Patent Publication Number: US-2023157830-A1

Title: Patient specific femoral prosthesis

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a divisional of U.S. patent application Ser. No. 16/732,672 filed Jan. 2, 2020, which is a continuation-in-part of U.S. patent application Ser. No. 16/587,683 filed Sep. 30, 2019, the disclosure of which is hereby incorporated by reference as if set forth in its entirety herein. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to customizable femoral components used in a total hip arthroplasty and more particularly to femoral implants having different core geometries within a casing that surrounds the core. 
     BACKGROUND 
     Joint arthroplasty is a well-known surgical procedure by which a diseased and/or damaged natural joint is replaced by a prosthetic joint. For example, in a hip arthroplasty surgical procedure, a prosthetic hip replaces a patient&#39;s natural hip. A typical prosthetic hip includes an acetabular orthopaedic prosthesis and/or femoral head orthopaedic prosthesis. A typical acetabular orthopaedic prosthesis includes an acetabular cup, which is secured to the patient&#39;s natural acetabulum, and an associated polymer bearing or ring. 
     A typical femoral component includes a stem having a neck and an elongate body extending distally from the neck, and a femoral head configured to be positioned on the neck of the stem. The stem of the femoral component is secured to a patient&#39;s femur. In some examples, the stem can be surrounded by an outer sleeve that defines an outer surface of the femoral component in the medullary canal of the femur. The femoral head can articulate in the acetabular cup to replicate the motion of a natural hip joint. 
     Examples of hip prostheses are shown and described in U.S. Pat. Nos. 10,213,314 and 10,213,310 
     SUMMARY 
     According to one aspect of the disclosure, an orthopaedic system includes a prosthetic femoral stem and a prosthetic femoral head configured to engage a patient&#39;s natural acetabulum or an acetabular prosthetic component. The femoral stem includes an outer casing configured to engage a patient&#39;s femur. The outer casing defines a longitudinal axis that is configured to be positioned in a coronal plane of the patient&#39;s femur when the femoral stem is implanted in the patient&#39;s femur. In some embodiments, an outer casing surface of the outer casing defines the longitudinal axis. The femoral stem also includes a neck configured to receive the prosthetic femoral head to position the prosthetic femoral head at a predetermined position relative to the longitudinal axis of the outer casing and/or the coronal plane. The femoral stem may be manufactured to place the neck at a number of selectable angles to move the prosthetic femoral head in an anterior-posterior direction relative to the longitudinal axis of the outer casing and/or the coronal plane, in a medial-lateral direction, and/or in an inferior-superior direction. The selectable angles may shift the neck anteriorly or posteriorly relative to the longitudinal axis of the outer casing and/or the coronal plane, medially or laterally, and/or inferiorly or superiorly. The selectable angles may also adjust a degree of tilt of the neck relative to the longitudinal axis of the outer casing. The degree of tilt may cause the neck to be pivoted in any direction (anterior, posterior, medial, lateral, inferior or superior) relative to the outer casing to change the position of the femoral head. 
     In one example, a femoral prosthesis includes an elongate core body that extends along a central core body axis from a proximal core body end to a distal core body end opposite the proximal core body end. The core body includes a medial core body side and a lateral core body side opposite the medial core body side. The medial and lateral core body sides extend from the proximal core body end to the distal core body end. The core body is configured to be received in a medullary canal of a femur. The femoral prosthesis further includes a neck that extends out with respect to the proximal core body end. The femoral prosthesis further includes a porous casing that encases at least a portion of the core body. The porous casing defines an inner casing surface that faces the core body and an outer casing surface opposite the inner casing surface. The inner surface of the porous casing extends along a central inner casing axis that is substantially coincident with the central core body axis. The outer surface of the porous casing extends along a central outer casing axis that intersects the central inner casing axis within an outer perimeter of the core body with respect to a side elevation view of the stem component that includes the proximal core body end and the distal core body end. 
     In another embodiment, a femoral prosthesis can include a core body and a casing that surrounds at least a portion of the core body. The casing can be additively manufactured to produce a plurality of femoral prostheses that include substantially identical core bodies, but also define at least one respective geometry that differs from the other of the femoral prostheses. 
     In one example, the femoral implant can include a core that includes the core body and a neck that extends out with respect to the core body at a fixed angle. The at least one respective geometry can include a selectable neck angle that is defined by a central neck axis and a central axis of an outer casing surface of the casing. Alternatively or additionally, the at least one geometry can include a neck offset measured from the casing to the neck along a direction substantially parallel to the central neck axis. Alternatively or additionally still, the at least one geometry can include a rotational position of the core body in the casing. 
     In another example, the casing can define an inner casing surface that faces the core and extends along a central inner casing axis. The core body can extend along a core body axis that is substantially coincident with the central inner casing axis. The outer casing surface can extend along a central outer casing axis that is angularly offset with respect to the central inner casing axis. 
     In another example, the casing can define a thickness that extends from the inner casing surface to the outer casing surface. The thickness can increase in a distal direction at one of a medial side of the casing and a lateral side of the casing, and can decrease in the distal direction at the other of the medial side of the casing and the lateral side of the casing. 
     In another example, the casing can define a thickness that extends from the inner casing surface to the outer casing surface. The thickness can increase in a distal direction at one of a medial side of the casing and a lateral side of the casing, and can decrease in the distal direction at the other of the anterior side of the casing and the posterior side of the casing. 
     In another embodiment, a femoral prosthesis includes an elongate core body that defines a medial core body side and a lateral core body side opposite the medial core body side substantially along a medial-lateral direction. The femoral prosthesis further includes a neck that extends out with respect to the elongate core body. The femoral prosthesis further includes a porous casing that encases at least a portion of the core body. The porous casing can define an inner casing surface that faces the core body and an outer casing surface opposite the inner casing surface. The porous casing can define an anterior casing surface and a posterior casing surface opposite the anterior casing surface substantially along an anterior-posterior direction. The medial core body side can define a first distance from the anterior side along the anterior-posterior direction and a second distance from the posterior side along the anterior-posterior direction that is different than the first distance. 
     In one example, the core body can be angulated such that the medial core body side defines a first distance from an anterior side of the casing along an anterior-posterior direction and a second distance from a posterior side of the casing along the anterior-posterior direction that is different than the first distance. 
     In another embodiment, a first femoral prosthesis and a second femoral prosthesis each define a medial side and a lateral side opposite the medial side along a medial-lateral direction, and an anterior side and a posterior side opposite the anterior side along an anterior-posterior direction. Each of the first and second femoral prostheses include a core having a core body elongate along a core body axis, the core body defining an outer core body surface. The core further has a neck that is monolithic with the core body, wherein the neck extends out with respect to the core body along a central neck axis. The core of the first femoral prosthesis is substantially identical to the core of the second femoral prosthesis. The first femoral prosthesis and the second femoral prosthesis each further include a porous casing that encases at least a portion of the core body. The porous casing defines an inner casing surface that extends along the outer core body surface, and an outer casing surface that is opposite the inner casing surface. The outer casing surface defines a central outer casing axis. Each of the first femoral prosthesis and the second femoral prosthesis includes a geometry that includes at least one of a selectable neck angle defined by the central neck axis and the central outer casing axis, a tilt angle along that is defined by the core body axis and the central outer casing axis, and a neck offset that extends from the neck to the casing along the central neck axis, and a rotational position of the core body relative to the outer casing surface about an axis that substantially perpendicular to each of the anterior-posterior direction and the medial-lateral direction. The geometry of the first femoral prosthesis is different than the geometry of the second femoral prosthesis. 
     In one example, the first femoral prosthesis defines a first selectable neck angle, and the second femoral prosthesis defines a second selectable neck angle different than the first selectable neck angle. 
     In another example, the first femoral prosthesis defines a first neck offset from the casing to the neck along the central neck axis, and the second femoral prosthesis defines a second neck offset from the casing to the neck along the central neck axis that is different than the first neck offset. 
     In another example, the core of second femoral prosthesis is rotated about the axis of rotation with respect to first femoral prosthesis. 
     In another example, the core of the first femoral prosthesis is tilted along the anterior-posterior direction in the outer casing of the first femoral prosthesis so as to define a first tilt angle, and the core of the second femoral prosthesis is tilted along the anterior-posterior direction in the outer casing of the second femoral prosthesis so as to define a second tilt angle that is different than the first tilt angle. 
     In another example, the casing defines an anterior casing side and a posterior casing side opposite the anterior casing side along the anterior-posterior direction, and the core body defines a medial core body side and a lateral core body side opposite the medial core body side. The medial core body side of the second femoral prosthesis can be spaced further from the anterior casing side than the medial core body side of the first femoral prosthesis is spaced from the anterior casing side. 
     Each of the first femoral prosthesis and the second femoral prosthesis can further include a collar that extends at least medially out with respect to the outer core body surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The detailed description particularly refers to the following figures, in which: 
         FIG.  1    is an exploded perspective view of a femoral prosthesis 
         FIG.  2 A  is a sectional elevation view of the femoral prosthesis illustrated in  FIG.  1   , taken along line  2 A- 2 A; 
         FIG.  2 B  is a sectional elevation view of a femoral prosthesis similar to the femoral prosthesis illustrated in  FIG.  2 A , but showing a different neck angle; 
         FIG.  3    is an exploded perspective view of a femoral prosthesis similar to the femoral prosthesis illustrated in  FIG.  1   ; 
         FIG.  4    is a perspective view of a portion of a porous casing of the femoral prosthesis illustrated in  FIGS.  1  and  3   ; 
         FIG.  5    is an exploded perspective view of the femoral prosthesis illustrated in  FIG.  1   , further showing a plurality of collars; 
         FIG.  6 A  is a sectional elevation view of the femoral prosthesis illustrated in  FIG.  1   , showing one of the collars of  FIG.  5    attached to the core; 
         FIG.  6 B  is a sectional elevation view of the femoral prosthesis illustrated in  FIG.  1   , showing a collar monolithic with the casing; 
         FIG.  6 C  is a sectional elevation view of the femoral prosthesis illustrated in  FIG.  1   , showing a collar monolithic with the core; 
         FIG.  7 A  is a sectional side elevation view of a portion of the femoral prosthesis illustrated in  FIG.  1   , wherein the stem component defines a first selectable neck angle; 
         FIG.  7 B  is a sectional side elevation view of the femoral prosthesis illustrated in  FIG.  7 A , but wherein the stem component defines a second selectable neck angle; 
         FIG.  7 C  is a sectional elevation view of the femoral prosthesis illustrated in  FIG.  1   , wherein the stem component defines a neutral selectable neck angle position 
         FIG.  8 A  is a sectional side elevation view of a portion of the femoral prosthesis illustrated in  FIG.  1   , wherein the stem component defines a first tilt position; 
         FIG.  8 B  is a sectional side elevation view of the femoral prosthesis illustrated in  FIG.  8 A , but wherein the stem component defines a second tilt position different than the first tilt position; 
         FIG.  8 C  is a sectional elevation tilt angle view of the femoral prosthesis illustrated in  FIG.  1   , wherein the stem component defines a third neutral tilt position; 
         FIG.  9 A  is a sectional plan view of the femoral prosthesis illustrated in  FIG.  1   , wherein the stem component defines a first rotational position; 
         FIG.  9 B  is a sectional side elevation view of the femoral prosthesis illustrated in  FIG.  8 A , but shown wherein the stem component defines a second rotational position different than the first rotational position; 
         FIG.  9 C  is a sectional side elevation view of the femoral prosthesis illustrated in  FIG.  8 B , but shown wherein the stem component defines a third neutral rotational position; 
         FIG.  10 A  is a sectional plan view of the femoral prosthesis illustrated in  FIG.  1   , wherein the stem component defines a first neck offset; 
         FIG.  10 B  is a sectional side elevation view of the femoral prosthesis illustrated in  FIG.  10 A , but shown wherein the stem component defines a second neck offset; and 
         FIG.  11    is a simplified block diagram of a method for implanting a femoral prosthesis illustrated in  FIG.  1   . 
     
    
    
     DETAILED DESCRIPTION 
     While the concepts of the present disclosure are susceptible to various modifications and alternative forms, specific exemplary embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the concepts of the present disclosure to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. Further, the term “at least one” stated structure as used herein can refer to either or both of a single one of the stated structure and a plurality of the stated structure. 
     While the concepts of the present disclosure are susceptible to various modifications and alternative forms, specific exemplary embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the concepts of the present disclosure to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     References in the specification to “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. 
