Abstract:
The present invention relates to a tibial prosthesis useful in knee replacement surgeries. The prosthesis includes one or more cement introduction ports which may be used to deliver and control delivery of bone cement to a prosthesis-bone interface after the prosthesis has been positioned on a resurfaced area of a tibia bone. The prosthesis is suitable for implantation using arthroscopic as well as open surgical procedures. The prosthesis may be used as a unicondylar implant in either compartment of the knee or in both compartments of the knee.

Description:
[0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 61/067,740 filed Feb. 29, 2008; U.S. Provisional Application Ser. No. 61/067,741 filed Feb. 29, 2008; and U.S. Provisional Application Ser. No. 61/067,742 filed Feb. 29, 2008, the entire disclosure of each of which is incorporated herein by this specific reference. 
     
    
       [0002]    The present invention generally relates to prosthetic implants and, more particularly, to tibial prostheses for human knee joints. 
       BACKGROUND OF THE INVENTION 
       [0003]    It has become a common practice to implant medical prostheses to resurfaced articular surfaces of knees, for example, during knee replacement surgery. Many of the prior art prosthetic implants require large incisions to provide adequate access to the joint space to accommodate the implant as well as the surgical tools required during the surgery. In addition, conventional knee replacement procedures often involve resection or removal of substantial amount of bone or cartilage tissue in order to accommodate the relatively large prosthetic implant designs typically used today. Such substantial removal of bone can cause increased surgical trauma to a patient and may increase time required for recovery and rehabilitation. In addition, excessive removal of bone tissue may lead to failure of the prosthetic implant due to subsidence thereof into the underlying bone tissue. Unfortunately, this often necessitates additional surgery, for example, revision surgery, in order to replace the failed implant. 
         [0004]    Bone cement is typically used to secure implant components to a resurfaced bone. Misalignment of components may occur when too much or too little bone cement is placed on the implant and the implant positioned on the bone surface. If excess bone cement is used, bone cement may escape from between the bone and the edges of the implant requiring additional surgical steps or processes to remove the escaped cement. Alternatively, if too little bone cement is used, the inadequate amounts of bone cement may result in inadequate fixation of the implant to the bone, resulting in the loosening of the implant, necessitating revision surgery to correct. 
         [0005]    Caspari et al U.S. Pat. No. 5,336,266 discloses tibial and femoral knee joint prosthesis which include open channels through which bone cement can be passed to an inner surface of the implant to at least assist in fixing the implant to the tibia/femur bone. Caspari et al discloses a two piece tibial implant including a polymeric insert fitted into a metal implant body. Caspari et al employs a sharp rim on the implant to form a seal around the cement receiving chamber. In spite of such structure, the Caspari et al devices tend to have problems, for example, with cement leakage, too much or too little cement being injected, uneven distribution of the cement, which can cause discomfort and/or other harm to the patient and/or revision surgery. 
         [0006]    There is still an unmet need for better prosthetic implants, for example, tibial prosthetic implants useful in knee replacement surgery. 
       SUMMARY OF THE INVENTION 
       [0007]    Accordingly, it is an object of the present invention to overcome at least some of the above-mentioned disadvantages associated with prior art devices and surgical procedures. The present invention provides new, for example, improved or enhanced, tibial prosthesis devices for a human knee joint, and which may be, and preferably are, structured to be implantable by means of arthroscopic surgical techniques as well as conventional, open surgical techniques. The present prosthetic devices may be used as unicondylar implants in either compartment of the knee or in both compartments of the knee. 
         [0008]    Advantageously, the present devices may be sized and structured to reduce the required size of surgical incisions and/or reduce the amount of bone that must be removed during surgery, when compared to prior art implant devices and surgical procedures. 
         [0009]    The present devices may be structured to prohibit or substantially prevent or reduce undesirable leakage of bone cement away from the implant, for example, leakage of bone cement into a joint space adjacent the implant. For example, the device may include structure effective to facilitate delivery of bone cement to the appropriate interface region between the implant device and the resurfaced region of the bone, for example, the tibia bone. 
