Abstract:
Expandable medical implants for supporting bone structures may include a first member and a second member. The second member may be configured to receive the first member and may be moveable along the longitudinal axis relative to the first member. One of the first and second members may include a plurality of teeth and the other of the first and second members may include at least one tooth. At least a portion of one of the first and second main bodies may be elastically deformable to selectively engage and disengage the at least one tooth and the plurality of teeth. At least one tooth and the plurality of teeth may be shaped to deform the elastically deformable portion when both increasing and when decreasing the overall implant height by moving the second member relative to the first member along the longitudinal axis.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to the field of replacing portions of the human structural anatomy with medical implants, and more particularly relates to an expandable implant and method for replacing bone structures such as one or more vertebrae or long bones. 
       BACKGROUND 
       [0002]    It is sometimes necessary to remove one or more vertebrae, or a portion of the vertebrae, from the human spine in response to various pathologies. For example, one or more of the vertebrae may become damaged as a result of tumor growth, or may become damaged by a traumatic or other event. Excision of at least a generally anterior portion, or vertebral body, of the vertebra may be referred to as a corpectomy. An implant is usually placed between the remaining vertebrae to provide structural support for the spine as a part of a corpectomy.  FIG. 1  illustrates four vertebrae, V 1 -V 4  of a typical lumbar spine and three spinal discs, D 1 -D 3 . As illustrated, V 3  is a damaged vertebra and all or a part of V 3  could be removed to help stabilize the spine. If removed along with spinal discs D 2  and D 3 , an implant may be placed between vertebrae V 2  and V 4 . Most commonly, the implant inserted between the vertebrae is designed to facilitate fusion between remaining vertebrae. Sometimes the implant is designed to replace the function of the excised vertebra and discs. All or part of more than one vertebrae may be damaged and require removal and replacement in some circumstances. 
         [0003]    Many implants are known in the art for use in a corpectomy procedure. One class of implants is sized to directly replace the vertebra or vertebrae that are being replaced. Another class of implants is inserted into the body in a collapsed state and then expanded once properly positioned. Expandable implants may be advantageous because they allow for a smaller incision when properly positioning an implant. Additionally, expandable implants may assist with restoring proper loading to the anatomy and achieving more secure fixation of the implant. Implants that include insertion and expansion members that are narrowly configured may also provide clinical advantages. In some circumstances, it is desirable to have vertebral endplate contacting surfaces that effectively spread loading across the vertebral endplates. Effective implants should also include a member for maintaining the desired positions, and in some situations, being capable of collapsing. Fusion implants with an opening may also be advantageous because they allow for vascularization and bone growth through all or a portion of the entire implant. 
         [0004]    Expandable implants may also be useful in replacing long bones or portions of appendages such as the legs and arms, or a rib or other bone that is generally longer than it is wide. Examples include, but are not limited to, a femur, tibia, fibula, humerus, radius, ulna, phalanges, clavicle, and any of the ribs. 
       SUMMARY 
       [0005]    In a first exemplary aspect, an expandable medical implant for supporting bone structures is disclosed. The implant may have an overall implant height adjustable along a longitudinal axis and may include a first member having a first outer end, a first inner end, and a first main body extending therebetween. The first outer end may be configured to cooperatively engage a first bone structure, and the first main body may define the longitudinal axis. A second member may have a second outer end, a second inner end, and a second main body extending therebetween. The second outer end may be configured to cooperatively engage a second bone structure. The second inner end may be configured to receive the first inner end of the first member. The second member may be moveable along the longitudinal axis relative to the first member. One of the first and second main bodies may include a plurality of teeth and the other of the first and second main bodies may include at least one tooth. At least a portion of one of the first and second main bodies may be elastically deformable to selectively engage and disengage the at least one tooth and the plurality of teeth. At least one tooth and the plurality of teeth may be shaped to deform the elastically deformable portion when both increasing and when decreasing the overall implant height by moving the second member relative to the first member along the longitudinal axis. 
