The L4 myotome is tested by ankle dorsiflexion, the ISNCSCI key movement for L4, mainly through tibialis anterior. L4 also helps knee extension and foot inversion. Walking on the heels is a quick functional check.
| Nerve root | L4 |
|---|---|
| Area | Ankle dorsiflexion (ISNCSCI key muscles: ankle dorsiflexors) |
| How to test | The patient pulls the foot up toward the shin against the examiner's hand on the top of the foot; heel walking can be used as a screen. Strength is graded 0-5 on the Medical Research Council scale and compared side to side. |
| Muscles | |
| Nerve Supply | Deep fibular nerve; Femoral nerve |
Lifts the foot at the ankle and clears the toes during the swing phase of walking.
L4 radiculopathy, from an L3-L4 disc or a far lateral L4-L5 disc, gives weak dorsiflexion and a reduced patellar reflex. Foot drop has many causes, including L4 or L5 root lesions, common fibular nerve palsy, sciatic nerve injury and central causes. 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 of the L4 root causing weak dorsiflexion and inversion, medial leg numbness and a reduced patellar reflex.
Weakness of the ankle dorsiflexors causing the toes to drag, compensated by a high stepping gait.
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