Abstract:
A prosthesis assembly in one embodiment includes a stem configured to be implanted in a bone and including a first coupling portion, a head having a bearing surface configured to mate with at least one of a natural opposing joint component and a prosthetic opposing joint component, the head further having a second coupling portion, a coupler including a third coupling portion and a fourth coupling portion, the third coupling portion configured to couple with the second coupling portion, and an insert including (i) a fifth coupling portion configured to couple with the fourth coupling portion in any of a plurality of rotational orientations in combination with any of a plurality of roll angles and any of a plurality of pitch angles, and (ii) a sixth coupling portion configured to couple with the first coupling portion only when the insert assumes a predetermined rotational orientation with respect to the stem.

Description:
FIELD 
     The present disclosure relates to joint prostheses, and particularly to prostheses having articulating head components. More specifically, the disclosure relates to a system for achieving variable positions for the head component of a joint prosthesis relative to a bone-engaging portion of the prosthesis. 
     BACKGROUND 
     Repair and replacement of human joints, such as the knee, shoulder, elbow and hip, has become a more and more frequent medical treatment. Longer life spans mean that the joints are subjected to wear and tear over an extended period of time. Additionally, participation in sports activities results in a greater likelihood of serious joint injuries. Treatment of injuries, wear, and disease in human joints has progressed from the use of orthotics to mask the problem, to fusion of the joint, to the use of prostheses to replace the damaged joint component(s). 
     As the success rate for total or partial joint replacements has increased, so too has the need for modularity and universality in the joint prosthesis. Patient variety means that no single size or configuration of joint prosthesis provides optimum results for each patient. The physical dimensions of a patient&#39;s joint components vary, as do the bio-mechanic relationship between the components within a particular joint. By way of example, in a shoulder prosthesis, the relationship between the articulating humeral and glenoid components can be significantly different between patients. These relationships are especially important where only one component of the joint is being replaced and must integrate with the existing natural opposing joint component. 
     For instance, in many shoulder surgeries, only the humeral component is replaced, leaving the glenoid component intact. In this case, it is imperative that the articulating surface of the humeral component match the articulating surface of the glenoid component as perfectly as possible, both statically and dynamically. With a typical humeral prosthesis, version and inclination are adjusted by the geometry of the head of the prosthesis. In other words, certain pre-determined head geometries are available that can be selected for a mating glenoid component. Unless a virtually infinite variety of pre-determined head geometries are maintained in inventory, the resulting humeral prosthesis will rarely provide an optimum fit with the glenoid component of the shoulder joint. 
     In a typical surgical procedure, a trial component is used to determine the optimum component configuration for the permanent prosthetic device. In most cases, the surgeon is able to make a selection of components and configurations that fits the joint in an acceptable manner. In some cases, however, the functionality of the fit cannot be fully assessed until the surgery is completed and the patient has had an opportunity to utilize the repaired joint. In some cases, a revision surgery is necessary to replace a prosthetic device that is not optimally sized or configured for the particular patient. One type of revision surgery requires removal of the entire prosthesis from the bone and replacement with a different prosthesis. 
     There is a significant need for a joint prosthesis that is both modular and universal. A further need exists for a prosthesis that is easily manipulated during the surgery and capable being configured in a nearly infinite number of version and inclination angle combinations. Additionally, a need exists for a prosthetic device that is easily modified during a revision surgery. Yet a further need exists for a prosthetic device that is modifiable during a revision surgery without the need to completely remove the entire prosthetic assembly from the bone of the patient. 
     SUMMARY 
     A method and assembly for achieving variable positions of a head component of a joint prosthesis relative to a bone-engaging portion of the prosthesis is disclosed. In a one embodiment, a prosthesis assembly includes a stem configured to be implanted in a bone and including a first coupling portion, a head having a bearing surface configured to mate with at least one of a natural opposing joint component and a prosthetic opposing joint component, the head further having a second coupling portion, a coupler including a third coupling portion and a fourth coupling portion, the third coupling portion configured to couple with the second coupling portion, and an insert including (i) a fifth coupling portion configured to couple with the fourth coupling portion in any of a plurality of rotational orientations in combination with any of a plurality of roll angles and any of a plurality of pitch angles, and (ii) a sixth coupling portion configured to couple with the first coupling portion only when the insert assumes a predetermined rotational orientation with respect to the stem. 