         [0010]    The devices of the invention may be structured to reduce occurrence of subsidence of the implant device. For example, the devices may be structured to require or to be used in combination with no more than a minimal, or substantially a minimal, resection of bone such that bone architecture is left substantially intact and better able to adequately support the implants. In one embodiment, the present devices may be used with less resection of bone relative to another implant device, for example, an identical implant device, without one or more of the structural features of the present devices. 
         [0011]    Another object of the present invention is to reduce surgical trauma by providing devices, for example, tibial prostheses, that reduce the required size of surgical incisions and/or that reduce the amount of bone that must be removed during implantation when compared to prior art tibial prosthetic devices or identical prosthetic devices which are without one or more structural features of the present devices. Advantageously, the present devices may be surgically implanted into an articular surface of a knee using either conventional open surgical methods or arthroscopic surgical methods. In some preferred embodiments of the invention, the devices comprise tibial prostheses which are structured, for example, sized, shaped or otherwise configured, to be implantable through a single surgical incision, or skin portal, which may be less than about 40 mm, or less than about 30 mm or less than about 25 mm. 
         [0012]    Yet another object of the present invention is to provide an implant that, in the event that revision surgery is required, would allow the use of a standard unicompartment replacement knee prosthesis. In one aspect of the invention, the present implant devices are structured to require a minimal or substantially minimal resection of bone such that the bone architecture is left substantially intact leaving more bone stock available for use in revision surgery when compared to prior art devices or identical prosthetic devices which are without one or more structural features of the present devices, and prior art surgical procedures. 
         [0013]    Accordingly, prosthetic implants, for example, tibial prosthesis devices, are provided. In one useful aspect of the invention, the devices useful in knee replacement surgery comprise a proximal articulating region, hereinafter sometimes referred to a proximal region; and a distal fixation region, hereinafter sometimes referred to as a distal region, substantially opposing the proximal region and structured to substantially interface with a resurfaced region of a bone, such as a tibia bone. The proximal region provides a prosthetic articulating surface of a resurfaced bone, for example, a resurfaced tibia bone. The distal region, substantially opposing the proximal region, is generally structured to substantially interface with a resurfaced region of a bone, for example, a tibia bone, and may be implanted on or into a resurfaced region of a bone, for example, a tibia bone. 
         [0014]    In one embodiment, the present tibial prosthetic devices include a peripheral sidewall between the proximal region and the distal region and including a substantially straight sidewall portion and a curved or substantially curved sidewall portion, so as to form a somewhat semi-circular or D-shaped configuration of the device, and defining an area approximating a resurfaced area of a tibia bone. 
         [0015]    The present prosthetic devices may be structured to be effective to facilitate introduction of and effective containment of bone cement used to bond the device to a resurfaced region of a bone, for example, a tibia bone. For example, at least one port may be positioned and structured for receiving and passing bone cement introduced or injected through the port or ports during the surgical procedure, for example, after the device is placed in contact with or on the tibia bone. Further, the present devices may be structured to facilitate containing the bone cement and substantially preventing undesirable leakage thereof into the joint space. For example, the device may be structured to prevent undesirable extrusion of cement exterior to the device after implantation of the device. 
         [0016]    In one aspect of the invention, the present prosthetic devices comprise at least one port, for example, defined by a bore, positioned to facilitate introduction or injection of bone cement, for example, through the at least one port, to the distal region. In one embodiment, the at least one port, or each of the ports if more than one port is employed, includes an inlet, an outlet and a closed or substantially closed passageway there between, that is between the inlet and the outlet, in the device. 
         [0017]    In some embodiments, the inlet of the at least one port is structured and positioned to receive bone cement, for example, from a cement injection system allowing delivery of cement, for example, from the proximal region or outside the proximal region, to the distal region, for example, while the implant is positioned on the prepared tibial surface. 
