Abstract:
A system and method for immobilizing adjacent spinous processes in accordance with the present invention can supplement primary fusion devices and methods by immobilizing spinous processes while bone from adjacent vertebral bodies grows together. The system requires less extensive surgical procedures than other common supplemental devices, and preferably does not require bone or ligament removal. One such system comprises three spacers positioned between spinous processes and adjustably connected with a plate positioned on either side of the spinous processes. Each plate includes grips, with each grip positioned adjacent to the spinous process, forming a clamp with a grip connected with the opposing plate.

Description:
PRIORITY CLAIM  
       [0001]    This application claims priority to the following U.S. Provisional Patent Application:  
         [0002]    U.S. Provisional Patent Application No. 60/446,868, entitled “A System and Method for Immobilizing Adjacent Spinous Processes,” Attorney Docket No. KLYC-01086US0, filed Feb. 12, 2003. 
     
    
     
       CROSS-REFERENCED CASES  
         [0003]    The following U.S. Patent Applications are cross-referenced and incorporated herein by reference:  
           [0004]    U.S. patent application Ser. No. 09/829,321, entitled “SPINE FIXATION DEVICE AND METHOD” by David Yun, filed Apr. 9, 2001 (Attorney Docket No. KLYC-01049US0);  
           [0005]    U.S. Provisional Patent Application No. 60/421,921, entitled “INTERSPINOUS PROCESS APPARATUS AND METHOD WITH A SELECTABLY EXPANDABLE SPACER”by James F. Zucherman, Ken Y. Hsu, and Charles J. Winslow, filed Oct. 29, 2002 (Attorney Docket No. KLYC-01056US0;  
           [0006]    U.S. patent application Ser. No. 09/579,039, entitled SUPPLEMENTAL SPINE FIXATION DEVICE AND METHOD by James F. Zucherman, Ken Y. Hsu, Charles J. Winslow and Henry A. Klyce, filed May 26, 2000 (Attorney Docket No. KLYC-01033US0);  
           [0007]    U.S. patent application Ser. No. 09/842,819, entitled SUPPLEMENTAL SPINE FIXATION DEVICE AND METHOD by James F. Zuchernan, Ken Y. Hsu, Charles J. Winslow and Henry A. Klyce, filed Apr. 26, 2001 (Attorney Docket No. KLYC-01033US4);  
           [0008]    U.S. patent application Ser. No. 09/982,418, entitled SUPPLEMENTAL SPINE FIXATION DEVICE AND METHOD by James F. Zucherman, Ken Y. Hsu, Charles J. Winslow, Steve Mitchell, Scott Yerby and Henry A. Klyce, filed Oct. 18, 2001 (Attorney Docket No. KLYC-01033US5);  
           [0009]    U.S. Provisional Patent Application No. 60/306,262, entitled SUPPLEMENTAL SPINE FIXATION DEVICE AND METHOD by James F. Zucherman, Ken Y. Hsu, Charles J. Winslow, Steve Mitchell, Scott Yerby and Henry A. Klyce, filed Jul. 18, 2001 (Attorney Docket No. KLYC-01033US3);  
           [0010]    U.S. Provisional Patent Application No. 60/421,915, entitled INTERSPINOUS PROCESS IMPLANT WITH RADIOLUCENT SPACER AND LEAD-IN TISSUE EXPANDER by James F. Zucherman, Ken Y. Hsu, Charles J. Winslow, John Flynn and Steve Mitchell, filed Oct. 29, 2002 (Attorney Docket No. KLYC-01077US0); and  
           [0011]    U.S. patent application Ser. No. 10/230,505, entitled DEFLECTABLE SPACER FOR USE AS AN INTERSPINOUS PROCESS IMPLANT AND METHOD by James F. Zucherman, Ken Y. Hsu, Charles J. Winslow and John Flynn, filed Aug. 29, 2002 (Attorney Docket No. KLYC-01056USB).  
           [0012]    1. Technical Field  
           [0013]    The present invention relates to methods and systems for immobilizing adjacent spinous processes which, byway of example only, supplement a primary spine fusion device, such as an interbody fusion device.  
