Abstract:
Systems and methods for reducing pressure within a spinal disc are described. In accordance with one implementation, a spinal disc system comprises an aperture within a spinal disc body, and the aperture is configured to permit nucleus pulposus to flow from the disc body through the aperture. In accordance with another implementation, a method of reducing pressure within a spinal disc comprises forming an aperture within a spinal disc body, and permitting at least a portion of the nucleus pulposus to flow from the disc body through the aperture.

Description:
TECHNICAL FIELD 
       [0001]    This application relates generally to spinal disc systems and methods for reducing pressure within a spinal disc. 
       BACKGROUND 
       [0002]    A human spinal column includes vertebral bodies alternating with intravertebral discs extending from the neck to the pelvis. The discs generally form strong joints, separate, cushion and allow flexure and torsion between the vertebrae. 
         [0003]    When functioning properly, the vertebrae and discs allow a person to bend forward, backward, sideways and to twist. To accomplish this, the discs typically permit adjacent vertebrae six degrees of motion: vertical (compressing to absorb shock and tension), bending forward and backward, bending to the sides and twisting. The cervical and lumbar discs also can be thicker anteriorly to contribute to lordosis. Thoracic discs usually are more uniform. Unfortunately, disc disease may limit spinal motion or cushioning or permit the motion with pain. 
         [0004]    Each intervetebral disc usually has a central area composed of a colloidal gel, called the nucleus pulposus, on a surrounding collagen-fiber composite structure, the annulus fibrosus. The nucleus pulposus typically occupies 25-40% of the disc&#39;s total cross-sectional area. The nucleus pulposus usually contains 70-90% water by weight and may mechanically function like an incompressible hydrostatic material. The annulus fibrosis surrounds the nucleus pulposus and typically resists torsional and bending forces applied to the disc. The annulus fibrosis thus often serves as the disc&#39;s main stabilizing structure. The annulus fibrosus usually resists hoop stresses due to compressive loads and the bending and torsional stresses produced by a person bending and twisting. The fibers of the annulus form lamellae, individual layers of parallel collagen fibers, that attach to the superior and inferior end plates of adjacent vertebrae. Vertebral end-plates separate the disc from the vertebral bodies on either side of the disc. 
         [0005]    The anterior longitudinal ligament, which is anterior to the vertebral bodies, and the posterior longitudinal ligament, which is posterior to the vertebral bodies and anterior to the spinal cord function to hold the spinal structure together. The muscles of the trunk provide additional support. 
         [0006]    Trauma or disease may displace or damage spinal discs. A disc herniation occurs when annulus fibers weaken, and the inner tissue of the nucleus (nucleus pulposus) bulges out of the annulus. The herniated nucleus may compress a spinal nerve, which could result in pain, lack of sensation, loss of muscle control or even paralysis. Alternatively, disc degeneration may result when the nucleus deflates. Subsequently, the height of the nucleus decreases often causing the annulus to buckle in areas where the laminated plies are loosely bonded. This also may cause chronic and severe back pain. Further, the disc may rupture, resulting in a portion of the nucleus pulposus flowing through the fractured annulus, outside the disc to compress nerves and/or the spinal cord. This material may irritate the spinal nerve or spinal cord when tit flows into a posterior region of the disc. 
         [0007]    Whenever the nuclear tissue is herniated or the disc degenerates, the vertical disc space typically narrows and the adjacent vertebra may lose much of their normal stability. In many cases, to alleviate pain from degenerated or herniated discs, a surgeon removes the nucleus by performing a discectomy, which requires surgical dissection. The healing from such a surgery usually causes scar tissue which may compress the same or nearby nerves and/or spinal cord (which were being affected by the now-removed nucleus) and cause chronic pain and nervous system dysfunction. Other times, if the disc is compressed, the surgeon may perform a surgical fusion of two or multiple adjacent vertebrae together. While this treatment may or may not alleviate the pain and nervous dysfunction, the patient often loses all disc motion in the fused segment. Ultimately, this procedure places greater stress on the discs adjacent to the fused segment as the adjacent discs compensate for lack of motion. 
         [0008]    In the case of severe disc degeneration, the height of the disc often is flattened to such an extent that the adjacent vertebral body bones touch and eventually grow together. This may stop pain by stopping the movement of the disc between the vertebral bones, and is known as an auto-fusion. 
