Abstract:
Disclosed are embodiments of an improved joint prosthesis that can provide the option to improve initial stability without removing the implant or altering the preparation. Embodiments of improved joint implant components can comprise one or more expandable, hollow segmented posts. Methods of implant fixation are also disclosed. Disclosed methods can provide the opportunity for establishing initial biologic fixation (bone ingrowth), and can also provide an adjunct fixation through injecting cement down the center of the post if initial stability is not achieved or is questionable.

Description:
FIELD 
     The disclosed technology relates generally to a joint prosthesis. More specifically, the disclosure relates to a joint prosthesis comprising one or more hollow segmented posts and a method of implanting the same. 
     BACKGROUND 
     Joint implants have been designed to replace articular surfaces of many human and animal joints. These implants include replacements for hip, knee, elbow, shoulder, ankle, and other joints. Prosthetic joint implants generally must both replace the bearing surface of the joint for motion and provide some method of fixing the implant to the bone. 
     Conventional methods of fixing the implant to the bone has been accomplished by two primary methods: bone cement (e.g., PMMA) or bone ingrowth through porous surfaces (biologic fixation). Bone cement is mixed in the operating room and injected into the preparation sites for the implants. The strength of a joint implant&#39;s fixation using bone cement is at a maximum shortly after implantation (usually after around 24 hours). Over time, the cement can fatigue and break down, leading to loosening and wear of the implants. 
     Biologic fixation for prostheses eliminates the need for cement and possibly avoids the long term complications associated with cement fixation. Conventional biologic fixation methods include fixation through a porous surface created by layers of sintered beads, plasma sprayed surface, titanium wire, and other micro and macro surfaces providing for a mechanical lock with bone. Bone ingrowth within the first 10-12 weeks after surgery essentially determines whether the implant will be stable long term. In order to be successful, the porous surfaces or macro surfaces must be well designed for bone attachment and the implant must be very stable during this early post-operative time period. If there is too much motion between the implant and the bone, a fibrous tissue interface will occur rather than bone ingrowth. Should that happen, the long term success will be in jeopardy as loosening due to pain and micromotion can create a need for revision. 
     For stability to be consistently achieved during the preparation of the bones for the implant insertion, very precise instruments and very consistent surgical techniques are required. In many cases this cannot consistently be achieved due to many variables including surgeon error, worn instruments, and patient issues. In some cases, discovery of a problem may come after insertion of the implant. For example, during surgery, after the bones have been prepared for biologic fixation, trial implants placed and evaluated, and the final implants selected and inserted into their corresponding preparations, the surgeon may discover that the patient&#39;s joint is not suitable for biologic fixation. 
     However, addressing these problems usually requires removing the implant and/or attempting further preparation to the bony beds. Different bone preparation techniques are required for cement fixation, and thus switching from one method to the other mid-surgery typically requires removing the implant and essentially starting over from the beginning. Further, conventional joint implants are subject to post-operative loosening due to, for example, inadequate stability due to initial patient activity. There thus remains a need for an improved joint implant that can address these and other disadvantages in the prior art joint implants and implantation methods. 
     SUMMARY 
     Disclosed are embodiments of an improved joint prosthesis that can provide the option to improve initial stability without removing the implant or altering the preparation. Embodiments of joint implant components can include one or more hollow segmented posts positioned on one or more bone fixation surfaces. The segmented posts can include a central opening configured to receive cement for initial stability of the implant. Cement can be injected at the time of implantation, at a time after implantation (e.g., during later revision surgery), or not at all. The segmented posts can be expandable to form or increase a press fit within a bore or hole drilled in the patient&#39;s bone, thereby further increasing stability of the implant in some embodiments. 
     One embodiment of a joint implant component comprises a bone-engaging or bone fixation surface configured to engage with a patient&#39;s bone and at least one post (e.g., a fixation post) protruding outwardly from the bone fixation surface. The post can comprise at least two segments, each segment being separated by a gap, and the segments can define a central opening through the centers of said segments. Thus, the post can be a hollow segmented post. The segments of each fixation post can be substantially aligned with one another. 
     In some embodiments, the at least one post comprises at least a first and second post protruding from the bone fixation surface, the first and second posts being positioned on opposite portions of the joint implant from each other. The first and second posts can be positioned substantially parallel to one another in some specific embodiments. At least one post can be positioned tangentially to the bone fixation surface, substantially parallel to a longitudinal axis of the joint implant, and/or transversely to a major axis of the joint implant. The segments of each post can be positioned relative to one another such that they are configured to receive a cement injection needle within the central opening through the segments. 
     In some embodiments, the joint implant can comprise at least a first implant member and a second implant member, the first and second implant members being configured to articulate with each other (e.g., the joint implant can be a bicompartmental joint implant). Unicompartmental and tricompartmental joint implants are also disclosed. In embodiments with more than one implant component, the first implant member can comprise a first bone fixation surface and the second implant member can comprise a second bone fixation surface, and both the first and second bone fixation surfaces can comprise at least one post protruding from said first and second bone fixation surfaces. In some embodiments, each segment of the fixation post is substantially C-shaped. 
     Some embodiments of joint prostheses include porous surfaces. For example, at least part of one fixation post can include a porous surface (e.g., a porous coating). In some embodiments, at least a portion of the bone fixation surface comprises a porous coating. For example, portions of the bone fixation surface between fixation posts can comprise a porous coating or treatment. 
     The fixation posts can be configured to be expandable from a first position to a second position, wherein the diameter of the central opening is increased in the second position with respect to the first position. Such expansion can contribute to initial implant stability within a patient&#39;s bone by increasing the press fit between the post and a hole drilled in the patient&#39;s bone. 
