Figure 25a. (a, b) Anteroposterior (a) and lateral (b) radiographs of the left knee show a cruciate-retaining total knee prosthesis with resurfacing of the patella (AMK; DePuy). Lytic lesions are seen in the medial femoral condyle and in the patella, as well as asymmetric appearance of tibial tray polyethylene (arrow), findings consistent with small particle disease. Note a moderate-size dense joint effusion on the lateral view. (c, d) Anteroposterior (c) and lateral (d) radiographs of the same knee demonstrate bone grafting of the medial femoral condyle and the patella and revision of the polyethylene liner. Note the polyethylene locking mechanism clip, which locks the tibial polyethylene into the tibial base plate (arrow).