Chronic knee effusion and aspiration: the effect on quadriceps inhibition.

Inhibition of the non-weight-bearing quadriceps was studied in ten patients with chronic knee effusions. The muscles were tested with the knees both flexed and extended, before and after joint aspiration. More inhibition was seen when the knees were extended (p less than 0.005). There was no relationship between muscle inhibition and the size of effusion, pain experienced during contraction or the extent of weakness. Aspiration of joints did not reduce the amount of inhibition. Acute effusions have previously been shown to cause muscle inhibition, even when pain-free, and we suggest that the known changes in the compliance of chronically effused joints are responsible for the observed differences in the effect of acute and chronic effusions.