Revision of failed patellar components.

In the majority of revision knee replacements, the existing patellar component is well fixed and it is possible to retain the existing patellar component when specific criteria are met. If the patellar component is loose, malpositioned, or damaged, it should be revised. The decision regarding whether to implant another prosthesis or to perform an alternative procedure is dependent on an assessment of remaining patellar bone stock. Patellae with severe bone deficiency, which preclude adequate fixation of another patellar implant, occur in approximately 10% of revision knee replacements. Specific techniques include patellar resection arthroplasty, the gull-wing osteotomy, structural bone grafting of the patella, morcellized bone grafting of the patella, or use of a porous metal augmentation baseplate. Whether the patellar revision being performed is an isolated procedure or is part of revision arthroplasty, optimal positioning of the femoral and tibial component is important for proper patellar kinematics.