Abstract:
A tool provides for coupling a first prosthetic to a second prosthetic. The tool can include a first arm having a first concave bearing surface configured to apply a force in a first direction. The tool can also include a second arm having a hook shaped member. The hook shaped member can have a second concave bearing surface configured to apply a force in a second direction opposite the first direction. The first arm and the second arm can be generally parallel, and the first arm can be translatable with respect to the second arm. The tool can include a translation force mechanism, which can apply force to the first arm and the second arm so as to cause generally parallel translation of the first arm and second arm.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 13/025,597, filed on Feb. 11, 2011. U.S. patent application Ser. No. 13/025,597 is a continuation of U.S. patent application Ser. No. 10/999,297, filed on Nov. 29, 2004, which is a continuation-in-part of U.S. patent application Ser. No. 10/464,043, filed Jun. 18, 2003 (now abandoned), which is a continuation of U.S. patent application Ser. No. 09/828,745, filed Apr. 9, 2001 now issued as U.S. Pat. No. 6,656,225 on Dec. 2, 2003, which claims the benefit of U.S. Provisional Application 60/195,444, filed on Apr. 10, 2000. The disclosures of the above applications and patent are hereby incorporated by reference as if fully set forth herein. 
    
    
     FIELD 
     The present disclosure relates to prostheses for the elbow joint, and more specifically to prostheses for replacing a proximal head of the radius. 
     BACKGROUND 
     Trauma to the elbow joint frequently involves damage to the ligamentous support of the elbow and fractures of the osseous structures responsible for the skeletal integrity of the elbow joint. The proximal aspect of the radius, or radial head, is frequently injured either in isolation or in combination with injury to other bony or ligamentous structures of the elbow joint. The radial head may also be fractured in association with injuries to the forearm axis, including disruptions of the interosseous membrane between the radius and the ulna. Whether in isolation or in combination with other injuries, fractures of the radial head can be difficult to treat. 
     Fractures of the radial head are either reconstructable or unreconstructable. Despite various technical advances in the reconstruction of radial head fractures, a certain percentage of fractures are not amenable to reconstruction due to the degree comminution or severity of the fracture. In general, unreconstructable radial head fractures result from high energy trauma and are therefore frequently associated with significant injuries to other osseous or ligamentous structures of the elbow joint or forearm. In these cases, restoration of the stabilizing function of the radial head is critical to allow the ligaments of the elbow or forearm to heal in appropriate relationships, thereby restoring stability to the elbow or forearm. This stabilizing function depends, in part, upon re-establishing the appropriate distance between the capitellum and the proximal shaft of the radius. 
     Prosthetic replacement of the radial head has evolved rather slowly. The first widely used prosthetic radial head was introduced in the 1970&#39;s and was composed of silicone. Silicone implants placed in various joints throughout the body led to “silicone synovitis,” in which the silicone induced an inflammatory response within the joint. Further, silicone radial head prostheses were found to be incapable of resisting the stresses to which the radial head is subjected, rendering it less useful in stabilizing the injured elbow or forearm. 
     The difficulties apparent with silicone led to experimentation with metal radial head implants. These prostheses are fashioned from a single piece of metal (often titanium) and include a stem and a head portion. The head portion is shaped to approximate the anatomy of the radial head. These metallic prostheses are capable of resisting the compressive stresses to which the radial head is subjected, as has been demonstrated in several biomechanical studies. However, significant problems remain with these prostheses. 
     Anatomic and radiographic studies of the dimensions of the radial head reveal a disparity with currently available metallic prostheses. Therefore it has been difficult to restore appropriate anatomic alignments within the elbow. Therefore restoration of the appropriate relationship between the capitellum and proximal shaft of the radius has been very difficult to achieve with these prostheses. Additionally, the fact that these prostheses are fashioned from a single piece of metal has led to technical difficulties with insertion and removal. Surgeons have had difficulty with matching both the size of the stem to the canal of the proximal radius and the size of the head portion to the patient&#39;s native radial head. Removal of these non-modular components frequently requires release of the lateral ligaments of the elbow and the annular ligament, which binds the neck of the proximal radius to the proximal ulna. Thus the elbow is frequently destabilized during removal of these prostheses. 
     Designers of prosthetic joint replacements in the hip, shoulder, knee and fingers have circumvented the above mentioned difficulties by employing the use of modular components. Modularity allows for each aspect of a prosthesis to be sized appropriately to its recipient anatomic site. The concept of modularity has only recently been applied to commercially available radial head prostheses. Currently available modular radial head prostheses employ a mechanism by which the head component is impacted over and onto the stem component. The surgical exposure must therefore allow sufficient room for the head to be maneuvered over the stem prior to being impacted. With impaction, the height of the prostheses may be decreased, resulting in an increased distance between the capitellum and the proximal end of the radius. Increasing this distance alters the bony anatomy such that the ligaments of the elbow joint are not held in their appropriate lengths and tensions. Instability of the elbow or inappropriate healing of the ligaments may result. Furthermore, removal of these prostheses is accomplished in the same manner as the above mentioned metallic implants, often requiring destabilization of the lateral aspect of the elbow joint. 
