Abstract:
Methods and devices are disclosed for the optimization of shoulder arthroplasty component design through the use of computed tomography scan data from arthritic shoulders.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is a divisional application of U.S. patent application Ser. No. 14/300,805 filed Jun. 10, 2014, which is a continuation-in-part of U.S. patent application Ser. No. 13/818,738 filed Feb. 25, 2013 which is a 371 application of PCT/US11/049686 filed Aug. 30, 2011 which claims priority from U.S. Provisional Patent Application No. 61/379,222 filed Sep. 1, 2010, and U.S. Provisional Patent Application No. 61/379,634 filed Sep. 2, 2010. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
       [0002]    Not Applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The invention relates to a method for the optimization of joint arthroplasty component design, and more particularly to a method for the optimization of shoulder arthroplasty component design through the use of computed tomography scan data. 
         [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 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 “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]    One alternative to total shoulder replacement is referred to as shoulder hemiarthroplasty. In one version of this procedure, the humeral head is replaced with a generally hemispherical head that may or may not include a connected stem. The glenoid cavity of the scapula is not replaced with a glenoid component, but may be refinished in a way that gives it a smooth surface and a shape which matches the generally hemispherical replacement head. Another version of this procedure can use a glenoid component with resurfacing of the humeral head. 
         [0008]    Several deficiencies have been found in currently available shoulder arthroplasty systems including glenoid sizes (primary and reverse) and humeral sizes that are not based on the anatomic distribution. In addition, the advent of reverse arthroplasty for the treatment of proximal humerus fractures has also changed the requirements for an appropriate fracture stem. Specific design features are necessary to make the fracture stem appropriate for hemiarthroplasty and reverse arthroplasty use. Although resurfacing of the humerus has become popular, the designs are not based on an anatomic distribution. The instrumentation that is currently available is inadequate and may lead to significant malposition in version and inclination. 
         [0009]    Prior magnetic resonance imaging and cadaveric studies of glenohumeral anatomy have been performed on shoulders without arthritis (Iannotti et al., “The normal glenohumeral relationships. An anatomical study of one hundred and forty shoulders”,  J Bone Joint Surg Am.  1992; 74:491-500; Hertel et al., “Geometry of the proximal humerus and implications for prosthetic design”,  J Shoulder Elbow Surg.,  July/August 2002, pp. 331-338; and Boileau et al., “The Three-Dimensional Geometry Of The Proximal Humerus—Implications For Surgical Technique And Prosthetic Design”,  J Bone Joint Surg  [Br], 1997; 79-B:857-865). However, in reality, shoulder arthroplasty is not performed on normal shoulders. Shoulder arthroplasty is performed in patients with arthritis in the setting of cartilage loss and usually associated bone loss. In order to make properly sized implants that will accommodate patients with arthritis, it is important to understand the anatomy of these patients. 
         [0010]    Typically, the designing surgeon has used a system with three glenoid sizes. In one study, it was determined that the distribution of glenoid components used in total shoulder arthroplasty was as follows: 4% large, 40% medium, and 56% small. One can see that based on component use, the sizing of these implants is not optimal. If glenoid component sizes are not optimal, there may be issues related to perforation of the glenoid by fasteners used in attaching the glenoid component to the scapula. In addition, certain components may be too large for smaller patients resulting in component overhang and potentially leading to violation of important neurovascular structures. Thus, it could be hypothesized that the preference for small glenoid components may result from the desire to avoid glenoid perforation and/or avoid component overhang. However, larger glenoid components can lead to a better fitting prosthesis and greater stability. 
         [0011]    There has been increasing interest in the use of augmented glenoid components in shoulder arthroplasty. Bone graft has been used in the past to manage bone deficiency; however there has been a high rate of graft resorption. It has also been clearly recognized that removal of the remaining hard cortical bone to create a neutral surface can compromise fixation by leaving the surgeon with only soft cancellous bone resulting in insufficient implant support for certain patients. In addition, excess reaming results in medialization and shortening the remaining rotator cuff lever arm with functional implications. Therefore, there has been increasing interest in the use of augmented glenoid components. 
         [0012]    In  FIG. 5A , one example augmented glenoid component  102  for use in a total shoulder system is shown. The glenoid component  102  has a single component plastic body  104 . A concave articular surface  105  of the body  104  provides a smooth bearing surface for the head portion of the humeral component implanted into the humerus. The thickness of the plastic body  104  gradually increases from an anterior edge  106  to a posterior edge  108  thereof thereby creating a relatively smooth, arcuate-shaped medial base surface  110  from which a number of posts or pegs  112  extend. It can be seen that the augmented glenoid component  102  has an augment that has a defined slope along the entire posterior surface of the glenoid. An augment thickness can be defined as the thickness of the posterior edge  108  minus the thickness of the anterior edge  106 . 
         [0013]    In  FIG. 5B , another example augmented glenoid component  114  for use in a total shoulder system is shown. The augmented glenoid component  114  includes a body  116  having a concave articular surface  118  on one end thereof. The concave surface  118  of the body  116  provides a smooth bearing surface for the head portion of the humeral component implanted into the humerus. The body  116  includes a step  120  on or from a body surface  122  opposite the concave surface  118 . The step  121  forms a portion of the posterior edge  121  of the body  116 . The augmented glenoid component  114  also includes an anchor peg  123  and a plurality of stabilizing posts pegs  124 . It can be seen that the augmented glenoid component  114  has an augment that is a step on the posterior aspect of the glenoid. An augment thickness can be defined as the thickness of the posterior edge  121  minus the thickness of the anterior edge  117 . 
         [0014]    In  FIGS. 6A and 6B , an example augmented glenoid component  130  for use in a reverse shoulder system is shown. The glenoid component  130  includes a baseplate  132  in which the thickness of the baseplate  132  gradually increases from a first edge  133  to an opposite second edge  134  thereof. The baseplate  132  has a surface  136  from which a peg  138  extends. The baseplate  132  is secured in a glenosphere  139  forming the glenoid component  130 . The glenosphere  139  has an convex articular surface  137  that provides a smooth bearing surface for the concave articular portion of the humeral component implanted into the humerus. An augment thickness can be defined as the thickness of the second edge  134  minus the thickness of the first edge  133 . 