     Referring to  FIGS.  1 - 2 A , a femoral prosthesis  10  of a hip prosthesis includes a femoral stem component  16  that is configured to be implanted into the medullary canal  21  of a patient&#39;s femur  23 . The femoral prosthesis  10  can further include a head component  18  that is configured to attach to the femoral stem component  16 . The head component  18  can define an outer articulation surface  25  that is configured to articulate along a complementary bearing surface of an acetabular prosthetic component that is implanted in the patient&#39;s acetabulum. In one example, the outer articulation surface  25  can be three-dimensionally curved. For instance, the outer surface can be substantially spherically shaped. An acetabular prosthetic component generally includes an outer shell configured to engage the acetabulum of the patient and an inner bearing or liner coupled to the shell that is configured to engage the femoral head component  18  to form a ball and socket joint that approximates the natural hip joint. 
     The femoral prosthesis  10  can define a medial side  11  and a lateral side  13  opposite the medial side  11  along a medial-lateral direction. Thus, the femoral prosthesis  10 , and the elements thereof, defines a medial direction that is oriented from the lateral side  13  to the medial side  11 , and a lateral direction that is oriented from the medial side  11  to the lateral side  13 . The femoral prosthesis can further include an anterior side  15  and a posterior side  27  opposite the anterior side  15  along an anterior-posterior direction that is substantially perpendicular to the medial-lateral direction. Thus, the femoral prosthesis  10 , and the elements thereof, defines an anterior direction that is oriented from the posterior side  27  to the anterior side  15 , and a posterior direction that is oriented from the anterior side  15  to the posterior side  27 . The anterior and posterior sides  15  and  27  each extend from the medial side  11  to the lateral side  13 . Similarly, the medial and lateral sides each extend from the anterior side  15  to the posterior side  27 . 
     Unless otherwise indicated herein, the term “substantially,” “approximately,” and derivatives thereof, and words of similar import, when used to describe a size, shape, angle orientation, distance, spatial relationship, or other parameter includes the stated size, shape, angle, orientation, distance, spatial relationship, or other parameter, and can also include a range up to 10% more and up to 10% less than the stated parameter, including 5% more and 5% less, including 3% more and 3% less, including 1% more and 1% less. The term “substantially” in the context of substantially perpendicular axis includes perpendicular, and can also include up to +/−25 degrees from perpendicular. The term “substantially identical” and derivatives thereof as used herein refer to being designed to be identical in size and shape, and thus within manufacturing tolerances. Thus, the term “different” when used in connection with a comparison to different sizes, orientations, angles, shapes, or other value means that the compared values are different than each other by design, and thus outside of manufacturing tolerances. 
     The femoral prosthesis  10  can further include a collar  14  that extends medially outward from the femoral stem component  16 . In other examples, the femoral stem component  16  can include the collar  14 . In use, an orthopaedic surgeon may assemble a femoral prosthesis  10  using the various components before implanting the assembled femoral prosthesis  10  in the patient&#39;s femur  23 . For example, in some patients, the femoral prosthesis  10  may include only the stem component  16  and the femoral head component  18 . For other patients, the orthopaedic surgeon may couple one of the collar  14  to the stem component  16  to address specific additional needs of a patient. 
     The stem component  16  defines a medial side  42  and a lateral side  44  opposite the medial side  42  substantially along a medial-lateral direction. The medial and lateral sides  42  and  44  of the stem component  16 , respectively, define respective portions of the medial and lateral sides  11  and  13 , respectively, of the femoral prosthesis. The stem component  16  further defines an anterior side  46  and a posterior side  48  opposite the anterior side  46  substantially along an anterior-posterior direction. The anterior and posterior sides  46  and  46 , respectively, of the stem component  16  define a portion of the anterior and posterior sides  15  and  27 , respectively, of the femoral prosthesis  10 . The elements of the stem component  16  described below can similarly define respective anterior and posterior sides. The medial side  42  and the lateral side  44  are spaced from each other a first distance, and the anterior side  46  and the posterior side  48  are spaced from each other a second distance that is less than the first distance. 
     The stem component  16  can include an elongate core body  34  and a neck  28  that extends out with respect to the elongate core body  34 . For instance, the neck  28  can extend out from the core body  34 . The core body  34  can thus extend distally from the neck  28 . Alternatively, the stem component  16  can further include a shoulder  32  that is disposed between the core body  34  and the neck  28 . Thus, the neck  28  can extend out from the shoulder  32  that, in turn, extends out from the core body  34 . Further, the core body  34  can extend distally from the shoulder  32 . Either way, it can be said that the core body  34  extends distally with respect to the neck  28 . The core body  34  is configured to be received in the medullary canal  21  of the patient&#39;s femur  23 . The neck  28  can extend out with respect to the core body  34  at a fixed neck angle  40 . 
     The neck  28  includes a trunnion  30  that extends superiorly and medially. The stem component  16  can define a proximal end  17 . The proximal end  17  can be defined by the trunnion  30  in some examples. The trunnion  30  is configured to attach to the femoral stem component  16 . The trunnion  30  is shaped to receive the femoral head component  18  by being positioned in a matching bore (not shown) of the femoral head component  18 . The bore and the trunnion  30  can have matching tapers such that the femoral head component  18  may be secured to the stem component  16  via a Morse taper locking connection. In other embodiments, the trunnion  30  and the surface lining the bore of the femoral head component  18  may be threaded. 
     The core body  34  can extend distally to a distal core body end  37  of the core body  34 . The stem component  16  can further include a casing  33  that encases at least a portion of an entire length of the core body  34 . In the illustrative embodiment, the core body  34  and the surrounding casing  33  are shaped to be received in the medullary canal  21  patient&#39;s femur  23  via a press-fit to secure the stem component  16 , to the patient&#39;s femur  23 . In other embodiments, the core body  34  and the surrounding casing  33  may be secured to the femur  23  via other attachment means such as, for example, bone cement. The stem component  16  can define a distal end  19  that is opposite the proximal end  17 . The distal end  19  of the stem component  16  can be defined by the casing  33  in some examples. In other examples, for instance whereby the casing does not extend along the entire length of the core body  34 , the distal end of the stem component  16  can be defined by the casing  33 . Thus, the stem component  16 , the core body  34 , and the casing  33  can define a proximal direction from the distal end  19  to the proximal end  17 . Conversely, the stem component  16 , the core body  34 , and the casing  33  can define a distal direction from the proximal end  17  to the distal end  19 . 
     As will be described in more detail below, the casing  33  extends over at least a portion of the core body  34 . Thus, the casing  33  defines an inner casing surface  108  that faces an outer core body surface  109  of the core body  34 , the casing  33 , and an outer casing surface  110  opposite the inner casing surface  108 . The casing  33  can be additively manufactured so as to encase the core body  34 . For instance, the casing  33  can be additively manufactured onto the core body  34  so as to define a coating having an inner casing surface  108  that extends along the outer core body surface  109 . Accordingly, the inner casing surface  108  can be coated onto the outer core body surface  109  after the casing has been additively manufactured onto the core body  34 . Thus, the inner casing surface  108  can face the outer core body surface  109 . Alternatively, as illustrated in  FIG.  3   , the casing  33  can be additively manufactured as a separate component  61  that is sized and configured to receive the core body  34 . Thus, the casing  33  of the separate component  61  defines the inner casing surface  108  prior to attaching the casing  33  to the core body  34 . The inner casing surface  108  of the casing  33  of the separate component  61  faces the core body  34  when the casing  33  receives the core body  34 . Whether the casing  108  is additively manufactured onto the core body  34  or additively manufactured as the separate component  61 , it can be said that the casing  33  encases at least a portion of the core body  34 . The neck  28  can extend out with respect to the elongate core body  34 . For instance, the neck  28  can extend out from the core body  34 . Alternatively, the elongate body  34  can include the shoulder  32  that extends from the inner core body  34 , such that the neck extends out from the shoulder  32 . 
     Referring again to  FIGS.  1 - 2 B , the core body  34  can define a proximal core body end  35  and a distal core body end  37  opposite the proximal core body end  35 . The proximal core body end  35  can be disposed at an interface between the core body  34  and the shoulder  32 . Alternatively, in instances whereby the stem component  16  does not include the shoulder, the proximal core body end  35  can be disposed at an interface between the core body  34  and the neck  28 . The core body  34  can define a distal core body end  37  opposite the proximal core body end  35  along a central core body axis  39 . Thus, the elongate core body  34  can be elongate along the central core body axis  39  from a proximal core body end  35  to the distal core body end  37 . 
     Referring again to  FIGS.  1 - 2 A , the distal core body end  37  can be spaced from the distal end  19  of the stem component in the proximal direction. For instance, the casing  33  can define a distal casing end  49  that is disposed distal of the distal core body end  37 . The central core body axis  39  extends through the core body  34  from the proximal core body end  35  to the distal core body end  37 . The central core body axis  39  extends centrally through the core body  34  with respect to a medial core body side  54  of the core body  34  and a lateral core body side  56  of the core body  34 . The medial core body side  54  and the lateral core body side  56  can be opposite each other substantially along the medial-lateral direction. The medial core body side  54  and the lateral core body side  56  each extend from the proximal core body end  35  to the distal core body end  27 . The medial core body side  54  and the lateral core body side  56  can define a portion of the medial side  42  and a lateral side  44  of the stem component  16 . That is, the central core body axis  39  can extend centrally through the core body  34  with respect to a side elevation view of the core body  34  that includes the medial core body side  54  and the lateral core body side  56 . Further, the central core body axis  39  can be centrally disposed with respect to the anterior and posterior sides, respectively, of the core body  34 . The medial and lateral core body sides  54  and  56  can extend from the side and the posterior side of the core body  34 . 
     The core body  34  can further include an anterior core body side  57  and a posterior core body side  59  (see  FIGS.  9 A- 9 C ). The anterior core body side  57  and the posterior core body side  59  can be opposite each other substantially along the anterior-posterior direction that is substantially perpendicular to the medial-lateral direction. The anterior core body side  57  and the posterior core body side  59  can define respective portions of the anterior side  46  and a posterior side  48  of the stem component  16 , for instance at locations of the core body  34  that protrude from the casing  33 . In one example, such locations can be at a superior end of the core body  34  that defines the proximal core body end  35 . The anterior core body side  57  and the posterior core body side  59  can extend from the medial core body side  54  to the lateral core body side  56 . 
     The central core body axis  39  can define any suitable shape depending on the design of the core body  34 . For instance, the central core body axis  39  can be curved in one example. The central core body axis  39  can have a constant curvature. Alternatively, the central core body axis  39  can have curvatures that vary along its length. Alternatively, the central core body axis  39  can be straight and linear. Alternatively still, the central core body axis  39  can include a plurality of straight and linear segments that are angled with respect to each other. Alternatively still, the central core body axis  39  can include one or more straight and linear segments and one or more curved segments. 
     The casing  33  can also define a first or medial casing side  70  and a second or lateral casing side  72 . The medial casing side  70  and the lateral casing side  72  are opposite each other along the medial-lateral direction. The medial and lateral casing sides  70  and  72 , respectively, of the casing  33  can define at least a portion of the medial and lateral sides  42  and  44 , respectively, of the stem component  16 . The outer casing surface  110  at the medial and lateral casing sides  70  and  72  can taper toward each other as they extend distally. 
     The casing  33  can further include an anterior casing side  71  and a posterior casing side  73 . The anterior casing side  71  and the posterior casing side  73  can be opposite each other substantially along the anterior-posterior direction that is substantially perpendicular to the medial-lateral direction. The anterior casing side  71  and the posterior casing side  73  can define respective portions of the anterior side  46  and a posterior side  48  of the stem component  16 . The anterior casing side  71  and the posterior casing side  73  can extend from the medial casing side  70  to the lateral casing side  72 . 
     In one example, the neck  28  can extend out from the core body  34  so as to define an inner core  31 . For instance, the neck  28  can be monolithic with the core body  34  so as to define the inner core  31 , which can be a single unitary structure. The inner core  31  can further include the trunnion  30 . The trunnion  30  can be monolithic with the neck  28  and the core body  34 . The inner core  31  can further include the shoulder  32 . The shoulder  32  can be monolithic with the trunnion  30 , the neck  28 , and the core body  34  so as to define the inner core  31 . Thus, the inner core  31  can be a single monolithic structure. Thus, it should be appreciated that the casing  33  can encapsulate at least a portion of an overall length of the core  31  as defined from the distal core body end  37  to the proximal end  17  of the trunnion  30 . In one example, the inner core  31  can be made of any suitable biocompatible material, such as a metal. Further, the inner core  31 , including the core body  34 , the neck  28 , the trunnion  30 , and the shoulder  32 , can be a forged metal. In one example, the inner core  31  can be made of stainless steel, cobalt chromium, titanium, tantalum, niobium, or alloys thereof. It is recognized, of course, that the inner core  31  can be made of any suitable alternative material, and fabricated using any suitable fabrication method as desired. 
