Abstract:
Methods for spinal stabilization operative to prevent lateral bending, extension, and rotation across two or more adjacent vertebrae are described. Broadly, the method includes placing two or more anchors at each vertebral level, passing one or more sutures through each anchor at each level, applying tension to the sutures and joining the sutures in a cross-braced arrangement over the disc space between two or more vertebrae to prevent lateral bending, extension, and rotation of the spinal segment. The sutures can be welded in any combination of diagonal and vertical patterns across the adjacent vertebrae. In some embodiments, two or more sutures can be threaded through some of the suture anchors such that multiple vertebral levels can be joined in a cross-braced arrangement. Two or more sutures can also be used in multiple anchors in two adjacent vertebrae to provide additional reinforcement or stabilization across different portions of the two vertebrae. The sutures reinforcing different portions of the vertebrae can have different breakage strength and different elastic properties. The invention may be used on the cervical, thoracic, lumbar, or sacral regions of the spine.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of provisional application 60/861,499, filed Nov. 28, 2006, entitled “Annulus and Spinal Ligament Reconstruction.” This application is related to co-pending application 60/808,795, filed May 26, 2006, entitled “Fastening Assemblies for Disc Herniation Repair and Methods of Use.” The application is also related to U.S. Pat. Nos. 6,248,106 and 6,423,065. All of the above-referenced patent and applications are hereby expressly incorporated by reference in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The subject invention resides in methods and apparatus for reconstructing the annulus fibrosis (AF) of a spinal disc and the ligaments of the spine. The invention is particularly well suited to the prevention of extrusion of material or devices placed into the disc space and to the prevention of excessive spinal motion. 
       BACKGROUND 
       [0003]    The human intervertebral disc is an oval to kidney bean-shaped structure of variable size depending on the location in the spine. The outer portion of the disc is known as the annulus fibrosis (AF). The annulus fibrosis is formed of approximately 10 to 60 fibrous bands or layers. The fibers in the bands alternate their direction of orientation by about 30 degrees between each band. The orientation serves to control vertebral motion (one half of the bands tighten to check motion when the vertebra above or below the disc are turned in either direction). 
         [0004]    The annulus fibrosis contains the nucleus pulposus (NP). The nucleus pulposus serves to transmit and dampen axial loads. A high water content (approximately 70-80%) assists the nucleus in this function. The water content has a diurnal variation. The nucleus imbibes water while a person lies recumbent. Nuclear material removed from the body and placed into water will imbibe water swelling to several times its normal size. Activity squeezes fluid from the disc. The nucleus comprises roughly 50% of the entire disc. The nucleus contains cells (chondrocytes and fibrocytes) and proteoglycans (chondroitin sulfate and keratin sulfate). The cell density in the nucleus is on the order of 4,000 cells per microliter. 
         [0005]    The intervertebral disc changes or “degenerates” with age. As a person ages, the water content of the disc falls from approximately 85% at birth to approximately 70% in the elderly. The ratio of chondroitin sulfate to keratin sulfate decreases with age, while the ratio of chondroitin  6  sulfate to chondroitin  4  sulfate increases with age. The distinction between the annulus and the nucleus decreases with age. Generally disc degeneration is painless. 
         [0006]    Premature or accelerated disc degeneration is known as degenerative disc disease. A large portion of patients suffering from chronic low back pain are thought to have this condition. As the disc degenerates, the nucleus and annulus functions are compromised. The nucleus becomes thinner and less able to handle compression loads. The annulus fibers become redundant as the nucleus shrinks. The redundant annular fibers are less effective in controlling vertebral motion. This disc pathology can result in: 1) bulging of the annulus into the spinal cord or nerves; 2) narrowing of the space between the vertebra where the nerves exit; 3) tears of the annulus as abnormal loads are transmitted to the annulus and the annulus is subjected to excessive motion between vertebra; and 4) disc herniation or extrusion of the nucleus through complete annular tears. 
         [0007]    Current surgical treatments for disc degeneration are destructive. One group of procedures, which includes lumbar discectomy, removes the nucleus or a portion of the nucleus. A second group of procedures destroy nuclear material. This group includes Chymopapin (an enzyme) injection, laser discectomy, and thermal therapy (heat treatment to denature proteins). The first two groups of procedures compromise the treated disc. A third group, which includes spinal fusion procedures, either remove the disc or the disc&#39;s function by connecting two or more vertebra together with bone. Fusion procedures transmit additional stress to the adjacent discs, which results in premature disc degeneration of the adjacent discs. These destructive procedures lead to acceleration of disc degeneration. 
