Abstract:
Embodiments of the invention include expandable, implantable devices and methods. Devices expand linearly and laterally to provide secure fixation between or among anatomical structures. In some embodiments, an implant replaces one or more vertebral bodies, or portions of vertebral bodies, of the spine.

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 skeletal structures such as one or more vertebrae or portions of vertebrae. 
       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. Removal, or excision, of a vertebra may be referred to as a vertebrectomy. Excision of 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 or vertebrectomy.  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 . In some cases, the implant inserted between the vertebrae is designed to facilitate fusion between remaining vertebrae. In other cases, especially when treating tumors, the ultimate goal of the procedure is spinal stability, regardless of fusion. A successful procedure may decrease pain, preserve or enhance neurological function and allow a patient greater mobility without an external orthosis. Sometimes an implant is designed to replace the function of the excised vertebra and discs. All or part of more than one vertebra may be damaged and require removal and replacement in some circumstances. If only a portion of a vertebral body and adjacent discs are removed and replaced, the procedure is called a hemi-vertebrectomy. 
         [0003]    Many implants are known in the art for use in vertebrectomy and corpectomy procedures. One class of implants is sized to directly replace the vertebra or vertebrae that are being replaced, without in situ expansion. Another class of implants is inserted in a collapsed state and then expanded once properly positioned. Expandable implants may be advantageous because they allow for a smaller incision and entry path when positioning an implant. A smaller incision may be particularly useful with a posterior approach, as illustrated in  FIG. 2 .  FIG. 2  is an illustration from the posterior of a portion of a human spine, with one thoracic vertebra removed. To support the remaining vertebral structure, an implant may be placed through the window W, avoiding the nerve root N. The nerve root N, may be mobilized to increase the size of the window W slightly, but excess movement may risk damage to the nerve root N. Therefore, for a posterior approach, an initially small expandable implant may have particular utility. A posterior approach may be preferred for patients with circumferential tumors or for patients more susceptible to the risks associated with a more extensive anterior approach. Similarly, initially small implants enabling minimal tissue disruption may be useful from any surgical approach to reduce trauma to surrounding tissues and to enhance patient recovery. 
         [0004]    Once in position and expanded, it may be advantageous for a corpectomy or vertebrectomy implant to, as nearly as possible, fill the space vertically between the remaining vertebrae and laterally among the remaining soft tissues. Lateral expansion may increase the contact area between the implant and vertebral endplates. This expansion may reduce the potential for subsidence of the device into the adjacent vertebrae. However, it may be important that the lateral expansion not impinge on the spinal cord or nerve roots. In some instances, it may be useful to control lateral expansion to a particular distance or volume. 
         [0005]    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, though not necessarily, 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. Use of the mechanisms described and claimed herein are equally applicable to treatment or repair of such bones or appendages. Similarly, expandable implants may be useful in at least some spinal fusion procedures where a spinal disc is replaced without replacing a vertebral body. 
       SUMMARY 
       [0006]    One embodiment of the invention is an expandable medical implant for supporting skeletal structures. The expandable medical implant may include a laterally rigid component and a membrane defining a volume and having an upper surface and an opposite lower surface. The membrane may be coupled adjacent to the laterally rigid component. The expandable medical implant may also include a port in the expandable medical implant for receiving a fluid that drives or maintains expansion of the expandable medical implant, and a fill material that occupies at least the membrane and provides support between the upper surface and the lower surface. The volume defined by the membrane is exclusive of the laterally rigid component. 
         [0007]    An embodiment of the invention is a means for occupying a vertebral space. The means may include a linearly expandable means for occupying at least a portion of a space between vertebrae and for providing protection to neural structures, and a laterally expandable means coupled adjacent to the linearly expandable means. The laterally expandable means may be for receiving and containing a fill material between the linearly expandable means posteriorly and soft tissues surrounding a spinal column. 
