Patent Publication Number: US-2017360485-A1

Title: Spinal implants and methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 12/013,351, entitled “SPINAL IMPLANTS AND METHODS” and filed on Jan. 11, 2008 which is a continuation-in-part of U.S. patent application Ser. No. 11/293,438, entitled “INTERSPINOUS DISTRACTION DEVICES AND ASSOCIATED METHODS OF INSERTION” and filed on Dec. 2, 2005, which is a continuation-in-part of U.S. patent application Ser. No. 11/257,647, entitled “INTERSPINOUS DISTRACTION DEVICES AND ASSOCIATED METHODS OF INSERTION” and filed on Oct. 25, 2005, each of which is incorporated in full by reference herein. 
     The present application is also a continuation-in-part of U.S. patent application Ser. No. 11/934,604, entitled “SPINOUS PROCESS IMPLANTS AND ASSOCIATED METHODS” and filed Nov. 2, 2007 which is incorporated in full by reference herein. 
     The present application further claims the benefit of U.S. Provisional Patent Application No. 60/884,581, entitled “SPINAL STABILIZATION” and filed Jan. 11, 2007, U.S. Provisional Patent Application No. 60/621,712, entitled “INTERSPINOUS DISTRACTION DEVICES AND ASSOCIATED METHODS OF INSERTION,” and filed on Oct. 25, 2004; U.S. Provisional Patent Application No. 60/633,112, entitled “INTERSPINOUS DISTRACTION DEVICES AND ASSOCIATED METHODS OF INSERTION,” and filed on Dec. 3, 2004; U.S. Provisional Patent Application No. 60/639,938, entitled “INTERSPINOUS DISTRACTION DEVICES AND ASSOCIATED METHODS OF INSERTION,” and filed on Dec. 29, 2004; U.S. Provisional Patent Application No. 60/654,483, entitled “INTERSPINOUS DISTRACTION DEVICES AND ASSOCIATED METHODS OF INSERTION,” and filed on Feb. 21, 2005; U.S. Provisional Patent Application No. 60/671,301, entitled “INTERSPINOUS DISTRACTION DEVICES AND ASSOCIATED METHODS OF INSERTION,” and filed on Apr. 14, 2005; U.S. Provisional Patent Application No. 60/678,360, entitled “INTERSPINOUS DISTRACTION DEVICES AND ASSOCIATED METHODS OF INSERTION,” and filed on May 6, 2005; and U.S. Provisional Application No. 60/912,273; entitled “FUSION PLATE WITH REMOVABLE OR ADJUSTABLE SPIKES” and filed Apr. 17, 2007, each of which is incorporated in full by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to spinal implants and associated methods. 
     BACKGROUND 
     The vertebrae of the human spine are arranged in a column with one vertebra on top of the next. An intervertebral disc lies between adjacent vertebrae to transmit force between the adjacent vertebrae and provide a cushion between them. The discs allow the spine to flex and twist. With age, spinal discs begin to break down, or degenerate resulting in the loss of fluid in the discs and consequently resulting in them becoming less flexible. Likewise, the disks become thinner allowing the vertebrae to move closer together. Degeneration may also result in tears or cracks in the outer layer, or annulus, of the disc. The disc may begin to bulge outwardly. In more severe cases, the inner material of the disc, or nucleus, may actually extrude out of the disc. In addition to degenerative changes in the disc, the spine may undergo changes due to trauma from automobile accidents, falls, heavy lifting, and other activities. Furthermore, in a process known as spinal stenosis, the spinal canal narrows due to excessive bone growth, thickening of tissue in the canal (such as ligament), or both. In all of these conditions, the spaces through which the spinal cord and the spinal nerve roots pass may become narrowed leading to pressure on the nerve tissue which can cause pain, numbness, weakness, or even paralysis in various parts of the body. Finally, the facet joints between adjacent vertebrae may degenerate and cause localized and/or radiating pain. All of the above conditions are collectively referred to herein as spine disease. 
     Conventionally, surgeons treat spine disease by attempting to restore the normal spacing between adjacent vertebrae. This may be sufficient to relieve pressure from affected nerve tissue. However, it is often necessary to also surgically remove disc material, bone, or other tissues that impinge on the nerve tissue and/or to debride the facet joints. Most often, the restoration of vertebral spacing is accomplished by inserting a rigid spacer made of bone, metal, or plastic into the disc space between the adjacent vertebrae and allowing the vertebrae to grow together, or fuse, into a single piece of bone. The vertebrae are typically stabilized during this fusion process with the use of bone plates and/or pedicle screws fastened to the adjacent vertebrae. 
     Although techniques for placing intervertebral spacers, plates, and pedicle screw fixation systems have become less invasive in recent years, they still require the placement of hardware deep within the surgical site adjacent to the spine. Recovery from such surgery can require several days of hospitalization and long, slow rehabilitation to normal activity levels. 
     More recently, investigators have promoted the use of motion preservation implants and techniques in which adjacent vertebrae are permitted to move relative to one another. One such implant that has met with only limited success is the artificial disc implant. These typically include either a flexible material or a two-piece articulating joint inserted in the disc space. Another such implant is the spinous process spacer which is inserted between the posteriorly extending spinous processes of adjacent vertebrae to act as an extension stop and to maintain a minimum spacing between the spinous processes when the spine is in extension. The spinous process spacer allows the adjacent spinous processes to move apart as the spine is flexed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various examples of the present invention will be discussed with reference to the appended drawings. These drawings depict only illustrative examples of the invention and are not to be considered limiting of its scope. 
         FIG. 1  is a perspective view of a spinal implant according to the present invention; 
         FIG. 2  is a cross sectional view of the spinal implant of  FIG. 1  showing the implant in a first position; 
         FIG. 3  is a cross sectional view of the spinal implant of  FIG. 1  showing the implant in a second position; 
         FIG. 4  is an elevation view of a spinal implant according to the present invention showing the implant in a first position; 
         FIG. 5  is an elevation view of the spinal implant of  FIG. 4  showing the implant in a second position; 
         FIG. 6  is a perspective view of a spinal implant according to the present invention; 
         FIG. 7  is a cross sectional view of the implant of  FIG. 6 ; 
         FIG. 8  is a perspective view of a spinal implant according to the present invention; 
         FIG. 9  is a perspective view of a spacer component of the spinal implant of  FIG. 8  in a first position; 
         FIG. 10  is a perspective view of a spacer component of the spinal implant of  FIG. 8  in a second position; 
         FIG. 11  is an elevation view of a core component of the spinal implant of  FIG. 8  in a first position; 
         FIG. 12  is a perspective view of a spinal implant according to the present invention; 
         FIG. 13  is a perspective view of the spinal implant of  FIG. 12  illustrating one method of insertion; 
         FIG. 14  is a perspective view of the spinal implant of  FIG. 12  illustrating another method of insertion; 
         FIG. 15  is a perspective view of an alternative configuration for the retention members of the spinal implant of  FIG. 12 ; 
         FIG. 16  is a perspective view of a spinal implant according to the present invention; 
         FIG. 17  is an elevation view of a spinal implant according to the present invention in a first position; 
         FIG. 18  is an elevation view of the spinal implant of  FIG. 17  in a second position; 
         FIG. 19  is a perspective detail view of one end of the spinal implant of  FIG. 17  showing the first and second positions superimposed on one another 
         FIG. 20  is a perspective view of a spinal implant according to the present invention; 
         FIG. 21  is a perspective view of the spinal implant of  FIG. 20  shown implanted in a first position; 
         FIG. 22  is a perspective view of the spinal implant of  FIG. 20  shown implanted in a second position; 
         FIG. 23  is a perspective view of a spinal implant according to the present invention in a first position; 
         FIG. 24  is a perspective view of the spinal implant of  FIG. 23  in a second position; 
         FIG. 25  is a perspective view of a spinal implant according to the present invention in a first position; 
         FIG. 26  is a perspective view of the spinal implant of  FIG. 24  in a second position; 
         FIG. 27  is a perspective view of the spinal implant of  FIG. 26  in a third position; 
         FIG. 28  is a cross sectional view of a spinal implant according to the present invention in a first position; 
         FIG. 29  is a cross sectional view of the spinal implant of  FIG. 28  in a second position; 
         FIG. 30  is a perspective view of a spinal implant according to the present invention in a first position; 
         FIG. 31  is a side elevation view of the spinal implant of  FIG. 30  in the first position; 
         FIG. 32  is a front elevation view of the spinal implant of  FIG. 30  in the first position; 
