Tibial resection guide alignment apparatus and method
BACKGROUND OF THE INVENTION 
     This invention relates to total knee replacement or arthroplasty and particularly to an alignment apparatus and method for aligning a resection guide used in resecting the tibial plateau. 
     In total knee replacement or arthroplasty, the proximal surface of the tibia is removed or resetted and an implant affixed over the resected surface. The implant includes artificial articulating surfaces to replace the natural articulating surfaces which have been removed. The resection of the proximal surfaces of the tibia must leave a surface having a specific posterior slope and varus/valgus angle that are unique to every patient. Also the depth of the cut must be specifically tailored for the thickness of the implant in order to properly position the artificial articulating surfaces. 
     Due to the critical nature of the cut required through the tibial plateau, a saw guide block or resection guide is preferably fixed to the tibia and used to guide a saw blade in making the cut. The resection guide includes a planar guide surface that guides the saw blade in the appropriate plane to produce the desired resected surface. The resection guide itself must be aligned with its planar guide surface in the plane necessary to provide the desired cut, and alignment devices have been developed to align the resection guide with respect to the surgically exposed tibia. Using the alignment instrument, the resection guide is aligned primarily to match natural landmarks of the tibial plateau and lower leg. 
     The alignment devices include means for adjusting the posterior/anterior slope of the resection guide, the depth of the resection guide&#39;s guide surface below the top of the tibia, and the varus/valgus or lateral/medial slope. Tibial resection guide alignment devices fall into two broad categories, extramedullary mounted devices and intramedullary mounted devices. The extramedullary devices are connected outside the patient&#39;s tibia while the intramedullary alignment devices include an intramedullary rod that is positioned down the central canal of the tibia and the alignment mechanism suspended from the rod. In either type of alignment device, the resection guide was first attached to the device, the device was connected to the patient, and then the alignment device was operated to provide the desired alignment. Once the resection guide was aligned, it was temporarily fixed in place on the anterior side of the tibia and the alignment device removed to allow the cutting or resection operation. 
     An intramedullary or extramedullary mount is generally a matter of preference for the particular surgeon. Prior alignment guides were restricted to one type of mount, either intramedullary or extramedullary. Therefore, to meet surgeon preference, two sets of tools had to be available. Furthermore, the prior intramedullary mounted alignment guides did not provide fine adjustments for cutting depth and slope. 
     SUMMARY OF THE INVENTION 
     It is a general object of the invention to provide a tibial resection guide alignment apparatus and method that overcomes the above problems and others associated with prior alignment devices. More particularly, it is an object of the invention to provide a tibial resection guide alignment apparatus that may be mounted both extramedullar or intramedullar. Another object of the invention is to provide a tibial resection guide alignment apparatus that includes an intramedullary mounting arrangement and still provides for fine depth and slope adjustments. 
     In order to accomplish these objects, the apparatus according to the invention provides both fine slope and depth adjustment mechanisms adjacent to a guide block mount upon which the resection guide is mounted for alignment. The position of the fine adjustment mechanisms near the guide block mount allow the device to be supported by an intramedullary rod or extramedullary mounting arrangement and still provide the desired fine adjustment. The varus/valgus adjustment mechanism is removed from the area of the guide block mount at the end of the extramedullary mounting device and therefore fine varus/valgus adjustment is available only with the extramedullary mount associated with the device. 
     The apparatus includes an elongated base member with a carriage member slideably mounted on the base member along a depth adjustment axis. A depth adjustment mechanism associated with the carriage may be operated to move the carriage along the depth adjustment axis and fix the carriage at a desired position along the axis. A guide block mount to which the resection guide is removably connected is pivotally connected to the carriage so that it may pivot about a slope adjustment axis extending perpendicular to the depth adjustment axis. A slope adjustment mechanism is associated with the carriage and may be operated to pivot the guide block mount about the slope adjustment axis and thereby adjust posterior/anterior slope, and to fix the guide block mount in the desired position about the axis. 
     With the posterior/anterior slope adjustment and depth adjustment mechanisms both associated with the base member, the base member may be connected to the patient&#39;s tibia through either an intramedullary mount or an extramedullary mount and provide the two fine adjustments. With either the intramedullary or extramedullary mount, the alignment device includes an arm connected to the base member in a position to extend over the surgically exposed proximal end of the tibia. The arm includes an opening for receiving an intramedullary rod and also includes members for gripping the proximal end of the tibia. The extramedullary mount includes a separate extramedullary member which may be removably connected to the base member, and a bottom assembly connected to the extramedullary member by which the device may be connected around the patient&#39;s lower leg or ankle. Varus/valgus adjustment is provided in the connection between the extramedullary member and the bottom assembly. 
     The preferred form of the invention includes both a depth stylus and a slope stylus that may be connected to the guide block mount or resection guide itself. The slope stylus includes an elongated slope stylus member preferably lying in the plane of the planar guide surface on the resection guide when the guide is properly connected to the guide block mount. An extension member positions the slope stylus member adjacent to the tibial plateau so that the stylus member provides a visual indication for comparison to the natural posterior/anterior tibial slope. The depth stylus member includes a stylus end that terminates in a plane parallel to the planar guide surface of the resection guide and spaced above such guide plane a distance equal to the thickness of the prosthesis to be implanted. 