     In order to reap the benefits of modularity in radial head prosthetic replacement, a reliable and surgically appropriate method to secure the stem of the prostheses to the head of the prostheses and which allows for accurate restoration of the appropriate spatial relationships between the bones of the elbow is required. 
     SUMMARY 
     A modular prosthesis system for replacement of a head portion of a proximal radius includes a monolithic stem component, a head component, and a locking mechanism formed by the stem component and the head component. The stem component defines a stem anchoring portion having a longitudinal axis and configured to couple to the proximal radius, and a dovetail-shaped first mounting portion on a first end face that extends in a first direction transverse to the longitudinal axis. The head component has a dovetail-shaped second mounting portion on a second end face opposite the first end face slidably engaged with the first mounting portion along the first direction. One of the first and second mounting portions intersects the longitudinal axis. The locking mechanism is formed at an interface between the stem component and the head component and is engaged through relative translational movement between the stem component and the head component along the first direction. 
     A method of use for a modular prosthesis for replacement of a head portion of a proximal radius includes coupling a stem anchoring portion of a monolithic stem component having a longitudinal axis to a resected portion of the proximal radius, and coupling a dovetail-shaped first mounting portion on a first end face of a head component that extends in a first direction transverse to the longitudinal axis to a dovetail-shaped second mounting portion on a second end face of the stem component that extends in the first direction. The coupling the first mounting portion includes slidably engaging the first mounting portion with the second mounting portion by moving the head component in the first direction, and connecting the head component and the stem component by moving the head component in the first direction after the slidably engaging until a locking mechanism formed by the stem component and the head component at an interface is engaged, wherein one of the first and second mounting portions intersects the longitudinal axis. 
     Further provided is a tool for coupling a first prosthetic to a second prosthetic. The tool can include a first arm having a first concave bearing surface configured to apply a force in a first direction. The tool can also include a second arm having a hook shaped member. The hook shaped member can have a second concave bearing surface configured to apply a force in a second direction opposite the first direction. The first arm and the second arm can be generally parallel, and the first arm can be translatable with respect to the second arm. The tool can include a translation force mechanism, which can apply force to the first arm and the second arm so as to cause generally parallel translation of the first arm and second arm. 
     According to various aspects, provided is a tool for coupling a first prosthetic to a second prosthetic. The tool can include a first arm including a substantially U-shaped member at a first distal end for contacting the first prosthetic and a hinge near a first proximal end. A slider can be coupled to the first arm between the hinge and the U-shaped member. The tool can also comprise a second arm including a hook shaped member at a second distal end for contacting the second prosthetic and a handle at a second proximal end. The second arm can define a track between the handle and the hook shaped member. The slider can be movably received within the track so that the first arm is movable relative to the second arm. The hinge can couple the first arm to the handle so that application of a force to the handle moves the first arm relative to the second arm to couple the first prosthetic to the second prosthetic in a first orientation. 
     Also provided is a tool for coupling a first prosthetic to a second prosthetic. The tool can comprise a first arm including a substantially U-shaped member at a first distal end for applying a force to the first prosthetic in a first direction and a hinge near a first proximal end. The tool can also comprise a second arm including a hook shaped member at a second distal end for applying a force to the second prosthetic in a second direction different than the first direction. The second arm can also include a handle at a second proximal end. The second arm can define a passage between the handle and the hook shaped member, which can receive the first proximal end of the first arm therethrough. The movement of the first proximal end relative to the handle can translate the first arm relative to the second arm in a generally parallel direction to couple the first prosthetic to the second prosthetic when the tool is in a first orientation and to decouple the first prosthetic from the second prosthetic when the tool is in a second orientation. 
     Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the disclosure, are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a front view of a stem component; 
         FIG. 2  is a side view of the stem component from a perspective perpendicular to that of  FIG. 1 ; 
         FIG. 3  is a top view of the stem component; 
         FIG. 4  is a front view of an inner core of a head component; 
         FIG. 5  is a side view of the inner core of the head component from a perspective perpendicular to that of  FIG. 4 ; 
         FIG. 6  is a top view of the inner core of the head component; 
         FIG. 7  is a front view of an outer shell of the head component; 
         FIG. 8  is a side view of an outer shell of a head component from a perspective perpendicular to that of  FIG. 7 ; 
         FIG. 9  is an exploded perspective view of an assembly of a stem component, a inner core, and an outer shell; 
         FIG. 10  is a perspective view of an assembled prostheses; 
         FIG. 11  is a front view of an assembled prostheses; 
         FIG. 12  is a side view of an assembled prostheses from a perspective perpendicular to that of  FIG. 11 ; 
         FIG. 13  is a top view of an assembled prostheses; 
         FIG. 14  is a posterior oblique view of a human elbow depicting a radial head prostheses in position within a proximal radius bone and articulating with a capitellum of a distal humerus; 
         FIGS. 15 and 16  are perspective views of a tool that can be used to insert or remove a head component from a stem component via a translational force; 
         FIG. 17  is a perspective view of the head component showing the outer shell body completely enveloping the inner core; 
         FIG. 18  is similar to  FIG. 17  but shows the head component disassembled; 
         FIG. 19A  is a perspective view of the head component showing the inner core extending beneath the outer shell body; 
         FIG. 19B  is similar to  FIG. 19A  but shows a mechanical fastener securing the outer shell body to the inner core; 
         FIG. 19C  is similar to  FIG. 19A  but shows the head components as a single piece; 
         FIG. 20  is similar to  FIG. 19  but shows the head component disassembled; 
         FIG. 21A  is a perspective view of the head component, the stem component and a collar component; 
         FIG. 21B  is similar to  FIG. 21A  but shows an alternative configuration between the head component, the stem component and the collar component; 
         FIG. 22  is similar to  FIG. 21A  but the components are assembled; 
         FIG. 23  are perspective views of exemplary alternative connections between components of the modular prosthesis; 
         FIG. 24  is similar to  FIG. 21A  but shows an angled collar component; 
         FIG. 25  is similar to  FIG. 24  but the components are assembled; 
         FIGS. 26A-26D  are perspective views of exemplary alternative connections between the head component, the stem component and the collar component; and 
         FIG. 27  is perspective view of a kit including a plurality of head components, stem components and collar components having various sizes, shapes and configurations. 
