Abstract:
A modular prosthetic acetabular cup for use in restorative hip replacement has an augment which can be attached to an acetabular cup outer shell to provide an acetabular cup with a cross section of a desired configuration. The augment can be attached to the acetabular cup by a coupling element having an outer dovetail portion which slidably engages a groove formed within the augment preferably open to at least a first end thereof. The inner end of the coupling element can engage screw holes of the acetabular cup. The groove of the augment further includes a second end having a gradually increasing distance from the outer surface of the shell and the inner surface of the augment on moving towards the second end of the augment.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to artificial joint implants. More particularly, this invention relates to modular, multi-component acetabular cup joint implants. Specifically, this application relates to the use of modular augments to fill bone defects in the acetabulum. 
       BACKGROUND OF THE INVENTION 
       [0002]    Prosthetic acetabular cups are well known for use in total hip arthroplasty. In such a surgery the head of the femur is replaced by a prosthetic femoral component which includes a part-spherical ball designed to engage the bearing component of a prosthetic acetabular cup. 
         [0003]    During primary total hip arthroplasty generally an acetabular cup with a hemispherical outer surface is utilized with either bone cement or by a press-fit within a prepared acetabulum. In either case the outer shell of the prosthetic acetabular cup can include apertures for receiving bone screws or pins which aid in fixation of the outer shell within the acetabulum. Once fixed the bearing liner, usually a polyethylene insert having a part spherical inner recess adapted to receive the prosthetic head of the femoral component, is inserted within the shell. 
         [0004]    In some cases during primary and especially during revision total hip arthroplasty the acetabulum may include a bone defect such as the presence of a void usually in the superior or superior/posterior acetabular region. Such voids or defects may be caused by superior or superior/posterior migration of a previously implanted primary acetabular prosthesis such as may be encountered during revision surgery. In those circumstances, the surgeon typically must fill the superior portion of the acetabulum with bone grafts, ream a hemispherical cavity, and insert a new acetabular cup outer shell. Not only is this time consuming and expensive but exposes the patient to additional risk since bone allografts may present potential health risks due to spread of infectious diseases. Additionally, there may be defects in the inferior acetabular which can be filled by augments. 
         [0005]    It is desirable to use a sterilized, preferably metallic, augment which can be coupled to the outer surface of the shell in the superior or superior/posterior direction to fill such defects. Such modular acetabular cups are shown in U.S. Pat. Nos. 5,176,711, 5,370,704 and 5,326,368. These patents disclose augments which can be attached to the outer surface of the shell. 
       SUMMARY OF THE INVENTION 
       [0006]    A first aspect of the present invention is an acetabular implant. Preferably including a shell, a coupling element, and an augment. The shell preferably has an inner recessed surface for receiving a bearing component, which in turn receives a femoral head, and a part spherical outer surface. The augment has an inner surface that generally conforms to the outer surface of the shell. The coupling element preferably has an enlarged inner end which may be enlarged or threaded and an outer tapered portion. The inner end can be configured to mount to an inner surface of the shell while the tapered outer portion can be configured to extend outwardly from the outer surface of the shell. The augment may further include a groove open toward the shell forming an inner bottom surface and a plurality of inner side surfaces inside the augment. The groove can have a first end and a second end, the first end can be configured to receive the outer tapered portion of the coupling element while the second end can be configured so that movement of the coupling element towards the second end compressively engages and locks the outer tapered portion of the coupling element to the inside of the groove. Thus, the inner surface of the augment compressively engages to the outer shell surface. 
         [0007]    The enlarged outer portion of the coupling element and the groove of the augment can have a dovetail shape. Alternatively, the outer portion and groove can have a T-shape. 
         [0008]    The distance from the bottom surface at the first end of the groove to the inner surface of the augment adjacent the shell outer surface is less than a distance from the bottom surface at the second end of the groove to the inner surface of the augment. The distance from the bottom surface of the groove to the inner surface of the augment preferably gradually increases as the groove extends towards the groove second end. 