    
    
     These and other objects, advantages, and features of the invention will be apparent from the following description of the preferred embodiments, considered along with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is isometric drawing showing a tibial resection guide alignment apparatus embodying the principles of the invention. 
     FIG. 2 is a partial longitudinal section view taken along line 2--2 in FIG. 1. 
     FIG. 3 is a view in section taken along line 3--3 through the varus/valgus adjustment mechanism. 
     FIG. 4 is a partial longitudinal section view of the guide block mount with the depth stylus in position for providing a depth indication. 
     FIG. 5 is a partial longitudinal section view similar to FIG. 4 but showing the slope stylus in position for providing a visual indication of the guide slope. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2 show the tibial resection guide alignment apparatus 10 including a base member 12 having a base opening 14 extending along its length along a depth adjustment axis D. A carriage member 16 is slideably received over the base member 12. The apparatus 10 also includes a guide block mount 20 pivotally connected to the carriage 16 so as to pivot about a slope adjustment axis S extending perpendicular to the depth adjustment axis D. The base member 12 also has associated with it depth adjustment means 22 for positioning the carriage along the depth adjustment axis D, and slope adjustment means 24 for positioning the guide block mount about the slope adjustment axis S. Also, resection guide connecting means 26 associated with the guide block mount 20 allows a resection guide 28 (shown in phantom) to be connected to the guide block mount for alignment. 
     The slope adjustment means 24 includes the nut 18 received in the base opening 14 and a slope adjustment member 30 threaded through the carriage member 16 and the nut, and terminating in a pivot connection 32 to the guide block mount 20. The threaded slope adjustment member 30 may be threaded in and out through the carriage member 16 and nut 18 to force the guide block mount 20 to pivot about the slope adjustment axis S and provide fine posterior/anterior slope adjustment for the resection guide 28 connected to the guide block mount 20. 
     The depth adjustment means 22 includes slots 40 extending along a portion of the base member 12 through which the threaded slope adjustment member 30 passes, and a threaded depth adjustment member 42. The depth adjustment member 42 is threaded through the base opening 14 and rotateably connected at one end to the nut 18. The depth adjustment member 42 threads in and out through the base member 12 to provide fine depth adjustment by forcing the nut 18 through the base member opening 14 and along with the nut, the carriage member 16, threaded slope adjustment member 30, and the guide block mount 20. 
     The resection guide connecting means 26 includes a connecting member 44 extending through an opening through the guide block mount 20 and terminating in a threaded end section 48. The threaded end section 48 is adapted to cooperate with a female threaded opening on the resection guide 28. The resection guide 28 is connected to the guide block mount 20 in this form of the invention by aligning the resection guide on the bottom surface of the guide block mount and turning the threaded connecting member 44 to start the threaded end 48 into the female threaded opening on the resection guide 28 and draw the resection guide tightly against the bottom surface of the guide block mount 20. Also, the resection guide connecting means 26 preferably includes an alignment feature 50 formed on the bottom surface of the guide block mount 20. The alignment feature 50 registers with openings formed on the top of the resection guide 28 to allow the resection guide to be connected in only one position on the guide block mount 20 and ensure that the resection guide 28 is properly connected. 
     A connecting arm member 60 is connected to a top end of the base member 12. The connecting arm 60 extends in the direction in which the guide block mount 20 is separated from the base member 12 and includes an end section 62 which is adapted to extend over the top of a surgically exposed proximal end of a tibia when the base member is properly connected to the tibia in an operating position. A slot in the connecting arm 60 accepts the threaded connecting member 44 with a knurled end 45 of the threaded connecting member extending conveniently above the connecting arm. Preferably two or more engagement or spike members 64 extend downwardly from the end section 62 of the connecting arm 60 in position to be driven into the top of the proximal end of the tibia with the base member in the operating position extending downwardly along the anterior side of the tibia. Also, the connecting arm 60 includes an opening 66 extending through the arm end section 62 for receiving an intramedullary mounting rod 68 (shown in phantom). 
     To accommodate extramedullary mounting, the apparatus 10 also includes an extension member 70 connected to the base member 12 and extending downwardly from the base member in a plane defined substantially by the depth adjustment axis D and the connecting arm 60. The extramedullary mounting arrangement also includes an extramedullary mounting member 72 that may be removably connected to extension member 70 and locked in place with a suitable locking mechanism 74. The locking mechanism allows the overall length of the extramedullary mounting structure to be adjusted to the length of the tibia. A bottom assembly 76 extends at substantially a fight angle to the axis of the extramedullary mounting member 72 and includes a cradle assembly 78 for securing around the patient&#39;s ankle or lower leg. The bottom assembly 76 may also include a receptacle 80 extending in the opposite direction from the ankle cradle assembly 78 for receiving an alignment rod (not shown) which a physician may use in aligning the device 10 on a patient&#39;s tibia. 
