Functional Bracing — A General Overview (originally posted as a three-part document on Bob's ACL WWWBoard)

(Previous versions of document were entitled "Functional Knee Bracing — Brace biomechanics; finding the best orthosis for your needs")

Posted By: Michael Frind <frind@execulink.com>

Version 8b: January 4, 2002, with some revisions added November 22, 2002, May 7, 2003, and also December 12, 2003.

(Version 9 is currently in preparation, and will incorporate further revisions. New features will include diagrams and hotlinks. Version 9 should be ready sometime in early 2004.)

The following document comprises a summary of my findings related to functional knee bracing. (The material was originally posted as three separate text files; the link to each subsequent part was found at the bottom of its predecessor. Here, all portions have been amalgamated into the single document you are now reading. A hotlink to a list of brace manufacturers is provided at the conclusion of the final portion.)  Readers of the following document will find it convenient to print out a copy first, and then read with a pen or pencil in hand. Note that searching for any text string (e.g. if you want information on a particular model of brace) can be done using Edit/Find in Internet Explorer, or Edit/Find In Frame in Netscape.

The modern functional knee brace is more a product of biomechanics and engineering than of pure biomedicine. Used appropriately, and with understanding, functional braces are extremely beneficial to anyone with any history of knee-ligament injury (irrespective of whether this includes partial or full tears, surgical or non-invasive conservative treatment). The goal of this document is to cover the fundamentals of brace biomechanics, as well as to provide an in-depth analysis of brace design.  (Please note that no one has yet done a definitive, scientifically-absolutely-rigorous, comparative on-leg study of all [or even most of] the functional braces on the market.  Because a proper scientific experiment can test for only one variable [which would have to be the model of brace], and because in the case of health sciences must involve a sufficiently large sample population [in order to address the inevitable variability inherent in having human subjects], and also because of the inherent complexity of bracing as well as brace-leg interaction, doing such a study would entail the enormous capital expenditure of outfitting hundreds of people with every brace model to be studied.  For this reason, it makes more sense to evaluate knee bracing from a combination of both biomechanical engineering and personal-use experiences of brace-wearers—and this synthesis is what this document seeks to provide.)

The world of functional knee-bracing is both surprisingly complex as well as remarkably multi-faceted. There are many models on the market; most are adequate at serving various intended purposes, some are good but only in certain areas, and a few are excellent all-around. The range of products includes numerous well-established and thoroughly-refined models, as well as a handful of newcomers. Although there are many models available on the market, only relatively few are well-known and available in all areas; fewer still are both widely available and well-engineered.

In this document, I will examine, in reasonable detail, functional bracing from the combined viewpoints of structural engineering, orthopedic biomechanics, and ergonomics. To ensure a balanced analysis of overall design as well as utilitarian functionality, I will reserve detailed explications for bracing that I have been able to repeatedly observe first-hand, in actual on-leg service. (This is in addition to off-leg examinations of bracing). Quite by necessity, in-depth discussions are reserved for the more-common braces. (Please note: There are several firms which produce custom-made braces which look promising, but for which I do not have enough information. This lack of information would be due to either the model being very new on the market, or simply not being widely available [and hence not well-known, thus with no track record]. I will endeavour to report on such braces as additional information becomes available.) Please remember that merely because a given brace (because of the specific nature of its attributes) requires more space for description than a product from another manufacturer should not be taken to imply any type of endorsement for either product.

Because there are so many considerations germane to functional bracing, and because there are some similarities between certain models, it is impractical to exhaustively describe each model separately. Rather, I have chosen to discuss the salient points in detail, with background topics covered as needed. The result is an explication organized by design considerations, with various brace models being examined as case studies throughout. Model-specific caveats and concerns are addressed in the appropriate context. I believe that the following document provides an overview that is both intensive and extensive, as well as objective, thoughtful, practical, balanced, coherent, relevant, and adequately thorough.

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Perhaps the most common complaint about functional knee bracing relates to its general inability to protect the knee from twisting. (There is one exception to this; I will discuss it later.) The main reason behind said inability is simply shearing of the leg's soft tissues. Because the human knee's anterior cruciate ligament carries most of the responsibility for controlling torsion at the knee, it is most commonly injured via this mode of forcing. (In fact, it is possible to injure one’s ACL merely by vigorously swinging handheld weights in the transverse plane.) Clearly, the ACL-compromised knee is especially vulnerable to torsion. Since externally-worn bracing generally cannot guarantee immunity to twisting (with the aforementioned exception), it follows that wearing a brace to compensate for an ACL-deficient knee's vulnerability to torsion constitutes a recipe for serious problems.

Of course, the human knee can be injured via mechanisms other than twisting. (Because the ACL is also responsible for limiting extension and anterior drawer [and in MCL-compromised knees sideways forcing as well], the ACL does not require twisting in order to incur injury.) Functional bracing is very valuable in that it is superb for protecting the knee from hyperextension (assuming, of course, that the appropriate extension blocks are used) and sideways forcing. This means that a well-fitted brace, when teamed with diligently-done rehabilitation and strong upper-leg musculature, is very useful in the context of sports. This is particularly true for sports in which contact may occur (accidentally or intentionally), since incidents of hyperextension and sideways forcing tend to occur unexpectedly—thus leaving the athlete unable to prepare for them by tensing the appropriate musculature.  (There are additional biomechanical considerations that reinforce the value of bracing; I will delve into these later.)

In contrast, incidents involving twisting are often under the control of the athlete.  (The athlete can, for example, learn to land jumps with good knee flexion, and can develop the habit of only pivoting on the front of the shoe.  Keeping the knees bent also reduces the risk of the knee being hyperextended, and enables the knee to flex in order to absorb shock.  Rapidly flexing the knees while changing direction results [due to the inertia of the upper body] in a momentary reduction in force on the feet—this can be used to advantage because it enables one to pivot while exerting less torque on the knee.) Because the modes of forcing that bracing is ideally suited for protecting against are exactly those which tend to be hardest to foresee, a brace can provide the wearer with a certain degree of confidence.

In fact, bracing is valuable for any knee which harbours any history of ligamentous injury (regardless of how treated); a major reason for this is that any such injury will tend to leave the joint predisposed towards further injury and/or premature degeneration. (The degeneration concern is so severe that it alone is often cited as a reason for ACL reconstruction.)

Although even in the unstable ACLless knee a brace will likely improve stability significantly, bracing is most beneficial when used in a knee that has at least some serviceable ACL tissue. (Because a functional brace is very effective at preventing sideways movement of the knee, and because ACL give-outs usually involve the knee twisting inwards, a close-fitting functional brace can in fact keep an ACLless knee quite stable.) For anyone with a fully-ACL-deficient knee, the utility of bracing is only optimized when the appliance is teamed with reconstructive surgery—and so the brace can find itself useful both before and after surgery, as well as in the long term.  (Note: Brace manufacturers often use the terms “support” and “control”. I prefer to describe this as restraint against specific modes of abnormal motion, and protection against potentially-injurious forcing.  In any case, when discussing the biomechanics underlying the brace-leg system, it is essential to specify the forces meant.)

The human knee has the distinction of being the body’s most-vulnerable-to-serious-injury joint. No other joint must contend with such long lever arms: the tibia and femur can act as frighteningly-efficient wrenches (given that they are several times longer than a car-tire wrench). Also, the knee must handle dynamic loadings as high as twenty times the body’s static weight. This situation is exacerbated by the fact that kinetic energy increases with the square of velocity (which explains why stopping distances quadruples when speed is doubled, and why high speed is a major factor in everything from car crashes to hockey and alpine-skiing injuries), and also by the closely-related fact that impulse is defined as force divided by time.  (This explains how a hammer works.  Consider also the astonishing fact that a slice of bread falling from a table hits the ground with a force equal to fifty times its weight.  The implications for the human knee are clear.)

The knee’s staggering predisposition to injury does not end there.  The joint has a complete lack of native bony stability, and so depends heavily on ligaments for stability.  The knee-surrounding musculature is important for stability, but keep in mind that said muscles are only of value if activated in time and if biomechanically reasonably able to counteract the force in the first place.  During an injury situation, especially one in which the athlete may not be able to foresee the forcing (e.g. impact from the front or side), the muscles may not be activated appropriately, thus leaving the ligaments entirely responsible for maintaining the knee’s intactness—that is, unless a brace is worn.

So, the knee’s unique set of attributes not only make it very vulnerable to major injuries—they also make this joint difficult to rehabilitate, and hence more likely to be haunted by the effects of previous injuries. Finally, note that a reconstructed ligament cannot be expected to attain quite the same strength as its natural counterpart (although it is possible to train to have stronger muscles than pre-injury); also, note that revision reconstructions do not have the high success rate of first-time reconstructions. Clearly, preventing injury/re-injury should be a high priority.

The benefit of bracing also deserves to be examined in the context of biomechanics. Case in point: hyperextension (herein defined as extension beyond the knee’s natural limit). Hyperextension is something which the flexors (hamstrings) are normally responsible for protecting against. (The hamstrings are also essential for countering anterior-drawer forces; this I will discuss later. Note also that, in this document, I use the term “hamstrings” to denote all the knee-flexors located in the thigh [including the gracilis and sartorius].) However, as the knee approaches extension, the angle at which the hamstrings operate changes. At full extension, the hamstrings are mechanically at a great disadvantage. So, once the knee is at full extension, it is disproportionately vulnerable to further extension. This is a major concern, because hyperextension is a major cause of ACL injury/re-injury. Fortunately, a good functional knee brace provides very dependable protection against hyperextension.

Hyperextension is not limited to high-impact sports.  It can occur in the most banal of situations, for example while walking on uneven terrain.  To understand how this type of hyperextension occurs, it is necessary to consider that normal human gait entails a brief quadriceps activation upon landing.  (This serves to absorb shock, and also prevents the knee from flexing entirely…or else we would end up squatting with each step we take.)  However, if the person accidentally steps into an unseen depression in the ground, the quadriceps activation occurs while the foot is still in the air.  This results in an unwanted extension force exerted on the knee.  In a normal knee, this is not likely to present any problems…but in a knee which harbours an injured or newly-reconstructed ACL, the incident could engender pain and possible injury.  (Note that if the ACL is fully torn, or if it has been recently reconstructed, the ACL-protective hamstring reflex will be missing…thus the knee will be very vulnerable to hyperextension.  Once the knee is reconstructed and has become reinnervated, diligently-done proprioceptive training is necessary in order to regain the ACL-related neurological functioning.)

Sideways forcing is also a mode which the knee is intrinsically vulnerable to: it depends almost entirely on its collateral ligaments for arresting valgus- (i.e. inwards-) and varus- (i.e. outwards-) directed forcing. No muscle-tendon units are capable of providing any significant degree of protection against sideways forcing, although a brace will again protect very reliably here. (Note that if the MCL is torn, the ACL is additionally called upon to resist sideways forcing. A knee with MCL-tearing history would thus also benefit from the protection of functional bracing.)

Note that ACL-related giving-way incidents often tend to involve a certain amount of inwards forcing of the knee, in addition to twisting.  This type of inwards forcing is something which a brace, if equipped with a snug-fitting medial condyle pad, can counteract—and this might mean the difference between an ACL-deficient knee giving way repeatedly and not giving out, or between a freshly-reconstructed ACL being reinjured and not incurring damage.   It is advisable for anyone being fitted with a functional brace to ensure that various thicknesses of interchangeable condyle pads will be provided with the brace.

There are numerous other reasons why using a brace, for any knee with a ligament-injury history, is foresightful. The importance of preserving the knee’s bone-covering articular cartilage (which sustains permanent damage with the bone-bruising that tends to accompany knee give-outs) and menisci (which are often torn in conjunction with ACL tearing, and which can be further damaged if a reconstructed ACL is re-torn, or if an unstable knee is allowed to give out repeatedly) cannot be overemphasized. (The menisci are essential for absorbing shock as well as distributing compressive and shear forces over the articular-cartilage surface. Also, they contribute to overall joint stability, and enable the synovial fluid to lubricate the joint efficiently. Note that a loss of even a quarter a meniscus can engender a quadrupling in stresses on the articular cartilage…with the end result being osteoarthritis. Also note that meniscal damage is very often irreparable; thus even a single meniscal tear might result in extensive cartilage removal—hence permanent consequences inasmuch as knee longevity is concerned.  And, note that modern biomedicine has yet to develop a proven method to reliably restore articular or meniscal cartilage to its pristine pre-injury condition.) Because of the very strong correlation between ACL injury and meniscal loss, and because of the very strong relationship between such injuries and premature degenerative changes, it is extremely wise to do everything possible to prevent knee injury/re-injury.

Functional knee braces are often used in the context of rehabilitation from ACL reconstruction. In this realm, it is important to note that the graft, as a sliver of tendon, initially derives much of its tensile-strength rating from the means with which it is anchored to the bone. The first several post-op weeks are marked by tissue death (due to avascular necrosis, or lack of blood); thereafter, the graft serves as scaffolding for ingrowth of new ligament tissue. Nerves and blood vessels grow into the graft. This process of incorporation proceeds rapidly at first, then slowly later on; overall, it takes 1-2 years for the graft to become optimally serviceable. (Incidentally, the gradual increases in stressing, integral to any concerted rehabilitation/physiotherapy programme, are essential on a cellular level. Tissue remodelling—that is, the formation of tensile fibres oriented parallel to direction of tension—cannot occur if the ligament does not receive the appropriate incremental increases in stressing.) The fact that the nascent ligament’s mechanical properties require quite some time to develop fully is another good reason in support of the use of a functional brace. Furthermore, considering the enormous costs of ACL reconstruction (including the cost of surgery itself, the inconvenience and pain to the patient, etc.), and considering that a functional brace can prevent ACL re-injury (and it can do this for a tiny fraction of the cost of another reconstruction), it is surprising that the use of such braces is not universal in ACL-reconstruction rehabilitation.

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The term “functional brace” is usually reserved for braces which contain some type of hard framework which encases the leg in such a way that said framework comprises a single (albeit hinged) unit. Functional braces are intended to be worn during activities (either athletic or everyday), and thus by definition must be comfortable to wear. These requirements make them very distinct from rehabilitative-type full-leg braces.

A basic classification scheme of functional knee orthoses is as follows:

Custom-made functional knee braces (e.g. Innovation Sports CTi2, DonJoy Defiance, OrthoTech Performer [was discontinued mid-September 2000], Townsend Premier, Lenox Hill Avenger Custom, Flextech/Flexguard F1, Townsend Original/Air/Ultra Air, Omni Avant Garde, Karl Hager Double X, EMT Stealth, Biedermann/Montana Ultratech). These braces are well-suited for athletic use, and are great for protection from hyperextension and lateral forcing. Being specifically made to fit the specific patient, they are fabricated either from a leg cast or via a series of at least a dozen measurements. They cost the most; however, they are designed for comfort, durability, efficacy and dependability. Most come with lifetime frame-and-hinge warranties; some demonstrate very solid engineering and incorporate well-thought-out design principles. (Note: Breg and Bledsoe do not produce genuinely custom-made braces, although I will touch on these firms’ pseudo-custom braces. Truly-custom-made braces are the focus of this document.)

