Abstract:
A two piece humeral component for use in shoulder arthroplasty which is adapted to be implanted into a humerus and engaged by a glenoid component of a scapula. The humeral component includes a body having a first articulating surface and a second medial surface opposite the first articulating surface. The first articulating surface is adapted to be engaged by the glenoid component and the second medial surface is adapted to be secured to mounting portion. The mounting portion has a first surface and a second medial surface. The first surface is adapted to be fixably engaged to the second mounting portion of the humeral component. The second medial surface is adapted to be secured to the humerus. A peg which has a first end adapted to engage a cavity found in the humerus is disposed on the mounting portion&#39;s second medial surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/308,340, filed Jul. 27, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to an apparatus and method for shoulder arthroplasty and, more particularly, to a humeral component and other associated surgical components and instruments for use in shoulder arthroplasty. 
     2. Discussion of the Related Art 
     A natural shoulder joint may undergo degenerative changes due to a variety of etiologies. When these degenerative changes become so far advanced and irreversible, it may ultimately become necessary to replace a natural shoulder joint with a prosthetic shoulder joint. When implantation of such a shoulder joint prosthesis becomes necessary, the natural head portion of the humerus is resected and a cavity is created in the intramedullary canal of the host humerus for accepting a humeral component. The humeral component includes a head portion used to replace the natural head of the humerus. Once the humeral component has been implanted, the humeral cavity positioned at the scapula socket may also be resurfaced and shaped to accept a glenoid component. The humeral component generally includes an articulating surface which engages an articulates with the socket portion of the glenoid component. 
     It is generally known in the art to provide a shoulder joint prosthesis having a humeral component, as discussed above. However, current prior art humeral components along with the associated surgical components and instruments utilized during shoulder arthroplasty suffer from many disadvantages. 
     For example, since the humeral component is subject to various types of loading by the glenoid component, the humeral component must offer a stable and secure articulating surface. To achieve this, some humeral components provide a post or stem attached to a lateral surface of the prosthetic humeral head. These humeral components are generally a single piece system with a single stem, which is inserted and cemented into a hole bored deeply into the intramedullary cavity. However, such existing humeral components also exhibit several disadvantages. For example, these types of stemmed humeral components utilize a large stem to stabilize and secure the humeral component to the humerus. Such humeral components increase the amount of bone tissue removed, while also increasing the labor and complexity of the shoulder arthroplasty. Other stemmed humeral components may offer a larger diameter stem. However, the larger diameter stem also requires excess bone tissue to be removed which may not be practical in some patients. 
     Other prior art humeral components, such as that disclosed in WO 01/67988 A2 sets out a stemless humeral component or head that provides an integral cruciform shape that includes two planar intersecting fins. While this type of humeral component addresses the amount of bone tissue removed, this type of system provides little versatility or adjustments to a surgeon performing the shoulder arthroplasty. Moreover, this type of system does not provide additional enhanced fixation other than the planar intersecting fins. 
     Additionally, most prior art humeral components only rely on the stem to secure the humeral component into the intramedullary canal, via a cement mantle or bone attachment. The stem may also include grooves or holes, which act as an anchor, once the stem is cemented within the intramedullary canal. The medial surface of most humeral components are thus generally overlooked to enhance cement fixation and are therefore generally smooth. Although some humeral components may include a few longitudinal grooves and others may include both grooves and depressions on the medial surface, such surface enhancements only utilize or texture a portion of the medial surface, thereby not advantageously using the entire medial surface. 
     What is needed then is a modular humeral component and associated surgical components for use in shoulder arthroplasty which do not suffer from the above-mentioned disadvantages. This in turn, will provide a humeral component which is stable and secure, reduces the overall amount of bone tissue required to be removed, increases a surgeon&#39;s available components utilizing a single sized post, reduces the overall surgical time and complexity, increases overall medial surface area, enhances and increases post strength without increasing overall post diameter, provides a fully enhanced or textured medial surface for enhanced cement fixation or bone fixation and increased overall stability, provides for a uniform cement mantle, and provides increased tensile and shear strength. It is, therefore, an object of the present invention to provide such a humeral component and associated surgical components for use in shoulder arthroplasty. 
