Clonus is characterised by a series of involuntary muscular contractions due to a sudden stretch placed upon a muscle.
With the patient supine or in a seated position, the examiner rapidly dorsiflexes the patient’s foot and holds it in that position for a few seconds.
This procedure can also be carried out at the quadriceps by stretching through the patella, 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 serotonergic drugs.