Abstract:
This invention relates generally to spine surgery and, in particular, to methods and apparatus for treating spinal stenosis.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 11/540,318, filed Sep. 28, 2006, now pending, which claims the benefit of the filing date under 35 USC 119(e) of provisional application entitled “Methods and Apparatus for Treating Spinal Stenosis,” Ser. No. 60/722,065, filed Sep. 28, 2005, the entire contents of which is fully incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    I. Field of the Invention 
         [0003]    This invention relates generally to spine surgery and, in particular, to methods and apparatus for treating spinal stenosis. 
         [0004]    II. Discussion of the Prior Art 
         [0005]    Spinal stenosis is a narrowing of spaces in the spine which results in pressure on the spinal cord and/or nerve roots. This disorder usually involves the narrowing of one or more of the following: (1) the canal in the center of the vertebral column through which the spinal cord and nerve roots run, (2) the canals at the base or roots of nerves branching out from the spinal cord, or (3) the openings between vertebrae through which nerves leave the spine and go to other parts of the body. Pressure on the spinal cord and/or exiting nerve roots may give rise to pain or numbness in the legs and/or arms depending on the location within the spine (e.g. cervical, thoracic, lumbar regions). While spinal stenosis generally afflicts those of advanced age, younger patients may suffer as well. 
         [0006]    A variety of treatments have been undertaken to alleviate or minimize the effects of spinal stenosis. One such technique is a laminectomy, which involves removing the lamina portion from the pathologic region. By removing the lamina, this procedure enlarges the spinal canal and thus relieves the pressure on the spinal chord and/or compressed nerves. While generally effective, some consider lamimectomy disadvantageous in that, as with any procedure involving bone removal, the resulting region of the spine may be further compromised from a mechanical standpoint. Moreover, elderly patients frequently have co-morbidities that increase the likelihood of complications, such as increased back pain, infection, and prolonged recovery. 
         [0007]    Still other efforts at treating spinal stenosis involve placing spacer devices within the inter-spinous space to indirectly decompress the stenotic condition. These systems are characterized by being secured at the superior and inferior spinous processes. Having both ends of the spacer device coupled to the respective spinous processes disadvantageously limits both flexion and extension of the spine at that location, when it is believed that limiting extension is the key to relieving spinal stenosis. Moreover, the prior art inter-spinous spacers are typically constructed from materials (e.g. metal) with properties substantially different than that of the spinous processes themselves, which raises questions of whether the spinous processes will remodel around the spacer and thereby lose their ability to distract and thereby alleviate spinal stenosis. 
         [0008]    The present invention is directed at overcoming, or at least improving upon, the disadvantages of the prior art. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention is directed at treating spinal stenosis involving an inter-spinous spacer dimensioned to distract a stenotic inter-spinous space and further characterized as being affixed to only one of the two adjacent spinous processes to prevent spinal extension and allow spinal flexion. The inter-spinous spacer of the present invention may be used in the cervical, thoracic and/or lumbar spine. Although shown and described throughout this disclosure with the inter-spinous spacer affixed to the superior spinous process, it will be appreciated that the inter-spinous spacer of the present invention may also be affixed to the inferior spinous process without departing from the scope of the invention. Various mechanisms may be used to affix the inter-spinous spacer of the present invention to the given spinous process, including but not limited to one or more tethers (e.g. wire, cable, suture, allograft tissue, or other single or multi-filament members), one or more screws and/or any of a variety of clamping mechanisms. 
         [0010]    According to an important aspect of the present invention, the inter-spinous spacer of the present invention is designed to fuse to the spinous process to which it is affixed over time, resulting in what is called “hemi-fusion” in that the spacer will be fused to only one spinous process. This is facilitated by abrading the surface of the spinous process (to preferably cause bleeding) where it will mate with the inter-spinous spacer of the present invention. This junction will fuse over time based, in part, on the fusion-enabling design and/or material of the inter-spinous spacer of the present invention. More specifically, the inter-spinous spacer of the present invention may be constructed from bone (e.g. allograft) material, which is readily known to enable fusion upon implantation. The inter-spinous spacer may also be constructed from non-bone materials (e.g. polyaryletheretherketone (PEEK) and/or polaryletherketoneketone (PEKK)) which are physically designed to promote fusion. This is accomplished, by way of example, by providing an interior lumen within the inter-spinous spacer which is dimensioned to receive fusion-inducing materials and which is in communication with the abraded surface of the given spinous process. Such fusion-promoting materials may include, but are not necessarily limited to BMP, demineralized bone matrix, allograft cancellous bone, autograft bone, hydroxy appetite, coral and/or other highly porous substances. 
