Patent Publication Number: US-2023149177-A1

Title: Humeral implant anchor system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 16/580,367, filed Sep. 24, 2019, which is a continuation of U.S. patent application Ser. No. 15/192,628, filed Jun. 24, 2016 (now U.S. Pat. No. 10,456,264) claiming priority to U.S. Provisional Application No. 62/192,797, filed Jul. 15, 2015, and as a continuation-in-part of PCT Application No. PCT/US2014/072443, filed Dec. 26, 2014, which claims to the priority benefit of U.S. Provisional Application No. 61/931,500, filed Jan. 24, 2014, all of which are hereby incorporated by reference in their entirety herein. 
    
    
     BACKGROUND 
     Field 
     The present disclosure relates to stemmed and stemless humeral components of a shoulder joint prosthesis. 
     Description of the Related Art 
     In a shoulder joint, the head of the humerus interacts with the glenoid cavity of the scapula in a manner similar to a “ball and socket” joint. Over time, it may become necessary to replace the shoulder joint with a prosthetic shoulder joint including a humeral component. 
     Traditionally, the humeral component is a single body implant having a humeral head and a stem. The stem is configured to be inserted into an intramedullary canal of the humerus. In certain cases, insertion of the stem disadvantageously requires bone to be removed to fit the stem to the canal due to patient-to-patient anatomical variation. Another disadvantage of this approach is that integration of the stem into the bone through a natural process of bone ingrowth can make it difficult to remove the humeral component if it becomes necessary to replace the humeral component with another device. Even when no removal was expected, this approach had the disadvantage of only achieving implant security after sufficient time had passed to allow for sufficient bone ingrowth. 
     A stemless humeral component may be used to address some of the disadvantages of conventional humeral components. Stemless humeral components can decrease the amount of bone loss in preparing the humerus to receive the component and decrease the complexity of the joint replacement procedure. 
     Stemless humeral component designs can be more challenging to secure to the humerus. Conventional stemless designs rely on bone ingrowth for strength. While such designs perform well over time, there is a risk in the early days and weeks after surgery where such ingrowth has not yet occurred that the stem and stemless humeral component will be dislodged from the humerus. Dislodgement may also occur due to excessive wear, forces applied thereto during a revision surgery or other high load conditions. 
     SUMMARY 
     Accordingly, there is a need for a stemless humeral component or prosthesis designed to preserve bone in initial implantation while enhancing initial pull-out resistance. Preferably enhanced initial dislodgement resistance will also provide excellent long term fixation. 
     The present disclosure relates to various embodiments of a stemless humeral shoulder assembly that can minimize bone loss and provide excellent initial pull-out resistance and long term fixation. Advantageously, the humeral shoulder assemblies described herein provide adequate compression, increase rotational and longitudinal stability, and encourage bone ingrowth. 
     Certain aspects of the disclosure are directed toward a prosthesis mounting system having a base member adapted to be driven into bone. The base member can include a central portion having a lumen extending along a longitudinal axis and a peripheral portion connected to the central portion. Further, the prosthetic mounting system can include an anchor having an inner passage sized to be advanced along the longitudinal axis of the base member. The anchor can have at least one thread surrounding the inner passage. When the anchor is coupled with the base member, the thread extends outward of the central portion of the base member. 
     In one embodiment, a stemless humeral shoulder assembly is provided. The assembly includes a base member and an anchor member. The base member has a distal end that can be embedded in bone and a proximal end that can be disposed at a bone surface. The base member has a plurality of spaced apart arms projecting from the proximal end to the distal end. The anchor member is advanceable into the base member to a position disposed within the arms. The anchor member is configured to project circumferentially into the arms and into a space between the arms. The anchor member is exposed between the arms when advanced into the base member. The assembly includes a recess projecting distally from a proximal end of the anchor member to within the base member. The recess is configured to receive a mounting member of an anatomical or reverse joint interface. 
     In another embodiment, a humeral shoulder assembly is provided that includes a stem and an anchor. The stem has a proximal region to be disposed in the metaphysis of a humerus, a distal end configured to be disposed in a canal of a humerus and a proximal end. The proximal end is to be disposed at a bone surface. The proximal region of the stem has a plurality of spaced apart projections disposed adjacent to the proximal end. The anchor is advanceable into the stem to a position disposed within the projections. The anchor is configured to project circumferentially into the projections and into a space between the projections. The anchor is exposed between the projections when advanced into the stem. The humeral shoulder assembly includes a recess that projects distally from a proximal end of the anchor to within the stem. The recess is configured to couple with an articular component. 
     In another embodiment, a prosthesis mounting system is provided that includes a stem and an anchor. The stem is adapted to be driven into bone. The stem has a central portion that includes a lumen. The lumen extends along a longitudinal axis. A peripheral portion of the stem is connected to the central portion. The stem extends distally of the central portion. The anchor has an inner passage sized to be advanced along the longitudinal axis. The anchor having at least one thread surrounding the inner passage. When the anchor is coupled with a proximal portion of the stem, the thread extends outward of the central portion of the base member. 
     Certain aspects of the disclosure are directed toward methods for treating a shoulder joint. The methods can include accessing a humeral head, resecting the humeral head, driving a base member into the humeral head, and advancing an anchor member into the base member. When the anchor member is advanced into the base member, a lateral projection of the anchor member can be disposed through the base member and can be embedded in bone adjacent to the base member. In certain aspects, the methods can also include securing a joint interface to the base member and/or the anchor member. 
     In another method for treating a shoulder joint, an end portion of a humerus is accessed. A stem is driven into the end portion of the humerus such that a portion of the stem extends into a canal of the humerus. An anchor member is advanced into the stem such that a lateral projection thereof is disposed through the stem and is embedded in bone adjacent to the stem. A joint interface is secured to the stem and/or the anchor member. 
     As described above, in certain aspects the stemless humeral component can be modular to provide more options for the surgeon during a revision surgery. For example, the modular humeral component can include a stemless fixation component adapted to be secured in the head of the humerus and a spherical head removably attached to the fixation component. During the revision surgery, the modular approach can make it easier to convert an anatomic shoulder prosthesis to a reverse shoulder prosthesis. 
     In any of the above-mentioned aspects, the anchor member can include a helical structure advanceable to engage corresponding surfaces of the arms. In certain aspects, the anchor can include a cylindrical sleeve and the helical structure can include at least one thread (e.g., one thread, two threads, three threads, or four threads) projecting laterally therefrom. 
     Any feature, structure, or step disclosed herein can be replaced with or combined with any other feature, structure, or step disclosed herein, or omitted. Further, for purposes of summarizing the disclosure, certain aspects, advantages, and features of the inventions have been described herein. It is to be understood that not necessarily any or all such advantages are achieved in accordance with any particular embodiment of the inventions disclosed herein. No aspects of this disclosure are essential or indispensable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects and advantages are described below with reference to the drawings, which are intended to illustrate but not to limit the inventions. In the drawings, like reference characters denote corresponding features consistently throughout similar embodiments. The following is a brief description of each of the drawings. 
         FIG.  1 A  is a perspective view of one embodiment of a stemless humeral shoulder assembly shown mounted in a humerus; 
         FIG.  1 B  is a cross-sectional view of  FIG.  1 A , showing the stemless humeral shoulder assembly disposed in the humeral head; 
         FIG.  2    is a perspective view of the stemless humeral shoulder assembly of  FIGS.  1 A and  1 B ; 
         FIG.  3    is an exploded view of the stemless humeral shoulder assembly of  FIG.  2   ; 
         FIG.  4    is a top view of the base member of the shoulder assembly of  FIG.  2   ; 
         FIG.  5    is a first side view the base member of  FIG.  4   ; 
         FIG.  6    is a second side view of the base member of  FIG.  4   ; 
         FIG.  6 A  is a cross-section of the base member shown in  FIG.  6    through line  6 A- 6 A in  FIG.  4   ; 
         FIG.  7    is a top perspective view of an anchor member of the shoulder assembly of  FIG.  2   ; 
         FIG.  8    is a side view of the anchor member of  FIG.  7   ; 
         FIG.  9    is a bottom view of the anchor member of  FIG.  7   ; 
         FIGS.  10 A- 10 H  illustrate steps of various methods of implantation of the stemless humeral shoulder assembly of  FIG.  2   ; 
         FIG.  11    is a top perspective view of another embodiment of a stemless humeral shoulder assembly; 
         FIG.  12    is a top perspective view of a base member of the stemless humeral shoulder assembly of  FIG.  11   ; 
         FIG.  13    is a top view of the base member of  FIG.  12   ; 
         FIG.  13 A  is a side view of the base member of  FIG.  12   ; 
         FIG.  14    is a top perspective view of an anchor member of the stemless humeral shoulder assembly of  FIG.  11   ; 
         FIG.  15    is a top view of the anchor member of  FIG.  14   ; 
         FIGS.  16 A- 16 C  illustrate steps of various methods of implantation of the stemless humeral shoulder assembly of  FIG.  11   ; 
         FIG.  17    is a top perspective view of another embodiment of a stemless humeral shoulder assembly; 
         FIG.  18    is a top perspective view of a base member of the stemless humeral shoulder assembly of  FIG.  17   ; 
         FIG.  19    is a top view of the base member of  FIG.  18   ; 
         FIG.  20    is a side view of the base member of  FIG.  18   ; 
         FIG.  21    is a bottom view of the base member of  FIG.  18   ; 
         FIG.  22    is a cross-sectional view of the base member of  FIG.  19    along line  22 - 22 ; 
         FIG.  23    is a top perspective view of an anchor member of the stemless humeral shoulder assembly of  FIG.  17   ; 
         FIGS.  24 A- 24 B  illustrate tool and component combinations that can be provided in various methods of implantation of the stemless humeral shoulder assembly of  FIG.  17   ; 
         FIG.  25    illustrates an adaptor or centering pin that can be used to align a driver with a base member, as discussed herein; 
         FIG.  26    illustrates the performance of various embodiments of stemless humeral shoulder assemblies; 
         FIG.  27    is a cross-sectional view of another embodiment of a shoulder assembly having a locking device disposed between a base member and an anchor member thereof to reduce or eliminate disengagement of the anchor member from the base member; 
         FIG.  27 A  is an enlarged view of the locking device shown in  FIG.  27    taken through line  27 A- 27 A; 
         FIG.  28    is a top perspective view of an anchor member assembly of the shoulder assembly of  FIG.  27   ; 
         FIG.  29    is a side view of a shoulder assembly having another embodiment of a locking device; 
         FIG.  30    is a side view of an anchor member of the shoulder assembly of  FIG.  29   ; 
         FIG.  31    is a top view of a shoulder assembly having another embodiment of a locking device; 
         FIG.  32    is a bottom perspective view of a tool for actuating a locking structure of the locking device of the shoulder assembly of  FIG.  31    from a disengaged configuration to an engaged configuration; 
         FIGS.  33  and  34    are a top perspective and side views of a humeral implant including the anchor member; 
         FIG.  35    is a side view of a stem of the humeral implant of  FIG.  33    without anchor member; 
         FIG.  36    is a view showing the components of a stemless humeral implant having one or more surfaces formed by additive manufacturing; and 
         FIG.  37    is a top perspective view of another embodiment of a humeral implant with a stem, at least a portion of the implant being formed by additive manufacturing. 
