PATENT DOCUMENT

Abstract:
A spinal implant which is configured to be deployed between adjacent vertebral bodies. The implant has at least one extendable support element with a retracted configuration to facilitate deployment of the implant and an extended configuration so as to expand the implant and effectively distract the disc space, stabilize the motion segments and eliminate pathologic spine motion. The implant has a minimal dimension in its unexpanded state that is smaller than the dimensions of the neuroforamen through which it typically passes to be deployed within the intervertebral space. The implant is provided with a locking system having a plurality of linked locking elements that work in unison to lock the implant in an extended configuration. Bone engaging anchors also may be provided to ensure secure positioning.

Full Description:
RELATED APPLICATION DATA 
       [0001]    This application is a continuation-in-part of U.S. Nonprovisional patent application Ser. No. 12/787,281, filed on May 25, 2010, entitled “Adjustable Distraction Cage with Linked Locking Mechanisms,” which is a continuation-in-part of International Application No. PCT/US2009/67446, designating the United States, filed Dec. 10, 2009, entitled “Lockable Expanding Spine Cage,” and U.S. Nonprovisional patent application Ser. No. 12/380,840, filed on Mar. 4, 2009, entitled “Lockable Spinal Implant,” which is a nonprovisional of U.S. Provisional Patent Application Ser. No. 61/201,518, filed on Dec. 10, 2008, entitled “Lockable Spinal Implant.” 
         [0002]    This application is also related to U.S. patent application Ser. No. 11/692,800, filed Mar. 28, 2007, entitled “Selectively Expanding Spine Cage, Hydraulically Controllable in Three Dimensions for Vertebral Body Replacement,” which is a continuation-in-part of U.S. Nonprovisional patent application Ser. No. 11/535,432, filed Sep. 26, 2006, entitled “Selectively Expanding Spine Cage, Hydraulically Controllable in Three Dimensions for Enhanced Spinal Infusion,” which is a nonprovisional of U.S. Provisional Patent Application Ser. No. 60/720,784, filed Sep. 26, 2005, entitled “Selectively Expanding Spine Cage, Hydraulically Controllable in Three Dimensions for Enhanced Spinal Infusion.” 
         [0003]    Each of the above listed applications is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0004]    The invention relates to devices and methods for stabilizing the vertebral motion segment. More specifically, the field of the invention relates to an expandable spinal implant with locking elements configured to lock the implant in an expanded configuration within an intervertebral space to provide controlled spinal correction in three dimensions for improved spinal intervertebral body distraction and fusion. 
       BACKGROUND 
       [0005]    A conventional spine cage or implant is characterized by a kidney bean shaped body which is typically inserted posteriorly through the neuroforamen of the distracted spine after a trial implant creates a pathway. Existing devices for interbody stabilization have important and significant limitations, including inability to expand and distract the end plates or to fix the device in place to prevent relative movement between the device and an adjacent vertebral body. Current devices for interbody stabilization include static spacers composed of titanium, PEEK, and high performance thermoplastic polymer produced by VICTREX, (Victrex USA Inc, 3A Caledon Court; Greenville, S.C. 29615), carbon fiber, or resorbable polymers. Moreover, current interbody spacers do not maintain interbody lordosis and can contribute to the formation of a straight or even kyphotic segment and the clinical problem of “flatback syndrome.” Separation of vertebral end plates increases space available for the neural elements, specifically the neural foramen. Existing static cages do not reliably improve space for the neural elements. Therefore, what is needed is a spinal implant that will provide space for the neural elements posteriorly between the vertebral bodies, or at least maintain the natural bone contours to avoid neuropraxia (nerve stretch) or encroachment. 
         [0006]    Conventional devices for intervertebral body stabilization include poor interface between bone and the biomaterial of the device. Conventional static interbody spacers form a weak interface between bone and biomaterial. Although the surface of such implants is typically provided with a series of ridges or coated with hydroxyapetite, the ridges may be in parallel with applied horizontal vectors or side-to-side motion. That is, the ridges or coatings on the implant offer little resistance to movement applied to either side of the end plates. Thus, nonunion is common in allograft, titanium and polymer spacers, due to motion between the implant and host bone. 
       SUMMARY OF THE DISCLOSURE 
       [0007]    This invention is generally directed to a spinal implant for insertion between superior and second vertebral end plates after partial or total removal of a spinal disc. The spinal implant embodying features of the invention has a contracted configuration for easy installation between adjacent vertebral bodies and an expanded configuration to support the vertebrae in a desirable position. More specifically, the implant has a plurality of inter-engagable elements which locks the implant in an expanded configuration to hold the vertebral or joint sections in the desired positions. 
         [0008]    The invention is particularly directed to a spinal implant suitable for placement between superior and interior vertebral bodies. The spinal implant has a first member or top plate for engaging an end of the superior vertebral body and a second member or base for engaging an end of the inferior vertebral body and has one or more extendable support elements preferably with one or more top end plates that engage vertebral bodies in the expanded configuration. The one or more extendable support elements have a first contracted configuration to facilitate deployment of the implant between the superior and inferior vertebral bodies and safely past sensitive neural elements and a second or an extended configuration to engage the end plates of the vertebral bodies. The implant has a locking system with linked locking elements that mechanically engage or interlock with the extendable support element or the first member to lock the implant between the superior and inferior vertebral bodies in an expanded configuration. 
         [0009]    The extendable support element(s) may be extended in a variety of ways such as with fluid pressure, e.g. hydraulic fluid or gas, by mechanical force, such as a threaded connection with a rotating driving member or other suitable means. Fluidic displacement is preferred. The extendable support element(s) are disposed in cylinders which support and guide the extendable support elements when they are extended. However, the locking system is separate from the extendable support member and cylinder receiving the supporter member, although the extending support member may initiate the locking system and the support member and cylinder may have lock support members attached thereto. 
         [0010]    In one exemplary system, the spinal implant having features of the invention comprises an inferior pressure applying member or base with a first bone engaging surface, one or more extendable support members cooperating with the base and a superior pressure applying member such as a top end plate with a second bone engaging surface that is coupled to the at least one extendable member. The spinal implant preferably has a plurality of engaging locking elements that are configured to independently lock one or more of the extendable support members or pressure applying members in an extended configuration to thereby provide desired disc height between adjacent vertebrae. 
         [0011]    The spinal implant or selectively expanding spine cage (SEC) embodying features of the invention is particularly suitable for posterior or transforaminal insertion between superior and inferior vertebral end plates as described in copending application Ser. No. 11/535,432, filed Sep. 26, 2006, and Ser. No. 11/692,800, filed Mar. 28, 2007. The implant has a contracted or unexpanded configuration which allows easy deployment and is typically about 0.5 to about 1 cm in maximum short transverse dimension so as to enable minimally invasive insertion posteriorly between vertebral pedicles through a working space of approximately 1 cm in diameter. 
         [0012]    In one exemplary embodiment, the spinal implant for placement between adjacent vertebral bodies as described above has an upper locking member with stepped supporting surfaces on the underside thereof and a lower locking member with stepped supporting surfaces on the top side thereof which are configured to engage the stepped supporting surface of the upper locking member to lock the implant in an extended configuration. Extension of the expandable members, such as bellows or pistons; or other appropriately sized mechanisms, such as cams or screws, to raise the superior pressure applying member increases longitudinal spacing between the upper and lower locking members. Relative motion, rotational or linear, between the upper and lower locking members causes the stepped supporting surfaces of the lower locking members and the stepped supporting surfaces of the upper locking members to re-engage to fix the locking members in an increased spaced apart relationship and thereby lock the implant in the extended configuration. 
         [0013]    Since the vertebral end plates are held together at one end by a ligament much like a clamshell, as the implant expands against the vertebral end plates, the amount of vertical expansion can be adjusted to create the desired anterior/posterior correction angle. 
         [0014]    A minimally invasive downsized insertion tool, such as described in the above referenced applications, both inserts the unexpanded implant posteriorly and provides the hydraulic or mechanical lines communicating with the interior of the implant. The insertion tool may also provide a line for communicating the liquid or slurry bone graft material into the intervertebral space for subsequent fusion. Advantageously, hydraulic lines are small size tubing to allow for high hydraulic pressure without danger of the lines bursting. 
         [0015]    Due to the mechanical advantage provided by a hydraulic system or a proximally operated mechanical system, the implant has minimized size and diameter in its unexpanded state that is smaller than the diameter of a prepared neuroforamen. The implant thus can be inserted transforaminally and engaged between the end plates of the adjacent vertebra to effectively distract the intervertebral area, restore space for neural elements, stabilize the motion segment and eliminate pathologic segmental motion. The implant enhances spine arthrodesis by creating a rigid spine segment. 
         [0016]    The implant is preferably provided with a hollow interior to enable a comparatively large quantity of bone growth conductive or inductive agents to be contained therein that through openings communicate directly to adjacent bone. Importantly, this results in fixation forces greater than adjacent bone and soft tissue failure forces. The implant can be used to promote fusion, and/or to correct deformities such as scoliosis, kyphosis, and spondylolisthesis. 
         [0017]    The clinical goals of the implant and the method for its insertion provide a minimally invasive risk of trauma to nerve roots, reduce pain, improve function, and permit early mobilization of the patient after fusion surgery. The fixation elements maintain the implant in a desired position until healing (fusion or arthrodesis) occurs. At this point, the implant is incorporated inside bone and its role becomes quiescent. 
         [0018]    Thus, a feature of the invention is that an implant can be inserted posteriorly between vertebral pedicles in only a working space of about ½ cm and then be expanded from about 100% to about 200%, typically about 160%, of its original insertion size and locked in that position to provide a closely controlled full range of permanent spinal correction in three dimensions. These and other advantages of the invention will become more apparent from the following detailed description and the accompanying exemplary drawings. 
         [0019]    In other embodiments of the invention, extendable, locking, bone engaging anchors are provided to ensure that the implant is positively engaged with the bone after insertion. 
         [0020]    In one implementation, the present disclosure is directed to a lockable, extendable spinal implant for placement between first and second vertebral bodies. The implant includes: first and second bone engaging members each having a surface configured to respectively engage opposed first and second vertebral bodies; extension means acting between the first and second bone engaging members to control extension of the bone engaging members between contracted and extended configurations; first and second fixed lock members fixed to one of the first and second bone engaging members and extending towards the opposite bone engaging member, the fixed lock members being spaced apart and each having a fixed locking surface; first and second moveable lock members captured between the first and second bone engaging members for cooperation with the fixed lock members, each moveable lock member having a moveable locking surface configured to engage an opposed fixed locking surface on one the fixed lock member to prevent contraction of the extension means; a locking actuator configured to engage the moveable locking surfaces with the fixed locking surfaces; and a link member operatively connected between the first and second moveable lock members to coordinate movement therebetween. 
