Abstract:
A spinal fixation and fusion assembly includes a bone anchoring member, a cylindrical rod and a cap. The bone anchoring member comprises an elongated body that is made entirely of bone type material. The elongated body includes a main shaft, a conical shaped distal end, a flared out proximal end, and a through-opening extending along an axis from the proximal end to the distal end. The cylindrical rod is shaped and dimensioned to be received within the through-opening and is made entirely of metal. The cap is made entirely of metal and is attached to a proximal end of the cylindrical rod.

Description:
CROSS REFERENCE TO RELATED CO-PENDING APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional application Ser. No. 61/346,523 filed May 20, 2010 and entitled “SYSTEM AND METHOD FOR FACET FUSION”, the contents of which are expressly incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a system and a method for facet fixation and fusion, and more particularly to a system and a method that utilizes a bone allograft product for bone-to-bone facet fusion. 
       BACKGROUND OF THE INVENTION 
       [0003]    The human spine includes individual vertebras that are connected to each other. Under normal circumstances the structures that make up the spine function to protect the neural structures and to allow us to stand erect, bear axial loads, and be flexible for bending and rotation. However, disorders of the spine occur when one or more of these spine structures are abnormal. In these pathologic circumstances, surgery may be tried to restore the spine to normal, achieve stability, protect the neural structures, or to relief the patient of discomfort. The goal of spine surgery for a multitude of spinal disorders especially those causing compression of the neural structures is often decompression of the neural elements and/or fusion of adjacent vertebral segments. Fusion works well because it stops pain due to movement at the facet joints or intervertebral discs, holds the spine in place after correcting deformity, and prevents instability and or deformity of the spine after spine procedures such as discectomies, laminectomies or corpectomies. Discectomy and fusion or corpectomy and fusion are most commonly performed in the cervical spine but there is increasing application in the thoracic and lumbar spine, as well. 
         [0004]    Several spinal fixation systems exist for stabilizing the spine so that bony fusion is achieved. The majority of these fixation systems utilize fixation elements such as rods wires or plates that attach to screws threaded into the vertebral bodies, facets or the pedicles. In some fixation systems the facet joints are compressed together and attached together via spinal fixation elements  82   a ,  82   b , shown in  FIG. 1 . However, in most prior art methods of facet fixation, compression and fixation does not result in actual bone-to-bone contact and fusion between superior and inferior facets. Accordingly, there is a need for a system and a method for bone-to-bone facet fixation that results in facet fusion between superior and inferior facets and spinal stabilization. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention relates to facet fixation and fusion methods and facet fixation and fusion devices, and in particular to cylindrical or multi-faceted components made of bone allograft material for the achievement of bone-to-bone facet fixation. 
         [0006]    In general, in one aspect, the invention features a spinal fixation and fusion assembly including a bone anchoring member, a cylindrical rod and a cap. The bone anchoring member comprises an elongated body that is made entirely of bone type material. The elongated body includes a main shaft, a conical shaped distal end, a flared out proximal end, and a through opening extending along an axis from the proximal end to the distal end. The cylindrical rod is shaped and dimensioned to be received within the through opening and is made entirely of metal. The cap is made entirely of metal and is attached to a proximal end of the cylindrical rod. 
         [0007]    Implementations of this aspect of the invention may include one or more of the following features. The elongated body may have a cylindrical cross section, rectangular cross section, or polygonal cross section. The elongated body may include screw threads, spikes, teeth, barbs, bumps, indentations, straight protrusions, helical protrusions, or combinations thereof. The main shaft may have a parallelepiped shape, the distal end may be an inverted truncated rectangular pyramid extending from the bottom surface of the main shaft, and the proximal end may be an inverted truncated rectangular pyramid extending from the top surface of the main shaft. The main shaft may have a polygonal shape, the distal end may be an inverted truncated polygonal pyramid extending from the bottom surface of the main shaft, and the proximal end may be an inverted truncated polygonal pyramid extending from the top surface of the main shaft. The spinal fixation assembly may further include a conical cap made entirely of metal and being attached to a distal end of the cylindrical rod. The conical cap comprises screw threads. The bone type material may be one of allograft bone material, biocompatible materials, synthetic bone growth promoting material, bone-polymer composite material, autograft bone material, xenograft bone material, polymers, resorbable material, non-resorbable material, or combinations thereof. The metal may be one of titanium, cobalt, stainless steel, chrome, alloys thereof, shape-memory alloy, ceramic-metallic composite materials, or combinations thereof. 