     Disclosed concepts can be applied to any type of joint implant prosthesis. For example, any of the following specific implant components can be provided with one or more hollow, expandable fixation posts according to the present disclosure: an elbow implant component, an acetabular cup, a femoral hip stem, a shoulder humeral stem, a femoral knee implant component, a tibial knee implant component, or an ankle tibial implant component. Of course this list is non-exhaustive, and any other type of joint implant or implant component can include one or more fixation posts according to the present disclosure. 
     One embodiment of a joint implant component comprises a post portion configured to engage with a patient&#39;s bone, the post portion comprising a plurality of segments positioned around the circumference of the post portion and spaced apart by a plurality of longitudinal slits extending along at least a portion of the length of the post portion. The joint implant component can also comprise a taper portion coupled to the post portion, wherein the post portion and taper portion are arranged such that a longitudinal central opening extends through the post portion and taper portion. The segments of the post portion can be expandable from a first configuration to an expanded configuration. The diameter of the central opening can be increased in the expanded configuration with respect to the first configuration. 
     The segments can be positioned relative to one another such that they are configured to receive a cement injection needle within the central opening. In some embodiments, at least a part of the post portion can have a porous surface. One specific embodiment of a joint implant component comprises a femoral hip stem. 
     In some embodiments, the taper portion can comprise internal threads within the central opening. Such threads can be configured to engage with a threaded expansion tool that can be used to expand the post portion from the first configuration to the expanded configuration. 
     Some embodiments can comprise a curved annular portion positioned between the taper portion and the post portion, wherein the curved annular portion is configured to engage with a surface of a patient&#39;s bone. 
     Methods of implant fixation are also disclosed. Disclosed methods can provide the opportunity for establishing initial biologic fixation (bone ingrowth), and can also provide an adjunct fixation through injecting cement down the center of the post if initial stability is not achieved or is questionable. 
     One method of replacing at least part of a patient&#39;s joint with one or more joint implant components can comprise preparing the implant site to receive the one or more joint implant components and implanting the joint prosthesis wherein at least a portion of the implant component is positioned at least partially within a hole drilled into a patient&#39;s bone, wherein the joint implant component comprises a bone fixation surface and at least one segmented post protruding from the bone fixation surface, and wherein the post comprises at least two segments, each segment being separated by a gap, and wherein the segments define a central opening through the center of said segments. 
     Some methods can comprise expanding the at least one segmented post from a first configuration to a second configuration, wherein the diameter of the central opening is increased in the second configuration with respect to the first configuration. In some embodiments, expanding the at least one segmented post can comprise drawing a tapered expansion tool through at least part of the segmented post. 
     Some methods can comprise evaluating whether biologic fixation is suitable as the sole fixation method at the time of implantation, and injecting cement into the central opening. For example, an implant site can be prepared for biologic fixation, and disclosed embodiments of joint implant components can be implanted at the site. If it is determined that biologic fixation is not suitable for that patient, conventional methods would require removal of the implant, and re-preparation of the implant site for cement fixation. Disclosed methods, on the other hand, can allow for use of bone cement without requiring removal of the implant component or further alteration of the implant site. 
     In some methods, the joint replacement can be completed and a follow up evaluation some time after completion of the joint replacement can be conducted to determine whether the joint prosthesis is sufficiently stable. Cement can be injected into the central opening, for example, at a time after initial implantation. For example, if a follow-up evaluation reveals that bone ingrowth has been insufficient for long-term implant stability, revision surgery can be conducted to increase fixation of the implant within the patient&#39;s bone. In some embodiments, cement can be injected into one or more of the hollow segmented posts. In some embodiments, fibrous growth may need to be removed from the fixation posts before cement can be injected. 
     The foregoing and other objects, features, and advantages of the invention will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of one component of a joint prosthesis having hollow segmented posts according to the present disclosure. 
         FIG. 2  is a perspective view of a second component of a joint prosthesis having hollow segmented posts. 
         FIG. 3  is an exploded view of a simplified schematic representation of an elbow joint prosthesis. 
         FIG. 4  is a side elevation view of a joint prosthesis implanted in a subject&#39;s joint. 
         FIG. 5  is a perspective view of an alternative joint prosthesis according to the present disclosure. 
         FIG. 6  is a perspective view of an alternative joint prosthesis according to the present disclosure. 
         FIG. 7  is a perspective view of an alternative joint prosthesis according to the present disclosure. 
         FIG. 8  is a perspective view of an alternative joint prosthesis according to the present disclosure. 
         FIG. 9  is a perspective view of an alternative joint prosthesis according to the present disclosure. 
         FIG. 10  is a perspective view of an alternative joint prosthesis according to the present disclosure. 
         FIG. 11  is a black and white scanning electron micrograph (SEM) photo of a plasma spray porous surface. 
         FIG. 12  is a black and white SEM photo of a sintered bead porous surface. 
         FIG. 13  is a black and white SEM photo of a fiber metal porous surface. 
         FIG. 14  is a black and white SEM photo of a porous surface having a tantalum structure with interconnected porosity. 
         FIG. 15  is a perspective view of cement being implanted into a joint prosthesis according to the present disclosure. 
         FIG. 16  is a side elevation view of a hollow segmented post in an unexpanded configuration. 
         FIG. 17  is a side elevation view of a hollow segmented post in an expanded configuration. 
         FIG. 18  is a perspective view of one example of an expansion tool that can be used to expand a hollow segmented post from an unexpanded to an expanded configuration. 
