Patent Publication Number: US-2022233323-A1

Title: Glenoid implant anchor post

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of co-pending U.S. patent application Ser. No. 17/586,126, filed Jan. 27, 2022, which is a continuation of U.S. patent application Ser. No. 17/488,749, filed Sep. 29, 2021, which is a divisional application of U.S. patent application Ser. No. 16/700,267, filed on Dec. 2, 2019 (now U.S. Pat. No. 11,160,662), which is a continuation of U.S. patent application Ser. No. 15/379,359, filed on Dec. 14, 2016 (now U.S. Pat. No. 10,524,922), which is a divisional application of U.S. patent application Ser. No. 12/398,750, filed on Mar. 5, 2009 (now U.S. Pat. No. 9,545,311), the entireties of which are incorporated by reference herein. 
    
    
     FIELD OF DISCLOSURE 
     The present invention relates generally to an apparatus and device for securing a glenoid implant to a glenoid, and in particular, to an anchor with deformable portions that are adapted to form a cement-less connection with the glenoid. 
     BACKGROUND 
     In a healthy shoulder joint, the humeral head of the humerus interacts with the glenoid of the scapula to form a “ball and socket” joint. The humeral head abuts and articulates with the glenoid to allow a wide range of motion in the shoulder. In an unhealthy shoulder joint, the interaction between the glenoid and the humerus are compromised, requiring repair or replacement. Total shoulder replacement is one method used to replace shoulder joints that have been damaged beyond repair due to trauma or disease. Typically, a total shoulder replacement procedure includes providing a glenoid component and a humeral component that interact with each other at an articulating surface. 
     Conventionally, glenoid components have been designed as two-piece components made of plastic and metal. Due to difficulties in designing a mechanism to lock the two pieces together, the assembly can fail over time. Replacement of the glenoid component requires that the patient undergo an additional surgical procedure and be subjected to additional recovery time and costs. One-piece glenoid components have also been developed that fixate to a glenoid and provide an articulating surface for the humeral component. Bone cement is commonly used to secure the glenoid component to the glenoid for both two-piece and one-piece components. 
     U.S. Pat. No. 6,911,047 (Rockwood Jr. et al.) discloses a glenoid component having an anchor peg and stabilizing pegs to secure the glenoid component to a glenoid without the use of bone cement. The anchor peg disclosed in Rockwood Jr. et al. includes a body portion having a plurality of fins at a proximal end of the body portion. When the glenoid component is positioned within the glenoid and scapula, the fins provide resistance to removal forces on the glenoid component. The stabilizing pegs are positioned within the glenoid around the anchor peg to prevent movement of the body portion relative to the glenoid. 
     SUMMARY 
     The present invention is directed to a prosthesis with an anchor having deformable portions that engage with cortical bone at a glenoid. 
     In some embodiments, the present prosthesis is adapted to form a cement-less connection with a glenoid. The deformable portions are optionally structured for substantially unidirectional deformation. That is, the deformable portions resist deformation in the direction of removal. The anchor is optionally modular so that it is easily customized for patients of varying sizes. For example, different patients may have cortical bone of varying thicknesses and/or glenoids of varying depths. 
     In one embodiment, the present invention is a prosthesis that mechanically couples with both cancellous bone and cortical bone of a glenoid. The prosthesis includes a head portion comprising a rear surface and an articular surface, an anchor member, and a plurality of deformable fins extending radially outward from the anchor member. The anchor member includes a proximal end and a distal end. The proximal end is connected to the rear surface of the head portion. The plurality of deformable fins extend radially outward from the anchor member and include at least a first proximal fin adjacent to the rear surface of the head portion positioned to engage with the cortical bone. The plurality of deformable fins may also include at least one distal fin located proximate the distal end of the anchor member positioned to engage with the cancellous bone. 
     In another embodiment, the present invention is a prosthesis for securement to a glenoid and includes a head portion and an anchor. The head portion has a first surface and a second surface. The anchor extends from the first surface of the head portion and includes a proximal end connected to the first surface of the head portion, a distal end opposite the proximal end and a set of proximal fins. The set of proximal fins extend radially from the proximal end of the body portion. The anchor may also include a set of distal fins extending radially from the distal end of the body portion. The anchor is configured to engage the glenoid. 
     In an alternative embodiment, the present invention is an implant positionable between a glenoid and a humeral component. The implant includes a head portion and an anchor. The head portion has a first surface engageable with the glenoid and a second surface engageable with the humeral component. The anchor extends substantially perpendicularly from the first surface of the head portion and has a first end attached to the first surface, a second end opposite the first end, and a first set of flexible flanges positioned proximate the first end of the anchor. The anchor may also include a second set of flexible flanges positioned proximate the second end of the anchor. 
     The present invention is also directed to a method of fixating a prosthesis to a glenoid. The method includes aligning an anchor of the prosthesis with a bore formed in the glenoid and inserting the anchor in the bore such that a first surface of the prosthesis engages the glenoid. The anchor includes a first deformable fin and a second deformable fin. The first deformable fin is implanted within cancellous bone and the second deformable fin is implanted proximate cortical bone. 
     Terminology such as “first,” “second,” “third,” etc., is used herein to designate particular components being described. Because various components of the embodiments described herein can be positioned in a number of different orientations and in a number of different sequences, this terminology is used for the purposes of illustration and is not intended to be read in a restrictive manner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view of a glenoid component positioned between a glenoid and a humeral component in accordance with an embodiment of the present invention. 
