Abstract:
An implantable spinous process stabilization assembly includes a body, a bent arm and a straight arm. The body includes first and second crosspieces arranged parallel to each other, a first plate extending in a direction at right angle to first ends of the first and second crosspieces, first and second rings extending from second ends of the first and second crosspieces, respectively and a second plate extending from a base of the first and second rings, at right angle to the first and second crosspieces and in an opposite direction to the first plate&#39;s direction. The bent arm and the straight arm are configured to pivot around an axis perpendicular to the first and second rings and to set first and second pivot angles with the first and second plates, respectively, thereby defining first and second spaces configured to receive and lock onto first and second spinous processes, respectively.

Description:
CROSS REFERENCE TO RELATED CO-PENDING APPLICATIONS 
     This application claims the benefit of U.S. provisional application Ser. No. 60/784,557 filed Mar. 21, 2006 and entitled “SPINOUS PROCESS FIXATION DEVICE”, the contents of which are expressly incorporated herein by reference. 
     This application is also a continuation in part of U.S. application Ser. No. 11/609,418 filed on Dec. 12, 2006 and entitled SPINOUS PROCESS FIXATION IMPLANT, the contents of which are expressly incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a system and a method for spinal stabilization through an implant, and more particularly to spinal stabilization through attachment of the implant to the spinous processes along one or more vertebras. 
     BACKGROUND OF THE INVENTION 
     The human spine comprises individual vertebras  330  (segments) that are connected to each other to form a spinal column  329 , shown in  FIG. 12A . Referring to  FIGS. 12B and 12C , each vertebra  330  has a cylindrical bony body (vertebral body)  332 , three winglike projections (two transverse processes  333 ,  335  and one spinous process  334 ), left and right facet joints  346 , lamina  347 , left and right pedicles  348  and a bony arch (neural arch)  336 . The bodies of the vertebrae  332  are stacked one on top of the other and form the strong but flexible spinal column. The neural arches  336  are positioned so that the space they enclose forms a tube, i.e., the spinal canal  337 . The spinal canal  337  houses and protects the spinal cord and other neural elements. A fluid filled protective membrane, the dura  338 , covers the contents of the spinal canal. The spinal column is flexible enough to allow the body to twist and bend, but sturdy enough to support and protect the spinal cord and the other neural elements. The vertebras  330  are separated and cushioned by thin pads of tough, resilient fiber known as inter-vertebral discs  340 . Disorders of the spine occur when one or more of the individual vertebras  330  and/or the inter-vertebral discs  340  become abnormal either as a result of disease or injury. In these pathologic circumstances, fusion of adjacent vertebral segments may be tried to restore the function of the spine to normal, achieve stability, protect the neural structures, or to relief the patient of discomfort. 
     Several spinal fixation systems exist for stabilizing the spine so that bony fusion is achieved. The majority of these fixation systems utilize rods that attach to screws threaded into the vertebral bodies or the pedicles. In some cases plate fixation systems are also used to fuse two adjacent vertebral segments. This construction usually consists of two longitudinal plates that are each placed laterally to connect two adjacent pedicles of the segments to be fused. This system can be extended along the sides of the spine by connecting two adjacent pedicles at a time similar to the concept of a bicycle chain. Current plate fixation systems are basically designed to function in place of rods with the advantage of allowing intersegmental fixation without the need to contour a long rod across multiple segments. Both the plating systems and the rod systems add bulk along the lateral aspect of the spine limits access to the pars and transverse processes for decortication and placement of bone graft. In order to avoid this limitation many surgeons decorticate before placing the rods, thereby increasing the amount of blood loss and making it more difficult to maintain a clear operative field. Placing rods or plates lateral to the spine leaves the center of the spinal canal that contains the dura, spinal cords and nerves completely exposed. In situations where problems develop at the junction above or below the fused segments necessitating additional fusion, the rod fixation system is difficult to extend to higher or lower levels that need to be fused. Although there are connectors and techniques to lengthen the fixation, they tend to be difficult to use and time consuming. 
