Abstract:
Apparatus for reconstructing a joint, the apparatus comprising:
       an implant body having a bone contacting surface; and   a plurality of fixation elements secured to the implant body and extending into the host bone at a plurality of angles, wherein all angles are not equal to one another, so as to create immediate stability between the implant body and the host bone.

Description:
REFERENCE TO PENDING PRIOR PATENT APPLICATIONS 
       [0001]    This patent application claims benefit of: 
         [0002]    (i) pending prior U.S. Provisional Patent Application Ser. No. 61/599,816, filed Feb. 16, 2012 by Thomas Eickmann et al. for TIBIAL BASE CONSTRUCT FOR KNEE JOINT PROSTHESIS (Attorney&#39;s Docket No. MOBIUS-1 PROV); and 
         [0003]    (ii) pending prior U.S. Provisional Patent Application Ser. No. 61/730,836, filed Nov. 28, 2012 by Thomas Eickmann et al. for CEMENTLESS BASEPLATE (Attorney&#39;s Docket No. MOBIUS-5 PROV). 
         [0004]    The two (2) above-identified patent applications are hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0005]    This invention relates to orthopaedic prostheses in general, and more particularly to tibial baseplates for knee joint prostheses. 
       BACKGROUND OF THE INVENTION 
       [0006]    Joint replacement surgery seeks to replace some or all of a natural joint with prosthetic components so as to provide long-lasting function and pain-free mobility. 
         [0007]    For example, in the case of a prosthetic total hip joint, the head of the femur is replaced with a prosthetic femoral stem component, and the socket of the acetabulum is replaced by a prosthetic acetabular cup component, whereby to provide a prosthetic total hip joint. 
         [0008]    In the case of a prosthetic total knee joint, the top of the tibia is replaced by a prosthetic tibial component, and the bottom of the femur is replaced by a prosthetic femoral component, whereby to provide a prosthetic total knee joint. 
         [0009]    The present invention is directed to orthopedic prostheses for restoring the knee joint and, in particular, to improved prosthetic tibial components. 
         [0010]    Looking now at  FIG. 1 , there is shown a prior art prosthetic total knee joint  5  which generally comprises a prosthetic tibial component  10  secured to the top end of a resected tibia  15 , and a prosthetic femoral component  20  which is secured to the bottom end of a resected femur  25 . 
         [0011]    A typical prior art prosthetic tibial component  10  is shown in greater detail in  FIGS. 2 and 3 . Prior art prosthetic tibial component  10  generally comprises a metal base construct  30  and a polyethylene bearing construct  35 . 
         [0012]    More particularly, metal base construct  30  generally comprises a baseplate  40  having a top surface  42  and a bottom surface  43 , a stem  45  and a plurality of posts  50  descending from bottom surface  43  of baseplate  40  and into resected tibia  15 , a plurality of screws  55  passing through baseplate  40  and into resected tibia  15 , a pair of rails  60  running along top surface  42  of baseplate  40  and defining a groove  65  therebetween, and a pair of end walls  70  connected to top surface  42  of baseplate  40 . Preferably bottom surface  43  of baseplate  40  (and, optionally, stem  45  and/or posts  50 ) comprises a porous material so as to allow bone ingrowth into baseplate  40  (and/or stem  45  and/or posts  50 ), whereby to facilitate osseo-integration of the baseplate (and/or stem  45  and/or posts  50 ) with resected tibia  15  over time. 
         [0013]    Polyethylene bearing construct  35  comprises a flat bottom surface  75  having a recess  80  in which is disposed a tongue  85 . Tongue  85  is sized to slidingly fit in groove  65  of metal base construct  30  ( FIG. 3 ), whereby polyethylene bearing construct  35  may be slidingly secured to metal base construct  30 . Note that end walls  70  act as stops for polyethylene bearing construct  35  when tongue  85  of polyethylene bearing construct  35  is advanced into groove  65  of metal base construct  30 . It should be appreciated that the aforementioned “tongue-in-groove” locking mechanism between polyethylene bearing construct  35  and metal base construct  30  (i.e., tongue  85  of polyethylene bearing construct  35  and groove  65  of metal base construct  30 ) is only one of the many different locking mechanisms used in the art to secure a polyethylene bearing construct to a metal base construct, and is shown here for purposes of example but not limitation. 
