Abstract:
A device and a method for stabilizing lumbar and thoracic vertebra or individual bones in human spine or bone column is provided for the purpose of fixing a vertebra or individual bone with respect to other vertebra or individual bones and with respect to other parts of the spinal or bone column. While providing spinal stabilization, the stabilizer allows axial load sharing or construct dynamized action. The device allows the vertebra or individual bones to be held in compression allowing subsidence along the plate axis or to be fixed with respect to the plate for rigid stabilization. The vertebra or individual bones will be prevented from distraction by a stop lock clamp. The device may be configured as a fully or partially rigid system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent claims the benefit of U.S. provisional application Ser. No. 60/348,180 filed on Jan. 14, 2002 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     REFERENCE TO A MICROFICHE APPENDIX 
     Not Applicable 
     FIELD OF THE INVENTION 
     This invention relates to implant assemblies for use in stabilizing bone members to treat patients with ruptured or degenerated intervertebral bone discs and to replace vertebrae or individual bone bodies damaged by fracture, tumor or degenerative processes. Specifically, the invention relates to dynamized vertebral or individual bone implants and methods of implanting them to form a support in the spinal column or bone column and to promote fusion, healing, and bone growth in the human spine or bone column, incorporating an elongated member such as a plate. 
     BACKGROUND OF THE INVENTION 
     When surgery is needed, the discs are removed and replaced with grafts that will heal or fuse with the vertebra or individual bones. This implanted graft provides realignment and stabilization while healing takes place. Those surgeries that use implanted stabilizers, along with a graft are more successful than those that do not use a stabilizer. Surgeries that maintain compression between the vertebra or individual bones during healing are the most successful. 
     Devices that support all of the vertebra or individual bone&#39;s force leaving no force on the intervertebral or individual bone&#39;s graft are called “stress shielding” devices. Devices that support or share a portion of the spinal load in parallel with the graft are called “load sharing” devices. Devices that allow axial subsidence of the implant and support most of the load on the individual bone grafts are referred to as providing “dynamized” action. 
     The present invention allows the surgeon to select any of these three conditions at the time of surgery, by selecting the bone screw nut and positioning the stop Lock clamp. The present patent will restrict distraction, lateral translation, and rotational shear, reducing the stretching rupture and shear tearing of the forming nutrient blood vessels while allowing compression during the healing process. 
     SUMMARY OF THE INVENTION 
     The present patent relates to a spinal stabilizing device, and a method of implanting it on the posterior, or lateral side of the human spine or bone column. This device includes a rectangular shaped plate to allow axial subsiding motion without rotation or shear translation. The plate is for placement adjacent to and along the spinal or bone column, and having a longitudinal axis. The plate includes an open slot substantially parallel to the plate axis extending substantially the entire longitudinal dimension of the plate, leaving the plate ends the same thickness as the plate rails. The plate is raised above the individual bones by the thickness of a bone screw driving portion and the thickness of a plate guide. The stabilizer further includes a plate guide with two tubes attached to the plate guide and extending perpendicular to the plane of the plate guide and having inner diameters which slidably engage machine screws and outer diameters which will slidably engage the plate slot. The plate guide also including an “L” shaped extension, referred to as the outrigger arm extending perpendicular to and in the plane of the plate guide anteriorly, for placement of an anterior bone screw which is fixed to the plate guide through a locking means. This system also includes a bone screw having a bone threaded portion which engages the bone, a driving portion, and a machine thread stud portion extending through the plate guide tubes, so that the screw&#39;s driving portion abuts the vertebra or individual bones, and the machine thread portion engages the tubes and protrudes above the tubes. Also provided are two different nuts with a threaded hole extending through the body portion for threaded engagement with the machine threaded portion and a flange substantially concentric with the nut&#39;s thread. One nut includes an undercut and is referred to as a clamp nut, the second nut, which does not have an undercut, is referred to as a sliding nut. If a sliding nut is used it will clamp against the tube, leaving clearance between the plate and the plate guide allowing for dynamized motion. If a clamp nut is used, the nut will not contact the Tube, but will clamp the plate to the plate guide for rigid clamping. At the time of implantation the device is adapted to either rigidly fix the vertebra or individual bones or to allow selected axial subsiding action. Stop Lock clamps are provided to control the displacement of the plate with respect to the plate guides and to add torsional rigidity to the implant and improve pullout resistance by virtue of its orientation relative to the Posterior Bone Screws. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features, advantages, and objects will be evident from the following specification. 
