A system for repairing a defect on an articular surface of a patient's bone, said system comprising: a reamer comprising a shaft and a cutting head extending generally radially outward from an end thereof, said cutting head having at least one cutting surface; and a guide block comprising: a body having an exterior surface configured to engage against said articular surface of said bone; a protrusion extending generally from said body and configured to be received in a first bore formed in said articular surface along a reference axis; and a first excision passageway extending through a guide bushing extending through a first cavity in said body along a first working axis, characterized in that said first excision passageway is configured to receive said shaft and allow said shaft to only move along said working axis; that a first opening disposed within said exterior surface of said body and aligned with said first excision passageway, said first opening configured to receive said cutting head between said body and said articular surface and to allow said cutting head to pass through said guide block and into the articular surface below the guide block to form an excision site in said articular surface centered around said first working axis; and that said reamer comprises indicia on said shaft configured to be aligned with said first excision passageway to define a depth of said excision site formed by said reamer in said articular surface. a reamer comprising a shaft and a cutting head extending generally radially outward from an end thereof, said cutting head having at least one cutting surface; and a guide block comprising: a body having an exterior surface configured to engage against said articular surface of said bone; a protrusion extending generally from said body and configured to be received in a first bore formed in said articular surface along a reference axis; and a first excision passageway extending through a guide bushing extending through a first cavity in said body along a first working axis, characterized in that said first excision passageway is configured to receive said shaft and allow said shaft to only move along said working axis; that a first opening disposed within said exterior surface of said body and aligned with said first excision passageway, said first opening configured to receive said cutting head between said body and said articular surface and to allow said cutting head to pass through said guide block and into the articular surface below the guide block to form an excision site in said articular surface centered around said first working axis; a body having an exterior surface configured to engage against said articular surface of said bone; a protrusion extending generally from said body and configured to be received in a first bore formed in said articular surface along a reference axis; and a first excision passageway extending through a guide bushing extending through a first cavity in said body along a first working axis, characterized in that said first excision passageway is configured to receive said shaft and allow said shaft to only move along said working axis; that a first opening disposed within said exterior surface of said body and aligned with said first excision passageway, said first opening configured to receive said cutting head between said body and said articular surface and to allow said cutting head to pass through said guide block and into the articular surface below the guide block to form an excision site in said articular surface centered around said first working axis; and that said reamer comprises indicia on said shaft configured to be aligned with said first excision passageway to define a depth of said excision site formed by said reamer in said articular surface.