Abstract:
Disclosed in one embodiment, dynamic braces are used in multiple levels to maintain proper vertebral spacing. Such dynamic braces aid in permitting a substantial range of motion in flexion, extension, rotation, anterior-posterior translation and/or other desired types of spinal motion.

Description:
CROSS-REFERENCED TO RELATED APPLICATIONS  
       [0001]     The present application is related to and claims priority from the following commonly assigned patent applications: U.S. Provisional Patent Application 60,775,877, entitled “Multi-Level Spherical Linkage Implant System,” filed on Feb. 23, 2006; U.S. Provisional Patent Application 60793829, entitled “Micro Motion Spherical Linkage Implant System,” filed on Apr. 21, 2006; U.S. patent application Ser. No. 11,443,236, entitled “System and Method for Dynamic Skeletal Stabilization,” filed on May 30, 2006; U.S. Provisional Patent Application 60,814,753, entitled “Multi-Level Spherical Linkage Implant System,” filed on Jun. 19, 2006; the disclosures of which are hereby incorporated by reference.  
         [0002]     The present application is related to the following commonly assigned patent applications: U.S. patent application Ser. No. 10,914,751, entitled “System and Method for Dynamic Skeletal Stabilization,” filed on Aug. 9, 2004; U.S. Provisional Patent Application 60,637,324, entitled “Three Column Support Dynamic Stabilization System and Method of Use,” filed on Dec. 16, 2004; U.S. Provisional Patent Application 60,656,126, entitled “System and Method for Dynamic Stabilization,” filed on Feb. 24, 2005; U.S. Provisional Patent Application 60,685,705, entitled “Four-Bar Dynamic Stabilization Device,” filed on May 27, 2005; U.S. Provisional Patent Application 60,685,760, entitled “Slidable Post Dynamic Stabilization Device,” filed on May 27, 2005; U.S. Provisional Patent Application 60,693,300, entitled “Spherical Plate Dynamic Stabilization Device,” filed on Jun. 22, 2005; U.S. Provisional Patent Application 60,692,943, entitled “Spherical Motion Dynamic Spinal Stabilization Device,” filed on Jun. 22, 2005; U.S. Provisional Patent Application 60,711,812, entitled “Dynamic Spinal Stabilization Alignment Instrument,” filed on Aug. 26, 2005; U.S. Provisional Patent Application 11,303,138, entitled “Three Column Support Dynamic Stabilization System and Method,” filed on Dec. 16, 2005; U.S. Provisional Patent Application 60,775,879, entitled “Aligning Cross-Connector,” filed on Feb. 23, 2006; U.S. Provisional Patent Application 60,775,877, entitled “Multi-Level Spherical Linkage Implant System,” filed on Feb. 23, 2006; U.S. Provisional Patent Application 60,786,898, entitled “Full Motion Spherical Linkage Implant System,” filed on Mar. 29, 2006; U.S. Provisional Patent Application 60,793,829, entitled “Micro Motion Spherical Linkage Implant System,” filed on Apr. 21, 2006; U.S. patent application Ser. No. 11,443,236, entitled “System and Method for Dynamic Skeletal Stabilization,” filed on May 30, 2006; U.S. Provisional Patent Application 60,814,943, entitled “Aligning Cross-Connector,” filed on Jun. 19, 2006; U.S. Provisional Patent Application 60,814,753, entitled “Multi-Level Spherical Linkage Implant System,” filed on Jun. 19, 2006; U.S. Provisional Patent Application 60,831,879, entitled “Locking Assembly,” filed on Jul. 19, 2006; U.S. patent application Ser. No. 11,467,798, entitled “Alignment Instrument for Dynamic Spinal Stabilization Systems,” filed on Aug. 28, 2006; U.S. Provisional Patent Application 60,825,078, entitled “Offset Adjustable Dynamic Stabilization System,” filed on Sep. 8, 2006; U.S. Provisional Patent Application 60,826,807, entitled “Offset Adjustable Dynamic Stabilization System,” filed on Sep. 25, 2006; U.S. Provisional Patent Application 60,826,817, entitled “Offset Adjustable Dynamic Stabilization System,” filed on Sep. 25, 2006; U.S. Provisional Patent Application 60,826,763, entitled “Alignment Instrument for Dynamic Spinal Stabilization Systems,” filed on Sep. 25, 2006; U.S. Provisional Patent Application 60,863,284, entitled “Alignment Instrument for Dynamic Spinal Stabilization Systems,” filed on Oct. 27, 2006; and U.S. Provisional Patent Application 60,883,314, entitled “Dynamic Linking Member for Spine Stabilization System,” filed on Jan. 3, 2007, the disclosures of which are hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION  
       [0003]     This disclosure relates to skeletal stabilization and, more particularly, to systems and method for stabilization of human spines and, even more particularly, to dynamic stabilization techniques.  
