Abstract:
A method for providing vertebral disc annular fibrosis tensioning and lengthening that restores the loss of disc height and provides disc regeneration. In one non-limiting embodiment, the method includes inserting pedicle screws into the vertebral bodies of adjacent vertebra and positioning a spring in compression between and in contact with the pedicle screws so that the spring bias forces the pedicle screws apart to provide a distractive force that increases the height of the disc space and promotes the disc regeneration.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation 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 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates generally to a method for providing vertebral disc annular fibrosis tensioning and lengthening and, more particularly, to a method for providing vertebral disc annular fibrosis tensioning and lengthening device that includes mounting pedicle screws in opposing vertebra and positioning a spring member in compression between the pedicle screws so as to provide a distractive force to the vertebra. 
         [0004]    2. Discussion of the Related Art 
         [0005]    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 back can bend and rotate. 
         [0006]    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 unyielding, the preferred contemporary treatments are primarily surgical, particularly fusion and/or disc replacement. 
         [0007]    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. 
         [0008]    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. 
         [0009]    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 taller 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. 
         [0010]    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. 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. 
       SUMMARY OF THE INVENTION 
       [0011]    In accordance with the teachings of the present invention, a method for providing vertebral disc annular fibrosis tensioning and lengthening is disclosed that restores the loss of disc height and provides disc regeneration. In one non-limiting embodiment, the method includes inserting pedicle screws into the vertebral bodies of adjacent vertebra and positioning a spring in compression between and in contact with the pedicle screws so that the spring bias forces the pedicle screws apart to provide a distractive force that increases the height of the disc space and promotes the disc regeneration. 
         [0012]    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 
         [0013]      FIG. 1  is a perspective view of a pedicle screw employed in a vertebral disc annular fibrosis tensioning and lengthening device of the invention; 
           [0014]      FIG. 2  is a perspective view of a spring employed in the vertebral disc annular fibrosis tensioning and lengthening device of the invention; 
           [0015]      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; 
           [0016]      FIG. 4  is a cross-sectional side view of the vertebral disc annular fibrosis tensioning and lengthening device shown in  FIG. 3 ; 
           [0017]      FIG. 5  is a top view of the vertebral disc annular fibrosis tensioning and lengthening device shown in  FIG. 3 ; 
           [0018]      FIG. 6  is a perspective view of a vertebral disc annular fibrosis tensioning and lengthening device, according to another embodiment of the present invention; 
           [0019]      FIG. 7  is a side view showing a vertebral disc annular fibrosis tensioning and lengthening device of the invention inserted within adjacent vertebrae; 
           [0020]      FIG. 8  is a top view of two vertebral disc annular fibrosis tensioning and lengthening devices of the invention inserted within the adjacent vertebrae; 
           [0021]      FIG. 9  is a side view of a vertebral disc annular fibrosis tensioning and lengthening device, according to another embodiment of the present invention; and 
           [0022]      FIG. 10  is a top view of a spring member for the vertebral disc annular fibrosis tensioning and lengthening device shown in  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0023]    The following discussion of the embodiments of the invention directed to a method for providing vertebral disc annular fibrosis tensioning and lengthening is merely exemplary in nature, and is in no way intended to limit the invention or its applications or uses. 
         [0024]      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 ) of the invention. 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 align the pedicle screw  10 , 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  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, as would be well understood to those skilled in the art. 
         [0025]      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 of the invention. 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. An example of a suitable alloy includes about 50% nickel and about 50% titanium. 
         [0026]      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 of the present invention. 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. The diameter of the spring  32  can be any diameter suitable for the purposes described herein. 
         [0027]    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. 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. The spring  30  operates as a compressible link and the posterior ring  42  operates as a rigid link. 
         [0028]      FIG. 6  is a perspective view of a vertebral disc annular fibrosis tensioning and lengthening device  50 , according to another embodiment of the present invention, 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 . 
         [0029]      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. 
         [0030]    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. Further, multiple devices  40  can be provided between a series of adjacent vertebra to provide an expansive force to more than one disc. 
         [0031]    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. 
         [0032]    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. 
         [0033]    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 Wolffs law. The link also allows parallel distraction of the disc, distraction along the coronal plane of the disc tissue, puts the annulus fibrous in tension and provides torsional rotation of the vertebral construct. Also, the tensioning of the annular fibrosis in the manner as described above provides uniform distraction distances within the sagittal plane of the disc. Further, the pedicle screws can be replaced with any suitable mounting member. 
         [0034]    By a more general description, the vertebral disc annular fibrosis tensioning and lengthening device includes a caudle vertebral body attachment member and a cephelad 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. 
         [0035]      FIG. 9  is a side view of a vertebral disc annular fibrosis tensioning and lengthening device  80 , according to another embodiment of the present invention. The device  80  includes pedicle screws  82  each having a screw body  84  and a screw head  86 . An annular mounting portion  88  is provided between the screw head  86  and the screw body  84 . The device  80  also includes a spring member  90  having a spring  92  and end plates  94  and  96 .  FIG. 10  is a top view of the spring member  90 . The spring  92  can be any suitable spring, such as a helical spring. Holes  98  and  100  are provided through the end plates  94  and  96 , respectively. A U-shaped coupling member  102  is attached to the end plate  94  and a U-shaped coupling member  104  is attached to the end plate  96 . The U-shaped coupling members  102  and  104  have a size that conforms to the diameter of the annular mounting portion  88 . The surgeon will use a suitable tool (not shown) that is inserted in the holes  98  and  100  to compress the spring  92  and position the U-shaped coupling members  102  and  104  around the annular mounting portions  88  so as to provide a separation force to the pedicle screws  82  for the reasons discussed above. 
         [0036]    As discussed above, the pedicle screws  10  include the holes  24  for facilitating bone growth therein. Such a concept eliminates or reduces the halo around the known pedicle screws that reduces the joining of the screw to the bone. With the holes  24 , the screw will act more like natural bone and increase the integrity of the bonding between the screw and the vertebra. 
         [0037]    The holes  24  are one example for accepting bone growth in a surgical screw. Other configurations can also be employed for pedicle screws, and for other screws permanently placed in a bony structure to provide bone interdigitation. Suitable examples include an non-smooth or porous surface on the screw body, interdigitation cavities formed by the addition of sintered beads on the outside of the screw body, interdigitation cavities formed by laser processing, interdigitation cavities formed by machining grooves, a roughened surface provided by sand blasting, a hydroxyapetite coating, etc. Further, the screws are not limited to pedicle screws, but can be screws for other surgical applications, such as maxio-facial applications, hip fractures, podiatric fusions and fraction repair, periarticular fracture fixation, arthroplasty device anchoring, long bone fracture repair, cervical fusion construct anchoring, tendon anchoring, etc. 
         [0038]    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.