Abstract:
A spinal-fixation system comprises a dual parallel bridging that runs along a posterior length of the spine and is anchored with cables looped through a dorsal corner of the spinal canals of respective adjacent vertebrae.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to surgical methods and devices to stabilize vertebra, and more particularly to plates and rods anchored by cables for immobilizing human spine vertebrae. 
     2. Description of Related Art 
     Degenerative disc disease accounts for more than 100,000 low back spinal fusion procedures in the United States annually, according to Columbia, Colo. hospitals. The intervertebral disc is a pad of cartilage-type material situated between spinal bones. Each disc serves as a connector, spacer, and shock absorber for the spine. A soft, jelly-like center is contained by outer layers of fibrous tissue. Healthy discs help allow normal turning and bending. Trauma or injury to the spine can cause discs to tear, bulge, herniate, and even rupture. This can be quite painful, as the soft center of the disc leaks, putting pressure on the adjacent nerve roots and spinal cord. 
     A damaged disc can cause nerve dysfunction and debilitating pain in the back, legs and arms. Typical treatments that provide relief and allow patients to function again include back braces, medical treatment, physical therapy and surgery to remove the disc. A conventional surgical solution removes the bad disc and promotes new bone growth in the space to fuse the adjacent vertebrae together. 
     One conventional approach implants one or more metal rods to bridge across a damaged portion of the spine. Such rods lock the bridged-over spinal vertebrae so they cannot twist or flex on their intervertebral discs. In some cases, such discs may have been removed and the object of the spinal fixation is to promote bone growth that fuses the vertebrae together. Such a system is described by Erik Wagner, et al., in U.S. Pat. No. 5,989,250, issued Nov. 23, 1999. Bone hooks and bone screws secured to individual vertebrae serve as anchors for a bridging spinal-rod. The rods are dressed to follow along the lamina inside the two parallel canals formed by the posterior spinous processes of each vertebrae. A similar system is described by Robert Howland in U.S. Pat. No. 5,030,220, issued Jul. 9, 1991. 
     DePuy AcroMed, a subsidiary of Johnson &amp; Johnson, markets several spinal-fixation systems and devices. For example, the ISOLA Spinal System is a rod-based, thoracic and lumbar multi-level fixation system. Dr. Kiyoshi Kaneda&#39;s Anterior Spine Stabilization System is another that is universally used for tumor and trauma spinal fixation. The ACROMED Cable System by Matthew Songer, MD, uses multi-strand cable for cervical, thoracic and lumbar fixation. The ACROPLATE Anterior Cervical System uses a titanium plate on the cervical anterior, and is secured with bi-cortial screws. 
     Edward Benzel, et al., describe a spinal column retainer in U.S. Pat. No. 5,800,433, issued Sep. 1, 1998. A pair of parallel fenestrated support rods are secured to each vertebrae with a middle plate. A number of holes in each plate allow bone screws to be used to secure the plate to the respective vertebrae. Such plates do not span between vertebrae, the rods do that. Set screws in the plates allow the plates to be locked to each rod, and thus will resist twisting and/or sliding. 
     Erik Wagner, et al., also describe in U.S. Pat. No. 6,030,389, issued Feb. 29, 2000, a bone plate device for human spine stabilization. Such plates are anchored with bone screws that are angled to one another so that they will bed deeply into the strongest bone material. 
     A direct rod-to-bone attachment screw is described by Robert Songer, et al., in U.S. Pat. No. 5,662,653, issued Sep. 2, 1997. A bone screw resembling an eye-bolt is screwed into the vertebrae and fenestrated support rod is threaded through the eye-loops. Clamps in the eye-loops open to receive the rods and lock them within. 
     All such bone screw dependent systems suffer from screw breakout and screw backout problems. Various ingenious techniques and devices have been developed to mitigate these problems, but cable-anchored approaches seem to be superior. 
     Some prior-art spinal-fixation systems pass loops of heavy cable or wire under the spinal lamina and through the spinal canal. This, of course, must be done without disturbing the nerves or spinal cord. There is a little spare room in the spinal canal not required by the spinal cord. Each thoracic vertebrae in the back, for example, has a vertebral canal with a small space in the posterior (dorsal) corner, adjacent to the lamina. There a cable can be safely passed through. But just forward of this is the spinal cord which is very delicate and absolutely cannot tolerate being squeezed or disturbed. 
     A surgical cable system and method is described by Erik Wagner, et al., in U.S. Pat. No. 6,053,921, issued Apr. 25, 2000. A metal crimp or collet is used to secure a cable in a loop. A tensioning device allows the cable to be tightened around vertebral bone. 
     The anchor wires of prior art spinal-fixation systems are conventionally twisted around opposite ends and the fenestrated support rods. Such can easily slip and twist on the usually smooth rods. The alternative anchor cables are multi-strand wires that cannot simply be twisted together. Various cable clamps and locks have been marketed commercially to secure such cables to the rods. A bone-banding cable is described by Leo Whiteside, et al., in U.S. Pat. No. 5,772,663, issued Jun. 30, 1998. 