       BACKGROUND  
       [0004]     The human spine is a complex structure designed to achieve a myriad of tasks, many of them of a complex kinematic nature. The spinal vertebrae allow the spine to flex in three axes of movement relative to the portion of the spine in motion. These axes include the horizontal (bending either forward/anterior or aft/posterior), roll (bending to either left or right side) and vertical (twisting of the shoulders relative to the pelvis).  
         [0005]     In flexing about the horizontal axis, into flexion (bending forward or anterior) and extension (bending backward or posterior), vertebrae of the spine must rotate about the horizontal axis, to various degrees of rotation. The sum of all such movement about the horizontal axis of produces the overall flexion or extension of the spine. For example, the vertebrae that make up the lumbar region of the human spine move through roughly an arc of 15° relative to its adjacent or neighboring vertebrae. Vertebrae of other regions of the human spine (e.g., the thoracic and cervical regions) have different ranges of movement. Thus, if one were to view the posterior edge of a healthy vertebrae, one would observe that the edge moves through an arc of some degree (e.g., of about 15° in flexion and about 5° in extension if in the lumbar region) centered around a center of rotation. During such rotation, the anterior (front) edges of neighboring vertebrae move closer together, while the posterior edges move farther apart, compressing the anterior of the spine. Similarly, during extension, the posterior edges of neighboring vertebrae move closer together, while the anterior edges move farther apart, compressing the posterior of the spine. Also during flexion and extension, the vertebrae move in horizontal relationship to each other, providing up to 2-3 mm of translation.  
         [0006]     In a normal spine, the vertebrae also permit right and left lateral bending. Accordingly, right lateral bending indicates the ability of the spine to bend over to the right by compressing the right portions of the spine and reducing the spacing between the right edges of associated vertebrae. Similarly, left lateral bending indicates the ability of the spine to bend over to the left by compressing the left portions of the spine and reducing the spacing between the left edges of associated vertebrae. The side of the spine opposite that portion compressed is expanded, increasing the spacing between the edges of vertebrae comprising that portion of the spine. For example, the vertebrae that make up the lumbar region of the human spine rotate about an axis of roll, moving through roughly an arc of 10° relative to its neighbor vertebrae, throughout right and left lateral bending.  
         [0007]     Rotational movement about a vertical axis relative to the portion of the spine moving is also natural in the healthy spine. For example, rotational movement can be described as the clockwise or counter-clockwise twisting rotation of the vertebrae during a golf swing.  
         [0008]     The inter-vertebral spacing (between neighboring vertebrae) in a healthy spine is maintained by a compressible and somewhat elastic disc. The disc serves to allow the spine to move about the various axes of rotation and through the various arcs and movements required for normal mobility. The elasticity of the disc maintains spacing between the vertebrae, allowing room or clearance for compression of neighboring vertebrae, during flexion and lateral bending of the spine. In addition, the disc allows relative rotation about the vertical axis of neighboring vertebrae, allowing twisting of the shoulders relative to the hips and pelvis. Clearance between neighboring vertebrae maintained by a healthy disc is also important to allow nerves from the spinal chord to extend out of the spine, between neighboring vertebrae, without being squeezed or impinged by the vertebrae.  
         [0009]     In situations (based upon injury or otherwise) where a disc is not functioning properly, the inter-vertebral disc tends to compress, and in doing so pressure is exerted on nerves extending from the spinal cord by this reduced inter-vertebral spacing. Various other types of nerve problems may be experienced in the spine, such as exiting nerve root compression in the neural foramen, passing nerve root compression, and ennervated annulus (where nerves grow into a cracked/compromised annulus, causing pain every time the disc/annulus is compressed), as examples. Many medical procedures have been devised to alleviate such nerve compression and the pain that results from nerve pressure. Many of these procedures revolve around attempts to prevent the vertebrae from moving too close to each other thereby maintaining space for the nerves to exit without being impinged upon by movements of the spine.  
         [0010]     In one such procedure, screws are embedded in adjacent vertebrae pedicles and rigid rods or plates are then secured between the screws. In such a situation, the pedicle screws (which are in effect extensions of the vertebrae) then press against the rigid spacer which serves to distract the degenerated disc space, maintaining adequate separation between the neighboring vertebrae, so as to prevent the vertebrae from compressing the nerves. This prevents nerve pressure due to extension of the spine; however, when the patient then tries to bend forward (putting the spine in flexion), the posterior portions of at least two vertebrae are effectively held together and are not allowed to move as a natural healthy spine. Furthermore, the lateral bending or rotational movement between the affected vertebrae is significantly reduced, due to the rigid connection of the spacers and rods. Overall movement of the spine is reduced as more vertebras are distracted by such rigid spacers. This type of system not only limits the patient&#39;s movements, but also places additional stress on other portions of the spine (typically, the stress placed on adjacent vertebrae without spacers being the worse), often leading to further complications at a later date.  