         [0015]    In  FIGS. 6C and 6D , another example augmented glenoid component  130 A for use in a reverse shoulder system is shown. The glenoid component  130 A includes a baseplate  132 A in which the thickness of the baseplate  132 A gradually increases from a first edge  133 A to an approximately central section and then the thickness is approximately constant to an opposite second edge  134 A thereof. The baseplate  132 A has a surface  136 A from which a peg  138 A extends. The baseplate  132 A is secured in a glenosphere  139 A forming the glenoid component  130 A. The glenosphere  139 A has an convex articular surface  137 A that provides a smooth bearing surface for the concave articular portion of the humeral component implanted into the humerus. An augment thickness can be defined as the thickness of the first edge  134 A minus the thickness of the second edge  133 A. 
         [0016]    However, significant deficiencies have been found in currently available augmented glenoid components that are not based on an anatomic distribution. The currently available commercial designs for augmented glenoids are not designed based on the specific dimensions of glenoid bone loss present in patients undergoing shoulder arthroplasty. In order to make properly sized augmented glenoid components that will accommodate patients with arthritis, it is important to understand the anatomy of these patients. One issue that continues to be raised is that no one has ever defined on average where this transition zone begins between native bone and worn bone. This would allow one to design an augment that is shaped according to the defects that actually exist and covers the appropriate amount of glenoid worn rather than being based on guesswork. Ideally, to design proper augmented glenoids one needs to define the bone loss based on the anatomy of patients actually undergoing shoulder arthroplasty. In order to make properly sized augmented glenoid components that will accommodate patients with arthritis, it is important to understand the anatomy of these patients. 
         [0017]    Thus, there exists a need for a method for the optimization of joint arthroplasty component design, and in particular, there exists a need for a method for the optimization of shoulder arthroplasty component design. 
       SUMMARY OF THE INVENTION 
       [0018]    The present invention addresses the foregoing needs by providing methods for the optimization of joint arthroplasty component design. 
         [0019]    In one aspect, the invention provides a method for manufacturing a prosthetic component for replacing a part of a bone of a joint in a subject. The method comprises: (a) obtaining an axial image of the bone of the joint; (b) orienting on the image a reference angle from a body of the bone to create a neutral face plate line that extends from a first border of the bone to an opposite second border of the bone; (c) measuring a length of the neutral face plate line; and (d) manufacturing the prosthetic component to include a base surface and an opposed articular surface wherein a width of the base surface is a predetermined percentage of the length of the neutral face plate line. For example, the width of the base surface may be the same or less than the length of the neutral face plate line. 
         [0020]    In another aspect, the invention provides a method for manufacturing a prosthetic component for replacing a part of a bone of a joint in a subject. The method comprises: (a) obtaining an axial image of the bone of the joint; (b) orienting on the image a reference angle from a body of the bone to create a neutral face plate line that extends from a first border of the bone to an opposite second border of the bone; (c) orienting on the image a first reference line perpendicular to the neutral face plate line and extending over the bone in the image; (d) measuring a first reference length of the first reference line from the neutral face plate line perpendicular to a depth of a cavity in the bone; and (e) manufacturing the prosthetic component to include an articular section and a projection extending away from the articular section wherein a length of the projection is a predetermined percentage of the first reference length. For example, the length of the projection is typically less than the first reference length. 
         [0021]    In another aspect, the invention provides a method for manufacturing a glenoid component for replacing a part of a scapula of a shoulder joint in a subject, the method comprises: (a) obtaining a sagittal image of the glenoid of the scapula; (b) orienting on the image a first reference line that extends perpendicularly from an inferior border of the glenoid image over the scapula in the image; (c) orienting on the image a second reference line that perpendicularly intersects the first reference line and that extends from a first border of the scapula to an opposite second border of the scapula; (d) measuring a length of the second reference line; and (e) manufacturing the glenoid component to have a width that is a predetermined percentage of the length of the second reference line. For example, the width of the glenoid component may be the same or less than the length of the second reference line. 
         [0022]    In another aspect, the invention provides a method for manufacturing a prosthetic component for replacing a part of a bone of a joint in a subject. The method comprises: (a) obtaining a coronal image of the bone of the joint; (b) orienting on the image a first reference line that extends from a first border of a head of the bone to an opposite second border of the head of the bone; (c) orienting on the image a 90 degree reference angle from an inferior position of the first reference line to create a second reference line that extends over the image of the bone; (d) orienting on the image a third reference line that extends over the image of the bone from the second reference line to a superior aspect of a tuberosity of the bone; (e) measuring a length of the third reference line; and (f) manufacturing the prosthetic component to include a protruding section wherein a length of the protruding section is a predetermined percentage of the length of the reference line. 
         [0023]    In another aspect, the invention provides a method for manufacturing a prosthetic component for replacing a part of a bone of a joint in a subject. The method comprises: (a) obtaining a coronal image of the bone of the joint; (b) orienting on the image a first reference line that extends from a first border of a head of the bone to an opposite second border of the head of the bone; (c) orienting on the image a ninety degree reference angle from an inferior position of the first reference line to create a second reference line that extends over the image of the bone; (d) orienting on the image a third reference line that extends over the image of the bone from the second reference line to a superior border of a tuberosity of the bone; (e) orienting on the image a fourth reference line that extends over the image of the bone from the third reference line to a side border of the tuberosity of the bone; (f) measuring a length of the fourth reference line; and (g) manufacturing the prosthetic component to include a protruding section wherein a diameter of the protruding section is a predetermined percentage of the length of the fourth reference line. 
