Abstract:
An orthopaedic instrument includes a metallic load-bearing member and a non-metallic support structure formed integrally with the load-bearing member such that the load-bearing member is permanently attached to the non-metallic support structure. The non-metallic support structure enables the orthopaedic instrument to be lighter than an all-metal instrument while the metallic load bearing member provides wearability comparable to an all-metal instrument.

Description:
FIELD OF THE INVENTION 
     This invention relates to the field of orthopaedics and more particularly to methods and instrumentation used in orthopaedic procedures. 
     BACKGROUND 
     Bones can become damaged as a result of accident or illness. Such damage can be, for example, to the articular cartilage covering the ends of the bones at a joint as well as the intra-articular cartilage between the ends of the adjacent bones of the joint. When the damage to the joint is severe, a joint endoprosthesis can be implanted to improve the comfort and mobility of the patient. 
     Joint endoprostheses have been developed to replace native tissue of several human joints. There are a variety of knee prostheses, hip prostheses, shoulder prostheses, ankle prostheses and wrist prostheses available to relieve patient suffering. Such devices are made by and available from, for example, DePuy Products, Inc. and DePuy Orthopaedics, Inc. of Warsaw, Ind. 
     Standard joint endoprostheses include metal components that are affixed to the articulating ends of the bones of the joint and commonly include a bearing component positioned between the metal components. Standard bearing components of joint endoprostheses have a surface against which one of the metal components articulates. For example, hip endoprostheses include a metal femoral component to be affixed to the proximal femur and a metal cup to be affixed to the acetabulum. Many of these standard hip endoprostheses include a liner in the acetabular cup against which the femoral component articulates. Knee prostheses commonly include a femoral component to be affixed to the distal femur and a tibial component to be affixed to the proximal tibia. Bearings are typically between the femoral and tibial components. Similar systems with bearings are available to replace other joints in the body. Such endoprosthesis systems are commercially available from DePuy Orthopaedics, Inc. of Warsaw, Ind. 
     Orthopaedic prosthetics are also used to replace bone lost in the treatment of various bone cancers. These orthopaedic prosthetics may include elements of a joint endoprosthesis as well as components to replace intercalary bone loss. Such prosthetics are made by and available from DePuy Products, Inc. and DePuy Orthopaedics, Inc. of Warsaw, Ind. 
     Trauma products are also available for treating patients suffering traumatic injury, such as bone fractures. Trauma products frequently include orthopaedic components such as bone screws, bone nails, bone plates and fixators, for example. Such trauma products are commercially available from DePuy Trauma and Extremities of Warsaw, Ind. 
     Each of the foregoing types of devices typically requires a specialized set of instruments to ensure that the devices are properly implanted. Moreover, each of the different devices may require instruments of different sizes so as to ensure proper placement of the devices for different bone sizes. Accordingly, a large number of instruments are maintained in inventory, either at the care facility or under the control of a representative of the instrument manufacturer merely to support the implantation of the orthopaedic prosthetics. 
     Additionally, for a single surgery, such as a hip, knee, shoulder, and other joint replacement surgery (partial or total), six or more trays of instruments and trial implants may be required to be available for potential use. Prior to use in a subsequent procedure, each tray has to be re-sterilized even if the particular tray was not utilized during a prior procedure. 
     Therefore, a large number of instruments, some of which may be rarely used, must still be made available. The maintenance of a large inventory, while necessary, is not advantageous for many reasons. The instruments used in surgical procedures, for example, are typically fabricated from a metal such as stainless steel using traditional manufacturing processes such as machining, turning, and drilling. Although the foregoing materials and processes result in the production of effective instruments, the instruments are very heavy and expensive. Accordingly, the required instrument inventory is both extensive and expensive. Moreover, the instruments are heavy making movement of the instruments about a care facility cumbersome. 
     By way of example, patella drill guide instruments are regularly used in orthopaedic procedures. Typically, these instruments are produced by machining a stainless steel block. The areas that are subjected to the highest wear or load, however, are the actual guide holes. Thus, the bulk of the stainless steel merely adds to the weight and the expense of the device. Additionally, spikes are typically desired to be provided in order to facilitate stability of the guide during use. Because patella drill guide instruments are made of stainless steel, the addition of spikes requires welding the spikes onto the stainless steel block and then polishing and finishing the weld. Thus, the manufacturing steps and associated costs of the patella guide instruments are increased. 