         [0011]     In other procedures, dynamic stabilization devices are used. Typically, such devices do not allow multiple levels of stabilization of the vertebrae and do not allow for interchangeability of dynamic and fusion type systems for multiple levels.  
         [0012]     What is needed is a dynamic system that provides for dynamic stabilization and/or fusion of the spine at multiple levels, while increasing the ease of insertion by allowing for adjustability of components during implantation and accounting for variations in patient anatomy.  
       SUMMARY  
       [0013]     In response to these and other problems, there is presented certain aspects which may provide methods and spine stabilization systems for maintaining spacing between multiple consecutive vertebrae, while allowing movement of the vertebrae relative to each other in at least two and preferably three axes of rotation.  
         [0014]     In one embodiment, dynamic braces are used in multiple levels to maintain proper vertebral spacing. The dynamic braces are designed to allow the vertebrae to which it is attached to move through natural arc, which may travel on an imaginary surface of a sphere or another curved surface. Accordingly, such dynamic braces aid in permitting a substantial range of motion in flexion, extension, rotation, anterior-posterior translation and/or other desired types of spinal motion.  
         [0015]     These and other features, and advantages, will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings. It is important to note the drawings are not intended to represent the only aspect of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following Detailed Description taken in conjunction with the accompanying drawings, in which:  
         [0017]      FIG. 1  is a perspective view of one side of a multi-level dynamic stabilization system;  
         [0018]      FIG. 2A  is a detailed perspective view of one embodiment of a brace which may be used in the dynamic stabilization system of  FIG. 1  illustrated in a neutral position;  
         [0019]      FIG. 2B  is a perspective view of the brace illustrated in  FIG. 1  illustrated in a flexed position;  
         [0020]      FIG. 2C  is a perspective view of the brace illustrated in  FIG. 1  illustrated in a lateral bending position;  
         [0021]      FIG. 2D  is a perspective view of the brace illustrated in  FIG. 1  illustrated in a rotational position;  
         [0022]      FIG. 3  is a cross sectional view of a component that may be incorporated in the dynamic stabilization system of  FIG. 1  and  4 ;  
         [0023]      FIG. 4  is a perspective view of an alternative embodiment of a multi-level dynamic stabilization system;  
         [0024]      FIG. 5  is a detailed perspective view of a component which may be used in the dynamic stabilization system of  FIG. 1  and  4 ;  
         [0025]      FIG. 6A  is a perspective view of a limiter element which may be incorporated into the dynamic stabilization system of  FIG. 1  and  3 ;  
         [0026]      FIG. 6B  is an enlarged perspective view of an alternative embodiment of a dynamic brace which may be incorporated into the dynamic stabilization system of  FIG. 1  and  4 ;  
         [0027]      FIG. 7  is a perspective view of both sides of a multi-level dynamic stabilization system; and  
         [0028]      FIG. 8  is a perspective view of the dynamic stabilization system shown in  FIG. 7  implanted in multiple consecutive vertebrae;  
         [0029]      FIG. 9  is a perspective view of an alternative embodiment illustrating a connection between a pedicle screw and the rods, which may be incorporated into the dynamic stabilization system of  FIG. 1  and  4 ;  
         [0030]      FIG. 10  is a top view of a kit for a multi-level dynamic stabilization system. 
     
    
     DETAILED DESCRIPTION  
       [0031]     For the purposes of promoting an understanding of the principles of the present inventions, reference will now be made to the embodiments, or examples, illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the inventions as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates.  
         [0032]     Referring now to  FIG. 1 , there is shown one embodiment of a spine stabilization system  10  which may be secured to one side of the spine. The spine stabilization system  10  may be used to link and stabilize three or more vertebrae. As illustrated, the spine stabilization system  10  may incorporate three or more bone anchors  12   a - 12   c , three or more anchor heads  26   a - 26   c  that couple to the bone anchors  12   a - 12   c  and two or more dynamic braces  16   a - 16   b  that are positioned between anchor heads  26   a - 26   c  via rod or link members. Additionally, the various components of the spine stabilization system  10  may be manufactured from medical grade implantable polymers or metals, such as titanium, PEEK, cobalt chrome, nitinol, and stainless steel. As will be explained below in greater detail, the spine stabilization system  10  provides stabilization for three or more vertebrae, thus enabling multi-level spine stabilization.  
