Abstract:
IM tibia revision tools include a trial stem extender having multiple notches which serve both as depth witness marks and holders for a stop clip, a collection of different sized tibial templates, each template adapted to receive an angular offset positioning guide, a collection of offset bushings, each bushing each bushing having a different offset distance and each being adapted to cooperate with the trial stem extender and the angular offset positioning guide, a neutral bushing for locating the position of the implant boss relative to the tibia and for reaming the tibia to accept the boss of the implant, a fin punch guide and fin punch for preparing the tibia to receive the keel of the tibial component, and a tool for translating the angular offset measurement to the tibial component. Tibial components according to the invention have three parts: the baseplate portion, the offset portion, and the stem portion. Each portion is provided in a variety of sizes and the portions may be mixed and matched according to the measurements made with the tools described above. Methods for using the tools and the tibial components are also disclosed.

Description:
This application is a continuation of U.S. Ser. No. 09/170,572 filed Oct. 13, 1998, now U.S. Pat. No. 6,063,091. 
     This application is related to co-owned Ser. No. 09/049,705, filed Mar. 28, 1998, entitled Methods and Tools for Femoral Imtermedullary Revision Surgery now U.S. Pat. No. 6,258,095, the complete disclosure of which is hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to methods and tools used in knee arthroplasty. More particularly, the invention relates to methods and tools used in revision surgery where an artificial tibial component is removed and replaced. The invention also relates to improved tibial components. 
     2. Brief Description of the Prior Art 
     Total knee arthroplasty involves the replacement of portions of the patellar, femur and tibia with artificial components. In particular, a proximal portion of the tibia and a distal portion of the femur are cut away (resected) and replaced with artificial components. As used herein, when referring to bones or other body parts, the term “proximal” means closest to the heart and the term “distal” means more distant from the heart. When referring to tools and instruments, the term “proximal” means closest to the practitioner and the term “distal” means more distant from the practitioner. 
     There are several types of knee prostheses known in the art. One type is sometimes referred to as a “resurfacing type”. In these prostheses, the articular surface of the distal femur and proximal tibia are “resurfaced” with respective metal and plastic condylar-type articular bearing components. These knee prostheses provide adequate rotational and translational freedom and require minimal bone resection to accommodate the components within the boundaries of the available joint space. 
     The femoral component is a metallic alloy construction (cobalt-chrome alloy or 6A14V titanium alloy) and provides medial and lateral condylar bearing surfaces of multi-radius design of similar shape and geometry as the natural distal femur or femoral-side of the knee joint. 
     The tibial component usually includes a distal metal base component and a proximal interlocking plastic, e.g. UHMWPE (ultra high molecular weight polyethylene), component or insert. The plastic tibial plateau bearing surfaces are of concave multi-radius geometry to more or less match the articular geometry of the mating femoral condyles. Both the femoral and tibial components are usually provided with intermedullary (IM) stem options. 
     After preparing the distal surface of the femur and the proximal surface of the tibia, an opening is made into the medullary canal of the femur, and an opening is made into the medullary canal of tibia. The interior surface and the IM stem of the femoral component are usually covered with a polymeric cement and the IM stem is inserted into the medullary canal of the femur until the interior surface of the femoral component meets the distal surface of the femur. The tibial component is similarly usually cemented to the proximal surface and medullary canal of the tibia. 
     Occasionally, the components are press fit without the use of cement. The use of cement has advantages and disadvantages. Press fit components rely on bone quality to obtain good fixation. Sometimes it is impossible to obtain good fixation with a press fit component and sometimes a press fit component will fail early because of failure of successful biological ingrowth. Cement assures good fixation but puts strain along the component stem. In addition, as described below, cement complicates the removal of a failed component. 
     Often, due to normal wear over time, the prosthetic knee must be replaced via a procedure known as revision surgery. When the primary cemented prosthetic is removed, the proximal surface of the tibia and the distal surface of the femur typically exhibit cavernous defects. Absent the use of bone graft, the proximal surface of the tibia and the distal surface of the femur must be carefully resected to remove cavernous defects before a replacement knee can be installed. 
     In addition, the intramedullary (IM) canals must be broached or reamed to remove any remaining cement or cavernous defects existing in the canals before a replacement knee can be installed. 
     According to the state of the art, after the primary prosthetic is removed, the proximal tibia is resected with a lateral template. The medullary canal is reamed and the reamer is tapped in place with a mallet. A proximal resection guide is attached to the reamer and proximal resection is completed via slots in the guide. Preparation of the distal femur is described in the above referenced related application. 
