Patent Abstract:
The present invention is a rotating track cutting guide system that maintains precise alignment of a bone saw with bone tissue. The rotating track cutting guide generally includes a track subassembly and cutting guide subassemblies attachable to the bone that is to be cut. The track subassembly supports an oscillating surgical saw driver. The track subassembly is removably securable to cutting guide subassemblies which are attachable to the desired bone to facilitate a series of controlled cuts. The design of the track subassembly stabilizes the oscillating saw driver and enables it to both rotate in the plane of the saw blade and move linearly along the track.

Full Description:
This application claims priority to U.S. Provisional Application No. 60/314,475 filed Aug. 23, 2001, the contents of which are incorporated herein in their entirety by this reference. 

   FIELD OF THE INVENTION 
   The present invention relates to instrumentation used for precision bone cutting. More specifically, the invention relates to a cutting guide apparatus for guiding a bone saw to allow for the surgical preparation of bone joint structures to facilitate the implantation of artificial joint prostheses. 
   BACKGROUND OF THE INVENTION 
   In total knee arthroplasty, a damaged knee joint is replaced with a prosthesis to reproduce natural knee function. Multiple faceted cuts are made on the femur and at least one cut is made to the tibia to prepare the bone surface for application of the knee replacement prosthesis. These cut surfaces are preferably precisely angularly aligned to each other and are planar to enable satisfactory mating with the prosthesis. 
   In preparing the joint for a prosthesis, a series of cuts are made to the inferior end of the femur and the superior end of the tibia. Exemplary femoral cuts are depicted in FIG.  1 . Initially the femur is cut to create a flat surface (annotated “A” in the drawings) generally perpendicular to the longitudinal mechanical axis of the bone. Next, two flat cuts are made generally parallel to the longitudinal mechanical axis of the femur: one at the rear of the knee to remove the posterior femoral condyles B and another at the front of the knee C. Lastly, two chamfered cuts D, D′ are made at approximately a forty-five degree angle at the juncture of the perpendicular and the anterior and posterior planes (or “planed femoral surfaces”). The superior end of the tibia is cut off perpendicular to the longitudinal mechanical axis of the tibia in a fashion similar to femoral cut A. 
   Skeletal joints are subject to high degrees of mechanical stress. The secure attachment of joint replacement structures to the bone is, therefore, critical in determining the long-term success of the surgical procedure. The accuracy with which the bone ends are shaped is essential to achieving a secure connection between the existing bone and an implanted prosthesis. 
   A number of studies have documented the correlation between imprecise bonding surface preparation and later complications for joint replacement patients. Knee implant malpositioning due to deficient bone resecting technique contributes to poor long-term results by influencing a prosthesis&#39; function, load distribution, wear and fixation. 
   These discoveries have led researchers to propose standards that improve the likelihood of post-surgical success. Sandborn et al. recommended that the gap between the bone and a porous-coated knee implant not exceed 0.5 mm for optimal bone ingrowth. P. M. Sandborn et al.,  The Effect Of Surgical Fit On Bone Growth Into Porous Coated Implants , 12 Trans. Orthop. Res. Soc., 217 (1987). Cooke et al proposed a maximum cutting error of ±1 mm for proper bone fixation into a porous-coated prosthesis. T. D. Cooke et al.,  Universal Bone Cutting Device For Precision Knee Replacement Arthroplasty And Osteotomy . 7 J. Biomed. Eng. 45, 50 (1985). These levels of accuracy are currently difficult to achieve. 
   Unfortunately, these currently exists as much as a ten-fold discrepancy between the precision of the implant manufacturing tolerances (±0.2 mm) and the bone cutting process. Bone cements are often used to fill the gap between resected bone tissue and the prosthesis. Even with the use of bone cement, however, an uneven cement mantle due to poor bone cutting can result in early prosthesis loosening. 
   To aid the surgeon in making the precise multiple bone cuts required for this type of surgery, various guides and devices have been proposed. An initial group of devices are secured to the saw driver and to the patient and/or the surgical table. A second group includes cutting guides that guide the saw blade, typically within a close fitting slot. 
   The first group includes, for example, U.S. Pat. No. 4,457,307, issued to Stillwell, which discloses a bone cutting device for total knee replacements that is secured to the femur throughout its use. With this device, cuts are made both to the femur and the tibia. The Stillwell design requires removal of a large amount of soft tissue and a substantial number of calculations and adjustments in order to make the cuts required for total knee replacement surgery. 
   U.S. Pat. No. 4,574,794, issued to Cooke et al., discloses a guide for supporting a bone saw driver. The Cooke guide includes a complex system of parallel guide rods secured to the operating table as well as to the long bones of the leg and the bones of the foot. The device requires extensive fixation to the bone and numerous calculations to generate the desired cuts on the knee joint. U.S. Pat. No. 5,007,912, issued to Albrektsson et al., discloses a cutting device mounted to a frame. The frame is connected to the patient&#39;s femur and to the operating table. Similar to the Cooke device, this system requires extensive manipulation of the saw driver and the patient to create the required cuts. 
   U.S. Pat. No. 5,092,869, issued to Waldron, discloses a surgical saw guide, including retractable guide pins mounted in guide pin holders which stabilize the saw for translational movement along a linear axis. 
   U.S. Pat. Nos. 5,228,459 and 5,304,181, issued to Caspari et al., disclose an apparatus that is affixed to the tibia and the ankle that includes a rack and pinion mechanism to linearly advance a surgical milling device to make the appropriate surface cuts for total knee replacement surgery. The &#39;181 patent discloses refinements to the device of the &#39;459 patent. 
   U.S. Pat. No. 5,653,714, issued to Dietz et al., discloses a multi-component assembly that slides and pivots a milling head in order to make the cuts required for knee replacement surgery. 
   The second group of cutting guide systems includes devices such as that disclosed in U.S. Pat. No. 5,925,049, issued to Gustilo et al. The Gustilo patent discloses slotted cutting guides which are secured to the bone end by screws or other fixtures. Slotted cutting guides assist in orienting the blade of a surgical bone saw during the cutting process. 
   Despite these efforts, there remains room for improvement in the creation of precise and accurate bone cuts with current cutting technologies. 