         FIG. 2  is a perspective view of the glenoid component in accordance with an embodiment of the present invention. 
         FIG. 3  is a side view of the glenoid component implanted in the glenoid in accordance with an embodiment of the present invention. 
         FIG. 4  is a side view of an alternative glenoid component in accordance with an embodiment of the present invention. 
         FIG. 5  is a perspective view of an alternative glenoid component in accordance with an embodiment of the present invention. 
         FIG. 6  is a perspective view of an alternative glenoid component in accordance with an embodiment of the present invention. 
         FIG. 7A  is a perspective view of an alternative glenoid component in accordance with an embodiment of the present invention. 
         FIG. 7B  is a side view of the alternative glenoid component of  FIG. 7A  in accordance with an embodiment of the present invention. 
         FIG. 8  is a perspective view of an alternative glenoid component in accordance with an embodiment of the present invention. 
         FIG. 9A  is a perspective view of an alternative glenoid component in accordance with an embodiment of the present invention. 
         FIG. 9B  is a side view of a stepped hole configuration in accordance with an embodiment of the present invention. 
         FIG. 9C  is a side view of the alternative glenoid component of  FIG. 9A  positioned within the stepped hole configuration of  FIG. 9B  in accordance with an embodiment of the present invention. 
         FIG. 10  is an exploded side view an alternative glenoid component in accordance with an embodiment of the present invention. 
         FIG. 11  is a graph of load versus displacement during insertion of the glenoid component in accordance with an embodiment of the present invention. 
         FIG. 12  is a graph of load versus displacement during removal of the glenoid component in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an exploded view of a glenoid component  10  positioned between a glenoid  12  of a scapula S and a humeral component  14 . While the humeral component  14  illustrated in  FIG. 1  is a prosthesis, the present glenoid component  10  can also engage with an anatomical humeral head. Therefore, reference to the humeral component  14  herein should be construed to include an anatomical humeral head. 
     The glenoid component  10  is attachable to the glenoid  12  and functions as an artificial surface for engagement with the humeral component  14 . The glenoid component  10  can be secured to the scapula S without the use of bone cement and provides structural resistance from being removed from the scapula S. 
     The glenoid component  10  includes a head portion  16 , an anchor  18 , a first stabilizing pin  20   a , a second stabilizing pin  20   b  and a third stabilizing pin  20   c  (collectively referred to as “stabilizing pins  20 ”). The head portion  16  includes a first articulating surface  22  and a second surface  26 . The first articulating surface  22  engages the humeral head  24  of the humeral component  14 , which includes a stem  28  implanted in a humerus H, to allow rotation and movement of a shoulder. 
     The anchor  18  and stabilizing pins  20  of the glenoid component  10  extend from the second surface  26  of the head portion  16  of the glenoid component  10  and secure the glenoid component  10  to the glenoid  12 . In the illustrated embodiment, the glenoid  12  and scapula S include an anchor hole  30  and a plurality of stabilizing holes  32   a ,  32   b ,  32   c  (referred to collectively as “32”) to accept the anchor  18  and the stabilizing pins  20 , respectively. In an alternate embodiment, the present glenoid component  10  can be implanted without the pre-drilled holes  30 ,  32 . 
     Referring more particularly to  FIG. 2 , but still also in reference to  FIG. 1 ,  FIG. 2  shows a perspective view of the glenoid component  10 , which functions to provide a replacement surface to articulate with the humeral component  14 . The first articulating surface  22  of the head portion  16  is concave and configured to engage the humeral head  24  of the humeral component  14 . The first articulating surface  22  is thus formed to accept at least a portion of the humeral head  24  within the concavity of the first articulating surface  22 . The second surface  26  of the head portion  16  is preferably configured with the same shape as the glenoid  12  of the scapula S, which is usually convex. 
     In the illustrated embodiment, the anchor  18  extends substantially perpendicularly from the second surface  26  of the head portion  16  and secures the glenoid component  10  to the glenoid  12 . In other embodiments, the anchor  18  may extend at various other angles relative to the second surface  26  of the head portion  16 . The anchor  18  is preferably positioned substantially at the center of the second surface  26  of the head portion  16  and is in the form of a cylindrical shaft  34  having a proximal end  36 , a middle section  38  and a distal end  40 . The shaft  34  is attached to the head portion  16  at the proximal end  36  and tapers at the distal end  40  to facilitate insertion of the anchor  18  into the anchor hole  30  of the glenoid  12 . In one embodiment, the distal end  40  of the anchor  18  includes a conical tip, or other shape that facilitates insertion into the glenoid  12 , with or without the pre-drilled hole  30 . Alternatively, the anchor  18  can have a tapered or stepped structure. 
     In the illustrated embodiment, the anchor  18  has a substantially consistent diameter. Distal fins  44  extend radially outward from the distal end  40  of the shaft  34  and proximal fins  42  extend radially outward from the proximal end  36  of the shaft  34 . In the illustrated embodiment, the set of proximal fins  42  includes a first proximal fin  42   a  and a second proximal fin  42   b . The set of distal fins  44  includes a first distal fin  44   a , a second distal fin  44   b , a third distal fin  44   c  and a fourth distal fin  44   c.    
