Fatigue fracture of the femoral component in a mobile bearing knee prosthesis.

Stress fracture of the femoral component is a rare complication following total knee arthroplasty. We report one such complication which occurred 6.5 years after primary implantation of an uncemented meniscal Low Contact Stress (LCS) prosthesis. The fracture affected the medial condyle of the femoral component, and a large osteolytic lesion was present in the underlying femoral condyle. The patient underwent revision arthroplasty with a cemented constrained condylar knee, which is still in place with a satisfactory result 12 years later. This complication appears to be very rare, although a number of cases probably go unreported. From data available in literature, it appears that stress fractures of the femoral component have predominantly affected the medial condyle, following uncemented implantation of fixed-bearing as well as mobile-bearing knees. Different mechanisms may be involved: specific design features of the implant, failure of bone ingrowth in uncemented components, and osteolysis from particulate wear debris.