         [0008]    Prosthetic disc replacement offers many advantages. The prosthetic disc attempts to eliminate a patient&#39;s pain while preserving the disc&#39;s function. Current prosthetic disc implants either replace the nucleus or replace both the nucleus and the annulus. Both types of current procedures remove the degenerated disc component to allow room for the prosthetic component. Although the use of resilient materials has been proposed, the need remains for further improvements in the way in which prosthetic components are incorporated into the disc space to ensure strength and longevity. Such improvements are necessary, since the prosthesis may be subjected to 100,000,000 compression cycles over the life of the implant. 
         [0009]    Current nucleus replacements (NRs) may cause lower back pain if too much pressure is applied to the annulus fibrosis. As discussed in co-pending U.S. patent application Ser. No. 10/407,554 and U.S. Pat. No. 6,878,167, the content of each being expressly incorporated herein by reference in their entirety, the posterior portion of the annulus fibrosis has abundant pain fibers. 
         [0010]    Herniated nucleus pulposus (HNP) occurs from tears in the annulus fibrosis. The herniated nucleus pulposus often allies pressure on the nerves or spinal cord. Compressed nerves cause back and leg or arm pain. Although a patients symptoms result primarily from pressure by the nucleus pulposus, the primary pathology lies in the annulus fibrosis. 
         [0011]    Surgery for herniated nucleus pulposus, known as microlumbar discectomy (MLD), only addresses the nucleus pulposus. The opening in the annulus fibrosis is enlarged during surgery, further weakening the annulus fibrosis. Surgeons also remove generous amounts of the nucleus pulposus to reduce the risk of extruding additional pieces of nucleus pulposus through the defect in the annulus fibrosis. Although microlumbar discectomy decreases or eliminates a patient&#39;s leg or arm pain, the procedure damages weakened discs. 
       SUMMARY 
       [0012]    A portion of the annulus fibrosis and a portion of the ligaments of the spine are excised to allow insertion of materials and devices into the disc space. For example, a portion of the anterior half of the annulus fibrosis and a portion of the anterior longitudinal ligament (ALL) are excised to enable insertion of bone growth promoting materials and fusion devices in interbody fusion procedures. Removal of portions of the annulus fibrosis and anterior longitudinal ligament increase the flexibility of the spine and allow excessive motion of the spine. For example, removal of the tissues mentioned permits excessive spinal extension, lateral bending, and axial rotation. Destabilizing the spine decreases the chance of a successful fusion. The invention may be used to increase the stiffness of the operated segment of the spine. Increasing the stiffness of the spine facilitates spinal fusion. 
         [0013]    A portion of the annulus fibrosis and a portion of the anterior longitudinal ligament are also excised to enable insertion of motion preserving devices into the disc. For example, Total Disc Replacements (TDRs) and Nucleus Replacements (NRs) are often inserted through the anterior portion of discs. Excessive spinal extension, lateral bending, and axial rotation following excision of the spinal tissues and insertion of motion preserving devices into the disc space places excessive force on the facets of the spine. Biomechanical studies show the forces across the facets at the operated level of the spine can be doubled by motion preserving devices and the techniques used to insert such devices. Excessive force on the facets may lead to degeneration of the facets. Degeneration of the facets may cause low back pain. 
         [0014]    The present invention provides methods for spinal stabilization operative to prevent lateral bending, extension, and rotation across adjacent vertebrae. Broadly, the method includes placing two or more anchors at each vertebral level, passing one or more sutures through each anchor at each level, applying tension to the sutures and joining the sutures in a cross-braced arrangement over the disc space to prevent lateral bending, extension, and rotation of the spinal segment. 
         [0015]    In some embodiments, six anchors can be used to join multiple levels of vertebrae. Two anchors are placed in each vertebra. The anchors placed in the cranial and caudal vertebrae each have at least one elongate member, such as a suture, extending therethrough. The anchors in the medial vertebra have at least two elongate members extending therethrough. Tension is applied to the elongate members and the elongate members extending from the medial anchor are attached in a crossing pattern with the elongate members extending from the cranial and caudal anchors having left and right generally vertically extending segments and diagonal connections between upper and lower end regions of each vertically extending segment. 