         FIG. 19  is a perspective view of another embodiment of a joint prosthesis according to the present disclosure. 
         FIG. 20  is a top plan view of the joint prosthesis of  FIG. 19 . 
         FIG. 21  shows an elevation view of one embodiment of an expansion tool that can be used to expand the joint prosthesis of  FIGS. 19-20 . 
         FIG. 22  is an elevation view of the expansion tool of  FIG. 21  in place within a joint prosthesis. 
         FIG. 23  is an elevation view of a joint prosthesis implanted within a patient&#39;s bone. 
         FIG. 24  is an elevation view of the joint prosthesis of  FIG. 23 , after partial expansion of the prosthesis. 
         FIG. 25  is an elevation view of an expanded joint prosthesis implanted into a patient&#39;s bone. 
     
    
    
     DETAILED DESCRIPTION 
     As used in this application and in the claims, the singular forms “a,” “an,” and “the” include the plural forms unless the context clearly dictates otherwise. Additionally, the term “includes” means “comprises.” Although the operations of exemplary embodiments of the disclosed method may be described in a particular, sequential order for convenient presentation, it should be understood that the disclosed embodiments can encompass an order of operations other than the particular, sequential order disclosed. For example, operations described sequentially may in some cases be rearranged or performed concurrently. Further, descriptions and disclosures provided in association with one particular embodiment are not limited to that embodiment, and may be applied to any embodiment disclosed herein. Moreover, for the sake of simplicity, the attached figures may not show the various ways in which the disclosed system, method, and apparatus can be used in combination with other systems, methods, and apparatuses. 
     To address the problems discussed above with conventional joint prostheses, the present disclosure concerns a joint prosthesis designed to facilitate bone ingrowth (e.g., designed to be secured within a patient&#39;s joint via biologic fixation), and yet is also designed to facilitate cement fixation, either at the time of initial implantation, or some time after implantation. Disclosed joint prostheses and methods enable a surgeon to prepare a treatment site for biologic fixation, insert a joint prosthesis, and evaluate whether biologic fixation seems appropriate for the particular patient. If the surgeon determines at this stage in surgery that cement fixation is necessary, a surgeon using a conventional joint prosthesis would be required to remove the prosthesis, re-prepare the treatment site, and begin again. On the other hand, a surgeon using one of the presently disclosed joint prostheses and methods would advantageously be able to inject cement into the joint prosthesis without needing to remove the implant or alter the bone preparation already completed. In this manner, disclosed embodiments of joint prostheses can allow a surgeon to adapt to individual patient needs, while potentially shortening the time required for surgery. 
     Disclosed embodiments of joint prostheses and methods of using the same can be used with both human and animal joints. Additionally, the disclosed principles can be applied to any joint prosthesis and are not limited to the specific examples described herein. Unicompartmental, bicompartmental, and tricompartmental joint prostheses can all be designed to include one or more hollow segmented posts, as will be described further. 
     By way of illustration, one embodiment of a joint prosthesis in the form of a bicompartmental elbow implant is shown in  FIGS. 1-4 .  FIG. 1  shows one embodiment of a humeral component  100 , and  FIG. 2  shows one embodiment of a radioulnar component  200 . As shown in  FIG. 3  (which is a simplified representation), the humeral component  100  and the radioulnar component  200  can be configured to interact with one another to form an articulating prosthetic elbow joint  400 , which is shown implanted in  FIG. 4 . 
     In the example shown in  FIGS. 1-4 , the humeral component  100  and the radioulnar component  200  each includes two fixation posts  102 ,  202  protruding outwardly from respective bone-engaging surfaces  104 ,  204 . While  FIGS. 1-4  illustrate each joint prosthesis component  100 ,  200 , having two fixation posts, in alternative embodiments, each component  100 ,  200  may have more or fewer fixation posts. For example, in one alternative embodiment, a first joint prosthesis component can comprise one or more fixation posts, while a second joint prosthesis component can be provided without any fixation posts. In another specific example, a first joint component can comprise one fixation post and a second joint component can comprise two or more fixation posts. A suitable number of fixation posts can be determined based on the particular joint application and can vary for different designs of joint prostheses. 
     Returning to  FIGS. 1-4 , the humeral component  100  can comprise a bone-engaging surface  104  opposite an articulating surface  106 . The radioulnar component  200  can comprise a bone-engaging surface  204  opposite an articulating surface  206 . As shown in  FIGS. 3-4 , the joint prosthesis  400  is designed such that, when implanted, the articulating surface  106  of the humeral component  100  and the articulating surface  206  of the radioulnar component  200  interact with one another such that the humeral component  100  can move with respect to the radioulnar component (e.g., the articulating surfaces  106 ,  206  slide back and forth against one another), thereby providing joint movement. The interaction of the humeral component  100  and the radioulnar component  200  is shown in  FIG. 3 , in exploded view. 
     The bone-engaging surfaces  104 ,  204  each can engage with a bone at the implantation site. In the particular example shown in  FIGS. 1-4  (and as best seen in  FIG. 4 ), the bone-engaging surface  104  engages with a humerus  408  and the bone-engaging surface  204  engages with the radius and/or ulna  410 . In other embodiments (e.g., with other types of joint implants according to the present disclosure), the bone engaging surfaces can engage with different bones, as determined by the particular joint the joint implant is designed to replace. 