     
    
    
     DETAILED DESCRIPTION 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the disclosure, its application or uses. 
     Before the present disclosure is disclosed and described, it is to be understood that this disclosure is not limited to the particular configurations, process steps and materials disclosed herein as these may vary to some degree. It is also to be understood that the terminology used herein is used for the purpose of describing particular embodiments only, and is not intended to be limiting as the scope of the present disclosure. The disclosure will be limited only by the appended claims and equivalents thereof. 
     It must be noted that, as used in this specification and the appended claims, singular forms of “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. 
     “Radial head” is defined as the essentially cylindrical protrusion found at the proximal end of a radius bone. The term “radial head” can also be used to modify or describe the prostheses of the present disclosure. 
     “Longitudinal axis” is an imaginary line that is defined by the center of the stem component in the direction of intramedullary canal insertion. Thus, the “longitudinal axis” is also roughly defined as running parallel to a centerline running between the proximal and distal end of the radius bone. 
     “Transverse axis” or “assembly axis” is an axis that intersects the longitudinal axis. The transverse axis can be linear or non-linear. For example, if non-linear, the axis can be arcuate, provided the assembly axis intersects the longitudinal axis. Thus, angles &gt;0° and &lt;180° qualify as “transverse.” However, for practical purposes, the transverse axis can be from 45° to 135° with respect to the longitudinal axis in order to significantly benefit from the modular assembly benefits described herein. In many instances, an essentially perpendicular transverse axis with respect to the longitudinal axis will be present. 
     “Protuberance” can include any protuberance functional with the present disclosure, particularly with respect to certain locking mechanisms. For example, such protuberances can be convexities. 
     “Concavity” is intended to describe an open space defined by a mounting portion of a stem component, or an inner core. With respect to a locking mechanism, the concavity can be configured to inversely match and accept a protuberance, though this is not required. 
     “Intramedullary” shall mean the within the marrow cavity of a bone. 
     “Native” is used to describe the condition of the bone or the head of a bone prior to damage or removal. 
     For the purposes of promoting an understanding of the principles of the disclosure, reference will now be made to the exemplary embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended. Any alterations and further modifications of the inventive features illustrated herein, and any additional applications of the principles of the disclosure as illustrated herein, which would occur to one skilled in the relevant art and having possession of this disclosure, are to be considered within the scope of the disclosure. 
     In order to remedy the shortcomings of prosthetic radial head replacement, a radial head prosthesis is disclosed that enables the assembly without having to significantly remove or manipulate bone and tissue as part of an overhead assembly. By implementing a sliding mechanism for the assembly of the modular radial head prostheses as described herein, improvement over the commercially available prosthetics can be achieved. Specifically, a sliding mechanism in conjunction with a locking mechanism enables the secure attachment and reasonable removal of a head component from an intact stem component, without the disadvantages associated with head component insertion along the longitudinal axis. 
     With the above descriptions and definitions in mind, a stem component  10  is shown in  FIG. 1 . Generally, the stem component  10  comprises an anchoring portion  12  and a mounting portion  14 . The anchoring portion  12  is the portion that is anchored within a canal of the proximal radius, providing support to the radial head prosthetic as a whole. In this embodiment, the anchoring portion  12  is tapered and can be coated or textured to allow bone ingrowth after insertion into the radius bone of a patient. The anchoring portion can be cemented, press fit, and/or impacted into the intramedullary canal as is known by those skilled in the art. If a cement is used, then a cement such as, for example, methyl methacrylate, can be used. If desired, various sized broaches (not shown) can be provided such that the surgeon can sound the diameter of the proximal radial shaft, thereby selecting an appropriate sized stem component. In this embodiment, the mounting portion  14  is configured as a dovetail shaped mount when viewed from the front perspective shown in  FIG. 1 . On each side of the mounting portion  14  are the stem protuberances  16   a ,  16   b . Though not required, the entire stem component  10  (i.e., the anchoring portion  12 , the mounting portion  14 , and the stem protuberances  16   a ,  16   b ) can be constructed of a rigid material such as metal, alloy, or ceramic. If the rigid material is metal or alloy, appropriate materials can include, for example, titanium, stainless steel, and cobalt chrome. 
