Patent Publication Number: US-2020297507-A1

Title: Expandable vertebral implant

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/270,620, filed Sep. 20, 2016, which is a continuation application of U.S. patent application Ser. No. 13/711,204, filed Dec. 11, 2012. 
     This application is also a continuation of U.S. patent application Ser. No. 15/270,620, filed Sep. 20, 2016, which is a continuation-in part of U.S. patent application Ser. No. 14/940,322, filed on Nov. 13, 2015, which is a continuation of U.S. patent application Ser. No. 13/845,645, filed on Apr. 3, 2013, now U.S. Pat. No. 9,216,095, which is a continuation-in-part of U.S. patent application Ser. No. 13/451,230, filed on Apr. 19, 2012, now U.S. Pat. No. 8,518,120, which is a continuation-in-part of U.S. patent application Ser. No. 13/440,158, filed on Apr. 5, 2012, now U.S. Pat. No. 8,679,183, which is a continuation-in-part of U.S. patent application Ser. No. 13/273,994, filed on Oct. 14, 2011, now U.S. Pat. No. 9,358,126, which is a continuation-in-part of U.S. patent application Ser. No. 12/823,736, filed on Jun. 25, 2010, now U.S. Pat. No. 8,685,098, which is a continuation of U.S. patent application Ser. No. 12/579,833, filed on Oct. 15, 2011, now U.S. Pat. No. 8,062,375. The disclosures of all are being incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to stabilizing adjacent vertebrae of the spine by inserting an intervertebral spacer, and more particularly an intervertebral spacer that is adjustable in height. 
     BACKGROUND OF THE INVENTION 
     Bones and bony structures are susceptible to a variety of weaknesses that can affect their ability to provide support and structure. Weaknesses in bony structures have numerous potential causes, including degenerative diseases, tumors, fractures, and dislocations. Advances in medicine and engineering have provided doctors with a plurality of devices and techniques for alleviating or curing these weaknesses. 
     In some cases, the spinal column requires additional support in order to address such weaknesses. One technique for providing support is to insert a spacer between adjacent vertebrae. 
     SUMMARY OF THE INVENTION 
     In accordance with the disclosure, a joint spacer for therapeutically maintaining a separation of bones of a joint, comprises a frame having distal and proximal ends defining a longitudinal axis extending therebetween; a carriage slideably retained within the frame and having at least one ramped surface, the carriage further including a threaded portion; an actuator screw threadably engaged with the frame, the actuator screw configured to bear against the carriage to cause the carriage to slideably move within the frame when the actuator screw is rotated; a first endplate configured to engage a first bone of the joint, and having at least one surface mateable with the at least one carriage ramped surface, whereby when the carriage is slideably moveable by rotation of the actuator screw, the at least one endplate ramped surface slides against the at least one carriage ramped surface to cause the first endplate to move along an axis transverse to the longitudinal axis to increase a height of the spacer; and a second endplate configured to engage a second bone of the joint. 
     In one embodiment thereof, the carriage includes at least two ramped surfaces, and the second endplate includes at least one ramped surface mateable with at least one of the at least two ramped surfaces of the carriage, whereby when the carriage is slideably moved by rotation of the actuator screw, the at least one second endplate ramped surface slides against the at least one additional carriage ramped surface to cause the second endplate to move along an axis transverse to the longitudinal axis to increase a height of the spacer. 
     In other embodiments thereof, the first endplate is configured to abut the frame as the first endplate is moved along an axis transverse to the longitudinal axis, whereby the first endplate moves substantially only along an axis transverse to the longitudinal axis; the first endplate includes at least one aperture through which a fastener may pass to secure the first endplate to a bone of the joint; the spacer further includes a blocking mechanism to prevent backing out of a fastener passed through the first endplate; and the first endplate includes one or more projections configured to engage bone of the joint when the implant is positioned between bones of the joint. 
     In further embodiments thereof, at least one of the first and second endplates is composed of two interconnected portions of dissimilar materials; one of the dissimilar materials is metallic and includes at least one aperture through which a fastener may be passed to attach the implant to a bone of the joint; and one dissimilar material is polymeric, and another dissimilar material is metallic. 
     In yet further embodiments thereof, the actuator screw includes a flange, and the carriage includes a flange rotatably mateable with the actuator screw flange; the spacer further includes a thrust washer interposed between the actuator screw and the carriage; the spacer further includes a polymeric material configured to press against the actuator screw to reduce a potential for unintended rotation of the actuator screw; and the spacer further includes a plate having at least one aperture sized and dimensioned to receive an elongated fastener for fastening the spacer to bone of the joint, the plate being releaseably detachable from the spacer to reduce an profile of the spacer during insertion of the spacer into the body, the plate attached to the spacer inside the body. 
     In other embodiments thereof, the plate and the frame include mating portions of a twist-lock connector operable to connect the plate to the frame when the spacer is inside the body; the plate and the frame include mating portions of a snap-fit interference connector operable to connect the plate to the frame when the spacer is inside the body; the plate includes hinged portions, the hinged portions foldable to reduce a profile of the plate during insertion of the plate into the body; the at least one surface mateable with the at least one carriage ramped surface is at least one ramp; the at least one carriage ramp is disposed upon at least one cam, the cam rotatable to bear the at least one carriage ramp against the at least one surface of the first endplate; the first endplate includes a rotatable portion having first and second transverse axes of different lengths; and the rotatable portion is passable through an interior of the spacer. 
     In other embodiments thereof, the first endplate includes an aperture sized and dimensioned to receive an elongated fastener operable to pass through the aperture to affix the spacer to bone of the joint, the aperture movable with the first endplate as the first endplate is moved along the axis transverse to the longitudinal axis; and the first endplate includes a first portion having at least one aperture through which a fastener may pass to secure the first endplate to a bone of the joint, and a second portion configured to support bone of the joint, the first and second portions mutually connected by a dovetail connection. 
     In additional embodiments thereof, the spacer further includes a rotatable plate having at least two apertures through each of which a fastener may pass to secure the spacer to a bone of the joint, the rotatable plate rotatable after the spacer has been implanted within the body, to overlie the at least two apertures with bone of the joint; the spacer further includes a rotatable plate having at least two apertures through each of which a fastener may pass to secure the spacer to a bone of the joint, the rotatable plate rotatable after the spacer has been implanted within the body, to overlie the at least two apertures with bone of the joint; the spacer further includes at least one rotatable plate having an aperture through which a fastener may pass to secure the spacer to a bone of the joint, the rotatable plate rotatable after the spacer has been implanted within the body, to overlie the aperture with bone of the joint; and the spacer further includes at least two plates rotatably connectable to the spacer, each plate slidably connected to the other by a dovetail joint, each plate having at least one aperture through which a fastener may pass to secure the spacer to bone of the joint, the plates rotatable after the spacer has been implanted within the body, and each of the at least two plates slideable with respect to the other, to overlie the aperture of each plate with bone of the joint. 
