Note: If you are looking for Michael Frind's detailed evaluations of functional knee bracing, please check the Interim Archive.

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

For a list of knee-brace manufacturers, click here.

Click here for a diagram and calculations showing anterior-drawer-counteraction forcing being exerted by a functional knee brace on an ACL-injury-history knee. (Contrary to the marketing by a certain knee-brace maker based in Vista, California, such anterior-drawer-counteraction forcing can be exerted by nearly any hard-shell, dual-upright-type knee brace. Additional comments are provided in the document.)

Click here for a diagram showing anterior-drawer-counteraction forcing being exerted by a functional knee brace on an ACL-injury-history knee. (Contrary to the marketing by a certain knee-brace maker based in Vista, California, such anterior-drawer-counteraction forcing can be exerted by nearly any hard-shell, dual-upright-type knee brace.)

Click here for a diagram showing posterior-drawer-counteraction forcing being exerted by a functional knee brace on a PCL-injury-history knee. (Contrary to the marketing by a certain knee-brace maker based in Vista, California, such anterior-drawer-counteraction forcing can be exerted by nearly any hard-shell, dual-upright-type knee brace.)

Click here for a diagram showing how a functional knee brace (with an adjustable extension-limitation device built into the hinges) protects the knee against hyperextension.

For articles dealing with MCL injuries (for which rehabilitation typically involves the use of bracing and no surgery), please see Injuries Involving the MCL and Treatment Thereof.

The Effects of a Functional Knee Brace During Early Treatment of Patients With a Nonoperated Acute Anterior Cruciate Ligament Tear: A Prospective Randomized Study, Linda R Swirtun et al.; Clinical Journal of Sports Medicine, Lippincott Williams & Wilkins Inc.; September 2005, Vol 15(5), pages 299-304. Comments: This Scandinavian study shows that full-ACL-tearing (without reconstruction) patients benefit subjectively (i.e. knee feels more stable, which could imply a proprioceptive benefit) from the wearing of a strutted sleeve-type brace. However, no quantitative, objective benefits were noted. Keep in mind that the Bauerfeind SofTec Genu is an off-the-shelf elasticized-fabric sleeve with side struts, and thus is fundamentally different from a rigid hinged-shell-type functional knee brace. A sleeve-type device should not be counted on to provide the reliable protection against injurious hyperextension and sideways forcing that is expected of any well-designed functional knee brace. This study was funded by the German firm Bauerfeind.

Team Physician's Corner - The Use of Knee Braces, Part 1: Prophylactic Knee Braces in Contact Sports, Soheil Najibi and John P. Albright; American Journal of Sports Medicine, Baltimore; April 2005, Vol 33, pages 602-611. Comments: This study looks specifically at prophylactic knee braces, as widely used for college football and other collision-type team sports. These braces are typically primitive hinged-strut (either just one hinged-strip-of-sheet-metal strut, or perhaps one on each side of the knee, but typically no actual frame) off-the-shelf braces specifically intended to prevent injury via sideways forcing or hyperextension (which are generally referred to as contact-type injuries). However, keep in mind that functional knee braces also provide this same protection, and so functional braces are very often used prophylactically as well. But functional braces (which typically have shells which surround the leg as well as struts and hinges on both sides of the knee, and thus are structurally and mechanically far superior to both single-upright and two-hinged-strut-but-no-actual-frame prophylactic braces) are designed to fit the knee more closely than prophylactic ones, and even a base-model off-the-shelf functional brace can be expected to fit more comfortably than a prophylactic brace. (Granted, a custom-made functional brace, the most expensive option, can be expected to be the most comfortable, as well as the most lightweight and most protective of all.) The reader should keep in mind that designs of all types of knee braces vary greatly. The prophylatic category, in particular, has recently seen the arrival of a number of shell-type prophylactic braces which are structurally very similar to full-fledged off-the-shelf functional knee braces (and which are being marketed for motocross use); however, such high-end prophylactic braces are not covered by the studies Najibi and Albright looked at. (Further comments are provided with the article.)