         [0008]    Another embodiment of the invention is a method of occupying a vertebral space. The method may include introducing a vertebral prosthesis comprising a laterally rigid expandable component and an adjacent membrane having an upper surface and an opposite lower surface into the vertebral space. The method may also include introducing a fluid into the vertebral prosthesis to expand or maintain expansion of the laterally rigid expandable component, and introducing a fill material into the vertebral prosthesis to provide a non-fluidic structural support between the upper surface and the opposite lower surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is an elevation view of a segment of a lumbar spine. 
           [0010]      FIG. 2  is a posterior perspective view of a portion of a human spine. 
           [0011]      FIG. 3  is a perspective view of an embodiment of an expandable medical implant. 
           [0012]      FIG. 4  is a perspective view of the laterally rigid component embodiment of  FIG. 3 . 
           [0013]      FIG. 5  is an enlarged perspective view of the implant of  FIG. 4 . 
           [0014]      FIG. 6  is a plan view of the superior end of the implant of  FIG. 3 . 
           [0015]      FIG. 7  is a plan view of the inferior end of the implant of  FIG. 3 . 
           [0016]      FIG. 8  is a plan view of the superior end of the implant of  FIG. 4 . 
           [0017]      FIG. 9  is a plan view of the superior end of the implant of  FIG. 4  with a portion of the end material removed to illustrate the interior or the implant. 
           [0018]      FIG. 10  is a perspective view of an embodiment of an expandable medical implant. 
           [0019]      FIG. 11  is a plan view of the inferior end of the implant of  FIG. 10 . 
           [0020]      FIG. 12  is a perspective view of an embodiment of an expandable medical implant. 
           [0021]      FIG. 13  is a plan view of the superior end of an embodiment of an expandable medical implant. 
           [0022]      FIG. 14  is a perspective view of an embodiment of an expandable medical implant. 
           [0023]      FIG. 15  is a plan view of the superior end of the implant of  FIG. 14 . 
           [0024]      FIG. 16  is a perspective view of the expandable medical implant of  FIG. 3  in a state prior to expansion. 
           [0025]      FIG. 17  is a perspective view of the laterally rigid component embodiment of  FIG. 16 . 
           [0026]      FIG. 18  is a perspective view illustrating an embodiment of an expandable medical implant being introduced through a generally posterior approach. 
           [0027]      FIG. 19  is a perspective view illustrating an embodiment of an expandable medical implant expanded between vertebrae. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]      FIGS. 3-9  illustrate one embodiment of an expandable medical implant  1  for supporting skeletal structures. The expandable medical implant  1  shown includes a laterally rigid component  3  and a membrane  5 . The illustrated laterally rigid component  3  is a bellows. In some embodiments, the expandable medical implant  1  will be oriented with the membrane  5  toward the anterior of the spinal column, as noted by the letter A, and with the laterally rigid component  3  toward the posterior of the spinal column, as noted by the letter P. The specified orientations are for illustrative purposes only and may be altered in various other embodiments. The longitudinal axis, or linear expansion direction L, of the laterally rigid component  3  is also illustrated. In  FIGS. 3 and 4 , the laterally rigid component  3  is shown in an expanded state. Expansion of the laterally rigid component  3  may be realized by introduction of a fluid into the laterally rigid component  3 , may result from elasticity in the material from which the component is made, from internal or external biasing devices, or from any other effective device for generating expansion. 
         [0029]    As shown in  FIGS. 3 ,  4 , and  6 - 9 , the cross-sectional shape of the embodiment of the laterally rigid component  3  is concave-convex. However, in other embodiments, the cross-sectional shape of the laterally rigid component  3  may be any functional shape, such as but not limited to, generally round, oval, rectangular, triangular, polygonal, or combinations of these shapes. 
         [0030]    The laterally rigid component  3  illustrated in  FIG. 4  is defined herein as “laterally rigid” because it appreciably resists forces applied lateral to its linear axis L. Other devices that expand linearly and resist forces applied laterally to their linear axes L, are telescoping devices of  FIGS. 10-15 . These, and any other devices that provide resistance to lateral forces, are contemplated in embodiments of the present invention and are within the scope of the claims herein. Other devices that may meet these limitations include, but are not limited to, reinforced elastomeric bodies, such as a polymer body impregnated with or in combination with reinforcing fibers, or passively expanding bodies driven by the expansion of other connected components. Resistance to lateral forces may be useful in the illustrated embodiments for protecting posterior neural structures such as, but not limited to, the spinal cord, spinal canal, and nerve roots. 