         FIG. 33  is a perspective view of the spinal-implant of  FIG. 30  in a second position; 
         FIG. 34  is a perspective view of a spinal implant according to the present invention in a first position; 
         FIG. 35  is a perspective view of the spinal implant of  FIG. 34  in a second position; 
         FIG. 36  is a perspective view of the spinal implant of  FIG. 34  in a third position; 
         FIG. 37  is a perspective view of the spinal implant of  FIG. 34  implanted in a spine; 
         FIG. 38  is a perspective view of a spinal implant according to the present invention; 
         FIG. 39  is a front elevation view of the spinal implant of  FIG. 38  implanted in a spine; 
         FIG. 40  is a cross sectional view of a spinal implant according to the present invention implanted in a spine; 
         FIG. 41  is a cross sectional view of a spinal implant according to the present invention implanted in a spine; 
         FIG. 42  is a front elevation view of a component of a spinal implant according to the present invention being implanted in a spine; 
         FIG. 43  is a front elevation view of the fully assembled implant of  FIG. 42  implanted in a spine; 
         FIG. 44  is a perspective view of a spinal implant according to the present invention in a first position; 
         FIG. 45  is a perspective view of the spinal implant of  FIG. 44  in a second position; 
         FIG. 46  is a perspective view of the spinal implant of  FIG. 44  in a third position; 
         FIG. 47  is a perspective view of a spinal implant according to the present invention in a first position; 
         FIG. 48  is a perspective view of the spinal implant of  FIG. 47  in a second position; 
         FIG. 49  is a perspective view of a spinal implant according to the present invention in a first position; 
         FIG. 50  is a side elevation view of the spinal implant of  FIG. 49  in a second position; 
         FIG. 51  is a perspective view of a spinal implant according to the present invention in a first position; 
         FIG. 52  is a perspective view of the spinal implant of  FIG. 51  in a second position; 
         FIG. 53  is a perspective view of a spinal implant according to the present invention in a first position; 
         FIG. 54  is a perspective view of the spinal implant of  FIG. 53  in a second position; 
         FIG. 55  is an exploded perspective view of a spinal implant according to the present invention; 
         FIG. 56  is a front elevation view of the spinal implant of  FIG. 55  in a first position; 
         FIG. 57  is a front elevation view of the spinal implant of  FIG. 55  in a second position 
         FIG. 58  is an exploded perspective view of a spinal implant according to the present invention; 
         FIG. 59  is an exploded perspective view of a spinal implant according to the present invention; 
         FIG. 60  is a right perspective view of a spinal implant according to the present invention; 
         FIG. 61  is a left perspective view of the spinal implant of  FIG. 60 ; 
         FIG. 62  is a left perspective view of a spinal implant according to the present invention; 
         FIG. 63  is a right perspective view of the spinal implant of  FIG. 62 ; 
         FIG. 64  is a perspective view of a spinal implant according to the present invention; 
         FIG. 65  is a perspective view of a spinal implant according to the present invention; 
         FIG. 66  is a front elevation view of the spinal implant of  FIG. 65 ; 
         FIG. 67  is a front elevation view of a spinal implant according to the present invention; 
         FIG. 68  is a flow diagram of a method of inserting a spinal implant according to the present invention; 
         FIG. 69  is a front elevation view of a spinal implant according to the present invention; and 
         FIG. 70  is a perspective view of an alternative embodiment of the spinal implant of  FIG. 69 . 
     
    
    
     DESCRIPTION OF THE ILLUSTRATIVE EXAMPLES 
     Embodiments of spinal implants according to the present invention include a spacer and one or more retention members. Throughout this specification, the spinal implant will be referred to in the context of a spinous process implant. However, it is to be understood that the spinal implant may be configured for insertion into the cervical, thoracic, and/or lumbar spine between adjacent spinous processes, transverse processes, and/or other vertebral structures. The spacer may be provided in a variety of sizes to accommodate anatomical variation amongst patients and varying degrees of space correction. The spacer may include openings to facilitate tissue in-growth to anchor the spacer to the vertebral bodies such as tissue in-growth from the spine. For example, the spacer may be configured for tissue in-growth from superior and inferior spinous processes to cause fusion of the adjacent spinous processes. The openings may be relatively large and/or communicate to a hollow interior of the spacer. A hollow interior may be configured to receive bone growth promoting substances such as by packing the substances into the hollow interior. The openings may be relatively small and/or comprise pores or interconnecting pores over at least a portion of the spacer surface. The openings may be filled with bone growth promoting substances. 
     The spacer may have any suitable cross-sectional shape. For example, it may be cylindrical, wedge shaped, D-shaped, C-shaped, H-shaped, include separated cantilevered beams, and/or any other suitable shape. The shape may include chamfers, fillets, flats, relief cuts, and/or other features to accommodate anatomical features such as for example the laminae and/or facets. 
     The spacer may be incompressible, moderately compressible, highly compressible, convertible from compressible to incompressible, and/or any other configuration. For example, the spacer may be compressible into a compact configuration for insertion between adjacent bones and then expandable to space the bones apart. The spacer may be allowed to flex to provide a resilient cushion between the bones. The spacer may be locked in the expanded condition to prevent it from returning to the compact configuration. 
     The retention member may extend transversely from the spacer relative to a spacer longitudinal axis to maintain the spacer between adjacent spinous processes. A single retention member may extend in one or more directions or multiple extensions may be provided that extend in multiple directions. One or more retention members may be fixed relative to the spacer longitudinally and/or radially. One or more retention members may be adjustable relative to the spacer and/or other retention members longitudinally and/or radially to allow the retention members to be positioned relative to the spinous processes. The retention members may be deployable through and/or from within the spacer to allow the spacer to be placed and the retention members deployed in a minimally invasive manner. The retention members may include one or more screws, pins, nails, bolts, staples, hooks, plates, wings, bars, extensions, filaments, wires, loops, bands, straps, cables, cords, sutures, and/or other suitable retention member. The retention members may be made of metals, metal alloys, polymers, and/or other suitable materials. The retention members may grip bone and/or soft tissue, abut bone and/or soft tissue, facilitate tissue ingrowth and/or ongrowth, and/or otherwise retain the implant. 
     The retention members may cooperate with fasteners engageable with the spinous processes and/or soft tissue. Such fasteners may include one or more screws, pins, nails, rivets, bolts, staples, hooks, sutures, wires, straps, clamps, spikes, teeth, adhesives, and/or other suitable fasteners. The fasteners may be integrated into the retention members or they may be modular. The retention members and/or fasteners may be adjustable, replaceable, and/or removable and may be employed in one direction and/or on one side of the implant or in multiple directions and/or on multiple sides of the implant to allow tailoring of the kind and quality of fixation of adjacent bones. For example, the implant may be placed such that it acts only as a spacer between adjacent bones, as an elastic restraint between adjacent bones, or as a rigid fixation between adjacent bones. The spacer, retention members, and/or fasteners may advantageously be made of different materials. 
     Cerclage may be used to stabilize the spinal implant and/or to provide other benefits. For example, wires, straps, bands, cables, cords, and/or other elongated members may encircle the pedicles, laminae, spinous processes, transverse processes, and/or other spinal structures. The cerclage may be relatively inextensible to provide a hard check to spine flexion or the cerclage may be relatively extensible to provide increasing resistance to flexion. The cerclage may be relatively flexible and drapeable such as a woven fabric or it may be relatively rigid such as a metal band. The cerclage may have shape memory properties that cause it to resume a prior set shape after implantation. The cerclage may be independent of the spinous process implant or may engage it. For example, the cerclage may pass through a hollow interior of the spinous process implant and/or engage the extension. 