         [0006]    In another exemplary aspect, the implant may include a locking member configured to selectively inhibit deformation of the elastically deformable portion to prevent a change in the overall implant height. The locking member may be a sleeve extending about and slidable along the perimeter of the second member. 
         [0007]    In yet another exemplary aspect, an expandable medical implant for supporting bone structures is disclosed. The implant may include a first member, a second member, and a third member. The first member may have a first outer end configured to cooperatively engage a first bone structure and a first inner end configured to engage the second member. The second member may have a second outer end configured to cooperatively engage a second bone structure and a second inner end configured to engage the first member. The second member may be axially moveable along the longitudinal axis relative to the first member to increase the overall implant height. The second member may include an elastically deformable portion that elastically deforms during the axial movement. The third member may be configured to selectively inhibit deformation of the elastically deformable portion to inhibit axial movement and an increase in the overall implant height. 
         [0008]    In one aspect, the second member may receive the first member, and the third member may extend about a perimeter of the second member. In another aspect, the first and second members may each include a plurality of selectively engagable teeth, and the third member may be configured to selectively maintain the plurality of selectively engagable teeth in an engaged state. 
         [0009]    In yet another aspect, an expandable medical implant for supporting bone structures is disclosed. The implant may include an inner member having a first inner end and an opposite first outer end configured to cooperatively engage with a first bone structure. The first member also may include an outer surface having outwardly protruding teeth disposed thereon. An outer member may have a second inner end and an opposite second outer end configured to cooperatively engage with a bone structure. The second inner end may be configured to receive the first inner end of the inner member. The outer member may have an inner wall surface including inwardly protruding teeth. The outer member may be configured to elastically deform to selectively engage and disengage the inwardly protruding teeth between the outwardly protruding teeth during axial extension. 
         [0010]    In some aspects, the inwardly and outwardly protruding teeth are configured to engage and disengage when the outer member is axially displaced in either direction relative to the inner member. Also, in some aspects, a locking member may be disposed about the outer member. The locking member may be sized to limit elastic deformation of the outer member. 
         [0011]    In yet another exemplary embodiment, a method of implanting an expandable medical implant for supporting bone structures is disclosed. The implant may include first, second, and third members and the first and second members may define a longitudinal axis. The first member may have at least one tooth, and the second member may have a plurality of teeth. The method may include placing the implant between the bone structures and displacing the first member along the longitudinal axis relative to a second member such that one of the first and second members elastically deforms to selectively engage and disengage the at least one tooth with the plurality of teeth. The third member may be associated with the first or second member to selectively inhibit elastic deformation and to secure the at least one tooth in an engaged position with the plurality of teeth. 
         [0012]    In yet another exemplary aspect, an expandable medical implant for supporting bone structures is disclosed. The implant includes a first member, a second member, and a third member. The first member may have a first outer end configured to cooperatively engage a first bone structure and a first inner end configured to engage the second member. The second member may have a second outer end configured to cooperatively engage a second bone structure and a second inner end configured to engage the first member. The second member may be axially moveable along the longitudinal axis relative to the first member to increase the overall implant height. The third member may be configured to apply a radial load that increases frictional resistance between the first and second members to selectively inhibit axial movement and an increase in the overall implant height. 
         [0013]    In yet another exemplary embodiment, a method of implanting an expandable medical implant for supporting bone structures is disclosed. The implant may include first, second, and third members, the first and second members defining a longitudinal axis. The method may include the steps of placing the implant between the bone structures and displacing the first member along the longitudinal axis relative to a second member. The third member may be associated with the first or second member to increase frictional resistance between the first and second members and to inhibit further displacement. 
         [0014]    Further aspects, forms, embodiments, objects, features, benefits, and advantages may be found in related U.S. patent application Ser. No. ______ (Attorney Docket No. P25412/MSDI-755), which has a common inventive entity and the same filing date as the present application, and which is incorporated herein by reference in its entirety. 
         [0015]    Further aspects, forms, embodiments, objects, features, benefits, and advantages of the present invention shall become apparent from the detailed drawings and descriptions provided herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is an elevation view of a segment of a lumbar spine. 
