The purpose of this study was to investigate changes in muscle strength of the quadriceps femoris after intraarticular acupuncture treatment of the affected joint in subjects with unilateral osteoarthritic knee. Isometric muscle strength was measured by standard dynamometry at 90 degree knee flexion when the subjects contracted the quadriceps muscle slowly and maximally without any pain.
In the preliminary experiment, the repeated measurement yielded a high reliability coefficient (correlation coefficient r=0.95, there is no significant difference between the two means) in the affected knee as well as the normal side for 19 patients with osteoarthritic knee.
Nine subjects, whose muscle strength of the affected side had fallen by more than 20% compared with the normal side, participated in the study. An acupuncture needle was inserted into the point where the tenderness of the affected meniscus was marked. The results revealed a noticeable increase in muscle strength of the quadriceps femoris in the affected side from 14.3±2.2kg before acupuncture to 22.9±3.0kg after intraarticular acupuncture (p<0.001), with no significant change in the normal side from 26.0±2.4kg to 27.1±2.8kg (p>0.05).
A hypothesis was formulated that the dicreased muscle strength of the quadriceps femoris in the osteoarthritic knee results from reflex inhibition from joint receptors and that intro-articular acupuncture has a disinhibition effect on this inhibition of the extensor muscle activity.