Dynamic activity of unloader knee braces in genu varum subjects: New insights to improve compliance in medial knee osteoarthritis patients?

Abstract

Using unloader knee braces with 3-point pressure in knee osteoarthritis patients is debated. The main reason is discomfort resulting in poor compliance. Studying the external knee adduction moment (EKAM) curve, gold standard in the medial knee load estimation, should be helpful to reduce this discomfort. Reducing constraint solely during the stance phase of gait (combined with an inactivation during large knee flexion) should indeed considerably improve comfort. Thus, the objective of this study was to validate both a method for measuring dynamic activity of new unloader knee braces and to highlight the biomechanical effectiveness of these orthoses. A specific tool incorporated into the brace at the leg interface was developed to quantify knee moments in situ. This tool was beforehand validated in accuracy and retest reliability A kinematic and kinetic analysis was performed on 8 healthy subjects (genu varum) throughout 7 knee valgus braces conditions (and a control condition without orthosis). Each orthosis was endowed of one, two or three mechanisms resulting in all possible combinations (valgus pad and/or cable on the external hinge and/or distraction on the medial hinge). The relative absolute mean bias of the tool was approximatively 4% (accuracy) and the standard error of measurement was close to 1.3% (retest reliability). Femoro-tibial angle in static position, 1st and 2nd EKAM pics, level arm and adduction angle at pics moment as well as maximum knee flexion were significantly reduced by some orthosis ( P < 0.001). The valgus orthosis moment varied significantly at 2nd EKAM pic depending on to the orthosis worn ( P < 0.006). Reported accuracy and retest reliability appear suitable to measure dynamic constraints induced by a knee orthosis. Thereby, biomechanical parameters allow us to point out the benefit of some new unloading knee orthoses, especially the device based on both lateral valgus pad and medial distraction.