         [0014]    In use, the top end of tibia  15  is resected, and metal base construct  30  is secured to tibia  15 , i.e., by advancing stem  45  and posts  50  into resected tibia  15  until bottom surface  43  of baseplate  40  is seated against resected tibia  15 . Note that the parallel dispositions of stem  45  and posts  50  facilitates advancement of stem  45  and posts  50  into the resected tibia. Next, screws  55  are advanced through baseplate  40  and into resected tibia  15 , whereby to secure metal base construct  30  to resected tibia  15 . Then polyethylene bearing construct  35  is locked onto metal base construct  30 , e.g., by sliding tongue  85  of polyethylene bearing construct  35  into groove  65  of metal base construct  30  until polyethylene bearing construct  35  engages end walls  70  of baseplate  40 . 
         [0015]    Ideally, baseplate  40 , stem  45  and posts  50  osseo-integrate with resected tibia  15  over time, thereby providing stable attachment of prosthetic tibial component  10  to resected tibia  15 . 
         [0016]    Unfortunately, in many patients, micromotion of baseplate  40 , stem  45  and posts  50  relative to resected tibia  15  inhibits osseo-integration. In addition, micromotion can lead to the development of a fibrous membrane at the interface of the prosthesis and the resected tibia. This fibrous membrane further inhibits bony ingrowth into the prosthesis, and the result is a loose and painful joint. In many patients, the consequences of the aforementioned micromotion between the prosthesis and the bone (i.e., lack of proper osseo-integration, development of a fibrous membrane between the prosthesis and the resected tibia, and the resulting pain for the patient) ultimately requires revision surgery. 
         [0017]    As a result, in many cases, clinicians apply bone cement (typically polymethylmethacrylate, also known as PMMA) between bottom surface  43  of baseplate  40  and the top of resected tibia  15 , and/or around stem  45  and/or posts  50 . However, since this bone cement is interposed between the prosthesis and the tibia, it inhibits the aforementioned osseo-integration process, thereby reducing the possibility of long-term biological fixation via bony ingrowth. Furthermore, over time, bone cement can deteriorate, thereby causing loosening of the prosthesis, significant pain for the patient and, in many cases, ultimately requiring revision surgery. 
         [0018]    Thus there is a need for a new and improved tibial baseplate assembly for a knee joint prosthesis which can provide for immediate cementless fixation of the tibial baseplate to the resected tibia while effectively eliminating micromotion between the prosthesis and the tibia, thereby providing an early post-operative environment where bony ingrowth can occur, providing long-term, biological fixation between bone and prosthesis which has the potential to provide a lifetime result for the patient. 
       SUMMARY OF THE INVENTION 
       [0019]    The present invention comprises the provision and use of a new and improved tibial baseplate assembly for a knee joint prosthesis which provides for immediate cementless fixation of the tibial baseplate to the resected tibia while effectively eliminating micromotion between the prosthesis and the tibia, thereby providing the environment for long-term biological fixation via bony ingrowth into the prosthesis surface. 
         [0020]    The present invention also comprises the provision and use of a new and improved prosthetic tibial component which comprises a base construct and a bearing construct, wherein the base construct comprises a novel tibial baseplate assembly which provides for immediate cementless fixation of the tibial baseplate to the resected tibia while effectively eliminating micromotion between the prosthesis and the tibia, thereby providing the environment for long-term biological fixation via bony ingrowth into the prosthesis surface. 
         [0021]    The present invention also comprises a novel method for reconstructing a knee joint, wherein the novel method comprises the provision and use of an improved prosthetic tibial component which comprises a base construct and a bearing construct, and further wherein the base construct comprises a novel tibial baseplate assembly which provides for immediate cementless fixation of the tibial baseplate to the resected tibia while effectively eliminating micromotion between the prosthesis and the tibia, thereby providing the environment for long-term biological fixation via bony ingrowth into the prosthesis surface. 
