Abstract:
Methods and devices are disclosed for joint (e.g., shoulder) arthroplasty. In one aspect, there is provided a device for determining inclination and/or version of a prosthetic head with respect to a prosthetic stem. In another aspect, there is provided a joint (e.g., shoulder) prosthesis. In another aspect, there is provided a method for setting an inclination angle and/or a version angle of a prosthetic head with respect to a stem implanted or to be implanted in a bone of a joint (e.g., shoulder).

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. patent application Ser. No. 61/774969 filed Mar. 8, 2013. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
       [0002]    Not Applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The invention relates to a prosthesis and method for variable inclination and/or version of the humeral head component for shoulder arthroplasty, glenosphere for the shoulder, radial head for the elbow, or femoral head for hip arthroplasty. 
         [0005]    2. Description of the Related Art 
         [0006]    Various prostheses for the replacement of the shoulder joint are known. In one example shoulder prosthesis, the upper portion of the humerus is replaced by a humeral component including (i) a stem, or cleat, that extends into a bore formed within the humerus and (ii) a generally hemispherical head portion that is connected to the stem. The hemispherical head of the humeral component articulates with a complementary concave section of a glenoid component mounted within the glenoid cavity of the scapula. This type of shoulder prosthesis may be called a “primary” or “total” prosthesis. In another example shoulder prosthesis, often called a hemiarthroplasty, a hemispherical head of the humeral component articulates with the native glenoid. In another example shoulder prosthesis, often called a “reverse” or “inverted” prosthesis, the glenoid component includes a convex section that articulates with a complementary concave section of the head of the humeral component. 
         [0007]    There has been demonstrated to be a significant theoretical as well as practical need to have variable inclination of the humeral component in shoulder arthroplasty. This has been demonstrated in strong marketplace acceptance as well as a clear demand for this feature in shoulder arthroplasty. Elbow and hip arthroplasty shares a similar need for variable adjustments. In addition, there is a future trend toward patient specific instrumentation in shoulder, elbow, and hip arthroplasty. Variable inclination would be a very desirable, if not necessary, component of any shoulder arthroplasty system to allow the surgeon to exactly match the inclination chosen for the humeral head component on the pre-operative plan and to match the instrumentation for that individual patient. 
         [0008]    However, a review of competitive systems in the marketplace reveals that the range of inclination provided by these systems does not properly address the range of humeral head component inclination encountered at the time of shoulder arthroplasty. In addition, many of the ranges provided by shoulder arthroplasty systems are not physiologic and may result in significant component malposition. The range of inclination in currently available systems appears randomly chosen without a true anatomic basis. 
         [0009]    In addition to a lack of understanding of the proper range of inclination necessary for a humeral component, the method to achieve this inclination has associated challenges. There are several potential strategies to change the inclination of the humerus available in the marketplace. Each of these methods has disadvantages. 
         [0010]    One can manufacture a variety of humeral stems that have a fixed amount of inclination. However, this can result in a significant increase in inventory requiring multiple stem inclinations for a wide breadth of stem diameters. 
         [0011]    In one alternative method, a set screw can be used within the stem to lock in the inclination angle of the humeral component. This can make the set screw the “weak link” in the design and could be problematic during attempted removal. 
         [0012]    In another alternative method, one can use a screw through a lateral opening in the humeral stem and into the humeral head component to fix the amount of inclination. This can result in making humeral head component removal impossible without removing the humeral stem. This system may be used without the set screw; however, the manufacturer recommends impacting the head and stem together prior to insertion in the humerus. However, the lateral opening in the humeral stem remains, making removal of the humeral stem much more difficult used with cement. 
         [0013]    In yet another alternative method, complex assembly can be performed with a locking mechanism connecting the humeral stem and humeral head component requiring more than ten steps. This method also does not allow one to place the stem in the humeral canal independent of the humeral head component. This decreases the ability to place sutures in the rotator interval and may have an effect on stability and outcome. 
