The L5 myotome is tested by extension of the big toe, the ISNCSCI key movement for L5, through extensor hallucis longus. L5 also supplies the hip abductors (gluteus medius and minimus) and contributes to dorsiflexion. There is no standard tendon reflex that tests L5 reliably, though the medial hamstring reflex is sometimes used.
| Nerve root | L5 |
|---|---|
| Area | Long toe extension (ISNCSCI key muscle: extensor hallucis longus) |
| How to test | The patient lifts the big toe up while the examiner presses down on the toenail; hip abduction can be tested side-lying. Strength is graded 0-5 on the Medical Research Council scale and compared side to side. |
| Muscles | |
| Nerve Supply | Deep fibular nerve; Superior gluteal nerve; Tibial nerve |
Lifts the toes, steadies the pelvis during walking and helps lift the foot.
L5 radiculopathy, most often from an L4-L5 disc, gives weak big toe extension and hip abduction, with a Trendelenburg gait in severe cases. Testing hip abduction and foot inversion helps separate an L5 root lesion from a common fibular nerve palsy, which spares them. Myotome charts vary slightly between sources, and most muscles receive more than one root, so a single root lesion usually weakens rather than paralyses.
Compression at L4-L5 causing weak big toe extension and hip abduction, with numbness on the top of the foot.
Compression at the fibular neck causes foot drop but leaves hip abduction and ankle inversion intact.
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