Knee extension and flexion torque as a function of thigh asymmetry

Although tape measurement of thigh girth is a common component of a clinical knee examination, the implications of thigh girth asymmetry are not well understood. The purpose of this study was to examine the relationship between thigh girth asymmetry and torque asymmetry for extension and flexion of the knee. Thirty subjects with thigh girth asymmetry of at least 2 cm, measured at a site 15 cm proximal to the superior pole of the patella, were studied. Subjects were measured for girth at 10 sites along each thigh. Knee flexion and extension torque production were also tested on a Cybex II isokinetic dynamometer. Girth asymmetry was determined by the difference in measurements between the subjects' smaller and larger thighs. Percent girth asymmetries varied by site, with the greatest average girth asymmetry (asymmetry = 5.94%) at 16 cm proximal to the superior patellar pole. Percent peak torque asymmetries were computed from the differences between subjects' stronger vs. weaker thighs. Correlations and regressions of both extension and flexion torque asymmetries upon girth asymmetry sites showed higher associations and less error for more proximal measurements. Fair to moderate correlation coefficients (r = .37-.42, p < .05) were statistically significant for extension torque asymmetry compared with girth asymmetry at sites 12, 14, 16, and 20 cm proximal to the patella and for flexion torque asymmetry only at the 14-cm site. Although girth and torque asymmetries were found to be somewhat related, percent girth asymmetry provided only a limited prediction of percent peak torque asymmetry.