Abstract:
An intervertebral spacer for positioning between vertebral members. The spacer may include contact surfaces that are configured to contact against the vertebral members. A fluid cylinder may be positioned between the first and second contact surfaces and configured to contain a fluid. The fluid cylinder may include an outer cylinder with an open first end that telescopingly receives an inner cylinder. The spacer is configured to maintain the distance between the contact surfaces at a desired amount.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation of co-pending application Ser. No. 12/848,499, filed on Aug. 2, 2010, which itself is a continuation of application Ser. No. 11/412,671, filed on Apr. 27, 2006, now U.S. Pat. No. 7,794,501. Each of these applications is herein incorporated by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    The present application is directed to devices and methods for stabilizing vertebral members, and more particularly, to intervertebral implants and methods of use for replacing an intervertebral disc, vertebral member, or combination of both to distract and/or stabilize the spine. 
         [0003]    The spine is divided into four regions comprising the cervical, thoracic, lumbar, and sacrococcygeal regions. The cervical region includes the top seven vertebral members identified as C1-C7. The thoracic region includes the next twelve vertebral members identified as T1-T12. The lumbar region includes five vertebral members L1-L5. The sacrococcygeal region includes nine fused vertebral members that form the sacrum and the coccyx. The vertebral members of the spine are aligned in a curved configuration that includes a cervical curve, thoracic curve, and lumbosacral curve. Intervertebral discs are positioned between the vertebral members and permit flexion, extension, lateral bending, and rotation. 
         [0004]    Various conditions may lead to damage of the intervertebral discs and/or the vertebral members. The damage may result from a variety of causes including a specific event such as trauma, a degenerative condition, a tumor, or infection. Damage to the intervertebral discs and vertebral members can lead to pain, neurological deficit, and/or loss of motion. 
         [0005]    Various procedures include replacing the entirety or a section of a vertebral member, the entirety or a section of an intervertebral disc, or both. One or more replacement implants may be inserted to replace the damaged vertebral members and/or discs. The implants reduce or eliminate the pain and neurological deficit, and increase the range of motion. 
       SUMMARY 
       [0006]    The present application is directed to an intervertebral spacer for positioning between first and second vertebral members. One spacer includes a first contact surface and a second contact surface. A fluid chamber is positioned between the first and second contact surfaces and is configured to contain a fluid. The fluid chamber includes an outer member with an open end, a sidewall, and a closed end. The outer member telescopingly receives an inner member. A slot is positioned in the sidewall of the outer member and extends inward from the open end. A seal is positioned in the slot to prevent the fluid from leaking from the fluid chamber. 
         [0007]    Another spacer includes first and second contact surfaces. A fluid chamber is positioned between the first and second contact surfaces and is configured to contain a fluid. The fluid chamber includes an outer member with an open end that telescopingly receives an inner member. A slot extends through the outer member and intersects with the fluid chamber. An elongated retaining mechanism extends across the slot and includes longitudinal first and second sections with the first section of the retaining mechanism positioned in the outer member on a first side of the slot and the second section of the retaining mechanism positioned in the outer member on an opposing second side of the slot. The outer member is movable relative to the outer member to adjust a width of the slot. 
         [0008]    Another spacer includes first and second contact surfaces. A fluid chamber is positioned between the first and second contact surfaces and is configured to contain a fluid. The fluid chamber includes an outer member with an open first end that telescopingly receives an inner member. A slot extends through the outer member at the open first end and intersects with the fluid chamber. A seal is positioned in the slot to prevent the fluid from leaking from the fluid chamber. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a perspective view of an exemplary intervertebral spacer in a retracted position disposed between two vertebral members. 
           [0010]      FIG. 2  is a perspective view of an exemplary intervertebral spacer in an extended position disposed between two vertebral members. 
           [0011]      FIG. 3  is an exploded perspective view of an exemplary intervertebral spacer. 
           [0012]      FIG. 4  is a perspective view of an inferior member for an exemplary intervertebral spacer. 
           [0013]      FIG. 5  is a perspective view of a superior member for an exemplary intervertebral spacer. 
           [0014]      FIG. 6  is a detail view of one exemplary intervertebral spacer. 
           [0015]      FIGS. 7 and 8  illustrate an exemplary method of inserting the intervertebral spacer. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    The present application relates to implants for replacing an intervertebral disc, vertebral member, or combination of both, and to methods of inserting the same. The implant comprises an intervertebral spacer  10  that can be inserted between vertebral bodies in a compact configuration as shown in  FIG. 1  and subsequently expanded to contact the adjacent vertebral bodies as shown in  FIG. 2 . 
