Abstract:
A method of manufacturing a distal femoral knee prosthesis includes the initial step of forming a rough prosthesis workpiece member that has the approximate size and shape of a final polished distal femoral prosthesis. The rough prosthesis workpiece member can be a casting, forging or a rough machined part. The prosthesis member is then attached to a fixator and movably supported adjacent a rotary grinder. Relative motion between the rotary grinder and the prosthesis is controlled with a computer. An articular surface of the prosthesis is shaped by engaging the prosthesis with the rotary grinder. The workpiece is primarily polished to remove &#34;scallops&#34; that form on the outer surface during a shaping with the rotary grinder. The prosthesis workpiece member is then secondarily polished until the articular surface provides a highly polished mirror finish.

Description:
BACKGROUND OF THE INVENTION: 
     1. Field of the Invention 
     The present invention relates to surgical orthopedic implants and methods of manufacturing same. Even more particularly, the present invention relates to an improved orthopedic joint implant component (e.g. femoral component) having a non articulating surface that fastens the implant to the patient&#39;s bone tissue adjacent the joint to be replaced and an articulating surface that engages a corresponding implant member (e.g. tibial component) and wherein the articulating surface is dressed using a programmable CNC multi-axis grinder that cuts multiple parallel grooves in the articulating surface of a blank (e.g. cast, forged, machined) as the blank is oscillated about a first axis on a fixture and translated during such oscillation to define the shape of the articular surface being cut, subsequent method steps including a coarse polishing to remove &#34;peaks&#34; formed by the grinder, followed by a fine polishing of the articular surface. 
     2. General Background 
     Prosthetic joint devices are well known in the art. One of the most common types of joint prosthetic devices is a knee prosthesis that includes a femoral component and a tibial component. The femoral component typically has a &#34;J&#34; shape and includes a distal articulating surface with anterior, distal and posterior condylar portions. The non-articulating surface of the prosthesis includes a number of flat intersecting surfaces that mate with similarly shaped surfaces surgically formed on the patient&#39;s distal femur. 
     One of the problems that has plagued the manufacture of femoral knee implants is that of proper sizing and shaping. The distal femoral articulating surface is a complex structure. In the past, sizing and shaping this structure has been a highly labor intensive process that requires a number of manual polishing steps. However, these polishing steps are typically performed by workers that do not exactly duplicate the same shape each time. Variations can occur even at the same factory between two different workers. 
     SUMMARY OF THE INVENTION 
     The present invention solves this prior art problem by providing a highly effective and controllable method of manufacturing a distal femoral knee prosthesis. 
     The method of the present invention begins with the formation of a rough prosthesis workpiece member that has the approximate size and shape of a final polished distal femoral prosthesis. 
     The workpiece can be a cast metallic part for example. The prosthesis member is attached to a fixator. The fixator is movably supported adjacent a rotary grinder wheel. A computer is used to control relative motion between the rotary grinder and the prosthesis workpiece member. 
     A curved &#34;J&#34; shaped articular surface of the prosthesis member is formed by engaging the prosthesis with the rotating rotary grinder wheel. 
     In the preferred method, the grinding wheel sculpts the articular surface by forming a plurality of generally parallel grooves adjacent one another. This also forms &#34;peaks&#34; at the intersections of two adjacent grooves sculpted by the grinding wheel. The articulating surface of the workpiece is preliminarily polished to remove peaks that occur between adjacent grooves cut by the rotary grinder wheel. Thereafter, the articular surface is secondarily polished until it has a highly polished mirror finish. 