         [0021]    In another implementation, the present disclosure is directed to a lockable, extendable spinal implant for placement between first and second vertebral bodies. The implant includes: first and second bone engaging members each having a surface configured to respectively engage opposed first and second vertebral bodies; first and second pistons disposed on one the bone engaging member and cooperating with mating cylinders disposed on the opposite bone engaging member, the pistons moveable between a contracted configuration within the cylinders and an extended configuration extending from the cylinders; first and second arcuate, fixed lock members, each having a fixed locking surface, mounted to one of the bone engaging members, each disposed around one the piston, the fixed lock members extending towards the opposite bone engaging member; first and second moveable lock members, each formed around one the cylinder for cooperation with the fixed lock members, each moveable lock member having a moveable locking surface configured to engage an opposed fixed locking surface on one the fixed lock member to prevent contraction of the extension means; at least one biasing element acting on at least one the moveable lock member to bias the member into engagement with its associated fixed lock member; and a link member operatively connected between the first and second moveable lock members to coordinate movement therebetween and force the other moveable lock member into engagement with its associated fixed lock. 
         [0022]    In still another implementation, the present disclosure is directed to a lockable, extendable spinal implant for placement between first and second vertebral bodies. The implant includes: first and second bone engaging members each having a surface configured to respectively engage opposed first and second vertebral bodies; first and second pistons disposed on one the bone engaging member and cooperating with mating cylinders disposed on the opposite bone engaging member, the pistons moveable between a contracted configuration within the cylinders and an extended configuration extending from the cylinders; first and second arcuate, fixed lock members, each having a fixed locking surface, mounted to one of the bone engaging members, each disposed inside one the piston, the fixed lock members extending towards the opposite bone engaging member; first and second moveable lock members, each formed inside one the cylinder for cooperation with the fixed lock members, each moveable lock member having a moveable locking surface configured to engage an opposed fixed locking surface on one the fixed lock member to prevent contraction of the extension means; at least one biasing element acting on at least one the moveable lock member to bias the member into engagement with its associated fixed lock member; and a link member operatively connected between the first and second moveable lock members to coordinate movement therebetween and force the other moveable lock member into engagement with its associated fixed lock. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    For the purpose of illustrating the invention, the drawings show aspects of one or more embodiments of the invention. However, it should be understood that the present invention is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein: 
           [0024]      FIG. 1  is a perspective view of an intervertebral implant in a contracted configuration embodying features of the invention. 
           [0025]      FIG. 2  is a perspective view of the implant shown in  FIG. 1  in an expanded configuration. 
           [0026]      FIG. 3  is an exploded perspective view of the implant shown in  FIG. 1 . 
           [0027]      FIG. 4A  is a top view of the implant shown in  FIG. 1 . 
           [0028]      FIG. 4B  is a side cross-sectional view through line  4 B- 4 B of the implant shown in  FIG. 4A . 
           [0029]      FIG. 5A  is a perspective view of a lower part of the implant shown in  FIG. 1  with upper portions and bottom face removed. 
           [0030]      FIG. 5B  is a bottom view of the lower portion shown in  FIG. 5A . 
           [0031]      FIG. 6A  is a perspective view of the upper portion of the implant shown in  FIG. 1  with the lower portion removed. 
           [0032]      FIG. 6B  is an enlarged perspective view of the staircase-like lower lock support shown in  FIG. 3 . 
           [0033]      FIG. 7  is a partial side view of one of the locking mechanisms of the implant shown in  FIG. 2 . 
           [0034]      FIGS. 8A-9B  are partial side views of the locking mechanism in  FIG. 7  shown in different expanded and locked configurations. 
           [0035]      FIGS. 10A and 10B  of the locking mechanism illustrate the expanded but unlocked configuration in  FIG. 10A  and the expanded and locked configuration in  FIG. 10B . 
           [0036]      FIGS. 11A and 11B  are perspective views of the lower lock support and spring locking actuator illustrating the operation thereof. 
           [0037]      FIG. 11C  is a perspective view of an alternative locking mechanism and locking actuator embodying features of the invention. 
           [0038]      FIGS. 12A-12C  are perspective views of alternative lower lock support designs embodying features of the invention. 
           [0039]      FIGS. 13A-13B  are perspective and side views respectively of an alternative implant embodying features of the invention which has an articulating top end plate. 
           [0040]      FIG. 14A  is an exploded perspective view of yet another alternative implant embodying features of the invention which has the lower lock supports within the extendable pistons. 
           [0041]      FIG. 14B  is a top view of the implant shown in  FIG. 14A . 
           [0042]      FIG. 14C  is a side cross-sectional view through line  14 C- 14 C of the implant shown in  FIG. 14B . 
           [0043]      FIG. 15  is a perspective view of an alternative implant design having features of the invention wherein the locking mechanism surrounds a central opening in the top end plate. 
           [0044]      FIG. 16  is a perspective view of an alternative implant design having features of the invention wherein the expanding piston is centrally located and locking mechanisms are provided on both sides of the expanding piston. 
           [0045]      FIG. 17  is a simplified schematic illustration of an alternative implant design having ratchet and pawl locking members between the top and bottom plates of the implant. 
           [0046]      FIG. 18  is a perspective view of an alternative implant design with ratchet and pawl locking members between the top and bottom plates of the implant. 
           [0047]      FIG. 19  is a cross-sectional perspective view of an implant design with ratchet and cantilevered spring members between the top and bottom plates of the implant. 
           [0048]      FIGS. 20A-29  schematically illustrate various means for locking an expanding member of implants in extended configurations embodying features of the invention. 
           [0049]      FIG. 30  is a perspective view of yet another alternative implant design having features of the invention wherein the locking mechanism has straight upper and lower interfitting lock supports. 
           [0050]      FIG. 31A-31G  illustrate an alternative implant locking mechanism in which a wire-form surrounds a pair of upper support members with grooves configured to receive the wire-form. 
           [0051]      FIGS. 32A and 32B  are perspective views of a further alternative embodiment of the present invention including locking, conical bone engaging anchors. 
           [0052]      FIGS. 33A-C  are perspective views showing alternative bone engaging anchors. 
           [0053]      FIGS. 34A and 34B  are perspective cross-sectional views of another alternative embodiment of the present invention including locking, screw-threaded bone engaging anchors. 
           [0054]      FIGS. 35A and 35B  are perspective views of yet another embodiment of the present invention including locking, telescoping bone engaging surfaces. 
           [0055]      FIGS. 36A and 36B  are cross-sectional views of another exemplary embodiment of the present invention shown in a collapsed and an expanded configuration respectively. 
           [0056]      FIG. 36C  is a posterior perspective view of the embodiment in  FIG. 36B , shown in an expanded state. 
           [0057]      FIGS. 37A and 37B  are end views of a lift mechanism according to a further exemplary embodiment of the present invention, shown in a collapsed and an expanded configuration respectively. 
           [0058]      FIGS. 38A and 38B  are end views of a cross section of another embodiment of the present invention utilizing the lift mechanism shown in  FIGS. 37A and 37B , shown in a collapsed and an expanded configuration, respectively. 
           [0059]      FIGS. 39A and 39B  are top views of the respective embodiments shown in  FIGS. 38A and 38B  with the top plate removed. 
           [0060]      FIG. 40  is an anterior perspective view of the embodiment shown in  FIG. 38B . 
           [0061]      FIG. 41  is a posterior perspective view of still another exemplary embodiment of the present invention, shown in an expanded configuration. 
           [0062]      FIG. 42  is a perspective view of a lift mechanism of the embodiment of  FIG. 41 . 
           [0063]      FIGS. 43A and 43B  are cross-sectional views of the embodiment of  FIG. 41  shown in a collapsed and an expanded configuration, respectively. 
           [0064]      FIG. 44  is an exploded perspective view of another embodiment of the current invention. 
           [0065]      FIG. 45A  is a partial inferior perspective of another embodiment of the present invention. 
           [0066]      FIG. 45B  is a partial top view of the embodiment shown in  FIG. 45A . 
           [0067]      FIG. 46A  is an exploded perspective view of another embodiment of the current invention. 
           [0068]      FIGS. 46B and 46C  are superior perspective views of the embodiment shown in  FIG. 46A  in the collapsed and expanded configurations respectively. 
           [0069]      FIG. 47  is an exploded perspective view of another embodiment of the current invention. 
           [0070]      FIG. 48  is an exploded perspective view of another embodiment of the current invention 
           [0071]      FIG. 49  is an exploded perspective view of another embodiment of the current invention. 
           [0072]      FIG. 50A  is a side view of an alternative implant design in a collapsed configuration having an articulating top plate. 
           [0073]      FIG. 50B  is a side view of the implant shown in  FIG. 50A  in an expanded configuration. 
           [0074]      FIG. 50C  is a top view of the implant shown in  FIG. 50B . 
           [0075]      FIG. 50D  is a side cross-sectional through line  50 D of the implant shown in  FIG. 50C . 
           [0076]      FIG. 51A  is a side view of an alternative implant in a collapsed configuration having an articulating top plate. 
           [0077]      FIG. 51B  is a side view of the implant shown in  FIG. 51A  in an expanded configuration. 
           [0078]      FIG. 52A  is a side view of an alternative implant in a collapsed configuration embodying features of the invention which has two separated top plates. 
           [0079]      FIG. 52B  is a side view of the implant shown in  FIG. 52A  in a slightly expanded configuration. 
           [0080]      FIG. 52C  is a side view of the implant shown in  FIG. 52B  in a more expanded configuration. 
           [0081]      FIG. 52D  is a side view of the implant shown in  FIG. 52C  in a fully expanded configuration. 
           [0082]      FIG. 52E  is a top view of the implant shown in  FIG. 52D . 
           [0083]      FIG. 52F  is a side cross-sectional through line  52 F of the housing  111  of the implant shown in  FIG. 52E . 
           [0084]      FIG. 53  is a side view of an alternative implant design in a fully expanded configuration having two separated top plates. 
