A system for repairing a defect on an articular surface of a trochlear region, comprising a guide block comprising a body having an exterior surface configured to engage with the saddle portion and ridge portions of the patients trochlear region, a protrusion extending generally from the body and configured to be received in a first bore formed in the articular surface along a reference axis, and a first cavity extending through the body configured to establish a first working axis displaced from the reference axis, wherein the exterior surface of the body and the protrusion are configured to secure the location of the guide block about the patients trochlear region. A method for preparing an implant site in bone, comprising: establishing a reference axis extending from the bone creating a bore in the bone by reaming about the reference axis and securing a guide block about the articular surface.