         [0009]    The shell can include an aperture or a plurality of apertures extending from the inner surface of the shell to the outer surface of the shell. The enlarged inner end of the coupling element can be configured to engage a recessed surface surrounding an aperture of the inner surface of the shell. The recessed surface can be a part-spherical depression and the enlarged inner end of the coupling element can preferably have a part-spherical surface for engaging the part-spherical depression. Any of the apertures can be a threaded hole and the enlarged inner end of the coupling element can be threaded for engaging any of the apertures. 
         [0010]    The enlarged inner end of the coupling element can be received within an aperture of the shell and can be shaped eccentrically so that it can be locked into the aperture by rotating the coupling element approximately  90  degrees. 
         [0011]    An alternate embodiment of the acetabular implant aspect of the present invention preferably including a shell with at least one aperture in the shell, a coupling element, and an augment. The shell preferably can have an inner surface for receiving a bearing element which in turn receives a femoral head and an outer surface that generally conforms to a bottom surface of an augment. The coupling element preferably has an enlarged inner end and a tapered outer portion. The enlarged inner end can be configured to mount to the shell from the inside while the tapered outer portion can be configured to extend outwardly beyond the outer surface of the shell. The augment preferably has an inner surface generally conforming to the outer surface of the shell which typically is spherically shaped. The augment further includes an arcuate groove having an inner bottom surface and a plurality of inner side surfaces inside the augment. The groove has a first end and a second end, the first end can be configured to receive the tapered outer portion of the coupling element while the second end of the groove can be configured to cause the coupling element to be placed under tension to couple the augment to the shell outer surface. The side surfaces of the arcuate groove of the augment extends generally perpendicular to the generally hemispherical outer surface of the shell, however, in the preferred embodiment, the depth of the groove changes to develop the tension in the coupling element. 
         [0012]    Yet another acetabular implant embodiment preferably includes a shell, at least one aperture in the shell, a coupling element, and an augment. The shell has an inner surface for receiving a bearing component which in turn receives a femoral head and part spherical outer surface. The coupling element preferably has an enlarged inner end and a tapered outer portion. The inner end can be configured to mount to the outer surface of the shell by insertion from the outside of the shell while the outer portion can be configured to extend outwardly from the outer surface of the shell. While the inner end of the coupling element is preferably enlarged it may also be threaded to engage a threaded bore in the shell. The augment preferably has an inner surface generally conforming to the shape of the outer surface of the shell. The augment may further include an arcuate groove open to the bottom and having an inner bottom surface and a plurality of inner side surfaces inside the augment. The groove has a first end and a second end, the first end is configured to receive the tapered outer portion of the coupling element while the second end of the groove is configured to cause the coupling element to be placed under tension to thereby couple the augment to the shell. This is caused by tension between the enlarged tapered portion of the coupling element and the inside of the groove. The augment preferably includes at least one coupling element extending from the bottom surface of the augment into the at least one channel of the shell. 
         [0013]    The method includes placing the enlarged inner end of the coupling element into an aperture of the shell. A first method of assembling the augment would include pushing the coupling element through the shell from the inside, then putting the groove and the augment over the tapered outer portion of the coupling element. This is accomplished by placing the open end of the groove, which is where the bottom surface of the groove is closest to the inner surface of the augment (and then sliding the augment towards the equator of the acetabular cup shell outer surface so that the coupling element moves toward the part of the groove which has a bottom surface spaced farther away from the inner surface of the augment. If both the inner surface of the groove and the outer enlarged surface of the coupling element have matching tapers, this allows a more positive locking between the two parts. A force such as that applied by the surgeon with a mallet can be used to impact the augment driving the coupling element towards the end of the groove furthest from the inner augment surface thereby locking the two pieces together. Disassembly can occur by applying the force in the opposite direction. Essentially whether the coupling element is first inserted into the shell or first inserted into the augment is a matter of design choice. 