     In yet further embodiments thereof, at least one of the carriage ramped surfaces is operative to push a piercing element through an aperture in the first endplate, the piercing element operative to pierce bone of the joint to secure the spacer within the body; the spacer further includes a bone screw having bone engaging threads and gear teeth, and the actuator screw including gear teeth engageable with the gear teeth of the bone screw, the actuator screw thereby rotated when the bone screw is threaded into bone of the joint; the spacer further includes a plate having an aperture through which a fastener may be passed to connect the spacer to bone of the joint, the plate including a dovetail portion; and the first endplate including a dovetail portion mateable with the dovetail portion of the plate, the plate and the first endplate thereby securely connectable to each other; and the spacer further includes a channel formed within the first endplate, the channel sized and dimensioned to receive an elongate portion of a fastener operative to secure the spacer within the body. 
     In other embodiments thereof, the spacer further includes at least one elongate rotatable deployer pivotally connected to the frame; at least one piercing element connected to the deployer, the at least one piercing element operable to pierce bone of the joint when the rotatable deployer is rotated within the body; the at least one piercing element is pivotally connected to the deployer to thereby enter bone of the body at a desired angle relative to a plane of the first endplate; the at least one rotatable deployer rotates about a common axis with respect to the actuator screw; the at least one rotatable deployer rotates when the actuator screw is rotated; and the at least one rotatable deployer rotates independently of the actuator screw. 
     In yet further embodiments thereof, the first endplate is pivotally connected to the frame; the first endplate pivots about the pivotal connection, about an axis extending transverse to the longitudinal axis; and the first endplate is connected to the frame to allow roll, pitch, and yaw movement of the first endplate with respect to the frame. 
     In another embodiment of the disclosure, a joint spacer for therapeutically maintaining a separation of bones of a joint, comprises a frame having distal and proximal ends defining a longitudinal axis extending therebetween; a carriage slideably retained within the frame and having at least one ramped surface, the carriage further including a flange; an actuator screw threadably engaged with the frame, the actuator screw including a flange rotatably mateable with the carriage flange, whereby the carriage is slideably moved when the actuator screw is rotated; a first endplate configured to engage a first bone of the joint, and having at least one ramped surface mateable with the at least one carriage ramped surface, whereby when the carriage is slideably moved by rotation of the actuator screw in a first direction, the at least one endplate ramped surface slides against the at least one carriage ramped surface to cause the first endplate to move along an axis transverse to the longitudinal axis to increase a height of the spacer; and a second endplate configured to engage a second bone of the joint. 
     In various embodiments thereof, when the actuator screw is rotated in an opposite, second direction, the at least one endplate ramped surface is slideable against the at least one carriage ramped surface to cause the first endplate to move along an axis transverse to the longitudinal axis to decrease a height of the spacer; the first endplate includes a metallic portion having an aperture through which a fastener may be passed for connecting the implant to body tissue, the first endplate further having a polymeric portion connected to the metallic portion, the polymeric portion sized and dimensioned to support a bone of the joint; the frame and the first endplate include mateable dovetailed portions configured to maintain an orientation of the first endplate and the frame when the first endplate is positioned proximate the frame. 
     In another embodiment of the disclosure, a method for therapeutically maintaining a separation of bones of a joint, comprises inserting a spacer between bones of the joint, the spacer including—a frame having distal and proximal ends defining a longitudinal axis extending therebetween; a carriage slideably retained within the frame and having at least one ramped surface, the carriage further including a flange; an actuator screw threadably engaged with the frame, the actuator screw including a flange rotatably mateable with the carriage flange, whereby the carriage is slideably moved when the actuator screw is rotated; a first endplate configured to engage a first bone of the joint, and having at least one ramped surface mateable with the at least one carriage ramped surface, whereby when the carriage is slideably moved by rotation of the actuator screw in a first direction, the at least one endplate ramped surface slides against the at least one carriage ramped surface to cause the first endplate to move along an axis transverse to the longitudinal axis to increase a height of the spacer; and a second endplate configured to engage a second bone of the joint; the spacer inserted when the first endplate is positioned proximate the frame; and slideably moving, by rotation of the actuator screw, the at least one endplate ramped surface against the at least one carriage ramped surface to cause the first endplate to move along an axis transverse to the longitudinal axis to increase a height of the spacer to maintain a separation of bones of the joint. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which: 
         FIG. 1  depicts a perspective view of a spacer in accordance with the disclosure, including bone fasteners, the spacer in a reduced height, or compressed configuration; 
         FIG. 2  depicts the spacer of  FIG. 1 , in an increased height, or expanded configuration; 
         FIG. 3  depicts a front view of the spacer of  FIG. 1 ; 
         FIG. 4  depicts a front view of the spacer of  FIG. 2 ; 
         FIG. 5  depicts a cross-section taken through a center of the spacer of  FIG. 2 ; 
         FIG. 6  depicts a top view of the spacer of  FIG. 1 ; 
         FIG. 7  is a diagram of a possible implantation location in the body, for the spacer of  FIG. 1 ; 
         FIG. 8  depicts an embodiment of a spacer in accordance with the disclosure, including a fixation plate that is removeably connectable to a remainder of the spacer, the fixation plate shown removed; 
         FIG. 9  depicts a connector for connecting the fixation plate to a remainder of the spacer, with respect to  FIG. 8 ; 
         FIG. 10  depicts the spacer of  FIG. 8 , the fixation plate attached; 
         FIG. 11  depicts a reverse side of the spacer of  FIG. 10 ; 
         FIG. 12  depicts a front view of the spacer of  FIG. 10 ; 
         FIG. 13  depicts a side view of an embodiment of a spacer in accordance with the disclosure, the spacer including a detached fixation plate having a snap-fit attachment; 
         FIG. 14  depicts the spacer of  FIG. 13 , the fixation plate snap-fit into attachment; 
         FIG. 15  depicts the fixation plate of  FIG. 13 ; 
         FIG. 16  depicts a hinged fixation plate in accordance with the embodiment of  FIG. 13 ; 
         FIG. 17  depicts the hinged fixation plate of  FIG. 16 , the hinged portions folded, and further showing barbs upon the hinged portion; 