     In the illustrated embodiment, the sets of distal fins  44  and proximal fins  42  are spaced from each other by the middle section  38  of the shaft  34 . In an alternate embodiment, the sets of proximal and distal fins  42 ,  44  extend the full length of the shaft  34  without being separated by the middle section  38 . 
     Both sets of proximal and distal fins  42 ,  44  are flexible and are configured to bend or deform when force is exerted against them. Deformation of the proximal and distal fins  42   a ,  42   b ,  44   a ,  44   b ,  44   c ,  44   d  can be plastic or elastic. For example, in one embodiment, the proximal and distal fins  42   a ,  42   b ,  44   a ,  44   b ,  44   c ,  44   d  deform plastically upon insertion into the glenoid  12  and retain a generally curved configuration, such as illustrated in  FIG. 3 . Alternatively, the proximal and distal fins  42   a ,  42   b ,  44   a ,  44   b ,  44   c ,  44   d  return to their un-deformed configuration after implantation. 
     In the illustrated embodiment, the proximal and distal fins  42   a ,  42   b ,  44   a ,  44   b ,  44   c ,  44   d  have substantially the same diameter. Consequently, the proximal and distal fins  42   a ,  42   b ,  44   a ,  44   b ,  44   c ,  44   d  are co-axial with each other and the outside edges are aligned. Although  FIG. 2  depicts the set of proximal fins  42  as including two fins  42   a ,  42   b  and the set of distal fins  44  as including four fins  44   a ,  44   b ,  44   c ,  44   d , the sets of proximal fins and distal fins  42 ,  44  may include any number of fins. 
     In one embodiment, the shaft  34  and the proximal and distal fins  42   a ,  42   b ,  44   a ,  44   b ,  44   c ,  44   d  of the anchor  18  are integrally formed with the head portion  16 . For example, the glenoid component  10  can be molded as a single unitary structure or machined from a monolithic piece of material. In another embodiment, the shaft  34  and the proximal and distal fins  42   a ,  42   b ,  44   a ,  44   b ,  44   c ,  44   d  are separate components (See e.g.,  FIG. 10 ). In an alternate embodiment, the proximal and distal fins  42   a ,  42   b ,  44   a ,  44   b ,  44   c ,  44   d  are molded from a first material while the head portion  16  is molded from a second material. In this embodiment the first material preferably has a higher stiffness than the second material. 
     The glenoid component  10  of the present application can be manufactured from a variety of materials, such as for example polyethylene or ultra-high molecular weight polyethylene (“UHMWPE”), such as disclosed in U.S. Pat. No. 6,911,047, the disclosure of which is incorporated herein by reference. 
     The stabilizing pins  20  prevent the glenoid component  10  from moving relative to the glenoid  12  once the glenoid component  10  is implanted in the glenoid  12  and the scapula S. The stabilizing pins  20  preferably extend substantially perpendicularly from the second surface  26  of the head portion  16  and are positioned around the anchor  18 . Each of the stabilizing pins  20   a ,  20   b ,  20   c  includes a body  46   a ,  46   b ,  46   c  (collectively referred to as “bodies  46 ”), respectively, having a proximal end  48   a ,  48   b ,  48   c  (collectively referred to as “proximal ends  48 ”), respectively, and a distal end  50   a ,  50   b ,  50   c  (collectively referred to as “distal ends  50 ”), respectively. Each of the bodies  46  of the stabilizing pins  20  is attached at its proximal end  48  to the head portion  16  of the glenoid component  10 . The stabilizing pins  20  optionally include an indent or series of indents  52  to accept and lock in bone cement, maintaining the stabilizing pins  20  in position. 
     The stabilizing pins  20  are preferably shorter than the anchor  18  and in one embodiment extend only slightly past the set of proximal fins  42  of the anchor  18 . Similar to the distal end  40  of the anchor  18 , the distal ends  50  of the stabilizing pins  20  are also tapered to facilitate insertion of the stabilizing pins  20  into the stabilizing holes  32  of the glenoid  12 . In one embodiment, the distal ends  50  of the stabilizing pins  20  have a conical tip, or other shape that facilitates insertion into the glenoid  12 , with or without pre-drilled hole  32 . 
     The stabilizing pins  20  may be arranged in any configuration on the second side  26  of the head portion  16  around the anchor  18 . In one embodiment, the stabilizing pins  20  are positioned such that the first stabilizing pin  20   a  is positioned farther from the anchor  18  than the second and third stabilizing pins  20   b ,  20   c . In another embodiment, the stabilizing pins  20  are positioned around the anchor  18  along a periphery of the head portion  16  substantially equidistant from the anchor  18  and each adjacent stabilizing pin  20   a ,  20   b ,  20   c . Although  FIG. 2  depicts the glenoid component  10  as including three stabilizing pins  20 , the glenoid component  10  may include any number of stabilizing pins, including zero, without departing from the intended scope of the present invention. When the glenoid component  10  does not include any stabilizing pins, any means for preventing rotation of the glenoid component  10  relative to the glenoid  12  may be used. For example, the glenoid  12  may be milled in an oval shape and the glenoid component  10  may be key implanted into the bone. 