     Turning to  FIG. 2 , a side view of the stem component  10  shown. As can be seen, the stem protuberances  16   a  are configured to span a distance of approximately one half of the depth of the mounting portion. The stem protuberance  16   b  (not shown) is configured similarly. In  FIG. 3 , a top view of the stem component  10  is shown. As the mounting portion  14  is configured in a dovetail-type shape, the stem protuberances  16   a ,  16   b  are not visible from this perspective, and thus, are shown as dashed lines. 
     The stem component shown in  FIGS. 1-3  has the dual purpose of attaching the prostheses to the radius bone, as well as to provide a mechanism to mount a head component (not shown) to the stem component. Though the head component can be a single unit, in the embodiment shown in the subsequent figures, the head component comprises an outer shell and an inner core. The practical reason for this is that it is often desirable to have a rigid outer shell, while having a less rigid inner core when utilizing the locking mechanism described in  FIGS. 1-13 . However, if the locking mechanism does not utilize compressible protuberances as part of the locking mechanism, the inner core can be a rigid material as well.  FIGS. 3-6  show an embodiment of the inner core, and  FIGS. 7-8  show an embodiment of the outer shell. However, the inner core and the outer shell will generally be pre-assembled prior to surgery. 
     Turning specifically to  FIG. 4 , an inner core  20  of a head component is shown. An inner core body  22  defines the shape of the inner core  20  and can be constructed of a polymeric resin, such as, for example, a high molecular weight polyethylene. Additionally, the outer dimension of the inner core body  22  can be cylindrical in shape. Attached to the inner core body are a pair of inner core protuberances  24   a ,  24   b . The inner core body  22  and the inner core protuberances  24   a ,  24   b  define an inner core open channel or groove  26  that can be slidably connected to the mounting portion (not shown) of the stem component (not shown). The inner core protuberances  24   a ,  24   b  can be constructed of the same material as the inner core body  22 , though this is not required. Thus, the inner core body  22  and the inner core protuberances  24   a ,  24   b  can be a single polymeric or copolymeric unit. Whatever the structure, in this embodiment, the inner core protuberances  24   a ,  24   b  are constructed of a compressible material so that the inner core protuberances  24   a ,  24   b  can pass by the stem protuberances (not shown) as part of a locking mechanism. 
     As can be seen more clearly in  FIGS. 5 and 6 , the inner core protuberances  24   a ,  24   b  are configured such that they span only a portion of the depth of the open channel  26 . Thus, the inner core protuberances  24   a ,  24   b  are positioned opposite the stem protuberances (not shown) such that when the head component is in place on the stem component, all of the protuberances act together to form a locking mechanism. 
     As shown in this embodiment, the inner core open channel  26  does not traverse completely through the inner core body  22 . Thus, the inner core groove  26  is just long enough such that when the mounting portion of the stem component (not shown) is tracked within the inner core open channel  26 , the mounting portion and the inner core  20  will be coaxial. 
     In  FIGS. 7 and 8 , a radial head component  30  is shown. An outer shell body  32  is fashioned to approximate the dimensions of a damaged or removed radial head. Thus, the outer dimension is roughly cylindrical, having a slightly concaved top portion  37  for natural articulation with the capitellum (not shown). Because outer shell body  32  is the portion of the prostheses that will articulate with the capitellum upon joint movement, this structure can be constructed of a biologically acceptable rigid material. Such a material can include, for example, metal, alloy, or ceramic. If the rigid material is metal or alloy, appropriate materials can include, for example, titanium, stainless steel, and cobalt chrome. The outer shell body  32  also defines an inner hollow  34  that accepts the inner core (not shown) when the head component is fully constructed. Additionally, an outer shell open channel or groove  36  is present that essentially matches the inner core open channel or groove (not shown) such that the mounting portion (not shown) can be inserted into the aligned grooves. For example, the outer shell body  32  and the inner core (not shown) can both be cylindrical components that define dovetail shaped grooves, which substantially fits the dovetail shaped mount of the stem component. If the inner core  20  and the outer shell body  32  are two different materials (as in the present embodiment), then the two components can be fitted together with a bonding cement, friction fit, and/or other known techniques. The outer shell open channel or groove  36  can be present at only one edge of the outer shell body  32  and its edges can be tapered to avoid damage to the articular cartilage of the proximal radio-ulnar joint. As mentioned, the outer shell body  32  should be composed of metal suitable for biologic implantation, and be shaped to approximate the dimensions of the radial head. If the surgeon requires assistance in selecting an appropriately sized head component, then an estimate of the patient&#39;s anatomy can be ascertained using plastic trials (not shown) provided for this purpose. Though not required, the edges of the outer shell groove  36  can be tapered to avoid damage to the proximal radio-ulnar joint. 