         FIG. 18  depicts an embodiment of a spacer in accordance with the disclosure, including cams operative to increase a height of the spacer, the spacer in a reduced height configuration; 
         FIG. 19  depicts the spacer of  FIG. 18 , the cams actuated to increase a height of the spacer; 
         FIG. 20  depicts an embodiment of a spacer in accordance with the disclosure, the spacer including rotatable endplate portions; 
         FIG. 21  depicts an end view of the spacer of  FIG. 20 ; 
         FIG. 22  depicts the spacer of  FIG. 21 , the rotatable endplate portion rotated; 
         FIG. 23  depicts an embodiment of a spacer in accordance with the disclosure, having endplates that translate together with endplates, as endplates are moved to increase a height of the spacer; 
         FIG. 24  depicts the spacer of  FIG. 23 , the spacer expanded to have an increased or expanded height; 
         FIG. 25  depicts a side view of an embodiment of a spacer in accordance with the disclosure, the spacer having connectable fixation portions and endplate support portions; 
         FIG. 26  depicts a cross-section of the spacer of  FIG. 25 ; 
         FIG. 27  illustrates an embodiment of a spacer including connectable fixation portions and endplate support portions, the portions connectable by a dovetailed connection; 
         FIG. 28  depicts a cross-section of the device of  FIG. 27 ; 
         FIG. 29  depicts an embodiment of a spacer of the disclosure, including a rotatable fixation plate; 
         FIG. 30  depicts the spacer of  FIG. 29 , the fixation plate rotated; 
         FIG. 30A  depicts an embodiment of a spacer of the disclosure, including two rotatable fixation plates, rotated to a deployment position; 
         FIG. 31  depicts an embodiment of a spacer of the disclosure including two rotatable fixation portions connected by a sliding dovetail connection; 
         FIG. 32  depicts the spacer of  FIG. 31 , the fixation portions relatively displaced and rotated; 
         FIG. 33  depicts a cross-section the spacer of  FIG. 31 ; 
         FIG. 34  depicts an embodiment of a spacer of the disclosure, including deployable piercing elements; 
         FIG. 35  depicts the spacer of  FIG. 34 , the piercing elements deployed; 
         FIG. 36  depicts an embodiment of a spacer of the disclosure, including a bone fixation device having gear teeth mateable with gear teeth of an endplate actuator screw; 
         FIG. 37  depicts the spacer of  FIG. 36 , the bone fixation device deployed to engage bone, and to increase a height of the spacer; 
         FIG. 38  depicts an embodiment of a spacer of the disclosure, including a dovetail connection between a fixation portion, and a bone endplate support portion; 
         FIG. 39  depicts the fixation portion of the spacer of  FIG. 38 ; 
         FIG. 40  depicts the bone endplate support portion of the spacer of  FIG. 38 ; 
         FIG. 41  depicts an embodiment of a spacer in accordance with the disclosure, including channels in endplate portions; 
         FIG. 42  depicts a top view of an embodiment of a spacer in accordance with the disclosure having deployment arms rotatably supporting piercing elements; 
         FIG. 43  depicts a cross section of the spacer of  FIG. 42 ; 
         FIG. 44  depicts the spacer of  FIG. 43 , the piercing elements deployed; 
         FIG. 45  depicts an embodiment of a spacer in accordance with the disclosure, including a deployment arm having a common axis with an actuator screw; 
         FIG. 46  depicts a cross section of the spacer of  FIG. 45 ; 
         FIG. 47  depicts the spacer of  FIG. 46 , the piercing elements deployed; 
         FIG. 48  illustrates an alternative spacer in accordance with  FIG. 45 , the deployment arm independently rotatable; and 
         FIG. 49  illustrates an embodiment of a spacer in accordance with the disclosure, an endplate pivotable about a transverse axis. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As required, detailed embodiments are disclosed herein; however, it is to be understood that the disclosed embodiments are merely examples and that the systems and methods described below can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present subject matter in virtually any appropriately detailed structure and function. Further, the terms and phrases used herein are not intended to be limiting, but rather, to provide an understandable description of the concepts. 
     The terms “a” or “an”, as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms “including” and “having,” as used herein, are defined as comprising (i.e., open language). 
     With reference to  FIGS. 1-7 , spacer  100  is operative, when positioned between adjacent bones of a joint, such as for example vertebrae  10 ,  12  (shown in  FIG. 7 ), to stabilize a joint formed between adjacent vertebrae. Spacer  100  has a collapsed state or height, illustrated in  FIGS. 1 and 3 , and an expanded state or height, illustrated in  FIGS. 2, 4 and 5 . Spacers  100  of the disclosure may be inset into the intervertebral disc space at a collapsed height, and then expand axially (superior/inferior) to restore height loss in the disc space. Spacer  100  provides distraction as well as achieves optimal separation of adjacent vertebrae, or disc height restoration. When inserted in a collapsed state, Spacers  100  have a reduced height profile which reduces adverse impact to tissue adjacent to and within the joint space during insertion, while presenting the least visually blocking or physically obstructing profile. Spacer  100  may be reduced in height after implantation, for example by inserting a tool through a minimal incision, to perform a therapeutic height adjustment. Spacer  100  may also be reduced in height to a compressed configuration, to facilitate removal from the body. Spacer  100  supports the cortical rim of adjacent vertebrae, and distributes forces across the vertebra, thereby maximizing vertebral endplate preservation. 
     Spacer  100  includes two separable endplates  110 ,  112 . A surface  114  of an endplate  110 ,  112  can be provided with teeth or other projections  116  which can penetrate body tissue to reduce a likelihood of migration of spacer  100  after implantation. Spacer  100  is further secured with one or more fasteners, such as bone screws  300 , which pass through an adapter, such as bone screw socket  118  within spacer  100 , and into body tissue of the patient. In the embodiment illustrated in  FIGS. 1-5 , two sockets  118  for two bone screws are provided, although one or more than two fasteners and fastener adapters, may be provided. Bone screws  300  can be retained in connection with spacer  100  by blocking fasteners  120 . Bone screw  300  can be a polyaxial screw, and sockets  118  correspondingly shaped, whereby bone screw  300  may be inserted into body tissue at an optimal angle with respect to spacer  100 , whereby optimal purchase may be obtained, or certain body tissue may be avoided. 
     Endplates  110 ,  112  are moveably connectable to an actuator  150  operable to change a relative relationship of endplates  110  and  112 . Actuator  150  includes a frame  152  rotatably supporting an actuator screw  154 , and a moveable carriage  156 . As actuator screw  154  rotates within frame  152 , carriage  156  slides within frame  152 , driven by cooperation between threads  158  upon actuator screw  154 , and mating threads  160  within frame  152 . An implantation tool engagement surface  330  may be provided upon or within spacer  100 , configured to receive a tool to enable secure manipulation of spacer  100  during implantation or removal from the body. 
