Clonus test at the knee

Clonus is characterised by a series of involuntary muscular contractions due to a sudden stretch placed upon a muscle.

Test procedure:
With the patient supine and their leg being tested straight, the examiner rapidly moves the patients patella distally using the web of his/her hand, and holds this position for a few seconds.
This procedure can also be carried out at the calf, and at the wrist flexors.

Test findings (Positive & Negative results):
The presence of clonus in a patient is a pathological finding, and warrants further investigations.
A clonus is characterised by rhythmic contractions of the muscle that is being stretched, sustained for a minimum of five seconds.

The presence of clonus is a sign of an upper motor neurone lesion, and can also appear after ingesting potent serotogenic drugs.