     Referring now to  FIGS.  2 A- 2 B , the neck  28  can extend out with respect to the core body  34 , and in particular the proximal core body end  35 , along a central neck axis  29  that combines with the central core body axis  39  to define any desirable fixed neck angle  40  with respect to a side elevation view of the stem component  16  that includes the distal end  19  of the stem component  16 , the proximal end  17  of the stem component  16 , the medial side  42  of the stem component  16 , and the lateral side  44  of the stem component  16 . For instance, the neck  28  can extend out from the proximal core body end  35 . Alternatively, the shoulder  32  can be disposed between the proximal core body end  35  and the neck  28 . Thus, the neck  28  can extend out from the shoulder  32  that, in turn, extends out from the proximal core body end  35 . Because the neck  28  and the core body  34  can be monolithic with each other, or otherwise secured to the core body  34 , the neck angle  40  can be referred to as a fixed neck angle. That is, the fixed neck angle  40  cannot be altered without redesigning the core  31 . In one example, the central neck axis  29  can be coplanar with the central core body axis  39  such that the axes  29  and  39  intersect each other so as to define the fixed neck angle  40 . Alternatively, the central neck axis  29  and the central core body axis  39  can be non-coplanar with each other. Either way, the axes  29  and  39  intersect each other with respect to a side elevation view of the stem component  16  that includes the distal end  19  of the stem component  16 , the proximal end  17  of the stem component  16 , the medial side  42  of the stem component  16 , and the lateral side  44  of the stem component  16 . Further, because the inner casing surface  108  of the casing  33  can extend along the outer core body surface  109  of the core body  34 , central neck axis  29  and the central inner casing axis  112  can define the angle  40 .  FIG.  2 A  illustrates the neck  28  extending out from the core body  34  at a first fixed neck angle  40 .  FIG.  2 B  illustrates the neck  28  extending out from the core body  34  at a second fixed neck angle  40  different than the first fixed neck angle  40 . 
     The inner casing surface  108  can extend along a central inner casing axis  112 . For instance, the inner casing surface  108  can be elongate along the central inner casing axis  112 . The central inner casing axis  112  extends centrally through the casing  33  at a location centrally disposed with respect to the inner casing surface  108 . For instance, the central inner casing axis  112  extends centrally through the casing  33  at a location centrally disposed with respect to the inner casing surface  108  at the medial casing side  70  and the inner casing surface  108  at the lateral casing side  72 . That is, the central inner casing axis  112  extends through the casing  33  at a location centrally disposed with respect to the inner casing surface  108  along a sectional side elevation view of the casing  33  that includes the medial casing side  70  and the lateral casing side  72 . Further, the central inner casing axis  112  can be centrally disposed with respect to the anterior casing side  71  and the and posterior casing side  73 . Thus, it can be said that the inner casing surface  108  at the medial casing side  70  and the lateral casing side  72  combine to at least partially define the central inner casing axis  112 . It can also be said that the inner casing surface  108  at the anterior casing side  71  and the posterior casing side  73  can also combine to partially define the central inner casing axis  112 . Because the casing  33  can be coated onto the outer core body surface  109 , the central inner casing axis  112  can be substantially coincident with the central core body axis  39 . Thus, the fixed neck angle  40  can be defined by the central neck axis  29  and either or both of the central inner casing axis  112  and the central core body axis  39 . 
     It is recognized that either or both of the central neck axis  29  and either or both of the central core body axis  39  and the central inner casing axis  112  can be curved where they intersect. Thus, the neck angle  40  can be measured by respective tangents to the central neck axis  29 , the central core body axis  39 , and the central inner casing axis  112  where they intersect, when the axes are curved where they intersect. In this regard, all angles disclosed herein defined by one or more curved axes can be measured by respective tangents of the one or more curved axes where the axes intersect. The central neck axis  29  can be coincident with a central axis of the trunnion axis. Alternatively, the trunnion  30  can be oriented such that the central axis of the trunnion is angularly offset with respect to the central neck axis  29 . 
     As described above, the core body  34  extends along an overall length from the proximal core body end  35  to the distal core body end  37 . The casing  33  can encase at least a portion of the overall length of the core body  34  up to an entirety of the overall length of the core body  34  from the proximal core body end  35  to the distal core body end  37 . In particular, the casing  33  can surround the core body  34  along a plane that is oriented perpendicular to the central core body axis  39 . Further, in some examples, the casing  33  can encapsulate the distal core body end  37 . Thus, the distal casing end  49  can be disposed distal of the distal core body end  37 . Further, the distal end  19  of the stem component  16  can be defined by the distal casing end  49 . Alternatively, the casing  33  can terminate proximal of the distal core body end  37 , such that the distal casing end  49  is spaced from the distal core body end  37  in the proximal direction. The casing  33  can further define a proximal casing end  51  opposite the distal casing end  49 . The proximal casing end  51  can terminate at the shoulder  32  in some examples. Thus, the casing  33  can extend in the distal direction from the shoulder  32  to the distal casing end  49 . In the event that the inner core  31  does not include the shoulder  32 , the casing  33  can extend in the distal direction from the neck  28  to the distal casing end  49 . In other examples, the casing  33  can extend to a location proximal of the neck  28 . For instance, the casing  33  can encapsulate an entirety of the core  31 . Thus, in this example, the proximal casing end  51  can define the proximal end  17  of the stem component  16 . 
     As described above, the casing  33  can be additively manufactured. In one example, the casing  33  can be made of a porous material  53  as described in U.S. patent application Ser. No. 16/365,557 filed Mar. 26, 2019, the disclosure of which is hereby incorporated by reference as if set forth in its entirety herein. Because the casing  33  is made of the porous material  53 , the casing  33  can be referred to as a porous casing. Additive manufacturing processes can include, by way of example, powder bed fusion printing, such as melting and sintering, cold spray 3D printing, wire feed 3D printing, fused deposition 3D printing, extrusion 3D printing, liquid metal 3D printing, stereolithography 3D printing, binder jetting 3D printing, material jetting 3D printing, and the like. 
     In one example, referring to  FIG.  4   , the porous material  53  of the casing  33  can be defined by a porous three-dimensional structure that can comprise a plurality of connected unit cells. Each unit cell can define a unit cell structure  200  that includes a plurality of lattice struts  210  and a plurality of internal structs  220  so as to define a first geometric structure  230  and a plurality of second geometric structures  240  that are disposed within the first geometric structure  230 . In one example, the first geometric structure  230  can include the plurality of lattice struts  210 . The lattice struts  210  cooperate to define the first geometry. Each of the plurality of second geometric structures  240  can define an internal volume that is substantially equal to the internal volumes of the other second geometric structures  240 . Each second geometric structure  240  can be formed by a plurality of the internal struts  220  and a plurality of the lattice struts  210 . In one example, the first geometric structure can be a rhombic dodecahedron, and the second geometric structure can be a rhombic trigonal trapezohedron. It should be appreciated, of course, that the first and second geometric structures can vary as desired. Further, it should be appreciated that the unit cells that make up the casing  33  can have any suitable alternative geometry as desired. 
     The porous material  53  can be a metal powder that can be used to form the casing  33 . In one example, the metal powders can include, but are not limited to, titanium, titanium alloys, stainless steel, cobalt chrome alloys, tantalum, or niobium powders. As illustrated in  FIGS.  2 A- 2 B , the porous material  53  can have a porosity suitable to facilitate bony ingrowth into the femoral prosthesis  10  when the core  31  is disposed in the medullary canal  21 , but can be sufficiently solid such that the femoral prosthesis  10  has a desired rigidity. It is appreciated, of course, that the porous material can be any suitable alternative biomedical material. For instance, the porous material  53  can be a powder that can be used to form the casing  33 . In one example, the powder can be a metallic powder. Alternatively, the powder can be a polymeric powder, such as polyetheretherketone (PEEK). For instance, the PEEK can be a composite-reinforced PEEK. The composite has an elastic modulus of approximately 21.5 GPa and an ultimate tensile strength of approximately 223 MPa. Thus, the casing  33  has an elastic modulus that is similar to that of a patient&#39;s femur. In other embodiments, the casing  33  can be formed of any suitable composite or polymeric material having a low elastic modulus, such as, for example, a glass-filled polymer such as glass-filled PEEK, a non-reinforced polymer such as neat PEEK, or any other suitable reinforced or non-reinforced polymer. 
     In one example, the casing  33  can be additively manufactured directly onto at least a portion of the core body  34  so as to define a porous coating  50  that surrounds the core body  34 . Alternatively, as illustrated in  FIG.  3   , the casing  33  can be manufactured as a separate sleeve  52  that can be coupled to the inner core  31 . In particular, the sleeve  52  can define an internal void  55  that receives the inner core  31 , such that the casing  33  surrounds at least a portion of the core  31  in the manner described herein. The sleeve  52  can be adhesively attached to the inner core  31  or attached using any suitable mechanical device such as one or more screws or other fasteners. 
     Referring now to  FIG.  5 - 6 C  generally, and as described above, the femoral prosthesis  10  can further include one of a plurality of collars  14 . For instance, referring now to  FIGS.  5  and  6 A , the collars  14  can include a stabilizing collar  22  and a trochanter collar  24  that may be selectively secured to the femoral stem component  16 . As described in greater detail below, each collar  14  is configured to be coupled to the stem component  16  in a fixed, immoveable position relative to the stem component  16 . Alternatively, the collar  14 , including one of the stabilizing collar  22  and the trochanter collar  24 , can be monolithic with the inner core  31  or the casing  33 . When the femoral prosthesis  10  is implanted in the patient&#39;s femur  23 , the collar  14  is configured to engage the patient&#39;s femur  23  to provide additional stability for the femoral prosthesis  10 . It should be appreciated that in other embodiments the plurality of collars  14  of the femoral prosthesis  10  may include additional collar configurations, including collars of different sizes and shapes. 
     In an illustrative embodiment, each collar  14  can formed from a resorbable material that may be assimilated into the body over time. In the one example, each collar  14  can be made of a rigid polymer such as polyetheretherketone (PEEK). The collar  14  can be additively manufactured as described above with respect to  FIG.  4   . Thus, the collar  14  can be a porous PEEK. As a result, each collar  14  is capable of providing more stability than a stem component  16  alone and is easier to manipulate in the event that a revision hip replacement is necessary. In other embodiments, one or more of the collars  14  may be formed from a medical-grade metallic material such as stainless steel, cobalt chrome, or titanium, although other metals or alloys may be used. In this regard, the collar  14  can be made from the same material as the casing  33 . Thus, the collar  14  can be referred to as a porous collar. Further, the collar  14  can be additively manufactured as described herein with respect to the casing  33 . 
     Referring to  FIG.  5 - 6 A , the shoulder  32  can be configured to be secured to one of the collars  14 . For instance, the stem component  16  includes a groove  88  that is formed at least in the anterior side and the posterior side of the stem component  16 . The groove  88  can be defined at the shoulder  32  or any suitable alternative location of the stem component  16 . The groove  88  can be sized to receive portions of the collar  14  to secure the collar  14  to the stem component  16  via a press-fit or other suitable mechanical connection. 
     The collar  14  can include one of a stabilizing collar  22  and a trochanter collar  24  in one example. Each of the collars  22  and  24  is configured to engage a surgically prepared proximal surface  90  of the patient&#39;s femur  23  (see  FIGS.  2 A- 2 B ) when the femoral prosthesis  10  is positioned in the patient&#39;s femur  23 . In other embodiments, however, the trochanter collar  24  may not engage the surgically prepared proximal surface of the patient&#39;s femur  23  and may be configured to only engage a portion of the patient&#39;s trochanter. 
     For instance, each of the collars  22  and  24  can include a base  94  that is configured to attach to the stem component  16 . The base  94  is configured to be received in the groove  88 . The base  94  defines an aperture  96  that is configured to receive the stem component  16 , such that at least one inner wall  95  of the base  94  that at least partially defines the aperture  96  is received in the groove  88  of the stem component  16 . 
     The stabilizing collar  22  can define an opening formed at a lateral end of its base  94  so as to define a pair of arms  97  and  99  that are spaced from each other. Thus, the arms  97  and  99  can combine to define the at least one inner wall  95  that is received in the groove  88  to couple the stabilizing collar  22  to the stem component  16 . The aperture  96  defines an open-ended slot  101  between the arms  97  and  99  that is configured to receive the stem component  16  as the stabilizing collar  22  is moved along the lateral direction so as to receive the stem component  16  in the slot  101 . 