         [0011]    The present invention overcomes the drawbacks of the prior art by treating spinal stenosis while allowing spinal flexion with an implant constructed from materials with properties substantially closer to the properties of the spinous processes themselves than prior art devices. This advantageously minimizes the risk of the spinous processes remodeling around the inter-spinous spacer of the present invention, which advantageously prevents and/or minimizes the risk of a loss of distraction that may otherwise occur. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Many advantages of the present invention will be apparent to those skilled in the art with a reading of this specification in conjunction with the attached drawings, wherein like reference numerals are applied to like elements and wherein: 
           [0013]      FIG. 1  is a perspective view of an inter-spinous spacer according to a first embodiment of the present invention in use affixed to a superior spinous process of a human spine; 
           [0014]      FIG. 2  is a perspective view of the inter-spinous spacer of the present invention shown in  FIG. 1 ; 
           [0015]      FIG. 3  is a side view of the inter-spinous spacer of the present invention as shown in  FIG. 1 ; 
           [0016]      FIG. 4  is a front view of the inter-spinous spacer of the present invention as shown in  FIG. 1 ; 
           [0017]      FIG. 5  is a top view of the inter-spinous spacer according to the present invention as shown in  FIG. 1 ; 
           [0018]      FIG. 6  is a cross-sectional view of the inter-spinous spacer of the present invention as taken through lines A-A of  FIG. 5 ; 
           [0019]      FIG. 7  is a perspective view illustrating the inter-spinous spacer shown in  FIG. 1  with fusion-promoting materials disposed within an inner lumen according to one aspect of the present invention; 
           [0020]      FIG. 8  is a perspective view of an inter-spinous spacer according to a second embodiment of the present; 
           [0021]      FIG. 9  is a side view of the inter-spinous spacer according to the present invention as shown in  FIG. 8 ; 
           [0022]      FIG. 10  is an end view of the inter-spinous spacer according to the present in invention as shown in  FIGS. 8-9 ; 
           [0023]      FIG. 11  is a perspective view of an inter-spinous spacer according to a third embodiment of the present invention in use affixed to a superior spinous process of a human spine; 
           [0024]      FIG. 12 . is a frontal view of the inter-spinous spacer according to the present in invention as shown in  FIG. 11 , in place in between the two spinous processes; 
           [0025]      FIG. 13 . is a side view of the inter-spinous spacer according to the present in invention as shown in  FIG. 11 , in place in between the two spinous processes; 
           [0026]      FIG. 14 . is a side view of the inter-spinous spacer according to the present in invention as shown in  FIG. 11 , in place in between the two spinous processes with fusion inducing material packed inside; 
           [0027]      FIG. 15  is a front view of the inter-spinous spacer according the present invention as shown in  FIG. 11 ; 
           [0028]      FIG. 16  is a top view of an inter-spinous spacer according the present invention as shown in  FIG. 11 ; 
           [0029]      FIG. 17  is a back side view of an inter-spinous spacer according the present invention as shown in  FIG. 11 ; 
           [0030]      FIG. 18  is bottom view of an inter-spinous spacer according the present invention as shown in  FIG. 11 ; 
           [0031]      FIG. 19  is a side view of an inter-spinous spacer according the present invention as shown in  FIG. 11 ; 
           [0032]      FIG. 20  is perspective view of an inter-spinous spacer according the present invention as shown in  FIG. 11  including visualization markers; 
           [0033]      FIGS. 21-23  illustrate an exemplary insertion tool in use with the inter-spinous spacer of  FIG. 11 , according to one embodiment of the present invention; 
           [0034]      FIGS. 24-27  illustrate an exemplary sizer tool for use when implanting the inter-spinous spacer as shown in  FIG. 11 ; according one embodiment of the present invention; 
           [0035]      FIGS. 28-29  illustrate an alternate attachment device for use with the inter-spinous spacer shown in  FIG. 11  according to an alternate embodiment of the present invention; 
           [0036]      FIG. 30  illustrates a posterior fluoroscopy view taken during implantation of the inter-spinous spacer of  FIG. 11  demonstrating the alignment of markers (including the formation of a “T”) to aid in placement; and 
           [0037]      FIG. 31  illustrates a lateral fluoroscopy view taken during implantation of the inter-spinous spacer of  FIG. 11  demonstrating the position of markers (including the formation of a backwards “L”) to aid in placement. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0038]    Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. The spinal alignment system disclosed herein boasts a variety of inventive features and components that warrant patent protection, both individually and in combination. 
