Quadriceps femoris activation in healthy women with genu varum and women with osteoarthrosis and genu varum.

This study was designed to determine whether abnormalities in individual or group activation of the knee extensors might be associated with the development of osteoarthrosis of the knee with varus deformity. The study consisted of nine healthy women with normal tibial alignment, nine agematched healthy women with genu varum and nine women with osteoarthrosis (OA) of the knee and genu varum. The outcome measures were normalized quadriceps femoris surface EMG amplitude parameters, recorded during maximal voluntary static and dynamic knee extension movements at 0° and 90° s(-1), expressed as a percentage and peak torque and rate of tension development at 0° s(-1). Under static conditions, the normalized EMG amplitudes, peak torque and rate of tension development of the knee extensors in those with OA differed significantly from the same parameters recorded for the healthy controls (P < 0.001). Although not significantly different under dynamic conditions (P = 0.1), there was a large effect size of f = 0.40 between the EMG amplitudes of the knee extensors of the two healthy groups, with a neglible effect size between the EMG amplitudes as well as a trend towards reduced tension-generating capacity of the knee extensors in those with varus deformity, irrespective of joint status. The latter findings suggest that the neural integration mechanisms governing the contractural pattern of the extensors surrounding a varus knee may abnormally reflect various aspects of the disease process of osteoarthrosis.