Ankle clonus in patients with spinal cord and supraspinal lesions: An electromyographic analysis

Document Type


Publication Source

Archives of Physical Medicine and Rehabilitation

Publication Date






First Page


Last Page



Spasticity accompanying supraspinal lesions has been shown to differ from that in the spinal cord patient. In this study, ankle clonus, one of the signs of spasticity, has been evaluated electromyographically in patients with both types of lesions to determine if their clonic responses were different in terms of the mechanisms mediating the response, frequency of the clonus and the contributions of the ankle flexor and extensor muscles. Ankle clonus was produced by manually forcing the ankle into dorsiflexion and sustained with a bias force applied to the ball of the patient's foot. Clonic responses of patients with supraspinal lesions were found not to be different from those responses elicited in patients with spinal cord lesions. Ankle clonus consisted of repetitive phasic EMG discharges of the gastrosoleus muscle, involving in in some cases, reciprocal phasic activity in the tibialis anterior muscle. In every patient the following applied: (1) there occurred, during the first clonic discharges, a progressive shortening of the time interval between successive discharges: (2) the durations of the clonic discharges were similar; (3) the frequency of the discharges was variable by altering the bias force; and (4) ankle clonus could be inhibited with progressively increasing bias forces. The mechanisms mediating ankle clonus appear similar regardless of the site of the central nervous system lesion, although the existence of clonic responses in ankle flexor and extensor muscles may vary with the level of the lesion.

This document is currently not available here.