     FIG. 1 is an isometric view of a two-level dynamized spinal stabilization system. 
     FIG. 2 is an isometric exploded view of a two-level dynamized spinal stabilization system. 
     FIG. 3 is a lateral view of a two-level dynamized spinal stabilization system with a lateral attachment to lumbar vertebra or individual bones. 
     FIG. 4 is an anterior cross-sectional view of a two-level dynamized spinal stabilization system with a lateral attachment to lumbar vertebra or individual bones and Bone Screws through the vertebra or individual bones, taken along the line  4 — 4  of FIG. 3 
     FIG. 5 is an axial cross-sectional view of a dynamized spinal stabilization system, taken along the line  5 — 5  of FIG.  3 . 
     FIG. 6 a  is an enlarged axial cross-sectional view of the circled area of FIG. 5 showing a sliding nut. 
     FIG. 6 b  is an enlarged axial cross-section view of the circled area of FIG. 5 showing a dynamized spinal stabilization system with a clamping nut. 
     FIG. 7 a  is an enlarged view of FIG. 6 a.    
     FIG. 7 b  is an enlarged view of FIG. 6 b.    
     FIG. 7 c  is an enlarged view of FIG. 5 showing an upper saddle clamp. 
     FIG. 8 a  is an axial cross-sectional view of a stop lock clamp, taken along the line  8 — 8  of FIG.  3 . 
     FIG. 8 b  is an enlarged view of FIG. 8 a.    
     FIG. 8 c  is a view of FIG. 8 b  showing an upper and lower stop lock saddle clamp 
     FIG. 9 a  is an isometric view of a plate guide with an optional boss. 
     FIG. 9 b  is an isometric view of the bottom of a plate guide showing two spikes. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     For the transfer of knowledge and an understanding of the principles of the present invention, the illustrated drawings and the specifications referenced will describe one specific size and embodiment of a working model of the dynamized stabilizer, which has been constructed for demonstration and reduction to practice. It will be understood that no limitation of the scope of the invention is intended. These specifications contain an organized, written description of the invention, and of the manner and process of making and using it. It is presented in such full, clear, concise, and exact terms as to enable any person skilled in the art of manufacturing and implantation of medical devices to make and use the stabilizer described in the best mode contemplated by the inventors. 
     The best mode material for the stabilizer is titanium alloy Ti-6AI-4V. It is the most bio-compatable of all metals due to its total resistance to attack by human and animal body&#39;s. It also has high strength, low density, flexibility, low modulus of elasticity, and a low thermal coefficient of expansion. Other advantages of this material are its decreased interference with metal detectors and with magnetic resonance imaging (MRI) used for postoperative evaluation. Ti-6AI-4V is best in the alpha-beta phase, which can be heat-treated to obtain the desired properties. Details of the fabrication methods and dimensions of the model are given in the section titled Dynamized Bone Stabilizer Manufacturing Method. 
     The invention will be presented in these specifications in the following order: 
     The Dynamized Spinal Stabilization System  10 . 
     The Plate Guide  20 , Including The Guide Tubes  22 , And The Outrigger Arm  28 , 
     The Plate  30 . With The Slot  34 . 
     The Bone Screws  40 . Including The Bone Thread End  42 , The Drive Feature  44 , And The Machine Threaded Stud Portion  46 . 
     Dynamizing And Rigidizing Action including: The Sliding Nut  48  And The Clamp Nut  49 . 
     The Clamp Nut and the Sliding Nut. 
     Stop Lock clamps  50   
     The Graft  62 . 
     Dynamized Bone Stabilizer Manufacturing Method. 
     Dynamized Bone Stabilizer Implanting Method 
     The Dynamized Spinal Stabilization System 
     Referring generally to FIGS. 1,  2 , and  3 , one embodiment of the dynamized stabilizer implant system  10  of the present patent is illustrated. The system is implanted on vertebra or individual bones  60  on the spinal or bone column  61 . In this embodiment the system  10  includes a bone plate  30  having a longitudinal axis  31  substantially parallel to the spinal or bone column axis  63 , a plate guide  20  with two tubes  22 , an outrigger arm  38 , an anterior screw  47 , a bone screw  40 , two different nuts  48  and  49 , and a graft  62 . Also included is a stop lock clamp  50  including an upper clamp  52 , a lower clamp  54 , and a stop screw  56 . 