Off-the-shelf functional braces (e.g. Townsend Rebel, Innovation Sports Edge and C180 and MVP, DonJoy Legend/Goldpoint, OrthoTech Vortex [discontinued], Lenox Hill Precision Lite, Omni Spectrum, Breg Tradition, Exotec Audacity 2, Flextech/Flexguard Inferno [now simply known as Flexguard], Bledsoe ACL/Ultimate/Force). These braces are economical (sometimes referred to as “cost-sensitive”) alternatives to the high-end custom braces. The off-the-shelf (also known as “pre-sized”, “semi-custom”, “patient-ready” or “ready-to-fit”) braces are best suited to people whose legs are not unusual in shape, and whose knee angulation (or alignment) is normal (i.e. neither knock-kneed nor bow-legged). Some of the off-the-shelf braces (e.g. Breg Tradition/X2K "Custom", Flextech Flexguard [formerly Inferno], Townsend Rebel) have aluminum frames, which the clinician can bend to shape. Others (such as the Townsend GS) are sold in kit form; the clinician heats and forms it around a cast of the patient's leg. Still other models (most notably the CTi Edge) have semi-flexible components which conveniently and easily (and usually satisfactorily) accommodate not only a considerable variety of leg sizes/shapes, but changes over time as well.  Although this document does touch briefly on off-the-shelf braces, models in this category are the focus of a separate document.

Hinged neoprene-sleeve braces (e.g. Innovation Sports PlayTuf, Townsend Sport, Anatech/Stromgren Stabilized Sleeve, DonJoy Playmaker, Mueller B5333, Bauerfeind SofTec). These braces, which can be considered a subset of the off-the-shelf category, range from available-at-any-pharmacy neoprene sleeves (with basic metal side struts), to more elaborate models which include stronger metal side struts and more-sophisticated hinging.  These braces also have the advantage of being generally economical to purchase.  (The most elaborate ones have hinges similar to those of the hardshell functional braces, and can be quite expensive.)  For non-heavy-duty sports use, they are convenient. Still, it must be kept in mind that these braces, given their obvious lack of hardshell construction, usually cannot provide full protection from hyperextension and sideways forcing. Also, the neoprene-sleeve braces are often prescribed merely because they retain heat and so encourage additional blood flow; in this way, they can promote faster healing. (Note: the hinged neoprene sleeves can also include arrangements for forcing a maltracking patella towards either side. Neoprene sleeves equipped in this way are often called “patellofemoral braces”.)

Finally, there is also the category of bracing for unilateral osteoarthritis. Such orthoses are designed to force the knee sideways so as to transfer the axial loading to the undamaged compartment. Both off-the-shelf and custom models exist; many are physically nearly identical to regular functional bracing (except for the lateral-forcing modification). Braces exclusive to this category I have discussed in other posting documents.

One reason behind prescription of bracing in general is that of proprioception. The ACL, injury of which is a common reason for bracing, is far more than just a restraint against inwards tibial rotation, excessive extension, and anterior drawer. Being replete with tension-sensing nerve endings, it is essential for keeping the brain apprised of goings-on within the knee, and by implication within the leg as a whole. Such data-relaying is known proprioception; without it, biomechanical efficiency is compromised. (The quadriceps-avoidance gait, a classic hallmark of full ACL deficiency, is but one example of this. Proprioception is essential for balance and for optimal muscle-activation timing, and thus for injury-prevention too.) Additionally, the ACL's nerve endings are responsible for activating the ACL-protective hamstring reflex. (This is termed dynamic stabilization of the knee, and it is important in high-stress movements such as jumping.  Note that during many activities, both the hamstrings and quadriceps are used simultaneously, thus assisting the ligaments in keeping the knee together.  This effect is most apparent during activities in which the foot is bearing weight.  Exercises making use of this phenomenon are known as closed-kinetic chain, and are safest for rehab of injury-history knees.)  Obviously, full ACL tearing leaves the knee vulnerable to further injuries; the only way to regain said proprioceptive capabilities is to have the ligament reconstructed and thoroughly rehabilitated (and even then, it can take several years for significant proprioception to return). But bracing can be helpful here: by stimulating the nerve endings underneath the skin, it will cause some signals to be sent to the brain. However, it is not known conclusively whether such supplementary information can result in improvements in muscle activation/timing.

Occasionally, one hears about concerns pertaining to whether or not wearing a brace will engender muscle weakness. The effect of a brace on degree of muscle activation (and subsequent development) is still an area of considerable research. For background in this area, a good paper to read is by DeVita et al, American Journal of Sports Medicine, Nov/Dec 1998.  (This article can be viewed on-line, in this board’s On-Line Knee-Injury-Article Library.) The authors found that the wearing of a brace encourages more use of hip musculature and less use of quadriceps; they concluded that bracing could be helpful in developing gait adaptations. (The authors point out that activation of the quadriceps tends to strain the ACL, and so by encouraging slightly reduced quadriceps use, the brace would indirectly reduce ACL strain. Apparently, there is no notable effect on the hamstrings; this is appropriate because hamstring activation is very beneficial in protecting the ACL.)  However, it must be remembered that normal use of a functional brace is usually defined as intermittent (e.g. only for sports). One would have to wear a functional brace 24 hours/day (or at least, continuously while awake)—as well as avoid exercise—in order to engender the possibility of a negative impact on leg-muscle strength.  (It is the knee injury itself, combined with the inevitable trauma of surgery, that engenders the recalcitrant atrophy often observed with knee injuries.)

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The first question pertains to the choice of custom versus off-the-shelf brace. As a rule of thumb, a custom model is preferable in any case. While a custom-made brace is always the best choice if the leg is oddly-shaped, some off-the-shelf braces can in fact accommodate unusual leg shapes surprisingly well. It is most important that the brace's frontal- (or coronal-) plane alignment (i.e. valgus-varus angle; I prefer to avoid using “knee angle”, in order to distinguish it from the angle at which the knee is flexed at any given point in time) matches that of the wearer’s knee; this factor alone often rules out off-the-shelf bracing. (Currently, only one off-the-shelf brace [the ISI OAsys] has this type of adjustability, but it is sold as an osteoarthritis brace.)  (The term “Q-angle”, denoting quadriceps-pull angle, is sometimes incorrectly used to denote inwards knee anglement.  Although a large Q-angle is usually caused by knock-kneedness, the two are not synonymous. I will return to this topic later.) 

Additionally, it is imperative that the brace's shape and contours fit the user’s leg. Close fit is also important in ensuring that the brace will compress the leg's soft tissues as uniformly as possible, thus resulting in the leg’s approximately-round cross-section being only minimally distorted. (Of course, the more soft tissue that surrounds the bones, the harder it is to grip the bones and control their movement. For obese people, extended-version full-shell braces are best.) A brace that fits poorly will be uncomfortable, may migrate, and would be a hindrance to activity. For high-level athletics, custom bracing is always the best choice.

Regardless of the type of brace, a very important factor is the clinician (or orthotist). If this person is not experienced with selecting, fitting, and adjusting bracing (whether of the custom or off-the-shelf type), then even the best-engineered brace could be troublesome. (Note that functional knee braces are medical devices. Furthermore, most braces [and in fact, all of the really good ones] are rigid-framed. I wish to emphasize that the selection, fabrication and fitting of functional knee braces is extremely different from that of finding footwear. Shoes are not medical devices; moreover, they are flexible as well as off-the-shelf. Anyone who likens the selection and purchase of footwear to that of obtaining a functional brace should not be entrusted to the fitting of custom-made knee orthoses. It also goes without saying that salespeople/vendors/orthotists/clinicians/physicians/therapists should not receive financial rewards for selling certain models of braces. I firmly believe that the attributes of the various braces should dictate the model chosen.  The goal of this document is thus to elucidate the characteristics of the braces, so as to facilitate informed decision-making.)

Off-the-shelf braces are usually fitted via a single measurement, usually taken at the knee's condyles. Some braces use several measurements above and below the knee; such braces may provide a closer fit than the single-measurement type. (One example is the Breg Tradition/X2K “Custom”, which requires a mere four data points; this brace is far from truly custom-made.) However, even if six measurements are taken, the brace still only qualifies as off-the-shelf. A set of merely six points is inadequate for plotting leg shape well.

Custom-made braces are made from casts or a detailed set of measurements. Overall, what is important is not so much whether casting or measuring is used, but rather the sophistication and accuracy (correctness) involved.  The consequences are not only germane to how well the brace will fit upon delivery, but also how comfortable it will be to wear during activities. 

Casting is the method used by Townsend Design, OrthoTech, Omni and Generation 2, EMT, Lenox Hill, Flextech/Flexguard, Karl Hager, and a number of other firms. (The cast is used for making a positive mould of the patient's leg; this is then modified in order to serve as basis for the orthosis. Usually the mould-modification is done by hand [e.g. Townsend], but it can also be done by a computer-controlled lathe [e.g. Lenox Hill].) The major advantage of casting is that it is virtually foolproof; this makes it ideal for use by a clinician who is somewhat inexperienced. Casting is also good in that it captures leg contours accurately (even though some of this detail is redundant to the brace fabrication and fitting). The disadvantage of casting is that cast-modification (if done by hand) depends greatly on the judgement of the individual orthotist at the factory; the result is that there could be some variability in closeness of fit obtained. (I consider minor drawbacks, such as cost of cast shipping, to be nugatory.)

Another means with which a brace can be fitted is via a measurement process. The caveat is that the measuring process must be sophisticated enough to represent the leg accurately. This means that a handful of measurements is inadequate. For a full-shell brace, at least twenty measurements are needed for a really good fit. I consider the only custom-made braces that have adequately-sophisticated measuring systems to be the CTi2 and the Defiance. Of these two, I consider the CTi2's system to be the most reliable and capable of capturing leg dimensions (in all three planes: frontal/coronal, transverse, and sagittal) both accurately and reproducibly (thus precisely); however, the Defiance’s system is also well-proven. (Incidentally, some custom-made braces, most notably those from Omni, can be obtained via simple digital photographs: one snapshot is taken from the front of the knee, and another is taken from the side. The drawback with such as system is that it cannot reliably take into account the three-dimensional structure of the knee. To accurately record the three-dimensional leg via such imaging, it would be necessary to take a third photograph from the top or bottom.)

DonJoy's popular open-framed Defiance is made via a measuring gadget known as the CCMI (Custom Contour Measuring Instrument) Mark II, which is clamped to the leg in the weight-bearing position, whence dial gauges are read and recorded. (The device takes a mere 15 measurements, a minimum as far as I am concerned.  However, as will be discussed subsequently, the Defiance’s sits-solely-on-soft-tissues design means that it can be fitted adequately with less measurements than the CTi2.) Meanwhile, the CTi2 is made from measurements taken with a proprietary Coordinates Measuring System gadget. The data include 24 separate measurements; this consists of 22 leg-size measurements (taken with the leg extended horizontally, but with certain measurements taken with specific muscles activated), along with patient weight and height. (Here we can see the importance of a trained and experienced clinician. Because leg shape is affected by which muscles are activated, it is important that only the appropriate muscles be activated [and only at the appropriate time] during the measuring process.  Please remember that how the leg feels while in the measuring device closely parallels how the leg will feel while in the brace.  This means that if the measuring device is set to squeeze at the knee, a painfully tight brace will be the result.)  Note that although the Defiance’s measuring and fabrication system records patient height and weight, said two pieces of data do not directly impact the final product.  (The CTi2 can in fact be requested to be made longer or shorter than it would normally be made for a person of a given height.)

Braces fabricated from measurements are made from a numerical model of the patient's leg. This is a fundamentally different procedure from the traditionalistic fully-manual casting. With the CTi2, for example, the measurements are input directly into a computer program, and a type of numerical model is made of the patient's leg. This digital process makes it possible to reproducibly modify the virtual “cast” of the leg, because it is done via a codified numerical procedure. (In order for any brace to fit snugly, the recorded leg shape must in any case be modified somehow; thus numerical modification accomplishes on computer what casting does with plaster.) The numerical model is utilized for setting up a series of sophisticated jigs, and the brace is hand-fabricated on these. (With the Defiance, two heated carbon-fibre tubes are inflated by compressed air and moulded by a specially-designed framework which is set according to parameters from computer processing of the CCMI dataset.  The hinges are then inserted into the tubes, and riveted in.  This design, while economical to fabricate, tends to make it difficult to modify the brace later on.  Also, it is not as strong as the integrated-directly-into-the-frame installation of hinging, as used by Townsend, Innovation Sports, and many other firms.)

In the end, a CTi2 brace made from two-dozen measurements is no less labour-intensive than one that is made directly from cast (e.g. Townsend Original/Air). (Note: the Defiance’s fabrication system requires much less hand labour than does the CTi2’s. The major reason for this is that, unlike with models such as the Original/Air and CTi2, the Defiance’s fabrication does not involve customized hand-layup of the carbon-fibre woven fabric.)

At this point, one might wonder: which is better—casting or measuring? This is not an easy question to answer, since both systems have their own unique merits. The engineering philosophy behind casting is slightly different than for measuring, albeit both systems have the goal of reproducing the leg’s relevant physical parameters as faithfully as possible. However, both depend heavily on the skill of the clinician. With a measuring protocol, the measuring device must be used correctly; thus clinician skill is key. Granted, measuring devices are easier to misuse than plaster-soaked gauze. But lest anyone think casting is foolproof, it must be remembered that a skilled orthotist/clinician must be careful to correctly mark (on the under-cast stockinette) certain bony landmarks.  With this in mind, casting is really not that foolproof after all.  And, of course, serious problems will result if the stockinette shifts during the plaster-gauze-wrapping process.

A brace made from carefully-taken measurements (on a biomechanically-sound measuring protocol) will fit as well as one that is made from a cast. Besides being reproducible and consistent (due to its basing on a numerical algorithm for its dimensioning), a well-planned measuring system also brings a unique advantage: it can take into account the leg-contour changes caused by muscle activation. So, a casting process has a disadvantage: it is impossible for a cast to record what happens when individual muscles are tensed. While a good measuring system can record the leg-shape changes due to specific muscle activations, a cast merely takes an average of everything.