         [0033]     Each of the bone anchors  12   a - 12   c  may have a distal threaded section that is secured into a patient&#39;s vertebrae. In certain embodiments, the proximal end of each bone anchor  12   a - 12   c  may be shaped to couple in a polyaxial manner to an anchor head (such as anchor heads  26   a - 26   c ). One such example of a bone anchor coupled in a polyaxial manner to a anchor head is disclosed in application Ser. No. 10/990,272 entitled “An Implant Assembly and Method for use in an Internal Structure Stabilization System” filed on Nov. 16, 2004, the disclosure of which is hereby incorporated by reference for all purposes. The bone anchors  12   a - 12   c  may be pedicle screws or other suitable bone anchoring devices such as plates, rods, hooks, or nails.  
         [0034]     In certain embodiments, the anchor heads  26   a - 26   c  may have a generally smooth outer surface and a threaded internal surface. In some embodiments, the anchor heads  26   a - 26   c  may have a central hole or bore extending along its longitudinal center axis creating a cylindrical shaped head. The central hole may receive the proximal end of bone anchors  12   a - 12   c  from either direction. In certain embodiments the cylindrical shaped head may have an elongated slot on one or both sides of the head which may be perpendicular to the central hole. The elongated slot may be dimensioned to receive one or more rods  14   a - 14   c.  In yet other embodiments, which will be described in greater detail below, rods  14   a - 14   c  may be shaped so they may couple to anchor heads  26   a - 26   c  in a polyaxial manner.  
         [0035]     The rods  14   a - 14   c  may be adjusted vertically as needed to accommodate various placements of connecting members  18   a - 18   d  and, as will be explained later, accommodate a strategic placement of the braces  16   a - 16   b.  The rods  14   a - 14   c  may also slide within anchor heads  26   a - 26   c  to allow for adjustability during implantation. As will be explained below, in certain embodiments the connecting members  18   a - 18   d  may also slide relative to the bone anchors  12   a - 12   c  to accommodate various distances between bone anchors. The final position of rods  14   a - 14   c  and anchor heads  26   a - 26   c  may be secured by locking elements  28   a - 28   c.  The locking elements  28   a - 28   c  may be locking caps or other suitable locking elements known to those skilled in the art. In certain embodiments, the locking elements  28   a - 28   c  may have a threaded external surface that mates with a threaded internal surface of the respective anchor heads  26   a - 26   c.    
         [0036]     In certain embodiments, one or more dynamic braces  16   a - 16   b  may be provided that couple either directly or indirectly with the anchor heads  26   a - 26   c.  As illustrated in  FIG. 2A , for instance, the brace  16   a  may couple to the rods  14   a  and  14   b  by adjustable connecting members  18   a  and  18   b , respectively. In certain embodiments, the adjustable connecting members  18   a - 18   b  enables the brace  16   a  to be adjusted vertically along the rods  14   a - 14   b  to accommodate different distances in pedicle screw placement due to the various anatomies of patients. Furthermore, the adjustable connecting members  18   a - 18   b  may rotate about the rods  14   a - 14   b , which in turn may allow the brace  16   a  to pivot in relation to rods  14   a - 14   b.    
         [0037]     Turning briefly to  FIG. 3 , there is shown a section view of the connecting member  18   a  that may be used in certain embodiments. The connecting member  18   a  may allow the surgeon to adjust the dynamic brace  16   a  easily once implanted within patient&#39;s body. The axial adjustability of connecting member  18   a  reduces the total number sizes required for the braces  16   a  (and  16   b ) in order for surgeons to account for the differences in anatomy among patient populations. The connecting member  18   a  may comprise a body  30  with an adjustable arm  32  that is sized to receive and clamp the rod  14   a.  In certain embodiments arm  32  may pivot between an open and closed position to allow for the insertion of rod  14   a.  The rod  14   a  may also be able to slide between arm  32  and the body  30  without adjusting the position of arm  32  or the body  30 . The arm  32  may be fastened to the body  30  by a fastener  34  such as a screw, bolt, rod, collet or other suitable fastener known to those skilled in the art. When tightened, the fastener  34  may exert a compressive force on the arm  32  which transfers the force to rod  14   a  rigidly locking rod  14   a  in place with respect to the connecting member  18   a . The connecting member  18   a  may also allow for an end of a dynamic brace  16   a  to rotatably couple to the body  30 . A fastening device  36  such as a dowel pin, screw, bolt, or other suitable fastening device known to those skilled in the art may be used to secure link member  20   a  or  22   a  of the dynamic brace  16 A to connecting member  18   a  while still allowing for rotation of dynamic brace  16   a  relative to connecting member  18   a.    
