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Clonus

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

Clonus is said to occur if there are sustained rhythmical contraction of muscles after a sudden stretch; it signifies the hypertonia of an upper motor neurone lesion. It may be present at the ankle or knee:

  • ankle clonus
    • thigh is externally rotated, knee is bent
    • the examiner dorsiflexes the foot - if clonus is present then there is recurrent ankle plantar flexion movement as long as the examiner retains the foot in dorsiflexion

  • patella clonus - less common than ankle clonus:
    • the examiner holds the patient's patella between thumb and index finger - rest other hand - left - on top of patient's quadriceps
    • sharply pull down patella - if clonus is present then there is sustained rhythmical contraction of quadriceps as long as the examiner maintains downward pressure on the patella

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