Unusual manifestations of proximal tibiofibular joint synovial cysts

Synovial cysts emanating from the proximal tibiofibular articulation are commonly symptomatic and may progress to compromise peroneal nerve function. They may cause diagnostic confusion when they present as intraosseous masses or as soft tissue masses causing extrinsic bony erosion. Twelve cases treated surgically are reviewed. Electromyography and nerve conduction studies were valuable in localizing the lesions to the knee when no mass was palpable. Of the six cases involving the peroneal nerve, three required loupe or microscopic dissection of the cyst from within the epineurium. Two other cases had bony changes. Magnetic resonance imaging, though not diagnostic, is valuable in planning the dissection.