Common Peroneal Nerve Palsy Due to a Proximal Tibiofibular Joint Ganglion Cyst in a Recreational Runner: A Case Report

Common peroneal nerve (CPN) palsy is one of the most frequent lower-limb compression neuropathies in athletes, typically occurring at the fibular neck. Proximal tibiofibular joint (PTFJ) ganglion cysts are a well-recognized but rare extraneural cause of CPN compression, especially in runners. We report a 36-year-old female recreational long-distance runner who presented with a six-month history of progressive lateral knee pain that acutely evolved into foot drop. Examination revealed severe weakness in ankle dorsiflexion and eversion (Medical Research Council grade 1/5) and sensory loss over the dorsum of the foot. Electrophysiological studies demonstrated a >50% conduction block of the CPN at the fibular head with slowed velocity and signs of denervation. Magnetic resonance imaging (MRI) showed a large (6 × 1.1 cm), multiloculated cyst arising from the PTFJ and compressing the CPN. The patient opted for conservative management: an ultrasound-guided aspiration of the cyst with corticosteroid injection was performed, followed by a rehabilitation program. This yielded fast improvement; within one month, her foot drop had resolved, and dorsiflexion strength improved significantly. By three months, pain had nearly resolved and gait had normalized, although the cyst recurred on imaging; a second aspiration was done. At six months, motor function remained normal with only mild residual paresthesia, and surgical excision was recommended for definitive treatment. This case highlights that image-guided aspiration combined with rehabilitation can lead to swift and meaningful recovery in CPN palsy despite severe initial neurologic deficits, though cyst recurrence is common if the articular connection is not addressed. PTFJ ganglion cysts, although rare, should be considered in the differential diagnosis of foot drop in athletes.