     The bone-engaging surfaces  104 ,  204  can comprise one or more portions configured to encourage bone growth. For example, central portion  112  and edge portions  114  of the humeral component  100 , as well as portion  216  of the radioulnar component  200  can comprise a porous coating. In some embodiments, only a portion of the bone-engaging surfaces  104 ,  204  is treated with such porous coatings. In some embodiments, substantially all of the bone-engaging surfaces  104 ,  204  are treated with one or more porous coatings. In some embodiments, at least a portion of the surfaces of one or more fixation posts  102 ,  202  can include one or more porous coatings. Examples of suitable porous coatings are shown in  FIGS. 11-14  and include a plasma spray porous surface ( FIG. 11 ), a sintered bead porous surface ( FIG. 12 ), a fiber metal porous surface ( FIG. 13 ), and a porous tantalum structure with interconnected porosity ( FIG. 14 ). 
     One or more fixation posts  102 ,  202  can be positioned on the bone-engaging surfaces  104 ,  204  of joint components  100 ,  200 . Humeral component  100  can include two fixation posts  102  positioned on the bone-engaging surface  104 . In some embodiments, as shown in  FIG. 1 , the two fixation posts  102  can be positioned substantially parallel to one another, adjacent opposite ends  118 ,  120  of the humeral component  100 . The posts  102 ,  202  can protrude outwardly from the bone-engaging surface  104 ,  204  and each can be formed of at least two substantially aligned segments  122 ,  222 , respectively, separated from each other along the bone-engaging surface  104 ,  204  by respective gaps  124 ,  224 . 
     Each segment  122 ,  222  can be a partially closed segment having two free ends. For example, each segment  122  can have free ends  121 ,  123  and each segment  222  can have free ends  221 ,  223 . Each segment  122 ,  222  can be, for example, a C-shaped structure integrally formed with or coupled to the bone-engaging surface  104 ,  204  (e.g., by welding). In other embodiments, each segment can be, for example, a substantially elliptical, oval, circular (e.g., O-shaped with a small gap between two free ends), angular, triangular, square, rectangular, V-shaped, or D-shaped structure coupled to the bone-engaging surface of a joint implant component. Other shapes can also be suitable. 
     The segments  122 ,  222  can be substantially aligned with one another so as to form respective central openings  126 ,  226  through the centers of the segments  122 ,  222 . Each central opening  126 ,  226  can be, for example, a substantially cylindrical opening. Each central opening  126 ,  226  is discontinuous due to the gaps  124 ,  224  between adjacent segments  122 ,  222 , but each opening  126 ,  226  nonetheless can be configured to receive a cylindrical object such as a cement injection needle. The fixation posts  102 ,  202  and central openings  126 ,  226  can also be configured to receive ingrowing bone. For example, bone can grow into the segments  122 ,  222  between the free ends and/or between the segments (e.g., in gaps  124 ,  224 ). Thus, the humeral and radioulnar components  100 ,  200  and their fixation posts  102 ,  202  can be configured for biologic fixation and/or for cement fixation. 
     The fixation posts  102 ,  202  can be positioned tangential to the bone-engaging surface  104 ,  204  in some embodiments. The orientation of the fixation posts  102  can be at least partially defined with respect to a major axis X and a minor axis Y. Generally, major axis X corresponds to the longest dimension of the joint component, and the minor axis Y is perpendicular to the major axis X. In the case of the humeral component  100  of  FIG. 1 , the overall cross-sectional shape of the component  100  can be substantially half of an ellipse (e.g., when viewed from the side), and the major axis X passes through foci proximate to opposite ends  118 ,  120 , as well as the center of the implant component  100 . As in  FIG. 1 , the fixation posts  102  can be positioned such that they cross (e.g., are transverse to) the major axis X. In  FIG. 1 , the fixation posts  102  are positioned substantially parallel to the minor axis Y (e.g., substantially perpendicular to the major axis X). In other embodiments, the fixation posts can be positioned to cross the major axis X at a non-perpendicular angle to the major axis X. 
     Fixation posts  102 ,  202  can be expandable from a first position to a second position, wherein the diameter of the central opening is increased in the second position with respect to the first position, as will be described further below in connection with  FIGS. 16-17 . One or more segments  122 ,  222  of the respective fixation posts  102 ,  202  can be provided with internal threads (e.g., the surface of the segments  122  facing the central opening  126  can be threaded). 
       FIGS. 5-10  show alternative examples of embodiments of joint implants (or joint implant components) that include one or more fixation posts in various positions on the joint implant (e.g., on the bone-engaging surface of one or more joint implant components). These embodiments are exemplary only, and many other configurations and implant types are possible. 
       FIG. 5  shows a prosthetic femoral hip stem  500  having a longitudinal axis Z. The femoral hip stem  500  can include one or more fixation posts  502  positioned on and protruding outwardly from a bone-engaging surface  504 . The fixation posts  502  can be positioned substantially parallel to the longitudinal axis Z in some embodiments. While only one fixation post  502  is visible in  FIG. 5 , the femoral hip stem  500  can include one or more additional fixation posts  502  spaced around the implant. 
     The fixation post  502  can include at least two substantially aligned segments  522  (e.g., C-shaped segments) separated from each other along the bone-engaging surface  504  by a gap  524 . The segments  522  of a fixation post  502  can define a central opening through the centers of the segments  522 . While the embodiment shown in  FIG. 5  includes three substantially aligned segments  522 , other embodiments can include one or more fixation posts having more or fewer segments. As with all described embodiments, at least a portion of the joint implant  500  (e.g., the bone-engaging surface) and/or at least a portion of the one or more fixation posts  502  can be porous. For example, at least a portion of the joint implant  500  and/or at least a portion of the fixation post  502  can be treated with a porous coating, such as the porous coatings shown in  FIGS. 11-14 . Fixation post  502  can be expandable, in accordance with  FIGS. 16-17 . 
