Abstract:
A spinous process spacer implant and method of use are provided. The implant can be configured to be placed between adjacent spinous processes. The implant can comprise at least one pair of notches that can be positioned such that portions of the adjacent spinous processes are engaged therewithin to maintain a size of a desired space between the adjacent spinous processes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. application Ser. No. 11/308,767, filed May 1, 2006, which claims the benefit of U.S. Provisional Application No. 60/676,538, filed on May 2, 2005, the entireties of each of which are hereby incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Inventions 
         [0003]    This invention generally relates to a device and method for the treatment of spinal stenosis. 
         [0004]    2. Description of the Related Art 
         [0005]    Spinal stenosis is a narrowing of the spinal canal. While this in itself does not necessarily cause symptoms, swelling and nerve inflammation results when the narrowing leads to compression of the spinal cord and nerve roots. 
         [0006]    While spinal stenosis can be found in any part of the spine, the lumbar and cervical areas are most commonly affected. Patients with lumber spinal stenosis may feel pain, weakness, or numbness in the lower extremities. Symptoms often increase when walking short distances and decrease when the patient sits, bends forward or lies down. Although some people are born with spinal stenosis, it generally occurs as the gradual result of “wear and tear” on the spine during everyday activities, primarily affecting people over 50 years of age. 
         [0007]    Non-surgical treatments of spinal stenosis include medication, steroid injections, and physical therapy. While surgical options are available, they are invasive. Due to the inherent risks involved with such procedures, surgery is usually considered only after other non-invasive procedures have failed. 
         [0008]    Published application number 2001/0039452 by Zucherman discloses a spinal distraction implant that alleviates pain associated with spinal stenosis by expanding the volume in the spinal canal or neural foramen. In the Zucherman device, a body portion is adapted to seat between the adjacent spinous processes while a wing portion is adapted to prevent lateral movement of the body portion, thereby holding it in place between the adjacent spinous processes. 
         [0009]    Although the Zucherman device achieves spinal distraction, it nonetheless presents some limitations. It is a non-biological, multi-piece design, subject to wear and implantation complexity. Furthermore, the expansive geometry of the device may not lend itself to minimally invasive surgical techniques seeking to conserve muscle mass and soft tissue in the regions adjacent the spinous processes. 
       SUMMARY 
       [0010]    A spinous process spacer device for surgical implantation between the spinous processes of adjacent upper and lower vertebrae is disclosed. The spacer device maintains a desired space between the adjacent spinous processes. It comprises a tubular member having an axis, a length, an axial lumen coextensive with the length, an outer diameter, an upper end and a lower end. The upper and lower ends each have a pair of diametrically opposed notches (cut outs) along the outer diameter of the spacer device. The pair of diametrically opposed notches in the upper end is aligned with the pair of diametrically opposed notches in the lower end. When properly positioned, the pairs of diametrically opposed notches are dimensioned to receive a portion of the spinous processes, thereby maintaining the desired space between adjacent spinal processes. 
         [0011]    The features of the invention believed to be novel are set forth with particularity in the appended claims. However the invention itself, both as to organization and method of operation, together with further objects and advantages thereof may be best understood by reference to the following description taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0012]    The abovementioned and other features of the inventions disclosed herein are described below with reference to the drawings of the preferred embodiments. The illustrated embodiments are intended to illustrate, but not to limit the inventions. The drawings contain the following figures: 
           [0013]      FIG. 1  illustrates a spinal column having a collapsed disc and stenotic central canal. 
           [0014]      FIG. 2  illustrates the spinous process spacer implant of the present invention. 
           [0015]      FIG. 3   a  illustrates the final configuration of spinous process spacer positioned between adjacent spinous processes.  FIG. 3   b  is an enhancement indicating the engagement of the spinous processes with the spinous process cutout portion of the implant. 
           [0016]      FIG. 4  illustrates the spinous process spacer positioned and constrained with optional cables. 
           [0017]      FIG. 5  illustrates the introduction of successively larger diameter dilators until the appropriate distraction is achieved. 
           [0018]      FIG. 6  illustrates the insertion and placement of the rotation cannula over the last dilator used. 
           [0019]      FIG. 7  illustrates the position of the rotation cannula between adjacent spinous processes after the dilators have been removed. 
           [0020]      FIG. 8  illustrates the insertion and initial placement of the implant with the rotation instrument. 
           [0021]      FIG. 9  illustrates the configuration upon rotating the implant 90 degrees using the rotation instrument. 
           [0022]      FIG. 10  illustrates the final configuration of the implant upon removal of the cannula and rotation instrument. 
           [0023]      FIG. 11  illustrates the empty rotation cannula. 
           [0024]      FIG. 12  illustrates the rotation cannula with the implant inserted into the extensions for the lateral spinous process stabilizers. 
           [0025]      FIG. 13  illustrates the rotation instrument. 
           [0026]      FIG. 14  illustrates the rotation instrument with the implant inserted between its prongs. 
           [0027]      FIG. 15  illustrates the rasping device. 
       