           [0014]    2. Background  
           [0015]    A common procedure for handling pain associated with degenerative spinal disk disease uses devices for fusing together two or more adjacent vertebral bodies. The procedure is known by a number of terms, one of which is interbody fusion. Interbody fusion can be accomplished through the use of a number of methods and devices known in the art. These methods and devices include screw arrangements, solid bone implant methodologies, and fusion devices which include a cage or other mechanism packed with bone and/or bone growth inducing substances. One or more of the above are implanted between adjacent vertebral bodies in order to fuse the vertebral bodies together, thereby alleviating associated pain.  
           [0016]    It can be advantageous to associate with such primary fusion devices and methods, supplemental devices which assist in the fusion process. These supplemental devices assist during the several month period when bone from the adjacent vertebral bodies is growing together through the primary fusion device in order to fuse the adjacent vertebral bodies. During this period it is advantageous to have the vertebral bodies held immobile with respect to each other so that sufficient bone growth can be established.  
           [0017]    Such supplemental devices can include hook and rod arrangements, screw arrangements, and a number of other devices which include straps, wires, and bands, all of which are used to immobilize one portion of the spine relative to another. All of these devices generally require extensive surgical procedures in addition to the extensive procedure surrounding the primary fusion implant.  
           [0018]    It is advantageous for a device and procedure for supplemental spine fixation to be as simple and easy to perform as possible, and optimally such a device and procedure leaves bone, ligament, and other tissue which comprise and surround the spine intact. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    Further details of embodiments of the present invention are explained with the help of the attached drawings in which:  
         [0020]    [0020]FIG. 1 is a side view of a system in accordance with one embodiment of the present invention positioned about adjacent spinous processes;  
         [0021]    [0021]FIG. 2A is a top view of the system shown in FIG. 1;  
         [0022]    [0022]FIG. 2B is a close-up view of two grips positioned on opposite sides of a spinous process as shown in FIG. 2A;  
         [0023]    [0023]FIG. 3 is a side view of an alternative embodiment of the invention with an expanding spacer;  
         [0024]    [0024]FIG. 4A is a side view of an alternative embodiment of the invention with a slot for positioning a pin having lobed cut-outs;  
         [0025]    [0025]FIG. 4B is a side view of an alternative embodiment of the invention with a slot for positioning a pin having a knurled periphery; and  
         [0026]    [0026]FIG. 5 is a representation of a method for immobilizing adjacent spinous processes in accordance with one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0027]    [0027]FIGS. 1-2B illustrate a system for immobilizing adjacent spinous processes in accordance with one embodiment of the present invention. The system  100  comprises a scaffold formed by two plates  104   a,b  adjustably connected by pins  110  inserted through slots  106  in each plate. Each plate  104   a,b  is positioned generally along a plane parallel to a plane formed by the major axis of the spinous processes, with a first plate  104   a  positioned on one side of protruding adjacent spinous processes, and a second plate  104   b  positioned on an opposite side of the adjacent spinous processes, such that the spinous processes are sandwiched between the two plates. Each plate  104   a,b  includes two grips, each grip  214   a,b  comprising part of a clamp adapted for gripping the spinous processes to prevent shifting of the system  100  relative to the spine and to assist in immobilizing the adjacent spinous processes.  
         [0028]    As shown in FIG. 2B, a clamp comprises a grip  214   a  from a first plate  104   a  and a grip  214   b  from a second plate  104   b . The grip  214   a  from the first plate  104   a  is oriented such that the grip substantially opposes a face of a spinous process. The grip  214   b  from the second plate  104   b  is oriented such that the grip substantially opposes the opposite face of the spinous process. The grips  214   a,b  are spaced along the length of the plates  104   a,b  such that each pair of grips  214   a,b  is positioned about a spinous process. In other embodiments, and in the same way that spacers  102  are moveable in slots  106 , the grips  214   a,b  can be moveably connected to grip slots in the plates  104   a,b , thereby allowing each grip  214   a,b  to be moved laterally relative to every other grip  214   a,b , thus allowing each grip  214   a,b  to be substantially centered with respect to an associated spinous process.  