         [0038]     This adjustability will aid in allowing the brace to align or “point” towards a center of rotation, as shown in U.S. patent application Ser. No. 11/443236 entitled “System and Method for Dynamic Stabilization” filed on May 30, 2006, which is hereby incorporated by reference. Alignment tools may also be used to assist with the alignment process. Such tools are described in U.S. Provisional Patent Application 60,711,812, entitled “Dynamic Spinal Stabilization Alignment Instrument,” filed on Aug. 26, 2005; U.S. patent application Ser. No. 11,467,798, entitled “Alignment Instrument for Dynamic Spinal Stabilization Systems,” filed on Aug. 28, 2006; U.S. Provisional Patent Application 60,826,763, entitled “Alignment Instrument for Dynamic Spinal Stabilization Systems,” filed on Sep. 25, 2006, which are herby incorporated by reference for all purposes. Once the desired distance and angle of rotation is achieved the connecting members  18   a - 18   b  may be locked in place with respect to the rods  14   a - 14   b  by a fastener  34  or other locking means known to those in the art.  
         [0039]     In certain embodiments, therefore, the connecting members  18   a  and  18   b  may be adjusted so that the bone anchor which is secured to the vertebra may rotate about a center of rotation as more fully described in the PCT Patent Application No. PCT/US2005/027996, entitled, “System and Method for Dynamic Skeletal Stabilization” filed on Aug. 8, 2005. The connecting members  18   a - 1   8   d  may also allow the surgeon to adjust or orient the brace  16   a - 1   6   b  to prevent the braces  16   a - 1   6   b  from interfering with neighboring anatomy of the spine, especially during movement of the spine.  
         [0040]     Turning back to  FIG. 2A , in the certain embodiments, the dynamic brace  16   a  may be offset from a longitudinal axis that passes through the adjacent bone anchors. Such an offset may allow for the brace to be larger or more easily placed because the distance and space between adjacent bone anchors and/or vertebrae is limited, especially in smaller patients. In certain embodiments, the dynamic brace  16   a  may incorporate a first link member  20   a  and a second link member  22   a.  In some embodiments, the link members  20   a  and  22   a  may be hinged or pivotably connected to each other at their proximal ends, respectively. For instance, the link members  20   a  and  22   a  may be secured together by a pin  24   a  (as shown in  FIG. 2C  and  FIG. 2D ). Although a pin  24   a  is shown, any other suitable fastening device known to those skilled in the art may be used that will allow rotational movement.  
         [0041]     Referring to  FIGS. 2A through 2D , there is shown one embodiment of the dynamic brace  16   a  illustrating the range of motion of adjacent vertebrae that may be enabled by the spine stabilization device  10  between two vertebra.  FIG. 2A  illustrates the brace  16   a  when the two adjacent vertebrae are in a neutral position. In some situations, the brace  16   a  may be initially implanted by a surgeon when the patient is in the neutral position.  FIG. 2B  illustrates the brace  16   a  when the two adjacent vertebrae move from a neutral to a flexion position (when the patient is bending forward). As the spine moves from a neutral to flexion position the link members  20   a  and  22   a  may pivot away from one another, increasing the resulting angle between the two link members. The link members  20   a  and  22   a  may also rotate in relation to the rods  14   a - 14   b.    FIG. 2C  illustrates the brace  16   a  when the two adjacent vertebrae are in a lateral bending position (when the patient is bending towards the right or left).  FIG. 2D  illustrates the brace  16   a  when the two adjacent vertebrae are in a rotational motion (when the patient is turning to the right or left).  
         [0042]     As explained above, the relative position and angles of the link members  20   a  and  22   b  may be adjusted by moving the connecting members  18   a - 18   b  either axially or rotationally and then locking them in place, thus effecting the amount of motion allowed by dynamic brace  16   a.    
         [0043]     In certain embodiments, one of the dynamic braces  16   a  or  16   b  may be replaced by a rigid element such as a rod or a plate that couples to one or more anchor heads (a hybrid system).  FIG. 4  illustrates one possible embodiment of a hybrid dynamic stabilization system  100 . The hybrid dynamic stabilization system  100  is similar to the dynamic stabilization system  10  as described above, except the lower dynamic brace has been replaced by a rod  14   d  which may extend from anchor head  26 A thru the anchor head  26   b  to the link member  18   a.  Thus, this system  100  allows for fusion between the first anchor head  26   a  and the second anchor head  26   b  while still allowing for dynamic stabilization between the second anchor head  26   b  and the third anchor head  26   c.  Thus, the rod  14   d  directly links the two anchor heads  26   a  and  26   b . As illustrated, the connecting member  18   a  may couple the rod  14   d  to the dynamic brace  16   b.  Thus, fusion may be achieved at the lower vertebra level with rod  14   d,  while motion is preserved at the upper vertebra level with the dynamic brace  16   b  or vice versa. The interchangeability of the multilevel dynamic stabilization system  10  gives a surgeon the desired flexibility required when addressing different clinical needs.  