         [0018]    Without wishing to limit the invention to any particular theory of operation, it is believed that the structure and/or location or position of the present at least one port of the present devices is useful in facilitating one or more benefits provided by the present devices, such as providing for enhanced passing of bone cement to an appropriate location between device and bone, enhanced containment of the bone cement, reduced leakage, for example, unwanted leakage, of bone cement around the periphery of the device or implant near the cement port at the bone implant interface, for example, into the joint space and/or reduced extrusion of the bone cement exterior of the device. For example, it is believed that the closed passageway between the inlet and outlet of the present port or ports provides better control of bone cement injection, bone cement containment or positioning between device and bone, bone cement leakage and/or bone cement extrusion outside the device relative to an identical prosthesis device in which the at least one port including a closed passageway is replaced by an open channel. The devices disclosed in Caspari et al U.S. Pat. No. 5,336,266, noted above, employ an open channel for injecting bone cement into the devices. 
         [0019]    In one embodiment, the at least one port comprises two ports, for example, in a substantially side-by-side relationship, which generally extend through the device, for example generally through or adjacent a sidewall, for example, the peripheral sidewall and/or the distally extending sidewall. The port or ports may extend at an oblique or obtuse angle with respect to the support region. The ports may be located approximate a juncture of the straight sidewall portion and the curved sidewall portion of the device, for example, along the curved sidewall portion. In one embodiment of the invention, when the device has been implanted into the tibia bone, the inlet of at least one port is located at the anterior of the tibial component, for example, near the proximal region of the device. 
         [0020]    The use of more than one port, for example, two ports, may be advantageous. For example, when a single port is used, the overall diameter of the port is greater for a given area of cement flow relative to using two smaller ports, for example, set side-by-side. Using such a side-by-side dual or two port system, for example, two substantially equally sized ports, allows for less bone resectioning and/or results in less trauma to the patient relative to using a device with a single port to provide the same area for cement flow. 
         [0021]    The use of at least dual or two ports may allow the use of a double pronged insertion instrument to hold and/or manipulate the device or implant during surgery. A dual pronged instrument may provide a better grip and/or allow for finer control of the device or implant during surgery. Dual or two closed ports may allow irrigation and/or suction of the implant bone interface. Pulse lavage may be used effectively. 
         [0022]    When the device is implanted into a tibia bone, the at least one port may be, and often is, located at an anterior region of the joint, for example, the knee joint. 
         [0023]    In one embodiment, the distal region of the present device includes a support region comprising a fixation structure effective to enhance fixation of the device to a resurfaced region of a bone relative to an identical device without the fixation structure. The fixation structure may form a plurality of channels in the support region in communication with the at least one port. Thus, the bone cement introduced or injected through the port or ports may flow into and through the channels in facilitating fixation of the device to a resurfaced area of a bone. The fixation structure may comprise a plurality of undercuts or distally extending projections effective to facilitate bone cement from, for example, introduced or injected from, the at least one port, forming a cement bond, for example, an enhanced cement bond, between the device and a resurfaced region of a bone, for example, relative to an identical device without such undercuts or projections, such as an identical device having a support region with a featureless, planar distal surface. 
         [0024]    In one embodiment, the channels in the support region may be formed by a appropriate positioning/ordering of the undercuts or projections. Therefore, a prosthetic device which includes both such channels and such undercuts or projections can be provided and is included within the scope of the present invention. 
         [0025]    The present devices do not require that a through hole be provided for inserting a bone screw through the device into a tibia bone. In one embodiment, the present device includes no through hole, that is, the device is free of a through hole, for inserting a bone screw through the device into a tibia bone. This feature of the present devices facilitates maintaining the integrity of the bone remaining after the device is implanted, and reduces surgical trauma. 
         [0026]    In some embodiments of the invention, the distal region includes a distally extending sidewall at least partially or even substantially entirely circumscribing the support region. A recess at least partially or even substantially entirely circumscribing the support region, for example, inside of the peripheral sidewall and/or distally extending sidewall, may be present. The recess may comprise a groove which at least partially or even substantially entirely circumscribes the support region. The peripheral sidewall/distally extending sidewall and recess provide structure effective to at least facilitate containment of bone cement used to secure the implant device to the resurfaced tibia bone, as well as prevent undesirable leakage of bone cement into the joint space. 
