Abstract:
In accordance with one or more implementations of the present invention, a flexible mesh bag including a catenoidal central portion ( 106 ) and two bulbous end portions ( 104, 108 ) may be employed as a spinal spacer. The mesh may be percutaneously implanted between adjacent spinous processes ( 202, 204 ) to correct the position and orientation of a spine and thereby relieve any discomfort associated with spinal stenosis. Additionally, the mesh may be filled with a bone graft material to permit bone fusion for long-term stability.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to methods and devices for the treatment of spinal stenosis. 
         [0003]    2. Description of the Related Art 
         [0004]    Spinal stenosis is a condition in which the spinal canal is narrowed, resulting in compression of the spinal cord and corresponding nerves. Possible causes of spinal stenosis include osteoarthritis, degenerative disc disease and other conditions associated with aging. Many people suffering from spinal stenosis often have spinous processes of adjacent vertebra that are abnormally close. Pressure on the spinal cord may be reduced by implanting a device that separates the spinous processes. 
         [0005]    World Intellectual Property Organization (WIPO) Publication WO 2005/009300 describes a prosthesis inserted between spinous processes to prevent back pain. The prosthesis is comprised of an elastic material and includes a rigid central rod extended along its horizontal axis. The elastic material prevents leakage of liquids and gases and may be composed of rubber or silicon. Additionally, the prosthesis may have a dumbbell shape and may include expandable pockets within end sections and within a central section of the prosthesis. Prior to implantation, the pockets are filled with a substance, such as ethyl ether, that expands when exposed to body heat. The end sections are positioned along the sides of the spinous processes and the central section is positioned between the spinous processes. 
         [0006]    WIPO Publication 2007/110604 discloses an expandable spacer including a flexible enclosure and a central tubular section extending along the horizontal axis of the enclosure. The flexible enclosure includes two end sections and a central section that may adapt to the shape of spinous processes when inserted between them. Further, the length of the central tubular section may be adjusted to stretch the flexible member so as to reduce the cross-sectional area of the spacer during insertion. After the spacer is inserted between spinous processes, the length of the central tubular section is reduced and the flexible enclosure is injected with a settable polymer resin through the central tubular section. Subsequent to polymerization, the end sections of the flexible enclosure retain the spacer in place and the pressure of the central section may control the separation between the spinous processes. 
         [0007]    U.S. Pat. No. 5,549,679 discloses methods for treating spinal degeneration by inserting an expandable implant between vertebral bodies. The method may begin by boring out a portion of a degenerated disc and portions of neighboring vertebral bodies. Thereafter, the implant is inserted within the bored cavity and a bone graft material is injected within the implant. The implant is elliptical in shape and is porous, thereby enabling ingress and egress of fluids to permit growth of blood vessels, fibrous tissue and bone through the implant. The implant is sealed after it has been filled with the material. The patent also states that the filled implant may alternatively be positioned against the exterior lamina bone of adjacent vertebra to promote bone grafting of adjacent vertebra. 
         [0008]    U.S. Pat. No. 7,226,481 and related U.S. Publication No. 2006/0149379 disclose methods for treating several spinal abnormalities including compression fractures by employing an implant similar to the patent described in U.S. Pat. No. 5,549,679. The references further describe inserting the implant within the vertebral body between vertebral end plates to displace diseased or damaged tissue or bone when filled with bone graft material. 
       SUMMARY OF THE INVENTION 
       [0009]    It is an object of the invention to provide methods and implants for bone grafting the spinous processes to promote long term relief of back pain due to spinal stenosis. 
         [0010]    It is further object of the present invention to provide minimally invasive surgical methods and implants for treating spinal stenosis by adjusting the position of adjacent vertebra. 
