For a brief overview of knee anatomy, physiology, and biomechanics, please click here.

The Effect of Anterior Cruciate Ligament Deficiency on the In Vivo Elongation of the Medial and Lateral Collateral Ligaments, Samuel K. Van de Velde et al.; American Journal of Sports Medicine; February 2007, Vol 35, page 294-300. Comments: In this study, the authors looked at how knee motion was affected by loss of the ACL. They found that unaddressed ACL deficiency predisposes the knee to further ligamentous injuries, most notably MCL injury. Leaving the ACL chronically torn results in increased MCL stresses, therefore eventually causing the MCL to stretch out, hence worsening the joint looseness (laxity) and exacerbating instability. They note that an ACL reconstruction should aim to restore normal knee motion in all six degrees of freedom. (A good discussion of the six degrees of freedom can be found in DeFrate-AJSM-Aug06.shtml.)

Outcomes of Anterior Cruciate Ligament Injuries to Running Backs and Wide Receivers in the National Football League, James L. Carey et al.; American Journal of Sports Medicine; December 2006, Vol 34, page 1911-1917. Comments: This eye-opening study found that about 20% of professional NFL football players who incur an ACL injury never return to playing. Although this translates into a success rate (where "success" is defined not only as a successful ACL reconstruction and rehabilitation, but a full return to all pre-injury activities) of about 80%, it should be kept in mind that those who do return perform at a level roughly 33% below their original level. Granted, these are highly trained athletes with access to top-notch surgeons and physiotherapists and trainers. But it underscores the reality of knee injuries, and it shows that even the best of athletes either cannot or choose not to return to the activities in which they tore their ACLs. Given that football is a collision sport as well as a cutting-type sport, it is understandable that someone injured in this activity might be leery of returning to it. What is unknown here is the proportion of players who never returned to the sport out of concern for long-term knee health and not actual ability of the knee. It is interesting to note that the very best, most powerful players generally seemed to be the most injury-prone. The authors point out that the best players are the fastest (remember that kinetic energy, hence injury severity, increases with speed squared), and that they are the most agile as well as the most powerful. This means that they place high demands on their knees (hard pivoting, rapid direction changing, sudden stops and starts made possible by extremely powerful musculature). These are the types of elite athletes who could probably tear their ACLs just by forcefully extending their knees against massive resistance (e.g. sled-pressing a whole rack full of the heaviest weights). Keep in mind that although the muscles can be strengthened by training, knee-ligament strength remains relatively constant. And, as this football-player situation shows, even the strongest leg musculature, while helpful in protecting against joint injuries, cannot protect against all types of knee-ligament tears.

Clinical Outcome at a Minimum of Five Years After Reconstruction of the Anterior Cruciate Ligament, Kurt P. Spindler et al.; Journal of Bone and Joint Surgery (American Edition); August 2005, Vol 87, page 1673-1679. Comments: This study used patient questionnaires and other data (knee-evaluation scores, instrumented tests, intra-articular findings) to quantify progress at greater than five years after ACL reconstruction. The authors found that a worse-than-ideal outcome could be predicted by subsequent weight gain, the presence of a felt or heard pop at the time of injury (such strident noises imply that especially high kinetic energy was involved, which implies that other structures could have been damaged concomitantly with the original ACL injury), and no change in educational level since the injury. Curiously, that authors did not find a correlation between cartilage damage (i.e. meniscal tearing or articular-cartilage damage via bone-bruising, irrespective of whether treated or not) and a worse outcome. However, it is worth bearing in mind that such cartilage damage can bring effects in a time frame longer than five years. Consider, for example, the 2002 study by Pinczewski, which found that tibiofemoral joint-space narrowing (an early harbinger of osteoarthritis) can be found five years after certain types of ACL reconstruction procedures. A patient with such joint-space narrowing might not notice anything amiss at all, and might think the knee is perfectly fine. The only sign of articular-cartilage erosion (and resulting joint-space narrowing) would be on an X-ray image taken years after the ACL has been reconstructed. In any case, it is still safe to say that any meniscal tearing or articular-cartilage damage will predispose the knee to developing premature osteoarthritis. Ideally, anyone with any knee-ligament injury would be followed up for the remainder of their life (including X-rays every five years to determine joint-space narrowing progression).

The Effect of Anterior Cruciate Ligament Reconstruction on the Risk of Knee Reinjury, Warren R. Dunn; American Journal of Sports Medicine, Baltimore; December 2004, Vol 32, p. 1906-1914 Comments: This article, which looks at knee injuries in a population of militarians, shows that ACL reconstruction brings the benefit of preventing further injuries (e.g. meniscal tearing) to the knee. The benefits of ACL reconstruction are especially apparent if the surgery is undertaken within about 3 months of the actual injury. (If the knee is left ACL-deficient for longer periods of time, loosening of the secondary restraints will occur. This concern is especially the case if the knee is giving way on a regular basis, yet it is still present even if the person is able to keep the knee from giving out, e.g. through avoidance of certain movements. Although ACL reconstruction is still very beneficial even in a knee which has been ACLless for many years, the sloppiness in the knee motion might make repair of the stretched-out secondary restraints indicated.)