     The implant may be supplemented with bone growth promoting substances to facilitate fusion of adjacent vertebrae between spinous processes, laminae, transverse processes, facets, and/or other spinal structures. The bone growth promoting substances may be spaced from the implant, placed adjacent the implant, sandwiched between the implant and underlying bone, placed inside the implant, coated onto the implant, and/or otherwise placed relative to the implant. If it is coated onto the implant it may cover the entire implant or only selected portions of the implant such as the spacer, retention members, fasteners, and/or other portions. 
     As used herein, bone growth promoting substances may include bone paste, bone chips, bone strips, structural bone grafts, platelet derived growth factors, bone marrow aspirate, stem cells, bone growth proteins, bone growth peptides, bone attachment proteins, bone attachment peptides, hydroxylapatite, calcium phosphate, statins, and/or other suitable bone growth promoting substances. 
     The spinal implant and any associated cerclage or other components may be made of any suitable biocompatible material including among others metals, resorbable ceramics, non-resorbable ceramics, resorbable polymers, and non-resorbable polymers. Some specific examples include stainless steel, titanium and its alloys including nickel-titanium alloys, tantalum, hydroxylapatite, calcium phosphate, bone, zirconia, alumina, carbon, bioglass, polyesters, polylactic acid, polyglycolic acid, polyolefins, polyamides, polyimides, polyacrylates, polyketones, fluropolymers, and/or other suitable biocompatible materials and combinations thereof. 
     The spinal implant may be used to treat spine disease in a variety of surgical techniques including superspinous ligament sacrificing posterior approaches, superspinous ligament preserving posterior approaches, lateral approaches, and/or other suitable approaches. The spinal implant may be used to treat spine disease by fusing adjacent vertebrae or by preserving motion between adjacent vertebrae. It may include only an extension stop such as a spacer, only a flexion stop such as flexible cerclage elements, or both a flexion and extension stop. The spinous process implant may be used to reduce loads on the facet joints, increase spinous process spacing, reduce loads on the disc, increase disc spacing, and/or otherwise treat spine disease. Techniques for the spinal implant may include leaving the tissues at the surgical site unmodified or modifying tissues such as trimming, rasping, roughening, and/or otherwise modifying tissues at the implant site. 
     For example,  FIGS. 1-3  illustrate a spinal implant  100  including a spacer  102  and a plurality of retention members in the form of first and second plate extensions  104 ,  105  and deployable retention members  106 ,  108 , and  110 . The spacer  102  has a generally cylindrical body  112  having a proximal end  114 , a distal end  116 , and a longitudinal spacer axis  118  extending therebetween. The distal end  116  tapers to an edge to facilitate inserting the spacer  102  between two bones, e.g. adjacent spinous processes. The distal end is defined by a superior facet  120 , an inferior facet  122 , and lateral facets  124  (one shown). 
     The first plate extension  104  projects radially outwardly from the spacer  102  adjacent the proximal end and the second plate extension  105  projects radially outwardly from the spacer  102  opposite the first plate extension  104 . The plate extensions  104 ,  105  may be integral with the spacer  102  as shown in  FIGS. 1-3  or modular and separable from the spacer  102 . The plate extensions  104 ,  105  provide an insertion stop by abutting the spinous processes  126 ,  128 . 
     The deployable retention members  106 ,  108 ,  110  may be pre-installed within the spacer  102  or inserted into the spacer  102  intraoperatively. Preferably they are pre-installed and retracted within the spacer  102  as shown in  FIG. 2 . Each deployable retention member  106 ,  108 ,  110  is directed into a channel  130 ,  132 ,  134  that communicates from the interior of the spacer  102  out through the distal end  116  to the exterior of the spacer  102 . The deployable retention members  106 ,  108 ,  110  are joined at their proximal ends  136  so that they move together. The interior of the spacer includes a cavity  137  that houses the deployable retention members  106 ,  108 ,  110  in the un-deployed position. The cavity  137  is threaded and receive an actuator screw  138  in axial translating relationship. 
     In use, the spinal implant  100  is inserted between adjacent spinous processes  126 ,  128  as shown. The actuator screw  138  is then rotated so that it translates along the spacer axis  118  and pushes the deployable retention members  106 ,  108 ,  110  distally through the channels  130 ,  132 ,  134 . The spacer  102  includes a pair of sockets  139  at its proximal end  114  for receiving a tool for applying a counter torque to the spacer  102  while the actuator screw  138  is rotated. The channels  130 ,  132 ,  134  may be curved to cause the deployable retention members  106 ,  108 ,  110  to bend away from the spacer axis  118  and grip the spinous processes  126 ,  128  and/or surrounding soft tissue. The deployable retention members  106 ,  108 ,  110  may also be pre-bent and then elastically straightened as they are loaded into the un-deployed position of  FIG. 2 . Upon being deployed, they may then return to their pre-bent shape. The deployable retention members  106 ,  108 ,  110  may advantageously be made of a superelastic material such as Nitinol. They may also respond to the patient&#39;s body temperature to change shape from the straight configuration of  FIG. 2  to the curved configuration of  FIG. 3 . Soft tissue may also grow around, adhere to, scar around, and/or otherwise grip the deployable retention members  106 ,  108 ,  110  over time. Deployable retention member  110  is split at its distal-end to form a loop  140  that opens upon being deployed from the spacer  102  to facilitate tissue growth into and around the loop  140  for increased retention strength. A plurality of holes  142  are formed through the plate extensions  104 ,  105  for receiving fasteners for attaching the plate extensions  104 ,  105  to the surrounding bone and/or soft tissue. Such fasteners may include any of the fasteners listed above. A pin  144  is shown in one of the holes  142  in  FIG. 3 . 
       FIGS. 4-5  illustrate a spinal implant  200  similar in form and function to that of  FIGS. 1-3 . The spinal implant  200  includes a spacer  202 , deployable retention members  204 , and spacer end pieces  206 . The spacer  202  and end pieces  206  are generally cylindrical and are aligned along a spacer axis  208  and connected by a threaded shaft  210  that threadably engages the end pieces  206 . The threaded shaft  210  is mounted to the spacer  202  for axial rotation and includes a driver engaging end  212 . The deployable retention members  204  are fixed in the spacer  202  and are slidably received in channels  214  in the end pieces  206 . 
     In use, the spinal implant  200  is inserted between adjacent bones such as spinous processes  220 ,  222 . A driver (not shown) is engaged with the driver engaging end  212  of the threaded shaft  210  and rotated to move the end pieces  206  toward the spacer  202  causing the retention members  204  to extend out of the channels  214  away from the spacer axis  208  as shown in  FIG. 5 . A tool (not shown) may be engaged with one or more sockets  224  in one of the end pieces  206  or notches  226  in the spacer  202  to apply a counter torque while the threaded shaft  210  is rotated. 
       FIGS. 6-7  illustrate a spinal implant  300  similar in form and function to that of  FIGS. 1-3 . The spinal implant  300  includes a spacer  302 , a core  304 , and deployable retention members  306  extending from the core  304 . The deployable retention members  306  include a plurality of wires projecting in a radial array from a core/spacer axis  308  at each end of the core  304 . In the illustrative example, which have been designed for interspinous placement, there are no wires projecting anteriorly to avoid impingement with the facets and/or other spinal structures. The core  304  and deployable retention members  306  are received in a passageway  309  through the spacer  302  parallel to the spacer axis  308 . 
     In use, the spacer  302  is positioned between adjacent bones such as spinous processes  310 ,  312 . The core  304  and deployable retention members  306  may be partially pre-inserted as shown in  FIG. 7  such that after the spacer  302  is positioned the core is advanced to deploy the deployable retention members  306 . Alternatively, the core and deployable retention members  306  may be separate from the spacer  302  and inserted after the spacer is placed. In either case, a tube  314  may optionally be used to hold the deployable retention members  306  and/or core  304  prior to deployment. As shown in  FIG. 7 , the tube  314  may be engaged with the spacer  302  in alignment with the passageway  309  and the core  304  and deployable retention members  306  pushed from the tube  314  into the passageway  309  until the deployable retention members  306  deploy from the opposite end of the passageway  309 . The tube  314  may be withdrawn to permit the remaining deployable retention members  306  to deploy. 