         [0029]    Each grip  214   a,b  is adjustably connected with an associated plate  104   a,b  by a threaded bolt  116  having preferably a hexagonal head for engaging the bolt  116 . Twisting the threaded bolt  116  in a first direction drives the bolt  116 , and consequently the grip  214   a,b , toward the spinous process. Twisting the threaded bolt  116  in a direction opposite the first direction drives the grip  214   a,b  away from the spinous process. In other embodiments, the grip  214   a,b  can be connected to the plate  104   a,b  by a slotted screw. In still other embodiments, the grip  214   a,b  can be connected to the plate  104   a,b  by a socketed screw. One of ordinary skill in the art can appreciate the myriad of different fasteners that can be used to adjustably connect each grip  214   a,b  with an associated plate  104   a,b.    
         [0030]    The bolts  116  are provided through a threaded bore in the plates  104   a,b . Turning the bolts  116  moves the bolts and the grips  214   a,b  secured thereto relative to the plates  104   a,b . The ends of the bolts  116  can be either fixedly or rotatably secured to the grips  214   a,b . The bolts  116  can be rotatably secured to the grips  214   a,b  as is know in the art. For example, the ends of the bolts can include a circumferential lip that is received in an undercut groove in a bore of the grips  214   a,b . The lip is free to rotate in the groove of the bore. Where the bolts  116  are fixedly secured to the grips  214   a,b , the grips  214   a,b  are preferably circular in cross-section (as the bolts  116  are tightened, the grips  214   a,b  rotate relative to the plates  104   a,b  and thus relative to the spinous processes). One of ordinary skill in the art can appreciate the different means for adjustably connecting the grip  214   a,b  with the plate  104   a,b.    
         [0031]    The plates  104   a,b  and threaded bolts  116  can be made of stainless steel, titanium, and/or other biologically acceptable material such as polyetheretherketone (PEEK). In one embodiment, the grips  214   a,b  can similarly be comprised of a biologically acceptable material such as stainless steel, titanium, and/or other material such as PEEK, with the surface that comes into contact with the spinous process having a roughened or uneven surface. The contacting surface can, for example, be knurled or it can contain spikes to allow the grips  214   a,b  to engage the bone of the spinous processes. In other embodiments, the grips  214   a,b  can be comprised of silicon or other biologically acceptable polymer or material (such as presented below with respect to the spacers). The material can be somewhat deformable and can conform to the surface of the spinous processes.  
         [0032]    As shown in FIGS. 1 and 2A, the system  100  has a single clamp positioned at each of two spinous processes, each clamp being comprised of two grips  214   a,b  on opposite sides of an associated spinous process. However, in other embodiments, a plurality of clamps (with associated grips  214   a,b ) can be positioned at selected spinous processes. Thus, for each surface of each spinous process there can be two or more grips. With several grips, each grip can be tightened against a portion of the surface of a spinous process independently of the other adjacent grip that is tightened against a different portion of the same surface of the spinous process. This system can accordingly accommodate uneven surfaces of the spinous processes with each grip tightened against a portion of a surface of a spinous process that is not even with another portion of the surface of the spinous process.  
         [0033]    Referring again to FIG. 1, the plates  104   a,b  are secured together with pins  110 . A pin  110  can have a threaded bore for receiving a screw or bolt having a hexagonal, slotted, or other type of head at each end of the pin  110 . Alternatively, one or both ends of the pin  110  can be threaded for receiving a nut, or lug for example, or other fastener. The pin  110  can be made of a material similar to the plates  104   a,b , for example, the pin  110  can be made of stainless steel, titanium or other biologically acceptable material. At least one fastener for each pin  110  is tightened so that the pins pull the plates  104   a,b  toward one another as desired. Alternatively, the pins  110  can have a main body diameter thicker than the height of a slot  106  with a thinner threaded end for passing through the slot, thereby predefining a space between plates  104   a,b.    