       SUMMARY 
       [0009]    In accordance with one implementation, a spinal disc system comprises an aperture within a spinal disc body, and the aperture is configured to permit nucleus pulposus to flow from the disc body through the aperture. 
         [0010]    In accordance with another implementation, a method of reducing pressure within a spinal disc comprises forming an aperture within a spinal disc body, and permitting at least a portion of the nucleus pulposus to flow from the disc body through the aperture. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    In the drawings, which are discussed below, one or more implementations are illustrated. The drawings are not necessarily to scale and certain features may be removed, exaggerated, moved, or partially sectioned for clearer illustration. It is understood that the spinal disc stent is not limited to the implementations depicted in the drawings herein, but rather it is defined by the claims appended hereto and equivalent structures. 
           [0012]      FIG. 1  is side view of a human spinal column. 
           [0013]      FIG. 2  is an enlarged view of a portion of the column of  FIG. 1 , illustrating vertebrae alternating with vertebral discs and a stent implanted within the wall of one disc. 
           [0014]      FIG. 3  is a perspective, partially sectioned view of  FIG. 2 , taken generally along the view of line  3 - 3  of  FIG. 2 , with the stent removed for clarity. 
           [0015]      FIG. 4  is a sectional view taken generally along line  4 - 4  of  FIG. 3 . 
           [0016]      FIG. 5  is a partially sectioned side view of selected vertebrae and a disc of  FIG. 2 , illustrating the disc in a first configuration. 
           [0017]      FIG. 6  is a partially sectioned side view of selected vertebrae and a disc of  FIG. 2 , illustrating the disc in a second configuration. 
           [0018]      FIG. 7  is the view of  FIG. 4 , illustrating an aperture formed within the wall of a disc, and showing an optional stent, according to an implementation. 
           [0019]      FIG. 8  is the view of  FIG. 4 , illustrating a cannula for implanting a stent within the wall of a disc, according to an implementation. 
           [0020]      FIG. 9  is an enlarged sectional view of  FIG. 8 , illustrating the stent of  FIG. 2 , according to an implementation. 
           [0021]      FIG. 10  is an enlarged sectional view taken of  FIG. 8 . 
           [0022]      FIGS. 11-13  illustrate exemplary additional implementations of stents. 
           [0023]      FIG. 14  is a perspective view of a plugging portion, according to an implementation. 
       
    
    
       [0024]    Like reference symbols in the various drawings indicate like elements. 
       DETAILED DESCRIPTION 
       [0025]    While the specification concludes with claims particularly pointing out and distinctly claiming subject matter, the spinal disc stent will now be further described by reference to the following detailed description of exemplary implementations taken in conjunction with the above-described accompanying drawings. The following description is presented to enable any person skilled in the art to make and use the spinal disc stent. Descriptions of specific implementations and applications are provided only as non-limiting examples and various modifications will be readily apparent to those skilled in the art. The general principles defined herein may be applied to other implementations and applications without departing from the spirit and scope of the spinal disc stent. Thus, the spinal disc stent is to be accorded the widest scope encompassing numerous alternatives, modifications, and equivalents consistent with the principles and features disclosed herein. For purpose of clarity, details relating to technical material that is known in the technical fields related to the spinal disc stent have not been described in detail so as not to unnecessarily obscure the present application. 
         [0026]      FIG. 1  illustrates a human spinal column  20 . The spinal column  20  includes vertebral bodies  22  alternating with intravertebral discs  24  extending from the neck region to the pelvis (not shown). The vertebral bodies  22  typically include seven cervical vertebrae  30  in the neck,  12  thoracic vertebrae  32  below the neck, five lumbar vertebrae  34  of the lower back, one sacrum  36  below the lumbar region and one coccyx  38 . 