       FIGS. 8-11  illustrate a spinal implant  400  similar in form and function to that of  FIGS. 1-3 . The spinal implant  400  includes a generally cylindrical hollow spacer  402  having a first end  404 , a second end  406 , and a spacer axis  408  extending from the first end  404  to the second end  406 . A core  410  is positionable within the spacer  402  along the spacer axis  408 . Optionally, a plurality of deployable retention members  412  project radially away from the spacer axis  408  at each end of the core  410 . The spacer  402  is made of a compressible material such as a superelastic metal or polymer such that it can be compressed to facilitate insertion. For example, as shown in  FIG. 9 , the prongs  420  of a tool (not shown) may be inserted into the spacer  402  and spread apart to stretch the spacer  402  into a flattened elliptical shape. The spacer  402  may then be inserted and the prongs removed to allow the spacer  402  to recover to its original shape. Depending on the modulus of the spacer  402  and the loads exerted on it by the surrounding bones, it may recover to its full pre-insertion height and distract the bones or it may only recover partially. The core  410  may then be inserted to maintain the spacer  402  at its recovered height. The core  410  may be sized to press into the spacer  402  and thereby prevent any compression of the spacer  402  post-insertion or the core may be sized to allow a predetermined amount of compression of the spacer  402  to provide a resilient spacer. The optional deployable retention members  412  may be omitted and the spinal implant  400  used in the condition shown in  FIG. 10 . Preferably, the core  410  includes deployable retention members  412  in the form of filaments that can be deployed as an array of loops projecting radially outwardly from the spacer axis  408  at each end of the core  410 . The retention members  412  may retain the space  402  in place by physically blocking withdrawal. The retention members  412  may also retain the spacer  402  due to tissue growth around the retaining members  412 . 
       FIG. 11  illustrates one way of arranging the deployable retention members  412 . A plurality of rings  422  are mounted on the core  410  with at least one of the rings  422  being axially translatable along the core  410 . The rings are connected by a plurality of filaments  424  spiraling around the core  410 . 
     In use, the spacer  402  is inserted between adjacent bones such as adjacent spinous processes and the core  410  is inserted into the spacer  402 . At least one ring  422  is moved toward another ring  422  causing the filaments  424  to bend away from the core and form the array of loops as shown in  FIG. 8 . Alternatively, the retaining members  412  may be folded down parallel to the spacer axis  408  similar to the embodiment of  FIG. 7 . 
       FIGS. 12-14  illustrate a spinal implant  500  similar in form and function to that of  FIGS. 1-3 . The spinal implant  500  includes a spacer  502  having a generally cylindrical hollow body  504  including a first end  506 , a second end  508 , and a spacer axis  510  extending from the first end  506  to the second end  508 . The ends of the spacer  502  are tapered to facilitate insertion between adjacent bones. A plurality of channels  512  extend through the body  504  from the first end  506  to the second end  508  generally parallel to the spacer axis  510 . Deployable retention members  514  are engageable with channels  512  in axially slidable relationship. In the illustrative example of  FIGS. 12-14 , the channels  512  and deployable retention members  514  have complimentary rectangular cross sectional shapes. The deployable retention members  514  are curved to extend radially away from the spacer axis  510  and grip the spinous processes. 
     In use, the deployable retention members  514  are straightened and/or retracted to allow the spinal implant  500  to be inserted between the spinous processes. This may be accomplished in a variety of ways. As shown in  FIG. 13 , the deployable retention members  514  may be withdrawn partway through the channels  512  forcing them to straighten. They may include a stop to prevent them from being withdrawn completely. After the spacer  502  is inserted between the spinous processes, the deployable retention members  514  may be fed through the channels  512  and allowed to resume their curved configuration. Alternatively the deployable retention members  514  may be separated from the spacer  502  completely and not introduced until after the spacer  502  has been inserted. As shown in  FIG. 14 , the deployable retention members  514  may be straightened and the spinal implant  500  inserted through a tube  520  and into the space between the spinous processes.  FIG. 12  illustrates the spinal implant  500  post-insertion with the deployable retention members  514  fully deployed.  FIG. 15  illustrates a spinal implant  600  similar to that of  FIGS. 12-14 . Spinal implant  600  has deployable retention members  602  in the form of wires rather than the rectangular ribbon-like deployable retention members  514  of  FIGS. 12-14 . 
       FIG. 16  illustrates a spinal implant  700  similar to that of  FIGS. 12-14 . Spinal implant  700  includes a spacer  702  having a passageway  704  through the spacer  702  parallel to a spacer axis  706 . After the spacer  702  is inserted between adjacent spinous processes, a preformed deployable retention member  708  in the form of a wire is inserted through the passageway  704  from a first end to a second end of the passageway so that it emerges from the second end and returns to its preformed shape to extend transverse to the spacer axis  706  beyond the outer surface of the spacer  702 . The end of the deployable retention member may also extend transverse to spacer axis  706  at the first end of the spacer axis so that the deployable retention member may extend on both sides of a process to capture the process. Alternatively, a set screw or other mechanism may be provided to fix the deployable retention member  708  in the passageway  704  after the deployable retention member  708  has been deployed. In the illustrative embodiment the deployable retention member  708  is preformed into a coil. 
       FIGS. 17-19  illustrate a spinal implant  800  similar to the previous embodiments. The spinal implant  800  includes a spacer  802  having first and second ends  804 ,  806  and a spacer axis  808  extending therebetween. The spacer  802  may be wedge shaped, cylindrical, elliptical, rectangular, and/or any other suitable shape. The shape may be based on anatomical considerations. Deployable retention members are provided in the form of a terminal portion  810 ,  812  extending from each end  804 ,  806  of the spacer  802 . The terminal portions  810 ,  812  have a compact position or shape closer to the spacer axis  808  as shown in  FIG. 17  and an expanded position or shape further from the spacer axis  808  as shown in  FIG. 18 .  FIG. 19  illustrates the compact and expanded positions superimposed for comparison. In the illustrative embodiment of  FIGS. 17-19  the terminal portions  810 ,  812  are provided as coils such as a conventional helical spring coil and the compact position corresponds to a coil being tightly wound and the expanded position corresponds to the coil being loosely wound. However, the terminal portions  810 ,  812  may be shaped as a flange, solid disc, protrusion, bar, or the like as a matter of design choice. The spinal implant  800  is implanted with at least one of the terminal portions  810 ,  812  in the compact position. Once placed, one or both terminal portions are allowed to expand. For example, the coils may unwind due to their own spring tension. Alternatively, the coils may be activated, such as e.g. by heat, to expand. The spacer  802  separates adjacent spinous processes and the expanded terminal portions  810 ,  812  maintain the spacer  802  between the spinous processes. 
     While the terminal portions  810 ,  812  may be separate devices, in the illustrative embodiment of  FIGS. 17-19 , the terminal portions  810 ,  812  are connected through a passageway  814  formed through the spacer  802  along the spacer axis  808 . In this embodiment, the terminal portions  810 ,  812  are the ends of a continuous coil placed within the passageway  814 . The coil may be designed to be in tension such that the terminal portions tend to seat against the spinous processes to hold the spacer  802  firmly in place. 
     The termination portions  810 ,  812  may be formed of any number of materials, but superelastic materials such as shape memory metal alloys or polymers are advantageous. In particular, shape memory materials can be designed having a first small shape to allow less traumatic implantation of the device. Once implanted, activation of the shape memory material would cause the terminal portions  810 ,  812  to move from the compact position to the expanded position. Moreover, for a continuous coil embodiment, the coil may be configured to retract and thereby seat the terminal portions against the spinous process. 
     The spacer  802  may be provided with one or more surface grooves  816  to receive, e.g., the prongs of a surgical distraction tool so that the spacer may be placed along the prongs after the spinous processes have been distracted. 
       FIGS. 20-22  illustrate an alternative arrangement to that of  FIGS. 17-19  in which a spinal implant  900  includes a spacer  902  and a coil  904  wrapped around the outside of the spacer  902 . The coil  904  may have shape memory properties allowing it to be transformed from a compact position to an expanded position or it may always be biased toward the expanded position. In the case where it is always biased toward the expanded position, the coil  904  may be maintained in the compact position by a sleeve  906  or other surrounding structure. The spinal implant  900  is placed between adjacent bones, e.g. spinous processes  910 ,  912 , in the compact position ( FIG. 21 ) and allowed, or activated, to transition to the expanded position ( FIG. 22 ) to maintain the spacer  902  between the bones. Alternatively, the spacer  902  may be removed after the spinal implant is implanted or the spacer  902  may be omitted entirely such that just the coil  904  serves as both a spacer and retention member. 