         [0044]      FIG. 5  is a detailed view illustrating one component which may be incorporated in dynamic stabilization system  10  to limit the amount of movement allowed by the dynamic brace  16   a.  In order to stabilize adjacent vertebrae, a force must be applied to the vertebra to keep them separated during movement of the spine. The force may increase or decrease as the spine moves through its natural motions. In certain embodiments, a limiter element  40   a  (or  40   b ) may act to apply a force to aid in the distraction of adjacent vertebrae by limiting or applying a force on the dynamic brace  16   a - 16   b  in either extension or flexion, or both. The limiter element  40   a  (or  40   b ) may incorporate additional elements to aid in either flexion or extension. For example,  FIG. 5  shows the limiter element  40   a  which may work in conjunction with the limiter element  40   b.  In this illustrative example, the limiter element  40   a  may be a helical spring or isomeric dampener positioned between the ends of the rods  14   b  and  14   b.  The limiter element  40   b  may be a torsional spring coupled to the joint  23   a.  In other embodiments, the limiter elements  40   a  (or  40   b ) may be a spring (such as a torsion spring, leaf spring or compression spring), a tension band, bumper or other device that limits or controls the force acting on the dynamic brace  16   a - 16   b  either in flexion and/or extension of the spine. In certain embodiments, one limiter element  40   a  (or  40   b ) may apply a force during flexion of the spine while the other limiter  40   a  (or  40   b ) applies a force during extension of the spine. Both limiters  40   a - 40   b  may also apply a limiting force during rotation and lateral bending of the spine.  
         [0045]     In certain embodiments, the limiter element  40   a  or  40   b  may incorporate a soft or a hard stop. For example the complete compression of a spring (or a spring with a certain spring constant) may provide a stop that prevents any further movement of the spine in either extension or flexion (or rotation or lateral bend). The limiter elements  40   a - 40   b  may also be so rigid as to allow very little or no motion of dynamic braces  16   a - 16   b  which may aid in promoting fusion of the attached vertebrae. A locking element may also be provided, such as a set screw, to convert the dynamic braces  16   a - 16   b  to a fusion brace by restricting any motion.  
         [0046]     In yet other embodiments, for instance, the pin element  24   a  may be replaced with a locking element which effectively converts the dynamic brace to a rigid element might be provided. Thus, at a later date, the surgeon may quickly convert the dynamic brace into a static or fused brace.  
         [0047]      FIG. 6A  and  FIG. 6B  illustrate an alternate embodiment of a dynamic brace and a limiter or torsion spring, as described more fully in U.S. Provisional Application 60/883,314 entitled “Dynamic Linking Member for Spine Stabilization System” filed on Jan. 3, 2007, the disclosure of which is hereby incorporated by reference. A limiter or torsion spring  1010  may be incorporated into a dynamic brace  1000  to control the force required exerted between a first linking member  1002  and a second linking member  1004  of the dynamic brace. The first linking member  1002  and the second linking member  1004  may be pivotably coupled to each other with pin  1018 . In this embodiment, the limiter  1010  may have a top wall  1076  and a bottom wall  1078  with an open space  1080  in-between. The top  1076  and bottom  1078  walls may be connected by two opposite side walls which have dampening members  1070  and  1072  that extend along the longitudinal axis of the limiter  1010 . In the present example, the dampening members  1070  and  1072  extend along a curved or arcuate longitudinal axis. The space  1080  in-between the top  1076  and bottom  1078  walls of torsion spring  1010  may be dimensioned to receive a shaped end of one of the linking members of the dynamic brace.  
         [0048]      FIG. 6B  shows an enlarged front view of one embodiment of the joint of linking members  1002  and  1004  assembled with the limiter  1010 . In certain embodiments, the limiter  1010  may have a slot  1074  that extends through its top wall  1076 . Slot  1074  of the limiter  1010  may align with a hole on the second linking member  1004 . The tension of the limiter  1010  may be adjusted by adjusting the position of the slot  1074  relative to the hole on the second linking member  1004  and the limiter adjustment member  1016 . The limiter adjustment member  1016  may be inserted through slot and into the hole of second linking member  1004  to secure the limiter to the second linking member  1004 .  
         [0049]     The distal end of the dampening members  1070  and  1072  may mate or contact protrusions  1042   a  and  1042   b  of first linking member  1002 . Dampening members  1070  and  1072  may exert a force against protrusions  1042   a  and  1042   b , respectively. As the first and second linking members  1002  and  1004  move towards each other (as shown by large arrow in  FIG. 6B ), one dampening member  1070  may compress against protrusion  1042   b , while other dampening member  1072  may relax or extend, as shown in  FIG. 6B . Dampening member  1072  may compress and exert a force against protrusion  1042   a , if first and second linking members  1002  and  1004  are moved in the opposite direction. The amount of force exerted on protrusions  1042   a  and  1042   b  by dampening members  1070  and  1072  (respectively) may be adjusted by adjusting the position of slot  1074  relative to limiter adjustment member  1016 . For example, if member  1016  is positioned further away from one end of slot  1074 , as shown in  FIG. 6B  then dampening member  1072  may be compressed more (and member  1074  may be compressed less) than if member  1016  was positioned in the middle (or at the other end) of slot  1074 .  