         [0008]    In general, in another aspect, the invention features a spinal fixation and fusion assembly including a bone anchoring member and a cylindrical member. The bone anchoring member includes an elongated body made entirely of metallic material. The elongated body comprises a threaded portion at the distal end, a head at the proximal end, and a lag portion extending between the threaded portion and the head. The cylindrical member surrounds the lag portion of the bone—anchoring member and is made entirely of bone type material. The cylindrical member comprises a through opening extending along an axis from its proximal end to the distal end and the through opening includes inner threads and is dimensioned to receive said lag portion of the bone anchoring member. The spinal fixation may further include a polyaxial washer surrounding the head of the bone anchoring member, and the polyaxial washer includes spikes extending from its bottom surface. 
         [0009]    In general, in another aspect, the invention features a spinal fixation and fusion assembly including a bone anchoring member and a cylindrical member. The bone anchoring member includes an elongated body and the elongated body is made entirely of bone type material. The elongated body comprises a threaded portion at the distal end, a head at the proximal end, and a lag portion extending between the threaded portion and the head. The cylindrical member surrounds the lag portion of the bone—anchoring member and is made entirely of bone type material. The cylindrical member comprises a through opening extending along an axis from its proximal end to the distal end and the through opening comprises inner threads and is dimensioned to receive said lag portion of the bone anchoring member. 
         [0010]    In general, in another aspect, the invention features a spinal fixation and fusion method including forming an opening extending through first and second adjacent vertebral bodies and then inserting a spinal fixation and fusion assembly into the formed opening. The spinal fixation and fusion assembly comprises a bone anchoring member, a cylindrical rod and a cap. The bone anchoring member comprises an elongated body comprised entirely of bone type material and the elongated body comprises a main shaft, a conical shaped distal end, a flared out proximal end, and a through opening extending along an axis from the proximal end to the distal end. The cylindrical rod is shaped and dimensioned to be received within the through opening and is comprised entirely of metal and the cap is comprised entirely of metal and is attached to a proximal end of the cylindrical rod. 
         [0011]    In general, in another aspect, the invention features a spinal fixation and fusion method comprising forming an opening extending through first and second adjacent vertebral bodies and inserting a spinal fixation and fusion assembly into said formed opening. The spinal fixation and fusion assembly comprises a bone anchoring member and a cylindrical member. The bone anchoring member comprises an elongated body comprised entirely of metallic material. The elongated body comprises a threaded portion at the distal end, a head at the proximal end, and a lag portion extending between the threaded portion and the head. The cylindrical member surrounds the lag portion of the bone anchoring member. The cylindrical member is comprised entirely of bone type material and comprises a through opening extending along an axis from its proximal end to the distal end and the through opening comprises inner threads and is dimensioned to receive said lag portion of the bone anchoring member. The spinal fixation and fusion assembly further includes a polyaxial washer surrounding the head of the bone anchoring member, and the polyaxial washer comprises spikes extending from its bottom surface. 
         [0012]    In general, in another aspect, the invention features a spinal fixation and fusion method comprising forming an opening extending through first and second adjacent vertebral bodies and then inserting a spinal fixation and fusion assembly into said formed opening. The spinal fixation and fusion assembly comprises a bone anchoring member and a cylindrical member. The bone anchoring member comprises an elongated body comprised entirely of bone type material. The elongated body comprises a threaded portion at the distal end, a head at the proximal end, and a lag portion extending between the threaded portion and the head. The cylindrical member surrounds the lag portion of the bone anchoring member. The cylindrical member is comprised entirely of bone type material and comprises a through opening extending along an axis from its proximal end to the distal end and the through opening comprises inner threads and is dimensioned to receive said lag portion of the bone anchoring member. 
         [0013]    In general, in another aspect, the invention features a facet fixation and fusion method comprising forming a first opening extending through a facet joint of first and second adjacent vertebral bodies and then forming a second opening extending through the first and second adjacent vertebral bodies. The second opening is adjacent to the first opening. Next, inserting a first spinal fixation assembly into the first opening, and then inserting a second spinal fixation and fusion assembly into the second opening. The first fixation assembly comprises a bone anchoring member and a polyaxial washer. The bone anchoring member comprises an elongated body having a threaded portion at the distal end, a head at the proximal end, and a lag portion extending between the threaded portion and the head. The polyaxial washer surrounds the head. The first fixation assembly is comprised entirely of metallic material. The second fixation and fusion assembly comprises a cylindrical elongated body comprised entirely of bone type material. The first and second openings may intersect each other, or may be non-intersecting. The first and second openings may have parallel or non-parallel trajectories. The first and second openings are formed through a double-barreled cannula. 
