Abstract: A method and surgical instrument is provided for the in situ clamping engagement and reaming of the human patella bone in preparation for the installation of a patellar button prosthesis, the clamp including a rectangular frame wherein a pair of handles are mounted for parallel movement whereby to move their respective jaws into clamped engagement with the opposite faces of the patella, and a guide head defining a fixed stop; and a reaming device including a reamer shaft disposed for rotation relative to the guide head, a depth adjustment head connected to the shaft and adapted to abut the fixed stop, and a reamer blade mounted to the shaft. The shaft is provided with indicia to indicate the thickness of the patella that will remain after the resection.