A system for repairing a defect on an articular surface of a patient's trochlear region, the system comprising a guide block comprising a body having an exterior surface configured to engage with the saddle portion and ridge portions of the patient's 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 patient's 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； securing a guide block about the articular surface； establishing a first working axis extending from the bone using the guide block, the first working axis is displaced from the reference axis； and creating a first socket in the bone by reaming about the first working axis, wherein the first socket partially overlaps with the bore.