       FIG. 6  shows one embodiment of an acetabular cup  600  having a longitudinal axis Z. The acetabular cup  600  can include one or more fixation posts  602  positioned on a bone-engaging surface  604 . The fixation posts  602  can be positioned substantially parallel to the longitudinal axis Z in some embodiments. While two fixation posts  602  are visible in  FIG. 6 , the acetabular cup  600  can include one or more additional fixation posts  602  spaced around the implant. The fixation posts  602  can each include at least two substantially aligned segments  622  (e.g., C-shaped segments) separated from each other along the bone-engaging surface  604  by a gap  624 . The segments  622  of a fixation post  602  can define a central opening through the segments  622 . While the embodiment shown in  FIG. 6  includes three substantially aligned segments  622  forming each fixation post  602 , other embodiments can include one or more fixation posts having more or fewer segments. Fixation posts  602  can be expandable, in accordance with  FIGS. 16-17 . 
       FIG. 7  shows one embodiment of a femoral knee implant  700  that can interact with the knee tibial implant  800  of  FIG. 8  to form a complete prosthetic knee implant. Femoral knee implant  700  can include a bone-engaging surface  704  configured to engage with a patient&#39;s femur and one or more fixation posts  702  protruding from the bone-engaging surface  704 . Similarly, the knee tibial implant  800  can include one or more fixation posts  802  protruding from a bone-engaging surface  804  configured to engage with a patient&#39;s tibia. The fixation posts  702 ,  802  can each include at least two substantially aligned segments (e.g., C-shaped segments) separated from each other along the bone-engaging surface  704 ,  804  by a gap. The segments of a fixation post  702 ,  802  can define a central opening through the segments. Fixation posts  702 ,  802  can be expandable, in accordance with  FIGS. 16-17 . 
       FIG. 9  shows a prosthetic shoulder humeral stem  900  having a longitudinal axis Z. The shoulder humeral stem  900  can include one or more fixation posts  902  positioned on and protruding from a bone-engaging surface  904  configured to engage with a patient&#39;s bone (e.g., the humerus). The fixation posts  902  can be positioned substantially parallel to the longitudinal axis Z in some embodiments. While only one fixation post  902  is visible in  FIG. 9 , the shoulder humeral stem  900  can include one or more additional fixation posts  902  spaced around the implant. The fixation post  902  can include at least two substantially aligned segments  922  (e.g., C-shaped segments) separated from each other along the bone-engaging surface  904  by a gap  924 . While the embodiment shown in  FIG. 9  includes four substantially aligned segments  922 , other embodiments can include one or more fixation posts having more or fewer segments. The segments  922  of a fixation post can be arranged to define a central opening through the segments  922 . Fixation posts  902  can be expandable, in accordance with  FIGS. 16-17 . 
       FIG. 10  shows a prosthetic ankle tibial implant  1000  having a bone-engaging surface  1004  configured to engage with a patient&#39;s bone (e.g., the tibia). The bone-engaging surface  1004  can include one or more fixation posts (e.g., hollow, segmented posts)  1002  protruding outwardly from the bone-engaging surface  1004 . The fixation posts  1002  can be formed from two or more adjacent, substantially aligned segments  1022  (e.g., C-shaped segments) separated from each other along the bone-engaging surface  1004  by a gap  1024 . Fixation posts  1002  (e.g., segments  1022  of the fixation posts  1002 ) can be expandable, in accordance with  FIGS. 16-17 . 
     As shown in  FIG. 10 , a first fixation post  1002  can be positioned near a first edge portion  1018  and a second fixation post  1002  can be positioned near a second edge portion  1020  opposite the first edge portion  1018  of the ankle tibial implant  1000 . A major axis X and a minor axis Y can be associated with the ankle tibial implant  1000 , and one or more of the fixation posts can be positioned to cross (e.g., be positioned transverse to) the major axis X. In the specific embodiment shown in  FIG. 10 , the fixation posts are positioned substantially perpendicular to the major axis X, but other arrangements are also suitable. For example, fixation posts can be positioned at a non-perpendicular angle to the major axis X in some embodiments. 
     Fixation posts  1002  each comprise three substantially aligned segments  1022 , but in alternative embodiments, the fixation posts  1002  can comprise more or fewer segments. The fixation posts  1002  can be configured such that the interior of the segments  1022  forms a central opening  1026  (e.g., a substantially cylindrical opening  1026 ) that can be configured to receive a cylindrical object (e.g., a bone cement injection needle) and/or biologic tissue (e.g., bone ingrowth from the patient&#39;s bone). The fixation posts  1002  can be positioned tangentially to the bone-engaging surface  1004 , with the open portions of the segments  1022  facing outward (e.g., facing away from the bone-engaging surface  1004 ). Such arrangements of the segments  1022  of the fixation posts  1002  can facilitate expansion of the fixation posts  1002 , as will be described further below. 
     Any of the disclosed embodiments of joint implants having one or more hollow, segmented fixation posts can be configured such that the fixation posts are expandable from an original position to an expanded position. For example,  FIG. 16  shows a schematic elevation view of one segment  1622  of a fixation post positioned on a joint implant component  1600 , with the fixation post in its original position within a hole  1628  drilled into a patient&#39;s bone  1630 . 
