Sustained clonus in the ankles is an important neurological finding – learn how to recognize it!

Brisk reflexes can be a sign of an upper motor neuron injury – such as a brain or spinal cord injury. A classic finding of pathologic hyperreflexia is sustained clonus involving the achilles tendon at the ankle.

Clonus is an involuntary, repetitive muscle contraction which occurs with forced flexion – most commonly seen in the ankle, but it can be found at other joints in extreme cases of hyperreflexia.

In the video below, the examiner is just putting rapid, sustained pressure against the foot – the rhythmic twitching is clonus.

Sustained, pathologic clonus.

Sustained clonus is rated as 4+ on the reflex scale. Be aware that a few beats of clonus in the ankles can be a normal finding in some poeple, especially in those with otherwise brisk reflexes at baseline.

Another example of 4+ clonus.

This patient was found to have severe cervical spine stenosis causing increased lower extremity reflexes.

Photo credit: Photo by Zun Zun on Pexels.