         [0014]    The details of one or more embodiments of the invention are set forth in the accompanying drawings and description below. Other features, objects and advantages of the invention will be apparent from the following description of the preferred embodiments, the drawings and from the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Referring to the figures, wherein like numerals represent like parts throughout the several views: 
           [0016]      FIG. 1  depicts a prior art system for face fixation; 
           [0017]      FIG. 1   a  and  FIG. 1   b  are perspective views of a first embodiment of the spine fixation and fusion device according to this invention; 
           [0018]      FIG. 2   a  and  FIG. 2   b  are perspective views of the second embodiment of the spine fixation and fusion device according to this invention; 
           [0019]      FIG. 3   a ,  FIG. 3   b , and  FIG. 3   c  are perspective views of a third embodiment of the spine fixation device according to this invention; 
           [0020]      FIG. 4   a  and  FIG. 4   b  are perspective views of the fourth embodiment of the spine fixation and fusion device according to this invention; 
           [0021]      FIG. 5   a  and  FIG. 5   b  are perspective views of the fifth embodiment of the spine fixation and fusion device according to this invention; 
           [0022]      FIG. 6   a  is a perspective view of the sixth embodiment of the spine fixation and fusion device according to this invention; 
           [0023]      FIG. 6   b  is a perspective view of the embodiment of  FIG. 6   a  having a metal cap at the top end; 
           [0024]      FIG. 6   c  is a side cross-sectional view of the embodiment of  FIG. 6   b;    
           [0025]      FIG. 7   a  and  FIG. 7   b  are perspective views of the seventh embodiment of the spine fixation and fusion device according to this invention; 
           [0026]      FIG. 8  is a perspective view of the eighth embodiment of the spine fixation and fusion device according to this invention; 
           [0027]      FIG. 9   a  and  FIG. 9   b  are perspective views of the ninth embodiment of the spine fixation and fusion device according to this invention; 
           [0028]      FIG. 9   c  is a cross-sectional side view showing the installation of the spine fixation device of  FIG. 9   b;    
           [0029]      FIG. 9   d  is a cross-sectional side view showing the fully installed spine fixation device of  FIG. 9   b;    
           [0030]      FIG. 10   a  and  FIG. 10   b  are an exploded view and perspective view of a tenth embodiment the spine fixation and fusion device according to this invention, respectively; 
           [0031]      FIG. 11   a  through  FIG. 11   e  are perspective views of the first method steps of inserting the fixation and fusion device of this invention in and through the facet joint; 
           [0032]      FIG. 12   a  through  FIG. 12   h  are perspective views of the second method of inserting the fixation and fusion device of this invention in and through the facet joint; 
           [0033]      FIG. 13   a  through  FIG. 13   i  are perspective views of the third method of inserting the fixation and fusion device of this invention in and through the facet joint; and 
           [0034]      FIG. 14  is a perspective view of inserting a fixation and fusion device through the facet joint in a more lateral trajectory. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0035]    Referring to  FIG. 1 , spinal fixation elements  82   a ,  82   b  are used to secure together first and second facet joints  46   a ,  46   b  of two adjacent vertebras  30   a  and  30   b . The spinal fixation elements  82   a ,  82   b  are inserted along directions  60 ,  70 , respectively. In most cases, directions  60 ,  70  are symmetrically positioned to the left and right of the spinal midline  80 . In this prior art example, fixation elements  82   a ,  82   b  are facet screws and are placed in a trans-facet way for connecting adjacent vertebras  30   a ,  30   b . In other examples, fixation elements  82   a ,  82   b , may be staples, wires, or pins, and they may connect adjacent or non-adjacent vertebras via trans-facet, intra-facet, trans-laminar, trans-facet-pedicular, trans-pedicular, or through any other vertebral location. 
         [0036]    The present invention describes a new facet fixation and fusion device that is shaped and formed to be implanted into the vertebrae through the facet joint and into the pedicle in order to provide both spine fixation and fusion through the facet joint. The new facet fixation and fusion device is made of allograft material, which is actual bone material harvested from human donors. 
         [0037]    Referring to  FIG. 1   a , a new facet fixation and fusion device comprises a cylindrical dowel  100  made of allograft bone material. The cylindrical dowel  100  includes an elongated cylindrical body  101  having a rounded conical shaped distal end portion  102  and a flared out proximal end portion  104 . Distal end portion  102  tapers to a smaller diameter than the diameter of the cylindrical body  101 . In the embodiment of  FIG. 1   b , cylindrical dowel  100  includes a through opening extending along axis  107  from the proximal end  104  to the distal end  102 . 