     The Plate Guide 
     Referring generally to FIGS. 2,  3 , and  4  the plate guide  20  is an “L” shaped plate, the top face of the plate guide surface  21  interfaces the lower face of the plate  30  and the plate guide tube  22  outer diameter interfaces with the plate slot  34  sides. When the plate guide is clamped, the interface surfaces are static. When the device is free the interface is dynamic sliding. Sliding does not allow rotation or horizontal translation of the plate relative to the vertebrae or individual bones, This device will allow axial sliding of the bone screws  40  and plate guides  20 . 
     The plate guide  20  has two tubes  22  fixed to it and extending perpendicular outward from the plane of the plate guide. The two fixed guide tubes  22  prevent plate  30  rotation and lateral sliding. The guide tubes give guidance to plate  30  through plate slot  34 . The tubes have through holes  27  that allow the bone screw machine threads  46  to protrude above the top of the tubes. The inner diameters of the tubes slidably engage and interface with the machine threaded stud portion  46  of the bone screw  40 . The tube length protrusion shown as  70  in FIG. 7 a  prevents the sliding nut  48  from direct plate to plate guide clamping by restricting the sliding nut from compressing the plate. 
     The outrigger arm  28  of the plate guide  20  comprises a contiguous metal piece curved  23  to fit the lateral or anterior curvature of the vertebral body  60 . An anterior (ventral) bone screw  47  clearance hole  25  and one or more spikes  29 , shown in FIG. 9 b,  on the lower surface fixes the outrigger arm  28  into place. 
     The outrigger arm  28  extends perpendicular to and substantially in the plane of the plate guide  20  anteriorly, for placement of an anterior bone screw  47  which is fixed to the plate guide through a locking means. The anterior bone screw serves to provide rotational, and pullout resistance to the plate guides. An optional malleable portion in the plate guide arm between the posterior bone screws  40  and the anterior bone screw  47  to allow the outrigger arm  28 , to better conform to the vertebra or the individual bone&#39;s curve. An additional two-hole plate guide  26 , shown in FIG. 3 allows the plate guide to be set at an angle with the plate  30 . In another embodiment the plate may have an integral boss  24 , with drilled holes in place of the tubes  22 , as shown in FIG. 9 a.  The spikes  29 , shown in FIG. 9 b,  are driven into the vertebra or individual bones stabilizing the outrigger arm  28  prior to or during bone screw placement. 
     The Plate 
     Referring generally to FIG. 2 the plate  30  has a rectangular cross section with a slot  34  creating two rails  35 , shown in the section view of FIG. 6 a.  The plate end  32  is semicircular with rounded ends and a width equal to that of the plate rail. The plate lower face interfaces with the plate guide&#39;s upper surface  21 . The plate upper face interfaces with the nut flange  57 . The plate also has two substantially parallel side faces with a thickness of sufficient strength to substantially eliminate bending. The plate  30  is machined from a single piece of titanium. It has an through guide Slot  34  parallel to its longitudinal axis  31  to receive and contain the tube portion  22  of the plate guide  20 . Unlike stabilizing plates with preformed holes that dictate the location of the bone screws  40 , this plate allows the bone screws  40  to be infinitely positioned axially to place the bone screws into the desired position of the vertebra or individual bones  60 . The plate may be bent  23  at the time of manufacture or at the time of surgery to accommodate spinal curvatures. 
     The Bone Screws 
     Referring generally to FIGS. 2,  4 , and  5 , the bone screw  40 , having a bone threaded portion  42  which engages the bone  60 , a driving portion  44  with a hexagonal head, a machine threaded stud portion  46 , which is not threaded at the tube/stud interface, and a top drive feature  45 . The bone screw portion is threaded into the bone in pairs with the screw&#39;s centerline distance equal to the guide plate tubes centerline distance. The bone screws  40  are driven in to the bone until the screw&#39;s driving portion  44  abuts the vertebra or individual bones. All or some of the bone screws may be self-tapping. The machine threads extend above the plate guide tube  22  so that the nuts  48  and  49  can have threaded engagement and interface with the screw machine thread portion. Two different nuts with threaded holes and flanges  57  as shown in FIGS. 6 a,    6   b,    7   a,  and  7   b  are provided. For final adjustment after implantation the final height is adjusted using the top drive feature. 
     Dynamizing and Rigidizing Action 
     Referring generally to FIGS. 7 a,  and  7   b,  in the dynamized installation the sliding nut  48  clamps tight against the end of guide tube  22  allowing clearance  70 , shown in FIG. 7 a,  between the plate  30  and the plate guide  20 . The guide tubes  22  diameters are smaller then the plate slot  34  width to maintain clearance between the plate slot and the tube. Installing sliding nuts  48  will allow the plate  30  to slide relative to the plate guide  20 . 