         [0024]    In another aspect, the invention provides a method for manufacturing a prosthetic component for replacing a part of a bone of a joint in a subject. In the method, the prosthetic component is formed to include a base surface and an opposed articular surface wherein a width of the base surface is a predetermined percentage of a length of a neutral face plate line. The length of the neutral face plate line used by the manufacturer in forming the prosthetic component has been determined by (i) obtaining an image of the bone of the joint, (ii) orienting on the image a reference angle from a body of the bone to create the neutral face plate line, wherein the neutral face plate line extends from a first border of the bone to an opposite second border of the bone, and (iii) measuring the length of the neutral face plate line. The predetermined percentage of the length of a neutral face plate line used by the manufacturer in forming the prosthetic component can be 100% or less, 90%-99%, or 80%-99%. The predetermined percentage can be greater than, equal to, or less than 100%, and can take into account a range of data values observed when analyzing a number of images for the measurement of interest. For example, the predetermined percentage can be selected to include any number of standard deviations above a mean of the collected measurement data. The joint can be arthritic. In one form, at least a section of the base surface of the prosthetic component is flat. For example, the base surface of the prosthetic component can be flat around a central post that extends away from the base surface of the prosthetic component. The neutral face plate line can correspond to a width of a flat neutral face plate formed by removing a portion of the bone during arthroplasty. In one version of the method, the bone is the scapula, and the joint is the shoulder. The prosthetic component can be a glenoid component. The image can be a computed tomography scan slice, and the reference angle can be 90 degrees. In one version of the method, the neutral face plate line is a straight line positioned completely within a perimeter of the image of the bone from the first border of the bone to the second border of the bone. At least a section of the straight line is spaced from a portion of the perimeter of the image of the bone, and the portion of the perimeter of the image of the bone represents a natural articular surface of the bone. 
         [0025]    In another aspect, the invention provides a method for manufacturing a prosthetic component for replacing a part of a bone of a joint in a subject. In the method, the prosthetic component is formed to include an articular section and a projection extending away from the articular section wherein a length of the projection is a predetermined percentage of a first reference length. The first reference length used by the manufacturer in forming the prosthetic component has been determined by (i) obtaining an image of the bone of the joint, (ii) orienting on the image a reference angle from a body of the bone to create a neutral face plate line that extends from a first border of the bone to an opposite second border of the bone, (iii) orienting on the image the first reference line, the first reference line being perpendicular to the neutral face plate line and extending over the bone in the image, (iv) measuring the first reference length of the first reference line from the neutral face plate line perpendicular to a depth of a cavity in the bone. The predetermined percentage of the first reference length can be 100% or less, 90%-99%, or 80%-99%. The predetermined percentage can be greater than, equal to, or less than 100%, and can take into account a range of data values observed when analyzing a number of images for the measurement of interest. For example, the predetermined percentage can be selected to include any number of standard deviations above a mean of the collected measurement data. The projection can be a post. In one version of the method, the prosthetic component is formed such that the length of the projection is a predetermined percentage of a second reference length. The second reference length used by the manufacturer in forming the prosthetic component has been determined by (i) orienting on the image a second reference line parallel to the first reference line and extending over the bone in the image, (ii) measuring the second reference length of the second reference line from the neutral face plate line to the depth of a cavity in the bone. In one version of the method, the bone is the scapula, and the joint is an arthritic shoulder, and the prosthetic component is a glenoid component. The image can be a computed tomography scan slice. In one version of the method, the neutral face plate line is a straight line positioned completely within a perimeter of the image of the bone from the first border of the bone to the second border of the bone. At least a section of the straight line is spaced from a portion of the perimeter of the image of the bone, and the portion of the perimeter of the image of the bone represents a natural articular surface of the bone. 
         [0026]    In another aspect, the invention provides a method for manufacturing a glenoid component for replacing a part of a scapula of a shoulder joint in a subject. In the method, the glenoid component is formed to have a width that is a predetermined percentage of a length of a second reference line. The length of the second reference line used by the manufacturer in forming the prosthetic component has been determined by (i) obtaining an image of the glenoid of the scapula, (ii) orienting on the image a first reference line that extends perpendicularly from an inferior border of the glenoid image over the scapula in the image, (ii) orienting on the image the second reference line, the second reference line perpendicularly intersecting the first reference line and extending from a first border of the scapula to an opposite second border of the scapula, and (iii) measuring the length of the second reference line. The predetermined percentage of the length of the second reference line can be 100% or less, 90%-99%, or 80%-99%. The predetermined percentage can be greater than, equal to, or less than 100%, and can take into account a range of data values observed when analyzing a number of images for the measurement of interest. For example, the predetermined percentage can be selected to include any number of standard deviations above a mean of the collected measurement data. The second reference line intersects the first reference line at about 10 to 18 millimeters above the inferior border of the glenoid image. The second reference line preferably intersects the first reference line at about 14 millimeters above the inferior border of the glenoid image. The image can be a computed tomography scan slice. 
         [0027]    In another aspect, the invention provides a method for manufacturing a prosthetic component for replacing a part of a bone of a joint in a subject. In the method, the prosthetic component is formed to include a protruding section wherein a first length of the protruding section is a predetermined percentage of a length of the third reference line. The length of the third reference line used by the manufacturer in forming the prosthetic component has been determined by (i) obtaining an image of the bone of the joint, (ii) orienting on the image a first reference line that extends from a first border of a head of the bone to an opposite second border of the head of the bone, (iii) orienting on the image a 90 degree reference angle from an inferior position of the first reference line to create a second reference line that extends over the image of the bone, (iv) orienting on the image the third reference line, the third reference line extending over the image of the bone from the second reference line to a superior aspect of a tuberosity of the bone, and (v) measuring the length of the third reference line. In one version of the method, the prosthetic component is formed such that a second length of the projection is a predetermined percentage of a fourth reference length wherein the second length of the projection is perpendicular to the first length of the projection. The fourth reference length used by the manufacturer in forming the prosthetic component has been determined by (i) orienting on the image a fourth reference line perpendicular to the third reference line and extending over the bone in the image from the third reference line to a perimeter of the bone in the image, and (ii) measuring the fourth reference line to determine the fourth reference length. In one version of the method, the bone is the humerus, the joint is the shoulder, the length of the third reference line is a superior-inferior length of a greater tuberosity of the humerus, and the fourth reference length is a medial-lateral length of the greater tuberosity of the humerus. In one version of the method, the joint has been fractured, and the protruding section includes a plurality of fins for immobilizing fracture fragments. 
