Bone resection apparatus and method for knee surgery

Abstract

A bone resection apparatus and its method of use for knee surgery are presented. In one aspect of the invention, the apparatus includes a spacer and a tibial cut guide. The spacer has a first surface engageable with the cut distal femoral bone and a second surface opposite the first surface engageable with the uncut proximal tibial bone in joint articulating relationship. The spacer further includes a cut guide support. The tibial cut guide has a cutter guide defining a cut plane and a support engaging element engageable with the cut guide support. The cut guide support and support engaging element cooperate to position the cut plane in relative to the first surface.

1 . An apparatus for guiding a bone cut during knee joint replacement surgery in which a portion of the distal femur and a portion of the proximal tibia are removed and replaced with prosthetic components, the knee joint comprising a tibia and a femur and having a medial/lateral axis, an anterior/posterior axis, and a proximal/distal axis, rotation about the medial/lateral axis corresponding to posterior slope rotation, and rotation about the anterior/posterior axis corresponding to varus/valgus rotation, the apparatus comprising:
 a spacer having a first surface engageable with the cut distal femoral bone, a second surface opposite the first surface engageable with the uncut proximal tibial bone in joint articulating relationship, and a cut guide support; and   a tibial cut guide having a cutter guide defining a cut plane and a support engaging element engageable with the cut guide support, the cut guide support and support engaging element cooperating to position the cut plane in predetermined posterior slope angular relationship to the first surface.   
     
     
         2 . The apparatus of  claim 1  wherein the first surface comprises a planar seating portion. 
     
     
         3 . The apparatus of  claim 2  wherein the second surface comprises an arcuate condylar surface arching away from the planar seating portion generally in the shape of an anatomic femoral condyle. 
     
     
         4 . The apparatus of  claim 3  wherein the condylar surface is curved in a sagittal plane to match, the general anterior/posterior curvature of an anatomic femoral condyle. 
     
     
         5 . The apparatus of  claim 4  wherein the condylar portion is curved in a frontal plane to match the general medial/lateral curvature of an anatomic femoral condyle. 
     
     
         6 . The apparatus of  claim 4  further comprising a plurality of spacers having different curvatures to permit selection of a spacer that best matches a patient's anatomy. 
     
     
         7 . The apparatus of  claim 3  wherein the spacer has a condylar thickness, the apparatus further comprising a plurality of spacers having different condylar thicknesses. 
     
     
         8 . The apparatus of  claim 1  wherein the cut guide support comprises an elongated member having a longitudinal axis and projecting outwardly from the spacer. 
     
     
         9 . The apparatus of  claim 8  wherein the longitudinal axis of the cut guide support forms a predetermined tibial posterior slope angle relative to the first surface. 
     
     
         10 . The apparatus of  claim 9  wherein the apparatus further comprises a plurality of spacers having different posterior slope angles between zero and ten degrees. 
     
     
         11 . The apparatus of  claim 8  wherein cut guide support comprises a non-circular cross section and the tibial cut guide comprises a body having a front surface, a back surface, and an aperture through the body from the front surface to the back surface, the aperture having a non-circular cross section for receiving the support, the aperture and support permitting linear translation of the cut guide relative to the spacer and maintaining a fixed angular relationship between the cut guide and the spacer. 
     
     
         12 . The apparatus of  claim 8  wherein cut guide support comprises a circular cross section and the tibial cut guide comprises a body having a front surface, a back surface, and an aperture through the body from the front surface to the back surface, the aperture having a circular cross section for receiving the support, the aperture and support permitting linear translation of the cut guide relative to the spacer, varus/valgus rotation of the cut guide relative to the spacer, and maintaining a fixed posterior slope angular relationship between the cut guide and the spacer. 
     
     
         13 . The apparatus of  claim 11  wherein the body further includes a saw slot extending through the body from the front surface to the back surface, the saw slot defining a cut plane, the cut plane being oriented parallel to the longitudinal axis of the support. 
     
