Abstract:
A tibial prosthesis including a tibial component including a tray having first and second opposing surfaces and a stem extending from the second surface of the tibial component, a tibial conversion module including a receiver portion defining a stem-receiving cavity for slideable engagement with the stem of the tibial component, wherein the stem of the tibial component is positioned within the stem-receiving cavity at a first end of the receiver portion, and an extension peg engaged with the stem-receiving cavity at a second end of the receiver portion that is opposite the first end of the receiver portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     The present application claims priority to U.S. Provisional Application No. 60,752,849, filed Dec. 21, 2005, titled “Tibial Component With a Conversion Module for a Knee Implant”, the entire contents of which is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention relates to total knee implants. In particular, the invention relates to a polyethylene tibial component with a conversion module that allows the incorporation of a metal extension peg into the assembly.  
       BACKGROUND  
       [0003]     In general, total knee implants consist of three components: a femoral component, a tibial component, and a patellar component. Tibial components often fall into the categories of either metal-backed (modular) or all-polyethylene (also referred to as “all-poly”) tibial components. Metal-backed or modular tibial components often have a metal tray supporting a plastic modular piece that articulates with the femoral component. An all-poly tibial component, as the name implies, is a non-modular one-piece component made entirely of polyethylene plastic.  
         [0004]     It has been shown that the long-term results of all-polyethylene tibial components have some advantages over metal-backed tibial components. For example, all-polyethylene components are often cheaper, easier to manufacture, and can exhibit better wear characteristics than metal-backed tibial components. However, in order to add to the stability of the tibial component, such as for revision cases or in cases where there is significant bone loss in the proximal tibia, it can be advantageous to include an extended metal tibial stem or peg in the implant. In many cases, the attachment of such a metal component directly to a polyethylene component can be difficult and may result in unsatisfactory attachment conditions. Thus, it has been known to use a tibial component that includes a polyethylene or other plastic portion with an attached metal backing to allow for attachment of an extended metal tibial stem or peg to the metal backing portion of the tibial component. However, there is a need to provide a knee implant assembly that allows a metal peg to be attached to an all-poly tibial component, thus offering the advantages of both metal-backed and all-poly tibial components.  
       SUMMARY  
       [0005]     The present invention relates to total knee implants that include a metal adaptor or tibial conversion module that allows a metal intramedullary peg to be used in an assembly that includes an all-polyethylene tibial component. The intramedullary peg adds to the stability of the all-poly tibial component, which can be particularly advantageous for revision cases or in cases where there is significant bone loss in the proximal tibia. Plastic or metal blocks and wedges can also be used with the implant assembly to fill bony defects.  
         [0006]     The metal adaptor or conversion module can be designed for all-poly tibial components with or without dovetail cuts on the underside. The conversion unit can also be used for all-poly tibial components wherein a ridge along the periphery of the underside has been incorporated which is designed to prevent bone cement from migrating during implant insertion.  
         [0007]     In one aspect of the invention, a tibial prosthesis is provided that includes a tibial component including a tray having first and second opposing surfaces and a stem extending from the second surface of the tibial component, a tibial conversion module including a receiver portion defining a stem-receiving cavity for slideable engagement with the stem of the tibial component, wherein the stem of the tibial component is positioned within the stem-receiving cavity at a first end of the receiver portion, and an extension peg engaged with the stem-receiving cavity at a second end of the receiver portion that is opposite the first end of the receiver portion. The tibial component and tibial conversion module are preferably made of different materials, such as polyethylene for the tibial component and metal for the tibial conversion module.  