     The defects in the tibia are measured and the cutting guide is moved down 6 to 10 mm. A flat cut from anterior to posterior is made. A tibial template is attached to the reamer and reference marks are typically in pen. A flat cut and sagittal cut are made relative to the reference marks. Another template is attached to the reamer and anterior and posterior holes are drilled for securing a wedge resection guide. A wedge cut is then made. The template is replaced and aligned with the marks. A revision mask punch guide is attached to the template and a revision box chisel is used to prepare for a stem. 
     Those skilled in the art will appreciate that revision surgery is difficult because (1) the type and location of cavernous defects make it difficult to match the exterior surfaces of the tibia and femur to the interior surfaces of the prosthetic, (2) the femur and tibia must be resected with reference to the IM canal, and (3) the use of multiple templates and guides during the course of the procedure makes it very difficult to keep all the cuts in proper alignment relative to the IM canal. 
     In particular, with respect to the tibia, resection of the proximal tibia results in the creation of a tibial plateau in which the IM canal is no longer centrally located. If a normal tibial component is installed, portions of the tibial component will overhang the resected tibial plateau. 
     In order to compensate for this problem, it is known in the art to provide tibial components with offset IM stems. However, the relative location of the IM canal relative to the perimeter of the tibial plateau may be offset in any direction, anterior, posterior, medial, or lateral, depending on the individual bone. It is impossible or at least impractical to provide an offset stem tibial component for every possible variation in the relative location of the IM canal. 
     Moreover, it is difficult to estimate the offset of the IM canal in order to choose an appropriate offset tibial component. 
     According to the state of the art, offset tibial components are selected by trial and error, a tedious procedure which prolongs surgery. For example, as shown in FIG. 1, a relatively symmetrical tibial plateau  10  exhibits the IM canal  12  in a central location. After resection of the tibial plateau, the location of the IM canal may be located off center as shown in FIGS. 2 and 3 where canals  12 ′ and  12 ″ are seen to be located off center relative to the plateaus  10 ′ and  10 ″ respectively. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide methods and tools for performing IM revision surgery. 
     It is also an object of the invention to provide tools for IM revision surgery which maintain proper alignment with the IM canal while multiple resection cuts are made, tools for determining the offset location of the IM canal relative to the tibial plateau, tools which enhance the accuracy of IM revision surgery and enhance the stability of the revision implant. 
     It is another object of the invention to provide methods for performing IM revision surgery in which a minimum number of tools are used. 
    
    
     The methods and tools of the invention provide accurate location of bone cuts so that the revision prosthetic is correctly oriented relative the IM canal and the bone cuts. Moreover, the tools and methods provide accurate measurements for use in selecting the appropriate tibial component and for adjusting the angular offset of the tibial component according to the measurements. Additional objects and advantages of the invention will become apparent to those skilled in the art upon reference to the detailed description taken in conjunction with the provided figures. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic plan view of a relatively symmetrical tibial plateau; 
     FIG. 2 is a view similar to FIG. 1 showing a slightly offset IM canal; 
     FIG. 3 is a view similar to FIG. 1 showing a more dramatically offset IM canal; 
     FIG. 4 is a perspective view of the resection guide tower attached to the tool stem; 
     FIG. 5 is a perspective view of the impactor/extractor; 
     FIG. 6 is a broken perspective transparent view of the guide tower installed in the IM canal of the tibia; 
     FIG. 7 is a view similar to FIG. 6 with the optional collar attached to the tool stem; 
     FIG. 8 is a broken perspective view of the cutting block attached to the tool stem; 
     FIG. 9 is a view similar to FIG. 8 showing the optional extra medullary referencing tool attached to the cutting block; 
     FIG. 10 is a broken perspective transparent view of a trial stem extender and trial stem inserted into the IM canal of the tibia; 
     FIG. 11 is a broken perspective view showing the tibial template and offset positioning guide placed over the trial stem on the tibial plateau; 
     FIG. 12 is a view similar to FIG. 11 showing the 4 mm offset bushing installed in the angular offset positioning guide; 
     FIG. 13 is a perspective view of the 4 mm, 6 mm. and 8 mm offset bushings; 
     FIG. 14 is view similar to FIG. 12 showing the optional stop clip attached to the trial stem extender; 
     FIG. 15 is an enlarged broken perspective view of the 4 mm offset bushing installed in the angular offset positioning guide indicating an angular offset of 320 degrees and showing the template pinned to the tibia; 
     FIG. 16 is a view similar to FIG. 15 showing the 4 mm offset bushing removed and the boss reamer bushing in its place; 
     FIG. 17 is a view similar to FIG. 16 showing the boss reamer (or optionally an offset boss reamer) in the reamer bushing; 
     FIG. 18 is a view similar to FIG. 17 with the reamer, bushing, and angular offset guide removed from the template and with the fin punch guide and fin punch in their place; 
     FIG. 19 is an exploded perspective view of a tibial component according to the invention; 
     FIG. 20 is an exploded perspective view of the component stem and wrench; 
     FIG. 21 is an exploded perspective view of the tibial component and the tool for translating the angular offset to it; and 
     FIG. 22 is a sectional view of the component and tool of FIG.  21 . 
    
    
     DETAILED DESCRIPTION 
     An illustrative embodiment of the invention is set forth hereinafter. The illustrative embodiment makes reference to specific measurements for tool diameters, cut depths, etc., which are intended only to give those skilled in the art an appreciation for the operating principals of the invention without any intent of limiting the spirt or scope thereof. It is applicants&#39; intention that the invention only be limited by the appended claims and not any of the exemplary measurements set forth in the illustrative embodiment of the invention. 
     According to the methods of the invention, the previous tibial component is removed from the tibia and the IM canal of the tibia is reamed as described in the parent application hereto. 
     Referring now to FIG. 4, after the tibial IM canal is prepared, based on the diameter and reaming depth of the last IM reamer used, an appropriate tool stem  20  is chosen for attachment to the resection guide tower  22 . The tower  22  has a boss  24  with a pair of surface grooves  26 , a stem  28  with a pair of surface grooves  30 , and an upstanding shaft  32  therebetween. The boss  24  has interior threads (not shown) and the stem  20  is provided with engaging exterior threads (not shown). According to one embodiment of the invention, the boss  24  has a diameter of 15 mm and several stems  20  of different diameter are provided for attachment to the tower  22 . 
     Turning now to FIGS. 5 and 6, the resection guide tower  22  with the attached tool stem  20  is installed in the IM canal  34  of the tibia  36  with the aid of the impactor/extractor  40 . The tool  40  has a proximal handle  42 , a distal coupling  44 , and a sliding mass  46 . The coupling  44  has a slot  44   a  which is dimensioned to receive the stem  28  of the tower  22 , and a pair of distal shoulders  44   b  which are dimensioned to fit into the slots  30  of the stem  28 . A spring loaded latch  44   c  is located adjacent to the slot  44   a.    
     The tool  40  is removably attached to the tower  22 . The stem  20  of the tower is then inserted into the IM canal  34  and the sliding mass  46  of the tool  40  is slid distally. The force of the accelerated mass  46  impacts the coupling  44  and drives the stem  20  of the tower  22  into the IM canal  34 . If necessary, the mass is slid several times until the stem  22  is fully inserted into the IM canal  34 . After the tower is installed, as shown in FIG. 6 the impactor/extractor tool is uncoupled from the tower. 
     In situations where the IM canal opening is enlarged and does not provide adequate support or a good reference point to seat the tower, a tibial collar  48 , shown in FIG. 7, is attached to the boss  24  by engaging the grooves  26 . The tibial collar  48  is shaped and dimensioned to cover the tibial plateau  37 . In addition to stabilizing the tower  22 , the collar  48  aids in preliminary sizing of the tibial plateau  37 . 
     Once the tower  22  is properly installed, a tibial cutting block  50  (which is provided in separate left and right versions) is attached to the upstanding shaft  32  of tower  22  as shown in FIGS. 8 and 9 by means of a cam lock  52  and the two ⅛″ drill bits  54 ,  56  inserted into holes  58 ,  60 . If desired, as shown in FIG. 9, a handle  70  and rod  72  are attached to the cutting block  50  so that an optional visual EM alignment inspection can be made. 
     With the cutting block  50  so secured, a typical 2 mm clean-up cut can be made using the proximal surface  62  of the cutting block as a guide. According to a preferred embodiment of the invention, three degrees of posterior slope is built into the cutting block and this is why separate left and right cutting blocks are provided. Slots  64 ,  66  are provided for optional wedge cuts. After the clean-up cut and wedge cuts (if desired) are made, the cutting block  50  and the tower  22  are removed from the tibia  36 . The removal of the cutting block and tower is effected with the aid of the impactor extractor  40 . 