     In a further embodiment, a prosthesis assembly kit includes at least one stem configured to be implanted in a bone, the at least one stem including a keyed stem coupling portion, a plurality of heads, each of the plurality of heads having a bearing surface configured to mate with at least one of a natural opposing joint component and a prosthetic opposing joint component, each of the plurality of heads further having a head coupling portion, at least one first coupler including an upper coupling portion and a lower coupling portion, the upper coupling portion configured to couple with the head coupling portion of each of the plurality of heads, and at least one insert including (i) a non-keyed insert coupling portion configured to couple with the lower coupling portion of each of the at least one first couplers in any of a plurality of rotational orientations in combination with any of a plurality of roll angles and any of a plurality of pitch angles, and (ii) a keyed insert coupling portion configured to couple with the keyed stem coupling portion of each of the at least one stems. 
     In yet another embodiment, a method of forming a prosthesis includes implanting a stem in a bone, the stem including a first coupling portion, determining a desired orientation of a head with respect to the stem, coupling the head with a first coupling portion of a coupler, coupling a second coupling portion of the coupler with an insert, aligning a key member of the coupled insert with the implanted stem, and coupling the aligned insert with the implanted stem. 
     The above-noted features and advantages, as well as additional features and advantages, will be readily apparent to those skilled in the art upon reference to the following detailed description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The illustrative devices will be described hereinafter with reference to the attached drawings which are given as non-limiting examples only, in which: 
         FIG. 1  depicts a perspective exploded view of a prosthesis assembly including a stem, an insert, a coupler and a head incorporating principles of the invention; 
         FIG. 2  depicts a side plan view of the stem of  FIG. 1 ; 
         FIG. 3  depicts a partial cross sectional view of the stem of  FIG. 1  showing a coupling receptacle with a key feature; 
         FIG. 4  depicts a partial top plan view of the stem of  FIG. 1  showing the coupling receptacle with the key feature; 
         FIG. 5  depicts a cross sectional view of the insert of  FIG. 1  showing an inner coupling receptacle and an outer coupling wall with a key feature; 
         FIG. 6  depicts a bottom plan view of the insert of  FIG. 5  showing the periphery of the outer coupling wall and the key feature; 
         FIG. 7  depicts a cross sectional view of the coupler of  FIG. 1  showing an upper coupling wall and an lower bulbous coupling; 
         FIG. 8  depicts a bottom plan view of the coupler of  FIG. 7  showing the bulbous coupling to be circular in plan view; 
         FIG. 9  depicts a cross sectional view of the head of  FIG. 1  showing an upper articulating surface and a lower surface including a coupling receptacle and a recessed area; 
         FIGS. 10-13  depict a procedure of coupling of the head of  FIG. 1  with the coupler of  FIG. 1  and coupling the coupler of  FIG. 1  with the insert of  FIG. 1  which may be accomplished prior to implantation in accordance with principles of the invention; 
         FIGS. 14-15  depict a procedure of alignment the key member of the insert of  FIG. 1  with the key member of the stem of  FIG. 1  and coupling of the insert with the stem; 
         FIGS. 16-19  depict the combinations of version and inclination angles at which the coupler of  FIG. 1  may be coupled with the insert of  FIG. 1 ; 
         FIG. 20  depicts a perspective view of a removal tool that may be included in a kit and used to decouple the head of  FIG. 1  from the coupler of  FIG. 1 ; 
         FIG. 21  depicts a partial cross sectional view of the assembled prosthesis assembly of  FIG. 1  showing a gap into which the prongs of the removal tool of  FIG. 20  may be inserted to decouple the head of  FIG. 1  from the coupler of  FIG. 1 ; 
         FIG. 22  depicts a partial cross sectional view of the assembled prosthesis assembly of  FIG. 1  showing a gap into which the prongs of the removal tool of  FIG. 20  may be inserted to decouple the head of  FIG. 1  from the coupler of  FIG. 1  when the axis of the head is not aligned with the axis of the stem receptacle; 
         FIG. 23  depicts a perspective view of the removal tool of  FIG. 20  positioned to decouple the head of  FIG. 1  from the coupler of  FIG. 1 ; 
         FIG. 24  depicts a partial cross sectional view of the assembled prosthesis assembly of  FIG. 1  with the end portions of the prongs of the removal tool of  FIG. 20  inserted in the gap between the head and the stem; 
         FIG. 25  depicts a partial cross sectional view of the assembled coupler and insert of  FIG. 1  with portions of the prongs of the removal tool of  FIG. 20  inserted between the stem and the shoulder portion of the coupler for decoupling of the coupler and the insert; 