         [0031]      FIGS. 3-5  illustrate a nozzle  2  extending from the laterally rigid component  3 . A similar nozzle may, alternatively or in addition, extend from the opposite end of the laterally rigid component  3 . The illustrated nozzle  2  is open to the interior of the laterally rigid component  3 . A balloon  11  is shown extending from an open, distal end of the nozzle  2 . The balloon  11  shown is in fluid communication with the interior of the laterally rigid component  3 . The nozzle  2  and balloon  11  of some embodiments are configured to extend from the laterally rigid component  3  and into an endplate of an adjacent vertebra. The balloon  11  may be filled with a material, such as a flowable material, to assist in attachment of the laterally rigid component  3  to the adjacent vertebra. In some embodiments, the balloon  11  is filled separately from the laterally rigid component  3  or the membrane  5 . The balloon  11  may additional have a therapeutic effect on the vertebra. For example, and without limitation, the balloon  11 , alone or in combination with the nozzle  2 , may help to stabilize the vertebra. The material used to inflate the balloon  11  may be a curable material or may be a material that is used to expand the balloon  11 , but does not cure in place. Once expanded, the balloon  11  may also receive additional materials that permanently fill the balloon  11 , or that have an additional therapeutic effect on the vertebra. Any of the materials for use in the balloon  11  may also be a fill material  100  as described in detail below. The balloon  11  may in whole or in part be non-permeable, semi-permeable, or permeable to allow the flowable material or the fill material  100  to contact the vertebra. In addition to or instead of the nozzle  2  or balloon  11 , an end of an embodiment of the laterally rigid component  3  my include teeth, spikes, ridges, indentations, roughening, knurling, or any other device for enhancing fixation between a vertebra and the laterally rigid component  3 . The embodiments of  FIGS. 10-15  illustrate spikes  22  on the end of laterally rigid components. 
         [0032]    The membrane  5  is illustrated in an expanded configuration in  FIG. 3 . The membrane  5  defines a volume and has an upper surface  6  and an opposite lower surface  4 . The membrane  5  is shown coupled laterally adjacent to the laterally rigid component  3 . The illustrated membrane  5  and the laterally rigid component  3  are adjacent, with the volume defined by the membrane  5  exclusive of the laterally rigid component  3 , as defined herein. In some embodiments, it is advantageous for the membrane  5  and the laterally rigid component  3  to be configured in different volumes such that expansion of the respective devices may be controlled independently or enacted sequentially or in parallel. The membrane  5  of some embodiments is configured to be placed between vertebrae and expanded such that the upper surface  6  contacts a first vertebra and the opposite lower surface  4  contacts a second vertebra to provide support between the vertebrae. Lateral expansion of the membrane  5  is also accomplished in some embodiments. For example, in  FIG. 3  anterior expansion, as well as medial-lateral expansion, and intervening radial expansions, are illustrated. As used herein, the term lateral means directions approximately normal to the linear expansion direction L. 
         [0033]    The membrane  5  may be constructed, in whole or in part, of a non-permeable material. The membrane  5  may include compliant or non-compliant balloon materials such as those commonly used to manufacture coronary and Kyphoplasty medical devices. Such materials may include, but not be limited to, mylar, rubber, polyurethane, vinyl, latex, polyethylenes, ionomer, and polytetraphthalate (PET), as well as less flexible materials such as Kevlar®, PEBAX®, stainless steel, titanium, nickel-titanium alloys, and other metals and alloys and/or ceramics. A compliant membrane may include reinforcing to limit one or both of the size and shape of the membrane to a clinically advantageous extent. A non-compliant membrane may expand more elastically to more completely fill an irregular opening, depending on the amount of material introduced into the membrane. 
