Abstract:
A spinal distraction device is provided having a generally H-shaped cross section that maintains a desired space between adjacent spinous processes. The distraction device includes a body and two pairs of parallel sidewalls. The sidewalls create channels for receiving respective spinous processes. The distraction device is fused to the spinous processes with fixation devices.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims priority to U.S. Provisional Patent Application Ser. No. 60/722,208, filed Sep. 29, 2005, which is hereby incorporated in its entirety by reference herein. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to devices for improving the spinal stability of a patient. More particularly, the present invention relates to a spinal distraction device that may be implanted between adjacent spinous processes and is particularly well suited for percutaneous delivery.  
       BACKGROUND OF THE INVENTION  
       [0003]     As people age, they often experience degenerative conditions affecting the spinal structures. The conditions often cause pain and discomfort that may, in severe cases, be debilitating. Those conditions may include, for example, spinal stenosis, facet arthropathy and degenerative disc disease.  
         [0004]     Spinal stenosis is the thickening of the bones that make up the spine. That thickening often reduces the size of the passageways through which the spinal column, nerves and blood vessels pass. Those passageways include the central spinal canal and lateral foramena. In some cases, the space may be reduced to such a degree that the spinal column, nerves and/or blood vessels become impinged, or compressed, causing pain and/or numbness.  
         [0005]     Facet arthropathy (degeneration and arthritis of the facet joints) and degenerative disc disease often contribute to the instability of the spine. That instability may exacerbate or independently cause compression of the spinal cord, nerves and/or blood vessels within and surrounding the spine.  
         [0006]     The methods used to treat those spine conditions vary depending on the severity. For example, in less severe cases, non-surgical methods such as modifying activities or administering anti-inflammatory medications may be utilized. However, treatment of more severe cases often includes major surgical procedures such as spinal decompression surgery.  
         [0007]     A common problem with such procedures is that they are very invasive and require the severing of tissues surrounding the vertebral bodies causing the compression. As a result, the patient is oftentimes subjected to lengthy rehabilitation. In addition, some patients, especially elderly patients, may not have the stamina to endure such invasive procedures or lengthy rehabilitation.  
         [0008]     Other efforts have focused on creating distraction devices for maintaining a desired space between adjacent spinous processes. One such example of a distraction device is described in U.S. Pat. No. 6,699,247 to Zucherman et al. The distraction device described in that patent includes an expandable structure that includes two saddles facing opposite directions. The opening of each saddle is oriented to face a spinous process and the device is expanded to increase the space between the spinous processes. The saddles may be tethered to the spinous processes to inhibit migration of the device while allowing relative motion between each spinous process and the associated saddle and between the spinous processes. The device is also constructed from a flexible material to allow for that relative motion.  
         [0009]     A disadvantage of the device is that where fusion between the spinous processes is desired, the device is inadequate because it is designed and constructed so that there is relative movement.  
       SUMMARY OF THE INVENTION  
       [0010]     In view of the foregoing, it is an object of the present invention to provide a spinal distraction device that overcomes the drawbacks of previously known treatments and devices, and which may be implanted using open surgical, minimally invasive or percutaneous implantation techniques.  
         [0011]     It is also an object of the present invention to provide a percutaneously deliverable spinal distraction device that may be constructed from bone allograft.  
         [0012]     It is a further object of the present invention to provide a spinal distraction device that allows for fusion of the device with the adjacent spinous processes.  
         [0013]     These and other objects of the present invention are accomplished by providing a spinal distraction device constructed from bone allograft. The device has an H-shaped cross-section that provides channels, each of which is designed to receive a spinous process. The device also includes apertures for receiving fixation devices, such as screws, sutures or wire.  
         [0014]     In one embodiment, the distraction device includes a body portion and two pairs of parallel side walls. The side walls create channels for receiving the adjacent spinous processes. Apertures are also provided through the side walls for receiving fixation screws.  
