Wear debris associated with a large lateral femoral condyle cyst following an Oxford medial unicompartmental knee replacement.

A 63-year-old gentleman presented with a history of worsening left knee pain almost 5 years following bilateral uni-compartmental knee replacements. X-Rays revealed a fracture of the medial tibial plateau and revision surgery was undertaken. A large cyst was found in the lateral femoral condyle, which extended from the weight bearing area in the lateral compartment to the margin of the trochlea. Histology of the lesion revealed a central degenerate cyst with multiple particles of polyethylene and cement debris around its periphery. Cyst progression in association with wear debris is a rare problem following unicompartmental knee replacement. The findings at the time of revision in this case demonstrate that the complications of unicompartmental arthroplasty may affect all compartments of the knee.