Functional Bracing After Anterior Cruciate Ligament Reconstruction: A Prospective, Randomized, Multicenter Study, Edward R. McDevitt et al.; American Journal of Sports Medicine, Baltimore; December 2004, Vol 32, pages 1887-1892. Comments: This study looks at young military-academy people who underwent ACL reconstruction; half of these people used knee bracing (rehabilitative/postoperative brace after surgery, followed by an off-the-shelf functional brace worn daily starting at 6 weeks and carrying on until 6 months post-op (and thereafter during strenuous activities only); the other half used a knee immobilizer (removed for exercises thrice daily) for three weeks. The authors found no difference in clinical outcome between the two groups, but they did note that their population size is too small to conclude that functional bracing does not influence the reinjury or complication rates after ACL reconstruction. It would have been interesting to have had more information regarding the mechanisms of injury pertaining to the "subsequent injuries" section, in particular the ACL-graft tears noted in two nonbraced people; because functional braces protect very reliably against sideways forcing and injurious hyperextension, if the subsequent injuries in these two nonbraced people were of these types, then bracing would indeed have prevented these injuries. Another thought-provoking aspect about this study is that the functional braces used were of the off-the-shelf variety only. (Because different braces employ different designs, materials, and construction, the protective capabilities of the various off-the-shelf braces on the market at not all the same. It would have been nice to know the make/model of functional brace used, but this information might have been deliberately omitted. Only the make/model of rehabilitative brace was given.) Given that there are always some people who have legs shaped in a way that is wholly or partly incompatible with off-the-shelf bracing, it seems very improbable that all the people in the braced group would have happened to have been endowed with leg sizes/shapes that were truly suited to comfortable wearing of off-the-shelf bracing. Since all members of the braced group were expected to wear their knee braces on a daily basis until six months post-op, one would have expected that custom-made knee bracing would have at least been offered to those with non-average leg shapes. Because all-day wearing of bracing requires the brace to fit perfectly and be comfortable, the fact that exclusively off-the-shelf braces were provided raises the question of whether 100% of the members of the braced group were diligent in wearing their braces as instructed. And finally, the study's approach to bracing is a bit disappointing in that it treats functional knee bracing as a "black box". Simply giving a patient a functional brace and saying "here it is, wear it" is inherently inadequate. Rather, the patient must understand the limitations and capabilities of the brace, as well as the underlying reasons therefor. In particular, the patient should be reminded that because of the bone-surrounding shear-prone soft tissues of the leg, it is inherently inappropriate to expect a used-in-isolation brace to protect against twisting-type knee injuries.

Immediate Effects of a Knee Brace With a Constraint to Knee Extension on Knee Kinematics and Ground Reaction Forces in a Stop-Jump Task, Bing Yu et al.; American Journal of Sports Medicine, Baltimore; July 2004, Vol 32, pages 1136-1143. Comments: This intriguing study shows that retrofitting a knee brace, by adding a spring that engages as the knee is extended, engenders greater knee flexion during the landing of single-leg jumps. Landing a jump activates the quadriceps group (which contract eccentrically in order to absorb the kinetic energy of landing). The quads pull on the patellar tendon; this pulling generates forwards shearing on the knee. However, due to the biomechanics of the knee, this forwards shearing force decreases as the knee is more flexed. Because said shearing stresses the ACL (just like the Lachmann and anterior-drawer tests do), it was hoped that landing a jump with a more-flexed knee would translate into less stress on the ACL. This was seen as a potential advantage especially for female athletes, who tend to land jumps with inadequate knee flexion. But the authors found that the use of the extension-constraining knee brace, regrettably, did not reduce the ground-reaction forces, nor did it reduce the resultant forces and moments at the knee joint. (Moments are twisting forces, therefore torques.) The authors note that simply landing jumps with knees more flexed due to the modified brace is not a panacea, and there is still much research to be done in this regard. (More details can be found in this article's discussion section, which should be read with extra care.)