           [0017]      FIG. 2  is an exploded side view of an exemplary expandable implant. 
           [0018]      FIG. 3  is a cross-section view of an outer member of the exemplary implant shown in  FIG. 2 . 
           [0019]      FIG. 4  is a cross-section view of a locking member of the exemplary implant shown in  FIG. 2 . 
           [0020]      FIG. 5  is a cross-section view of the assembled exemplary implant shown in  FIG. 2  in a first position. 
           [0021]      FIG. 5A  is a cross-section view showing additional detail of the assembled exemplary implant shown in  FIG. 5   
           [0022]      FIG. 6  is a cross-section view of the assembled exemplary implant shown in  FIG. 2  in a second position. 
           [0023]      FIG. 7  is an elevation view of an alternative locking member. 
           [0024]      FIG. 8  is an elevation view of another alternative locking member. 
           [0025]      FIG. 9  is a cross-sectional view of another embodiment of an exemplary expandable implant. 
           [0026]      FIG. 10  is a cross-sectional view of yet another embodiment of an exemplary expandable implant. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments, or examples, illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates. 
         [0028]    Referring now to  FIG. 2 , there is shown an expandable implant  100  in accordance with one aspect of the present invention. The expandable implant  100  may include an inner member  102 , an outer member  104 , and a locking member  106 , extending along a longitudinal axis L. The inner member  102  may be formed as a tube and may include an inner end  108  configured to cooperate with the outer member  104 , and an outer end  110  configured to cooperatively interface with a bone structure, such as a vertebral body, either through additional components such as end plates or by directly abutting the bone structure. A main body extends between the inner and outer ends  108 ,  110 . Ridges or outwardly protruding teeth  112  may extend about the outer perimeter or surface of the inner member  102 . As can be seen, the outwardly protruding teeth  112  are outward facing protrusions that form valleys  113  therebetween. In  FIG. 2 , the outwardly protruding teeth  112  are formed as triangular shaped protrusions. However, other shapes of outwardly protruding teeth  112  may be used, including for example, frustums, rounded, truncated, or sinusoidal shaped teeth, among others. 
         [0029]    The outer end  110  of the inner member  102  may include a flange  116  that may abut the adjacent vertebral body, thereby distributing any loads carried by the bones over a wider surface area. The flange may be sized to cooperate with a standard distracter tool (not shown) that would be used to distract the expandable device once it is placed within a spinal column. In the embodiment shown, only one flange is disposed at the outer end  110 . However, in other embodiments, the inner member  102  may include more than one flange. For example, in one embodiment, a second flange may be formed on the inner member slightly offset from the outer end  110  of the inner member  102 . A distracter tool would then be able to fit between the two flanges to more securely hold the inner member  102  during implantation of the expandable implant  100 . 
         [0030]    In some embodiments, modular end plates (not shown) may be disposed adjacent the outer end  110  of the inner member  102  to engage the bone structure. In some embodiments, the end plates may include bone fixation features, such as for example, teeth or fins configured to engage the bone structures. 
         [0031]    Adjacent the outer end  110 , the inner member  102  may include optional gaps or windows  114  that provide access to a hollow interior  116  (shown in  FIG. 5 ). The windows  114  may allow graft material to be introduced into the hollow interior  116  after implantation of the expandable implant  100 . In addition, the windows  114  may provide access for other biological activity and vascularization. 
         [0032]    In some embodiments the outwardly protruding teeth  112  may be axially spaced apart from the inner end  108  and may be disposed centrally or toward the outer end  110  of the inner device  102 . As such, the outwardly protruding teeth  112  may be formed along any part or the outer perimeter of the inner member  102 . In some embodiments, the outwardly protruding teeth  112  may be disposed adjacent the outer end  110  in place of the shown windows  114 . Also, in some embodiments, the outwardly protruding teeth  112  may be formed of separate adjacent ridges extending radially about the perimeter of the inner member  102  as shown in  FIG. 2 , or alternatively, may be one or more spirally formed teeth extending about the perimeter of the inner member  102 . 