Granted, casting is better at capturing every nuance of the patient's leg contours—however, keep in mind that how well the resulting brace matches said contours will depend on the care taken in cast-making as well as on the individual orthotist's mould-modification prowess. And, remember that long-term brace fit is not necessarily commensurate with initial fit. The catch is that what defines long-term fit is not the little nuances in leg contour—but rather the ability of the brace to fit a leg which will inevitably change slightly (and perhaps even significantly) over time. This means that an initially-snug fit may not be so comfortable in the long run. (Of course, a greater-than-minor change in leg shape will likely require the brace to be sent back to the factory for modification or refabrication.  For this reason, it is best to have a warranty on fit that is as long as possible. The longer said warranty is, the less concern there is regarding leg-shape/size changes affecting brace fit.) Although any manufacturer will remake a screwed-up brace free of charge, obtaining a correct fit the first time saves inconvenience.

Obviously, long-term fit of a brace is contingent upon overall design (which in turn comprises a number of factors). Here is where a relatively thick lining contributes to an advantage in long-term adaptability. I personally would prefer a brace that is made with a thick foam lining (such as the CTi2) and which still fits closely (yet not quite as closely as, say, a Townsend Air/Original), as opposed to a brace with a thinner lining (e.g. Townsend Air/Original, Flextech/Flexguard F1) and which will be more sensitive to minor changes in muscle dimension (also as a consequence of how its shape interacts with the leg, as discussed elsewhere). (Although thicker linings will make a brace bulkier, with good design this can be used advantageously—since the hinges are by necessity the thickest parts of any brace, using a thick foam lining [especially in the members surrounding the hinges] will result in hinges which do not protrude with respect to the frame. [Note: since I wear two braces, I consider the issue of hinge protrusion significant because of potential tripping hazard.]  A thick foam liner also provides improved protection against direct impact.)

Regardless of whether the leg is casted or measured, it is imperative that the leg’s valgus-varus angle be captured accurately. (The valgus-varus angle is the angle the shaft of the femur makes with the tibial shaft, when viewed from the front. Note that this is distinct from the Q-angle, for which measurement takes into account the pelvis, hip, spine and ankle. Although the most-common cause of a sharp Q-angle is indeed knock-kneedness, other factors come into play; thus it is important not to confuse Q-angle with valgus-varus angle. Note that in this document, I use the term “knockkneedness” to denote inwards knee alignment.  Technically, the term “knock-kneed”, also known as genu valgum, is limited to cases where the person, when standing erect, cannot put his/her feet together because the knees are touching.)

The human knee is not merely a saggital-plane (i.e. front-to-back) hinge. As it extends, the tibia rotates externally, thus in effect making the knee more knock-kneed. (This is the screw-home mechanism; because it makes the joint close-packed, it is helpful for purposes of standing.) Since practical considerations limit a dual-hinge knee brace to saggital-plane motion, it is imperative that the brace have enough room on the medial side (so that the medial side of the knee doesn’t impinge on the inside of the brace’s medial hinge). This explains why, for bracing, the casting or measuring must be done with the knee straight. (In cases where the injury makes it impossible to attain full extension, near-full extension is still adequate.) Brace manufacturers design their orthoses with the knee’s screw-home mechanism in mind, and thus allow enough medial-side hinge clearance.

Other braces which are ordered via casting are the Omni Avant Garde, the Lenox Hill Avenger, the Flexguard F1, the Biedermann/Montana Ultratech, the Karl Hager Double X, the EMT Stealth (which I am still in the process of gathering data for), and formerly the Orthotech Performer.  (Note: Because in 2000 Orthotech was bought out by DonJoy, the Performer is no longer available.  I rated the Performer as superior to the Defiance, albeit not as good as the Innovation Sports CTi2 and Townsend Air/Original.)

Townsend's open-framed brace, the Premier, is available via casting as well as a new tracing protocol. The Premier's tracing device is quite sophisticated, and will yield reliable results if used carefully. Condyle width is measured via a caliper-like device, and coronal/frontal-plane measurements are traced with a pencil in a sliding holder; shape is recorded via leaded strips, which are then traced. One drawback of Townsend’s tracing system is that its accuracy will be affected by distortions introduced via faxing; I suggest traditional casting be used for the Premier. (Note: Townsend's Rebel-99 Pro, an aluminum-framed version of the graphite-foamcore Premier, is available in custom and off-the-shelf versions. However, the custom model is custom-formed from off-the-shelf aluminum members, rather than being made from scratch.)

Examples of custom-made braces with which I am very familiar with (and personally know people who use them) are the Innovation Sports CTi2 (this is the model I wear), the Townsend Air/Original (very good but also heavier than average; the Air is almost identical to the Original, and thus I tend to consider these two models as one), the Townsend Premier (a very light and comfortable open-frame brace; many similarities to Townsend's Ultra Air), the DonJoy Defiance (despite its odd frame design, this brace is very popular; I consider this model to be merely adequate), the Omni Avant Garde (the frame is structurally weak, but comfortable for some), and the Lenox Hill Custom 2 (the now-discontinued predecessor to the Avenger).

The distinction between full-shelled and open-shelled is an important one. I herein define a full-shelled brace as having a lower shell which covers a substantial portion of the tibial crest. The amount of tibial-crest coverage is usually about one-third of the tibial-crest length (but then this depends on patient height); a general rule of thumb is that in a full-shell brace, the tibial-crest portion of the lower shell extends from the lowermost part of the brace up to the tibial tuberosity (the bony protruberance below the patella).

In covering a large portion of the shinbone's bony ridge, the full-shell brace takes advantage of this landmark as a solid reference. Because bones tend not to change over time (although they can), whereas soft tissues are very prone to rapid dimensional changes (e.g. due to muscular activation), it is logical to design a brace to interface as closely as possible with as much as of the tibial crest as possible. And, because ligaments connect bones, it makes fundamental sense to design a brace to grip as much bone as possible. Since the tibial crest is the only part of the leg (besides the knee joint itself) in which the bone is not covered by thick layers of soft tissue, it makes sense to design the brace’s lower shell to grip the tibial crest tightly.  Only if the brace interfaces with the tibial crest can it reliably remain in place on the leg.

Full-shelled braces can get sweaty in hot weather, while open-shelled models tend to stay cooler in hot weather. However, a compromise must be made. The major drawback of an open-shelled brace is its propensity towards fit problems, due to the lack of reliable tibial-crest registration.  (Registration is the location of the correctly-worn brace with respect to the leg’s anatomical landmarks.)  Open frames, by virtue of their reduced skin-contact area, can be prone to pressure-point problems. (Pressure is force divided by area, thus less area means more pressure.) A full-shell brace will always provided better soft-tissue containment, and thus better-defined restraint against abnormal motion. And, an open-shelled brace will not provide the same degree of protection during high-impact activities as its full-shelled counterpart. Open-framed braces also have the disadvantage in that their ability to protect the knee (from side impacts) tends to be highly sensitive to the closeness of fit. With regards to frontal impacts (especially to lower leg), full-shell braces always offer the best protection.

Open-shelled braces, as discussed earlier, can be prone to difficult-to-resolve fitting problems.  This is especially the case if the orthosis has no ability to grip the tibial crest—an oddity which only the DonJoy Defiance has.  The Defiance’s trouble-prone design makes this the only model which completely lacks tibial-crest registration. In other words, the Defiance's lower shell can move (with respect to the leg bones) both translationally (i.e. distal-proximally [up-down], anterior-posteriorly [front-to-back], and medial-laterally [side-to-side], as well as rotationally (i.e. roll, pitch, and yaw).  The resulting poor consistency of on-leg registration (i.e. location of the brace with respect to the leg's bones) raises serious questions with regards to how dependably this brace can perform its duties without hampering the user’s activities. 

Furthermore, the Defiance's design means the brace's frame sits exclusively on soft tissues. (Because soft tissues are deformable, it is evident that the need for proper fit is not so acute as it would be with a brace that registers on the tibial crest.) Since soft tissues (i.e. muscle) are exactly the most changeable (i.e. due to muscle activation) feature of the leg, the Defiance’s lower shell will move with respect to the leg each time the calf muscles are activated. (A brace's lower shell should always remain stationary with respect to the tibia.) The result is that the Defiance's suboptimal lower-shell design makes the whole brace prone to migration; each time the leg is flexed, the lower shell moves. (The only solution is keep the strapping just below the knee very tight. One additional drawback of this model is that the strap just below the knee does not attach to pivoted buckles, and thus will not follow this area’s rear contour very well.) Additionally, the Defiance’s simple pin-type hinge motion means that the brace’s top shell will piston with respect to the thigh. As the brace migrates down the leg, this pistoning will be exacerbated (because the brace hinges will be further misaligned with the knee motion) to the point where the wearer will be forced to pull the brace up and overtighten the strapping.

Defiance-wearers often indicate that they must wear their braces uncomfortably tight—and the need for keeping the straps so tight, in conjunction with the just-discussed biomechanical drawbacks of this model, means the Defiance user will likely be forced to endure chafing and irritation.  (Keep in mind that if the brace is irritating to wear, then the user will likely avoid wearing it…thus nullifying its protective capabilities.)  The more the brace moves around, the less predictable its function becomes…and the less it protects the knee.  We have already seen how the Defiance’s frame design makes it the most prone-to-migration of all braces, by far.  I would not be surprised if a poll of brace-users would show that those wearing the Defiance experienced the greatest number of knee re-injuries.

Long-term muscle changes (due to rehab) will also result in shifting of the Defiance’s frame with respect to the leg bones. The Defiance’s floats-on-fleshy-tissue design is such that although the brace is quite forgiving of clinician errors (i.e. bad measurements), it is quite sensitive to both correct strap tightness as well as changes in muscle girth.  Note that changes in muscle size are more likely to occur in some parts of the leg than others, thus raising concerns about the entire brace frame being shifted over time (in addition to the just-discussed concerns of rubbing and migration). But because the Defiance has absolutely no tibial-crest registration, movement of the brace’s frame with respect to the leg will be such that the cause of the poor fit [i.e. location on the brace frame] will be nearly impossible to trace.  So, the owner of a problematic Defiance must be prepared to expect that the brace will remain problematic forever.

Because the Defiance has no anterior tibial shell at all, it depends entirely on strapping to exert its compressive forces on this portion of the leg.  Specifically, this means that the brace’s tibial-crest strap (i.e. the one immediately below the kneecap) must exert considerable pressure on the often-sensitive tibial-crest region—and this is particularly the case with the Defiance, whose straps must be kept tighter than the corresponding straps in other braces.  (The tibial-crest area is often sensitive to pressure, on account of the presence of surgical hardware from ACL reconstruction…especially in the case of people who have undergone patellar-tendon ACL reconstruction.  So, the Defiance’s design brings major drawbacks indeed.  In contrast, with a full-shell brace, it is easy to cut out certain areas of padding in the sensitive regions.)

In the realm of providing protection against sideways forcing and hyperextension, the Defiance is entirely adequate. In the end, the Defiance is not “bad” per se—after all, there are many people who have worn this brace and found it satisfactory—but rather, from the viewpoints of engineering design and technical sophistication, it has been superseded by quite a few of its competitors.

One more issue regarding the Defiance in particular: DonJoy has recently introduced a heavily-promoted “Knee Guarantee”, in which the company will pay the insurance deductible of anyone who, while wearing a Defiance, re-tears a reconstructed ACL and undergoes revision reconstruction.  I think such a guarantee makes a mockery of the person’s long-term knee health, and for a number of reasons.  First of all, anyone who has undergone ACL reconstruction knows how demanding and gruelling it is, and that $1000 is peanuts inasmuch as the total cost (which must include not only the surgery costs [which in some jurisdictions is covered by government insurance anyway], but also lost working hours, inconvenience, rehab costs, various out-of-pocket expenditures, and so on) is concerned.  Secondly, the agony of re-tearing an already-once-reconstructed ACL is many orders of magnitude greater than what can be addressed in dollar values…one only need remember that each time a knee gives out, damage is done to articular and meniscal cartilage—and such damage makes the knee more arthritis-prone in the future.  Thirdly, DonJoy’s “Knee Guarantee” could be dangerous in that it might cause Defiance users (especially young people) to consider themselves immune to ACL reinjury and thus to take uncalculated risks.  Fourthly, it must be remembered that revision ACL reconstructions are fraught with technical difficulties and various other problems, and thus do not carry the 90-95% success rate that first-time ACL reconstructions (if done via autografting) do.  In short, I think DonJoy’s “Knee Guarantee” should be ignored when considering the Defiance brace.  I strongly recommend choosing a brace on the basis of technical merit and thoughtfulness of engineering design, the fundamentals of which this three-part document seeks to cover.

(For continuation, please see part 2, below)

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Functional Bracing — A General Overview (part 2/3)

(Part 2 of 3)

There are a few features that are common to all braces. The most obvious is that the appliance requires straps which serve to clamp it to the limb. It is unavoidable, however, that some restriction on the joint's range of motion is caused by said strapping (most notably the strapping just above and below the knee). This means that it is essentially impossible to squat or kneel while wearing any knee brace.  However, aside from this, a correctly-used brace will allow normal knee motion—but will restrain against excessive extension as well as certain modes of abnormal forcing.

The issue of strapping also leads to the topic of how to best anchor the brace to prevent slippage down the leg (also known as migration). The most proven means is via the tightest strap being located directly below the knee, so that the brace effectively rests on the gastrocnemius/soleus (i.e. calf) muscle group. This arrangement is biomechanically far more efficaceous and appropriate than anchoring the appliance above the knee. Consider that the hamstring and quadriceps, the two major muscles involved with the knee, are such that their moving tendons are located just above the joint. This means that having a brace apply sufficient compression for brace anchorage, in this area, would reduce efficiency of this musculature.  Note that the gastrocnemius is a biarticulate muscle: it operates both the knee and ankle, albeit predominantly the latter. The biomechanics of the gastrocnemius are such that comparatively little movement of the muscle occurs at the knee end. So, having the brace sit on the gastrocnemius will result in far less interference with componentry that moves underneath the skin (as compared to anchoring a brace by compressing tissue above the knee). Gastrocnemial suspension also accomplishes the side benefit of pain relief through below-knee compression, thus serving the same function as the popular Cho-Pat strap (and related products). Being most important as well as tightest (hence fastest to wear out), the strap just below the knee should be attached to pivoted buckles for easy replacement and user comfort, and should be no less than 1.5 inches wide (for durability and user comfort).

A synopsis of general hints for brace-wearing would read as follows: most importantly, the strap immediately below knee should be tightest. Bottommost strap should be moderately tight, also the strap just above the knee.  (Should the knee be violently hyperextended, the straps above and below the knee would be in tension.  Therefore, during high-risk activities such as contact/collision sports, adequate tightness in both of these straps is necessary in order to preclude anterior-posterior shearing of the knee.  However, during other activities, this is not a major concern.)   The topmost strap should be no more that slightly-to-moderately tight; overtightening said strap will cause the brace to be forced downwards due to the distal conical tapering of the thigh.  (For the case of the ACL-injury-history knee, there is the additional issue of counteracting anterior drawer [so as to reduce strain on the partly-torn or freshly-reconstructed ACL, or in the case of the fully-ACLless knee, to prevent injury to secondary restraining structures].  Counteracting anterior-drawer forcing requires the strap immediately above the knee (or the auxiliary anterior-drawer-counteracting devices, as available on some braces) to be rather tight.   However, because of the presence of the hamstring tendons and also the soft tissues behind the knee, in practice it is quite difficult to significantly counteract anterior drawer.  In general, then, for knees which have a significant amount of native laxity and hence which naturally tend to hyperextend or which exhibit a forwards-shifting-prone tibia, the user is advised to ensure that both the upper and lower-cruciate straps are snug.