         [0008]     In another aspect of the invention, a tibial prosthesis is provided that includes a tibial component comprising a tray having first and second opposing surfaces and a stem extending from the second surface of the tibial component, a tibial conversion module comprising at least one engagement component slideably engaged with the second surface of the tibial component at a first end of the tibial conversion module, and an extension peg engaged with a second end of the tibial conversion module. The tibial component and tibial conversion module are preferably made of different materials, such as polyethylene for the tibial component and metal for the tibial conversion module. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The present invention will be further explained with reference to the appended Figures, wherein like structure is referred to by like numerals throughout the several views, and wherein:  
         [0010]      FIG. 1  is an exploded perspective view of the components of one embodiment of a knee implant of the present invention;  
         [0011]      FIG. 2  is another perspective view of the knee implant components shown in  FIG. 1 , further including directional arrows to indicate the component locations relative to each other when assembled;  
         [0012]      FIG. 3   a  is a perspective view of a knee implant assembly of the present invention;  
         [0013]      FIG. 3   b  is a bottom perspective view of the knee implant illustrated in  FIG. 3   a;    
         [0014]      FIG. 4  is a bottom perspective view of one embodiment of the tibial component of the knee implant of the invention;  
         [0015]      FIG. 5  is perspective view of one embodiment of the tibial conversion module of the invention;  
         [0016]      FIG. 6  is a perspective view of one side of the tibial conversion unit shown in  FIG. 5 ;  
         [0017]      FIG. 7  is another bottom perspective view of an embodiment of the tibial component of the knee implant of the invention;  
         [0018]      FIG. 8  is a perspective view of an embodiment of the extension peg of the invention;  
         [0019]      FIG. 9  is an exploded perspective view of the components of another embodiment of a knee implant of the present invention;  
         [0020]      FIG. 10  is another perspective view of the knee implant components shown in  FIG. 9 , further including directional arrows to indicate the direction components can be moved relative to each other for assembly and to illustrate one exemplary order of steps involved in assembling the knee implant;  
         [0021]      FIG. 11  is a perspective view of the tibial conversion module of  FIG. 9 ;  
         [0022]      FIG. 12  is a bottom perspective view of the tibial component of  FIG. 9 ;  
         [0023]      FIGS. 13   a  and  13   b  are two perspective views of a knee implant assembly, including a tibial wedge on one side of the bottom surface of the tibial component;  
         [0024]      FIG. 14  is another perspective view of the conversion module of  FIG. 9 , showing an opening in the bottom shank;  
         [0025]      FIG. 15  is a perspective view of the extension peg of  FIG. 9 ; and  
         [0026]      FIGS. 16-20  are perspective views of a variety of embodiments of tibial wedges and/or tibial components that can be used with the knee implant assemblies of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0027]     Referring now to the Figures, wherein the components are labeled with like numerals throughout the several Figures, and initially to  FIGS. 1-3   b , one exemplary embodiment of a knee implant assembly  10  of the present invention is illustrated. As is best illustrated in the exploded views of  FIGS. 1 and 2 , the assembly  10  generally includes a tibial component  12 , a tibial conversion module or unit  14 , and an extension peg  16 .  FIG. 2  further includes a directional arrow  18  showing the direction the tibial component  12  moves relative to the tibial conversion module  14  to mate with the tibial conversion module  14 , and a directional arrow  20  showing the direction the extension peg  16  moves relative to the tibial conversion module  14  to mate with the tibial conversion module  14 , which will be described in further detail below.  FIGS. 3   a  and  3   b  illustrate the knee implant assembly  10  in its assembled configuration.  
         [0028]     In accordance with the present invention, the tibial component  12  is preferably made entirely or primarily of polyethylene, and can be manufactured using any known forming techniques, such as molding. It is contemplated, however, that materials other than polyethylene are incorporated into the structure of the tibial component  12 . For example, metal particles may be incorporated into the material that makes up the tibial component  12  to provide additional strength to the structure. However, in order to achieve at least some of the desirable properties for which polyethylene may be chosen, the tibial component  12  may be made of entirely of polyethylene.  
         [0029]     The tibial conversion module  14  is preferably made entirely or primarily of metal, such as stainless steel or titanium, where it is preferable that the entire module  14  is made of the same metal. However, it is possible that the conversion module  14  is made of more than one material, where certain portions are made from particular materials to give certain strength characteristics to the module  14 . The conversion module  14  may be machined or molded into its desired configuration. The module  14  also includes features for engagement with the tibial component  12 , which will be described below.  
         [0030]     As shown in  FIG. 4 , the tibial component  12  has a first or top surface  42  and a second or bottom surface  44  that is generally opposite the top surface  42 . Surfaces  42 ,  44  can be generally parallel to each other as shown, or may be offset or angled relative to each other. The bottom surface  44  of the tibial component  12  has multiple grooves  24  that extend generally from one side of the tibial component  12  to its opposite side, although it is contemplated that the grooves extend across only a portion of the tibial component  12  in one or more directions. However, in order to be able to engage with another component in the system in a sliding type of engagement, the grooves  24  can preferably have at least one end that terminates at a face of the tibial component  12 . This is particularly advantageous if the grooves  24  have a dovetail configuration, as is illustrated in  FIG. 4  so that a mating dovetail shaped component can engage with it. Alternatively, the grooves  24  may be rectangular, curved, or otherwise shaped. The particular design and pattern of the underside grooves  24  may vary from one system to another, but are generally provided for engagement with another component and/or for use as anchoring points or channels for bone cement or other adhering material when the tibial component  12  is implanted. The grooves  24  may extend in one or both directions relative to the length and width of the component  12 , and may intersect with each other at one or more locations. Thus, a dovetail configuration is only one of a number of possible configurations for the grooves  24 . The number of grooves, the arrangement of the grooves, and the relative length and widths of the grooves may vary slightly or considerably from the grooves  24  illustrated in  FIG. 4 .  
