End-stage osteoarthritis of the knee presenting with foot drop

This report describes the case of a 78-yearold man who presented with a 6 week history of a swelling on the lateral aspect of his right knee, and a painless right-sided foot drop. Examination revealed a fluctuant swelling at the level of the fibular head with absent power in the anterior tibial and peroneal compartments. Imaging of the right knee displayed end-stage arthritis and a multi-loculated swelling over the fibular head. This swelling was explored and was found to be compressing the peroneal nerve. The lesion was excised and histological examination revealed it to be a ganglion with evidence of degeneration and trauma. The patient tolerated the procedure well, and is showing evidence of recovery of anterior and lateral compartment function. The purpose of this report was to illustrate a unique presentation of osteoarthritis. We propose that the ganglion in this case had resulted in a significant decrease in normal joint sensation. Subsequent instability of the knee resulted in trauma to the ganglion causing a progressive increase in its size, and a corresponding compressive neuropathy of the common peroneal nerve.