Effect of Functional Bracing on Subsequent Knee Injury in ACL-Deficient Professional Skiers, Mininder Kocher et al.; Journal of Knee Surgery; April 2003, Vol 16/2, p. 87-92. Comments: In this study of ACL-deficient (without reconstruction) alpine skiers, Kocher et al. found an increased likelihood of re-injury in those who did not use functional knee bracing. They recommend the use of functional knee bracing for professional skiers (e.g. ski patrollers, ski instructors). The brace used in this study was the Innovation Sports CTi2, with no options (i.e. without the optional twist-controlling alpine-ski-boot attachment). It is reasonable to conclude that the findings of this study would apply to all custom-made dual-upright, full-tibial-shell functional knee braces (examples of which include, besides the ISI CTi2, the Townsend Air/Original, the DeRoyal Flextech F1, and the Karl Hager Double X). In fact, the study results probably apply to any brace which protects reliably against sideways forcing and injurious hyperextension (which includes nearly all functional braces, potentially including off-the-shelf models, if properly fitted to the leg).

The Effect of Anterior Cruciate Ligament Deficiency and Functional Bracing on Translation of the Tibia Relative to the Femur During Nonweightbearing and Weightbearing, Bruce D. Beynnon et al.; The American Journal of Sports Medicine, Baltimore; January 2003, Vol 31, p. 99-105. 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 presence of the hamstring tendons makes it difficult for a brace to exert large amounts of anterior-drawer-counteraction forcing. (The hamstring tendons are easily palpated by hand. When the knee is fully extended, a brace can exert some anterior-drawer-counteraction forcing, but as the knee is progressively flexed, the hamstring tendons become more and more of an impediment to the brace exerting anterior-drawer-counteraction forcing. Also, as the knee is more flexed, the biomechanics of how the brace can exert anterior-drawer forcing means that the brace becomes less effective at doing this; when the knee is flexed at 90 degrees, the brace can exert no anterior-drawer-counteraction forcing at all. Fortunately, the hamstrings are biomechanically best positioned to counteract anterior drawer when the knee is flexed to 90 degrees. The importance of strong hamstrings is clear.) The 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. (Further comments are provided in the article document.)

Effects of Knee Bracing on the Sensorimotor Function of Subjects with Anterior Cruciate Ligament Reconstruction, Gloria K.H. Wu et al.; American Journal of Sports Medicine, Baltimore; Sep/Oct 2001, Vol 29/5, p. 641. Comments: This thought-provoking study found, for people at five months post-ACL-reconstruction and under isokinetic testing, that knee bracing can improve the static proprioception of the knee joint. However, there is no enhancement of the contractile function of the musculature. Also noteworthy: the fact that a similar proprioceptive effect was noted (by the subjects in the testing) irrespective of whether a placebo (fake) or genuine brace was worn is evidence that the proprioception enhancement (or surrogate proprioception) can be obtained by almost anything worn on the knee -- that is, anything from a high-end custom-made functional brace to a simple neoprene sleeve. (Of course, a simple neoprene sleeve would not provide any protection against sideways forcing nor against injurious hyperextension.)