         [0031]     In the configuration of  FIG. 4 , the grooves  24  can be used as anchoring points for bone cement, and also provide a means of engaging with or attaching to the tibial conversion module  14 . As shown in  FIG. 5 , the tibial conversion module  14  has pair of skids  26  with a dovetail cross-section that corresponds to the dovetail shape of the grooves  24  on the corresponding tibial component  12 . The tibial conversion module  14  preferably also has a locking ramp  28 , as shown in  FIG. 6 , which is used in the structural attachment of the various components, as described below.  
         [0032]     In one assembly sequence of the invention, the tibial conversion module  14  is assembled onto the tibial component  12  (see  FIG. 2 ) by engaging the skids  26  with grooves  30  and  32  provided on the bottom surface of the tibial component  12 , which are best shown in  FIG. 7 . These grooves  30 ,  32  are specifically spaced and sized for engagement with corresponding skids, such as skids  26 . This engagement of the skids  26  in the grooves  30  and  32  prevents the tibial component  12  and the conversion module  14  from being separated in the vertical direction. As the tibial conversion module  14  is slid further onto the tibial component  12 , the locking ramp  28  engages a back edge  34  of the tibial component  12 . The tibial conversion module  14  and the tibial component  12  are further slid relative to each other until the locking ramp  28  engages with a locking cavity  36  of the tibial component  12 , thereby locking the two components together. The locking ramp  28  may include a feature that inhibits or prohibits the disengagement of the locking function once it has been engaged. It is understood, however, that a wide variety of configurations can be used for both the conversion module and tibial component to hold them together, including other mechanical or other types of engagement configurations between the components. It is desirable, however, that the engagement of the components is secure enough that the components cannot come apart, even under a variety of different loading conditions.  
         [0033]     When the tibial conversion module  14  and the all-poly tibial component  12  are attached to each other, the tibial conversion module  14  allows the extension peg  16  to be attached to the assembly, as shown in  FIGS. 3   a  and  3   b . The tibial conversion module  14  may have a tapered shank  38  (see  FIG. 6 ), which is configured for engagement with a tapered hole  40  in extension peg  16  (see  FIG. 8 ), thereby forming a Morse taper type of connection. Thus, the present invention is able to offer the advantages of both an all-polyethylene tibial component and a metal-backed tibial component. In another alternative connection, the tapered hole  40  can be threaded to mate with threads on the outer surface of extension peg  16  to attach the components to each other. A wide variety of alternative connection configurations can also be used for attachment of the extension peg  16  to the tibial conversion module  14 , such as may include pins, clips, screws, and other engagement components and configurations. Further, while this embodiment illustrates the tapered shank  38  of the conversion module  14  as being insertable into the tapered hole  40  of extension peg  16 , the components may instead essentially be reversed so that the shank  38  of the conversion module  14  has a hole for internal connection of an extension peg  16 , such as with a friction fit, a threaded connection, or another engagement configuration.  
         [0034]      FIGS. 9-17  illustrate another exemplary embodiment of a knee implant assembly  100  of the invention and its individual components. Implant assembly  100  generally includes a conversion module  101 , a tibial component  102 , a tibial wedge  103 , and an intramedullary peg  104 . The tibial wedge  103  is an optional component of the system and is particularly adaptable for filling bony defects in the proximal tibia.  
         [0035]     The conversion module  101  is preferably a metal component that is engageable with an extending post  114  of tibial component  102 . The tibial component  102  is preferably made entirely or primarily of polyethylene. The intramedullary (IM) peg  104  is preferably made entirely or partially of metal or another material that provides the desired structural integrity to the assembly. The optional tibial wedge or wedges  103  can be made of polyethylene, metals, plastics, combinations thereof, and the like. Thus, the use of a conversion module  101  allows for an assembly that provides a number of advantages in that the tibial component  102  can be made of polyethylene, yet it can be securely attached to a metal intramedullary peg  104  via the intermediate conversion module  101 . It is contemplated, however, that these components may be made of different materials or combinations of materials, and/or that the components may all be made of the same material as each other, as desired. In any case, the materials that make up the components can be selected to provide the desired properties (e.g., strength, weight, and the like) to the final knee implant assembly.  