       
    
    
     DETAILED DESCRIPTION 
       [0085]      FIGS. 1-10B  illustrate an example of an intervertebral implant  10 , a Selectively Expandable Cage (SEC), having features of the invention. The implant  10  generally includes a housing  11 , a housing base  12 , an interlocking top end plate  13 , a bottom end plate  14 , an interior cavity  15  within the housing  11  and a pair of cylinders  16 . The top and bottom end plates are the bone engaging members of the implant, providing surfaces for engaging vertebrae above and below the implant when placed in the patient. Upper lock supports  17  are attached to the underside of the top end plate  13  thus forming fixed lock members and have multi-stepped lower support surfaces  18  much like an inverted staircase. Lower lock supports  20 , having multi-stepped upper support surfaces  21  surround cylinders  16  much like an upright staircase. The multi-stepped support surfaces form the locking surfaces of the lock supports. Pistons  22  are secured to the under surface of top end plate  13 . Seal members  23  are slidably disposed within the cylinders  16  and are mounted on pistons  22 . The upper surface  24  of bottom end plate  14  is provided with locking actuator channels  25  which partially receive spring locking actuators  26 . The base  12  of the housing  11  has arcuate slots  27  which are configured to slidably receive the depending elements  28  or locking actuator transfer element of the lower lock supports  20  and partially receive the spring locking actuators  26 . Depending elements  28  engage the forward end  30  of spring locking actuators  26 . The spring locking actuators  26  are initially in a compressed configuration so that upon the extension of the top end plate  13  and the attached upper lock supports  17 , the lower lock supports  20  rotate about the cylinders  16  due to the force applied by the biased spring locking actuator  26  thus forming moveable lock members. This causes the lock support surfaces  21  of the lower lock supports  20  to engage support surfaces  18  of the upper lock supports so as to lock the top end plate  13  in an extended configuration. The support surfaces  18  of the upper lock supports  17  and the support surfaces  21  of the lower lock supports  20  are tiered with multiple steps so that the implant  10  can be locked at several different expanded heights. The underside stepped support surfaces  18  of the upper lock support  17  may be provided with increasing riser height (alignment faces  46 ) in the upward direction to provide smaller incremental expansion near the end of the piston expansion. In addition or alternatively, the stepped support surfaces  21  of the lower lock support  20  may be provided with decreasing riser height in the upward direction for the same reason. A variety of riser heights of the upper lock support  17  or lower lock support  20  can be provided. The lowermost stepped support surface  18  of the upper lock support  17  and the uppermost stepped support surface  21  of the lower lock support  20  may be provided with various lengths and widths to ensure better support. 
         [0086]    As can be seen in  FIG. 2  there are two sets of upper lock supports  17  attached to the top end plate  13  and there are two sets of lower lock supports  20  in this embodiment, but a single set or more than two sets of upper and lower lock supports can also be used to lock the implant  10  in the expanded state. Also shown, for example, in  FIG. 2  are cylinders  16  and pistons  22 , which provide one example of extension means in embodiments of the present invention. Other examples of extension means are described herein below in connection with alternative embodiments of the invention. 
         [0087]    The implant  10  is configured to be implanted between opposing vertebral bodies in the spine to facilitate bony fusion between those vertebral bodies. The implant  10  is shown in its collapsed or contracted configuration in  FIG. 1  and in one example of its expanded configuration in  FIG. 2 . In the collapsed state, the implant  10  can be inserted easily into the intervertebral body space through a minimal incision and with minimal tissue removal. Once in that space, the implant  10  can be expanded against the two opposing vertebral bodies to distract them and thereby restore height to the intervertebral space. This provides stable opposition of the implant  10  to both vertebral bodies and optimizes the bony fusion process. The fusion process can also be enhanced by filling the interior cavity  15  with autologous bone graft, a bone growth enabling matrix, and/or bone growth stimulating substances prior to and/or after insertion into the body. 
         [0088]    Further details of individual parts of the implant  10  are depicted in  FIGS. 3 ,  4 A and  4 B. Pistons  22  are attached to the underside of the top end plate  13  which are configured to support seal members  23  which run inside of cylinders  16  located in the housing  11 . When the cylinders  16  are pressurized as will be described in more detail below, the seals  23  running inside the cylinders  16  and pistons  22  slidably disposed within the seals are vertically displaced, translating the top end plate  13  vertically above the housing  11 . Lower lock supports  20  are located around the outer wall of the cylinders  16 . When the top end plate  13  is vertically displaced, which in turn displaces the attached upper lock supports  17 , the lower lock supports are rotated by the biased locking actuators  26  to a locking position. Arcuate locking actuator channels  25  in the top surface of bottom plate  14  and the arcuate slots  27  in the housing base  12  confines the locking actuators  26  to the housing  11 . 
         [0089]    Additional details of the housing  11  are depicted in  FIGS. 5A and 5B . The housing  11  comprises an outer wall  31  and cylinders  16  which are secured to housing base  12 . The outer wall  31  supports a leading nose  32  on the distal end and a delivery boss  33  on the proximal end. The leading nose  32  has inwardly directed side tapered faces  34  and top tapered face  35  and bottom tapered face  36 . These tapered faces  34 ,  35  and  36  enable non-traumatic insertion of the implant  10  past neural elements and between the vertebral bodies. The delivery boss  33  contains a delivery tool anchor  37  which allows secure attachment of the implant  10  to a delivery tool (not shown), which is illustrated in co-pending application Ser. No. 11/535,432, filed Sep. 26, 2006, and Ser. No. 11/692,800, filed Mar. 28, 2007 for insertion into a vertebral space. The delivery boss  33  also contains pressure input ports  38  which are used to deliver a pressurized fluid to the interiors of cylinders  16 . The outer wall  31  of the housing  11  also provides side openings  40  which provide space for bony in-growth into central cavity  15  in the housing  11  and provide radiolucent openings for the radiographic imaging of the process of bony in-growth. The housing base  12  also contains pressure channels  41  which deliver pressurized fluid from the pressure input ports  38  to the interior of cylinders  16 . Although the housing base  12  of implant  10  is depicted with independent pressure channel  41  for each cylinder  16 , other embodiments can contain one or more branching pressure channels for delivering pressurized fluid to two or more cylinders  16 . As previously mentioned, the housing base  12  also has locking actuator slots  27  which hold and guide the locking actuators  26 . The locking actuator slots  27  contain a wider portion, locking actuator opening  42 , to enable insertion of the locking actuator  26  into the channels defined by the locking actuator slots  27  in housing base  12  and the locking actuator channels  25  in the bottom end plate  14 . The housing base  12  also has optional alignment bosses  19  which align the bottom end plate  14  to the housing  11  via optional alignment holes  9 . 
         [0090]      FIGS. 6A and 6B  illustrate further details of the top end plate  13  and the lower lock support  20 . The two sets of pistons  22  and upper lock supports  17  are joined by connecting members or struts  44 . The pistons  22  have seal bosses  45  on which the seals  23  are mounted. The upper lock supports  17  have tiered lower support surfaces  18  and risers or alignment faces  46 . The tiered or stepped support surfaces  18  of the upper lock supports  17  engage the stepped or tiered support surfaces  21  of the lower lock supports  20 . The alignment faces  46  of the upper lock support are configured to engage the alignment faces  47  of the lower lock supports  20 . The uppermost support surface of the lower lock support  20  has a lock support stop  50  which engages with the lower most alignment faces  46  of the upper lock support to prevent the lower lock support  20  from over rotating as it engages the upper lock support  17 . The bottom of the lower lock support  20  also has the locking actuator transfer element  28  which engages the forward end  30  of the spring locking actuator  26  to transfer the actuation force from the locking actuator  26  to the lower lock support  20 . 
         [0091]      FIGS. 7 through 10B  show details of the selectively expanding locking sequence of implant  10  with the housing  11  removed. The collapsed configuration is shown in  FIG. 7  with the support surfaces  18  of the upper lock support  17  resting on the support surfaces  21  of the lower lock support  20 . The locking actuator  26  is a biasing element, such as a spring, that engages the depending element or locking actuator transfer element  28  to urge the alignment faces of the lock supports in a direction where they contact. Thus, in one exemplary embodiment, the alignment faces  47  of the lower lock supports  20  are forced against the alignment faces  46  of the upper lock support  17 . The lock support stops  50  fit within the lower lock stop relief  52  (shown best in  FIG. 6A ) on the top end plate  13 . When the cylinders  16  are pressurized, the pistons  22  raise the top end plate  13  and attached upper lock supports  17  (straight arrow) moving the support surfaces  18  of the upper lock support  17  off of the support surfaces  21  and moving the lower alignment faces  46  past the upper alignment faces  47 . When the alignment faces  46  of the upper lock support  17  have cleared the alignment faces  47  of the lower lock support  20 , the locking actuators  26  (in this embodiment a compressed coiled spring) engaging the locking actuator transfer element  28  force the lower lock supports  20  to rotate (curved arrow in  FIGS. 8B and 9B ). The support surfaces  21  of the rotating lower lock supports  20  move to the next lower level of the support surfaces  18  of the raised upper lock supports  17  until the alignment faces  47  of the lower lock supports  20  engage the next level of the alignment faces  46  of the upper lock supports  17 . The lower lock support  20  and upper lock support  17  then lock the top end plate  13  at this expanded level. This process repeats itself at each locking level ( FIGS. 8A ,  8 B,  9 A,  9 B and  10 A) until the top level (or somewhere between) is reached as shown in  FIG. 10B . At this top level, the locking actuators  26  engage the locking actuator transfer elements  28  and the lower lock supports  20  are rotated so the lowermost alignment surface  46  of the upper lock support  17  engages lock support stop  50  of the uppermost support surface  21  of the lower lock support  20 . At this highest locked level only the lowest support surfaces  18  of the upper lock supports  17  and the highest support surfaces  21  are engaged providing all of the locking support. As can be seen from  FIGS. 10A and 10B  the lowest support surfaces  18  of the upper lock supports  17  and the highest support surfaces  21  of the lower lock supports  20  can be wider than the other support faces to provide sufficient support material when only these two faces are engaged. 