         [0028]    In another aspect, the invention provides a method for manufacturing a prosthetic component for replacing a part of a bone of a joint in a subject. In the method, the prosthetic component is formed to include a head and a stem connected to the head. The head has a longitudinal head axis and the stem has a longitudinal stem axis. The head axis and the stem axis are angled to create an inclination angle between the head axis and the stem axis. The inclination angle used by the manufacturer in forming the prosthetic component has been determined by (i) obtaining an image of the bone of the joint, (ii) orienting on the image a first reference line that extends from a first border of a head of the bone to an opposite second border of the head of the bone, (iii) orienting on the image a 90 degree reference angle from an inferior position of the first reference line to create a second reference line that extends over the image of the bone, (iv) orienting on the image the third reference line, the third reference line extending over the image of the bone from the second reference line to a superior aspect of a tuberosity of the bone, and (v) measuring an angle between the first reference line and the third reference line, wherein the angle is equal to the inclination angle. In one version of the method, the bone is the humerus, and the joint is an arthritic shoulder. The image can be a computed tomography scan slice. 
         [0029]    In another aspect, the invention provides a method for manufacturing a prosthetic component for replacing a part of a bone of a joint in a subject. In the method, the prosthetic component is formed to include an articular head and an opposed base surface. The head has a longitudinal head axis, and the head axis and the base surface are angled to create an inclination angle between the head axis and the base surface. The inclination angle used by the manufacturer in forming the prosthetic component has been determined by (i) obtaining an image of the bone of the joint, (ii) orienting on the image a first reference line that extends from a first border of a head of the bone to an opposite second border of the head of the bone, (iii) orienting on the image a 90 degree reference angle from an inferior position of the first reference line to create a second reference line that extends over the image of the bone, (iv) orienting on the image the third reference line, the third reference line extending over the image of the bone from the second reference line to a superior aspect of a tuberosity of the bone, and (v) measuring an angle between the first reference line and the third reference line, the angle being equal to the inclination angle. In one version of the method, the bone is the humerus, and the joint is an arthritic shoulder. The image can be a computed tomography scan slice. 
         [0030]    In another aspect, the invention provides a method for manufacturing a prosthetic component for replacing a part of a bone of a joint in a subject. In the method, the prosthetic component is formed to include a body having a base surface, an outer surface opposite the base surface, a first side edge extending between the base surface and the outer surface, and a second side edge extending between the base surface and the outer surface. The second side edge is opposite the first side edge. A first thickness of the first side edge is less than a second thickness of the second side edge by an augment thickness. The augment thickness is determined by (i) obtaining an image of the bone of the joint, (ii) orienting on the image a reference angle from a body of the bone to create a first reference line parallel to a bone surface, wherein the first reference line extends from a first border of the bone to an opposite second border of the bone, (iii) orienting on the image a second reference line from the first reference line to an eroded region of the bone surface, (iv) determining a length of the second reference line, and (v) selecting the augment thickness based on the length of the second reference line. The augment thickness can be equal to the length of the second reference line. The image can be a computed tomography scan axial slice, and the reference angle can be 90 degrees. The first side edge can be an anterior edge, and the second side edge can be a posterior edge. 
         [0031]    In one version of the method, the augment thickness extends from the second side edge to a location on the base surface between the first side edge and the second side edge. The location can be determined by (vi) identifying on the image a junction between the eroded region of the bone surface and a native region of the bone surface, and (vii) determining a reference point on the first reference line where a third reference line intersects the first reference line, the third reference line extending perpendicularly from the junction to the first reference line. The location can be determined by (viii) calculating a percentage of a fourth reference line from the first border of the bone to the reference point with respect to a length of the first reference line, and (ix) selecting the percentage to be an amount of the body having the augment thickness. 
         [0032]    In one version of the method, the augment thickness increases from the first side edge to the second side edge thereby defining an augment angle between the outer surface and the base surface. The augment angle can be determined by orienting on the image an angle reference line from the first border to where the second reference line intersects the bone surface and by selecting the augment angle as an angle between the first reference line and the angle reference line. 
         [0033]    In one version of the method, the augment thickness increases from the first side edge to the second side edge at a step discontinuity. 
         [0034]    The bone can be the scapula, the joint can be the shoulder, and the prosthetic component can be a glenoid component. The outer surface can be a concave bearing surface for articulating with a humeral head component of a total shoulder arthroplasty system. The glenoid component can be a glenoid baseplate dimensioned to be secured to a glenosphere of a reverse shoulder arthroplasty system. 
         [0035]    In another aspect, the invention provides a method for manufacturing a prosthetic component for replacing a part of a bone of a joint in a subject. In the method, the prosthetic component is formed to include a body having a base surface, an outer surface opposite the base surface, a first side edge extending between the base surface and the outer surface, and a second side edge extending between the base surface and the outer surface wherein the second side edge is opposite the first side edge. A first thickness of the first side edge is less than a second thickness of the second side edge by an augment thickness. The augment thickness can be determined by (i) obtaining an image of the bone of the joint, (ii) orienting on the image a neutral face plate line, (iii) orienting on the image a first reference line, the first reference line being parallel or within 20 degrees of parallel to the neutral face plate line, the first reference line extending from a first border of the bone to an opposite second border of the bone, (iv) orienting on the image a second reference line from the first reference line to a bone surface, the second reference line intersecting the first reference line a predetermined distance from the first border of the bone, (v) determining a length of the second reference line, and (vi) selecting the augment thickness based on the length of the second reference line. The augment thickness can be equal to the length of the second reference line. 
