Abstract:
A prosthesis is attached to bone by means of a stem that expands in a bone structure in response to the insertion of a pin.

Description:
RELATED APPLICATION  
       [0001]    This application claims the benefit of the filing date of copending United States Provisional Patent Application Serial No. 60/322,170, filed Sep. 11, 2001, entitled “Modular Prosthesis for Bone Structures.” 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to prosthetic implants and, in particular, to an implant for a glenoid cavity of a shoulder joint.  
         BACKGROUND OF THE INVENTION  
         [0003]    A shoulder joint consists of a ball-and-socket type coupling of the humerus to the scapula. The humerus forms the ball, and the socket is formed at the glenoid cavity of the scapula. Injury or disease may cause the destruction or deterioration of the glenoid cavity, making normal functioning and use of the joint painful or not possible. In this situation, a replacement joint surface for the glenoid cavity may be desired.  
           [0004]    Modular prosthetic implants of the glenoid cavity of a shoulder joint, which are targeted at repairing the glenoid cavity of the scapula, are known. For example, multiple section glenoid implants that incorporate a single or multiple stem structures on a medial side of the prosthesis to aid fixation to a scapula bone have been used. Stemmed implants typically require considerable resection (removal of bone) of the scapula to insure a proper fit. Further, stemmed structures require bone cement, bone screws or their combination to secure the implant to the scapula.  
         SUMMARY OF THE INVENTION  
         [0005]    The invention provides a prosthesis that can be used in any joint requiring an implant. The prosthesis can be secured to bone without use of additional fasteners or bone cement. The prosthesis also makes possible an implant that requires less resection of bone.  
           [0006]    One aspect of the invention provides a prosthetic implant for a bone structure. The implant comprises a base that includes at least one stem adapted to engage at least one void created in the bone structure. The stem has an exterior peripherally surrounding an interior lumen. The implant also includes a pin that fits into the interior lumen and, when fitted, expands the exterior of the stem. Expansion of the stem compresses surrounding bone structure, to thereby secure the base to the bone structure.  
           [0007]    In one embodiment, the implant further includes a cap from which the pin depends. Fitting the pin into the interior lumen of the stem couples the cap to the base. The cap can include a bearing surface. In this arrangement, the pin depends from the cap from a surface that faces away from the bearing surface. The cap and base can also include nesting surfaces that rest together when the base is coupled to the cap.  
           [0008]    Another aspect of the invention provides a method of mounting a prosthesis in a bone structure. The method provides an implant that includes a base having at least one stem having an exterior peripherally surrounding an interior lumen, and a pin that fits into the interior lumen. The method locates the implant on the bone structure by placing the stem into a void formed in the bone structure. The method secures the implant by inserting the pin in the interior lumen of the stem to expand the exterior of the stem within surrounding bone structure. The method is useful, e.g., for installing an implant in a glenoid cavity of a shoulder joint.  
           [0009]    Another aspect of the invention provides systems and methods for installing a prosthetic implant for the glenoid cavity of a shoulder joint.  
           [0010]    In one embodiment, the invention provides a prosthetic implant for the glenoid cavity of a shoulder joint. The implant can comprise, for example, a base and a cap.  
           [0011]    In this arrangement, the base has, for example, three stems protruding in a generally perpendicular manner from an inferior surface of the base. The stems are located in such a manner as to engage prepared cavities in the bone, for example, three reamed holes in a scapula. The stems fit into the prepared cavities with a secure fit. Each stem has side exposed to bone. The exposed side is, for example, textured to enhance fixation to new bone growth. Each stem also has a hollow interior and open top. The hollow interior and open top are adapted to receive a pin. A superior surface of the base has openings corresponding with the open top and hollow interior of the stems. There is, for example, a slight taper at the openings to facilitate engagement of the pin.  
           [0012]    In one embodiment, the cap of the modular prosthesis has a bearing surface and an opposite facing mounting surface. The bearing surface of the cap is adapted to engage a bone or separate implant and is generally contoured to receive such implant or bone. The mounting surface has, for example, an indentation adapted to receive the superior surface of the base, whereby the superior surface of the base is nested in the indentation of the cap.  