         [0033]    In some embodiments, the inner member  102  is not entirely hollow, but may be solid or alternatively, may be partially hollow. For example, it may be hollow only at the outer end  102  to provide vascularization and grafting at the interface of the vertebral body and the outer end  110 . 
         [0034]      FIG. 2  shows a side view and  FIG. 3  shows a cross-sectional view of the outer member  104 . The outer member  104  may be a tubular device having an inner end  118 , an outer end  120 , and a main body  122 . The inner end  118  may be configured to cooperatively receive the inner member  102 , and the outer end  120  may be configured to cooperatively interface with a bone structure, either directly or through additional components, such as end plates. 
         [0035]    The outer member  104  includes a hollow center  124  formed by an inner wall  126 . The hollow center  124  is sized to receive the inner end  108  of the inner member  102 . Upward or downward movement of the inner member  102  relative to the outer member  104  increases or decreases the overall height of the expandable implant  100 . 
         [0036]    The main body  122  of the outer member  104 , in the embodiment shown, is divided into a flexible section  128  and an optional window section  130 . The flexible section  128  is identified by slots  132  longitudinally extending from the inner end  118  toward the outer end  120 . The slots  132  divide the flexible section  128  into a plurality of cantilevered segments  134  extending from the window section  130  that are capable of elastically deforming, as is explained below. 
         [0037]    Each cantilevered segment  134  may include inwardly protruding teeth  136  on the inner wall  126  that radially extend inward. In the embodiment shown in  FIGS. 2 and 3 , the inwardly protruding teeth  136  are sized and spaced to correspond to and mesh between the outwardly protruding teeth  112  on the inner member  102 , as discussed below with reference to  FIG. 5 . In the embodiment shown, the inwardly protruding teeth  136  are spaced apart from each other about twice the distance of the spacing of the teeth  112  on the inner member  102 . However, in other embodiments, the teeth  136  are spaced closer to each other, or further apart from each other. 
         [0038]    Because the inwardly protruding teeth  136  are formed on the cantilevered elements  134 , when the inner and outer members  102 ,  104  are assembled together, axial movement of the outer member  104  relative to the inner member  102  causes the on the cantilevered elements  134  to elastically deform so that the inwardly protruding teeth  136  alternating engage and disengage the valleys  113 , thereby ratcheting between the outwardly protruding teeth  112  of the inner member  102 . In some embodiments, the teeth  112 ,  136  may have a zero angle or reverse angle to allow ratcheting in a single direction. 
         [0039]    As shown in  FIGS. 2 and 3 , a locking nub  138  lies about the exterior of the perimeter of the flexible section  128 . The locking nub  138  orients the locking member  106  in a position to secure the cantilevered segments  134  from flexing and disengaging the inner member  102 . This reduces any chance of undesired increase or decrease of the overall height of the expandable implant  100 . 
         [0040]    The window section  130  includes windows  140  providing access to the interior of the expandable implant  100  after the implant is placed within a spinal column. Like the windows  114  of the inner member  102 , the windows  140  allow the introduction of grafting material, as well as access for biological activity, such as vascularization. 
         [0041]    A flange  142  disposed at the outer end  120  of the outer member  104  provides a wide support area to distribute loads on the bone structure. In addition, it provides a location for a standard distraction type device (not shown) to apply a distraction force to separate the inner and outer members  102 ,  104  to increase the height of the expandable implant  100 . As described above with reference to the inner member  102 , the outer member  104  may include more than one flange. In some embodiments, modular end plates (not shown) may be disposed adjacent the outer end  120  of the outer member  104  to engage the bone structure. 
         [0042]    Although in the embodiment shown, the slots  132  extend only about halfway along the height of the main body  122  of the outer member  104 , in other embodiments, the slots extend less than half the length or more than half of the length of the main body  122 . The length of the slots  132  may be partially dependent on the material and wall thickness of the outer member  104  because the slots should be long enough to allow enough elastic deformation to ratchet the inwardly protruding teeth  136  into and out of engagement with the outwardly protruding teeth  112  of the inner member. 