         [0036]    In one version of the method, the augment thickness extends from the second side edge to a location on the base surface between the first side edge and the second side edge. The location can be determined by (vii) identifying on the image a junction between the eroded region of the bone surface and a native region of the bone surface, and (viii) determining a reference point on the first reference line where a third reference line intersects the first reference line, the third reference line extending perpendicularly from the junction to the first reference line. The location can be determined by (viii) calculating a percentage of a fourth reference line from the first border of the bone to the reference point with respect to a length of the first reference line, and (ix) selecting the percentage to be an amount of the body having the augment thickness. 
         [0037]    In one version of the method, the augment thickness increases from the first side edge to the second side edge thereby defining an augment angle between the outer surface and the base surface, and the augment angle can be determined by orienting on the image an angle reference line from the first border to where the second reference line intersects the bone surface and by selecting the augment angle as an angle between the first reference line and the angle reference line. The augment thickness may increase from the first side edge to the second side edge at a step discontinuity. 
         [0038]    In the method, the bone can be the scapula, the joint can be the shoulder, and the prosthetic component can be a glenoid component. The outer surface can be a concave bearing surface for articulating with a humeral head component of a total shoulder arthroplasty system. The glenoid component can be a glenoid baseplate dimensioned to be secured to a glenosphere of a reverse shoulder arthroplasty system. 
         [0039]    In one version of the method, the image is a computed tomography scan coronal slice. The first reference line can be about 10 degrees from parallel to the neutral face plate line. In one version of the method, the first side edge of the prosthetic component body is an inferior edge, and the second side edge is a superior edge. The predetermined distance can be about 20 millimeters to about 40 millimeters. 
         [0040]    In another aspect, the invention provides a method for manufacturing a prosthetic component for replacing a part of a bone of a joint in a subject. In the method, the prosthetic component is formed to include a body having a base surface, an outer surface opposite the base surface, a first side edge extending between the base surface and the outer surface, and a second side edge extending between the base surface and the outer surface wherein the second side edge is opposite the first side edge. A first thickness of the first side edge is less than a second thickness of the second side edge by an augment thickness. The augment thickness increases from the first side edge to the second side edge thereby defining an augment angle between the outer surface and the base surface. The augment angle can be determined by (i) obtaining an image of the bone of the joint, (ii) orienting on the image a neutral face plate line, (iii) orienting on the image a first reference line, the first reference line being parallel to the neutral face plate line, the first reference line extending from a first border of the bone to an opposite second border of the bone, (iv) orienting on the image a second reference line from the first reference line to a bone surface, the second reference line intersecting the first reference line a predetermined distance from the first border of the bone, (v) orienting on the image an angle reference line from the first border to where the second reference line intersects the bone surface, and (vi) selecting the augment angle based on a measured angle between the first reference line and the angle reference line. The image can be a computed tomography scan coronal slice. 
         [0041]    In one version of the method, when the measured angle is in the range of 0 to 10 degrees superior tilt, the augment angle is selected as about 10 degrees. In another version of the method, when the measured angle is between 10 and 15 degrees superior tilt, the augment angle is selected as about 15 degrees. In another version of the method, when the measured angle is in the range of 15 to 20 degrees superior tilt, the augment angle is selected as about 20 degrees. 
         [0042]    In one version of the method, the bone is the scapula, the joint is the shoulder, and the prosthetic component is a glenoid component. The glenoid component can be a glenoid baseplate dimensioned to be secured to a glenosphere of a reverse shoulder arthroplasty system. The first side edge of the prosthetic component body can be an inferior edge, and the second side edge can be a superior edge. 
         [0043]    The methods of the present disclosure can be used in a number of different joints in addition to the shoulder. For example, the methods may be used in the elbow, wrist, hand, spine, hip, knee, ankle, and/or foot. When the joint is the elbow, the bone can be selected from the ulna, radius, and humerus. When the joint is the wrist, the bone can be selected from the radius, ulna, and carpal bones. When the joint is the hand, the bone can be selected from phalanges, metacarpals, and carpals. When the joint is the spine, the bone can be a vertebrae. When the joint is the hip, the bone can be selected from the femur and the pelvis/acetabulum. When the joint is the knee, the bone is selected from the femur, tibia and patella. When the joint is the ankle, the bone can be selected from the talus, the tibia and the fibula. When the joint is the foot, the bone can be selected from phalanges tarsals and metatarsals. 
         [0044]    The method of the present disclosure allows one to design an augment that is shaped according to the defects that actually exist and covers the appropriate amount of glenoid worn rather than being based on guesswork. This disclosure facilitates design in three ways: (1) it defines the angle of glenoid erosion; (2) it defines the depth of glenoid erosion; and (3) it defines what percent of the glenoid has an eroded surface. This information will significantly improve the ability to design an augmented glenoid component. 
         [0045]    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 
         [0046]      FIG. 1  is a cross-sectional view of one embodiment of a shoulder prosthesis suitable for use in the invention. 
           [0047]      FIG. 2  shows a tracing of a computed tomography (CT) axial two-dimensional (2D) CT slice of the scapula and humerus with measurement lines according to the invention shown in broken lines. 
           [0048]      FIG. 3  shows a tracing of a 2D CT sagittal slice of the scapula with measurement lines according to the invention shown in broken lines. 
           [0049]      FIG. 4  shows a tracing of a CT 2D coronal slice of the scapula and humerus with measurement lines according to the invention shown in broken lines. 
           [0050]      FIG. 5A  is a side sectional view of a prior art augmented glenoid component. 
           [0051]      FIG. 5B  is a side view of another prior art augmented glenoid component. 
           [0052]      FIG. 6A  is an exploded side view of yet another prior art augmented glenoid component. 
           [0053]      FIG. 6B  is a side view the augmented glenoid component of  FIG. 6A  in the assembled configuration. 
           [0054]      FIG. 6C  is an exploded side view of yet another prior art augmented glenoid component. 
           [0055]      FIG. 6D  is a side view the augmented glenoid component of  FIG. 6C  in the assembled configuration. 
           [0056]      FIG. 7  shows a tracing of a computed tomography (CT) axial two-dimensional (2D) CT slice of the scapula and humerus with measurement lines according to the invention shown in broken lines. 
           [0057]      FIG. 8  shows a tracing of a 2D CT coronal slice of the scapula with measurement lines according to the invention shown in broken lines. 
           [0058]      FIG. 9  shows another tracing of a CT 2D coronal slice of the scapula and humerus with measurement lines according to the invention shown in broken lines. 
       