   Devices that guide the saw body tend to be complex and cumbersome to set up, adjust and use. Orthopedic surgery is a physically demanding, labor intensive and time-consuming endeavor. Added instrument complexity tends to lead to longer procedures, which results in surgeon fatigue and a greater chance of surgical error. 
   Surgical cutting guides tend to obstruct the surgeon&#39;s view of the cutting site. This increases the risk of inadvertent damage to surrounding tissue, and can reduce the accuracy of a cut. 
   The oscillating saw used by orthopedic surgeons can be guided along a surgical cutting guide by hand. Some cutting guides utilize slots to provide a measure of blade control during surgery. There are numerous limitations with this cutting methodology. The very nature of resting an oscillating saw blade against another surface while the saw blade is in motion creates a certain degree of imprecision. 
   Also, to allow clearance for the saw in the kerf, surgical bone saw teeth are set. That is, alternate teeth are offset from the center of the blade so that the resulting cut is slightly wider than the blade, to prevent the blade binding in the kerf. Consequently, the guide slot must be wide enough to receive the set of the teeth. This creates enough clearance for the blade to toggle within the slot and substantially reduce the precision of the cut. 
   The surgeon&#39;s hand motions can cause the blade to toggle during the procedure and generate a non-planar bone surface. Vibrations generated by the oscillating saw driver are transmitted to the hands of the surgeon and to the cutting guide, affecting the quality of the resected bone surface. 
   In addition, inadvertent blade contact with the inner slot surface of a cutting guide dulls the blade teeth and damages the guide slot. Contact between the blade and guide can also result in a temporary loss of blade control. Consequently, it is difficult to maintain the saw oriented in the desired plane and angle. 
   Additionally, current cutting guide sets contain a large number of precision machined parts. These parts are expensive and their multiplicity creates both added expense and complexity. It would be preferable if the orthopedic surgeon had available a simpler cutting guide system with relatively few parts. 
   Thus, there is a need for a surgical saw guide that allows for the precise faceting of bone ends to facilitate the implantation of orthopedic prostheses. The guide should be simple to set up and use while creating precision planar cuts in bone tissue. It is preferred that the guide minimize saw blade damage and wear and that the guide minimize vibrational energy transfer to the surgeon&#39;s hands and the patient&#39;s bone. It would be preferable to minimize the amount of visual obstruction presented by the cutting guide. 
   SUMMARY OF THE INVENTION 
   The present invention fulfills the above needs by providing a rotating track cutting guide system that maintains precise alignment of a bone saw with bone tissue. The rotating track cutting guide system generally includes a track subassembly and cutting guide subassemblies attachable to the bone that is to be cut. The track subassembly supports an oscillating surgical saw driver. The track subassembly is removably securable to cutting guide subassemblies which are attachable to the desired bone to facilitate a series of controlled cuts. The design of the track subassembly stabilizes the oscillating saw driver and enables it to both rotate in the plane of the saw blade and move linearly along the track. In conjunction with specially designed cutting guide subassemblies, use of the track subassembly enables a surgeon using the rotating track cutting guide system to perform all the necessary surgical cuts required for a knee replacement with great accuracy and precision. The rotating track cutting guide system is adaptable to an open frame design to improve visibility of the surgical site during resection. Although the rotating track cutting guide system will be described in the context of total knee arthroplasties, it should be understood that the invention may be applied to various other surgical procedures. 
   The track subassembly includes a rotating driver carriage that supports an oscillating saw driver. The driver carriage rests upon a track that has an alignment member that enables the track to removably attach to various positioning and cutting guides. The alignment member allows immediate fixation of the track onto the cutting guide subassembly, while fastening members provide for ready attachment and removal. The use of a stabilizing track in conjunction with cutting and positioning guides results in a synergistic effect that enables the user to resect bone to great accuracy and precision along a plane. 
   The present invention provides a cutting platform whereby the oscillating saw driver, the cutting guide and the bone to be cut are fixed relative to one another except in the plane in which the cut is being made. The stabilization of movement affords the surgeon excellent control and enables the physician to perform precise and accurate cuts. 
   Further, the rotating track cutting guide system minimizes blade damage and wear caused by inadvertent contact between the blade and the cutting guide. The resulting retention of blade sharpness throughout the procedure produces a smoother, flatter, more precisely cut bone surface than is otherwise achievable. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1   a  is a perspective view of a resected distal femur showing facets created in preparation for placement of a knee prosthesis; 
       FIG. 1   b  is a profile view of a distal femur and a proximal tibia uncut; 
       FIG. 1   c  is a profile view of a resected distal femur and a proximal tibia as faceted for total knee arthroplasty; 
       FIG. 2  is a side perspective view of a rotating track cutting guide system of the present invention positioned as attached to a femur, with phantom lines depicting a femur and a saw apparatus; 
       FIG. 3  is a top perspective view of a track subassembly in accordance with the present invention; 
       FIG. 3   a  is a detail view of a second embodiment of the end of the track subassembly (taken at the position of  3   a  of FIG.  3 ); 
       FIG. 4  is a perspective view of the track subassembly as depicted in  FIG. 2 , but with the subassembly inverted, phantom lines depicting a saw apparatus; 
       FIG. 5  is an exploded top perspective view of a driver carriage used in accordance with the present invention; 
       FIG. 6  is an exploded front perspective view of the distal femur and proximal tibia cutting guide subassembly and track in accordance with the present invention; 
       FIG. 6   a  is a perspective view of an alternative embodiment of a distal femur and proximal tibia cutting guide, attached to an intramedullary alignment system (depicted in phantom); 
       FIG. 7  is rear perspective view of an anterior and posterior femoral cutting guide subassembly in accordance with the present invention; 
       FIG. 8  is top perspective view of a posterior cutting guide in accordance with the present invention; 