         [0039]      FIG. 1  illustrates a perspective view of a spinous process spacer  10  of the present invention in use between two spinous processes in a human spine. The spacer assembly  10  includes a spacer  12 , a primary spinous process tether  14 , and two side tethers  15  (only one of which is shown in  FIG. 1 ). The spacer  12 , as illustrated in  FIGS. 2-6 , is generally cylindrical and includes a main chamber  16 , a pair of insertion tool apertures  18 , a fusion notch  20 , and a pair of tether lumens  22 . As will be described in greater detail below, the spacer  12  is (according to a preferred embodiment) coupled to only the superior spinous process such that the spacer  12 , with no coupling to the inferior spinous process. This is accomplished, but way of example only, by securing the primary spinous process tether  14  to the superior spinous process (as a first step of affixation), followed by passing one side tether  15  through each of the tether lumens  22 , in between the superior spinous process and the primary spinous process tether  14 , and finally tightening each side tether  15  until the spacer  12  is generally transverse to the longitudinal axis of the spine. 
         [0040]    The spacer  12  may be of bone or non-bone construction. The bone embodiment involves manufacturing the spacer  12  from a suitable allograft, including but not limited to clavicle, rib, humerus, radius, ulna, metacarpal, phalanx, femur, tibia, fibula, or metatarsal bone. The non-bone embodiment involves manufacturing the spacer  12  from suitable non-bone materials, including but not limited to polyaryletherketone (PEEK) and polyaryletherketoneketone (PEKK). In either event, the spacer  12  is designed to fuse to the superior spinous process over time, resulting in what is called “hemi-fusion” in that the spacer  12  will be fused to only one spinous process. This may be augmented by disposing any number of suitable fusion-inducing materials within the spacer  12 , including but not limited to BMP1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 . . . n, demineralized bone matrix, allograft cancellous bone, autograft bone, hydroxy appetite, coral and/or other highly porous substance. 
         [0041]    Although shown and described with regard to the superior spinous process, it will be appreciated that the spacer  12  may also be coupled to only the inferior spinous process without departing from the scope of the present invention. The spacer  12 , once positioned, serves to distract the inter spinous process space, which advantageously restores foraminal height in stenotic patients and may also indirectly decompress the intervertebral space. 
         [0042]    As depicted in  FIGS. 2-3 , the main chamber  16  extends through the lateral sides of the spacer  12 . The main chamber  16  may be provided in any of a variety of suitable shapes in addition to the generally cylindrical shape shown, including but not limited to a generally oblong, triangular, rectangular shape and/or combinations thereof. The main chamber  16  may be dimensioned to receive fusion inducing materials  32 , as best illustrated in  FIG. 8 . Again, such fusion inducing materials may include, but are not necessarily limited to BMP1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 . . . n, demineralized bone matrix, allograft cancellous bone, autograft bone, hydroxy appetite, coral and/or other highly porous substance. The fusion inducing materials may be packed into main chamber  16  before and/or after fixing spacer  10  to the spinous process. The pair of insertion tool apertures  18  may be located on either the posterior or anterior side of the spacer  12  and extend a portion of the way through the spacer  12 . The fusion notch  20  includes a slot or indent to receive a portion of an upper spinous process or other vertebral feature to enhance fusion. The notch  20  may be located generally on the top surface towards the middle portion of the spacer  12 . The notch  20  helps center the spacer  12  relative to the superior spinous process. 