     Accordingly, there is a need for a spinal stabilization device that does not add bulk to the lateral aspect of the spine and does not limit access to the pars and transverse processes for decortication and placement of bone graft. 
     SUMMARY OF THE INVENTION 
     In general, in one aspect, the invention features an implantable assembly for stabilization of spinous processes, including a body, a bent arm and a straight arm. The body includes first and second crosspieces arranged parallel to each other, a first plate extending in a direction at right angle to first ends of the first and second crosspieces, first and second rings extending from second ends of the first and second crosspieces, respectively, and a second plate extending from a base of the first and second rings, at right angle to the first and second crosspieces and in an opposite direction to the first plate&#39;s direction. The second ends are arranged opposite to the first ends. The straight arm and bent arm are configured to pivot around an axis perpendicular to the first and second rings and to set first and second pivot angles with the first and second plates, respectively, thereby defining first and second spaces configured to receive first and second spinous processes, respectively. 
     Implementations of this aspect of the invention may include one or more of the following features. The straight arm extends along the first plate&#39;s direction and comprises a ring and a plate extending from a portion of the ring so that the plate&#39;s plane is perpendicular to the ring&#39;s plane. The straight arm plate comprises a first surface arranged opposite to a first surface of the first plate of the body. The bent arm comprises a bent shaft, a ring extending from a first end of the bent shaft and a plate extending form a second end of the bent shaft so that the plate&#39;s plane is perpendicular to the ring&#39;s plane. The bent arm plate comprises a first surface arranged opposite to a first surface of the second plate of the body. The straight arm ring and the bent arm ring are configured to be received within a gap formed between the first and second body rings. The assembly may further include a post member configured to pass through concentrically aligned through-bore openings formed in the first body ring, the straight arm ring, the bend arm ring and the second body ring. The post comprises outer threads configured to engage inner threads formed in the through-bore openings of the first body ring, the straight arm ring, the bend arm ring and the second body ring, consecutively, thereby locking and preventing the pivoting of the straight arm and the bent arm around the axis. The first surface of the first body plate, the first surface of the straight arm plate, the first surface of the second body plate and the first surface of the bent arm plate comprise protrusions configured to engage and frictionally lock the plates onto the first and second spinous processes positioned in the first space between the first body plate and the straight arm plate and the second space between the second body plate and the bent arm plate, respectively. The first and second crosspieces are dimensioned to fit between the first and second spinous processes and comprise edges sculpted to conform to the shape of the spinous processes. The first and second pivot angles comprise values between zero and 90 degrees. The assembly may be assembled prior to being implanted between the first and second spinous processes, or after being implanted between the first and second spinous processes. The assembly may further include a first locking member configured to lock the first plate&#39;s top end and the straight arm plate&#39;s top end to the first spinous process. The first locking member comprises a long bolt configured to be threaded through bolt holes formed through the first plate&#39;s top end, the first spinous process and the straight arm plate&#39;s top end and locks the first plate&#39;s top end, the first spinous process and the straight arm plate&#39;s top end by engaging a first nut after it exits the straight arm plate&#39;s bolt hole. The assembly may further include a second locking member configured to lock the second plate&#39;s bottom end and the bent arm plate&#39;s bottom end to the second spinous process. The second locking member comprises a long bolt configured to be threaded through bolt holes formed through the second plate&#39;s bottom end, the second spinous process and the bent arm plate&#39;s bottom end and locks the second plate&#39;s bottom end, the second spinous process and the bent arm plate&#39;s bottom end by engaging a second nut after it exits the bent arm plate&#39;s bolt hole. The first and second locking members may be staples, cables, sutures, pins or screws. The first and second plates, the straight arm and the bent arm may have adjustable lengths. The first and second crosspieces may have adjustable heights. The assembly may further include an extension body and the extension body may have first and second crosspieces arranged parallel to each other, a first plate extending in a direction at right angle to first ends of the first and second crosspieces, first and second rings extending from second ends of the first and second crosspieces, respectively, and a second plate extending at right angle to the first ends of the first and second