     Referring to FIGS. 1, 2, and 3, the preferred extramedullary mounting arrangement also includes varus/valgus adjusting means 84 associated with the bottom assembly 76 and the extramedullary mounting member 72. The varus/valgus adjusting mechanism 84 comprises a threaded adjustment member 86 connected to knurled knobs 88, and a slide device 90 that is threaded over the threaded adjustment member and is connected to the ankle cradle assembly 78. Turning the threaded adjustment member 86 using the knurled knobs 88 causes the threaded slide device 90 to move laterally along the threaded adjustment member 88 therefore moving the ankle cradle assembly laterally as well. 
     Referring now to FIGS. 4 and 5, the apparatus preferably includes a combination depth stylus and slope stylus 100 that may be connected to the resection guide 28 through a stylus connecting member 102. The stylus connecting member 102 preferably includes an end section 104 adapted to extend into an opening through the resection guide 28. The preferred combined depth stylus and slope stylus 100 includes an elongated center section 106 having a slot 108 through which the device may be connected to the top of the stylus connecting member 102. The top of the stylus connecting member 102 includes a reduced diameter section 110 that may extend through the slot 108 with a cap member 112 threaded over the reduced diameter section 110 to fix the combined stylus 100 in the desired position. In addition to the central section 106 of the unitary stylus 100, the stylus includes a depth stylus section 114. The depth stylus section 114 has an end 116 that terminates in a depth plane extending parallel to the plane G of the resection guide 28 guide surface when the guide is properly connected on the guide block mount 20. The depth plane X is also separated from the plane G of the resection guide a distance equal to an implant thickness. The opposite end of the unitary stylus 100 includes a slope stylus section 118 terminating with an elongated slope member 120 that lies in the plane X defined by the guide surface of the resection guide 28 properly received on the guide block mount 20. 
     The operation of the apparatus 10 and the method of the invention may now be described with reference to FIGS. 1-5. First, the resection guide 28 is connected in position on the guide block mount 20 using the connecting member 44. With the resection guide 28 in place, the apparatus 10 is positioned with the end 62 of the connecting arm 60 extending over the surgically exposed proximal end of the patient&#39;s tibia T (FIGS. 4 and 5) and with the base member 12 extending downwardly on the anterior side of the tibia. With the base member 12 properly centered in front of the tibia, the connecting arm end section 62 is driven downwardly driving the spikes 64 into the proximal end of the tibia. At this point, the intramedullary rod 68 is inserted through opening 66 or the extramedullary mounting member 72 is attached over the rod 70 extending from the base member 12. Either mounting method stabilizes the base member 12 in front of the tibia T where the fine posterior/anterior slope adjustment and depth adjustment can be made to properly align the resection guide 28. 
     With the base member 12 stabilized on the anterior side of the tibia T, the stylus 100 is rotated to position the elongated slope stylus member 120 over, or adjacent to, the tibial plateau and the threaded depth adjustment member 42 is rotated to position the slope stylus member 120 just above the tibia as shown in FIG. 5. With the elongated slope stylus member 120 adjacent to the tibial plateau, the slope adjustment member 30 may be threaded in or out to provide fine slope adjustment until the slope of the elongated slope stylus member 120 matches the slope of the natural tibial plateau. Once the slope is matched, the stylus 100 is rotated again to position the depth stylus section over the proximal end of the tibia as shown in FIG. 4. The threaded depth adjustment member 42 can then be turned to move the resection guide 28 and guide block mount 20 downwardly parallel to the depth adjustment axis D until the depth stylus end 116 contacts the proximal end of the tibia T. Both the slope and depth of the resection guide 28 is now set and the resection guide may be temporarily fixed by suitable means to the anterior side of the tibial plateau prior to releasing the guide 28 from the guide block 20 and removing the alignment apparatus 10. 
     Where the extramedullary mount is used, the apparatus 10 also provides a fine varus/valgus angle adjustment through the adjustment mechanism 84 associated with the bottom assembly 76 and the bottom of the extramedullary mounting member 72. By sliding the end of the extramedullary mounting member 72 connected to the bottom assembly 76 along an axis extending perpendicular to the mounting member, the lateral/medial or varus/valgus angle of the attached resection guide 28 may be adjusted. A rod (not shown) may be inserted in the receptacle 80 for providing an alignment reference for the varus/valgus adjustment. 
     The above described preferred embodiments are intended to illustrate the principles of the invention, but not to limit the scope of the invention. Various other embodiments and modifications to these preferred embodiments may be made by those skilled in the art without departing from the scope of the following claims. For example, the resection guide 28 may be secured to the guide block mount 20 by any arrangement that allows the guide 28 to be released readily for removing the apparatus 10. Also, the extramedullary mounting arrangement may include any suitable bottom assembly for providing the desired extramedullary connection. Further, the slope stylus and depth stylus may be separate devices rather than the unitary device shown in the figures. The slope stylus and depth stylus may, in any event, be mounted on the resection guide directly or on the guide block mount.