     In the preferred method, the rotary grinder and the fixator each have central longitudinal axes. These axes are maintained generally parallel during a shaping of the articular surface of the prosthesis member with the grinder wheel. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a further understanding of the nature and objects of the present invention, reference should be had to the following detailed description, taken in conjunction with the accompanying drawings, in which like parts are given like reference numerals, and wherein: 
     FIG. 1 is a perspective view of the preferred embodiment of the apparatus of the present invention; 
     FIG. 2 is a fragmentary perspective view of the preferred embodiment of the apparatus of the present invention; 
     FIG. 3 is a fragmentary schematic view illustrating the grinding step of the method of the present invention; 
     FIG. 4 is a perspective view of a prosthesis workpiece to be finished using the method of the present invention; 
     FIG. 5 is another perspective view of a prosthesis workpiece to be finished using the method of the present invention; 
     FIG. 6 is a perspective view of another prosthesis to be finished using the method of the present invention; 
     FIG. 7 is a fragmentary exploded perspective view of the preferred embodiment of the apparatus of the present invention; 
     FIG. 8 is a fragmentary sectional view of the preferred embodiment of the apparatus of the present invention illustrating the attachment between the prosthesis component and grinding fixture; 
     FIG. 9 is a fragmentary sectional view of the preferred embodiment of the apparatus of the present invention illustrating the attachment between the prosthesis component and grinding fixture; 
     FIG. 10 is a fragmentary perspective end view of the preferred embodiment of the apparatus of the present invention illustrating the grinding fixture; 
     FIG. 11 is a fragmentary perspective view of the preferred embodiment of the apparatus of the present invention illustrating the coarse polishing fixture portion thereof; 
     FIGS. 12-13 are schematic views illustrating the coarse polishing step of the method of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1-3 show the preferred embodiment of the apparatus of the present invention designated generally by the numeral 10. Prosthesis grinding apparatus 10 includes a grinding fixture 20 supported between work head 14 and a tailstock 11A in a conventional programmable CNC multi-axis grinder 11 that includes for example a pair of spaced apart rotary grinding wheels 12, 13 and spaced apart holding portions 14, 15. The holding portions 14, 15 interface with end portions of the grinding fixture 20 after prosthesis component workpieces 21, 22 are attached thereto. Workpieces 20,21 include femoral component workpiece 21 and femoral component workpiece 22. 
     Programmable grinder 11 can include fluid dispensers for dispensing a desired cooling fluid to the grinding apparatus as is known in the art. Such fluid dispensers 16, 17 are typically supplied with commercial available programmable grinders 11, a fluid dispenser 16, 17 being positioned respectively above each grinding wheel 12, 13. 
     In FIG. 2, the axis of rotation 18 of grinding wheel 12 is illustrated. The grinding wheel 12 rotates about axis 18. Wheel 12 also moves in an anterior/posterior direction relative to the workpiece 21 along an anterior/posterior direction created by relative movement between path 19 and 50 in FIG. 2. 
     In combination with the rotary movement of grinder 12 and its for and aft movement along path 19, there is also provided relative movement between grinding wheel 12 and prosthesis component 21 by moving grinding fixture 20. In FIG. 2, arrows 49 indicate schematically lateral/medial movement of grinding fixture 20 relative to wheel 12. The plane of wheel 12 is designated as 12A. Curved arrow 50 schematically illustrates rotation in an anterior posterior direction of the component 21 relative to wheel 12. 
     The programmable grinder 11 can thus be programmed to rotate the wheel 12 at a desired speed, move the wheel for and aft along the path 19 a desired degree during cutting of the prosthesis 21, and rotate the grinding fixture 20 about its central longitudinal axis. This combination presents various anterior, distal, and posterior articulating surfaces of the femoral component workpiece 21 to the grinding wheel 12. In this fashion, grooves or scallop is formed in the articulating 23 surface of the selected component workpiece 21 or 22 as shown in FIG. 3. The grooves or scallops are designated as 51 in FIG. 3. Grooves 51 are spaced apart by measure that is designated by the arrows 52 in FIG. 3 as groove spacing. Further, each of the grooves have a thickness that is designated by the arrows 53 in FIG. 3. 
     In FIGS. 4-6, two femoral component workpiece 21, 22 are shown for purposes of illustration. In FIG. 4, femoral component workpiece 21 is provided with threaded attachments 37, 38 and with a bone ingrowth surface that is comprised of a plurality of non-articulating surfaces 28-35. In FIGS. 5 and 6, femoral component workpiece 22 is provided with unthreaded, smooth attachment posts 47, 48. 
     In FIG. 4, the femoral component workpiece 21 includes an outer, articulating surface 23 that is to be dressed using the method and apparatus of the present invention. The articulating surface 23 includes an anterior end surface 24, a distal end surface 25, and a pair of spaced apart posterior condylar surfaces 26, 27. The non-articulating surfaces 28-35 include anterior non-articulating surface 28, chamfer surfaces 29 and 32-33, distal non-articulating surfaces 30, 31 and posterior condylar non-articulating surfaces 34, 35. Transverse bar 36 can form a connection between condylar portions of the prosthesis workpiece 24 that are covered with exterior condylar surfaces 26, 27 and with the surfaces 34, 35. 