           [0013]    Also protruding in a generally perpendicular fashion, and being rigidly attached to the cap, is at least one pin. The pin is adapted to be received by a corresponding opening on the base. When the pin is inserted in the opening of the base, and is fully engaged with the open top and hollow interior of the stem, an interference fit is created in the bone, because the pin forces the stem to expand inside the void of the bone. This expansion creates a compressive mechanical lock of the prosthesis in the bone.  
           [0014]    The use of an expanding pin that is integral to the prosthesis for fastening the prosthesis to the bone eliminates the need for additional fasteners or bone cement. However, if desired, additional fastening means can be used.  
           [0015]    The material of the cap and base need not be identical. Materials commonly used in the prosthetic arts can be used, including, but not limited to, metals, ceramics, titanium, titanium alloys, tantalum, chrome cobalt, surgical steel  
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is an anterior and exploded view of the shoulder region of a human skeleton.  
         [0017]    [0017]FIG. 2 is an exploded perspective showing the present invention highlighting the bearing surface.  
         [0018]    [0018]FIG. 3 is a perspective and exploded view of the present invention highlighting the pins and stems.  
         [0019]    [0019]FIG. 4 is an exploded view showing the assembly of the modular prosthesis in relation to the shoulder region of a human skeleton.  
         [0020]    [0020]FIG. 5 is a detailed cross sectional view depicting the stem inserted in a bone.  
         [0021]    [0021]FIG. 6 is a detailed cross sectional view depicting the assembled modular prosthesis in the scapula, highlighting the expanded pins of the top portion engaged with the stem of the bottom portion of the prosthesis of this invention.  
         [0022]    [0022]FIG. 7 is an exploded view of an insertion assembly embodying features of the present invention.  
         [0023]    [0023]FIG. 8 is an assembled view of the assembly shown in FIG. 7.  
         [0024]    [0024]FIG. 9 is a perspective view illustrating the use of an insertion tool to place the cap component onto the base component implanted within the glenoid cavity.  
         [0025]    [0025]FIG. 10 illustrates the use of a hammer to mount the cap onto the base.  
         [0026]    [0026]FIG. 11 illustrates the manipulation of the insertion tool to release the cap component.  
         [0027]    [0027]FIG. 12 illustrates the removal of the insertion tool from the glenoid cavity and further illustrating the cap and base components of the modular prosthesis implanted within the glenoid cavity.  
         [0028]    Other objects, advantages, and embodiments of the invention are set forth in part in the description which follows, and in part, will be obvious from this description, or may be learned from the practice of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]    [0029]FIG. 1 shows a shoulder skeleton in an exploded view. An upper portion of an arm bone or humerus  12  is shown. The humerus has a ball  14  that is rotatably received by a glenoid cavity  15 . The ball  14  is adjacent to a greater tubercle  16  and a lesser tubercle  18 .  
         [0030]    Opposite the humerus  12  is the shoulder blade or scapula  13 . The intersection of the scapula  13  and the humerus  12  is known as the shoulder joint  11 . The scapula  13  has a coracoid process  17  protruding toward the humerus  12 . As mentioned, the humerus  12  rotatably engages the scapula  13  at the glenoid cavity  15 . Working with the ball  14 , the glenoid cavity  15  is the socket for the shoulder joint  11 , which is referred to as a ball and socket joint.  
         [0031]    [0031]FIGS. 2 and 3 show one embodiment of the present invention. In this embodiment, a modular prosthesis  21  comprises a base  23  and a cap  41 . The base  23  has three stems  27  which, in use, engage the glenoid cavity at defined holes adapted to receive the stems  27 , as will be described later. As FIGS. 2 and 3 show, the stems  27  are desirably ribbed or threaded.  
         [0032]    Each stem  27  has a hollow interior  31  and an exposed side  33 . Each stem  27  intersects a superior surface  35  and passes through an inferior surface  25  of the base  23 . The orientation of the stems  27  with respect to each other is not critical. A factor, for example, used to determine the orientation of each stem  27  would be the particular geometry of the glenoid cavity of a selected patient.  