       FIG. 17  shows a schematic elevation view of the segment  1622  of a fixation post in its expanded configuration  1622 ′ within the hole  1628  drilled into a patient&#39;s bone  1630 . The original position of segment  1622  is shown in  FIG. 17  in phantom, for reference. In expanding the segment  1622 ′, the free ends  1621 ′,  1623 ′ can be moved farther apart from one another than the free ends  1621 ,  1623  were in the original configuration. Such expansion of the fixation post segments generally involves permanent expansion (e.g., permanent deformation) as opposed to elastic deformation. In this manner, once the segments  1622  are expanded to an expanded configuration, they generally do not return to their original positions. 
     As shown in  FIGS. 16-17 , by expanding a fixation post (e.g., by expanding some or all of the segments  1622  that form a fixation post), one or more of the expanded segments  1622 ′ can engage with the patient&#39;s bone  1630  (e.g., the surface of the bone  1630  facing the hole  1628 ) such as to provide frictional engagement between the segment  1622 ′ and the bone  1630 . Such frictional engagement can provide further stability for the joint implant component  1600 . Thus, any of the disclosed embodiments of fixation posts can increase stability (e.g., fixation) of the joint implant and/or joint implant components. 
     While  FIG. 16  shows a visible gap between the segment  1622  and the hole  1628 , the hole  1628  is generally drilled to provide a press fit engagement with the fixation post, and  FIG. 16  shows a gap for clarity, and to emphasize the expansion of the segment  1622 . Thus, expansion of the segments  1622  can increase the strength of the fixation of the joint implant component  1600  to the bone  1630 . 
       FIG. 18  shows one embodiment of an expansion tool  1836  that can be used to expand segments of a fixation post, such as shown in  FIGS. 16-17 . Expansion tool  1836  can comprise a central portion  1838 , an enlarged tapered portion  1840 , and a threaded portion  1842 . Threaded portion  1842  can be configured to engage with, for example, a thumb screw  1844 . Threaded portion  1842  and central portion  1838  can be configured to fit within the central opening of a fixation post. A handle portion  1846  can be provided at one end of the expansion tool  1836 , opposite the threaded portion  1842 . The expansion tool  1836  can be long enough that the handle portion  1846  can extend out one end of a fixation post, while at least a portion of the threaded portion  1842  can extend out the opposite end of the fixation post. A thumb screw  1844  or other device can be used to engage with the threaded portion  1842  and turn the expansion tool  1836  so as to pull it at least partially into the central opening of a fixation post. As the expansion tool  1836  is pulled into a fixation post, the enlarged tapered portion  1840  can cause the segments of the fixation post to expand, as the enlarged tapered portion is pulled into the segments, forcing them to expand outwardly. One or more segments of a fixation post can be expanded in this manner, and then the expansion tool  1836  can be removed from the fixation post. If desired, the expansion tool  1836  can be inserted in the opposite end of the fixation post to expand one or more segments of the other end of the fixation post. In this manner, one or more the segments on either end of the fixation post can be expanded. In some embodiments, an expansion tool can expand all of the segments of a fixation post. 
     Any other suitable tool or device can also be used to expand one or more segments of one or more fixation posts on a joint implant component in a similar or other fashion. For example, in one alternative embodiment, the segments can be provided with internal threads that can engage a tapered tool, without the need for a separate thumb screw device as described above. In other embodiments, a tapered tool can be inserted, such as by a hammer, into the fixation post in order to expand one or more segments. 
       FIGS. 19-20  show another embodiment of a joint implant component  1900  comprising one or more hollow segmented fixation posts. Implant component  1900  is particularly adapted to be a femoral hip implant for example purposes, but the described concepts can be applied to other types of joint implants as well. While the joint implant embodiments shown in  FIGS. 1-10  generally include fixation posts that can be inserted and expanded in a hole tangential to the implant surface, the embodiment of  FIGS. 19-20  provide a joint implant having an expandable fixation post that can be inserted into a hole that is perpendicular to the osteotomy surface, or inserted into a blind- or through-hole. 
     Joint implant component  1900  can include a taper portion  1946  coupled to a post portion  1948 , both being substantially parallel to the longitudinal axis of the implant component  1900 . The post portion  1948  is at least partially inserted in a patient&#39;s bone (and thus is configured to engage with a patient&#39;s bone), and at least a portion of the taper portion  1946  rests outside of the bone. Taper portion  1946  can include internal threads  1950  for, by way of example, receiving another joint implant component (e.g., a metal femoral head configured to engage with an acetabulum) and/or for engaging with an expansion tool. Implant component  1900  can include a curved annular portion  1952  positioned between the taper portion  1946  and the post portion  1948 . The curved annular portion  1952  can be configured as a bone-engaging surface configured to engage with a patient&#39;s bone. The post portion  1948  can protrude outwardly from the curved annular portion  1952 . 
     Post portion  1948  can include a plurality of longitudinal slits  1956  positioned between adjacent segments  1954  (e.g., at least a portion of each of the segments  1954  is separated from an adjacent segment  1954  by a gap  1956 ). The longitudinal slits  1956  can extend along at least a portion of the length of the post portion  1948 . The longitudinal slits  1956  can also provide additional surfaces for bone ingrowth (e.g., bone can grow through the slits  1956  and into the central opening  1958 ). 
     In this manner, the segments  1954  can be positioned around the circumference of the post portion  1948  such that the segments  1954  can define a central opening  1958  through the center of the segments  1954 . The central opening  1958  can be configured to receive, for example, a cement injection needle. Longitudinal central opening  1958  can extend through the post portion  1948 , taper portion  1946 , and curved annular portion  1952 . However, the central opening  1958  need not have a constant diameter through the entire implant component  1900 . For example, the diameter of the central opening  1958  can be larger within the taper portion  1946  than it is within the post portion  1948 . 