Knee Stability Controlled by Hamstrings and Functional Knee Brace, Michael R. Torry et al.; Journal of Prosthetics and Orthotics; July 2001, Vol 13/4, p. 90-96. Comments: Torry et al. note that knee-joint stability is a complex synergy of leg-musculature forces (dynamic stabilization, ligaments (and the posterior edges of the menisci, in ACL-deficient knees), bony geometry (which is influenced by anatomical variations as well as flexion angle; note that the knee in any case has very little native bony stability), and externally applied forces (e.g. from a knee brace, taping of the knee, or collisions with external objects). This study tries to disentangle the interrelationship between hamstring contractions and a functional knee brace, in stabilizing (defined herein as reducing anterior drawer) the ACL-deficient knee. The researchers found that while 50% contracted hamstrings provide better anterior-drawer-counteraction forcing than a functional knee brace, the use of a brace resulted in a reduction of anterior tibial displacement similar to that of the unaffected knee; therefore wearing a functional knee brace may reduce the demand for increased muscular output during critical knee-strenuous situations. (This applies particularly in the absence of appropriate muscular stabilization, a scenario which, in real life situations, could conceivably correspond to unanticipated-forcing incidents -- as might be encountered in any team sport where contact or collisions tend to occur. Note, too, that functional bracing is already well-known to provide protection against sideways forcing and hyperextension -- protection which is also extremely desirable during any type of unexpected-forcing situation.) It is reasonable to conclude that the findings of this study apply not only to the as-studied Innovation Sports Edge brace, but to other dual-hinged, dual-upright, shell-type knee braces (both off-the-shelf and custom-made) as well. (This study was partly funded by California-based brace manufacturer Innovation Sports and by a grant from the National Football League Charities. Note that field modifications of the bracing were done in order to enable anterior-drawer testing with the KSS device to be done.) One complaint about this study is that because the anterior-drawer-counteraction forcing of any knee brace is directly dependent on tightness of certain straps (specifically those located immediately above and below the knee), more detail about strap tension and related aspects should have been included. It is not enough to simply specify the make and model of brace studied; indeed, how the brace is fitted and worn probably influences the anterior-drawer-counteraction forcing obtained far more than the overall brace design. Using a force transducer to determine strap tension (and its variations throughout the range of motion) would have been helpful in this regard. In summary, even though a functional knee brace's major role is to protect against sideways forcing and injurious hyperextension, this study shows that bracing can be very helpful in terms of counteracting the excessive anterior displacement (anterior drawer) that is a hallmark of ACL deficiency.

Assessment of functional knee bracing: an in vivo three-dimensional kinematic analysis of the anterior cruciate deficient knee, Dan K. Ramsey et al.; Clinical Biomechanics, Elsevier Science, Holland; January 2001, Vol 16, p. 61-70. Comments: This innovative study, the first knee-bracing study to use bone pins (one implanted into the tibia and another in the femur, and protruding through the skin and tipped with markers designed to be seen by three-dimensional infrared motion-recording cameras) comes to the conclusion that many others have come to: that functional knee bracing cannot be depended on to control forwards sliding of the tibia (also known as anterior tibial translation). Note that this same conclusion can also be arrived at by via a simple biomechanical analysis which takes into account the inherent difficulty in applying forwards forcing to the distal end of the femur. Said difficulty arises largely as a consequence of the hamstring tendons, whose presence makes it nearly impossible for the brace strap (the one located immediately above and behind the knee) to exert the required forwards forcing on the distal end of the femur. Although it is easy for any brace to exert the necessary rearwards forcing on the proximal end of the tibia (i.e. at the tibial tuberosity, hence just below the kneecap), this is of little value unless the brace can exert a force of equal magnitude (but in the opposite direction) above and behind the knee. Once again, this limitation is imposed by simple physical principles, particularly with regards to how the soft tissues of the leg impede any external device's ability to control movement of the leg bones. These same physical principles also explain why used-in-isolation functional braces are well-suited to protecting against sideways forcing and injurious hyperextension, but not against twisting. In other words, what a brace can and cannot do is heavily influenced by the general anatomy of the leg. (This means that a brace's limitations do not constitute a "failure". So, instead of saying that "knee braces fail when high loads are encountered or when load is applied in an unpredictable manner", the authors should be saying something similar to the following: "As would be expected from a simple biomechanical analysis, and as shown by our study and the findings of other researchers, it is inappropriate to expect a functional knee brace to be capable of exerting sufficient anterior-drawer-counteraction forcing to protect an ACL-deficient knee against pathological forwards tibial translation, just as it is inappropriate to expect any externally-worn used-in-isolation knee brace to be able to grip the leg bones well enough to protect against twisting-type injuries. Because braces seek to control the motion of the leg bones, the inherent limitations of functional knee bracing are primarily a consequence of the interference resulting from the presence of various soft-tissue structures.") Further comments are provided in the study.