     Once a cable has been passed, a device can be used to secure the cables like that described by Robert J. Songer, et al., in U.S. Pat. No. 5,116,340, issued May 26, 1992. Surgical cables looped through spinal vertebrae are conventionally secured by Songer crimping pliers. 
     All the United States Patents cited herein are incorporated by reference. Such Patents themselves cite many prior art patents and technical documents that will assist the reader in understanding and implementing embodiments of the present invention. These are lodged in the file wrappers of those Patents. 
     What is needed is a spinal-fixation system that combines thoracic and lumbar posterior plates or bars anchored with cables or wires that individually pass through the spinal canals of adjacent vertebrae. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a spinal-fixation system for immobilizing at least two adjacent thoracic or lumbar vertebrae. 
     Another object of the present invention is to provide a spinal-fixation system anchored with cables or wires that pass through the spaces of the spinal canal of adjacent vertebrae. 
     Briefly, a spinal-fixation system embodiment of the present invention comprises a dual parallel bridging that runs along a posterior length of the spine and is anchored with cables looped through a dorsal corner of the spinal canals of respective adjacent vertebrae. 
     An advantage of the present invention is that a spinal-fixation system is provided that securely immobilizes the spine of a patient. 
     Another advantage of the present invention is that a spinal-fixation system is provided that makes it safer and easier for a surgeon to immobilize damaged portions of the spine. 
     The above and still further objects, features, and advantages of the present invention will become apparent upon consideration of the following detailed description of specific embodiments thereof, especially when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A and 1B are right and left side diagrams representing the spine of a patient having a spinal implant embodiment of the present invention; 
     FIG. 2 is a cross-sectional view of a stabilization implant embodiment of the present invention similar to that shown in FIG. 1; 
     FIGS. 3A and 3B are partial cross-sectional diagrams of an embodiment of the present invention that attaches anchoring cables directly to fenestrated support rods; 
     FIG. 4 is a perspective diagram of a spinal fixation system similar to that of FIGS. 3A and 3B; 
     FIGS. 5A and 5B are partial cross-sectional diagrams of an embodiment of the present invention that attaches anchoring cables with crimps; 
     FIG. 6 is a perspective diagram of a spinal fixation system similar to that of FIGS. 5A and 5B; and 
     FIG. 7 is an assembly diagram of a spinal fixation system in an alternative embodiment of the present invention that uses a smooth rod and cable anchors. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1A and 1B illustrate a spinal-fixation system embodiment of the present invention, and is referred to herein by the general reference numeral  100 . The spinal-fixation system  100  immobilizes portions of the human L 1 -L 5  lumbar vertebrae and T 1 -T 12  thoracic vertebrae as represented by a series of vertebrae  101 - 106 . C 1 -C 7  is also feasible. In FIG. 1, it is assumed that vertebrae  102 - 105  are to be immobilized relative to one another. As few as two adjacent such vertebrae could be immobilized by the system  100 , e.g., to promote intervertebral bone-fusion growth. FIG. 1A shows only the right-side half of the preferred system, and FIG. 1B shows the left-side half. The corresponding elements in each half are interchangeable, and so they are numbered alike. 
     A fenestrated rod or plate  108  is secured to each corresponding vertebrae  102 - 105  by a respective loop of cable  110 - 113 . Each such cable has a top tie portion  114  that is secured to the fenestrated rod or plate  108 , a superior-vertebral-notch portion  115 , a spinal canal portion  116 , an inferior-vertebral-notch portion  117 , and a bottom-tie portion  118 . If the cables  110 - 113  comprise single-strand wire, the top and bottom tie portions  114  and  118  may be secured by twisting them together. If the cables  110 - 113  comprise multi-strand cable, the top and bottom tie portions  114  and  118  may be secured by crimps and/or collets. 
     The fenestrated rod or plate  108  is constructed in one embodiment with a flat-bar stock having a series of cable holes. Such holes are spaced apart and occur at intervals that suit good cable anchor deployment. In other embodiments it is a metal rod with many transverse holes drilled through. 
     The approach and departure angles of cable portions  115  and  117  are preferably set to minimize wiggle and slack between the vertebrae  102 - 105  and the fenestrated rod or plate  108 . Preferred materials include surgical-grade stainless steel, titanium, and polyethylene. The flat-bar stock itself is preferably relieved of sharp edges on all corners and edges. The outside edges along the length may be necked together at a variety of strategic points to give clearance to posterior spinous processes. 
     The fenestrated rod or plate  108  is constructed in another embodiment with a rod stock having a series of clamp-on ears. Such ears have cable loop holes and are spaced apart on the rod to occur at intervals that suit good cable anchor deployment. Here too, the approach and departure angles of cable portions  115  and  117  are preferably set to minimize wiggle and slack between the vertebrae  102 - 105  and the fenestrated rod or plate  108 . Preferred materials include surgical-grade stainless steel, titanium, and polyethylene. 