         [0022]    In one preferred form of the invention, there is provided apparatus for reconstructing a joint, the apparatus comprising: 
         [0023]    an implant body having a bone contacting surface; and 
         [0024]    a plurality of fixation elements secured to the implant body and extending into the host bone at a plurality of angles, wherein all angles are not equal to one another, so as to create immediate stability between the implant body and the host bone. 
         [0025]    In another preferred form of the invention, there is provided a method for reconstructing a joint, the method comprising: 
         [0026]    providing apparatus comprising:
       an implant body having a bone contacting surface; and   a plurality of fixation elements to be secured to the implant body and extend into the host bone at a plurality of angles, wherein all angles are not equal to one another, so as to create immediate stability between the implant body and the host bone;       
 
         [0029]    positioning the implant body against a host bone; and 
         [0030]    creating immediate stability between the implant body and the host bone using the plurality of fixation elements. 
         [0031]    In another preferred form of the invention, there is provided apparatus for reconstructing the knee joint, the apparatus comprising: 
         [0032]    a tibial baseplate; and 
         [0033]    at least two fixation elements for securing the tibial baseplate to a bone, wherein the at least two fixation elements are secured to the tibial baseplate and extend into the tibia at angles which are not parallel to one another. 
         [0034]    In another preferred form of the invention, there is provided a method for reconstructing the knee joint, the method comprising: 
         [0035]    providing apparatus comprising:
       a tibial baseplate; and   at least two fixation elements for securing the tibial baseplate to a bone, wherein the at least two fixation elements are secured to the tibial baseplate and extend into the tibia at angles which are not parallel to one another;       
 
         [0038]    positioning the tibial baseplate against a resected tibia; and 
         [0039]    securing the tibial baseplate to the resected tibia using the at least two fixation elements, wherein the at least two fixation elements are secured to the tibial baseplate and extend into the tibia at angles which are not parallel to one another. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0040]    These and other objects and features of the present invention will be more fully disclosed or rendered obvious by the following detailed description of the preferred embodiments of the invention, which is to be considered together with the accompanying drawings wherein like numbers refer to like parts, and further wherein: 
           [0041]      FIG. 1  is a schematic side view showing a prior art prosthetic total knee joint; 
           [0042]      FIG. 2  is a schematic partially-exploded perspective view showing a prior art prosthetic tibial component; 
           [0043]      FIG. 3  is a schematic front view showing a prior art prosthetic tibial component secured to a resected tibia; 
           [0044]      FIG. 4  is a schematic front view showing a new and improved tibial baseplate assembly for a knee joint prosthesis; 
           [0045]      FIG. 5  is a view like that of  FIG. 4 , except that the baseplate of the tibial baseplate assembly is shown semi-transparent; 
           [0046]      FIG. 6  is a schematic lateral view showing the new and improved tibial baseplate assembly of  FIG. 4 ; 
           [0047]      FIG. 7  is a schematic posterior view showing the new and improved tibial baseplate assembly of  FIG. 4 ; 
           [0048]      FIG. 8  is a schematic medial view showing the new and improved tibial baseplate assembly of  FIG. 4 ; 
           [0049]      FIG. 9  is a schematic bottom view showing the new and improved tibial baseplate assembly of  FIG. 4 , with the baseplate of the tibial baseplate assembly being shown semi-transparent; 
           [0050]      FIG. 10  is a schematic top view showing the new and improved tibial baseplate assembly of  FIG. 4 , with the baseplate of the tibial baseplate assembly being shown semi-transparent; 
           [0051]      FIG. 11  is a partial schematic front view showing a peg secured to the baseplate of the new and improved tibial baseplate assembly of  FIG. 4 ; 
           [0052]      FIG. 11A  is a schematic front view showing a template for use in forming holes in the resected tibia for receiving the pegs of the new and improved tibial baseplate assembly of  FIG. 4 ; 
           [0053]      FIG. 11B  is a schematic front view showing a peg secured to the baseplate of the new and improved tibial baseplate assembly of  FIG. 4  using a hole formed by the template shown in  FIG. 11A ; 
           [0054]      FIG. 12  is a schematic view showing an alternative form of pegs secured to the baseplate of the new and improved tibial baseplate assembly of  FIG. 4 ; 
           [0055]      FIG. 13  is a schematic bottom view showing the components of  FIG. 12 ; 
           [0056]      FIG. 14  is a view like that of  FIG. 12 , except showing one of the pegs about to be secured to the baseplate; 
           [0057]      FIG. 15  is a schematic perspective view showing pegs and a bone screw securing the baseplate of the new and improved tibial baseplate assembly to the resected tibia; and 
           [0058]      FIG. 16  is a schematic lateral view showing pegs and a bone screw securing the baseplate of the new and improved tibial baseplate assembly to the resected tibia. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0059]    The present invention comprises the provision and use of a new and improved tibial baseplate assembly for a knee joint prosthesis which provides for immediate cementless fixation of the tibial baseplate to the resected tibia while effectively eliminating micromotion between the prosthesis and the tibia. 