         [0016]    In some embodiments, the sutures are joined by welding. In some embodiments, a mesh patch can be placed between the sutures and the vertebrae to provide a cushion between the sutures and the bone and reduce friction on the sutures and the suture welds. In some embodiments, the material for the mesh can be selected such that connective tissue will grow into and over the mesh in vivo, forming a synthetic tendon-like layer that further cushions and protects the sutures. In some embodiments, an anti-adhesion patch can be placed over the exposed portions if the sutures and the suture anchors. 
         [0017]    In an alternative embodiment, multiple anchors and sutures can be used to provide additional stabilization/fixation across two adjacent vertebrae. In some embodiments, six or more anchors can be placed in two adjacent vertebrae, each anchor having at least one suture extending therethrough. The sutures can be arranged in any combination of vertical and diagonal patterns across the two adjacent vertebrae and joined together to prevent lateral bending, extension, and rotation of the spinal segment. Tension can be applied to the sutures prior to joining them together to vary the resistance to spinal extension, lateral bending and axial rotation extension as necessary. In some embodiments, the sutures can be made of different material and have different properties. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1A  is a lateral view of a suture anchor with a single eyelet. 
           [0019]      FIG. 1B  is a lateral view of a suture anchor with two eyelets 
           [0020]      FIG. 2A  is an anterior view of an embodiment for joining three adjacent vertebrae, 
           [0021]      FIG. 2B  is an anterior view of the embodiment in  FIG. 2A  with the sutures welded together in a cross-braced pattern. 
           [0022]      FIG. 2C  illustrates an anterior view of the embodiment in  FIG. 2B  with an anti-adhesion cover placed over the fixation sutures and suture anchors. 
           [0023]      FIG. 2D  illustrates a lateral view of the embodiment in  FIG. 2A . 
           [0024]      FIG. 3A  is an anterior view of an alternative embodiment for joining multiple vertebrae of the spine using two sutures in each suture anchor. 
           [0025]      FIG. 3B  is an anterior view of the embodiment in  FIG. 3A  with the first sutures welded together in a cross-braced pattern and the second sutures welded together in a vertical pattern. 
           [0026]      FIG. 4A  is an anterior view of an alternative embodiment for joining two adjacent vertebrae using three anchors in each vertebrae. 
           [0027]      FIG. 4B  is an anterior view of an alternative embodiment for joining two adjacent vertebrae using three anchors in each vertebrae. 
           [0028]      FIG. 5A  is an anterior view of an alternative embodiment for joining two adjacent vertebrae using three anchors in each vertebrae and a second set of sutures in the central anchors. 
           [0029]      FIG. 5B  is an anterior view of the embodiment in  FIG. 5A  showing the first sutures welded together in a cross-braced pattern and the second sutures welded together in a vertical pattern. 
           [0030]      FIG. 6A  is an anterior view of an alternative embodiment for joining two adjacent vertebrae using three anchors in each vertebrae and using two sutures in each suture anchor. 
           [0031]      FIG. 6B  is an anterior view of the embodiment in  FIG. 6A  showing the first sutures welded together in a cross-braced pattern and the second sutures welded together in a vertical pattern. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]      FIG. 1A  is a lateral view of a suture anchor  1  with one eyelet  5 .  FIG. 1B  is a lateral view of a suture anchor  10  with two eyelets  5  and  7 . The suture anchors comprise anchor  1  and  10  having a first portion capable of being inserted into or otherwise attached to a bone, such as vertebrae. Anchor  1  has a second portion with opening  5  adapted to receive a suture therethrough. Anchor  1  also has a second portion with openings  5  and  7  each adapted to receive a suture therethrough. In one embodiment, anchor  10  is a screw having two holes through the head of the screw. 
         [0033]    The anchors  10  can vary in size from about 3 to about 12 mm in diameter and about 4 to about 40 mm in length. For example, anchors having a diameter of about 3 mm and a length of about 7 mm can be used in the anterior portions of cervical vertebrae. Additionally, anchors having a diameter of about 8 mm and a length of about 35 mm can be used in the anterior portions of lumber vertebrae. The anchors are preferably made of an MRI-compatible material. For example, the anchors can be made of titanium, plastic, or other material. The anchors can additionally be coated with a material, such as hydroxyappetite, that promotes the in-growth of bone. In an alternative embodiment, the anchors can be hollow and filled with a material that promotes bone in-growth. 