     SUMMARY OF THE INVENTION 
     In accordance with the teachings of the present invention, an apparatus and method for shoulder arthroplasty is disclosed. The apparatus and method employs a modular humeral component and other associated surgical components for use in the shoulder arthroplasty. In this regard, the modular humeral component is adapted to be implanted into a humerus and engaged by a glenoid portion of a scapular component. 
     In one preferred embodiment, a modular humeral component is used for shoulder arthroplasty such that the humeral component is adapted to be implanted into a humerus and engage a glenoid component. The humeral component includes a head member having a first articulating surface and a second fixation surface, which is opposite to the first articulating surface. The first articulating surface is adapted to engage the articulating surface of the glenoid component and the second fixation surface is adapted to engage a fixation component. The fixation component has a first surface adapted to be secured to the head member and a second surface that is generally opposite the first surface. The second surface includes a fixation member adapted to be secured to the humerus. 
     Use of the present invention provides an apparatus and method for shoulder arthroplasty, and specifically, a modular humeral component and associated surgical components for use in shoulder arthroplasty. As a result, the aforementioned disadvantages associated with the currently available humeral components and associated surgical components for shoulder arthroplasty have been substantially reduced or eliminated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Still other advantages of the present invention will become apparent to those skilled in the art after reading the following specification and by reference to the drawings in which: 
     FIG. 1 is a perspective view of the humeral component according to the teachings of the preferred embodiment of the invention shown implanted in a skeletal structure; 
     FIGS. 2 a - 2   c  are views of the fixation member of humeral component of FIG. 1; 
     FIGS. 3 a - 9  are alternate embodiments for the fixation member of the humeral component of the present invention; 
     FIGS. 10-12 represent alternate peg configurations for the fixation member of the humeral component of the present invention; 
     FIGS. 13 and 14 represent alternate texturing, which is usable in the humerical components of the present invention; 
     FIGS. 15 and 16 represent cross-sectional views of implanted humeral components of the present invention; 
     FIGS. 17 through 22 depict an alternate embodiment of the present invention having an insert member disposed between the head and the base member; 
     FIGS. 23 a - 23   e  depict another alternate embodiment of the present invention having flanges disposed on a shelfless base member; 
     FIGS. 24-26 b  illustrate a method for preparing the humerus implantation of the humeral component using associated surgical components according to the teachings of the preferred embodiment of the present invention; and 
     FIGS. 27-28 further illustrate methods for implanting the humeral components into the prepared humerus according to the teachings of the preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiments concerning an apparatus and method for shoulder arthroplasty is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     FIG. 1 depicts the components used in the shoulder arthroplasty of the current invention. As shown, the modular humeral component  31  has a base member  32  and a head member  33 . The base member  32  has a fixation peg  34 , which is used to attach the humeral component to the resected portion  36  of the humerus  38 . If a total shoulder arthroplasty is performed, a glenoid component  40  is first implanted into the scapula  42  using techniques well known in the art. The glenoid component  40  is preferably of the type disclosed in U.S. Pat. No. 5,800,551, which is hereby incorporated by reference, or other suitable conventional glenoid components. The humeral component  31  is designed to allow rotational and transitional movement of the head member  33  with respect to the glenoid component  40 . 
     FIGS. 2 a - 2   c  depict the base member  32  of one embodiment of the current invention. The base member  32  is defined by a shelf member  44 , which may have a plurality of through holes  46 . The shelf member  44  can have at least one mating member  48  for engaging the head member  33  of the humeral component  31 . It is preferred that the mating member  48  be a defined Morse Taper or other suitable attaching mechanism. In addition to the mating member  48 , each base member  32  has a fixation peg  34  disposed on the lower lateral surface  50  of shelf member  44 . The fixation peg  34  is generally perpendicular to the shelf member for its entire length of the fixation peg  34 . As depicted in FIGS. 2 a - 3 , the shelf member  44  of the base member  32  can define flat lower lateral surface  50  and flat generally parallel upper surfaces  51 . FIG. 3 a  shows the second embodiment of the current invention, which has a cavity  52  defined in the shelf member  44 . The cavity  52  is preferably the female side of a Morse Taper, which would engage a male Morse Taper on the head member  33 . 