     In FIG. 4, the attachment posts 37, 38 are threaded. These threaded posts 37, 38 must be protected from damage when component 21 is subjected to programmable grinder 11 according to the method of the present invention as will be described more fully hereinafter. 
     In FIG. 6, component 22 includes smooth surfaces 41-46 and smooth posts 47, 48. The surface 41 is an anterior surface. The surfaces 42-43 and 45 are chamfer surfaces. Surface 44 is a distal non-articulating surface. Surface 46 is a posterior non-articulating surface. In each of the workpiece of FIGS. 4 and 6, the rear non-articulating surfaces 28-35 and 41-46 are surfaces that register with similarly shaped cut surfaces on the patient&#39;s distal femur as prepared by a surgeon. 
     In FIG. 5, workpieces 21, 22 is shown and more specifically the articulating surface 23 thereof. The present invention provides an improved method for shaping such workpieces 21, 22 having articulating surfaces 23. These workpieces 21, 22 which begin as castings, rough machinings, forgings or the like. For example, if workpieces 21, 22 begin as castings, they can have projecting portions 39, 40 that are formed during casting and which must be removed as part of the method of the present invention. 
     FIG. 7 illustrates a more detailed view of grinding fixture 20. Grinding fixture 20 has an enlarged end portion 54 held by grinder 11 holder 14. End portion 54 provided a recess 55 that can be engaged by a torquing member for imparting rotation to the grinding fixture 20 as generated by the programmable grinder 11. The grinding fixture 20 includes an elongated bar 56 having a plurality of cylindrically shaped openings 57-60, each of the openings 57-60 having a central longitudinal axis that is perpendicular to the axis of rotation of the grinding fixture 20. In FIG. 2, the axis of rotation of grinding fixture 20 is defined by arrow 49. 
     Because each of the cylindrical openings 57-60 has an axis that is perpendicular to the axis of rotation of fixture 20, this similarly places each of the non-articulating surfaces 28-35 of prosthesis workpiece 21 and 41-46 of prosthesis 22 at right angles to the anterior posterior travel path 19 of grinding wheel 12 and also at right angles to the plane of grinding wheel 12 designated as 12A in FIG. 2. 
     FIGS. 8-9 show the connection formed between a post 37, 47 of a component workpiece 21 or 22 and the elongated transverse bar 56 of fixture 20. In FIG. 9, the sectional view illustrates the connection formed between component 22 and bar 56 of fixture 20. When a component workpiece 21 is to be connected to fixture 20 and the component workpiece 21 has threaded attachment posts such as 37, a thread protector 61, 62 is threadably attached to the threaded attachment post 37, 38. Thread protector 61, 62 provides an internal threaded bore with internal threads that match the external threads of the posts 37, 38. 
     Each of the thread protectors 61, 62 can have a hexagonal drive portion 63, 64 to aid in a solid attachment of the particular thread protector 61, 62 to a selected of the threaded posts 37, 38. 
     In FIG. 9, a thread protector 61 has been applied to a threaded attachment post 37. In order to complete an attachment of the workpiece 21 to the grinding fixture 20, the user places annular sleeve 65 or 66 over the thread protector 61, 62 as shown in FIGS. 7 and 9. 
     Threaded sleeves 67, 68 then extends over the thread protector 61 and ferrule 65 as shown in FIG. 9. The threaded sleeve 67, 68 have external threads 69, 70 that engage corresponding internal threads 71 that line a portion of the selected opening 59, 60 as shown in FIG. 9. Each of the threaded sleeves 67, 68 each provide beveled annular surfaces 74, 75 respectively that engage the outer surface of ferrules 65, 66 for forming a wedge lock connection therewith. As the user tightens the selected threaded sleeve 67, 68, the selected components 21, 22 is rigidly connected to grinding fixture 20. 
     In FIG. 8, a connection is shown between prosthesis component workpiece 22 having a smooth attachment post 47 and the grinding fixture 20. In FIG. 8, annular sleeve 65 connects directly to the unthreaded attachment post 47. Threaded sleeve 67 then engages the threads 71 of bar 56 to form a wedge lock connection between the beveled annular surface 74 of sleeve 67 and the outer surface of the annular sleeve 65. 