         [0060]    The present invention also comprises the provision and use of a new and improved prosthetic tibial component which comprises a base construct and a bearing construct, and further wherein the base construct comprises a novel tibial baseplate assembly which provides for immediate cementless fixation of the tibial baseplate to the resected tibia while effectively eliminating micromotion between the prosthesis and the tibia. 
         [0061]    The present invention also comprises a novel method for reconstructing a knee joint, wherein the novel method comprises the provision and use of an improved prosthetic tibial component which comprises a base construct and a bearing construct, and further wherein the base construct comprises a novel tibial baseplate assembly which provides for immediate cementless fixation of the tibial baseplate to the resected tibia while effectively eliminating micromotion between the prosthesis and the tibia. Looking now at  FIGS. 4-11 , there is shown a novel base construct  105  for use in conjunction with a bearing construct (e.g., the polyethylene bearing construct  35  discussed above) so as to form a prosthetic tibial component for a prosthetic total knee joint. 
         [0062]    Novel base construct  105  comprises a novel tibial baseplate assembly  110  for mounting to the resected tibia and receiving a bearing construct (e.g., the polyethylene bearing construct  35  discussed above). Novel tibial baseplate assembly  110  generally comprises a baseplate  115  having a top surface  120  and a bottom surface  125 , and at least two fixation elements  130  extending downwardly from bottom surface  125  of baseplate  115  for receipt in a resected tibia (not shown) so as to cementlessly secure baseplate  115  (and hence novel base construct  105 ) to the resected tibia while effectively eliminating micromotion between the prosthesis and the tibia. In accordance with the present invention, and as will hereinafter be discussed in further detail, at least two of the fixation elements  130  extend downwardly from bottom surface  125  of baseplate  115  in a non-parallel manner. Such non-parallel disposition of at least two of the fixation elements  130  ensures that baseplate  115  is cementlessly secured to the tibia while effectively eliminating micromotion between the prosthesis and the tibia. Preferably bottom surface  125  of baseplate  115  (and, optionally, one or more of the at least two fixation elements  130 ) comprise a porous material so as to allow bone ingrowth into baseplate  115  (and/or one or more of the at least two fixation elements  130 ), whereby to facilitate osseo-integration of the baseplate  115  (and/or one or more of the at least two fixation elements  130 ) with the resected tibia over time. 
         [0063]    A pair of rails  135  run along top surface  120  of baseplate  115  and define a groove  140  therebetween. A pair of end walls  145  are connected to top surface  120  of baseplate  115 . Rails  135  and end walls  145  are intended to facilitate securing a bearing construct (e.g., such as the aforementioned polyethylene bearing construct  35 ) to baseplate  115  via a “tongue-in-groove” locking mechanism (e.g., via disposition of tongue  85  of polyethylene bearing construct  35  into groove  140  of baseplate  115 ), although such a “tongue-in-groove” locking mechanism is only one of the many different locking mechanisms which may be used to secure a bearing construct (such as the polyethylene bearing construct  35 ) to baseplate  115 , and hence it should be appreciated that rails  135  and end walls  145  are shown here for purposes of example but not limitation. 