       FIG. 9  is a bottom perspective view of the posterior cutting guide in accordance with the present invention; 
       FIG. 10  is a front perspective view of an anterior cutting guide in accordance with the present invention; 
       FIG. 11  is rear perspective view of the anterior cutting guide in accordance with the present invention; 
       FIG. 12  is an exploded, top perspective view of the anterior cutting guide with the detachable femoral anterior reference in accordance with the present invention; 
       FIG. 13  is a bottom perspective view of the detachable anterior reference in accordance with the present invention; 
       FIG. 14  is a top perspective view of a chamber cutting guide subassembly in accordance with the present invention; 
       FIG. 15  is a cross-sectional view of the chamfer cutting guide subassembly of the present invention taken along line  15 — 15  of  FIG. 14 ; 
       FIG. 16  is a perspective view of an alternative embodiment of a distal femur and proximal tibia cutting guide and track in accordance with the present invention; 
       FIG. 17  is a perspective view of a first alternative embodiment of the rotating track cutting guide system including a multipurpose cutting guide and multipurpose track, with phantom lines depicting a bone saw and a femur; 
       FIG. 18  is a perspective view of the multipurpose cutting guide and multipurpose track of  FIG. 17  assembled, with phantom lines depicting a bone saw and a femur; 
       FIG. 19  is a perspective view of a second alternative embodiment of the multipurpose track subassembly in accordance with the present invention, with phantom lines depicting a bone saw and a femur; 
       FIG. 20  is a graph summarizing experimental results for a precision comparison between the rotating track cutting guide and a prior art cutting system, each system cutting plastic-coated knees; 
       FIG. 21  is a graph summarizing experimental results for a precision comparison between the rotating track cutting guide and a prior art system, each system cutting cadaver knees; 
       FIG. 22  is a profile view of a third alternative embodiment of the rotating track cutting guide system engaged to a femur; and 
       FIG. 23  is a perspective view of the embodiment of  FIG. 22  with a bone saw and a femur depicted in phantom. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The rotating track cutting guide system  30  of the present invention, as depicted in the drawings, generally includes a track subassembly  32  and a variety of bone cutting guides. Bone cutting guides include an anterior and posterior femoral (APF) cutting guide  36 , a distal femur and proximal tibia (DFPT) cutting guide  38  and a chamfer cutting guide  40 . Track subassembly  32  is adapted to be removably affixed to any of the bone cutting guides. Bone cutting guides are adapted to be removably affixed to bone structures via clamps (not shown), screws (not shown), pins (not shown), drill bits  33  or any other means known to those skilled in the orthopedic arts. Bone cutting guides may be adapted to receive handlebars  35 . 
   Referring to  FIGS. 2 ,  3  and  4 , track subassembly  32  supports an oscillating saw driver  42  and is depicted attached to distal femur and proximal tibia cutting guide  38  which is, in turn, attached to femur  44 . Oscillating saw driver  42  drives saw blade  46 . 
   Track subassembly  32  generally includes track  48  and driver carriage  50 . Driver carriage  50  is slidably carried on track  48  and is adapted to support oscillating saw driver  42 . Oscillating saw driver  42  may be, for example, a 3M oscillating head L120B in combination with a 3M Maxi Driver II L100. Track  48  is adapted to be removably attachable to any of cutting guides  36 ,  38 ,  40 . 
   Referring to  FIG. 5 , driver carriage  50 , includes superior driver brace  52 , inferior driver brace  54  and endcap  56 . Superior driver brace  52  presents counterbored holes  58 ,  60 ,  62 ,  64  adapted to receive threaded fasteners  66 ,  68 ,  70 ,  72  through top brace face  73 . Threaded fasteners  66 ,  68 ,  70 ,  72  thread into fastening holes  74 ,  76 ,  78 ,  80  in inferior driver brace  54 , to secure superior driver brace  52  to inferior driver brace  54 . Inner brace contact surfaces  77 ,  79  of superior driver brace  52  and inferior driver brace  54  conform to oscillating saw driver  42 . 
   Endcap  56  includes superior circular plate  81 , inferior circular plate  82  and cylindrical spacer  84 . Inferior circular plate  82  presents counterbored hole  86  adapted to receive threaded fastener  88 . Counterbored hole  86  is located proximate the center of inferior circular plate  82 . Threaded fastener  88  is receivable into threaded bore  90  located in inferior driver brace  54 . 
   Referring particularly to  FIG. 3 , track  48  presents track slot  92 , alignment peg  94 , and counterbored alignment hole  96  adapted to receive fastener  97 . Track  48  further presents superior track face  98 , inferior track face  100 , front track face  102 , back track face  104 , inner track face  106  and side track faces  108 . Track slot  92 , as defined by inner track faces  106 , is of appropriate width to slidably receive cylindrical spacer  84 . The thickness of track  48 , as defined as the distance between superior track face  98  and inferior track face  100 , is adapted to be received between superior circular plate  80  and inferior circular plate  82 . 
   Front end  110  of track  48  is adapted to be secured to bone cutting guides  36 ,  38 ,  40 . Front end  110  includes alignment peg  94  and counterbored alignment hole  96 . Counterbored alignment hole  96  receives threaded fastener  97 . In another embodiment, depicted in  FIG. 3   a , front end  110 ′ includes alignment pins  114 , recesses  116  and alignment clips  118 . 
   Referring to  FIG. 6 , distal femur and proximal tibia cutting guide  38  generally includes positioning guide  120  and cutting guide  122 . DFPT cutting guide  38  is adapted to receive track  48 . 
   Positioning guide  120  presents attachment shelves  124 ,  126 , peg holes  128 ,  130 , track fastening holes  132 ,  134 , pin holes  136 ,  138 , diagonal pin holes  144 ,  146 , handlebar holes  148 ,  150 , and guide fastening holes  152 ,  154 . Guide fastening holes  152 ,  154  are adapted to receive guide fasteners  156 ,  158 . 
   Cutting guide  122  presents cutting slot  160 , intramedullary attachment holes  162 ,  164  and counterbore guide holes  166 ,  168 . Also shown in phantom in  FIG. 6   a  is intramedullary alignment system  170 . Intramedullary alignment system  170  includes intramedullary alignment rod  172 , bracket  174  and angle positioner  175 . 
   Referring to  FIG. 16 , another embodiment of DFPT cutting guide  38 ″ is shown. This embodiment of DFPT cutting guide  38 ″ presents attachment slots  176 ,  178 , attachment bosses  180 ,  182 , and attachment clip receivers  184 ,  186 . This embodiment further presents diagonal pin holes  144  and handlebar holes  148  and slot  160  similar to the initial embodiment. 
