The effect of valgus braces on medial compartment load of the knee joint - in vivo load measurements in three subjects.

Knee osteoarthritis occurs predominately at the medial compartment. To unload the affected compartment, valgus braces are used which induce an additional valgus moment in order to shift the load more laterally. Until now the biomechanical effect of braces was mainly evaluated by measuring changes in external knee adduction moments. The aim of this study was to investigate if and to which extent the medial compartment load is reduced in vivo when wearing valgus braces. Six components of joint contact load were measured in vivo in three subjects, using instrumented, telemeterized knee implants. From the forces and moments the medio-lateral force distribution was calculated. Two braces, MOS Genu (Bauerfeind AG) and Genu Arthro (Otto Bock) were investigated in neutral, 4° and 8° valgus adjustment during walking, stair ascending and descending. During walking with the MOS brace in 4°/8° valgus adjustment, medial forces were reduced by 24%/30% on average at terminal stance. During walking with the GA in the 8° valgus position, medial forces were reduced by only 7%. During stair ascending/descending significant reductions of 26%/24% were only observed with the MOS (8°). The load reducing ability of the two investigated valgus braces was confirmed in three subjects. However, the load reduction depends on the brace stiffness and its valgus adjustment and varies strongly inter-individually. Valgus adjustments of 8° might, especially with the MOS brace, not be tolerated by patients for a long time. Medial load reductions of more than 25% can therefore probably not be expected in clinical practise.