         [0011]    These and other related objects are achieved according to the invention by a method for treating spinal stenosis including the steps of inserting a porous implant in interspinus space and filling the implant with a material to secure the implant and to adjust the position and orientation of adjacent vertebra. In accordance with one aspect of the present invention, the implant may be porous. According to another aspect of the present invention, the implant may include a central portion positioned between adjacent spinous processes and two end portions positioned along the sides of the implant to provide stability. Utilizing an implant with a central section and end sections in accordance with aspects of the present invention provide a significant advantage over the prior art. For example, as discussed above, prior art methods merely separate spinous processes with a foreign object. In contrast, the porosity of an exemplary implant of the present invention may permit bone grafting of adjacent spinous processes, thereby providing a durable and natural means for relieving spinal cord compression due to osteoarthritis and other causes of spinal stenosis, as discussed more fully below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The advantages, nature, and various additional features of the invention will appear more fully upon consideration of the illustrative embodiments now to be described in detail in connection with accompanying drawings. In the drawings: 
           [0013]      FIG. 1A  is a diagram of an exemplary implant in a filled state in accordance with an aspect of the present invention; 
           [0014]      FIG. 1B  is a diagram depicting an alternate view of an implant in a filled state in accordance with an aspect of the present invention; 
           [0015]      FIG. 2  is a diagram illustrating an exemplary implant in a filled state inserted between spinous processes in accordance with an aspect of the present invention; 
           [0016]      FIG. 3  is a diagram illustrating a cross-sectional view of an exemplary implant in a filled state in accordance with an aspect of the present invention; and 
           [0017]      FIG. 4  is a high-level flow diagram illustrating an exemplary method for treating spinal stenosis in accordance with an aspect of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0018]    The present invention provides methods and devices for treating spinal stenosis. According to one exemplary embodiment of the present invention, an implant may be inserted between the spinous processes of adjacent vertebra to adjust the position and orientation of the spinous processes, thereby relieving compression of the spinal cord. With reference to  FIG. 1A  and  FIG. 1B , a view of an expanded implant  100  that is filled to a desired volume according to one aspect of the present invention is illustrated. 
         [0019]    As depicted in  FIGS. 1A and 1B , the implant  100  may be configured in a dumbbell or hour-glass shape, comprising four portions, described here from right to left: a fill insertion lip  102 ; a first end portion  104 ; a central portion  106 ; and a second end portion  108 . The fill insertion lip  102  or fill opening may include an elliptical opening with a diameter sufficient to permit the insertion of a filling tube so that the implant  100  may be filled with a material to a desired volume. Moreover, the lip may be self-closing upon withdrawal of the tube or may be sealed as is known in the art. U.S. Pat. No. 5,549,679, for example, describes several known methods for sealing an implant. 
         [0020]    Returning to  FIGS. 1A and 1B , the first and second end portions  104  and  108  may be in a bulbous, elliptical configuration and may include corresponding elliptical cavities. The central portion may be in a catenoidal configuration and may include a corresponding catenoidal cavity, as shown in  FIGS. 1A and 1B . According to one aspect of the present invention, the thinnest width of the central portion cavity may be approximately half as large as the diameter of one or both end portions. Further, the length of the central portion may be approximately one-third the length of the implant  100 . However, it should be appreciated that the central portion and end portions need not be related as described above. For example, the width of the central portion may range from 2 mm and 15 mm, the length of the central portion may range from 2 mm to 17 mm, the widths of either end portion may be between 4 mm and 30 mm, and the length of the implant  100  may range from 8 mm to 56 mm. 
         [0021]    With reference to  FIG. 2 , an illustration of a filled implant  100  inserted in an interspinous space is depicted. For example, as shown in  FIG. 2 , the central portion  106  of the filled implant  100  may be inserted between adjacent spinous processes  202  and  204  to adjust the position and orientation of the processes and the end portions  104  and  108  may be in contact with the sides of spinous processes  202  and  204  with sufficient surface pressure to secure the implant  100  in a proper location. Moreover, as shown in  FIG. 2 , the fill opening may permit access to a continuous space within said mesh bag. As discussed more fully below, the implant  100  may be porous to permit bone grafting of adjacent vertebra through the implant  100 . 