         [0014]    Thus, there exists a need for an improved prosthesis and method that provide for variable inclination and/or version of the humeral head component in shoulder arthroplasty, as well as a need for variability in elbow and hip arthroplasty. 
       SUMMARY OF THE INVENTION 
       [0015]    The present invention addresses the foregoing needs by providing improved methods and devices for joint (e.g., shoulder) arthroplasty. There is provided a joint (e.g., shoulder) prosthesis. There is also provided a device for determining inclination and/or version of a prosthetic head with respect to a prosthetic stem, There is also provided a method for setting an inclination angle and/or a version angle of a prosthetic head with respect to a stem implanted or to be implanted in a bone of a joint (e.g., shoulder). 
         [0016]    In one aspect, the invention provides a joint prosthesis including a stem dimensioned to be implanted in a first bone of a joint of a subject; a prosthetic head having an outer surface dimensioned for articulation with an articular surface of a natural or artificial joint surface of a second bone of the joint; an adapter dimensioned to be impacted into a depression in an end surface of the prosthetic head opposite the outer surface of the prosthetic head thereby forming an interference fit between the adapter and the depression; and a mounting stud having a first end and a second end wherein the first end is dimensioned for impaction into a socket in the adapter thereby forming an interference fit between the first end and the socket, and the second end is dimensioned for insertion into an opening in the stem. 
         [0017]    In one version of the joint prosthesis, the second end of the mounting stud is dimensioned for impaction into the opening in the stem thereby forming an interference fit between the second end and the stem. 
         [0018]    In another version of the joint prosthesis, the first end of the mounting stud includes a spherical surface. The spherical surface of the first end of the mounting stud can be rotated in the socket to set inclination and/or version of the head with respect to the stem before forming the interference fit between the first end of the mounting stud and the socket. 
         [0019]    In another version of the joint prosthesis, the second end of the mounting stud includes an outer surface that tapers inward from an intermediate section to an outermost section of the second end of the mounting stud. 
         [0020]    In another version of the joint prosthesis, the mounting stud includes circumferential reference indicia at or adjacent a junction of the spherical surface of the first end of the mounting stud and the outer surface of the second end of the mounting stud. 
         [0021]    In another version of the joint prosthesis, a longitudinal axis of the second end of the mounting stud forms an oblique angle with respect to an axis of the prosthetic head when the interference fit is formed between the first end and the socket. 
         [0022]    In another version of the joint prosthesis, the socket of the adapter is offset with respect to a central longitudinal axis of the adapter. 
         [0023]    in another version of the joint prosthesis, the adapter has a circular outer surface and the depression has a circular inner surface such that the adapter can be rotated in the depression to set radial offset of the head with respect to the stem before forming the interference fit between the adapter and the depression. 
         [0024]    In another version of the joint prosthesis, the head includes at least one first reference marking for alignment with a second reference mark on the adapter. 
         [0025]    The joint prosthesis is suitable for use in different joints. For example, the first bone may be the humerus, and the second bone may be the scapula. The first bone may be the scapula, and the second bone may be the humerus. The first bone may be the femur, and the second bone may be the pelvis. The first bone may be the humerus, and the second bone may be the radius. 
         [0026]    In another aspect, the invention provides a device for determining an inclination and/or a version of a prosthetic head with respect to a stem wherein the inclination and/or the version are used when the prosthetic head is coupled to the stem. The prosthetic head has an outer surface for articulation with an articular surface of a natural or artificial joint surface of a bone of a joint of a subject. The device can include a body having a well; and a joint element having a first end and a second end wherein the first end is positioned in the well, and the second end is movable between positions wherein a longitudinal axis of the second end is angled with respect to an axis of the body. 
         [0027]    One version of the device includes a retainer having an opening extending between a first side and an opposed second side of the retainer wherein the retainer is arranged in the well, and the retainer is dimensioned for translation in the well. The first end of the joint element is dimensioned to be positioned between the body and the first side of the retainer such that the second end of the joint element extends through and outwardly of the opening of the retainer, and the second end of the joint element is dimensioned to be movable between positions where the longitudinal axis of the second end is angled with respect to an axis of the opening of the retainer. The retainer can have an oblong shape with a pair of parallel sides. 