     In the embodiment of  FIGS. 1-6 , endplates  110  and  112  are formed in two connected portions, including a portion  122 ,  122 A which can be polymeric, for example PEEK, and a fixation portion  124 ,  124 A, which can be metallic, for example titanium, although other materials may be used. For example, material used for fixation portion  124  should withstand the bending forces exerted by a fastener, for example bone screw  300 , passing therethrough. In contrast, endplate material advantageously resiliently withstands a pressure applied by weight of the body. In this regard, both materials could also be polymeric, for example, but of different types of polymer. 
     The portions  122 ,  124  or  122 A and  124 A are joined in the embodiment shown by screws, a mechanical interlock, adhesive, or other fasteners, possibly in combination, as explained further herein. Metallic portions  124 ,  124 A can provide greater strength for portions of spacer  100  which are under relatively greater stress, for example portions through which a fastener may pass to anchor spacer  100  within the body. While portions  122 ,  122 A,  124 ,  124 A are described as polymeric or metallic, it should be understood that other materials may be used, and that the portions can be of similar or dissimilar materials, as described further herein. 
     With reference to  FIGS. 1 and 3 , it may be seen that spacer  100  is in a compressed state, having a lower height relative to an expanded state, as shown in  FIGS. 2 and 4 . A functioning of device  100  may be best understood with reference to  FIG. 5 , which is a cross-section through the center of spacer  100 . Endplates  110  and  112  are provided with ramps  164 , sized to slidingly receive ramps  168  disposed upon carriage  156 . While three mating ramps  164 ,  168  are illustrated for each endplate  110 ,  112 , it should be understood that one, two, or more than three sets of ramps  164 ,  168  may be provided. Mating ramps  164 ,  168  operate to enable a reduction or increase in height by sliding against each other as actuator screw  154  is rotated. Interlocking flanges  204 ,  204 A rotatably couple actuator screw  154  and carriage  156 , whereby actuator screw may rotate and advance or retard in connection with frame  152 , concomitantly advancing or retarding carriage  156  along a longitudinal axis of spacer  100  extending from a distal end  186  and a proximal end  182  of frame  152 . A reduction in height is further fostered by a pressure exerted by body tissue. 
     As may further be seen in  FIG. 5 , ramps  164  can include channels  164 A within endplates  110 ,  112 , and ramps  168  may include dovetail portions  168 A which extend into ramps  164 . By projecting a dovetail portion  168 A of ramp  168  into channels  164 A, endplates are moveably affixed to carriage  156 . Dovetail portions  168 A and channels  164 A may further support a predetermined relative orientation of endplates  110 ,  112  when in a compressed or expanded configuration, while they are being expanded, and when spacer  100  is inserted and removed from the body. It should further be understood that a relative orientation of endplates  110 ,  112  may be substantially parallel, or may be non-parallel, for example to produce an effective lordosis. Further, planes defined by an interior portion of endplates  110 ,  112  may be relatively parallel, but bone contacting surfaces may be relatively non-parallel. 
     Carriage  156  is alternatively or further supported by frame  152  by lateral engagement means, in the embodiment shown there are two support screws  174  engaged with carriage  156 , and passable through respective channels  176  formed in frame  152 . 
     A hex driver (not shown) is inserted into engagement with an end of actuator screw  154  at a proximal end  182  of frame  152 . As actuator screw  154  is turned, distal end  172  bears against a thrust washer  184 , and an end portion of frame  152 . As actuator screw  154  rotates in one direction, carriage  156  is driven along actuator screw by interaction of threads  158  and  160  and flanges  204 ,  204 A. As carriage  156  moves, endplates  110 ,  112  are urged to move along ramps  168 , and  168 A if present, causing endplates  110 ,  112  to thereby moving relatively apart, and to increase a height of spacer  100 . Endplates  110 ,  112  are moved relative to carriage  156  by abutting against an end portion  186  of frame  152 . End portion  186  can include an internal ramped surface  170  mateable with a ramp  168 , as shown in this embodiment, thereby providing additional stability in an expanded configuration. 
     In a given orientation, one of endplate  110  and  112  is an upper endplate with respect to an orientation in a standing patient. However, spacer  100  may, in some embodiments, be implantable in either of opposite orientations, and therefore designations of upper and lower are provided for ease of understanding, only. It should further be understood that only one of endplate  110 ,  112  may be moveable with respect to the other. For example, in one embodiment, ramps  168 ,  168 A may not be provided, and endplate  112  may be attached to frame  152 . 
       FIG. 7  illustrates a spacer  100  of the disclosure implanted between adjacent vertebrae  10 ,  12 . Frame  152  defines a distal or leading end  186  which is inserted first into the body, and a proximal or trailing end  182  which passes last into the body, the distal and proximal ends defining a longitudinal axis extending therebetween. Spacer  100  can be inserted into the body, and into a position between vertebrae, using minimally invasive methods, for example using a small incision, and spacer  100  may be passed through a cannula or other structure which maintains a pathway through body tissue. Spacer  100  may be inserted into the spinal column through any approach, including anterior, anterolateral, lateral, posterolateral, or posterior. A portion of the disc annulus, and nucleus pulposus may be removed in order to form a space into which spacer  100  may be inserted. 
     Spacer  100  can be inserted when configured to have a lower height profile, as shown in  FIGS. 1 and 3 , whereby an extent of distraction of body tissue may be reduced during insertion. Moreover, to the extent that spacer  100  is used to open a pathway towards an implantation site, trauma to adjacent tissue is reduced relative to inserting a spacer having a final height profile. Once spacer  100  is positioned between adjacent vertebrae, actuator screw is rotated by a tool. The tool may be positioned entirely within the body, or can extend from in interior of the body to outside the body, for example having a driving tip at one end and having a handle at an opposite end, with a shaft extending into the body between each end. 
     Once actuator screw  154  has been rotated to separate endplates  110 ,  112  a desired amount, the tool is removed. At this point, actuator screw  154  may be secured in place, for example using a mechanical block, or an adhesive, to prevent unintended rotation of actuator screw  154 . As carriage  156  is slideably moved by rotation of actuator screw  154 , ramps  164 ,  168  of endplates  110 ,  112  slide against each other, to cause the endplate to move along an axis transverse to the longitudinal axis of the frame, to increase a height of the spacer. Rotation of actuator screw  154  in an opposite direction causes movement along an axis transverse to the longitudinal axis of the frame to decrease a height of the spacer. 
     In  FIG. 6 , it may be seen that spacer  100  has an elongated, narrow profile, facilitating insertion from a lateral approach. Bone ingrowth apertures  332  may be provided, to promote the ingrowth of bone of the patient to further stabilize spacer  100 , or to achieve fusion, should that be a therapeutic objective. 