     
    
    
     DETAILED DESCRIPTION 
     While the present description sets forth specific details of various embodiments, it will be appreciated that the description is illustrative only and should not be construed in any way as limiting. Furthermore, various applications of such embodiments and modifications thereto, which may occur to those who are skilled in the art, are also encompassed by the general concepts described herein. Each and every feature described herein, and each and every combination of two or more of such features, is included within the scope of the present invention provided that the features included in such a combination are not mutually inconsistent. 
       FIG.  1 A  shows a humeral shoulder assembly  100  that has been implanted in an exposed face F of a humerus H. The assembly  100  has a recess  104  in which further components of a prosthetic shoulder joint can be secured. The configuration of the assembly including the recess  104  enable the humerus H and a corresponding scapula to be fitted with either an anatomical shoulder or a reverse shoulder configuration either initially or as part of a revision procedure.  FIG.  1 B  shows that in certain applications, the shoulder assembly  100  can be fully retained within a head h of the humerus H. In other words, the distal-most portion of the assembly  100  is disposed in the humeral head h. The assembly  100  does not have members that protrude beyond the head h into the intramedullary canal. This arrangement is less invasive and simplifies the procedure compared to a procedure involving a humeral component with a stem, as discussed elsewhere herein. 
       FIGS.  2 - 9    elaborate on advantageous structures and variations of the shoulder assembly  100  that can be employed in the stemless approach of  FIGS.  1 A- 1 B . Methods of using the shoulder assembly  100  are discussed below in connection with  FIGS.  10 A- 10 H . Shoulder assemblies capable of being at least partly delivered over a guide wire are discussed below in connection with  FIGS.  11 - 16 C .  FIGS.  17 - 24 B  illustrate shoulder assemblies where a joint interface mounting platform or recess is disposed on a base member and an anchor member is provided primarily or solely for bone securement function.  FIG.  25    shows an adaptor that can be used in connection with several embodiments and methods of applying shoulder assemblies.  FIG.  26    illustrates the performance of certain embodiments compared to a prior art design. While incremental differences in these embodiments and methods are discussed below, it is to be understood that features of each embodiment can be combined with features of the other embodiments, as appropriate. 
     I. Assemblies Having Reinforced 
     II. Bone Engaging Anchor Members 
       FIGS.  2  and  3    show more detail of components of the shoulder assembly  100  that among other features and advantages provides an anchor member with an inwardly positioned cylindrical member that reinforces outwardly positioned helical structures as discussed below. 
     The assembly  100  has a base member  108  and an anchor member  112 .  FIG.  3    shows that the base member  108  and anchor member  112  are separable components that can be applied to the patient separately, e.g., assembled in multiple steps within the bone as discussed below. The base member  108  has a distal end  120  and a proximal end  124 . The distal end  120  is configured to be embedded in the head of a humerus. The proximal end  124  is configured to be disposed adjacent to a face of the humerus or another bone surface. The base member  108  has a plurality of spaced apart arms  128  projecting from the proximal end  124  to the distal end  120 . The base member  108  also has a central portion, e.g., a cylindrical member  130 , that forms part of the recess  104 , as discussed in more detail below. In the illustrated embodiment, the arms  128  are equally spaced about the cylindrical member  130 . The arms  128  can be spaced apart by about 120 degrees. The base member  108  and the other base members discussed below can have three arms. The base member  108  and the other base members discussed below can have one or a plurality of arms  128 . In various embodiments, the base member  108  and the other base members discussed below can have two, three, four, five, or six arms. The arms  128  preferably are thin in the circumferential direction such that large gaps are provided between the arms. 
       FIGS.  3  and  4    show the proximal end  124  of the base member  108  in more detail. In particular, the proximal end  124  can include a peripheral member  140  disposed about the outer periphery of the proximal end  124 . The peripheral member  140  can be coupled with proximal ends  144  of the arms  128  (see  FIGS.  5 - 6 A ) to provide a unitary structure. In one embodiment, the peripheral member  140  comprises an annular structure  145  that is tapered such that a convex surface  146  is provided between proximal and distal portions of the peripheral member  140 . The convex surface  146  extends from a bone engaging side of the peripheral member  140  to a proximal side of the peripheral member  140 . The proximal side of the peripheral member  140  is disposed adjacent to but may be spaced from another joint component, such as a portion of an assembly including an anatomical or reverse shoulder joint humeral interface. 
     In one embodiment, the proximal end  124  can include a plurality of guide members  148  that can be coupled with the peripheral member  140 . The guide members  148  can include plate-like projections extending radially inwardly from an arcuate segment of the peripheral member  140 . The guide members  148  can be coupled with, attached to or a monolithic extension of an inner edge of the peripheral member  140 . In one embodiment, the base member  108  includes three guide members  148 . The guide members  148  can include an angled or lead surface  152  that is angled relative to a transverse plane of the proximal end  124 . As used in this context, a transverse plane of the proximal end  124  is a plane that extends perpendicular to a longitudinal axis A (see  FIGS.  5  and  6 A ) of the cylindrical member  130 . The angle of the lead surface  152  is selected to match the angle of a distal face of a helical structure of the anchor member  112  as discussed further below in connection with  FIGS.  6 A and  8   . 
     In one embodiment, each of the guide members  148  includes a flat surface  156 . Each of the flat surfaces  156  can be disposed on a transverse plane of the proximal end  124 . The flat surfaces  156  can extend between an outer portion  160  coupled with the peripheral member  140  and an inner portion  168  disposed adjacent to the cylindrical member  130 . In the illustrated embodiment, each inner portion  168  of three guide members  148  is spaced from the cylindrical member  130  by a corresponding gap  172 . The gaps  172  partly define an annular volume (projecting distally into the page in  FIG.  4   ) in which a cylindrical portion of the anchor member can be disposed, as discussed further below. 
       FIG.  3    shows that the flat surface  156  can be disposed at an elevation distal of (or below) the proximal-most aspect of the peripheral member  140 . The distance between the proximal-most aspect of the peripheral member  140  and the flat surface  156  can provide a space into which at least a portion of the anchor member  112  can be recessed. In one embodiment, a proximal end  180  of the cylindrical member  130  is disposed at about the same elevation of the proximal-most aspect of the peripheral member  140 . In some embodiments, an outside surface of the cylindrical member  130  and an inside surface of the peripheral member  140  define side surfaces of an annular space into which a proximal portion of the anchor member  112  can be received.  FIG.  2    shows that the annular space bounded by the outside surface of the cylindrical member  130  and the inside surface of the peripheral member  140  provides a substantially flush, e.g., stepless, profile or transition from the inner and proximal-most aspect of the peripheral member  140  to an outer periphery  182 A of the anchor member  112  and from an inner periphery  182 B of the anchor member to the proximal end  180  of the cylindrical member  130 . The flush profile enables other components of a shoulder joint to be drawn down adjacent to but preferably spaced from the assembly  100 . 
       FIG.  4    shows that the guide members  148  generally are spaced apart by arcuate openings  192 . The openings  192  extend from a lower end of one of the angled surfaces  152  to an end of an adjacent guide member  148 . As discussed further below, the openings  192  permit laterally extending portions of the anchor member  112  to be advanced into the base member  108 . In certain embodiments, the laterally extending projections include one or more, e.g., three, threads that can be advanced through the openings to engage with the base member  108  at a position distal of the guide members  148 .  FIG.  4    shows that the arms  128  are disposed distal of but accessible through the openings  192 . The arms  128  are located at a circumferential position between the angled surface  152  of a first guide member  148  and a non-angled surface of a second guide member  148 , where the second guide member is adjacent to the first guide member. Preferably, the circumferential position of the arms  128  is closer to the circumferential position of the non-angled surface of the second guide member  148  as shown. In this context, the circumferential position is determined by projecting these structures to the plane upon which the non-angled surface  148  is disposed.  FIG.  6 A  shows that a proximal portion of the arms  128  is located distal of the distal-most aspect of the angled surface  152 . 
       FIG.  6 A  shows one of the arms  128  in more detail. In some embodiments, the arms  128  are each identical. In other embodiments, the arms differ from each other. For example, in the single thread configurations of  FIGS.  11  and  17    the arms differ from each other in having slots advanced distally from a first arm to a next arm in the direction of rotation of an anchor member to accommodate the path of the helical member or thread, as discussed below in connection with those embodiments. The arms  128  have a plurality of slots  202 , e.g., three slots disposed between proximal and distal ends thereof.  FIG.  6 A  shows that the proximal-most slot  202  can be different from the two slots  202  disposed distal thereof in that the proximal-most slot  202  is bounded by a lower surface  218 A discussed below but not by a corresponding upper edge formed in the arm  128 . As noted above, the arm  128  is coupled with the peripheral member  140  at a proximal end  144  of the arm  128 . In one embodiment, a unitary structure is provided. In such a structure, a continuous structure can be provided from within the peripheral member  140  to within a proximal portion of the arm  128  so that there are no welds or joining lines or boundaries in this area. Such an arrangement simplifies the structure and eliminates potential areas for concentration of stress and potentially failure. 
     An outer edge  210  of the arms  128  provides a continuously arcuate sloping surface in one embodiment. The sloping surface can facilitate insertion of the base member  108  into an exposed humeral face F as discussed above and further below in connection with  FIGS.  10 A- 10 H . An inner edge  214  of the arm  128  can include one or a plurality of, e.g., three, laterally extending faces or surfaces  218 A,  218 B,  218 C. 