       FIG. 3  shows a side view of the glenoid component  10  implanted through the glenoid  12  and into the scapula S. In practice, to attach the glenoid component  10  to the glenoid  12 , the anchor hole  30  and the plurality of stabilizing holes  32  are preferably first drilled or otherwise formed in the glenoid  12 . The anchor hole  30  is preferably sized to have a diameter D AH  slightly larger than a diameter Ds of the shaft  34  of the anchor  18  but smaller than a diameter D F  of the distal and proximal fins  42   a ,  42   b ,  44   a ,  44   b ,  44   c ,  44   d  of the anchor  18 . Because the proximal and distal fins  42   a ,  42   b ,  44   a ,  44   b ,  44   c ,  44   d  are flexible, even though the diameters D F  of the proximal and distal fins  42   a ,  42   b ,  44   a ,  44   b ,  44   c ,  44   d  are larger than the diameter D AH  of the anchor hole  30 , the proximal and distal fins  42   a ,  42   b ,  44   a ,  44   b ,  44   c ,  44   d  can pass through the anchor hole  30  by exerting an extra amount of force on the glenoid component  10  and causing the proximal and distal fins  42   a ,  42   b ,  44   a ,  44   b ,  44   c ,  44   d  to deform. 
     The stabilizing holes  32  are drilled around the anchor hole  30  and are sized to accept the stabilizing pins  20 . The stabilizing pins  20  may be press fit or interference fit into the stabilizing holes  32 . Optionally, bone cement may also be utilized to help maintain the stabilizing pins  20  within the stabilizing holes  32 . If it is desired to use bone cement to aid in securing the glenoid component  10  to the glenoid  12 , the bone cement can be applied at the indents  52  of the bodies  46  of the stabilizing pins  20  to increase the area of contact between the stabilizing pins  20  and the bone cement in order to increase the bond to secure the stabilizing pins  20  within the stabilizing holes  32 . 
     The anchor hole  30  and the stabilizing holes  32  are drilled such that when the glenoid component  10  is positioned with respect to the glenoid  12 , the anchor  18  is aligned with the anchor hole  30  and the stabilizing pins  20  are aligned with the stabilizing holes  32 . In one embodiment, a drill guide or pattern may be used to properly position and align the anchor hole  30  and the stabilizing holes  32  in the glenoid  12  to correspond with the positions and alignments of the anchor  18  and stabilizing pins  20  of the glenoid component  10 , respectively. 
     After the anchor hole  30  and the stabilizing holes  32  have been formed in the glenoid  12  and the scapula S, the glenoid component  10  is positioned in front of the glenoid  12  such that the anchor  18  and stabilizing pins  20  of the glenoid component  10  are aligned with the anchor hole  30  and the stabilizing holes  32 , respectively, of the glenoid  12 . As the glenoid component  10  is directed towards the glenoid surface  12 , the conical tip at the distal end  40  of the shaft  34  of the glenoid component  10  first enters the anchor hole  30 . When the set of distal fins  44  contact the cortical bone  12   a , each of the distal fins  44   a ,  44   b ,  44   c ,  44   d  deforms sequentially in order to pass through the anchor hole  30 . Once the set of distal fins  44  are advanced past the cortical bone  12   a , they engage with the softer cancellous bone  12   b.    
     The distance “d” between the first proximal fin  42   a  and the second surface  26  of the head portion  16  corresponds generally to the thickness of the cortical bone  12   a . The distance “d” is generally between about 1 to about 4 millimeters, and preferably between about 2 to about 3 millimeters. In the embodiment of  FIG. 10 , the distance “d” is adjustable by substituting a different spacer  306 . 
     The proximal fins  42   a ,  42   b  provide resistance against the smaller diameter D AH  of the anchor hole  30  so enough force must be exerted in order to engage the proximal fins  42   a ,  42   b  with the cortical bone  12   a . Once past the anchor hole  30 , the set of proximal fins  42  pass through the cortical bone  12   a  and into the cancellous bone  12   b  of the scapula S. In one embodiment, the first proximal fin  42   a  is positioned in the cortical bone  12   a  and the second proximal fin  42   b  is positioned adjacent to the cortical bone  12   a.    
     In order to fully insert the anchor  18  through the anchor hole  30 , the stabilizing pins  20  must be aligned with stabilizing holes  32  such that the stabilizing pins  20  engage with respective stabilizing holes  32 . Thus, as the anchor  18  is advanced into the anchor hole  30 , the stabilizing pins  20  are simultaneously advanced into the stabilizing holes  32 . Because the stabilizing pins  20  have a substantially consistent diameter and the stabilizing holes  32  are sized to accept the stabilizing pins  20 , extra force is not required to advance the stabilizing pins  20  into the scapula S. The glenoid component  10  is advanced into the scapula S until the second surface  26  of the head portion  16  abuts the glenoid  12  and the anchor  18  and stabilizing pins  20  are fully inserted into the scapula S. When the anchor  18  is positioned through the anchor hole  30  and the stabilizing pins  20  are positioned through the stabilizing holes  32 , the stabilizing pins  20  prevent rotation or movement of the glenoid component  10  relative to the glenoid  12 . 