     In a rigid installation the clamping nut  49 , shown in FIG. 7 b,  is undercut with a clearance  71  preventing the nut from clamping against the tube  22 . This clamping forces the plate  30  against the plate guide  20  clamping them together rigidly to preventing relative motion between the plate and the plate guide. Installing the clamp nut  49  will prevent motion between the plate and the plate guide. 
     In the preferred embodiment sliding or rigidity can be selected or changed by the specific nut,  48  or  49 . Because of the metal-to-metal clamping with either nut there is no need for additional nut locking devices. 
     The Clamp Nut and The Sliding Nut 
     Referring generally to FIGS. 1,  2 ,  4 ,  7   a,  and  7   b.  The nuts consist of a hexagonal portion and a flange portion  57  and an internal thread. The nut flange interfaces with the plate  30  upper face and the nut threaded portion interfaces with the machine threaded stud portion  46 . The sliding nut  48  also interfaces with the top of the guide tube  22  and dynamically sliding with the plate upper face. The clamp nut  49  interfaces statically clamped with the plate upper face. The clamp nut  49  has an undercut that clears the tube  22  top allowing the nut to clamp the plate  30  directly to the plate guide  20  thereby rigidizing the vertebra or individual bones  60 . Because of the metal-to-metal clamping of the sliding nut  48  and the guide tube; and the metal to metal clamping of the clamp nut  49  to the plate the nuts do not require anti-rotational locks, such as auxiliary screw connectors, cams, wedges or locking caps. The plate heights are adjusted by rotateing the bone screw with a driving wrench on the top drive 
     An optional upper saddle clamp  41 , shown in FIG. 8 b,  may be used with the clamp nut  49  for additional rigidity between the bone screw  40  and the plate  30 . The saddle clamp has flanges which trap the plate rails from spreading. The metal-to-metal clamping of the bone screw  40  to the Plate  30  provides a fully rigid bone stabilizer system. 
     Stop Lock Clamps 
     Referring generally to FIGS. 2,  4 ,  8   a,  and  8   b,  the stop lock clamp assembly  50  is a clamp consisting of an upper clamp  52 , a lower clamp  54 , and a screw  56  that pulls the upper and lower clamps against the plate  30 . This rigid clamp will prevent or stop the plate guide  20  from distracting yet will allow it to freely subside, maintaining compression between the vertebra or individual bones  60  and the graft  62  to allow for any graft resorbtion and settling. The stop lock clamp will also increase plate rigidity and serve as a travel limit stop for the bone screw  40 /plate guide  20  assembly with respect to the plate  30 . The graft should be compressed before tightening the lock clamp screw  56 . An optional upper stop lock saddle clamp  59  and a lower stop lock saddle clamp  58 , shown FIG. 8 c,  will add rigidity to the system  10  and will prevent the plate slot from widening. 
     The Graft 
     Referring generally to FIG. 4, for consistency in this patent the word stabilizer or implant refer to the plate-screw assembly  10 , whereas the word graft  62  refers to the interbody material replacing the removed disc or vertebra. The graft is pieces of human bone, a piece of calcium, a synthetic material, a protein/DNA/gene sequence, or a metal device. These devices act as a bone growth enhancer and share the vertebra or individual bone&#39;s load to maintain the disc space along with the stabilization system of the present invention. The graft must maintain its height until the healing is complete. The plate  30  must also help to keep the graft in place. The vertebra or individual bone&#39;s end plates are cartilage, which must be removed so the graft has live healthy bone to grow with. An expandable interbody can be used to initially compress the construct. 
     Dynamized Bone Stabilizer Manufacturing Method 
     The components are made of titanium alloy Ti-AI6-V4. They are machined from rod and bar stock. Ti-AI6-V4 can be machined by the customary methods. However it requires slow speeds, heavy feeds to reduce work hardening, and an ample supply of coolant. Because heavy feeds create large loads on the tool bits, the machine tools and setups must be very rigid to avoid chattering. The tool bits must remain sharp therefor carbide tool bits are recommended. Ti-AI6-V4 can be welded only in a clean inert atmosphere. The recommended welding process is TIG (Tungsten electrode Inert Gas). 
     A recommended titanium supplier is Tico Titanium, inc. Tyco can furnish bar and rod stock or near net cut titanium shapes with excellent edge finish and a high degree of intricacy or size tolerance using abrasive water-jet cutting systems operated by CAD systems. Water-Jet cut titanium materials are preferred because the cold cutting process does not change the properties of the material. 
