anklejerk

Ankle jerk, also known as the Achilles reflex, is a deep tendon reflex elicited by tapping the Achilles tendon at its insertion on the calcaneus. The tap stretches the gastrocnemius-soleus complex, activating muscle spindles and triggering a monosynaptic reflex arc through the tibial nerve and the S1 spinal segment, producing plantar flexion of the foot.

Testing is usually performed with the patient seated or lying prone, the leg relaxed and the foot in slight plantar flexion. The examiner strikes the distal Achilles tendon with a reflex hammer. A normal response is a rapid, symmetric plantar flexion of the foot.

Interpretation of the ankle jerk is clinical: a reduced or absent reflex can reflect peripheral nerve or nerve-root dysfunction, especially involving S1–S2, and is seen in conditions such as diabetic neuropathy, chronic alcoholism, or posterior tibial nerve injury. An exaggerated response may occur with upper motor neuron lesions or certain metabolic states. Clonus at the ankle, if present, suggests upper motor neuron involvement. The ankle jerk is part of a standard neurological examination and is interpreted alongside other reflexes and signs, with decreased reflexes being more common in aging.