         [0034]    Likewise the membrane  5  may be constructed, in whole or in part, of a permeable material, which allows a certain amount of fill material  100  to pass through the membrane  5 . All or a portion may be made permeable by fabricating a material, including but not limited to, the membrane materials listed above, into a fabric, weave, mesh, composite, bonded fiber assembly, or any other manufacture known to those skilled in the art. For example, all or part of the upper surface  6  and the opposite lower surface  4  may be constructed of a permeable material to allow fill material  100  to move through the membrane  5  and to come into contact with vertebrae. 
         [0035]      FIGS. 6 and 7  illustrate, respectively, superior and inferior ends of an expanded expandable medical implant  1 . The laterally rigid component  3  shown includes an upper cap  16  and a lower cap  14 . The upper and lower caps  16 ,  14  may be non-permeable or permeable to some degree, with similar functions to, and made from similar materials with, the membrane  5  discussed above. The upper and lower caps  16 ,  14  may be made from the same material as the rest of the laterally rigid component  3 , or may be made from a separate material.  FIG. 8  illustrates an upper cap  16  made from an at least partially permeable woven or mesh material. As illustrated, two mesh ends  17  are integrated into the upper cap  16  to allow passage of some of the fluid or fill material  100  to contact an adjacent vertebra. Alternately, or in addition, the upper cap  16  may be expanded or stretched into contact with an adjacent vertebra to conform to the contours of the vertebral endplate so as to provide an improved interface between the expandable medical implant  1  and the vertebra.  FIG. 9  shows the upper end cap  16  of  FIG. 8  with the two mesh ends  17  removed to illustrate the interior of an embodiment of the laterally rigid component  3 . The interior shown includes a chamber  13  which is open along the length of the laterally rigid component  3  between the upper and lower caps  16 ,  14 . In this embodiment, the chamber  13  is open whether the laterally rigid component  3  is in an expanded or unexpanded state. The interior edge  15  of the bellows defines an inner periphery of the chamber  13 . In some embodiments, elasticity in the material along the interior edges  15  of the bellows may sever as a biasing force to bias the laterally rigid component  3  toward an expanded or unexpanded state, as may be advantageous in various circumstances. For example, it may be advantageous to bias the laterally rigid component  3  toward an unexpanded state to provide a low profile device for insertion. Other devices may be used to expand the device as needed. In other circumstances, it may be preferred to bias the laterally rigid component  3  toward an expanded state. With such an embodiment, another component may be used to keep the laterally rigid component  3  in an unexpanded state while it is inserted. Then following insertion, the laterally rigid component  3  may be released and allowed to increase toward its expanded state. 
         [0036]      FIGS. 6 and 7  illustrate the membrane  5  being coupled laterally adjacent to the laterally rigid component  3 . In the embodiment of  FIG. 6 , an adhesive may be applied between the membrane  5  and the laterally rigid component  3  at a first point  18  near the upper surface  6  of the membrane  5 . As illustrated in  FIG. 7 , the membrane  5  may be coupled to the laterally rigid component  3  with an adhesive applied at a second point  19  near the lower surface  4  of the membrane  5 . 
         [0037]    Embodiments of the expandable medical implant  1  also include a port  7  for receiving a fluid. As used in association with this function, a fluid may be a paste, gel, liquid, suspension, granular mixture, or similar substance. A substance as described herein will be considered a fluid even if it later cures or hardens to a non-fluidic state. As illustrated in  FIGS. 3-9 , the port  7  is connected to the laterally rigid component  3 . In other embodiments, the port  7  may connect to the membrane  5 , or to another portion of the expandable medical implant  1 . The fluid received through the port  7  in some circumstances will drive expansion of the expandable medical implant  1 . This may be accomplished by pressurizing the laterally rigid component  3  or the membrane  5 , or by pressurizing both. In other embodiments, the fluid may be used to maintain expansion generated by some other force such as expansion from elasticity in the material from which the laterally rigid component  3  or membrane  5  are made, from biasing devices internal or external to the laterally rigid component  3  or membrane  5 , or from any other effective device for generating expansion. The illustrated port  7  includes a relief  8  that may be useful in detaching the port  7  from the laterally rigid component  3  after expansion of the implant, but prior to completion of the surgical procedure. The relief  8  provides both a tactile indication of an appropriate location to detach the port  7  and a reduced material thickness that allows for less resistance to cutting, breaking, or otherwise removing the port  7 . The port  7  may also serve as an extension of the expandable medical implant  1  useful in manipulating the expandable medical implant  1  into a clinically effective location. 