crosspieces in an opposite direction to the first plate&#39;s direction. The second ends are arranged opposite to the first ends. The assembly may further include a second straight arm extending along the extension body second plate&#39;s direction and comprises a ring and a plate extending from a portion of the ring so that the plate&#39;s plane is perpendicular to the ring&#39;s plane. The second straight arm plate comprises a first surface arranged opposite to a first surface of the second plate of the extension body. The second straight arm is configured to pivot around an axis perpendicular to the extension body&#39;s first and second rings and to set a third pivot angle with the second plate of the extension body thereby defining a third space configured to receive a third spinous processes between the extension body&#39;s second plate and the second straight arm&#39;s first plate. The ring of the second straight arm is configured to be received within a gap formed between the extension body&#39;s first and second rings. The assembly may further include a second post member configured to pass through concentrically aligned through-bore openings formed in the extension body&#39;s first ring, the second straight arm ring and the extension body&#39;s second ring. The first surface of the extension body second plate, and the first surface of the second straight arm plate comprise protrusions configured to engage and frictionally lock the plates onto the third spinous process positioned in the third space between the extension body second plate and the straight arm plate. The extension body&#39;s first and second crosspieces are dimensioned to fit between the second and third spinous processes and comprise edges sculpted to conform to the shape of the spinous processes. The assembly may further include a third locking member configured to lock the extension body second plate&#39;s bottom end and the second straight arm plate&#39;s bottom end to the third spinous process. The third locking member comprises a long bolt configured to be threaded through bolt holes formed through the second straight arm plate&#39;s bottom end, the third spinous process and the extension body second plate&#39;s bottom end and locks the extension body second plate&#39;s bottom end and the second straight arm plate&#39;s bottom end to the third spinous process by engaging a third nut after it exits the second straight arm plate&#39;s bolt hole. The first plate of the extension body is attached to the second plate of the body. The first plate of the extension body is attached to the second plate of the body with the second locking member. The extension body first plate comprises a first surface having a spur configured to be received within a slot formed in the second plate of the body. The protrusions may teeth, spikes, serrations, rough coatings or ridges. The body, the extension body and the straight and bent arms may be made of stainless steel, titanium, gold, silver, alloys thereof, or absorbable material. 
     In general, in another aspect, the invention features a method for stabilizing spinous processes of a spinal column, including providing a body, a straight arm and a bent arm. The body comprises first and second crosspieces arranged parallel to each other, a first plate extending in a direction at right angle to first ends of the first and second crosspieces, first and second rings extending from second ends of the first and second crosspieces, respectively, wherein the second ends are arranged opposite to the first ends, and a second plate extending from a base of the first and second rings, at right angle to the first and second crosspieces and in an opposite direction to the first plate&#39;s direction. The method also includes engaging a first surface of the first plate with a first lateral surface of a first spinous process and a first surface of the second plate with a second lateral surface of a second spinous process. Next, engaging a first surface of the bent arm with a first lateral surface of the second spinous process and then engaging a first surface of the straight arm with a second lateral surface of the first spinous process. The bent arm and the straight arm are configured to pivot around an axis perpendicular to the first and second rings and to set first and second pivot angles with the first and second plates, respectively, thereby defining first and second spaces configured to receive the first and second spinous processes, respectively. 
     Among the advantages of this invention may be one or more of the following. The assembly stabilizes vertebras by attaching plates to the spinous processes of the vertebras. This stabilization device does not add bulk to the lateral aspect of the spine and does not limit access to the pars and transverse processes for decortication and placement of bone graft. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and description below. Other features, objects and advantages of the invention will be apparent from the following description of the preferred embodiments, the drawings and from the claims 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring to the figures, wherein like numerals represent like parts throughout the several views. Various embodiments of the present invention will now be discussed with reference to the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. 