See also the September 2004 article Histology of the Torn Meniscus -- A Comparison of Histologic Differences in Meniscal Tissue Between Tears in Anterior Cruciate Ligament–Intact and Anterior Cruciate Ligament–Deficient Knees, by Meister et al., in the Meniscal Injuries: Causes, Consequences and Treatments section

See also the April 2004 article Prospective Evaluation of 1485 Meniscal Tear Patterns in Patients With Stable Knees, Michael H. Metcalf et al., in the Meniscal Injuries: Causes, Consequences and Treatments section

(Point-Counterpoint Debate-Style article) Anterior cruciate ligament reconstruction: A cynical view from the British Isles on the indications for surgery, Donald H. Johnson, Nicola Maffulli, John B. King, and K. Donald Shelbourne. Arthroscopy; February 2003, Vol 19/2, page 203. Comments: This excellent and highly readable discussion of whether or not to reconstruct a fully torn ACL brings forth a plethora of very thought-provoking points. Many, many patients with unstable and deteriorating knees find themselves confronted with a surgeon whose recommendation seems to give more weight to financial concerns. Dr. Shelbourne, a famous knee expert and highly articulate researcher, brings forth numerous good reasons in favour of prompt ACL reconstruction. He also does an excellent job of refuting the widespread misinterpretations stemming from Noyes' "rule of thirds". He points out the regrettable aspect that in some countries (in this example, the United Kingdom), the government-bean-counter-imposed restrictions on ACL reconstruction (i.e. "ACL reconstruction shall only be done for already-severely-damaged knees") naturally means that the results of ACL reconstruction are not as good as they could be. ACL reconstruction brings the best possible results only when the knee is not allowed to incur the damage of repeated giving-way incidents. So, health-insurance accountants who consider ACL reconstruction to be too expensive must be reminded of the enormous long-term costs that come with the accelerated knee degeneration that is an inevitable consequence of a knee that manifests itself as unstable. Shelbourne concludes his brilliant missive by deftly pouncing on Maffulli and King's use of dated, obsolete references.

The effects of time course after anterior-cruciate-ligament injury in correlation with meniscal- and articular-cartilage loss, George A.C. Murrell; American Journal of Sports Medicine, Baltimore; Jan/Feb 2001, Vol 29/1, p. 9 Comments: This article provides an excellent overview of the degeneration of the ligament-injury-history knee. Said deterioration is a known consequence of the damage that the bone-covering articular cartilage often (more than 85% of the time) incurs in conjunction with ACL rupture. Meniscal tearing commonly accompanies full ACL tearing; if it leads to partial or full menisectomy, the consequences for the articular cartilage invariably prove frighteningly severe.

See also the July 2000 article Results of anterior cruciate ligament reconstruction based on meniscus and articular-cartilage status at the time of surgery: Five- to fifteen-year evaluations, by Shelbourne, in the Meniscal Injuries: Causes, Consequences and Treatments section.

Eighteen-to twenty-four-year follow-up after complete rupture of the anterior cruciate ligament, Wolfgang Maletius; American Journal of Sports Medicine, Baltimore; Nov/Dec 1999, Vol 27/6, p. 711 Comments: Maletius and Messner provide good insight into the cartilage-deleterious effects of knee instability. The study is one of the few that look at ACL injuries in the long term, and it clearly shows that evidence of progressively-worsening arthritic degeneration can be depended on to eventually accompany any type of full-ACL tearing (irrespective of how treated). (Of course, ACL reconstruction has advanced tremendously within the past two decades; primitive ACL-suturing attempts, crude extraarticular reconstructions, and biomechanically-horrendous artificial ligaments have thankfully been relegated to the status of mere historical curiosities. In this study, some of the patients did not undergo any surgery for their full ACL tearing; nearly all of the patients who did undergo the decidedly unsophisticated surgeries of the day experienced a very dismal failure at some point in time.) It was found that after 20 years of ACLlessness, well over half of the knees harboured compromised menisci. Maletius et al. note that the incidence of osteoarthritis is many times higher in people with full-ACL-rupture histories, as compared to the general population. The authors also point out that the Lachman test, particularly if performed without anesthesia, depends somewhat on the examiner's tactile abilities. It was noted that isolated ACL injuries are usually rare; thus whenever an ACL injury occurs, other structures (e.g. MCL, articular cartilage, trabecular/subcortical bone) are often injured along with it.

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