Abstract:
The present invention involves a system and method for implanting an interspinous spacer configured to self-distract a stenotic interspinous space. The present system includes, but is not necessarily limited to, an interspinous spacer and insertion instrumentation for assisting in the implantation and positioning of the interspinous spacer within an interspinous space.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is an non-provisional patent application and claiming the benefit of priority from commonly owned and co-pending U.S. Provisional Patent Application Ser. No. 61/105,011, entitled “Systems and Methods for Treating Spinal Stenosis,” and filed on Oct. 13, 2008, the entire contents of which is hereby expressly incorporated by reference into this disclosure as if set forth in its entirety herein. 
    
    
     FIELD 
     This invention relates generally to spine surgery and, in particular, to methods and apparatus for treating spinal stenosis. 
     BACKGROUND 
     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. 
     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 cord and/or compressed nerves. While generally effective, some consider laminectomy 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. 
     Still other efforts at treating spinal stenosis involve placing spacer devices within the interspinous space to indirectly decompress the stenotic condition. Typically implanting these spacers requires perforating the supraspinous ligament running along the apices of the spinous processes. The use of one or more additional instruments to distract the interspinous space prior to implanting the spacer is also generally required. The present invention is directed at overcoming, or at least improving upon, the disadvantages of the prior art. 
     SUMMARY OF THE INVENTION 
     The present invention is directed at treating spinal stenosis involving an interspinous spacer configured to self-distract a stenotic interspinous space. According to an important aspect of the present invention, the interspinous spacer of the present invention is designed to fuse over time to the spinous processes of the affected spinal level. This is facilitated by abrading the surface of the spinous process where it will mate with the interspinous spacer of the present invention. This junction will fuse over time based, in part, on the fusion-enabling design and/or material of the interspinous spacer of the present invention. The interspinous 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 interspinous spacer which is dimensioned to receive fusion-inducing materials and which is in communication with the abraded surfaces of the given spinous processes. Such fusion promoting materials may include, but are not necessarily limited to BMP (bone morphogenic protein), demineralized bone matrix, allograft cancellous bone, autograft bone, hydroxyapetite, coral and/or other highly porous substances. 
     The spacer may be used in either an open or minimally invasive spinal fusion procedure. In either type of procedure, a working channel is created in a patient that reaches a targeted spinal level. After the creation of the working channel, the interspinous space is prepared by removing at least a portion of the interspinous ligament and preferably abrading the superior and inferior spinous processes. Abrading the spinous processes includes abrading the inferior portion of the superior spinous process and the superior portion of the inferior spinous process where they will communicate with the fusion promoting materials packed in the main cavity through a superior fusion aperture and inferior fusion aperture. Abrading removes the hard cortical bone from the surface of the bone exposing the softer bleeding cancellous bone underneath which is better adapted for fusion. As new bone generates to heal the abraded portion, the new bone may communicate with the fusion promoting materials and grow into the main cavity of the spacer, thus fixing the spacer to both the superior and inferior spinous processes. 