         [0092]      FIGS. 11A and 11B  illustrate the operation of locking actuator  26 . In this embodiment the spring locking actuator  26  is compressed into an arc beneath the lower lock support  20 . One end of the spring locking actuator  26  is constrained by the housing  11  (not shown) and the other is engaged with the locking actuator transfer element  28 . When the lower alignment faces  46  of the upper lock support  17  are raised above the upper alignment faces  47  of the lower lock support  20  by the extension of piston  22 , the locking actuator  26  pushes against the locking actuator transfer element  28  and rotates the lower lock support  20  in a clockwise direction (arrow) as viewed from above. It should be noted that in the embodiment of the current implant as described thus far, the angular orientation of the tiered upper and lower support surfaces  18  and  21  can vary when there is more than one set of supports. As shown in  FIG. 3  the proximal lower support surfaces  21  are oriented clockwise as viewed from above and the distal lower support surfaces  21  are oriented counter-clockwise. This opposite orientation provides enhanced locking support for rotational forces applied to the implant. 
         [0093]    An alternative locking actuator  26   a  is shown in  FIG. 11C  as a torsion spring. This locking actuator  26   a  has constraining tab  53  secured to the lower lock support  20  and constraining tab  54  secured to the housing  11 . Just as the compression spring shown in  FIGS. 11A and 11B  applies a force to the lower lock support  20  to rotate it, the torsion spring in  FIG. 11C  does the same. An extension spring would work equally as well as a locking actuator  26   a . Spring actuators can be made of an appropriate biocompatible material such as stainless steel, NITINOL, titanium or a suitable polymer. Locking actuators are not limited to springs. A wide variety of mechanisms can be used to actuate the lower lock supports  20 , including but not limited to, a linear drive, an externally actuated tensile member, a worm gear, an inflated member such as a balloon or bellows, a magnet, a rotational drive such as a micro motor, a super elastic shape memory element, and the like. 
         [0094]      FIG. 12A through 12C  show variations of the lower lock support  20  described above. In  FIG. 12A  a tri-set lock support  20   a  is shown whereby there are three sets of upper support surfaces  21   a , upper alignment surfaces  47   a  and lock support stops  50   a  rather than the two sets described above. This tri-set lower lock support  20   a  has two advantages over the two sets design, 1) there are three support columns rather than two locking the implant  10  in an expanded state thereby creating a more stable lock and 2) the tri-set lower lock support  20   a  has to move or rotate much less for each locking level. This last advantage is significant when the locking actuator is a spring such as spring locking actuator  26  as this places less strain on the spring to achieve the required locking force at each step. Each lower lock support column will have a corresponding upper lock support column (not shown). The upper support surfaces  21  and lower support surfaces  18  are not limited to two or three sets of surfaces. Any number of sets of support surfaces including a single set may be employed. 
         [0095]      FIG. 12B  shows an inter-digitating lower lock support  20   b . Each of the inter-digitating upper support surfaces  21   b  on the inter-digitating lock support  20   b  is paired with an inter-digitating stop  50   b  which when paired with matching inter-digitating support surfaces and stops of an upper lock support (not shown) prevents the inter-digitating support surfaces  21   b  from moving relative to the inter-digitating support surfaces of an upper lock support to unlock the implant without the inter-digitating lower support faces first lifting above the inter-digitating stop  50   b . This design provides an enhanced locking feature. Upper alignment surfaces  47   b  are again provided. 
         [0096]    Generally the lower support surfaces  18  and the upper support surfaces  21  are horizontal to maximize vertical support in the locked implant. However, the locking support  20   c  shown in  FIG. 12C  provides an enhanced locking feature by providing inclined support surfaces  21   c  which have a slope relative to the horizontal which requires matching inclined lower support surfaces on the upper lock supports (not shown) to be lifted above the inclined upper support surfaces  21   c  before the upper lock support can be rotated to unlock the implant. 
         [0097]      FIGS. 12A and 12C  show various lengths of locking actuator transfer elements or depending elements  28 . The locking actuator transfer element  28  can vary in length depending on how much engagement is desired between the locking actuator transfer element  28  and the locking actuator slots  27 . The locking actuator transfer element  28  includes one or more transfer element tabs  29   a  and  29   c  which vertically constrain the lower lock support  20  to the locking actuator slots  27  in the housing  11 . The wider locking actuator opening  42  described above (see  FIG. 5B ) enables insertion of the locking actuator transfer element  28  with transfer element tabs  29   a  and  29   c  into the locking actuator slots  27  in housing base  12  at the rotational position where the locking actuator transfer element  28  is aligned with the locking actuator opening  42 . In other rotational positions the transfer element tabs are constrained by lateral extensions on the sides of the narrower locking actuator slots  27 . In this manner the locking actuator transfer element  28  provides both the function of transferring force from the locking actuator  26  to the lower lock support  20  as well as constraining the lower lock support  20  to the housing  11 . This later function prevents the frictional forces between the lower alignment faces  46  and the upper alignment faces  47  created by the biased spring locking actuator  26  from lifting the lower lock support  20  along with the upper lock support  17  when the upper lock support  17  is lifted by the piston  22 . 
         [0098]    As an alternative to the locking actuator transfer element  28 , the embodiment shown in  FIG. 12B  depicts a locking actuator guide channel  80 . This locking actuator guide channel  80  engages a tensile member (not shown) which transfers actuation force from the locking actuator  26  to the lower lock support  20 . Tensile members can be any of a number of known elements such as sutures made of polymers or natural materials, metal cable, plastic or metal rod and the like. 
         [0099]      FIGS. 13A and 13B  illustrate an alternative design of an implant  110  embodying features of the invention. The implant  110  has independent actuation of the distal piston  122   a  and proximal piston  122   b . The two pistons  122   a  and  122   b  are interconnected by an articulating top end plate  113  which allows independent lift and locking of each side of the implant  110 . This independent lift and locking of both ends of the implant  110  enables the implant to conform to intervertebralend plates that have uneven lateral heights between them. Further, this independent lift and locking allows the implant  110  to be used to create varying lateral heights between vertebralend plates which can be useful to compensate for a scoliosis in the spine. 
         [0100]    Implant  110  has a housing  111  which has an alternative delivery tool anchor  160  located in it as well as alternative pressure input ports  137 . A variety of anchor designs or pressure ports can be used with any of the embodiments of the current device without departing from the scope of this invention. Lock and unlock access ports  138  are also located on this housing  111 . These ports are used to guide lock and unlock mechanisms (not shown) which can be manipulated externally to the implant  110  to actuate the lower lock support  120  to not only move it under the upper lock support  117  to hold the piston  122   b  and articulating end plate  113  in an expanded position, but also to move the lower lock support  120  away from the upper lock support  117  to allow the piston  122   b  and articulating end plate  113  to collapse back into the housing  111 . This later action may be desirable to remove the implant  110  from or reposition the implant within the intervertebral space. A variety of lock/unlock mechanisms can be used with the current invention such as but not limited by, a tensile member including suture thread and metallic cable, a compressive member such as a metallic or polymer rod, pressurized fluid, a rotating drive, a super elastic shape memory element, and the like. 
         [0101]      FIGS. 14A-14C  depict yet another alternative implant  210  that embodies features of the invention. Implant  210  has an interfacing top plate  213  which connects to separate and freely rotating pistons  222  via the piston capture plate  270  on the interfacing top plate  213  and the piston heads  271  on the rotating pistons  222   ab . The rotating pistons  222   ab  also interiorly contain upper lock supports  217  with support faces  218  and alignment faces  246 . Seals  223  are mounted on the rotating pistons  222   ab  and the seals  223  and rotating pistons  222   ab  fit into internal cylinders  216  that are located on the housing  211 . The internal cylinders  216  have lower lock supports  220  with support surfaces  221  and alignment faces  247  as well as lower retaining features  273 . The housing  211  also contains one or more pressure input ports  238 . 
         [0102]    In use, the implant  210  is inserted into the intervertebral body space in a collapsed state and fluid pressure is delivered through the pressure input port(s)  238  to the internal cylinder(s)  216  to raise the seal(s)  223  and rotating piston(s)  222   ab  out of the internal cylinder(s) thereby raising the interfacing top plate  213  and expanding the implant  210 . Once the rotating pistons  222   ab  have been raised such that the lower alignment faces  246  of the upper lock supports  217  have cleared the upper alignment surfaces  247  of lower lock supports  220 , an actuator (not shown) rotates the rotating pistons  222   ab  such that the lower support surfaces  218  of the upper lock supports  217  are moved above the upper support surfaces  221  of the lower lock supports  220 , to thereby lock the implant  210  in the expanded configuration. The actuator can be one or more tensile members such as suture threads or cables that extend from the user into the implant  210  through the lock and unlock access ports  238  on the interfacing top plate  213  to the piston head  271 . Applying tension to one or more tensile members when the piston is in an extended configuration will rotate the piston heads  271  such that the support surfaces  218  of upper lock supports  217  are moved above the support surfaces  221  of the lower lock supports  220  thereby locking the implant  210 . Alternatively or in addition to applying tension to lock the implant  210  in an expanded configuration, applying tension to one or more tensile members will rotate the piston heads  271  such that the lower support surfaces  218  are moved away from the upper support surfaces  221  thereby unlocking the implant  210  and allowing the rotating pistons  222   ab  to seat back into the internal cylinders  216  such that the implant  210  is once again in a collapsed configuration. 
         [0103]      FIG. 15  illustrates an alternative implant design  310  embodying features of the invention which has a housing  311 , top end plate  313  and pistons  322  similar to the prior embodiments. This implant  310  has upper lock supports  317  and lower lock supports  320  within a central portion of the implant. The upper lock supports  317  are secured to the top end plate  313  and the lower lock supports  320  are secured to the base  314  with depending elements (not shown) as was described above and are moved as in the prior embodiments. 
         [0104]      FIG. 16  illustrates an alternative implant design  410  embodying features of the invention which has a housing  411 , top end plate  413  and a centrally located piston  422  similar to the prior embodiments. This implant  410  has upper lock supports  417  and lower lock supports  420  distal and proximal to the centrally located cylinder  416  and piston  422 . The upper lock supports  417  are secured to the top end plate  413  and the lower lock supports  420  are secured to the base  412  and are moved as in the prior embodiments via depending elements (not shown) as was described above. 
         [0105]      FIG. 17  shows another alternative implant  510  which has a pair of pistons  522  and which has a locking support system which includes ratchets  521  on the base  512  and pawls  517  pivotally mounted to and depending from the top end plate  513 . Expansion of the pistons  522  causes the free ends  518  of pawls  517  to engage recesses  520  in the ratchets  521  so as to lock the top end plate  513  in an extended configuration. 
