Compressive neuropathy of the tibial nerve and peroneal nerve by a Baker's cyst: case report.

We report a case of Baker's cyst that induced compression of both the tibial and common peroneal nerves. The patient presented with calf atrophy and foot drop over a 6-month period. These signs and symptoms could have been mistaken for those of spinal origin. Based on an electrodiagnostic study and magnetic resonance imaging, compression of nerves by an asymptomatic Baker's cyst measuring 6x4 cm was confirmed. This cyst communicated with the articular joint which was also associated with a medial meniscal lesion. We treated the patient arthroscopically by performing partial medial meniscectomy, and through the posterolateral and the posteromedial portal, decompression of the Baker's cyst was performed. Approximately 6 weeks after the arthroscopic decompression, the cyst recurred. Therefore open resection was performed. At 1-year follow-up, the patient had considerable improvement in motor as well as sensory function and showed no evidence of recurrence. Although the electrodiagnostic studies showed an improvement in symptoms, the patient continued to complain of lower leg weakness owing to delayed diagnosis and cyst decompression. We believe that Baker's cysts should also be considered in the differential diagnoses of patients who present with neuromuscular dysfunction in the calf and leg.