Abstract:
An anterior thoracic/lumbar system comprising a thin plate and fasteners for securing the plate to vertebrae or other osseous material. The plate may be hinged along the central axis, with a pair of collinear holes on each portion of the plate. Each of the holes accommodates a bolt which is screwed into the vertebrae and secured to the plate using a nut.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims benefit from U.S. Provisional Patent Application Serial No. 60/279,157, filed Mar. 27, 2001, which application is incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates generally to devices for use in spinal surgery, and, in particular, to a hinged anterior thoracic/lumbar plate which is implantable within a patient for stabilization of the spine.  
           [0004]    2. Description of the Related Art  
           [0005]    Eighty-five percent of the population will experience low back pain at some point. Fortunately, the majority of people recover from their back pain with a combination of benign neglect, rest, exercise, medication, physical therapy, or chiropractic care. A small percent of the population will suffer chronic low back pain. The cost of treatment of patients with spinal disorders plus the patient&#39;s lost productivity is estimated at 25 to 100 billion dollars annually.  
           [0006]    Seven cervical (neck), 12 thoracic, and 5 lumbar (low back) vertebrae form the normal human spine. Intervertebral discs reside between adjacent vertebra with two exceptions. First, the articulation between the first two cervical vertebrae does not contain a disc. Second, a disc lies between the last lumbar vertebra and the sacrum (a portion of the pelvis).  
           [0007]    Motion between vertebrae occurs through the disc and two facet joints. The disc lies in the front or anterior portion of the spine. The facet joints lie laterally on either side of the posterior portion of the spine. The osseous-disc combination of the spine coupled with ligaments, tendons, and muscles are essential for spine function. The spine allows movement (flexation, lateral bending, and rotation), supports the body, and protects the spinal cord and nerves.  
           [0008]    The disc changes with aging. As a person ages the water content of the disc falls from approximately 85 percent at birth to 70 percent in the elderly. The ratio of chondroitin sulfate to keratin sulfate decreases with age. The ratio of chondroitin 6 sulfate to chondroitin 4 sulfate increases with age. The distinction between the annulus and the nucleus decreases with age. These changes are known as disc degeneration. Generally disc degeneration is painless.  
           [0009]    Premature or accelerated disc degeneration is known as degenerative disc disease. A large portion of patients suffering from chronic low back pain is thought to have this condition. As the disc degenerates, the nucleus and annulus functions are compromised. The nucleus becomes thinner and less able to handle compression loads. The annulus fibers become redundant as the nucleus shrinks. The redundant annular fibers are less effective in controlling vertebral motion. The disc pathology can result in: 1) bulging of the annulus into the spinal cord or nerves; 2) narrowing of the space between the vertebrae where the nerves exit; 3) tears of the annulus as abnormal loads are transmitted to the annulus and the annulus is subjected to excessive motion between vertebrae; and 4) disc herniation or extrusion of the nucleus through complete annular tears. Disc herniation can also cause arthritis of the facet joints, which, in turn, may cause back pain.  
           [0010]    The problems created by disc degeneration, facet arthritis, and other conditions such as spondylolysis, spondylolisthesis, scoliosis, fracture, tumor, or infection are frequently treated by spinal fusion. Such problems may include pain in the back or legs, nerve injury, risk of future nerve injury, or spinal deformity. The goal of spinal fusion is to successfully “grow” two or more vertebrae together. To achieve this, bone from the patient&#39;s body (spine or iliac crest) or from cadavers is grafted between vertebrae. Alternatively, bone graft substitutes, such as hydroxyapatite and bone morphogenetic protein, may be used. The bone graft is placed between the vertebrae in the disc space and/or over the posterior elements of the vertebrae (lamina and transverse processes). The surgeon scrapes the vertebrae to create bleeding. Blood flows into the bone graft. The scraped bone, blood clot (hematoma), and the bone graft simulates a fracture. As the patient heals, the “fracture” causes the vertebrae to be fused and heal together.  