         FIG. 26  depicts a partial cross sectional view of the insert and stem of  FIG. 1  with a threaded decoupler partially threaded into the threaded bore of the insert for decoupling of the insert and the stem; 
         FIG. 27  depicts a side plan view of an alternative insert that may be used to couple the head of  FIG. 1  with the stem of  FIG. 1  with the axis of the head parallel to the axis of the stem receptacle; 
         FIG. 28  depicts a partial cross sectional view of the alternative coupler of  FIG. 27 ; 
         FIG. 29  depicts a partial cross sectional view of the stem and head of  FIG. 1  assembled using the coupler of  FIG. 27 ; 
         FIG. 30  depicts a perspective view of a removal tool that may be included in a kit and used to decouple the coupler of  FIG. 1  from the insert of  FIG. 1  or that insert of  FIG. 27 ; 
         FIG. 31  depicts a side plan view of a decoupler with a threaded stem and a flange that may be included in a kit and used to decouple the coupler of  FIG. 1  from the insert of  FIG. 1  or the insert of  FIG. 27 ; 
         FIG. 32  depicts a partial cross sectional view of the insert and stem of  FIG. 1  with the decoupler of  FIG. 31  threaded into the threaded bore of the insert for decoupling of the insert and the stem; and 
         FIG. 33  depicts a partial cross sectional view of the insert of  FIG. 27  and the stem of  FIG. 1  with the decoupler of  FIG. 31  threaded into the threaded bore of the insert for decoupling of the insert and the stem. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. 
     DETAILED DESCRIPTION 
     For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the invention is thereby intended. It is further understood that the present invention includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the invention as would normally occur to one skilled in the art to which this invention pertains. 
       FIG. 1  depicts a perspective view of a humeral prosthesis assembly  100 . The assembly  100  is the humeral component of a shoulder prosthesis that can be implanted in the humerus bone of a patient for articulating engagement with the natural glenoid or with a glenoid prosthesis. The assembly  100  includes a stem  102  configured to be implanted within the humerus bone in an acceptable manner. The assembly  100  further includes an insert  104 , a coupler  106  and an articulating head component  108 . 
     With further reference to  FIGS. 2-4 , the stem  102  includes a shaft  110  and a platform area  112 . The platform area  112  includes an upper surface  114  that faces toward the glenoid component of the joint when the stem  102  is implanted within a patient. The upper surface  114  defines a tapered bore  116  that includes a key member  118 . 
     The insert  104 , shown in  FIGS. 1 ,  5 , and  6 , includes an outer wall  120  which generally tapers from an upper portion  122  to a lower portion  124 . A tapered bore  126  opens to the upper portion  122  and a threaded bore  128  opens at one end to the lower portion  124  and opens at the other end to the tapered bore  126 . A key member  130  is located near the lower portion  124 . 
     The coupler  106  includes an upper coupling portion  132  and a lower coupling portion  134  joined by a middle portion  136  as shown in  FIGS. 7 and 8 . The upper coupling portion  132  includes a bore  138  and a tapered outer wall  140 . The middle portion  136  includes a shoulder portion  142  which tapers inwardly from the tapered outer wall  140  to a neck portion  144 . The lower coupling portion  134  is bulbous shaped when viewed in profile ( FIG. 7 ) and circular when viewed in plan (see  FIG. 8 ). 
     Referring to  FIGS. 1 and 9 , the articulating head component  108  includes an outer articulating surface  148 , which is shaped to articulate with a glenoid component, and a lower surface  150 . The lower surface  150  includes a protuberance  152  defining a tapered bore  154 . A recessed area  156  extends between the protuberance  152  and a lip  158  which circumscribes the lower surface  150 . 
     Assembly of the humeral prosthesis assembly  100  in one embodiment may be performed once the stem  102  has been implanted within the bone of a patient. A trial (not shown) is used to determine the head size and the version and inclination angle combination of the head that provides the desired joint configuration. The coupler  106  may then be joined with the articulating head component  108  of the desired size by aligning the tapered bore  154  with the upper coupling portion  132  as shown in  FIG. 10 . 
     The tapered bore  154  and the outer wall  140  of the upper coupling portion  132  in this embodiment have a five degree taper. The tapered bore  154  and the outer wall  140  thus provide for a Morse taper coupling. Accordingly, movement of the articulating head component  108  in the direction of the arrow  160  onto the upper coupling portion  132  provides the configuration of  FIG. 11 . The articulating head component  108  and the coupler  106  are then firmly coupled by impacting the articulating head component  108  onto the coupler  106 . 