Because in practice the brace’s hinge motion might not quite perfectly align with that of the knee (remember that everyone’s leg shape and knee motion is slightly different), a slight degree of pistoning is to be expected.  The amount of this sliding motion (between the thigh and the brace’s upper shell) should be so minor to be undectable, or at least not objectionable.  The brace’s upper-shell straps should be loose enough (in practice, this means moderately snug, since soft-tissue shearing will be present as well) to enable the brace’s upper shell to slide slightly with respect to the femur.  I will return to the topic of brace-frame and hinge-design interrelationship later.

Secure anchorage of the brace’s lower is assisted by designing the brace’s lower shell to interface as closely as possible with the tibial crest.  This again highlights the benefit inherent in a full-shell brace: good registration with respect to the shinbone, and hence greatly-reduced concern about the brace moving each time the leg changes shape due to muscle activation.  (Open-shell braces, which tend not to have a furrow which cups the tibial crest, depend very heavily on carefully-tightened straps for consistent anchorage.)  For a full-shell brace, the lower shell should have a furrow which aligns with the tibial crest.  (An additional indentation to match the tibial tuberosity [i.e. the bony bump just below the kneecap] is unnecessary if the brace’s frame padding is reasonably thick.  Furthermore, such an indentation would make the brace very migration-sensitive — that is, if it were to migrate [even if merely due to a minor cause such as worn-out Velcro strapping], pressure points would develop.  For this reason, a thickly-padded simple furrow, in a full-shelled brace, is best.)

The tightness of the brace’s strapping clearly plays a role in all aspects of functional knee brace use; however, it should be noted that strap tightness is difficult to quantify.  The same strap tightness (tension), applied to two different braces, will not necessarily engender the same amount of soft-tissue compression.  This is affected by the design elements of the various braces, and in fact, some braces have various options.  (The CTi2 is an example here: it can be worn with just a pad attached to the strap immediately below and behind the knee.  Or, a leg-encircling sleeve [the manufacturer calls it an AMS Y-wrap] can be used in conjunction with the strap.  The use of such a sleeve results in more uniform compression around the circumference of the leg, thereby making the brace more comfortable for long-term wearing or intense activity.  This is good for the brace-wearer, but it can complicate things for the medical researcher who is investigating the various braces.  When looking at strap tightness and its impact on the performance of different braces, it can be very difficult to make apples-to-apples comparisons.)

A number of studies which seek to compare various models of braces have been done.  Standardization of strap tightness using a simple Newton spring scale (basically just a metal spring with a scale and pointer) is insufficient, because such a procedure fails to take into account a basic aspect of brace design—namely, how far the strap-attachment points are from the sides of the leg, and also how far anterior or posterior said points are.  Some brace designs use straps attached to the outside of the frame, which naturally means that in order to achieve the same degree of tissue compression (as compared to a brace in which the straps are attached to the inside of the frame), the straps themselves must be tighter.  (In this case, making the straps tighter simply results in the brace frame sides being pulled inwards.  But having the straps attach inside the frame can result in fittings which can mechanically irritate the skin, and can make said straps hard to replace.)  Because custom-brace fit and leg shape and highly individual, the optimal tightness of each strap is something which the brace user will discover through experience.

The human knee is not a simple (that is, uniaxial) pin hinge. Accordingly, a hinged brace should be designed with this in mind. The better the brace motion matches that of the natural knee, the less slippage (between the brace and the skin, or even below the skin—in the form of shearing underneath of the skin) there will be, and so the less rubbing (pistoning) there will be. Technically (and anatomically/physiologically), there is some person-to-person variation in the roll-and-glide of the human knee—and so it is infeasible for a brace hinge to absolutely perfectly mimic everyone’s knee motion anyway. (Of course, it is also very difficult to ensure that the brace is always worn perfectly positioned; consider that the exact position of the brace on the leg can vary slightly depending on strap tightness, muscle size, et cetera.)  Still, it is well worthwhile for the brace’s hinge to be designed to mimic the average roll-and-glide motion of the knee.  Clearly, a natural-motion hinge is superior to a simple pin-motion-type hinge.  I am surprised that only some manufacturers (most notably Townsend and Innovation Sports, along with smaller manufacturers EMT, Lenox Hill, Biedermann/Montana, Flextech/Flexguard, also Exotec) use hinges that are designed to take the knee's natural roll-and-glide movement into account. (How well the hinges of these firms match the knee's motion varies somewhat, and is discussed subsequently.) Why DonJoy, Karl Hager, Breg, Omni and others are so smitten by primitive geared-polycentric hinges (which provide nothing more than simple pin-hinge-type motion) is beyond me—although I note that some of these firms dismiss the benefits of incorporating anatomically-correct hinge motion into knee bracing.

So, the need for good tibial-crest anchorage is clear.  But even if the brace does not grip the tibial crest itself (i.e the Defiance), it is worthwhile to grip the lower leg more firmly than the thigh.  Most braces are in fact designed to grip one half of the leg more firmly than the other. The idea here is to permit a controlled amount of slippage, yet only in one half of the brace. For nearly all braces, the lower member is the one that is firmly (or most firmly) affixed to the leg. If the bracing does not have an anatomically-correct hinge motion, then its top shell will piston noticeably (and possibly objectionably). The action of the thigh muscles (combined with the thigh’s downwards-tapered conical shape) could cause the appliance to migrate. However, if the brace’s hinge motion is anatomically correct, then the top shell will only piston very slightly—such a slight degree of movement would not be noticed by the wearer.

In addition to the aforementioned advantages of firmly anchoring the lower half of the brace, this anchoring concept is the most compatible with the design goal of making the brace most amenable to long-term thigh-girth changes.  With the brace’s upper shell purposely being slightly loose, the orthosis can easily accommodate minor changes due to hamstring and quadriceps rehabilitation.  (While some manufacturers [Flextech/Flexguard, EMT] do incorporate padded protrusions [which are theoretically supposed to grip above the knee] in the upper halves of their brace shells, there is really only one brace [Omni] which does not depend chiefly on time-proven gastrocnemial-muscle suspension.) The braces of Omni provide another case study in mediocre design.  Because Omni is quite a commonly-used brace, it is worth devoting a few paragraphs to this firm’s notably-marginal products.

Omni makes its braces, with an elastic upper portion which bridges the two lateral struts, such that the upper half of the appliance grips the thigh firmly. This means that the pistoning occurs on the lower half of the leg; this is not biomechanically optimal. Omni's braces are also strange in that they all lack solid upper members. However, because one can literally move an Omni brace's two upright struts independently, the design is not structurally sound. The arrangement is such that said brace must be on the leg to have any semblance of side-to-side strength. And, the brace's strength is partially contingent upon the firmness of the leg's soft tissues. (Of course, said firmness varies with which muscles are activated.) I would choose bracing that does not have this type of drawback. All of the other braces (except those of Generation 2) are made such that the appliance is strong in coronal (or frontal) plane bending. (The coronal or frontal plane is the plane that is parallel to the floor if you lie on your back.)

Full-shelled custom-made braces are designed to compress the leg as uniformly as possible. In addition to minimizing distortion of the leg’s cross-section, this reduces pressure on any one area. Furthermore, full-shelled braces have the advantage (over open-shelled ones) of spreading out the pressure they exert over as large an area as possible. (This is why a full-shelled brace will be more comfortable than an open-shelled one, assuming both fit well and are approximately equal in weight.) Given that many brace-users have undergone ACL reconstruction, and given that said surgical procedure can make certain parts of the leg sensitive to pressure, the concern of how this affects brace choice arises. Again, full-shell custom-made braces have the advantage—and particularly if such braces have a thick lining. So, if a person’s tibial crest has a sensitive region (due to the presence of surgical hardware such as screws, or due to bone spurs as a consequence of Osgood-Schatter’s disease), with a full-shell brace, the solution is simply to cut out the portion of the liner in that area. This could be done very easily with the CTi2, and also with the Townsend Air (although the Air has a thinner liner). Note that such padding modifications cannot be done with open-shelled braces. With open-shelled braces, tibial-crest sensitivities (e.g. due to surgical hardware) would occur where the brace has straps…thus making such bracing extremely uncomfortable to wear.

A well-designed brace will extend quite far both above and below the knee. Of course, the shorter the brace is made, the less purchase on the leg it has. This translates into less efficacy in arresting hyperextension and protecting against lateral forcing. (A longer frame means more leverage. Because a longer orthosis has more leverage, the total skin-contact area can be correspondingly reduced.  A too-short brace would not protect adequately against sideways forcing and hyperextension, a brace that covers the entire leg would be uncomfortable.) This means that, for a person of average height, a functional brace's frame must extend about 16 inches. Most functional brace brace frames, both open- and full-framed types, satisfy this requirement. (Many custom braces, for example the Defiance and CTi2, can be ordered as super-short versions; such versions are only appropriate for very small people. Other models, such as the CTi2 and the braces of Townsend Design, can be made shorter or longer by special request.)  People involved in high-impact contact-type sports might wish to request that their knee bracing be made a few inches longer than normal.

The topic of brace shape (and its effect on brace use) also merits consideration. For brace users who expect to be straddling something (for example, a horse or small motorized vehicle), the problem of inside-upper-thigh chafing can be especially acute. Towards this end, some manufacturers (e.g. Townsend) allow special-request modifications to their functional braces. The CTi2's frame design already avoids the inside-upper-thigh region, and thus is already well-suited to equestrian activities. Open-shelled braces such as the Defiance and Townsend Rebel are not amenable to special-request frame-shape modifications.

In order to obtain high strength-to-weight ratios, most braces on the market are made from advanced synthetic materials with some non-corroding metals. The braces of Innovation Sports and Townsend (save for the Rebel series) are made from carbon-fibre and epoxy resins, along with titanium hinges. (Hinge pins are stainless steel.)  Such construction engenders bracing that is not only durable and light, but is resistant to extremely corrosive substances such as seawater.  DonJoy, Flextech/Flexguard, Karl Hager, and Lenox Hill use these materials as well, though in some models combined with various high-strength plastics and aluminum. Omni and EMT also use synthetic composites, as do many other firms. (For increased durability, some braces can be ordered with additional reinforcement, for extra-heavy-duty collision sports.  Townsend and Innovation Sports are the most accommodating of such special requests.)  Amongst all the brace manufacturers, Generation 2 stands out in its parsimonious choice of materials: in using plain high-carbon steel (which rusts); the shell of its old 3-plane model uses polyethylene (which is what food-storage containers are made from), albeit the new Extreme does employ a flexible carbon-fibre composite. (Except for the shell material, the Extreme is identical to the old 3-plane.)

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The Innovation Sports CTi2 and Townsend Air, two of the most common braces, are good examples of full-shell bracing; however, the executions are strikingly different. Let’s take a moment to examine these two models (which I both rank as being top-notch for full-shell bracing). (The Air is a slightly modified version of the Original [which is the brace upon which Jeff Townsend founded his firm]; the only alterations are a tibial-shell hole, a slightly shorter lower shell, and two lower-shell straps instead of three. I consider the two models to be the same.) Both the CTi2 and Air grasp the lower leg very solidly. In the Air, titanium struts extend from the hinges to halfway up and down the upper and lower shells; the carbon-fibre shells are bonded as well as riveted to this. This makes for a strong but heavier-than-average design. The Air envelops the leg from side to side; besides giving this model a somewhat limited ability to accommodate to leg-size changes (although some heating and remoulding is possible), this means that chafing in the inside-upper-thigh region (notable for its soft and easily-irritated tissue) could be a problem. This would make the Air a poor choice for horseback-riders, unless the previously-discussed special modifications are requested.

Meanwhile, the CTi2 employs a lobed frame, with frontal members, combined with upper and lower lateral arms; although still a full-shell design, this model covers slightly less skin than the Air/Original. Here, the titanium hinges are integrated directly into the framing, thus avoiding the need for long metal side struts. The CTi2’s carbon-fibre framing contains a foam core—this gives it a very high strength-to-weight ratio. (The CTi2 is noticeably lighter than the Original/Air. In fact, the CTi2 is the lightest of all full-shell braces; its light weight is very favourably comparable to that of open-shelled braces.) The CTi2's frame is notable for its absence of medial hard components at the uppermost and lowermost extremes; this completely eliminates the potential for chafing in the sensitive inside-upper-thigh region; it also avoids the possibility of the brace frame being contacted by a shoe (on the non-brace-wearing leg) during running. (The CTi2’s design is in fact very effective at restraining bone motion. In the thigh, the femur’s shaft angles sharply towards the outside—right inside the brace.) Additionally, the CTi2’s upper strap incorporates another pragmatic feature: an elastic section which permits the brace to accommodate muscle-activation-induced transient thigh-girth changes. (Incidentally, by avoiding having the uppermost and lowermost edges of the frame extend around the medial sides of the leg, the CTi2's design means that the brace depends on having its top and bottom straps adequately tight for protection against outwards forcing. However, outwards forcing is so extremely rare, whereas inwards forcing is very common. [Consider, for example, that LCL injuries are extremely rare, whereas MCL injuries are very common.])

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It is well-known that the ACL-deficient knee is highly vulnerable to twisting (predominantly inwards rotation of the tibia). Likewise, a knee that is undergoing rehabilitation from ACL reconstruction is also sensitive to twisting. Unfortunately, no brace can guarantee protection against torsion. (The only exception to this occurs when a brace is connected, in a twist-resisting fashion, to an alpine-ski boot. I will discuss this special case later.) The root problem (as mentioned earlier) is that there is simply too much shear in the soft tissues which surround the leg bones. (A secondary factor is that when the lower leg is rotated [i.e. foot is abducted and adducted], the fibula rotates around the tibia.  Other factors include the amount of friction between the skin and the brace lining, and the amount of tenseness [hence firmness] of the leg muscles during the twisting incident.)  However, a brace which can grip the tibial crest (shinbone, at front of leg) has a very slight hope of reducing the degree of twisting (along the longitudinal axis of the tibia), yet only during situations when the knee is flexed. The reason for this is that in these specific cases, the upper half of the brace is prevented from rotating (about the tibia's axis) by impinging on the sides of the thigh—so, as long as the leg is adequately flexed, the brace will have some resistance to rotation (about the tibia's longitudinal axis) because said rotation-inhibition is independent of how well it grips the upper leg. This is good in theory—however, as I found by experimentation, things do not work out quite that nicely in practice.

