Comments: This is the first study to specifically investigate the effect of functional knee bracing exerting anterior-drawer-counteraction forcing (i.e. rearwards force on tibial tuberosity simultaneously with a forwards force just above the rear of the knee), in the context of moving from a non weight-bearing position to the stance phase of gait (i.e. transition to weight-bearing). It is important to note that during this transition, the typical ACL-deficient knee manifests an average of 4.6 mm of anterior tibial translation...an amount that qualifies as abnormal by any standard. The authors used three different off-the-shelf knee orthoses: the DonJoy Legend and Townsend Rebel (both open-style rigid-frame braces), and the Bauerfeind SofTec Genu (a frameless soft sleeve with embedded hinged struts). They concluded that bracing is ineffective in preventing this abnormal anterior tibial translation (forwards tibial sliding) during the transition period. Such an inability of bracing is to be expected, given the inherent difficulty in applying a forwards compressive force just above the rear of the knee; in this region, the distal end of the femur is surrounded by thick soft tissues; moreover, the hamstring tendons (easily palpated by hand) impede any brace's attempts at exerting anterior-drawer-counteraction forcing. This authors note that ACLless people often can gain partial control over their abnormal anteroposterior laxity while wearing a brace during certain well-controlled situations, but will likely continue to experience abnormal forwards tibial sliding during activities. Once again, it is clear that there is no substitute for a serviceable ACL. While functional knee braces are beneficial from the viewpoint of protecting against sideways forcing and injurious hyperextension, anyone with a dysfunctional ACL would be well-advised to combine the use of bracing with prompt ACL reconstruction.

So, the findings of this study agree (i.e. that bracing does not protect against abnormal amounts of forwards tibial sliding, particularly during the critical transition to weightbearing portion of gait) with what would be expected from a simple biomechanical analysis of brace-leg interaction. Such a fundamental analysis would also indicate that that a functional brace does not provide immunity against injuries involving the exertion of forwards-tibial-sliding forces (e.g. the "boot-induced ACL tear" of alpine skiers) or twisting (e.g. planting-and-twisting, as in myriad cutting-type sports such as soccer and basketball). In short, the bone-surrounding soft tissues of the leg are the most significant limiting factor inasmuch as the capabilities of functional bracing are concerned. Other factors to consider include muscle strength, neuromuscular firmware considerations (proprioception, muscle-activation timing, speed and order of muscle firing, etc.), skills and other learned abilities, and other aspects. Nuances of brace design may also play a role, particularly if the bracing being investigated is custom-made, for example full-tibial-shell versus open-frame design.

Note, too, that what a brace can do with regards to anterior drawer (forwards tibial sliding) depends on exactly how the brace straps (in particular those just above and below the knee) have been tightened. So, tightening the strap just above and behind the knee, in such a way as to apply a forwards force just above the rear of the knee as well as a simultaneous rearwards force on the tibial tuberosity (just below the patella), will result in more anterior-drawer counteraction than if all the straps were merely tightened moderately. Unfortunately, the authors did not have a meaningful means of standardizing brace-strap tightness. (Note that such standardization would ideally be based on actual compression exerted on the tissues. Because different braces utilize different frame designs, simply using a spring-tension scale is insufficient. Clearly, simply applying the braces to the legs, even with the aid of a trained orthotist, is not enough. Issues of brace fit also come to mind; all the braces in this study were of the off-the-shelf variety, and so it would have been extremely unlikely that the individual braces used in this study would have properly fitted all subjects.) Also important is the angle at which the knee happens to be flexed at a given point in time, since it becomes increasingly difficult for a brace to exert anterior-drawer-counteraction forcing as the knee is progressively more flexed. Of course, twisting, the most troubling cause of ACL tears, is something which a used-in-isolation brace is not capable of providing much protection against, given the easily-sheared soft tissues that surround the leg bones; however, twisting was beyond the scope of this study.

Note that the subjects in this study were required to have no history of fractured tibia or femur (in either leg). The reason for this is that when a tibia or femur heals from a fracture, there is usually some lasting shape deformity...and this tends to affect the knee biomechanically afterwards, for the rest of the person's life. Furthermore, the forces involved in fracturing a tibia or femur can also affect the knee. So, for example, a frontal impact below the knee could fracture the tibia, but it could also cause ligamentous injury to the knee via hyperextension-type forcing.