         [0043]    According to another embodiment, shown in  FIGS. 9-11 , the spacer  12  may be provided with a second notch  21  opposite the fusion notch  20 . The second notch  21  is capable of resting on the inferior spinous process during use, which may assist in maintaining the spacer  12  in a fully centered position relative to the inferior spinous process. As best shown in  FIG. 9 , the fusion notch  20  may be further provided with slots  23  extending into the main chamber  16 . When the spacer  12  is coupled to the superior spinous process, these slots  23  will establish direct communication between the fusion-inducing compounds provided within the main chamber  16  and the lower aspect of the superior spinous process, which advantageously augments the ability of the spacer  12  to fuse to the superior spinous process (particularly if the spacer  12  is constructed of non-bone materials). 
         [0044]    As best shown in  FIG. 6 , the tether lumens  22  each extend at an angle through the top surface of the spacer  12  and into the main chamber  16 . Each tether lumen  22  may be provided in any of a variety of suitable shapes in addition to the cylindrical shape shown, including but not limited to oblong, triangular, rectangular and/or any combination thereof. The tethers  14 ,  15  may comprise any number of suitable materials and configurations, including but not limited to wire, cable, suture (permanent and/or bioresorbable), allograft tissue and/or other single or multi-filament member. Suture thread may include any number of components capable of attaching to a spinous process, including but not limited to ordinary suture threads known to and used by those skilled in the art of wound closure. Suture thread may be of any length necessary to effectively fuse the spacer  12  to the particular spinous process. 
         [0045]    The spacer  12  according to the present invention may be constructed of allograft bone and formed in a generally cylindrical shape. The spacer  12  of the present invention may be provided in any number of suitable shapes and sizes depending upon a particular patient and the shape and strength characteristics given the variation from cadaver to cadaver. The spacer  12  may be dimensioned for use in the cervical and/or lumbar spine without departing from the scope of the present invention. The spacer  12  may be dimensioned, by way of example only, having a length ranging between 6-20 mm and a height ranging between 20-25 mm. 
         [0046]    When constructed from allograft, the spacer  12  may be manufactured according to the following exemplary method. A belt sander may first be used to reduce any high spots or imperfections to standardize the shape of the bone. Cut the allograft bone to length using the band saw. Remove the cancellous material from the inner canal to create the main chamber  16 . Using calipers, measure the struts and create a size distribution of spacers  12 . Machine the insertion tool apertures  18 . Set-up a standard vice for holding the implant across its width on the mill. Use a 3/32″ ball end mill to create the insertion tool apertures  18  (same as cervical allograft implant). Insert the spacer  12  into the vice and tighten. Calculate the centerline of the 20 or 25 mm long spacer  12 . Create the holes 2.26 mm away from each side of the centerline (4.52 mm hole to hole distance). Create a notch  22  for the spinous process. Set-up the cervical allograft holding fixture that uses the insertion tool apertures  18  and vice to hold the spacer  12  across its width on the mill. Use a ¼″ flat end mill to create the notch  22 . Calculate the centerline of the 20 or 25 mm long spacer  12 . Insert the spacer  12  onto the fixture using the insertion tool apertures  18  and tighten the vice. This automatically verifies the correct sizing/spacing of the insertion tool apertures  18 . Measure the spacer  12  height. Calculate the cut depth to create the desired spacer  12  size. Cut the flat on the spacer  12  to the desired depth. Remeasure the spacer  12  to insure proper cut depth. Drill the angled lumens  22  in face of spacer  12 . Remove the spacer  12  from the cervical allograft fixture and tighten into the standard vice. Using a battery powered or corded drill with a 1/16″ drill bit, drill through the front face to the canal on both sides. Belt sand the face if needed to create a flat surface for the drill bit to engage the spacer  12 . 
         [0047]    Turning now to  FIG. 11  there is shown in perspective view an example of a spacer  112  according to another embodiment of the present invention. Spacer  112  includes a posterior side  113 , anterior side  114 , lateral sides  115 , a main chamber  116 , and a fusion notch  120 . Spacer  112  is further provided with a plurality of apertures including, but not necessarily limited to, three pairs of insertion tool apertures  118   a ,  118   b , and  118   c , tether lumens  122 , and fusion apertures  124 . 
