This specification covers the basic material descriptions, device geometry (axisymmetric and nonsymmetric), and in-vivo performance characteristics of patellar resurfacing prosthetic devices used to provide a functioning articulation between the bones of the patella and the femur. This specification does not cover the details for quality assurance, design control, and production control contained in 21 CFR 820 and ISO 9001. All devices conforming to this specification shall be fabricated from materials with adequate mechanical strength and durability, corrosion resistance, and biocompatibility. In the evaluation of their safety and efficacy, patella prosthesis shall adhere to the minimum acceptance criteria specified for the following failure modes: dislocation or laterial subluxation; component disassociation; fixation failure; device fracture; and articular surface wear.