         [0022]    In accordance with a preferred embodiment the implant  100  is a porous, elastic, flexible and expandable bag that may exhibit strong tension characteristics when filled. For example, the implant  100  may be composed of any one or more of a polymeric fiber, fabric, metal and/or material used for surgical stitching. Further, it should be understood that the implant is composed of materials that are bio-compatible and meet all regulatory requirements. As depicted in  FIGS. 1A and 1B , the implant may also include perforations in a mesh configuration. The perforations are of a sufficient size to prevent outflow of fill material while permitting the growth of blood vessels and bones through the implant in both the end portions and the central portion when filled with a bone graft particulate. For example, the pores may be sized between about 0.25 mm to about 5.0 mm. Bone grafting of adjacent spinous processes provides a significant advantage over merely separating spinous processes with a foreign object. For example, bone grafting of spinous processes enables the corresponding vertebrae to maintain a position and orientation for long-term relief of compression of a spinal cord due to a spinal stenosis condition. 
         [0023]    With reference to  FIG. 3 , a cross-section of the filled implant showing the distribution of granular bone substitute utilized for bone grafting is illustrated. As depicted in  FIG. 3 , the implant perforations permit bone growth through the implant. In addition, the bone graft material inserted within the implant may comprise bone graft materials known in the art. For example, the bone graft material may include one or more of hydroxyapatite, morselized bone graft cortical, cancellous, bone morphogenic protein and calcified or decalcified bone derivative. 
         [0024]    Referring now to  FIG. 4 , a high-level method  400  for treating spinal stenosis is described. At step  402 , the implant may be inserted in interspinous space in a variety of ways. For example, the implant may be inserted in interspinous space by inserting a guide tube percutaneously with an open end positioned between adjacent spinous processes. Subsequently, a fill tube having a diameter that is smaller than the diameter of the guide tube may be directed through the guide tube with the implant in a collapsed or empty state attached at the end of the fill tube. The implant may be attached to the fill tube by mating threads included along the inner surface of fill insertion lip  102  with threads included on the outer surface of the fill tube as is known in the art. Known attachment means and sealing means are described, for example, in U.S. Pat. No. 5,549,679. 
         [0025]    After the implant is percutaneously pushed through the opening in the guide tube and situated in a proper position between the spinous processes, the implant may be filled with bone graft material in accordance with step  404 , described more fully below. For example, the implant may be placed in a proper location and filled in to a desired volume and size by utilizing positioning methods know to those of ordinary skill in the art, such as, for example by including radiopaque materials within the implant and monitoring the implant in accordance with radiographic techniques. 
         [0026]    It should also be noted that in other implementations, insertion of the guide tube may be omitted. For example, an incision may be made through a patient&#39;s soft tissue and the fill tube may be inserted through the incision with the implant tucked within the tube. 
         [0027]    At step  404 , with reference to  FIG. 2 , the implant may be filled with a bone graft material to a desired volume. For example, packing the implant with a material enables adjustment of the width of the central portion of the implant. The implant may be filled until the spinous processes are spaced a distance sufficient to relieve compression of the spinal cord due to spinal stenosis. Moreover, as the implant is filled over time, the bulbous end portions become increasingly rigid, thereby providing an increasing degree of stabilization along either side of the spinal processes. In this way the implant may adjust the position and orientation of the spinous processes. Further, the central portion of the implant may be positioned between adjacent spinous processes and the end portions may be positioned along the sides of the spinous processes to promote bone grafting as discussed above. In addition, the spinous processes with which the implant is in contact may be filed prior to filling the implant to enhance bone grafting, as is known in the art.  FIG. 2  illustrates the implant inserted between spinous processes and filled to a desired volume. 
         [0028]    At step  406 , the implant may be sealed. For example, the fill insertion lip may be self sealing upon removal of the fill tube, as is known in the art. 
         [0029]    Advantageously, method  400  may be performed percutaneously, thereby providing a minimally invasive procedure for implanting a spinal support device for the treatment of spinal stenosis. 
         [0030]    Having described preferred embodiments for the treatment of spinal stenosis, materials used therein and methods for utilizing the same (which are intended to be illustrative and not limiting), it is noted that modifications and variations can be made by persons skilled in the art in light of the above teachings. It is therefore understood that changes may be made in the particular embodiments of the invention disclosed which are within the scope and spirit of the invention as outlined by the appended claims. Having thus described the invention with the details and particularity required by the patent laws, what is claimed and desired protected by Letters Patent is set forth in the appended claims.