         [0048]      FIGS. 12-14  depict spacer  112  in use in the inter spinous process space of a patient. Spacer  112  is designed to fit between a superior spinous process and an inferior spinous process and may be dimensioned in any number of suitable shapes and sizes to accomplish this. The spacer  112  may be positioned in any of the cervical, thoracic, and/or lumbar spine and sizes may vary accordingly. When in position, a properly sized spacer  112  distracts the inter spinous process space, restoring the foraminal height in stenotic patients and indirectly decompresses the intervertebral space. By way of example only, spacer  112  may be dimensioned having a length ranging between 6-20 mm and a height ranging between 20-25 mm. 
         [0049]    Spacer  112  is preferably constructed of non-bone material. Suitable non-bone materials may include, but are not necessarily limited, to polyaryletherketone (PEEK) and polyaryletherketoneketone (PEKK). Numerous advantages may be gained by constructing spacer  112  out of materials such as PEEK and PEKK. The stiffness properties of PEEK and PEKK closely match that of bone. This reduces substantially the likelihood that the spinous process will remodel around spacer  112  causing a re-narrowing of the foraminal height and potentially resulting in revision surgeries. PEEK and PEKK are also substantially radiolucent which allows for improved post operative visualization of fusion between the implant and the superior spinous process. Finally, by using the non bone material with strategically placed apertures, fusion may be confined to areas where it is useful. By way of example only, spacer  112  may include fusion apertures only along the top (and potentially posterior side  113 ) such that fusion occurs only between the superior spinous process and spacer  112 . In this manner, extension is limited without disadvantageously limiting flexion as well. 
         [0050]    As depicted in  FIG. 13 , the main chamber  116  extends through the lateral sides  115  of the spacer  112 . Main chamber  116  may be provided in any of a variety of suitable shapes in addition to the generally cylindrical shape shown, including but not limited to a generally oblong, triangular, rectangular shape and/or combinations thereof. Main chamber  116  may be dimensioned to receive fusion inducing materials  32 , as best illustrated in  FIG. 14 . Again, such fusion inducing materials may include, but are not necessarily limited to BMP1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 . . . n, demineralized bone matrix, allograft cancellous bone, autograft bone, hydroxy appetite, coral and/or other highly porous substance. The fusion inducing materials  32  may be packed into main chamber  16  before and/or after fixing spacer  10  to the spinous process. The fusion inducing material  32  packed within main chamber  16  may communicate openly with the superior spinous process through any of the insertion tool apertures  118   a ,  118   b ,  118   c , fusion apertures  124 , and/or tether apertures  122 . Through this communication, fusion may occur from the superior spinous process into the main chamber  116 , permanently fixing spacer  112  in position. 
         [0051]    With reference to  FIGS. 15-19 , the various features of spacer  112  will now be described according to one preferred embodiment.  FIG. 16  is a view of the top of spacer  112 . Fusion notch  120  may be located generally on the top surface towards the middle portion of the spacer  112 . Fusion notch  120  generally comprises a slot or indent dimensioned to receive an inferior portion of a superior spinous process. The notch  120  helps center the spacer  112  relative to the superior spinous process and may assist in limiting side-to-side motion of spacer  112  prior to fusion. Fusion notch  120  includes main fusion aperture  124   a . Main fusion aperture  124   a  extends into main chamber  116  and is the main avenue for fusion between main chamber  116  and the superior spinous process. Secondary fusion apertures  124   b  may be located along the top of spacer  112  near the four corners of fusion notch  120  and extend into main chamber  116 . Secondary fusion apertures  124   b  may provide additional routes for fusion to the superior spinous process. Tether apertures  122  may be located along the top center of spacer  112  near either side of fusion notch  120 . Tether apertures  122  are dimensioned to receive tethers  14 ,  15  to temporarily fix spacer  112  in position until fusion to the superior spinous process occurs, permanently fixing spacer  112  in place. 
         [0052]    Main fusion aperture  124   a , secondary fusion apertures  124   b , and tether apertures  122  may each be provided in any of a variety of shapes in addition to the generally circular shapes shown, including but not necessarily limited to, generally square, rectangular, oblong, triangular, and/or any combination thereof. 