     When the sets of proximal and distal fins  42 ,  44  of the anchor  18  are positioned within the scapula S, the proximal and distal fins  42   a ,  42   b ,  44   a ,  44   b ,  44   c ,  44   d  are bent towards the glenoid  12 , securing the glenoid component  10  to the scapula S. The anchor  18  of the glenoid component  10  is positioned in the scapula S such that the sets of distal and proximal fins  42 ,  44  are embedded in the cancellous bone  12   b , which has low density and strength and fills the inner cavity of the scapula S. Because the set of proximal fins  42  is located proximate the second surface  26  of the head portion  16 , the set of proximal fins  42  is located adjacent and proximate the cortical bone  12   a , which is dense and forms the surface of the scapula S. The first proximal fin  42   a  abuts the cortical bone  12   a , providing resistance to prevent the set of proximal fins  42  from passing through the anchor hole  30  and removing the anchor  18  from the scapula S. In addition, in the deformed state, the proximal fins  42   a ,  42   b  also function to stabilize the shaft  34  and prevent the shaft  34  from bending when side loaded. Because the set of proximal fins  42  substantially continuously abuts against the cortical bone  12   a , the glenoid component  10  provides increased resistance to removal from the scapula S compared to a glenoid component that does not include a set of proximal fins. 
     In addition, over time, as the glenoid component  10  remains within the scapula S, tissue will grow into the spaces between the fins  42   a ,  42   b ,  44   a ,  44   b ,  44   c ,  44   d  and provide further resistance to pulling out the anchor  18  from the anchor hole  30 . The combination of the configuration of the sets of proximal and distal fins  42 ,  44  within the scapula S and the tissue that grows around the fins  42   a ,  42   b ,  44   a ,  44   b ,  44   c ,  44   d  eliminates or reduces the need to use bone cement or other adhesive means to secure the glenoid component  10  to the glenoid  12 . Likewise, the indents  52  in the bodies  46  of the stabilizing pins  20  also provide an area for tissue to grow, further increasing the force required to remove the glenoid component  10  from the scapula S. 
     Referring back to  FIG. 1 , once the glenoid component  10  is fixed to the glenoid  12  and the scapula S, the first articulating surface  22  of the head portion  16  of the glenoid component  10  acts as an articulating or bearing surface for engaging the humeral head  24  of the humeral component  14 . The glenoid component  10  thus functions as a replacement for the natural glenoid of the scapula S, allowing the glenoid component  10 , the glenoid  12  and the humeral component  14  to interact similarly to a natural shoulder socket. 
       FIG. 4  shows a side view of an alternative glenoid component  100 . The glenoid component  100  functions substantially similarly to the glenoid component  10  of  FIGS. 1 and 2  and includes a head portion  102 , an anchor  104  and a plurality of stabilizing pins  106   a ,  106   b  (not shown),  106   c . The anchor  104  includes a shaft  108  having a proximal end  110 , a middle section  112  and a distal end  114 . A set of proximal fins  116  extends radially from the proximal end  110  of the shaft  108  and a set of distal fins  118  extends radially from the distal end  114  of the shaft  108 . The sets of proximal and distal fins  116 ,  118  are optionally separated by the middle section  112  of the shaft  108 . 
     The anchor  104  of the glenoid component  100  is substantially similar to the anchor  18  of the glenoid component  10  of  FIGS. 1 and 2  except that each of the first proximal fin  116   a  and the first, second and third distal fins  118   a ,  118   b  and  118   c  includes a rib feature  120  to create preferential deformation of the fins  116   a ,  118   a ,  118   b  and  118   c . The rib features  120  function to transfer load between the proximal fins  116   a ,  116   b , and between the distal fins  118   a ,  118   b ,  118   c ,  118   d , to reduce fin deformation in response to a removal force  121 . For example, when the glenoid component  10  is being pulled away from the glenoid  12  ( FIG. 1 ), the rib feature  120  of the first proximal distal fin  116   a  abuts the second proximal fin  116   b , reducing deformation arising from the removal force  121 . Likewise, the rib feature  120  of the first distal fin  118   a  abuts the second distal fin  118   b , the rib feature  120  of the second distal fin  118   b  abuts the third distal fin  118   c  and the rib feature  120  of the third distal fin  118   c  abuts the fourth proximal fin  118   d , reducing deformation of the respective first, second and third distal fins  118   a ,  118   b ,  118   c  in response to the removal force  121 . The fins  116   a ,  118   a ,  118   b ,  118   c  are substantially uni-directionally deformable. As used herein, “uni-directionally deformable” or “uni-directional deformation” refer to a structure that deforms in a first direction, but resists deformation in an opposite second direction. 
       FIG. 5  shows a perspective view of an alternative glenoid component  200 . The glenoid component  200  functions substantially similarly to the glenoid component  10  of  FIGS. 1 and 2  and includes a head portion  202 , an anchor  204  and a plurality of stabilizing pins  206   a ,  206   b ,  206   c . The anchor  204  includes a shaft  208  having a proximal end  210 , a middle section  212  and a distal end  214 . A set of proximal fins  216  extends radially from the proximal end  210  of the shaft  208  and a set of distal fins  218  extends radially from the distal end  214  of the shaft  208 . The proximal and distal fins  216 ,  218  are optionally separated by the middle section  212  of the shaft  208 . 
     The anchor  204  of the glenoid component  200  is substantially similar to the anchor  18  of the glenoid component  10  of  FIGS. 1 and 2  except that each of the proximal and distal fins  216   a ,  216   b ,  218   a ,  218   b ,  218   c ,  218   d  includes one or more cut-outs  220 . As the glenoid component  10  is pushed into the scapula S, additional force is needed to pass the proximal and distal fins  216   a ,  216   b ,  218   a ,  218   b ,  218   c ,  218   d  through the anchor hole  30 . By reducing the surface area of the proximal and distal fins  216   a ,  216   b ,  218   a ,  218   b ,  218   c ,  218   d , the amount of force required to insert the glenoid component  10  is also reduced. 