     The dimensions of the working model are described below. It will be understood that no limitation of the scope of the invention is intended by these specifications. 
     The plate is 4.5 mm (0.187 inch) thick, 12.7 mm (0.500 inch) wide, and 108 mm (4.25 inch) long. 
     The plate slot is 6.5 mm (0.255 inch) wide. 
     The guide plate is 2.5 mm (0.100 inch) thick, 22.8 mm (0.900 inch) long, and 12.7 mm (0.500 inch) wide. 
     The guide plate tubes are 6.3 mm (0.250 inch) outer diameter, 4.83 mm (0.190 inch) inner diameter, and 5 mm (0.200 inch) long. 
     The outrigger is 2.5 mm (0.100 inch) thick, 5 mm (0.200 inch) wide, and 15 mm (0.600 inch) long. 
     The bone screw is 22 mm (0.86 inch) long with: 
     a 5 mm (0.197 inch) diameter bone thread 10 mm (0.394 inch) long. 
     a 2 mm (0.080 inch) thick, 9.5 mm (0.375 inch) hexagonal wrench feature. 
     a 4.7 mm (0.187 inch) diameter, 6.5 mm (0.652 inch) long stud length, and a 10 mm (0.4 inch) thread length. 
     Dynamized Bone Stabilizer Implanting Method 
     Referring generally to FIGS. 2,  3  and  4 , the plate  30  is attached lateral to the vertebra or bone body  60  with the bone screws  40  through the sliding plate guides tubes  22 . The bone screws  40  are threaded into the vertebra or individual bones  60  from a lateral exposure with bicortical purchase. The method is described as a two level fusion involving three adjacent vertebra or individual bone segments with the discs replaced by interbody grafts  62 . 
     First the interbody graft  62  is placed and spinal alignment is confirmed. Next posterior (posterior-lateral) bone screw  40  pilot holes are drilled through a template or drill guide that will ensure proper posterior bone screw  40  alignment, with the adjacent vertebra or individual bone segment&#39;s posterior bone screws. Proper posterior bone screw alignment will prevent the plate guide  20  from binding in the plate slot  34 . Bone screw  40  pilot hole drilling to direct bone screw placement is well known to those practiced in the art. The pilot holes are tapped with an internal thread and then the posterior screws are placed. Self-tapping bone screws do not require that the pilot hole be tapped. Two posterior bone screws  40  are placed per vertebra or individual bone segments  60 . the plate guides  20  are then placed over the posterior bone screws  40  at each segment. The posterior bone screws are adjusted by rotating the bone screw by the middle drive feature  44  or the top drive feature  45  to control the plate guide  20  height. The plate  30  is loaded onto the plate guide tubes  22 . The plate guide tubes slidably engage the plate internal slot  34 . 
     The plate  30  is loaded onto the plate guide tubes  22 . Plate preloading results in maintenance of construct compression. Each sliding vertebra or individual bone segment&#39;s posterior bone screws  40  are then secured firmly to the plate guide tubes  22  with a bone screw-sliding nut  48 . The loading is carried out with a compression tool means followed by placement of a stop lock clamp  50 , or by subsequent expansion of an expandable interbody means. If needed the stop lock clamp is slid against the plate guide  20  during compression, and then the stop lock clamp is clamped in place, holding the construct in compression. Construct compression techniques and interbody device distraction are well known to those practiced in the art. The outrigger  28  is then secured with the anterior bone screw  47 . Each segment screw to be rigidized with respect to the plate  30  is clamped using the bone screw clamp nut  49 . 
     The final adjustment of the plate guide heights are made by loosening the two nuts on the plate guide to be adjusted, then rotating the bone screw with a driving wrench on the top drive feature until the plate guide is at the required level. The wrench should be held while the nuts are being retightened. 
     Implanting Method Options: 
     (1) Referring to FIG. 7 a,  if unidirectional preloaded dynamized action is desired, sliding nuts  48  are threaded onto bone screw  40  and tightened. A compression tool means is used to draw the vertebra or individual bone segments  60  toward each other until the desired preload is reached. This compression prevents motion in the direction of the stop lock clamp  50  to maintain preload as shown in FIGS. 3 and 4. 
     (2) Referring to FIG. 7 b,  If rigidizing is desired, clamp nuts  49  are threaded onto bone screw machine threaded stud portion  46  and tightened. The clamp nuts clamp against the plate thereby restricting motion of the plate with the plate guide  20 .