         [0053]      FIG. 16  illustrates the posterior side  113  of spacer  112 . The posterior side  113  may include 3 separate pairs of insertion tool apertures  118   a ,  118   b , and  118   c . As will be described in more detail below, having three pairs of insertion apertures allow different insertion approaches to be utilized without needing to make available separate tools and/or spacers with alternate aperture configurations. Insertion tool apertures extend into main chamber  116  and may serve as additional fusion routes after insertion, this may further solidify and strengthen the fusion between the superior spinous process and spacer  112 . 
         [0054]      FIG. 17  illustrates the anterior side  114  of spacer  112  and  FIG. 18  illustrates the bottom of the spacer. The anterior side  114  is preferably free of any apertures (except, secondary fusion apertures  124   b  may be located near the top of spacer  112  on the anterior side). When positioned in the inter spinous process space, the anterior side  114  faces the spinal canal. Bone growth along the anterior side could potentially interfere with the spinal canal and the delicate neural tissue located inside, which could result in pain and/or further surgery for the patient. The lack of communication to main chamber  116  caused by the absence of apertures on the anterior side  114  advantageously prevents bone growth in the area. Likewise, the bottom of spacer  112  is also aperture free and does not communicate with main chamber  116 . This advantageously prevents bone growth in the area and fusion to the inferior spinous process will not occur. Again, this allows the spinal segment to maintain flexion ability while still correcting the stenosis. The bottom of spacer  112  may preferably have a concave surface such that the distance from top to bottom of spacer  112  is greater neareast the lateral sides  115  and lesser near the center. The concave bottom may rest along the inferior spinous process and helps maintain spacer  112  in a centered position relative to the inferior spinous process.  FIG. 19  illustrates again a lateral side  115  with main chamber  116  extending therethrough. 
         [0055]    To assist in visualization of spacer  112 , both during and after surgery, spacer  112  may include at least one marker. Preferably, spacer  112  includes a top marker  126  and two side marker  128 . Markers  126 ,  128  may be comprised of biocompatible radio-opaque material, such as for example only, titanium (or other metals or polymers). Marker  126  may be positioned along the center of spacer  112  within fusion notch  120 . Preferably marker  126  extends through spacer  112  down to the bottom surface. Markers  128  may be located in the lateral sides below main chamber  116 . During and after placement of the spacer  112 , markers  128  and  128  may be utilized to correctly orient spacer  112 . 
         [0056]    Utilizing X-ray fluoroscopy and/or other suitable imaging techniques from the posterior (or the back of the patient) perspective of the spacer  112 , the marker  126  situated in the center and extending from fusion notch  120  to the bottom surface should make a line between the superior spinous process and the inferior spinous process viewable on the fluoroscopy screen when the spacer  112  is properly positioned, as pictured in  FIG. 30 . Markers  128  should be positioned on each side of the superior and inferior spinous process in the inter spinous process space. Drawing an imaginary line between markers  128  and connecting that line to an imaginary line extending marker  126  to it should form an upside down “T” if properly positioned. From a lateral view, the depth of the spacer  112  in the interspinous space may be verified. Marker  126  runs along the posterior side  113  of spacer  112 . One or both of markers  128  may be positioned in the lateral side  115  near the posterior side  113 . In one embodiment, one marker  128  is positioned near the posterior side  113  and one marker  128  may be positioned near the anterior side  114 . On a lateral fluoroscopy view taken during surgery the position of the markers  126  and  128  may be viewed in relation to the posterior end of the spinous processes and the more anterior vertebral elements to ensure spacer  112  is neither too far anteriorly nor to far posoteriorly. Drawing an imaginary line between markers  128  and connecting that line to an imaginary line extending marker  126  to it should form an backwards “L” if properly positioned, as pictured in  FIG. 31 . 