     The illustrative aperture  96  of the trochanter collar  24  can define a closed through-hole  105  that extends through its base  94 . The through-hole  105  can be defined by the inner wall  95  of the trochanter collar  24 . The through hole  105  can receive the stem component  16  along one of the proximal direction and the distal direction. The inner wall  95  can ride along the stem component  16  until the inner wall  95  is resiliently forced into the groove  88  of the stem component  16 , thereby securing the trochanter collar  24  to the stem component  16 . 
     The stabilizing collar  22  can further include an abutment member  102  that extends medially out from the base  94 . Thus, the abutment member  102  can further extend out with respect to the neck  28  in any suitable predetermined direction. For instance, the abutment member  102  can extend medially out with respect to the neck  28 . The abutment member  102  can be substantially coplanar with the base  94 . The abutment member  102  can define an inferior surface  103  that is configured to abut the surgically prepared proximal surface  90  of the patient&#39;s femur  23  during use. 
     The trochanter collar  24  can be configured as a calcar attachment, and can further include an abutment member  104  that extends out from the base  94 . For instance, the abutment member  104  can extend away from the base  94  along any suitable predetermined direction and cooperates with the base  94  so as to define a non-orthogonal angle  117 . When the trochanter collar  24  is coupled to the stem component  16 , the abutment member  104  extends medially and superiorly out with respect to the neck  28 . The abutment member  104  of the trochanter collar  24  can define an inferior surface  103  that is configured to abut the surgically prepared proximal surface  90  of the patient&#39;s femur  23  during use. It should be appreciated that the aperture  96  of the stabilizing collar  22  can alternatively define a through-hole, and the aperture  96  of the trochanter collar  24  can alternatively define an open-ended slot. 
     In still other examples, such as is shown in  FIG.  6 B , the collar  14  can be monolithic with one the casing  33 . Alternatively still, as illustrated in  FIG.  6 C , the collar  14  can be monolithic with the inner core  31 . Alternatively still, as illustrated in  FIG.  10 A , the femoral prosthesis  10  can be devoid of a collar. 
     As will now be described with reference to  FIGS.  7 A- 10 B , a plurality (i.e., greater than one) of different femoral prostheses  10 , such as first and second femoral prostheses, can be fabricated from the same core  31 . The femoral prostheses  10  can further be customized for different patients. For instance, the femoral prostheses can define at least one respective geometry that differs from the other of the femoral prostheses. 
     As illustrated in  FIGS.  7 A- 7 C , the geometry can include a selectable neck angle  162 . Thus, while the fixed neck angle  40  can be the same for the first and second femoral prosthesis  10 , the selectable neck angle  162  of a first femoral prosthesis  10  can be different than the selectable neck angle  162  of a second femoral prosthesis  10 . The selectable neck angle  162  can be different than the fixed neck angle. As illustrated in  FIG.  7 A , a first femoral implant  10  defines a first selectable neck angle  162   a . As illustrated in  FIG.  7 B , a second femoral implant  10  defines a second selectable neck angle  162   a . As illustrated in  FIG.  7 C , a third femoral implant  10  defines a neutral selectable neck angle position having a third selectable neck angle that is different than each of the first and second selectable neck angles. The term “selectable” in connection with any of the geometries described herein, including the neck angle, indicate a geometry within a range of permissible geometries for the femoral prosthesis  10 . 
     Alternatively or additionally, as illustrated in  FIGS.  8 A- 8 C , the geometry can include a tilt angle  165  of the core body  34 , and thus of the core  31 , with respect to the outer casing  33  along the anterior-posterior direction. In particular, as illustrated in  FIG.  8 A , the inner core  31  of a first femoral prosthesis  10  can define a first tilt position along the anterior-posterior direction relative to the outer casing surface  110 . As illustrated in  FIG.  8 B , the inner core  31  of a second femoral prosthesis  10  can define a second tilt position along the anterior-posterior direction relative to the outer casing surface  110 . The second tilted position can be different than the first tilted position. Thus, the first tilted position can be defined by a first tilt angle  165   a , and the second tilted position can be defined by a second tilt angle  165   b  that is different than the first tilt angle  165   a . As illustrated in  FIG.  8 C , the inner core  31  of a third femoral prosthesis can define a third tilt position along the anterior-posterior direction relative to the outer casing surface  110 . The third tilt position can be a neutral position of the inner core with respect to the outer casing surface  110 . As described herein, the outer casing surface  110  of each of the first, second, and third femoral implants can be substantially identical to each other. It is appreciated that the tilt positions and corresponding tilt angles 
     Alternatively or additionally still, referring to  FIGS.  9 A- 9 C , the geometry can include a rotational position  166  of the core body  34 , and thus of the core  31 . In particular, the inner core  31  can define a rotational position  166  relative to the outer casing surface  110  about an axis of rotation  167  that is oriented in a directed substantially perpendicular to each of the medial-lateral direction and the anterior-posterior direction. Accordingly, the rotational positions  166  can be defined in a plane that defined by the anterior-posterior direction and the medial-lateral direction. The first femoral prosthesis  10  can define a first rotational position  166   a , and the second femoral prosthesis  10  can define a second rotational position  166   b  that is different than the first rotational position  166   a.    
     Alternatively or additionally yet, as illustrated in  FIGS.  10 A- 10 B , the geometry can include a neck offset  164 . The neck offset  164  extends from the core  31  to the neck  28  substantially along the central neck axis  29 . Thus, the first femoral prosthesis  10  can define a first neck offset  164   a , and the second femoral prosthesis  10  can define a second neck offset  164   b  that is different than the first neck offset. As will be described in more detail below, each of the geometries can determine at least one or both of a position and an orientation of the neck  28  with respect to the outer casing surface  110 . 
     Referring again to  FIGS.  7 A- 10 B  generally, because the trunnion  30  can extend out from the neck  28  at a fixed position with respect to the neck  28 , each of the geometries of the femoral prosthesis  10  described herein can further determine at least one or both of a position and orientation of the neck  28  with respect to the outer casing. Further still, because the head component  18  can be coupled to the trunnion  30 , each of the geometries of the femoral prosthesis  10  described herein can further determine a position of the head component  18 , and an orientation of the stem component  16  with respect to the head component  18  when the head component is received by the acetabular prosthesis. 
     While first and second femoral prostheses  10  having a different one or more up to all of the geometries are used as examples, but it should be appreciated that a plurality of femoral prostheses  10  can have one or more up to all different geometries. Thus, it will be appreciated that a plurality of femoral prostheses  10  can be constructed using substantially identical inner cores  31  and can still be customized to better fit different specific patient anatomies. The femoral prosthesis  10  can be referred to as a patient specific femoral prosthesis. For large differences in patient anatomies greater than the difference attained by the geometries described herein, as can occur in patients having significant age differences and gender differences, cores  31  of the type described herein can be produced having different sizes. However, the ability for the resulting femoral prosthesis to have at least one of the geometries can result in a reduced number of stock keeping units (SKU) of the inner core  31  while allowing the femoral prosthesis  10  to accommodate a greater number of different patient anatomies that are currently accommodated using a greater number of SKUs than previously achieved. Further, in some examples, the outer casing surface  110  of the femoral prostheses  10  can have substantially the same size and substantially the same shape, such that femoral prostheses  10  having substantially the same size and shaped cores  31  can also define substantially the same size and shaped prosthesis  10 . 
     It is recognized that each femoral prosthesis  10  can be fabricated for a specific patient anatomy. Thus, an orthopaedic implant system can include a plurality of femoral prostheses  10  that can be produced at different times, including a first femoral prosthesis and a second femoral prosthesis that is different than the first femoral prosthesis. The different prostheses  10  of the orthopedic implant system can be produced non-contemporaneously. For instance, different femoral prostheses  10  can be fabricated days, weeks, months or even years apart. Further, the femoral prostheses  10  of the orthopedic implant system can be packaged and delivered separately to different healthcare providers. Therefore, it is recognized that the plurality of femoral prostheses of the orthopedic implant system can be produced that are not provided in a single kit in some examples. In other examples, it is recognized that a plurality of the femoral prostheses  10  described herein of the orthopedic implant system can be provided in a kit, such that a healthcare provider can have an inventory of the femoral prostheses  10  with one or more different respective geometries among the plurality of respective geometries described herein. 
     Referring now to  FIGS.  7 A- 7 C  in particular, and as described above, the femoral prosthesis, can include a selectable neck angle  162  with respect to the casing  33 . Thus, the neck  28  can extend out from the core body  34  both at the fixed neck angle  40  and at the selectable neck angle  162 . As will now be described, the outer casing  33  can define the selectable neck angle  162 . For instance, the outer casing  33  can be fabricated such that the core  31 , and thus the neck  28 , can define any suitable selectable orientation with respect to the outer casing. 
     The outer casing surface  110  of the casing  33  can extend along a longitudinal axis of the casing  33  that is the central outer casing axis  114 . For instance, the outer casing surface  110  can be elongate along the central outer casing axis  114 . The central outer casing axis  114  extends centrally through the casing  33  at a location centrally disposed with respect to the outer casing surface  110 . For instance, the central outer casing axis  114  can extend centrally through the casing  33  at a location centrally disposed with respect to the outer casing surface  110  at the medial casing side  70  and at the lateral casing side  72  of the casing  33 . That is, the central outer casing axis  114  extends through the casing  33  at a location centrally disposed with respect to the outer casing surface  110  along a neck angle view. In one example, the neck angle view can be a sectional side elevation view of the casing  33  that includes the medial casing side  70  and the lateral casing side  72 , and the proximal and distal ends of the casing  33 . Thus, the central outer casing axis  114  can be centrally disposed with respect to the outer casing surface  110  at anterior casing side  71  and at the posterior casing side  73 . Thus, it can be said that the outer casing surface  110  at the medial casing side  70  and at the lateral casing side  72  can at least partially define the central outer casing axis  114 . When implanted in a patient&#39;s femur, the central outer casing axis  114  is positioned in the coronal plane of the patient&#39;s femur. As described in more detail below, the outer casing surface  110  at the anterior casing side  71  and the posterior casing side  73  can also at least partially define the central outer casing axis  114 . 
     The selectable neck angle  162  can be defined by the central neck axis  29  and the central outer casing axis  114 . The central neck axis  29  can be coplanar with the central outer casing axis  114  such that the axes  29  and  114  intersect each other so as to define the selectable neck angle  162 . Alternatively, the central neck axis  29  and the central outer casing axis  114  can be non-coplanar with each other. For example, the central neck axis  29  may extend anteriorly out of plane with the central outer casing axis  114  to position the femoral head anteriorly relative to the outer casing and hence the coronal plane of the patient&#39;s femur. In another example, the central neck axis  29  may positioned in a plane offset from, but extending parallel to, the plane of the central outer casing axis  114  (e.g., the coronal plane of the patient&#39;s femur when the femoral stem is implanted in the patient&#39;s body). 
     It should be appreciated that the axes  29  and  114  intersect each other with respect to the neck angle view. In some examples, the neck angle view can be a side elevation view of the stem component  16  that includes the distal end  19  of the stem component  16 , the proximal end  17  of the stem component  16 , the medial side  42  of the stem component  16 , and the lateral side  44  of the stem component  16 . In one example, the selectable neck angle  162  can be selected by determining an orientation of the core  31  with respect to the casing  33  about an axis that is oriented substantially along the anterior-posterior direction. It is further appreciated that axes  29  and  114  intersect each other inside an outer perimeter of the core body  34  with respect to the side elevation neck angle view of the stem component that includes the proximal core body end  35 , the distal core body end  37 , the medial core body side  54 , and the lateral core body side  56 . The outer perimeter of the core body  34  is defined by the proximal core body end  35 , the distal core body end  37 , the medial core body side  54 , and the lateral core body side  56 . 
     The femoral prosthesis  10  can be customized such that the neck  28  can define any suitable selectable neck angle  162  as desired to position the prosthetic femoral head at a predetermined position relative to the longitudinal axis of the outer casing and/or the coronal plane of the patient&#39;s femur. In particular, the casing  33  can be fabricated such that the core  31  defines any suitable predetermined selectable neck angle  162 . For instance, as illustrated in  FIG.  7 A , the core body  34  can define a first selectable neck angle  162   a  within the casing  33 . As illustrated in  FIG.  7 B , the core body  34  can define a second selectable neck angle  162   b  within the casing  33  that is different than the first selectable neck angle  162   a . As illustrated in  FIG.  7 C , the core body  34  can be substantially centrally disposed within the casing  33 , and defines an associated third selectable neck angle. The core body  34  can define any suitable number of selectable neck angles  162  that are different than each of the first and second selectable neck angles  162 . The selectable neck angles  162  defined by the core body  34  within the casing  33  can be defined with respect to a neck angle view that is defined by a sectional side elevation view that extends through both the core body  34  and the casing  33  and includes the medial core body side  54  and the lateral core body side  56 , and the proximal and distal ends of the core body  34 . The sectional side elevation view can further include the medial casing side  70  and the lateral casing side  72 . 