     In one embodiment, radial cut-outs  220  are machined through all of the proximal and distal fins  216   a ,  216   b ,  218   a ,  218   b ,  218   c ,  218   d  in order to reduce the surface area. Although  FIG. 5  depicts the cut-outs  220  as being positioned substantially symmetrically around the anchor  204 , the cut-outs  220  may be positioned anywhere around the anchor  204  without departing from the intended scope of the invention. In addition, there may be any number of cut-outs  220  machined from the proximal and distal fins  216   a ,  216   b ,  218   a ,  218   b ,  218   c ,  218   d.    
       FIG. 6  shows a perspective view of an alternative glenoid component  400 . The glenoid component  400  functions substantially similarly to the glenoid component  10  of  FIGS. 1 and 2  and includes a head portion  402 , an anchor  404  and a plurality of stabilizing pins  406   a ,  406   b ,  406   c . The anchor  404  includes a shaft  408  having a proximal end  410 , a middle section  412  and a distal end  414 . A set of proximal fins  416  extends radially from the proximal end  410  of the shaft  408  and a set of distal fins  418  extends radially from the distal end  414  of the shaft  408 . The sets of distal and proximal fins  416 ,  418  are optionally separated by the middle section  412  of the shaft  108 . 
     The anchor  404  of the glenoid component  400  is substantially similar to the anchor  18  of the glenoid component  10  of  FIGS. 1 and 2  except that the proximal end  410  of the shaft  408  of the anchor  404  includes a stabilizing boss  420 . The stabilizing boss  420  has a diameter DB that is larger than the diameter Ds of the shaft  408  but smaller than the diameters D F  of the sets of proximal and distal fins  416 ,  418 . The stabilizing boss  420  functions to aid in stabilizing the shaft  408  in a radial load condition. In one embodiment, the stabilizing boss  420  has a diameter substantially equal to the diameter of the anchor hole  30  D AH  ( FIG. 3 ) to help prevent the shaft  408  from bending when side loaded. 
       FIGS. 7A and 7B  show a perspective view and a side view, respectively, of an alternative glenoid component  500 . The glenoid component  500  functions substantially similarly to the glenoid component  10  of  FIGS. 1 and 2  and includes a head portion  502 , an anchor  504  and a plurality of stabilizing pins  506   a ,  506   b ,  506   c . The anchor  504  includes a shaft  508  having a proximal end  510 , a middle section  512  and a distal end  514 . A set of proximal fins  516  extends radially from the proximal end  510  of the shaft  508  and a set of distal fins  518  extends radially from the distal end  514  of the shaft  508 . The proximal and distal fins  516 ,  518  are optionally separated by the middle section  512  of the shaft  508 . 
     The anchor  504  of the glenoid component  500  is substantially similar to the anchor  18  of the glenoid component  10  of  FIGS. 1 and 2  except that the diameters of the proximal fins  516   a ,  516   b ,  516   c  are not the same. In the illustrated embodiment, the first and second proximal fins  516   b ,  516   b  have a smaller diameter than the diameter D F  of the third proximal fin  516   c . The smaller diameters of the first and second proximal fins  516   a ,  516   b  function to stabilize the shaft  508  of the anchor  504  and to prevent the shaft  508  from bending from side loading. In one embodiment, the diameters of the first and second proximal fins  516   a ,  516   b  are substantially equal to the diameter of the anchor hole  30  D AH . Although  FIGS. 7A and 7B  depict only the first and second proximal fins  516   a ,  516   b  as having a different diameter than the rest of the proximal and distal fins  516   c ,  518   a ,  518   b ,  518   c ,  518   d , any of the proximal and/or distal fins  516   a ,  516   b ,  516   c ,  518   a ,  518   b ,  518   c ,  518   d  may have varying diameters. 
       FIG. 8  shows a perspective view of an alternative glenoid component  600 . The glenoid component  600  functions substantially similarly to the glenoid component  10  of  FIGS. 1 and 2  and includes a head portion  602 , an anchor  604  and a plurality of stabilizing pins  606   a ,  606   b ,  606   c . The anchor  604  includes a shaft  608  having a proximal end  610 , a middle section  612  and a distal end  614 . A set of proximal fins  616  extends radially from the proximal end  610  of the shaft  608 . 
     The anchor  604  of the glenoid component  600  is substantially similar to the anchor  18  of the glenoid component  10  of  FIGS. 1 and 2  except that the anchor  604  does not include a set of distal fins. Thus, the middle section  612  and the distal end  614  of the shaft  608  are smooth with no radial extensions. The embodiment shown in  FIG. 8  illustrates that distal fins are not required to fixate the glenoid component  600  to the glenoid  12  ( FIG. 1 ). When the anchor  604  does not include any distal fins, initial fixation can still be achieved using only the set of proximal fins  616 . 