     As a further example, known femoral distal cutting block instruments require a number of precision machining operations to produce the base block and pawl. Likewise, finishing guides require machining operations to form the various plates as well as turning operations to manufacture screws needed for assembly of the finishing guide. 
     The problems associated with the need to maintain a large inventory of heavy instruments is further compounded by the fact that some instruments are needed merely to manipulate other instruments. One such instrument is a tibial tray trial. The tibial tray trial includes a tray instrument which is machined in several steps as well as a handle instrument. The handle instrument is designed to be attached to the tray instrument and then to be removed once the tray instrument is in the desired position. Thus, additional instruments are required. Additionally, the release mechanism used, in addition to being heavy, includes a number of additional components, thereby increasing the complexity of the instrumentation. 
     In addition to the foregoing limitations, any delay due to the shipping and re-sterilization of the instruments adds to the cost of providing the instruments. Also, as implant systems or instruments are modified or replaced, the inventory of such systems or instruments must also be replaced. 
     Therefore, a need exists for an orthopaedic instrument which is lighter than an all-metal instrument but which provides wearability comparable to the all-metal instrument. A further need exists for an instrument which is inexpensive and which is easy to manufacture. A further need exists for new complex instrumentation to be rapidly and inexpensively produced. 
     SUMMARY 
     Orthopaedic instrumentation and a method of manufacturing the instrumentation is disclosed. In one embodiment, an orthopaedic instrument includes a metallic load-bearing member and a non-metallic support structure formed integrally with the load-bearing member such that the load-bearing member is permanently attached to the non-metallic support structure. 
     In a further embodiment, an orthopaedic instrument includes at least one metallic work piece including a working surface and a surface interlock feature and a non-metallic support structure integrally formed with the surface interlock feature such that the at least one metallic work piece is permanently embedded in the non-metallic support structure. 
     In one method, manufacturing an orthopaedic instrument includes machining a metallic load-bearing member, generating a surface interlock feature on the metallic load-bearing member and forming a non-metallic support member into contact with the surface interlock feature. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts an exploded perspective view of a patella drill guide instrument with load-bearing members which are interlocked with a support member using a variety of different surface features in accordance with principles of the present invention; 
         FIG. 2  depicts a perspective view of one of the load-bearing members of  FIG. 1  which incorporates pyramid shaped protrusions used to form interlocks with the support member of  FIG. 1  to inhibit axial and rotational movement of the load-bearing member with respect to the support member; 
         FIG. 3  depicts a perspective view of one of the load-bearing members of  FIG. 1  which incorporates a groove to form an interlock with the support member of  FIG. 1  to inhibit axial movement of the load-bearing member with respect to the support member; 
         FIG. 4  depicts a perspective view of one of the load-bearing members of  FIG. 1  which incorporates a number of protuberances to form interlocks with the support member of  FIG. 1  to inhibit rotational and axial movement of the load-bearing member with respect to the support member; 
         FIG. 5  depicts a perspective view of one of the load-bearing members of  FIG. 1  which incorporates axially extending teeth to form interlocks with the support member of  FIG. 1  to inhibits rotational movement of the load-bearing member with respect to the support member; 
         FIG. 6  depicts a perspective view of an alternative load-bearing member that is sized such that the upper and lower surfaces of the load-bearing member form interlocks with a support member to inhibit axial movement of the load-bearing member with respect to the support member; 
         FIG. 7  depicts a partial side cross-sectional view of the load-bearing member of  FIG. 2  integrally formed with the support member of  FIG. 1  showing the interlocks between the pyramid shaped protrusions of the load-bearing member and the support member which inhibit axial movement of the load-bearing member with respect to the support member in accordance with principles of the present invention; 
         FIG. 8  depicts a partial top cross-sectional view of the load-bearing member of  FIG. 2  integrally formed with the support member of  FIG. 1  showing the interlocks between the pyramid shaped protrusions of the load-bearing member and the support member which inhibit rotational movement of the load-bearing member with respect to the support member in accordance with principles of the present invention; 
         FIG. 9  depicts a partial side cross-sectional view of the load-bearing member of  FIG. 3  integrally formed with the support member of  FIG. 1  showing the interlocks between the groove of the load-bearing member and the support member which inhibit axial movement of the load-bearing member with respect to the support member in accordance with principles of the present invention; 
         FIG. 10  depicts a partial top cross-sectional view of the load-bearing member of  FIG. 3  integrally formed with the support member of  FIG. 1  showing the absence of interlocks between the outer periphery of the load-bearing member and the support member; 
