Clonus

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