         [0027]      FIGS. 2-8  illustrate a portion of the vertebral bodies  22  as adjacent vertebral bodies  40 ,  42  and  44  with alternating discs  46  and  48 , which are a portion of the discs  24 . As seen in  FIGS. 3-8 , each disc  24  has a nucleus pulposus  60  surrounded by a disc body, or annulus fibrosus,  62 . As seen in  FIG. 4 , the column  20  also includes posterior longitudinal ligaments  64  and anterior longitudinal ligaments  68 , which generally maintain the positions of the vertebral bodies  22  relative to discs  24 . Other ligaments, which are not discussed, are also typically present. The disc body  62  includes a generally circular lower portion  70 , a generally circular upper portion  72 , and a generally annular disc wall  74  ( FIG. 4 ). The disc wall, as illustrated in  FIGS. 3 ,  7  and  8 , is composed of fibrous tissue, or annulus fibrosus, and includes an inner surface  76  and an outer surface  78 . The disc  24  inner surface  76  defines a chamber  80  where the nucleus pulposus  60  is positioned. Further, the disc  24  includes a disc annulus central portion  82  which includes at least a portion of the chamber  80 . 
         [0028]    As seen in  FIG. 2 , the spinal column  20  includes a posterior region and an anterior region. In an implementation, a stent  100  may permit the nucleus pulposus  60  to flow into the anterior region of the column  20 . In some implementations, a stent is not needed and the nucleus pulposus  60  may flow into the anterior region of the column  20  through the aperture. 
         [0029]      FIG. 7  illustrates an aperture  90  formed through the annular disc wall  74  from the inner surface  76  to the outer surface  78 . The aperture  90  is generally defined by an inner surface  92 . In some implementations, the aperture  90  may be created by a stent, burn hole, drill hole, incision or puncture with balloon dilation or any other suitable manner of forming the aperture  90 . 
         [0030]      FIGS. 2 and 8  also illustrate an implementation of a disc stent  100 . As shown, the stent  100  includes a helical body  102  generally defining an axis A-A and having a first end  104 , a second end  106 , and an outer surface  108  ( FIGS. 9 and 10 ). In the implementation illustrated, the stent  100  is a biocompatible material, as discussed in greater detail below. 
         [0031]      FIGS. 5 and 6  illustrate relative axial motion between vertebral bodies  40 ,  42  and the deflection of the disc  24 . In  FIGS. 5 and 6 , the sectional shape of the inside surface  76  of the chamber  80  is exaggerated for clarity of illustration. In  FIG. 5 , the disk  40  is at a “normal” position relative to the disc  42  and the chamber  80  is illustrated as being generally circular in section. In  FIG. 6 , the disc  40  is forced toward the disc  42  with a force F as the disc  46  is deformed and the chamber  80  is distorted toward a more ellipsoidal section. As the disc  46  deforms, the disc wall  74  and the aperture  90  may also distort. Accordingly, the stent  100  may need to be radially flexible in order to maintain an axial position within the disc wall  74 . Further, in an implementation, a coating  110  may be applied to the outer surface  108  of the stent  100  to promote adhesion between the stent  100  and the inner surface  92  of the aperture  90  to restrict axial motion (along the axis A-A of  FIG. 9 ) of the stent  100  relative to the aperture  90 , thereby desirably retaining the stent  100  within the disc wall  74 . In some implementations, the stent  100  may be desired to remain within the aperture  90  for only a few (1-12) weeks, and some relative movement between the stent  100  and the inner surface  92  of the disc aperture  90  may be permitted. 
         [0032]      FIG. 9  illustrates the stent  100  interposed at least partially within the aperture  90 . As illustrated, after the stent  100  is implanted, the stent  100  will deflect radially outward and the aperture  90  may deflect radially inward until the outer surface  108  of the stent  100  contacts and interferes with the inner surface  92  of the aperture  90 . The outer surface  108  of the stent  100  may have a relatively smooth, semi-smooth, rough, or semi-rough surface, as desired, to desirably retain the stent  100  within the aperture  90 . 
         [0033]      FIG. 10  illustrates a device  120  including a cannula  122  and a plunger  124 . In some implementations, the cannula  122  includes a deployment end  130  and an opposing operating end (not shown). To deploy the stent  100  within the aperture  90 , the stent  100  is first radially compressed and inserted into the deployment end  130  of the cannula  122 . Then the cannula  122  is advanced into the body of the patient and into the disc  46 , through the disc annulus central portion  82  and into the aperture  90 . The plunger  124  may be then used to maintain the position of the stent  100  relative to the aperture  90  as the cannula  122  is retracted, generally in the direction R of  FIG. 10 . As the deployment end  130  is retracted past the stent body  102 , the stent body  102  may radially deform outwardly as the stent outer surface  108  interferes with the inner surface  92  of the aperture  90 . 