       FIG. 9A  shows a perspective view of an alternative glenoid component  700 . The glenoid component  700  functions substantially similarly to the glenoid component  10  of  FIGS. 1 and 2  and includes a head portion  702 , an anchor  704  and a plurality of stabilizing pins  706   a ,  706   b ,  706   c . The anchor  704  has a diameter DA and includes a shaft  708  having a proximal end  710 , a middle section  712  and a distal end  714 . A set of proximal fins  716  extends radially from the proximal end  710  of the shaft  708  and has a diameter D F . 
     The anchor  704  of the glenoid component  700  is substantially similar to the anchor  18  of the glenoid component  10  of  FIGS. 1 and 2  except that rather than having a set of distal fins extending radially from the distal end  714  of the shaft  708 , the distal end  714  includes a plurality of grooves  718   a ,  718   b ,  718   c ,  718   d  (collectively referred to as “grooves  718 ”) machined into the shaft  708 . The grooves  718  may be machined into the distal end  714  of the shaft  708  by any means known in the art. In one embodiment, the grooves  718  are machined into the shaft  708  by step drilling. Similar to the glenoid component  600  shown in  FIG. 8 , initial fixation of the anchor  704  of the glenoid component  700  can still be achieved using just the set of proximal fins  716 . After the initial fixation, long term fixation is achieved through bone in-growth into the grooves  718 . Although  FIG. 9  depicts the distal end  714  of the shaft  708  as including four grooves  718 , the distal end  714  of the shaft  708  may include any number of grooves. 
       FIG. 9B  shows a side view of a stepped hole configuration  800  created through the cortical bone  12   a  and within the cancellous bone  12   b .  FIG. 9C  shows a side view of the anchor  704  of the glenoid component  700  positioned within the stepped hole configuration  800 . The stepped hole  800  is sized to receive the anchor  704  of the glenoid component  700  and initially reduce the amount of force required to insert the anchor  704  of the glenoid component  700  into the scapula S. The stepped hole  800  includes a proximal portion  802  having a first diameter SH 1  and a distal portion  804  having a second diameter SH 2  bone  12   b . The proximal portion  802  is located through the cortical bone  12   a  and the cancellous bone  12   b  and the distal portion  804  is located within the cancellous bone  12   b . The first diameter SH 1  is greater than the second diameter SH 2  and slightly smaller than the diameter D F  ( FIG. 9B ) of the set of proximal fins  716 . The second diameter SH 2  is substantially the same size as the diameter DA of the anchor  704 , allowing easily insertion of the distal end  714  of the anchor into the stepped hole  800 . Because the diameter D F  of the set of proximal fins  716  is greater than the first diameter SH 1  of the stepped hole  800 , as the proximal end  710  of the anchor  704  is inserted into the stepped hole  800 , there is “lock-up” of the set of proximal fins  716  under the cortical bone  12   a.    
     Once the anchor  704  is positioned in the stepped hole, the relative sizes of the second diameter SH 2  of the stepped hole  800  and the anchor DA allows for bone ingrowth into the recessed grooves  718  at the distal end  714  of the shaft  708 . Although the stepped hole  800  is discussed with relation to glenoid component  700 , the stepped hole  800  may be used with other glenoid components in which the proximal end of the anchor has a greater diameter than the distal end of the anchor. For example, the stepped hole configuration  800  may also be used with the glenoid component  600  shown in  FIG. 8 . In one embodiment, the step hole  800  is formed using a step drill.  FIG. 10  shows an exploded side view of an alternative glenoid component  300 . In order to accommodate patients of various shapes and sizes, the glenoid component  300  may have a modular design. The glenoid component  300  functions substantially similarly to the glenoid component  10  of  FIGS. 1 and 2  and includes a head portion  302 , an anchor portion  304  and a plurality of stabilizing pins  306   a ,  306   b  (not shown),  306   c . The head portion  302  is preferably a single piece of material, while the anchor portion  304  is formed of a plurality of modular pieces. 
     In the embodiment shown in  FIG. 10 , the anchor portion  304  includes a first spacer  308 , a first proximal fin  310   a , a second proximal fin  310   b , a second spacer  312  and a set of distal fins  314 . The first spacer  308  sets an offset between a second surface  326  of the head portion  302  and the first proximal fin  310   a  corresponding generally to a thickness of the cortical bone  12   a  ( FIG. 3 ). 
     Each of the modular pieces  308 ,  310   a ,  310   b ,  312 ,  314  of the anchor portion  304  includes a bore  316  running through the center of the pieces  308 ,  310   a ,  310   b ,  312 ,  314  such that they can be maintained together and fixed to the head portion  302  by a screw  318 . Although  FIG. 10  shows the glenoid component  300  as including the modular pieces  308 ,  310   a ,  310   b ,  312 ,  314 , the glenoid component  300  may include any number of modular pieces without departing from the intended scope of the present invention. For example, the glenoid component  300  may include additional spacers to accommodate a patient with larger proportions or may include only one spacer to accommodate a patient with smaller proportions. Various spacers may also be provided having varying thicknesses. In another embodiment, additional fins may be included adjacent the set of distal fins  314  or one of the proximal fins  310   a ,  310   b.    
     The embodiment of  FIG. 10  is particularly well suited for building the glenoid component  300  from multiple materials. For example, the head portion  302  can be made from a first material and one or more of the other pieces  308 ,  310   a ,  310   b ,  312 ,  314  can be made from one or more second materials. Forming the pieces  308 ,  310   a ,  310   b ,  312 ,  314  separately also facilitates formation of various structures to achieve uni-lateral deformation. 
