Abstract: A system is disclosed for preparing a natural patella for implantation of a patellar prosthesis. Substantially the same amount of bone removed from the natural patella is replaced by the prosthesis so that the reconstructed patella will replicate the natural one in diameter and thickness. To this end, the patella is held stationary and two operations are performed simultaneously. First, a posterior side of the patella is resected to form a prosthesis receiving surface for reception of a fixation surface of the patellar prosthesis. Second, a mounting bore is formed into the resected surface of the patella for reception of fixation members of the patellar prosthesis. A reamer is guided for movement between a first position spaced from the posterior surface of the patella and a second position in operative engagement with the patella at which formation of both the receiving surface and of the mounting bore therein has been completed.