     One or more portions of the joint implant component  1900  can comprise a porous surface, such as one or more of the porous surfaces shown in  FIGS. 11-14 . For example, one or more portions of the joint implant component  1900  can comprise a plasma spray porous surface ( FIG. 11 ), a sintered bead porous surface ( FIG. 12 ), a fiber metal porous surface ( FIG. 13 ), and/or a porous tantalum structure with interconnected porosity ( FIG. 14 ). Such portions of porous surface coatings or treatments can increase bone ingrowth in and around the segments  1954  of the post portion  1948 . For example, at least a portion of the outer, bone-engaging surfaces of segments  1954  can comprise a porous coating. In some embodiments, at least a portion of the inner surface of the segment  1954  (e.g., facing the central opening  1958 ) can comprise a porous coating. In some embodiments, each segment  1954  can comprise one or more recesses  1955 . Such recesses  1955  can be configured to encourage bone growth in and around the post portion  1948  of the implant component  1900 . 
     The segments  1954  can be arranged around the circumference of the post portion  1948 , and can be configured to expand radially outward to increase the diameter of a central opening  1958  of the joint implant component  1900  (e.g., by increasing the space between adjacent segments  1954 ). 
     For example, an expansion tool  2160  shown in  FIG. 21  can be used to expand the segments  1954  of the joint implant component  1900  from a first configuration to an expanded configuration, wherein the diameter of the central opening  1958  of the post portion  1948  is increased in the expanded configuration with respect to the diameter of the central opening  1958  in the first configuration. 
     One embodiment of an expansion tool  2160  can comprise a tapered portion  2162 , a threaded portion  2164 , and an internal opening  2166  configured to engage with, for example, a screwdriver head  2168 . The expansion tool  2160  can be inserted into the implant component  1900  such that the threaded portion  2164  of the expansion tool  2160  engages with the internal threads  1950  of the implant component  1900 .  FIG. 22  shows the expansion tool  2160  positioned at least partially inside the central opening  1958  of the implant component  1900 . As shown in  FIG. 22 , at least a portion of the tapered portion  2162  of the expansion tool  2160  can be positioned inside the central opening  1958  of the post portion  1948  of the implant component  1900  (e.g., inside the segments  1954 ). 
     In order to expand the post portion  1948  of the implant component (e.g., in order to move the segments  1954  radially outward and increase the gap between the segments), a screwdriver head  2168  or other tool can be inserted through the central opening  1958  at the end  1970  adjacent the taper portion  1946  of the implant component  1900 . The screwdriver head  2168  can engage with the expansion tool  2160  via the internal opening  2166 . Turning the screwdriver head  2168  can cause the expansion tool  2160  to be drawn through the central opening  1958  of the implant component  1900 , in a longitudinal direction towards the end  1970  adjacent the taper portion  1946 , due to engagement of the threaded portion  2164  of the expansion tool  2160  with the internal threads  1950  of the implant component  1900 . As the expansion tool  2160  is pulled through the segments  1954 , the segments  1954  are forced radially outward by the tapered portion  2162  of the expansion tool  2160 . 
       FIGS. 23-24  further illustrate expansion of an implant component  1900  in place within a patient&#39;s bone  2330  (e.g., femur  2330 ). A hole  2328  can be drilled into a patient&#39;s bone  2330  and sized such that the post portion  1948  of the implant component  1900  can be inserted into the hole  2328  by hand in some embodiments. When inserted, at least a portion of the post portion  1948  of the implant component  1900  can be positioned within a hole  2328  drilled into a patient&#39;s bone  2330 . In some embodiments, the annular portion  1952  can rest against a surface  2372  of bone  2330 . Annular portion  1952  can be enlarged so as to prevent insertion of the taper portion  1946  in the hole  2328  (e.g., the annular portion  1952  can serve as a stopper, preventing the implant  1900  from being inserted too far into a patient&#39;s bone  2330 ). 
     The expansion tool  2160  can be positioned within the central opening  1958  of the implant component  1900  before the post portion  1948  is inserted into the hole  2328  in the patient&#39;s bone  2330 . In this manner, once the post portion  1948  is inserted into the bone  2330 , a screwdriver head  2168  can be inserted through the end  1970  adjacent the taper portion  1946  (e.g., the portion of the implant component  1900  that is arranged outside of the bone  2330 ). The screwdriver head  2168  can engage with the internal opening  2166  of the expansion tool, and as the screwdriver head  2168  is turned ( FIG. 24 ), the expansion tool  2160  can be drawn through the central opening  1958  of the implant component  1900 , towards the end  1970  of the taper portion  1946 . As the expansion tool  2160  is drawn through the segments  1954  of the post portion  1948 , the segments  1954  are moved radially outward, increasing the size of the longitudinal slits  1956  (e.g., the gap) between adjacent segments  1954 , thereby increasing the diameter of the central opening  1958  within the post portion  1948  and increasing the frictional engagement or press fit of the post portion  1948  with the patient&#39;s bone  2330 . 
     As shown in  FIG. 25 , the expansion tool can be drawn entirely through the implant component  1900 , leaving the expanded implant component  1900  in the hole  2328  of the bone  2330 . Once the expansion tool is removed, further procedures can be performed to complete the joint replacement. For example, a second implant component  2574  can be arranged to couple with the implant component  1900 . For example, in the specific embodiment shown, a femoral head  2574  (e.g., a cobalt chrome femoral head) can be screwed into the internal threads  1950  within the taper portion  1946  of the implant component  1900 . The femoral head  2574  can then engage with one or more additional implant components, such as a prosthetic acetabulum. 