         FIG. 1  is a posterior view of a portion of the spine with one embodiment of a spinous process fixation device of the present invention affixed thereto; 
         FIG. 2  is a perspective anterior view of the body of the device of  FIG. 1 ; 
         FIG. 3  is a perspective anterior view of the straight arm of the device of  FIG. 1 ; 
         FIG. 4  is a perspective posterior view of the straight arm of  FIG. 3 ; 
         FIG. 5  is a perspective anterior view of the bent arm of the device of  FIG. 1 ; 
         FIG. 6  is a perspective posterior view of the bent arm of  FIG. 5 ; 
         FIG. 7  is a perspective posterior view of the body of  FIG. 2  with the straight arm of  FIG. 3  and the bent arm of  FIG. 5  attached; 
         FIG. 8  is a cross-sectional view of the assembly of  FIG. 7  as seen from a caudal perspective; 
         FIG. 9  is a posterior view of a portion of the spine with a spinous process fixation device according to an alternative embodiment of the present invention affixed thereto; 
         FIG. 10  is a perspective posterior view of the extension body of  FIG. 9 ; 
         FIG. 11  is a perspective view of the extension body of  FIG. 9  with the straight arm of  FIG. 3  attached; 
         FIG. 12A  is a side view of the human spinal column; 
         FIG. 12B  is an enlarged view of area A of  FIG. 12A ; and 
         FIG. 12C  is an axial cross-sectional view of a lumbar vertebra. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention relates to a system and a method for a spinous process fixation implant. 
     Referring to  FIG. 1 , a posterior view illustrates a portion of the spine with an embodiment of the present invention. A spinous process fixation device  10  includes a body  12 , a bent arm  14 , and a straight arm  16 . A short bolt  20 , two long bolts  22   a ,  22   b,  and nuts  24   a ,  24   b  hold the elements of the device  10  together. Each long bolt  22   a ,  22   b  also passes through one spinous process  4   a ,  4   b  securing the device  10  to the vertebrae  2   a,    2   b , respectively. 
       FIGS. 2 through 8  display the device  10  in more detail. As seen in  FIG. 2 , the body  12  has an anterior side  36  and a posterior side  38 . It includes a pair of crosspieces  40 ,  42 . At a right angle to one end of the crosspieces  40 ,  42  is a first plate  44 . At the opposite end of the crosspieces  40 ,  42 , a pair of rings  48 ,  50  extends from the crosspieces. In the embodiment depicted in  FIGS. 1 and 2  the rings are located at one end of the crosspieces, however in alternative embodiments they could be located at either end or in the center of the crosspieces, or anywhere on the body  12  which places them in the vicinity of or between the spinous processes when the device is implanted. A second plate  46  extends from the base of the rings  48 ,  50 , at a right angle to the crosspieces  40 ,  42 , and in the opposite direction from the first plate  44 . Each crosspiece  40 ,  42  has edges  66  which are rounded and sculpted to correspond with the geometry of the spinous processes and lamina around which they will fit once implanted. 
     The first plate  44  is a substantially flat, rectangular surface extending perpendicularly from the crosspieces  40 ,  42 . It has a first side  52  and a second side  54 , and ends in a rounded terminus  56 . A first bolt hole  58  passes through the first plate  44  near the terminus  56 . Surrounding the bolt hole  58  on the first side  52  is a plurality of teeth  60  which protrude out of the surface of the first side. Indented into the second side  54 , between the bolt hole  58  and the terminus  56 , is a kidney-shaped first slot  62  (not visible in  FIG. 2 ). 
     At the opposite end of the crosspieces  40 ,  42  from the first plate  44  are the rings  48 ,  50 . The first ring  48  is a rounded extension of the first crosspiece  40 , and the second ring  50  is a rounded extension of the second crosspiece  42 . The rings  48 ,  50  are parallel to each other and a gap  68  between them is sized to hold portions of a straight arm  16  and a bent arm  14 , as seen in  FIG. 2 . The first ring  48 , which lies on the posterior side  38 , has a circular first bore  70 . This first bore  70  is sized to receive a short bolt  20 . The second ring is on the anterior side  36 , and has a circular second bore  72 . This second bore  72  is larger in diameter than the first bore  70 , and is sized to receive a short bolt  20  plus a portion of the straight arm  16 . 