To get an idea of how braces perform in the realm of twisting, I did simple on-leg twist tests of several popular braces. This involved gently twisting the brace with the knee at various angles, with the upper half unstrapped from the leg. The CTi2 (without the ski-boot attachment) and Townsend Air offered the most resistance to twisting, but only by a slight margin. The observed edge in terms of twist resistance might be expected, given that both the CTi2 and Air both cup the tibial crest very well. (Incidentally, Townsend's Air has a ridge [named an anti-rotation tibial bolster] inside the lower shell [so positioned that it protrudes medially to the tibial shaft], which is intended to confer maximum ability to resist twisting. I was unable to observe any effect from this bolster ridge, even in on-leg testing of a nearly a half-dozen of each of these two models.) The only brace which provided a truly useful twist-arresting capability (herein defined as able to protect against injury) was the ski-boot-attachment-equipped CTi2; however, this is a special case because it applies only to alpine skiing.

The DonJoy Defiance twisted the most. (This is not surprising, given the absence of a solid member around the tibial crest.) Two other models (Omni Avant Garde, Generation 2 3-plane) tested between these extremes. My conclusion is simple: no brace (unless attached to an external device, as a ski boot) can be depended on to provide protection against twisting—and this agrees with what published studies report. (Note: Of course, this experiment's small sample size [minimum five each of CTi2, Air/Original, and Defiance; so far, three each of Omni and Generation 2] means that it could easily be argued that the results are not statistically valid. The testing is only for comparison purposes; it does not have the resolution to provide quantitative measurements. The testing did not involve a sophisticated apparatus; the experiment was not a formal scientific one. [In fact, there has yet to be a definitive and rigorously-thorough study of the effect of all brace models on knee twisting.] All on-leg tests of braces were performed on friends and acquaintances who happen to wear bracing and who were, of course, willing. (It is true that people’s leg shapes vary quite a bit; this too affects how well a brace could hope to control twisting.  I continue to test bracing at every opportunity; the numbers of braces tested continues to accrue. A few other models have been tested less than three times, and thus are not mentioned in this context.)

The rule of thumb that a functional brace cannot inhibit twisting is true in all cases where the device is used in isolation as an externally-mounted orthosis. However, as indicated above, there is one exception: if the brace were connected to external devices, for example an ankle cast that surrounds the foot and a shell that encases the torso, then (depending on the dynamics of the system) said arrangement can indeed have an arresting effect on torsional forces. This is not so far-out as it seems: for example, the CTi2 can be ordered with an alpine-ski-boot attachment which connects the brace directly to the ski boot; this device is effective at preventing the flexed knee from being twisted, as it transfers the torsion directly from brace to boot. When the knee is flexed (e.g. skier's tuck position), the sides of the brace impinge compressively on the sides of the thigh; this ensures that the brace cannot rotate with respect to the tibia's longitudinal axis. This effectively shields the knee from twisting, thus ensuring that the bindings release well before injury occurs. (The protection of the ski-boot attachment is present as long as the knee is at least somewhat flexed; normal alpine skiing provides adequate knee flexion to ensure good effectiveness of such a ski-boot attachment.) Although the CTi2 is still the only brace available with such a device, with a little ingenuity and access to a machine shop it should be possible to contrive a suitable brace-to-boot attachment for any full-shelled knee brace. (A few points to keep in mind: note that correctly-adjusted ski bindings cannot guarantee that the knee will not be twisted; the reason for this is that the binding is unable to detect the torque at the knee [because the torque on said joint depends on the angle at which it is flexed]—in other words, the binding cannot “see” the twisting at the knee. Also note that the CTi2’s ski-boot attachment system is far more effective than any of the heavily-advertised new “knee-friendly” ski boots.) Finally, an important aspect of alpine-skiing injury prevention is training in recognition and avoidance of specific ACL-injury precursors; in said sport, as in most sports, twisting is not the only cause of knee injuries. For more information, visit the injury-prevention section of this forum’s On-Line Knee-Injury Article Library. Alpine skiers should note that although anterior drawer is sometimes cited as a cause of skiing-type ACL injuries, nearly all anterior-drawer-entailing ski injuries also involve twisting…and so the protective benefit of a twist-inhibiting ski-boot attachment is indeed very much desirable.

In addition to the ACL-deficient knee's distinct vulnerability to twisting (as well as sensitivity to hyperextension and sideways forcing), there is also the issue of anterior drawer to consider. The ACL is important in preventing the tibia from sliding forward with respect to the femur. While it is difficult (for reasons mentioned previously) for a brace to stop twisting, it is easy to design a brace to counteract anterior drawer. (Note: the issue of anterior drawer is less of a concern in a knee that has been reconstructed and fully rehabilitated than in a knee that harbours a partly-torn or fully-torn or freshly-reconstructed ACL. With regards to reconstructions, strength [after completion of rehab] is at least as important as tightness.) 

To fulfill the goal of providing anterior-drawer counteraction, an ACL functional brace is designed to force the distal (bottom) end of the femur forwards, while simultaneously pulling rearwards on the tibial tuberosity (the proximal end of the tibia). This anterior-posterior (sagittal-plane) shearing removes some of the loading on the ACL—but of course, it adds loading to the PCL. (Because the PCL is much stronger than the ACL, it is rarely injured. So, additional loading on it is not a problem—unless it too is injured. Of course, for people who have exclusively PCL deficiencies, the brace could be designed to shear in the opposite direction from an ACL brace. People who have both ACL and PCL injuries simply tighten the strapping in such a way that the brace does not exert any anterior-posterior shearing forces.)

In the realm of anterior-posterior shearing for ACL compensation, some brace manufacturers promote their products tirelessly. (DonJoy is particularly notable in having termed its shearing conceptualization “the Four Points of Leverage”. This is cute: it implies that the DonJoy Defiance has some wonderful property which no other brace has. In reality, of course, almost any brace can be made to shear the knee in the sagittal plane. The Defiance is not special in this regard.) With any brace, the amount of sagittal-plane shearing obtained depends on the tightness of the appropriate strapping. (The sagittal plane is parallel to the floor, if you lie on your side.)

The hamstrings, if appropriately activated when the knee is at least partly flexed, can pull the tibia backwards. Because one of the ACL's roles is to prevent the tibia from sliding too far forwards, this means good ACL protection is conferred by strong and appropriately-activated hamstrings.  (The issue of muscle activation depends on proprioception, as discussed earlier.)  However, the biomechanics of the system play a major role here: at increasing extension, the hamstrings become less and less effective at counteracting anterior drawer (and also at arresting hyperextension). This means a fully-extended knee is extremely vulnerable to ACL injury. Interestingly, full extension also happens to be the point at which a brace has the best hope of being able to counteract anterior shearing, if the strap just above the knee is kept very tight. (Of course, for people who have undergone ACL reconstruction and have successfully rehabilitated their knees, the issue of anterior-drawer counteraction is likely to be a moot point. But the importance of strong hamstrings is paramount in any case.)

One manufacturer (Innovation Sports) has tried to take further advantage of this phenomenon by designing an unusual dynamically-activated gadget (for its CTi2 brace). The arrangement comprises a pad which sits just in front of the tibial crest. When the hamstrings are activated, the increased muscle bulk tightens a cable, which in turn pulls rearwards on the aforementioned pad. The only catch is that in order for this system to be really effective, the hamstrings would have to be specially trained (via biofeedback training or otherwise) to fire simultaneously with the quadriceps (and to an extent greater than they normally would in an ACL-compromised knee). For the average user, this ACL-cable device, albeit ingenious, is not likely to make a very significant difference. But for someone with well-developed and appropriately-trained hamstrings, it could confer some protection against anterior-drawer forcing.

Recently, Innovation Sports came out with the XCL system, which uses a crossed pair of behind-the-knee straps for purposes of counteracting ACL-injury-induced anterior-drawer laxity. The XCL system is available on the CTi2 as well as on several off-the-shelf models. The idea is that the action of extending the knee causes the strapping to tighten, thereby pulling the tibial tuberosity backwards while simultaneously pushing the distal end of the femur forwards. The novel aspect of the design is this: the XCL system uses the extension of the knee (powered by the quadriceps group) to help counteract anterior drawer (which is normally counteracted by the hamstring group). Compared to the idea behind the ACL cable, this represents a very different concept: using the quadriceps to assist the hamstrings in protecting the ACL.

Using the leg’s musculature to counteract anterior-drawer movement (also known as subluxation) is technically not difficult to conceive, but it requires thoughtful engineering in order to ensure good execution. The concept of a dynamic brace is not new; Bledsoe has been promoting it for a while now (in its off-the-shelf braces). But the Innovation Sports XCL system is unique in its elegance and simplicity. Bledsoe's concept involves the hinge exerting the force via a shearing motion, this results in serious hinge-alignment problems. Bledsoe’s hinge-shifting design is intended to shift the tibia rearwards as the knee is extended, but the forcing is not applied gradually enough nor there any assurance that it would be applied when it is most needed—in other words, the Bledsoe hinge’s increase in anterior-drawer-counteracting forcing is not synchronized with the user’s knee reaching full extension. Additionally, Bledsoe’s hinge design is based on an invalid assumption of constant torque (at the knee) as the joint extends; in reality, the quadriceps cause a torque that varies with factors such as knee-flexion angle and the amount of weight being borne by the foot. Bledsoe’s system also brings the drawback of not being adjustable—there is no way for the user to fine-tune the hinge to shift at the point in the range of motion where it is most needed. The Bledsoe shifting hinge also brings its own risks: besides engendering considerable friction, if it seizes, it could cause the quadriceps to work very hard [in order to try to get the hinge moving again] and this could cause an ACL-injurious anterior-drawer forcing. Innovation Sports’ XCL system solves these concerns because it applies a gradually-increasing anterior-drawer-counteracting force [and this force will appear at the correct point in the range of motion because the wearer would adjust it to do so]. The XCL system has another advantage: it is nearly impossible for the wearer to incorrectly adjust it; if not correctly adjusted [e.g. if the crossing straps not adequately tightened], then the brace will merely function as if the XCL system had not been installed.) From both the perspectives of engineering design and biomechanics/ergonomics, the Innovation Sports XCL system is far superior to Bledsoe’s hinge-shifting concept.

Another point: the XCL system provides anterior-drawer counteraction specifically during the portion of range of motion (i.e. full extension) in which the hamstrings are biomechanically least able to do anything about it. The hamstrings cannot exert a rearwards force on the distal end of the femur when the knee is at full extension—and thus anterior drawer is most likely to be a problem at full extension.  So, it indeed makes sense to devise the anterior-drawer-counteracting mechanism in such a way that it functions maximally at full extension.  Additionally, the XCL system serves to limit extension (and it does this more gently than the abrupt stop of the brace’s standard hinge-based extension-blocking feature).  Again, this makes sense because at full extension, the hamstrings are least able to prevent further extension.

The XCL system is intended primarily for people who are fully ACL deficient but have not had reconstructive surgery—in other words, people who are undergoing conservative treatment for full ACL tearing. The XCL system would not be as beneficial for people who have already had ACL reconstruction. (After all, modern ACL reconstructions are much tighter than they were in the past. And besides, anterior-drawer counteraction capabilities of any brace are limited by the fact that the posterior of the femur's distal end is surrounded by soft tissue. In other words, although it is easy to exert a rearwards force on the tibial tuberosity, it is not so easy to exert the necessary forwards force just above the back of the knee.) However, for some people, the XCL option might be helpful during the initial rehab phases of ACL reconstruction. Actually, in the context of rehab, the XCL system brings another advantage: because it makes demands on the quadriceps, it would help with development of stronger quadriceps muscles. This is a distinct benefit, because people with freshly-reconstructed ACLs often tend to walk with knees too straight, due in part to surgery-induced atrophy of the leg muscles. By walking with the knees extended, less demands are placed on the quadriceps (think how tiring it would be to walk with knees deeply flexed: the quads would tire very quickly).  But such stilt-legged walking leaves the knee vulnerable to insults such as injury via hyperextension; however, the XCL-strapping system, if adjusted so that it tightens as full extension is approached, would prevent this from becoming a problem.  The fully-extended position also places the knee at greater risk for injury via sideways forcing.  (At full extension, the lever arm formed by the tibia and femur are positioned in such a way as to make the knee most vulnerable to these modes of forcing.  However, the brace-wearing itself, in reliably protecting the knee against sideways forcing and hyperextension, would take care of this concern. (The XCL option is something which one can try out and easily remove if desired. Simply removing the crossing straps converts the brace back to a normal one.  The CTi2’s XCL-strap and ACL-cable systems cannot be used simultaneously, only one can be used at any given time.  However, it is possible to specially request the brace to be equipped with both options [but make sure that said request is clearly indicated on the requisition form], and then to try each out separately.)

I have always maintained that functional knee bracing should only be depended on for protection from lateral forcing and hyperextension (except for the aforementioned ski-boot-attachment case). In my own experience, such situations frequently occur in contact-containing sports. On numerous occasions, my braced knees have taken violent impacts from the side. Opposing players have fallen on my outstretched legs. I have fallen into holes on geological field trips. (Imagine a knee giving out while on a field trip in the middle of nowhere, and with attainment of the nearest vestige of civilisation requiring a substantial trek.) I have found functional bracing to be of great value in situations where the knee can be forced into hyperextension or impacted from the side.

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The major benefit of bracing is, of course, reduction in likelihood of knee failure—irrespective of whether said giving-way occurs as a consequence of the ACL having been torn previously, or as a consequence of tearing an ACL graft. (As we have already discussed, hyperextension and side impacts are where a brace is of greatest value.) Besides the issues related to safety and inconvenience, there is the issue of cartilage damage to consider. Because each episode of knee collapse (whether occurring in conjunction with ACL tearing or subsequent to it) tends to bring meniscal tearing and/or erosion as well as osteochondral (bone-cartilage-interface) damage (and perhaps damage to other ligaments and structures too), it is important that the knee be kept stable. All types of cartilage damage are harbingers of arthritis. (This, along with the close interdependency of the knee’s componentry, explains why in cases where the ACLless knee is grossly unstable, ACL reconstruction is so often indicated.)

The baneful spectre of osteoarthritis is reason enough to do everything possible to ensure that a knee which harbours any ligament-injury history is never re-injured. Unfortunately, the knee’s status as most-vulnerable-to-serious-injury joint ensures the permanence of cartilage-related damage. The reconstructed-and-rehabilitated knee is not immune to eventual degeneration (due to the osteochondral damage which nearly always accompanies ACL tearing). Furthermore, if a reconstructed-and-rehabilitated knee goes through additional ACL-tearing-and-reconstruction cycles, degeneration occurs much more rapidly. This, combined the well-known fact that revision ACL reconstructions tend to have a lower success rate than first-time reconstructions, should provide sufficient motivation to protect the knee.