     The angle of the surfaces  152 ,  218 A,  218 B,  218 C can be configured to facilitate advancement of a lateral extent of the anchor member  112  along a helical path. For example, initial advancement of a lateral portion of the anchor member  112  can cause a leading edge surface of the anchor member  112  to slide along the surface  152  shown in  FIG.  6 A . Continued advancement can cause the leading edge surface of the anchor member  112  to approach and then slide across the surface  218 A shown in  FIG.  6 A . Continued advancement can cause the leading edge surface of the anchor member  112  to approach and then slide across a surface  218 B of an arm  128  disposed adjacent to and on a first side of the arm  128  shown in  FIG.  6 A . Continued advancement can cause the leading edge surface of the anchor member  112  to approach and then slide across a surface  218 C of an arm  128  disposed adjacent to and on a second side of the arm  128  shown in  FIG.  6 A . Once the anchor member  112  slides across the surface  218 C of each arm  128 , the anchor member  112  can continue to rotate an additional 5-15 degrees to further compress the entire construct into the bones. Advancement is complete when a proximal face of the threads  340  (see  FIG.  8   ) contacts an upper surface  222 B,  222 C of the slots  202  (see  FIG.  6 A ). 
     At least some of the surfaces  218 A,  218 B,  218 C can be disposed in laterally projecting recesses or channels of the arms  128 . For example, the surface  218 B extends laterally outwardly from the inner edge  214  of the arms  128 . A corresponding surface  222 B can extend outwardly from the inner edge  214  adjacent to the surface  218 B. The surfaces  218 B,  222 B can be substantially parallel along their length. The surfaces  218 B,  222 B can be spaced apart by a short distal-proximal distance. The short distal-proximal distance can be about the same as the thickness of lateral protrusions (e.g., threads) of the anchor member  112  discussed below. In these embodiments both of the surfaces  218 B,  222 B play a role in guiding the advancement of the anchor member  112 . The face  222 B can have an angled surface similar to that of the surface  218 B. For example, the angle of the face  222 B can be the same angle as that of the face  218 B. 
     In one embodiment, each of the faces  218 A,  218 B,  218 C has a length as measured radially away from the axis A that differs from the length of the other faces. The distal-most face  218 C can have the shortest length. The proximal-most face  218 A can have the longest length. A face  218 B disposed between the distal- and proximal-most faces  218 C,  218 A can have an intermediate length. These lengths can correspond to the tapered profile of the base member  108 , e.g., with the arms  128  having a generally convex shape from proximal to distal as viewed from the side. The lengths of the faces  218 A,  218 B,  218 C can correspond to the profile of the lateral projection of the anchor member  112 , which is some embodiments may be tapered. 
     In one embodiment, the proximal-most face  218 A does not have a corresponding face on the arm  128  disposed proximal thereof. A lower surface of the guide member  148  disposed adjacent to but clockwise of the arm  128  can abut a proximal side of a thread while a distal side of the thread advances along the face  218 A. In this sense, each of the faces  218 A,  218 B,  218 C has a corresponding surface that together guide a thread of the anchor member  112  as discussed further below. 
     In the embodiment of  FIGS.  1 - 10 H , each arm has a plurality of, e.g., three faces  218 A,  218 B,  218 C. The face  218 A of each of the arms  128  is disposed at the same elevation as the corresponding face  218 A of adjacent arms  128 . The face  218 B of each of the arms  128  is disposed at the same elevation as the corresponding face  218 B of adjacent arms  128 . The face  218 C of each of the arms  128  is disposed at the same elevation as the corresponding face  218 C of adjacent arms  128 . This construction defines a plurality of helical paths on the base  108  for guiding helical members, as appropriate for certain embodiments. Other embodiments have different helical paths, such as a single path as discussed below in connection with the embodiments of  FIGS.  11  and  17   . Rather, a plurality of spaced-apart surfaces reside on and/or define the helical path. In one right-hand configuration, a first helical path is defined by a face  218 A of a first arm  128 , a face  218 B of a second arm  128  adjacent to but disposed clockwise of (as defined above) the first arm, and a face  218 C of a third arm  128  adjacent to but disposed counter-clockwise of (as defined above) the first arm. In one embodiment, the first helical path also includes the lead surface  152  disposed above and circumferentially between the first and third arms  128 . A second helical path can extend from a surface  152  to the second arm  128  to a face  218 C of the first arm  128 . A third helical path can extend from a surface  152  of the third arm  128  to a face  218 C of the second arm  128 . Each of the surfaces on the helical paths can have substantially the same angle relative to a transverse plane of the base  108 . In some embodiments, the angle of the faces  218 A,  218 B,  218 C can be different. 
     In other embodiments of the base member  108 , three left-handed helical paths can be provided, each one commencing with an oppositely oriented surface similar to the surfaces  152  and traversing counter-clockwise to a face  218 A below and on the arm  128  immediately counter-clockwise of the oppositely oriented surface, then to the face  218 B on the next arm  128  and then to the face  218 C on the next arm  128 . In this context, the “next arm  128 ” is the arm circumferentially spaced from and immediately counter-clockwise of the arm from which the path extends. 
     Unlike a conventional mating screw structure, only very small segments of the helical path involve contact between the faces  218 A,  218 B,  218 C and a mating structure. This arrangement enhances the surface area of the anchor thread contacting bone when the assembly  100  is disposed in the bone. 
       FIG.  5    shows that a gap  232 A is provided between the inner edge  214  and the cylindrical member  130  below the face  218 A. A gap  232 B is provided between the inner edge  214  and the cylindrical member  130  below the face  218 B. A gap  232 C is provided between the inner edge  214  and the cylindrical member  130  below the face  218 C. The gap  232 C is substantially the same width as the gaps  232 A,  232 B. In one embodiment, the gaps  232 A,  232 B,  232 C are substantially the same as the gap  172 . The gaps  172 ,  232 A,  232 B,  232 C define part of a cylindrical space configured to receive part of the anchor member  112  as discussed further below. The gap  232 C enables a distal portion of the anchor member  112  to be advanced distal of the face  218 C. 
       FIG.  6 A  shows that in some embodiments, the cylindrical member  130  has a threaded recess  250  formed in a lower portion thereof. The threaded recess  250  enables a component to be advanced into engagement with the base member  108 . The component can be another component of a prosthetic joint or can be a tool used in placement of one or more components of the shoulder assembly  100 . The recess  250  can engage a guide tool  432  (see  FIG.  25   ) in one technique, discussed in more detail in connection with  FIG.  10 F . 
       FIGS.  2  and  7 - 9    illustrate features of the anchor member  112  which, as discussed above, is advanceable into the base member  108  to a position disposed within the arms  128 . The anchor member  112  includes a proximal face  300 , a helical structure  304  disposed distally of the proximal face  300 , and a cylindrical sleeve  308  configured to be disposed around the recess  104 . In some embodiments, the sleeve  308  is configured to be advanced over and receive the cylindrical member  130  as discussed further below. 
     The proximal face  300  comprises the proximal side of a disc structure  312  disposed at the proximal end of the anchor member  112 . The disc structure  312  is configured to be disposed in a space partly bounded by the flat surfaces  156 , the inner face of the peripheral member  140 , and the outer face at the proximal end  180  of the cylinder member  130  of the base member  108  (see  FIG.  3   ). The disc structure  312  can have a thickness (proximal-to-distal distance) substantially the same as the distance from the flat surfaces  156  to the proximal most aspect of the peripheral member  140 . The anchor member  112  is configured such that regions  320  ( FIG.  9   ) of the distal surface of the disc structure  312  are advanced into a position to abut the flat surfaces  156  of the base member  108  when the shoulder assembly  100  is assembled. 
       FIGS.  8  and  9    show the helical structure  304  in more detail. In one embodiment, the helical structure  304  includes three spaced apart helical protrusions  332 A,  332 B,  332 C. In this embodiment, the anchor member  112  has a triple lead configuration. Other embodiments can have a single lead (as in the embodiments discussed in connection with  FIGS.  11  and  17    below), a double lead, or a quadruple lead configuration. Distal ends of the three helical protrusions  332 A,  332 B,  332 C can be seen in  FIG.  9   . Each of these helical protrusions  332 A,  332 B,  332 C has progressively larger diameter from a distal end to a proximal end thereof in the illustrated embodiment. The larger size toward the proximal end enables the helical protrusions to project farther laterally into the faces  218 A,  218 B,  218 C of the arms  128 . The smaller size toward the distal end enables the disruption of bone toward the distal end to be minimized. The helical protrusions can be threads in some embodiment. 
       FIG.  8    shows distal and proximal faces  336 ,  340  of one of the helical protrusions. The distal face  336  is configured to be advanced along one or guided by one of the helical paths described above. The distal face  336  is angled relative to a transverse (e.g., perpendicular) cross-sectional plane of the anchor member  112 , which angle may be selected to match the lead surface  152 , as discussed above. For example, the distal face  336  can slide along the lead surface  152 , one of the faces  218 A, one of the faces  218 B, and one of the faces  218 C. The proximal face  340  can slide along or be guided by the surface  228 B ( FIG.  6 A ) or another distally-oriented face disposed in one of the arms  128  or on a lower surface of the guide member  148 . 
       FIG.  8    shows that a spiral or helical surface  342  extends between adjacent helical protrusions  332 A,  332 B,  332 C. The spiral surface  342  can extend from the base of a distal surface  336  of the helical protrusion  332 B to the base of the proximal surface of the helical protrusion  332 C. The spiral surface  342  has a proximal to distal dimension that is about the same as the proximal-distal dimension of the side surface  214  between the surfaces  218 A,  228 B (See  FIG.  6 A ). The proximal to distal dimension of the spiral surface  342  is about 50% larger than and in some cases twice as large as the proximal to distal dimension of the helical protrusions  332 A,  332 B,  332 C. 
       FIG.  2    shows that the anchor member  112  projects into the arms  128  and into a space between the arms when the anchor member and the base member are assembled. The anchor member  112  is exposed between the arms  128  when advanced into the base member  108 . More specifically, a plurality of elongate segments  352  of the helical protrusions  332 A,  332 B,  332 C are not covered by the faces  218 A,  218 B,  218 C,  222 B of the arms  128  but rather are located in an open area between the arms. The exposed segments  352  create areas of engagement with the bone that vastly increase the initial pull-out force of the assembly  100  when initially placed. This improved initial pullout force greatly reduces the chance of dislodgement, as discussed below in connection with  FIG.  26   . 
