L5 Radiculopathy vs Common Peroneal Nerve Palsy: Clinical Differentiation
Nerve Injuries · 7 min read · 2026-03-14
The Foot Drop Dilemma
A patient presents with foot drop. Is it an L5 radiculopathy or a common peroneal nerve palsy? This is one of the most clinically important differentials in lower limb neurology, and students who understand the anatomy never get it wrong.
Why This Matters
The management is entirely different. An L5 radiculopathy may need spinal imaging and potentially surgical decompression. A peroneal nerve palsy at the fibular head often resolves with conservative management and avoidance of compression.
Common Peroneal Nerve Palsy
The common peroneal nerve wraps around the fibular neck — the most superficial point of any major peripheral nerve. Compression here (leg crossing, tight casts, surgical positioning) causes:
- Foot drop: weakness of tibialis anterior (dorsiflexion) and extensor hallucis longus
- Eversion weakness: peroneus longus and brevis are affected
- Sensory loss: lateral leg and dorsum of the foot
- Inversion is PRESERVED: tibialis posterior is supplied by the tibial nerve
L5 Radiculopathy
An L5 nerve root lesion (disc herniation, foraminal stenosis) produces:
- Foot drop: tibialis anterior weakness (same as peroneal palsy)
- Eversion weakness: can also be present
- BUT inversion is ALSO weak: tibialis posterior is supplied by L5 via the tibial nerve
- Hip abduction weakness: gluteus medius is L5-innervated
- Sensory loss: may extend to the medial foot and buttock (broader dermatomal pattern)
- Back pain or radicular symptoms: pain radiating down the posterolateral leg
The Key Differentiator: Inversion
This is the single most important test. Ask the patient to invert the foot against resistance:
- Normal inversion → common peroneal nerve palsy (tibial nerve territory is spared)
- Weak inversion → L5 radiculopathy (the root supplies both tibial and peroneal divisions)
Additional Clues
Clinical Pearl
Test hip abduction in the side-lying position. If gluteus medius is weak along with foot drop, you're dealing with an L5 root problem, not a peripheral nerve issue. The peroneal nerve has nothing to do with the hip.
Summary
Foot drop with preserved inversion = peroneal palsy. Foot drop with weak inversion = think L5. Add hip abduction testing and sensory mapping for confirmation.