         [0017]      FIGS. 3-5  illustrate one exemplary embodiment of the intervertebral spacer  10 . The intervertebral spacer  10  comprises an inferior member  12  and a superior member  60  movable with respect to the inferior member  12  from a retracted position to an extended position. As will be described in more detail below, the inferior member  12  includes a first cylinder  22 , and the superior member  60  includes a second cylinder  72  that is insertable into the first cylinder  22 . The cylinders  22  and  72  together define a expansion chamber. When fluid is introduced into the expansion chamber, the superior member  60  is urged away from the inferior member  12 . While cylinders  22  and  72  are shown having a circular cross-section, those skilled in the art will appreciate that the cylinders  22  and  72  can have other shapes, such as square, rectangular, oval, kidney-shape, etc. 
         [0018]      FIG. 4  illustrates details of one embodiment of the inferior member  12 . The inferior member  12  comprises a body  14  including a bottom surface  15  that contacts an adjacent vertebral body. The bottom surface  15  can be textured to grip the vertebral body. For example, teeth, ridges, or grooves can be formed in the bottom surface  15  to improve gripping capability. The body  14  has an oblong configuration including a central section  16  and wing sections  18  and  20 . Cylinder  22  is formed in the central section  16 . A fluid port  24  is formed in the central section  16  for introducing fluid into the expansion chamber formed by cylinders  22  and  72 . A one-way valve  26  ( FIG. 3 ) is disposed in the fluid port  24  that allows introduction of fluid, such as a saline solution, into the expansion chamber, and prevents fluid from exiting the expansion chamber. One or more cavities  30  may be formed in the wing sections  18  and  20  to reduce weight and material requirements. 
         [0019]    A slot  32  is formed in the wing section  18 . Slot  32  divides the wing section  18  into first and second clamping portions  34  and  36 , respectively, and intersects both the wall and bottom of the cylinder  22 . A compressible seal  50  is disposed within the slot  32  to prevent fluid from leaking from the expansion chamber. Clamping portion  34  includes a recessed surface  38 . A pair of spaced-apart ears  40  project outward from the recessed surface  38  for mounting a pin  42 . The ends of the pin  42  are firmly secured in openings formed in the ears  40 . Any suitable techniques for securing the pin  42  can be used. A screw hole  44  extends inward from the recessed surface  38  to receive a locking screw  46 . The screw hole  44  crosses the slot  32  such that the screw hole  44  is divided into two portions  44   a ,  44   b . Portion  44   b  of the screw hole  44  is threaded. When the locking screw  46  is tightened, the clamping portions  34  and  36  are pulled together, causing a slight contraction of the cylinder  22 . As will be hereinafter described, this clamping arrangement functions as a locking mechanism to lock the superior member  60  firmly in place once proper height adjustment has been made. 
         [0020]    The superior member  60 , shown in  FIG. 5 , comprises a plate  62  having a top surface  64  that engages an adjacent vertebral body. The top surface  64  can be textured to grip the vertebral body. For example, small teeth, ridges, or grooves can be formed in the top surface  64  to improve gripping capability. The top plate  62  is shaped to generally correspond to the shape of the inferior member  12 . The top plate  62  includes a central section  66  and wing sections  68  and  70 . A cylinder  72  extends from the bottom surface of the top plate  62 . Cylinder  72  is sized to fit within the cylinder  22  in the inferior member  12 . In one embodiment, the interior dimension of the cylinder  22  and exterior diameter of the cylinder  22  are sized to close tolerances such that a seal is formed between the interior wall of cylinder  22  and outer surface of cylinder  72 . However, those skilled in the art will appreciate that a ring seal  52  may be used to form a fluid tight seal between cylinders  22  and  72 . An annular groove  54  may also be formed in the outer surface of the cylinder  72  to position the seal  52 . 
         [0021]    A mechanism can be provided to prevent the inferior member  12  and superior member  60  from separating. In one embodiment, a pair of resilient fingers  74  extends downward from the bottom surface of the top plate  62  of superior member  60 . The enlarged ends  76  of the resilient fingers  74  are configured to engage the locking tabs  28  on the inferior member  12 . When the superior member  60  is assembled with the inferior member  12 , the ends of the locking fingers  74  contact the locking tabs  28 . Camming surfaces  78  on the enlarged ends  76  of the locking fingers  74  cause the resilient fingers  74  to flex outward and pass over the locking tabs  28 . Once the enlarged ends  76  have passed over the locking tabs  28 , the resilient fingers  74  return to their original position, thereby preventing separation of the superior member  60 . Thus, the resilient fingers  74  and locking tabs  28  cooperate to retain the superior member  60  in place. 