In cases where a partial tear has left the knee stable, functional bracing provides much-needed protection against certain modes of forcing. (This describes my own situation: partial tearing in both knees.) In cases where the ACL has been reconstructed, a brace protects against re-injury via non-twisting means (and in the aforementioned special case, twisting too); such protection is particularly helpful during the early phases of rehabilitation. In cases where the knee is left completely ACL-less forever, the brace still provides tangible benefits, although it obviously cannot replicate the missing ligament function. But in any case, if the knee is kept stable, then the risk of cartilage damage (both meniscal and articular) is minimized. (Note that direct compression of the knee, as might occur when jumping with a locked knee, is one way in which cartilage damage can occur without a lot of violent twisting. In this case, however, ligament damage could still be likely. This is one example of a situation where no protection is conferred without proper technique.) Also note that, for reconstructed ACLs, stretching (as opposed to partial tearing) tends to be the more-common incomplete-ACL-damage injury, whereas for natural ACLs, partial tearing seems to be more common than stretching. (Another point: nearly all of the body’s soft tissues, ligaments included, are viscoelastic. This means they are elastic if rapidly stressed [but not to the point of full rupture], yet can be stretched out if the force if applied over time. [This explains why effective stretching of musculature is best done slowly, without bouncing.] In engineering terminology, elastic modulus increases slightly with strain rate.)

In the human knee, the cruciate ligaments are only supplied with blood from one end. This alone makes healing very difficult. Furthermore, consider the enormous moment-arm forces and dynamic loadings that a knee must contend with—and it is not surprising that torn cruciate-ligament fibres do not regain their lost tensile strength. (In the usual best case, they merely fill in with scar tissue.) This, of course, means that a serious partial ACL tear is unable to heal on its own. If the knee's stability has been retained (as in my own situation), then it is sometimes possible to get by without surgical reconstruction; however, the weakened knee’s vulnerability demands careful management as well as good protection.

If a brace is to be used on a still-stable knee which harbours partially-torn cruciate ligaments, then it should be selected with careful consideration for long-term use (i.e. not just durability, but also adaptability to leg-size changes). Although the permanently-increased vulnerability of any ligament-injury-history knee makes indefinite wearing of a brace (during knee-strenuous-activities) worthwhile, some ACL-reconstruction patients find themselves desirous of discontinuance of brace-wearing once a certain temporal milestone has been reached. In any case, a brace design shows that thought has been given to long-term use is very much desirable. (Of course, easily swapped pads and simple-to-replace strapping facilitate maintenance and well as fine-tuning of fit.) With many carbon-fibre-and-resin braces, minor leg-size changes can be field-accommodated by the clinician. Usually, parts can be heated (with a heat gun) and, using appropriate jigs and clamps, carefully reformed. Long-term brace use also makes lifetime frame-and-hinge warranties an absolute must.

The CTi2, despite having an appearance that some consider imposing and bulky, again provides an interesting case study in overall well-thought-out design. This model’s lobed design is very efficient, given that its upper shell closely cups the femur [which runs from the knee outwards to the hip region], while its lower shell provides maximum contact with the bony tibial crest.  The CTi2 is one model which, albeit being fully-custom made and having a very rigid frame, is quite amenable to adapting to leg-girth changes. The CTi2's design is such that at the points where the muscles are thickest (and hence where any possible size changes over time will be greatest) the brace only encircles about one-third of the leg—and this is on the lateral/frontal aspect. Of course, major muscle-size changes would indeed affect fit. (For the clinician, this model brings the advantage in that it is convenient to modify focally, i.e. without affecting parts which are not to be modified.) Of course, with any brace design, very great leg-size changes would require the appliance to be sent back to the factory for modifications or refabrication.

(For continuation, please see part 3, below.)

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Functional Bracing — A General Overview (part 3/3)

(Part 3 of 3)

As some manufacturers emphasize in their literature, the standard bane of brace-wearers is migration. Migration is a gradual distal (i.e. towards the foot) movement of the appliance, most often as a consequence of running and jumping. (The harder the foot slams into the ground, the greater the likelihood of migration. I’ll delve into this shortly.)

For a truly-custom-made brace, the cause of brace migration will either be a poorly-fitted brace of improper wearing procedure (or both); however, some designs (discussed elsewhere) will tend to be more prone to migration than others. Generally, the single-most-important criterion is that the strap immediately below the knee be tightest. (With use, the strapping's Velcro fastener begins to wear; the resulting migration can be solved merely by replacing the strap.) It should be noted that the solution is not simply one of having all straps maximally tight; besides being uncomfortable, this would make the distally-tapered thigh force the brace downwards with each activation of the thigh musculature (thus resulting in the brace working its way down the leg).

However, if the frame's shape is not quite right, then migration can occur as well. Here, the topic of fit is paramount; close fit is important in the tibial-crest region. (This is why a fully-custom-made brace will always have far less likelihood of migration problems than will an off-the-shelf brace. (My own braces have never given me migration problems.) Curiously, some braces have been promoted as being guaranteed not to slip down the patient's leg. Most notable among these is the Townsend Premier (but not the Air which, because of its considerable weight, would tend to be more prone to migration).

The issue of brace weight is not a trivial one. Each time the brace-wearing leg hits the ground (especially while running) the brace must be decelerated. (Conversely, each time the foot is lifted, the brace must be accelerated upwards.) Therefore, the inertia of the brace must be taken into account. Inertia is defined in physics as a body’s desire to stay at rest or in uniform motion. Inertia increases with mass. So, we can easily see that adding weight to a brace makes it more prone to migration. Because lighter braces are less likely to migrate anyway, a “no-migration guarantee” means more if it applies to a heavier brace. The ideal brace combines the advantage of a full-shell design with the lightest possible construction.

I suppose a discussion of brace weight (or more technically, mass) would not be complete without data on the various models.  I have been weighing braces (using a kitchen scale) at every opportunity.  Custom-made braces, by virtue of their handcrafting, tend to vary slightly in mass; additionally, the influence of brace size must be taken into account.  The heaviest braces are those of Breg (all-aluminum); however, all of Breg’s braces (including those sold as “custom”) actually fall into the off-the-shelf category.  The Generation 2 Extreme and 3-plane are also rather heavy.  Townsend’s Original model is next-heaviest.  The Townsend Premier and CTi2 are indistinguishable weight-wise.  The DonJoy Defiance is lightest, but only by a small margin (a few tens of grams, compared to the CTi2…the difference is unlikely to be noticeable to the user).  How much a brace feels like it weighs depends on its design (open versus full-shell) and fit, both of which directly influences how the orthosis behaves on the leg.  Because the CTi2’s full-shell design makes for a more intimate (and hence comfortable) fit, I would not be surprised if the Defiance were to feel heavier.  (An interesting sidenote: the Defiance’s frame is not strong enough to support someone standing on the frame in such a way as to force the hinges together.  In contrast, the CTi2’s markedly-stronger frame can easily support someone standing on the brace in this fashion.  Townsend’s Original is strong enough to support such crushing-type abuse.)

Besides migration, one other common concern about functional bracing is its effect on intensely-demanding activities. All functional braces have straps which encircle the rear of the leg. The strapping in the knee region will tend to cause some inhibition of flexion—this will occur with all braces. This means that squatting (fully) while wearing bracing is infeasible. However, the amount of flexion permitted by bracing is wholly adequate for participation in jumping-type sports. The amount of flexion impingement caused by functional braces does not vary appreciably between models.

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Townsend makes its braces with an unusual feature: the strap just below (and behind) the knee is riveted either to the inside of the frame, or is wrapped around the front and riveted there (depending on the model). This allows said strap to cup as much of the leg as possible, thus compressing the soft tissue as uniformly as possible (thereby helping to preserve the limb's cross-section during brace-wearing). Unfortunately, this design has a drawback: it means that, in all of Townsend's braces, the strap immediately below the knee is riveted to the frame. This means that the user is obligated to return the entire brace to the factory each time said strap wears out. (Since the requirement of gastrocnemius-muscle suspension means that the strap just below the knee is the one that must be tightest, this strap tends to wear out fastest. With Townsend’s braces, this problem is exacerbated by having this strap only 1 inch wide, instead of 1.5 inches wide. This concern would be greatest with the heaviest model [Air] because there is more weight to suspend.) With the Air/Ultra Air models, all straps (except for the one immediately below the knee) are user-replaceable; with the Premier, all straps are riveted directly to the frame. Anyone contemplating the Premier for long-term wearing might wish to consider its sister model, the Ultra Air, instead. (For the Air/Ultra Air, it is possible to request loops, or chafes, to be installed for both sides of the just-below-the-knee strap, thus making all of these models' straps user-replaceable—something which I think should be a standard feature to begin with.) Because straps are a wear-and-tear item, it is pointless not to make them user-replaceable.

Townsend’s Premier also has another drawback (albeit not a major one). Although this model is very light and strong, it is nearly impossible to heat and reshape. (This is due to its type of foamcore construction.) The Ultra Air, meanwhile, has a solid-core graphite construction, which means that although it will be heavier, it will also be amenable to heating and remoudling.

Incidentally, the now-no-longer-made OrthoTech Performer had also been promoted as guaranteed not to migrate.  It is mentioned here only to illustrate contrast in design.  (Had it not been discontinued, the Performer would have benefited from natural-motion hinging.) The Performer had an unusual feature: a “supra-patellar suspension strap”, which if overtightened caused the brace to ride on the user’s kneecap and thus tended to force the patella downwards. In the long term, this could theoretically have caused patellar-tracking problems.  The Performer had a removable gastrocnemial force plate which (if used) compressed the calf muscle into the brace's lower shell. (Incidentally, the CTi2 PCL/combined-instability model has a similar gastrocnemial force-plate, albeit for a different reason.)

I maintain that any, suitably-selected, well-fitted and properly-worn custom-made functional brace will not shift on the leg. (For people who have really thin legs—and particularly those who have very little calf-muscle definition—a custom-made brace is always a better choice than an off-the-shelf brace. People who have large thighs and small calves are also best-served by custom bracing, as are those whose legs are in any way unusual in shape. With some braces, such as the CTi2, the aforementioned gastrocnemial force plate is available upon request; said plate is helpful for thin-legged people.)

Townsend's Air model (and also the Original variant and Ultra Air model), formerly only available with a dirt-ingression-prone slot-cam hinge, can now be ordered with a four-bar-linkage-type hinge (which is mechanically similar to that of the CTi2). (Both slot-cam and linkage-type hinges have anatomically-correct motion, although in the former the sliding surfaces are alternatingly covered and uncovered. The linkage-type hinge will provide a smoother movement, as well as much better resistance to dirt-caused wear.) Note that on the Air/Original model, the thin shell linings mean that the relative hinge protrusion is still quite noticeable (even though hinge-unit thickness is no greater than that of other braces).

The Defiance's fundamentally biomechanically-poor design has already been discussed. However, its frame design brings further disadvantages. Being the only brace which has its lower member traversing the rear of the calf, it is the only brace which requires the wearer to remove footwear for brace donning and doffing. A more significant concern is this design's glaring incompatibility with alpine ski boots: it tends to cause chafing of skin. (Although a short-calf version is available, keep in mind that the shorter the brace is, the less protection against hyperextension (and also, sideways forcing) it can confer.)

Lenox Hill produces two custom-made braces. One happens to be the oldest design in the realm of functional knee bracing, and is known as the LH1 Derotation brace. (The term “derotation” is a trademark of this firm.) The LH1 brace is anachronistic and ungainly in appearance, and consists of little more than straps and metal struts; curiously, it is still made. (With little in the way of a shell, the LH1 will not be very effective at preventing hyperextension or sideways forcing.) The newest model is the made-from-cast Avenger Custom (a successor to the LH2 Custom 2); although an improvement (and heavily marketed), it still leaves a few things to be desired.

With regards to the traditional open-shell-versus-full-shell design, the Avenger falls into a bit of a grey area, although I still consider this model to be open-shelled. The reason for this has to do with the lower-shell design: two horizontal members, albeit only the lower one connects the two upright struts. The upper-tibial-crest section (which Lenox Hill calls a “T-bar”) extends from the medial side almost to the lateral side—with nothing but a strap connecting it to the lateral member. Fine-tuning the fit in the difficult-to-fit tibial-crest area thus requires flexing this part of the lower frame (which could otherwise be made to be more rigid, as well as stronger). The major problem with this design is that the amount of sagittal-plane movement (of said T-bar) varies with location from the medial side. In other words, if the user desires more room on the medial side (say, 3 mm) and less on the lateral side (say, only 1 mm) of the upper tibial crest, this cannot be easily accommodated. This issue is important, because this region will experience maximal compression from the brace (as a requirement of brace anchorage); also, this region might be home to surgical hardware (or, in the case of patellar-graft ACL reconstructions) donor-site soreness. Another point of concern: the Avenger's frame, despite being made of “prepreg” (i.e. sheets that arrive pre-impregnated with resin) carbon-fibre material, is not amenable to heating and reshaping—as can be done with many other carbon-fibre-based shells. This means that any changes to the brace's frame (even those needed as a consequence of muscle-size changes) always require the appliance to sent back to the manufacturer.

Another problem with the Avenger is that the strap just below the knee is rather narrow. Because this strap is the one which is responsible for anchoring the brace (i.e. the brace sits on the gastrocnemius muscle), it would be most comfortable if its width were 1.5 inches. (This comment also applies to several other braces, as noted earlier.)

The Avenger uses a four-bar linkage-type hinge which promises an anatomically-correct motion; however, I note that Lenox Hill's incarnation of the four-bar hinge includes a pin which slides in a slot, and thus is vulnerable to dirt ingress. (Any hinge which contains sliding parts which are alternatingly covered and uncovered [as opposed to being continually in contact], is prone to wear problems.) Furthermore, the Avenger’s overall design is not very sophisticated: because the brace is made of prepreg carbon-fibre, there is no hand-layup involved...in contrast to what is done with true high-end custom-made braces.  Construction-wise, the Avenger is thus somewhat comparable to the C180, an off-the-shelf hardshell brace that is the most basic of the products made by Innovation Sports.

I think the Avenger, despite being an improvement on the Custom 2, is still not an optimized design. Also, given that it is a new model (and thus has no track record), I would suggest going with a proven and well-refined model (such as a custom brace from Townsend or Innovation Sports [or OrthoTech, if it were not to have been bought out]). However, the Avenger's design is better than the designs of Generation 2 and DonJoy.

A few final points: the Avenger only comes with a five-year frame-and-hinge warranty. Given that most custom-made functional braces come with lifetime warranties, this alone constitutes a serious shortcoming. Another point of concern is that the Avenger does not come with a free-refit period. The Avenger is simply made according to the submitted cast. This means that if any error occurs, or if the patient's leg changes shape (due perhaps to rehab), then the patient is responsible for costs (which, given that the Avenger uses a type of carbon-fibre material that is not designed to be amenable to heating and reshaping, could mean purchasing an entirely new brace altogether). Considering that most manufacturers provide free-refit warranties (ranging from Innovation Sports' one year to DonJoy’s four months), Lenox Hill's refusal to provide any type of free-refit period is indeed disheartening.