           [0011]    Spinal instrumentation may be placed onto or into the spine to immobilize the vertebrae that are going to be fused. Immobilization leads to a higher fusion rate and speeds a patient&#39;s recovery by eliminating movement. The use of spinal fixation plates or rods for correction of spinal deformities and for fusion of vertebrae is well known. Typically, a rigid plate is positioned to span bones or bone segments that need to be immobilized with respect to one another. Bone screws may be used to fasten the plate to the bones. Spinal plating systems are commonly used to correct problems in the lumbar and cervical portions of the spine, and are often installed posterior or anterior to the spine.  
           [0012]    One technique of treating these disorders is known as surgical arthrodesis of the spine. This can be accomplished by removing the intervertebral disk and replacing it with bone and immobilizing the spine to allow space to connect the adjoining vertebral bodies together. The stabilization of the vertebrae to allow fusion is often assisted by a surgically implanted device to hold the vertebral bodies in proper alignment and allow the bone to heal, much like placing a cast on a fractured bone. Such techniques have been effectively used to treat the above described conditions and in most cases are effective at reducing the patient&#39;s pain and preventing neurologic loss of function.  
           [0013]    Several types of anterior spinal fixation devices are currently in use. One technique involves placement of screws completely through the vertebral body, called bicortical purchase. The screws are placed through a titanium plate but are not attached to the plate. This device is difficult to place, and over-penetration of the screws can result in damage to the spinal cord. The screws can back out of the plate into the surrounding tissues as they do not fix to the plate. Several newer generation devices have used a unicortical purchase of the bone, and in some fashion locking the screw to the plate to provide stability and secure the screw from backout. Problems have resulted from over rigid fixation and stress shielding, resulting in nonunion of the bony fusion, chronic micromotion during healing, resulting in stress fracture of the fixation device at either the screw to the plate resulting in screw backout, or inadequate fixation strength and resultant collapse of the graft and angulation of the spine.  
           [0014]    Another technique involves formation of a medical construct using surgical rods and connectors. Such systems include a pair of rods which are placed on opposite sides of the portion of the spine which is intended to be fused. Pedicle, lateral, and oblique mounting means are used to secure the rods relative to the desired portion of the spine which will be fused by the fixation system. However, this construct extends outwardly further than a plate/screw system, potentially affecting the surrounding muscle, and causing pain to the patient.  
           [0015]    Plates and screws are often placed onto the anteriolateral portion of the spine to facilitate spinal fusion. Generally, they are placed across one or two disc spaces in the treatment of fractures and tumors. Most of the present systems use screws with nuts for the posterior portion of the vertebrae. The screws with nuts are commonly called bolts by those skilled in this art. Screws, without nuts, are placed through the anterior portion of the plate. The posterior bolts are generally thought to rigidly fix the plate to the screws. Some surgeons believe that the rigid bolt/plate construct provides more spinal stability. However, while screws without nuts are easier to insert, they also are known to back out, causing potential failure of the fusion. Devices have been devised to hold the screws within the plate. It is believed that there are no systems in the marketplace which uses an all bolt construct.  
           [0016]    A typical device which is used for spinal fixation is taught in U.S. Pat. No. 4,611,581. This device consists of a simple plate having a series of openings for receiving threaded portions of force transmitting members which securely lock in a part of the bone of the vertebra in which they are mounted and a threaded portion which projects outwardly from the vertebrae. The vertebra is pulled into the desired relationship with adjacent vertebrae by tightening a nut on the outwardly projecting end portion of the force transmitting member.  
           [0017]    Another typical device used is shown in U.S. Pat. No. 6,306,136. This patent discloses an implant which is used particularly as an anterior cervical plate, having a solid plate consisting of two sliding parts, each of which has holes for anchoring screws in two adjacent vertebrae. The sliding parts are provided with a screw and slot for limiting the sliding travel between the parts.  
           [0018]    Another vertebrae connecting plate is taught in U.S. Pat. No. 5,147,361. This plate has a small thickness, and uses set screws which are screw engaged in threaded holes within the connecting plate to prevent any loosening of the screws within the plate.  
         SUMMARY OF THE INVENTION  
         [0019]    It is therefore an object of the present invention to provide a plate system for spinal surgery, which has a low profile and comfortably fits a patient&#39;s anatomy.  
           [0020]    It is a further object of the present invention to provide a plate system which is easily implanted within a patient.  