     Some additional unique features of the assembly  100  include helical surfaces in the anchor member  112  that mate only in very small and spaced apart areas of the base member  108  while exposing a majority of the helical surface to allow the exposed areas to be disposed directly in the bone for direct contact therewith. In some embodiments, a portion of the helical surface is disposed within the arms  128  and not exposed but a majority of the helical surface is exposed to be embedded in bone. The percentage of the surface area of the exposed segments  352  to the total area of the helical protrusions  332 A,  332 B,  332 C is between about 80 and 98% in some embodiments. The percentage of the area of the exposed segments  352  to the total area of the helical protrusions  332 A,  332 B,  332 C is between about 85 and 95% in some embodiments. The percentage of the area of the exposed segments  352  to the total area of the helical protrusions  332 A,  332 B,  332 C is about 91% in some embodiments. Similarly, the ratio of the length of the exposed segments  352  to the total length of the helical protrusions  332 A,  332 B,  332 C is between about 0.8 and about 0.98, e.g., between about 0.85 and about 0.95, e.g., about 0.9 in various embodiments. It may be desirable to further enhance engagement of the assembly  100  and other assemblies herein by increasing the ratios and percentages discussed in this section. Higher percentages and ratios can be provided by decreasing the distance between threads such that each thread has more turns. The percentage and ratios discussed in this passage are also applicable to the other embodiments discussed below. 
     Also, the structure provided herein enables the threads to extend a large distance from the center of the recess  104 . For example, the lateral extent, e.g., radius of the helical protrusions  332 A,  332 B,  332 C can be at least 50% of the lateral extent, e.g., radius of the peripheral member  140 , for example, at least about 50% and/or less than or equal to about 75%. In some embodiments, the lateral extent of at least one of the helical protrusions  332 A,  332 B,  332 C can be at least about 50%, such as between about 50% and about 55%, of the diameter of the peripheral member  140 . In some embodiments, the lateral extent of at least one of the helical protrusions  332 A,  332 B,  333 C can be at least about 60%, such as between about 60% and about 65%, of the diameter of the peripheral member  140 . In some embodiments, the lateral extent of the helical protrusions  332 A,  332 B,  333 C can be at least about 70%, such as between about 70% and about 75%, of the diameter of the peripheral member  140 . In certain embodiments, as shown in  FIG.  8   , the diameter of each of the helical protrusions  332 A,  332 B,  332 C can vary from the proximal face  300  to the distal end  310  of the anchor  112 . For example, the diameter of a portion of the helical protrusions  332 A,  332 B,  332 C near the proximal face  300  can be greater than the diameter of a portion of the helical protrusions  332 A,  332 B,  332 C near the distal end  310 . The percentage can be measured against any portion of the protrusions  332 A,  332 B,  332 C. In some embodiments, the lateral extent of the helical protrusion  332 C can be between about 50% and 55% of the diameter of the peripheral member  140 , while the lateral extent of the helical protrusion  332 A can be between about 70% and 75% of the diameter of the peripheral member  140 . 
       FIG.  7    shows that the proximal face  300  of the anchor member  112  can include a driver interface  364  to facilitate advancing the anchor member  112  into the base member  108 . The driver interface  364  can take any suitable form, for example, as three spaced apart recesses. The recesses can be cylindrical recesses extending into the disc member  312 . 
       FIGS.  10 A- 10 H  illustrate methods of implanting the humeral shoulder assembly  100  into the humerus H. Prior to the step illustrated by  FIG.  10 A , surgical access has been provided to the humerus H and the humerus has been prepared. Preparing the humerus H can include cutting off a joint-facing portion of the humeral head h. The joint facing portion can be further prepared, for example by providing a countersunk region CS in the exposed face F. The countersunk region CS enhances a low profile application of the assembly  100  as discussed further below. A pin  400  is placed in a central region of the countersunk region CS.  FIG.  10 B  shows that the pin  400  may be used to guide a reamer to create a well at the base of the pin.  FIG.  10 C  shows the well having received a tool  404  that has been advanced into the face F to modify the well to receive the base member  108 . For example, the tool  404  has a plurality of, e.g., three, radial projections  406  to create channels radiating from the well as shown in  FIG.  10 D . Preferably the projections  406  have an edge profile similar to that of the arms  128 , e.g., with a convex edge from proximal to distal when viewed from the side similar to the edge  210 . 
       FIG.  10 D  show the expose humeral face F with the pin  400  and tool  404  removed so that a created recess CR in the face F is shown. The recess CR is configured to permit the base  108  to be advanced with ease into the face F of the humeral head h as shown in  FIG.  10 E . More specifically, the recess CR is shaped to match the shape of a portion of the base member  108  that projects distally. For example,  FIG.  4    shows that the arms  128  can be equally spaced about the base member  108 , e.g., outer ends thereof coupled with the peripheral member  140  can be spaced circumferentially by about 120 degrees. The arms  128  can be thin at radially outer portions thereof and can be joined adjacent to the distal end  120  of the base member  108 . Accordingly, the radial projections of the recess CR created by the radial projections  406  of the tool  404  can be narrow and spaced apart by the same amount as the arms  128 , e.g., about 120 degrees apart. 
     Although the projection  406  and corresponding projections of the recess CR are generally straight, radial projections, the projections  406  could be curved and/or can extend away from a central region to in a non-radial direction matching the shape and orientation of any projections of the base member  108 . 
     Preferably, the insertion of the base member  108  into the recess CR can be achieved with ease, e.g., without an impactor or any other tools, but rather by hand force. The base member  108  advantageously is symmetrical about the axis A (see  FIGS.  4  and  5   ). This allows the surgeon to insert the base member  108  in any orientation provided that the arms  128  and the projections in the recess CR are aligned. Other configurations have a preferred orientation, as discussed further below. 
       FIGS.  10 E- 10 F  show that the countersunk region CS is configured to receive the peripheral member  140  in a recessed position. For example, the countersunk region CS has a bone recessed area, which is recessed by about the proximal-distal dimension  416  (shown in  FIG.  6   ) of the peripheral member  140 . By recessing the base member  108 , the base member and/or the humeral shoulder assembly  100  can positioned as desired relative to the face F of the humeral head h, e.g., with a small gap or flush mounted. Flush-mount enables a joint interface coupled with the assembly  100  to be positioned close to the face F, e.g., with little to no gap therein. Consistent and accurate positioning of the assembly  100  and joint interface can be important factors in properly locating the prosthetic joint interface. 
       FIG.  10 F  shows that after the base member  108  has been inserted into the face F of the humerus a subsequent step can involve coupling the guide tool  432  with the base member.  FIG.  25    shows details of one embodiment of the guide tool  432 . The guide tool  432  preferably includes a guide body  436  disposed at a proximal portion thereof. The guide body  436  projects outside and proximally of the base member  108  and is configured to guide the anchor member  112  to be advanced thereover. In one form, the guide body  436  is a cylindrical member. A distal portion  440  of the guide tool  432  is configured to be coupled with the base member  108 . In particular, a threaded distal portion  444  is configured to mate with the threads in the threaded recess  250  (see  FIG.  6 A ). A tapered portion  448  facilitates insertion of the guide tool  432  into the cylindrical member  130  of the base member  108 . More particularly as shown in  FIG.  6 A , the cylindrical member  130  can be tapered on an inside surface thereof, such that the recess formed in the member  130  is narrower at the distal end than at the proximal end thereof. Stated another way, a wall surrounding the recess in the cylindrical member  130  is closer to the axis A near the threads  250  than near the proximal end of the recess. Similarly, the outside surface of the tapered portion  448  is closer to a central longitudinal axis B of the guide tool  432  than is a proximal portion of the tapered portion  448 . The tapers match such that if the guide tool  432  is inserted into the cylindrical member  130  with the axis A, B offset, the surface  448  and the inside surface of the recess in the cylindrical member  130  match to align these axes before the threads  444  and the threads in the recess  250 . 
       FIG.  10 G  shows the anchor member  112  engaged with the base member  108 . This configuration results from advancement of the anchor member  112  over the guide tool  432  in one method. In one embodiment, a method step includes coupling a driver with the driver interface  364  on the proximal face  300  of the anchor member  112 . The driver can take any suitable form, e.g., can include a plurality of protrusions configured to mate with recesses of the driver interface  364 . The driver can be configured to snap into or onto the anchor member  112  at the driver interface  364 . Embodiments of a driver are discussed below in connection with  FIGS.  16 B and  24 B . Preferably, the driver has a ratchet mechanism such that the surgeon can continuously hold the tool and need not release the handle to re-grip it to apply additional turns to the anchor member  112 . However, one advantage of the three thread design of the anchor member  112  is that less rotation of the anchor member is required as compared to a two thread design or a one thread design to fully seat the anchor member in the base member  108 . 
     In one method, the surgeon observes the face F of the humerus and advances the anchor member  112  until some fluid is observed to emerge from the recess CR and/or around the assembly  100 . The emergence of fluid suggests that the anchor member  112  is fully seated in the bone in a way providing excellent initial bone retention. Such retention provides enhanced pull-out force. 
       FIG.  26    illustrates the initial pull-out force  1510  for Embodiment A, a variant of the shoulder assembly  100  in which the anchor member  112  has a single continuous thread. Portions of the helical structure  304  project into the open area defined between the arms  128  and engage the bone thereby increasing the initial pull-out force of the assembly  100  when initially placed. As shown in  FIG.  26   , the peak force corresponding to the initial pull out force  1510  of Embodiment A is at least ten times greater than the peak force corresponding to the initial pull out force  1500  of the prior art design having a base member and no anchor thread. 
     As discussed above, the assembly  100  enables a variety of joint interface components. The surgeon can couple an anatomical joint interface with the assembly  100 , e.g., by positioning an anchor portion of the anatomical joint interface in the recess  104 . In some cases, a reverse shoulder configuration is better for the patient. The surgeon can dispose an anchor portion of a reverse configuration shoulder joint interface in the recess  104 .  FIG.  10 H  shows an adaptor  464  coupled with the recess  104 . The adaptor  464  can be seated with a concave socket portion  468  that can be coupled with a convex head implanted in the scapula in the reverse shoulder configuration. 
