Comments: This article shows that a functional knee brace can protect the ACL at the relatively low strain levels engendered by moderate anterior-drawer-applied and twisting-type loadings. (Testing was done at a fixed angle of the knee, and so the length change of various portions of the ACL throughout the range of motion would not be an issue here.) Note that the forces applied in this study were relatively low: 140 Newtons. Things are very different at high loadings. (Of course, laboratory studies with living people must involve relatively low loadings, because no one wants to incur injury in a laboratory study. But the general consensus is that, with regards to anterior-drawer-type and twisting-type injury scenarios at high loadings [hence involving very high forces, as would occur during a high-speed pivoting manoeuver, for example], it is not a good idea to expect a knee brace to provide immunity to ACL injury.) This study used ligament-healthy knees with normal ACLs. Measuring of ACL strain was done with transducers attached directly to the ACLs (a method first used in the 1992 study by Beynnon et al., available here in the Knee Library as Beynnon-JBJS-Oct92); the subjects required surgery in any case for meniscal- and articular-cartilage issues, and so attaching the transducers (and then removing them afterwards) did not involve any extra surgery. The authors note that this study challenged the ACL, as the forces were similar to those produced during certain isometric quadriceps-contraction exercises. Although these forces amount 25-33% of the ACL-failure strain values, in terms of what an ACL might be exposed to during high-demand activities, they are still comparatively small. Note, too, that because the ACL contains tension-sensitive nerve endings which are capable of triggering the hamstring reflex, at high loadings this protective reflex will be activated.

The fact that the authors conclude that brace-strap tension does not matter initially raises the question of whether some additional mechanism (for example, proprioception and muscle activation) was at work here; however, the authors point out that this study did not take into account the influence of leg-muscle activation, as local anesthesia was used. (One additional concern arises: the fact that the subjects underwent minor surgery could have affected the muscle-activation patterns as well; any joint surgery can be expected to have an influence on how the surrounding musculature is recruited, at least for a number of weeks or months after the surgery.) It is intuitively obvious that in order for a brace to exert anterior-drawer-counteraction forcing, the strap immediately above and behind the knee must exert a forwards force, while the lower shell of the brace (or strap, depending on brace design) must simultaneously exert a rearwards force on the tibial tuberosity...and, of course, the forcing applied would have to be influenced by strap tightness (in addition to other factors, such as brace design).

Note that several other studies into knee bracing have touched on the issue of strap tightness on anterior-drawer-counteraction forcing, and the effect of strap tightness has been found to be significant. But no one has yet done a study which compares different functional-brace designs and which takes into account not only strap tightness, but the interdependency of brace-frame design and strap tightness, because different frame designs require different strap tensions in order to produce a given anterior-drawer-counteraction force. In other words, the issue of strap-tightness standardization is complex, and in any case calls for an approach far more sophisticated than the simplistic spring-scale strap-tensioning procedure which Beynnon and his group used in this study! Because different knee braces employ different designs and construction techniques, the strap-tightening methodology appropriate to one brace is not necessarily ideal for another brace. Furthermore, the issue of how the brace interfaces with a given person's leg deserves serious thought...in other words, especially for an off-the-shelf brace such as the GoldPoint used in this study, leg size and shape/contour should be taken into account too. (The only general constant is that the strap immediately below the knee should be tightest, to ensure good anchorage of the brace on the leg; also, the topmost strap should not be too tight or else the entire brace will be forced down the leg.) Clearly, Beynnon's method of simply using a spring scale to measure and equalize strap tension across the different braces being tested leaves much to be desired. One possibility worth pursuing might entail using some type of tissue-compression sensor underneath each strap, and therefore tightening each strap so that a certain tissue compression is generated (perhaps at maximum muscle activation or a certain reliably reproducible percentage thereof).

It would also seem intuitively obvious that if a brace were worn with the straps extremely loose (so loose that the brace was nearly about to slip down the leg), then no anterior-drawer-counteraction forcing would be exerted. (And, if the wearing of a knee brace stimulates skin-subsurface nerve endings and therefore affects muscle-activation patterns, then this could account for the strap-tension-does-not-matter finding of this study. The November 1998 AJSM article by DeVita, available here in the Knee Library, shows that knee bracing does indeed influence muscle-activation patterns.)

The aforementioned proprioception and strap-tightness issues also mean that it would be very insightful to repeat this study with various types of knee braces, as well as with simple neoprene sleeves and even basic taping of the knee. (This study looked at only one brace: the off-the-shelf DonJoy GoldPoint, provided by the manufacturer for the study. Keep in mind that the general findings of this study would be expected to apply to other frame-type functional knee braces as well, and so there is no advantage to DonJoy products. Note that DonJoy provides a heavily condensed one-page synopsis of this study to its representatives, as document 00-0180. A comparision of said DonJoyesque synopsis with the unabridged full-text version given here in the Knee Library shows that the former leaves out a lot of important points.) Please make certain to read the fourth paragraph of the Discussion section of this article very closely. The Discussion section also describes the influence of weight-bearing on the strains exerted on the ACL.

Although the study did find that bracing provides an ACL-protective effect in response to tibial torque (i.e. twisting of the knee), this was done with the knee in non-weightbearing, at the torque involved was a mere 6 Nm. However, note that in a real-life plant-and-twist injury, such as in cutting-type sports, the torque would be much, much greater...and, of course, the knee would be bearing weight. In the end, it is best to consider functional bracing as protection against sideways forcing and injurious hyperextension. With regards to protecting the ACL against twisting-type injuries, it is well worthwhile to learn to pivot with a knee-friendly technique: that is, to plant only on the front portion of the foot while pivoting. Remember that functional knee bracing cannot grip the leg bones well enough (due to the bone-surrounding shear-prone soft tissues) to protect the knee against plant-and-twist-type injuries.