         [0064]    As noted above, novel tibial baseplate assembly  110  comprises at least two fixation elements  130  extending downwardly from bottom surface  125  of baseplate  115  for receipt in a resected tibia (not shown) so as to cementlessly secure baseplate  115  (and hence novel base construct  105 ) to the resected tibia while effectively eliminating micromotion between the prosthesis and the tibia. In accordance with the present invention, at least two of the fixation elements  130  extend downwardly from bottom surface  125  of baseplate  115  in a non-parallel manner. Such non-parallel disposition of at least two of the fixation elements  130  ensures that baseplate  115  is cementlessly secured to the tibia while effectively eliminating micromotion between the prosthesis and the tibia. 
         [0065]    In one preferred form of the invention, fixation elements  130  comprise a stem  150 , a post  155  and a plurality of pegs  160 . 
         [0066]    Stem  150  is preferably formed integral with baseplate  115  and comprises a substantially straight body extending downwardly from bottom surface  125  of baseplate  115 . Stem  150  extends at a right angle to bottom surface  125  of baseplate  115 . Stem  150  may have a circular cross-section or other cross-section, straight or tapered sides or edges, and a pointed, rounded or flat distal end. Stem  150  is preferably located intermediate bottom surface  125  of baseplate  115  so as to extend into the intramedullary canal of the tibia when baseplate  115  is set on the resected tibia. In one preferred form of the invention, substantially the entire outer surface of stem  150  comprises a porous coating so as to facilitate osseo-integration of the surrounding bone into the stem. 
         [0067]    Post  155  is preferably formed integral with baseplate  115  and comprises a substantially straight body extending downwardly from bottom surface  125  of baseplate  115 . Post  155  extends at a right angle to bottom surface  125  of baseplate  115 . Post  155  may have a circular cross-section or other cross-section, straight or tapered sides or edges, and a pointed, rounded or flat distal end. Post  155  is preferably located intermediate bottom surface  125  of baseplate  115  so as to extend into the tibia when baseplate  115  is set on the resected tibia. In one preferred form of the invention, substantially the entire outer surface of post  155  comprises a porous coating so as to facilitate osseo-integration of the surrounding bone into the stem. 
         [0068]    Each peg  160  comprises an elongated body  165  having a distal end  170  and a proximal end  175  ( FIG. 11 ). Elongated body  165  preferably has a circular cross-section. Distal end  170  of elongated body  165  is preferably rounded so as to facilitate advancement into a hole formed in the tibia (see below), and proximal end  175  of elongated body  165  includes an inward taper  178  and an outer screw thread  180  proximal to inward taper  178 . A non-circular recess  185 , for receiving a driver (not shown), is formed in proximal end  175  of elongated body  165 . Pegs  160  are intended to be releasably secured to baseplate  115  via the aforementioned screw thread  180  and, to this end, baseplate  115  comprises a plurality of threaded bores  190  extending therethrough. In accordance with one preferred form of the present invention, each threaded bore  190  extends at a non-perpendicular angle to the plane of baseplate  115 , such that when pegs  160  are screwed into threaded bores  190 , pegs  160  will extend at non-perpendicular angles to the plane of baseplate  115 . Furthermore, in one preferred form of the invention, threaded bores  190  extend non-parallel to one another, such that pegs  160  also extend non-parallel to one another. 
         [0069]    In order to provide sufficient stability to pegs  160 , baseplate  115  preferably comprises collars  195  about each of the threaded bores  190 , with collars  195  being formed integral with baseplate  115  and extending distally from baseplate  115 , coaxial with threaded bores  190 . Collars  195  terminate in a tapered shoulder  200  for mating with inward taper  178  of pegs  160 . 
         [0070]    In one preferred form of the invention, substantially the entire outer surface of pegs  160  comprise a porous coating so as to facilitate osseo-integration of the surrounding bone into the peg. 
         [0071]    And in one preferred form of the invention, collars  195  comprise a porous coating so as to facilitate osseo-integration of the surrounding bone with the collar. 