     The methods described above, e.g., in connection with  FIGS.  10 A- 10 H , can include additional steps and employ additional tools as discussed below. The shoulder assembly  100  also can be adapted to be compatible with other methods herein, e.g., having a guidewire passage suitable for employing over-the-wire methods discussed below. 
     The assembly  100  and the methods described above can be modified by incorporation of structures and methods discussed in connection with the embodiments below. 
     III. Assemblies Having Guidewire Delivery Capability 
     IV 
       FIG.  11 - 16 C  show a stemless shoulder assembly  500  and methods similar to the shoulder assembly  100  and methods discussed above except as described differently below. The assembly  500  is configured to allow a guidewire to be used to advance components thereof into a prepared humeral face F, providing for an efficient and accurate procedure. The assembly  500  includes a recess  504 , a base member  508 , and an anchor member  512 . As discussed more below, a thread or other helical protrusion  532  extends from the anchor member  512  into engagement with the base member  508  and into an open area where it can engage bone. In this embodiment, the anchor member  512  has a single lead configuration. Other embodiments can have a multiple lead configuration, e.g., including a double lead, a triple lead, or a quadruple lead configuration. 
       FIGS.  12 ,  13  and  13 A  show features of the base member  508  that facilitate delivery of the base member and/or the anchor member  512  over a guidewire. For example, the base member  508  has a plurality of arms  528 A,  528 B,  528 C that extend between a distal and a proximal end  520 ,  524  of the base member  508 . The arms  528 A, B, C are coupled with a sleeve  530  disposed adjacent to the distal end  520  of the base member  508 . The sleeve  530  has an opening at a proximal end  534  thereof extending into a lumen  538 . The lumen  538  extends from the opening at the proximal end  534  to an opening at the distal end  520  of the sleeve  530 . The lumen  538  is accessible through an open space  542  disposed between the arms  528 A, B, C and between the proximal end  534  of the sleeve  530  and the proximal end  524  of the base member  508 . The space  542  provides access to the lumen  538  by a direct path, e.g., a path perpendicular to the plane of the proximal end  524  of the base member  508 . 
       FIG.  12    shows that the base member  508  includes a guide surface  548  and a lead surface  552  in some embodiments. The guide and lead surfaces  548 ,  552  can be regions of a continuous guide member and can be a continuous expanse without a change in orientation between them. The guide surface  548  can be substantially flat, e.g., disposed on a plane that is perpendicular to a longitudinal axis C of the lumen  538 . The lead surface  552  can be angled to match the pitch of the helical protrusion  532  (see  FIG.  14   ) on the anchor member  512 . The guide member or the guide and lead surfaces  548 ,  552  can be disposed adjacent to a periphery of the base member  508 , e.g., between a peripheral member  540  and the axis C. In one embodiment, the guide and lead surfaces  548 ,  552  are coupled at outer edges thereof with an inner edge of the peripheral member  540 . In one embodiment, a circumferential gap  544  is provided between ends of the guide and lead surfaces  548 ,  552 . The gap  544  is configured to permit the helical protrusion  532  (see  FIG.  14   ) to be advanced along the lead surface  548  to a top laterally extending surface  560 A of the first arm  528 A, which is disposed beneath the gap  544 . 
       FIG.  13 A  show the path from the lead surface  552  to the top surface  560 A through the gap  544  is a first segment of a helical path about the axis C. A second segment of the helical path extends from the top laterally extending surface  560 A to a top laterally extending surface  560 B on the arm  528 B. A third segment of the path extends from the top laterally extending surface  560 B to a top laterally extending surface  560 C of the arm  528 C. A fourth segment of the path extends from the top laterally extending surface  560 C to a laterally extending surface  564 A of the arm  528 A below the surface  560 A. The laterally extending surface  564 A is a mid-level surface on the arm  528 A. The helical path through the base  508  extends in the same manner across a plurality of mid-level surface corresponding to the surface  564 A and a plurality of surfaces at a lower level of the arms to a distal end point on or adjacent to or at a laterally extending surface  568 C. The helical path described above accommodates a single helical protrusion, e.g., thread, of the anchor member  512 . An advantage of this design is that only a single thread must traverse a gap in the proximal surface of the base portion  508 . Also, the thread is much longer than the thread of the anchor member  112  and is generally at a shallower angle and so may be advanceable along the helical path with less torque than is required for the anchor member  112 . 
       FIGS.  14  and  15    show further details of the anchor member  512 . In particular, the anchor member  512  has a proximal face  600  having a tapered annular surface. The proximal face  600  can include a driver interface  604  that can take any suitable form, such as any of those described above. For example, driver interface  604  can include a plurality of recesses.  FIG.  15    shows that the recess  504  can extend from the proximal face  600  to a distal end having an aperture  608  formed therein. The aperture  608  can be configured to receive a guidewire such that the anchor member  512  can be advanced over a wire, as discussed further below. 
       FIGS.  16 A-C  illustrate various methods of implanting the shoulder assembly  500 . The method can include compatible steps of any of the methods discussed above in connection with  FIGS.  10 A- 10 H , including initial preparation of a humeral head with a recess to receive a guidewire  650 . The guidewire  650  can take any suitable form and is sometimes known as a Kirschner wire or K-wire. The guidewire  650  is placed into a recess extending distally into a face of a humeral head. Once in place, the base member  508  is advanced over the proximal end  654  of the guidewire  650 , e.g., an opening at the distal end of the lumen  538  is advanced over the proximal end  654  of the guidewire  650 . The lumen  538  is sized so that the base member  508  can easily slide along the length of the guidewire  650  to a position corresponding to the position of the base member  108  in  FIG.  10 E . 
     Thereafter, the base member  508  is advanced into the bone. For example, if a recess have been formed that has a profile similar to that of the base member  508 , the base member can be urged into the recess with low force, e.g., with hand force and without impactors or with light force from the impactor. In some methods, the gap  544  is oriented with respect to the anatomy. For example, the gap  544  can be disposed at a lower elevation (caudad) compared to the position of the guide surface  548 . 
       FIG.  16 B  illustrates further step in which a cannulated driver  662  is advanced over the guidewire  650 . The cannulated driver  662  preferably has an interface configured to mate with the driver interface  604  on the anchor member  512 . The driver  662  can have a plurality of prongs extending distally therefrom to engage recesses in the face  600  of the anchor member  512 . In one step, the surgeon couples the driver  662  with the anchor member  512 . Once so coupled, the driver  662  and the anchor member  512  are advanced over the guidewire  650 . An initial step of advancing the driver  662  and the anchor member  512  over the guidewire  650  includes inserting the proximal end  654  of the guidewire  650  into the aperture  608  in the anchor member  512 . Continued advancement of the driver  662  and the anchor member  512  causes the guidewire  650  to be advanced through the driver  662  and out of a proximal end  668  thereof. 
     Once the driver  662  and the anchor member  512  are adjacent to the proximal portion of the base member  508 , the distal portion of the helical protrusion  532  is placed against the guide surface  548  and/or the lead surface  552  and through the gap  544  and from there along the helical path discussed above. Once fully advanced, the cannulated driver  662  can be removed leaving the shoulder assembly  500  in place as shown in  FIG.  16 C . Thereafter the guidewire  650  is removed to allow subsequent steps to proceed, including attachment of a joint interface as discussed above. 
     Among the additional advantages of the shoulder assembly  500  is providing a single sleeve-like structure in the anchor member  512  rather than co-axial sleeve one in each of the base and anchor members. In particular, in the assembly  500  only the anchor member  512  includes a cylindrical structure. The cylindrical structure of the assembly  500  reinforces the helical protrusion  532  and also comprises the recess  504 . This provides a simpler construction having fewer components. Also, there is no chance for multiple cylinders to be slid over each other to become misaligned, leading to binding or increased torque requirements for advancing the anchor member  512  into the base member  508 . 
     V. Assemblies Having Reinforced Base Members 
     VI 
       FIGS.  17 - 24 B  illustrate an embodiment of a humeral shoulder assembly  1000  in which distally projecting arms are more rigid by virtue of being coupled to each other and directly to a cylinder member at intermediate positions. This structure retains the direct bone engagement of exposed threads while making the arms more rigid. 
       FIG.  17    illustrates the assembly  1000  having a base member  1008  and an anchor member  1012 . The base member  1008  and the anchor member  1012  are separable components that can be applied to the patient separately, e.g., assembled in multiple steps within the bone in techniques similar to those discussed above. 
       FIGS.  18 - 22    illustrate various views of the base member  1008 . The base member  1008  has a distal end  1020  configured to be embedded in bone and a proximal portion  1024  to be disposed adjacent to the face F of the humerus H or another bone surface. 
     As shown in  FIG.  20   , the base member  1008  can have a plurality of spaced apart arms  1028  projecting from the proximal portion  1024  to the distal end  1020  of the base member  1008 . Each arm  1028  can define an outer edge  1210  having an arcuate sloping surface. The sloping surface can facilitate insertion of the base member  1008  into an exposed humeral face F as discussed above in connection with  FIGS.  10 A- 10 H . Further, each arm can define an inner edge  1214 . The inner edge  1214  of a distal portion  1046  of each of the arms can be connected to form the distal end  1020  of the base member  1008  (see  FIG.  21   ). 
     The inner edge  1214  of each arm  1208  can include one or more laterally extending recesses  1218 A,  1218 B,  1218 C. The number of laterally extending recesses can vary between different arms  1028 . For example, as shown in  FIG.  20   , a first arm can include a first recess  1218 A and a second recess  1218 B, while a second arm can include only one recess  1218 C. The recesses  1218 A,  1218 B of the first arm can be longitudinally displaced from the recess  1218 C of the second arm to accommodate a helical structure  1304  of the anchor member  1012  (see  FIG.  17   ). Additionally, the outermost edge of each of the laterally extending recesses  1218 A,  1218 B,  1218 C can be equidistant from the longitudinal axis of the base member  1008  to accommodate an anchor member  1012  having a substantially constant outer diameter along the helical structure  1304  (see  FIG.  17   ). 
