One case and one study of an atrophy of the vastus medialis (VM), which might be caused not by disuse but by neurophysiological factors, are presented in this paper. (1) A 17-year-old boy showed an acute atrophy of the VM on day 3 after injury of ligaments and menisci of his left knee. This atrophy was demonstrated on MR imaging. (2) The right knee of 11 healthy students was braced for 8 weeks to investigate effects of knee bracing on muscle. Cross-section area of the VM was significantly (p<0, 05) in 8-week braced side. Reflex inhibition of the VM via modulation of afferent activity of the capsule or ligament and meniscus, in response to capsular compression with bracing or acute swelling or injury to the mechanoreceptors in involved tissues, might lead to this muscle atrophy.
