Electromyographic observations in patients with foot pain syndromes.

Abductor hallucis muscle EMGs were performed in control subjects and in patients with chronic foot pain (9 affected by the disease of the metatarsophalangeal joint of the big toe, 6 affected by chronic foot strain) to investigate pathophysiological mechanisms of muscle pain syndromes. Unlike control subjects, patients showed an abnormal involuntary activity when standing. All patients presented a decrease of abnormal EMG activity when postural changes were induced either by variations in body weight distribution on the feet, or by changes of position in the weight-bearing foot achieved by arch supports or by boards of variable thickness applied under the forefeet or the heels. Anaesthesia of the metatarsophalangeal joint of the hallux (injection into the joint cavity of 2-3 ml 0.50% bupivacaine) reduced the abnormal EMG activity only in patients with hallux valgus, whereas it did not affect muscular activity in the other patients. Present results support the idea of the role of abnormal muscular activity in causing and maintaining chronic pain and suggest that alterations of postural mechanisms and of afferent input, in particular that arising from joint receptors, are involved in the genesis of this abnormal muscular activity.