The medial hamstring reflex is a stretch reflex in which a tap on the medial hamstring tendons behind the knee makes the semitendinosus and semimembranosus contract. It mainly tests L5 and the tibial part of the sciatic nerve. It is useful because L5 otherwise has no standard tendon reflex.
| Nerve root | L5 (L5-S1) |
|---|---|
| Area | Medial hamstring tendons at the back of the knee (posteromedial knee) |
| How to test | With the patient lying with the knee slightly bent and relaxed, the examiner places a thumb on the medial hamstring tendons and strikes the thumb, feeling for contraction. |
| Muscles | |
| Nerve Supply | Sciatic nerve (tibial division) |
Tests the L5 reflex arc, filling the gap left by the standard knee and ankle reflexes.
A reduced medial hamstring reflex on one side supports an L5 radiculopathy, especially when knee and ankle reflexes are normal. It is harder to elicit than the standard reflexes and is often absent in healthy people, so only a clear asymmetry is meaningful. Tendon reflexes are graded 0 (absent) to 4+ (clonus), with 2+ normal; symmetry matters more than the absolute grade.
Compression of the L5 root, usually at L4-L5, can reduce the medial hamstring reflex along with big toe extension weakness.
Damage to the sciatic nerve reduces hamstring reflexes and weakens knee flexion and all muscles below the knee.
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