     Polymeric insets, or a polymeric square nut, for example PEEK, can be provided, engageable with threads  158  or other portion of actuator screw  154 , to provide additional friction to prevent height loss under load, particularly under cyclic loading. Similarly, once bone screws  300  have been inserted, blocking elements  196  may be rotated to extend over an end of bone screw head  302 , preventing screw  300  from backing out. To enable insertion of bone screw  300 , a notched portion  196 A is formed in blocking element, and which may be rotated into a position adjacent aperture  118 . A similar mechanical block (not shown) may be provided for actuator screw  154 . 
     With reference to the figures, it may be seen that sockets  118  move with endplate  110  or  112 , as spacer  100  expands to a final height, whereby sockets  118  overlie cortical bone of vertebrae  10 ,  12  after spacer  100  is expanded. 
     In an embodiment, spacer  100  of the disclosure provides an actuator that translates relative to the body by means of a threaded actuator screw  154 . Ramps  168 ,  168 A on a carrier  152  mate with ramps  164 ,  164 A on endplates  110 ,  112 . Linear translation of carriage  152  causes endplates  110 ,  112  to expand spacer  100  along an S/I axis with respect to the body. 
     In one embodiment, two bone screws  300  are used to provide fixation into adjacent vertebral bodies, a screw extended from each of endplates  110  and  112 . Spacer  100  can thus be narrow, to therapeutically fit between vertebrae when inserted from a lateral approach. However, one screw, or more than two screws  300  may be used. Bone screws  300  can have spherical or otherwise curved heads, facilitating insertion at a desired angle, or may be provided to mate with socket  118  in a fixed orientation, for example depending on a diameter of a neck portion of screw  300 . Cam type blocking fasteners  196  can be used to block bone screws  300  from backing out after being inserted. 
     Referring now to  FIGS. 8-12 , a spacer  100 A is similar to spacer  100 , however a fixation plate  210  is rotatably fastened to a collar  212  extending from frame  152 A. The collar includes an interlock  214 , in the example shown a twist-lock connector, although any means of mechanically fastening fixation plate  210  to the remainder of spacer  100 A may be used, provided that fixation plate  210  and actuation screw  154  may be rotated as described herein. Fixation plate  210  enables spacer  100 A to be inserted into the body with fixation plate  210  rotated to have a longitudinal axis aligned with a transverse axis of spacer  100 A, whereby the combined spacer  100 A and fixation plate  210  may have a reduced height, and whereupon a reduced sized incision may be used to implant spacer  100 A with fixation plate attached. After implantation, fixation plate  210  may be rotated, for example about 90 degrees, so that sockets  118  overlie bone of adjacent vertebrae. Rotation may be any amount, however, for example 45 to 135 degrees. 
     Alternatively, spacer  100 A may be implanted without fixation plate  210  attached, and through a reduced size incision, with less disturbance to body tissue. Fixation plate may then be attached to spacer  100 A in situ. In this manner, fixation plate  210  may be inserted through the same entry as spacer  100 A, with fixation plate  210  aligned along a longitudinal while being passed through the incision. Once positioned proximate spacer  100 A, fixation plate  210  may be reoriented to be attached to spacer  100 A, and rotated to align sockets  118  with bone. Rotation of fixation plate  210  can be performed after expansion of spacer  100 A, facilitating alignment of sockets  118  with bone. 
     It should be understood that the various embodiments described herein with respect to spacer  100  and frame  152  may be applied equally to spacer  100 A and frame  152 A, and any other variants thereof described herein, and are described separately only to facilitate an understanding of each embodiment. More particularly, various embodiments of this disclosure are intended to be combinable in a manner that would be apparent to the practitioner and therapeutic for the patient. 
     In one embodiment, fixation plate  210  may only be attached to spacer  100  when a longitudinal axis of fixation plate  210  is substantially aligned with a transverse axis of spacer  100 , and when fixation plate  210  is rotated to overlie bone, fixation plate  210  is securely affixed to spacer  100 . For example, in  FIG. 9 , an embodiment of interlock  214  is illustrated, including flanges  216  which engage mating flanges  218  disposed upon fixation plate  210 . Flanges  216 , and or the mating flanges, can be ramped or cammed, so that when engaged, fixation plate  210  and spacer  100  become progressively more tightly interconnected. 
     In another embodiment, shown in  FIGS. 13-17 , fixation plate  210  is preliminarily held in place using a snap-fit connector  220 , functioning to secure fixation plate to spacer  100 , or cooperating with interlock  216 . Snap-fit connector  220  forms at least a preliminary connection between fixation plate  210  and spacer  100 , to facilitate handling by the medical practitioner. A plate mounting screw  334  may be connected, for example threaded into a threaded bore of actuator screw  154 , to further secure fixation plate  210  to a remainder of spacer  100 . Fixation plate may be rotated when connected by snap-fit connector  220 . Set screws  226  may be passed through apertures  226 A to affix fixation plate  210  once it has been rotated. Snap fit connector  220  comprises extension tangs  222  extend from spacer  100 , and form a resilient interference fit with snap-fit aperture  224  upon fixation plate  210 . Snap-fit aperture  224  may be formed upon spacer  100 , and extension tangs may extend from fixation plate  210 . Additionally, references to spacer  100  should be considered to include similar embodiments, including spacer  100 A. 
     With reference to  FIGS. 16 and 17 , fixation plate  210 A includes, in another embodiment of the disclosure, folding or hinged portions  228  which may contain sockets for bone screws  300  or other fastener. When inserting fixation plate  210 A, hinged portions  228  are folded either on a lateral, longitudinal, or other axis of the fixation plate along one or more hinges  230 , as shown in  FIG. 11 , to reduce a maximum dimensional profile of fixation plate  210 A. In this manner, fixation plate  210 A may pass through a reduced size incision as compared to a requirement for an unfolded fixation plate. In an embodiment, tangs or barbs  232  may extend from fixation plate  210  or  210 A. to engage body tissue, for example cortical bone of a vertebra, to provide further fixation and stability when bone screws are passed through the fixation plate and into body tissue. Additionally, hinged portions  228  may be angled to permit a bone fastener passed therethrough, for example bone screw  300 , to enter bone of the joint at a beneficial or desired angle. 
     Referring now to  FIGS. 18-19 , one or more expansion cams  240  are disposed between endplates  110 ,  112 . A tool is inserted into a socket  242  which may be rotated to rotate the cam (as shown by arrows) to separate endplates  110 ,  112 . Expansion cams  240  can be supported upon a shaft (not shown) connected to frame  152 . Endplates  110 ,  112  can be supported and guided by ramp channels  164 A,  168 A, as described with respect to  FIG. 5 . 