       FIGS. 23-24  illustrate a spinal implant  1000  including a spacer  1002  having a proximal end  1004 , a distal end  1006 , and a spacer axis  1008  extending therebetween. Optionally, the distal end  1006  may be tapered as shown to facilitate insertion between adjacent bones. The spinal implant  1000  includes one or more deployable retention members mounted for rotation to the spacer  1002  for rotation between a compact or stowed position ( FIG. 23 ) and an expanded or deployed position ( FIG. 24 ). In the illustrative embodiment of  FIGS. 23-24 , the deployable retention members are in the form of wires  1010  mounted to brackets  1012  extending radially away from the spacer axis  1008 . The wires  1010  extend between the brackets  1012  generally parallel to the spacer axis  1008  and then bend transverse to the spacer axis  1008  at the proximal and distal ends  1004 ,  1006 . The spacer  1002  includes an annular groove  1014  adjacent the distal end and the wires  1010  are curved distally to engage the groove  1014  in the compact or stowed position. As shown in  FIG. 23 , the groove  1014  may receive the wires  1010  so that their curved portions are completely recessed to ease implantation. The proximal ends of the wires  1010  are positioned behind the proximal end  1004  of the spacer  1002  in the compact or stowed position to ease implantation. After the spinal implant  1000  is inserted between adjacent bones, e.g. spinous processes, the wires  1010  are rotated from the stowed position to the deployed position to maintain the spacer  1002  between the bones. In the illustrative embodiment of  FIGS. 23-24  the proximal ends of the wires can be accessed after implantation to rotate the wires  1010 . The wires may maintain their position due to friction with the brackets  1012  or an additional locking mechanism may be provided. For example, detents  1016  may be provided to receive the wires and help maintain them in position, e.g. in the deployed position. 
       FIGS. 25-27  illustrate a spinal implant  1100  including a spacer  1102  having a first end  1104 , a second end  1106 , and a spacer axis  1108  extending therebetween. One or more deployable retention members in the form of end pieces are mounted to the spacer  1102  for rotation between a stowed position nearer the spacer axis  1108  and a deployed position further from the spacer axis. For example, the spinal implant may include a pair of outer end pieces  1110  and a pair of inner end pieces  1112  with one outer and one inner end piece at each end of the spacer. The outer end pieces  1110  are mounted for rotation about an axis  1114  offset from the spacer axis  1108  so that they move nearer to or further from the spacer axis  1108  as they rotate. For example, the outer end pieces  1110  may be mounted on a common shaft  1116  so that they rotate together. The inner end pieces  1112  may be similarly mounted for rotation about an offset axis  1118  on a common shaft  1120 . Preferably the inner pieces  1112  are mounted on a shaft  1120  that is offset from both the spacer axis  1108  and the shaft  1116  that the outer end pieces  1110  are mounted on so that the inner and outer end pieces  1112 ,  1110  move away from the spacer axis  1108  in different directions. In the example of  FIGS. 25-27 , the inner end pieces  1112  have been relieve; e.g. to include notches  1122  ( FIG. 27 ); to clear the shaft of the outer end pieces  1110  so that they may be rotated to a stowed position that is coaxial with the spacer  1102  as shown in  FIG. 25 . In use, the spinal implant  1100  is inserted between adjacent bones, e.g. spinous processes, in the stowed position of  FIG. 25 . Once the spacer  1102  is in the desired location one or more of the outer and inner end pieces  1110 ,  1112  may be rotated to the deployed position to maintain the spacer  1102  in position. Driver engaging sockets  1124  are provided to facilitate rotating the end pieces. Any number of end pieces may be provided up to and including an implant  1100  in which the entire spacer is made up of a series of end pieces. The end pieces may be selectively rotated to achieve the desired fit with the adjacent bones. The end pieces may be mounted to separate shafts or otherwise mounted for independent rotation. The end pieces may be mounted to a shaft so that they slip when a torque threshold is met. For example, the end pieces may be mounted for predetermined slipping such that if a plurality of end pieces are being rotated together on a common shaft and one abuts a bone, the abutting end piece may slip on the shaft and thereby permit the other end pieces to be rotated fully into the deployed position. 
       FIGS. 28-29  illustrate a spinal implant  1200  similar to that of  FIGS. 25-27 . The spinal implant  1200  includes a spacer  1202 , a proximal end  1204 , a distal end  1206 , and a spacer axis  1208  extending therebetween. A fixed retention member in the form of a plate or bar shaped extension  1210  extends radially away from the spacer axis  1208  adjacent the proximal end  1204 . A deployable retention member in the form of an end piece  1212  is mounted at the distal end  1206 ; The end piece.  1212  is preferably tapered as shown to facilitate insertion between adjacent bones. The end piece  1212  is mounted to the spacer  1202  for rotation about an end piece rotation axis  1214  transverse to the spacer axis  1208 . For example, the distal end  1206  of the spacer may include a distal face  1216  transverse to the spacer axis  1208  and a trunnion  1218  projecting outwardly normal to the distal face  1216 . The end piece  1212  includes a complimentary proximal face  1220  with a socket  1222  for receiving the trunnion  1218 . The end piece  1212  is rotatable about the rotation axis  1214  from a compact or stowed position as shown in  FIG. 28  in which the end piece  1212  extends generally parallel to the spacer axis  1288  to an expanded or deployed position as shown in  FIG. 29  in which the end piece  212  extends generally transverse to the spacer axis  1208 . To facilitate rotation of the end piece  1212 , a shaft  1224  extends from the end piece  1212  through a passageway  1226  in the spacer  1202  to the proximal end  1204 . The shaft  1224  may extend parallel to the rotation axis  1214  or it may bend as shown. A bent shaft may include a flexible portion, a universal joint, a bevel gear, and/or some other arrangement to permit transmitting torque through the bend. A driver engaging socket  1228  is provided at the end of the shaft to engage a tool for rotating the end piece. 
       FIGS. 30-33  illustrate a spinal implant  1300  similar to that of  FIGS. 28-29 . The spinal implant  1300  includes a spacer  1302  having a proximal end  1304 , a distal end  1306 , and a spacer axis  1308  extending therebetween. A plurality of deployable retention members are provided at each end in the form end pieces  1310 ,  1312  mounted for rotation about axes transverse to the spacer axis  1308 . As revealed through the broken away portion of the spacer  1302  in  FIG. 30 , the end pieces are mounted to gears  1314  that engage additional gears  1316  on a drive shaft  1318 . As the drive shaft  1318  is rotated, the end pieces  1310 ,  1312  rotate away from the spacer axis  1308  from the stowed position of  FIGS. 30-32  to the deployed position of  FIG. 33 . 
       FIGS. 34-37  illustrate another spinal implant  1400  including a spacer  1402  having a first end  1404 , a second end  1406 , and a spacer axis  1408  extending therebetween. The spacer  1402  is in the form of a cylinder, rectangle, wedge, cone, and/or some other suitable shape and is compressible transverse to the spacer axis  1408 . In the illustrative example of  FIGS. 34-37  the spacer is hollow and made of an elastic material, preferably a superelastic and/or shape memory material. The spinal implant  1400  includes one or more arms  1410  extending away from the ends  1404 ,  1406  of the spacer  1402 . The arms are also preferably made of an elastic material such as a superelastic and/or shape memory material. In a compact or stowed position ( FIG. 34 ), the spacer  1402  is compressed radially toward the spacer axis  1408  and the arms  1410  extend outwardly generally parallel to the spacer axis  1408 . In an expanded or deployed position ( FIG. 36 ) the spacer  1402  is expanded away from the spacer axis  1408  and the arms  1410  extend transverse to the spacer axis  1408 . In use, the spinal implant  1400  is inserted between adjacent bones; e.g. spinous processes  1420 ,  1422 ; in the compact position and then allowed or activated to transition to the expanded position ( FIG. 37 ). In the illustrative example of  FIGS. 34-37 , the arms  1410  have a pre-formed shape in which they arch or curve back over the spacer  1402  to grip the spinous processes. In the illustrative example, the arms  1410  also have holes  1424  to receive fasteners similar to the embodiment of  FIGS. 1-3 . The spacer  1402  may also receive a core (not shown) to maintain a minimum expanded height similar to the embodiment of  FIGS. 9-12 . 