         [0106]      FIG. 18  illustrates another alternative implant design  610  which is similar to that shown in  FIG. 17 . In this embodiment the free end of the pawl  617  has a plurality of teeth  618  to provide greater effective contact between the pawl  617  and the ratchet  621  for locking of the implant  610 . 
         [0107]      FIG. 19  is a cross section embodiment, showing implant  710  embodying features of the invention. In this embodiment the pistons  722  are surrounded by upper lock support  717  which has at least one cantilever extension ending at the support surface  718 . The support surfaces  718  are captured by the recessed support surfaces  721  which are located on the inner wall of the housing  711 . Once the pistons  722  are expanded in an upward direction, the support surfaces  718  of the upper lock support  717  engages the recessed support surfaces  721  locking the implant  710  in place. The upper lock support  717  can be rotated relative to the piston  722  and housing  711  to disengage the support surfaces  718  from the support surfaces  721  to unlock the implant  710  and lower the pistons  722  as needed. Alternatively the implant  710  can be unlocked by rotating the upper lock support constraints  775  relative to the upper lock support  717  to press on the cantilever extensions and disengage the support surfaces  718  from the support surfaces  721 . 
         [0108]      FIGS. 20A-31B  illustrate a variety of suitable means for locking extendable members such as pistons in extended configurations.  FIGS. 20A ,  20 B,  21 A,  21 B, and  22 - 31 B show variations of lower lock supports and upper lock supports. In each of these variations there are support surfaces on the lower lock supports which engage support surfaces on the upper lock supports. 
         [0109]    In  FIGS. 20A and 20B  support surfaces  818  comprise grooves set into the upper lock support  817 . The lower lock support  820  is a U-shaped tong which is configured to advance (as indicated by the arrow in  FIG. 20A ) towards the upper lock support  817  and to engage one of the grooves with its upper support surface  821  for locking an implant not shown in these drawings. Lower lock support  820  is withdrawn (as indicated by the arrow in  FIG. 20B ) from the groove to disengage the lower lock support and unlock the implant. 
         [0110]    In the variation shown in  FIG. 21A , the lower lock support  920  is a plate with an upper lock clearance opening  970  that is shaped to allow passage of the cylindrical flat-sided upper lock support  917  through the lower lock support  920  (arrow). As shown in  FIG. 21B , once the lower lock support  920  is positioned at the desired location it can be rotated approximately 90° (arrow) to engage the support surfaces of the lower lock support  920  with the support surfaces  918  of the upper lock support  917 . The shape of the upper lock support  917  and mating upper lock clearance opening  970  on the lower lock support  920  are not restricted to the profile shown in  FIGS. 21A and 21B  nor is the locking actuation restricted to 90° rotation of one of the elements but can vary to any number of shapes that allow passage in one configuration but constraint when one of the elements is moved to another configuration. 
         [0111]    In  FIG. 22 , the upper lock support  1017  is a cylinder with notches cut to create support surfaces  1018 . The lower lock support  1020  is a pivoting pin  1070  with a pawl  1071  for the lower support surface  1021 . In the configuration shown, the support surface is biased as indicated by the arrow  1072  to allow the upper lock support  1017  to rise with an expandable member of an implant and to prevent the upper lock support from dropping. This allows the device to lock at each level when the subsequent support surface  1018  of the upper lock support  1017  engages the support surface  1021  of the lower lock support  1020 . In this variation having features of the present invention, the upper lock support  1017  can also be lowered by moving the pivoting pin  1070  of the lower lock support  1020  away from the upper lock support  1017  to disengage the support surface  1021  from the support surface  1018 . 
         [0112]      FIG. 23  shows yet another embodiment having features of the invention where the lower lock support  1120  is a pin configured to engage (arrow) support surfaces  1118  located in the upper lock support  1117 . The lower lock support  1120  does not have to engage the full thickness of the upper lock support  1117  as shown in this figure, nor does the support surface  1118  have to extend through the entire thickness of the upper lock support  1117  but rather can engage any portion of the upper lock support  1117  that is sufficient to lock an implant in position. This embodiment also allows a variety of shapes of pins  1120  and matching support surfaces  1118 . 
         [0113]    In  FIG. 24  the lower lock support  1220  is a grip with two pivoting jaws  1270 , the ends of which have support surfaces  1221 . The upper lock support  1217  has a series of notches which have the support surfaces  1218 . A lock actuator such as a compressive spring (not shown) can apply force (as shown by the arrows  1272 ) to the grip base extensions  1273  to lock the device. This variation having features of the invention allows the upper lock support  1217  to move upwards but prevents downward motion thereof. Downward motion of the upper lock support  1217  can be allowed by reversing the force on grip base extensions  1273 . 
         [0114]    Not all locking systems embodying features of the invention require the engagement of support surfaces of the upper lock supports directly on top of the support surfaces of the lower lock supports. A frictional support can be created to lock the device as shown in  FIGS. 25 through 32 . 
         [0115]    In  FIG. 25  the upper lock support  1317  has one or more flat surfaces as the support surfaces  1318 . The lower lock support  1320  has one or more pivoting pawls that have a support surface  1321  that engage the support surface  1318  and supports a load (arrow). 
         [0116]    In  FIG. 26  the upper lock support  1417  has an exterior support face  1418  which is gripped by the support face  1421  on the inner diameter of the wrapped lower lock support  1420 . This lower lock support  1420  can be a torsion spring that in its free state grips the upper lock support  1417  and releases the upper lock support when a force (arrows) is applied to one or more of its ends  1470  as shown to increase the spring&#39;s inner diameter. The reverse is possible where in its free state the lower lock support  1420  allows movement of the upper lock support  1417  inside the inner diameter. When a tensile force is applied to the ends  1470  to reduce the inner diameter, the lower lock support grips the support surface  1418  of the upper lock support  1417  to lock the implant. 
         [0117]      FIGS. 27A and 27B  show another variation which can be described as a canted washer type device. The lower lock support  1520  is a plate with an upper lock clearance opening  1570  which allows relative movement of the upper lock support  1517  as shown in  FIG. 27A . When the lower lock support  1520  is canted as shown in  FIG. 28B , the edge of the upper lock clearance opening  1570  comprises a lower support surface  1521  which engages the upper support surface  1518  which is the outer surface of the upper lock support  1517  locking it relative to the lower lock support  1520 . 
         [0118]    Yet another variation of the gripping lock of the current invention is shown in  FIG. 28 . In this variation the lower lock support  1620  comprises one or more jaws which have support surfaces  1621  that are configured to be forced against the support surface  1618  of the upper lock support  1617  to produce friction to lock the device in place. 
         [0119]      FIG. 29  illustrates a lower lock support  1720  which comprises a pivot and pawl as has been detailed above. The end of the pawl comprises a lower support surface  1721  which engages an upper support surface  1718  on the upper lock support  1717 . In this embodiment the upper lock support  1717  is rotated counter clockwise by an expanding element (not shown). This rotation in turn raises the piston  1722  which expands the implant. In this manner the upper lock support  1717  is integrated into the lifting mechanism to engage the lower lock support  1720  and lock the implant as it expands. 
         [0120]      FIG. 30  illustrates yet another alternative implant  1810 , similar to that shown in  FIG. 1  except that the upper locking member  1817  and lower locking member  1818  have a linear shape rather than the arcuate shape of the prior embodiments. The implant  1810  generally has a housing  1811 , a top plate  1813 , a bottom plate  1814 , pistons  1822  and cylinders  1816 . The upper locking member  1817  has support surfaces  1818  and the lower locking member  1820  has support surfaces  1821 . The implant  1810  has a locking actuator (not shown). 
         [0121]      FIGS. 31A-31G  illustrate another implant  1910  embodying features of the invention which have upper locking members  1917  with grooves  1970  having support surfaces  1918  and lower locking member  1920  with locking surfaces  1921 . The lower locking member  1920  is a wire-form which encircles the exterior of both upper locking members  1917  and is configured to seat within the grooves  1970 . Expansion of the lower locking member  1920  (arrows in  FIG. 31B ) by the locking actuator (not shown) causes the lower locking member  1920  to be pulled out of the groove  1970  and allows the upper locking member  1917  to rise with the expansion of the implant. Release of this expansion of the lower locking member  1920  (arrows in  FIG. 31A ) allows the lower locking member  1920  to seat back into the groove  1970  locking the implant  1910 . 
         [0122]      FIG. 31G  illustrates a detail of an alternative implant  1910   a  embodying features of the invention which have upper locking members  1917   a  with grooves  1970   a  having support surfaces  1918   a  and lower locking member  1920   a  with locking surfaces  1921   a . The lower locking member  1920   a  is a wire-form which encircles the exterior of both upper locking members  1917   a  and is configured to seat within the grooves  1970   a . The support surface  1918   a  locks on the support surface  1921   a  when there is a compressive or downward force (hollow arrow) on the upper locking member  1917   a  locking the implant  1910   a . Upward force or extension (solid arrow) of the upper locking member  1917   a  causes the lower locking member  1920   a  to ride on the disengaging surface  1919   a  and out of the groove  1970   a  allowing the upper locking member  1917   a  to rise with the expansion of the implant  1910   a.    
         [0123]    In a further aspect of the present invention, a piston/cylinder and locking arrangement as described above may be used to deploy extendable bone anchors. For example, implant  10 A with conical bone engaging anchors  60  as shown in  FIGS. 32A and 32B  may be constructed with pistons  22  and cylinders  16  as described above in connection with implant  10  and shown, for example, in  FIGS. 2 ,  3  and  4 B. Implant  10 A has a housing  11  as previously described and may include other previously described features such as interior cavity  15  for bone growth stimulating substances. However, in this embodiment, instead of upper interlocking end plate  13 , the two pistons  22  individually terminate with conical bone engaging anchors  60 . The bone engaging anchors, including sharp leading tip  62 , form surface for engaging the vertebral body. 
         [0124]    As shown in  FIG. 32A , bone engaging anchors  60  are in a contracted configuration, within housing  11 , to facilitate insertion of implant  10 A. Using hydraulic actuation as previously described, bone engaging anchors  60  are moved to an extended configuration as shown in  FIG. 32B , wherein at least leading tip  62  extends beyond housing  11  to engage and anchor in the bone. In order to ensure that the bone engaging anchors remain firmly engaged in the bone, locking mechanisms including multi-stepped upper and lower lock supports  17 ,  20  as previously described in connection with implant  10  and shown, e.g. in  FIGS. 6A-12C , are provided to support each anchor  60  in the extended configuration. With this arrangement, the extended and locked anchor  60  helps to retain the implant in place. 