         [0036]      FIG. 10  shows one exemplary sequence of assembling the different components together into a knee implant assembly  100 , where the first step is illustrated with directional arrow  120 . In this step, the conversion module  101  is pressed onto the extending post  114  of the tibial component  102  until a surface  106   a  of conversion module  101  is in contact with a surface  106   b  of a tray or plate of tibial component  102  (shown in  FIGS. 11 and 12 ). The surfaces  106   a  and  106   b  are preferably designed to allow complete or nearly complete contact between them. That is, the surfaces  106   a  and  106   b  can be manufactured so that they have surfaces that can be generally or completely flush when they come into contact with each other, which helps to minimize or prevent rotation in the coronal and/or sagittal planes. In the illustrations of  FIGS. 11 and 12 , the surface  106   b  of tibial component  102  comprises a number of raised and recessed areas, which can vary widely from that shown; however, the selection of a configuration for the surface  106   b  is preferably selected or designed to cooperate with a corresponding surface  106   a . For one example, the surface  106   b  can have a portion of its surface that is recessed in an identical or nearly identical pattern to the outer surface shape and size of the surface  106   a . In this way, the surface  106   a  can mate with the surface  106   b  in the recessed area, thereby providing close contact between the conversion module  101  and the tibial component  102 .  
         [0037]     A second (optional) step in assembling the knee implant assembly  100  is illustrated with directional arrow  122 . In this step, a locking element or screw  105  is threaded, pressed, or otherwise engaged with the assembly of the conversion module  101  and tibial component  102  to secure these pieces to each other. In this embodiment, the conversion module  101  is provided with a mating feature or aperture that can engage with a pin or set screw  105  to lock the conversion module  101  and the tibial component  102  to each other. This attachment of the module  101  to the tibial component  102  may be accomplished in a number of different ways, such as by friction or interference fit between the two components, for example. These alternative attachment methods may be used instead of or in addition to using a device such as a locking element or screw. That is, in one embodiment, the conversion module  101  can act like a pocket or pouch for accepting tibial component  102  and no other attachment mechanisms are used. This is possible because the main forces will be downward on the assembly after it is implanted in a patient, thereby pressing the tibial component  102  into conversion module  101 .  
         [0038]     A third step in assembling the knee implant assembly  100  is illustrated with directional arrow  124 . In this step, the intramedullary peg  104  is pressed or otherwise secured to the conversion module  101  by interference fit or threaded fasteners, for example. As with the embodiment of  FIG. 1 , this attachment may be accomplished using a number of different techniques and configurations that provide for secure attachment of the components under a variety of loading conditions. In another example, the conversion module  101  has a tapered hole  108 , shown in  FIG. 14 , which can mate with a tapered shank  109  of the intramedullary peg  104  (see  FIG. 15 ), which thereby forms a Morse taper type of connection.  
         [0039]     A fourth step in assembling the knee implant assembly  100  is illustrated with directional arrow  126 . In this optional step, a desired number of tibial wedges  103  can be slid or otherwise moved onto the assembly until the wedge or wedges  103  come in contact with the bottom surface of the tibial component  102 . The wedge or wedges  103  can be secured to the bottom surface of the tibial component  102 , as desired and as will be discussed in further detail below. The tibial wedge or wedges  103  are selected or designed for use depending on the size and type of bony defect in the proximal tibia that needs to be filled.  
         [0040]     It is understood that this assembly sequence described above is intended to be one exemplary assembly sequence, and that the steps may be performed in a different order. For example, tibial wedges  103  may be secured to the tibial component  102  prior to the intramedullary peg  104  being secured to conversion module  101 . In addition, because one or more tibial wedges  103  may or may not be necessary for a particular patient, this step may be performed multiple times with wedges of the same or different sizes and shapes, or may be not be performed at all if wedges are not needed.  
         [0041]     It should be noted that the embodiments of  FIGS. 2 and 10  illustrate different ways of attaching the tibial components  12  and  102  to the conversion modules  14  and  101 , respectively, where the entire assemblies can be embedded in bone cement when implanted in the patient. That is, the portion of the assemblies  10  and  100  from the bottom surface of tibial component  12  or  102  down to the extension peg  16  or intramedullary peg  104  can be embedded in bone cement. In this situation, other than the locking mechanisms discussed above, the tibial components  12  or  102  will be connected or attached to the conversion modules  14  or  101 , respectively, due to the properties of the bone cement in which they are embedded.  