     With reference to  FIG. 12 , the lower coupling portion  134  of the coupler  106  is then aligned with the tapered bore  126  of the insert  104  and the articulating head component  108  and the coupler  106  are moved in the direction of the arrow  162 . Insertion and impacting of the lower coupling portion  134  within the tapered bore  126  results in the configuration of  FIG. 13 . Specifically, the lower coupling portion  134  has a diameter that is larger than the diameter of the tapered bore  126  at a location spaced apart from the upper portion  122  of the insert  104 . Thus, while a Morse taper coupling is not formed, the lower coupling portion  134  may be firmly secured within the tapered bore  126  by application of sufficient force. Preferably, the force used to secure the lower coupling portion  134  within the tapered bore  126  is greater than the force used when forming a Morse taper coupling. 
     Once the head  108 , the coupler  106  and the insert  104  have been coupled, the lower portion  124  of the insert  104  is aligned with the tapered bore  116  as shown in  FIG. 14 . The key member  130  and the key member  118  are configured such that the lower portion  124  may be fully inserted into the tapered bore  116  in a single rotational configuration. Accordingly, the insert  104  must be rotated as necessary to align the key member  130  and the key member  118 . Consequently, the axis of the bore  116  is collocated with the axis of the insert  104 . 
     The tapered bore  116  and the outer wall  120  of the insert  104  in this embodiment have a ten degree taper. The tapered bore  116  and the outer wall  120  thus provide for a Morse taper coupling. Accordingly, movement of the insert  104  in the direction of the arrow  164  into the tapered bore  116  provides the configuration of  FIG. 15 . The insert  104  and the stem  102  are then firmly coupled by impacting the articulating head component  108  to force the articulating head component  108 , the coupler  106  and the insert  104  toward the stem  102 . 
     Alternatively, the coupler  106  and the insert  104  may be positioned with the implanted stem  102  prior to coupling the head  108  with the coupler  106 . The head  108  is then positioned and coupled with the previously positioned coupler  106  and the insert  104 . This alternative may be used in rescission surgeries to allow for a smaller incision to be used to access the surgical site. 
       FIG. 15  depicts a configuration wherein the axes of the tapered bore  154  of the articulating head component  108 , the coupler  106 , the insert  104  and the tapered bore  116  are substantially aligned. Because the articulating head component  108  and the coupler  106  form a Morse taper coupling as discussed above, the articulating head component  108  will assume a specific axial alignment with respect to the coupler  106  when the articulating head component  108  is coupled with the coupler  106 . Likewise, because the insert  104  and the stem  102  form a Morse taper coupling as discussed above, the insert  104  will assume a specific axial alignment with respect to the stem  102  when the insert  104  is coupled with the stem  102 . 
     Therefore, the axial alignment of the articulating head component  108  with respect to the stem  102  may be established by controlling the axial alignment of the coupler  106  with the insert  104 . Moreover, the key members  118  and  130  establish a specific rotational alignment of the insert  104  with respect to the stem  102 . Therefore, the rotational orientation of the articulating head component  108  with respect to the stem  102  may be established by controlling the rotational alignment of the coupler  106  with the insert  104 . Accordingly, the desired axial and rotational alignment of the articulating head component  108  with respect to the stem  102  may be established by controlling the rotational and axial alignment of the coupler  106  with the insert  104 . 
     Rotational and axial alignment of the coupler  106  with the insert  104  is discussed more fully with initial reference to  FIG. 16 .  FIG. 16  depicts the geometric center  170  of the lower coupling portion  134 . The lower coupling portion  134  is formed such that the diameter of the lower coupling portion  134  along a plane that includes the geometric center  170  and is located between the axes  172  and  174  is greater than a diameter of the tapered bore  126  at a location between the upper portion  122  of the insert  104  and the bottom of the tapered bore  126 . 
     Accordingly, the coupler  106  may be coupled with the insert  104  with any axial or rotational alignment so long as the lower coupling portion  134  is oriented within the tapered bore  126  such that a plane that includes the geometric center  170 , and is perpendicular to the axis  176  of the insert  104 , is located between the axes  172  and  174 . 
     By way of example, the axis  180  of the coupler  106  is aligned with the axis  170  (the axis  180  is depicted as offset from the axis  170  in  FIG. 16  for purpose of clarity). Additionally, the plane  182 , which includes the geometric center  170 , is perpendicular to the axis  176  of the insert  104  and is located between the axes  172  and  174 . Accordingly, the coupler  106  and the insert  104  may be coupled in the configuration shown in  FIG. 16 . 