         [0050]     In certain embodiments the limiter spring  1010  may be molded or machined from an elastomeric or polymeric material. Dampening members  1070  and  1072  may be molded or machined from the same material as the rest of torsions spring  1010  or may be manufactured from a metallic material such as nitinol, stainless steel or titanium. Dampening members  1070  and  1072  may achieve its dampening characteristics through its wave-like design as shown in  FIG. 6A  and/or the material properties of the material it is manufactured from. In other embodiments, dampening members  1070  and  1072  may include various types of springs designs, such as torsion springs, compression springs or wave springs.  
         [0051]     It is understood that the various components described above such as bone anchor  12   a - 12   c , anchor heads  26   a - 26   c , rod  14   a - 14   c , braces  16   a - 16   b , connecting member  18   a - 18   d,  dampening element  40   a  and  40   b  and locking member  28   a -c may be assembled together as required by a surgeon to create a dynamic stabilization system  10 . These components are interchangeable and some components may not be used in a system and some components may be used more than once.  FIG. 7  illustrates one example of a multi-level dynamic stabilization system  10  for securing to both sides of the spinous process. As illustrated, both sides of the spine stabilization system are similar, but as described above, depending on the patient needs, a surgeon may construct a different multi-level dynamic stabilization system on either side of the spine as illustrated in  FIG. 8 .  
         [0052]     In the example illustrated in  FIG. 7 a  bone anchor  12   a  may be multiaxially coupled to a anchor head  26   a , which may receive a rod  14   a  that may be coupled to connecting member  18   a.  Connecting member  18   a  may be coupled to one side of dynamic brace  16   a.  A second connecting member  18   b  may be used to couple to an opposing side of dynamic brace  16   a.  Second connecting member  18   b  may be coupled to a second rod  14   b  which may slide into a slot of a second anchor head  26   b  which is coupled to a second bone anchor  12   b  which is secured within a vertebra of the next level. Second rod  14   b  may extend through the slot in second anchor head  26   b . The end portion of second rod  14   b  may couple to a third connecting member  18   c  which couples to a side of a second brace  16   b.  The opposing side of second brace  16   b  may couple to a fourth connecting member  18   d  which may receive a third rod  14   c.  The third rod  14   c  may then couple to a third anchor head  26   c  which is multi-axially coupled to a third bone anchor  12   c  which is secured to the next level vertebra.  
         [0053]     The system may be implanted in either an open or a minimally invasive manner. Furthermore, either the entire system or portion of the system may be assembled outside the body and adjusted once implanted. The surgeon may slide rods  14   a - 14   c  within anchor heads  26   a - 26   c  and may slide and/or rotate the connecting members  18   a - 18   d  along the rods  14   a - 14   c  until the desired orientation of the dynamic braces  16   a - 16   b  is achieved (for example the dynamic brace(s) points toward the center of rotation for that vertebral level). The surgeon may also adjust the anchor heads  26   a - 26   c  to achieve the desired orientation of the dynamic stabilization system  10 . Once the desired position is achieved the locking members  28   a - 28   c  and connecting members  18   a - 18   d  may be tightened to fix the orientation of the dynamic stabilization system  10 . This process of connecting various components of the dynamic spinal stabilization system  10  may be continued along the spine to additional levels (including cervical vertebrae). A second dynamic stabilization system  10  may be implanted on the opposite side of the spine for multiple levels (three or more vertebrae) as is shown in  FIG. 7 .  FIG. 8  further illustrates both sides of the spine stabilization device as implanted into multiple vertebrae  50   a - 50   c.  The dynamic stabilization system as shown in  FIG. 7  and  FIG. 8  may be easily modified. For example, the limiter element  40   a - 40   b  may be added to any number of dynamic braces  16   a  (or  16   b ) as described above.  
         [0054]      FIG. 9  illustrates an alternative embodiment  50  showing another coupling mechanism. Rods  14   a - 14   c  described above may be substituted for rods  52  and  54 . In this alternative embodiment, the rod  52  may be fixedly secured to the screw head  58 . In certain embodiments, there may be a side slot  59  formed within a wall of the screw head  58 . As illustrated, the rod  54  may have an enlarged or spherical portion  60 . Spherical portion  60  may be received by and fit within a proximal opening  62  of the screw head  58 . Screw head  58  may be multiaxially coupled to bone anchor  56  as described earlier. The combination of spherical portion  60  and multiaxial screw head  58  allows for two points of adjustability at the same location. In other words, when a single rod is used (e.g. rod  14   b  as illustrated in  FIG. 1 ), the position and alignment of the rod must be “balanced” between the adjacent levels. However, if a single rod is replaced with the screw head  58  and a rod  54 , each of the respective ends may be adjusted independently. This flexibility allows components to line up easier and in the desired orientation.  