     Turning to  FIG. 9 , an exploded view of an embodiment of the present disclosure is shown. Specifically, the radial head component  30  is shown having an outer shell body  32 , which defines an outer shell hollow  34 . The outer shell hollow  34  fits over an outer dimension of the inner core body  22  of the inner core  20 . Once the outer shell body  32  and the inner core  20  are fitted together such that the outer shell open channel  36  aligns with the inner core open channel  26 , the entire head component (which comprises these two components) can be fitted on the mounting portion  14  of the stem component  10 . Though not required, the locking mechanism can be at an interface between the mounting portion  14  and the inner core  20 . As shown in this figure, a pair of the stem protuberances  16   a ,  16   b  can pass over a pair of the inner core protuberances  24   a ,  24   b , as the inner core protuberances  24   a ,  24   b  are configured to compress. Once the stem protuberances  16   a ,  16   b  completely pass over the inner core protuberances  24   a ,  24   b , the stem protuberances can lock into a pair of inner core concavities  25   a ,  25   b , respectively. The inner core concavities  25   a ,  25   b  are configured in dimension to inversely match the stem protuberances  16   a ,  16   b  such that a locking action occurs. Thus, an abutment of the protuberances occurs and can prevent unwanted motion between the head component and the stem component after the prostheses is inserted. The protuberances also serve to prevent the head component from slipping off the stem component without intentional force, e.g., during removal by a surgeon. With this and other similar designs, the stem component can be placed in a canal of the radius bone, followed by the fitting of the head component. 
       FIG. 10  shows the stem component, the inner core  20  and the outer shell body  32  in a completed assembly configuration. As can be seen, the cylindrical inner core  20  component fits centrally within the outer shell body  32 . Thus, when the mounting portion  14  of the stem component  10  is inserted fully within the core and shell, all three components will be configured coaxially. Though the outer shell body  32  and the inner core  20  are shown as two separate components, in practice, the outer shell body  32  and the inner core  20  can be assembled and sterilized prior to attachment to the mounting portion  14  of the stem component  10 . Thus, the surgeon would only be required to slide the assembled head component onto the stem component  10  by lining up the open channels  26 ,  36  with the mounting portion  14 , and sliding the radial head component  30  into place. In  FIGS. 11-13 , additional views of an assembled prosthesis are shown. 
     When assembling the head component onto the mounting portion  14 , due to elastic deformation of the inner core protuberances  24   a ,  24   b , all of the protuberances  16   a ,  16   b ,  24   a ,  24   b  can be slid past opposing protuberances under sufficient translational force. In this embodiment, the protuberances are shaped such that the force required to press the protuberances past their opposing protuberances is intentional and reasonable, but not excessive. 
       FIG. 14  is a posterior oblique view of the human elbow depicting the radial head prostheses in position within the proximal radius bone  38  and articulating with the capitellum  39  of the distal humerus. As can be seen, the anchoring portion  12  is within the medullary canal of the proximal radius  38 , and the radial head  30  is articulating with the capitellum  39  of the distal humerus. 
     In  FIGS. 15 and 16 , a tool  40  is shown that can be used with the prostheses of the present disclosure is shown. In  FIG. 15 , the tool  40  is positioned in a first orientation with respect to proximal radius  38  for inserting the radial head component  30  onto the mounting portion  14 . In  FIG. 15 , the tool  40  is positioned in a second orientation with respect to the proximal radius  38  for removing the radial head component  30  from the mounting portion. 
     Specifically, with respect to  FIG. 15 , a first arm  42  and a second arm  44  are shown that enable or surgeon to create translational force  45  to be placed on the radial head component  30 . The first arm  42  and the second arm  44  are tracked parallel to one another by a track  46  and a slider  48 . The second arm  44  is connected to a handle  52  by a hinge  50 . The handle  52  is designed such that by applying a squeezing force  51 , translational force  45  is applied to the head component  30 . Thus, in this embodiment, the translational force mechanism is a lever. At the end of the first arm  42  is a pulling member  54  that acts to stabilize the proximal radius  38  (or alternatively, the mounting portion  14 ). At the end of the second arm  44  is a pushing member  56  for pushing the radial head component  30  onto the mounting portion  14 . 
     In  FIG. 16 , the same tool  40  as described in  FIG. 15  can be used by flipping it upside down. Thus, the first arm  42  now acts to provide the translational force  45  and the second arm  44  stabilizes the proximal radius  38  (or alternatively, the mounting portion  14 ). Thus, the arms are characterized as the first arm  42  and the second arm  44  for convenience only. It would be apparent to one skilled in the art that the first arm or the second arm can function as the stabilizer. Likewise, the first arm or the second arm can act to provide desired translational force. 
     The use of such a tool is particularly helpful when a locking mechanism such as that described in  FIGS. 1-13  is in place. Locking and unlocking can be carried out as previously described. Specifically, in the present embodiment, the tool can press the components onto one another while maintaining alignment of the dovetail shaped mount and groove. In the absence of intentional and sufficient pressure to translate the head component off of the stem component, the rigidity provided by the polyethylene is sufficient to secure the modular components to each other. Removal is accomplished by generating sufficient translational pressure on the head component with the use of a specially designed handle. This tool binds the far end of the head component while stabilizing the proximal radius bone, and thereby the stem component. Translational force is generated which presses the protuberances of the inner core past the protuberances of the mounting portion, thereby releasing the head component from the stem component. 