         [0028]    Another version of the device includes a fastener movable between a first position in which the fastener allows the retainer to translate in the well and a second position in which the fastener prevents translation of the retainer in the well. The fastener may be a screw that when in the second position causes the first end of the joint element to be immobilized between the body and the retainer. 
         [0029]    In one version of the device, the first end of the joint element includes a spherical bearing surface, and the second end of the joint element includes an outer diameter that decreases from an intermediate section to an outermost section of the second end of the joint element. The second end of the joint element may be dimensioned to contact an inner surface of an opening in the stem. 
         [0030]    In one version of the device, the body and the retainer include reference markings for determining a positional relationship of the retainer with respect to the body. 
         [0031]    The device is suitable for determining an inclination and/or a version of a prosthetic head with respect to a stem of a prosthesis for different joints. For example, the prosthetic head may articulate with the scapula when the joint is the shoulder. The prosthetic head may articulate with the humerus when the joint is the shoulder. The prosthetic head may articulate with the pelvis when the joint is the hip. The prosthetic head may articulate with the radius when the joint is the elbow. 
         [0032]    In another aspect, the invention provides a method for setting an inclination angle and/or a version angle of a prosthetic head with respect to a stem implanted or to be implanted in a bone of a joint of a subject. The method uses a trial device including (i) a body having a well, and (ii) a joint element having a first end and a second end wherein the first end is positioned in the well, and the second end is movable between positions wherein a longitudinal axis of the second end is angled with respect to an axis of the body. The second end of the joint element is inserted in an opening in the stem, and the joint element is immobilized with respect to the body. A mounting stud is secured to the prosthetic head in a fixed position with respect to the prosthetic head so as to match an orientation of the immobilized joint element with respect to the body. An end of the mounting stud may be secured in the opening in the stem. 
         [0033]    In one version of the method, the trial device further includes a retainer arranged in the well, and the first end of the joint element may be immobilized between the body and the retainer. The retainer may be dimensioned for translation in the well, and the method may comprise preventing translation of the retainer in the well. A fastener may be movable into a position in which the fastener prevents translation of the retainer in the well. 
         [0034]    In another version of the method, a template is placed over the immobilized joint element, and a position of a reference line on the template with respect to a first reference point on the body is noted. The template is then placed over the mounting stud, and the reference line is aligned with a second reference point on the prosthetic head. The mounting stud is then secured to the prosthetic head in the fixed position with respect to the prosthetic head. The template may include an opening, and the opening may be placed over the immobilized joint element before noting the position of the reference line on the template with respect to the first reference point on the body. The opening may be placed over the mounting stud before aligning the reference line with the second reference point on the prosthetic head. 
         [0035]    In another version of the method, the mounting stud can be moved to a first angle with respect of the prosthetic head before the mounting stud is secured to the prosthetic head in the fixed position. The first angle is about the same (e.g., ±20°, or ±10°, or ±5°) as a second angle of the immobilized joint element with respect to the body. The first angle can be determined using a first reference circle surrounding the mounting stud, and the second angle can be determined using a second reference circle surrounding the joint element. The first angle can be determined using a first reference circle surrounding the mounting stud and a reference line on the template, and the second angle can be determined using a second reference circle surrounding the joint element and the reference line on the template. 
         [0036]    The method is suitable for setting an inclination angle and/or a version angle of a prosthetic head with respect to a stem implanted or to be implanted in a bone of various joints of a subject. The bone can be the scapula, and the joint can be the shoulder. The bone can be the humerus, and the joint can be the shoulder. The bone can be the femur, and the joint can be the hip. The bone can be the humerus, and the joint can be the elbow. 