     In some examples, a permissible range of selectable neck angles  162  can be determined such that the at least a portion of the core body  34  is encapsulated by the casing at all of the selectable neck angles  162  within the permissible range of selectable neck angles  162 . In one example, the permissible range of selectable neck angles  162  can be a substantially 30 degree range. That is, the central neck axis  29  can be angularly offset from the central outer casing axis from a position substantially 15 degrees offset from the central outer casing axis  114  in a respective negative direction to a position substantially 15 degrees offset from the central outer casing axis  114  in a respective positive direction that is opposite the respective negative direction. In this regard, it should be appreciated that the core body  34  can be sized substantially smaller than the footprint defined by the outer casing surface  110  along the medial-lateral direction to achieve a broader range of selectable neck angles  162 . As the size of the core body  34  in the casing is increased with respect to the outer casing surface  110  along the medial-lateral direction, the range of selectable neck angles  162  can decrease. 
     It should be further appreciated that the selectable neck angle  162  in the range of selectable neck angles  162  can define a respective medial-lateral thickness profile of the casing  33 . In particular, the casing  33  can define a thickness  113  along the length of the core body  34  that is a function of the selectable neck angle  162  relative to the casing  33 . The thickness  113  of the casing  33  can extend from the inner casing surface  108  to the outer casing surface  110  along the medial-lateral direction. As described above, the outer casing surface  110  can define at least a portion of the outer surface of the femoral prosthesis  10 . Further, the outer casing surface  110  can be nonparallel with respect to the inner casing surface  108 . It should be appreciated that as the orientation of the core body  34  varies to correspondingly vary the selectable neck angle  162 , the thickness of the casing  33  can similarly vary along the length of the casing  33 . Further, the thickness  113  of the casing  33  can be maintained above a minimum thickness along an entirety of the medial and lateral casing sides  70  and  72 , respectively. Alternatively, portions of the core body  34  can protrude through the casing  33 , and in particular through the medial and lateral casing sides  70  and  72 . Accordingly, the outer casing surface  110  can be interrupted by core body  34 , and thus can be discontinuous in some embodiments. 
     As illustrated in  FIG.  7 A , the casing  33  can be fabricated such that the central core body axis  39  is angularly offset from to the central outer casing axis  114  with respect to the neck angle view. Thus, the central core body axis  39  can intersect the central outer casing axis  114  in the core body  34  with respect to the neck angle view. Because the neck  28  extends out from the core body  34  at the fixed neck angle  40 , the angular offset of the central core body axis  39  can further define a first selectable neck angle  162   a . In one example, the central core body axis  39  can define a first angular offset with respect to the central outer casing axis  114 . In particular, the central core body axis  39  can extend medially with respect to the central outer casing axis  114  as it extends in the distal direction. The first angular offset can be referred to as a negative angular offset in a negative direction. Further, the central inner casing axis  112  can be similarly angularly offset with respect to the central core body axis  39 . For instance, the central inner casing axis  112  can define the first angular offset with respect to the central outer casing axis  114 . 
     As used herein, the term “angular offset” and derivatives thereof refers to a design in which two different axes are intended to be angularly offset, and thus outside of manufacturing tolerances. Thus, the term “angular offset” and derivatives thereof connotes that the angular offset is greater than an angular offset of two axes that are designed to be coincident with each other but might be offset due to manufacturing tolerances. In one example, the term “angular offset” can include an offset of at least approximately 1 degree, such as at least approximately 2 degrees. 
     Further, with continuing reference to  FIG.  7 A , the thickness  113  of the casing at the medial casing side  70  can decrease as the casing  33  extends in the distal direction. The thickness  113  of the casing at the lateral casing side  72  can increase as the casing extends in the distal direction. The terms “increase” and “decrease” and derivatives thereof when used in connection with dimensions or measurements connotes that the distance or measurement increases or decreases, respectively, an amount greater than manufacturing tolerances of a distance or measurement that is designed to be constant. 
     As illustrated in  FIG.  7 B , the core body  34  can be oriented such that the central core body axis  39  is angularly offset from the central outer casing axis  114  with respect to the neck angle view so as to define a second angular offset that is different than the first angular offset. Thus,  FIG.  7 B  illustrates a second selectable neck angle  162   b  that is different than the first selectable neck angle  162   a  of  FIG.  7 A . The central core body axis  39  can intersect the central outer casing axis  114  in the core body  34  so as to define the second selectable neck angle  162   b . In one example, the second angular offset can be opposite the first angular offset. In particular, the central core body axis  39  can extend laterally with respect to the central outer casing axis  114  as it extends in the distal direction so as to define the second angular offset. The second angular offset can be referred to as a positive angular offset in a positive direction. Further, the central inner casing axis  112  can be similarly angularly offset with respect to the central core body axis  39 . For instance, the central inner casing axis  112  can define the second angular offset with respect to the central outer casing axis  114 . Further, the thickness  113  of the medial casing side  70  can increase as the casing  33  extends in the distal direction. The thickness  113  of the lateral casing side  72  can decrease as the casing extends in the distal direction. The core body  34  of the femoral prosthesis illustrated in  FIG.  7 B  can be substantially identical to the core body  34  of the femoral prosthesis illustrated in  FIG.  7 A   
     Accordingly, it should be appreciated that a plurality of different femoral prostheses  10  can be manufactured having different selectable neck angles. For instance, the respective core bodies  34  of each of the plurality of cores  31  having substantially the same fixed neck angle can be encased by respective casings  33  that are fabricated about their respective outer core body surfaces  109 , such that when the casings  33  are inserted into the medullary canal of a femoral bone at substantially the same relative orientation with respect to the bone, the respective necks having the same fixed neck angle will extend medially and superiorly at different angles with respect to the central axis of the femur. In one example, the casings  33  can have substantially identically sized and shaped outer casing surfaces  110 . 
     The relative orientations of the central core body axis  39 , the central inner casing axis  112 , and the central outer casing axis  114  described above can be determined with respect to a sectional side elevation view of the stem component  16  that includes the medial casing side  70  and the lateral casing side  72 . Further, an angle defined by the central outer casing axis  114  and either or both of the central core body axis  39  and the central inner casing axis  112  can be curved where they intersect when viewed along the sectional side elevation view. Thus, the angle can be measured by respective tangents of one or more up to all of the central outer casing axis  114  and either or both of the central core bony axis  39  and the central inner casing axis  112 , when curved, where they intersect. It is further recognized that the central core body axis  39  can be angularly offset with respect to the central inner casing axis  112 . For instance, it is recognized that portions of the inner casing surface  108  can be spaced from the outer core body surface  109 , such as when the casing  33  is additively manufactured as a separate component  61  as shown in  FIG.  3   . 
     As illustrated in  FIG.  7 C , the core body  34  defines a third selectable neck angle  162   c  that is different than each of the first and second selectable neck angles  162   a  and  162   b . In particular, the core body  34  can be oriented with respect to the casing  33  such that the central core body axis  39  is oriented parallel with the central outer casing axis  114  with respect to the neck angle view. Thus, the core body  34  can be said to be centrally disposed in the casing  33  with respect to the neck angle view. In some examples, the central core body axis  39  can be coincident with the central outer casing axis  114  with respect to the neck angle view. Further, the central inner casing axis  112  can be parallel to or coincident with the central core body axis  39  with respect to the neck angle view. Further, the thickness  113  of the medial casing side  70  of the casing  33  can be substantially constant along an entirety of the length of the core body  34 . Thus, the third selectable neck angle  162   c  can be equal to the fixed neck angle  40 . Similarly, the thickness  113  of the lateral casing side  72  can be substantially constant along an entirety of the length of the core body  34 . In one example, the thickness of the casing  33  at the medial casing side  70  is greater than the thickness of the casing  33  at the lateral casing side  72 . In other examples, the thickness of the casing  33  at the medial casing side  70  is less than the thickness of the casing  33  at the lateral casing side  72 . As described above, the inner core  31  of the femoral prosthesis illustrated in  FIG.  7 C  can be substantially identical to the inner core  31  of the femoral prosthesis illustrated in each of  FIG.  7 A  and  FIG.  7 B . That is, the inner core shown in  FIGS.  7 A- 7 C  can have the substantially same size and shape. 
     With continuing reference to  FIGS.  7 A- 7 C , it should be appreciated a method can be provided for fabricating the femoral prostheses  10  that each includes the core body  34  that is configured to be inserted into the medullary canal  21  of the femur  23 . The femoral prostheses  10  can include substantially equally sized and shaped core bodies  34  having different orientations in the respective casings  33 . A method of fabricating the femoral prosthesis  10  can include the step of applying the porous casing  33  onto the core body  34  so as to define the inner casing surface  108  that faces the core body  34  and the outer casing surface  110  opposite the inner casing surface  108 , such that the central core body axis  39  of the core body  34  is angularly offset with respect to the central outer casing axis  114  defined by the outer casing surface  110 . The angular offset between the central core body axis  39  and the central outer casing axis  114  similarly determines the selectable neck angle  162 . 
     For instance, the first femoral prosthesis can include a first core body and a first neck that extends out with respect to the first core body at the fixed neck angle  40  and at a first selectable neck angle  162   a . The second femoral prosthesis can include includes a second core body and a second neck that extends out with respect to the second core body at the fixed neck angle  40  and at a second selectable neck angle  162   b  different than the first selectable neck angle  162   a.    
     The method can include the step of manufacturing a first porous casing  33  onto a first core body  34  so as to define a first femoral prosthesis  10  whereby 1) a first neck  28  extends out with respect to the proximal end of the first core body  34  at a fixed neck angle  40 , and 2) the first porous casing  33  defines a first inner casing surface  108  that faces the first core body  34  and a first outer casing surface  110  opposite the first inner casing surface  108 , wherein the first outer casing  33  extends along a first central outer casing axis  114 , and the first neck  28  extends from the first core body  34  at a first selectable neck angle  162   a  with respect to the first central outer casing axis  114 . 
     The method can include the step of manufacturing a second porous casing  33  onto a second core body  34  so as to define a second femoral prosthesis  10  whereby 1) a second neck  28  extends out with respect to the proximal end of the second core body  34  at the fixed neck angle  40 , and 2) the second porous casing  33  defines a second inner casing surface  108  that faces the second core body  34  and a second outer casing surface  110  opposite the second inner casing surface  108 , wherein the second outer casing  33  extends along a second central outer casing axis  114 , and the second neck  28  extends from the second core body  34  at a second selectable neck angle  162   b  with respect to the second central outer casing axis  114  that is different than the first selectable neck angle  162   a.    
     Referring now to  FIGS.  8 A- 8 C , and as described above, the core body  34  and thus the inner core  31  of the femoral prosthesis,  10  can be tilted along the anterior-posterior direction with respect to the casing  33 . As described above, the central outer casing axis  114  extends centrally through the casing  33  at a location centrally disposed with respect to the outer casing surface  110 . For instance, the central outer casing axis  114  can extend centrally through the casing  33  at a location centrally disposed with respect to the outer casing surface  110  at the anterior casing side  71  and at the posterior casing side  73  of the casing  33 . That is, the central outer casing axis  114  extends through the casing  33  at a location centrally disposed with respect to the outer casing surface  110  along a tilt angle view. The tilt angle view can be defined by a sectional side elevation view of the casing  33  that includes the anterior casing side  71 , the posterior casing side  73 , and the proximal and distal ends of the casing  33 . Thus, the central outer casing axis  114  can be centrally disposed with respect to the outer casing surface  110  at the anterior casing side  71  and at the posterior casing side  73 . Accordingly, it can be said that the outer casing surface  110  at the anterior casing side  71  and at the posterior casing side  73  can at least partially define the central outer casing axis  114 . As described above, the outer casing surface  110  at the medial and lateral casing sides can also at least partially define the central outer casing axis  114 . 
