the term “ allograft ”, as used herein , is intended to mean a graft taken from a different individual of the same species . the term “ sagittal plane ”, as used herein , is the plane which splits the body into left and right segments . the mid - sagittal , or median plane splits the body into equal left and right halves . the term “ coronal plane ”, as used herein , is the plane that separates the body into anterior and posterior ( front and back ) segments . the coronal plane is perpendicular to the sagittal plane . the term “ posterior process fusion ”, as used herein , describes the fusion of adjacent spinous processes firstly to the spinous process spacer implant , and eventually to each other via the growth of tissue through the axial conduit of the implant . fig1 illustrates a spinal column having a collapsed disc and stenotic central canal . fig2 illustrates the spinous process spacer implant of the present invention . fig3 a illustrates the final configuration of spinous process spacer positioned between adjacent spinous processes . fig3 b is an enhancement indicating the engagement of the spinous processes with the spinous process cutout portion of the implant . fig4 illustrates the spinous process spacer positioned and constrained with optional cables . fig5 illustrates the introduction of successively larger diameter dilators until the appropriate distraction is achieved . fig6 illustrates the insertion and placement of the rotation cannula over the last dilator used . fig7 illustrates the position of the rotation cannula between adjacent spinous processes after the dilators have been removed . fig8 illustrates the insertion and initial placement of the implant with the rotation instrument . fig9 illustrates the configuration upon rotating the implant 90 degrees using the rotation instrument . fig1 illustrates the final configuration of the implant upon removal of the cannula and rotation instrument . fig1 illustrates the rotation cannula with the implant inserted into the extensions for the lateral spinous process stabilizers . fig1 illustrates the rotation instrument with the implant inserted between its prongs . the function of the spinous process spacer ( 20 ) can be understood by appreciating the problem illustrated in fig1 . a cross section of the spinal cord ( 10 ) in the mid - sagittal plane is shown with the vertebral body ( 11 ) on the right and the spinous process ( 12 ) on the left . a normal disc ( 16 ) above ( or cephalad to ) the vertebral body ( 11 ) is shown pairing with a normal interspinous process space ( 13 ). in the same manner , a collapsed disc ( 17 ) pairs with a collapsed interspinous process space ( 14 ). this unbalanced arrangement results in one or more types of narrowing such as the stenotic central canal shown at ( 15 ). the spinous process spacer ( 20 ) spreads the spinous processes ( 12 ) adjacent to the collapsed interspinous process space ( 14 ) apart , thereby restoring anatomical alignment of the anterior and posterior spinal anatomy and alleviating the narrowing of nerve pathways that may have been generating severe pain and loss of function . the spinous process spacer ( 20 ) of the present invention is shown in fig2 . basically a tubular member ( 21 ) having an axial conduit ( 22 ), the desired interspinous process space ( 26 ) is defined by the depth of diametrically opposed spinous process cutouts , or , more simply termed “ notches ” ( 23 ), cut out of each end . the spinous processes ( 12 ) seat in these notches ( 23 ) when the spinous process spacer ( 20 ) is deployed in its final position as illustrated in fig3 - 4 . the remaining tubular sections flanking the notches ( 23 ) function as lateral spinous process stabilizers ( 24 ). optional holes ( 25 ) for mechanical attachment ( 40 ) to the adjacent spinous processes ( 12 ) are provided as well . attachment can be effected by suturing , cabling or other suitable means as is indicated in fig4 . the tubular geometry of the spinous process spacer ( 20 ) not only serves to strengthen the spacer in the axial direction but also provides more stabilization against unintended rotation than the substantially flat “ h ” shaped designs of the prior art . moreover , the axial conduit ( 22 ) offers a fillable space for bone growth - promoting materials . finally , the spinous process spacer ( 20 ) can be made of allograft or other suitable biological material to further promote integration of the spinous process spacer ( 20 ) into surrounding tissue . there are many techniques suitable for deployment of the spinal process spacer ( 20 ), the choice of which is dependent upon individual circumstances . basically , the following steps must be executed . the collapsed interspinous process space ( 14 ) must be adequately distracted . an appropriately sized spinous process spacer implant ( 20 ) must be secured in an implant holder . the holder and implant must be placed within the distracted space so that the axis of the spinous process spacer implant ( 20 ) is parallel to the adjacent spinous processes . finally the spinous process spacer implant ( 20 ) is rotated 90 degrees in the mid - sagittal plane so that its axis is now perpendicular to the spinous processes ( 12 ), and positioned so that the spinous processes ( 12 ) rest within the