         [0033]    The superior surface  35  is adapted to interface with the cap  41 . Moreover, the stems  27  and the respective hollow interior  31  are adapted to receive corresponding pins  43  carried by the cap  41 . The pins  43  are sized to create an interference fit within the stems  27 , once seated in the corresponding hollow interior  31  of the respective stem  27 . The insertion of the pins  43  into the stems  27  causes a compression of the surrounding bone matter of the scapula. As FIGS. 2 and 3 show, the pins  43  are desirably ribbed or threaded.  
         [0034]    The cap  41  also has a bearing surface  45  which is adapted to rotatably receive the ball  14  of the humerus  12 , as FIG. 1 shows.  
         [0035]    In one embodiment, to ensure proper seating of the cap  41  in the base  23 , and to ensure proper orientation of the bearing surface  45 , the base  23  has a superior surface  35  adapted to seat with the mounting surface  47  of the cap  41 .  
         [0036]    [0036]FIG. 4 depicts an embodiment of the modular prosthesis fitted to bone. The scapula  13  has been adapted to receive the prosthesis at the glenoid cavity  15 . The glenoid cavity  15  may, for example, be sculpted or resected by a surgeon to ensure proper alignment of the base section  23  of the prosthesis. By any suitable means known in the relevant art, corresponding mounting holes  19  are drilled, reamed or otherwise shaped into the glenoid cavity  15 . Each hole  19  is oriented to receive a stem  27  of the base  23 . As FIG. 4 shows, the base  23  is oriented such that the single (apex) stem  27  of the triangular array of stems  27  occupies the top (superior) position. The cap  41  then fits over the base section  23 . Pins  43  on the cap  41  align with corresponding hollow  31  stems  27  of the base, while the mounting surface of the cap  43  seats on the superior surface  35  of the base  23 .  
         [0037]    As FIGS. 5 and 6 show, as the pins  43  engage the openings  37  surrounding the hollow inside  31  of each stem  27 , the stem  27  swells and thereby places the surrounding bone matter of the scapula  13  in compressive opposition to the stem  27 , thus creating a coupling of the prosthesis to the scapula  13 . The humerus  12  then rests against the bearing surface  45  of the cap  41 .  
         [0038]    For the pins  43  to properly engage the openings  37 , sufficient leverage must be applied to the cap  41  when seating the cap  41  onto the base  23 . Toward this end, an insertion tool  48  is desirably provided, as shown in FIGS. 7 and 8.  
         [0039]    The insertion tool  48  comprises a handle component  50  and a carrier component  52 . The handle  50  is configured for grasping and of a length that assists in providing a desired angle and sufficient leverage for seating the cap  41 .  
         [0040]    As FIGS. 7 and 8 show, the carrier component  52  is adapted to mate with the cap  41  and can be variously configured. In the illustrated embodiment, the carrier  52  has a top surface  54  and a bottom surface  56 . The top surface  54  is adapted to mate with the bearing surface  45  of the cap  41 . In the illustrated embodiment, a pair of clasps  58  extend from the carrier component  52  and serve to couple a mating surface  56  on the circumferential margin of the cap  41  in a snap-fit engagement. This arrangement allows the cap  41  to be selectively removable from the carrier  52 .  
         [0041]    In use, as shown in FIG. 9, the base  23  is implanted into the glenoid cavity  15  of the scapula  13 , as previously described. The cap  41  is coupled to the carrier  52  of the insertion tool  48 .  
         [0042]    The insertion tool  48  is then used to advance (shown by phantom lines in FIG. 9) the cap  41  into the glenoid cavity  15  and to place the cap  41  onto the base  23 .  
         [0043]    To mount and secure the cap  41  onto the base  23 , force is exerted on the end of the handle  50 , e.g., with a hammer  62 , as shown in FIG. 10.  
         [0044]    As represented by arrows in FIG. 11, the handle  50  is manipulated from side to side to release the cap  41  from the carrier  52 . Finally, the insertion tool  48  is withdrawn, as FIG. 12 shows.  
         [0045]    The foregoing is considered as illustrative only of the principles of the invention. Furthermore, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.