         [0037]    In one non-limiting embodiment, it is an advantage of the invention to use a humeral head assembly with a taper to set the inclination/version of a shoulder prosthesis. This construct allows for the use of a pre-existing stem design. The variable inclination is a part of the humeral head assembly. The use of a taper within the humeral head assembly provides the ability to not only change humeral inclination but also humeral version. This eliminates the need to create a separate humeral stem to allow adjustment for inclination and version. A taper of the humeral head assembly has the ability to rotate and then lock in place at the desired inclination/version in the humeral head. This allows the surgeon to maximize intraoperative flexibility by using one stem design to achieve the desired amount of inclination and version. This has the benefit of decreasing humeral component inventory and allows changing humeral inclination/version without removing the stem. 
         [0038]    The proper range of inclination can be established with patient studies in order to properly define the range of inclination that will accommodate patients. This can facilitate the accurate and efficient design of a variable inclination system to determine the exact range of inclination that is necessary for the system. 
         [0039]    Adjustment of humeral inclination has become a clear need in the shoulder arthroplasty marketplace. Significant deficiencies have become recognized in the currently available systems including a range of inclinations that are not based on the anatomic distribution. Moreover, the currently available systems used to create variable inclination have significant technical drawbacks. Therefore, the method of the invention has been designed to address these significant market needs. In addition, applications that may benefit from similar adjustability include the glenosphere of the shoulder, radial head of the elbow, femoral head of the hip, and the like. 
         [0040]    These and other features, aspects, and advantages of the present invention will become better understood upon consideration of the following detailed description, drawings, and appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0041]      FIG. 1  is a cross-sectional view of a conventional shoulder prosthesis. 
           [0042]      FIG. 2  is an anterior view, partially in cross section, of one embodiment of a shoulder prosthesis according to the invention. 
           [0043]      FIG. 3  is a view of the shoulder prosthesis of  FIG. 2 , taken along line  3 - 3  of  FIG. 2 . 
           [0044]      FIG. 4  is a bottom view of a trial head assembly used in implanting a shoulder prosthesis according to the invention. 
           [0045]      FIG. 5  shows a template and components of a humeral head assembly kit of a shoulder prosthesis according to the invention. 
           [0046]      FIG. 6  is a top perspective view of a step in assembling a humeral head assembly of a shoulder prosthesis according to the invention. 
           [0047]      FIG. 7  is a top view of a step, subsequent to  FIG. 6 , in assembling a humeral head assembly of a shoulder prosthesis according to the invention. 
           [0048]      FIG. 8  is a top perspective view of a step, subsequent to  FIG. 7 , in assembling a humeral head assembly of a shoulder prosthesis according to the invention, 
           [0049]      FIG. 9  is a top perspective view of a step, subsequent to  FIG. 8 , in assembling a humeral head assembly of a shoulder prosthesis according to the invention. 
       
    
    
       [0050]    Like reference numerals will be used to refer to like parts from Figure to Figure in the following description of the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0051]    Looking first at  FIG. 1 , there is shown an example conventional shoulder prosthesis  10 . The upper portion of the humerus  12  is replaced by a humeral component  14  including a stem  16  that extends into a bore formed within the humerus  12 . Typically, the stem  16  is fixed within the bore formed within the humerus  12 . The stem  16  has a longitudinal stem axis S. A generally hemispherical head  18  is connected to the stem  16 . Alternatively, the head  18  is integral with the stem  16 . The hemispherical head  18  has a base surface  19  and a longitudinal head axis H. The hemispherical head  18  of the humeral component  14  articulates with a complementary concave section  22  of a glenoid component  24  that is fixed within the glenoid cavity of the scapula  26  using cemented or uncemented posts  28 . The glenoid component  24  includes a base surface  27  opposite the concave section  22  that serves as an articular surface of the glenoid component  24 . 
