II. Definitions
- Clonus
- Involuntary Muscle movement rapidly alternating Muscle Contraction and relaxation (typically 5-7/sec)
- Sustained Clonus
- Following persistent stimulus (e.g. ankle dorsiflexion), Clonus persists (10 beats or more)
- Unsustained Clonus
- Following persistent stimulus (e.g. ankle dorsiflexion), Clonus may occur briefly and rapidly extinguish
III. Technique: Ankle Clonus
- Patient lies supine, relaxed with knee in slight flexion
- Examiner grasps the foot and suddenly forces the ankle into dorsiflexion and holds the foot in that position
IV. Findings: Abnormal Ankle Clonus
- Rhythmic ankle flexion and extension for at least 3 beats of Clonus before it extinguishes
V. Causes: Sustained Ankle Clonus
-
Upper Motor Neuron Lesion
- Cerebrovascular Accident
- Multiple Sclerosis
- Cerebral Palsy
- Encephalopathy
- Other systemic conditions
VI. References
- Degowin and Degowin (1987) Bedside Diagnostic Exam, Macmillan Publishing, New York, p. 818