         [0125]    A variety of alternatives are possible for the bone engaging anchor according to the invention as illustrated in  FIGS. 33A-C . For example, implant  10 B in  FIG. 33A  includes bone engaging anchors formed as spike  60 A and blade  60 B. Blade  60 B can be particularly effective in preventing motion along the insertion path after deployment. In this case, the length of the blade  60 B is aligned in the direction shown by arrow A. This is substantially orthogonal to the direction of implantation (arrow B) and would resist movement in that direction. Implant  10 F, shown in  FIG. 33B  includes further possible variations. In this embodiment, the bone engaging anchors are formed as barbed spikes  60 C. Barbs  61  along the shaft of the spikes resist forces that tend to move the tissue away from the implant along the axis of the anchor (much as the screw threaded anchor described below would also resist this force). Also included in implant  10 F is a lateral bone engaging anchor  63  for anchoring in laterally oriented tissue. In the illustrated embodiment, lateral anchor  63  includes a plain spike  60 A. Lateral anchor  63  is formed in the same manner and with the same components, i.e. piston, cylinder, locking mechanism, etc. as elsewhere described in this application, except that the components are oriented laterally as shown. To provide support for the bone anchor components in this lateral embodiment, housing  11  includes a central member  11 A that divides interior cavity  15  into two portions. In the configurations of implants  10 B and  10 F, the top of piston  22  can also become a bone engaging surface when the anchor member is fully received within the bone.  FIG. 33C  shows a further alternative implant  10 G, including anchors  65  extending obliquely from housing  11 , rather than orthogonally. This oblique arrangement is helpful in resisting side to side rotational forces (for example when the patient/spine bends towards the side) and expansion forces. Once again, obliquely extending anchors  65  are essentially identical to other bone engaging anchors described herein except for the oblique orientation. Here, holes  68  are provided in top end plate  66  for the spikes to pass through. In general, bone engaging anchors according to embodiments of the invention should have a relatively small termination (e.g. tip  62 ) relative to the size of the piston diameter so that the force on the piston created by the hydraulic fluid is proportionally a much greater force at the small anchor termination to enhance its ability to extend into hard bony tissues. It will also be appreciated by persons skilled in the art that the various features of the bone engaging elements, e.g. spike, blade, barbs, etc., described herein may be combined in any desired combination, in addition to the exemplary combinations shown in the figures of the present application. 
         [0126]    In another alternative embodiment, illustrated in  FIGS. 34A and 34B , implant  10 C includes screw-threaded members  64  as bone engaging anchors. Implant  10 C also illustrates a further alternative wherein the bone engaging surfaces, such as the anchors, extend from opposite sides of the implant. In this exemplary embodiment, interlocking end plate  13  is replaced with an integrated top end plate  66 . Holes  68  are provided for threaded member  64  to pass through. Persons of ordinary skill in the art will appreciate that holes  68  will be located as needed; in the illustrated embodiment one is in top end plate  66  and the other in bottom end plate  14 . 
         [0127]    Threaded members  64 , as bone engaging anchors extend outwardly from pistons  22 . In order to rotate the threaded anchors into the bone when the pistons are extended, the inner wall of housing  11  is provided with a screw-threaded surface  70  that mates with corresponding threads  71  cooperating with pistons  22 . As previously described, seals  23  act between the pistons  22  and cylinders  16  to prevent leakage of hydraulic fluid. When fluid is pressurized within the cylinders as described for prior embodiments, the piston is extended, but also driven in a circular motion by the engagement between threaded surfaces  70  and  71 . The screw-threaded member  64  is thus driven into adjacent bone as it is extended to anchor the implant. 
         [0128]    Once again, locking mechanisms as previously described and shown, for example, in  FIGS. 6A-12C , may be employed to prevent the bone engaging anchors from becoming unengaged from the bone. In the cross-sectional views of  FIGS. 34A and 34B , upper and lower lock supports  17 ,  20  are visible around the outside of the piston and cylinders. Alternatively, depending on the depth and pitch of the threaded portions, use of a separate locking mechanism may not be required. As persons of ordinary skill will appreciate, the configuration of the threads alone may be sufficient to prevent the anchors from backing out. 
         [0129]      FIGS. 35A and 35B  illustrate a further aspect of the present invention wherein locking mechanisms as described are utilized to secure telescoping bone engaging surfaces in place. As used herein, telescoping refers to nested, extendable members including at least one intermediate member between a base and bone engaging member. 
         [0130]    Referring first to  FIG. 35A , implant  10 D has substantially planar bone engaging members  72 . Bone engaging members  72  are thus similar to the bone engaging members of implant  10 , but instead individually actuated without interlocking end plate  13 . The piston/cylinder arrangement is also similar to that previously described except that here upper piston  74  is received in intermediate piston  80 . Intermediate piston is in turn received in cylinder  16  as was previously described for piston  22 . Upper piston  74  is sealed against intermediate cylinder  78  of intermediate piston by upper piston seals  76  (see  FIG. 35B ). 
         [0131]    The telescoping bone engaging members  72  are secured by locking mechanisms in a similar manner to the earlier described embodiments, with the addition of an upper lock support  82  for the upper piston. Intermediate piston  80  is supported by upper lock support  17  and lower lock support  20  as previously described. Upper lock support  82  includes upper and lower lock supports  84 ,  86 . Thus, upper piston  74  is secured to upper lock support  84  of the upper lock set. Lower lock support  86  of the upper lock set is mounted on top of upper lock support  20  of the lower lock set. One difference from the earlier described embodiments is that separate spring actuators  26  are not required for the upper lock set as they may be rotated along with the lower lock set by actuators  26 . 
         [0132]    Implant  10 E, as shown in  FIG. 35B  includes a further variation in which the planar portion of upper bone engaging surface  88  is effectively annular with a conical anchor  90  at the center. Advantages of embodiments of the present invention including bone engaging anchors include the ability of the anchors to be extended lateral from the long axis of the implant (i.e., the insertion axis) with a relatively high force using the relatively small connection to the implant of the hydraulic line. This is an advantage over other methods that require larger access or larger connections to the implant for lager tools or non-hydraulic extension forces to extend the anchors into the hard, bony tissue. 
         [0133]    Although the previously described embodiments of the invention included cylinders  16  and pistons  22  expanded with a pressurized fluid as the mechanism used to lift the top end plate away from the bottom end plate, embodiments of the present invention are not limited to only such lift mechanisms. In  FIGS. 36A-C  an alternative embodiment of the present invention comprising implant  10 F is shown wherein a pair of bellows  92  replaces the piston and cylinder pairs previously described. One end of bellows  92  is attached to housing  11  and the other end to top end plate  13 . A pressurized fluid added via pressure input ports  38  is directed through bellows orifice  94  into the inside of bellows  92  causing the bellows to expand. The expanding bellows forces top end plate  13  away from housing  11  and lower lock supports  20  are rotated to lock the device in the expanded configuration as was previously described. Bellows  92  can be made of any biocompatible material such as the 316 series of stainless steels, titanium or a titanium alloy, a cobalt chromium alloy, or an implantable polymeric material. The bellows can be of an accordion-like folding configuration as shown in  FIGS. 36A-C  or any other regular or irregular configuration which can fit inside of the housing and lock supports in the collapsed configuration and expand sufficiently when pressurized to lift top end plate  13  the desired amount away from housing  11 . Lower lock supports  20  and upper lock supports  17  provide a confining geometry for bellows  92 , which allows use of an irregular bellows configuration. With a bellows arrangement as shown in  FIGS. 36A and 36B , the amount of lift is not limited as is the case in a cylinder and piston to the amount that the collapsed cylinder and piston overlap. 
         [0134]    Other exemplary embodiments do not rely on the use of a pressurized fluid for expansion. For example,  FIGS. 37A and 37B  show an alternative rotating cam lift mechanism  93 . Cam lift mechanism  93  includes cam  96  with a substantially curved cam surface  95  and a substantially flat top surface  97 , rotating shaft  98 , and shaft supports  99 . Cam  96  is attached to rotating shaft  98 , and shaft  98  is supported by and rotates within shaft supports  99 . In an implant  10 G ( FIG. 40 ) using this mechanism, the shaft supports  99  are anchored to the inside of housing  11  and rotation of shaft  98  (depicted by curved arrows) rotates the curved cam surface  95  against the bottom of top end plate  13  and moves top end plate  13  away from housing  11  as shown in  FIGS. 38A-38B ,  39 A- 39 B and  40 . The shape of cam  96  determines both the amount of lift that is possible and the relative amount of lift to the amount of rotation of the cam. The cam is not limited by 90 degrees of rotation depicted in the figures. Any shape of a cam that is rotated by any amount from as little as 10 degrees to as much as 355 degrees is possible without departing from the scope of the present invention. Shaft rotation can be accomplished by several means as will be discussed in more detail below. Use of cam lift mechanism  93  as the lifting mechanism along with lower and upper locking supports  20  and  17  for implant  10 G allows the lift mechanism to support only the initial lifting loads and not have to support the repetitive long-term supporting loads on implant  10 G which are borne by the locking supports. Cam  96  does not require a substantially flat top surface  97  as shown in the exemplary embodiment to support top end plate  13 , but such a surface provides a rotational endpoint for the surgeon rotating shaft  98 . 
         [0135]    Another alternative embodiment is implant  10 H shown in  FIGS. 41 ,  43 A and  43 B. Implant  10 H uses a rotating screw lift mechanism  193  as shown in  FIG. 42 . This mechanism includes shaft  98 , shaft supports  99 , worm gears  170  attached to shaft  98  and a shaft input end  178  at one end of shaft  98 . The mechanism also includes lift screws  172 , which have lower lift threads  174  and transfer gear  176  and supporting boss  186 . Applying a torque via shaft input end  178  turns shaft  98 , which turns the attached worm gears  170 . Worm gears  170  turn transfer gear  176  on lift screw  172 . Lift screw  172  is contained within housing  11  by way of its supporting boss  186 , which is seated in housing bearing  188 . Rotation of lift screw  172  transfers force from lower lift threads  174  to upper lift threads  182  on upper lift nut  180 . Upper lift nut  180  is attached to top end plate  13  so that rotation of shaft input end  178  lifts upper end plate  13  away from housing  11 . The relative pitch of worm gears  170  and matching transfer gears  176  and the lower lift threads  174  and matching upper lift threads  182  can be varied to achieve the desired amount of lift relative to the amount of rotation and torque. The torque can be applied by any means well known by those skilled in the art including but not limited to electric motor, pneumatic or hydraulic turbine, or manual rotation of an actuator. Shaft input end  178  is shown as a hexagonal post, but any alternative input end can be used without departing from the scope of the present invention, such as, but not limited to, a square or star-shaped post, a square, star or hexagonal-shaped socket, or a keyed shaft. 