         [0014]    The augment can be adapted to engage an acetabular cup to provide a modular acetabular cup device that substantially conforms to the shape of the existing cavity in the pelvis and provides a cross section of a desired configuration. The augment preferably includes an open part-spherical surface that terminates in a base section. The acetabular cup can have a part-spherical outer surface that includes a locking system which engages the augment to substantially prevent relative movement between the acetabular cup and the augment. Such a locking system may include extending ribs, anti-rotation keys, dove-tail joints, mechanical fasteners or taper members. 
         [0015]    The outer surface of the augment can be spherical or oval shaped to enable the device of the invention to substantially conform to cavities of various configurations. The outer surface of the augment can be at least partially oval in cross section and extend up to about 90 degrees to a polar axis through the center of the augment through an arc around the rim of the cup of about 180 degrees. Optionally, a layer of bone cement may be provided between the acetabular cup and the augment. 
         [0016]    Both the cup component and augment also may include additional stabilizers such as spikes, fins or pegs. Both the cup component and the augment further may include bone ingrowth surfaces, such as sintered beads, cast mesh, or plasma sprayed surfaces. The stabilizers and the ingrowth surfaces can be formed of cobalt-chrome alloys or titanium alloys coated with known osteo-conductive materials, such as hydroxyapatite or tri-calcium phosphate. 
         [0017]    Coatings such as bone morphogenic proteins (BMP) can be added to the ingrowth coatings. Specifically, OP-1 brand of bone morphogenic protein sold by Stryker Corporation may be used. 
         [0018]    The modular acetabular cup of the invention may be packaged in a kit for convenient use. The kit may include a sterile container that carries one or more augments and acetabular cups of various sizes and configurations and devices for securing other cups/augments against each other to prevent relative movement as described above. The kit also may include mechanical fasteners such as bone screws and the like. Tools for tightening these fasteners also may be included in the kit. The sterile tray containing the acetabular cup, augments, and other components is placed in an outer envelope and is sealed with a cover to establish a package, all in a manner well known in the packaging of surgical items to be brought into the sterile environment of an operating room. 
         [0019]    It will be seen that the present invention provides a modular acetabular cup that can be fitted into bone cavities that have a variety of shapes without the need to have available multiple acetabular cups and also to reduce the sculpturing of the acetabular cavity to a specific shape prior to or during the implant procedure. Use of the modular acetabular cups of the invention thereby simplifies the implant procedure and reduces the time required to implant an acetabular cup device. The modular acetabular cups of the invention also enable development of the most appropriately shaped implant, reduces the need to carry an inventory of differing shaped acetabular cup type implants, and reduces the use of bone grafts. 
         [0020]    These and other aspects of the present invention will be apparent from the detailed description to follow, together with the accompanying drawings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    There follows a detailed description of preferred embodiments of the present invention which are to be read together with the drawings therein: 
           [0022]      FIG. 1  is an exploded view of the acetabular implant of the present invention comprising an augment, coupling element and shell; 
           [0023]      FIG. 2  is an assembled view of the acetabular implant of  FIG. 1 ; 
           [0024]      FIG. 3  is a cross-sectional view of the coupling element shown in  FIG. 1 ; 
           [0025]      FIG. 4  is a bottom view of an assembled system according to a second embodiment of the coupling system with the augment of  FIG. 1 ; 
           [0026]      FIG. 5  is a cross-sectional view of the assembly of  FIG. 4  along lines  5 - 5 ; 
           [0027]      FIG. 6  is a cross-sectional view along lines  6 - 6  of  FIG. 5 ; 
           [0028]      FIG. 7  is a side view of the shell and a second augment embodiment of the present invention in a partially assembled position; 
           [0029]      FIG. 8  is an end view of the assembled system of  FIG. 7 ; 
           [0030]      FIG. 9  is a bottom view of the augment of  FIGS. 7 and 8 ; 
           [0031]      FIG. 10  is a top view of the augment shown in  FIG. 9 ; 