    
    
       [0059]    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 
       [0060]    Looking first at  FIG. 1 , there is shown one example embodiment of a shoulder prosthesis  10  suitable for use in the invention. 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 . The stem  16  can be monolithic with the head  18 , or the stem  16  and the head  18  can formed as separate parts. 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  (shown cutaway) 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 . 
         [0061]    Proper design and selection of the hemispherical head  18  and the glenoid component  24  can be achieved using the method of the invention. In one non-limiting example method of the invention, eleven measurements are obtained using CT slices. The eleven measurements are as follows: (1) glenoid version; (2) anterior-posterior (AP) diameter at the articular surface; (3) anterior-posterior width at a neutral face plate; (4) depth of the glenoid vault from a neutral face plate; (5) depth of the glenoid vault from a neutral face plate with a diameter of the center post (an example center post diameter being five millimeters); (6) superior-inferior glenoid height; (7) determination of the anterior-posterior width fourteen millimeters from the inferior border of the glenoid; (8) humeral head diameter; (9) humeral head thickness; (10) greater tuberosity length of the humerus; (11) greater tuberosity width of the humerus; and (12) humeral inclination. 
         [0062]    Proper design and selection of an augmented glenoid component can be achieved using the method of the invention. In one non-limiting example method of the invention, measurements are obtained using CT slices as shown in  FIGS. 7-9 . 
         [0063]    The degree of anterior-posterior glenoid wear has been defined in a series of patients undergoing shoulder arthroplasty. This angle allows one to determine a specific anatomic range of augments to accommodate anterior-posterior bone loss in patients undergoing anatomic total shoulder arthroplasty and reverse shoulder arthroplasty. 
         [0064]    Superior glenoid wear may occur in patients with rotator cuff insufficiency undergoing reverse shoulder arthroplasty. Previously, there was no information on the specific range of inferior-superior glenoid wear among these patients. Therefore, in order to design a glenoid baseplate that accommodates the anatomy of these patients and allows for proper fit with minimal bone removal, it is critical to understand the anatomic distribution in these patients. Thus, a method has been developed and utilized among patients who have undergone reverse arthroplasty of the shoulder to determine the anatomic distribution. The concept of superior wear angle and depth expands and is an extension on the neutral face plate concept described herein. 
         [0065]    The most frequently used glenoid baseplate in the United States has a diameter of 25 millimeters. Therefore, one may determine the angle of an augmented glenoid component by placing an angle to the most medial aspect of the glenoid 25 millimeters from the inferior aspects of the glenoid compared to one parallel to the faceplate of the glenoid. However, the method is not limited to 25 millimeter diameter circular baseplates. One may determine the angle of an augmented glenoid component by placing an angle to the most medial aspect of the glenoid about 20 to about 40 millimeters from the inferior aspects of the glenoid compared to one parallel to the faceplate of the glenoid. This would accommodate circular baseplates having a 20-40 millimeter diameter, or oval baseplates having a major axis up to 40 millimeters. In cases where superior glenoid erosion has resulted in loss of the superior aspect of the glenoid, the scapular spine can be used with a standardized population based average to determine the inclination plane of the glenoid face. 
         [0066]    Various combinations of these measurements are used for manufacturing a prosthetic component for replacing a part of a bone of a joint in a subject (e.g., mammal). The prosthetic component 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. 
       EXAMPLES 
       [0067]    The following Examples have been presented in order to further illustrate the invention and are not intended to limit the invention in any way. 
       Example A 
     1. Glenoid Version 
       [0068]    Using an axial 2D CT scan of a human shoulder, the mid point of the glenoid was determined. A first line was then drawn through the midpoint and parallel to the scapular body. The first line intersects a second line drawn parallel to the joint surface. The glenoid version was the angle between the first line and the second line, and was recorded in degrees. 
       2. Anterior-Posterior (AP) Width at the Articular Surface 
       [0069]    Using an axial 2D CT scan of a human shoulder, the diameter (AP width) was measured at the mid-point of the glenoid in millimeters. 
       3. Anterior-Posterior (AP) Width at a Neutral Face Plate 
       [0070]    Looking at  FIG. 2 , an axial 2D CT scan of a human shoulder was obtained and a 90 degree angle A (shown in broken lines) was oriented from the scapular body  26  and then placed on the glenoid  30  to create a neutral face plate  32  (shown in broken lines) that runs from one side border  34  to the other side border  36  of the glenoid  30 . This width was then measured in millimeters. This measurement is important to determine the true AP width of the glenoid after creating a flat neutral face plate by removing bone during arthroplasty. This is what occurs at surgery according to the method of the invention, yet this measurement has never been previously described. Prior measurements have been made of the articular surface only of the glenoid. This explains why many glenoid component sizes are too large. The measurement at a neutral faceplate is usually several millimeters less than the measurement at the articular surface due to reaming or removing glenoid bone to make the surface flat to place the glenoid component  24 . 
         [0071]    When manufacturing a glenoid component, a manufacturer can be supplied with the length of the neutral face plate  32  which provides a true AP width of the glenoid after creating a flat neutral face plate by removing bone during arthroplasty. A predetermined percentage of the length of the neutral face plate  32  can be used to machine or mold the glenoid component to have a selected width for the base surface  27  (see  FIG. 1 ). 
       4. Depth of the Glenoid Vault from a Neutral Face Plate 
       [0072]    Still looking at  FIG. 2 , a line  38  (shown in broken lines) was started at the neutral face plate  32  and was drawn medially to determine the depth of the glenoid vault  40 . Previous reports have mentioned only the depth from the articular surface which overstates the depth of the glenoid. This explains why many central posts or peripheral pegs of glenoid components that are currently in the market are too long and perforate the glenoid. Prior designs have not been designed based on patients with arthritis and associated bone loss who have undergone shoulder arthroplasty. 
         [0073]    When manufacturing a glenoid component, a manufacturer can be supplied with the length of the line  38 . A predetermined percentage of the length of the line  38  can be used to machine or mold the glenoid component to have a selected longitudinal length for the post  28  (see  FIG. 1 ). 
       5. Depth of the Glenoid Vault from a Neutral Face Plate with a Diameter of 5 Millimeters 
       [0074]    Still looking at  FIG. 2 , a five millimeter line  42  (shown in broken lines) was placed within the vault parallel to the line  38 . This will show one the depth of the glenoid vault that one can drill back to a five millimeter diameter. This allows accurate determination of the safe length for a central post or screw. Other post diameters are allowed in the design, five millimeters is used only as an example. 
         [0075]    When manufacturing a glenoid component, a manufacturer can be supplied with the length of the line  42 . A predetermined percentage of the length of the line  42  can be used to machine or mold the glenoid component to have a selected length for the post  28  (see  FIG. 1 ). 
       6. Superior-Inferior Glenoid Length 
       [0076]    The height of the glenoid was measured in millimeters. 
       7. Determination of the AP Width Fourteen Millimeters from the Inferior Border of the Glenoid 
       [0077]    Turning to  FIG. 3 , a 2D CT scan of a human shoulder was obtained and on the sagittal cut, an anterior-posterior width on line  46  (shown in broken lines) was measured. Line  46  was perpendicular to and fourteen millimeters up line  50  (shown in broken lines) from the inferior border  48  of the glenoid  30 . This measures the anterior-posterior width of the glenoid fourteen millimeters above the inferior rim of the glenoid. This allows determination of the appropriate width of a glenoid base plate for reverse arthroplasty. 
         [0078]    When manufacturing a glenoid component, a manufacturer can be supplied with the length of the line  46 . A predetermined percentage of the length of the line  46  can be used to machine or mold the glenoid component to have a selected width for the base surface  27  (see  FIG. 1 ). 
       8. Humeral Head Diameter and 9. Humeral Head Thickness 
       [0079]    Turning to  FIG. 4 , a 2D CT scan of a human shoulder was obtained and on the coronal slice the diameter of the humeral head was measured in millimeters at line  52  (shown in broken lines). A line  54  (shown in broken lines) was then drawn perpendicular from line  52  to the surface  56  of the humeral head. The length of line  54  (here measured in millimeters) gives one the thickness of the humeral head. 
       10. Greater Tuberosity Length and 11. Greater Tuberosity Width 
       [0080]    A 90 degree line  58  (shown in broken lines) was taken off the most inferior aspect of the humeral head cut. A line  62  (shown in broken lines) was then placed from the superior aspect of the greater tuberosity (intersection with the superior end point of line  52 ) to intersect this line  58 . This line  62  shows the true distance of the greater tuberosity in length (superior-inferior). Next a line  64  (shown in broken lines) was taken 90 degrees to this line  62  to show the maximum diameter of the greater tuberosity. This line  64  shows the true distance of the greater tuberosity in width (medial-lateral). This facilitates designing a humeral component that maximizes tuberosity healing as well as anatomic component shape. This data also facilitates the design of different size humeral components specifically for fracture cases to improve tuberosity healing. This would include different size “fins” or other components to accommodate and secure fracture fragments based on the size of the patient. 
       12. Measurement of Humeral Inclination 
       [0081]    On  FIG. 4 , taking the angle B between lines  52  and  62  in degrees and adding 90° defines the inclination angle of the humeral head in degrees (i.e., angle B in degrees+90°=the inclination of the humeral head). This measurement can determine the true range of inclination necessary for humeral component design. 
         [0082]    When manufacturing a humeral component, a manufacturer can be supplied with the inclination angle of the humeral head. The inclination angle of the humeral head can be used to machine or mold the humeral component to have a selected angle, or a selected range of angles (for adjustable humeral inclination) between the longitudinal head axis H (see  FIG. 1 ) and the longitudinal stem axis S (see  FIG. 1 ) or the longitudinal head axis H and the base surface  19  (see  FIG. 1 ). 
       Results 
       [0083]    Using the measurement technique of Examples 1-12, a review of 800 patients who have undergone shoulder arthroplasty (436 total shoulder arthroplasties, 210 reverse shoulder arthroplasties, and 154 hemiarthroplasties) was completed and is shown in Table 1 below. In addition, statistical analysis revealed that when evaluating for specific anatomic ratios there were very tight confidence intervals. This can be further used to ensure proper component design as shown in Table 2. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Anatomic Measurements of 800 Shoulders 
               