         [0015]     In another embodiment, the distraction device includes a body portion and two pairs of parallel side walls, the side walls create channels for receiving the adjacent spinous processes. In this embodiment, an aperture is provided through the body portion for receiving a suture that is used to fuse the device within the space between the adjacent spinous processes. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     The above and other objects and advantages of the present invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference numerals refer to like parts throughout, and in which:  
         [0017]      FIG. 1  is a side view of an exemplary spinal distraction device of the present invention implanted between adjacent spinous processes;  
         [0018]      FIG. 2  is a perspective view of the spinal distraction device of  FIG. 1 ;  
         [0019]      FIG. 3  is a side view of the spinal distraction device of  FIG. 1 ;  
         [0020]      FIG. 4  is another side view of the spinal distraction device of  FIG. 1 ;  
         [0021]      FIG. 5  is a side view of another exemplary embodiment of a spinal distraction device of the present invention implanted between adjacent spinous processes;  
         [0022]      FIG. 6  is a perspective view of the spinal distraction device of  FIG. 5 ;  
         [0023]      FIG. 7  is a side view of the spinal distraction device of  FIG. 5 ; and  
         [0024]      FIG. 8  is another side view of the spinal distraction device of  FIG. 5 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]     The present invention is directed to a spinal distraction device  1  that is used to maintain a desired space between adjacent spinous processes, as shown in  FIG. 1-4 . Distraction device  1  may be implanted between adjacent vertebrae V 1  and V 2  to maintain a desired space between the vertebrae. In particular, the distance between a superior spinous process P 1  of a superior, or upper, vertebra V 1  and an inferior spinous process P 2  of inferior, or lower, vertebra V 2  is maintained by distraction device  1 .  
         [0026]     Distraction device  1  is generally H-shaped and generally includes a main body portion  2 , a pair of superior side walls  3 , and a pair of inferior side walls  4 . Body portion  2  is a generally columnar member that has a height H 1  corresponding to the desired space between adjacent spinous processes. As shown, body portion  2  has an oval cross-section, but it shall be appreciated that body portion  2  may have any cross-sectional shape, such as a rectangle, circle or semi-circle and body portion  2  may be tubular.  
         [0027]     Side walls  3  extend upward from a top surface  5  of body portion  2 . Side walls  3  are generally parallel and spaced from each other by a distance W 1 . Side walls  3  and top surface  5  combine to define a superior channel  6  having a width corresponding to distance W 1 .  
         [0028]     One or more apertures  7  may be provided through superior side walls  3 . Apertures  7  are configured to receive fixation devices, such as screws or sutures, for the purpose of fusing side walls  3  to the adjacent spinous process P 1 . It shall be appreciated that one aperture  7  may be provided that extends through only one of side walls  3 . In addition, although apertures  7  are shown generally aligned, it shall be appreciated that apertures  7  need not be aligned and may be offset so that multiple fixation devices may be inserted through side walls  3 .  
         [0029]     Side walls  4  extend downward from a bottom surface  8  of body portion  2 . Side walls  4  are generally parallel and spaced from each other by a distance W 2 . In addition, side walls  4  are generally parallel to side walls  3  such that distraction device  1  has an H-shaped cross-section, as shown in  FIG. 3 . Side walls  4  and bottom surface  8  together define an inferior channel  9  having a width W 2 .  
         [0030]     Apertures  10  may also be provided through side walls  4 . Similar to apertures  7 , apertures  10  are configured to receive fixation devices, such as screws or sutures, for the purpose of fusing side walls  4  to the adjacent spinous process P 2 . It shall be appreciated that one aperture  10  may be provided that only extends through one of side walls  4 . In addition, although apertures  10  are shown generally aligned, it shall be appreciated that apertures  10  may be offset so that multiple fixation devices may be inserted through side walls  4 .  
         [0031]     Superior channel  6  is configured to receive a lower portion of spinous process P 1 . In particular, distance W 1  approximates the width of spinous process P 1  so that there is limited relative lateral motion between side walls  3  and spinous process P 1 . In addition, side walls  3  have a height H 2  sufficient for fixation of side walls  3  with spinous process P 1  by fixation screws  11  that extend through apertures  7 .  
         [0032]     Similarly, inferior channel  9  is configured to receive an upper portion of spinous process P 2 . Distance W 2  approximates the width of spinous process P 2  so that there is limited relative lateral motion between side walls  4  and spinous process P 2 . Furthermore, side walls  4  have a height H 3  sufficient for fixation of side walls  4  with spinous process P 2  by fixation screws  11  that extend through apertures  10 . It shall be appreciated that fixation screws  11  may be any fixation screw known in the art.  
         [0033]     Distraction device  1  is formed from a material that is preferably osteoconductive and/or osteoinductive, such as bone allograft. The material choice helps to ensure fusion between distraction device  1  and the adjacent spinous processes P 1  and P 2 . Distraction device  1  may be formed from the allograft material and packaged by any method known in the art. For example, the device may be kept frozen or freeze-dried until just prior to its implantation.  