     Once the interspinous space has been prepared, a sizer instrument may be used to determine the appropriate size of the spacer required to achieve the desired correction. According to one aspect of the present invention, the implant may be inserted in a horizontal position having an initial height dimensioned to fit within the undistracted interspinous space and then rotated to a vertical position thereby distracting the interspinous space to the desired height. To accomplish this, the surgeon will use an insertion instrument to guide the spacer in between the spinous processes, leading with the bottom surface and guiding the bottom surface around the supraspinous ligament. The spacer is then axially rotated so the top side of spacer faces the posterior side of the spine and the lateral sides of the implant are positioned on either side of the supraspinous ligament. Spacer is then rotated to its final vertical position allowing the spacer to distract the spine at the spinal processes and prevent over extension. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  is a perspective view of an interspinous spacer according to one example embodiment and in use and affixed between a superior spinous process and an inferior spinous process of a human spine; 
         FIG. 2  is a perspective view of the interspinous spacer according to the embodiment shown in  FIG. 1 ; 
         FIG. 3  is a posterior view of the interspinous spacer according to the embodiment shown in  FIG. 1 ; 
         FIG. 4  is an anterior view of the interspinous spacer according to the embodiment shown in  FIG. 1 ; 
         FIG. 5  is a side view of the interspinous spacer according to the embodiment shown in  FIG. 1 ; 
         FIG. 6  is a bottom view of the interspinous spacer according to the embodiment shown in  FIG. 1 ; 
         FIG. 7  is a top view of the interspinous spacer according to the embodiment shown in  FIG. 1 ; 
         FIG. 8  is a cross-sectional view of the interspinous spacer according to the embodiment shown in  FIG. 1 ; 
         FIG. 9  is a perspective view of the interspinous spacer according to the embodiment shown in  FIG. 1  with markers exploded; 
         FIG. 10  is a perspective view of an insertion instrument according to one example embodiment used to install the interspinous spacer of  FIG. 1 ; 
         FIG. 11  is a posterior view of the insertion instrument attached to the interspinous spacer of  FIG. 1  in preparation for introduction to a target site; and 
         FIGS. 12-14  illustrate in progressive fashion the insertion of the spacer in a first orientation having a diminished height and then the rotating of the spacer to effect distraction of the interspinous space, according to one example embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     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 implant system disclosed herein boasts a variety of inventive features and components that warrant patent protection, both individually and in combination. 
       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. Spacer  10  includes a top surface  11 , posterior side  12 , bottom surface  13 , lateral sides  14 , and anterior side  16 . Top surface  11  may further include superior fusion notch  20 , and bottom surface  13  may further include inferior fusion notch  22 . Spacer  10  may be further provided with a plurality of fusion apertures including, but not limited to, superior fusion aperture  21 , inferior fusion aperture  23  and posterior fusion apertures  24  all linked to a main cavity  17 . Insertion apertures  26  may be provided on lateral sides  14 . As will be described in greater detail below, spacer  10  may preferably be coupled to both a superior and inferior spinal process. This may be accomplished, by way of example only, by snugly positioning spacer  10  between both spinous processes and allowing boney ingrowths to form between the superior and inferior spinous processes through spacer  10 . 
     In a preferred embodiment, spacer  10  is constructed of non-bone material. Suitable non-bone materials may include, but are not necessarily limited to, polyaryletherketone, polyetheretherketon (PEEK) and polyaryletherketoneketone (PEKK). Numerous advantages may be gained by constructing spacer  10  out of materials such as PEEK and PEKK. One advantage is the stiffness properties of PEEK and PEKK closely match that of bone which substantially reduces the likelihood that the spinous process will remodel around spacer  10  causing a re-narrowing of the foraminal height and potentially resulting in the potential need for revision surgery. PEEK and PEKK are also substantially radiolucent which allows for improved post operative visualization of fusion between the superior and inferior spinous processes through spacer  10 . 
     Spacer  10  is designed to maintain the interspinous space between the spinous processes and prevent over extension while boney fusion takes place between the spinous process over time. The fusion process may be augmented by disposing any number of suitable fusion-inducing materials  28  within the main cavity  17 , including but not limited to BMP (bone morphogenic protein)  1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11 ,  12 ,  13 ,  14  . . . n, demineralized bone matrix, allograft cancellous bone, autograft bone, hydroxyapetite, coral and/or other highly porous substance. The fusion inducing material  28  may be packed within main cavity  17  to thereby communicate openly with the superior and inferior spinous processes through any of the insertion instrument apertures  26  and/or fusion apertures  21 ,  23  and  24 . Through this communication, fusion may occur between the superior and inferior spinous processes through the main cavity  17 , fixing spacer  10  in position. The cross section of the main cavity  17  is shaped and dimensioned to allow for a sufficient amount of bone growth to form through the cavity, thus fusing and securing the spacer  10  in the interspinous process space. By way of example, the main cavity  17  is shown as being elliptical in shape with a length dimension of approximately 5 mm and a height dimension ranging from approximately 3 mm and 5 mm. Although the main cavity  17  is shown and described as being elliptical in shape with the aforementioned dimensions, the main cavity  17  may be any shape and dimensions appropriate to allow secure bone fusion of the spacer  10  to the surrounding spinous processes without departing from the scope of the present invention. 