         [0027]    In one advantageous aspect of the invention, one or both of the peripheral sidewall and the distally extending sidewall, for example, the distally extending sidewall, includes a flow control structure effective in controlling the flow of bone cement from the distal region. Such flow control structure is effective in enhancing the fixation of the present prosthesis device to the bone, for example, relative to an identical prosthesis device without the flow control structure. For example, the device may be structured to control flow of bone cement, that is to allow a limited or controlled flow of bone cement, for example, from the distal region, as discussed elsewhere herein, as well as prevent undesirable extrusion of bone cement exterior to the device, for example, into the joint space, after implantation of the device. The flow control structure, for example and without limitation, may include one or more notches and/or one or more sidewall grooves and/or one or more flow control ports into which the bone cement, for example, a limited or controlled amount of the bone cement, may enter to form an improved or enhanced bond, such as an improved or enhanced cement bond, between the bone, for example, the resurfaced region of the tibia bone, and the device. 
         [0028]    Various embodiments of the present invention are described in detail in the detailed description and additional disclosure below. Any feature or combination of features described herein are included within the scope of the present invention provided that the features included in any such combination are not mutually inconsistent as will be apparent from the context, this specification, and the knowledge of one of ordinary skill in the art. In addition, any feature or combination of features may be specifically excluded from any embodiment of the present invention. Additional advantages and aspects of the present invention are apparent in the following detailed description, drawings, examples, and additional disclosure. 
         [0029]    Many of the aspects and advantages of the present invention may be more clearly understood and appreciated with reference to the following Detailed Description and accompanying Drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]      FIG. 1  is a top plan view of a tibial prosthesis device in accordance with the present invention showing a proximal region, for example, an articulating surface, of the device. 
           [0031]      FIG. 2  is a cross-section of the device taken along line  2 - 2  of  FIG. 1 . 
           [0032]      FIG. 3  is a perspective view of the device of  FIG. 1  showing the proximal region of the device. 
           [0033]      FIG. 4  is a perspective view of the device of  FIG. 1  showing the distal fixation region, including the support region, of the device. 
           [0034]      FIG. 5  is a bottom plan view of the device of  FIG. 1  showing the distal fixation region of the device. 
           [0035]      FIG. 6  is a side elevational view of the device. 
       
    
    
     DETAILED DESCRIPTION 
       [0036]    Turning now to the drawings, an exemplary embodiment of a tibial prosthesis device in accordance with the invention is shown generally at  10 . The device  10  includes a curved peripheral wall or sidewall  16  and a generally straight peripheral wall or sidewall  18 , which together form, in cross-section, a generally semi-circular shape, or a generally D-shape, which approximates a resurfaced area of a bone, for example, a resurfaced area of a tibia bone, on or into which the device is to be implanted. 
         [0037]    Resurfacing of the tibia bone in preparation for implantation of tibial prosthesis device  10  may be performed using conventional techniques, for example conventional, open surgical techniques. In one embodiment, such preparation may be performed using the arthroscopic surgical devices and methods described in the co-pending U.S. provisional patent application Ser. No. 61/067,741, filed Feb. 29, 2008, entitled INSTRUMENTS AND METHOD FOR ARTHROSCOPY OF THE KNEE and commonly owned herewith, the entire disclosure of said application being incorporated herein by this specific reference. 
         [0038]    The device  10  further comprises a distal fixation region or distal region  20 , shown perhaps most clearly in  FIGS. 4 and 5 , and a proximal articulating region or proximal region  22 , shown in  FIGS. 1 and 3 . The distal region  20  is generally structured to interface with and be implanted onto or in a resurfaced region or area of a tibia bone. The proximal region  22  of the device  10 , which substantially opposes the distal region  20 , is slightly curved inwardly toward the center, for example, concave, and provides an articulating surface of the device  10 , for example, with a femur bone or a femoral prosthesis device (not shown), after the device  10  is implanted on or into a resurfaced region of a tibia bone. 