         [0043]    The locking member  106  is a sleeve configured to extend about the exterior of the outer member  104 . Sized to provide a sliding fit, the locking member  106  cooperates with the outer member  104  to allow or inhibit deflection of the cantilevered segments  134  and to allow or inhibit a change the overall height of the expandable implant  100 . 
         [0044]      FIG. 4  shows a cross-section of the locking member  106 . As can be seen, an interior surface  143  of the locking member  106  includes a tapering lip  144  and a recess  146 . The tapering lip  144  and recess  146  cooperate with the locking nub  138  to secure the locking member  106  in place about the flexible section  128  of the outer member  104 . As explained further below, the tapering lip  144  of the locking member  106  may be slid over the locking nub  138  until the locking nub  138  fits within the recess  146 . 
         [0045]      FIGS. 5 and 6  each show cross-sectional views of the assembled expandable device  100  at different stages of implantation. In  FIG. 5 , the expandable implant  100  is in a locked condition, while in  FIG. 6 , the expandable implant  100  is an unlocked condition. 
         [0046]    Referring to  FIG. 5 , the locking member  106  extends about the exterior of the outer member  104 . The locking member  106  slides along the outer perimeter of the outer member  104  between a locked and an unlocked position. 
         [0047]    When in the locked position, as shown in  FIG. 5 , the locking member  106  is disposed in a position to restrict substantial deflection of the cantilevered elements  134  of the outer member  104 . More specifically, the locking member  106  may be located about the flexible section  128  of the outer member  104 . In  FIG. 5 , the locking member  106  is located so that the recess  146  is secured about the locking nub  138 , inhibiting any undesired movement of the locking member  106  relative to the outer member  104 . Thus, the locking member  106  also inhibits any movement of the flexible section  128  of the outer member  104  that would disengage the inwardly protruding teeth  136  from the outwardly protruding teeth  112 . 
         [0048]    In contrast, as shown in  FIG. 6 , when the locking member  106  is in the unlocked position, the locking member  106  does not restrict substantial deflection of the cantilevered elements  134 . In this embodiment, the locking member  106  is the unlocked position when, as shown in  FIG. 6 , the locking member  106  is not disposed about the flexible section  128 . Here, instead of being disposed about the flexible section  128 , the locking member is disposed about the window section  130 . 
         [0049]    Referring to  FIGS. 5 and 5A , the inwardly protruding teeth  136  of the outer member  104  are disposed between and engaged with the outwardly protruding teeth  112  of the inner member  102 . In the embodiment shown and as seen best in  FIG. 5A , the outwardly protruding teeth  112  and inwardly protruding teeth  136  are formed of two flat surfaces forming the exemplary triangular teeth. These surfaces form angles Θ between their surfaces and a line drawn parallel to the longitudinal axis L. In one example, the angles Θ are equal, while in other embodiments, they are not equal, such as when the teeth have a zero angle or reverse angle. In order to provide simple ratcheting when increasing or decreasing the overall height of the implant  100 , the angles Θ may be between the range of 10° and 80°. In some embodiments, the angles Θ are within the range of 20° and 70°. 
         [0050]    In the embodiment shown, the inwardly protruding teeth  136  are spaced apart to protrude into alternating valleys  113  formed between the outwardly protruding teeth  112  of the inner member  102 , as is shown in  FIG. 6 , rather than adjacent valleys  113 . Accordingly, adjacent inwardly protruding teeth  136  on the outer member  104  mesh into non-adjacent valleys  113  formed by the outwardly protruding teeth  112  of the inner member  102 . 
         [0051]    Because the inwardly protruding teeth  136  are formed on the cantilevered elements  134 , axial movement of the outer member  104  relative to the inner member  102  causes the cantilevered elements to elastically deform so that the inwardly protruding teeth  136  alternating engage and disengage the valleys  113  between the outwardly protruding teeth  112  of the inner member  102 , thereby ratcheting. Furthermore, the shape of the outwardly protruding teeth  112  and the inwardly protruding teeth  136 , as well as the angles Θ of the outwardly and inwardly protruding teeth  112 ,  136 , allow the teeth to move relative to each other along the longitudinal axis L to not only increase the overall height of the implantable member  100 , but also to decrease the overall height of the implantable member  100 . 