           [0021]    It is a further object of the present invention to provide a plate system which is easily positioned and establishes a secure connection between vertebrae.  
           [0022]    It is still a further object of the present invention to provide a plate system that is top loading and top tightening.  
           [0023]    It is a still further object of the present invention to provide a plate system which is easily adaptable to the lumbarithoracic region of the spine.  
           [0024]    These and other objects and advantages of the present invention will be readily apparent in the description that follows. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    [0025]FIG. 1 is a lateral view of a prior art spinal plate installed in vertebrae of a spine;  
         [0026]    [0026]FIG. 2 is an anterior to posterior view of the plate shown in FIG. 1;  
         [0027]    [0027]FIG. 3 is an exploded lateral view of the plate and associated devices shown in FIG. 1;  
         [0028]    [0028]FIG. 4 is an end view of the plate and devices of FIG. 3 in the assembled position;  
         [0029]    [0029]FIG. 5 is a perspective partially assembled view of the spinal plate of the present invention along with C-rings;  
         [0030]    [0030]FIG. 6 is another perspective partially assembled view of the system of FIG. 5 along with locking nuts;  
         [0031]    [0031]FIG. 7 is a perspective view of the spinal plate system of FIG. 5 in its assembled position;  
         [0032]    [0032]FIG. 8 is a lateral view of the plate system of the present invention with two bolts installed;  
         [0033]    [0033]FIG. 9 is a lateral view of the plate system of the present invention during the installation of two C-rings;  
         [0034]    [0034]FIG. 10 is a lateral view of the plate system of the present invention with the nut installed on the lower posterior bolt;  
         [0035]    [0035]FIG. 11 is a lateral view of the plate system with the two posterior bolts installed;  
         [0036]    [0036]FIG. 12 is a lateral view of the plate system with C-rings for the anterior bolts;  
         [0037]    [0037]FIG. 13 is a lateral view of the plate system of the present invention completely installed;  
         [0038]    [0038]FIG. 14 is a sectional view of the system shown in FIG. 13;  
         [0039]    [0039]FIG. 15 is a fragmentary view of an anterior hole of plate of the present invention showing the beveled orientation through the plate;  
         [0040]    [0040]FIG. 16 is a lateral view of the plate system having slotted holes on the anterior section of the plate;  
         [0041]    [0041]FIG. 17 is a lateral view of an alternative embodiment of the plate system of the present invention;  
         [0042]    [0042]FIG. 18 is a side view of the plate shown in FIG. 17 partly in phantom;  
         [0043]    [0043]FIG. 19 is a cross-sectional view of the plate shown in FIG. 17;  
         [0044]    [0044]FIG. 20 is a plan view of a plate of the present invention which is angled for use on a kyphotic spine;  
         [0045]    [0045]FIG. 21 is a plan view of a plate of the present invention which is angled for use on a lordotic spine; and  
         [0046]    [0046]FIG. 22 is a plan view of another embodiment of a spine plate according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0047]    FIGS.  1 - 4  represent a common prior art method currently used for spinal stabilization. Referring now to FIGS. 1 and 2, there is shown a spinal plate  10  which has been placed across several vertebrae  12 ,  14 . Plate  10  contains a series of openings  16  which are intended to receive bone anchoring hardware. As can be clearly seen in FIG. 1, two of openings  16  are positioned against vertebra  12 , while two of openings  16  are positioned against vertebra  14 . A bone graft  18  which replaced a vertebra is positioned between vertebrae  12 ,  14 .  
         [0048]    Most prior art spinal plate systems use a combination of screws and bolts to attach spinal plates to the posterior portion of the vertebrae. Referring again to FIG. 1, a pair of screws  20 , having a threaded section  21 , are installed through the anterior portion of plate  10 , while a pair of bolts  22  are installed through the posterior portion of plate  10 . Each bolt  22  consists of a lower threaded section  23  and an upper threaded post  24  which is affixed in position by a nut  26 . The threaded sections of  21 ,  23  of screws  20  and bolts  22  are anchored into the bone of vertebrae  12 ,  14 . When placed within the spine, bolts  22  and screws  20  converge to resist pull-out, as can be clearly seen in FIG. 4. This combination is believed to provide more spinal stability, as bolts rigidly affix the spinal plate to the screws, which are much easier to insert in the procedure.  