     The tilt angle  165  can be defined by the central core body axis  39  and the central outer casing axis  114 . The central core body axis  39  can be coplanar with the central outer casing axis  114  such that the axes  39  and  114  intersect each other so as to define the tilt angle  165 . Alternatively, the central core body axis  39  and the central outer casing axis  114  can be non-coplanar with each other. Either way, the axes  39  and  114  intersect each other with respect to the tilt angle view. In some examples, the tilt angle view can be a side elevation view of the stem component  16  that includes the distal end  19  of the stem component  16 , the proximal end  17  of the stem component  16 , the anterior side  46  of the stem component  16  and the posterior side  48  of the stem component  16 . In one example, the tilt angle  165  can be selected by determining an orientation of the core  31  with respect to the casing  33  about an axis that is oriented substantially along the anterior-posterior direction. It is further appreciated that axes  39  and  114  intersect each other inside a respective outer perimeter of the core body  34  with respect to the side elevation tilt angle view of the stem component that includes the proximal core body end  35 , the distal core body end  37 , the anterior core body side  57  and the posterior core body side  59 . The respective outer perimeter of the core body  34  is defined by the proximal core body end  35 , the distal core body end  37 , the anterior core body side  57 , and the posterior core body side  59 . 
     The femoral prosthesis  10  can be customized such that the core body  34  and thus the inner core  31  can define any suitable tilt angle  165  as desired. In particular, the casing  33  can be fabricated such that the core  31  defines any suitable tilt angle  165  as desired. For instance, as illustrated in  FIG.  8 A , the core body  34  can define a first tilt angle  165   a  within the casing  33 . As illustrated in  FIG.  8 B , the core body  34  can define a second tilt angle  165   b  within the casing  33  that is different than the first tilt angle  165   a . As illustrated in  FIG.  8 C , the core body  34  can be in a neutral tilt position whereby the core body is substantially centrally disposed within the casing  33  with respect to the tilt angle view. The core body  34  of  FIG.  8 C  can be substantially identical to the core body  34  of  FIGS.  8 A and  8 B . The tilt angles  165  defined by the core body  34  within the casing  33  can be defined with respect to a respective sectional side elevation tilt angle view that extends through both the core body  34  and the casing  33  and includes the anterior core body side  57  and the posterior core body side  59 . The sectional side elevation tilt angle view can further include the anterior casing side  71  and the posterior casing side  73 . 
     In some examples, a permissible range of tilt angles  165  can be determined such that the at least a portion of the core body  34  is encapsulated by the casing at all of the tilt angles  165  within the permissible range of tilt angles  165 . In one example, the permissible range of tilt angles  165  can be a substantially 30 degree range. That is, the central core body axis  39  can be angularly offset from the central outer casing axis  114  from a position substantially 15 degrees offset from the central outer casing axis  114  in a respective positive direction to a position substantially 15 degrees offset from the central outer casing axis  114  in a respective negative direction that is opposite the respective positive direction. In this regard, it should be appreciated that the core body  34  can be sized substantially smaller than the footprint defined by the outer casing surface  110  along the anterior-posterior direction to achieve a broader range of tilt angles  165 . As the size of the core body  34  in the casing is increased with respect to the outer casing surface  110  along the anterior-posterior direction, the range of tilt angles  165  can decrease. 
     It should be further appreciated that the tilt angle  165  in the range of tilt angles  165  can define a respective anterior-posterior thickness profile of the casing  33 . In particular, the casing  33  can define a thickness  119  along the length of the core body  34  that is a function of the tilt angle  165  relative to the casing  33 . The thickness  119  of the casing  33  can extend from the inner casing surface  108  to the outer casing surface  110  along the anterior-posterior direction. As described above, the outer casing surface  110  can define at least a portion of the outer surface of the femoral prosthesis  10 . Further, the outer casing surface  110  can be nonparallel with respect to the inner casing surface  108 . It should be appreciated that as the orientation of the core body  34  varies to correspondingly vary the tilt angle  165 , the thickness of the casing  33  can similarly vary along the length of the casing  33 . Further, the thickness  119  of the casing  33  can be maintained above a minimum thickness along an entirety of the anterior and posterior casing sides  71  and  73 , respectively. Alternatively, portions of the core body  34  can protrude through the casing  33 , and in particular through the anterior and posterior casing sides  71  and  73 . Accordingly, the outer casing surface  110  can be interrupted by core body  34 , and thus can be discontinuous in some embodiments. 
     As illustrated in  FIG.  8 A , the casing  33  can be fabricated such that the central core body axis  39  is angularly offset from to the central outer casing axis  114  with respect to the tilt angle view. Thus, the central core body axis  39  can intersect the central outer casing axis  114  in the core body  34  with respect to the tilt angle view. The central core body axis  39  and the central outer casing axis  114  can define a first tilt angle  165   a  with respect to the tilt angle view. In one example, the central core body axis  39  can define a first angular tilt offset with respect to the central outer casing axis  114  in the tilt angle view. In particular, the central core body axis  39  can extend anteriorly with respect to the central outer casing axis  114  as it extends in the distal direction. The first angular tilt offset can be referred to as a negative angular tilt offset in a negative tilt direction. Further, as the central inner casing axis  112  can be coincident with the central core body axis  39 , the central inner casing axis  112  can be similarly angularly offset with respect to the central outer casing axis  114 . Thus, the central inner casing axis  112  can define the first tilt angle  165   a  with respect to the central outer casing axis  114 . 
     As used herein, the term “angular tilt offset” and derivatives thereof refers to a design in which two different axes are intended to be angularly offset with respect to the tilt angle view, and thus outside of manufacturing tolerances. Thus, the term “angular tilt offset” and derivatives thereof connotes that the angular tilt offset is greater than an angular tilt offset of two axes that are designed to be coincident with each other but might be offset with respect to the tilt angle view due to manufacturing tolerances. In one example, the term “angular tilt offset” can include an offset of at least approximately 1 degree, such as at least approximately 2 degrees. 
     Further, with continuing reference to  FIG.  8 A , the thickness  119  of the casing at the anterior casing side  71  can decrease as the casing  33  extends in the distal direction. The thickness  119  of the casing at the posterior casing side  73  can increase as the casing extends in the distal direction. The terms “increase” and “decrease” and derivatives thereof when used in connection with dimensions or measurements connotes that the distance or measurement increases or decreases, respectively, an amount greater than manufacturing tolerances of a distance or measurement that is designed to be constant. 
     As illustrated in  FIG.  8 B , the core body  34  can be oriented such that the central core body axis  39  is angularly offset from the central outer casing axis  114  with respect to the tilt angle view so as to define a second tilt angle  165   b  that is different than the first tilt angle  165   a . The central core body axis  39  can intersect the central outer casing axis  114  in the core body  34  with respect to the tilt angle view so as to define the second tilt angle  165   b . In one example, the second tilt angle  165   b  can be opposite the first tilt angle  165   a . In particular, the central core body axis  39  can extend posteriorly with respect to the central outer casing axis  114  as it extends in the distal direction so as to define the second tilt angle  165   b . The second tilt angle  165   b  can be referred to as a positive tilt angle in a positive direction. Further, as the central inner casing axis  112  can be coincident with the central core body axis  39 , the central inner casing axis  112  can be similarly angularly offset with respect to the central core body axis  39 . For instance, the central inner casing axis  112  can define the second tilt angle  165   b  with respect to the central outer casing axis  114 . Further, the thickness  119  of the anterior casing side  71  can increase as the casing  33  extends in the distal direction. The thickness  119  of the posterior casing side  73  can decrease as the casing extends in the distal direction. As described above, the inner core  31  of the femoral prosthesis illustrated in  FIG.  8 B  can be substantially identical to the inner core  31  of the femoral prosthesis illustrated in  FIG.  8 A . 
     Accordingly, it should be appreciated that a plurality of different femoral prostheses  10  can be manufactured having different tilt angles. For instance, the respective core bodies  34  of each of the plurality of cores  31  can have substantially the same size and shape, but can define different tilt angles with respect to the respective outer casings  33 . Further, the respective outer casings  33  can have substantially identically sized and shaped outer casing surfaces  110 . 
     The relative orientations of the central core body axis  39 , the central inner casing axis  112 , and the central outer casing axis  114  described above with respect to the tilt angle can be determined in the sectional side elevation tilt angle view of the stem component  16  that includes the anterior casing side  71  and the posterior casing side  73 , and the proximal and distal ends of the casing  33 . Further, the tilt angle defined by the central outer casing axis  114  and either or both of the central core body axis  39  and the central inner casing axis  112  can be curved where they intersect when viewed along the tilt angle view. Thus, the angle can be measured by respective tangents of one or more up to all of the central outer casing axis  114  and either or both of the central core body axis  39  and the central inner casing axis  112 , when curved, where they intersect. It is further recognized that the central core body axis  39  can be angularly offset with respect to the central inner casing axis  112 . For instance, it is recognized that portions of the inner casing surface  108  can be spaced from the outer core body surface  109 , such as when the casing  33  is additively manufactured as a separate component  61  as shown in  FIG.  3   . 
     As illustrated in  FIG.  8 C , the core body  34  can define a neutral tilt position in the casing  33 . In particular, the core body  34  can be oriented with respect to the casing  33  such that the central core body axis  39  is oriented substantially parallel with the central outer casing axis  114  along the sectional side elevation tilt angle view. In some examples, the central core body axis  39  can be substantially coincident with the central outer casing axis  114 . Further, the central inner casing axis  112  can be parallel to or coincident with the central core body axis  39 . Further still, the thickness  119  of the anterior casing side  71  of the casing  33  can be substantially constant along an entirety of the length of the core body  34 . Similarly, the thickness  119  of the posterior casing side  73  can be substantially constant along an entirety of the length of the core body  34 . In one example, the thickness of the casing  33  at the anterior casing side  71  is greater than the thickness of the casing  33  at the posterior casing side  73 . In other examples, the thickness of the casing  33  at the anterior casing side  71  is less than the thickness of the casing  33  at the posterior casing side  73 . The core body  34  of the femoral prosthesis illustrated in  FIG.  8 C  can be substantially identical to the core body  34  of the femoral prosthesis illustrated in  FIGS.  8 A and  8 B . 
     With continuing reference to  FIGS.  8 A- 8 C , it should be appreciated a method can be provided for fabricating the femoral prostheses  10  that each includes the core body  34  that is configured to be inserted into the medullary canal  21  of the femur  23 . The femoral prostheses  10  can include substantially identically sized and shaped core bodies  34  having different tilt angles in the respective casings  33 . A method of fabricating the femoral prosthesis  10  can include the step of applying the porous casing  33  onto the core body  34  so as to define the inner casing surface  108  that faces the core body  34  and the outer casing surface  110  opposite the inner casing surface  108 , such that the central core body axis  39  of the core body  34  is angularly offset with respect to the central outer casing axis  114  defined by the outer casing surface  110  with respect to the tilt angle view. The angular offset between the central core body axis  39  and the central outer casing axis  114  similarly determines the tilt angle  165 . 
     For instance, the first femoral prosthesis can include a first core body  34  having a first core body axis  39  that has a first orientation in the respective first porous casing  33  with respect to the tilt angle view, and a femoral prosthesis that includes a second core body  34  having a second core body axis  39  that has a second orientation in the respective second porous casing  33  with respect to the tilt angle view. The second orientation is different than the first orientation with respect to the respective casing  33 . Thus, the first femoral prosthesis defines the first tilt angle, and the second femoral prosthesis defines the second tilt angle that is different than the first tilt angle. 
     The method can include the step of manufacturing the first porous casing  33  onto the first core body  34  so as to define the first femoral prosthesis  10  whereby the first core body axis  39  defines the first tilt angle  165   a  with respect to the outer central casing axis  114 . The method can include the step of manufacturing the second porous casing  33  onto the second core body  34  so as to define the second femoral prosthesis  10  whereby the second core body axis  39  defines the second tilt angle with respect to the outer central casing axis  114 . 
     Referring now to  FIGS.  9 A- 9 C , and as described above, the femoral prosthesis  10  can include the rotational position  166  with respect to the casing  33 . Thus, the neck  28  can extend out from the core body  34  at the fixed neck angle  40  and at the rotational position  166  with respect to the outer casing surface  110 . Further, because the inner casing surface  108  can extend along the outer core body surface  109 , the central neck axis of the neck  28  can extend out from the central inner casing axis  112  at the fixed neck angle  40  (see  FIGS.  1 - 2 B ). As will now be described, the outer casing  33  can define the rotational position  166 . For instance, the outer casing  33  can be fabricated such that the core  31 , and thus the neck  28 , can define any suitable orientation with respect to the outer casing  33  about the axis of rotation  167 . The axis of rotation  167  can be defined by the central core body axis  39 , or can be offset from the central core body axis  39 . As the inner core  31  defines the rotational position  166  is adjusted in a range of permissible rotational positions  166 , the neck  28  defines a position in a range of permissible selective positions that revolve about the axis of rotation  167 . 
