summary TKA Patellar Prosthesis Loosening is a complication following TKA that is more common with metal-backed patellar components. Diagnosis is made with plain radiographs of the knee. Treatment is generally revision arthroplasty of the patellar component. Epidemiology Incidence 0.6-5% of cases more common with metal-backed patellae Etiology Cause subclinical infection maltracking or overstuffing, leading to high shear Risks obesity lateral release joint-line elevation postoperative flexion >100° poor bone stock asymmetric patellar resection inadequate implant fixation (small pegs) secondary osteonecrosis and osteolysis Presentation Symptoms persistnent knee pain Imaging Radiographs recommended views lateral tangential findings loss of radiolucent space in patellofemoral joint with contact between patella bone and femoral component seen on lateral view dissociated patellar component patellar component adjacent/superficial to patella seen on lateral and tangential views thinning of polyethylene seen on tangential view Treatment Operative revision of patellar component if revision fails, resection of patellar component