         [0038]    Referring to  FIG. 2   a , a new facet fixation and fusion device comprises a cylindrical dowel  110  made of allograft bone material. The cylindrical dowel  110  includes an elongated cylindrical body  111  having a conical shaped distal end portion  112  and a flared out conical head portion  114 . Distal end portion  112  tapers to a smaller diameter than the diameter of the cylindrical body  111  and includes threads  113  that are designed to screw the dowel  110  into an opening extending through the facet joints, as will be described below. Head portion  114  has a flat top  114   a  and a diameter at the top larger than the diameter of the cylindrical body  111 . In the embodiment of  FIG. 2   b , cylindrical dowel  110  includes threads  113  that are oriented perpendicular to the dowels main axis  117 . 
         [0039]    Referring to  FIG. 3   a , a new facet fixation and fusion device comprises a cylindrical dowel  120  made of allograft bone material. The cylindrical dowel  120  includes an elongated cylindrical body  121  having a rounded conical shaped distal end portion  122  and a flared out proximal end portion  124 . Cylindrical body  121  includes barbs  123  or bumps  126  extending throughout the entire body  121  or covering only segments of the cylindrical body, as shown in  FIGS. 3   b  and  3   c . Distal end portion  122  tapers to a smaller diameter than the diameter of the cylindrical body  121 . In the embodiment of  FIG. 3   c , distal end portion  122  includes indentations  127 . In the embodiments of  FIG. 5   a  and  FIG. 5   b , cylindrical body  121  includes elongated straight or helical patterned protrusions  129 ,  128  surrounding the elongated body, respectively. In one example, protrusions  128 ,  129  are crush ribs that dig into the side walls of the opening  192  made in the facet joint, shown in  FIG. 11   d.    
         [0040]    Referring to  FIG. 4   a , a new facet fixation and fusion device comprises a parallelepiped-shaped dowel  130  made of allograft bone material. The parallelepiped-shaped dowel  130  includes an elongated body  131  having a rectangular cross-section, rectangular top and bottom surfaces and four rectangular sides  131   a ,  131   b ,  131   c ,  131   d . The distal end portion  132  comprises an inverted truncated rectangular pyramid extending from the bottom surface of the elongated body  131  and the proximal end portion  134  comprises an inverted truncated rectangular pyramid extending from the top surface of the elongated body  131 . 
         [0041]    Referring to  FIG. 4   b , a new facet fixation and fusion device comprises a polygonal-shaped dowel  130  made of allograft bone material. The polygonal-shaped dowel  140  includes an elongated polygonal body  141 , which in this case has a hexagonal cross-section, hexagonal top and bottom surfaces and six rectangular sides  141   a ,  141   b ,  141   c ,  141   d ,  141   e ,  141   f . The distal end portion  142  comprises an inverted truncated polygonal pyramid extending from the bottom surface of the elongated body  141  and the proximal end portion  144  comprises an inverted truncated polygonal pyramid extending from the top surface of the elongated body  141 . The edges  143  between two adjacent side surfaces (i.e.,  141   a ,  141   b  or  131   a ,  131   b ) form a rigid and sharp edge that bites into the side walls of opening  192  in the facet joint. 
         [0042]    Referring to  FIG. 6   a , a new facet fixation and fusion device  150  comprises a combination of a cylindrical metallic rod  152  surrounded by an outer cylindrical body  155  made of allograft bone material. The outer cylindrical body  155  includes a through opening  153  extending along axis  151  from the proximal end  154  to the distal end  156 . In the embodiment of  FIG. 6   b , the device  150  also includes a metal cap  158  that connects to the metal cylinder  152  inside the through opening  153 , as shown in the cross-sectional view in  FIG. 6C . 
         [0043]    Referring to  FIG. 7   a , a new facet fixation and fusion device  150  comprises a cylindrical metallic rod  152  surrounded by an outer cylindrical body  155  made of allograft bone material. The device  150  also includes a “bulleted” conical shaped metallic cap  157  at the distal end of the cylindrical body  155 . The outer cylindrical body  155  includes a through opening  153  extending along axis  151  from the proximal end  154  to the distal end  156 . 
         [0044]    In the embodiment of  FIG. 7   b , the device  150  also includes a metal cap  158  which connects to the metal cylinder  152  inside the through opening  153 . In this embodiment the conical metallic cap  157  also includes screw threads  159  surrounding its outer surface. In the embodiment of  FIG. 8 , the cylindrical body  155  includes longitudinally extending metallic spikes or teeth  161  protruding from the sides of the cylindrical body  155 . 