     A procedure that can be followed for the insertion of the modular radial head prostheses is as follows. If necessary, after resection of a substantially unreconstructable radial head bone, a proximal edge of the radius bone can be removed by transverse sawing or some other removal technique. After the damaged radial head has been removed, the medullary canal of the bone can then be broached with one or more of a series of broaches, the shapes of which approximate the various stem sizes available. Once an appropriate size stem component size has been selected, the anchoring portion can be inserted into the proximal radius bone such that the mounting portion protrudes from the proximal radius bone. The head component can then selected based upon parameters such as proper ligament tensioning, circumference, and height. If desired, this assessment can be assisted with the use of plastic trials made available for this purpose. After an appropriately sized head component is selected, the forearm can be rotated so that the mounting portion is positioned to receive the head portion, i.e., an assembled outer shell/inner core combination or a single piece head component. If the head component comprises an outer shell and an inner core, the head component can either be assembled at the time of manufacture or by the surgeon. In any event, the outer shell groove and the inner core groove should be position such that the grooves line up for accepting the mounting portion. Once the stem component is in place and the proper head component is assembled and selected, the head component is then translated onto the stem component fully. If a locking mechanism is used such as that described in  FIGS. 1-13 , a click will be palpable as the stem protuberances and the inner core protuberances slip fully past each other. The prostheses will then be secure within the canal of the proximal radius bone and is positioned to articulate with the capitellum of the distal humerus. 
     With the above figures and surgical procedures in mind, a modular prostheses system for replacement of the radial head portion of the radius bone is disclosed comprising a stem component and a head component. The stem component comprises an anchoring portion and a mounting portion, and the head component can have an open channel configured to connect to the mounting portion along an assembly axis that is transverse to a longitudinal axis of the stem component. The connection can be by a sliding motion. Though the system requires only that the assembly axis be transverse to the longitudinal axis of the stem component, for practical purposes, the transverse angle will generally be from about 45° to 135° with respect to the longitudinal axis. This is due to the fact that as you approach angles closer to parallel with the longitudinal axis, the head component becomes more difficult to put in place. In many incidences, the assembly axis will intersect the longitudinal axis at essentially a perpendicular angle. 
     The system can further comprise a locking mechanism to prevent the open channel of the head component from indeliberately sliding on the mounting portion once connected to the mounting portion. This is desirable because once the prosthesis has become part of the functioning elbow joint, any slippage could require surgery for repair. Thus, the only circumstance wherein sliding should be allowed should occur at the hand of the surgeon, with deliberate action. The locking mechanism can be configures such as that shown in  FIGS. 1-13 , or by any other locking mechanism known by those skilled in the mechanical arts. For example, after sliding the head component onto the mounting portion, the head component can be locked in place with a pin or screw. 
     In a one embodiment, the mounting portion can be configured for allowing the head component to slide along a single axis via the open channel. Such an embodiment is shown in  FIGS. 1-13  where the dovetail-shaped mounting portion is inversely matched with a dovetailed-shaped groove. Thus, head component can be slid onto the mounting portion along a single axis only. 
     Though not required, the head component can be inserted and removed from the mounting portion with a specially designed tool. Thus, the system of the present disclosure can further comprise a tool for inserting and removing the head component while the stem component is in place within a radial canal. Such a tool can comprise a first arm for inserting the head component onto the mounting portion or removing the head component from the mounting portion; a second arm for stabilizing the radius bone; and a translational force mechanism for moving the first arm while the second arm stabilizes the radius bone. The terms “translation” and “stabilizing” are used loosely depending on whether the tool is being used for insertion or removal of the head component, the arm acting to provide the translational force and the arm act to provide stabilization can be changed. Thus, the terms are relative as to the action, rather than to the specific structure. For example, when insertion of the head component is being carried out, the first arm carrying out the translational insertion does so by a pushing force, and the second arm stabilizes the radius bone by a pulling force. Conversely, when removal of the head component is being carried out, the first arm removes the head component by a pulling force (i.e., the tool is flipped over, and the second arm stabilizes the radius bone by a pushing force). 
     As part of the system, a method for fitting a damaged radius bone with a modular radial head prostheses is disclosed comprising the steps of securing a stem component partially within a proximal intramedullary canal of the damaged radius bone such that a mounting portion of stem component is exposed above the damaged radius bone; selecting a head component that will provide a desired result; and sliding the head component onto the mounting portion in a direction along an assembly axis that is transverse to a longitudinal axis of the stem component. Typically, a preliminary step of removing a radial head of the damaged radius bone is carried out prior to fitting the radius bone with the prostheses of the present disclosure, though there can be circumstances where this preliminary step is not necessary. Additionally, before securing the stem component within the intramedullary canal, it may be desirable to carry out the preliminary step of sizing the stem component to securely fit within the proximal canal. This can be done using a set of broaches designed for this purpose. The stem component can be secured within the intramedullary canal by one of a number of techniques including the use of cement, firm pressure into the canal, or impacting the stem component into the canal, for example. 
     Once the stem component is in place, the next step of selecting an appropriate head component is carried out. Considerations can include assessing a desired tensioning of one or more ligaments attached to the radius bone and/or assessing the height and shape of the head component to be used. Aid in this area can be provided by the use of trials designed for this purpose. Such trials can be plastic structures configured to approximate the size and shape of the head component to be ultimately placed on the mounting portion. It is appreciated that the trials can be made of other suitable materials. 
