Corpus: Achilles reflex

The Achilles reflex is a deep tendon reflex that causes contraction of the calf muscles, resulting in plantar flexion of the foot at the ankle joint after a tap on the Achilles tendon. It is mediated by the tibial nerve and involves motor neurons in the S1 spinal segment, with contributions from the neighboring L5 and S2 segments.

The Achilles reflex can be tested with the patient in a sitting, kneeling, or lying position.

• In the sitting position, the patient sits on the examination couch with their legs dangling freely. Alternatively, the patient may kneel on a stool.
• The examiner dorsiflexes the foot slightly to stretch the Achilles tendon.
• The reflex is elicited by delivering a firm but not excessive tap with a reflex hammer on the Achilles tendon just above the heel bone (calcaneus).
• The test should be repeated several times at approximately 2-second intervals.
• The opposite side should then be tested for comparison.
• If the reflex response is weak, the patient can be asked to perform the Jendrassik maneuver to enhance the reflex.

For the lying position, the examiner places the patient’s lower leg over the opposite shin with the foot slightly turned outward.

• Absent reflex: Possible causes include S1 nerve root compression due to a lumbar disc herniation, peripheral nerve damage, or Achilles tendon rupture.
• Diminished reflex: May indicate peripheral neuropathy.
• Exaggerated reflex: Suggests an upper motor neuron lesion, indicating involvement of the pyramidal tract.