         [0038]    As shown in  FIGS. 4 ,  5 ,  8 , and  9 , a transfer opening  9  is provided between the laterally rigid component  3  and the membrane  5 . In some embodiments, the transfer opening  9  is a hole through which a fluid or fill material  100 , or both, may pass. Passage may occur in either direction between the laterally rigid component  3  and the membrane  5  in various embodiments. As illustrated, fluid, fill material  100  or both enter the laterally rigid component  3  through the port  7  and pass through the transfer opening  9  into the membrane  5 . In some embodiments, a valve is provided at the transfer opening  9  to control flow between the laterally rigid component  3  and the membrane  5 . The valve may be controlled by direct manipulation or through instrumentation connected through the port  7 . The valve may also be pressure actuated such that flow is allowed through the transfer opening  9  above a certain pressure. 
         [0039]    The fill material  100  may enter the expandable medical implant  1  as a fluid, and then harden or cure in the implant. In some embodiments, a non-hardenable and non-curing fluid is used to expand, or to hold expansion in, the implant or one or some of the components of the implant. A fill material  100  may then be introduced into at least the membrane  5  to provide support between the upper surface  6  and the lower surface  4 . The fill material  100  may be a paste, gel, liquid, suspension, granular mixture, or similar substance. Non-limiting examples of fill materials  100  include bone cement, paste, morselized allograft, autograft, or xenograft bone, ceramics, or various polymers. An example bone cement is polymethylmethacrylate (PMMA), which may be made from methylmethacrylate, polymethylmethacrylate, esters of methacrylic acid, or copolymers containing polymethylmethacrylate and polystyrene. Additional non-limiting examples of the fill material  100  include semi-rigid flowable or hardenable material such as silicone or various types of urethane materials. It should further be understood that other types of fill materials  100  which are not necessarily hardenable or curable may be used in association with the present invention. For example, the fill material may comprise beads or small particles or grains of material, some of which may, in aggregate, achieve a harder consistency as a result of interlocking or compaction. In some embodiments, the fill material may also include a bone growth promoting substance. The use and components of such bone growth promoting substances are described in more detail below. 
         [0040]      FIGS. 10 and 11  show another embodiment of an expandable medical implant  21 . An inferior side of the implant is illustrated in  FIG. 11 , as well as in  FIG. 10 . The expandable medical implant  21  shown includes a laterally rigid component  23  and a membrane  25 . The illustrated laterally rigid component  23  is a telescoping body with spikes  22  for enhanced connection to an adjacent vertebral body. In some embodiments, the expandable medical implant  21  will be oriented with the membrane  25  toward the anterior of the spinal column and with the laterally rigid component  23  toward the posterior of the spinal column. The specified orientations are for illustrative purposes only and may be altered in various other embodiments. The laterally rigid component  23  is shown in an expanded state. Expansion of the laterally rigid component  23  may be realized by introduction of a fluid into the laterally rigid component  23 , may result from a biasing device resident in the laterally rigid component  23 , or from any other effective device for generating expansion. The membrane  25  is essentially similar to the membrane  5  described in greater detail above. A port  27  coupled to the laterally rigid component  23  is also illustrated. A relief  28  is depicted that provides both a tactile indication of an appropriate location to detach the port  27  and a reduced material thickness that allows for less resistance to cutting, breaking, or otherwise removing the port  27 . Similar to the previous embodiment, an adhesive may be applied between the membrane  25  and the laterally rigid component  23 .  FIGS. 10 and 11  illustrate an embodiment where the adhesive may be applied at a point  29  near a lower surface  24  of the membrane  25 . 