   Referring to  FIG. 7 , APF cutting guide  36  generally includes posterior cutting guide  188  and anterior cutting guide  190 . Posterior cutting guide  188  generally includes body  192  and posterior condyle referencing paddles  194 ,  196 . 
   Referring particularly to  FIGS. 8 and 9 , body  192  presents condyle cutting slots  198 ,  200 , sizing slot  202  and notch  204 . Notch  204  is located between posterior condyle referencing paddles  194 ,  196 . Attachment shelves  206 ,  208  are located at the juncture between posterior condyle referencing paddles  194 ,  196  and body  192 . Each attachment shelf  206 ,  208  further includes fastening holes  210  and peg holes  212 . Attachment shelves  206 ,  208  are adapted to receive track  48 . 
   Sizing slot  202  includes inner sizing slot grooves  214 ,  216  and inner sizing slot top face  218 . Inner sizing slot top face  218  presents a plurality of sizing holes  220 . Body  192  further presents handlebar attachments  222 ,  224  and diagonal fixation pinholes  226 ,  228  oriented diagonally inward therethrough. 
   Referring to  FIGS. 10 ,  11  and  12 , anterior cutting guide  190  generally includes sizing ledge  230  and guide body  232 . Sizing ledge  230  generally includes sizing side ridges  234 ,  236 , sizing ledge top face  238  and sizing ledge bottom face  240 . Sizing ledge top face  238  presents sizing holes  242  therethrough. Sizing ledge  230  is dimensioned so as to be slidably received into sizing slot  202  as depicted in  FIGS. 8 and 9 . 
   Guide body  232  includes inner ring  244  and attachment ledge  246 . In a first embodiment of anterior cutting guide  190 , inner ring  244  is cut entirely through the thickness of guide body  232 . In a second embodiment inner ring  244  is cut partially through the thickness of guide body  232 , and a cutting slot  248  is cut through the remaining thickness. In the second embodiment attachment buttress  250  is present. 
   Attachment ledge  246  includes fastening hole  252  and peg hole  254 . Attachment ledge  246  is adapted to receive track  48 . 
   Attachment ledge  246  is also adapted to receive detachable femoral reference  256 . Referring to  FIG. 13 , detachable femoral reference  256  generally includes body  258 , L-bracket  260  and attachment slot  262 . 
   Referring to  FIGS. 14 and 15 , chamfer cutting guide  40  generally includes side plates  264 ,  266 , attachment guide plates  268 ,  270  and central guide plate  272 . Side plates  264 ,  266  each present handlebar hole  274  and diagonal fixation hole  276 . Attachment guide plate  268  presents anterior fastening hole  278  and anterior peg hole  280 . Attachment guide plate  270  presents posterior fastening hole  282  and posterior peg hole  284 . Central guide plate  272  presents a plurality of guide positioning holes  286 . Attachment guide plate  268  and central guide plate  272  define anterior cutting slot  288 . Attachment guide plate  270  and central guide plate  272  define posterior cutting slot  290 . Bottom side attachment guide plates  268 ,  270  and central guide plate  272  define bone contacting face  292 . 
   Referring to  FIGS. 17 and 18 , another embodiment of rotating track cutting guide system  30  is depicted. This embodiment generally includes multipurpose cutting guide  294  and multipurpose track  296 . 
   Multipurpose cutting guide  294  is generally an open frame guide. Multipurpose cutting guide  294  includes perpendicular cut adaptor  300  and chamfer cut adaptors  302 . Multipurpose cutting guide  294  defines a plurality of alignment rod receivers  304 . Perpendicular cut adaptor  300  includes perpendicular rod receivers  306 . Chamfer cut adaptors  302  include chamfer rod receivers  308 . Multipurpose cutting guide  294  defines a window  310 . Window  310  has a superior edge  312  and an inferior edge  314 . 
   Multipurpose track  296  is generally similar to track  48  except for the addition of a terminal block  316  secured at the end thereof. Terminal block  316  supports alignment rods  318  and presents upper edge  320 . In one embodiment, depicted in  FIG. 19  terminal block  316  also is perforated by guide slot  322 . Guide slot  322  is sized to receive saw blade  46 . 
   Referring to  FIGS. 22 and 23 , an additional embodiment of the present invention includes curved track  324 . Driver carriage  50  is slidably and rotatably retained on curved track  324 . Otherwise this embodiment is similar in structure to the foregoing embodiments. 
   In operation, rotating track cutting guide system  30  is assembled in concert with oscillating saw driver  42 . Referring to  FIG. 5 , superior driving brace  52  and inferior driving brace  54  are separated and assembled to grip oscillating saw driver  42  as depicted in FIG.  4 . Saw blade  46  is attached to oscillating saw driver  42 . Track  48  may then be connected to any of bone cutting guides  36 ,  38 ,  40 . 
   Referring particularly to  FIGS. 2 and 6 , in preparing to make an initial cut on femur  44 , distal femur and proximal tibia cutting guide  38  is secured to femur  44  via clamps, screws, pins or drill bits or any other means known in the orthopedic arts. If desired, handle bars  35  may be secured to DFPT cutting guide  38  to allow an assistant to the surgeon to help support DFPT cutting guide  38  during the cutting process. Track  48  is secured to DFPT cutting guide  38  prior to cutting. 
   Referring particularly to  FIG. 6 , DFPT cutting guide  38  may be disassembled into positioning guide  120  and cutting guide  122 . For attachment, front end  110  of track  48  is inserted so that it rests on one of attachment shelves  124 ,  126  and so that alignment peg  94  engages into peg hole  128 ,  130 . Thereupon, a fastener  131  may be inserted through counterbored alignment hole  96  and threaded into track fastening hole  132 ,  134 . Once fastener  131  is tightened in place, cutting guide  122  is assembled to positioning guide  120 . This is achieved by inserting fasteners  156 ,  158  through cutting guide counterbored holes  166 ,  168  on cutting guide  122  and tightening fasteners  156 ,  158  against fastening holes  152 ,  154 . 
   Referring again to  FIGS. 2 ,  3  and  4 , oscillating saw driver  42  may then be moved linearly and rotationally in a fixed plane because of the interaction between driver carriage  50  and track  48 . End cap  56  is securely and slidably engaged to track slot  92 , thereby allowing driver carriage  50 , along with oscillating saw blade  46 , to move within a fixed plane aligned with cutting slot  160  if present. 
   Oscillating saw driver  42  may then be advanced through cutting slot  160  in order to make an initial planar cut across the inferior end of femur  44 . Because of the interconnection of rotating track cutting guide system  30  to femur  44 , this cut will be planar and smooth. 
   After this initial cut is made, distal femur and proximal tibia cutting guide  38  may be unfastened from femur  44  and removed. 
   Making the initial femoral cut with the alternate embodiment of DFPT cutting guide  38  depicted in inset  3   a  and  FIG. 16  requires a slightly different procedure. In this embodiment, positioning guide  120  and cutting guide  122  are combined into a single unit. DFPT cutting guide  38  is secured to femur  44  by the insertion of drill bits  33  into fastening holes  136 ,  138 . Track  48  is then inserted into attachment slot  176 ,  178 , and alignment of track  48  is achieved through the interaction of attachment bosses  180 ,  182  with recesses  116 . Upon insertion, alignment clips  118  engage attachment clip receivers  184 ,  186  to secure track  48  to DFPT cutting guide  38 . Thereafter, the initial femoral cut is made as described above. 
   Referring to  FIGS. 7-12 , anterior and posterior femoral cutting guide  36  is adapted to be placed against the planar resected bone surface previously produced by the use of DFPT cutting guide  38 . To properly orient APF cutting guide  36 , body  192  is placed on the resected bone surface so that posterior condyle referencing paddles  194 ,  196  are in contact with the condyles on femur  44  and notch  204  is aligned with the intercondylar notch on femur  44 . 
   After properly orienting anterior and posterior femoral cutting guide  36 , the size of femur  44  may be measured using detachable femoral reference  256 . Detachable femoral reference  256  is placed so that attachment slot  262  engages attachment ledge  246 . The femur  44  may then be sized by pressing posterior condyle referencing paddles  194 ,  196  against the femoral condyles and pressing L-bracket  260  of detachable femoral reference  256  against the anterior femoral surface. 
   Thereafter, APF cutting guide  36  is secured to femur  44  by any means known to the orthopedic arts. If necessary, handlebars  35  may be secured to handlebar attachments  222 ,  224  to enable an assistant to hold and restrain the motion of APF cutting guide  36  to provide additional stability during the cutting process. 
   Resection of the anterior portion of femur  44  may then be accomplished. Track subassembly  32  is secured to attachment ledge  246 . Oscillating saw driver  42  may then be advanced along track  48  to make the appropriate cut to the anterior region of femur  44 . 
   Resection of the posterior portion of the femoral condyles is accomplished by sequentially securing track subassembly  32  to attachment shelves  206 ,  208 . Oscillating saw driver  42  may then be advanced and rotated along track  48  as needed to accomplish the required posterior femoral condyle cuts. Once the required resections are made, APF cutting guide  36  is removed from femur  44 . 
   Next, referring to  FIGS. 14 and 15 , anterior and posterior chamfer cuts may be made to femur  44 . Chamfer cutting guide  40  is secured to the resected surface of femur  44  by use of any means known to the orthopedic art such that bone contacting face  292  is flush with the resected femur surface A. Track subassembly  32  is then secured to one of attachment guide plates  268 ,  270 . To make the posterior chamfer cut, track subassembly  32  is secured at anterior peg hole  280  and anterior fastening hole  278 . Oscillating saw driver  42  may then be advanced along track  48  and rotated as need be to make the required resection. The anterior chamfer cut is made in a similar fashion, attaching track subassembly  32  at posterior peg hole  284  and posterior fastening hole  282 . If desired, handlebars  35  may be secured at handlebar holes  274  in order to provide additional stabilization of chamfer cutting guide  40 . 
   To effect resection of the proximal portion of the tibia, a procedure similar to that used for resecting the distal portion of femur  44  is followed. 
   Referring to  FIGS. 17 and 19 , to utilize multipurpose cutting guide  294  for the initial femoral cut, multipurpose cutting guide  294  is secured to the anterior surface of femur  44  by any means known to the orthopedic arts. Note that the presence of window  310  provides convenient visibility of the bone structure for the surgeon. 
   Once multipurpose cutting guide  294  is in position, multipurpose track  296  may be engaged to multipurpose cutting guide  294  as depicted in FIG.  18 . Thereupon, oscillating saw driver  42  and saw blade  46  may be advanced along multipurpose track  296  in order to make the appropriate cuts. 
   Note, referring to  FIG. 18 , that when engaged, terminal block  316  and superior edge  312  combine to form an effective guide slot for saw blade  46 . In another alternate embodiment, depicted in  FIG. 19 , terminal block  316  includes guide slot  322  to provide additional stabilization of saw blade  46 . 
   After making the initial femoral cut, as depicted in  FIG. 17 , multipurpose cutting guide  294  may be relocated to make anterior and posterior femoral cuts. This orientation is depicted in FIG.  18 . After multipurpose cutting guide  294  is secured to femur  44  at the location of the initial femoral cut, multipurpose track  296  may be engaged to make the anterior femoral cut. Once the anterior femoral cut is completed, multipurpose track  296  may be removed, rotated 180°, around the longitudinal axis of multipurpose track  296  and replaced on multipurpose cutting guide  294  in order to make the posterior femoral cut. 
   After the posterior femoral cut is made, multipurpose track  296  may be removed and relocated so as to engage chamfer cut adaptor  302  in order to make a first chamfer cut. Thereafter, multipurpose track  296  may be located to the other chamfer cut adaptor  302  in order to make the second chamfer cut to this resected femur  44 . 
   Note that when placed on chamfer cut adaptors  302 , upper edge  320  of terminal block  316  provides support for saw blade  46  and superior edge  312  or inferior edge  314  also provide support for saw blade  46 . This additional support serves to improve the planar quality of the cuts made. 
   Multipurpose cutting guide  294  both reduces the number of parts necessary for the rotating track cutting guide system  30  and allows the anterior and posterior femoral cuts as well as the chamfer cuts to be made without the necessity of repositioning or replacing the cutting guide. 
   EXAMPLES 
   A quantitative assessment of the final design of the rotating track cutting guide system was performed to judge its effectiveness. Its capabilities were compared to cutting guides from a typical knee replacement system, the Exodus® System (Orthopaedic Innovations, Minneapolis, Minn.). Three experiments were performed to appraise the efficacy of the rotating track cutting guide system. The following experiments were performed:
         A. Precision Analysis: Evaluated the each system&#39;s capacity to reproducibly cut in the same plane.   B. Blade Wear Analysis: Examined the cutting guides&#39; success at reducing blade wear.   C. Femoral Component Fit Analysis: Provided information on the amount of contact between prosthesis and the resected bone surface to determine the accuracy with which the cut bone fit the prosthesis.
 