         [0049]    Most spinal plates available today use only screws, or the screw/bolt combination. In addition, as screws sometimes have a tendency to back out of the bone, devices are available to secure the screws in place.  
         [0050]    Referring now to FIGS.  5 - 7 , a hinged spinal plate system, generally designated at  30 , which embodies the principles of the present invention, is shown. This system is ideally suited for use in the lumbar/thoracic portion of the spinal column.  
         [0051]    Plate system  30  includes a thin plate  32  having two plate elements  32   a ,  32   b  which are removably coupled together along a hinged section  34 . Element  32   a , which contains generally rounded edges  35   a ,  35   b  and a cutaway section  35   c  has two generally circular through openings  36 , which are positioned collinearly along element  32   a . Element  32   b  also contains generally rounded edges  38   a ,  38   b  and a cutaway section  38   c , and has two generally circular through openings  40  positioned collinearly along element  32   b . Although openings  36 ,  40  are shown as circular in this embodiment, they may also consist of elongated slots. Cutaway sections  35   c ,  38   c  afford the surgeon a better view of the bone graft inserted between vertebrae, to insure that the bone graft is not projecting into the spinal cord or nerves. Plate  32  is generally constructed from an implant grade titanium alloy, such as Ti-6Al-4V, or possibly stainless steel ASTM F138.  
         [0052]    Along hinged section  34  of plate system  30  there is an opening  42  formed by a cutout section  42   a  in element  32   a  and a cutout section  42   b  in element  32   b . Opening  42  may be used if additional hardware is desired to increase the holding force of system  30  against the spine for greater stability, or to secure the bone graft.  
         [0053]    A series of bolts  50  are inserted through openings  36 ,  40  to secure plate  32  to the vertebrae. Bolts  50  contain a lower threaded portion  52  for threadedly engaging holes which are drilled into the appropriate vertebrae of the spine, and an upper threaded portion  54  which extends through plate  32  when it is in its proper location against the spine.  
         [0054]    A series of snap or C-rings  60  are used with bolts  50  to securely fasten plate  32  in its proper position. Snap or C-rings  60  are clipped onto upper threaded position  54  of bolts  50  after lower threaded portion  52  has been anchored within the appropriate vertebrae. Finally, a series of nuts  62  are threaded onto upper threaded portion  54  of bolts  50  to secure plate  32  in its proper position. It is possible that ordinary washers could be used in place of the C-rings with plate system  30 .  
         [0055]    The proper use of hinged plate system  30  is shown clearly in FIGS.  8 - 11 . Referring now to FIG. 8, a bone graft  63 , which replaces a removed vertebra, is inserted between vertebrae, and after the appropriate size of plate  32  has been selected, two bolts  50  are affixed within the appropriate vertebrae. Using openings  40  as a guide, a pair of holes are drilled into the vertebrae at a 15 degree anterior angulation, and bolts  50  are screwed into place through plate  32  to ensure that bolts  50  are placed in the proper location. The upper bolt  50  shown in FIG. 8 is preferably placed into the cephalad portion of opening  40  to allow for compression.  
         [0056]    It is conceivable that other fastening systems could be used to secure plate  32  to the spine. For example, several two part screw systems having an outer vertebral screw and a locking inner screw are taught in a patent application entitled ANATOMIC POSTERIOR LUMBAR PLATE, filed in the name of Bret A. Ferree on the same day as this application, and hereby incorporated by reference in its entirety, may be used in place of bolts  50  in the present invention, as these two part screws create a “bolt” as understood in relation to the present invention.  
         [0057]    Next, posterior element  32   b  of plate  32  is flipped upwardly away from the vertebrae, as shown in FIG. 4, or plate  32  may be removed, and snap rings  60  are applied to upper threaded portion  54  of bolts  50  to secure them in place. Plate  32  is then repositioned over the two bolts  50  which have been secured in place within the vertebrae. Nut  62  is then tightened onto lower bolt  50 , as can be seen in FIG. 10. The wrench used to tighten nut  62  onto lower bolt  50  is preferably cannulated to allow insertion of a screwdriver while tightening to prevent rotation of bolt  50  while nut  62  is threaded onto upper threaded portion  54  until it is tight against plate  32 . While compressing graft material, which has been inserted between the vertebrae, nut  62  is placed upon upper threaded portion  54  of upper bolt  50  and securely tightened against plate  32 .  