         FIG. 11  depicts a partial side cross-sectional view of the load-bearing member of  FIG. 6  integrally formed with a support member showing the interlocks between the upper and lower surfaces of the load-bearing member and the support member which inhibit axial movement of the load-bearing member with respect to the support member in accordance with principles of the present invention; 
         FIG. 12  depicts an exploded perspective view of a femoral trial instrument with a load-bearing member that is interlocked with a support member using protuberances and recesses in accordance with principles of the present invention; 
         FIG. 13  depicts a perspective view of an alternative embodiment of a femoral trial instrument incorporating rods as load-bearing members in accordance with principles of the present invention; 
         FIG. 14  depicts a perspective view of a rod that may be used as a load-bearing component in an instrument in accordance with principles of the present invention; 
         FIG. 15  depicts a partial side cross-sectional view of the load-bearing member of  FIG. 14  integrally formed with a support member showing a work surface of the load-bearing member extending above the support member in accordance with principles of the present invention; 
         FIG. 16  depicts a perspective view of a cutting guide block instrument with a load-bearing member that is interlocked with a support member and showing a work surface of the load-bearing member extending above the support member in accordance with principles of the present invention; 
         FIG. 17  depicts a partial side cross-sectional view of one of the load-bearing members of  FIG. 16  integrally formed with the support member wherein the interlock with the support member is formed by ledges of the support member which overhang a portion of the load-bearing member in accordance with principles of the present invention; 
         FIG. 18  depicts a perspective view of a finishing guide instrument with a load-bearing member that is interlocked with a support member and showing a work surface of the load-bearing member extending along various surfaces of the support member in accordance with principles of the present invention; 
         FIG. 19  depicts a perspective view of the load-bearing member of  FIG. 18 ; 
         FIG. 20  depicts an exploded perspective view of a cutting block instrument with a number of load-bearing members in accordance with principles of the present invention; 
         FIG. 21  depicts a perspective view of one of the load-bearing members of  FIG. 20  showing a number of holes that may be over-molded with the support member to provide an interlock between the load-bearing member and the support member in accordance with principles of the present invention; 
         FIG. 22  depicts a perspective view of a tibial cutting block instrument with a load-bearing member in accordance with principles of the present invention; 
         FIG. 23  depicts a perspective view of a tibial trial tray instrument with a support member that is partially removable to provide a one-time use instrument in accordance with principles of the present invention; 
         FIG. 24  depicts a perspective view of a keel punch guide instrument with a support member that is used to operate the load-bearing member with which it is interlocked in accordance with principles of the present invention; 
         FIG. 25  depicts a side cross-sectional view of the keel punch guide instrument of  FIG. 24 ; 
         FIG. 26  depicts a perspective view of a universal handle instrument with a support member that is used to hold the load-bearing member with which it is interlocked in accordance with principles of the present invention; 
         FIG. 27  depicts a side cross-sectional view of the universal handle instrument of  FIG. 26 ; and 
         FIG. 28  depicts a process that may be used to manufacture an instrument with a load-bearing member interlocked with a support member in accordance with principles of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an exploded view of a patella drill guide  100 . The patella drill guide  100  includes two guide portions  102  and  104  joined by a shaft  106 . The guide portions  102  and  104  include a number of spikes  108 . The guide portion  102  further includes load-bearing members  110 ,  112  and  114  while the guide portion  104  includes load-bearing members  116 ,  118  and  120 . The load-bearing members  110 ,  112 ,  114 ,  116 ,  118  and  120  are located within receptors  122 ,  124 ,  126 ,  128 ,  130  and  132 , respectively, which are formed in either the guide portion  102  or the guide portion  104 . 
     The load-bearing members  110 ,  112 ,  114 ,  116 ,  118  and  120  incorporate a variety of interlocks with the guide portions  102  and  104 . By way of example, the load-bearing member  110 , which is shown in  FIG. 2 , includes an outer periphery  134  which includes a number of pyramid shaped protrusions  136 . The pyramid shaped protrusions  136  provide an interlock with the guide portion  102 . In contrast, the inner bore  138  of the load-bearing member  110  is smooth. This is because the inner bore  138  is a work surface since in normal use the inner bore  138  may be in contact with other instruments. 
     The load-bearing member  112  shown in  FIG. 3  includes an outer periphery  140  that includes a groove  142  that circumscribes the load-bearing t  112 . The groove  142  defines an upper flange  144  and a lower flange  146 , each of these surface features is a part of an interlock. Additionally, referring to  FIG. 4 , the load-bearing member  120  includes an outer periphery  148  that includes a number of protuberances  150 , each of which is a part of an interlock. 