         [0034]    In one embodiment, anchors  1  and  10  can be used to join multiple levels of vertebrae.  FIG. 2A  is an anterior view of the spine with intradiscal devices inserted in the disc spaces between three adjacent vertebrae  100 ,  102  and  104 . Six suture anchors  1   a - d  and  10   a - b  are used to join the three adjacent vertebrae  100 ,  102  and  104 . The anterior portion of the annulus fibrosis  111  and the anterior longitudinal ligament  113  were excised to permit insertion of intradiscal devices  101  and  103 , such as a nucleus replacement NR), bone graft, spinal cage, or TDR, into the disc space between vertebrae  100  and  102  and the disc space between vertebrae  102  and  104 . Two suture anchors  1   a ,  1   b  were placed into the vertebra  100  cranial to the intradiscal device  101 , two suture anchors  10   a ,  10   b  were placed into vertebra  102  and two suture anchors  1   c ,  10   d  were placed into the vertebra  104  caudal to the intradiscal device  103 . The anchors  1   a - d  placed in the cranial and caudal vertebrae  100 ,  104  have a single eyelet for threading a single suture  6   a,b,e,f  each. The anchors  10   a,b  placed in the medial vertebrae  102  have two eyelets, as shown in  FIG. 1B , for threading two sutures  6   c,d  and  8   a,b  each. In some embodiments, the cranial and caudal anchors can also have two eyelets for threading a second suture. 
         [0035]    Sutures  6   a,b,e,f  are threaded through the single eyelets in anchors  1   a ,b,c,d respectively such that first and second ends of each suture  6   a,b,e,f  extend from anchors  1   a ,b,c,d. Sutures  6   c,d  are threaded through first eyelets in anchors  10   a,b  and sutures  8   a,b  are threaded through second eyelets in anchors  10   a,b  such that first and second ends of sutures  6   c  and  8   a  extend from anchor  10   a  and first and second ends of sutures  6   d  and  8   b  extend from anchor  10   b.    
         [0036]    In some embodiments, the sutures can be monofilament or multifilament configurations of nylon, polypropylene, polyester, polyethylene, or other material. For example in one embodiment, the sutures can be made from a #5 polyester multifilament material. In another embodiment, the sutures can be made of a #5resorbable multifilament suture such as VICRYL™ (Ethicon, N.J.). In other embodiments, suture materials can be selected for specific characteristics. For example, rigid, semi-rigid or elastic materials may be selected. In embodiments of the invention used in spinal fusion procedures relatively inelastic sutures are preferably used. In other embodiments, the sutures can be made of materials than can be welded together. 
         [0037]    In some embodiments, the sutures  6   a - f  and  8   a,b  can be different sizes and/or made of different materials such that the sutures have different tensile strength or other properties. For example, in one embodiment, one set of sutures  6   a - f  could be a #5 polyester multifilament material. The other set of sutures  8   a,b  could be made of VICRYL™. Alternatively, in some embodiments, one set of sutures could be more elastic than the second set of sutures. For example, one set of sutures  6   a - f  could reversibly stretch about 1 to about 10 mm. The other set of sutures  8   a,b  could reversibly stretch about 5 to about 8 mm. 
         [0038]    As shown in  FIG. 2B , the medial ends of sutures  6   a - f  and  8 - a ,b are joined in an axial and criss-crossed pattern over the disc space between vertebrae  100 ,  102  and  104 . In the illustrated embodiment, the medial ends of the sutures  6   a - b  and  6   c - d  from the anchors  1   a,b  and  10   a,b  were welded together over the disc space between vertebrae  100  and  102  and the lateral ends of the sutures  6   a - b  and  6   c - d  were welded together to create vertical fixation suture arms. Similarly, the medial ends of sutures  8   a - b  and  6   e - f  were welded together over the disc space between vertebrae  102  and  104  while the lateral ends of the sutures  8   a - b  and  6   e - f  were welded together to create vertical fixation suture arms. This configuration joins the three adjacent vertebrae  100 ,  102  and  104  and forms “Xs” over the disc space between vertebrae  100  and  102 , and between vertebrae  102  and  104 . The pattern of the sutures over the disc space advantageously provides an arrangement that resists and/or limits extension, lateral bending and torosional/rotational stresses. The vertical fixation suture arms resist extension of the spine. The diagonal fixation suture arms resist lateral bending, axial rotation as well as extension of the spine. 