     Spacer  10  and various features thereof are described according to one example, as illustrated in  FIGS. 2-8 .  FIG. 2  is a perspective view of the spacer  10 .  FIG. 3  is an illustration of posterior side  12  of spacer  10 . Superior fusion notch  20  may be located generally on the top surface  11  and centrally positioned between the two lateral sides  14 . Fusion notch  20  generally comprises of a slot or indent dimensioned to receive an inferior portion of a superior spinous process. Fusion notch  20  may help center spacer  10  relative to the superior spinous process and may assist in limiting lateral motion of spacer  10  prior to fusion. Fusion notch  20  includes superior fusion aperture  21  (best viewed in  FIG. 7 ) which extends into main cavity  17  and is the primary passage for fusion between main cavity  17  and the superior spinous process. One or more fusion apertures  24  may also be provided on posterior side  24 . Posterior fusion apertures  24  may provide an additional avenue for boney growth around the exterior of spacer  10  and may also be used to pack main cavity  17  with fusion promoting materials before and/or after insertion of spacer  10 . 
     The spacer  10  is shaped such that the greatest height between the top and bottom surface  11 ,  13  of the spacer  10  exist along the lateral sides  14 , forming legs  9  extending below a central body portion. The legs  9  of the spacer  10  are increasingly tapered as they converge towards the bottom surface  13  (best shown in  FIG. 5  and  FIG. 8 ). The anterior side  16  of the legs  9  taper towards the posterior side  12  of the legs  9 , having a taper angle α ( FIG. 5 ). By way of example only, angle α may be approximately 15 to 30 degrees. The posterior sides  12  of the legs  9  begin to taper towards the anterior sides  16  of the legs  9  near the bottom surface  13 , having a taper angle β ( FIG. 5 ). By way of example only, angle β may be approximately 20 to 40 degrees. The bottom surface  13  provides a rounded transition between the anterior and posterior sides  16 ,  12  of the legs  9 . Tapering of the legs  9  also occurs in the lateral direction due to the increasing radii of the inferior fusion notch and the medial surface, as will be discussed in more detail below. By way of example, the taper of legs  9  facilitate insertion and through and around tissue (e.g. supra spinous ligament) and distraction of the interspinous space during insertion. 
     An inferior fusion notch  22  is located generally along the inferior surface of the spacer and is generally positioned centrally between the lateral sides  14 . Inferior fusion notch  22  is generally comprised of an angled concave surface dimensioned to receive a superior portion of an inferior spinous process. Fusion notch  22  also helps center spacer  10  relative to the inferior spinous process and may assist in limiting lateral motion of spacer  10  prior to fusion. Inferior fusion notch  22  includes an inferior fusion aperture  23  which extends into main cavity  17  and is the primary passage for fusion between main cavity  17  and the inferior spinous process.  FIG. 3  illustrates the medial surface  15  having a generally concave configuration from the bottom surface of legs  9  to the inferior fusion notch  22 . By way of example only, the concave inferior fusion notch  22  may have a radius dimension of approximately 5 mm to 8 mm and the concave medial surfaces  15  may have a radius dimension of approximately 10 mm to 15 mm. The more narrow fusion notch  22  generally assists in maintaining the final positioning of the spacer  10  until fusion occurs while the broader arc of the medial surfaces  15  aid in the insertion of the spacer  10  within an interspinous process space, as described below. 