         [0034]     In order to implant distraction device  1 , access to superior spinous process P 1  and inferior spinous process P 2  is provided, for example using percutaneous surgical procedures known in the art. Thereafter, spinous process P 1  is distracted from spinous process P 2 . Next, distraction device  1  is introduced, for example via a cannula, into the space between spinous process P 1  and spinous process P 2 . Distraction device  1  is oriented such that superior spinous process P 1  is located within superior channel  6  and inferior spinous process P 2  is located within inferior channel  9 . After distraction device  1  is properly located, side walls  3  are fused to superior spinous process P 1  and side walls  4  are fused to inferior spinous process P 2  by implanting fixation screws  11  through apertures  7  and  10 , respectively.  
         [0035]     Another embodiment of a spinal distraction device  15  is shown in  FIGS. 5-8 . Distraction device  15  may be implanted between adjacent vertebrae V 3  and V 4  to maintain a desired space between the vertebrae, as shown in  FIG. 5 , and as described with respect to the previous embodiment above. Particularly, distraction device  15  maintains a space between a superior spinous process P 3  of a superior vertebra V 3  and an inferior spinous process P 4  of an inferior vertebra V 4  in a patient&#39;s spine.  
         [0036]     Similar to the previously described embodiment, distraction device  15  generally includes a body portion  16 , a pair of superior side walls  17 , and a pair of inferior side walls  18 . Body portion  16  is a generally columnar member that has a height H 4  corresponding to the desired space between adjacent spinous processes. Body portion  16  may have any cross-sectional shape, such as a rectangle, circle or semi-circle and body portion  16  may be tubular.  
         [0037]     An aperture  19  extending through body portion  16  may also be provided for fixing distraction device  15  to adjacent spinous processes with a suture, or wire, as will be described in greater detail below.  
         [0038]     Side walls  17  extend upward from a top surface  20  of body portion  16 . Side walls  17  are generally parallel and spaced from each other to form a superior channel  21  having a width W 3 .  
         [0039]     Side walls  18  extend downward from a bottom surface  22  of body portion  16 . Side walls  18  are generally parallel and spaced from each other to form an inferior channel  23  having a width W 4 . In addition, side walls  18  are generally parallel to side walls  17  such that distraction device  15  has an H-shaped cross-section, as shown in  FIG. 7 .  
         [0040]     Superior channel  21  is configured to receive a lower portion of spinous process P 3 . In particular, distance W 3  approximates the width of spinous process P 3  so that there is limited relative lateral motion between side walls  17  and spinous process P 3 . In addition, side walls  17  have a height H 5  sufficient to restrict lateral movement of distraction device  15  with respect to spinous process P 3 .  
         [0041]     Similarly, inferior channel  23  is configured to receive an upper portion of spinous process P 4 . Distance W 4  approximates the width of spinous process P 4  so that there is limited relative lateral motion between side walls  18  and spinous process P 4 . Furthermore, side walls  18  have a height H 6  sufficient to restrict lateral movement of distraction device  15  with respect to spinous process P 4 .  
         [0042]     Distraction device  15  may be introduced as described above with respect to the previous embodiment. After introduction, a suture, or wire, may be used to retain distraction device  15  in the space between superior spinous process P 3  and inferior spinous process P 4 . The suture may be woven through aperture  19  and additional apertures A 3  and A 4  drilled through spinous process P 3  and spinous process P 4 , respectively, as shown in  FIG. 5 . After the suture is woven through he apertures, they may be tied to secure the device. Alternatively, the suture may be woven through aperture  19  and over, or through, other vertebral features, thereby obviating the need for apertures A 3  and/or A 4 .  
         [0043]     Distraction device  15  is preferably formed from a material that is osteoconductive and/or osteoinductive, such as bone allograft. The material therefore promotes fusion between distraction device  15  and the adjacent spinous processes. Distraction device  15  may be shaped from a piece of bone allograft and stored frozen or freeze-dried as is well-known in the art.  
         [0044]     An advantage of distraction device  15  is that a smaller piece of allograft may be used because the side walls do not have to be long enough to support screw fixation.  
         [0045]     While preferred embodiments of the invention are described above, it will be apparent to one skilled in the art that various changes and modifications may be made.