             
          
           
               
                   
                   
                   
                   
                   
                   
                 10th 
                   
               
               
                 Variable 
                 Mean 
                 Std Dev 
                 Median 
                 Minimum 
                 Maximum 
                 Pctl 
                 90th Pctl 
               
               
                   
               
             
          
           
               
                 1. Glenoid version (degrees) 
                 10.66 
                 9.68 
                 10.00 
                 −27.00 
                 49.00 
                 0.00 
                 24.00 
               
               
                 2. AP width at articular surface (mm) 
                 28.71 
                 4.32 
                 28.50 
                 12.40 
                 41.20 
                 23.30 
                 34.20 
               
               
                 3. AP width at a neutral faceplate (mm) 
                 24.59 
                 3.83 
                 24.70 
                 12.00 
                 36.90 
                 19.80 
                 29.30 
               
               
                 4. Vault depth from a neutral face plate (mm) 
                 21.79 
                 4.30 
                 22.00 
                 6.10 
                 37.00 
                 16.30 
                 27.20 
               
               
                 5. Vault depth to a 5 mm diameter (mm) 
                 16.07 
                 4.2 
                 16.30 
                 2.00 
                 27.30 
                 10.80 
                 21.50 
               
               
                 6. Superior-Inferior: Glenoid Height (mm) 
                 34.61 
                 4.4 
                 34.20 
                 24.00 
                 50.10 
                 29.10 
                 40.60 
               
               
                 7. AP width 14 mm from inferior glenoid rim (mm) 
                 26.78 
                 3.14 
                 26.80 
                 15.00 
                 35.20 
                 22.80 
                 30.80 
               
               
                 8. Humeral head diameter (mm) 
                 43.47 
                 4.31 
                 43.00 
                 32.80 
                 56.00 
                 38.30 
                 49.60 
               
               
                 9. Humeral head thickness (mm) 
                 22.11 
                 2.76 
                 22.20 
                 14.20 
                 29.70 
                 18.80 
                 25.60 
               
               
                 10. Greater tuberosity superior-inferior (mm) 
                 33.61 
                 4.54 
                 33.10 
                 21.00 
                 47.00 
                 28.00 
                 40.00 
               
               
                 11. Greater tuberosity medial-lateral (mm) 
                 11.29 
                 2.01 
                 11.00 
                 6.30 
                 18.00 
                 8.90 
                 14.00 
               
               
                 12. Humeral Inclination (degrees) 
                 129.13 
                 5.72 
                 129.00 
                 115.00 
                 145.00 
                 121.00 
                 137.00 
               
               
                   
               
               
                 The 10th and 90th percentile refer to the range of data. 
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                 Overall - 95% 
               
               
                   
                 Overall 
                 Confidence 
               
               
                 Ratio 
                 Ratio 
                 Intervals 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Humeral head diameter/Humeral head 
                 1.98 
                 1.97, 2.00 
               
               
                 thickness 
               
               
                 Greater tuberosity medial-lateral (width)/ 
                 0.337 
                 0.334, 0.341 
               
               
                 Greater tuberosity superior-inferior (height) 
               
               
                 AP width at a neutral faceplate/ 
                 1.16 
                 1.14, 1.18 
               
               
                 Vault depth from a neutral faceplate 
               
               
                   
               
             
          
         
       
     