     Turning now to  FIGS. 20-22 , in an alternative embodiment, endplates  110 ,  112  include one or more rotating endplate sections  250 A,  250 B which engage body tissue to therapeutically increase a height of spacer  100 B. In the embodiment shown, two rotating endplates sections are illustrated, each containing a transverse dimension having a first width, and a second longitudinal dimension having a second, greater width. Spacer  100 B can be inserted into the body with sections  250 A,  250 B rotated to have a same or lesser height than a remainder of spacer  100 B, to reduce an incision size, and to fit within an opening formed between adjacent vertebrae. After spacer  100 B has been positioned between vertebrae, sections  250 A,  250 B may be simultaneously or consecutively rotated to contact body tissue, for example cortical bone, to distract the joint. Section  250 B is disposed on a proximal side of spacer  100 B, and may be rotated by inserting a tool, for example tool  252 , through or into a mating socket  254 , and rotating tool  252 . Sections  250 A,  250 B are rotatably coupled to spacer  100 B by a pivot shaft, which may be engaged by tool  252 , or by another mating engagement between section  250 A,  250 B and a remainder of spacer  100 B, for example a flange (not shown). 
     Section  250 A is inserted first into the body, and to facilitate insertion, and to reduce interference with body tissue, section  250 A may be rotated so that section  250 A and a remainder of spacer  100 B form a compressed or unexpanded profile. For example, section  250 A is rotated so that the longest dimension is transverse to an S/I orientation in the body, and is thus adapted to fit within a space formed between adjacent vertebrae prior to distraction. To distract the joint, tool  252  is inserted into an interior of spacer  100 B, and is engaged with a socket  254  associated with section  250 A, and is rotated to orient section  250 A so that a tallest dimension is aligned with an S/I axis of the patient, distracting the joint. 
     With reference to  FIG. 20 , in one embodiment, section  250 A fits between endplates  110 ,  112  when rotated in the transverse orientation, to facilitate insertion between vertebrae. After implantation, section  250 A is pushed distally to emerge from between endplates  110 ,  112 , whereupon it may be rotated to distract, aid in distraction, or maintain a separation of vertebrae. Tool  252  is connected to section  250 A by a tether  256 , operative to maintain section  250 A in contact with a remainder of spacer  100 B, in cooperation with a biasing element  258 , disposed within tool  252 . In  FIG. 20 , section  250 A is illustrated in three stages of insertion, illustrated by  250 A- 1 ,  250 A- 2 , and  250 A- 3 . In the first stage, illustrated as  250 A- 1 , tool  252  is engaged with section  250 A and begins pushing section  250 A along an interior of spacer  100 B defined between endplates  110 ,  112 . In the second stage, illustrated as  250 A- 2 , tool  252  has pushed section  250 A to an end of an interior of spacer  100 B. In the third stage, illustrated as  250 A- 3 , tool  252  has pushed section  250 A to emerge from between endplates  110 ,  112 , whereupon tool  252  may then rotate section  250 A to orient a long axis of section  250  along an S/I orientation within the body. Tether  256  may be secured within spacer  100 B to maintain section  250 A in position at a distal end of spacer  100 B. Tool  252  may then be disengaged from spacer  100 B and removed from the patient.  FIG. 21  illustrates section  250 A oriented transverse to an S/I orientation, to reduce a height of spacer  100 B.  FIG. 22  illustrates section  250 A rotated to distract or maintain a separation of vertebra. Projections  260  can be provided, oriented to pierce body tissue to foster maintenance of a position of spacer  100  within the body. 
     Referring now to  FIGS. 23-24 , fixation portions  124 ,  124 A separate relative to each other as endplates  110 ,  112  are expanded as described herein. In this embodiment, fixation portions  124 ,  124 A can slideably mate with an actuating section  208 , or may only be affixed to their respective endplate  110 ,  112 . One manner of forming a slidable mating connection is described with respect to  FIGS. 31-33 , herein. By remaining in a fixed position relative to their respective endplate  124 ,  124 A, portions  124 ,  124 A are properly aligned to secure a fastener through socket  118  into cortical bone of adjacent vertebrae  10 ,  12 . 
     In  FIGS. 25-26 , a manner of connecting endplates  110 ,  112  to fixation portions  124 ,  124 A is illustrated. Fixation portions  124 ,  124 A and endplates  110 ,  112  are mutually shaped to be mateably connected, for example by a coupling fastener  262 , in this embodiment a screw. In the embodiment shown, endplate  110  and fixation portion  124  are illustrated, however it should be understood that a similar or different connection mechanism may be employed for endplate  112  and fixation portion  124 A. 
     A similar connection between endplate  110  and fixation portion  124  may be seen in  FIG. 27 , in which it may also be seen that screw  300  can be countersunk within fixation plate  124 . Socket  118  may additionally be a polyaxial socket, and can include a blocking element  196 .  FIG. 28  illustrates that the in addition to, or in an alternative to the use of coupling fastener  262 , endplate  110 / 112  and fixation portion  124 / 124 A may be joined by shaped coupling, for example a dovetail, tongue-in-groove, or T-connection. As an alternative to coupling fastener  262 , an adhesive may be used, or alternatively, the shaped coupling may produce an interference fit between endplate  110 / 112  and fixation portion  124 / 124 A. While  FIG. 28  illustrates fixation portion  124  (or  124 A) inserted within endplate  110  (or  112 ), it should be understood that this configuration could be reversed, with endplate  110 / 112  inserted within fixation portion  124 / 124 A. 
     In  FIGS. 29-30 , fixation portions  124 ,  124 A swivel so that socket  118  can be positioned over cortical bone of a vertebra  10 ,  12 . In the illustration, portions  124 ,  124 A are connected, or are formed as a single rotating fixation plate  266 , and rotate together about a single pivot. In  FIGS. 29-30 , the pivot is centrally located about the same axis as actuator screw  154 , however the pivot may be located elsewhere. In one embodiment, an endplate pivot pin  274  extends between an endplate  110 / 112  and plate  266 , causing plate  266  to rotate about the central axis as endplate  110 / 112  is moved with respect to the central axis. Alternatively, as illustrated in  FIG. 30A , fixation portions  124 ,  124 A may be separate, and each pivot on its own pivot,  264 ,  264 A. In this embodiment, as well as other pivoting embodiments, one or more endplate pivot pins  274  may be provided to cause a controlled rotation of a rotatable plate, for example one or both of separated plates  124 ,  124 A. 
