Apparatus for performing an open wedge, high tibial osteotomy, the apparatus comprising a two-piece bearing implant comprising an upper bearing member and a lower bearing member, wherein the upper bearing member comprises a screw hole for securing the upper bearing member to an upper portion of bone, and the lower bearing member comprises a screw hole for securing the lower bearing member to a lower portion of bone, and further wherein the upper bearing member comprises an upper dovetail track and the lower bearing member comprises a lower dovetail track; and a wedge comprising an upper dovetail rail which is complementary to the upper dovetail track and a lower dovetail rail which is complementary to the lower dovetail track, in order that the wedge can be introduced between the upper and lower bearing members, so as to open a wedge-like opening between the upper and lower bearing members.