       Example B 
       [0084]    Glenoid wear typically occurs in a posterior pattern with osteoarthritis and a superior direction with rotator cuff insufficiency. Anterior wear may also occur as well as combined patterns, however posterior or superior wear patterns are the dominant wear patterns. 
         [0085]    There are two primary means to resurface a worn glenoid component: anatomic shoulder arthroplasty and reverse arthroplasty. Anatomic arthroplasty is typically done in the setting of a posterior wear pattern. Reverse arthroplasty may be done in a posterior or superior wear pattern. In order to design appropriately sized augmented components, one needs to know the dimensions of wear. 
       1. Design of an Augment for a Posteriorly Worn Glenoid 
       [0086]    The angle of the augment is determined by determining the version of the glenoid. Looking at  FIG. 7 , an axial 2D CT scan of a human shoulder was obtained. One orients a line  231  parallel to the scapular body  226  that intersects a line  232  parallel to the joint surface at 90 degree angle A 2 . The line  232  runs at least from a posterior side border  234  to an anterior side border  236  of the glenoid  230 . The thickness dimension of the augment is determined by measuring along line  238  in millimeters the amount of wear of the posterior aspect of the glenoid  230 . One can also determine where the junction  241  occurs between native bone and eroded bone. This facilitates design of the augment by determining what percent of the glenoid  230  should have an augmented surface. For example, a distance along line  232  from the posterior side border  234  to the anterior side border  236  can be determined, and then a distance along line  232  from the anterior side border  236  to a point P at a line  243  passing through the junction  241  and perpendicular to the line  232 . An augment angle can be determined from angle G between line  232  and an angle reference line  239  from the anterior side border  236  to the line  238  where line  238  intersects the bone. The thickness of the augment, angle, and percent of surface covered by the augment may be less depending on the amount that the surgeon would want to ream the glenoid. However, reaming weakens the bone as well as decreases the moment arm for the rotator cuff muscles. Therefore, there has been increasing interest for the use of augments rather than reaming glenoid bone. 
       2. Design of an Augment for a Superiorly Worn Glenoid 
       [0087]    Looking at  FIG. 8 , a coronal 2D CT scan of a human shoulder was obtained. One determines the thickness of an augment needed by measuring a set distance from the inferior part  242  of the glenoid  230 . For example, for a glenoid baseplate that is 25 millimeters in diameter, one can measure 25 millimeters (as dimension D of  FIG. 8 ) from the inferior part  242  of the glenoid  230  along a line  244  parallel to the neutral face plate  246  of the glenoid  230  for a baseplate placed in neutral tilt. One can then measure medially along line  248  from the line  244  to the bone surface to determine the thickness of the superior augment needed. One can determine the angle of an augmented glenoid by placing a line  249  creating an angle A 3  to the most medial aspect of the glenoid  230  compared to the line  244  parallel to the neutral face plate  246  of the glenoid  230 . One can also determine where the junction  251  occurs between native bone and eroded bone. This facilitates design of the augment by determining what percent of the glenoid should have an augmented surface. For example, a distance along line  244  from the inferior part  242  to the superior side border  256  can be determined, and then a distance along line  244  from the inferior part  242  to a point P 1  at a line  253  passing through the junction  251  and perpendicular to the line  244 . 
         [0088]    One can create a glenoid component with 10 degrees of inferior tilt as preferred by some surgeons. Looking at  FIG. 9 , a coronal 2D CT scan of a human shoulder was obtained. One determines the thickness of an augment needed by measuring a set distance from the inferior part  342  of the glenoid  230 . For example, for a glenoid baseplate that is 25 millimeters in diameter, one can measure 25 millimeters (as dimension D of  FIG. 9 ) from the inferior part  342  of the glenoid  230  along a line  344  that has 10 degrees of tilt with respect to the neutral face plate  346  of the glenoid  230  for a baseplate placed in 10 degrees of inferior tilt. One can then measure medially along line  348  from the line  344  to the bone surface to determine the thickness of the superior augment needed. One can determine the angle of an augmented glenoid by placing a line  349  creating an angle A 4  to the most medial aspect of the glenoid  230  compared to the line  344 . One can also determine where the junction  351  occurs between native bone and eroded bone. This facilitates design of the augment by determining what percent of the glenoid should have an augmented surface. For example, a distance along line  344  from the inferior part  342  to the superior side border  356  can be determined, and then a distance along line  344  from the inferior part  342  to a point P 2  at a line  353  passing through the junction  351  and perpendicular to the line  344 . 
       3. Glenoid Wear Patterns 
       [0089]    In a series of 50 consecutive shoulders that underwent reverse arthroplasty, CT scans indicated that there were 28 with no superior glenoid wear (56%) and 22 with superior glenoid wear (44%). Among the glenoids without wear, superior inclination averaged 8 degrees. Among the glenoids with superior wear, there were 3 with mild wear with 5-10 degrees superior inclination, 10 with moderate wear with 10-15 degrees superior inclination, and 9 with severe wear with greater than 15 degrees of superior inclination. Among the 9 with severe wear, two had wear greater than 20 degrees. 
         [0090]    This study revealed a high rate of superior glenoid wear in patients undergoing reverse arthroplasty (44%). The data derived from this method has provided insight for the range of augments necessary to accommodate patients undergoing reverse arthroplasty. 
         [0091]    The methodology has revealed the potential benefit of an augmented glenoid baseplate for the reverse arthroplasty not only in the setting of significant glenoid erosion but also in the patient with no glenoid erosion. An augmented glenoid can facilitate the inferior tilting of the glenoid component to decrease the chance of loosening—while maintaining better quality bone and preserving bone. 
         [0092]    Among shoulders with no wear, there was on average 8 degrees of superior tilt. A preferred amount of inferior inclination is approximately 10 degrees. One strategy would allow the surgeon to ream the glenoid to a neutral position and then use a 10 degree augmented glenoid to create the appropriate tilt. This allows the surgeon to provide optimal inferior tilt without removing more inferior bone—a bone preserving approach. This is particularly important in a large glenoid with a deep concavity. If an augmented glenoid is not used, an excessive amount of glenoid reaming may be necessary to create the appropriate inferior tilt. 
         [0093]    The method has also revealed that augments ranging up to 20 degrees can accommodate 96% of glenoids undergoing reverse arthroplasty without the need for bone grafting. In a deformity up to 20 degrees, the surgeon can ream back to 10 degrees of superior tilt and use an augment with a 20 degree angle. This would create 10 degrees of inferior tilt. This method has also facilitated creation of an algorithm to manage superior glenoid wear. See Table 3 below. 
         [0000]    
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Reverse Shoulder- Glenoid Bone Preserving Technique 
               
             
          
           
               
                   
                 Inclination 
                   
                   
               
               
                 Glenoid Wear 
                 Correction 
                 Treatment 
                 Outcome 
               
               
                   
               
               
                 Slight or no wear 
                 up to 10 degrees 
                 10 degree 
                 10 degrees 
               
               
                 (0-10 degrees 
                   
                 augmented glenoid 
                 inferior tilt 
               
               
                 superior tilt) 
               
               
                 Moderate wear 
                 up to 10 degrees 
                 15 degree 
                 10 degrees 
               
               
                 (10-15 degrees) 
                   
                 augmented glenoid 
                 inferior tilt 
               
               
                 Severe wear 
                 up to 10 degrees 
                 20 degree 
                 10 degrees 
               
               
                 (15-20 degrees) 
                   
                 augmented glenoid 
                 inferior tilt 
               
               
                   
               
             
          
         
       
     
         [0094]    Use of the method described herein for superior wear and inclination has revealed the optimum range of augments necessary for reverse shoulder arthroplasty with a superior wear pattern. In addition, this method has helped identify a bone preserving technique of placing the glenoid baseplate in patients with minimal to no wear. 
         [0095]    Thus, the invention provides a method for the optimization of shoulder arthroplasty component design. Use of this method and the data that it provides gives unique insight into the number, size and shape of glenoid components for total shoulder arthroplasty and reverse shoulder arthroplasty as well as humeral heads for shoulder arthroplasty and resurfacing arthroplasty. This method also provides valuable information for the optimal design, shape, and size of the proximal humeral body for a fracture stem to maximize tuberosity healing and humeral component design for hemiarthroplasty/total shoulder arthroplasty. A method for the optimization of an augmented glenoid design for shoulder arthroplasty is also provided. In the course of new product development, this method is a valuable resource that can be used to radiographically evaluate each new component design to ensure optimal fit prior to component production and product launch. While the invention is described herein as a method for the optimization of shoulder arthroplasty component design, it can be used for other joints (e.g., elbow, wrist, hand, spine, hip, knee, ankle, foot, etc. . . . ). 
         [0096]    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.