     With reference to  FIGS. 31-33 , rotating fixation plate  268  is formed in two slidingly mateable plates  268 A,  268 B. An exemplary interconnection between plates  268 A,  268 B is illustrated in  FIG. 33 , in which a dovetail or interlocking engagement  270  may be seen. In this embodiment, interlocked plates  268 A,  268 B are secured in connection with a remainder of spacer  100 , and rotate about, a pivot  272 . In one embodiment, pivot  272  is associated with actuator screw  154 . In a related embodiment, rotation of actuator screw  154  causes a rotation of plate  268  due to a mechanical connection between actuator screw  154  and plate  268 . In another embodiment, pivot  272  is formed coaxial with, but separate from actuator screw  154 . 
     Referring now to  FIGS. 34-35 , blades, spikes, pins, or piercing elements  276  are disposed within piercing guides  278  formed within spacer  100 , for example within endplates  110 ,  112 . Only relevant portions of spacer  100  are illustrated in  FIGS. 34-35 , to clarify this feature of the disclosure. In one form, piercing element  276 A passes through a portion of ramp  164 , and is pushed by ramp  168  as actuator screw  154  is rotated to engage mating ramps  164 ,  168 . Piercing element emerges through endplate  110  or  112  to pierce body tissue, for example cancellous or cortical bone of adjacent vertebrae  10 ,  12 . In this manner, spacer  100  is further affixed in a therapeutic location within the body. By providing additional fixation in the form of piercing elements  276 , spacer  100  is better adapted to function without supplemental support, as a standalone device, without for example other fixation or fusing devices. Additionally, piercing elements herein can provide sufficient fixation so that a fixation portion  124 ,  124 A can optionally be eliminated, and fixation exterior to the intervertebral space may be avoided. 
     In another embodiment shown in  FIGS. 34-35 , piercing element  280  is formed as a resilient curved member which is straightened as it is pushed by a portion of carriage  156 . During straightening, piercing element  280  elongates to pass through endplate  110 ,  112  to pierce body tissue. 
     In  FIGS. 36-37 , bone screw  300 A is formed with gear teeth  282  disposed to lie along a longitudinal axis of the screw, as well as standard bone engaging threads substantially transverse to this longitudinal axis. Actuator screw  154 A includes external gear teeth  284  mateable with gear teeth  282  of bone screw  300 A, whereby when either bone screw  300 A or actuator screw  154 A is rotated, endplates  110 ,  112  separate to increase a height of spacer  100 , and bone screw  300 A is simultaneously driven into body tissue to therapeutically secure implant  100  to bone. 
       FIGS. 38-40  illustrate a method of connecting endplate  110 / 112  to fixation portion  124 / 124 A, using a mortise and tenon or dovetail connection  286 . A keyed aperture  288  disposed within fixation portion  124  or endplate  110  mateably receives a correspondingly shaped projection  290  in the other of fixation portion  124  and endplate  110 . A similar connection may be formed between fixation portion  124 A and endplate  112 . Aperture  288  and projection  290  may form an interference fit, or may alternatively be secure in mating conformity using a set screw or adhesive, for example. 
     With reference to  FIG. 41 , it may be seen that one or both of endplate  110 ,  112  may be beveled, truncated, fenestrated, or shaped with a gap, groove, or channel  292  in endplate  110 ,  112 , dimensioned to permit passage of a bone screw  300 , whereby a maximum height of spacer  100 , with the exception of bone screw  300 , is defined by an expanded height of endplates  110 ,  112 . Channel  292  can allow passage of a shank  294 , or any other portion of bone screw  300  or other fastener, so that socket  118  does not lie at a height greater than an endplate  110 ,  112 . 
     Turning now to  FIGS. 42-44 , an embodiment of the disclosure includes one or more piercing elements  276 A, pivotally mounted to rotatable deployers  310 . Piercing elements  276 A may have any shape which is adapted to pierce, grip, or engage body tissue, including pin, spike, or blade configurations. Although drawn as separate blades in  FIG. 42 , it should be understood that elements  276 A may extend along a substantial length of a longitudinal axis of spacer  100 , and may be supported by one, two, or more deployers  310 . An axle, pin, or shaft  296  pivotably mounts deployer  310  to frame  152 , carriage  156 , or other mounting point of suitable strength, upon spacer  100 , so that deployers  310  may rotate about a longitudinal axis aligned with a longitudinal axis of spacer  100 , although mounting along a different axis can be provided. In  FIGS. 42-44 , spacer  100  is illustrated without endplates  110 ,  112  and associated ramps, to simplify the illustrations. It may be seen, however, that ramps  164 ,  168  may be reduced in size to allow room for one or more deployers  310 . 
     In use, a tool (not shown) is engaged with an engagement port  198  and is rotated to rotate a deployer  310 , to advance piercing element  276 A through an opening or gap in an endplate  110 / 112 . In one embodiment, piercing element  276 A is fixed to an end of deployer  310 , and enters body tissue at an angle with respect to a plane defined by an endplate  110 / 112 . In the embodiment shown, piercing element is pivotally mounted to deployer  310  at pierce pivot  312 , and can be guided, for example by guide  314 , which may be a shaped channel in endplate  110 / 112 , to enter body tissue, for example bone of a vertebra  10 / 12 , substantially perpendicular to a plane defined by an endplate  110 / 112 , or at a particular desired angle or within a range of angles. Piercing elements  276 A therapeutically secure implant  100  to bone or body tissue of the joint. 
       FIGS. 45-47  contain elements analogous to  FIGS. 42-44 , however deployer  310  rotates about a common axis with actuator screw  154 , and therefore relatively larger ramps  164 ,  168  can be maintained. Piercing elements  276 B may further be longer, as a length of an arm  316  of deployer  310 A may be longer. 
     In  FIG. 48 , a collar  320  is connected to deployer  310 A, and rotates about a common axis with actuator screw  154 , but may be rotated independently of actuator screw  154  using tool engagement port  322 . In another embodiment, actuator screw is directly connected to deployer  310 A, and causes deployment of piercing elements  276 A as endplates  110 ,  112  are expanded as described herein. In a yet further embodiment, actuator screw rotates deployer  310 A through a gear reduction (not shown), whereby deployer  310 A rotates about the common axis more slowly than actuator screw  154 , so that increased leverage may be applied to piercing elements  276 A. 
