Spontaneous Proximal Tibiofibular Joint Ganglion Cyst as a Rare Cause of Acute Foot Drop: A Case Report

Abstract

Case Description: 50 year old male with no significant past medical history developed acute onset right ankle pain while driving home from work with associated lateral knee pain that developed shortly thereafter. Over the next 24 hours the pain persisted while also developing ankle dorsiflexion weakness. The patient was evaluated in the emergency department 4 days after symptom onset with persistent pain and weakness. X-rays of the ankle and tibia/fibula were unremarkable. He was placed in a walking boot and referred to neurology, who recommended an electrodiagnostic (EDX) study. EDX was performed 4 weeks after symptom onset, at which time ankle dorsiflexion/toe extension strength was 0-1/5 and numbness was reported to the anterolateral leg and dorsal foot. Otherwise, strength testing was normal and he denied pain. EDX was remarkable for severe motor axonal deep peroneal neuropathy without axonal continuity to the extensor digitorum brevis (EDB) and decreased amplitude but preserved axonal continuity to the tibialis anterior (TA). A focused ultrasound was performed immediately following EDX which demonstrated a loculated fluid collection just anterior to the fibular neck with apparent extension to the proximal tibiofibular joint (PTFJ). Subsequent MRI confirmed a PTFJ ganglion cyst resulting in deep peroneal nerve compression between the mass and the proximal fibula. Setting(s): OutpatientPM&R clinic. Patient(s): A 50 year old male with acute unilateral foot drop. Assessment/Results: Surgical ganglion cyst excision was performed 10 weeks after symptom onset. At 4 weeks post-op, sensory changes had resolved and dorsiflexion/toe extension strength improved to 3/5. Discussion(s): The pathogenesis of PTFJ ganglion cysts remains uncertain, though a leading theory is joint degeneration causing increased joint pressure and subsequent cystic outpouching. In cases such as this, nerve decompression should be performed within 3 months for optimal recovery. Conclusion(s): PTFJ ganglion cysts are rare entities that can cause nerve entrapment to the peroneal nerve or its branches.