     The base member  1008  can also include a central portion (e.g., a cylindrical member  1030 ). As shown in  FIG.  22   , the cylindrical member  1030  can include an open proximal end  1034  and a closed distal end  1032 . The proximal end  1034  can define the proximal-most point of the base member  1008 . In certain aspects, the proximal end  1034  can include an annular groove  1076  ( FIG.  18   ) for receiving a c-ring that may be present to prevent loosening between the anchor member  1012  and the base member  1008 . A c-ring can be part of a locking device, as discussed further in connection with  FIGS.  27 - 27 A  below. Further, a threaded recess  1250  can be formed in the distal portion of the cylindrical member  1030 . The threaded recess  1250  enables a component to be advanced into a secure position of engagement with the base  1008 . The component can be part of a prosthetic joint interface or can be a tool used in placement of the shoulder assembly  1000 . For example, as shown in  FIG.  24 A , the recess  1250  can engage a guide tool  432  ( FIG.  25   ). The guide tool  432  can extend the length of the cylindrical member  1030  to facilitate insertion of the anchor member  1012  into the base member  1008 . 
       FIG.  20    shows that the outer wall of the cylindrical member  1030  can define a helical channel  1050  (e.g., groove or opening). The outer wall of the cylindrical member  1030  can connect to the inner edge  1214  of the arms  1028 , such that portions of the helical channel  1050  can align with each of the laterally extending recesses  1218 A,  1218 B,  1218 C to form a pathway for the helical structure  1304  of the anchor member  1112  (see  FIG.  17   ). 
       FIG.  19    illustrates that the proximal portion  1024  of the base member  1008  can include a peripheral member  1040  disposed about the outer periphery of the proximal portion  1024 . The peripheral member  1040  can be coupled with the proximal ends of the arms  1028  (see  FIG.  22   ) to provide a unitary structure. As shown in  FIG.  19   , the proximal portion  1024  can include a guide member  1048  that can be connected to the peripheral member  1040 . The guide member  1048  can be partially recessed from the proximal face of the peripheral member  1040  to provide a space into which a proximal disc structure  1312  of the anchor member  1012  can be positioned (see  FIG.  17   ). Further, the guide member  1048  can include a plate-like projection extending radially inwardly from the peripheral member  1040  to a proximal portion of the cylindrical member  1030 . For instance, the guide member  1048  can extend continuously from the inner edge of the peripheral member  1040  to the cylindrical member  1030  around at least about 50% of an inner diameter of the peripheral member  1040 . In an arcuate segment, the guide member  1048  can extend discontinuously from the inner edge of the peripheral member  1040  to the cylindrical member  1030 . For example, a gap  1072  can be defined adjacent to but radially inward of an arcuate segment of the guide member  1048  that is disposed between the peripheral portion  1040  and the gap  1072 . The gap  1072  facilitates insertion of the anchor member  1012  into the base member  1008 . 
     As shown in  FIG.  20   , the proximal end  1034  of the cylindrical member  1030  can be elevated above the proximal-most aspect of the peripheral member  1040 . When the anchor member  1012  is connected to the base member  1008  (see  FIG.  17   ), the proximal disc structure  1312  can fill the annular space bounded by the outside surface of the cylindrical member  1030  and the inside surface of the peripheral member  1040  to create a tapered, annular surface from proximal end  1034  of the cylindrical member  1030  to the peripheral member  1040 . This structure avoids inflection points in the side profile of the assembly  1000 , which is advantageous in reducing or eliminating gaps between the assembly  1000  and another component of a shoulder joint assembly coupled therewith. 
       FIG.  23    illustrates features of the anchor member  1012 , which has a proximal disc structure  1312 . The proximal disc structure  1312  can define a central opening  1316  that can surround the proximal end  1034  of the cylindrical member  1030  when the shoulder assembly  1000  is assembled. Further, the proximal disc structure  1312  can include a driver interface  1364  (e.g. a plurality of openings) for engaging a driving tool  450  (see  FIG.  24 B ). Rotating the driving tool  450  can advance the anchor member  1012  to rotationally engage the base member  1008 . 
     The anchor member  1012  can also include a continuous helical structure  1304  disposed distally of the proximal disc structure  1312 . In this embodiment, the anchor member  1012  has a single helical structure  1304 . Other embodiments can have a multiple helices, e.g., including a double helix, a triple helix, or a quadruple helix configuration. The inner edge of the helical structure  1304  can define the innermost edge of the anchor member  1012  distal of the disc structure  1312  in that the anchor member  1012  does not include a central body structure. In at least this sense, the anchor member  1012  has an open helix construction. The helical structure  1304  defines a substantially constant inner diameter and a substantially constant outer diameter in one embodiment. 
     When the shoulder assembly  1000  is assembled, the disc structure  1312  can abut the guide member  1048  of the base member  1008  and the helical structure  1304  can be disposed in the helical groove  1350  and the laterally extending recesses  1218 A,  1218 B,  1218 C of the base member  1008  (see  FIG.  17   ). Portions of the helical structure  1304  project into the open area defined between the arms  1208  and engage the bone, thereby increasing the initial pull-out force of the assembly  1000  when initially placed. As shown in  FIG.  26   , the peak force corresponding to the initial pull out force  1520  of the shoulder assembly  1000  is at least five times greater than the peak force corresponding to the initial pull out force  1500  of the prior art. 
       FIGS.  24 A- 24 B  illustrate tools that can be used to implant the shoulder assembly  1000  and corresponding methods. The method of using the tools can include compatible steps of any of the methods discussed above in connection with  FIGS.  10 A- 10 H  including creating a recess CR in the humeral head (see  FIG.  10 D ). Once the recess CR is created, the base member  1008  can be inserted into the face F of the humerus head h (similar to  FIG.  10 E ). Preferably, the insertion of the base member  1008  can be achieved without an impactor or any other tools, but rather just inserted by hand force. 
     After the base member  108  has been inserted into the recess CR, a subsequent step can involve coupling the guide tool  432  with the base member  1008  (see  FIG.  24 A ). As described above,  FIG.  25    illustrates one embodiment of the guide tool  432 . The guide tool  432  can extend the length of the cylindrical member  1030  to guide the anchor member  1112  into the base member  1008 . To advance the anchor member  1012  over the guide tool  432 , the method can include coupling a driver  450  with the driver interface  1364  (see  FIG.  24 B ). The driver  450  can take any suitable form, e.g., can include a plurality of protrusions configured to mate with openings of the driver interface  1364 . Preferably, the driver  450  has a ratchet mechanism such that the surgeon can continuously hold the tool and need not release the handle to re-grip it. Once the shoulder assembly  1000  is assembled, the driver  450  and the guide tool  432  can be removed. 
     The methods described above, e.g., in connection with  FIGS.  24 A- 24 B , can include additional steps and employ additional tools as discussed above. The shoulder assembly  1000  and/or the tool  450  also can be adapted to be compatible with other methods, e.g., with over-the-wire methods. For instance, the base member  1008  can have a lumen extending through the distal end  1020  to guide the base member into place. A channel in the tool  450  can be used in guiding the anchor member  1012  into place in the base member  1008 . 
     VII. Locking Devices to Reduce or Eliminate Disengagement 
     VIII. Of Base and Anchor Members 
       FIGS.  27 - 32    show features that can reduce or eliminate disengagement between a base member and an anchor member. These embodiments are illustrated in connection with the shoulder assembly  100 , but can be used in connection with any of the embodiments herein. Also, although the features are discussed separately they could be combined in some embodiments. 
       FIGS.  27  and  27 A  shows a shoulder assembly  1100  that includes a base member  1108 , an anchor member  1112 , and a locking device  1118  disposed adjacent to a proximal end  1124  of the base member  1108 . The locking device  1118  comprises a C-ring  1122  that is disposed partially in a recess or groove  1126  (See  FIG.  27 A ) of the anchor member  1112  and partially in a groove  1130  (see  FIG.  27 A ) of the base member  1108 .  FIG.  28    shows a partial assembly in which the C-ring  1122  is coupled with the anchor member  1112  prior to coupling the anchor member  1112  to the base member  1108 . In the illustrated embodiment, the C-ring  1122  is disposed in the anchor member  1112  prior to implantation.  FIG.  27 A  shows that the cross-sectional shape of the C-ring  1122  facilitates actuation of the C-ring  1122  during assembly. A distal face  1134  of the C-ring  1122  is angled relative to a plane oriented perpendicular to the distal-proximal direction of the assembly  1100 . In assembly, the anchor member  1112  is advanced into the base member  1108  until the distal face  1134  engages a proximal portion  1138  (See  FIG.  27 A ) of the base member  1108  and is deflected thereby into or deeper into the recess  1126  of the anchor member  1112 . This permits the anchor member  1112  to move relative to the base member  1108  until the C-ring  1122  moves to the position of the groove  1130 . The resilience of the C-ring  1122  causes the C-ring to return to an un-deflected configuration thereof.  FIG.  27 A  shows the final position of the C-ring  1122  with a portion disposed in the groove  1130  and a portion disposed in the groove  1126 . In this configuration, the anchor member  1112  is locked into the base member  1108  because further advancement of the anchor member  1112  into the base member  1108  is prevented by contact between a base face  1148  and an anchor face  1120  and because retraction of the anchor member  1112  from the base member  1108  is prevented by the C-ring  1122  in cooperation with grooves  1126  and  1130  (see  FIG.  27   ). 
     In other embodiments, the C-ring  1122  can be coupled with the base member  1108  prior to assembly of the anchor member  1112  with the base member  1108 . In such embodiments, a surface of the anchor member  1112  can be configured to deflect the C-ring  1122  into or deeper into the groove  1130 . In such embodiments, a proximal face of the C-ring  1122  may be angled relative to a plane oriented perpendicular to the distal-proximal direction of the assembly to facilitate deflection of the C-ring. Although a C-ring is illustrated, other structures that can be temporarily deflected into the recess  1126  or the recess  1130  can be used, such as spring loaded or resilient detents or members or other similar structures. 
       FIGS.  29  and  30    illustrate another embodiment of a shoulder assembly  1200  that has a base member  1208 , an anchor member  1212 , and a locking device  1218  comprising an interface between the anchor member  1212  and the base member  1208 . The locking device  1218  includes a distal projection  1220  disposed on a distal side of a helical protrusion  1232  (see  FIG.  30   ).  FIG.  30    shows that the distal projection  1220  can have a first face  1222  that is oriented generally proximal to distal and a second face  1226  that is disposed at an angle relative to a plane extending perpendicular to the proximal-distal direction of the anchor member  1212 . 