         [0052]    In use, the expandable implant  100  may be surgically placed within a patient to engage and stabilize bone structures. Typically, the expandable implant is introduced through an incision in a fully retracted position. By being fully retracted, the expandable implant  100  is at its smallest size, thereby allowing implantation through the smallest possible incision. 
         [0053]    In its fully retracted condition, the expandable implant  100  is positioned into the bone segment, such as a vertebral segment, in the space previously occupied by a vertebral body. For example, with reference to  FIG. 1 , the expandable implant may be positioned in place of vertebral body V 3  and the adjacent disks D 2  and D 3 . 
         [0054]    If during implantation, the locking member  106  was secured about the flexible section  128  of the outer member  104  as shown in  FIG. 5 , then the locking member may be axially slid to disengage the locking member  106  from the locking nub  138  of the outer member  104 , as is shown in  FIG. 6 . 
         [0055]    Once the bone engaging portions have been properly oriented, a distraction tool or spreader (not shown) is inserted to engage the flanges  116 ,  142  on each of the outer ends  110 ,  120  to urge them apart and into engagement with the intact vertebra. 
         [0056]    During distraction, as shown in  FIG. 6 , the cantilevered segments  134  ratchet as they elastically deform and the inwardly protruding teeth  136  disengage and reengage the outwardly protruding teeth  112 . Accordingly, the inwardly protruding teeth  136  ratchet in and out from the outwardly protruding teeth  112  and change the overall height of the implant  100 . 
         [0057]    Once the desired amount of expansion of the expandable device  100  has been obtained, the locking member  106  is axially slid to cover the flexible section  128  of the outer member  104 . The locking member  106  forces the inwardly protruding teeth  136  in place between the outwardly protruding teeth  112 , and the tapering lip slides over the locking nub  138  and the locking nub snaps into the recess  146 . 
         [0058]    If for any reason it becomes necessary to remove the expandable implant  100 , the locking member  106  can be axially slid off the locking nub  138  and off the flexible section  128 . The outer ends  110 ,  120  can be brought together while the teeth  112 ,  136  ratchet in a manner similar to the manner done during expansion. Once the implant is retracted a desired amount, the implant can be removed. 
         [0059]    It should be noted that although the outer member  138  is shown with a single locking nub  138 , in other embodiments, a second locking nub is disposed toward the outer end  120  of the outer member  104 . This second locking nub may be used to securely hold the locking member  106  is the unlocked position during placement or distraction of the implant  100 . In such an embodiment, the interior surface  143  of the locker member  106  may have a tapered lip  144  at each end and, in some embodiments, an additional recess may be employed. Alternatively, a single recess  146  may be used to secure the locking member  106  whether it is in the locked or unlocked position. 
         [0060]      FIGS. 7 and 8  show alternative embodiments of the locking member  106 .  FIG. 7  shows a locking member  150  formed of a band  152  and a gear box  154 . The band  152  may be formed of a biologically compatible metal or other material, and may include perforations  156 . The gear box  154  may include a worm-type gear  158  having teeth (not shown) that engage the perforations  156  in the band  152 . By turning the gear  158  with an appropriate tool, the gear  158  may pull the band  152  to tighten it about the exterior of the outer member  104 , thereby inhibiting deformation of the cantilevered segments  134 , and thereby maintaining the outwardly protruding teeth  112  and the inwardly protruding teeth  136  in an engaged or meshed position. 
         [0061]      FIG. 8  shows another alternative embodiment of a locking member. In  FIG. 8 , the locking member  160  is a clamping band. The locking member  160  includes a first band  162 , a second band  164 , a hinge  165 , and a fastener  166 . The first and second bands  162 ,  164  are joined at one end by the hinge  165 . The other ends of the bands  162 ,  164  may be bent and perforated to receive the fastener  166 . In the embodiment shown, the fastener  166  is a bolt and nut. In other embodiments, the locking member  160  includes only a single band, rather than multiple bands as shown in  FIG. 8 . The two ends of the single band may be still joined to each other using a bolt and nut or other fastening system. 