         [0039]    The ends of sutures  6   a - f  and  8   a,b  can be joined together by any suitable method known in the art such as a knot, crimping, melting, welding or otherwise fusing the two ends of the suture. In one embodiment, shown in  FIG. 21B , the ends of sutures  6   a - f  and  8   a,b  can be welded together. The weld is preferably caused by heat-generating or heat-conducting instruments. The heat may be generated ultrasonically or by other means. Instruments with special tips may be used to weld the sutures within deep areas of the body. For example, instruments that are about 15 to abut 45 cm in length may be needed to weld sutures in the abdomen. The welding instruments are preferably about 4 to about 8 mm in diameter. In some embodiments, tension can be applied to the sutures  6   a - f ,  8   a,b  before the sutures  6   a - f ,  8   a,b  are welded together. 
         [0040]    In addition, in some embodiments, as shown in  FIG. 2B , a piece of porous mesh material  16  can be placed between the fixation sutures  6   a - f ,  8   a,b  and the spine before welding the sutures  6   a - f ,  8   a,b  together. The mesh  16  acts as scaffolding for connective tissue in-growth from the annulus fibrosis  111 , the anterior longitudinal ligament  113 , and the vertebrae  100 ,  102 , and  104 . The pores within the mesh  16  are preferably about 0.1 to 2.0 mm in diameter. Mesh piece  16  may be made of synthetic materials such as polyester, polypropylene, ePTFE, or polyethylene. Alternatively, the mesh could be made of natural material such as autograft, allograft, or xenograft tissues such as acellular dermis, swine intestinal submucosa, ligaments, facia, or tendon. The mesh  16  should extend over both sides of the anterior longitudinal ligament  113  and the annulus fibrosis  111  on either side of the annular window. The connective tissue, the mesh  16 , and the fixation sutures  6   a -E,  8   a,b  at least partially reproduce the function of the annulus fibrosis and the anterior longitudinal ligament. The components also prevent extrusion of tissue that resides within the disc, such as the nucleus pulposus, or materials or devices that are placed within the disc, such as intradiscal devices  101  and  103 . Radio-opaque markers could be added to the mesh  16  and or the fixation sutures  6   a - f ,  8   a,b  to help identify the location of the components on x-ray. For example, metal wires or staples could be included in mesh or fixation sutures. Alternatively, radio-opaque materials such as barium or other contrast agents may be used to “dye” the mesh or fixation sutures. 
         [0041]    In some embodiments, the sutures and anchors may be covered with an anti-adhesion component as described in co-pending patent application 60/808,795, filed May 26, 2006, entitled “Fastening Assemblies for Disc Herniation Repair and Methods of Use,” hereby expressly incorporated by reference in its entirety. For example, an anti-adhesion cover  20  could be attached to the fixation sutures  6   a - f ,  8   a,b  and/or the porous mesh  16 . In some embodiments, the anti-adhesion cover can be a piece of ePTFE. Alternatively, the anti-adhesion cover could also be made of autograft, allograft, or xenograft tissues such as acellular dermis, swine intestinal submucosa, ligaments, facia, or tendon. 
         [0042]    In some embodiments, as shown in  FIG. 2C , two connecting sutures  22  and  24  can be used to connect the anti-adhesion patch  20  to mesh patch  16 . The connecting sutures  22  and  24  are passed through mesh patch  16  and anti-adhesion cover  20  and then joined together, for example by welding or any other suitable method, over the anti-adhesion cover  20  to hold the anti-adhesion cover against the vertebrae  100 ,  102  and  104  and annulus fibrosis  111 . Anti-adhesion component  20  is sized to extend over the anchors  1   a - d ,  10   a,b , mesh  16 , fixation sutures  6   a - f  and  8   a,b , the cut edges of the annulus fibrosis  111  and the cut edges of the anterior longitudinal ligament  113 . The mesh  16  and anti-adhesion  20  components may also be connected with alternative fastening methods known in the art. In an alternative embodiment a single connecting suture can be passed through the mesh patch  16  and anti-adhesion cover  20  and then welded, or otherwise joined, together to hold the anti-adhesion cover  20  against the vertebrae  100 ,  102  and  104  and annulus fibrosis  111 . Covering the stiff ends of the sutures with the anti-adhesion patch  20  protects the suture welds from peeling forces due to friction from adjacent structures and helps prevent injury to delicate structures such as nerves, blood vessels, and the esophagus that lie directly over the stiff ends of the sutures and exposed portions of the suture anchors. 
