Fracture of a metal backed patellofemoral component overlying an osteolytic lesion

The second-generation patellofemoral component used in total knee arthroplasty (TKA) uses porous tantalum, which has lower tensile and yield strengths compared to titanium used in the first-generation implant. However, there is a paucity of studies investigating the complications in either generation. This case involves a female patient with a history of right TKA with a second-generation metal backed patellofemoral component who presented with right knee pain. Exam findings demonstrated positive patellofemoral grind test, medial joint line tenderness, and end-range flexion and extension pain. Radiographs showed a fracture of the metal backing of the proximal lateral patellofemoral component. A revision TKA was performed. Intraoperatively, there was a bony defect in the superior lateral patella underneath the area of the fractured metal patellar component. We hypothesize that the bony defect of the patella resulted in a stress point in the metal backing of the patellofemoral component, eventually causing a fatigue fracture after sustaining repetitive bending forces. The patellar component was revised with a cemented component, which also addressed the bony defect. Surgeons using a cementless metal backed patellofemoral component should take measures to ameliorate any stress points by ensuring circumferential support of the component.