Differential Diagnosis of "Foot Drop": Implications for Peripheral Nerve Surgery.

At least 128,000 patients in the United States each year suffer from foot drop. This is a debilitating condition, marked by the inability to dorsiflex and/or evert the affected ankle. Such patients are rendered to a lifetime of relying on an ankle-foot orthosis (AFO) for walking and nighttime to prevent an equinovarus contracture. Contrary to popular belief, foot drop can be caused by more than just insult to the common peroneal nerve at the fibular head (fibular tunnel). It is a common endpoint for a diverse spectrum of nerve injuries, which may explain its relatively high prevalence. From proximal to distal, these conditions include lumbar spine nerve root damage, sciatic nerve palsy at the sciatic notch, and common peroneal nerve injury at the fibular head. Each nerve condition is marked by a unique clinical presentation, frequency, likelihood for spontaneous recovery, and cadre of peripheral nerve techniques. The ideal surgical technique other than neurolysis for compression remains elusive, with traditional peripheral nerve procedures marred by a wide spectrum of functional results. Based on a careful understanding of why past techniques have achieved limited success, we can formulate a working set of principles to help guide surgical innovation moving forward, such as fascicular nerve transfer.