     In use, the anchor member  1212  is advanced into the base member  1208  in the same manner as described above in connection with the assembly  100 . As the anchor member  1212  approaches the fully engaged position, the second face  1226  of the projection  1220  approaches a first side  1228 A of the arm  1228  of the base member  1208 . The second face  1226  passes across a lower lateral face of an upper-most slot of the arm  1228 . As the second face  1226  crosses the arm  1228  from the first side  1228 A, local deformation of at least one of the arm  1228  and the projection  1220  permits further advancement of the second surface  1226  relative to the arm until the first surface is disposed on the second side  1228 B of the arm  1228  (see  FIG.  29   ). The local deformation is preferably temporary such that the deformed structure(s) return toward their undeformed state(s). Once disposed on the second side  1228 B of the arm  1228 , the first face  1222  abuts a corresponding surface of the second side  1228 B of the arm  1228 . In this configuration, the anchor member  1212  is locked into the base member  1208  because further advancement of the anchor member  1212  into the base member  1208  is prevented by contact between an upper surface of the base member  1208  and an anchor face  1224  and because retraction of the anchor member  1212  from the base member  1208  is prevented by contact between the first face  1222  and the second side  1228 B of the arm  1228 . 
     The locking device  1218  is simple in construction in that a first portion of the interface is disposed on the anchor member  1212  and a second portion of the interface is disposed on the base member  1208  and thus does not require another separable component compared to the shoulder assembly  1100 . Also, the locking device  1218  does not require an additional discrete step in the locking of the base member  1208  to the anchor member  1212  because the final step of passing the projection  1220  from the first side  1228 A to the second side  1222 B is accomplished with the same rotation as is required in connection with the assembly  100 , though some additional force may be required to provide the local deformation discussed above. 
       FIGS.  31  and  32    show another embodiment of a shoulder assembly  1300  that has a base member  1308 , an anchor member  1312 , and a locking device  1318  comprising at least one, e.g., a plurality of deflectable prongs  1320  that can be deployed to span from one of the anchor member  1312  and the base member  1308  to the other of the anchor and base members. The spanning of the prong(s)  1320  causes a portion of the prong to be engaged with the base member  1308  and another portion to be engaged with the rotatable anchor member  1312  such that rotation of the anchor member in either direction is reduced or eliminated. 
       FIG.  31    shows that the prongs  1320  can be disposed on the anchor member  1312  about an inner periphery  1332  of a disc structure  1336  thereof. The base member  1308  can have a cylindrical member  1324 , similar to that discussed above in connection with the assembly  100 . The cylindrical member  1324  can have a plurality of scallops or recesses  1328  disposed on a side surface thereof. The recesses  1328  can extend entirely around the cylindrical member  1324  in one embodiment to enable the prong(s)  1320  to be engaged at a nearest recess  1328  rather than come precisely to rest at a specific rotational position and recess. In other embodiments, the base and anchor members  1308 ,  1312  could be provided with the same number or prongs and recesses, wherein the location of the prongs and recesses are provided at an expected fully engaged position of the anchor member  1312  relative to the base member  1308 . 
       FIG.  31    shows the prong(s)  1320  in a disengaged position. Any suitable technique or tool can be used to deploy the prongs  1320  across a gap between the anchor member  1312  and the base member  1308 .  FIG.  32    illustrates a tool  1400  that can be used to deploy the prongs  1320 . The tool  1400  includes a proximal user grip portion  1404 , which can be a cylindrical member or any other ergonomic gripping structure. The tool  1400  also includes a plurality of pins  1408  disposed on a distal portion thereof that are configured and positioned to engage driver interfaces  1364  disposed on the proximal face of the disc structure  1336 . The pins  1408  can be on an opposite side of the tool  1400  from the grip portion  1404 . The tool  1400  also includes a plurality of prong actuators  1412  disposed on the same side of the tool as are the pins  1408 . The prong actuators  1412  can each include a first, radially inward side  1416  and a second, radially outward side  1420 . An angled surface  1424  is disposed between the sides  1416 ,  1420 . The angled surface  1424  is configured to engage the prongs  1320  and deflect and in some cases deform them as the tool  1400  is advanced. For example, the radially outward side  1420  is configured and positioned to be inserted into a recess  1340  disposed in the proximal faces of the disc  1336  radially outward of the prongs  1320 . This initial insertion of the prong actuator  1412  into the recess  1340  can be up to a point where the angled surface  1424  first engages the prong  1320 . The radial distance from the first, radially inward side  1416  to the second, radially outward side  1420  is greater than the radial extent of the recess  1340 . The radial distance from the first, radially inward side  1416  to the second, radially outward side  1420  spans the recess  1340 , the gap between the anchor and base members  1312 ,  1308  and into the scallop or recess  1328 . Further advancement of the tool  1400  causes the angled surface  1424  to engage the prong  1320 . Still further advancement of the tool  1400  causes the prong  1320  to be deflected, e.g., bent or otherwise deformed into the recess  1328  of the base member  1308 . When so deflected, the prong  1320  spans from the disc structure  1336  of the anchor member  1312  to the recess  1328  of the base member  1308 . Because the base member  1308  is fixed in the bone, the coupling of the prong  1320  with the base member  1308  causes the anchor member  1312  also to be fixed relative to the bone. This prevents any backing out or unintended disengagement of the anchor member  1312  from the base member  1308 . 
     As illustrated, one embodiment of the locking device  1318  comprises six prongs  1320 . In other embodiments, one prong  1320  can be provided. In other embodiments, a plurality of prongs, e.g., two three, four, five, twenty, or more prongs  1320  can be provided. The prongs  1320  could be disposed on the base member  1308  and could be deflected, e.g., bent or otherwise deformed, into a scallop or recess disposed on the anchor member  1312  in other embodiments. In further embodiments, the prong  1320  can be configured as a spanning member that need not be formed as a part of either the base member  1308  or the anchor member  1312  but rather as a separate components installed at the proximal side of the assembly  1300 . As discussed above, the various locking devices discussed herein can be combined to provide multiple locking structures. 
     IX. Anchor Members which Lock to Stems 
     As demonstrated above, the unique anchor and base members described herein provide for excellent securement of joint implant to bone, e.g., of humeral implants to a resected humerus. The excellent securement provided by these implants is provided immediately after a procedure without the need to wait for bone ingrowth.  FIGS.  33 - 35    illustrate a humeral implant  1600  and components thereof. The humeral implant  1600  includes a stem and that combines the securement benefits of a stem with the securement benefits of the base and anchor member as discussed herein. 
       FIGS.  33  and  34    show the humeral implant  1600  includes a stem  1610 . The implant  1600  also includes an anchor member  1612 . As discussed further below, the anchor member  1612  is similar to other anchor members discussed above. The description of the features of the other anchor members discussed herein may be combined with or substituted for the features of the anchor member  1612  described below. 
     The anchor member  1612  has a proximal face  1614  and a distal threaded portion  1618 . The distal threaded portion  1618  can have a radially inner edge coupled with a cylindrical portion  1619  of the anchor member  1612 . A radial outer edge and an expanse between the inner and outer edges of the threaded portion  1618  are adapted to be advanced into and then to be embedded in bone. The implant  1600  provides high confidence in securement by combining the engagement between the threaded portion  1618  and the bone matter in the metaphysis with engagement between the distal portion  1636  of the stem  1610  and the bone matter surrounding the canal of the humerus. In the event the engagement between the threaded portion  1618  and the bone matter of the metaphysis is not sufficient, the stem  1610  provides additional securement. See  FIG.  26    and corresponding discussion for details of securement using such a threaded portion. The proximal face  1614  can have a tool interface  1620  that can be engaged by a driver to advance the anchor member  1612  into or remove the anchor member from the stem  1610 .  FIG.  34    shows that the proximal face  1614  can be flush with a proximal portion of the stem  1610  when fully advanced. That is, the face  1614  can be positioned so that it does not protrude proximally of a proximal most aspect of the stem  1610 , which is discussed further below.  FIG.  33    shows that the proximal face  1614  can be annular, providing an inner edge  1622  that allows access to a portion of the stem  1610  as discussed below. The inner edge  1622  can be disposed at the proximal end of the cylindrical portion  1619 . In one embodiment, the cylindrical portion  1619  projects from the inner edge  1622 .  FIG.  33    also shows that the proximal face  1614  includes an outer edge  1624  that can be received by and in some cases surrounded by an outer periphery of a proximal portion of the stem  1610 . 
     The stem  1610  is advantageous in providing multiple modes of securement to a bone, e.g., to a proximal humerus. Compared to the aforementioned stemless designs, the stem  1610  gives a surgeon an option in evaluating a patient to be able to quickly adapt a surgical plan to an implant providing more security or providing security to a different bone segment, such as a canal which may be more robust than the cancellous bone disposed at or just beneath the resection plane.  FIG.  35    shows that the stem  1610  includes a proximal portion  1632  and a distal portion  1636 . The distal portion  1636  is configured to be inserted through cancellous bone, for example through a resected humerus of a patient. A distal tip  1640  of the distal portion  1636  can be inserted to extend into an intramedullary canal of the humerus. In some embodiments the distal portion  1636  includes a central portion  1644  extending proximally from the distal tip  1640 , with one or more projections  1648  extending away from the central portion  1624 . The projections  1648  can include two, three, four or more projections  1648 . In some embodiments, the projections  1648  are evenly spaced around the central portion  1644 . For example, if there are three projections  1648 , they may be spaced apart by 120 degrees. The projections  1648  enable the distal portion  1636  to be inserted into the canal of a long bone, such as a humerus, along thin outer edges of the projections  1348  such that contact with the bone in the canal is initially line contact. This makes insertion of the distal portion  1636  easier because there is less friction between the stem  1610  and the bone. While this provides for relatively minimal surface contact, the anchor member  1612  provides excellent securement, as discussed further below. 
     The proximal portion  1632  includes a distal region that can have the same or a similar form to that of a proximal region of the distal portion  1636 . For example, the distal region of the proximal portion  1632  can have a central portion  1652  and one or a plurality of projections  1656 . The proximal portion  1632  also can have one or more, e.g., three, projections. In one use, the stem  1610  is configured such that when implanted in a long bone, e.g. in the humerus, the proximal portion  1632  is disposed in the metaphysis of the bone. That is, the bone may be resected and thereafter, the distal portion  1636  can be advanced into the canal of the humerus, leaving the proximal portion  1632  in the metaphysis. 