A. Precision Analysis
       

   The precision analysis evaluated a cutting guide&#39;s ability to cut consistently in the same plane. After distal femoral condyle resection in a simulated total knee arthroplasty, the angle between the lateral and medial femoral condylar planes was measured. The precision of the cut was defined as the absolute value of the angular difference between the two condylar planes. 
   Methods for Experiment A1 
   Twelve 1145 urethane foam knees (Pacific Research Laboratories, Inc., Vashon, Wash.) were used. The rotating track cutting guide system and the Exodus® System were each tested with six knees and six new K-2000-25 3M Maxi-driver® blades (Komet Medical, Savannah, Ga.). After securing each cutting guide to a femur, the distal femoral condyles were resected. A Craftsman® Magnetic Universal Protractor (Sears, Hoffman Estates, Ill.) measured the angle of the lateral and medial condylar planes with respect to the ground. The protractor had an accuracy of ±0.5° and was maintained in a consistent orientation when placed on each condyle. 
   When measuring the condylar plane orientation, the angle indicated by the protractor was read by two individuals to account for user error. Both individuals separately measured the angles associated with the resected medial and lateral condylar planes. Each individual then calculated the angular difference between the two condylar planes and these values from the two individuals were compared. If the angular difference values differed, then the angles associated with the resected medial and lateral condylar planes were re-measured by each individual. 
   Methods for Experiment A2 
   The same procedure in Experiment A1 was performed, except that femora from twelve 1107-2 plastic-coated urethane foam knees were used. The 1107-2 urethane foam knees had a hard urethane elastomer cortex and were intended to model real bones more closely than the urethane foam bones. 
   Methods for Experiment A3 
   The same procedure in Experiment A1 was performed, except that the femora from fresh-frozen cadaver knees were used. 
   Analysis for the Precision Experiments 
   For the precision analysis, the absolute value of the angular difference between the two condylar planes was computed. For all the knees, a Fisher&#39;s Exact Test of Independence was used. This analysis is two-tailed test using a 2×2 table and compared the rate of existence of a zero difference between the Exodus® System and the rotating track cutting guide system. The experimental hypothesis was that the rotating track cutting guide system would have a higher rate of zero angular difference than the Exodus® System. 
   
     
       
             
           
             
             
             
           
             
             
             
           
         
             
               TABLE 1 
             
           
           
             
                 
             
             
               Angular Difference (Degrees) Between the Condyles When Using the 
             
             
               Exodus ® System and the Rotating Track Cutting Guide to Resect 
             
             
               Foam Femora 
             
           
        
         
             
                 
               Exodus ® System 
               Rotating Track Cutting Guide System 
             
             
                 
                 
             
           
        
         
             
               Bone 1 
               0 
               0 
             
             
               Bone 2 
               0 
               0.5 
             
             
               Bone 3 
               0 
               0 
             
             
               Bone 4 
               0.5 
               0 
             
             
               Bone 5 
               0 
               0 
             
             
               Bone 6 
               0 
               — 
             
             
                 
             
           
        
       
     
   
   
     
       
             
           
             
             
             
           
             
             
             
           
         
             
               TABLE 2 
             
           
           
             
                 
             
             
               Angular Difference (Degrees) Between the Condyles When Using the 
             
             
               Exodus ® System and Rotating Track Cuffing Guide to Resect 
             
             
               Plastic-coated Femora 
             
           
        
         
             
                 
               Exodus ® System 
               Rotating Track Cutting Guide System 
             
             
                 
                 
             
           
        
         
             
