From the Research
Clonus can be tested at several locations in the body, with the ankle being the most common site, as well as the wrist, patella, triceps surae, and jaw, as noted in the study by 1. To test for ankle clonus, the examiner should support the patient's knee in a slightly flexed position, then quickly dorsiflex the foot and maintain pressure. Other sites for testing clonus include:
- The wrist, by quickly extending the wrist
- The patella, by sharply pushing the patella downward
- The jaw, by tapping the chin downward Clonus is characterized by rhythmic, involuntary muscle contractions in response to sudden stretching of the muscle, and indicates upper motor neuron dysfunction, which can occur in conditions like stroke, multiple sclerosis, spinal cord injury, or severe metabolic disturbances, as discussed in the study by 1. The presence of sustained clonus (more than 3-4 beats) is generally considered abnormal and suggests pathology in the central nervous system, particularly in the corticospinal tracts, as supported by the findings of 2. When testing for clonus, it's essential to ensure the patient is relaxed to avoid false positives from voluntary muscle tension. The exact mechanism of clonus remains unclear, but it is thought to be related to hyperactive stretch reflexes or central generator activity, as proposed by 3 and 4. Overall, testing for clonus is an important part of the neurological examination, and can provide valuable information about the integrity of the spinal cord and the presence of upper motor neuron dysfunction, as highlighted by the study by 2.