     
         14 . The apparatus of  claim 13  wherein the body further includes at least one fixation hole formed through the body from the front surface to the back surface, the at least one fixation hole having a longitudinal axis, the at least one fixation hole being oriented such that its longitudinal axis is parallel to the longitudinal axis of the support. 
     
     
         15 . An apparatus for use in knee surgery in which a portion of the distal femur and a portion of the proximal tibia are removed and replaced with prosthetic components, the apparatus comprising:
 an implant including a femoral component having a femoral component thickness and a tibial component having a tibial component thickness, the implant having an overall implant thickness which is the sum of the femoral component thickness, the tibial component thickness, and an additional joint laxity distance corresponding to a desired amount of joint laxity;   a spacer having a body including a planar seating surface, an arcuate condylar surface arching away from the seating surface generally in the shape of an anatomic femoral condyle, and an elongated support having a longitudinal axis, the spacer having a spacer thickness normal to the planar seating surface; and   a tibial cut guide having a body with a front surface, a back surface, and an aperture through the body from the front surface to the back surface having a longitudinal axis, the aperture being engageable with the support for linear translation parallel to the aperture longitudinal axis, a cutter guide slot extending through the body from the front surface to the back surface, the cutter guide slot defining a cut plane oriented parallel to the aperture longitudinal axis, the cut plane being spaced a predetermined distance from the aperture such that with the aperture engaged with the support the cut plane is spaced from the arcuate condylar surface a tibial resection distance.   
     
     
         16 . The apparatus of  claim 15  further comprising a plurality of spacers, each of the plurality of spacers having a different spacer thickness, each spacer being engageable with the cut guide to produce a different tibial resection distance. 
     
     
         17 . The apparatus of  claim 15  wherein with the aperture engaged with the support the cut plane is spaced from the planar seating surface a distance equal to the overall implant thickness. 
     
     
         18 . A method of performing knee surgery comprising:
 resecting a portion of the distal femoral bone;   inserting a spacer into the knee joint to abut the cut surface of the femoral bone, the spacer having an arcuate condylar portion facing away from the cut surface;   abutting the arcuate condylar portion with the proximal tibial surface;   mounting a tibial cut guide on the spacer to position a cut plane at a predetermined posterior slope angle and depth relative to the cut surface of the femoral bone;   and guiding a cutter in the cut plane with the cut guide to form a planar surface on the tibia.   
     
     
         19 . The method of  claim 18  further comprising before the step of mounting the tibial cut guide, the steps of:
 articulating the knee joint between flexion and extension such that the proximal tibial surface articulates with the arcuate condylar portion of the spacer to evaluate knee kinematics; and   placing the knee joint in extension.   
     
     
         20 . The method of  claim 18  further comprising mounting a femoral implant component on the femur and mounting a tibial implant component on the tibia, wherein inserting a spacer comprises inserting a spacer having a thickness corresponding to the femoral implant component thickness plus an additional thickness corresponding to a desired joint laxity such that the cut guide guides the cutter to remove a portion of tibial bone equal in thickness to the tibial implant component thickness. 
     
     
         21 . The method of  claim 18  further comprising mounting a femoral implant component on the femur and mounting a tibial implant component on the tibia, wherein inserting a spacer comprises inserting a spacer having a thickness greater than the femoral implant component thickness plus an additional thickness corresponding to a desired joint laxity such that the cut guide guides the cutter to remove a portion of tibial bone having a thickness less than the tibial implant component thickness. 
     
     
         22 . The method of  claim 18  further comprising mounting a femoral implant component on the femur and mounting a tibial implant component on the tibia, wherein inserting a spacer comprises inserting a spacer having a thickness less than the femoral implant component thickness plus an additional thickness corresponding to a desired joint laxity such that the cut guide guides the cutter to remove a portion of tibial bone having a thickness greater than the tibial implant component thickness. 
     
     
         23 . The method of  claim 18  wherein resecting a portion of the distal femoral bone comprises resecting a portion of the distal femur perpendicular to the mechanical axis of the femur. 
     
     
         24 . The method of  claim 18  further comprising rotating the tibial cut guide relative to the spacer to vary the varus/valgus angle of the cut plane relative to the cut surface of the femoral bone.