Document Title: Fleming-AJSM-Nov00

Article Title: The influence of functional knee bracing on the anterior-cruciate-ligament strain biomechanics in weightbearing and nonweightbearing knees

Author: Branden C. Fleming, Per A. Renstrom, Bruce D. Beynnon, Bjorn Engstrom, Glenn Peura.

Publication: The American Journal of Sports Medicine

ISSN: 03635465

Date: November/December 2000

(Figures included. Reference-denoting numbers appear in the same point size as document text.)

Volume: 28

Issue: 6

Pages: 815-824

Key Words: Knee, brace, ligament, functional, anterior-drawer counteraction.

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.)

ABSTRACT

Functional knee braces are commonly prescribed after anterior cruciate ligament injury or reconstruction; however, their ability to protect the ligament, or graft, remains unclear. Our objective was to evaluate the anterior-cruciate-ligament strain response in braced and unbraced knees during weightbearing and nonweightbearing in combination with three externally applied loads: 1) anterior-posterior shear forces, 2) internal-external torques, and 3) varus-valgus moments. The Legend brace was tested. All external loads were applied to the tibia with the knee flexed to 20 degrees. Reproducible data were obtained from 11 subjects. For anterior shear loads up to 130 Newtons, the brace significantly reduced strain values compared with the unbraced knee during nonweightbearing and weightbearing conditions. For internal torques of the tibia (up to 9 Newton-metres), strain in the braced knee was significantly less than in the unbraced knee when the knee was nonweightbearing only. The brace did not reduce strain values when the knee was subjected to external torques (9 Newton-metres) or varus-valgus moments (10 Newton-metres) in weightbearing and nonweightbearing knees. These data indicate that a functional knee brace can protect the anterior cruciate ligament during anterior-posterior shear loading in the nonweightbearing and weightbearing knee and during internal torques in the nonweightbearing knee.

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