         [0062]    In use, the locking member  160  is placed about the exterior of the cantilevered segments  134  and then tightened and fastened closed to inhibit deformation of the cantilevered segments  134 , and thereby maintain the outwardly protruding teeth  112  and the inwardly protruding teeth  136  in an engaged or meshed position. Other fastening systems may be used, including screws, buckles, and others. It should be noted that other locking members also may be used to inhibit disengagement of the outwardly protruding teeth  112  and the inwardly protruding teeth  136 . 
         [0063]      FIG. 9  shows another exemplary embodiment of an outer member  170  and a locking member  172 . The outer member  170  and locking member  172  are similar to those disclosed above with reference to  FIG. 2 , but cantilevered segments  174  of the outer member  170  are tapered so that the outer diameter of an inner end  176  is greater than the diameter of other portions of the main body. In addition, the locking member  172  includes a tapered inner surface  180  that matches the tapered surface of the outer member  170 . Accordingly, by sliding the locking member  172  downward over the tapering cantilevered segments  174 , the locking member  172  provides a holding force that inhibits expansion and disengagement of the outwardly protruding teeth and the inwardly protruding teeth. It should be noted that some embodiments of the outer member and locking member do not employ the locking nub  138  and the recess  146 . 
         [0064]      FIG. 10  shows another exemplary embodiment of an expandable implant  190 . The implant  190  includes an inner member  192 , an outer member  194 , and a locking member  196 . The inner member  192  and the outer member  194  are similar to those disclosed above with reference to  FIG. 2 , but they do not include ratcheting teeth. Instead, the inner member  192  and the outer member  194  have surfaces that are relatively free of engaging protrusions and allow movement without deformation of any cantilevered segments  198  of the outer member  194 . The locking member  196  may be configured to secure the inner member  192  and the outer member  194  to each other by applying a radial load that causes the inner and outer members  192 ,  194  to be secured to each other by friction. In this embodiment, the locking member  196  may have an adjustable radius. In some embodiments, the locking members  150  and  160  described with reference to  FIGS. 7 and 8  may be used to securely hold the outer and inner members  192 ,  194  in frictional engagement. Other locking members having an adjustable radius are also contemplated. Accordingly, by tightening the locking member  196  about the inner and outer members  192 ,  194 , the locking member  196  provides a holding force that frictionally inhibits expansion and sliding. 
         [0065]    In some embodiments, the inner member  102  is substantially solid such that while it is telescopically received within the outer member  104 , no material may be received within inner member  102 . Moreover, while the inner member  102  has been shown as telescopically received within tubular outer member  104 , it will be appreciated that in a further embodiment the respective configuration is inverted such that the cantilevered segments are provided on the inner member rather than the outer member. Moreover, while a substantially cylindrical structure has been shown for the purposes of illustration, in an alternative embodiment the tubular shapes may take the form of a rectangle, square, ellipse, diamond, oval, D-shape or any shape. Further, the shapes may conform and substantially match the adjacent bone or the bone structure that is being replaced. As a result, the definition of tubular is not intended to be limited to cylindrical but is instead intended to cover all components that may be utilized to reduce the present invention. 
         [0066]    While the present device has been described with respect to insertion between two vertebrae after removal of the intervening vertebrae and intervertebral disc, it is contemplated that the length of the device may be sized appropriate to span multiple vertebrae. Additionally, the device may find application in other orthopedic areas and the size and shape of the device may be made to substantially match the implantation site. For example, while the present embodiment has been illustrated as a substantially cylindrical device, it is contemplated that in certain spinal applications it is desirable that the device have a substantially D shaped cross-section as viewed from top to bottom such that the anterior portion of the device has an exterior convexly curved surface matching the anterior of the vertebral body while the posterior portion of the device is substantially flat or concave allowing it to be positioned closer to the spinal canal without protruding into the spinal canal. 