       FIG. 17  shows the coupler  106  pivoted in a direction away form the key member  130 , thereby generating an angle a between the axis  180  and the axis  170 . Nonetheless, the plane  182 , which includes the geometric center  170  and is perpendicular to the axis  176  of the insert  104 , is still located between the axes  172  and  174 . Accordingly, the coupler  106  and the insert  104  may be coupled in the configuration shown in  FIG. 17 . Similarly, the coupler  106  and the insert  104  may be coupled in the configuration shown in  FIG. 18  wherein the coupler  106  is pivoted in a direction toward the key member  130 , thereby generating an angle a between the axis  180  and the axis  170 . 
     Moreover, because the lower coupling portion  134  is circular when viewed from the bottom (see  FIG. 8 ), the coupler  106  may be pivoted from side to side with respect to the key member  130 . Thus, as shown in  FIG. 19 , the coupler  106  and the insert  104  may coupled in any desired combination of inclination and version angles that positions the axis  180  of the coupler  106  within a cone  184  originating from the axis  170  and having a cone angle of φ. In one embodiment, the coupler  106  may be positioned within about 15 degrees of the axis  180  in any direction, thereby providing a cone angle of about 30 degrees. The cone angle for a particular embodiment is typically limited by impingement of either the insert  104  on the shoulder  142  or impingement of the stem  102  on the lower surface  150 . Accordingly, the cone angle may be modified by selection of the shape and dimensions of, for example, the neck  144  and shoulder  142  of the coupler  106 , the protuberance  152 , the recessed area  156  and the platform  112 . 
     Disassembly of the assembly  100  is possible using the removal tool  200  of  FIG. 20 . The removal tool  200  includes a base  202  and a shaft  204 . Two prongs  206  and  208  extend outwardly from the base  202  and an impact knob  210  is located on the shaft  204 . The prongs  206  and  208  are spaced apart by a distance corresponding to the diameter of the tapered bore  116  and are narrowed at the distal end portions  212  and  214 , respectively. The distal end portions  212  and  214  are thus proportioned to fit within a gap  220  (see  FIG. 21 ) between the protuberance  152  and the upper surface  114  of the shaft  102 . Even when the articulating head component  108  is angled with respect to the shaft  102  as shown in  FIG. 22 , the gap  220  is present. 
     Accordingly, disassembly of the assembly  100  is accomplished by maneuvering the prongs  206  and  208  between the articulating head component  108  and the upper surface  114  of the stem  102  as shown in  FIG. 23 . The recessed area  156  facilitates the positioning of the distal end portions  212  and  214  of the prongs  206  and  208  between the protuberance  152  and the upper surface  114  of the shaft  102  as shown in  FIG. 24 . Once positioned, the impact knob  210  is impacted. The force of the impact is transferred through the inclined surfaces of the tapered prongs  206  and  208  to the protuberance  152  forcing the articulating head component  108  away from the stem  102 . The impact will typically break the coupling between the outer wall  140  of the coupler  106  and the tapered bore  154 , allowing the articulating head  108  to be removed from the coupler  106 . 
     The distance between the prongs  206  and  208  decreases from the distance at the distal end portions  212  and  214  and the distance at the base  202 . Specifically, the distance between the prongs  206  and  208  at a location between the distal end portions  212  and  214  and the base  202  corresponds to the diameter of the neck  144 . Accordingly, once the articulating head component  108  is removed, the prongs  206  and  208  are positioned adjacent to the neck  144  as shown in  FIG. 25 . The prongs  206  and  208  thus contact the shoulder portion  142  of the coupler  106 . If desired, the upper inner surface of the prongs  206  and  208  may be formed with an angle complimentary to the angle of the shoulder portion  142  as shown in  FIG. 25 . A subsequent impact on the impact knob  210  decouples the coupler  106  from the insert  104 . 
     Finally, the insert  104  is removed by insertion of a threaded decoupler  220  into the threaded bore  128  as shown in  FIG. 26 . As the threaded decoupler  220  is threaded into threaded bore  128 , the threaded decoupler  220  contacts the bottom of the tapered bore  116 . Additional rotation of the threaded decoupler  220  breaks the coupling between the insert  104  and the tapered bore  116 . 
     A new humeral prosthetic assembly may then be assembled using the stem  102  along with a new insert  104 , a new coupler  106 , and a new articulating head component  108 . The orientation of the new articulating head component  108  may be set in the manner described above. Instrumentation which may be used to couple the articulating head component  108  and the coupler  106  at the desired orientation with the insert  104  is described in U.S. Publication No. 2005/0288681, published on Dec. 29, 2005, which is herein incorporated by reference. 