     FIG. 3 b  shows the head member  33  which mates with the base member  32  of FIG. 3 a . It should be noted that a surgical kit of the components would contain numerous head members  33 , each having a varied radius of curvature, diameter, and height to allow a surgeon to optimize joint movement. Additionally, a surgical kit would contain the instruments needed for implantation (shown later). 
     The head member  33  and base member  32  must be made of bio-compatible materials such as, without limitation, titanium, titanium alloys, surgical alloys, stainless steels, bio-compatible ceramics, and cobalt alloys. Optionally, the base member  32  can additionally be made of materials such as biocompatible ceramics and resorbable and non-resorbable polymers and other anticipated bio-compatible metallic or polymeric materials. Should the base member  32  be made of non-metallic components, a fastener would be needed to couple the head  33  to the base  32 . 
     As shown in FIGS. 4-7, the shelf members  44  need not to be planar. FIGS. 4 and 5 show the base member  32  and having an interior concave surface  56  and a convex medial surface  58 . Base members, as disclosed in FIGS. 4 and 5 would be used in situations where maximum bone removal in the humerus  38  is required. In each situation, the head member  33  would have a convex medial surface  59  for engaging the concave surface  56 . It is envisioned as with all of the embodiments that the base members  32  and head member  33  can be coupled using the mating member  48 , i.e., Morse Taper. The use of the convex-concave interface provides a coupling interface which is self centering under a multitude of loading conditions. The interface reduces the occurrence of micro-motions which can disrupt the normal functioning of the joint prosthesis as well as lead to premature component failures. Any loads applied to the articulating surface of the head member  33 , are transferred as a perpendicular force into the base member  32  of the modular humeral component  31  through the non-planar shelf member  44 . 
     FIGS. 6 and 7 define base members  32  having the shelf member  60  having a convex outer surface  62 . Additionally shown is a concave inner surface  64  for mating with a resected head  36  of the humerus  38 . The base members as depicted in FIGS. 6 and 7 can be used when minimal bone removal is possible and will generally encapsulate the hemispheric shape cut into the humerus  38  as described later. As with the base members as shown in FIGS. 4 and 5, any loads applied to the articulating surface of the head member  33 , are transferred as a perpendicular force into the base member  32  of the modular humeral component  31 . 
     FIGS. 8 and 9 disclose alternate embodiments of the base member  32  for the humeral component  31 . FIG. 8 depicts the base member  32  having a convex outer surface  66  and a flat lateral surface  68 . The base members as depicted in FIGS. 2 a - 3  and  8  can be utilized when a moderate amount of bone material must be removed from the resected head  36  of the humerus  38 . FIG. 9 depicts the base member  32  having a flat upper surface  51  and a convex lateral surface  58 . This base member would readily utilize the head member  33  as used with the base member as depicted in FIG. 2 a . It is envisioned that either base member can have a defined male or female mating member  48  in the form of a Morse Taper. 
     FIGS. 10-12 depict possible configurations for the fixation peg  34 . FIG. 10 shows the fixation peg  34  defining a plurality of flutes  70  therein. As can be seen, the modular system does not need a shelf member  44 . Without the shelf member  44 , the base can have either a male or female Morse Taper. FIGS. 11 and 12 depict the fixation peg  34  being at a tapered prism with the base of the prism coupled to the lower lateral surface  50  of the shelf member  44 . 
     FIGS. 13 and 14 depict possible surface treatments for the lower lateral surface  50  of the shelf member  44  and fixation peg  34 . All of the possible fixation pegs  34  can have a porous coated region  72 , which will assist in the fixation of the component to the humerus  38 . Additionally, all of the lower lateral surfaces  50  of the shelf member  44  can define a waffle pattern  74  to assist in the incorporation of bone cement. Each fixation peg  34  extends from the lower lateral surface  50  to define or fill in a coupling region  75  having a diameter of about 0.50 inches. Each coupling region  75  also includes a sidewall  77  formed with and from the lower lateral surface  50 . The coupling region  75  provides a smooth flat surface for which the fixation peg  34  extends out, and reduces or eliminates any stress risers about each fixation peg  34 , which could be caused by positioning the lower lateral surface  50  immediately adjacent the fixation peg  34 . 