The influence of functional knee bracing on the anterior cruciate ligament strain biomechanics in weightbearing and nonweightbearing knees, Branden C. Fleming; The American Journal of Sports Medicine, Baltimore; Nov/Dec 00, Vol 28/6, p. 815. Comments: This article looks at the anterior-drawer-counteraction ability the DonJoy Legend off-the-shelf functional knee brace. Fleming et al. provide a concise discussion on the viscoelastic nature of knee ligaments and the usefulness of preconditioning (hence the need for warming-up prior to engaging in activities!). I note that the simple spring-scale standardization protocol used in ensuring that the brace straps were uniformly tight (between test subjects) is only suitable for use with a study which looks at only one model of brace, as this one does. (When comparing different models of braces, note that it is not biomechanically valid to tighten brace straps to uniform tension using a Newton spring scale, because the brace design itself mandates a specific strap tightness. Factors such as brace-frame width at the strap-attachment points, anterior-posterior location of strap-attachment points, and brace-frame stiffness all must be taken into account. In tightening the straps of any brace, the brace frame itself is being pulled inwards. This means that in order to obtain a certain tightness of the straps on the leg, the actual strap tension would have to vary from brace to brace.)

The effect of anterior cruciate ligament trauma and bracing on knee proprioception, Bruce D. Beynnon; The American Journal of Sports Medicine, Baltimore; Mar/Apr 99, Vol 27/2, p. 150. Comments: Beynnon et al. found that the wearing of a functional knee brace or neoprene sleeve brings a slight improvement in proprioception. (Proprioception was characterized by sensitivity of detection to having the knee moved passively.) They noted that loss of the ACL invariably raises the threshold to detection of passive motion, hence underscoring the importance of serviceable ACL tissue to optimal athletic performance.

The effect of knee bracing after anterior cruciate ligament reconstruction: A prospective, randomized study with two years' follow-up, May Arna Risberg; The American Journal of Sports Medicine, Baltimore; Jan/Feb 99, Vol 27/1, p. 76. Comments: Risberg et al. found that, in the context of rehabilitation from standard tendon-graft ACL reconstruction, the benefits of functional bracing vary with how the braces are used. Improvement in Cincinnati Knee Score was noted in the brace group; however, increased quadriceps-group atrophy was also correlated with brace use. The major problem with this study is that the functional bracing was continuously worn (or, more specifically, the patients were instructed to wear their bracing continuously for a couple of months) -- and this does not reflect the more-appropriate use of functional braces for knee-demanding activities only. Wearing any brace continuously, all day, day after day, can of course cause muscular atrophy...but wearing a brace only during knee-strenuous activities will not cause such atrophy. Also, note that this study only looked at the DonJoy GoldPoint brace, an off-the-shelf open-shell brace whose frame design has the same general attributes (most notably, a tendency to sit solely on the leg's soft tissues, hence an inability to grasp the tibial crest) as the DonJoy Defiance. When extrapolating the findings of this study to other knee braces, these points must be borne in mind. (Further comments are provided in the study.)

Functional knee brace effects during walking in patients with anterior cruciate ligament reconstruction, Paul DeVita; The American Journal of Sports Medicine, Baltimore; Nov/Dec 98, Vol 26/6, p. 778. Comments: The authors found that the wearing of a brace encourages more use of hip-centred musculature and less use of quadriceps (which are knee-centred); they concluded that bracing could be helpful in developing gait adaptations. The authors note 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. (Note that many muscle groups, including the quadriceps and hamstrings, actually operate more than one joint anyway. The hamstrings and quadriceps both mainly operate the knee, but they happen to operate the hip too. Only via the automatic co-contraction of the appropriate muscles can the human body ensure that the desired joint movements are obtained.) Apparently, wearing a brace causes no effect on the hamstrings; this situation is desirable because hamstring activation is very beneficial in protecting the ACL. Keep in mind that functional braces are mostly used intermittently (e.g. only for sports), and so would not engender lasting effects on the leg muscles. (The sometimes-heard "braces cause weak muscles" would only be true if the person would both discontinue exercising and wear bracing 24/7, or at least continuously while awake). Used judiciously and with understanding of the underlying biomechanical principles involved, knee-bracing does not cause harm and does provide valuable protection against side impacts and hyperextension.