         [0039]    The distal region  20  includes a support region  34  comprising a fixation structure, shown generally at  44 , for example, a regular or irregular fixation structure, effective to enhance fixation of the device  10  to a resurfaced region of a tibia bone relative to an identical device without the fixation structure. For example, the support region  34 , and the fixation structure  44  in particular, comprise a system or network or plurality of undercuts or distally extending projections  45  and channels  36 . For example, the plurality of undercuts or projections  45  form the channels  36 . In the shown embodiment, some of the channels  36  are positioned substantially parallel to each other and some of the channels are substantially perpendicular to each other. 
         [0040]    In any event, the fixation structure  44  is effective so that when bone cement, for example, bone cement in a fluid state, is introduced or injected into the distal region  20 , in particular the support region  34 , for example, through the ports  32 , discussed hereinafter, while the device  10  is located in or on a resurfaced region of a tibia bone, an enhanced cement bond between the device  10  and the tibia bone is obtained. 
         [0041]    Without wishing to limit the invention to any particular theory of operation, it is believed that the fixation structure  44 , such as the channels  36 /undercuts or projections  45  of fixation structure  44  shown in the drawings, provides the support region  34  with an increased amount of surface area, for example, relative to a substantially planar support region. Such increased surface area provides more area for the cement to bond with the device  10  and, ultimately, provides for an enhanced cement bond, for example, a cement bond of increased strength, between the device  10  and the tibia bone, for example, relative to an identical device having a planar support region. 
         [0042]    Bone cement useful with the present invention may be any suitable bone cement known to those of skill in the art. For example, the bone cement may be a grout-like material, such as polymethyl methacrylate material and/or other suitable biocompatible material known to those of skill in the art which is effective to provide long term, for example, permanent or substantially permanent, fixation of a prosthesis to a surface of a bone. 
         [0043]    In one especially advantageous aspect of the present invention, the device  10  is structured to be effective to facilitate introduction or injection and containment of bone cement during the surgical implantation procedure. 
         [0044]    For example, in the shown embodiment, the device  10  further comprises structure for facilitating introduction of bone cement to the distal region  20 . The device  10  comprises a port structure, shown generally at  32 , including at least one port, for example, two ports  32   a  and  32   b , for facilitating introduction or injection of bone cement to the distal region  20 . The ports  32   a  and  32   b  are defined by bores extending through a surface region, for example, an angled surface region  33 , of port structure  32 , which extends outwardly and distally from the proximal region  22  of the device  10 . The ports  32   a  and  32   b  include closed passageways defined by closed bore sidewalls  35   a  and  35   b , respectively, between inlets  37   a  and  37   b , respectively, and outlets  39   a  and  39   b  ( FIG. 5 ), respectively. 
         [0045]    In this embodiment, the ports  32   a  and  32   b  are disposed substantially directly adjacent one another, for example, in a substantially side-by-side relationship. The ports  32   a  and  32   b  are appropriately sized and positioned to facilitate introduction or injection of a suitable bone cement in a suitable amount to the bone/implant interface during surgical implantation of the device  10  on or into a resurfaced region of a tibia bone. Each of the ports  32   a  and  32   b  has an inlet  37   a ,  37   b  away from or outside of the distal region  20 , and an outlet  39   a ,  39   b  through which bone cement passes to be placed in the distal region  20 . Each of the ports  32   a  and  32   b  is oriented so that the closed passageway or bore  35   a ,  35   b  slants or slopes distally from the inlet to the outlet, for example, at an oblique or obtuse angle with respect to the support region  34 . This orientation may facilitate injection of the bone cement and/or containment of the bone cement in the desired location or locations. 
         [0046]    The ports  32   a  and  32   b  of the shown embodiment are located so that the inlets  37   a  and  37   b  are positioned outwardly from, and distally from the proximal region  22  of the device  10 . The ports  32   a  and  32   b  are positioned to facilitate introduction or injection of bone cement to the distal portion  20 . The ports  32   a  and  32   b  may have any of various geometric shapes and may pass through the device  10  at an oblique or obtuse angle relative to the support region  34 , for example, as shown in  FIG. 2 . 
