Sudden peroneal nerve palsy in a varus arthritic knee

Peroneal nerve palsy has been reported in association with traumatic and nontraumatic causes. We encountered a 75-year-old man whose peroneal nerve palsy developed suddenly following varus deformity of the arthritic knee. A review of the literature found 1 other report describing a progressive peroneal nerve palsy associated with a varus deformity of the knee due to arthritis. Our patient had progressive intractable knee pain; 3-compartment, severe degenerative changes in the knees; varus knee malalignment and laxity; right peroneal nerve palsy; and decreased sensation to light touch and pinprick on the dorsum of the right foot. The preoperative WOMAC score was 36. Nerve conduction studies confirmed acute peroneal neuropathy with conduction block at the fibular neck and secondary axonal degeneration. Magnetic resonance imaging of the knee showed osteophytes and cysts surrounding the fibular neck. Although their compression could be responsible for the nerve palsy, the sudden process made this less possible. Thus, the patient underwent total knee arthroplasty of both knees without exploration of the nerve. At 5-month follow-up, the WOMAC score was 78. The patient walked with a cane with no varus thrust, and his right knee had no varus laxity in full extension. The peroneal nerve did not retain its function. Sensory examination and postoperative nerve conduction studies showed no improvement.