         [0034]    The clamps are adjusted as desired either before or after the fastener(s) of the pins  110  are tightened, thereby allowing the clamps to grip the spinous processes, making the system  100  rigid. A spacer  102  is moveably and rotatably connected with each pin  110  between plates  104   a,b . The spacer  102  is substantially cylindrical in shape with an elliptical cross-section sized to conform to a gap between spinous processes in which the spacer  102  is to be inserted. The elliptical spacer  102  has opposite, slightly curved (or relatively flat) surfaces that can distribute the load placed on the spacer by the spinous processes between which the spacer  102  is positioned. The spacer  102  further has curved ends connecting the slightly curved surfaces. The curved ends point substantially posteriorly and anteriorly. The anteriorly pointing ends approach the spine. In other embodiments the spacer  102  can have an egg-shaped cross-section with the curved end pointing toward the spine being smaller that the curved end pointing posteriorly in order to allow the spacer  102  to more closely approach the spine. In still other embodiments, the spacer  102  can have a cross-section having an ovoid, oval or even spherical shape, for example. One of ordinary skill in the art can appreciate the different cross-sectional shapes with which the spacer  102  can be formed in order to distribute load within the spacer  102 .  
         [0035]    One advantage of using the spacer  102  depicted in FIG. 1 is that the spacer  102  can be partially rotated and repositioned with respect to the system  100  in order to optimize positioning of the spacer  102  between spinous processes. The system  100  is thus designed to account for the various spine structures found in patients. Without having to remove bone from the spine or make multiple adjustments to a hardware system, the spacers  102  and also the grips  214   a,b  allow the system  100  to easily conform to the structure of an associated spine. Further, ease of use and placement allow procedures for implanting the system  100  to be carried out more quicky and with less potential trauma to the surgical site. Still further, as indicated above, the spacers  102  can be located closer to the spine where the bone is stronger, thus affording maximum load bearing and stabilizing support relative to the spine. Such load bearing and stabilizing support is advantageous when the system  100  is used as an adjunct to the fusion of adjacent vertebral bodies. It is to be understood that the cortical bone or the outer bone of the spinous processes is stronger at an anterior position adjacent to the vertebral bodies of the vertebra than at a posterior position distally located from the vertebral bodies.  
         [0036]    Still further, for load bearing it is advantageous for the spacer  102  to be close to the vertebral bodies. In order to facilitate this and to accommodate the anatomical form of the bone structures, the spacer  102  rotates relative to the system  100  as the spacer  102  is inserted between the spinous processes and/or urged toward the vertebral bodies so that the spacer  102  is optimally positioned between the spinous processes and the system  100  is optimally positioned relative to the spinous processes. The shape of the spacer  102  is designed so that it conforms to the area that the spacer  102  is inserted into. However, one of ordinary skill in the art will appreciate that the spacer  102  is not limited to having an elliptical cross-section. For example, the spacer  102  can be substantially spherical in cross-section or egg shaped as set forth above.  
         [0037]    As can be seen in FIG. 1, the spacers  102  can be of various sizes. Thus for example, using imaging prior to surgery, the anatomy of the individual patient can be determined and the system  100  assembled to suit the particular patient. Additionally, during surgery the physician can be provided with a kit having different sized spacers  102  and the physician can assemble the system  100  with appropriately sized spacers  102  to fit the anatomy of the patient. In this embodiment the pins  110  can be comprised of rods with threaded bores at each end that receive bolts or screws used to secure the pins between two plates  104   a,b  with the spacer  102  rotatably mounted on the pins  110 .  
         [0038]    In other embodiments, the spacer  102  can be comprised of two portions adjustably connected by a hinge to allow expansion of the spacer  102 . For example, as shown in FIG. 3, the spacer  102  is comprised of a first portion  330  and a second portion  332  that together have a minor dimension that can be adjusted by rotating a ball  334  connected with a lead screw  336 , such that the ball  334  alternatively forces the minor dimension to expand or allows the minor dimension to collapse. Such a spacer is described in pending U.S. Patent Application No. 60/421,921, entitled “INTERSPINOUS PROCESS APPARATUS AND METHOD WITH A SELECTABLY EXPANDABLE SPACER” by James F. Zucherman, Ken Y. Hsu, and Charles J. Winslow, incorporated herein by reference.  
