This patient has sustained left ankle clonus in response to forced ankle dorsiflexion by the examiner.
About ankle clonus
Clonus is a rhythmic contraction of muscles in response to a briskly applied stress stimulus. Sustained clonus represents pathologic hyperreflexia. It is most commonly elicited at the ankle. To test for ankle clonus, briskly dorsiflex the patient’s ankle and maintain the ankle in that position.
Localization
Ankle clonus is a manifestation of extreme hyperreflexia due to corticospinal tract dysfunction, with the result of disinhibition of the spinal reflex arc. Like the extensor plantar response, clonus is a sign of upper motor neuron dysfunction.