Ankle jerk reflex

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Ankle jerk reflex (Achilles reflex) is tested by tapping the Achilles tendon while the foot is gently dorsiflexed. It’s a deep tendon, monosynaptic stretch reflex that checks the gastrocnemius muscle and its nerve supply. A normal result is a brisk plantarflexion (the foot pointing downward).

How to test:
- Have the patient relaxed.
- Hold the ball of the foot to put a little tension on the tendon, but don’t fully dorsiflex the ankle.
- Tap the tendon with a rubber hammer.
- If there’s no response, try a Jendrassik maneuver (the patient clasps their hands together and tries to pull them apart).

What it means:
- The reflex mainly tests the S1 (and S2) nerve roots.
- A reduced or absent reflex can indicate nerve problems such as sciatic nerve issues.
- It is graded on a 0–4 scale; 4 indicates ankle clonus (repetitive dorsiflexion and plantarflexion on sustained stimulation), which can occur with upper motor neuron problems above S1.

Clinical notes:
- A delayed or reduced reflex can be seen in hypothyroidism.
- The reflex is often absent in disk herniation at L5–S1.
- A reduced reflex may also suggest peripheral neuropathy.