         [0034]    In the implementation illustrated, the stent  100  is implanted entirely within the aperture  90  such that the entire circumference of at least a portion of the stent  100  is in contact with the disc wall  74 . Once the stent  100  is implanted into the aperture  90 , an aperture  140  ( FIG. 9 ) is formed which permits at least a portion of the nucleus pulposus  60  to flow through the aperture  140  from the chamber  80  to the anterior or lateral region ( FIG. 2 ). 
         [0035]    It may be desired to permit the nucleus pulposus  60  to flow through the aperture  140  from the chamber  80  to the anterior/lateral region for a limited amount of time. Accordingly, in some implementations, the aperture  140  may be desirably restricted. In some implementations, the stent  100  may be removed from the annulus fibrosus  74  and the aperture  90  may be permitted to close. In some implementations, the stent  100  may be collapsed or deformed such that the aperture  140  may restrict the flow of the nucleus pulposus  60 . In some implementations, all or substantially all of the nucleus pulposus  60  may be permitted to flow through the aperture  140 . 
         [0036]    In some implementations, the aperture  140  may be restricted by engaging a plugging portion with the stent  100 . A non-limiting example of a plugging portion is a threaded portion that is proportioned to threadably engage within a helical stent by rotating the plugging portion as the plugging portion is advanced into the stent  100 . Another non-limiting example of a plugging portion is illustrated in  FIG. 14 , where an elongated biocompatible material  160  is wadded or folded prior to insertion within the aperture  140 . In some implementations, the material  160  may desirably embed within the aperture  140  and may restrict the flow of the nucleus pulposus  60 . In some implementations, the stent  100  may be constructed of a biodegradable material that will degrade sufficiently within a desirable timeframe that permits the aperture  90  to close, thus restricting the flow of the nucleus pulposus  60 . That is, the aperture  90  may heal to restrict the flow of the nucleus pulposus  60 . In some implementations, the inner surface  92  of aperture  90  may be treated, such as by heating, freezing, or other suitable method to provide an opening to permit the flow of nucleus pulposus  60  therethrough, where the inner surface  92  treatment will delay the healing of the aperture  90  until about a desired amount of time has been expended. 
         [0037]    A non-limiting example of deforming the stent  100  is to melt or fuse the end  106  of the stent  100  with a device that may heat the end  106 . Many biocompatible and/or biodegradable materials are constructed of a material such as polyethylene terephthalate (PET) that will deform when subjected to a temperature above the softening point. A device such as a radiofrequency probe, laser or other suitable device may be advanced toward the stent  100  and used to briefly apply heat to the stent  100 , thereby deforming the stent  100  and closing or restricting the aperture  140 . If the device is inserted in the lumbar region, the device may be advanced either 1.) from a posterior-lateral region diagonally through the disc annulus central portion  82  to access the end  104 ; 2.) from a posterior-lateral region and toward the outer surface  78  of the disc wall  74  while not advancing the device through the disc annulus central portion  82  to access the end  106 ; or 3.) through the anterior region toward the stent  100  to access the end  106 . Although, in the lumbar region, it is possible to go through the spinal canal and the spinal fluid, it may be preferable to go around such structures. In the cervical region, the device may be inserted from the anterior portion of the neck for entry. Thus it may be inserted posteriorly through the anterior annulus into the nucleus pulposus. 
         [0038]    Another non-limiting example of deforming the stent  100  is to engage the stent  100  with a tool that mechanically deforms either the end  104  or end  106  by crushing or collapsing at least a portion of the stent  100  to restrict the aperture  140 . 
         [0039]    In some situations, the stent  100  may need to be dislodged. In some implementations, the stent  100  may be dislodged mechanically. In some implementations, the stent  100  may be pushed past the disc annulus and thus out of the disc anteriorly to stop or slow flow of nucleus pulposus  60  out of the disc. In some implementations, a hook or like device may be used to pull the stent  100  entirely into the nucleus pulposus  60  area to stop the flow of nucleus pulposus out of the disc. 