       FIGS. 38-39  illustrate a spinal implant  1500  including a spacer  1502  having one or more holes  1504  to receive fasteners similar to the embodiment of  FIGS. 1-3 . In the illustrative example of  FIGS. 38-39 , the spacer  1502  is a hollow cylinder with the holes  1504  extending through the wall of the cylinder and being arrayed around the ends of the spacer  1502 . The spacer  1502  may be secured by placing fasteners through the holes  1504  and into one or more adjacent bones and/or into surrounding soft tissue. The spacer  1502  may be secured at one end, at both ends, to tissue associated with one adjacent bone, to tissue associated with multiple adjacent bones, and/or any combination of securing arrangements. In the example of  FIG. 39 , the spacer  1502  is placed between adjacent spinous processes and sutured to the surrounding soft tissue  1506  at both ends. 
       FIG. 40  illustrates a spinal implant  1600  similar to that of  FIGS. 38-39 . The spinal implant  1600  includes a generally solid spacer  1602  and includes one or more transverse passageways  1604  for receiving one or more fasteners  1606 . Preferably the passageways  1604  communicate from the end of the spacer to the outer surface of the spacer transverse to the spacer axis as shown. The spacer  1602  may be attached to one adjacent bone, both adjacent bones, from one side or from two sides. For example, in a unilateral procedure a fastener may be placed into only one bone to maintain the spacer  1602  in position. Alternatively a fastener may be placed into each of the adjacent bones to maintain the spacer  1602  in position and also to hold the adjacent bones in position relative to one another. In the example of  FIG. 40 , screws are placed from each side of the spacer  1602  into adjacent spinous processes  1610 ,  1612 . 
       FIG. 41  illustrates a spinal implant  1700  similar to that of  FIG. 40 . Spinal implant  1700  includes a spacer  1702 , a retention member in the form of a flange  1704 , and holes  1706  through the flange for receiving fasteners  1708 . The holes  1706  may be parallel to the spacer axis (as shown) or transverse to the spacer axis. 
       FIGS. 42-43  illustrate a spinal implant  1800  including a base  1802  having a base axis  1804  and a hook  1806  having a portion  1808  extending generally transversely away from the base axis  1804  and a portion  1810  extending generally parallel to the base axis  1804 . The spinal implant  1800  further includes a spacer  1812  engageable with the base  1802 . The spacer  1812  may be cylindrical, rectangular, conical, and/or any other suitable shape. In the illustrative example of  FIGS. 42-43 , the spacer  1812  is generally conical and threadably engages the base  1802  in axial translating relationship. In use, the hook  1806  is placed around a portion of one or more adjacent bones, e.g. it may be inserted between adjacent spinous processes to catch on one of the spinous processes as shown in  FIG. 42 . The spacer spaces them apart a desired distance as shown in  FIG. 43 . The spinal implant  1800  allows unilateral and minimally invasive placement like the previous examples and adjustable spacing determined by the axial position of the conical spacer  1812 . 
       FIGS. 44-46  illustrate a spinal implant  1900  including a spacer  1902  and deployable retention members  1904 . The spacer  1902  includes a split body  1906  having a superior surface  1908  and an inferior surface  1910 . The superior surface  1908  and inferior surface  1910  are movably connected to a driver  1912 . The driver  1912  has a screw  1914  attached to it and extending from the driver  1912  between the superior surface  1908  and inferior surface  1910  into a threaded bore  1916  in a wedge  1918 . In operation, turning the driver  1912  causes the screw  1914  to thread into the bore  1916 , which causes the wedge  1918  to move between the superior surface  1908  and the inferior surface  1910 . As the wedge  1918  moves further between the surfaces  1908 ,  1910 , the surfaces  1908 ,  1910  separate to increase the height of the spacer  1902 . Combinations of channels  1920  and ribs  1922  provide stabilization for movement of the wedge  1918  relative to the surfaces  1908 ,  1910 . Retention of the spacer  1902  may be accomplished using the coils, flanges, discs, wires and/or other protrusions described above. For example, deployable retention members  1904  in the of form elastic wires that may be folded parallel to the spacer axis  1924  for insertion may provide lateral retention of the spacer  1902 . 
       FIGS. 47-48  illustrate a spinal implant  2000  including a spacer  2002 . The spacer  2002  is generally shaped as a cylinder or sleeve having a bore  2004 . A gap  2006 , or slot, extends the length of spacer  2002 . Bore  2004  may be a complete through bore or bore  2004  may allow for a central wall or plug (not shown) for stability. Spinal implant  2000  further comprises end caps  2010  having a generally conical shape or wedge shape. As end caps  2010  are pressed or threaded into bore  2004 , the shape of caps  2010  causes the diameter of spacer  2002  to expand, which is allowed because of gap  2006 . Gap  2006  could be filled with a suitable elastic material. Alternatively to shaped caps  2010 , caps  2010  could be made of an expandable material, such as shape memory alloys, spring steel, resins, polymers or the like to achieve the same result. Lateral retention of the spacer may be accomplished using the coils, flanges, discs, wires and/or other protrusions described above and below and will not be re-described relative to this embodiment. 
       FIGS. 49-50  illustrate a spinal implant  2100  similar to that of  FIGS. 47-48 . The spinal implant  2100  has a spacer  2102  in the form of a coiled sheet. The spacer  2102  is moveable from a compact position ( FIG. 49 ) in which the coil winds around itself multiple times and is closer to a spacer axis  2104  to an expanded position ( FIG. 50 ) by uncoiling the spacer such that it winds around itself fewer times and is further from the spacer axis  2104 , e.g. such that it forms a single continuous ring. The spacer has inner and outer hook shaped edges  2106 ,  2108  that can engage as shown in  FIG. 50  to limit the amount of expansion of the spacer  2102 . The spinal implant  2100  may also include plugs or cores as shown in prior examples to support the spacer  2102  against collapse. Lateral retention of the spacer may be accomplished using the coils, flanges, discs, wires and/or other protrusions described above and below and will not be re-described relative to this embodiment. 
       FIGS. 51-52  illustrate a spinal implant  2200  similar to that of  FIGS. 49-50 . The spinal implant  2200  includes a coiled sheet-like spacer  2202  having tabs  2204  projecting away from the sheet to engage slots  2206  to limit the amount of expansion of the spacer  2202 . The tabs  2204  and/or slots  2206  may be positioned at the inner and outer edges of the coiled spacer  2202  or they may be positioned at one or more positions intermediate the edges. For example, the spacer may have tabs  2204  at one end and slots placed at multiple locations to allow the spacer to be fixed at different sizes. The spinal implant  2200  may also include plugs or cores as shown in prior examples to support the spacer  2202  against collapse. Lateral retention of the spacer may be accomplished using the coils, flanges, discs, wires and/or other protrusions described above and below and will not be re-described relative to this embodiment. 
       FIGS. 53-54  illustrate a spinal implant  2300  including a spacer  2302 , having a spacer axis  2303 , formed of an elastic material, such as a polymer or resin material. For example, the spacer  2302  may be a hydrogel or other composite or polymer material such as a silicone material. A bore  2304  extends through the spacer  2302  into a base  2306 . The base  2306  is shown with a wedge or conical shape to facilitate insertion but which could be any shape including rounded or blunt. Deployable retention members in the form of elastic arms  2308  are attached to the base  2306 . In use, the base  2306  is inserted between adjacent bones, e.g. spinous processes, parallel to the spacer axis  2303 . As the arms  2308  pass the spinous process, they fold into a compact or stowed insertion position in which they are nearer the spacer axis  2303  and lie along the sides of the spacer  2302  generally parallel to the spacer axis ( FIG. 53 ). Once the arms  2308  pass the spinous process, they return to an expanded or deployed retention position in which they project outwardly transverse to the spacer axis  2303  ( FIG. 54 ). Preferably, the arms  2308  only fold in one direction to provide increased retention once inserted. The spinal implant  2300  further includes a plate  2310  having a projection  2312 , such as a threaded shaft, extendable through the bore  2304  and threadably engaging the base  2306 . Threading, for example, the screw into the base  2306  compresses the spacer  2302  causing the diameter of the spacer  2302  to increase, providing distracting forces on the spinous process. Lateral stability is provided by the plate  2310  and the arms  2308  which extend away from the spacer axis  2303  on either side of the spinous process. 
