Foot Drop: An Anatomical, Clinical, and Electrodiagnostic Approach to Localization.

Foot drop, characterized by weakness of ankle and toe dorsiflexion, is a clinical sign rather than a diagnosis and requires accurate neuroanatomic localization. Potential sites of injury include the L5 nerve root, lumbosacral plexus, sciatic nerve, and common fibular (peroneal) nerve. Because lesions at different levels can produce overlapping motor and sensory findings, incorrect localization may lead to inappropriate diagnostic testing or treatment. This narrative review presents an anatomical, clinical, and electrodiagnostic framework for localizing neurogenic foot drop, with particular emphasis on distinguishing L5 radiculopathy, common fibular neuropathy at the fibular head, fibular-division predominant sciatic neuropathy, and lumbosacral plexopathy. High yield examination findings include ankle inversion and hip abduction strength, while electrodiagnostic localization relies on strategically selected sensory and motor nerve conduction studies and needle electromyography of muscles representing competing anatomic levels. The short head of the biceps femoris is particularly useful for distinguishing a proximal fibular division sciatic lesion from a typical common fibular neuropathy at the fibular head. Ultrasound and magnetic resonance imaging provide complementary structural information when focal nerve pathology is suspected. Integrating examination, electrodiagnostic testing, and targeted imaging provides a systematic approach to localization and guides subsequent etiologic evaluation and management.