     In FIG. 2, a spinal-fixation system  200  comprises a symmetrical pair of bridgings  202  and  204  that lie along a posterior length of a portion of the spine of a patient between spinous processes. A set of respective cables, represented by left and right cables  206  and  208 , secure the bridgings  202  and  204  to a corresponding thoracic, lumbar, or cervical vertebrae  210 . Such spinal-fixation system  200  is similar to the spinal-fixation system  100  of FIG. 1, and is shown here in cross-section to better illustrate the intended use. The cables  206  and  208  pass through a dorsal corner or sublaminar space of a spinal canal area  212  posterior to a spinal cord  214 . A disc  216  is shown anterior to the spinal canal area  212 . 
     FIGS. 3A and 3B represent a spinal-fixation system embodiment of the present invention, and is referred to herein by the general reference numeral  300 . The system  300  includes a smooth rod  302  that functions like the fenestrated rod or plate  108  in FIG. 1. A cable  304  is the equivalent of cables  110 - 113  in FIG. 1, and is used to secure the rod  302  directly, e.g., to vertebrae  102 - 105  in FIG.  1  and vertebrae  210  in FIG.  2 . The rod  302  has a number of tapered holes  306  that each capture a pair of collet halves  308  and  310 . Many such tapered holes can be disposed all along the length of the rod to give the surgeon ample choices for optimum cable anchoring angles. 
     FIG. 3A shows the collet halves  308  and  310  disassembled, as before installation. FIG. 3B shows them locked into the tapered hole  306  by virtue of mutual friction with cable  304  and a tension applied to it. In some applications, it is preferable to snip off any excess loose-ends of the cable  304 . In alternative embodiments of the present invention, it is preferable to capture the collet halves  308  and  310  inside the tapered hole  306  with a snap-ring. This would simplify the job of the surgeon by eliminating small loose pieces, and the cable could be simply pushed through one-way to be locked-in. A tensioner and cable-cutter would be used for final adjustment. 
     FIG. 4 illustrates a spinal-fixation system embodiment of the present invention, and is referred to herein by the general reference numeral  400 . It is similar to systems  100 ,  200 , and  300 . A fenestrated support rod  402  is shown with a single cable loop  404  that represents any number of such loops attached to a single rod. Other cable loops can also be included at other radial angles to band-capture spinous processes to the left or right, as well as looping through the spinal canal as shown in FIGS. 1A,  1 B, and  2 . A pair of collets  406  and  408  lock the cable tightly into the rod  404 . Crimps or set-screws could also be used. 
     FIGS. 5A and 5B represent a spinal-fixation system embodiment of the present invention, and is referred to herein by the general reference numeral  500 . The system  500  includes a fenestrated rod  502 . An anchoring cable  504  is used to immobilize each involved vertebrae (e.g., vertebrae  102 - 105  in FIG.  1  and vertebrae  210  in FIG. 2) through a hole  506 . Many such holes  506  can be disposed all along the length of the rod  502  to give the surgeon ample choices for optimum cable anchoring angles. A crimp  508  is used at each cable end. 
     FIG. 5A shows the various pieces disassembled, as before installation. FIG. 5B shows them assembled. In some applications, it is preferable to snip off any excess loose-ends of the cable  504 . A conventional tensioner and cable-cutter can be used for final adjustment. 
     FIG. 6 illustrates a spinal-fixation system embodiment of the present invention, and is referred to herein by the general reference numeral  600 . It is similar to systems  100 ,  200 , and  300 . A fenestrated support rod  602  is shown with a single cable loop  604  representative of any number of such loops attached to a single rod. Other cable loops can also be included at other radial angles to band-capture spinous processes to the left or right, as well as looping through the spinal canal as shown in FIGS. 1A,  1 B, and  2 . A pair of cable crimps  606  and  608  lock the cable tightly into the rod  604 . 
     FIG. 7 illustrates a spinal-fixation system embodiment of the present invention, and is referred to herein by the general reference numeral  700 . It is similar to systems  100 ,  200 ,  300 , and  600 . A smooth rod  702  with no cable-holes of its own has a number of cable anchors, represented by cable anchors  704  and  706 . These can be positioned anywhere along the smooth rod  702  and locked into position with set-screws or clamps. A cable  708  is looped around a vertebrae that is involved in a spinal immobilization procedure. The loose ends of cable  708  are passed through two holes provided and cinched with crimps  710  and  712 , or other suitable clips or connectors. A cable  714  is shown before being installed into the cable anchor  706 . 
     Although particular embodiments of the present invention have been described and illustrated, such is not intended to limit the invention. Modifications and changes will no doubt become apparent to those skilled in the art, and it is intended that the invention only be limited by the scope of the appended claims.