Document Title: Torry-JPO-Jul01.shtml
Article Title: Knee Stability Controlled by Hamstrings and Functional Knee Brace
Authors: Michael R. Torry, PhD, Dennis D. O’Connor, MS. Jon J. Kedrowski, William I. Sterett, MD, J. R. Steadman, MD
Publication: Journal of Prosthetics and Orthotics
Date: July 2001
Volume 13, Number 4, pages 90-96
Keywords: knee stability, hamstring muscles, knee braces, biomechanics, functional knee bracing.

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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.

ABSTRACT

The purpose of this study was to determine the effectiveness of an off-the-shelf functional knee brace on preventing anterior tibial translation in anterior cruciate ligament-deficient knees (ACL-d) with greater than 6 mm of side-to-side difference, and the effect of a 50% maximal voluntary hamstring contraction on knee joint laxity. A therapist experienced in using the Knee Signature System (KSS) screened 14 patients who had been diagnosed arthroscopically with ACL deficiency. Nine patients (8 men, 1 woman; mean age, 32.9 years; mean mass, 75 kg; mean height, 177 cm) met the inclusion criteria. All participants were 240 ± 42 days post injury. Participants in the study were tested with no brace, with brace, and 50% maximal voluntary contraction (MVC) of the hamstrings. The uninjured limb was tested only in the unbraced condition. Repeated measures ANOVA (p less than or equal to .05) and a Bonferroni post hoc analysis was used to detect specific differences between conditions. Results indicate that a 50% hamstring contraction provided better control of anterior tibial displacement than a functional knee brace under the same loading conditions, but a brace may contribute significantly to reducing antetiordisplacement when the hamstring force is not sufficient.

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Copyright Journal of Prosthetics and Orthotics, American Academy of Orthotists and Prosthetists, July 2001. For details regarding copyright as it applies to this page, please visit the page entitled Site Terms of Use and Aspects of Copyright on this site.

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