         [0136]    As shown in  FIG. 44 , an alternative embodiment of the implant  10 I includes a linking element  202  that connects the lower lock supports  20 A and  20 B. The linking element  202  coordinates the action of the lower lock supports  20 A and  20 B. When the locking actuator  26  actuates the leading lower lock support  20 A, the linking element  202  in turn actuates the following lower lock support  20 B. In this embodiment the implant  10 I may require only a single locking actuator  26 , however plural locking actuators as described above (see, for example,  FIG. 3 ) may be employed for greater actuation force as needed. In addition to actuating the following lower lock support  20 B, the linking element  202  prevents the leading lower lock support  20 A from actuating until the alignment faces  46  of both the leading upper lock supports  17 A and the following upper lock supports  17 B each clear the alignment faces  47  of both the leading lower lock support  20 A and the following lock support  20 B. In this manner the linking element  202  ensures the coordinated actuation of the lower lock supports  20 A and  20 B to ensure that the implant  10 I will always lock at the same height on both sides. This can be advantageous for certain implants placed in the spine where an even expansion of the implant is desired. 
         [0137]    Linking plural lower lock supports, such as supports  20 A and  20 B, with a linking element  202  for even expansion in the manner described may be advantageous over an implant with a similarly sized single lock support  20 , and single cylinder  16  and piston  22  due to the increase in the number of support elements, the broader support base, and the increase in expansion force due to the increased number of cylinder and piston pairs. Increasing the size of a single lock support would still have disadvantages of a larger width that would limit the ability for implantation in minimally invasive surgery. Embodiments of the invention are not limited to just the pair of lower locking supports  20 A and  20  B as shown in, for example,  FIG. 33 . Rather, any number of sets of cylinders  16 , pistons  22 , upper lock supports  17 , and lower lock supports  20 , with a locking actuator  26  and the appropriate number of linking elements  202  are possible. 
         [0138]    For the embodiment illustrated in  FIG. 44 , linking element  202  is configured to fit inside attachment grooves  204  on the lower lock support  20 A, B. Alternatively, linking element  202  may be configured to rest on the outside diameter of the lower lock support  20 A, B. The linking element  202  can also be configured to run underneath the lower lock supports  20 A, B as shown in  FIGS. 45A-D . For implant  10 I in  FIG. 44  both of the lower lock supports  20 A and  20 B rotate in the same direction when actuated. Elements of an alternative implant shown in  FIGS. 45A-B  include lower lock supports  20  that actuate with rotation in opposite directions. The linking element  202  is guided between the lower lock supports  20  through a link channel  210  in housing  11  ( FIG. 45B ). The linking element  202  is constrained in the link channel  210  by a channel cover  208 . The linking element  202  is connected to the lower lock supports  20  by means of link pins  206 . 
         [0139]    The linking element can be made from any of a variety of implantable materials including: a titanium wire, a titanium cable, a stainless steel wire or cable, a nitinol wire, a braided or mono-filament suture from any manner of suture material such as silk, polyester, polypropylene, ePTFE, or UHWPE. An implantable material that has a tensile strength sufficient to transfer the actuation force from the leading lower lock support  20 A to the following lower lock support  20 B as well as flexibility sufficient to follow the link channel  210  and/or rotate around the lock supports  20  may be used. Linking element  202  can be attached to the lower lock supports  20  in a number of ways known to those practiced in the art, the selection of which depends on factors such as the linking element material and the lower lock support material. Suitable techniques include laser welding, resistance welding, adhesive bonding, crimping, attaching with clamps, pins, or screws, or being threaded through an opening and securing with a knot. 
         [0140]    Turning now to  FIGS. 46A , B and C an implant  10 J with an additional feature, an unlocking tether  212  is shown. Unlocking tether  212  is attached to the following lower lock support  20 B in attachment groove  204 . Unlocking tether  212  is attached in the opposite direction as the linking element  202  and can be attached in any of the ways described above for attaching the link element  202 . The proximal end  214  of the unlocking tether  212  exits the housing  11  of the implant  10 J through the unlock port  216 . The proximal end  214  can be actuated by an external force or mechanism (not shown). Actuation of the proximal end  214  of the unlocking tether  212  to translate it away from the implant  10 J causes rotation of the following lower lock support  20 B, which will tension and translate the linking element  202  which will rotate the leading lower lock support  20 A. In this manner the unlocking tether  212  can be used to unlock the implant  10 J so that it can collapse to a lower or to its original height. In  FIG. 46B  the implant  10 J is collapsed and the unlocking tether  212  is extended a maximum distance out of the unlock port  216 .  FIG. 46C  shows the same implant  10 J with the top plate  13  fully expanded above the housing  11  and locked. The unlocking tether  212  has shortened as it was drawn into the implant  10 J as the lower lock supports  20  rotated into locking position. Tensioning or pulling on the unlocking tether  212  will unlock the lower lock supports  20  and allow the top plate  13  to collapse back into the housing  11 . The ability to unlock and collapse the implant  10 J can be highly advantageous to a physician placing the device if there is a need to reposition or replace the device after it has been expanded in-vivo. 
         [0141]    Turning now to  FIG. 47 , another embodiment of an implant  10 K is shown with lower lock supports  20  that are located inside the cylinders  16  of the housing  11 . In this embodiment the linking element  202  is a solid bar that can transfer compressive as well as tensile loads. The locking actuator  26  rotates the leading lower lock support  20 A, which pushes on the linking element  202 . The linking element  202  in turn pushes and rotates the following lower lock support  20 B. The lower lock supports  20 A and  20 B engage the upper lock supports  17  that are located inside the pistons  22  (shown in  FIG. 14C ). The rotation of the following lower lock support  20 B pulls the unlocking tether  212  into the housing  11  through the unlocking port  38 . The unlocking tether  212  can be tensioned away from the housing  11  to reverse the process and unlock the implant  10 K. 
         [0142]    The use of tension and compression elements as described above are not the only means for coordinating the controlled locking and unlocking of the device. In  FIG. 48  an alternative embodiment of the implant  10 L is shown wherein thread gears  226 A and  226 B are used to both lock and unlock the lower lock supports  20  thus forming a combined linking and unlocking element. Threaded gears  226 A and  226 B are mounted on a shaft  224  that is contained in the base of the housing. The proximal end of shaft  224  has a keyed head  228  that can protrude from or rest in the locking port  222 . An external tool (not shown) can interface with the keyed head  228  to rotate it in either direction. Rotating the keyed head  228  will in turn rotate the shaft  224  and the threaded gears  226 A and  226 B. The threaded gears  226 A and  226 B transfer the force to the lower lock supports  20  through the geared bottom face  220 . In the embodiment shown in  FIG. 48  the threaded gear  226 A is oriented opposite of the threaded gear  226 B. This allows rotation of the shaft  224  to rotate the lower lock supports  20  in opposite directions relative to each other. It is obvious to those schooled in the art that the threaded gears  226 A and  226 B can be oriented in the same direction if it is desired to rotate the lower lock supports  20  in the same direction. In either case the shaft  224  can be rotated in one direction to rotate the lower lock supports  20  in the locking direction, and the shaft  224  can be rotated in the opposite direction to rotate the lower lock supports  20  in the unlocking direction. 
         [0143]    An unlocking tether as described herein can be engaged and tensioned by any number of means including but not limited to gripping the unlocking tether between articulating grips, a collet or split ring clamp, crimping the unlocking tether to a tensioning wire or rod and cutting the unlocking tether to disengage after use, mounting a magnet on the proximal end  214  ( FIG. 46A ) of the unlocking tether and engaging the magnet with a mating magnet attached to a tensioning wire of rod, adding a female or male thread to the proximal end  214  or the unlocking tether and engaging it with a mating thread on the end of a tensioning rod or wire, or providing a continuous unlocking tether all the way to the point external to the body for tensioning and then cutting the unlocking tether near the implant after use to disengage. It is obvious to those schooled in the art that the unlocking tether can alternatively be pushed or compressed rather than tensioned as long as it is configured to rotate the lower lock supports  20 A and B in the unlock direction and deliver sufficient load without buckling when pushed. 
         [0144]      FIG. 49  illustrates an alternative embodiment of an implant  10 M with a pushable unlocking tether  212   a . In this embodiment, unlocking tether  212   a  engages the proximal lower lock support  20 B to rotate it in the unlock direction when the unlocking tether  212   a  is advanced towards the proximal lower lock support  20 B. The link  202  transfers that rotation from the following lower lock support  20 B to the leading lower lock support  20 A. The link  202  contains engagement pins  230 , which extend into receiving slots  232  on the lower lock supports  20 A and  20 B in order to transfer the lateral movement of the link  202  into rotation of the lower lock supports  20 A and  20 B. In much the same way, the unlocking tether  212  can contain an engaging pin (not shown) to extend into a receiving slot (not shown) on the following lower lock support  20 B to transfer the lateral compressive force applied to the unlocking tether  212   a  into rotation of the lower lock supports  20 B. This is just one method for attaching or engaging the unlocking tether  212  to the lower lock support  20  the numerous methods previously described herein for attaching or engaging the link  202  to the lower lock supports  20  can be used for attaching or engaging the tether  212  as well. 
         [0145]    One advantage to pushing the unlocking tether  212   a  to unlock the implant  10 M is that the method for engaging the unlocking tether is simplified. Unlocking tether  212   a , which is pushed to unlock the implant  10 M can be contained within the implant  10 M and a push rod (not shown) can be easily directed into the implant  10 M through the unlock port  216  to actuate the unlocking tether  212   a  and unlock the implant  10 M such that it can collapse. This eliminates the need to attach to the unlocking tether  212   a  which is required when the unlocking tether  212   a  is tensioned to unlock the implant  10 M. 