The Flextech/Flexguard F1 is another carbon-fibre brace. It is custom-built on a cast-mould positive, using pre-preg carbon fibre material (like the Avenger). In some ways, the F1 is somewhat comparable to Townsend's Air/Original model (and is full-shell as well). Due to its similar construction, I would expect the F1 to weigh roughly as much as the Air/Original. The F1 claims to have a natural-motion hinge; I'll discuss my concerns subsequently. The F1, like the Air/Original, has significant hinge protrusion with respect to frame, and thus is not a good choice for bilateral wear. And, like the Air/Original, the F1 also has upper members which extend into the fleshy inside-upper-thigh area; this could result in some discomfort to the wearer. The F1's outward appearance has changed slighly, as a consequence of the Flextech firm having been bought out by Tennessee-based DeRoyal. The original F1 had some oddities, for example its small above-the-knee protrusions, which (by compressing at the bottom of the quadriceps) were supposed to ensure that the brace would not migrate. In practice, of course, these protrusions tended to interfere with the optimal functioning of the quadriceps, and often caused discomfort as well. The new F1 still has these upper-shell-interior protrusions, albeit they are now known as "positive lock supracondylar pads". For both the old and new versions of the F1, the main source of suspension was, and still is (like nearly all braces), via the gastrocnemius.

The upper-shell design of the Flextech/Flexguard F1 brings another drawback as well: it makes it difficult for the strap above (and behind) the knee to reliably exert a forwards, anterior-drawer-counteracting force. This is a source of concern for the majority of knee-brace users who have ACL injuries. Meanwhile, the F1's hinge is inherently somewhat primitive, as it is basically a modified version of the crude geared-polycentric hinge that is found on DonJoy, Breg, and Omni braces. The F1 hinge uses radially asymmetric gears. It cannot mimic the roll-and-glide motion of the knee quite as accurately as do the hinges of Townsend or Innovation Sports, but it is better than a plain geared-polycentric hinge. However, the major long-term concern with the F1 hinge is the same as with other geared polycentric hinges: a rather high risk of mechanical failure, due both to the grinding action of dirt in the gears and the alternating covering/uncovering of metallic parts during the hinge-motion cycle. Anyone contemplating purchasing this brace should insist upon a lifetime warranty against all possible types of hinge failure. Otherwise, the user must be extremely careful not to allow dirt to enter the hinges.

Because of the relative rarity of Flextech/Flexguard braces, I have yet to have the opportunity to examine an F1 (either the old or the new version) first-hand, and thus I am not able to evaluate it as rigorously as I would like. But if I were forced to choose only between the F1 and the Townsend Air/Original, I would choose the latter.

Karl Hager, a Canadian firm, carries two custom-made (both from cast) models which are worth mentioning. The older model is the Double X (which, from the front, looks like two crosses stacked vertically). This brace has one drawback: a very short lever arm in the sagittal plane. Hyperextension protection will thus not be as good as with other designs. The newer open-framed Accelerator solves this problem (but with the aforementioned drawbacks of open-shelled bracing); this brace's frame shape is not overly different from the Townsend Premier. Karl Hager's products would be much improved by the inclusion of hinges with anatomically-correct motion.

It seems that the modern functional knee brace is a North American product, since it is hard to find such braces made overseas. One German firm, Biedermann (well-known in prosthetics), has a model which is now fabricated under license by the American firm Montana Medical Brace. This full-shelled carbon-fibre brace is known as the Ultratech; it has anatomically-correct hinges and appears quite adequate. However, the frame design, combined with very thin members, makes this brace unsuited to contact sports. Also, the Ultratech exhibits considerable protrusion of hinges with respect to frame. I do not have enough information on this model to enable a more-profound evaluation.  (A British firm, Doyle International, does make knee bracing, yet only of the off-the-shelf variety.)

Thus far, the functional knee braces I have discussed in detail are truly custom-made. I wish to point out two firms (Breg and Bledsoe) which produce knee braces which are fundamentally off-the-shelf, yet which are often promoted as being custom-made (as mentioned earlier). (I find it disturbing that these firms can command the same amount of money for their pseudo-custom braces as do the manufacturers of true custom braces.) Furthermore, there are serious drawbacks with the underlying designs of the functional braces of these two firms; I will take the following two paragraphs to review these points briefly. (The following two paragraphs can be skipped without loss of continuity of this document.)

Breg produces the Tradition/X2K, an aluminum-framed off-the-shelf brace with two geared polycentric hinges. Said brace is available in a “custom” version. However, being made from only four measurements, this brace is far from custom-made. (A “Tradition/X2K Custom” is thus just a custom-bent off-the-shelf Tradition/X2K.) Secondly, the Tradition/X2K's cage-like design means that the appliance contacts the skin in only a few areas; this makes brace discomfort likely. Said cage-like design reduces the brace’s protective capabilities, and also makes for a bulky, unwieldy-looking appliance. Thirdly, the Tradition/X2K's knee-region straps (i.e. one strap just above the knee, another strap just below the knee) depend on single screws for their anchorage in the frame—this means the Tradition/X2K will not fit closely; also, its ability to arrest hyperextension (as well as counteract anterior drawer) would be lost if any one of said small screws comes out or otherwise fails. This design aspect (combined with the pin-hinge motion) also makes the Tradition/X2K prone to migration problems. The Breg Tradition/X2K (whether in off-the-shelf or custom guise) constitutes a marginal design, and is superseded by quite a few other braces. (Being made of stamped aluminum, the Tradition/X2K costs much less to fabricate than a hand-laid-up carbon-fibre brace such as from Townsend or Innovation Sports.)

Bledsoe produces several off-the-shelf knee braces, some of which are labelled “semi-custom”. (These models are bent as required, based on a mere half-dozen measurements.) Bledsoe's ACL brace is unremarkable except for one feature: a lever-and-hinge assembly which is designed to exert an anterior shearing force on the knee as a consequence of the brace being extended. Bledsoe promotes this as being superior to simply tightening the strap (in any other brace) immediately above and behind the knee. This reveals a fundamental reasoning flaw, because it neglects several important points, the most prominent of which are as follows: a brace's ability to counteract anterior drawer depends on the strap above-and-behind the knee being extremely tight (to the extent that it could affect biomechanical efficiency, as discussed earlier), and secondly, it ignores the basic fact that Bledsoe's hinge design is in any case no better than merely tightening the strap just above the knee (because a brace's ability to counteract anterior drawer is only significant at full and near-full extension). Another problem is that the hinge's motion will tend to cause the entire hinge body to move forward with respect to the knee axis; this shifting will engender discomfort. As if this were not troublesome enough, it should also be remembered that the hinge’s exertion of shearing is not free. The effort to operate the hinge-lever mechanism comes from the extensors, i.e. quadriceps muscles; this neglects the hamstrings, which are what should be doing the anterior-drawer-forcing counteraction in any case (but which are, because of biomechanical disadvantage [as discussed earlier], rather ineffective at doing so at full extension). By making the quadriceps contract more forcefully (at and near full extension) than would otherwise be necessary, the Bledsoe hinge could cause increases in anterior-drawer forcing—and thus could cause more (instead of less) strain on the ACL. This means that the purported benefits (which Bledsoe heavily promotes) are likely to be completely cancelled out. So, Bledsoe’s hinge design is no better than a simple pin hinge. Finally, the user can expect to find the Bledsoe hinge annoying—if not initially, then later on when its highly-stressed design begins to fail mechanically. (The one-year frame-and-hinge warranty, one of the shortest for any hardshell functional brace, is further cause for concern; it calls the hinge's mechanical durability into question.) Bledsoe's knee bracing, at best, qualifies as mediocre.

The world of functional knee bracing also includes a brace design which is a carry-over from the world of osteoarthritis bracing (in which the goal is to force the knee sideways): this design is from the firm Generation 2. Said firm steadfastly limits itself to single-hinge-and-strap designs, thus producing ligament bracing which tends to force the knee sideways. The Generation 2 Extreme (successor to the 3-plane), is notable for its hinge (which is designed to force the tibia inwards as the knee is flexed) and its Dynamic Force Strap (which, as its name implies, is designed to force the knee outwards as the joint approaches entension). In the Extreme ACL brace, if said spiralling strap is overtightened, it will force the knee outwards at extension, thus stressing the LCL. (In the normal knee, the tibia does rotate slightly inwards as the knee flexes; this inwards rotation is very slight—nowhere near the exaggerated inwards rotation of the Generation 2 hinge.)  The design also means the brace will tend to twist on the leg—thus making this orthosis very likely to be uncomfortable.  And, the Generation 2 design is also likely to cause chafing and binding; this, however, will depend on individual anatomical variations. Use of the single-hinge-and-strap design should be reserved for unicompartmental osteoarthritis.

In addition to the above drawbacks, Generation 2's single-hinge design is very weak from the point of view of lateral forcing. It is the quintessential example of poorly-applied engineering-design principles. (One more point: Generation 2 uses very flexible shells; these are promoted as being better able to adjust to leg-girth changes than are rigid dual-hinged brace frames. However, in discussions with people who have long-term experience with Generation 2's braces, it became clear that this firm's braces do not have any particularly good ability to adapt to leg-size changes. A correctly-fitted rigid-frame custom-made brace does not require frame-flexing to compensate for poor fitting. In other words, flexible brace-shell designs should be reserved for the world of off-the-shelf braces.)

With nearly all knee braces, the standard skin-interface (lining) material is made of a textured neoprene (chloroprene) rubber. The neoprene is durable and comfortable for most people; however, some people are allergic to it. Towards this end, manufacturers have alternative liners. The Townsend Premier, for example, comes with a suede liner. Townsend's Custom Design braces can be ordered with an Aliplast or suede liner. The DonJoy Defiance comes with a synthetic fabric-like lining. The CTi2 can be ordered with an ethylvinylacetate foam (known as Evazote) lining. Also, all braces can be worn with a thin undersleeve (which is sometimes referrred to as an “over/undergarment”); however, the use of such undersleeves can make certain models more prone to migrating.  It should be remembered that braces are not designed to be worn on top of clothing. Manufacturers also provide sundry accessories (e.g. patella cups, hinge guards) to protect the brace (and other people) during contact sports and impact situations; fully-padded oversleeves (which have the drawback of making the orthosis sweaty) are available for use in sports leagues which regulate use of orthoses.

Note that in the context of the ACL-injury-history knee, the inside condyle pad of the brace is specifically responsible for constraining inwards movement.  Because ACL-problem-related giving-way generally involves a combination of twisting and inwards movement, a close fit of the medial condyle pad could save a lot of grief.  (It is usually most comfortable to have snug fit at both the medial and lateral condyle pads.)  I suggest that, upon receipt of a functional brace equipped with interchangeable condylar padding, the various combinations of pads be tested, and those yielding a close but comfortable fit be employed.  (Note that different thickness of condyle pads can be used at the medial and lateral hinges.)

Some braces (e.g. Defiance, CTi2) are available with cup-shaped pneumatic (or padded) condyle pads; these might provide additional comfort for some people. Nearly all braces have standard flat condyle pads which can easily be interchanged (thus allowing the wearer to experiment and choose what is most comfortable).  Some (e.g. Townsend Air/Original) can be ordered both with or without condyle padding. (If ordered without such padding, then the hinges are placed closer to the knee; this makes future addition of condyle pads infeasible.  Because Townsend’s brace hinges protrude greatly with respect to the frame, the decision on whether or not to get condyle pads in a Townsendian brace must take into account that wearer’s knee-to-knee clearance during normal gait and whether or not said person is knock-kneed.  It also means that anyone contemplating choosing a Townsend brace would have to choose between having to deal with massively-protruding hinges, or having to live without the aforementioned protective advantage offered specifically by a snug-fitting medial condyle pad.) 

For aesthetically-minded folks, knee-brace shells can often be ordered with custom colouring. The Flextech/Flexguard F1 and Townsend's Custom Design Series braces are two examples of braces which can be inlaid with any patterned fabric. The CTi2 can be ordered with a custom paint job, as desired. All painted braces are available in a wide range of colours.

Hinge protrusion (with respect to the brace frame) is an important consideration for people whose knees are close together (e.g. knock-kneed, or genu valgum) or for people who must wear two braces (such as myself), or who tend to walk with legs close together. The hinges of Townsend and Omni tend to have large protrusions. (Townsend, despite having modified its hinge designs, still has enormous hinge protrusions.) The CTi2 and Defiance are examples of braces whose hinges do not protrude significantly with respect to the frame. This makes these models well-suited to bilateral use.

Athletes are often concerned about how a functional brace will integrate with their favourite sport.  Hockey and soccer players, for example, would be concerned about a brace interfering with their shinpads.  Being both a hockey player and a soccer player, I have found that my two CTi2s can be worn with protective padding (although it was necessary to lengthen the soccer-shinpad straps).  People whose sports entail straddling any object (e.g. snowmobile, motorcycle) or animal (horse) should keep in mind that a brace which does not have hard portions in the inside-upper-thigh region is most suitable.

All functional knee brace hinges can be set so that they limit extension.  By setting the hinges so that they stop at point which corresponds to the knee’s maximum safe extension, the knee is protected against hyperextension-type injury.  (On many occasions, this feature has spared me a lot of grief.) Because hyperextension is a major cause of ACL injury/re-injury, it behooves the user to ensure that the brace’s extension-blocking device is set correctly.

As is already known, the ACL-deficient knee is most vulnerable to twisting. Because this is exactly the mode of forcing that a brace is of least utility in protecting against, it is imperative that the ACL-deficient knee be protected (as well as is biomechanically possible, as discussed earlier) by strong leg muscles. (Maximum strength is important, but equally essential is stamina.) Diligently-maintained hamstrings and quadriceps muscles are essential in protecting the knee's cruciate ligaments—and particularly during acceleration/deceleration manoeuvres. Additionally, balanced muscle capacity is important. The hamstrings should have about two-thirds the strength of the quadriceps. (This point applies especially to females, who tend to have weak hamstrings. In any case, quadriceps tend to be strong because of their role in postural maintenance.) Since fatigue tends to increase injury risk, strength training should focus on endurance. (In cases where the ligament has been reconstructed, single-leg exercises become important indefinitely; it seems that a side-effect of the surgery is that the muscles develop a lasting proneness to atrophy.)