         [0058]    Holes for bolts  50 , which pass through openings  36 , are now drilled using the openings as a drill guide (FIG. 10). Bolts  50  can then be affixed into place through element  32   a  of plate  32  (FIG. 11). Element  32   a  is then flipped upwardly, as can be seen in FIG. 12, and snap rings  60  are secured in place on upper threaded portion  54  of bolts  50 . Element  32   a  of plate  32  can now be returned to its proper position against the vertebrae and nuts  62  are tightened to completely secure plate  32 . Alternatively, openings  40  within element  32   b  may be beveled, as can be seen in FIG. 15, such that element  32   a  can be lifted slightly while located on upper threaded portion  54  of bolt  50  and snap ring  60  inserted below plate  32  onto bolt  50 . This is clearly seen in FIG. 15. Optionally, another screw  70  can be inserted through opening  42  into bone graft  63  (or a cage if it has been inserted).  
         [0059]    [0059]FIG. 14 is a sectional view of a vertebra on which hinged plate system  30  has been installed. Bolts  50  can be seen penetrating the vertebra. The relative angularity between bolts  50  provides the proper force to securely hold plate system  30  in the proper orientation to promote healing. In addition, hinged section  34  assists to contour plate  32  to the convexity of the vertebrae, allowing plate  32  to more completely contact the vertebral surface.  
         [0060]    Other modifications can be made to plate  32  in order to simplify the installation process. For example, FIG. 16 shows plate  32  where openings  40  in element  32   a  are slotted toward rounded edges  35   a ,  35   b  such that element  32   a  can be easily flipped upwardly.  
         [0061]    An alternate embodiment of the spinal plate system of the present invention is shown in FIGS.  17 - 22 . Referring now to FIGS. 17 and 18, a spinal plate system, as indicated at  100 , is shown mounted in position on the spinal column of a patient. A unitary flat plate  102 , having a plurality of slots  104   a - e , is fastened at vertebrae  106 ,  108 , in a fashion as previously described, by a plurality of bolts  110 . A bone graft  112  is located between plate  102  and the spinal column. Plate  102  contains cutaway edge portions  113   a ,  113   b  to allow the surgeon to visualize the bone graft easily. Bolts  110 , which are shown mounted through slots  104   a - d , are held in place by a plurality of snap-rings  114 . Central slot  104   e  located in the central region of plate  102  may be used for an additional screw or bolt through a central vertebra or bone graft. In addition, the bottom surface of plate  102  may contain a friction surface to allow better contact with the bone structures.  
         [0062]    [0062]FIG. 19 shows a cross-sectional view of the plate of FIG. 17. Plate  102 , which is approximately 7 mm in thickness, is curved to allow for better contact with the vertebral surface. Also, anterior slot  104   a , which is approximately 7 mm in width, lies perpendicular to the upper and lower surfaces of plate  102 , while posterior slot  104   b , also approximately 7 mm in width, is angled approximately  150  anteriorly. The range of lengths available for plate  102  are from 60 mm to 110 mm, while the width across plate  102  at its widest portion is approximately 20 mm. The width across cutaway sections  112   a ,  112   b  is approximately 12 mm.  
         [0063]    Plate  102  can be shaped to more easily fit the spinal shape when used in different areas. FIG. 20 shows plate  102  which is angled 15° in the forward direction to compensate for kyphotic conditions, while FIG. 21 shows plate  102  which is angled 15° in the reverse direction to compensate for lordotic conditions. Finally, a shorter plate  102  is shown in FIG. 22, which may be used in situations where longer plates cannot be used or are not necessary.  
         [0064]    While the present invention has been shown and described in terms of preferred embodiments thereof, it will be understood that this invention is not limited to any particular embodiment, and that changes and modifications may be made without departing from the true spirit and scope of the invention as defined in the appended claims.