         [0043]    In an alternative embodiment, as shown in  FIG. 3A , the suture anchors  40   a,b,e,f  in the cranial and caudal vertebrae  100 ,  104  can have two eyelets for threading a second suture as well as the anchors  40   c,d  in the medial vertebra  102 . Here, sutures  36   a ,bc,d,e,f are threaded through the first eyelets in anchors  40   a,b,c,d ,e,f respectively such that first and second ends of each suture  36   a,b,c,d ,e,f extend from anchors  40   a,b,c,d ,e,f. Sutures  38   a,b,c,d ,e,f are threaded through second eyelets in anchors  40   a,b,c,d ,e,f such that first and second ends of sutures  38   a,b,c,d ,e,f also extend from anchors  40   a,b,c,d ,e,f. 
         [0044]    As shown in  FIG. 3B , the medial ends of sutures  36   a,b,c,d ,e,f and  38 - c ,d are joined in an axial and criss-crossed pattern over the disc space between vertebrae  100 ,  102  and  104 . In the illustrated embodiment, the medial ends of the sutures  36   a - b  and  36   c - d  from the anchors  40   a,b,c,d  were welded together over the disc space between vertebrae  100  and  102  to create diagonal fixation suture arms and the lateral ends of the sutures  36   a,b  and  36   c,d  were welded together to create vertical fixation suture arms. Similarly, the medial ends of sutures  38   c,d  and  36   e,f  were welded together over the disc space between vertebrae  102  and  104  diagonal fixation suture arms while the lateral ends of the sutures  38   c,d  and  36   e,f  were welded together to create vertical fixation suture arms. In addition, medial and lateral ends of the second sutures  38   a  and  38   e  and  38   b  and  38   f  in the second eyelets in suture anchors  40   a,b,e,f  were welded together to create vertical fixation suture arms joining the cranial and caudal vertebrae  100  and  102 . Tension can be applied to each of the sutures prior to welding. The sutures  38   a,b,e,f  are preferably longer than sutures  36   a,b,c,d ,e,f and  38   c,d  so that they can extend between vertebrae  100  and  104 . In some embodiments, the sutures  38   a,b,e,f  can also be made of a different material having different breakage strength. This configuration joins the three adjacent vertebrae  100 ,  102  and  104  in arrangement including “Xs” over the disc space between vertebrae  100  and  102 , and between vertebrae  102  and  104  as well as vertical suture arms extending between vertebrae  100  and  104 . The pattern of the sutures over the disc space advantageously provides an arrangement that resists and/or limits extension, lateral bending and torosional/rotational stresses. The vertical fixation suture arms resist extension of the spine. The diagonal fixation suture arms resist lateral bending, axial rotation as well as extension of the spine. 
         [0045]    In addition, as discussed above with respect to the embodiment in  FIGS. 2A-D , a piece of porous mesh material can be placed between the fixation sutures  36   a - f  and  38   a - f  and the spine before welding the sutures  36   a - f  and  38   a - f  together. Likewise, an anti-adhesion cover can be placed over the exposed portions of the sutures  36   a - f  and  38   a - f  and suture anchors  40   a - f  anchors to protect the suture welds from peeling forces due to friction from adjacent structures and helps prevent injury to delicate structures such as nerves, blood vessels, and the esophagus that lie directly over the stiff ends of the sutures and exposed portions of the suture anchors. 
         [0046]    In an alternative embodiment, multiple anchors and sutures can be used to provide additional stabilization/fixation across two adjacent vertebrae. As shown in  FIG. 4A , six anchors  30   a - f  can be used to join two adjacent vertebrae  100  and  102 . In alternative embodiments, more than six or less than four anchors can be used. Here, anchors  30   a,b,c  were placed in the cranial vertebra  100 . Anchors  30   d,e,f  were placed in the caudal vertebra  102 . Sutures  36   a,b,c,d ,e,f were threaded through anchors  30   a,b,c,d ,e,f respectively. First and second ends of sutures  36   b,e  from central anchors  30   b,e  were welded together to create a pair of vertical fixation members  36   be  across the central portion of vertebrae  100 , 102 . Medial ends of sutures  36   a  and  f  and of  36   c  and  d  were welded together to create diagonal fixation members  36   af  and  36   cd  extending across vertebrae  100  and  102 . Lateral ends of sutures  36   a  and  d  and of  36   c  and  f  were welded together to create vertical fixation members  36   ad  and  36   cf  extending across the lateral portions of vertebrae  100 ,  102 . Tension is applied to the ends of sutures  36   a - f  before welding together. A piece of porous mesh material  16  can be placed between the fixation sutures  36   a - f  and the spine before welding the sutures  36   a - f  together. As discussed above in detail with respect to the embodiments in  FIGS. 2A-D , an anti-adhesion cover, such as ePTFE can be placed over the exposed portions of the suture anchors  30   a - f  and sutures  36   a - f  to protect the suture welds from peeling forces due to friction from adjacent structures and help prevent injury to delicate structures such as nerves, blood vessels, and the esophagus that lie directly over the stiff ends of the sutures and exposed portions of the suture anchors. 