         [0072]    In use, when novel base construct  105  is to be installed in the patient, the top end of the tibia is resected, and a template  202  ( FIG. 11A ) is positioned against the resected tibia. Template  202  is used to form holes  203  in the resected tibia to receive pegs  160  and, if desired, to form holes in the resected tibia to receive stem  150  and/or post  155 . Preferably the axes of holes  203  formed in the resected tibia to receive pegs  160  are offset from the axes of the threaded bores  190  extending through baseplate  115  so that, when pegs  160  are thereafter screwed into threaded bores  190  ( FIG. 11B ), elongated bodies  165  of pegs  160  create a compressive force against the surrounding bone along the inside edge of the pegs such that compressive forces are generated between the underside of the baseplate and the superior surface of the resected tibia. By way of example but not limitation, if threaded bores  190  are set at an angle A to the plane of baseplate  115  ( FIG. 11B ), then holes  202  may preferably be set at an angle B relative to the plane of baseplate  115  ( FIG. 11A ), with B&gt;A, in order to create compression between baseplate  115  and the resected tibia when pegs  160  are screwed into threaded bores  190 . 
         [0073]    Next, the template is removed and pegs  160  are inserted into their seats formed in the resected tibia. Then baseplate  115  is positioned against the resected tibia so that the exterior threads  180  of pegs  160  engage the threaded bores  190  of baseplate  115 . Then a driver is used to screw pegs  160 , retrograde, into threaded bores  190  of baseplate  115 . It will be appreciated that pegs  160  will then extend at a non-perpendicular angle to the plane of baseplate  115 , and stem  150  and post  155  will extend at a perpendicular angle to the plane of baseplate  115 , thereby ensuring that at least two of the fixation elements  130  extend downwardly from bottom surface  125  of baseplate  115  in a non-parallel manner. By virtue of the fact that at least two of the fixation elements  130  extend downwardly from bottom surface  125  of baseplate  115  in a non-parallel manner, baseplate  115  will be cementlessly secured to the tibia while effectively eliminating micromotion between the prosthesis and the tibia. 
         [0074]    Significantly, by forming the seats  203  for pegs  160  so that their axes are offset from the axes of the threaded bores  190  extending through baseplate  115 , i.e., in the manner shown in  FIGS. 11A and 11B , where B&gt;A, pegs  160  can create a compressive force against the surrounding bone when pegs  160  are screwed into threaded bores  190  of baseplate  115 , whereby to create a compressive force holding baseplate  115  against the resected tibia. 
         [0075]    A bearing construct (e.g., the aforementioned polyethylene bearing construct  35 ) may then be locked into place on baseplate  115  (e.g., such as by using a “tongue-in-groove” locking mechanism or another locking mechanism), whereby to complete installation of novel base construct  105  in the patient. 
         [0076]    It should be appreciated that, if desired, and looking now at  FIGS. 12-14 , pegs  160  may have a porous coating formed along only a portion of their lengths, e.g., on a more proximal portion of their elongated bodies. In such a construction, the more distal portions of pegs  160  may have a relatively smooth exterior surface, whereby to facilitate disposition of pegs  160  in the resected tibia. 
         [0077]    It should also be appreciated that, if desired, and looking now at  FIGS. 15 and 16 , one or more pegs  160  may be replaced by a bone screw  205 . More particularly, in this form of the invention, bone screw  205  preferably comprises distal threads  210  for passing through threaded bore  190  of baseplate  115  and engaging the resected tibia below the baseplate, and proximal threads  215  for engaging threaded bore  190  of baseplate  115 , whereby to create downward compression between the baseplate and the bone. The head of the screw is unable to pass through the threaded hole, creating tension along the long axis of the screw as distal threads  210  work to advance the screw through the bone. It will be appreciated that, in this form of the invention, bone screws  205  are set antegrade, i.e., they are first passed through baseplate  115  and then into the resected tibia. 
       Modifications 
       [0078]    While the present invention has been described in terms of certain exemplary preferred embodiments, it will be readily understood and appreciated by those skilled in the art that it is not so limited, and that many additions, deletions and modifications may be made to the preferred embodiments discussed herein without departing from the scope of the invention.