         [0052]    Referring now to  FIGS. 2-3 , there is shown an example embodiment of a shoulder prosthesis according to the invention. The humeral component  34  includes a stem  36  that extends into a bore formed within the humerus  12 . The stem  36  has a longitudinal stem axis S. A humeral head assembly  37  has a generally hemispherical head  38 . The humeral head assembly  37  is connected to the stem  36 . The outer surface  41  of the hemispherical head  38  of the humeral component  34  articulates with a complementary concave section  22  of a glenoid component  24  that is fixed within the glenoid cavity of the scapula  26  as shown in  FIG. 1 . In the humeral head assembly  37 , the head  38  includes a depression  43  that receives an adapter  46  having a body  47  with a socket  48  that is eccentric, i.e., the central axis of the socket  48  is offset from the central axis of the body  47 . The humeral head assembly  37  also includes a mounting stud  51  having a first end  53  with a spherical bearing surface  54  and a second end  56  comprising a tapered shaft  57 . The first end  53  of the mounting stud  51  is secured in the socket  48  of the adapter body  47  by way of an interference fit formed by impacting the mounting stud  51  in the socket  48 . The second end  56  of the mounting stud  51  is secured in a stem opening  61  of the stem  36  by way of a taper lock formed by impacting the mounting stud  51  in the stem opening  61 . 
         [0053]    The parts of the humeral component  34  may be formed from, for example: (i) a metal or metal alloy such as a titanium alloy (e.g., titanium-6-aluminum-4-vanadium), a cobalt alloy, a stainless steel alloy, or tantalum; (ii) a nonresorbable ceramic such as aluminum oxide or zirconia; (iii) a nonresorbable polymeric material such as polyethylene; or (iv) a nonresorbable composite material such as a carbon fiber-reinforced polymers (e.g., polysulfone). The prosthetic component can be manufactured by machining an article formed from these materials, or by molding these materials in a suitable mold. 
         [0054]    In  FIG. 2 , taking the included angle in an anterior view between stem axis S and head axis H in degrees and subtracting from 180° is one way to define the inclination angle A inclination  of the humeral head  38  in degrees. The inclination angle of the humeral head  38  can be adjusted to have a selected angle between the longitudinal head axis H and the longitudinal stem axis S by assembling the humeral head assembly  37  with the socket  48  of the adapter body  47  in a selected position with respect to the head  38  and with the mounting stud  51  in a selected orientation in the socket  48  of the adapter body  47  as described below. 
         [0055]    In  FIG. 3 , taking the included angle in a medial view between stem axis S and head axis H in degrees is one way to define the version angle A version  of the humeral head  38  in degrees. The version angle of the humeral head  38  can be expressed as a positive or negative angle with respect to the stem axis S. The version angle of the humeral head  38  can be adjusted to have a selected positive or negative angle between the longitudinal head axis H and the longitudinal stem axis S by assembling the humeral head assembly  37  with the socket  48  of the adapter body  47  in a selected position with respect to the head  38  and with the mounting stud  51  in a selected orientation in the socket  48  of the adapter body  47  as described below. 
         [0056]    Referring now for  FIGS. 4-9 , a surgeon can implant the humeral component  34  so that the humeral component  34  articulates with a complementary concave section  22  of a glenoid component  24 . The fixing of the glenoid component  24  within the glenoid cavity of the scapula  26  can be done in a conventional manner. A method of the invention uses a trial head assembly  63  (see  FIG. 4 ). A trial head assembly  63  is prepared, and then the orientation of the adapter  46  and the mounting stud  51  of the humeral head assembly  37  are matched to the trial head assembly  63 . 