    
    
     DESCRIPTION OF THE NUMERALS USED IN THE FIGURES 
       [0000]    
       
           10 —spinal cord 
           11 —vertebral body 
           12 —spinous process 
           13 —normal interspinous process space 
           14 —collapsed interspinous process space 
           15 —stenotic central canal 
           16 —normal disc 
           17 —collapsed disc 
           18 —anterior side 
           19 —posterior side 
           20 —implant, spinous process spacer 
           21 —tubular member 
           22 —axial conduit 
           23 —spinous process cutout, notch 
           24 —lateral spinous process stabilizers 
           25 —holes for securement means 
           26 —desired interspinous process spatial distance 
           40 —means for securement to spinous processes 
           50 —dilators 
           60 —rotation cannula 
           80 —rotation instrument 
           110 —extension for lateral spinous process stabilizers 
           111 —rotation and removal grooves 
           112 —tapered leading edge of the extension 
           113 —open trailing edge of the extension 
           130 —prong 
           131 —saddle 
           150 —trial rasp 
           151 —bullet shaped leading edge 
           152 —implant shaped body 
           153 —stem 
           154 —handle 
           155 —rasping surface 
       
     
       DETAILED DESCRIPTION 
       [0061]    The term “allograft”, as used herein, is intended to mean a graft taken from a different individual of the same species. 
         [0062]    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. 
         [0063]    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. 
         [0064]    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. 
         [0065]    The function of the spinous process spacer ( 20 ) can be understood by appreciating the problem illustrated in  FIG. 1 . 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. 
         [0066]    The spinous process spacer ( 20 ) of the present invention is shown in  FIG. 2 . 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  FIGS. 3-4 . 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  FIG. 4 . 
         [0067]    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. 
         [0068]    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. 
         [0069]    A more detailed description of such a method is illustrated in the remaining  FIGS. 5-15 .  FIG. 5  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  FIG. 6 . 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.  FIG. 7  illustrates the position of the rotation cannula between adjacent spinous processes after the dilators have been removed. 
         [0070]    As shown in  FIGS. 11-12 , 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. 
         [0071]    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  FIGS. 13-14 , the rotation instrument ( 80 ) effects placement of the spinous process spacer ( 20 ) in the rotation cannula ( 60 ) as is shown in  FIG. 8 . A cross section of each prong ( 130 ) flanking the spinous process spacer ( 20 ) can be seen in the figure. 
         [0072]    The rotation cannula ( 60 ), shown in more detail in  FIGS. 11-12 , 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.  FIG. 9  illustrates the resulting configuration after the required 90 degree rotation has been performed. Finally,  FIG. 10  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. 
         [0073]    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. 
         [0074]    The trial rasp ( 150 ), shown in  FIG. 15 , 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 ). 
         [0075]    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. 
         [0076]    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 adjacent spine motion segment and consequently less risk of a condition known as “adjacent segment disease”, a serious side effect of more traditional methods. 
         [0077]    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.