         [0039]    The spacer  102  can be made of a polymer, such as a thermoplastic, and can be formed by extrusion, injection, compression molding and/or machining techniques. Specifically, the spacer  102  can be made of a polyketone such as PEEK. One type of PEEK is PEEK  450 G, which is an unfilled PEEK approved for medical implantation available from Victrex of Lancashire, Great Britain. Other sources of this material include Gharda located in Panoli, India. PEEK  450 G has appropriate physical and mechanical properties and is suitable for carrying and spreading the physical load between the spinous process. For example in this embodiment the PEEK has the following approximate properties:  
                                                       Density   1.3 g/cc           Rockwell M   99           Rockwell R   126           Tensile Strength   97           MPa Modulus of Elasticity   3.5 GPa           Flexural Modulus   4.1 Gpa                      
 
         [0040]    It should be noted that the material selected may also be filled. For example, other grades of PEEK available and contemplated include 30% glass-filled or 30% carbon-filled PEEK, provided such materials are cleared for use in implantable devices by the FDA or other regulatory body. Glass-filled PEEK reduces the expansion rate and increases the flexural modulus of PEEK relative to unfilled PEEK. The resulting product is known to be ideal for improved strength, stiffness, or stability. Carbon-filled PEEK is known to enhance the compressive strength and stiffness of PEEK and lower its expansion rate. Carbon-filled PEEK offers wear resistance and load carrying capability.  
         [0041]    As can be appreciated, other suitable biologically acceptable thermoplastic or thermoplastic polycondensate materials that resist fatigue, have good memory, are flexible and/or deflectable, have very low moisture absorption and have good wear and/or abrasion resistance, can be used without departing from the scope of the invention other materials that can be used include polyetherketoneketone (PEKK), polyetherketone (PEK), polyetherketoneetherketoneketone (PEKEKK), and polyetheretherketoneketone (PEEKK), and generally a polyaryletheretherketone. Further, other polyketones can be used, as well as other thermoplastics. Still further, silicon can also be used or the spacer can be made of titanium and/or stainless steel.  
         [0042]    Reference to appropriate polymers that can be used in the spacer can be made to the following documents, all of which are incorporated herein by reference: PCT Publication WO 02/02158 A1, dated Jan. 10, 2002 and entitled Bio-Compatible Polymeric Materials; PCT Publication WO 02/00275 A1, dated Jan. 3, 2002 and entitled Bio-Compatible Polymeric Materials; and PCT Publication WO 02/00270 A1, dated Jan. 3, 2002 and entitled Bio-Compatible Polymeric Materials. Other materials such as Bionate®, polycarbonate urethane, available from the Polymer Technology Group, Berkeley, Calif., may also be appropriate because of the good oxidative stability, biocompatibility, mechanical strength and abrasion resistance. Other thermoplastic materials and other high molecular weight polymers can be used.  
         [0043]    As mentioned above, each spacer  102  can be connected with a pin  110  that adjustably connects the first plate  104   a  with the second plate  104   b . In one embodiment, each plate  104   a,b  has three slots  106  spaced and sized such that the slots  106  span approximately the width of the gap between the associated adjacent spinous processes when a patient is standing up. The length of the slots  106  should allow for necessary adjustment of the spacers  102  so that the anatomy of the adjacent spinous processes can be accommodated with the spinous processes immobilized between the spacers  102 . In the system  100  shown in FIG. 1, the middle of three slots  106  is sized larger than the slots  106  on either end of the plates. However, in other embodiments, the slots  106  can be sized relative to one another based on the vertebral bodies that are intended to be immobilized.  