     The femoral prosthesis  10  can be customized such that the core body  34 , and thus the core  31 , can define any suitable rotational position  166  with respect to the axis of rotation  167 . In particular, the casing  33  can be fabricated such that the core body  34  defines any suitable predetermined rotational position  166  with respect to the outer casing surface  110 . 
     For instance, as illustrated in  FIG.  9 A , the core body  34  can define a first rotational position  166   a  within the casing  33 . Thus, the core  31 , including the neck  28 , can similarly define the first rotational position  166   a . As illustrated in  FIG.  9 B , the core body  34  can define a second rotational position  166  within the casing  33  that is different than the first orientation. Thus, the core  31 , including the neck  28 , can similarly define the second rotational position  166 . As illustrated in  FIG.  9 C , the core body  34  can define a third rotational position  166   c  within the casing  33  that is different than each of the first and second rotational positions  166   a  and  166   b , respectively. In particular, the core body  34  can be centrally disposed within the casing  33  so as to define the third rotational position  166   c . The core  31 , including the neck  28 , can similarly define the first, second, and third rotational positions. The rotational positions  166  of the core body  34  within the casing  33  can be defined with respect to a rotational view. The rotational view can be a sectional plan view that extends through both the core body  34  and the casing  33  and includes the anterior casing side  71 , the posterior casing side  73 , the medial casing side  70 , and the lateral casing side  72 . The sectional plan view can be along a plane that is substantially perpendicular with respect to the central core body axis. 
     In some examples, the range of rotational positions  166  can be determined such that the at least a portion of the core body  34  is encapsulated by the casing  33  at all of the rotational positions  166  within the range of permissible rotational positions  166 . The range of permissible rotational positions  166  can be determined such that the core body  34  does not protrude through the outer casing surface  110  at any of the rotational positions  166  in the range of permissible rotational positions  166 . Further, the range of permissible rotational positions  166  can be determined such that a thickness  115  of the casing  33  at the anterior and posterior casing sides  71  and  73 , respectively, can be maintained above a minimum thickness along an entirety of the anterior and posterior casing sides  71  and  73 , respectively. 
     Referring now to  FIGS.  9 A- 9 B  in particular, the range of rotational positions  166  can be defined by an angle of rotation  168 . The angle of rotation  168  can be defined by a central core body axis  169  and a central fixed casing axis  171 . The core body axis  169  can extend from the medial core body side  54  and the lateral core body side  56 . Further, the core body axis  169  can bisect each of the medial core body side  54  and the lateral core body side  56 . These sides can be referred to as the medial core body side  54  and the lateral core body side  56  even when angulated about the axis of rotation  167 , as they define the medial and lateral extent of the core body  34  when the core body  34  is in a neutral non-angulated position. It is recognized that the core body axis  169  has an orientation that varies depending on the rotational position  166  of the core body  34 . The fixed casing axis  171  can extend from the outer casing surface  110  at the medial casing side  70  to the outer casing surface  110  at the lateral casing side  72 . For instance, the fixed casing axis  171  can bisect the outer casing surface  110  at the medial casing side  70  and the outer casing surface  110  at the lateral casing side  72 . In one example, the angle of rotation  168  can be at least approximately 5 degrees up to at least approximately 15 degrees. 
     The range of rotational positions  166  as defined by the angle of rotation  168  can be a substantially 30 degree range. That is, the angle of rotation  168  can range up to approximately 15 degrees clockwise and approximately 15 degrees counterclockwise. For instance, the range of rotational positions  166  as defined by the angle of rotation  168  can be a substantially 20 degree range. That is, the angle of rotation  168  can range up to approximately 10 degrees clockwise and approximately 10 degrees counterclockwise. In some examples, the range of rotational positions  166  as defined by the angle of rotation  168  can be a substantially 20 degree range. That is, the angle of rotation  168  can range up to approximately 10 degrees clockwise and approximately 10 degrees counterclockwise. In other examples, the range of rotational positions  166  as defined by the angle of rotation  168  can be a substantially 10 degree range. That is, the angle of rotation  168  can range up to approximately 5 degrees clockwise and approximately 5 degrees counterclockwise. In still other examples, the range of rotational positions  166  as defined by the angle of rotation  168  can be a substantially 5 degree range. That is, the angle of rotation  168  can range up to approximately 2.5 degrees clockwise and approximately 2.5 degrees counterclockwise. 
     In this regard, it should be appreciated that the core body  34  can be sized substantially smaller than the footprint defined by the outer casing surface  110  to achieve a broader range of rotational positions  166 . As the size of the core body  34  in the casing is increased with respect to the outer casing surface  110 , the range of rotational positions  166  can decrease. 
     As illustrated in  FIG.  9 A , a first negative angle of rotation  168   a  can be counterclockwise, such that the core body  34  defines a negative first rotational position  166   a . The first rotational position  166   a  in the range of rotational positions  166  can define a respective first anterior-posterior thickness profile of the casing  33 . In particular, the casing  33  can define a thickness  115  along the length of the core body  34  that is a function of the rotational position  166  of the core body  34  relative to the casing  33 . The thickness  115  of the casing  33  can extend from the inner casing surface  108  to the outer casing surface  110  at the anterior casing side  71  and the posterior casing side  73 . As described above, the outer casing surface  110  can define at least a portion of the outer surface of the femoral prosthesis  10 . 
     As the rotational position  166  of the core body  34  varies, the thickness  115  of the anterior casing side  71  and the posterior casing side  71  can vary. When the core body  34  is in the first rotational position  166   a  illustrated in  FIG.  9 A , the thickness  115  of the casing  33  at the anterior casing side  71  can increase as the anterior casing side  71  extends in the medial direction from the lateral casing side  72  toward the medial casing side  70 . Thus, the medial core body side  54  can be spaced a first distance from the outer casing surface  110  at the anterior casing side  71  along the anterior-posterior direction. In particular, the anterior side of the medial core body side  54  can be spaced the first distance from the outer casing surface  110  at the anterior casing side  71  along the anterior-posterior direction. The lateral core body side  56  can be spaced a second distance from the outer casing surface  110  at the anterior casing side  71  along the anterior-posterior direction. In particular, the anterior side of the lateral core body side  56  can be spaced the second distance from the outer casing surface  110  at the anterior casing side  71  along the anterior-posterior direction. The first distance can be different than the second distance when the core body  34  is angulated about the axis of rotation  167 . In one example, for instance when the core body  34  is angulated to define the negative angle of rotation  168   a , the second distance can be less than the first distance. Alternatively, the thickness  115  of the casing  33  at the anterior casing side  71  can decrease less than it decreases when the core body  34  is in the second rotational position  166   b  described with respect to  FIG.  9 B . 
     Conversely, the thickness  115  of the casing  33  at the posterior casing side  73  can decrease as the anterior casing side  71  extends in the medial direction. Thus, the medial core body side  54  can be spaced a third distance from the outer casing surface  110  at the posterior casing side  73  along the anterior-posterior direction. In particular, the posterior side of the medial core body side  54  can be spaced the third distance from the outer casing surface  110  at the posterior casing side  73  along the anterior-posterior direction. The lateral core body side  56  can be spaced a fourth distance from the outer casing surface  110  at the posterior casing side  73  along the anterior-posterior direction. In particular, the posterior side of the lateral core body side  56  can be spaced the fourth distance from the outer casing surface  110  at the posterior casing side  73  along the anterior-posterior direction. The third distance can be different than the fourth distance when the core body  34  is angulated about the axis of rotation  167 . In one example, for instance when the core body  34  is angulated to define the first negative angle of rotation  168   a , the third distance can be less than the fourth distance. Further, the third distance can be substantially equal to the first distance, and the fourth distance can be substantially equal to the second distance. Alternatively, depending on the dimensions of the core body  34 , the position of the core body  34  with respect to the anterior and posterior casing sides  71  and  73 , respectively, and the location of the axis of rotation  167 , the third distance can be different than the first distance, and the fourth distance can be different than the second distance. The first distance, the second distance, the third distance, and the fourth distance can be measured in a plane that is oriented substantially perpendicular to the central core body axis  39 . The plane can bisect the core body  34  in some examples. 
     Referring now to  FIG.  9 B , a second positive angle of rotation  168   b  can be clockwise, and thus opposite the first negative angle of rotation  168   a  described above with respect to  FIG.  9 A . Thus, the core body  34  defines a positive second rotational position  166   b . The second rotational position  166   b  in the range of rotational positions  166  can define a respective second anterior-posterior thickness profile of the casing  33 . In particular, when the core body  34  is in the second rotational position  166  illustrated in  FIG.  9 B , the thickness  115  of the casing  33  at the anterior casing side  71  can decrease as the anterior casing side  71  extends in the medial direction. Thus, the medial core body side  54  can be spaced a first distance from the outer casing surface  110  at the anterior casing side  71  along the anterior-posterior direction. The lateral core body side  56  can be spaced a second distance from the outer casing surface  110  at the anterior casing side  71  along the anterior-posterior direction. The first distance can be different than the second distance when the core body  34  is angulated about the axis of rotation  167 . In one example, for instance when the core body  34  is angulated to define the positive angle of rotation  168   b , the first distance can be less than the second distance. direction 
     Conversely, the thickness  115  of the casing  33  at the posterior casing side  73  can increase as the anterior casing side  71  extends in the medial direction. Thus, the medial core body side  54  can be spaced a third distance from the outer casing surface  110  at the posterior casing side  73  along the anterior-posterior direction. The lateral core body side  56  can be spaced a fourth distance from the outer casing surface  110  at the posterior casing side  73  along the anterior-posterior direction. The third distance can be different than the fourth distance when the core body  34  is angulated about the axis of rotation  167 . In one example, for instance when the core body  34  is angulated to define the second positive angle of rotation  168   b , the third distance can be greater than the fourth distance. Further, the third distance can be substantially equal to the first distance, and the fourth distance can be substantially equal to the second distance. Alternatively, depending on the dimensions of the core body  34 , the position of the core body  34  with respect to the anterior and posterior casing sides  71  and  73 , respectively, and the location of the axis of rotation  167 , the third distance can be different than the first distance, and the fourth distance can be different than the second distance. 
     It should therefore be appreciated that when first and second femoral prostheses  10  define different first and second rotational positions  166   a  and  166   b , respectively, the core  31  of second femoral prosthesis  10  is rotated about the axis of rotation  167  with respect to first femoral prosthesis  10 . The central casing axis  171  can be referred to as a fixed central casing axis because the central casing axis  171  of the first femoral prosthesis  10  can have the same position and orientation as the central casing axis  171  of the second femoral prosthesis. Further, the medial core body side  54  of the first femoral prosthesis  10  can be spaced further from the anterior casing side  71  than the medial core body side  54  of the second femoral prosthesis is spaced from the anterior casing side  71 . The lateral core body side  56  of the second femoral prosthesis  10  can be spaced further from the anterior casing side  71  than the lateral core body side  56  of the first femoral prosthesis is spaced from the anterior casing side  71 . The medial core body side  54  of the second femoral prosthesis  10  can be spaced further from the posterior casing side  73  than the medial core body side  54  of the first femoral prosthesis is spaced from the posterior casing side  73 . The lateral core body side  56  of the first femoral prosthesis  10  can be spaced further from the posterior casing side  73  than the lateral core body side  56  of the second femoral prosthesis is spaced from the posterior casing side  73 . 
     As illustrated in  FIG.  9 C , the core body  34  can be positioned in a third rotational position  166   c  with respect to the casing  33 . For instance, the third rotational position  166   c  can define a neutral position whereby the core body axis  169  is substantially parallel to the fixed casing axis  171 . For instance, the core body axis  169  can be substantially coincident with the fixed casing axis  171 . Further, when the core body  34  is in the third rotational position, the thickness  115  of the anterior casing side  71  can substantially constant along the medial-lateral direction from the medial core body side  54  to the lateral core body side, depending on the geometry of the core body  34  and casing  33  with respect to the rotational view. Further, the thickness of the posterior casing side  73  can be substantially constant along the medial-lateral direction from the medial core body side  54  to the lateral core body side  56 , depending on the geometry of the core body  34  and casing  33  with respect to the rotational view. Further, the medial and lateral core body sides  54  and  56 , respectively, can be aligned along the medial-lateral direction. 