The Effect of Functional Knee Bracing on the Anterior Cruciate Ligament in the Weightbearing and Nonweightbearing Knee, Bruce D. Beynnon et al.; The American Journal of Sports Medicine, Baltimore, Maryland; May/Jun 1997, Vol 25/3, pp. 353-359. 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; 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. (For further comments, see article.)

A Functional Knee Brace Alters Joint Torque and Power Patterns During Walking and Running, Paul DeVita, Michael Torry et al.; Journal of Biomechanics, Pergamon Press, Elsevier Science; September 1996, Vol 29, pp. 583-588. Comments: This fascinating study (followed up by DeVita's 1998 AJSM study, also available here in the Knee Library) shows that functional knee braces do have some neuromuscular effects. DeVita notes that ACL deficiency causes substantial changes in muscle-activation patterns. Healthy (free of knee-injury histories) individuals were observed while walking with and without functional braces; the presence of bracing resulted in greater hip and ankle extensor torques, thus resulting in more work being done at the hip and less at the knee -- the same general pattern which arises as a consequence of ACL tearing. However, during running, the wearing of a brace did not result in decreased knee power.

The Effect of Functional Knee-Braces on Strain on the Anterior Cruciate Ligament in Vivo, Bruce Beynnon et al.; Journal of Bone and Joint Surgery (American Edition); October 1992, Vol 74-A, p. 1298-1312. Comments: This intriguing study involved implanting tiny Hall-effect transducers directly, via spikes, into the ACLs of the subjects. (These were people with normal ACLs who were scheduled to undergo either meniscectomy [extremely worrisome in its own right, even if only partial meniscus removal is done] or diagnostic/explorative arthroscopy. Loadings applied in the study consisted of anterior-posterior [i.e. in the sagittal plane] shearing, inwards tibial twisting, outwards tibial twisting, quadriceps contraction with knee held at 30 degrees, and active flexion-and-extension movements. These types of loadings cover some of the most common ACL-injury situations, except for those involving hyperextension.) The result of using an implanted Hall-effect transducer is a measurement of ligament tensile stresses in the most direct way possible. A strain-shielding effect was noted with some of the braces, but only at low loadings. One major concern with this study is that of tightness of the brace strapping and standardization therefor. Since different knee braces employ different designs and construction techniques, the strap-tightening methodology should consider this. (Note, too, that the straps on a given brace should not all be of the same tightness. Seasoned knee-brace users know 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.) In any case, simply using a spring scale to measure and equalize strap tension across the different braces being tested leaves much to be desired...and this particular study did not even do this. However, the topic of strap tension is touched on (albeit inadequately) in a successor study, available here in the Knee Library as Beynnon-AJSM-May97. One potential solution to the strap-tightness problem might entail using a tissue-compression sensor underneath each strap, thus enabling each strap to be tensioned so that a certain target value of tissue compression is generated (e.g. with muscles relaxed or perhaps maximally activated). Beynnon astutely points out that previous cadaver studies are hampered by their inability to account for muscular contractions. (Another problem with putting braces on cadavers is that soft tissues behave differently in a corpse than when alive, and so it is easy to greatly overtighten the strapping and thereby inadvertently generate spurious results in such a study. Note that when a brace is applied to the leg of a real live person, the soft tissues automatically compensate for minor misalignments of the brace hinges with respect to the exact movements of the leg bones; soft-tissue shearing also explains why the brace does not have to mimic the complex triplanar motion of the knee, albeit a hinge which accurately mimics the sagittal-plane roll-and-glide of the knee is advantageous because it reduces piston-type sliding of the brace's upper shell with respect to the thigh.) On a logistical note, keep in mind that some of the brace manufacturers of the products in this 1992 study no longer exist. Note, too, that the braces which are still available today have been revised or updated since the time of the study. (The Townsend brace studied is today known as the Townsend Original; note that Townsend's most popular brace is now the Premier, a model which is vastly different from the Original. The C.Ti. has been revised, and is now the CTi2; however, the CTi2 retains the same full-tibial-shell frame shape as its predecessor. The posterior-tibial-cuff design of the DonJoy 4-Point is the same as all the present-day DonJoy frame-type braces. Lenox Hill, today owned by USMC, still makes its trademark derotation brace, now named the Custom Classic, albeit it now has newer models too.) Beynnon et al. conclude by noting that soft-tissue compliance, in particular shearing of the soft tissues surrounding the leg bones, is likely to be the limiting factor in terms of the protection a brace can provide. This seat-of-the-pants conclusion is intuitively very logical (as well as rather obvious), and it explains why a used-in-isolation brace is useful for protecting against injurious hyperextension and sideways forcing, but not against twisting-type injuries.