         [0067]    Embodiments of the implant in whole or in part may be constructed of biocompatible materials of various types. Examples of implant materials include, but are not limited to, non-reinforced polymers, carbon-reinforced polymer composites, PEEK and PEEK composites, shape-memory alloys, titanium, titanium alloys, cobalt chrome alloys, stainless steel, ceramics and combinations thereof. If the trial instrument or implant is made from radiolucent material, radiographic markers can be located on the trial instrument or implant to provide the ability to monitor and determine radiographically or fluoroscopically the location of the body in the spinal disc space. In some embodiments, radiographic markers are placed to show the location of the locking member relative to the outer member. For example, radiographic markers may be disposed adjacent the locking nub  138  and the recess  146  so that a physician can determine easily whether the locking member is properly located. 
         [0068]    In some embodiments, the implant or individual components of the implant are constructed of solid sections of bone or other tissues. In other embodiments, the implant is constructed of planks of bone that are assembled into a final configuration. The implant may be constructed of planks of bone that are assembled along horizontal or vertical planes through one or more longitudinal axes of the implant. In some embodiments, the hollow centers  124  may contain grafting materials. Tissue materials include, but are not limited to, synthetic or natural autograft, allograft or xenograft, and may be resorbable or non-resorbable in nature. Examples of other tissue materials include, but are not limited to, hard tissues, connective tissues, demineralized bone matrix and combinations thereof. Examples of resorbable materials that may be used include, but are not limited to, polylactide, polyglycolide, tyrosine-derived polycarbonate, polyanhydride, polyorthoester, polyphosphazene, calcium phosphate, hydroxyapatite, bioactive glass, and combinations thereof. Implant may be solid, porous, spongy, perforated, drilled, and/or open. 
         [0069]    In some circumstances, it is advantageous to pack all or a portion of the interior and/or periphery of the implant with a suitable osteogenetic material or therapeutic composition. Osteogenic materials include, without limitation, autograft, allograft, xenograft, demineralized bone, synthetic and natural bone graft substitutes, such as bioceramics and polymers, and osteoinductive factors. A separate carrier to hold materials within the device can also be used. These carriers can include collagen-based carriers, bioceramic materials, such as BIOGLASS®, hydroxyapatite and calcium phosphate compositions. The carrier material may be provided in the form of a sponge, a block, folded sheet, putty, paste, graft material or other suitable form. The osteogenetic compositions may include an effective amount of a bone morphogenetic protein, transforming growth factor β1, insulin-like growth factor 1, platelet-derived growth factor, fibroblast growth factor, LIM mineralization protein (LMP), and combinations thereof or other therapeutic or infection resistant agents, separately or held within a suitable carrier material. A technique of an embodiment of the invention is to first pack the interior of an unexpanded implant with material and then place one or both end members if desired. 
         [0070]    Access to the surgical site may be through any surgical approach that will allow adequate visualization and/or manipulation of the bone structures. Example surgical approaches include, but are not limited to, any one or combination of anterior, antero-lateral, posterior, postero-lateral, transforaminal, and/or far lateral approaches. Implant insertion can occur through a single pathway or through multiple pathways, or through multiple pathways to multiple levels of the spinal column. Minimally invasive techniques employing instruments and implants are also contemplated. 
         [0071]    It is understood that all spatial references, such as “top,” “inner,” “outer,” “bottom,” “left,” “right,” “anterior,” “posterior,” “superior,” “inferior,” “medial,” “lateral,” “upper,” and “lower” are for illustrative purposes only and can be varied within the scope of the disclosure. 
         [0072]      FIG. 1  illustrates four vertebrae, V 1 -V 4 , of a typical lumbar spine and three spinal discs, D 1 -D 3 . While embodiments of the invention may be applied to the lumbar spinal region, embodiments may also be applied to the cervical or thoracic spine or between other bone structures. 
         [0073]    While embodiments of the invention have been illustrated and described in detail in the disclosure, the disclosure is to be considered as illustrative and not restrictive in character. All changes and modifications that come within the spirit of the invention are to be considered within the scope of the disclosure.