         [0041]      FIG. 12  illustrates an embodiment of an expandable medical implant  31  with a membrane  35  coupled to a laterally rigid component  33  by a number of tethers  39 . Each tether  39  may be made of any biocompatible material. The tethers  39  illustrated are strands, but in other embodiments may be loops, hooks, staples, fasteners of any kind, or any other component capable of connecting the membrane  35  with the laterally rigid component  33 . The operation and structures of the embodiment of  FIG. 12  are otherwise essentially similar to the operation and structures of the other similar embodiments described herein. 
         [0042]      FIG. 13  illustrates an embodiment of an expandable medical implant  41  with a membrane  45  coupled to a laterally rigid component  43  such that a void  46  is created between the membrane  45  and the laterally rigid component  43 . The membrane  45  may be coupled to the laterally rigid component  43  by any effective mechanism, including but not limited to an adhesive or tether. The void  46  may be filled with an osteogenic material or therapeutic composition. Filling may occur through an opening into the void  46  through the membrane  45 , the laterally rigid component  43 , or otherwise. Filling may be through a syringe or similar device, through direct placement, or by any other effective mechanism. 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 may also be used. These carriers may 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 osteogenic compositions may include an effective amount of a bone morphogenetic protein (BMP), transforming growth factor β 1 , insulin-like growth factor, 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. The operation and structures of the embodiment of  FIG. 13  are otherwise essentially similar to the operation and structures of the other similar embodiments described herein. 
         [0043]      FIGS. 14 and 15  illustrate an embodiment of an expandable medical implant  51  with a membrane  55  coupled to a laterally rigid component  53 . The operation and structures of the embodiment of  FIGS. 14 and 15  are essentially similar to the operation and structures of the other similar embodiments described herein, except that the membrane  55  is sized or otherwise constrained such that it will only fill one lateral side of a vertebral space into which it is placed. The contralateral side of such a vertebral space may be left open for an additional implant, or may include healthy bone material and not need to be excised or filled. The membrane  55  may include layers, internal fibers or structures, or non-expandable materials that limit its expansion to one or both of a specific size and shape. The embodiment of  FIGS. 14 and 15  shows a port  57  near an inferior end of the laterally rigid component  53  such that the implant may be expanded from an inferior vertebra toward a superior vertebra. Note that any of the embodiments of the invention disclosed herein may be deployed from an inferior, superior, or even medial position effectively and within the claims herein. In some embodiments, the size or shape of the membrane  55  may be limited to only fill any particular portion of a vertebral space, not necessarily just a lateral portion. 
         [0044]      FIGS. 16 and 17  show the expandable medical implant  1  of  FIG. 3  in an unexpanded or contracted state. Both the laterally rigid component  3  and the membrane  5  are unexpanded linearly. The membrane  5  is unexpanded laterally as well as linearly. The port  7  may be used to handle the expandable medical implant  1  or to guide the implant into a position where it can be effectively deployed. One manipulation of an embodiment of the expandable medical implant  1  is illustrated in  FIGS. 18 and 19 . 
         [0045]    Each of the embodiments disclosed herein may be described as a means for occupying a vertebral space. This may be accomplished with a linearly expandable means for occupying at least a portion of a space between vertebrae and for providing protection to neural structures in combination with a laterally expandable means coupled adjacent to the linearly expandable means. The laterally expandable means of some embodiments is for receiving and containing a fill material between the linearly expandable means posteriorly and soft tissues surrounding a spinal column. The soft tissues surrounding the spinal column may include, but are not limited to, one or more of ligaments, muscles, vessels, arteries, and neural structures. 
         [0046]    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, low density polyethylene, shape-memory alloys, titanium, titanium alloys, cobalt chrome alloys, stainless steel, ceramics and combinations thereof. If a 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 space. In some embodiments, the implant or individual components of the implant may be constructed of solid sections of bone or other tissues. 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. 