     The second plate  46  extends at a right angle from the rings  48 ,  50  and ends in a rounded terminus  76 . A second bolt hole  78  penetrates the plate  46  near the terminus  76 . On the first side  52 , in between the terminus  76  and the bolt hole  78  is a kidney-shaped second slot  82 . On the second side  54 , surrounding the second bolt hole  78  is a plurality of teeth  80 . 
     As seen in  FIGS. 1 and 2 , the rings  48 ,  50  form the pivot point for the body  12 . A pivotable straight arm  16  fits in the gap  68  between the rings  48 ,  50  of the body  12 , and extends in the same direction as the first plate  44 .  FIGS. 3 and 4  display the straight arm  16  in more detail. One end of the straight arm  16  is a ring  90 , and extending from a portion of the ring is a plate  96 , which forms the remainder of the straight arm. The ring  90  has an anterior side  92  and a posterior side  94 . In the center of the ring  90  is a bore  98 , sized to fit the short bolt  20 . A protruding annulus  100  surrounds the bore  98  and projects outward from the anterior side  92 . The bore  98 , through both the ring  90  and the annulus  100 , is encircled by a threaded wall  99  (threads not visible in  FIGS. 3 and 4 ). Surrounding the bore  98  on the posterior side  94  of the ring  90  is a radial spline  102 . 
     The plate  96  extends away from the ring  90  such that the plane of the plate is perpendicular to the plane of the ring. The plate has a first side  104 , a second side  106 , and ends in a terminus  108 . Adjacent to the terminus  108  is a bolt hole  110 , which is has a diameter to fit a long bolt  22 , but is elongated to allow the vertical placement of the arm  16  on the bolt  22  to be adjustable. A plurality of teeth  112  surround the bolt hole  110 , projecting outward from the first side  104 . 
     Returning briefly to  FIGS. 1 and 2 , a bent arm  14  also fits in the gap  68  between the rings  48 ,  50  of the body  12 .  FIGS. 5 and 6  show the bent arm  14  in more detail. The bent arm  14  is comprised of a bent shaft  122 , a ring  120  and a plate  124 . The shaft  122  is an elongated member which is bent at a right angle near its center. The shaft  122  has a first side  126  on the inside of the bend; a second side  128  is on the outside; and anterior  130  and posterior  132  sides. One end of the bent shaft  122  connects to a ring  120 , and the opposite end terminates in a plate  124 . The ring  120  also has an anterior side  130  which is a continuation of the anterior side of the shaft  122 , and a posterior side  132  which is a continuation of the posterior side of the shaft  122 . In the center of the ring  120  is a circular bore  138 , whose diameter is sized to fit a short bolt  20 . On the posterior side  132  of the ring  120 , a radial spline  146  surrounds the bore  138 . 
     At the opposite end of the shaft  122  from the ring  120  is the plate  124 . The plate  124  is generally rectangular, and has a first side  126  which is a continuation of the first side of the shaft  122 . A second side  128  is a continuation of the second side of the shaft  122 . The plate  124  ends in a terminus  144 . Passing through the first and second sides  126 ,  128  adjacent to the terminus  144  is a bolt hole  140 . The bolt hole  140  has a diameter to fit a long bolt  22  but is elongated along the long axis of the shaft  122  so the placement of the bent arm  14  can be adjustable relative to the bolt  22 . Surrounding the bolt hole  140  and projecting from the first side  126  is a plurality of teeth  142 . 
     As shown in  FIG. 7 , a body  12 , bent arm  14 , and straight arm  16  are assembled to form one embodiment of the spinous process fixation device. The ring  90  of the straight arm  16  is placed between the rings  48 ,  50  of the body  12 , and the protruding annulus  100  is fitted into the larger second bore  72  on the second ring  50 . The plate  96  of the straight arm  16  is positioned so it is approximately parallel to the first plate  44  of the body  12 . Next, the ring  90  of the bent arm  14  is slid in between the first ring  48  of the body  12  and the ring  90  of the straight arm  16 . The shaft  122  of the bent arm  14  fits between the crosspieces  40 ,  42  of the body  12 . The bent arm  14  is positioned so that its plate  124  is approximately parallel to the second plate  46  of the body  12 . 