         [0047]    Here, the vertical fixation members  36   be  from the central pair of anchors  30   b,e  resist extension of the spine. The vertical fixation members  36   ad  and  36   cf  from the lateral pairs of anchors  30   a,c,d,f  resist lateral bending and the diagonal fixation members  36   cd  and  36   af  resist axial rotation as well as lateral bending and extension of the spine. The flexible fixation members that extend from the anchors may have different breakage strength and different elastic properties. For example, the flexible fixation members  36   b,e  from the central pair of anchors  30   b,e  may have a higher breakage strength than the flexible fixation members  36   a,c,d,f  from the lateral pairs of anchors  30   a,c,d,f , thereby restricting extension of the spine more than lateral bending or axial rotation. In addition, the tension applied to each suture prior to welding can be varied depending on the breakage strength of the suture material and the desired resistance to motion in a certain direction. For example, more tension can be applied to the sutures comprising the vertical fixation members to create more resistance to spinal extension. Alternatively, more tension can be applied to the sutures comprising the diagonal fixation members to create more resistance to axial rotation or the sutures comprising the vertical fixation members on the lateral sides of the vertebrae to create more resistance to lateral bending as well as extension. 
         [0048]    In an alternative embodiment, the sutures  36   a,b,c,d ,e,f extending from suture anchors  30   a - f  can be welded together in any combination diagonal, horizontal and or vertical patterns across the adjacent vertebrae to alter the resistance to spinal extension, lateral bending and axial rotation extension as necessary. For example, as shown in  FIG. 4B  in one embodiment, lateral ends of sutures  36   c  and  36   f  and sutures  36   a  and  36   d  are welded together to create vertical fixation arms  36   cf  and  36   ad . Medial ends of sutures  36   a,c,d,f  are welded to first and second ends of sutures  36   b,e  to create diagonal fixation arms  36   ae ,bd,bf,ce. Such an embodiment emphasizes resistance axial rotation by providing an additional set of diagonal fixation arms across the two vertebrae. The diagonal fixation arms also lie over the opening in the annulus fibrosis and help prevent extrusion of material through the opening. 
         [0049]    In some embodiments, one or more of the multiple suture anchors in each vertebra can have two sutures extending therethrough for providing additional fixation arms across the two vertebrae. In one embodiment, as shown in  FIG. 5A , the central pair of anchors  40   a,b  each have two sutures  36   a,b  and  38   a,b  extending therethrough. As shown in  FIG. 5B , sutures  36   a - f  are arranged as described above in  FIG. 4B  with lateral ends of sutures  36   a,c,d,f  creating lateral vertical fixation arms and median ends of sutures  36   a,c,d,f  and both ends of sutures  36   b,e  creating diagonal fixation arms. In addition, first and second ends of sutures  38   a,b  are welded together to create central vertical fixation arms. Tension can be applied to the sutures prior to joining them together to vary the resistance to spinal extension, lateral bending and axial rotation extension as necessary. A piece of porous mesh material  16  can be placed between the fixation sutures  36   a - f  and  38   a,b  and the spine before welding the sutures  36   a - f  and  38   a,b  together. As discussed above in detail with respect to the embodiments in  FIGS. 2A-D , an anti-adhesion cover, such as ePTFE can be placed over the exposed portions of the suture anchors  30   a - d ,  40   a,b  and sutures  36   a - f  and  38   a,b  to protect the suture welds from peeling forces due to friction from adjacent structures and to help prevent injury to delicate structures such as nerves, blood vessels, and the esophagus that lie directly over the stiff ends of the sutures and exposed portions of the suture anchors. 