     With reference to  FIG. 49 , in an embodiment of the disclosure, endplates  110 ,  112  can pivot about an axis  324  extending transverse to a longitudinal axis of spacer  100 , or along an axis that extends along an S/I direction when spacer  100  is implanted within a patient. For example, one or more pivot pins  326  may extend from an endplate  110  to frame  152 , or may extend from endplate  110  to endplate  112 . In this manner, spacer  100  may accommodate an additional rotational degree of freedom, for example, spacer  100  may support six degrees of freedom of movement of adjacent vertebrae. This is accomplished in one embodiment by enabling movement of ramped surfaces  164 ,  168  with respect to each other, thereby enabling roll, pitch, and yaw of endplate  110 / 112  with respect to frame  152 . While rotation about this axis is explicitly supported in this embodiment, it should be understood that all embodiments herein can be configured to support rotation about axis  324 , as well. A rotating fixation plate, for example fixation plate  266 , can be provided in this embodiment, as with other embodiments of the disclosure. 
     Implants of the disclosure enable a continuous expansion and retraction over a range of displacements according to predetermined dimensions of a specific spacer  100  design. This provides the ability to distract vertebral bodies to a desired height, but also to collapse the spacer  100  for repositioning, if therapeutically advantageous for the patient. Endplates  110 ,  112  may be shaped to form planes or surfaces which converge relative to each, to provide for proper lordosis, coronal correction, or kyphosis and can be provided with openings through which bone may grow, and into which bone graft material may be placed. Spacer  100  may be used to distract, or force bones of a joint apart, or may be used to maintain a separation of bones created by other means, for example retractor. Endplates  110 ,  112  may additionally be curved to conform to the surface of body tissue, for example the surface of cortical bone, of the vertebra to be contacted, for improved fixation and load bearing. 
     Spacer  100  may be fabricated using any biocompatible materials known to one skilled in the art, having sufficient strength, flexibility, resiliency, and durability for the patient, and for the term during which the device is to be implanted. Examples include but are not limited to metal, such as, for example titanium and chromium alloys; polymers, including for example, PEEK or high molecular weight polyethylene (HMWPE); and ceramics. There are many other biocompatible materials which may be used, including other plastics and metals, as well as fabrication using living or preserved tissue, including autograft, allograft, and xenograft material. 
     Portions or all of the implant may be radiopaque or radiolucent, or materials having such properties may be added or incorporated into the implant to improve imaging of the device during and after implantation. 
     For example, metallic portions  124 ,  124 A of endplates  110 ,  112  may be manufactured from Titanium, or a cobalt-chrome-molybdenum alloy, Co—Cr—Mo, for example as specified in ASTM F1537 (and ISO 5832-12). The smooth surfaces may be plasma sprayed with commercially pure titanium, as specified in ASTM F1580, F1978, F1147 and C-633 (and ISO 5832-2). Polymeric portions  122 ,  122 A may be manufactured from ultra-high molecular weight polyethylene, UHMWPE, for example as specified in ASTM F648 (and ISO 5834-2). In one embodiment, PEEK-OPTIMA (a trademark of Invibio Ltd Corp, United Kingdom) may be used for one or more components of spacer  100 . For example, polymeric portions  122 ,  122 A can be formed with PEEK-OPTIMA, which is radiolucent, whereby bony ingrowth may be observed. Other polymeric materials with suitable flexibility, durability, and biocompatibility may also be used. 
     In accordance with the invention, implants of various sizes may be provided to best fit the anatomy of the patient. Components of matching or divergent sizes may be assembled during the implantation procedure by a medical practitioner as best meets the therapeutic needs of the patient, the assembly inserted within the body using an insertion tool. Implants of the invention may also be provided with an overall angular geometry, for example an angular mating disposition of endplates  110 ,  112 , to provide for a natural lordosis, or a corrective lordosis, for example of from 0° to 6° for a cervical application, although much different values may be advantageous for other joints. Lordotic angles may also be formed by shaping one or both of plates  110 ,  112  to have relatively non-coplanar surfaces. Expanded implant heights, for use in the vertebrae for example, may typically range from 3 mm to 25 mm, but may be larger or smaller, including as small as 2 mm, and as large as 30 mm, although the size is dependent on the patient, and the joint into which an implant of the invention is to be implanted. Spacers  100  may be implanted within any level of the spine, and may also be implanted in other joints of the body, including joints of the hand, wrist, elbow, shoulder, hip, knee, ankle, or foot. 
     In accordance with the invention, a single spacer  100  may be used, to provide stabilization for a weakened joint or joint portion. Alternatively, two, three, or more Spacers  100  may be used, at a single joint level, or in multiple joints. Moreover, Spacers  100  may be combined with other stabilizing means. 
     Additionally, spacer  100  may be fabricated using material that biodegrades in the body during a therapeutically advantageous time interval, for example after sufficient bone ingrowth has taken place. Further, spacer  100  is advantageously provided with smooth and or rounded exterior surfaces, which reduce a potential for deleterious mechanical effects on neighboring tissues. 
     Any surface or component of the invention may be coated with or impregnated with therapeutic agents, including bone growth, healing, antimicrobial, or drug materials, which may be released at a therapeutic rate, using methods known to those skilled in the art. 
     Devices of the disclosure provide for adjacent vertebrae to be supported during flexion/extension, lateral bending, and axial rotation. In one embodiment, spacer  100  is indicated for spinal arthroplasty in treating skeletally mature patients with degenerative disc disease, primary or recurrent disc herniation, spinal stenosis, or spondylosis in the lumbosacral spine (LI-ST). Degenerative disc disease is advantageously defined as discogenic back pain with degeneration of the disc confirmed by patient history and radiographic studies, with or without leg (radicular) pain. Patients are advantageously treated, for example, who may have spondylolisthesis up to Grade 2 at the involved level. The surgery position spacer  100  may be performed through an Anterior, Anterolateral, Posterolateral, Lateral, and/or posterior approach. 
     In a typical embodiment, spacer  100  has a uncompressed height, before insertion, of 2 to 25 mm, and may advantageously be provided in cross-sections of 23×32 mm, 26×38 mm and 26×42 mm, with 4, 8, 12, or 16 degree lordotic angles, although these are only representative sizes, and substantially smaller or larger sizes can be therapeutically beneficial. In one embodiment a spacer  100  in accordance with the instant disclosure is sized to be inserted using an MIS approach (a reduced incision size, with fewer and shorter cuts through body tissue). 
     Spacer  100  may advantageously be used in combination with other known or hereinafter developed forms of stabilization or fixation, including for example rods and plates. 
     All references cited herein are expressly incorporated by reference in their entirety. There are many different features to the present invention and it is contemplated that these features may be used together or separately. Unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. Thus, the invention should not be limited to any particular combination of features or to a particular application of the invention. Further, it should be understood that variations and modifications within the spirit and scope of the invention might occur to those skilled in the art to which the invention pertains. Accordingly, all expedient modifications readily attainable by one versed in the art from the disclosure set forth herein that are within the scope and spirit of the present invention are to be included as further embodiments of the present invention.