           [0032]      FIG. 11  is a cross-sectional view along lines  11 - 11  of  FIG. 9  showing the groove within the augment; 
           [0033]      FIG. 12  is a cross-sectional view along lines  12 - 12  of  FIG. 10  showing the groove varying in depth through the augment; 
           [0034]      FIG. 13  is a bottom view of a first shell embodiment; 
           [0035]      FIG. 14  is a cross-sectional view along lines  14 - 14  of  FIG. 13 ; 
           [0036]      FIG. 15  is an enlarged bottom view of the coupling element of the present invention; 
           [0037]      FIG. 16  is an end view of the coupling element of  FIG. 15 ; 
           [0038]      FIG. 17  is a side view of the coupling element of  FIG. 15 ; 
           [0039]      FIG. 18  is a bottom view of an augment and shell of a second embodiment of the present invention; 
           [0040]      FIG. 19  is a cross-sectional view of the assembly of  FIG. 18  along lines  19 - 19 ; 
           [0041]      FIG. 20  is a partial assembled view of the shell and augment of  FIGS. 18 and 19 ; 
           [0042]      FIG. 21  is an exploded isometric view of the augment, coupling element and shell of the embodiment of  FIG. 18  prior to assembly; 
           [0043]      FIG. 22  is an isometric view of the augment of the embodiment shown in  FIG. 18 ; 
           [0044]      FIG. 23  is a cross-sectional view of the augment shown in  FIG. 22  including a cross-sectional view of the shell and coupling element shown in  FIG. 19 ; 
           [0045]      FIG. 24  is a cross-sectional view along lines  24 - 24  of  FIG. 22 ; 
           [0046]      FIG. 25  is an end view of the augment of  FIG. 22 ; 
           [0047]      FIG. 26  is a bottom view of the augment of  FIG. 22 ; 
           [0048]      FIG. 27  is a cross-sectional view of the shell of  FIG. 18  showing the part spherical recess surrounding the aperture in the shell; 
           [0049]      FIG. 28  is a bottom view of the coupling element utilized in  FIG. 21 ; 
           [0050]      FIG. 29  is an end view of the coupling element of  FIG. 28 ; and 
           [0051]      FIG. 30  is a side view of the coupling element of  FIG. 28 . 
       
    
    
     DETAILED DESCRIPTION 
       [0052]    Referring to  FIG. 1 , there is shown an augment generally denoted as  50  which can be constructed of either a solid biocompatible metal with an externally treated or coated surface for bony attachment, or made entirely of a porous biocompatible metal for bony ingrowth. The augment  50  can be totally solid, but preferably it is bored out in strategic regions  71 , so as to allow bone screws to be placed through a shell  70  into bone without obstruction. The augment could also include additional screw holes  73  for screw placement through the augment  50  and into the bone without first passing through shell  70 . A polar hole  75  provided for an insertion tool attachment. 
         [0053]      FIGS. 1-3  show a preferred embodiment of the acetabular cup augment system.  FIG. 1 . is an exploded view of this embodiment of the acetabular cup augment system comprising augment  50 , a coupling element  60  which may be inserted into apertures  74  from the inside of shell  70 . In the preferred embodiment  FIGS. 1 and 3  show a tapered coupling element  60 . In this embodiment the coupling element  60  can be inserted from the interior of outer shell  70  and oriented so as to be slidable in groove  52  of augment  50 . For the assembly of the augment  50  to the acetabular shell  70 , as seen in  FIGS. 1 and 3 , preferred coupling element  60  has a shell mating feature. The preferred coupling element  60  has an inner part-spherical flanged portion  62  and an outer extension portion  64 . The inner portion  62  of the coupling element  60  is designed to fit into a recessed area  75 ′ around one of a plurality of apertures  74  of the shell  70  from the inside out. These apertures are normally used for bone screws. The extension portion  64  of coupling element  60  can fit through bores  74  and is outwardly tapered at its end  65  to interface with a tapered dovetail channel or groove  52  cut into an inner side surface  54  of the augment  50 . In the embodiment of  FIGS. 1-3  end  65  is inserted through holes  74  and therefore has a diameter smaller than hole  74 . The channel  52  of the augment  50  has side walls  53  of a varying depth. In the preferred embodiment the depth is greater at first end  55  and less at second end  57  of channel  52 . The inner facing surface  54  of the augment  50  is generally hemispherical to mate with the generally hemispherical outer surface  72  of shell  70 . In the preferred embodiment augment  50  includes a pair of bores  71  and  73  for receiving typical bone screws. 