Dynamic EMG analysis of anterior cruciate deficient legs with and without bracing during cutting, Thomas P. Branch et al.; American Journal of Sports Medicine, Baltimore, Maryland; January 1989, Vol 17/1, pp. 35-41. Comments: In this intriguing study involving the use of electromyography (i.e. measuring the electrical signals at the skin arising as a consequence of muscle activity) during gait, these authors found that functional bracing did not alter the proportions of EMG activity (i.e. ratios stayed the same) nor muscle-activation-timing patterns. (You might wish to compare these results with those of subsequent studies focused on functional knee bracing. See, for example, DeVita-AJSM-Nov98 and Beynnon-AJSM-Jan03, both available here in the Knee Library.) Bracing did appear to generate an overall reduction in muscle activity. Keep in mind that these findings apply to completely ACL-deficient knees, hence with no ACL reconstruction. The discussion section of this study is especially insightful, and should be read very carefully. The authors set out to investigate the effect of knee bracing on both normal gait (running) and cutting (planting and twisting). Accordingly, each subject was asked to run to a force plate, and side-step cut using the ACL-deficient leg, both with and without knee bracing being worn. The side-step cut is perhaps one of the least riskiest plant-and-twist manoeuvres for an ACL-compromised knee, since it produces an external rotation moment at the tibia, which decreases the pivot-shift phenomenon. (The pivot-shift sign, like forwards tibial sliding [anterior drawer], is a hallmark of ACL deficiency.) For unbraced ACL-deficient people, the authors observed that, during the stance phase of gait, activity in the medial portion of the hamstring group increased simultaneously with a decrease in firing of the quadriceps; during the swing phase of gait, the increase in hamstring activity was especially noticeable. Because tensing the hamstrings counteracts anterior drawer, and because tensing the quadriceps exacerbates the anterior-drawer problem, the motor-control centre of the brain is automatically modifying muscle activity in order to reduce anterior drawer in the ACL-deficient knee. When a knee brace is added, an overall decrease in muscular activity was noted. The authors conclude that this could be an indication that a braced ACL-deficient knee requires less muscular stabilization -- and this decreased need for muscular stabilization is desirable, and it demonstrates bracing to be advantageous. Because no changes in muscle timing occurred, the authors note that bracing does not seem to be exerting a direct proprioceptive effect. They conclude that the effect of the brace may arise due to mechanical action; for example, the brace may subtly alter limb position in such a way as to reduce the need for muscular stabilization during the cutting movement. (Knee braces can exert anterior-drawer-counteraction forcing, if the straps above and below the knee are tightened appropriately; however, there are practical limits to the amounts of such forcing that can be exerted. One point to keep in mind is that, as with most knee-bracing studies, no standardization of brace-strap tightness was done. Ideally, strap tightness would be calibrated on the basis of tissue compression generated, not on the basis of strap tension itself.) The authors emphasize the importance of strong hamstring musculature in the context of rehabilitation (and reinjury prevention) for any ACL-injury-history knee.

Site Terms of Use and Aspects of Copyright

Printing Hints and Tips