         [0057]    The trial head assembly  63  includes a body  65 . Looking at  FIG. 4 , one side of the body  65  has an generally oblong shaped well  66  with offset markings  67  (A,B,C,D,E) on parallel side sections of the well  66 . Opposite the side of the body  65  having the well  66 , there is a side of the body  65  that has a generally hemispherical surface identical or substantially similar to the outer surface  41  of the hemispherical head  38  of the humeral component  34 . A retainer  69  can slide in the well  66  of the body  65  as shown at L in  FIG. 4 . In the trial head assembly  63 , set screws  70  can lock the position of the retainer  69  in the well  66 . The oblong shape of the well  66  may prevent the retainer  69  from rotating within the well  66  while set screws  70  are tightened (similarly, pins, and the like, may be used that slide along tightly-clearanced slots to prevent rotation of the retainer  69 ). The retainer  69  has an opening  71 , and cross hair markings  72 . A ball joint element  75  of the trial head assembly  63  has a first end  77  with spherical bearing surface  78  and a second end  79  in the shape of a tapered shaft  80 . The second end  79  of the ball joint element  75  protrudes outwardly through the retainer opening  71 , and the first end  77  of the ball joint element  75  is positioned between the retainer  69  and the surface of the well  66 . When the set screws  70  are tightened, the second end  79  of the ball joint element  75  is secured by contact with a surface of the retainer  69  and the surface of the well  66 . Three concentric reference circles  81  surround the ball joint element  75  near the junction of the spherical bearing surface  78  and the tapered shaft  80 . 
         [0058]    Shown in  FIG. 5  is a transparent template  82  that can be used to match the orientation of the components of the humeral head assembly  37  and the trial head assembly  63 . The template  82  has an opening  83 , reference lines  84 , and cross hair markings  85 . The template  82  may take other forms, such as a platform with a non-marring, low-friction surface for the head to rest upon while it is being rotated to its maximum offset, while still retaining an opening  83 , and reference lines  84 . 
         [0059]    Preparing the trial head assembly  63  begins with ensuring that the two set screws  70  on the trial head assembly  63  are loose. One verifies that the ball joint element  75  rotates freely in all directions and the retainer  69  slides freely in the well  66 . The stem  36  is fixed within a bore formed within the humerus  12  (see  FIG. 2 ). The second end  79  of the ball joint element  75  is then seated in the stem opening  61  of the stem  36  which has been implanted in the humerus  12  of a patient. The body  65  of the trial head assembly  63  is adjusted to the desired radial offset, inclination and/or version in the patient, and the two set screws  70  are tightened to lock the offset and the angle of the ball joint element  75  of the trial head assembly  63 . The set screws  70  are accessible on a side of the body  65  opposite the retainer  69 . The trial head assembly  63  is then removed from the stem  36 . 
         [0060]    The trial head assembly  63  is then turned upside-down such that the retainer  69  and the ball joint element  75  are visible to the surgeon as in  FIG. 4 . The surgeon notes the four cross-hair markings  72  on the surface of the retainer  69 , ninety degrees apart. The offset is indicated by the position of the vertical markings of the cross hair markings  72  of the retainer  69  relative to the A, B, C, D, and E offset markings  67  on the body  65 . The surgeon also notes a reference angle indicated by the concentric reference circles  81  on the ball joint element  75 . In the non-limiting example configuration shown, there are three concentric reference circles  81  present on the ball joint element  75 , which can be of different colors such as black, red, and blue. The reference angle is read by noting the position of the concentric reference circles  81  at the location where one of the cross-hair markings  72  would intersect the inner opening  71  circumference of the retainer  69 . By noting the position of the concentric reference circles  81  at two of these orthogonal locations (i.e., two adjacent cross-hair markings  72 ), the reference angle is fully characterized. 
         [0061]    The humeral head assembly  37  is assembled to match the orientation of the ball joint element  75  in the trial head assembly  63 . The adapter  46  is inserted into the head  38 , and the adapter  46  is rotated so that the offset reference markings  44  on the head  38  align with the appropriate offset reference mark  49  on the adapter  46 . See  FIG. 6 . 
         [0062]    Still referring to  FIG. 6 , an impactor  88  is then used in the method of the invention. The impactor  88  has a round fiat end surface  89 , a first side wall  90  with an end surface  91 , and a second side wall  92  with an end surface  93 . The end surfaces  91 ,  93  of the impactor  88  are placed on top of adapter  46 , and a mallet is used to strike the fiat end surface  89  of the impactor  88  to seat the adapter  46  inside the depression  43  of the head  38 . 