     Subjecting a bone to high impact forces may cause further injury or fracturing of the bone. Additionally, applying high impact forces to an implanted stem could move the stem within the bone resulting in misalignment of the prosthesis. Coupling the insert  104  and the coupler  106  prior to implanting the insert  104  within the bone of a patient thus allows a much higher impact force to be used than would typically be used to form a couple while one of the components is implanted. The use of a higher force provides a stronger coupling which better resists further movement between the components. 
     Specifically, the impact force used to form the Morse taper coupling between the insert  104  and the stem  102  is passed through the coupler  106 . Because the axis of the coupler  106  may not be aligned with the axis  176  of the insert  104 , forming the Morse taper coupling applies a torque to the coupler  106  tending to change the alignment of the coupler  106 . Since the insert  104  and the coupler  106  may be coupled using a force higher than the force used to form a Morse taper coupling, however, passing the force necessary to couple the insert  104  to the stem  102  through the coupler  106  does not significantly change the alignment of the coupler  106  within the tapered bore  126 . 
     In the event the axis of the tapered bore  154  of the articulating head component  108  is desired to be parallel with the axis of the tapered bore  116 , the coupler  106  and insert  104  need not be used. Rather, the insert  230  shown in  FIGS. 27 and 28  may be used. The insert  230  includes an upper tapered wall portion  232  and a lower tapered wall portion  234 . A bore  236  extends from the upper surface  238  of the insert  230  to a threaded bore  240 . 
     The upper tapered wall portion  232  is configured with a taper that provides a Morse taper coupling with the tapered bore  154  while the lower tapered wall portion  234  is configured with a taper that provides a Morse taper coupling with the tapered bore  116 . The insert  230  may thus be used to couple the articulating head component  108  with the stem  102  as shown in  FIG. 28  wherein the insert  230  is coupled with the tapered bore  116  at a location above the key member  128 . 
     The humeral prosthesis assembly  100  is thus a modular system that can be used to provide a number of different orientations of an articulating head component with respect to a stem. Accordingly, a kit including stems  102  of different lengths, at least one insert  104 , at least one coupler  106 , at least one insert  230 , and a removal tool  200  provides a highly adaptable system that can accommodate a wide range of joint constructs. 
     Additional removal systems may be provided in a kit for use with the humeral prosthesis assembly  100 . By way of example, a removal tool  250  shown in  FIG. 30  may be used to decouple the insert  104  and the insert  230  from the stem  102 . The removal tool  250  includes a base  252  and a shaft  254 . Two prongs  256  and  258  extend outwardly from the base  252  and an impact knob  260  is located on the shaft  254 . The prongs  256  and  258  are similar to the prongs  206  and  208 . The prongs  256  and  258 , however, are much thicker than the prongs  206  and  208 . 
     The removal tool  250  is configured to work with a decoupler  262  shown in  FIG. 31 . The decoupler  262  includes a flange  264  and a stem  266 . The stem  266  includes a threaded portion  268 . Removal of the insert  104  is accomplished by insertion of the threaded portion  268  of the decoupler  220  into the threaded bore  128  as shown in  FIG. 32 . The prongs  256  and  258  are then positioned between the flange  264  and the upper surface  114  of the stem  102 . Once positioned, the impact knob  260  is impacted. The force of the impact is transferred through the inclined surfaces of the tapered prongs  256  and  258  to the flange  264  forcing the insert  104  away from the stem  102 . 
     Decoupling of the insert  230  is accomplished in a similar manner as the threaded portion  268  of the decoupler  220  is threaded into the threaded bore  240  as shown in  FIG. 33 . The prongs  256  and  258  are then positioned between the flange  264  and the upper surface  114  of the stem  102 . Once positioned, the impact knob  260  is impacted. The force of the impact is transferred through the inclined surfaces of the tapered prongs  256  and  258  to the flange  264  forcing the insert  230  away from the stem  102 . 
     If desired, a different removal tool may be provided for use with each of the inserts  104  and  230 . Moreover, other devices may be used to provide an impact to the flange  264 . 
     Although the present invention has been described with respect to certain preferred embodiments, it will be appreciated by those of skill in the art that other implementations and adaptations are possible. Moreover, there are advantages to individual advancements described herein that may be obtained without incorporating other aspects described above. Therefore, the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein.