Can a Fibular Osteophyte Cause Foot Drop?

Fibular neuropathy at the knee is the most common lower-extremity mononeuropathy and is typically caused by external compression or trauma. We report a case of recurrent left foot drop due to an intrinsic osseous lesion. A 57-year-old man presented with progressive left foot drop over two to three months, preceded by one year of intermittent, activity-dependent episodes. Examination revealed steppage gait, severe weakness of ankle dorsiflexion (anterior tibialis 2/5, extensor hallucis longus 0/5), and sensory loss in the superficial fibular nerve distribution, with sparing of deep fibular, sural, and plantar territories. Electrodiagnostic testing localized a fibular neuropathy at the knee, demonstrating focal slowing across the fibular head, absent or minimally recordable extensor digitorum brevis responses, and active denervation of fibular-innervated muscles distal to the knee. Knee radiographs identified a lateral fibular head osteophyte adjacent to the fibular nerve, suggesting intrinsic compression as the etiology. This case underscores the value of knee radiographs in patients with new-onset foot drop and electrodiagnostic evidence of fibular neuropathy localized at the knee.