     Fusion apertures  21 ,  23  and  24  may be provided in any of a variety of shapes in addition to the generally oval shapes shown, including but not necessarily limited to, generally square, rectangular, circular, triangular and/or any combination thereof. Insertion instrument apertures  18  are positioned along the lateral sides  14  to facilitate introduction of the spacer into a desired position. For example, the spacer may be introduced without sacrificing the supraspinous ligament. In a preferred embodiment, the insertion instrument aperture  18  is a non-circular shape. The non-circular shape of the insertion instrument aperture  18  restricts the relative rotation between the insertion instrument and the spacer while rotating the spacer  10  to the desired interspinous position during introduction. By way of example only, the insertion apertures  18  may have a square profile with height and width dimensions generally in the range of 3 mm to 5 mm. However, the shape and dimensions of the insertion apertures  18  may be any shape and dimension appropriate to permit the desired insertion and rotation of the spacer  10 . 
       FIG. 4  is an illustration of anterior side  16  of spacer  10 . The anterior surface is generally curved to accommodate a smooth transition during insertion and rotation of the spacer  10  into the desired position within the interspinous space. When positioned in the inter spinous space, the anterior side  16  faces the spinal canal. Preferably, there are no fusion apertures along the anterior side  16  of the spacer  10 , which protects the dura and prevents graft material from falling into the dura from within the spacer  10 . Both posterior side  12  and anterior side  16  have angled surfaces  27  and  29 , respectively, near lateral sides  14  to further accommodate the installation process as described below. For example, angled surfaces  27  and  29  ensure that there are no sharp edges that can damage any surrounding bone or tissue during implantation of the spacer  10 . The angled surfaces  27  and  29  also assist in clearance of the lamina and facet joints during introduction and positioning of the implant. 
     Both the anterior and posterior surfaces of the spacer  10  are generally convex to provide for a smooth transition during insertion and rotation of the spacer  10  into a desired position within the interspinous space. Preferably, the greatest distance between the convex anterior and posterior surfaces is less than the shortest distance between the inferior and superior fusion notches  22 ,  20 . This allows the spacer  10  to distract the spinous processes upon rotation from between an initial insertion position and a final position. The spacer is inserted in a horizontal position and then rotated into a vertical position, as will be discussed in greater detail below. According to one example, and by way of example only, 2 mm to 6 mm of distraction can be effected upon rotation of the spacer  10  within the interspinous process space. However, more or less distraction can be accomplished using the spacer  10  without departing from the scope of the present invention. 
       FIG. 5  is an illustration of a lateral side  14  of spacer  10 . Insertion apertures  26  may be provided on lateral sides  14  and preferably connect into main cavity. Apertures  26  are provided on both lateral sides  14  such that spacer  10  may be inserted from either side of the patient. Apertures  26  are dimensioned to receive insertion head  34  of insertion instrument  30  as described below.  FIG. 6  is a bottom view of spacer  10 .  FIG. 7  is a top view of spacer  10 . Top surface  11  of spacer  10  is generally curved and tapers at an angle to the lateral sides  14 . 
     As depicted in  FIGS. 5-8 , main cavity  17  may preferably be formed from horizontal cavity  18  and vertical cavity  19 . Horizontal cavity  18  preferably spans across insertion apertures  26 . Horizontal cavity  18  may be provided in any variety of shapes in addition to the generally square shape shown, including but not necessarily limited to, generally rectangular, circular, oblong, triangular and/or any combination thereof. Vertical cavity  19  preferably spans across fusion apertures  21  and  23 . Vertical cavity  19  may be provided in any variety of shapes in addition to the generally oblong shape shown, including but not necessarily limited to, generally rectangular, circular, oblong, triangular and/or any combination thereof. In a cross-sectional view, the main cavity  17  has a generally cross-shaped pattern. 
     To assist in visualization of spacer  10 , both during and after surgery, spacer  10  may include at least one marker.  FIG. 9  shows in exploded view, by example only, four markers situated within spacer  10 . Preferably, spacer  10  includes two top markers  40  and two side marker  42 . Markers  40  and  42  may be comprised of biocompatible radiopaque material, such as, for example only, titanium (or other metals or polymers). Markers  40  may be positioned along top surface  11  of spacer  10  on either side of fusion notch  20 . Markers  42  may be located in lateral sides  14  below main cavity  17  and preferably adjacent to bottom surface  13 . During and after placement of the spacer  10 , markers  40  and  42  may be viewable using X-ray fluoroscopy to ensure spacer  10  is correctly oriented in the interspinous space. 
