Abstract
Varus deformity is frequently observed in osteoarthritis of the knee joint. However, research regarding the role of the muscles in it is rare, and this study was attempted to analyze muscle functions.
To determine the muscle activities in the lower extremity, a surface electromyogram and integrated electromyogram were taken under isometric contraction while the subject was in the standing position. The integrated action potentials were measured in 91 knees of osteoarthritis with the FTA varying from 173°to 198°, and in 10 normal younger subjects with a FTA of 175°: The results and conclusions are as follows:
1) The integrated EMG activity of the quadriceps muscle, hamstrings, tensor fascia latae, adductor magnum and peroneus longus muscles in varus knees had a tendency to be more active than those in the normal knees, and the EMG activity of these muscles increased as the FTA increased. Moreover, the EMG ratio of the lateral muscle to the medial muscle in the quadriceps muscle and hamstring also increased as the FTA increased.
2) There was no significant difference between varus and normal knees in the EMG activity of the gastrocunemius and tibialis anterior muscles.
3) In cases with high tibial osteotomy, the EMG activity had returned to the normal pattern.
4) In the cases with lateral wedged insole, the EMG showed the same changes as with high tibial osteotomy.
5) It appears that the muscles in the lower extremity act as dynamic stabilizers of the knee in the malaligment of degenerative genu varum. The lateral muscles around the knee joint act as resistant forces against varus deformity through biofeedback mechanisms.
6) Muscle exercise of the muscles around the knee, not only the quadriceps but also other muscles, is thought to be important in the treatment of arthritic knee joint.