     With continuing reference to  FIGS.  9 A- 9 C , it should be appreciated a method can be provided for fabricating the femoral prostheses  10  that each includes the core body  34  that is configured to be inserted into the medullary canal  21  of the femur  23 . The femoral prostheses  10  can include substantially equally sized and shaped core bodies  34  having different rotational position  166  in the respective casings  33 . A method of fabricating the femoral prosthesis  10  can include the step of applying the porous casing  33  onto the core body  34  so as to define the inner casing surface  108  that faces the core body  34  and the outer casing surface  110  opposite the inner casing surface  108 , such that the core body axis  169  defines a respective orientation with respect to the fixed casing axis  171 . For instance, the core body axis  169  can be angularly offset with respect to the fixed casing axis  171  in a positive direction, a negative direction, or the core body axis  169  can be substantially coincident with the fixed casing axis  171 . 
     The method can include the step of manufacturing a first porous casing  33  onto a first core body  34  so as to define a first femoral prosthesis  10  whereby 1) a first neck  28  extends out with respect to the proximal end of the first core body  34  at a fixed neck angle  40 , and 2) the first porous casing  33  defines a first inner casing surface  108  that faces the first core body  34  and a first outer casing surface  110  opposite the first inner casing surface  108 . The core body axis  169  can define the respective orientation with respect to the fixed casing axis  171 . The method can further include fabricating a first femoral component  10  including the first porous casing and a first inner core  31  that includes the first core body  34  and the first neck  28 . 
     The method can include the step of manufacturing a second porous casing  33  onto a second core body  34  so as to define a first femoral prosthesis  10  whereby 1) a second neck  28  extends out with respect to the proximal end of the second core body  34  at a fixed neck angle  40 , and 2) the second porous casing  33  defines a second inner casing surface  108  that faces the second core body  34  and a second outer casing surface  110  opposite the second inner casing surface  108 . The core body axis  169  can define the respective orientation with respect to the fixed casing axis  171 . The method can further include fabricating a first femoral component  10  including the first porous casing and a first inner core  31  that includes the first core body  34  and the first neck  28 . The first and second femoral prostheses can further define different selectable neck angles  162  described above. 
     Referring now to  FIGS.  10 A- 10 B  in particular, and as described above, the femoral prosthesis, can include a neck offset  164 . For instance, the neck offset  164  can thus extend from the outer casing surface  110  of the outer casing  33  to the neck  28  substantially along the central neck axis  29 . The neck offset  164  can be defined by a distance from the casing  33  to the neck  28  substantially along the central neck axis  29 . In particular, the neck offset  164  can be defined by a distance from a proximal end of the casing  33  to the neck  28  substantially along the central neck axis  29 . As will now be described, a position of the core body  34  in the casing  33  can determine the neck offset  164 . For instance, the outer casing  33  can be fabricated such that the core body  34  can define any suitable position in the outer casing  33  that, in turn, determines the neck offset  164 . 
     As illustrated in  FIG.  10 A , a first neck offset  164   a  from the neck  28  to the casing  33  substantially along the central neck axis  29  can define a first distance. When the core  31  includes the shoulder  32 , the first distance can be defined by a minimum first neck offset  164   a  when the shoulder  32  abuts the casing  33 . Thus, the first neck offset  164   a  can be defined as the dimension of the shoulder  32  substantially along the central neck axis  29 . Alternatively, when the core  31  does not include the shoulder  32 , then the first neck offset  164   a  can be defined by the dimension of the neck  28  along the central neck axis  29  when the neck  28  abuts the casing  33 . Thus, the first neck offset  164   a  can be approximately zero in one examples. Alternatively, the neck  28  can be spaced from the outer casing surface  110  along the central neck axis  29  so as to define the first neck offset  164   a.    
     As illustrated in  FIG.  10 B , a second neck offset  164   b  from the neck  28  to the casing  33  substantially along the central neck axis  29  that is different than the first neck offset  164   a  of  FIG.  10 A . The second neck offset  164   b  can be greater than or less than the first neck offset  164   a . In the example illustrated in  FIG.  10 B , the second neck offset  164   b  is greater than the first neck offset  164   a . Further, because the neck  28  is positioned increasingly superiorly and medially as the neck offset  164  increases, the thickness  113  of the medial casing side  70  can decrease. 
     Thus, when a first femoral implant  10  or stem component  16  defines a first neck offset  164   a , and a second femoral implant  10  or stem component  16  defines a second neck offset  164   b  that is different than the first neck offset  164   a , a first thickness  113  of the medial casing side  70  from the inner casing surface  108  to the outer casing surface  110  is of the casing  33  of the first femoral implant  10  or stem component  16  is different than a second thickness  113  of the medial casing side  70  from the inner casing surface  108  to the outer casing surface  110  is of the casing  33  of the second femoral implant  10  or stem component  16 . For instance, when the first neck offset  164   a  is greater than the second neck offset  164   b , the first thickness  113  can be greater than the second thickness  113 . Conversely, when the first neck offset  164   a  is less than the second neck offset  164   b , the first thickness  113  can be less than the second thickness  113 . 
     It should be appreciated that while the neck offset  164  can at least partially determine a position of the neck  28  with respect to the outer casing surface  110  substantially along the central neck axis  29 , one or both of the selectable neck angle  162  and the rotational position  166  of the core body  34 , and thus of the core  31 , can further determine the position of the neck  28  and an orientation of the neck with respect to the outer casing surface  110 . Because the trunnion  30  extends from the neck  28  and is configured to be coupled to the head component  18 , one or more up to all of the neck offset  164 , the selectable neck angle  162 , and the rotational position  166  of the core body  34  can determine the position and orientation of the head component  18  relative to the outer casing surface  110 , and thus relative to the femur. 
     With continuing reference to  FIGS.  10 A- 10 B , it should be appreciated a method can be provided for fabricating the femoral prostheses  10  that each includes the core body  34  that is configured to be inserted into the medullary canal  21  of the femur  23 . The femoral prostheses  10  and in particular the stem components  16 , can include substantially equally sized and shaped cores  31 , but disposed in different locations in the respective outer casings  33  along the central neck axis  29  so as to define different respective neck offsets  164 . In this regard, the neck offset  164  can be referred to as a selectable neck offset. A method of fabricating the femoral prosthesis  10  can include the step of applying the porous casing  33  onto the core body  34  so as to define the inner casing surface  108  that faces the core body  34  and the outer casing surface  110  opposite the inner casing surface  108 , such that the neck  28  is offset from the casing  33  as desired. 
     The method can include the step of manufacturing a first porous casing  33  onto a first core body  34  so as to define a first femoral prosthesis  10  whereby 1) a first neck  28  extends out with respect to the proximal end of the first core body  34  at a fixed neck angle  40 , and 2) the neck  28  defines a fixed distance to the core body  34 . The first porous casing  33  defines a first inner casing surface  108  that faces the first core body  34  and a first outer casing surface  110  opposite the first inner casing surface  108 . The first femoral prosthesis can define the first neck offset  164   a  as described above. 
     The method can include the step of manufacturing a second porous casing  33  onto a second core body  34  so as to define a first second femoral prosthesis  10  whereby 1) a second neck  28  extends out with respect to the proximal end of the second core body  34  at the fixed neck angle  40 , and 2) the second neck  28  defines the fixed distance to the core body  34 . The second porous casing  33  defines a second inner casing surface  108  that faces the second core body  34  and a second outer casing surface  110  opposite the second inner casing surface  108 . The second outer casing surface  110  can be substantially equally sized and shaped with respect to the first outer casing surface  110 . The second femoral prosthesis  10  can define the second neck offset  164   b  as described above. Alternatively or additionally, the first femoral prosthesis  10  can include either or both of the first selectable neck angle  162   a  and the first rotational position  166   a  described above. Alternatively or additionally still, the first femoral prosthesis  10  can include either or both of the first selectable neck angle  162   a  and the first rotational position  166   a  described above. 
     With continuing reference to  FIGS.  10 A- 10 B , while the neck offset  164  provides one way to measure the different positions of substantially identical cores  31 , in still other examples the different positions can be defined by an offset from the casing  33 , and in particular from the proximal casing end  151 , to a portion  173  of the core  31  that includes the neck  28  and the trunnion  30 . The portion  173  of the core  31  can further include the shoulder  32 . As described above with respect to the neck offset  164 , the offset from the casing  33  to the portion of the core  31  can be oriented along a direction substantially parallel to the central neck axis  29 . 
     In this regard, it is recognized that a plurality of femoral prostheses can be designed and manufactured having substantially identical core bodies  34  that define different geometries when surrounded by respective casings  33 . The casings  33  can be additively manufactured onto the core bodies  34 . Alternatively, the casings  33  can be separately fabricated so as to receive the respective core bodies  34 . The geometries can be selected as one or more up to all of the first selectable neck angle  162   a  (see  FIGS.  7 B- 7 C ), the second selectable neck angle  162   b  (see  FIGS.  8 A- 8 C ), the rotational position  166  and resulting first and second angles of rotation  168   a  and  168   b  (see  FIGS.  9 A- 9 C ), and the first and second neck offsets  164   a  and  164   b  (see  FIGS.  10 A- 10 B ). 
     Referring now to  FIG.  11   , a method  170  for performing a hip arthroplasty is shown. The method  170  includes step  172 , in which an orthopaedic surgeon, or other member of a surgical team, may resect a proximal end of a patient&#39;s femur  23  to form the surgically prepared planar proximal surface  90 . As described above, the femoral prosthesis  10  may include a stem component  16  and a femoral head component  18 . Depending on the needs of the patient, the surgeon may also include the collar  14 , including one of the stabilizing collar  22  or trochanter collar  24  in the femoral prosthesis  10 . Alternatively, the femoral prostheses as fabricated can include the collar  14 . In some embodiments, such as the case in some revision hip arthroplasties, an orthopaedic surgeon will also prepare medial surface of a trochanter of the patient&#39;s femur  23 . At step  174 , the orthopaedic surgeon selects a stem component  16  and a femoral head component  18  based on surgical parameters determined before the surgical operation began and intra-operative data determined during the surgical operation. For instance, the stem component  16  can be any one of the first stem component that includes the first core body encased by the casing  33 , the second stem component that includes the second core body encased by the casing  33 , and the third stem component that includes the second core body encased by the casing  33  as described above with respect to  FIGS.  7 A- 7 C . 
     At step  176 , the orthopaedic surgeon may insert a broach through the planar proximal surface  90  of the patient&#39;s femur  23  to define a passageway in the medullary canal  21  of the patient&#39;s femur  23  sized to receive the selected femoral stem component  16  (see  FIGS.  2 A- 2 B ). The size of the broach used by the orthopaedic surgeon is determined based on the size of the selected femoral component. 
     At step  178 , the orthopaedic surgeon determines whether the femoral prosthesis  10  requires more stability than what is provided by the stem component  16  alone. If the femoral prosthesis  10  does not indicate desirability for additional stability, the surgeon may continue to step  174  in which the stem component  16  and the femoral head component  18  are implanted in the patient&#39;s femur  23 . If additional stability is desired, the surgeon continues to step  180  in which the surgeon selects a collar from the plurality of collars  14  to couple to the stem component  16 . Alternatively, the surgeon can select a femoral prosthesis that was manufactured with a collar  14 . Each of the collars of the plurality of collars includes the inferior surface  103  (see  FIG.  2 A ) configured to engage the planar proximal surface  90  of the patient&#39;s femur  23 . The plurality of collars  14  may include a number of different types of collars configured to provide different types of stability. For example, the stabilizing collar  22  includes a platform that provides a large surface area to engage the planar proximal surface  90  of the patient&#39;s femur  23 . In another example, the trochanter collar  24  includes an abutment member  104  configured to couple a trochanter of the patient&#39;s femur  23  to the femoral prosthetic assembly. 
     At step  182 , the orthopaedic surgeon may secure the selected collar to the stem component  16  such that the inferior surface  103  of the collar extends transversely to the central core body axis  39 . At step  184 , once the selected collar  14  is secured in a fixed position relative to the stem component  16 , the assembled femoral prosthesis  10  is positioned and implanted in the patient&#39;s femur  23  such that the inferior surface  103  of the selected collar engages with the planar proximal surface  90  of the patient&#39;s femur  23 . 
     While the disclosure has been illustrated and described in detail in the drawings and foregoing description, such an illustration and description is to be considered as exemplary and not restrictive in character, it being understood that only illustrative embodiments have been shown and described and that all changes and modifications that come within the spirit of the disclosure are desired to be protected. 
     There are a plurality of advantages of the present disclosure arising from the various features of the method, apparatus, and system described herein. It will be noted that alternative embodiments of the method, apparatus, and system of the present disclosure may not include all of the features described yet still benefit from at least some of the advantages of such features. Those of ordinary skill in the art may readily devise their own implementations of the method, apparatus, and system that incorporate one or more of the features of the present invention and fall within the spirit and scope of the present disclosure as defined by the appended claims.