         [0054]    To assemble the augment  50  to the shell  70 , the coupling element  60  is placed from the inside of shell  70  through one of the plurality of apertures  74  of shell  70  such that outer tapered portion  65  of coupling element  60  protrudes outwardly from the generally hemispherical outer surface  72  of shell  70 . The augment  50  is then placed against the outer surface  72  of the shell  70  adjacent the second end  57  of dovetail channel  52  such that the outwardly tapered portion  65  of the coupling element  60  is aligned in the groove or channel  52  of the augment  50 . Once positioned, the augment  50  is translated along the outer surface  72  of the shell  70 . Because the groove  52  has sidewalls  53  and a bottom surface  59  at end  55  further from the inner surface  54  of augment  50  than at end  57  the tapered portion  65  of the coupling element  60  rides deeper and deeper into the matching dovetail of groove  52 . Thus, coupling element  60  is tensioned as the augment is translated. The engagement places extension  60  into greater tension as the depth of the slot increases. As force is applied in moving augment  50  away from the polar hole  75  of shell  70  by moving the end  65  of coupling element  60  deeper in groove  52 , the tension eventually causes the pressure between shell  70  outer surface  72  and augment  50  inner surface  54  to build, creating a lock between the two components. As the groove  52  deepens matching side walls  64  of coupling element  60  extend from the dovetail section of the channel groove  52  to the inner surface  54  of augment  50 . 
         [0055]    In this embodiment, a plurality of coupling elements  60  can be provided having side wall portions  64  of varying length which can vary the location on surface  72  at which augment  50  locks onto the shell  70 . Thus the location along groove  52  between ends  55  and  57  at which the augment locks can be easily and predictably varied. Because inner spherical surface  54  matches outer spherical surface  72  this allows variable rotation of the augment  50  about one of the plurality of apertures  72  prior to translation and locking. This relationship also allows placement of coupling element  60  in any of a plurality of apertures  74  about the shell  70 . 
         [0056]      FIGS. 4-8  depict an alternative embodiment of the coupling element and augument of the acetabular cup augment system of  FIGS. 1-3 , including an augment  110 , coupling element  120 , and shell  130 . This alternative assembly of the second embodiment of the invention allows assembly of the coupling element  120  into a groove  112  of the augment  110  to be performed first. Then, once contained in the augment groove  112 , the coupling element  120  can be inserted from the outside (above surface  72 ) of shell  70  into a specialized oblong slotted screw hole  131  of the shell  130 . As best seen in  FIGS. 15-17  coupling element  120  includes a non-circular inner portion  122  which engages the hole  131 . 
         [0057]      FIGS. 15-17  show different views of the configuration of the coupling element  120  of the acetabular implant of  FIG. 4 . The coupling element  120  has an outwardly tapered end  124  to interface with the groove  112  of the augment and a flat end  122  preferably with a pair of spherical extension portions  126  to interface with at least one screw placement apertures  132  having the radial slot  134 . 
         [0058]    Hole  131  has an oblong shape which allows the inner end  122  of the coupling element to be inserted in the slotted hole  131  in a first orientation and rotated 90° to lock the coupling element  120  to shell  130 . Referring to  FIG. 4 , the shell  130  has a plurality of bone screw placement holes or apertures  132  to receive bone screws. At least one of these plurality of apertures is a hole  131  which has a radial extension  134  for receiving non-circular end  122  of coupling element  120 . The radial extensions  134  create a specialized slotted hole  131  for receiving the eccentric end  122  of coupling element  122 . Referring to  FIGS. 15-17  coupling element  120  is shown with elongate non-circular end  122  and dovetail end  124  for engaging groove  112 . The coupling element end  122  is aligned and inserted through the ends  134  of hole  131 , then turned 90 degrees to prevent disassembly. 