         [0047]    The ports  32   a  and  32   b  may be positioned generally outside of the patella-tibial articulation region of the knee joint when the device  10  is implanted or affixed to the resurfaced region of a tibia bone. The ports  32   a  and  32   b , in particular the inlets  37   a  and  37   b  of such ports, are located on angled surface  33 , which is positioned in proximity to the intersection of substantially straight sidewall  18  and substantially curved sidewall  16  of the device  10 . The angled surface  33  extends outwardly from the sidewalls  16  and  18 . In one embodiment, the angled surface  33  may be joined at least partially or substantially entirely to the curved sidewall  16 . 
         [0048]    Although two ports  32   a  and  32   b  are shown in the drawings, in other embodiments of the invention not shown, the device  10  may comprise only one port or, alternatively, three or more ports. All such embodiments are included within the scope of the present invention. 
         [0049]    The introduction or injection of the bone cement or bone cement material may be achieved through a pressurizing syringe or similar fluid mover. The bone cement injected may be a highly viscous material or a less viscous or a more fluid material, for example, relative to the highly viscous bone cement material conventionally introduced to bond an implant to bone. Injecting a more fluid material, such as a material which is flowable or readily flowable at normal or atmospheric pressure under the influence of gravity, is different from injecting highly viscous material, which is not readily flowable at such conditions. In one embodiment, the fluid or more fluid bone cement material has a viscosity (at room temperature) in a range of about 5,000 centipoise or less to about 50,000 centipoise or about 100,000 centipoise. The injected fluid bone cement material has increased effectiveness, for example, relative to highly viscous bone cement material, for example, injected highly viscous bone cement material, in filling interstitials or small regions between the prosthesis device and the bone, and/or in bonding with mating surfaces. 
         [0050]    In the past, a surgeon often had to wait a period of time for the bone cement to set-up or harden sufficiently to allow the surgeon to handle the cement effectively. Such “set up” bone cement, once applied, tends to have or has reduced bonding ability. 
         [0051]    The present invention allows the surgeon to take advantage of bone cement in a more fluid state. Such more fluid bone cement material, for example, more fluid bone cement material injected through one or more ports including closed passageways in the present prosthesis device, allows the pores in the bone to be filled with bonding material, as well as providing more adhesive properties to the implant itself. A marked or substantial increase in cement bond strength relative to conventional thumb packing techniques with “set up” bone cement have been shown when more fluid bone cement material is injected, for example, using the prosthesis devices of the present invention. 
         [0052]    In the shown embodiment, the distal region  20  further comprises a distally extending flange or sidewall  38 . Flange or sidewall  38  may be defined or considered as a distally extending portion of, and/or may be contiguous with, curved sidewall  16  and/or the straight sidewall  18 . The distally extending flange or sidewall  38  may substantially entirely circumscribe the recess  40 . The distally extending flange or sidewall  38  includes a flow control structure effective in providing for an amount, for example, a controlled or limited amount, of bone cement to flow from the distal region  20 . For example, the flow control structure may include a plurality of spaced apart, open ended notches  41  in distally extending flange  38  for receiving bone cement to form additional bonding regions between the device  10  and the resurfaced region of a tibia bone about the outer periphery of the device  10 . 
         [0053]    The distal region  20  further includes a groove or recess  40 , which may substantially entirely circumscribe the support region  34 . The recess  40  may be flush with and/or otherwise in communication with the notches  41 . This recess  40  provides additional space or volume in the distal region  20  for the introduction and containment of bone cement, which may result in an enhanced cement bond between the device  10  and the tibia bone. Since the recess  40  is in communication with the notches  41 , the recess provides a supply of bone cement to be received in the notches  41 . In general, recess  40  is effective in controlling the placement and containment of the bone cement introduced into the distal region  20  and in reducing the risk of undesirable leakage of the bone cement from the device  10  into the joint space. 
