CLONUS

Ankle clonus is elicited by stretching the Archille's tendon by dorsiflexing the foot. Sustained tension on the ligament will cause a rhythmic contraction of the gastrocnemius and soleus muscles causing the foot to alternate between dorsiflexion and plantarflexion.

Sustained clonus is a manifestation of upper motor neuron disease in which the normal cortical suppression of the reflex arc is diminished or absent. It is the defining characteristic of hyperreflexia.

Clonus can also be elicited by hyperextending the wrist (finger flexor clonus), and by thrusting the patella downward (quadriceps clonus).