     A load-bearing member may be provided with a variety of surface features to be used in providing an interlock in addition to those identified above. For example, the teeth  152  of the load-bearing member  154  shown in  FIG. 5  and the upper surface  156  and lower surface  158  of the load-bearing member  160  may form a part of an interlock. The interlocks are used to provide a surface which acts against the surrounding support structure, such as the guide portion  102 , so as to restrict movement of the load-bearing member with respect to the support structure. Thus, with reference to  FIG. 7 , an axial impact upon the load-bearing member  110  in the direction indicated by the arrow  162  or the arrow  164  is transferred from the pyramid shaped protrusions  136  to the guide portion  102 . Likewise, rotational forces as indicated by the arrows  166  or  168  which act upon the load-bearing member  110  are transferred from the pyramid shaped protrusions  136  to the guide portion  102  as shown in  FIG. 8 . In both instances, the load-bearing member does not move with respect to the support member. 
     The forces which act upon the load-bearing members will vary depending upon the particular orthopaedic instrument. Accordingly, a surface feature may be selected for a particular load-bearing member based upon the expected forces. For example, the pyramid shaped protrusions  136  may be selected when both rotational and axial forces are encountered. 
     For applications wherein axial forces are the major expected force, the groove  142  may be selected. Referring to  FIGS. 9 and 10 , an axial impact upon the load-bearing member  112  in the direction indicated by the arrow  170  or the arrow  172  is transferred from the upper flange  144  or the lower flange  146 , respectively, to the guide portion  102 . Rotational forces as indicated by the arrows  174  or  176  which act upon the load-bearing member  112 , however, are only transferred to the guide portion  102  through mechanisms at the juncture of the outer periphery  140  of the load-bearing member  112  and the guide portion  102  such as friction, adhesion, etc. Typically, an interlock will provide better resistance to movement than these mechanism. 
     Similarly, when the load-bearing member  160  is embedded within a support portion  180  of an orthopaedic instrument as shown in  FIG. 11 , an axial impact upon the load-bearing member  160  in the direction indicated by the arrow  182  or the arrow  184  is transferred from the upper surface  156  or the lower surface  158 , respectively, to the support portion  180 . Rotational forces which act upon the load-bearing member  160  are restricted by the outer periphery of the load-bearing member  160  and a portion of the upper surface  156  and the lower surface  158  through friction, adhesion, etc. 
     Another embodiment of an instrument is shown in  FIG. 12  which shows an exploded view of a femoral trial instrument  190 . The femoral trial instrument  190  includes a support member in the form of substrate  192  and a load-bearing member  194 . The load-bearing member  194  includes protuberances  196  and recesses  198 . The substrate  192  is formed around the protuberances  196  and within the recesses  198  to interlock the substrate and the load-bearing member  194 . The load-bearing member  194  in this embodiment provides rigidity for the femoral trial  190  while the substrate  192  is formed into the more complicated contours of the articulation surfaces. 
     In the embodiment of  FIG. 13 , a femoral trial instrument  200  includes a substrate  202  and load-bearing members  204  and  206 . The substrate  202  in this embodiment is formed from a more rigid material than the substrate  192 . This allows for the use of the smaller load-bearing members  204  and  206  which in this embodiment are metal rods such as the rod  208  of  FIG. 14 , which are bent into the desired shape. 
     Just like the substrate  192 , the substrate  202  is formed into the more complicated contours of the articulation surfaces. In this embodiment, however, the load-bearing members  204  and  206  do not have recesses or protuberances which are used to interlock the load-bearing members  204  and  206  with the substrate  202 . Rather, as shown in  FIG. 15 , the substrate is formed such that the lips  210  and  212  of the substrate  202  entrap the load-bearing members  204  and  206 . In an alternative embodiment, the load-bearing member may be located completely within the substrate. 
     Partial entrapment of a load-bearing member in the manner shown in  FIG. 15  may further be used to provide a work surface. The cutting guide block  210  shown in  FIG. 16  includes a substrate  212  and two load-bearing members  214  and  216 . The load-bearing members  214  and  216  extend above the surface of the substrate  212  to provide a work surface for contact with other instruments or devices. 