               Bone 1 
               0 
               0 
             
             
               Bone 2 
               0.5 
               0 
             
             
               Bone 3 
               0.5 
               0 
             
             
               Bone 4 
               1 
               0 
             
             
               Bone 5 
               0.5 
               0 
             
             
               Bone 6 
               0.5 
               0 
             
             
                 
             
           
        
       
     
   
                                               TABLE 3                   Angular Difference (Degrees) Between the Condyles When Using the       Exodus ® System and Rotating Track Cutting Guide to Resect       Cadaver Femora                Exodus System   Rotating Track Cutting Guide                        Bone 1   2.5   0       Bone 2   1.5   0       Bone 3   0   0.5       Bone 4   0   0       Bone 5   0.5   0       Bone 6   0   0                    
Discussion
 
   For the Precision Analysis using the foam femora and cadaver femora, no significant differences could be found between the performances of the two cutting systems. When the cadaver femora were resected, the largest indicator of the different levels of performance between the two cutting systems stemmed from the 2.5 degree angular difference between the resected medial condylar plane and the lateral condylar plane when using the Exodus® System. In our study, however, the sample size of six did not allow the results to be statistically significant. These results suggested that a larger sample size would be appropriate for a definitive statistical comparison. 
   The Fisher&#39;s Exact Test of Independence for plastic-coated bones indicated that the rotating track cutting guide system had a significantly higher rate of zero angular difference than the Exodus® System (P=0.015). The better performance of the rotating track cutting guide system in our study suggested that the rotating track cutting guide system cuts more precisely than the Exodus® System. 
   B. Blade Wear Analysis 
   The investigators made an examination of the blade wear associated with total knee arthroplasty. Reduced blade wear reflects the cutting guides&#39; effectiveness for minimizing blade damage. Retained blade sharpness results in the more precise cutting of bone and a smoother bone surface. 
   Methods for Experiment B1 
   Two new K-2000-25 3M Maxi-driver® blades and 12 new 1145 urethane foam knees were obtained. One blade and six knees were randomly assigned to the cutting guides of the Exodus® System. The rotating track cutting guide system&#39;s cutting guides used the remaining blade and knees. The blades for the Exodus® and the rotating track cutting guide system&#39;s guides were weighed before their use. After performing all the femoral and tibial cuts in a simulated total knee arthroplasty, each blade was soaked overnight in acetone, dried and weighed. Repeated weighing of the blade ensured that a consistent blade weight value was obtained. A total of six simulated knee arthroplasties were performed using each blade and system, and the blade was weighed after each of the six procedures. The change in blade weight provided an indication of the average amount of blade wear associated with the use of each instrumentation system after one total knee arthroplasty. 
   Methods for Experiment B2 
   This experiment was similar to Experiment B1, but required the use of 12 new 1107-2 plastic-coated urethane foam knees. For additional qualitative information on blade damage, scanning electron microscopy provided 20×images of the blade teeth. SEM images of each blade were taken before the first arthroplasty and after the sixth procedure. Providing descriptive rather than quantitative information on blade damage, the images depicted the cumulated blade wear associated with each instrumentation system. 
   Analysis for the Blade Wear Experiments 
   The mean blade wear loss for each cutting system was calculated from six total knee arthroplasties. For the foam and plastic-coated knees, a repeated measures ANOVA compared the performance between the two cutting systems. The hypothesis was that the rotating track cutting guide system would result in less blade weight loss compared with the Exodus® System. 
   Results 
   
     
       
             
           
             
             
             
           
             
             
             
           
         
             
               TABLE 4 
             
           
           
             
                 
             
             
               Blade Weight Loss Comparison Between the Exodus ® System and 
             
             
               the Rotating Track Cutting Guide System After Performing Total Knee 
             
             
               Arthroplasty on Six Foam Knees 
             
           
        
         
             
                 
               Exodus ® System 
               Rotating Track Cutting Guide System 
             
             
                 
                 
             
           
        
         
             
               Trial 1 
               1.65 mg 
               0.125 mg  
             
             
               Trial 2 
                1.2 mg 
               0.125 mg  
             
             
               Trial 3 
               0.85 mg 
               0.07 mg 
             
             
               Trial 4 
                2.5 mg 
               0.03 mg 
             
             
               Trial 5 
                0.7 mg 
                0.2 mg 
             
             
               Trial 6 
                1.6 mg 
                0.0 mg 
             
             
               Total 
                8.5 mg 
               0.55 mg 
             
             
               Mean 
               2.56 mg 
               0.16 mg 
             
             
                 
             
           
        
       
     
   
   
     
       
             
           
             
             
             
           
             
             
             
           
         
             
               TABLE 5 
             
           
           
             
                 
             
             
               Blade Weight Loss Comparison Between the Exodus ® System and 
             
             
               the Rotating Track Cutting Guide System After Performing Total Knee 
             
             
               Arthroplasty on Six Plastic-coated Knees. 
             
           
        
         
             
                 
               Exodus System 
               Rotating Track Cutting Guide System 
             
             
                 
                 
             
           
        
         
             
               Trial 1 
               −2.7 mg   
                0.3 mg 
             
             
               Trial 2 
               9.8 mg 
               1.55 mg 
             
             
               Trial 3 
               1.5 mg 
                 0 mg 
             
             
               Trial 4 
               0.7 mg 
                0.2 mg 
             
             
               Trial 5 
               0.4 mg 
                 0 mg 
             
             
               Trial 6 
               1.25 mg  
                0.1 mg 
             
             
               Total 
                11 mg 
               2.15 mg 
             
             
               Mean 
               4.1 mg 
               0.67 mg 
             
             
                 
             
           
        
       
     
   