         [0055]     In certain embodiments, the spherical portion  60  allows the rod  54  to be rotated and angularly positioned with respect to the screw head  58 . Screw head  58  may then also be rotated and angularly position independent of the rod  54  and the bone anchor  56 . Once properly positioned, the rod  54  may be secured to the screw head  58  with a locking means, such as a cap screw  64 . Although rods are described in the various embodiments, these rods may also include plates as well as rods of various cross sectional geometries.  
         [0056]     In certain embodiments the rod  54  may extend along a horizontal axis that is substantially perpendicular to a longitudinal axis of the bone anchor  56 . In other embodiments the rod  54  may extend at an angle to the horizontal axis. For example the rod may extend at an angle of 40 degrees below the horizontal axis to an angle of 40 degrees above the horizontal axis.  
         [0057]     Thus, in the alternative embodiment  50 , there is an additional degree of freedom which allows the rods to be individually angularly positioned with respect to each other. Such an additional degree of freedom may allow the dynamic brace or fusion rods for each level to be more easily adjusted so that each brace may be aligned with its respective center of rotation.  
         [0058]     In other embodiments screw head  58  may have a U shaped channel and rods  52  and  54  may be one component with a spherical portion located between its ends. In such an embodiment the spherical portion may include a single ball or two partial spheres that are located within screw head  58 . As stated above screw head  58  may also be multiaxially coupled to a bone anchor.  
         [0059]     Referring now to  FIG. 10  one embodiment of a multi-level dynamic stabilization kit  105  is shown. The kit  105  may include a plurality of any component described above, including a plurality of dynamic braces  110 , a plurality of rods of  140 , a plurality of connecting members  150 , a plurality of bone anchors with multi-axial heads pre attached  130 , a plurality of locking members  160 , and a plurality of limiter elements  120 . The limiter elements  120  in the kit  105  may have varying compressive and/or extension forces as to allow the surgeon to choose the amount force needed for the vertebrae to move in extension and flexion (as well as rotation and lateral bend). The rods  140  in the kit may consist of several rods having various lengths and/or bends which enables the surgeon to customize the multi-level dynamic stabilization system implanted. The kit  105  may also incorporate a tray with inserts for the various components. In certain embodiments the tray may be sterilizable and manufactured from metal or high temperature plastic. In other embodiments the surgeon may order a pre-sterile pack with all of the required implants in the pack to assemble the desired dynamic multi-level system.  
         [0060]     The foregoing description of the embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.  
         [0061]     For instance, in some embodiments, there may be a spine stabilization device comprising a plurality of rods coupled to bone anchors wherein each bone anchor is secured to one rod in a polyaxial manner. The spine stabilization device may further comprise braces rotatably coupled between rods by a connecting member, the braces comprising two spherical link members coupled together at the proximal ends thereof by a fastener such as a pin or a screw.  
         [0062]     In other embodiments, there may be a spine stabilization device wherein the braces are coupled together at the proximal ends thereof by a hinged mechanism.  
         [0063]     In yet other embodiments, there may be a spine stabilization device may further comprise a spring coupled between the rods for added flexibility and stability.  
         [0064]     In other embodiments, there may be spine stabilization device comprising: a plurality of rods; a plurality of bone anchors, wherein each bone anchor may be secured to one rod in a polyaxial manner; at least one end of each rod rotatably coupled to a brace adapted to span between two bone anchors; each brace comprising a first and second link member wherein the distal end of the first link member rotatably secures to a first rod near the bottom end thereof, the distal end of the second link member rotatably secures to a second rod near the upper end thereof, and the first and second link members are pivotably secured to each other at the proximal end thereof; means for securing the first and second link members together; and means for securing the brace to the rods; wherein the brace allows for movement between the first link member and the second link member such that the movement of the second link member with respect to the first link member is generally restricted to a three dimensional curved path having a substantially constant radius about a center of rotation positioned outside of the brace.  
         [0065]     Additionally, the means for securing the first and second link members together comprises a pin and the means for securing the brace to the rods is first and second link members together comprises a connecting member. In some embodiments, the connecting member comprises a body, an adjustable arm, means for securing the arm to the body, and means for securing the link member of the brace to the body of the connecting member.  
         [0066]     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly the appended claims are intended to include within their scope such processes machines, manufacture, compositions of matter, means, methods or steps.