When checking for clonus, should the knee be in flexion or extension?

When checking for clonus, the knee should be in slight flexion. This positioning allows for a more accurate assessment of the ankle's oscillatory responses without the influence of other muscle groups or joints. In slight flexion, the gastrocnemius muscle is less activated, enabling the clinician to better isolate the responses of the soleus and other deep plantar flexors, which are primarily responsible for clonus.

Positioning the knee in full extension might over-recruit the gastrocnemius and alter the responsiveness of the plantar flexors, potentially leading to misinterpretation of the clonus response. Similarly, flexing the knee too much can disrupt the typical pathway of muscle activation and may cause unintended movements in response to the stretch applied. Therefore, slight flexion is optimal for eliciting and observing clonus effectively, making it the preferred choice for accurate evaluation of this neurological sign.