[Electromyographic findings in muscles around the osteoarthritic knee: integrated electromyography and frequency analysis].

An evaluation of the muscular functions of the vastus medialis, vastus lateralis, rectus femoris, medial hamstring, and of the lateral hamstring was performed using electromyography in 33 knees of 26 female patients with osteoarthritis (OA group) and in 25 knees of 19 healthy female volunteers (control group). During standing on both feet, all muscles in the OA group showed higher IEMG (integrated electromyography) and higher LMR (IEMG of vastus lateralis/IEMG of vastus medialis ratio in the quadriceps; and lateral hamstring/medial hamstring ratio in the hamstrings) than the control group. These augmentary muscular activities ameliorated the varus deformity caused by the osteoarthritis. During maximum isometric voluntary contraction, the OA group showed lower extension and flexion torque of the knees and also lower IEMG than to the control group, while the IEMG of vastus lateralis was not lower. These findings indicated decreased muscular activities in the osteoarthritic knee, and that the activity of the quadriceps was maintained mainly by the vastus lateralis under such conditions. Frequency analysis of the myoelectric signal during maximum isometric voluntary contraction revealed a single peak of low frequency in the power spectrum density function of the quadriceps and double peaks of low and of high frequency in the hamstring. In the OA group, the peak height of the low frequency component was increased in the quadriceps and decreased in the hamstring. We concluded that the duration of the motor unit action potentials was affected in the osteoarthritic knee.