     Turning now to FIG. 10, after the cutting block and tower are removed from the tibia, a trial stem extender  74  is attached to the trial stem  20  (or another trial stem of the same size). The trial stem extender has a proximal coupling  76  for coupling to the impactor/extractor, and three pairs of circumferential grooves  78 ,  80 ,  82  which serve as witness marks and receivers for a stop clip (described below with reference to FIG.  14 ). The witness marks are useful in determining the length of the stem portion of the tibial component implant. 
     With reference to FIG. 11, with the trial stem and extender  74  in place, an appropriately sized tibial template  84  is selected. The templates  84  are provided in a variety of sizes to correspond to different sized tibial plateaus  37 . The size of the template  84  chosen may be based on the size of the collar  48  chosen above. According to the invention, therefore, several different sized templates  84  are provided. Each template  84  has a central circular opening  86  of standard size for receiving the offset positioning guide  88 . The offset positioning guide  88  is a generally cylindrical member with a plurality of circumferential markings  90  which indicate angles between 0 degrees and 360 degrees. For clarity, the angle values are not shown in the drawing, except for FIG. 15 which only shows one angle value. 
     In the presently preferred embodiment, the angle markings  90  are spaced 5 degrees apart (i.e. there are seventy-two markings about the perimeter of the offset positioning guide  88 ). As suggested by FIG. 15, in the preferred embodiment, the angle values are provided for every other angle marking  90 . The tibial template  84  is also provided with a plurality of pin receiving holes  92  (described below with reference to FIG.  15 ), and a coupling  94  for an optional EM alignment guide (like the guide  70 ,  72  shown in FIG.  9 ). 
     Turning now to FIGS. 12 and 13, the tools of the illustrative embodiment of invention include three offset bushings  96 ,  98 ,  100 . Each bushing is a substantially cylindrical member which is dimensioned to fit within the cylindrical offset positioning guide  88  as shown in FIG.  12 . 
     Each bushing  96 ,  98 ,  100  is provided with a circumferential indicator  96   a ,  98   a ,  100   a  and a throughbore  96   b ,  98   b ,  100   b  which is designed to receive the trial stem extender  74 . According to the invention, the throughbores are not centrally located relative to the center of the cylindrical bushings. Each bushing  96 ,  98 ,  100  has a throughbore  96   b ,  98   b ,  100   b  which is offset a different amount from the center of the cylindrical bushing. 
     According to the presently preferred embodiment, bushing  96  has a 4 mm offset, bushing  98  has a 6 mm offset, and bushing  100  has an 8 mm offset. The circumferential indicators  96   a ,  98   a ,  100   a  are preferably located on the same radius along which the throughbores  96   b ,  98   b ,  100   b  are offset. 
     As shown in FIGS. 12 and 14, an appropriate offset bushing, e.g.  96 , is chosen and fitted into the cylindrical offset positioning guide  88  with the trial stem extender  74  extending through the throughbore, e.g.  96   b . The appropriate bushing is chosen by visual assessment or by trial and error. Optionally, if the trial stem and extender  74  are unstable in the IM canal, a stop clip  102  may be attached to one of the grooves in the extender  74  as shown in FIG.  14 . 
     With the extender  74 , template  84 , cylindrical offset positioning guide  88 , and bushing  96  assembled as shown, the bushing is rotated relative to the cylindrical offset positioning guide  88  until the template  84  assumes a position relative to the tibial plateau  37  where there is minimum or no overhang. When the optimal (best) position is obtained, the template  84  is pinned to the tibia  36 , for example with ⅛″ drill pins (or headed nails)  104  through the pin receiving holes  92 . The angle indicated by the indicia  96   a  and  90  is noted before the bushing  96  and stem with extender  74  are removed. 
     According to the invention, a neutral (boss reaming) bushing  106  is provided. The neutral bushing  106  is substantially the same size and shape as the offset bushings  96 ,  98 ,  100 , but has a centrally located throughbore  107  and no radial indicia. The purpose of the neutral bushing is to act as a guide for reaming a hole in the center of the tibial plateau  37  for receipt of the boss portion of the tibial implant. Those skilled in the art will appreciate from the foregoing that the location of the center of the “boss hole” will be offset from the tibial IM in the angular direction indicated by the indicators  90 ,  96   a  at the step shown in FIG. 15 by an amount equal to the offset amount of the bushing  96  (e.g. 4 mm). 