     With all pieces  12 ,  14 ,  16  assembled thus, a short bolt  20  is slid into place from the posterior side  38  of the body  12 .  FIG. 8  shows a cross-sectional view of the bolt  20  where it intersects the body ring  48 , the bent arm ring  120 , and the straight arm ring  90 . The bolt  20  has a head  21 , and a shaft  23  which is encircled by threads  25 . The bolt  20  passes through the first bore  70  (of the body  12 ), through the bore  138  (of the bent arm  14 ), and finally to the bore  98  (of the straight arm  16 ). When the bolt  20  reaches the bore  98 , threads  25  on the shaft  23  engage with the threaded wall  99  of the bore  98 . The bolt  20  is turned until the head  21  meets the posterior ring  48  (of the body  12 ). As the bolt  20  is turned further, the engagement of the threads pulls the straight arm ring  90  posteriorly, tightening the straight arm ring  90 , the bent arm ring  120 , and the body ring  48  together. As the rings are tightened, the radial spline  102  on the straight arm  16  is pressed against the anterior side of the bent arm&#39;s ring  120 . Similarly, the radial spline  146  on the bent arm  14  is pressed against the anterior side of the body&#39;s posterior ring  48 . 
     The assembled components are implanted into the patient with the use of instrumentation (not shown) between two adjacent spinous processes  4   a ,  4   b , as seen in  FIGS. 1 and 7 . The crosspieces  40 ,  42  are placed between the spinous processes  4   a ,  4   b , so that the plates  44 ,  46 ,  96 ,  124  fall on the lateral sides of the spinous processes. One spinous process  4   a  lies between the first plate  44  (of the body) and the plate  96  (of the straight arm), and the other spinous process  4   b  lies between the second plate  46  and the plate  124  (of the bent arm). On each of the plates  44 ,  46 ,  96 ,  124 , the corresponding teeth  60 ,  80 ,  112 ,  142  face toward the lateral surface of the adjacent spinous process. At this point, the arms  14 ,  16  are pivoted as necessary to provide the desired fit of the plates to the spinous processes. The bolt  20  is tightened, clamping the teeth  60 ,  80 ,  112 ,  142  into the surfaces of the spinous processes. The radial splines  102 ,  146  are pressed into their adjacent surfaces. The protruding teeth and splines create additional friction which helps prevent the device from shifting or slipping. 
     Long bolts  22   a ,  22   b  may be added to this embodiment to further anchor the device on the spinous processes  4   a ,  4   b,  respectively. If they are added, appropriately sized holes must be drilled laterally through the spinous processes prior to placement of the device. Once the device is in place as described above, one long bolt  22   a  is threaded through the bolt hole  58  on the first plate  44  of the body  12 , through the drilled hole in the spinous process  4   a,  then out through the bolt hole  110  on the straight arm  16 . The second long bolt  22   b  is threaded through the bolt hole  78  on the second plate  46 , through the drilled hole in the spinous process  4   b , then out through the bolt hole  140  on the bent arm  14 . The fit of the device may be adjusted by loosening the short bolt  20  and pivoting the arms  14 ,  16  until the proper orientation is found. The elongated bolt holes  110 ,  140  on the arms allow for adjustment of the arms  14 ,  16  while still being able to receive the ends of the long bolts  22   a ,  22   b . The short bolt  20  is tightened, and nuts  24   a ,  24   b  are screwed on the ends of the long bolts  22   a ,  22   b,  respectively, and tightened. 
     In this embodiment of the invention, a plurality of bolts and nuts holds the elements of the device  10  together and secures them to the vertebrae. The use of bolts adds adjunctive tension to the plates, and adds additional strength during flexion and extension. However, pins, screws, cables, or other connecting elements may be implemented instead to connect and secure the elements of the device. 
     The primary indication of the device  10  is as an adjunctive fixation device, in association with an interbody fusion device. However, if desired, the device as described may also be use as a dynamic stabilization device, if the plates are not clamped down tightly on the spinous processes. The device  10  may also be used as described as an X stop, reducing pressure on the intervertebral disks during extension. 