     Alternatively to screw threading into the base  2306 , a bolt may be attached to the base and the plate  2310  and spacer  2302  compressed with a nut  2314 . Other mechanisms could also be used to compress the spacer  2302  including ratchets, press fits, rivets, and/or any other suitable mechanism. 
       FIGS. 55-57  illustrate a spinal implant  2400  including a base plate  2402  and a wedge plate  2404 . The base plate  2402  is shown as having a rectangular shape, but any shape is possible including, circular, elliptical, square, semi-circular, triangular, trapezoidal, random or the like. The base plate  2402  has a through hole  2406  (square in the example shown) and two attachment tabs  2408 . The attachment tabs have bores  2410 . 
     The wedge plate  2404  is shown as having a rectangular shape similar to the base plate  2402 , but the base plate  2402  and wedge plate  2404  do not necessarily have the same shape. Moreover, the wedge plate  2404  may have numerous possible shapes as explained with reference to the base plate  2402 . A wedge protrusion  2414  extends from a first side of the wedge plate  2404 . The wedge protrusion  2414  is shown with a generally triangular shape having a straight side, but other shapes are possible including sides that are rounded, beveled, curved, arched, convex, concave, or the like. The wedge protrusion  2414  has a superior surface  2416  and an inferior surface  2418  that generally converge as they travel away from the wedge plate  2404 . The wedge protrusion  2414  has a channel bore  2420  extending through a portion of the wedge protrusion  2414 . While not necessary and depending on anatomical factors, the channel bore  2420  may be located halfway between the superior surface  2416  and the inferior surface  2418 . The wedge protrusion  2414  and through hole  2406  are sized such that the base plate  2402  and wedge plate  2404  can abut, although in the typical implanted configuration, the base plate  2402  and wedge plate  2404  would not in fact abut as the bone, e.g. spinous process, would intervene between the base plate  2402  and wedge plate  2404  as shown in  FIG. 57 . 
     As best seen in  FIGS. 56 and 57 , the bores  2410  on attachment the tabs  2408  generally align with the channel bore  2420  when the wedge protrusion  2414  resides in the through hole  2406  such that a connector  2422  can extend through the bores  2410  and channel bore  2420  to connect the base plate  2402  and wedge plate  2404  during use. Typically, the connector  2422  comprises a screw and nut, but any conventional connector may be used. When first implanted, the base plate  2402  and wedge plate  2404  are aligned about a superior spinous process  2450  and an inferior spinous process  2452 . The connector  2422  connects the attachment tabs  2408  and the wedge protrusion  2414 . Ideally, but not necessarily, the connector  2422  is not tightened and the base plate  2402  and wedge plate  2404  may move with respect to each other, although in the initial condition they can only move closer together. Once the plates are aligned with the proper distraction, the connector  2422  may be tightened to lock the spinal implant  2400  in place. Ideally, but not necessarily, the supraspinous ligament remains intact to inhibit the spinal implant  2400  from moving posteriorly out of the interspinous process space. Alternatively, and optionally, base plate  2402  and wedge plate  2404  may comprise suture bores  2424  ( FIG. 57 ). A suture  2426  may be connected to the suture bores  2424  and traverse superior the spinous process  2450  and the inferior spinous process  2452 . Moreover, while only a pair of bores is shown with a pair of sutures, more may be provided. Moreover, the suture  2426  should be construed generically to refer to cables, wires, bands, or other flexible biocompatible connectors. Such sutures may be tied or locked using a tie, cable lock, or crimp. 
       FIG. 58  illustrates an alternative spinal implant  2500  similar in form and function to that of  FIGS. 55-57 . The spinal implant  2500  includes a base plate  2502  and a wedge plate  2504 . The base plate  2502  includes an attachment tab  2506  and a bore  2508 . The wedge plate  2504  has at least one wedge prong  2510 , but two wedge prongs  2510  are provided for improved device stability. The two wedge prongs  2510  form a prong channel  2512  to receive the attachment tab  2506  and provide some additional stability. The wedge prongs  2510  have channel bores  2514 . While both the attachment tab  2506  and the wedge prongs  2510  are shown as wedge shaped, both are not necessarily wedge shaped. The bore  2508  and channel bores  2514  align such that a connector  2516  can be fitted between them to couple the base plate  2502  and wedge plate  2504  together. Alternatively, the bore  2508  may be formed as a channel bore and the channel bores  2514  may be formed as a bore or they may all be channel bores to allow for lateral adjustment of the plates. 
       FIG. 59  illustrates an alternative spinal implant  2600  similar to that of  FIG. 58  but instead of bores and connectors, protrusions  2602  are formed inside the prong channel  2604  and on the attachment tab  2606 . The protrusions  2602  may be ribs, pins, shoulders, barbs, flanges, divots, detents, channels, grooves, teeth and/or other suitable protrusions. The protrusions  2602  may operate similar to a ratchet mechanism and may be configured so that the base plate and wedge plate can move towards each other and distract adjacent bones, e.g. spinous processes. The protrusions  2602  engage such that the plates do not move apart after they are pressed together. The prong channel  2604  may be widened, e.g. by prying it open, to disengage the protrusions  2602  and allow the plates to be separated. 
       FIGS. 60-61  illustrate a spinal implant  2700 . The spinal implant  2700  includes a spacer having a spacer axis  2701 , a first part  2702 , and a second part  2704 . The first part  2702  has a main body  2706  with a first end  2708  and a second end  2710 . One or more lateral walls  2712  extend out from the first part  2702  transverse to the spacer axis  2701  at the first end  2708 . The walls  2712  are adapted to extend along a superior and inferior spinous process on a first side. The second end  2710  is adapted to reside in a space between the superior and inferior spinous process. The second part  2704  includes a main body  2714  and has a first end  2716  and a second end  2718 . One or more lateral walls  2720  extend out from the second part  2704  transverse to the spacer axis  2701  at the first end  2716 . The walls  2720  are adapted to extend along a superior and inferior spinous process on a second side. The second end  2718  is adapted to reside in a space between the superior and inferior spinous process. The lateral wall  2712 ,  2720  may be shaped to accommodate anatomy. The second end  2710  of the first part  2702  and second end  2718  of second part  2704  abut or engage. A variety of features may be provided to enhance this engagement. For example, the second ends may include one or more channels and/or one or more protrusions that fit in the channels. A set screw or the like may threadably engage a bore extending through the first and second parts to maintain them in alignment. However, as explained below, a set screw and bore are optional. Interlocking channels and protrusions are optional as the ends may just abut or have interfering surfaces. The ends may be sloped transverse to the spacer axis  2701 , as shown, to facilitate insertion and/or to increase the abutment area. Some alternate examples will be described below relative to  FIGS. 62-67 . 
     Continuing with  FIGS. 60-61 , one or more through channels or bores  2722  extend through the first and second parts  2702 ,  2704 . A guidewire  2732  extends through the channels  2722  generally parallel to the spacer axis  2701 . The guidewire  2732  may be formed of wire, braided or twisted cable (made of metallic or polymer strands), suture material, a flat metallic or polymer band (either braided or solid) and/or other suitable materials and configurations. Multiple through channels may allow the guidewire  2732  to form a loop about the first end  2702  as shown in  FIG. 61 . The guidewire  2732  ends may be connected around the second end such as with a tie, crimp, knot, twist lock, cable lock, and/or other suitable connections. When the guidewire  2732  is not looped, the guidewire  2732  may be locked against both the first and second ends using a locking device such as a cable lock, crimp, knot, and/or any other suitable locking device. The guidewire  2732  maintains the first and second parts locked together. 