     Turning now to FIG. 17, with the template  84  pinned to the tibia  36  by drill pins  104  and with the neutral bushing  106  inserted in the offset positioning guide  88 , a boss reamer  110  (or optionaly an offset boss reamer) is inserted into the throughbore  107  of the neutral bushing  106 . The illustrative boss reamer  110  shown in FIG. 17 is 15 mm in diameter and has two depth markings shown,  112  and  114 . All of the tibial baseplates according to the illustrative embodiment of the invention have a 15 mm diameter boss, but different baseplates have bosses with different lengths. 
     Having chosen the appropriately sized template  84 , the practitioner will know which tibial baseplate will be used in the implant and will know how deep to ream the hole for the boss of the baseplate. Thus, at this stage of the method of the invention, the practitioner uses the reamer  110  to ream to the appropriate depth indicated by the appropriate depth mark  112  or  114 . 
     After reaming for the baseplate boss, the tibia is punched to make space for the baseplate fins or “keel”. The boss reamer  110 , the neutral bushing  106 , and the offset positioning guide  88  are removed and the template  84  is left pinned to the tibia. The fin punch guide  120 , shown in FIG. 18, is attached to the template  84 . The guide  120  has left and right fin guides  122 ,  124  and a central boss guide  126 . The fin punch  130  has left and right fins  132 ,  134  and a central boss  136 . 
     The punch  130  is inserted into the punch guide  120  as shown in FIG. 18 with the central boss  136  entering the central boss guide  126  and the left and right fins  132 ,  134  entering the left and right fin guides  122 ,  124 . With the punch  130  in place, it is struck with a mallet (or attached to the impactor/extractor), driven into the tibial plateau, and then removed. Optionally, if a wedge cut had not been performed at the start (i.e. during the steps described with reference to FIGS.  8  and  9 ), a wedge cutting guide (not shown) may be attached to the coupling  94  of the template  84  and a wedge cut performed at this stage of the procedure. 
     All of the apparatus are now removed from the tibia and the tibial component is prepared for implant into the tibia. As mentioned above and as shown in FIG. 19, the tibial component  140  includes the baseplate portion  142 , the offset portion  144 , and the stem portion  146 . It will be appreciated that the tibial component  140  is shown inverted and exploded in FIG. 19 to illustrate the manner in which it is assembled rather than the manner in which it is implanted. 
     The baseplate  142  can be seen to have a central boss  148  and a pair of fins  150 ,  152 . The offset portion  144  has a male coupling  154  which engages the boss  148 , and a female coupling  156  which mates with the stem portion  146 . The axes of the couplings  154  and  156  are offset by a certain amount, e.g. 4 mm, 6 mm, or 8 mm, corresponding to the offset bushings  96 ,  98 ,  100  shown in FIG.  13  and described above. Between the male coupling  154  and the female coupling  156  is a tightening nut  155  which is used to lock the angular position of the two couplings relative to each other as described in detail below with reference to FIGS.  21  and  22 . 
     According to the presently preferred embodiment, the stem  146  has a male coupling  158  at its proximal end and a trifurcated distal end  160 . The fluted stem  146  is preferably coupled to the offset component  144  with the air of a trifluted wrench  162  which is shown in FIG.  20 . 
     Turning now to FIG. 21, the offset portion  144  is fixedly attached to the stem portion  146  and loosely coupled to the baseplate portion  142 . The baseplate portion  142  is placed in the base  164  of an angular adjustment tool  166 . A turntable portion  168  of the tool  166  is placed over the stem portion  146 , the offset portion  144  and tightening nut  155 , engaging both the base  164  and baseplate portion  142 . The turntable  168  has a locking knob  170  and an angle indicator/wrench key  172 . 
     With the tool  166  assembled about the tibial component  140  as shown in FIG. 22, the angle indicator/wrench key  172  is turned until it indicates the angle previously noted at the step described with reference to FIG.  15 . When the angle has been so “dialed in”, the offset portion  144  is tightened to the baseplate  142  using the wrench  174  (FIG. 21) on the tightening nut  155 . The tibial component is now assembled and ready for implantation. Optionally, if wedge cuts had been made, one or more wedges may be added to the bottom of the baseplate  142  either before or after the assembly of the baseplate, stem, and offset portion. 
     There have been described and illustrated herein methods and tools for IM revision surgery involving tibial components. While particular embodiments of the invention have been described, it is not intended that the invention be limited thereto, as it is intended that the invention be as broad in scope as the art will allow and that the specification be read likewise. It will therefore be appreciated by those skilled in the art that yet other modifications could be made to the provided invention without deviating from its spirit and scope as so claimed.