         [0050]    Here, the second sutures  38   a,b  can be made of a different material than sutures  36   a - f  and thus have different properties. For example, sutures  38   a,b  can be reabsorbable, but have a higher initial breakage strength while sutures  36   a - f  are more elastic with a lower breakage strength. This pattern could be advantageous for providing an increased resistance to spinal extension during the initial period after a total disc replacement  101  has been inserted into the disc space and thereby increasing the chances for a successful replacement. Over time, the stiffer central vertical fixation arms will be reabsorbed, leaving only the more elastic diagonal and lateral fixation arms in place. These fixation arms  36   cf ,  36   ad , and  36   ae,bd,bf,ce  could be welded under only slight tension. In addition, the fixation arms  36   cf ,  36   ad , and  36   ae ,bd,bf,ce could be applied with the spine in an extended position. Slight tension of the fixation arms and applying the sutures with the spine in an extended position will enable full normal movement of the spine while preventing excessive extension, excessive axial rotation and excessive lateral bending of the spine. 
         [0051]    In an alternative embodiment, each of the multiple suture anchors in each vertebra can have two or more sutures extending therethrough for providing additional fixation arms across the two vertebrae. For example, as shown in  FIG. 6A , each anchor  40   a - f  in vertebrae  100 ,  102  has two openings for receiving two sutures through each anchor  40   a - f . Sutures  36   a - f  and  38   a - f  have been threaded through the two openings in each anchor  40   a - f , Alternatively, more than two sutures could be inserted into one or more of the anchors to provide additional fixation members across a portion of the two vertebrae. As discussed above, each of the two or more sutures  36   a - f  and  38   a - f  that extend from each anchor  40   a - f  can be made of different materials and have different breakage strength and/or different elastic properties. In some embodiments, the sutures with differing properties can be color-coded such that a surgeon can easily determine which sutures to join and how much tension to apply during an operation. For example, sutures  36   a - f  could be a first color while sutures  38   a - f  could be made of a different material and have a second color to denote their different mechanical and/or physical properties. 
         [0052]    As shown in  FIG. 6B , sutures  36   a - f  are arranged as described above in  FIG. 4B  with lateral ends of sutures  36   a,c,d,f  creating lateral vertical fixation arms and median ends of sutures  36   a,c,d,f  and both ends of sutures  36   b,e  creating diagonal fixation arms. In addition, first and second ends of sutures  38   a  and  d , of  38   b  and  e  and of  38   c  and  f  are welded together to create three pairs of central vertical fixation arms  38   ad ,  38   be  and  38   cf . Tension can be applied to the sutures prior to joining them together. The tension applied to each suture prior to welding can be varied depending on the breakage strength of the suture material and the desired resistance to motion in a certain direction. A piece of porous mesh material  16  can be placed between the fixation sutures  36   a - f  and  38   a - f  and the spine before welding the sutures  36   a - f  and  38   a - f  together. As discussed above in detail with respect to the embodiments in  FIGS. 2A-D , an anti-adhesion cover, such as ePTFE can be placed over the exposed portions of the suture anchors  40   a - f  and sutures  36   a - f ,  38   a - f  to protect the suture welds from peeling forces due to friction from adjacent structures and helps prevent injury to delicate structures such as nerves, blood vessels, and the esophagus that lie directly over the stiff ends of the sutures and exposed portions of the suture anchors. 
         [0053]    Here, the second sutures  38   a - f  can be made of a different material than sutures  36   a - f  and thus have different properties. For example, sutures  38   a - f  can be reabsorbable, but have a higher initial breakage strength while sutures  36   a - f  are more elastic with a lower breakage strength. As discussed above, this pattern could be advantageous for providing an increased resistance to spinal extension during the initial period after an intradiscal device  101  has been inserted into the disc space between vertebrae  100 , 102 . For example as shown in  FIG. 6A , where intradiscal device  101  is a nucleus replacement (NR) device the three additional vertical fixation arms  38   cf ,  38   be ,  38   ad  can advantageously provide additional resistance to spinal extension to allow the annulus fibrosis  111  to heal, thereby increasing the chances for a successful nucleus replacement. 
         [0054]    Although the foregoing invention has, for the purposes of clarity and understanding, been described in some detail by way of illustration and example, it will be obvious that certain changes and modifications may be practiced which will still fall within the scope of the appended claims.