Aseptic Loosening of the Patellar Component at the Cement-implant Interface

We present four cases of aseptic loosening at the implant-cement interface following patellar resurfacing. All patients initially had good results, but then presented with onset of a new anterior knee pain. The radiographs including flexed lateral and skyline view of the knee were normal in all the cases. After carefully ruling out infection, aseptic loosening at the cement-implant interface was diagnosed on further investigation. Aseptic loosening of the patellar button at the implant-cement interface can be difficult to diagnose with standard knee radiographs. During flexed lateral radiograph of the knee and the skyline view radiograph of the patellofemoral joint, the patella is compressed on the femur and thereby reducing the loose patellar button. This phenomenon has not been previously described. Patients presenting with new onset of knee pain after an initial good results following patellar resurfacing require further investigation to exclude loosening at the cement-implant interface as plain radiographs can be misleading.