     The fixation peg  34  includes a first end  79 , which is inserted into or engages a cavity or hole formed within a cavity in the humerus and a second end  81 , which extends from or is integral with the shelf member  44 . The first end  79  is semi-spherical and the second end has a 0.25 inch radius about the circumference of the second end  81  of the peg, which blends into a flat or smooth portion of the coupling region  75  to decrease the overall sheer stress of the fixation peg  34 . Optionally, should the fixation peg be non-metallic, embedded within the first end of each fixation peg  34  is a tantalum ball  83 . The tantalum ball  83  enables the humeral component  31  to be easily identified in an x-ray. 
     FIGS. 15 and 16 depict cross-sectional views of various embodiments of the current invention implanted into resected head  36  of humerus  38 . As depicted in FIG. 16, when a large amount of bone mass must be removed during the arthroplasty, the base member  32  as depicted in FIG. 9 can be used. As is shown, the base member  32  is fixed to the humerus  38  using a plurality of screws  85 . The lateral surface  59  of the head member  33  defines a cavity  52  for receiving the mating member  48  or Morse Taper post. 
     As with the base member depicted in FIG. 15, the base member  32  is held to the humerus  38  by use of screws  85  disposed through the holes  46 . FIG. 16 discloses the use of the base member  32  as depicted in FIG. 3 a  which is similarly held in place by use of fixation screws  85  to the humerus  38 . 
     FIGS. 17 through 18 show an alternate embodiment of the humeral component  109 . Base member  110  is shown having a modified Morse Taper cavity  116 . The humeral component  109  further has a head portion  112  with a male Morse Taper portion  121 . Disposed between the head portion  112  and the base member  110  is a coupling member  114 . Coupling member  114  has an outer surface  118  which acts as the male portion of a Morse Taper to bond with the cavity  116  of the base member  110 . Coupling member  114  further defines a female portion  120  of a Morse Taper which corresponds to the male portion  121  of the Morse Taper of the head portion  112 . The coupling portion  114  functions to move the center of curvature of the head portion  112  a fixed distance  123  from the center line of the base member  110 . This functions to effectively change the centering location of the head portion  112  with respect to the humerus  138 , thus allowing the surgeon more flexibility. 
     FIG. 17 a  shows the alternate humeral component  109  in its assembled configuration. FIG. 18 shows an exploded view of the alternate humeral component  109 , coupling member  114 , and base member  110 . Rotation of coupling member  114  allows for translation of the head portion  112  on the base member  110 . FIGS. 19 through 19 b  depict a head portion  112  having a female Morse Taper cavity  116  which engages a male Morse Taper  115  on alternate coupling member  114 . FIG. 19 a  depicts an assembled view of the alternate humeral component  109 . 
     FIGS. 21 through 21 b  depict an alternate embodiment of the humeral component  122 . Shown is the base member  124  which has a modified female cavity defining a Morse Taper  116 . The head portion  126  has a coupling male Morse Taper  132  disposed on the medial surface of the head component  126 . Disposed between the head portion  126  and the base portion  124  is the coupling member  128 . The coupling member  128  defines an outer surface  118  which functions as the male portion of the Morse Taper and couples to the female portion  116  of the base member  124 . The coupling member  128  further defines an interior cavity  130  which functions as a female Morse Taper for the male Morse Taper  132  of the head  126 . The interior cavity  130  of the coupling member has an offset angle  134 , which functions to rotate the center of curvature of the head portion  126  with respect to the base member  124 . Similarly, shown in FIG. 21 b  is a coupling member  114  having a male Morse Taper  115  being angled. 
     FIGS. 20 a  and  22  show the alternate humeral components  122  inserted into a resected humerus. As with the other humeral components, the base member is fixed to the head of the humerus using fasteners. 