       FIGS. 62-63  illustrate a spinal implant  2800  similar to that of  FIGS. 60-61  except that it includes a protrusion  2804  extending from the second part  2704  to engage a slot  2802  extending from the first part  2702  to stabilize the first and second parts relative to one another. 
       FIG. 64  illustrates a spinal implant  2900  similar to that of  FIGS. 60-61  except that the first part  2702  defines slot  2902  and the second part  2704  tapers to a blade-like nose  2904  that engages the slot  2902 . 
       FIGS. 65-66  illustrate a spinal implant  3000  similar to that of  FIGS. 60-6.1  except that the first part  2702  defines tapering side cutouts  3002  separated by a central wedge shaped wall  3004  and the second part  2704  tapers to a wedge shaped second end  3006 . The wedge shaped second end is divided by a groove  3008 . When the first and second parts are pressed together, the wall  3004  engages the groove  3008  and the wedge shaped second end  3006  engages the side cutouts  3002 . Also, in the embodiment of  FIGS. 65-66 , the first and second parts  2702 ,  2704  have one or more bores  3010 ,  3012  transverse to the spacer axis  2701  for receiving a fastener to lock the parts together. 
       FIG. 67  illustrates a spinal implant  3100  similar to that of  FIGS. 60-66  and shown in the implanted condition. The first and second parts  2702 ,  2704  are secured together with a single guide wire  3102  secured at each end by a crimp  3104 . Passageways  3106  are provided through the lateral walls  2712 ,  2720 . Sutures, wires, cables, bands, or other flexible biocompatible material  3108  may extend through the passageways  3106  and over and/or through a spinous process. The flexible biocompatible material  3108  may loop under or over a single process (as shown on the superior process  3110 ), may loop around a single process (as shown on the inferior process  3112 ), or may loop around both processes, or a combination thereof. The flexible biocompatible material  3108  may be locked using a locking device similar to those explained above. The flexible biocompatible material  3108  and guidewire  3102  may optionally be the same element. 
       FIG. 68  is a flowchart describing one exemplary methodology for implanting the spinal implants of  FIGS. 60-67 . First, the patient is prepared for implanting the spinal implant, step  3202 . Preparing the patient may include, for example, making one or more incisions providing access to the spinal segment, placing the guidewire, etc. The surgical site is distracted (or measured as distraction may be caused by the spacer itself) using conventional distraction tools, step  3204 . Once exposed, the interspinous process space is prepared to receive the spinal implant, step  3206 . This typically includes preparing the spinous processes to accept the spinal implant, which may include removing some portion of the spinous process, and removing muscle, tendons, and ligaments that may interfere with implanting the spinal implant and/or may provide force tending to unseat the spinal implant. The first part of the spinal implant is inserted, over or with the guidewire, to the surgical site through the incision or the like, step  3208 . Once at the site, the first part of the spinal implant is positioned or aligned such that the lateral walls are loosely abutting a first side of the superior and inferior spinous processes and the second end extends into the interspinous space, step  3210 . Generally, this means that the first part is implanted through the interspinous process space. The guidewire, which is attached to the first part of the spinal implant as explained above extends from the second end of the first part and is attached to the second part of the spinal implant. Thus, the surgeon inserts the second part along the guidewire, step  3212 . Note, the first part and second part may be positioned using tools or the surgeon may place the parts using hands and fingers. Using the guidewire, the protrusions (if any) on the second part are inserted into the channels of the first part (if any) to align the first part and second part of the spinal implant, step  3214 . Compressive force is applied to mate the first part and the second part, step  3216 . The compressive force may be applied by crimping the guidewire, threading a cable lock, a separate clamp, or the like. Once sufficiently compressed, the first part and second part are locked together, step  3218 . Optionally, excess guidewire may be cut and removed or looped around the adjacent superior and inferior spinous process to provide secured seating, step  3220 . Once mated in the interspinous space, the distraction of the spinal segment may be released, step  3222 , and the patient&#39;s surgical site may be closed, step  3224 . 
       FIG. 69  illustrates a spinal implant  3300 . The spinal implant  3300 , includes a superior spinous process seat  3302  and an inferior spinous process seat  3304 . As shown, seats  3302  and  3304  form a U and inverted U shape, but other shapes are possible including a square channel shape for each seat, a C-shape, and/or any other suitable shape, although it is believed the saddle shape as shown would work well. 
     Seat  3302  includes a surface  3306  which contacts the superior spinous process and walls  3308  traversing each side of the superior spinous process to capture superior spinous process in seat  3302 . Walls  3308  may be convergent, divergent or relatively parallel. Walls  3308  may be more akin to bumps, ribs, or shoulders to traverse only a minor portion of the spinous process or may be longer to traverse a major portion of the spinous process. Surface  3306  and walls  3308  may be discrete or shaped like a saddle forming a smooth surface in which spinous process can rest. Attached to one wall  3308  is a vertical distraction post  3310  extending towards inferior seat  3304 . While only one vertical distraction post  3310  is shown, multiple posts are possible. Moreover, if multiple posts are used, vertical distraction posts  3310  may reside on opposite sides of superior spinous process seat  3302 . While shown as a straight post, vertical distraction post  3310  may be curved or straight depending on anatomical considerations or the like. 
     Similar to seat  3302 , seat  3304  includes a surface  3306  which contacts the inferior spinous process and walls  3308  traversing each side of the inferior spinous process to capture inferior spinous process in seat  3304 . Attached to one wall  3308 , on the side corresponding to vertical distraction post  3310  is an attachment tab  3312 . Attachment tab  3312  has a vertical bore  3314  through which vertical distraction post  3310  extends. Seat  3304  can be moved closer to or further from seat  3302  along vertical distraction post  3310 . Attachment tab  3312  also comprises a horizontal bore  3316 . Horizontal bore  3316  intersects vertical bore  3314 . A seating device  3318  is insertable into horizontal bore  3316 . As shown horizontal bore  3316  is threaded to accept a set screw or the like. 
     In use, a surgeon would distract superior and inferior spinous processes and implant spinal implant  3300 . Seats  3302  and  3304  would be set at a desired distraction and, for example, set screw  3318  would be threaded into horizontal bore  3316  to apply seating force to seat vertical distraction post  3310  in vertical bore  3314  locking seats  3302  and  3304  at the set distraction distance. 
     Vertical distraction post  3310  and/or vertical bore  3314  may be arranged with a protrusion  3319  or detent to inhibit the ability of withdrawing vertical distraction post  3310  from vertical bore  3314 . 
       FIG. 70  illustrates alternative seats  3400  and  3402 . Seats  3400  and  3402  are designed to nest or interlock. In that regard, seat  3400  has one or more first blades  3404  or multiple surfaces spaced apart so first gaps  3406  separate first blades  3404 . Seat  3402  would similarly have one or more second blades  3408  or multiple surfaces. Seat  3402  is shown with a single second blade for convenience. Second plate  3408  is aligned with first gaps  3406  such that seats  3400  and  3402  may nest or interlock. Similarly, first blades  3404  could align with second gaps, not shown. Either first blades  3404  (as shown) or second blade  3408  may attach to a vertical distraction post  3410  and second blade  3408  (as shown) or first blades  3404  may attach to attachment tab  3412 . 
     Although examples of a spinal implant and its use have been described and illustrated in detail, it is to be understood that the same is intended by way of illustration and example only and is not to be taken by way of limitation. The invention has been illustrated in the form of a spinal implant for use in spacing adjacent spinous processes of the human spine. However, the spinal implant may be configured for spacing other portions of the spine or other bones. Accordingly, variations in and modifications to the spinal implant and its use will be apparent to those of ordinary skill in the art. The various illustrative embodiments illustrate alternative configurations of various component parts such as spacers, retention members, additional fasteners, and the like. In most cases, and as will be readily understood by one skilled in the art, the alternative configuration of a component part in one embodiment may be substituted for a similar component part in another embodiment. For example, the differently shaped or expandable spacers in one example may be substituted for a spacer in another example. Likewise the various mechanisms for deploying a retention member or for providing additional fasteners may be interchanged. Furthermore, throughout the exemplary embodiments, where component part mating relationships are illustrated, the gender of the component parts may be reversed as is known in the art within the scope of the invention. The following claims are intended to cover all such modifications and equivalents.