notches or , alternatively , the spinous process cutouts ( 23 ), and engagement is effected . a major benefit of this technique is that it gains access to the spinous process space via a lateral incision in the spinous process ligament . this preserves more of the spinous process ligament than a direct posterior approach . a more detailed description of such a method is illustrated in the remaining fig5 - 15 . fig5 illustrates a cross section of the mid - sagittal plane wherein dilators ( 50 ) have been placed between adjacent spinous processes ( 12 ). a rotation cannula ( 60 ) is placed over the largest dilator as shown in fig6 . the rotation cannula ( 60 ) is described in more detail in later paragraphs , but for the present discussion , suffice it to say that the rotation cannula ( 60 ) effects the above outlined steps of providing an implant holder and facilitating the required 90 degree rotation . fig7 illustrates the position of the rotation cannula between adjacent spinous processes after the dilators have been removed . as shown in fig1 - 12 , the rotation cannula ( 60 ) is substantially an open cylinder having a hollow rectangular cross member or , alternatively , an extension for the lateral spinous process stabilizers ( 110 ), wherein the spinous process spacer ( 20 ) is placed . the leading edge ( 112 ) of the cross member ( 110 ) is tapered to facilitate initial placement between the spinous processes ( 12 ). the trailing edge ( 113 ) is open . the long dimension of the rectangular cross member ( 110 ) is placed parallel to the affected spinous processes ( 12 ). with the spinous process spacer ( 20 ) saddled ( 131 ) between its prongs ( 130 ) as shown in fig1 - 14 , the rotation instrument ( 80 ) effects placement of the spinous process spacer ( 20 ) in the rotation cannula ( 60 ) as is shown in fig8 . a cross section of each prong ( 130 ) flanking the spinous process spacer ( 20 ) can be seen in the figure . the rotation cannula ( 60 ), shown in more detail in fig1 - 12 , is designed so that various grooves ( 111 ) allow the 90 degree rotation of the spinous process spacer ( 20 ) and removal of the rotation cannula ( 60 )/ rotation instrument ( 80 ) combination leaving only the spinous process spacer ( 20 ) in place . fig9 illustrates the resulting configuration after the required 90 degree rotation has been performed . finally , fig1 illustrates the placement of the spinous process spacer ( 20 ) upon removal of the cannula and rotation instrument . this lateral entry to the spinous process space combined with the 90 degree rotation of the spinous process spacer to its final position , will allow for greater preservation of the spinous process ligament and surrounding soft tissue anatomy than if the surgical approach is from a direct posterior approach . one of the most unique features of this invention is the fusion promoting features of its design , most particularly its axial conduit ( 22 ) which not only provides a pathway wherein fusion can occur , but also provides a fillable space wherein fusion - promoting biological material can be deployed . to further this end , an additional step in the deployment technique can be used . the trial rasp ( 150 ), shown in fig1 , is introduced into the interspinous process space ( 14 ) after distraction . having a bullet shaped leading edge ( 151 ) to facilitate insertion , its body ( 152 ) replicates the shape of the spinous process spacer ( 20 ), particularly the dimension matching the desired interspinous process spatial distance ( 26 ). the trial rasp ( 150 ) accomplishes several things . it tests the space for acceptance of the intended implant ( 20 ) by placing a trial in place which is representative of the size and shape of the actual implant ( 20 ). introduction of the trial rasp ( 150 ) and particularly the rasping surface ( 155 ) causes bleeding bone and enhances bone growth and fusion . it additionally shapes and prepares the affected area of the spinous process ( 12 ) to engage and mate more intimately with the notch ( 23 ). furthermore , it strips away soft tissue from the engagement area that might otherwise be caught between the implant ( 20 ) and the spinous process ( 12 ), thereby inhibiting fusion fusion resulting between the spinous process spacer implant and the two neighboring spinous processes ( 12 ), will be much less rigid than the traditional , more invasive , posterior lateral fusion or an interbody fusion . this lessened rigidity will serve to pose less risk upon the the adjacent spine motion segment and consequently less risk of a condition known as “ adjacent segment disease ”, a serious side effect of more traditional methods . while particular embodiments of the present invention have been illustrated and described , it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention . it is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention .
a spinous process spacer implant for relief of back pain is disclosed . the implant , a generally h - shaped device having grooved ends , is made of human allograft or other suitable artificial or natural material . it is sized for implantation between and optional attachment to adjacent spinous processes . the implant may be hollow in the center to allow for addition of suitable biological material .