         [0047]      FIG. 1  illustrates four vertebrae, V 1 -V 4 , of a typical lumbar spine and three spinal discs, D 1 -D 3 , and  FIG. 2  depicts a portion of a typical thoracic spine. Embodiments of the invention may be applied to the lumbar spinal region, and embodiments may also be applied to the cervical or thoracic spine or between other skeletal structures. 
         [0048]    Some embodiments may also include supplemental fixation devices in addition to or as part of the expandable medical implant for further stabilizing the anatomy. For example, and without limitation, rod and screw fixation systems, anterior, posterior, or lateral plating systems, facet stabilization systems, spinal process stabilization systems, and any devices that supplement stabilization may be used as a part of or in combination with the expandable medical implant. Embodiments of the invention may be useful in at least some spinal fusion procedures where a spinal disc is replaced without replacing a vertebral body. 
         [0049]      FIGS. 18 and 19  illustrate the introduction and expansion of an expandable medical implant into a vertebral space. The implant is placed through the window W, as described above, and past a nerve root N. The window W is created among the soft tissues of a segment of the spinal column. The expandable medical implant introduced is a vertebral prosthesis that includes the laterally rigid expandable component  3  and the adjacent membrane  5  with an upper surface and an opposite lower surface.  FIG. 18  shows a distal end of the expandable medical implant being introduced through the window W first. In other embodiments, another portion of the expandable medical implant may be introduced first and other translational and rotational manipulations may be conducted on the implant as it is introduced. 
         [0050]    Once the expandable medical implant has been introduced through the window W and positioned appropriately in the vertebral space, it may be expanded linearly and laterally. A linearly and laterally expanded implant is illustrated in  FIG. 19 . The embodiment illustrated may be expanded by introducing a fluid through the port  7  and into the laterally rigid component  3 . Introducing fluid through the port  7  may be caused by pressure or force generated by a syringe, injector, multi-stage injector, central pressurization reservoir, or any effective system or device. The fluid introduced to expand the laterally rigid component  3  may be fluid that is introduced only to expand the component, or in some instances, is a final fill material  100 . When the fluid introduce to expand the implant is not, or is not a component of, the fill material  100 , the fluid may be removed from the implant after the fill material  100  has been introduced. The introduced fluid may be one part of a multi-part fill material. The fluid or a fill material  100  may further be passed from the laterally rigid component  3  into the membrane  5  to linearly and laterally expand the membrane  5 . In some embodiments, flow into the laterally rigid component  3  and the membrane  5  are separately controlled so that one or the other may be selectively filled independent from the other. In some embodiments, an additional port, or a port replacing the port  7  in the laterally rigid component  3 , may connect with the membrane  5  directly. 
         [0051]    In some embodiments, introduction of the fill material  100 , by whatever mechanism that is effective, results in a non-fluidic structural support between the upper and lower surfaces of the membrane  5 . Even though a fill material  100  may be initially introduced as a fluid, embodiments of the invention provide for the fill material  100  to cure or harden as noted above and provide structural support. Other fill materials  100  may have a non-fluidic state as a result of interlocking of the particles with one another or with the membrane  5 , or may be non-fluidic as a response to compaction. 
         [0052]    The expandable medical implant is shown in  FIGS. 18 and 19  as being implanted from a generally posterior approach. However, embodiments of the invention may include implantation from any surgical approach, including but not limited to, posterior, lateral, anterior, transpedicular, lateral extracavitary, in conjunction with a laminectomy, in conjunction with a costotransversectomy, or by any combination of these and other approaches. 
         [0053]    Various method embodiments of the invention are described herein with reference to particular expandable medical implants. However, in some circumstances, each disclosed method embodiment may be applicable to each of the expandable medical implants, or to some other implant operable as disclosed with regard to the various method embodiments. 
         [0054]    Terms such as lower, upper, anterior, posterior, inferior, superior, lateral, medial, contralateral, and the like have been used herein to note relative positions. However, such terms are not limited to specific coordinate orientations, but are used to describe relative positions referencing particular embodiments. Such terms are not generally limiting to the scope of the claims made herein. 
         [0055]    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.