         [0045]    Referring to  FIG. 9   b , a new facet fixation and fusion device  160  comprises an elongated metallic screw  162  having a threaded distal portion  166 , a head  168  and a lag portion  167  extending between the head  168  and the distal portion  166 . The lag portion  167  is surrounded by an outer cylindrical body  164  made of allograft bone material. Cylindrical body  164  includes a through opening  165  extending along its longitudinal axis  169 . Opening  165  includes inner threads  163 . Fixation device  160  is placed in an opening  172  extending through the facet joints  175  and the opening  172  includes a countersink hole  171  at the top for housing the cylindrical body  164  and head  168  of the screw  162 . In this embodiment screw  162  also includes a polyaxial washer  170  surrounding the head  168 . Polyaxial washer  170  includes spikes  173  extending from its bottom surface. Spikes  173  are configured to engage the surrounding bone surface, as shown in  FIG. 9   d.    
         [0046]    Referring to  FIG. 10   a , a new facet fixation and fusion device  180  comprises an elongated allograft plug  182  having a threaded distal portion  186 , a head  188  and a lag portion  187  extending between the head  188  and the distal portion  186 . The lag portion  187  is surrounded by an outer cylindrical body  184  also made of allograft bone material. Cylindrical body  184  includes a through opening  185  extending along its longitudinal axis  189 . Opening  185  includes inner threads  183 . Fixation device  180  is placed in an opening extending through the facet joints and the opening includes a countersink hole at the top for housing the cylindrical body  184  and head  188  of the plug  182 , as was described above. 
         [0047]    A first method of inserting the facet fixation and fusion device of  FIG. 1   a  includes driving an opening  192  with an awl  194  through the inferior facet of vertebra  30   b , facet joint  46   b , and superior facet of vertebra  30   a , with a trajectory towards the pedicle of the inferior vertebra  30   a , as shown in  FIG. 11   a . Next, inserting a cannula  196  over the awl  194 , removing the awl  194  and inserting a drill bit  198  through the cannula  196 , as shown in  FIG. 11   b  and  FIG. 11C . Next, drilling a hole  192  with the drill bit  198  and then inserting the fixation device  100  into the hole  192  through the cannula  196  with the impacter  199 . Finally removing the impacter  199  and cannula  196  leaving behind the inserted fixation device  100 , as shown in  FIG. 11   e . The process is repeated for the other facet joint  46   a . This method is applied for inserting any of the above described fixation devices  100 ,  110 ,  120 ,  130 ,  140 ,  150 ,  160 ,  180 . 
         [0048]    Referring to  FIG. 12   a - FIG. 12   h , in a second method two adjacent openings  208 ,  209  are made instead of one. Openings  208 ,  209  may be intersecting each other or non-intersecting. The allograft fixation and fusion device  100  is inserted in opening  208  and a separate metallic facet screw  206  is inserted in the other opening  209 , as shown in  FIG. 12   e  and  FIG. 12   f , respectively. A double-barreled cannula  200  is used to reach the two openings. In the case of a cannulated allograft device  100  (shown in  FIG. 1   b ), a guide wire  211  is used for inserting the allograft device in the opening  208 , shown in  FIG. 12   h.    
         [0049]    A third method is used for inserting the two component fixation and fusion device  160  or  180 . Referring to  FIG. 13   a , first an opening is driven and a cannula  196  is inserted. Next, the opening is dilated with dilator  212 , shown in  FIG. 13   b , and then a drill bit  198  is inserted through the cannula  196  for drilling a hole  222 , shown in  FIG. 13   c . Next, a countersink hole  220  surrounding the top of the opening  222  is drilled, as shown in  FIG. 13   d  and then the cylindrical allograft sleeve  164  is inserted in the countersink hole  220 , as shown in  FIG. 13   e . Finally the metallic facet screw  162  or the allograft plug  188  is inserted in the cylindrical allograft sleeve  164 , as shown in  FIG. 13   f  or  FIG. 13   h , respectively. 
         [0050]    In another embodiment, two separate openings are drilled with different trajectories through the facet joint  46   b , as shown in  FIG. 14 . In this embodiment, one opening is used for the allograft device  180  and the other opening is used for the metallic facet screw  206 . The opening for the allograft device  180  has a more lateral trajectory extending through the facet joint  46   b , as shown in  FIG. 14 . 
         [0051]    Other embodiments include one or more of the following. The allograft bone material is substituted with other biocompatible materials including synthetic bone growth promoting material, bone-polymer composite material, autograft bone material, xenograft bone material, polymers, resorbable material, or non-resorbable material, or combinations thereof. The metallic components may be made of titanium, cobalt, stainless steel, chrome, or alloys thereof or shape-memory alloy, or ceramic-metallic composite materials, among others. 
         [0052]    Several embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.