     Any of the disclosed embodiments of fixation posts can be configured to receive cement (e.g., polymethylmethacrylate (PMMA), other non-resorbable cements, or a resorbable bone cement) to be injected into the hollow segmented posts. For example,  FIG. 15  shows a joint implant component  1500  having at least one hollow segmented fixation post  1502  comprising three segments  1522 . A needle  1532  can be inserted into the opening  1526  created by the segments  1522  and cement  1534  can be injected into the central opening  1526  defined by the segments  1522 . As shown in  FIG. 15 , the fixation post  1502  can be configured to allow the cement  1534  to at least partially fill in the opening  1526  and flow out through removed segments of the post  1502  (e.g., flow through the gaps  1524  between adjacent segments  1522 ). The fixation post  1502  can thereby contribute to fixation of the joint implant component  1500  to a patient&#39;s bone  1530  by increasing the press fit engagement with the bone and into the bone (e.g., via expansion of the fixation post), by allowing for the extrusion of bone cement  1534  from the center of the post  1526  into the surrounding bone  1530 , and/or by promoting or allowing bone ingrowth through the gaps between adjacent segments and into the fixation post and/or bone ingrowth into porous surface portions on the implant component. 
     Disclosed embodiments of a hollow segmented fixation post can provide initial fixation (e.g., via press fit engagement with the patient&#39;s bone) but also provide the option to inject cement down the center of the post, allowing the cement to flow out through the gaps between adjacent segments of the post, thereby providing a stable localized locking of the implant to the bone. Additionally, disclosed fixation posts can allow for biologic fixation (e.g., bone ingrowth) into and on the joint implant components. For example, in embodiments where cement is not injected into the opening of the fixation posts, bone can grow into the central opening of the fixation posts by growing through the gaps between the segments of the post. In other embodiments (for example, when cement is injected into the central opening), bone ingrowth can develop on, for example, porous surfaces on the joint component and fixation posts. Such bone ingrowth can improve long term fixation of the implant. 
     Disclosed embodiments of joint prostheses and joint implant components can comprise any suitable metal, plastic, ceramic, coatings, and/or combinations of these. Generally, materials for bearing surfaces of implant components can be selected that provide low-friction movement with minimal generation of wear debris. Specific examples of suitable materials include cobalt chrome alloys, ultra high molecular weight polyethylene (UHMWPE), titanium nitride coatings, molybdenum, titanium, cobalt, and/or alloys or combinations of these materials. Specific examples of surface combinations suitable for articulation with one another include titanium nitride coated metals and UHMWPE, ceramic and ceramic, metal and metal, and other combinations of these. 
     At least a portion of disclosed embodiments of joint implant components can include porous coatings or treatments, such as PCA beads (Bio-Vac, Inc of Michigan, USA), hydroxy apatite (HA), titanium plasma spray coating, and/or Resorbable Blast Media Coating. In some embodiments, these porous coatings or treatments can promote bone growth in and around the joint implant component. 
     Methods of replacing at least part of a patient&#39;s joint with one or more joint implant components are also disclosed. For example, one method comprises preparing the implant site to receive the one or more joint implant components and implanting the joint prosthesis wherein at least a portion of the implant component is positioned at least partially within a hole drilled into a patient&#39;s bone. Any of the disclosed embodiments of joint implant components can be used in such methods. For example, the joint implant component can comprise a bone-engaging surface and at least one segmented post protruding from the bone-engaging surface, wherein the post comprises at least two segments, each segment being separated by a gap, and wherein the segments define a central opening through the center of said segments. 
     In some methods, at least one segmented post can be expanded from a first configuration to a second configuration, wherein the diameter of the central opening is increased in the second configuration with respect to the first configuration. For example, an expansion tool, such as the expansion tools shown in  FIGS. 18 and 21 , can be used to expand one or more segments of the implant component, thereby increasing the press fit of the fixation post within the patient&#39;s bone. Thus, in some methods, the at least one segmented post can be expanded by drawing a tapered expansion tool through at least part of the segmented post. 
     Disclosed methods and joint implant components can provide a surgeon with flexibility as to whether to use biologic fixation or cement fixation for a particular implant component for a particular patient. Such flexibility can be provided without requiring the surgeon to remove the implant or re-prepare the bone surface if he or she decided mid-surgery to alter the fixation approach. For example, a patient&#39;s bone can be prepared assuming the implant component will be stabilized using biologic fixation. After preparation and insertion of the implant, the surgeon or other professional can evaluate whether biologic fixation is indeed suitable as the sole fixation method at the time of implantation. If it is determined at the time of implantation that biologic fixation may be insufficient as the sole means of implant fixation, cement can be injected into the central opening of the fixation post, without requiring removal of the implant component. 
     On the other hand, if a joint implant component was implanted intending to rely on biologic fixation, and a follow-up evaluation a period of time after completion of the joint replacement reveals that the joint prosthesis is insufficiently stable, cement can be injected into the substantially cylindrical opening of one or more of the fixation posts at a date after initial implantation. Such revision surgery may require clearing of fibrous or other growth from within one or more fixation posts in order to re-open the hollow post to accommodate injection of bone cement. 
     In view of the many possible embodiments to which the principles of the disclosed invention may be applied, it should be recognized that the illustrated embodiments are only preferred examples of the invention and should not be taken as limiting the scope of the invention. Rather, the scope of the invention is defined by the following claims. We therefore claim as our invention all that comes within the scope and spirit of these claims.