     After the plurality of grooves or scallops 51 are formed in the external surface 23 (i.e. the articulating surface 23 of the selected femoral component workpiece 21, 22 the component workpiece 21, 22 is first subjected to a coarse polishing. During the coarse polishing each component workpiece 21, 22 is affixed to a polishing fixture 80 as shown in FIG. 11. The connection between the selected component workpiece 21, 22 and the elongated bar like fixture 80 can be the same type of connection as with the fixture 20 as shown in FIGS. 7, 8, and 9. 
     In order to protect all but the articulating surface from the coarse polishing, urethane protector block 81 is added to the component workpiece 21 or 22 as shown in FIG. 11. Protector block 81 can be of urethane plastic for example and extend both in a lateral medial direction and in an anterior posterior direction so that all of the non-articulating surfaces 28-25 or 41-46 are covered and protected from contact with polishing media 90 during the coarse polishing. 
     In FIGS. 12-13, the coarse polishing method step is schematically shown. In FIGS. 12-13 there can be seen a motor drive 83 that powers and rotates a sun gear 85 within gear case 84. The gear case 84 includes motor driven sun gear 85 having axis of rotation 86. Sun gear 85 is powered to rotate and drive a plurality of four planetary gears 87, each having an axis of rotation 88. An outer housing gear 89 surrounds and engages the planetary gears 87 and sun gear 85. 
     In FIG. 12, a circular path 90 indicates the travel path followed by of each of the planetary gears 88. Curved arrow 91 indicates the direction of rotation of the sun gear 85. Curved arrow 92 indicates the direction of rotation of the planetary gears 87. 
     In FIG. 13, the planetary gear case 84 is shown having a plurality of extensions shafts 93 extending downwardly therefrom, each attached respectively to a planetary gear 87 within planetary gear case 84. Each of the extension shafts 93 carries a chuck 94 for holding a holding fixture 95. 
     The holding fixture 95 includes a vertical shaft 96, a plurality of circumferentially spaced, radially extending arms 97, and a plurality of holders 98 that can form an attachment with the polishing fixture 80. 
     The plurality of holding fixtures 95 are supported within a tank 99 that contains media 90, a commercially available polishing media. Rotation of the fixtures 95 within tank 99 and the contained media 90 removes the scallops formed on the articulating surface of each workpiece 21, 22. 
     After coarse polishing, the component workpiece 21, 22 can be finely polished using a commercially available computer controlled polishing machine such as shown and described in U.S. Pat. 4,753,044 which is incorporated herein by reference. 
     The following table lists the parts numbers and parts descriptions as used herein and in the drawings attached hereto: 
     
         ______________________________________PARTS LISTPart Number    Description______________________________________10             prosthesis grinder apparatus11             grinder .sup. 11A     grinder tailstocks12             grinding wheel .sup. 12A     plane of rotation13             grinding wheel14             grinder workhead15             tailstock center16             fluid dispenser17             fluid dispenser18             axis of rotation of          grinding wheel19             path20             grinding fixture21             femoral component workpiece22             femoral component workpiece23             articulating surface24             anterior end25             distal end26             posterior condylar surface27             posterior condylar surface28             non-articulating surface29             non-articulating surface30             non-articulating surface31             non-articulating surface32             non-articulating surface33             non-articulating surface34             non-articulating surface35             non-articulating surface36             transverse bar37             attachment post38             attachment post39             casting gate40             casting gate41             anterior surface42             chamfer surface43             chamfer surface44             distal surface45             chamfer surface46             posterior surface47             attachment post48             attachment post49             arrow50             curved arrow51             scallop52             scallop spacing53             scallop height54             enlarged end55             recess56             elongated bar57             opening58             opening59             opening60             opening61             thread protector62             thread protector63             hex drive64             hex drive65             ferrule66             ferrule67             threaded sleeve68             threaded sleeve69             external threads70             external threads71             internal threads72             conical socket73             conical socket74             annular surface75             annular surface80             polishing fixture81             protector block82             coarse polisher83             motor drive84             planetary gear case85             sun gear86             axis of rotation87             planetary gear88             axis of rotation89             housing gear90             circular path91             curved arrow92             curved arrow93             extension shaft94             chuck body95             holding fixture96             shaft97             arm98             holder99             tank100            media______________________________________ 
    
     Because many varying and different embodiments may be made within the scope of the inventive concept herein taught, and because many modifications may be made in the embodiments herein detailed in accordance with the descriptive requirement of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.