     While each of the embodiments of  FIGS. 4 through 10  are discussed as separate, alternative glenoid components to the glenoid component  10  shown in  FIGS. 1-3 , the individual structural features of each of the embodiments may be incorporated into any glenoid component. For example, the glenoid component  700  ( FIG. 9 ) having the distal grooves  718  may also include the stabilizing boss  420  ( FIG. 6 ) or the proximal fins  516   a  and  516   b  having decreased diameters ( FIG. 7 ) for increased stability. 
     EXAMPLES 
     The present invention is more particularly described in the following examples that are intended as illustrations only, since numerous modifications and variations within the scope of the present invention will be apparent to those skilled in the art. 
     Example 1—Insertion 
       FIG. 11  illustrates the load versus displacement of a glenoid component of the present invention and the load versus displacement of a comparative glenoid component during insertion into a foam structure designed to exhibit similar density properties of a scapula. The foam structure included an anchor hole for accepting an anchor of the glenoid component of the present invention and an anchor of the comparative glenoid component. 
     The glenoid component of the present invention included an anchor having a set of four distal fins extending from a distal end of the anchor and a set of two proximal fins extending from a proximal end of the anchor. The set of distal fins and the set of proximal fins are separated by a middle section of the anchor, such as illustrated in  FIG. 2 . The set of proximal fins were offset from a rear surface of the head portion by about 2.5 millimeters. 
     The comparative glenoid component was substantially similar to the glenoid component of the present invention except that the comparative glenoid component did not include a set of proximal fins positioned to engage with the cortical bone. The comparative glenoid component included only a set of four distal fins. 
     As can be seen in  FIG. 11 , the force required to advance the distal end of the glenoid component of the present invention and the distal end of the comparative glenoid component into the foam structure was comparable. Initially, the distal fins on both glenoid components contacted the anchor hole of the foam structure. To advance each of the distal fins through the anchor hole, the amount of force that was applied to the glenoid component increased, creating a first spike, a second spike and a third spike corresponding to the location of the first, second, and third distal fins along the distal end of the anchor. 
     As the glenoid component of the present invention was advanced further into the foam structure, however, the amount of force required to advance the anchor through the anchor hole increased in response to the first and second proximal fins engaging the anchor hole. The amount of force required to advance the proximal fins into the foam structure increased sharply as the first proximal fin and then the second proximal fin contacted the anchor hole, spiking to a required load of about 44.5 pounds and 39.5 pounds, respectively. 
     By contrast, the comparative glenoid component did not require additional force to advance the proximal end of the anchor into the anchor hole. Rather, the amount of force required to advance the comparative glenoid component into the foam structure steadily decreased to about 10 or about 11 pounds. On average, the glenoid component of the present invention required about 75% more force to insert the proximal end of the anchor through the anchor hole than required to insert the proximal end of the anchor of the comparative glenoid component through the anchor hole. 
     Example 2—Removal 
       FIG. 12  illustrates the load versus displacement of the glenoid component of the present invention and the load versus displacement of the comparative glenoid component during removal from the foam structure. 
     As can be seen in  FIG. 12 , the initial force required to pull the glenoid component of the present invention out from the foam structure spiked to about 39 pounds in the first millimeter of displacement, followed immediately by a spike of about 43.5 pounds at about 2 millimeters of displacement. In particular, a force of about 39 pounds was required to pull the first proximal fin through the anchor hole and a force of about 43.5 pounds was required to pull the second proximal fin through the anchor hole. These spikes all occurred within about 2 millimeters of displacement of the glenoid component of the present invention. 
     By contrast, the initial force required to move the comparative glenoid component relative to the foam structure increased more gradually, and only to an initial force of about 24 pounds within about 2 millimeters of displacement. It was not until the comparative glenoid component was displaced about 7.5 millimeters that the first distal fin engaged the anchor hole and increased the removal force to about 34 pounds. 
     As a practical matter, once the comparative glenoid component was displaced about 7.5 millimeters, the structural integrity of the prosthesis was compromised. The spike of about 34 pounds at 7.5 millimeters of displacement was too late to save the implant. 
     The glenoid component of the present invention provided a force about 71.5% greater than the comparative glenoid component, over less than half the displacement. As a result, the present glenoid component provided a significantly greater resistance to initial displacement than the comparative glenoid component. 
     Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range is encompassed within the inventions. The upper and lower limits of these smaller ranges which may independently be included in the smaller ranges is also encompassed within the inventions, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either both of those included limits are also included in the inventions. 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which these inventions belong. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present inventions, the preferred methods and materials are now described. All patents and publications mentioned herein, including those cited in the Background of the application, are hereby incorporated by reference to disclose and described the methods and/or materials in connection with which the publications are cited. 
     The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present inventions are not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed. 
     Other embodiments of the invention are possible. Although the description above contains many specificities, these should not be construed as limiting the scope of the invention, but as merely providing illustrations of some of the presently preferred embodiments of this invention. It is also contemplated that various combinations or sub-combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the inventions. It should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the disclosed inventions. Thus, it is intended that the scope of at least some of the present inventions herein disclosed should not be limited by the particular disclosed embodiments described above. 
     Thus the scope of this invention should be determined by the appended claims and their legal equivalents. Therefore, it will be appreciated that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural, chemical, and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims.