Patent Publication Number: US-7896904-B2

Title: Vertebral disc tensioning device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part application of U.S. patent application Ser. No. 11/646,750, filed Dec. 28, 2006, titled “Vertebral Disc Annular Fibrosis Tensioning and Lengthening Device.” 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a vertebral disc tensioning device and, more particularly, to a vertebral disc tensioning device that includes a pair of pedicle screws, screw head portions coupled to each screw, a rigid connector connecting the screw head portions and a spring member applying a bias to gradually separate the pedicle screws to restore disc space height over time. 
     2. Discussion of the Related Art 
     The human spine includes a series of vertebrae interconnected by connective tissue referred to as intervertebral discs that act as a cushion between the vertebrae. The discs allow for movement of the vertebrae so that the spine can bend and rotate. 
     The intervertebral disc is an active organ in which the normal and pathologic anatomies are well known, but the normal and pathologic physiologies have not been greatly understood. The intervertebral disc permits rhythmic motions required of all vertebrate animals in their various forms of locomotion. The disc is a high-pressure system composed primarily of absorbed water, an outer multilayered circumferential annulus of strong, flexible, but essentially inelastic collagen fibers, and an inner core of a hydrogel called the nucleus pulposus. The swelling of the contained hydrogel creates the high pressure that tightens the annular fibers and its laminations. Degeneration of discs in humans is typically a slow, complex process involving essentially all of the mechanical and physiologic components with loss of water holding capacity of the disc. Discogenic pain arises from either component, but is primarily due to altered chemistry. When this pain is severely disabling and refractory to non-operative, the preferred contemporary treatments are primarily surgical, particularly fusion and/or disc replacement. 
     Annular collagen fibers are arranged in circumferential belts or laminations inserting strongly and tangentially in right- and left-handed angulated patches into each adjacent vertebral body. Inside the annular ring is contained an aggrecan, glycosaminoglycan, a protein-sugar complex gel having great hygroscopic ability to hold water. The swelling pressure of this gel of the nucleus maintains the pressure within the annulus, forcing the vertebrae apart and tightening the annular fibers. This tightening provides the primary mechanical stability and flexibility of each disc of the spinal column. Further, the angulated arrangement of the fibers also controls the segmental stability and flexibility of the motion segment. Therefore, the motion of each segment relates directly to the swelling capacity of the gel and secondarily to the tightness of intact annulus fibers. The same gel is also found in thin layers separating the annular laminar construction, providing some apparent elasticity and separating the laminations, reducing interlaminar torsional abrasion. With aging or degeneration, nucleus gel declines, while collagen content, including fibrosis, relatively increases. 
     Disc degeneration, which involves matrix, collagen and aggrecan, usually begins with annular tears or alterations in the endplate nutritional pathways by mechanical or patho-physiological means. However, the disc ultimately fails for cellular reasons. As a person ages, the discs in the spine go through a degenerative process that involves the gradual loss of the water holding capacity of the disc, referred to as desiccation. As a result of this loss of water, the disc space height may partially collapse, which may lead to chronic back pain disorders and/or leg pain as a result of the nerves being pinched. 
     Progressive injury and aging of the disc occurs normally in later life and abnormally after trauma or metabolic changes. In addition to the chemical effects on the free nerve endings as a source of discogenic pain, other degenerative factors may occur. Free nerve endings in the annular fibers may be stimulated by stretching as the disc degenerates, bulges, and circumferential delamination of annular fibers occurs. This condition may lead to a number of problems. It has been shown that a person&#39;s disc is typically thicker in the morning when a person awakes. This phenomenon may be due in part to the reduction of body weight forces on the disc when lying in a recumbent position overnight that causes the disc height to restore. Therefore, the reduction of compressive forces on the disc may help to restore disc height. 
     As discussed above, as a person ages, the discs of the spine degenerate, and the disc space height collapses. Further, the ligaments and facets of the spine degenerate as well due to increased forces and stresses on these structures that occur as the disc loses its weight-bearing capacity. These problems lead to a reduction in the foramenal height of the vertebrae, often causing central or lateral canal stenosis. The foramen is an opening through the vertebrae that allows the nerve from the spinal cord to pass through. Because the nerve passes through the foramen, the nerve will often get pinched as the disc height decreases, leading to various types of back pain. Further, these problems often lead to difficulty in walking. Additionally, the lateral canal stenosis causes the nerve to get pinched in the spinal canal. These conditions often lead to neurogenic claudication, where the patient typically responds by walking shorter distances, then sitting down, and then flexing the spine by leaning over or by walking with the aid of a device, which helps to flex the spine. 
     The treatment of degenerative disc disease and associated spine ailments is one of the most costly medical conditions with an estimated annual direct cost in the United States of thirty-three billion dollars and a total annual societal cost exceeding one hundred billion dollars. Indeed, in one&#39;s lifetime most individuals will experience an episode of significant back and/or neck pain. 
     SUMMARY OF THE INVENTION 
     In accordance with the teachings of the present invention, a vertebral disc tensioning device is disclosed that restores the loss of disc height as a result of disc degeneration and other factors. In one embodiment, the device includes first and second pedicle screws each including a screw body portion and a ball head. The device also includes first and second screw head portions each including an internal threaded bore where the first screw is inserted in the first screw head portion and is pivotally mounted relative thereto and the second screw is inserted in the second screw head portion and is pivotally mounted thereto. The device also includes a rigid connector that couples the first and second screw head portions where bolts are threaded through the connector and into the internal threaded bores of the first and second screw head portions. The device also includes a spring assembly offset from the rigid connector that applies a bias to separate the pedicle screws. 
     Additional features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a pedicle screw employed in a vertebral disc annular fibrosis tensioning and lengthening device; 
         FIG. 2  is a perspective view of a spring employed in the vertebral disc annular fibrosis tensioning and lengthening device; 
         FIG. 3  is a side view of the vertebral disc annular fibrosis tensioning and lengthening device of the invention including two of the pedicle screws with the spring therebetween; 
         FIG. 4  is a cross-sectional side view of the vertebral disc annular fibrosis tensioning and lengthening device shown in  FIG. 3 ; 
         FIG. 5  is a top view of the vertebral disc annular fibrosis tensioning and lengthening device shown in  FIG. 3 ; 
         FIG. 6  is a perspective view of a vertebral disc annular fibrosis tensioning and lengthening device, according to another embodiment; 
         FIG. 7  is a side view showing a vertebral disc annular fibrosis tensioning and lengthening device of the invention inserted within adjacent vertebrae; 
         FIG. 8  is a top view of two vertebral disc annular fibrosis tensioning and lengthening devices of the invention inserted within the adjacent vertebrae; 
         FIG. 9  is a perspective view of a vertebral disc annular fibrosis tensioning and lengthening device, according to another embodiment; 
         FIG. 10  is a cross-sectional view of the vertebral disc annular fibrosis tensioning and lengthening device shown in  FIG. 9 ; 
         FIG. 11  is a perspective view of a plate member used in the device shown in  FIGS. 9 and 10 ; 
         FIG. 12  is a perspective view of a spring element used in the device shown in  FIGS. 9 and 10 ; 
         FIG. 13  is a perspective view of a vertebral disc annular fibrosis tensioning and lengthening device, according to another embodiment; 
         FIG. 14  is a broken-away, perspective view of a vertebral disc annular fibrosis tensioning and lengthening device, according to another embodiment; 
         FIG. 15  is a perspective view of a disc height restoration assembly; 
         FIG. 16  is a side view of a vertebral disc tensioning device, according to another embodiment; 
         FIG. 17  is a top view of the device shown in  FIG. 16 ; 
         FIG. 18  is an exploded perspective view of the device shown in  FIG. 16 ; 
         FIG. 19  is a cross-sectional view of the device shown in  FIG. 16 ; 
         FIG. 20  is a perspective view of a pedicle screw and screw head portion in the device shown in  FIG. 16 ; 
         FIG. 21  is a connector in the device shown in  FIG. 16 ; 
         FIG. 22  is a bolt in the device shown in  FIG. 16 ; 
         FIG. 23  is a spring assembly in the device shown in  FIG. 16 ; 
         FIG. 24  is a side view of the device shown in  FIG. 16  with the spring head portion pivoted relative to the connector; and 
         FIG. 25  is a cross-sectional view of the illustration shown in  FIG. 24 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The following discussion of the embodiments of the invention directed to a vertebral disc tensioning device is merely exemplary in nature, and is in no way intended to limit the invention or its applications or uses. 
       FIG. 1  is a perspective view of a pedicle screw  10  for use in a vertebral disc annular fibrosis tensioning and lengthening device ( FIG. 3 ). The pedicle screw  10  includes a threaded and tapered body portion  12  having a tip  14 . The body portion  12  includes a plurality of holes  24  that allow bone to grow therein when the screw  10  is threaded into the vertebral body so that the pedicle screw  10  is better anchored within the vertebra. The use of holes in the body portion of a pedicle screw to facilitate bone growth therein can be employed in other types of pedicle screws for other uses besides vertebral disc annular fibrosis tensioning and lengthening devices, such as spinal fusion pedicle screw and rod instrumentation, well known to those skilled in the art. The holes  24  can come in a variety of numbers, diameters and configurations. In one non-limiting embodiment, the diameter of the body portion  12  is about 8 mm and the diameter of the holes is about 1.0 mm. The pedicle screw  10  can include a bore  26  that extends through the body portion  12  to make it cannulated so that a K-wire (not shown) can extend therethrough to allow for percutaneous placement of the pedicle screw over a K-wire that has previously been placed through the vertebral pedicle. This will allow for a minimally invasive application of the device that causes less disruption of the normal anatomical structures of the spine and improved recovery, as is well understood to those skilled in the art. 
     The pedicle screw  10  further includes a screw head  16  having an extended cup shape defining a cavity  18 . The cavity  18  includes an open side  20  that fits a spring head (discussed below) and allows for mobility between the spring head and the cavity  18  of the screw head  16 . This will permit mobility and will not limit flexion, extension and/or rotational mobility of the spine, thus allowing for the creation of a posterior motion-preserving device for reasons that will become apparent from the discussion below. An annular recess  22  is formed around an outside of the head  16  also for reasons that will become apparent from the discussion below. The pedicle screw  10  can be made of any suitable material, such as titanium, stainless steel, etc., as would be well understood to those skilled in the art. The cavity  18  could be made of ceramics or cobalt steel to limit wear between the spring head and the cavity  18 . 
       FIG. 2  is a perspective view of a spring  30  having a cylindrical body  32  that is also part of the vertebral disc annular fibrosis tensioning and lengthening device. A series of slots  34  are cut into the body portion  32 , as shown, in an alternating configuration that allows the body portion  32  to be compressed and provide an expansive spring force. The spring  30  includes generally rounded ends  36  and  38  that are shaped to conform to the shape of the inner surface of the cavity  18 . The spring  30  can be made of any suitable material for the purposes described herein, such as nitinol, which is a flexible metal having a memory. Other materials may also be suitable, such as a shape memory alloy, polymers, hydrogels, etc., which could expand over time and allow for separation of the screw heads and disc height restoration. An example of a suitable alloy includes about 50% nickel and about 50% titanium. 
       FIG. 3  is a side view,  FIG. 4  is a cross-sectional view, side view and  FIG. 5  is a top view of a vertebral disc annular fibrosis tensioning and lengthening device  40 , according to an embodiment. The vertebral disc annular fibrosis tensioning and lengthening device  40  includes two of the pedicle screws  10  where the open sides  20  of the heads  16  face each other, as shown. The spring  30  is inserted into the cavities  18  of the heads  16  so that the ends  36  and  38  conform to the inner surface of the cavities  18 . The inner surface of the cavities  18  and the ends  36  and  38  can be coated with a suitable low friction material, such as chrome, cobalt, ceramic, etc., to prevent or reduce wear particle formation as the spring  30  and the pedicle screws  10  rub against each other. Initially, the spring  32  is compressed so that it provides an expansive force to separate the pedicle screws  10 . In one non-limiting embodiment, the expanded or relaxed length of the spring  30  is in the range of about 3 cm-4 cm, which is about the height of a normal lumbar disc. The diameter of the spring  32  can be any diameter suitable for the purposes described herein. 
     An oval posterior ring  42  is positioned within the recesses  22 , and operates to maintain the screws  10  in their proper orientation, and prevent the pedicle screws  10  from separating beyond a predetermined limit. The fixed diameter of the ring  42  allows for the tips  14  of the pedicle screws  10  to separate greater relative to the heads  16 . This imparts lordosis. Further, as the spring  30  causes the pedicle screws  10  to separate, the ring  42  maintains the top end of the pedicle screws  10  stationary to create a pivot and restore the height of the disc and lordosis of the spine. Also, the configuration and orientation of the spring  30 , the ring  42  and the screws  10  preserves the motion of the spine as the person performs normal physical movement in that it allows for continued flexion, extension, as well as axial rotation of the spine. The spring  30  operates as a compressible link and the posterior ring  42  operates as a rigid link. 
       FIG. 6  is a perspective view of a vertebral disc annular fibrosis tensioning and lengthening device  50 , according to another embodiment, where like elements to the vertebral disc annular fibrosis tensioning and lengthening device  40  are identified by the same reference numeral. In this embodiment, the heads  16  of the pedicle screws  10  include a slot  52 . The ring  42  is replaced with a dumbbell member  54  including a cylindrical body portion  56  and end portions  58  and  60 . The body portion  56  extends through the slots  52  so that the end portions  58  and  60  are positioned on outside sides of the heads  16 , and also operates to limit the expansion of the pedicle screws  10  and control the posterior aspects of the screws  10  and control the posterior aspects of the screws  10 , thus allowing restoration of the lordosis, i.e., normal curvature, of the spine. 
       FIG. 7  is a side view and  FIG. 8  is a top view of two of the vertebral disc annular fibrosis tensioning and lengthening devices  40  coupled to two adjacent lumbar vertebra  70  and  72  having a disc  68  therebetween. The pedicle screws  10  are threaded through pedicles  74  of the vertebra  70  and  72  and into the vertebral body  76 . Once the pedicle screws  10  are in place, then the spring  30  is positioned within the cavities  18  under compression, as discussed above. As the spring bias forces the vertebra  70  and  72  apart, the height of a disc space  78  between the vertebra  70  and  72  increases and is restored. Further, as the height of the disc space  78  increases, the disc  68  is able to regenerate due to reduced sheer or compressive forces applied to the disc  68 . The device  40  creates a controlled distraction force and distraction distance on the annulus fibrosis and a controlled dynamic motion of the vertebra. Further, the device  40  allows motion of the spine while maintaining the stress tension effect on the disc  68 . Particularly, the device  40  provides a tension force across a compromised vertebral disc providing a distractive force to elicit the stress tension effect on the annulus fibrosis. The pedicle screws and links therebetween are arranged in a parallelogram shape to provide the desired distraction. Because most systems work like a hinge, the front or anterior portion of the disc moves much more than the back or posterior portion of the disc. This is not a natural motion, so with the vertebral linkage of the invention, a parallel or near parallel motion of the disc can be achieved. In one non-limiting embodiment, the motion pathway is an arc of a radius much longer than the pedicle screw length. Although the device  40  is shown coupled to adjacent vertebra, the device  40  can extend across any suitable number of vertebrae to increase the disc space of more than one disc. 
     The device  40  can also be applied unilaterally to restore coronal alignment. This is particularly applicable to patients suffering from scoliosis where the curvature of the spine could be corrected by applying the device  40  to the concaved portion of the spine. Restoration of spinal alignment would ultimately open the neural foramina on the concaved side and help to alleviate symptoms of lower back pain experience by these patients. 
     Any suitable surgical procedure for placing the pedicle screws  10  can be used, including minimally invasive surgical procedures by making the pedicle screws  10  cannulated. In one known process of percutaneous pedicle screw instrumentation, a Jamshidi needle is used to dock on to the junction of the vertebrae between the facet complex and the transverse process of the vertebra. Gentle taps with a mallet cause the Jamshidi needle to be advanced through the pedicle  74 , making sure not to cross the medial border of the pedicle  74 , which can result in nerve root injury, until the junction between the pedicle base and the vertebral body is reached. Fluoroscopic visualization into the anterior posterior and lateral planes of the vertebra is used to see the orientation of the Jamshidi needle. The correct trajectory of the Jamshidi needle should place the tip of the needle in the center of the pedicle in the anterior posterior view when the tip of the Jamshidi needle lies at the pedicle vertebral body junction in the lateral view. 
     Once the junction between the base of the pedicle wall and the vertebral body is reached, the Jamshidi needle can be directed in a more medial fashion. The Jamshidi needle is typically passed to about one-half the depth of the vertebral body, and then a K-wire is passed down the Jamshidi needle and into the vertebral body a little farther to seat it into the bone. The Jamshidi needle is then removed. A series of cannulated muscle dilators are then passed over the K-wire to prevent the soft tissue from going into the threads of the tap. The pedicle is tapped and a cannulated pedicle screw is then passed down the dilators. 
     Although a specific type of spring has been described above for the vertebral disc annular fibrosis tensioning and lengthening device, the present invention contemplates any suitable linearly expandable link suitable for the purposes described herein. The link exerts a force creating a stress tension effect within the disc allowing it to regenerate according to Wolff&#39;s law. The link also allows parallel distraction of the disc, distraction along the coronal plane of the disc tissue, and puts the annulus fibrous in tension and provides torsional rotation of the vertebral construct. Further, the pedicle screws can be replaced with any suitable mounting member. By a more general description, the vertebral disc annular fibrosis tensioning and lengthening device includes a caudal vertebral body attachment member and a cephalad vertebral body attachment member having a non-rigid interconnection member therebetween that creates the tension stress effect on the annulus fibrosis. The posterior ring  42  acts as a rigid member coupled between the attachment members that also operates to provide the distractive force. 
       FIG. 9  is a perspective view and  FIG. 10  is a cross-sectional view of a vertebral disc annular fibrosis tensioning and lengthening device  80 , according to another embodiment, that illustrate other designs that provide the annular fibrosis tensioning and lengthening and restore the natural lordosis of the spine in the manner discussed above. The device  80  includes a pair of pedicle screws  82  each including a body portion  84  having a ball head  86 . The pedicle screw  82  also includes a pedicle screw head portion  88  having an internal threaded bore  90  through which the body portion  84  extends so that the ball head  86  is mounted on a shoulder  92  within the bore  90 , as shown. A collar  94  is threaded into the internal bore  90  of the pedicle screw head portion  88  and engages a slot  96  in the ball head  86  to rigidly hold the body portion  84  in place at a proper kyphotic angle. The body portion  84  includes an internal bore  98  that accepts the Jamshidi needle for the reasons discussed above. 
     When the pedicle screws  82  are properly placed in the vertebrae during the surgical procedure, a plate connector  100 , shown separated from the device  80  in  FIG. 11 , is positioned over the pedicle screw head portions  88  so that holes  102  and  104  in ends  108  and  110 , respectively, in the plate connector  100  line up with the bores  90  in the pedicle screw head portions  88 . Bolts  106  are then placed through the holes  102  and  104  and threaded into the threaded bores  90  in the pedicle screw head portions  88  to secure the plate connector  100  to the pedicle screws  82 . The plate connector  100  has a gradual U-shape, as shown, where the ends  108  and  110  are slightly angled upward to provide the proper orientation for the device  80  that sets the maximum distraction of the disc. 
     In order to provide the distraction, a U-shaped spring element  112 , shown separated from the device  80  in  FIG. 12 , is inserted between the pedicle screw head portions  88 , where legs  114  and  116  of the spring element  112  push against the head portions  88 , which cause the pedicle screw body portions  84  to pivot away from each other and cause the disc height to be restored in a lordotic manner. As the spring element  112  separates the pedicle screws  82  to provide the distraction, the pedicle screw head portions  88  pivot on the plate  100  to provide the desired distraction. Thus, the combination of the plate  100  and the spring element  112  provide the expandable and rigid link that operate in the manner as discussed above. 
       FIG. 13  is a perspective view of a vertebral disc annular fibrosis tensioning and lengthening device  120 , according to another embodiment, where like elements to the device  80  are identified by the same reference numeral. In the device  120 , the spring  112  and the plate  100  are combined or integrated into a single integrated element  122 . The plate part of the integrated element  122  is flat in this embodiment and includes end pieces  124  and  126  through which the bolts  106  are placed. The element  122  includes limit stops  128  and  130  that limit the amount of distraction of the disc and also prevent overloading during jumping and other high loading states. The spring part of the integrated element  122  includes a live spring element  132  that provide the disc distraction. In this embodiment, an increased spring effect is provided by a spring loop portion  134  that extends the length of the spring element  132  to increase the distractive force. 
     The device  120  also includes an optional wedge member  136  positioned between one of the screw head portions  88  and the integrated element  122 , as shown. The wedge  136  is placed by the surgeon to provide changes in both height and angulations simultaneously, if desirable. 
       FIG. 14  is a perspective view of a vertebral annular fibrosis tensioning and lengthening device  150 , according to another embodiment, where like elements to the devices  80  and  120  are identified by the same reference numeral. In this embodiment, the screw head portion  88  is replaced with a rounded screw head portion  152 . The screw head portion  152  includes a cylindrical cap portion  154  having an internal threaded bore  156 . A plate  158  is mounted to the cap portions  154  so that holes  160  and  162  in the plate  158  line up with the bores  156 . Bolts  164  are threaded into the bores  156  to secure the plate  158  to the screws  82 . A cylindrical spring element  168  having spaced apart slots  170  is positioned between the rounded screw head portions  152 , as shown, where the spring element  168  is held in place by the relative shape between the ends of the spring element  168  and the head portions  152 . The spring element  168  provides the distractive force and the plate  158  provides the pivot limiting force as described above. 
       FIG. 15  is a perspective view of a disc height restoration assembly  180  including a plurality of pedicle screws  182  each including a body portion  184  and a head portion  186 . The head portion  186  includes an open U-shaped channel  188  defining opposing side walls  190  and  192  that allow adjacent pedicle screws  182  to be positioned together, as shown. A clip member  194  is positioned over adjacent side walls  192  of adjacent pedicle screws  182  to clip the adjacent pedicle screws  182  together and provide a distracted force to the disc when the pedicle screws  182  are mounted to adjacent vertebrate. A spring element  196  is included. 
       FIG. 16  is a side view,  FIG. 17  is a top view,  FIG. 18  is a blown-apart perspective view and  FIG. 19  is a cross-sectional perspective view of a vertebral disc annular fibrosis tensioning and lengthening device  200 , according to another embodiment. The device  200  is operable to provide the disc tensioning and lengthening as discussed above to restore the natural lordosis of the spine. The device  200  includes a pair of pedicle screws  202  each having a body portion  204  and a ball head  206 . An internal bore  208  extends through the body portion  206  and the ball head  206  to accept a K-wire as discussed above. The device  200  also includes a screw head portion  210  having an internal threaded bore  212 .  FIG. 20  is a perspective view of one of the pedicle screws  202  and one of the screw head portions  210  separated from the device  200 . The body portion  204  of the screw  202  is inserted through a top end of the internal bore  212  until the ball head  206  rests against a narrowed shoulder  214  in the head portion  210  that allows the pedicle screw  202  to be pivoted relative to the screw head portion  210 , as discussed above. The screw head portion  210  further includes a lateral cavity  216  that accepts a spring, as will be discussed in detail below. The screw head portion  210  also includes a concave shaped top surface  218  also provided for reasons that will become apparent for discussion below. 
     The vertebral disc annular fibrosis tensioning and lengthening device  200  also includes a screw connector  220  shown separated from the device  200  in  FIG. 21 . The connector  220  includes a top plate  222  and opposing side plates  224  and  226 , as shown. A support member  228  is connected to the opposing side plates  224  and  226  opposite to the top plate  222 . In other words, the plates  224  and  226  are interconnected with a cross-link from a construct on one side of the spinal cord to the other. The connector  220  includes a first opening  230  provided in a convex shaped portion  232  at one end of the top plate  222  and a second opening  234  provided in a convex shaped portion  236  at an opposite end of the top plate  222  for reasons that will become apparent from the discussion below. The top plate  222  also includes a slot  240  through which a wedge  238  is inserted into the device  200  to adjust a spring travel, as will also be discussed below. 
     The device  200  also includes a pair of bolts  260 , where one of the bolts  260  is shown separated from the device  200  in  FIG. 22 . The bolt  260  includes a bolt body  262  and a bolt head  264 . An internal bore  266  extends through the bolt  260  and aligns with the bore  208  in the pedicle screw  202 . A half-mooned shaped collar  268  including an opening extending therethrough is positioned around the bolt body  262  just below the bolt head  264  of the bolt  260 , as shown. 
     The device  200  also includes a spring assembly  270  shown separated from the device  200  in  FIG. 23 . The spring assembly  270  includes a base portion  272  having a bore  274  therein. The spring assembly  270  also includes a plunger  276  having a cylindrical body portion  280  and a head portion  278 . A compressible spring member  282  including an internal bore  284  is provided between the head portion  278  and the base portion  272  where the body portion  280  extends through the bore  284  and into the bore  274 , as shown. A compression force between the plunger  276  and the base portion  272  causes the head portion  278  to push against the spring member  282  so that the body portion  280  extends farther into the channel  274 . 
     The device  200  is assembled so that the pedicle screws  202  are pivotally mounted within the screw head portions  210  and the spring member  282  is positioned within the opposing cavities  216  of the head portions  210  so that the head portion  278  of the plunger  276  is in one of the cavities  216  and the base portion  272  is in the other cavity  216  of the other screw head portion  210 . The connector  220  is then positioned over the screw head portions  210  so that the side plates  224  and  226  are provided at sides of the screw head portions  210  and the top plate  222  covers the cavities  216  to hold the spring assembly  270  within the device  200 . In this configuration, the shape of the concave shaped portions  232  and  236  conforms to the concave surfaces  218  of the screw head portions  210 . The bolts  260  are then threaded into the threaded openings  212  through the openings  230  and  234  to hold the connector  220  to the screw head portions  210 . A bottom end of the bolts  260  is rounded to conform with the shape of the ball heads  206 . Thus, the ball heads  206  can rotate within the screw head portions  210  on the shoulders  214 . When the bolts  260  are threaded into the openings  212 , the half-moon portions  268  conform to an upper surface of the concave portions  232  and  236 . Thus, the connector  220  provides the non-compressible link and the spring assembly  270  provides the compressible link as discussed above to provide the disc distraction and regeneration. The wedge  238  can be driven through the hole  240  to conform with the head portion  278  of the plunger  276  to reduce the travel of the spring  282  if desired. 
     In addition to the pedicle screw  202  being able to pivot relative to the screw head portion  210 , the assembly of the pedicle screw  202 , the screw head portion  210  and the bolt  260  can pivot relative to the connector  220 .  FIG. 25  is a cross-sectional view of the device  200  with the spring assembly  270  removed and  FIG. 24  is a side view of the device  200  showing this feature. As is apparent, the orientation and shaping of the concave surfaces  218  on the screw head portion  210 , the concave shaped portions  232  and  236  of the plate connector and the half-moon shape of the collars  268  allow the spring head portions  210  and the collars  268  to pivot relative to the connector  222  when the bolt  260  is threaded into the threaded bore  212 . 
     The foregoing discussion discloses and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the spirit and scope of the invention as defined in the following claims.