   Blade damage was also qualitatively assessed by examining SEM images. The images with the Rotating track cutting guide system exhibited less cumulative blade damage than the Exodus® System. 
   Discussion 
   In the Blade Wear Analyses, a repeated measures ANOVA yielded a statistically significant difference in the blade wear between the rotating track cutting guide system and the Exodus® System (P=0.03). When resecting foam knees, there was often an order of magnitude difference in the blade weight loss between the rotating track cutting guide system and the Exodus® System. Use of the rotating track cutting guide system and the Exodus® System to resect plastic-coated knees showed a similar difference. There also existed a consistent wear pattern between each cutting system when resecting foam bones. The wear pattern, however, became less consistent when resecting plastic-coated bones. Additionally, the negative difference after the first blade wear trial for the Exodus® System was most likely due to plastic residue that remained on the blade after cleaning. Given the small sample size, more definitive conclusions can only be made after testing a larger number of blades. 
   The SEM images provided visual information that the rotating track cutting guide system was more effective in the retention of blade teeth sharpness than the Exodus® System. For the blade used by the rotating track cutting guide system, there was no deformation of the teeth closest to the sides of the saw blade, unlike with the blade used by the Exodus® System. The blade used by the rotating track cutting guide system, however, did have one row of blade teeth that was significantly worn. This wear pattern was probably due to the interference of the saw blade with the posterior cutting guide slots on the anterior and posterior femoral cutting guide subassembly. The experimental design of the rotating track cutting guide system did not include a method to attach and use the track subassembly to help guide the saw blade to resect the posterior femoral condyles. Consequently, the row of damaged teeth probably occurred from the saw blade not being oriented and stabilized with a track. 
   C. Femoral Component Fit Analysis 
   This experiment indicated the effectiveness of the cutting instrumentation through a fit assessment of the femoral component onto the femur. Although the use of PMMA allows a surgeon a greater margin of error when cutting bone, an uneven cement mantle can result in early prosthesis loosening. For this analysis, Ultra Low Pressurex® film (Sensor Products, Inc., East Hanover, N.J.) provided an image of the contact between the underside of the femoral component and the resected femoral surface. Decreased cutting effectiveness during resection would result in reduced contact area. 
   Methods for Experiment C1 
   In this experiment, 12 new plastic-coated femora and 12 new K-2000-25 3M blades were obtained. Six blades and femora were randomly selected and used with the Exodus cutting guides. The rotating track cutting guide system used the remaining blades and bones. Each system was used to perform the distal, anterior, posterior, anterior chamfer and posterior chamfer femoral cuts. The two halves of the Ultra Low Pressurex® film, the Transfer Sheet and the Developer Sheet, were individually cut into 3″×4.5″ rectangles and folded to conform to the distal portion of the resected femur and to each other. After the Transfer Sheet and the Developer Sheet were gently placed upon one another to avoid inadvertent film activation, the femoral component was placed onto the distal femur. The high sensitivity Pressurex® film was used so that film activation would not depend solely on the impact force applied by the surgeon when placing the femoral component onto the bone. Contact between the underside of the femoral component and the resected femoral surface broke the chemical-filled microcapsules on the Transfer Sheet. This chemical reacted with the color developing material on the Developer Sheet and generated a residual red stain at the regions where the prosthesis and bone contacted. Unstained Pressurex® film indicated the location of the gaps between the implant and the cut bone. 
   Methods for Experiment C2 
   The same procedure as in experiment C1 was performed, except that fresh-frozen cadaver knees were used rather than plastic-coated knees. 
   Analysis 
   The contact area between the component and femur was calculated using SigmaScan® software. The data were normalized by dividing the contact area by the total area of the underside of the femoral component. After averaging the percent of contact data for the six femora with the two cutting systems, their means were compared. Plastic-coated knees required a two-sample t test for statistical analysis. The use of paired cadaver knees required a paired t-test for analysis. The hypothesis was that the rotating track cutting guide system would result in a higher percent of contact area than the Exodus® System 
   Results 
   Results of the femoral fit component fit analysis utilizing plastic coated femora and cadaver are summarized in graphs depicted as  FIGS. 20 and 21  respectively. 
   Discussion 
   For the Femoral Component Fit Analysis using plastic-coated bones, use of the rotating track cutting guide system resulted in statistically significant increased contact between the underside of the femoral component and the resected femur than the Exodus® System (mean 42% vs. 28%, P=0.039). In the Femoral Component Fit Analysis with cadaver bones, use of the rotating track cutting guide system also resulted in statistically significant increased contact between the underside of the femoral component and the resected femur than the Exodus® System (mean 44% vs. 31%, P=0.021). Both results indicated that proper use of the rotating track cutting guide system resulted in greater contact between the resected bone surface and the prosthesis. 
   The distribution of contact percentages between each system may be attributed to how the cutting systems were designed and manufactured. For the Exodus® System, the cutting guide must be manually adjusted to the appropriate size before performing the chamfer cuts. A millimeter of difference can influence whether the femoral component will fit onto the resected bone surface. Consequently, half a millimeter of difference in the sizing of the cutting guide may have caused the contact percentage to range from 20-40%. 
   For the rotating track cutting guide system, one of the diagonal fixation holes of the medium chamfer cutting guide subassembly broke. This occurred as cadaver femur  3  was being resected. Consequently, the rotational motion of the medium chamfer cutting guide subassembly during the resecting process resulted in a low area contact percentage between the resected femoral surface and the prosthesis. The remaining variability in the performance of the rotating track cutting guide system was probably due to minor rotational motion of the large chamfer cutting guide subassembly during surgery. 
   D. Experiment Summary 
   The various analyses provided insight into the capabilities of the rotating track cutting guide system. The results of the Precision Analysis suggested that the rotating track cutting guide system resected the distal femur more precisely than a conventional cutting system. The Blade Wear Analysis proved a clearer suggestion that the rotating track cutting guide system produced statistically significant less blade wear on a saw blade than the Exodus® System. Use of the rotating track cutting guide system also resulted in statistical significant increased contact between the underside of the femoral component and the resected femur surface. 
   The present invention may be embodied in other specific forms without departing from the spirit of any of the essential attributes thereof; therefore, the illustrated embodiments should be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention.

Technology Classification (CPC): 0