For ACL-reconstructed knees, optimal return to competitive sports requires specific proprioceptive training. And, for jumping-type sports, proper jumping technique (e.g. with legs well-flexed upon landing) is indispensable. (This is particularly essential for women, who tend to land with inadequate knee flexion. Other reasons female athletes are more likely than males to tear their ACLs include sharply valgus knees [due to wider pelvis], loose joints [hence more dependence upon ligaments for stability], narrow intercondylar notches [thus leading to the ACL being guillotined; this explains why notch-widening is a standard adjunct to ACL reconstruction], ligament-weakening [due predominantly to estrogen] at certain points in the menstrual cycle, possible vestibular-system-related predispositions to balance loss, and a greater likelihood to be playing competitive sports with players of wide age [hence physical-size] range. For further information, a good paper to read is Hewett et al., AJSM, Nov/Dec 1999.  This article can be found on this board’s On-Line Knee-Injury-Article Library. For female-athlete knee-injury prevention training programs, an excellent website to visit is www.sportsmetrics.net).

Other knee-protective strategies for athletes (especially in plant-and-twist-type team sports) involve pivoting only on the ball of the foot (instead of planting the entire shoe sole and twisting suddenly), keeping one’s knees as bent as possible, and reconsidering the use of deeply-cleated shoes (particularly when playing on artificial turf).  One suggestion is to look for shoes which have a larger number of smaller cleats.  Some manufacturers have devised shoes with small cleats arranged in a circular pattern, as well as with the cleats being shaped so as to enable the shoe to twist relatively easily in the grass (hence protecting the knee).  Such designs reconcile the need to protect the human body’s most vulnerable joint with that of providing the maximum grip on often-slippery turf. 

The use of functional knee bracing often raises the question of use of ankle bracing.  Please note that ankle braces are fundamentally different from knee braces, as the former work by restricting the range of motion (given that the ankle is designed as a swivel), while the latter do not impede normal motion (given that the knee merely flexes and extends, with only a very slight rotation as part of the screw-home mechanism that locks the knee when standing). Volleyball and basketball players, who often wear ankle braces prophylactically, should note that ankle bracing can increase the risk of knee injury—by stiffening the ankle, these devices can force the knee to compensate for the degrees of freedom removed from the ankle.  (This depends somewhat on the type of ankle brace; detailed discussion is beyond the scope of the current document.)  More significantly, by preventing the ankle from inverting or everting, the player (if he/she lands partially on a fellow player’s shoe) could trade an ankle injury for a knee injury (the braced ankle, rendered unable to deal with even a normal amount of inversion or eversion, results in the player losing balance and possibly injuring a knee).  And finally, because certain ankle braces place a hard piece of plastic underneath the sole, the shock-absorption ability of the shoe (something which shoe manufacturers have worked very hard to develop) can be lost…with potentially harmful consequences.

Foot orthotics have also proven themselves helpful with regards to preventing knee injuries, most notably in female athletes.  It seems that the athletes who tend to exhibit inwards rolling of the knees benefit most in this regard—henceforth the orthotics, by addressing the arch foot-collapsing which apparently occurs concomitantly with the inwards knee rolling, prevent the valgus movement of the knee upon jump-landing.  (Of course, foot orthotics are not a cure-all; furthermore, they must be used with understanding of the underlying biomechanical principles and implications.  Also, the type of orthotic is important: for example, a hard-plate-type orthotic will enable the arch to flex [which it must do in order to absorb shock], but if the hard portion extends under the calcaneus [heelbone], the shoe’s heel-shock-absorption capabilities can again be nullified.)  To be truly beneficial, foot orthotics must be prescribed by a doctor specializing in feet, and must be custom-made.

Another useful knee-injury-prevention technique, often used by alpine skiers in order to facilitate turning, involves preceding cutting movements with either a slight jump or rapid flexion of the knee.  (This takes advantage of the upper body’s inertia, thereby resulting in a momentary reduction in forces through the foot, and hence reduced potential for torquing of the knee.)  Good jump technique requires both good balance and well-developed musculature.  Keep in mind that, while landing a jump, the body is momentarily heavier (think of jumping up and down on a bathroom scale).  This temporary increase in apparent weight serves to plant the feet more firmly on the ground.  Because friction increases with normal force (in other words, the greater your apparent weight, the more traction you have), the result is increased risk of the knee being injured via twisting.  So, the need for landing a jump with good control is imperative.  (Incidentally, these momentary weight increases also occur when changing direction—in fact, they occur whenever the athlete accelerates.  Note that because acceleration is defined as having both magnitude and direction [i.e. it is a vector], merely changing direction also constitutes acceleration.  Deceleration, often implicated in ACL injuries, is simply negative acceleration.)   Once again, the paramount importance of good training cannot be overemphasized. 

To summarize, the four most-important aspects to develop in this regard are proprioception, muscle strength, endurance, and range of motion.  Because of the inherent complexity involved in planning and orchestrating high-quality rehabilitation from ACL reconstruction, it is imperative that the services of a knee-experienced physiotherapist be sought.  The deplorable parsimony of some insurance firms has resulted in a move towards home-based rehabilitation.  It must be emphasized that only with both motivation on behalf of the patient and access to top-quality rehabilitation (as well as, of course, a well-done reconstruction by a caring surgeon) can an optimal outcome be anticipated.

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My interest in functional bracing is a deeply personal one, and has nothing to do with my employment. Over two years ago, I was prescribed two functional braces, as a consequence of partial ACL/PCL tears in both knees. After a careful engineering-type analysis (decision-matrix approach), I narrowed down the choice of bracing to the Innovation Sports CTi2, Townsend Air/Original, and (now-discontinued) OrthoTech Performer. My final choice of the CTi2 was predicated on its amenability to bilateral use (due to the aforementioned non-protruding hinge design), fully-user-replaceable strapping, absence of concern of chafing in the inside-upper-thigh region, one-year fit guarantee, and excellent ability to accommodate leg-size changes. The CTi2's unique ski-boot attachment option I also consider very desirable. (General advantages of the CTi2 [some of which are shared by the Air/Original] are anatomically-correct hinging, lifetime frame-and-hinge warranty, and superb tibial-crest registration.) I have found the full shell to be strong and light, as well as durable, comfortable, and migration-resistant. My two CTi2s have served me well in competitive sports (soccer, hockey, basketball, etc.), as well as on geological field trips in remote areas (during which I have worn them for full-day hikes, without any problems).

Custom-made braces have the advantage of excellent frame-and-hinge warranties (whereas their off-the-shelf counterparts usually have shorter warranties). The custom braces of DonJoy, Innovation Sports, Townsend, and (formerly) OrthoTech all come with lifetime warranties. Lenox Hill provides a five-year warranty; Omni gives a ten-year warranty.

If you intend to wear the brace with some degree of frequency, then a brace which is designed such that the user can easily replace the straps is indicated. (Some models from Townsend and Lenox Hill have the straps riveted to the frame, and thus must be sent back to the factory for mere strap replacement.) Easily-replaceable padding is also a design advantage.

All manufacturers of custom bracing provide some timeframe within which refitting or refabrication will be done free of charge. (This is useful because muscle sizes change during rehabilitation.) For Townsend, the free-refit period is six months; for Innovation Sports, it is one year, and for DonJoy four months. Lenox Hill is notable in providing absolutely no free-refit period. Other manufacturers provide various warranties; be sure to contact them for more information.

Below is the hotlink to my list of knee-brace manufacturers. The websites are convenient because they contain identifying photographs of the various braces; the toll-free telephone numbers are useful for posing manufacturer-specific questions that might arise.

I wish you well in your quest for the functional brace that best suits your needs.

Feel free to e-mail me if you have any questions.

Yours truly, Michael Frind.

Note: Two relative newcomers on the brace market, the Generation 2 3DX and the EBI Alliance, I am presently in the process of evaluating. If you are contemplating purchasing either of these two models, I can send you my comments via e-mail.

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Functional Knee Bracing — List of brace manufacturers, with contact information…

This list is intended for use in conjunction with my tripartite write-up on functional knee bracing, as posted January 4, 2002 (with update on November 22, 2002).  (Note that because of space limitations, not all product offerings from all firms have been discussed.  However, said document’s analysis, in combining coverage of the fundamental technical points [in plain language] with in-depth case studies of selected brace models, serves as an overview of the essential points pertinent to all braces.)

List of brace-manufacturer contact numbers and website addresses (in no particular order). This list focuses on hardshell, hinged knee bracing.  

Updated November 22, 2002.

- Innovation Sports http://www.isports.com (Foothill Ranch, California). 1-800-222-4284, 1-800-331-5491.

- Townsend Design http://www.townsenddesign.com (Bakersfield, California). 1-800-432-3466, 1-800-840-2722

- DonJoy http://www.donjoy.com (Division of DJ Orthopedics; note that this firm has bought out OrthoTech from Johnson and Johnson, and has broken away from Smith and Nephew.) (Vista, California). 1-800-321-9549

- Lenox Hill (Poulsbo, Washington) http://www.lenoxhill.com 1-800-248-6463, 1-800-222-8837 (The Lenox Hill name is now part of Seattle Orthopedic Group, which is owned by the firm J.E. Hanger.)

- Omni Scientific http://www.omniscientific.com (Concord, California). 1-800-448-6664. (This firm is currently owned by the New Zealand-based firm Bodyworks.)

- Enhanced Medical Technologies (EMT) http://www.kneebraces.com (Agoura Hills, California). 1-800-888-5633, 1-818-889-2500.   (This firm is quite small, and thus has little market penetration.  The fact that very few people have used this firm’s braces means that there is insufficient information to evaluate this firm’s products in depth.)

- Breg http://www.breg.com (Vista, California). 1-800-321-0607, 1-760-599-3000. (Note that this firm’s “custom” braces, despite aggressive marketing, actually fall into the category of “off-the-shelf”.)

- Flextech/Flexguard/DeRoyal http://www.deroyal.com/Patient%20Care/flexguard/flexgard.htm (Newport Beach, California). 1-800-681-3539, 1-714-650-3052, 1-800-251-9864 (The street address I have on file is 861 Production Place.  This firm has recently been bought out by DeRoyal, a large medical/surgical-products conglomerate based in Powell, Tennessee.  In its former incarnation, Flextech was very secretive, thus leading me to wonder about its long-term stability.  Given its newly transferred ownership, it is hard to predict what may happen to the firm and its products in the long term.  I would recommend that anyone who is contemplating purchasing a Flextech/Flexguard brace call and ask about warranties and free-refit periods.

- Exotec (Professional Products Inc.) http://www.ezywrap.com (DeFuniak Springs, Florida). 1-800-234-9004, 1-850-892-2731

- Generation 2 USA http://www.gen2.com (Bothell, Washington). 1-800-462-7252.

- Generation 2 Canada http://www.g2orthotics.com or http://www.genii-orthotics.com (Richmond, British Columbia) 1-800-663-5982, 1-604-241-8152.

- Karl Hager Limb and Brace (Edmonton, Alberta) 1-780-452-5771.

- Bledsoe http://www.bledsoebrace.com (Grand Prairie, Texas) 1-888-253-3763, 1-972-647-0884 (Note that this firm’s product range does not include custom-fabricated bracing.  Also note that this firm’s marketing efforts include “educational” articles, available on its website.)

- Bauerfeind USA http://www.bauerfeind.com (Kennesaw, Georgia). 1-800-423-3405

- Zinco http://www.zinco.com (Pasadena, California). 1-626-405-0660

- Biedermann GmbH http://www.biedermann.com (Villingen-Schwenningen, Germany). This firm produces the custom-made semi-flexible-frame Ultratech brace. For the American market, said brace is manufactured under license by Montana Medical Brace.  

- Montana Medical Brace http://www.mmbrace.com (Bozeman, Montana) 1-800-555-9256, 1-406-586-8440

- Empi http://www.empi.com (Saint Paul, Minnesota). 1-800-328-2536 x 8556, 1-800-325-5663. (This firm currently only makes rehabilitative-type bracing.)

- Protonics/Inverse Technologies http://www.protonics.com (Lincoln, Nebraska). 1-800-222-5778. Note: this firm produces only special-purpose rehab braces. Products are produced in conjunction with Empi, Inc.

- Doyle International http://www.dil-kneebrace.com (Luton, Bedfordshire, United Kingdom)  44(0) 15 82 755 000.  (Note that all of this firm’s products fall into the off-the-shelf category.)

- Mueller Sports Medicine http://www.muellersportsmed.com (Prairie du Sac, Wisconsin) 1-800-356-9522. (This firm no longer produces hardshell knee bracing.)

- Anatech http://www.anatechinc.com (Richmond, British Columbia) 1-800-667-3442. (This firm produces only soft knee bracing.)

- Kinetic Research, Inc. http://www.oandp.com/commerci/kinetic/index.htm (Tampa, Florida) (This firm's webpage is sparse; little can be found about this firm.)

- United States Manufacturing Co. http://www.usmc.com/ortho-p.htm (Pasadena, California) 1-626-796-0477. (This firm's knee bracing is limited to special-purpose use.)

- Composit Orthotic Design (Montreal, Quebec). 1-514-369-3311

- Leading Edge Products (Grimsby, Ontario). (This firm is small.  I will report on its rather odd K-System brace in the future.)

- Extreme Velocity Sports http://www.bews.com/mxsouth/evstoc.htm (Santa Monica, California). 1-800-229-4387. Note: this firm produces bracing which is intended solely for use as off-the-shelf athletic protective equipment (i.e. not as medical orthoses).

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I have decided not to list the multitudinous firms which dedicate themselves purely to distribution of bracing. In any case, distribution arrangements can always be found by contacting the manufacturers directly. Brace vendors and clinics often tend to focus on limited geographic areas; only a few have wide-ranging service agreements—appropriately, these firms will market their products via the Internet.

There also exist orthotic shops which still produce their own functional knee braces. Most of these shops concentrate on custom-designed braces for major disabilities (e.g. cerebral palsy, polio), and make prostheses (artificial limbs) as well. (Townsend Design is one example of an established firm that, in addition to producing a well-known line of functional knee braces, also makes several orthoses for major disabilities.)

Note that (as of this posting) Breg, Bledsoe, Bauerfeind, Zinco, Empi and EVS do not have any truly custom-made braces in their products lines. Of course, this may, in time, change. (Remember that toll-free telephone numbers do not always apply to all interjurisdictional calls. The few firms which do not have websites will likely soon develop them.)

A formerly well-known name, Sutter, seems to have disappeared completely from the functional-knee-brace market. Albeit it is possible that this firm has amalgamated or merged, I have been unable to find any trace of its business activities. Also impossible to trace is the manufacturer of the Marquette Knee Stabilizer. I have a feeling this product line was absorbed by another firm.  Last year’s buyout of OrthoTech by DJ Orthopedics (DonJoy), illustrates this phenomenon nicely.  Fortunately, the two manufacturers of the top-ranked braces are unaffected by this takeover.  I hope that this favourable situation does not change in the future. As with any industry, the competitiveness of the marketplace dictates that product quality and customer service must be accompanied by overall corporate health.