Common Peroneal Nerve (Fibular Nerve)
The common peroneal nerve is the most common nerve causing footdrop, pain, tingling, and numbness in the lower extremity. 1, 2, 3
Why the Common Peroneal Nerve
- Peroneal neuropathy is the most common entrapment neuropathy of the lower extremity, making it the primary culprit when footdrop presents with sensory symptoms 1, 2
- The nerve is most vulnerable at the fibular head (neck of the fibula), where it winds superficially around the bone and is susceptible to compression from external pressure, trauma, or habitual leg crossing 1, 3
- Injury to this nerve causes sensory loss in the dorsum of the foot and lateral leg, along with the characteristic motor deficit of footdrop 2, 3
Clinical Presentation Pattern
The common peroneal nerve injury produces a distinctive constellation of symptoms:
- Motor deficit: Inability to dorsiflex the foot (footdrop) and evert the foot, resulting in a characteristic steppage gait 1, 2
- Sensory symptoms: Numbness and tingling in the dorsum of the foot and lateral lower leg, which distinguishes it from more proximal lesions 2, 3
- Pain: May be present at the site of compression (fibular head) or along the distribution of the nerve 2
Distinguishing from Other Causes
While other nerve lesions can cause footdrop, the common peroneal nerve is identified by:
- L5 radiculopathy: Would also cause hip abductor weakness and medial foot numbness (not just dorsal/lateral), plus back pain radiating down the leg 3
- Sciatic nerve injury: Would include hamstring weakness and posterior leg/plantar foot numbness in addition to footdrop 4, 3
- Anterior horn cell disease: Would show more widespread weakness without sensory symptoms 3
Diagnostic Confirmation
- Nerve conduction studies and EMG localize the lesion to the fibular head level and determine severity of axonal damage versus demyelination 1, 2, 3
- Physical examination reveals weakness of ankle dorsiflexion and foot eversion, with sensory loss over the dorsum of the foot and lateral leg 2, 3
- Tinel's sign at the fibular head may be positive, indicating nerve irritation at this site 2
Common Pitfalls
- Don't assume all footdrop is peroneal nerve injury: Always examine for proximal weakness (hip abductors, knee flexors) and check the pattern of sensory loss to rule out L5 radiculopathy or sciatic neuropathy 3
- Habitual leg crossing is frequently overlooked as the cause of compression—specifically ask about this behavior, as cessation often leads to improvement 3
- The American Society of Anesthesiologists notes that perioperative peroneal nerve injuries can occur from positioning during surgery, emphasizing the nerve's vulnerability to external compression 5