         [0146]      FIGS. 50A-D  illustrate an alternate embodiment of the implant  10 N embodying features of the invention. Similar to the implant  110  as shown in  FIGS. 13A and 13B , the top end plate  113  of the implant  10 N articulates relative to the distal piston  122 A and proximal piston  122 B. The ends of the articulating top plate  113  have spherical projections  2001 A and  20001 B which are contained within mating pockets  2002 A and  2002 B in the two pistons  122 A and  122   b . Split rings  2006 A and  2006 B are placed over the spherical projections  2001 A and  20001 B and into the pistons  122 A and  122 B to vertically constrain the articulating top plate  113  to the pistons. This geometry provides articulation of the top plate  113  along not only the long axis (the axis extending along the line  50 C in  FIG. 50C ), as with the implant  110  shown in  FIGS. 13A-B , but also provides articulation in a side-to-side direction, which is an advantage for providing congruence of the implant to the intervertebral space. Thus, the articulating top plate  113  is polyaxially movably coupled to the pistons  122 A and  122 B, allowing the plate  113  to articulate about at least two axes. 
         [0147]    Also shown in  FIG. 50D  are vertical constraints  2003 A and  2003 B which are attached to the distal piston  122 A and proximal piston  122 B. These two constraints  2003 A and  2003 B fit inside channels  2004 A and  2004 B in the housing  111 . The top portion of the channels  2004 A and  2004 B have a narrowed potion  2005 A and  2005 B that prevent the vertical constraints  2003 A and  2003 B from advancing out of the housing  111 . In this manner these vertical constraints  2003 A and  2003 B limit the maximum vertical movement of the pistons  122 A and  122 B relative to the housing  111 . 
         [0148]      FIGS. 51A-B  illustrate another alternative embodiment.  FIGS. 51A-B  illustrate an implant  10 P that can have features similar to features in the embodiments illustrated in  FIGS. 13A ,  14 A-C, and  49 . The implant  10 P has the articulating top plate  113  similar to that shown in  FIG. 13A  which pivots relative to the distal piston  122 A and proximal piston  122 B about a distal pivot pin  2101 A and a proximal pivot pin  2101 B. The implant  10 P has a distal piston  122 A and a proximal piston  122 B. As with the pistons  222   a  and  222   b  shown in  FIGS. 14A-C , the pistons  122 A and  122 B can have internal upper lock supports  217 . Unlike implant  210 , in the illustrated embodiment, the pistons  122 A and  122 B do not rotate relative to the housing  111  as is the case in the implant  210 . Instead, lower lock supports  20 A and  20 B similar to those shown in  FIG. 49  rotate relative to the housing  111  and the two pistons  122 A and  122 B to lock the height of the expanded implant. In this manner, benefits of several of the previously described embodiments are combined to provide and implant  10 P that can lock at different distal and proximal heights. 
         [0149]      FIGS. 52A-F  illustrate an alternative embodiment of the present invention, exemplified by implant  10 R. In this embodiment, implant  10 R can include a distal piston top plate  2222  that can be completely separate from a proximal piston top plate  2223 . As shown in  FIGS. 52B-D , the two piston top plates  2222  and  2223  can each expand to different heights relative to the housing  111 . Thus, the independently adjustable top plates and their respective pistons provide a simple construct that can achieve variable expansion similar to the articulating top plate  113  in implants  10 N and  10 P. 
         [0150]    In some embodiments, the extendable members, such as pistons  122 A and  122 B, may be actuated by a common actuator such as a single syringe or other pressurized fluid source, but constrained as described herein to rise to independent/different heights. Such constraint may be provided by specific constraint means as described, by a common top plate such as shown in  FIG. 50D  or a combination thereof. 
         [0151]    As shown in  FIG. 52F , the implant  10 R can include a proximal lower lock support  20 B that can have stepped support surfaces that have shorter increments than the stepped support surfaces on a distal lower lock support  20 A. The mating stepped support surfaces on the proximal upper lock support (not shown) in the proximal piston  122 B can also have shorter increments than the stepped support surfaces on the upper lock support in the distal piston  122 A. This variation in stepped support surface can be designed to produce a specifically desired expanded height difference between the expanded distal piston top plate  2222  and the expanded proximal piston top plate  2223 . In addition, the expanded height difference can vary with the amount of expansion. This variation can be valuable, for example, for creating lordotic congruence between the implant  10 R and the vertebral bodies as the amount of lordosis required for proper congruence and spinal foraminal opening can increase along with the increase in distance between the vertebral bodies. 
         [0152]    The implant  10 R can also have vertical constraints  2005 A and  2005 B which can be attached to the housing  111 . In the illustrated embodiment, the vertical constraints  2005 A and  2005 B can prevent wide portions  2003 A and  2003 B of the distal piston  122 A and proximal piston  122 B from advancing out of the housing  111 . In this manner, these vertical constraints  2005 A and  2005 B can limit the maximum vertical movement of the pistons  2222  and  2223  relative to the housing  111 . 
         [0153]      FIG. 53  illustrates yet another alternative embodiment. As shown in  FIG. 53 , an implant  10 S can have a distal piston  122 A that can have both a horizontal vertebral engagement surface  2240  and an angled vertebral engagement surface  2242 , such that the distal piston  122 A can have a variation in vertebral engagement surface angles. These variations in vertebral engagement surface angles can be beneficial for providing even better congruence between the implant  10 S and the vertebral bodies when a lordotic or variable height expansion is desired. The implant  10 S can also have a proximal piston  122 B with a higher horizontal vertebral engagement surface  2244  and a lower horizontal vertebral engagement surface  2246 , which can also improve congruence between the implant  10 S and the vertebral bodies when a lordotic or variable height expansion is desired. As will be recognized by a person of ordinary skill in the art, any combination of these varied vertebral engagement surfaces can be employed on either the distal piston  122 A, the proximal piston  122 B, the articulating top plate  113  or the posterior surface of the housing  111  to provide optimal vertebral body congruency. 
         [0154]    The features of the current invention have been described in terms of an implant comprised of a pair of cylinder/piston/lock/and related features, however it is obvious to those schooled in the art that the described features can be included in an implant with only a single set or more than two sets of these features. 
         [0155]    A lateral cage implant, as illustrated for exemplary embodiments of the present invention herein, is particularly advantaged by the use of anchors as described herein because the lateral approach to the spine is a long and narrow approach, which limits the ability of the surgeon to use other instrumentation to extend anchors from the cage (as can be done more readily, for example, with an anterior approach where the access is not as narrow). However, as will be appreciated by persons of ordinary skill in the art, while particular, additional advantages may be presented in connection with the lateral approach and cages designed therefore, anchors according to embodiments of the present invention are advantageous for any approach as they can produce the required extension forces regardless of patient anatomy or other restrictions on the use of alternative extension means by the surgeon. 
         [0156]    Elements of the description herein focused on the manner in which the locking elements are configured to lock the implant in extended configurations. Although this locking action resists the forces placed on the implant that would tend to force it back into a collapsed configuration, that is not the only force the locking elements address. Once inserted between vertebral bodies the implant is subject to lateral forces and torsion moments as well as compressive forces. The locking features along with the other elements of the invention are designed to resist all of these forces to provide an implant that provides stable fixation and distraction. 
         [0157]    A partial or complete discectomy is usually performed prior to the insertion of the spinal implant having features of the invention between vertebral bodies. The implant is introduced in its unexpanded state to enable it to be inserted posteriorly with minimal trauma to the patient and risk of injury to nerve roots. Once in place the implant can be expanded to provide both medial and lateral spinal correction. The implant has an unexpanded height of about 5 to about 15 mm, typically about 7 mm and is expandable to at least 130% to about 180% of the unexpanded height. Typically the implant is about 9 to about 15 mm wide, typically about 12 mm wide and about 25 to about 55 mm long, typically about 35 mm long to facilitate minimally invasive insertion and thereby minimize trauma to the patient and risk of injury to nerve roots. 
         [0158]    Additional details of the implant such as the attachment of hydraulic lines and lines for transmission of a slurry or liquid bone graft material, device and hydraulic fluid delivery accessories and the like can be found in co-pending application Ser. No. 11/535,432 filed on Sep. 26, 2006 and Ser. No. 11,692,800, filed on Mar. 28, 2007, which are incorporated herein by reference. 
         [0159]    It will be appreciated that the implant, including its various components should be formed of biocompatible, substantially incompressible material such as PEEK or titanium, and preferably type 6-4 titanium alloy or other suitable materials which will allow for long-term deployment within a patient. 
         [0160]    While the invention has been described in connection with what are presently considered to be the most practical and certain preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments and alternatives as set forth above, but on the contrary is intended to cover various modifications and equivalent arrangements included within the scope of the following claims. 
         [0161]    For example, while implants described herein are expanded by hydraulic fluid, other expansion means may be employed. For example, the screw mechanism described herein may be employed to expand scissor jacks within the implant to engagement adjacent vertebral surfaces. Further, the implant can be provided with load or pressure sensors that register differential pressure and pressure intensity exerted on the engaging surfaces of the SEC by the patient&#39;s vertebrae end plates to generate corrective signals, for example by computer control, that are used, e.g. by the surgeon or by a computer-controlled mechanism to realign the patient&#39;s spine. The invention may further include a system that makes these adjustments, responsive to sensor signals, in real time and on a continual basis, such that the shapes of the implant changes to realign the patient&#39;s spine or mechanism. Preferably, such system is contemplated for use in setting the positions of the pistons during installation of the implant. 
         [0162]    While particular forms of the invention have been illustrated and described herein, it will be apparent that various modifications and improvements can be made to the invention. Additional details of the spinal implant devices may be found in the patents and applications referenced herein. To the extent not otherwise disclosed herein, materials and structure may be of conventional design. 
         [0163]    Moreover, individual features of embodiments of the invention may be shown in some drawings and not in others, but those skilled in the art will recognize that individual features of one embodiment of the invention can be combined with any or all the features of another embodiment. Accordingly, it is not intended that the invention be limited to the specific embodiments illustrated. It is therefore intended that this invention be defined by the scope of the appended claims as broadly as the prior art will permit. 
         [0164]    Terms such as “element”, “member”, “component”, “device”, “means”, “portion”, “section”, “steps” and words of similar import when used herein shall not be construed as invoking the provisions of 35 U.S.C. §112(6) unless the following claims expressly use the terms “means for” or “step for” followed by a particular function without reference to a specific structure or a specific action. All patents and all patent applications referred to above are hereby incorporated by reference in their entirety.