     Referring to  FIGS. 17 through 20 , the inner core  20  and the outer shell body  32  of the radial head component  30  are shown. In the various embodiments, the outer shell body  32  can be comprised of ultra high molecular weight polyethylene. The outer shell body  32  can also be comprised of a suitable metal material such as cobalt chrome, titanium, or other biocompatible material. The inner core  20  can also be made of a material that is identical to the radial head component  30  ( FIG. 19B ) or as above described made of a softer material ( FIG. 19A ) that can otherwise be compressed when inserted over the stem protuberances  16   a ,  16   b  or any other biocompatible material, as above detailed and as shown in  FIG. 1 . 
     In other embodiments, the inner core  20  and the outer shell body  32  are comprised of the same material ( FIG. 19B ), for example, a metal such as cobalt chrome or titanium. By way of example, a mechanical fastener  60  can be used to secure the outer shell body  32  to the inner core  20  in lieu of the compressible inner core protuberances  24   a ,  24   b  ( FIG. 4 ). In addition, the head component  30  can be made of single piece of biocompatible material ( FIG. 19C ), such that the head component is a unitary construction. It is appreciated that a plurality of the fasteners  60  can be used to secure the outer shell body  32  to the inner core  20 . Moreover, other types of exemplary connections may be used such as chemical bonding, shrink fit and taper junctions. Furthermore, the outer shell body  32  can be configured to snap fit onto the inner core  20 , while another method can include mechanical threading on the inner core  20  with complementary mechanical threading on the outer shell body  32 . The outer body shell  32  of the radial head component  30  can also be configured to completely envelope the inner core  20 , as shown in  FIGS. 17 and 18 , or otherwise be positioned over the inner core  20  as to not cover the open channel  26  thus exposing varying lengths of the inner core  20 , as shown in  FIGS. 19A, 19B and 20 . 
     With reference to  FIGS. 21A through 24 , a collar component  62  can be used to connect the radial head component  30  to the stem component  10 . The collar component  62  can have a collar open channel  64  and a collar mounting location  66 , which are complementary to the head open channel  36  and the stem mounting location  14 , respectively. The collar component  62  can be configured to vertically align the radial head component  30  and the stem component  10 , as shown in  FIG. 22 . An angled collar component  68  can also be configured to provide a pre-determined angle between the radial head component  30  and the stem component  10 , as shown in  FIG. 25 . As such, the angled collar component  68  can be configured at various angles, for example, between vertical (i.e., 180°) and narrower angles to match the native geometry of the bones, as shown in  FIG. 14 . It can be appreciated that the radial head component  30  and the stem component  10  can attach to the collar component  62  or the angled collar component  68  regardless of its length or angle. 
     In the various embodiments, the radial head component  30  can have a unitary construction (i.e., one-piece), thus omitting the inner core  20  and outer shell body  32 . In this arrangement, the radial head component  30  can be constructed of metal such as cobalt chrome, titanium or any other suitable biocompatible material for implementation into the human body. By way of example, the radial head component  30  can be secured to either the stem mounting portion  14  or the collar mounting portion  66  of the collar component  62  with a suitable mechanical fastener  60 . 
     With reference to  FIGS. 21A and 21B , the head component  30  includes a first connection portion  70  that connects to a second connection portion  72  on the collar component  62 . The collar component  62  also includes a third connection portion  74  that connects to a fourth connection portion  76  on the stem component  10 . It can be appreciated that the second connection portion  72  can be distal from the third connection portion  74  and can be on opposite ends of the collar component  62 . As shown in  FIG. 21A , the first connection portion  70  can be the open channel  26  on the head component  30 . The second connection portion can be the collar mounting portion  66 . The third connection portion  76  can be the collar open channel  64 . The fourth connection portion  78  can be the mounting portion of  14  on the stem component  10 . As shown in  FIG. 21B , the first connection portion  70  can be a head component mounting portion  78 . The second connection portion can be the collar open channel  64 . The third connection portion  74  can be the collar mounting portion  66 . The fourth connection portion  76  can be a stem component open channel  80 . 
     It can be appreciated that the various components of the modular prosthesis system can use various connection portions with myriad configurations. By way of example, the mounting portion on the various components is configured in a T-shaped protrusion generally indicated by reference numeral  82 . A complementary open channel  84  is similarly configured in a T-shape to accept the T-shaped protrusion  82 . With reference to  FIG. 23 , it can be appreciated that other configurations are suitable such as, but not limited to, a cylindrical configuration  86 , a dove-tail configuration  88 , and a star shaped configuration  90 . It can also be appreciated that, regardless of the configuration, various fits can be used such as, but not limited to, an interference fit, a taper lock fit and a sliding fit secured by a mechanical fastener  60 . It can further be appreciated that the mechanical fastener  60  can be inserted through an aperture and contact the T-shaped protrusion. The mechanical fastener can also connect to the T-shaped protrusion such that the fastener  60  can be inserted through a fastener aperture  92  in the open channel and/or in the mounting location. It can be additionally appreciated that the fastener can be placed at various angles and position to further secure the components of the prosthesis. 
     It can be appreciated that the various components of the modular prosthesis can be scaled to fit the patients native bone structure. A collar length  94  ( FIG. 22 ) and a collar angle  96  ( FIG. 24 ) can be variable among multiple collar components  62 ,  68 , while the collar mounting location  66  and the collar open channel  64  can have a fixed dimension to facilitate interchangeability among other stem components  10  and head components  30 . With reference to  FIG. 20 , it can also be appreciated that an inner core length  98  can vary such that the inner core body  22  can be completely contained within the head component inner hollow  34  or extend beyond an outer body shell aperture  100 . It is further appreciated, that various dimensions such as length, diameter, thickness etc. can be varied to more closely match the native bone structure of the patient, as shown in  FIG. 14 . 
