A method for performing an open wedge, high tibial osteotomy, the method comprising:identifying a cutting plane through the tibia and a boundary line for terminating a cut made along the cutting plane, wherein the boundary line is located within the tibia, parallel to the anterior-posterior slope of the tibia and parallel to the sagittal plane of the patient;positioning a hollow cylinder adjacent to an exterior surface of the tibia and co-axial with the boundary line;positioning a fluoroscope so that its field of view is parallel to the anterior-posterior slope of the tibia, parallel to the sagittal plane of the patient, and co-axial with the hollow cylinder;imaging with the fluoroscope and observing the profile of the hollow cylinder so as to confirm that the hollow cylinder is aligned co-axial with the boundary line;advancing an apex pin through the hollow cylinder and into the tibia along the boundary line so as to provide a positive stop at the boundary line for limiting cutting along the cutting plane;cutting the tibia along the cutting plane, with the cut terminating at the boundary line;moving the tibia on either side of the cut apart so as to form a wedge-like opening in the tibia; andstabilizing the tibia.A method for performing an open wedge, high tibial osteotomy, the method comprising:identifying a cutting plane through the tibia and a boundary line for terminating a cut made along the cutting plane, wherein the boundary line is located within the tibia, parallel to the anterior-posterior slope of the tibia and parallel to the sagittal plane of the patient;positioning a hollow apex pin adjacent to an exterior surface of the tibia and co-axial with the boundary line;positioning a fluoroscope so that its field of view is parallel to the anterior-posterior slope of the tibia, parallel to the sagittal plane of the patient, and co-axial with the hollow apex pin;imaging with the fluoroscope and observing the profile of the hollow apex pin so as to confirm that the hollow apex pin is aligned co-axial with the boundary line;advancing the hollow apex pin into the tibia along the boundary line so as to provide a positive stop at the boundary line for limiting cutting along the cutting plane;cutting the tibia along the cutting plane, with the cut terminating at the boundary line;moving the tibia on either side of the cut apart so as to form a wedge-like opening in the tibia; andstabilizing the tibia.