         [0042]     Without the conversion module  101 , the tibial component  102  can function as a standard all-polyethylene tibial component  102  in a standard total knee implant. However, when the conversion module  101  of the invention, which is preferably metal, and the polyethylene tibial component  102  are assembled or connected to each other, the conversion module  101  allows the intramedullary peg  104  to be attached to the assembly as shown in  FIGS. 13   a  and  13   b.    
         [0043]     As set out above, one or more tibial wedges can be used as an optional component to fill bony defects in the proximal tibia, where the wedges can partially or completely cover the bottom face of the tibial component. With particular reference to the tibial wedge  103  of  FIGS. 16 and 17 , the top surface of the wedge  103  has multiple ridges  110  that can fit into grooves  111  of tibial component  102  (see  FIG. 12 ). These ridges  110  can minimize or prevent relative movement between the tibial component  102  and each tibial wedge  103 . The width of the ridges  110  can be at least slightly smaller than the width of the grooves  111  so that the space formed can be filled with cement, although it is also possible to provide a tighter friction fit between the ridges and grooves. However, if a space is provided, such space between the ridges  110  and the grooves  111  can be filed with bone cement or the like during assembly of tibial component  102  and tibial wedge  103 , which can help to maintain a secure attachment between the components.  
         [0044]     Tibial wedge  103  can further include a cavity  112  that corresponds with the shape of the flanges  113  of conversion module  101  shown in  FIG. 14 . These flanges  113  are wider than a cylindrical portion  120  of conversion module  101  and comprise the face  106   a  described above. The tibial wedge  103  can further include at least one groove  118  on the underside of tibial wedge  103 , at least some of which can be used as anchor points for bone cement, if desired.  
         [0045]      FIGS. 18-20  illustrate top and bottom perspective views of three exemplary types of tibial wedges that can be used with the knee implant assemblies of the invention. In particular,  FIG. 18  illustrates a “full-wedge” configuration of a wedge  130 . Wedge  130  includes a central aperture  132  that is shaped and sized to fit over the flanges of a conversion module, such as flanges  113  of conversion module  101 . In this way, a top surface  134  of wedge  130  can contact the bottom surface of tibial component  102  when assembled. This type of wedge can further include at least one ridge  136  that extends from the top surface  134  for contact and/or engagement with at least one corresponding groove on the bottom surface of tibial component  102 .  
         [0046]      FIG. 19  illustrates a “hemi-wedge” configuration of a wedge  140 . Wedge  140  is essentially the same as tibial wedge  103  described above, in that it includes a cavity  142  to mate with a flange  113  of conversion module  101 .  FIG. 20  illustrates a more triangular-shaped wedge  150 , which also includes a cavity  152  to mate with a flange  113  of conversion module  101 . As shown, the top and bottom surfaces of wedge  150  are not parallel to each other, but instead form a triangular or somewhat pie-shaped wedge, which can accommodate certain types of bony defects that are not accommodated by a wedge having parallel opposing surfaces. Both of the wedges  140 ,  150  can also include at least one ridge  144 ,  154 , respectively, that extend from one surface of their respective wedges for contact and/or engagement with at least one corresponding groove on the bottom surface of a tibial component with which they will come in contact. In any case, a wide variety of wedges can be used, which are selected for use depending on the needs of each particular patient. The wedges can be made of polyethylene, metals, plastics, combinations thereof, and the like, and can be constructed by molding, forming, or other manufacturing techniques specifically chosen to cooperate with the material chosen.  
         [0047]     In the embodiments of the invention described above, the tibial component is generally described as being entirely made of polyethylene, while the conversion module and extension peg are described as being made entirely of metal. However, it is considered to be within the scope of the invention that any of these components may include multiple materials, which are designed to function together to provide an overall desired strength for the assembly. For example, the conversion module may be constructed to be partially made of polyethylene and/or another non-metal material, as long as it can provide the desired structural strength to the knee implant assembly.  
         [0048]     The present invention has now been described with reference to several embodiments thereof. The entire disclosure of any patent or patent application identified herein is hereby incorporated by reference. The foregoing detailed description and examples have been given for clarity of understanding only. No unnecessary limitations are to be understood therefrom. It will be apparent to those skilled in the art that many changes can be made in the embodiments described without departing from the scope of the invention. Thus, the scope of the present invention should not be limited to the structures described herein, but only by the structures described by the language of the claims and the equivalents of those structures.