         [0059]    In  FIGS. 4-12  an alternative augment  110 ′ is depicted. The augment has a bottom surface dovetail groove  112  cut into an inner surface  114  of augment  110 ′ for receiving the dovetail end  124  of coupling element  120 . The inner surface  114  of augment  110 ′ is generally hemispherical and mates with the generally hemispherical outer surface  136  of shell  130 . The dovetail groove  112  allows the tapered sides of dovetail end  124  of the coupling element  120  to be placed in tension and wedges the augment tightly against the acetabular shell  130 . In the second embodiment, the end  124  of coupling element  120  must first be inserted into the deeper end  115  of the groove  112  of the augment  110 ,  110 ′, and then slid to end  113  and then end  122  is inserted into hole  131  of the acetabular shell  130 . The augment  110 ,  110 ′ is then turned 90° and slid along shell surface  136  so that end  124  of element  120  is moved towards the deeper end of the groove  112  as described above to lock the augment in place. 
         [0060]      FIGS. 11 and 12  are cross sectional views which depict the configuration of groove  112  of augment  110 ′. In  FIG. 11 , the groove  112  of the augment  110 ′ can be seen, which has a dovetail with a tapered dimension that is slightly larger than that of the tapered end  124  of the coupling element  120 . Therefore, the slightly smaller tapered end  124  of the coupling element  120  can fit into the groove  112  at a deeped end  115  and slid to end  113  can be wedged tightly against inner tapered side wall surfaces  117  of the augment  110 ′ as the tapered end  124  of the coupling element  120  is translated toward a second deeper end  115  of the groove  112  of the augment  110 . In the preferred embodiment end  115  is 0.195 inches deep and end  112  is about half that or 0.99 inches deep. The depth tapers gradually from end  112  to end  115 . 
         [0061]    Referring to  FIGS. 13 and 14  there is shown a bottom view of shell  13  with a single eccentric hole  131  for receiving end  122  of coupling element  120 .  FIG. 14  is a cross-sectional view through hole  132 . 
         [0062]      FIGS. 18-30  depict an alternate design of the acetabular cup augment system including an augment  240 , coupling element  250 , and shell  260 . This alternative assembly of the invention allows assembly of the coupling element  250  into any of a plurality of holes  262  in the shell having part-spherical seats to receive screws having part spherical heads.  FIGS. 28-30  show different views of the configuration of the coupling element  250 . The coupling element  250  has a tapered end  254  to interface with the groove  242  of the augment and a flat end  252  with the part-spherical end portion  256  to interface with one of a plurality screw hole apertures  262  of the shell  260  which have a corresponding part spherical recess. As shown in  FIGS. 29-30  this coupling element  250  has a part-spherical shape at its end  256 . As with the other augments, end  254  is a dovetail shape. 
         [0063]    Coupling element  250  is first inserted in the shell from the inside. The augment  240  as shown in  FIGS. 22 to 26  has the same tapered dovetail groove  242  cut into an inner side surface  244  of the augment for receiving the tapered end  254  of coupling element  250  as in the other embodiments. Likewise the inner side surface  244  is generally hemispherical and mates with the generally hemispherical outer surface  266  of shell  260 . The tapering increasing depth of dovetail groove  242  allows the end  254  of the coupling element  250  to be wedged tightly within groove  242  as described above. 
         [0064]      FIGS. 19 and 24  are cross sectional views which depict the configuration of augment  240 . In  FIG. 24 , the groove  242  of the augment  240  can be seen, which has a dovetail cross-section that, as described above, is slightly larger than that of the tapered end  254  of the coupling element  250 . Therefore, the slightly smaller tapered end  254  of the coupling element  250  can fit into the groove  242  at a first end  246  and can be wedged tightly against inner side surfaces  247  of the augment  240  as the tapered end  254  of the coupling element  250  is translated toward a second deeper end  248  of the groove  242  of the augment  240 . 
         [0065]    In all the embodiments described above a plurality of grooved augments of varying shapes and sizes can be provided to fill bone defects of various sizes. These augments can be provided in a kit of parts which can be placed in the operating theater. This kit would include outer shells of different sizes, coupling elements and augments to match each shell size. 
         [0066]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.