     With reference to  FIGS. 26A-26D , a threaded post  102  and a complementary threaded aperture  104  can be used to connect the collar component  62  to the head component  30  and the stem component  10 . With reference to  FIG. 26A , the first connection portion  70  of the head component  30  can include the threaded aperture  104 . The second connection portion  72  of the collar component  62  can include the threaded post  102  that can engage with and connect to the complimentary threaded aperture  104  on the head component  30 . The third connection portion  74  of the collar component  62  can include the above described T-shaped protrusion  82 . The fourth connection portion  76  of the stem component  10  can include the above described T-shaped channel  84 , which can connect with the T-shaped protrusion  82  included on the third connection portion  74  of the collar component  62 . It can be appreciated that the angled collar component  68  ( FIG. 26D ) can be similarly configured to the collar component  62  ( FIGS. 26A-26C ) and, thus, can be used interchangeably. 
     With reference to  FIG. 26B , the first connection portion  70  on the head component  30  can include the T-shaped protrusion  82 . The second connection portion  72  of the collar component  62  can include the complimentary T-shaped channel  84  that can connect with and engage the T-shaped protrusion  82  included on the first connection portion  70  of the head component  30 . The third connection portion  74  of the collar component  62  can include the threaded post  102 . The fourth connection portion  76  of the stem component  10  can include the complementary threaded aperture  104  that can engage to and connect with the threaded post  102  included on the third connection portion  74  of the collar component  62 . 
     With reference to  FIG. 26C , the first connection portion  70  of the head component  30  can include the threaded aperture  104 . The second connection portion  72  of the collar component  62  can include the threaded post  102  which can engage with and connect to the threaded aperture  104  included on the first connection portion of the head component  30 . The third connection portion  74  of the collar component  62  can also include the threaded post  102 . The first connection portion  76  on the stem component  10  can include the threaded aperture  104  that can engage with and connect to the threaded post  102  on the third connection portion  74  of the collar component  62 . 
     With reference to  FIG. 26D , the first connection portion  70  of the head component  30  can include the threaded aperture  104 . The second connection portion  72  of the angle collar  68  can include the threaded post  102 , which can engage with and connect to the threaded aperture  104 . The third connection portion of the angle collar  68  can also include the threaded post  102 . The fourth connection portion  76  of the stem component  10  can include the threaded aperture  104 , which can engage with and connect to the threaded post  102 . It can be appreciated that height  94  ( FIG. 26C ) and/or angle  96  of either the collar component  62  or angled collar component  68  can be varied to accommodate the native bone structure, as shown in  FIG. 14 . Moreover, the height  106  ( FIG. 26C ) of the threaded post  106  can be varied to further accommodate the modularity of the prosthesis. It can also be appreciated that the first connection portion  70 , the second connection portion  72 , the third connection portion  74  and the fourth connection portion  76  can be configured in various ways including, but not limited to, the respective threaded posts  102  and threaded apertures  104  and various combinations thereof. 
     With reference to  FIG. 27 , a kit  108  is shown including exemplary stem components  10 , collar components  62 , angled collar components  68  and head components  30 . The kit  108  can include a collection of various sizes and shapes of the above-mentioned components. For example, the kit  108  can include a plurality of angled collar component  68  having varying collar angles  94 . By way of further example, the kit  108  can include a plurality of head components  30  having varying shaped concave top portions  37  that complement the native bone to which they will contact. The kit  108  can also include a plurality of stem components  10  such that each of the stem components  10  has varying size anchor portions  12  in thickness, taper design and/or length. Moreover, the kit  108  can include a plurality of collar components  62  having varying collar lengths  92  to further accommodate the native bone structure. It can be appreciated that the kit  108  can include numerous head components  30 , angled collar components  68 , collar components  62 , and stem components  10  of various sizes, shapes and configurations so that the modular prosthesis system can be assembled to closely match the native bone structure. 
     The kit  108  provides the plurality of head components  30 , angled collar components  68 , collar components  62 , and stem components  10  that can be assembled and adjusted during a medical procedure to provide a fit that can be in-situ determined and adjusted. It can be appreciated that a medical professional can determine a proper length and angle and select among the components of the kit  108  to achieve the proper length and angle. Nevertheless, the medical professional can select and substitute components in-situ to adjust to achieve the proper length and angle. 
     The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the gist of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure. It is to be understood that the above-described arrangements are only illustrative of the application of the principles of the present disclosure. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the spirit and scope of the present disclosure and the appended claims are intended to cover such modifications and arrangements. Thus, while the present disclosure has been shown in the drawings and fully described above with particularity and detail in connection with what is presently deemed to be the most practical and preferred embodiment(s) of the disclosure, it will be apparent to those of ordinary skill in the art that numerous modifications, including, but not limited to, variations in size, materials, shape, form, function and manner of operation, assembly and use may be made, without departing from the principles and concepts of the disclosure as set forth in the claims.