         [0040]    In some implementations, the stent  100  may be removed with an additional surgical procedure to access the stent and remove, or by attaching a wire  170  ( FIG. 13 ) to the stent  100  at either the end  104  or the end  106 . In some implementations, the wire  170  may have a gripping portion  172  coupled to the end that opposes the end connected to the stent  100 . The gripping portion  172  may extend outside the patient, or may be left within the patient in a desired location. In some implementations, the gripping portion may be constructed of a MRI visible or other material to aid in locating the gripping portion  172  when the stent  100  is to be removed. In some implementations, when the stent  100  is to be removed, the gripping portion  172  may be coupled to a device to grasp the wire  170  and pull the stent  100  from the aperture  90 . In some implementations, all portions of the stent  100  may not be removed in this procedure, and the portions removed may permit the remainder of the stent  100  to collapse within the aperture  90 , thus restricting the aperture  140 . In some implementations, after the stent  100  (or portions thereof) are removed from the aperture  90 , the stent  100  and wire  90  may be removed from the patient or left inside the patient. In some implementations, the stent  100  may not cause any difficulty if the stent  100  were to be desirably left in the anterior region of the column  20 . 
         [0041]    In the implementation illustrated, the stent  100  may be implanted by advancing a device through the disc annulus central portion  82 , although the stent  100  may be implanted into the wall  74  by accessing the annular wall  74  from the anterior region. One possible reason for advancing the device  120  through the disc annulus central portion  82  prior to forming the aperture  90  is that the disc  46  may be located in the lower portion of the column  20  such that the disc  46  is more easily accessed from a posterior ( FIG. 2 ) region. However, in upper regions of the column  20 , the disc wall  74  may be desirably and/or more easily accessed from the anterior region. When the disc  74  is accessed from the anterior region, then the cannula  102  may not be advanced through the disc annulus central portion  82 . 
         [0042]    In the implementation illustrated, the stent  100  is helical. However, any other geometries or shapes, such as a woven cylindrical structure, a square or oval structure or other suitable structure may be used. Some other geometries are illustrated in  FIGS. 11-13 , although other suitable geometries are contemplated. Further, the stent  100  may be constructed of a metal helical core surrounded by a bioabsorbable helical sheathing to permit the stent  100  to bioabsorb, if desired. 
         [0043]    In some implementations, the stent  100  does not reinforce the disc or support the vertebrae, but rather is about as deformable as the disc  46  in order to remain within the disc wall  75  as the column  20  is articulated. 
         [0044]    Therefore, in some implementations, the diameter of the aperture  140  may be desirably varied based upon the expected viscosity or water content of the nucleus pulposus  60 . That is, generally, a patient in the age range of mid 40&#39;s may have a nucleus pulposus  60  that is relatively more liquid and an aperture  90  of a desired diameter may be formed to accommodate a stent  100  with a selected stent effective flow area. Additionally, a patient in the age range of mid 70&#39;s may have a nucleus pulposus  60  that is relatively less liquid and an aperture  90  of a larger diameter may be formed to accommodate a larger stent  100  with a larger stent effective flow area. In this manner, the stent diameter  140  and stent effective flow area may be varied to accommodate an expected viscosity or liquidity of the nucleus pulposus  60  of the particular patient. Further, the stent  100  may be supplied in a configuration that provides an aperture  140  with a larger stent effective flow area and the stent  100  (at either end  106 , end  104 , or a central portion) may be deformed to adjust the stent effective flow area as the stent  100  is implanted into the disc wall  74 , thereby providing a desired flow rate of the nucleus pulposus  60  for the particular patient. 
         [0045]    Although the steps of the method of implanting the stent  100  and restricting the aperture  140  may be listed in an order, the steps may be performed in differing orders or combined such that one operation may perform multiple steps. Furthermore, a step or steps may be initiated before another step or steps are completed, or a step or steps may be initiated and completed after initiation and before completion of (during the performance of) other steps. 
         [0046]    A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosures in this application. As a non-limiting example, in some implementations, the stent  100  may be coated with a chemotherapy material that may prevent or substantially prevent inflammation that may be caused when the nucleus pulposus is extruded from the annulus. As another non-limiting example, the stent  100  may be inserted.