achillesreflex

The Achilles reflex, also known as the ankle-jerk reflex, is a monosynaptic deep tendon reflex elicited by tapping the Achilles tendon. The reflex arc involves the gastrocnemius and soleus muscles (the triceps surae) via afferent fibers in the tibial nerve (S1–S2) and efferent fibers back to the muscles.

Testing typically involves the patient in a prone position with the foot relaxed, or seated with the knee flexed. The examiner places a hand under the foot or holds the leg and delivers a sudden tap to the Achilles tendon just above its insertion on the calcaneus with a reflex hammer. A normal response is brisk plantarflexion of the foot. Reflexes are commonly graded on a scale (0 to 4+), where 0 is absent and 4+ is hyperactive. An absent or diminished response may indicate peripheral neuropathy or radiculopathy (S1–S2) or may result from technical factors; an exaggerated response can indicate upper motor neuron lesions or spasticity, and may be accompanied by ankle clonus.

Clinical relevance centers on assessing the integrity of the S1–S2 spinal segments and peripheral nerves. Abnormal findings require correlation with patient history, other neurological signs, and potentially further testing, as factors such as age, diabetes, medications, and posture can influence the reflex.

Variations and limitations include age-related diminishment in responsiveness, and conditions around the ankle or prior procedures that can alter elicitation. The absence of a reflex is not definitive for serious disease, and the finding should be interpreted in the broader clinical context.