         [0044]    As described above, a pin  110  can be fitted into a slot  106  in each plate  104   a,b . The width of the slot  106  allows the pin  110  to be optimally positioned within the gap between spinous processes, while still being fixable to the plates  104   a,b . The pin  110  can be fixedly connected with each plate  104   a,b  by a bolt, screw, nut or other fastener, optionally coupled with a washer. To prevent the plates  104   a,b  and pins  110  from slipping and shifting relative to one another, a number of different type of slots can be employed to fix the pin  110  in position. As shown in FIG. 4A, one type of slot  106  that can be used is a slot having cut-outs, lobes, or scallops  440  sized such that the cut-outs, lobes or scallops  440  have diameters slightly larger than the diameter of the pin  110 , but are separated such that the adjacent cut-outs, lobes, or scallops are joined at a space narrower than the diameter of the pin  110  so that the pin  110  is prevented from sliding to the adjacent position. Another type of slot  106 , shown in FIG. 4B, includes knurls around each slot&#39;s periphery, intended to be used with a knurled washer placed between a fastener and a plate  104   a,b . The knurls on the respective surfaces grip each other when the fastener is tightened, preventing the pin  110  from moving in the slot  106 . One of ordinary skill in the art can appreciate the different means for fixing a pin  110  in a slot  106  to prevent the pin  110  from moving relative to the plate  104   a,b.    
         [0045]    In alternative embodiments, the system  100  can comprise one or two plates  104   a,b  with spacers  102  rotatably secured thereto (foregoing the use of grips). The system  100  can be implanted and the position of the spacers  102  can be adjusted relative to the slots  106 , the one or two plates  104   a,b , and the spinous processes in order to immobilize the spinous processes  
         [0046]    [0046]FIG. 5 is a block diagram showing steps for performing a method for inserting a system  100  into a patient in order to immobilize vertebral bodies in accordance with the present invention. As shown in first block  500 , a first, second and third spacer  102  is selected according to the size of the gap between spinous processes that each spacer  102  will occupy. Each spacer  102  is moveably connected with an associated pin  110  (step  502 ). An incision is made in the patient proximate to vertebral bodies to be immobilized (step  504 ), and the spinous processes and surrounding tissues are exposed. Each spacer  102  is then inserted into position between targeted spinous processes (step  506 ) and allowed to rotate and adjust to conform as closely as possible to the contours of the space. A first plate  104   a  is inserted into the patient and positioned such that a first end of each pin  110  fits into a slot  106  (step  508 ). Each pin  110  is fixedly connected to the first plate  104   a  by a fastener, for example a bolt or slotted screw (step  510 ). A second plate  104   b  is inserted into the patient and positioned such that a second end of each pin  110  fits into a slot  106  (step  512 ). Each pin  110  is fixedly connected to the second plate  104   b  by a fastener, for example a bolt or slotted screw (step  514 ). Finally, the grips  214   a,b  are incrementally tightened so that each clamp grips an associated spinous process (step  516 ). The incision is closed (step  518 ).  
         [0047]    In other embodiments, a method in accordance with the present invention can be applied where there are more or less than three spacers  102 , and/or more or less than two clamps. The configuration of a system  100  will depend on the area intended to be immobilized, and the requirements of the patient.  
         [0048]    Other methods of insertion, include having the system  100  fully assembled prior to insertion. For this method, the surgical site is prepared and then the system  100  is pushed down over the ends of the spinous processes until the system  100  rests in a desired location. At this point the grips  214   a,b  are tightened in place about the spinous processes.  
         [0049]    Still alternatively, the system  100  can be partially assembled with the spacers  102  assembled with a first plate  104   a . This subassembly is positioned alongside of the spinous processes and the spacers  102  are urged between the adjacent spinous processes. When the spacers  102  are positioned, the second plate  104   b  is secured to the system  100 .  
         [0050]    The foregoing description of preferred embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations will be apparent to one of ordinary skill in the relevant arts. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications that are suited to the particular use contemplated. Other features, aspects, and objects of the invention can be obtained from a review of the specification, the figures, and the claims. It is intended that the scope of the invention be defined by the claims and their equivalence.