     FIGS. 23 a - 23   e  depict another alternate embodiment of the present invention. Shown is a shelfless base member  232  which is formed by a fixation peg  234 . Each fixation peg  234  has three evenly spaced triangular fins  236  disposed thereon. The triangular fins  236  have an edge  239  which is coplanar to a top surface  238  of fixation peg  234 . Incorporated into a top surface  238  of the fixation peg  234  is a fixing mechanism  240 . 
     FIGS. 23 a  and  23   b  disclose fixing mechanism  240  in the form of a female Morse Taper as the fixation which functions to couple the head  30  onto the base member  232  (see FIG. 23 d ). As can be seen FIG. 23 e , the top surface  238  alternately can have a fixing mechanism  240  in the form of a male Morse Taper disposed thereon. It is envisioned that a head member  30  being used in this embodiment can have a lower surface  244  which has a porous coat, plasma spray, grit blast, or smooth surface to facilitate the coupling to the bone. 
     When the base member  240  is coupled to head member  30 , there is a defined gap between the lower surface  244  of the head  30  and the upper surface  238  of the base member  232 . After implantation, the lower surface  244  of head member  30  rests upon the resected bone, not the top surface  238  of the base member  232 . 
     The method for implanting the humeral component  31 , along with associate surgical components utilized will now be described with reference to FIGS. 24 a - 28 . The head of the humerus  38  is resected using a saw, chisel then planed flat or with a concavity. With the resected head  36  of the humerus  38  exposed, an alignment or guide hole  90  is first drilled substantially through the center of resected head  36  of the humerus  38  using a quick release drill bit  96  and driver  98 . Optionally, the resected head  36  of humerus  38  can be resected to provide a flat surface prior to the drilling of pilot hole  90 . 
     Once the guide hole  90  is drilled, the resected head  36  of humerus  38  is optionally reamed using a concave spherical reamer shaft  102  with the driver  98 . The concave reamer  102  includes a guide pin  104  and a roughened spherical surface.  106  substantially corresponding to the spherical shape of the lower medial surface of the shelf member  44  of base member  32 . An optional convex reamer surface  108  permits rasping or drilling of tight humeral cavities (see FIGS. 25 a  and  26   d ). Upon rotating the surface of the reamer, the bone of the resected head  36  of the humerus  38  is prepared to mate or conform with the shape of the lower lateral surface  50  of the shelf member  44  of the base member  32 . As depicted in FIGS. 25 a  and  26   d , the reamer  102  can have a convex shape or alternatively a flat shape, which reams a concave shape into the resected head  36  of the humerus  38 . Determining which reamer is used is a function of the preoperative degenerative changes in the humerus  38 . 
     With reference to FIGS. 27-28, which depict the insertion of the humeral components  30 , once the surface of the resected head  36  of the humerus  38  has been resected, the base member  32  is inserted into the guide hole  90 . It is envisioned that fixation peg  34  of the base member  32  can be forced into the guide hole  90  to displace the bone material around the intramedullary canal. Optionally, the guide hole  90  can also be reamed to a larger interior diameter to accept the base member  32  without displacement of the bone material by the fixation peg  34 . 
     Once the base member  32  has been inserted into the guide hole  90 , the optional screws  85  are disposed through the holes  46  to couple the base member  32  to the humerus  38 . At this point, a surgeon may use any number of test head portions and/or adapter portions to determine the proper size needed to mate with the glenoid component. Once a proper head member  33  size has been determined, the final head member  33  can be fixed to the shelf member  44  of the base member  32 . 
     FIGS. 26 and 27 show the use of the base member  32  as depicted in FIG.  3 . As can be seen, the base member of FIG. 3 is utilized when a minimal amount of bone is required to be removed. 
     The modular nature of the humeral component  31  of the present invention allow a set of various types of both replacement base members  32  and head members  33  to be formed. In using such a set, a surgeon can interoperably choose the appropriate base member depending on the patients particular degenerative condition. Additionally, the surgeon can then choose from a set of head members  33 , which both have the proper articulating surface radius and a proper coupling to the base member  32 . 
     The description of the invention is merely exemplary embodiments in the present invention. One skilled in the art would readily recognize from such discussion and from accompanying drawings and claims that various changes, modifications, variations may be made therein without the spirit and scope of the invention