         [0057]    The spinal apparatus  10  of the present invention may be introduced into a spinal target site through the use of any of a variety of suitable instruments having the capability to releasably engage the spacer  12 ,  112 . In a preferred embodiment, the insertion tool permits quick, direct, accurate placement of the spacers  12 ,  112  between an upper and lower spinous process. An exemplary insertion tool is shown and described in commonly owned U.S. Pat. No. 6,923,814 entitled “System and Method for Cervical Fusion,” which is expressly incorporated by reference as if set forth fully herein.  FIGS. 21-23  depict an exemplary insertion tool  200  for use with spacers  12 ,  112 . At a distal end  202 , insertion tool  200  includes a pair of prongs  204  dimensioned to engage insertion apertures  18  and  118   a ,  118   b ,  118   c  such that spacer  12 ,  112  becomes temporarily attached to the distal end  202  for insertion. As pictured in  FIG. 24  insertion apertures  118   a  are aligned laterally in the center of spacer  112  such that spacer  112  and insertion tool  200  mate at approximately the center point of the spacer. This configuration may be advantageous if approaching the inter spinous process space from a directly posterior approach. As pictured in  FIG. 23 , insertion apertures  118   b  (and  118   c ) are aligned vertically near the side of spacer  112 . This configuration may be advantageous if approaching from a more lateral direction. 
         [0058]    In order to use the spinal apparatus  10  of the present invention in a treatment of spinal stenosis, a clinician must first designate the appropriate spacer size  12 ,  112 . A clinician can utilize the spinal apparatus  10  in either an open or minimally invasive spinal fusion procedure. In either type of procedure, a working channel would be created in a patient that reaches a targeted spinal level. After the creation of the working channel, the interspinous space would be prepared. After preparation a sizer instrument is used to determine the appropriate size of the spacer  12 ,  112 . One exemplary sizer instrument  300  is illustrated by way of example only in  FIGS. 24-27 . Sizer instrument  300  includes a handle portion  302  and an implant portion  304 . Handle portion  302  may be configured in any variety of suitable shapes and sizes. Implant portion  304  may be provided in a variety of sizes matching the various sizes of spacer  112 . As pictured, sizer implant may be proved in an asymmetrical shape where the side opposite the handle  302  has a lesser height than the side to which handle  302  is attached. This may allow the implant portion  304  to be rotated into position with minimal interference from the spinous process. Although it is not shown, it is conceived that spacer  112  may also be provided in this asymmetrical fashion. 
         [0059]    Preparation of the inter spinous process space includes perforating the interspinous ligament between the superior and inferior spinous processes. The supraspinous ligament may preferably be left intact and distracted out of the way if necessary. A key part of the preparation includes abrading the inferior portion of the superior spinous process where it will communicate with the fusion inducing materials  32  packed in the main chamber  16 ,  116 . Abrading removes the hard cortical bone from the inferior surface of the superior spinous process and leaves bleeding bone which is better adapted for fusion. As new bone generates to heal the abraded portion it may grow into the main chamber  16 ,  116 , fixing spacer  12 ,  112  to the superior spinous process. 
         [0060]    In one embodiment described above the spacer  12 ,  112  is held in position with tethers  14 ,  15  attached to the spinous process through tether lumen  22 ,  122 . According to an alternate embodiment, pictured by way of example only in  FIGS. 30-31  an alternate securing mechanism may be used to fix spacer  12 ,  112  in place. The alternate securing mechanism includes a zip cable  400  and a pair of locking bases  402   404 . Base  402  may be integral with cable  400 . Base  402  is positioned on the top of spacer  12 ,  112  next to the fusion notch  20 ,  120  and fixed to the spacer  12 ,  112  via tether apertures  22 ,  122 . Base  402  is positioned over tether aperture  22 ,  122  and a locking pin  406  is inserted through the base into tether aperture  22 ,  122 . The step is repeated for base  404  on the opposite side of the fusion notch  20 ,  120 . Once both bases are in position and the spacer  12 ,  112  is positioned between the spinous processes, the zip cable  400  may be wrapped around the superior spinous process and fed through the opposing base  404 . Teeth  408  on the cable  400  prevent cable  400  from loosening and thus holds the spacer  12 ,  122  in place for fusion to occur. Any of a variety of suitable materials may be used to form the zip cable  400 , bases  402 ,  404 , and locking pins  406 . In one exemplary embodiment the cable  400  and bases  402 ,  404  are comprised of nylon and the locking pins  406  are comprised of titanium. 
         [0061]    When the spacer  12 ,  112  is positioned and inserted into the prepared space between the spinous processes it forces the spinous processes apart. The spine flexes as the spinous processes are forced apart and the neuroforamina and the spinal canal are enlarged as the spine is flexed. The spinal apparatus  10  holds the vertebrae in a flexed position, preventing extension but advantageously allowing flexion. 
         [0062]    While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined herein.