       FIG. 10  shows an example embodiment of an insertion instrument  30 . Insertion instrument  30  consists of insertion head  34  connected by an elongated body  36  to handgrip  38 . Insertion head  34  is oriented at a non-straight angle relative to the longitudinal axis  35  of the instrument  30 . The insertion head  34  is configured and shaped to be received by either insertion aperture  26  of the spacer  10 . The cross-sectional geometry of the insertion head  34  may be shaped in any of a variety of shapes in addition to the generally square shape shown, including, but not necessarily limited to, generally rectangular, oblong, triangular and/or any combination thereof, such that insertion head  34  matches the shape of the insertion aperture  26 . The insertion head  34  may include a slight increasing taper from the tip of head  34  to the body  36 . The tapered head  34  interacts with the insertion aperture  26  on the implant  10  to cause a friction fit connection and releasably maintain the spacer  10  on the insertion instrument  30  during the implantation process.  FIG. 11  shows insertion instrument  30  inserted into spacer  10  via insertion aperture  26 . It will be appreciated that the insertion instrument  30  may be connected to an insertion aperture  26  located on either side of the spacer  10 . Preferably, spacer  10  may be positioned on the insertion head  34  such that the vertical orientation of the spacer  10  forms a non-right angle with the longitudinal axis of the instrument  30 . This angular offset between the spacer  10  and the instrument  30  may facilitate the rotation of the spacer from the first insertion position to the second distraction position, which will be described in more detail below. 
     A clinician can utilize the spacer  10  in either an open or minimally invasive spinal fusion procedure. In either type of procedure, a working channel is created in a patient that reaches a targeted spinal level. After the creation of the working channel, the interspinous space is prepared. The interspinous space is prepared by removing at least a portion of the interspinous ligament and preferably abrading the superior and inferior spinous processes. Abrading the spinous processes includes abrading the inferior portion of the superior spinous process and the superior portion of the inferior spinous process. This allows the abraded surfaces to communicate with the fusion promoting materials packed in the main cavity  17  through a superior fusion aperture and inferior fusion aperture of the spacer  10 . Abrading removes the hard cortical bone from the surface of the bone and exposes the softer bleeding cancellous bone underneath, which is better adapted for fusion. As new bone generates to heal the abraded portion, the new bone may communicate with the fusion promoting materials and grow into the main cavity  17  of the spacer  10 , thus fixing the spacer  10  to both the superior and inferior spinous processes. 
     Once the interspinous space has been prepared, a sizer instrument may be used to determine the appropriate size of the spacer required to achieve the desired correction. According to one aspect of the present invention and illustrated in  FIGS. 12-14 , the spacer may be inserted in a horizontal position having an initial height less than the desired corrected height of the interspinous space and then rotated to a final vertical position thereby distracting the interspinous space to the desired height. To accomplish this, the surgeon will use an insertion instrument  30  to guide the spacer  10  in between the spinous processes, leading with the bottom surface  13  and guiding one of the legs  9  around the supraspinous ligament. The tapered end of leg  9  aids in passing the leg under the supraspinous ligament and can also distract the spinous processes if necessary. Once the first leg  9  is passed under the supra spinous process, the spacer  10  may be axially rotated in the transverse plane to an intermediate position. To get to the intermediate position, the spacer may be rotated approximately 90 degrees such that the top surface  11  faces the spinal canal. From the intermediate position, the spacer  10  may be adjusted into the final position by rotating the spacer again, this time in the sagittal plane. The spacer may be rotated approximately 90 degrees such that the top surface faces the superior spinous process above. As the spacer is rotated into the final position the height of the implant distracts the spinal processes and prevents over extension. X-Ray fluoroscopy or other suitable imaging techniques may be used to verify the spacer  10  is properly positioned. The instrument  30  is removed from the spacer  10  and the working channel is closed. 
     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.