     The projections  1656  can include similar or the same features discussed above in connection with the arms  128  projection from the proximal end of the anchor member  108 . For example, the projections  1656  can include lateral spaces to receive and guide the threaded portion  1618  of the anchor member  1612  to the advanced position as shown in  FIGS.  33  and  34   . A gap also can be defined between the inner edges of the projections  1656  and an outer surface of the central portion  1652 . The gap can accommodate the cylindrical portion  1619  of the anchor member  1612 . 
       FIG.  33    shows that the stem  1610  of the implant  1600  includes a peripheral rim  1660  disposed about, e.g., surrounding the central portion  1652 . The central portion  1652  can include a cylindrical member that is similar to the cylindrical member  130  in some embodiments. The peripheral rim  1660  preferably is coupled with each of the projections  1656 . The peripheral rim  1660  can be configured to provide structural integrity to the projections. The peripheral rim  1660  has a plurality of tool features  1664  disposed about the periphery. In one embodiment, the tool features  1664  include three features equally spaced about the rim. The features can be used to advance the stem  1610  distally into the humerus after the humerus has been resected. In the event the stem  1610  is to be explanted the tool features  1664  can be engaged to dislodge the stem from the humerus. 
     The stem  1610  also includes a recess  1666  in which an articular component, such as a glenosphere, can be anchored. The recess  1666  is similar to the recess  104  discussed above in certain embodiments. The recess  1666  can be disposed in the central portion  1652 . The central portion  1652  can have a tapered inner surface to provide a Morse taper connection with the articular component. 
     A method of implanting the implant  1600  can be similar to those discussed above. For example, the humerus can be resected at about the level of the metaphysis. Thereafter, access to the canal of the humerus can be provided or confirmed. After the access has been provided, the stem  1610  can be advanced through the resected surface of the humerus. For example, the tip  1640  can be urged through the resection plane and thereafter deeper into the humerus and further into the humeral canal. As the stem  1610  is advanced the projections  1648  engage the canal and act to center the distal portion  1636  of the stem in the canal. Advancement can be over a wire (in which case stem  1610  can be cannulated) as illustrated above in connection with  FIGS.  16 A- 16 C  or freehand. After the stem  1610  is situated in the bone such that the peripheral rim  1660  is about at the plane of the resection, the surgeon can confirm placement. If appropriate, the surgeon may further advance the stem by impacting the stem into the bone. After the stem  1610  is properly placed, the anchor member  1612  can be advanced into the proximal portion  1632  of the stem as discussed above. For instance, a tool can engage the features  1620  and then apply a torque to engage the thread start(s) of the anchor member  1612  with the thread guiding features of the projections  1656 . Full advancement of the anchor member  1612  can be confirmed by a positive stop of the cylindrical portion  1619  or by visible confirmation. The implant  1600  provides at least two independent modes or zones of securement. In one mode, the implant  1600  is secured in the cancellous bone of the humerus at the methaphysis by the threaded portion  1618  disposed within the proximal portion  1632  of the stem  1610 . The proximal portion  1632  thus corresponds to one zone of securement. This mode and zone of securement are similar to that discussed above in connection with  FIG.  26   . A second mode of securement is provided by the distal portion  1636  of the stem  1610 , wherein the stem can integrate with the bone matter surrounding the canal of the humerus. The distal portion  1636  thus corresponds to another zone of securement. 
     X. Assemblies Having Porous Titanium Structures 
       FIGS.  36 - 37    illustrate embodiments in which one or more components are at least partially formed by additive manufacturing. In certain additive manufacturing techniques a structure is assembled from components to create a three dimensional porous metal structure. The structure is formed by applying or creating individual layers that are later joined together through a suitable process, such as sintering. The layers can be laid down to progressively to form the three dimensional structure.  FIG.  36    shows a humeral implant  1700  including a base member  1708 , an anchor member  1712 , and a humeral head  1714 . In one embodiment, one or more features of the anchor member  1712  are formed by a process of additive manufacturing. More specifically, the spaced apart arms or projections  1728  of the anchor member  1708  and other structures that interact with the bone may be comprised of a unitary or monolithic porous titanium (Ti-6Al-4V). A bottom surface of a peripheral rim  1740  can be formed by additive manufacturing. As a result, the arms  1728  and/or the distal side of the rim  1740  can have a porous titanium structure that contacts a bone, e.g., a resected portion of the humerus. Porous titanium has a modulus similar to bone or of about 2.6 GPa. Matching the modulus of the porous titanium to the bone may enable better stress transfer from the implant to the bone, reducing wear on the bone, and increasing strength at the bone/implant interface. 
     The porous titanium structure can have a pore size from about 300 to about 800 μm, in embodiments from about 350 to about 750 μm, and in further embodiments from about 400 to about 700 μm. The porosity of the porous titanium structure may be optimized per implant geometry and anatomy and can be about 50%, 55%, 60%, 65%, 70%, 75%, and 80% porous. 
     Porous titanium can be formed by an additive manufacturing process, including a 3 dimensionally (3-D) printing process where layers of titanium are formed to create a three dimensional structure. The initial layer or layers are formed by such a method directly onto a portion or surface of the anchor member  1708 . The 3-D printing process includes direct metal laser sintering onto the implant, more specifically, the anchor member  1708 . First, blanks are formed by sintering titanium powder with a laser directly onto the substrate or anchor member. Next, in some techniques the blanks are machined, constructed or shaped to create a specific geometry of the bone-engaging surface. In some embodiments, the blanks are shaped to create either a stemless implant (as in  FIG.  36   ) or an implant with a stem that can couple with the anchor member discussed herein (as in  FIG.  37   ). Although the 3-D process is used herein to create stemmed or stemless members for implantation in the metaphysis and/or the canal of the humerus, other portions and surfaces of the implants may be formed with porous titanium, and are within the scope of this disclosure, including, but not limited to the anchor member or peripheral screws or portions thereof, central posts, and other structures that may be combined therewith. Once constructed, the porous structure and the solid substrate of baseplate comprise a monolithic, or one-piece structure. Alternatively, Electron Beam Melting (EBM) can be used to 3-D print a porous three dimensional structure on the implant. 
       FIG.  37    shows a humeral implant  1800  that is a modified embodiment of the humeral implant  1600 . The implant  1800  includes an anchor member  1812  and a stem  1810 . The stem  1810  includes a porous substrate  1814  that is disposed over a portion thereof. In one embodiment, the porous substrate is formed by additive manufacturing, e.g., 3-D printing as discussed above. The porous substrate  1814  can extend over a proximal portion of the stem  1810 . For example, the porous substrate can be disposed over the metaphyseal bone contacting surfaces of the portion of the base not embedded in a canal of the humerus in use. The proximal portion that is porous titanium can include some or all of a plurality of projections  1856 . The proximal portion that is porous titanium also can include some or all of a peripheral rim  1860 , e.g., a distal bone engaging side of the rim  1860 . The porous titanium substrate can also extend distally of the projections  1856  to a location at or just distal of the narrowing of the metaphysis. 
     In one embodiment, a kit is provided that includes a stemless humeral implant, such as the humeral shoulder assembly  100 , and a stemmed humeral implant such as the implant  1600  or the implant  1800 . By providing these components together in a kit a clinician can quickly adapt during a procedure from a stemless approach to a stemmed approach. For example, if the bone is not strong enough to support a stemless implant, the stemmed implant can be used without significant delay or use of much different components. In fact, the anchor member  112  could be used with either stem or stemless implants. Furthermore, some kits can include a variety of sizes of one or both of the stemless implant or the stemmed implant. For example, the base member  108  can come in different sizes to occupy an appropriate volume of the metaphysis of the specific humerus that is being treated by the surgeon. In some embodiments, the stem  1610  or the stem  1810  can be provided in a number of sizes such that the distal ends thereof reaches an appropriate depth in the canal of the humerus and/or fits in the canal with little or no preparation of the bone around the canal. 
     As used herein, the relative terms “proximal” and “distal” shall be defined from the perspective of the humeral shoulder assembly. Thus, distal refers the direction of the end of the humeral shoulder assembly embedded in the humerus, while proximal refers to the direction of the end of the humeral shoulder assembly facing the glenoid cavity. 
     Conditional language, such as “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements, and/or steps. Thus, such conditional language is not generally intended to imply that features, elements, and/or steps are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without user input or prompting, whether these features, elements, and/or steps are included or are to be performed in any particular embodiment. 
     The terms “approximately,” “about,” and “substantially” as used herein represent an amount close to the stated amount that still performs a desired function or achieves a desired result. For example, the terms “approximately”, “about”, and “substantially” may refer to an amount that is within less than 10% of, within less than 5% of, within less than 1% of, within less than 0.1% of, and within less than 0.01% of the stated amount. As another example, in certain embodiments, the terms “generally parallel” and “substantially parallel” refer to a value, amount, or characteristic that departs from exactly parallel by less than or equal to 15 degrees, 10 degrees, 5 degrees, 3 degrees, 1 degree, 0.1 degree, or otherwise. 
     Some embodiments have been described in connection with the accompanying drawings. However, it should be understood that the figures are not drawn to scale. Distances, angles, etc. are merely illustrative and do not necessarily bear an exact relationship to actual dimensions and layout of the devices illustrated. Components can be added, removed, and/or rearranged. Further, the disclosure herein of any particular feature, aspect, method, property, characteristic, quality, attribute, element, or the like in connection with various embodiments can be used in all other embodiments set forth herein. Additionally, it will be recognized that any methods described herein may be practiced using any device suitable for performing the recited steps. 
     For purposes of this disclosure, certain aspects, advantages, and novel features are described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the disclosure may be embodied or carried out in a manner that achieves one advantage or a group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein. 
     Although these inventions have been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that the present inventions extend beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the inventions and obvious modifications and equivalents thereof. In addition, while several variations of the inventions have been shown and described in detail, other modifications, which are within the scope of these inventions, will be readily apparent to those of skill in the art based upon this disclosure. It is also contemplated that various combination 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. Further, the actions of the disclosed processes and methods may be modified in any manner, including by reordering actions and/or inserting additional actions and/or deleting actions. 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. The limitations in the claims are to be interpreted broadly based on the language employed in the claims and not limited to the examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive.