Traditionally, when performing a partial knee replacement procedure, a practitioner first makes a horizontal femoral cut in the distal femur to remove diseased bone and provide a surface for receiving a femoral prosthesis. The proximal tibia is then cut to remove any diseased bone and provide a surface and sufficient clearance for receiving a tibial prosthesis. The femoral and tibial prostheses mate to form a replacement partial knee.
In this traditional procedure, the ultimate alignment of the leg after the prostheses are implanted is determined by the location of the tibial cut with respect to the femoral cut. After the femoral cut has been completed, the practitioner selects the location for the tibial cut based primarily on experience and with the understanding that tibial prostheses are available in a limited number of thicknesses. The tibial cut accordingly is made as close to the proximal end of the tibia as possible, based on how much of the tibia must be removed due to disease, plus whatever additional spacing is required to accommodate the closest standard sized tibial prosthesis. After the tibial cut is made, the prostheses are temporarily implanted and the alignment of the leg is analyzed. To adjust the leg alignment, the practitioner can replace the tibial prosthesis with one of a different thickness, can remove more bone, or can do both. This procedure is followed until the leg is in the desired alignment and balance.
Because the location of the tibial cut is independent of the location of the femoral cut, such a procedure may result in the practitioner making numerous cuts before the desired leg alignment and tension are attained. Also, as a result of this trial-and-error process, practitioners may at times remove more bone than necessary.
One method and instrumentation for making horizontal, femoral and tibial cuts is disclosed in U.S. Pat. Nos. 5,122,144 and 5,234,433, both to Bert et al. The Bert et al. patents disclose a first instrument for aligning and making the horizontal femoral cut, and a second instrument for aligning and making the horizontal tibial cut.