     With reference to  FIG. 17 , the load-bearing member  214  is shown with two ledges  218  and  220  at the surface  222  of the substrate  212 . A work portion  224  of the load-bearing member  214  extends outwardly from the surface of the substrate  212 . The ledges  218  and  220  define a chord  226  across the load-bearing member  214  which is shorter than at least one chord extending across the load-bearing member  214  and which is farther from the surface  222  of the substrate  212  than the chord  226 , such as the chord  228 . Accordingly, the ledges  218  and  220  interlock the load-bearing member  214  within the substrate  212  while the work surface  224  prevents other instruments or devices from contacting the substrate  212 . 
     An alternative work surface is shown in  FIG. 18  wherein a finishing guide instrument  230  includes a substrate  232  and a load-bearing member  234 . As shown in  FIG. 19 , the load-bearing member  234  is interlocked with the substrate  232  by a number of protuberances  236 . The load-bearing member  234  further includes a work surface portion  238  that extends along the entire length of the load-bearing member  234  from one arm  240  of the load-bearing member  234  to another arm  242 . 
       FIG. 20  shows a cutting block  240  which includes a housing  242 , a support substrate  244  and six load-bearing members  246 . The load-bearing members  246  include a number of through holes  248 . When assembled, the six load-bearing members  246  are located within the support substrate  244  which is inserted within a cavity  250  in the housing  242 . 
     In this embodiment, the use of protuberances on the load-bearing members  246  is not desired due to the spacing restrictions within the cutting block  240 . Additionally, the size of the support substrate  244  is limited by the size of the cavity  250 . Accordingly the holes  248  are used as surface features which form an interlock with the support substrate  244 . With reference to  FIG. 21 , the holes  248  are located within two end portions  252  and  254  which are separated by a work portion  256 . The substrate  244  is formed about the two end portions  252  and  254 . Thus, the substrate  244  extends inwardly from the end portions  252  and  254  to the dashed lines  258  and  260 , respectively. The substrate  224  also extends through each of the through holes  248 . Accordingly, the load-bearing member  246  is supported between two portions of the substrate  244  on either side of the end portions  252  and  254  and the two portions of the substrate are connected through the through holes  248 . 
     As a matter of design choice, the load-bearing member may comprise a more substantial portion of the instrument. By way of example,  FIG. 22  shows a tibial cutting block  262  which includes a body  264  and a cutting guide  266 . The cutting guide  266  is made from a non-plastic material such as stainless steel while the body  264  is made from a plastic material. 
     In this embodiment, the load-bearing member, cutting guide  266 , accounts for about one-half of the volume of the tibial cutting block  262 . Of the two major components, however, the support structure, body  264 , has a more complicated design. Accordingly, because the more complicated portion of the tibial cutting block  262  is molded rather than machined, the manufacture of the tibial cutting block  262  requires fewer costly manufacturing steps. 
     In a further embodiment of an instrument, a portion of the support structure is removable.  FIG. 23  depicts a tibial tray trial  270  which includes a manipulating handle  272  and a tray  274 . The manipulating handle  272  is connected to the tray  274  through a notch  276 . Load-bearing members  278  and  280  are located in the tray  274  for use as drill guides. In this embodiment, the tray  274  and the manipulating handle  272  are made from the same non-metallic material. 
     The non-metallic material is selected such that the tray  274  supports the load-bearing members  278  and  280  and such that the notched area provides sufficient strength and rigidity to manipulate the tray  274  into position. The material is further selected such that the connection between the manipulating handle  272  and a tray  274  can be broken at the notch  276  when sufficient force is concentrated at the notch  276 . Thus, once the tray  274  is in the desired position and fixed in place, force is applied to the manipulating handle  272  causing the manipulating handle  272  to snap at the notch  276 . Accordingly, the tibial tray  270  is a single use instrument. 
       FIG. 24  depicts an embodiment of an instrument wherein a support member is used to operate a load-bearing member. The keel punch guide  282  includes a guide  284  and a handle  286 . A pin  288  extends from an inner bore  290  of the handle  286  into the guide  284  as shown in  FIG. 25 . A thumb piece  292  is interlocked with the pin  288  and extends through an opening  294  in the handle  286 . A spring  296  is located within the inner bore  290 . The spring  296  is located about a centering pin  298  which extends into an inner bore  300  in the pin  288 . 
     In operation, the thumb piece  292  is used to force the pin  288  against the spring  296 . As the spring  296  is compressed, the pin  288  is moved further into the inner bore  290  of the handle  286  and the centering pin  298  is inserted within the inner bore  300 . When the keel punch guide  282  is in the desired position, the thumb piece  292  is released and the spring  296  forces the pin  288  toward and partially into the guide  284 . Accordingly, the interlock between the pin  288  and the thumb piece  292  must be sufficiently strong to allow the spring  296  to be compressed without failing. 