         [0063]    Looking at  FIG. 7 , the first end  53  of the mounting stud  51  is placed vertically onto the socket  48  of the adapter  46 , and the mounting stud  51  is pressed down using just enough force to barely seat it. The socket  48  may also be lined with a material, such as rubber, that may act to hold the stud  51  in place. The opening  83  of the transparent template  82  is placed over the second end  56  of the mounting stud  51 , and the reference lines  84  of the template  82  are used to align the maximum offset direction of the head  38  with the maximum offset direction of the body  65  of the trial head assembly  63 . The template  82  is removed, noting its position relative to the head  38 .  FIG. 7  shows how the trial head assembly  63  can be located adjacent the humeral head assembly  37  during assembly for reference. 
         [0064]    Turning to  FIG. 8 , an impactor ring  95  having an aperture  96  is placed over the mounting stud  51 , and rotated so the impactor ring  95  aligns with the indexing features of the adapter  46 . As noted above, the stud  51  should not change orientation during assembly, and the impactor ring  95  may be lined with a material, such as rubber, to prevent motion. The impactor ring  95  is pushed into the pocket of the adapter  46 . The template is re-placed over the mounting stud  51  in the same position as when the template  82  was removed. The cross-hair markings  85  on the transparent template  82  are referenced, and the mounting stud  51  is moved to the same angle of the ball joint element  75  of the trial head assembly  63  using concentric reference circles  59  which surround the mounting stud  51  near the junction of the spherical bearing surface  54  and the tapered shaft  57  of the mounting stud  51 . The template  82  is then removed. 
         [0065]    Looking at  FIG. 9 , the angle of the mounting stud  51  of the head  38  and the ball joint element  75  of the trial head assembly  63  are visually compared by looking at them horizontally from two orthogonal directions. If the angles match acceptably, one gently pushes down on the impactor ring  95 , applying even pressure around the mounting stud  51 . The impactor ring  95  holds the mounting stud  51  at the correct angle during the subsequent steps. One then visually re-confirms that the angle of the mounting stud  51  of the humeral head assembly  37  is still acceptable. 
         [0066]    The impactor  88  is positioned concentric with the impactor ring  95  with the end surfaces  91 ,  93  of the impactor  88  contacting the impactor ring  95 . One uses downward pressure to hold the impactor  88  in place with one hand, and then one strikes the end surface  89  of the impactor  88  with a mallet. This pushes down the impactor ring  95 , which in turn drives the mounting stud  51  into an interference fit with the socket  48  of the adapter  46 . The interference fit may be enhanced by modifying the surfaces of either the mounting stud  51 , or the socket  48 , by abrasive blasting, roughening the surfaces, cutting rough machining lines, or adding sharp blade-like structures to engage the opposing surface, and the like, or otherwise modifying the shape of either the mounting stud  51  or the socket  48 . The mounting stud  51  is fully seated when the top surface of the impactor ring  95  is approximately flush with the top surface of the adapter  46 . One then visually re-confirms that the angle of the mounting stud  51  of the humeral head assembly  37  is still acceptable. 
         [0067]    The impactor ring  95  can be removed by pinching two tabs  97  with the thumb and index finger and pulling upward. The humeral head assembly  37  is now ready for implantation. The second end  56  of the mounting stud  51  of the humeral head assembly  37  is secured in a stem opening  61  of the stem  36 . Seating the humeral head assembly  37  in the humeral stem  36  using a mallet further seats the assembled components together as in  FIG. 2 , 
         [0068]    Thus, the invention provides an improved prosthesis and method that provide for variable inclination and/or version and/or offset of the humeral head component in shoulder arthroplasty. While a human cadaveric validation has been done with respect to the methods and the shoulder arthroplasty components, the method could be used for other joints (e.g., hip, knee, elbow, foot, ankle, etc.). 
         [0069]    Although the present invention has been described in detail with reference to certain embodiments, one skilled in the art will appreciate that the present invention can be practiced by other than the described embodiments, which have been presented for purposes of illustration and not of limitation. Therefore, the scope of the appended claims should not be limited to the description of the embodiments contained herein.