         [0054]    The flow control structure, in the shown embodiment, includes open sidewall groove  48 . Open sidewall groove  48  in the outside of sidewall  18 , shown most clearly in  FIG. 3  and  FIG. 6 , is in communication with notches  41  and is positioned and structured to be effective to facilitate the introduction of, placement of and/or containment of bone cement used to bond the device  10  to a resurfaced region of the tibia bone by permitting bone cement, for example, a controlled or limited amount of bone cement, extruded through the notches  41  from the distal region  20  to flow around the outer periphery of the device  10 . 
         [0055]    In one embodiment, the sidewall groove  48  can be segmented into a plurality, that is two or more, spaced apart sidewall groove segments, for example, separated from each other by portions of the peripheral sidewall/distally extending sidewall without the sidewall groove. Such embodiment is included within the scope of the present invention. 
         [0056]    The flow control structure of device  10  includes control bores or flow control bores  50 . Flow control bores  50  provide additional bone cement passageways between the distal region  20 , for example, the recess  40  of the distal region, and the sidewall groove  48 . Such control bores  50  are effective in controlling the placement of bone cement around the outer periphery of the device  10  when the device is implanted on or into a tibia bone. 
         [0057]    The flow control structure in accordance with the present invention may include any one or more of the notches  41 , the sidewall groove  48  and the flow control bores  50 . 
         [0058]    As shown in the drawings, the device  10  is a single unitary structure and has no moving parts. The device  10  may be made of a durable, biocompatible material. The device  10  may be made from a polymeric material, for example, any suitable polymeric material. Examples of suitable materials include ultra high molecular weight polyethylene (UHMWPE), for example, cast conforming to ASTM F75 Specification. The device  10  may be present in any suitable size or sizes. 
         [0059]    Reference to the following U.S. patents and Published patent applications may provide additional disclosure which may be helpful in understanding one or more aspects of the present invention, each of said patents and publications being incorporated herein in its entirety by this specific reference: Bokros, U.S. Pat. No. 4,166,292; Matthews et al., U.S. Pat. No. 4,778,473; Hofmann et al., U.S. Pat. No. 4,963,152; Caspari et al., U.S. Pat. No. 5,171,276; Clark et al., U.S. Pat. No. 5,266,075; Clark et al., U.S. Pat. No. 5,393,302; Coates, U.S. Pat. No. 5,405,395; Clark, U.S. Pat. No. 5,643,273; Oudard et al., U.S. Pat. No. 5,766,256; Clark, U.S. Pat. No. 5,954,747; Clark et al., U.S. Pat. No. 6,306,138; Clark, U.S. Pat. No. 6,306,156; Musset et al., U.S. Pat. No. 6,423,096; Clark et al., U.S. Pat. No. 6,558,389; Johnson et al., U.S. Pat. No. 6,723,102; Clark et al., U.S. Pat. No. 6,780,188; Masini, U.S. Pat. No. 6,821,300; Sonnabend et al., U.S. Pat. No. 6,884,246; Carson et al., U.S. Pat. No. 6,923,817; Fell et al., U.S. Pat. No. 6,966,928; McCue et al., U.S. Pat. No. 7,083,652; Lipman et al., U.S. Pat. No. 7,105,027; Rosa et al., U.S. Pat. No. 7,141,053; Johnson et al., U.S. Pat. No. 7,297,164; Hayes, JR, et al., U.S. Publication No. 2002/0161448; Metzger et al., U.S. Publication No. 2003/0009232; Walker et al., U.S. Publication No. 2004/0243134; Walker et al., 2005/0192583; Walker et al., U.S. Publication No. 2005/0192584; Bernero et al., U.S. Publication No. 2006/0052875; Saadat et al., U.S. Publication No. 2007/0213735; Justin et al., U.S. Publication No. 2007/0288029. 
         [0060]    While this invention has been described with respect to various specific examples and embodiments, it is to be understood that the invention is not limited thereto and that it can be variously practiced.