       FIG. 26  depicts a universal handle  302  that includes a load-bearing member  304 , a support member  306  and an engagement mechanism  308 . The load-bearing member  304  includes a metal strike plate  310  which is located outwardly of the support member  306  and three flanges  312 ,  314  and  316  which form interlocks with the support member  306  as shown in  FIG. 27 . The load-bearing member  304  further includes a coupling portion  318  and a flange  320 . The flange  320  is positioned within an inner bore  322  along with a spring  324 . The flange  320 , the spring  324  and the engagement mechanism  308  are used to couple the universal handle  302  to other instruments. 
     The universal handle  302  is used to transfer impacts to an instrument or device to which the universal handle  302  is coupled. Accordingly, an operator may use a mallet to impact the metal strike plate  310  while the operator grasps the universal handle  302  about the support member  306 . The load-bearing member  304  transfers the force from the impact to the coupling portion  318  which in turn transfers the impact to the coupled instrument or implant. The flanges  312 ,  314  and  316  are configured to ensure solid fixation of the load-bearing member  304  within the support member  306  during such impacting. 
     In one method, the foregoing instruments are fashioned in like manner. With reference to  FIG. 28 , the method  330  begins at the step  332  with manufacturing the load-bearing member. The load-bearing member may be manufactured from metal materials including stainless steels, cobalt, chrome, nickel and others. The processes used in manufacturing the load-bearing member will depend upon the particular instrument as well as the type of metal. Some processes that may be used include machining, drilling, electrical discharge machining, grinding and stamping. 
     By way of example, the load-bearing members  110 ,  112 ,  114 ,  116 ,  118  and  120  are turned and the desired surface feature is formed thereon. The load-bearing member  194  may be machined by laser, water jet cutting, stamping or forming a blank into the desired shape and texturing the protuberances  196  and the recesses  198 . The load-bearing members  204  may be cut and stamped. The load-bearing members  246  may be manufactured by cutting the desired shape out of a metal sheet and drilling the through holes  248 . 
     Once the load-bearing member is machined, it is positioned within an injection mold at the step  334 . The positioning of the load-bearing member within the injection mold may be accomplished in any acceptable manner. For example, in a different technological field, U.S. Pat. No. 6,126,882 of Iwinski et al. discloses a method of molding a socket tool with a metal insert by placing the metal insert in a mold. Once the load-bearing member is positioned, a resin is injected into the mold at the step  336 . The type of resin is selected to provide the desired properties such as rigidity and strength while exhibiting reduced weight or ease of fabrication as compared to the metal used in the load-bearing member. Thus, different instruments may be produced using different resins. Acceptable resins include medical grade plastics and glass filled substrates such as polyamide polyphenylsulfone, polyethersulfone, polysulfone, polyketone and polyarylamide. 
     Care should be taken in the design of the injection mold to ensure adequate redundancy of interlocks and penetration of the injected resin into the surface features to form the desired interlock for he expected forces. Larger surface features such as the flanges  312 ,  314  and  316  in  FIG. 27  may function properly as a part of an interlock even with a small cavity in the molded support member. Thus, redundant flanges may not be needed. The ability of smaller surface features such as the through holes  248  to function properly as a part of an interlock may be seriously degraded, however, by the presence of a void in the molded support member. Thus, redundant through holes and more stringent engineering of the injection mold may be needed. 
     Once properly cured, the integral load-bearing member and support member are removed from the injection mold at the step  338 . If the instrument is substantially completed at the step  340 , then the process proceeds to the step  342  and ends. By way of example, molding the support material integrally with the load-bearing material may be the final manufacturing step for the embodiments of instruments such as the patella drill guide  100 , the femoral trials  190  and  200 , the finishing guide instrument  230 , the tibial cutting block  262  and the tibial trial tray  270 . 
     If subsequent assembly is required at the step  330 , then the instrument is assembled at the step  344  and the process ends at the step  342 . Embodiments of instruments which may require assembly after a molding step include the cutting block  240 , the keel punch guide  282  and the universal handle  302 . 
     While the present invention has been illustrated by the description of exemplary processes and system components, and while the various processes and components have been described in considerable detail, the applicants do not intend to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will also readily appear to those ordinarily skilled in the art. The invention in its broadest aspects is therefore not limited to the specific details, implementations, or illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the applicants&#39; general inventive concept.