         [0022]      FIG. 6  illustrates an alternate method of preventing separation of the inferior member  12  and superior member  60 . In this embodiment, an inwardly projecting lip  80  is formed at the top end of cylinder  22  and an outwardly projecting lip  82  is formed at the bottom end of cylinder  72 . In this embodiment, the superior member  60  can be assembled with the inferior member  12  by dipping the superior member  60  in a cold liquid, such as liquid nitrogen, to shrink the superior member  60 . When the superior member  60  shrinks, the lip  82  on cylinder  72  will pass through the lip  80  on cylinder  22 . The superior member  60  will then expand to its original size as it returns to ambient temperatures. 
         [0023]    The inferior member  12  and superior member  60  can be made of any suitable material, such as PEEK. The bottom of the inferior member  12  and/or top late  62  of the superior member  60  could be porous to allow the in-growth of bone. An embedded biologic coating, such as hydroxia appetite (HA), BMP, or calcium phosphate could be used to promote bone in-growth. The contact surfaces of the inferior and superior members  12  and  72  could also be textured to grip the adjacent vertebral bodies. 
         [0024]    In use, the superior member  60  is assembled to the inferior member  12  and placed in a compact configuration with the superior member  60  in a retracted position relative to the inferior member  12  as shown in  FIG. 1 . The intervertebral spacer  10 , in a compact configuration, is inserted through a cannula  150  into an intervertebral space between two vertebral bodies ( FIG. 1 ). Those skilled in the art will appreciate that the intervertebral spacer  10  can replace one or more disks and/or vertebral bodies. After the insertion of the intervertebral spacer  10 , fluid or compressed air is introduced into the expansion chamber to cause the superior member  60  to extend away from the inferior member  12  as shown in  FIG. 2 . The superior member  60  is raised until the contact surfaces of the inferior and superior members  12  and  60  are engaged with the adjacent vertebral bodies. Once the height of the intervertebral spacer  10  is properly adjusted, the locking screw  24  is tightened to lock the superior member  60  in a fixed position relative to the inferior member  12 . Tightening the locking screw  46  causes the cylinder  22  of the inferior member  12  to contract and clamp against the exterior surface of cylinder  22 . Thus, the cylinder  22  itself functions as a clamp that will lock the inferior and superior members  12 ,  60  in position, even in the event that fluid leaks from the expansion chamber. 
         [0025]      FIGS. 7 and 8  illustrate an exemplary insertion tool  100  to insert the intervertebral spacer  10 . The insertion tool  100  includes an elongate housing  102  having three lumens  106 ,  108 , and  110  formed therein. Access to the intervertebral space is gained through a cannula  150  inserted into the body.  FIGS. 7 and 8  illustrate the distal end of the cannula  150  and insertion tool  100 . The insertion tool  100  includes a hook member  102  that engages pin  42  on the intervertebral spacer  10 . As the intervertebral spacer  10  is advanced through the cannula  150 , the intervertebral spacer  10  initially assumes the position shown in  FIG. 7 . When the intervertebral spacer  10  exits from the end of the cannula  150 , a push rod  104  is used to rotate the intervertebral spacer  10  into the proper angular position. 
         [0026]    The hook member  102  and push rod  104  pass through the first lumen  106 . The second lumen  108  aligns with the locking screw  46 . The third lumen  110  aligns with the fluid valve  26 . After the intervertebral spacer  10  is properly positioned, a fluid delivery line can be inserted through lumen  110  and engaged with the fluid valve  26  to deliver fluid into the expansion chamber to expand the intervertebral spacer  10 . A tool can then be inserted through the middle lumen  108  to tighten the locking screw  42 . 
         [0027]    The embodiments described above include member  60  being a superior member and member  12  being inferior. In another embodiment, the orientation of these members  60 ,  12  may be interchanged with member  60  functioning as an inferior member and member  12  functioning as a superior member. 
         [0028]    One embodiment includes accessing the spine from a postero-lateral approach. Other applications contemplate other approaches, including posterior, anterior, antero-lateral and lateral approaches to the spine, and accessing other regions of the spine, including the cervical, thoracic, lumbar and/or sacral portions of the spine. 
         [0029]    The term “distal” is generally defined as in the direction of the patient, or away from a user of a device. Conversely, “proximal” generally means away from the patient, or toward the user. Spatially relative terms such as “under”, “below”, “lower”, “over”, “upper”, and the like, are used for ease of description to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the device in addition to different orientations than those depicted in the figures. Further, terms such as “first”, “second”, and the like, are also used to describe various elements, regions, sections, etc and are also not intended to be limiting. Like terms refer to like elements throughout the description. 
         [0030]    As used herein, the terms “having”, “containing”, “including”, “comprising” and the like are open ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features. The articles “a”, “an” and “the” are intended to include the plural as well as the singular, unless the context clearly indicates otherwise. 
         [0031]    The present invention may be carried out in other specific ways than those herein set forth without departing from the scope and essential characteristics of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.