     When the device  10  is used as an adjunctive fixation device, it may be desirable to add bone ingrowth surfaces to the edges  66  of the crosspieces  40 ,  42 . The bone ingrowth surfaces may be additive, such as but not restricted to plasma spray, laser deposition of metal, or a sintered bead coating. Alternatively, the bone ingrowth surfaces may be created by electrochemical etching or other removal processes. If the device is to be used as a dynamic stabilization device or an X stop, no bone ingrowth surfaces would be created. 
     An alternative embodiment of the device is depicted in  FIG. 9 , bolted through three spinous processes  4   a ,  4   b ,  4   c . This device is indicated when more than two adjacent spinous processes require fixation. The device  11  includes a body  12 , a bent arm  14 , two straight arms  16 , an extension body  18 , and a plurality of bolts  20   a ,  20   b ,  22   a ,  22   b ,  22   c  and nuts  24   a - 24   c . The embodiment shown in  FIG. 9  has one body  12  and one extension body  18 ; another embodiment could include one body  12  with two extension bodies  18 , one added on either end of the body  12 . Yet other embodiments could include one body  12  with one extension body  18  linked to it, and one or more extension bodies  18  linked to the first extension body  18  in succession, depending on how many spinous processes are to be fixed. 
       FIG. 10  shows the extension body  18  in greater detail. The extension body  18  has a posterior side  160  and an anterior side  162 . A first plate  164  occupies one end of the body, and a second plate  166  is at the opposite end. A posterior ring  168  and an anterior ring  170  lie perpendicular to the plates  164 ,  166 , with a gap  171  between them. A posterior crosspiece  172  connects the posterior ring  168  to the posterior edges of the plates  164 ,  166 , and an anterior crosspiece  174  connects the anterior ring  170  to the anterior edges of the plates  164 ,  166 . Each crosspiece  172 ,  174  has edges  175  which are rounded and sculpted to correspond with the geometry of the spinous processes and lamina around which they will fit once implanted. As with the body  12 , bone ingrowth surfaces may be created on the edges  175  if the device  11  is to be used as an adjunctive fixation device. 
     The first plate  164  is generally flat and rectangular, and one rectangular end terminates in a rounded terminus  176 . The plate  164  has a flat first side  184  and a flat second side  186 . Adjacent to the terminus  176  and passing through both sides  184 ,  186  is a bolt hole  178 . A spur  182  projects from the first side  184 , on the opposite side of the bolt hole  178  from the terminus  176 . 
     The second plate  166  extends in the opposite direction but on the same plane as the first plate  164 . The second plate  166  is also generally flat and rectangular, and ends in a rounded terminus  188 . Adjacent to the terminus  188 , a bolt hole  190  is open from the first side  184  to the second side  186 . Surrounding the bolt hole  190  are a plurality of teeth  192  which project outward from the first side  184 . 
     The rings  168 ,  170  are parallel to one another and are perpendicular to the plates  164 ,  166 , extending in the direction of the first side  164 . The posterior ring  168  has a central first bore  194  which is sized to fit the diameter of a short bolt  20   b . The anterior ring  170  has a central second bore  196  which is wider in diameter, sized to fit the annulus  100  on a straight arm  16  (as seen in  FIG. 4 ). 
     An extension body  18  linked to a straight arm  16  is depicted in  FIG. 11 . The straight arm, as seen also in  FIGS. 3 and 4 , has a ring  90  and a plate  96 . The ring  90  is put into the gap  171  between the rings  168 ,  170  of the extension body  18 . The annulus  100  on the ring  90  fits into the second bore  196  on the anterior ring  170 . A circular washer  200  fits into the remainder of the gap  171 , between the ring  90  and the posterior ring  168 . A short bolt  20   b  is inserted from the posterior side  160  through the bore  194 , the washer  200 , and the bores  98 ,  196 . The straight arm  16  is pivoted on the bolt  20   b  so its plate  96  is approximately parallel to the plate  166  on the extension body  18 . 
     In this embodiment of the invention, the rings  168 ,  170  are located at one end of the crosspieces  172 ,  174 . The rings  168 ,  170  and their associated short bolt  20  form a pivot point for adjusting the fit of the plates  96 ,  166  around the spinous process. In alternative embodiments of the invention, the rings and therefore the pivot point could be located at the center of the crosspieces, at the other end of the crosspieces, or any other location on the extension body which puts the pivot point in the vicinity of or between the spinous process. 
     Referring to  FIGS. 7 ,  9  and  11 , the extension body  18  with the attached straight arm  16  is connected to the body  12  by lining up the first plate  164  of the extension body  18  with the second plate  46  of the body  12 . The first side  184  of the extension body  18  is placed against the first side  52  of the body  12 , so that the bolt holes  78 ,  178  line up. The spur  182  on the extension body  18  fits into the slot  82  on the body  12 . A long bolt  22   b  is passed from the second side  186  of the extension body and through both bolt holes  78 ,  178 . It then passes through the hole in the spinous process  4   b  and through the bolt hole  140  on the bent arm  14 . 
     Several adjustments may be made to fit the device to the spinous processes. The longitudinal angle of the extension body  18  relative to the body  12  is adjusted by pivoting the extension body  18  around the long bolt  22   b . The spur  182  slides within the slot  82 , allowing for some adjustment but preventing slippage beyond a certain point. Once the correct angle is found, a nut  24   b  is added to the end of the bolt  22   b  and tightened. 
     After the angle adjustment is made to the extension body  18 , the final long bolt  22   c  connects the second plate  166  to the straight arm  16 . It is threaded from the second side  186  of the extension body  18  through the bolt hole  190 , through the hole in the spinous process  4   c , then through the bolt hole  110  on the straight arm  16 . 
     The angle of the straight arm  16  attached to the extension body  18  is adjusted by pivoting it around the short bolt  20   b . The elongated shape of the bolt hole  110  allows for some movement of the straight arm  16  while still allowing the long bolt  22   c  to reach through the hole  110 . Once the correct fit is found, the short bolt  20   b  is tightened. As it is tightened, the radial spline  102  on the straight arm  16  is pressed into the washer  200 , creating additional friction. A nut  24   c  is added to the end of the long bolt  22   c  and tightened. As the nut  24   c  is tightened, the plates  96 ,  166  and their teeth  112 ,  192  are pressed in and grip the spinous process  4   c.    
     The fit of the spinous fixation device on the spinous processes is determined by two factors: the size of the component pieces and their ability to be pivoted. The body, extension body, straight arm and bent arm components are all available in small, medium and large sizes. All three sizes are of a standard depth (posterior to anterior direction) but increase in length from small to large. The lateral width of the device is determined by the pivotability of the components around the short bolts. The elongated bolt holes on the ends of the straight and bent arms allow those pieces freedom to be pivoted laterally yet still be connectable to the long bolts. 
     The device is conformed to the lordotic or kyphotic angle of the spine by the pivotability of the components around the long bolts. The plates of the body and the extension body (or bodies, if three or more spinous processes are fixed) are swiveled posteriorly or anteriorly at infinite increments to fit the spine prior to the tightening of the long bolt. The spur and slot mechanism which engages when an extension body is linked to a body allows for several degrees of rotation but prevents slipping. 
     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. As such, the described embodiments are to be considered in all respects only as illustrative and not restrictive. Other embodiments are within the scope of the following claims. For example, vertebras  2   a  and  2   b  may be any two vertebras, including lumbar L1-L5, thoracic T1-T12, cervical C1-C7 or the sacrum. The fixation assembly  10  may extend along multiple vertebras. The body structure  12  may be also configured as a mirror image of the structure in  FIG. 1 , with the pivoting straight arm  16  located on the right side of spinous process  4   a  and bend arm  14  located on the left side spinous process  4   b  of the  FIG. 1 . Plates  44 ,  46   96 ,  124  may have adjustable lengths. Crosspieces  40 ,  42  may have adjustable heights. 
     Several embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.