Patent Publication Number: US-2023157833-A1

Title: Minimally invasive posterior cervical facet arthrodesis shim implant and tools therefor

Description:
FIELD OF THE INVENTION 
     The invention pertains to surgical implants and tools for the distraction and fusion of cervical facet, foramen, and vertebrae. 
     BACKGROUND 
     Cervical spinal surgery since the late 1950s and early 1960s has steadily transitioned from primarily posterior based to primarily anterior based. Posterior based surgery has the following major advantages: minimal critical structures in the surgical field, familiar anatomy, and access to multiple levels. However, posterior based surgery has the following major disadvantages: dissection or approach related post-operative pain and large or limited arthrodesis option (for example, lateral mass screws and surface area available for fusion). Anterior based cervical surgery addresses some of the deficits, particularly pain and infection rates. Thus, the trend in the United States has been a shift towards more anterior cervical surgery and towards less posterior cervical surgery. 
     However, certain unique risks still remain with anterior surgery: injury to esophagus, injury to trachea, dysphagia/dysphonia, injury to recurrent laryngeal nerves, carotid artery injury, internal jugular vein injury, vagus nerve injury, adjacent level disease, non-unions, implant failure, implant prominence, dural injury, spinal cord injury to name a few. Thus, there has been a reemergence of posterior based surgery, particularly minimally invasive posterior surgery, to address the issues that may arise with anterior surgery. 
     Common indications for posterior minimally invasive surgery (MIS) include anterior cervical non-unions, patients at high risk for non-unions (for example, smokers), and/or isolated foraminal stenosis which may lead to radiculopathy. In theory, given that the facet surface area of the posterior spine is equal to or larger than the surface area of the disc space anteriorly in between the uncus, one could minimize the rate of cervical non-unions or even treat anterior non-unions via a posterior MIS. In theory, if stenosis is present at the foraminal level, indirect decompression via a posterior MIS would elevate the facet joint and increase the foraminal height as has been shown in the literature. In theory, given the minimal disruption of soft tissue with posterior MIS, the infection rates and post-operative pain issues would match or surpass that of anterior based surgery. 
     Two general technologies are currently in use for minimally invasive cervical facet arthrodesis. The first are manufactured allografts, made from human bone that is compacted and machined. See for example “FacetLift” implants from Medtronic. These implants have clear disadvantages. The implants are brittle and can fracture during insertion. In addition, these implants are radiographically lucent, which can make intra-operative assessments challenging and post-operative fusion rates difficult to observe. And, these implants have small pore sizes (or no pores at all) from the machining process and can result in limited or no bone in-growth and bone fusion. 
     An alternative cervical facet implant are metal (usually titanium) implants, for example the “CAVUX®” (referred to as “DTRAX®” in some literature), “HONOUR® ORB,” “Valeo® II C”, “UNIFLEX® Cervical cage” and others. See, for example, WO 2015/047818 and WO 2009/148619. These implants do not provide for efficient bone in-growth. Rather, they typically have bone on-growth or through-growth through a limited graft window, which is less efficient at bone fusion. In addition, the shape of prior art implants is not conducive to safe implantation. In some instances, these implants require harsh insertion techniques, such as malleting that reduce the control of the implantation procedure. The cervical facet joints frequently have minor imperfections and bone spurs, and prior art devices can unnecessarily damage these features during implantation. 
     SUMMARY OF THE INVENTION 
     The inventive implants provide a novel combination of features that address the shortcomings in the prior art discussed above. In various embodiments, the inventive implants include a titanium or tantalum alloy body that has a similar modulus of elasticity as natural bone and provides good radiologic contrast. In an embodiment, the inventive implants include a rounded nose that limits tissue damage during insertion. In an embodiment, the inventive implants include serrated surfaces on the superior and inferior faces. In an embodiment, the body of the inventive implants may be porous, roughened, and coated with an osteoconductive material such as hydroxyapatite (HA) and/or tricalcium phosphate (TCP). In an embodiment, the body of the inventive implant includes a graft window spanning the entire thickness of the implant. 
     In an embodiment, implants and methods are provided for treating stenosis with or without radiculopathy comprising surgical distraction of the relevant cervical vertebrae and insertion of the implant of claim  1 . In an embodiment, this invention provides a shim implant for the fusion of a cervical facet joint, comprising a generally rounded or box-shaped body having a distal face, a proximal face, superior and inferior surfaces in a generally parallel orientation, and two side faces in a generally parallel orientation, wherein a transverse axis can be defined as a line perpendicular to the side faces. The distal face may have a rounded profile defined by an arc having a radius on a transverse axis. The proximal face may have one or more insertion device engagement features. The superior and inferior surfaces each comprise serrations with a plurality of grooves on a transverse axis generally spanning the entire length of a transverse axis. The implant may be fabricated from titanium metal or alloy or tantalum metal or alloy, and may have a roughened surface, and is coated with hydroxyapatite or tri-calcium phosphate or both and is porous to allow for bone in-growth. 
     In an embodiment, the implant may have a graft window comprising a perforation spanning the distance between the superior and inferior surfaces. In an embodiment, the implant may have a rounded profile of the distal face is biased towards the inferior surface. In an embodiment, the insertion device engagement features comprise one or more holes in the proximal face. The insertion device engagement features may comprise three holes aligned on a transverse axis on the proximal face. At least one hole may have female screw threads for engaging a male threaded tool. The threaded hole may be a central hole in a group of three holes. 
     In an embodiment, each surface of the implant may be roughened with a macro surface roughener or nano-coating. In an embodiment, the hydroxyapatite or tri-calcium phosphate coating has a thickness of approximately 35 µm. The porous material may have pore sizes ranging in 200 to 900 µm. 
     In an embodiment, a set of tools is provided for implanting the implant described above. The tools include a chisel and one or more tongs and rasps. An entry chisel is provided with a distal end with smooth inferior and superior surfaces, and a uniform cross-sectional profile, wherein the chisel has a shaft with rounded superior and inferior surfaces and flattened sides, and wherein the chisel shaft has two cannulation channels running the entire length thereof for accepting a guidewire. In an embodiment, a first tong has two prongs at a distal end that are smooth or roughened, and a channel in the shaft along the entire length of the tong, and the interior cross-section of the channel matches the uniform cross-sectional profile of the chisel, such that the chisel can be inserted in the channel in the first tong from a proximal end of the first tong to a nested position. The rounded superior and inferior surfaces and flattened sides of the chisel maintain rotational stability that prevents the chisel from rotating when in place. When nested, the distal tip of the chisel may be aligned with the prongs. The chisel nested in the first tong may be inserted into a channel in a proximal end of a first decorticator, wherein the first decorticator has a jagged distal end with teeth and the proximal end has a handle for manual manipulation of the decorticator, and wherein the chisel and first tong are aligned with the distal edge of the first decorticator, and wherein a facet joint between two vertebrae is decorticated from a posterior approach. The first decorticator may then be withdrawn leaving the chisel nested in the first tong embedded in the facet joint and the chisel may then be withdrawn. Next, a rasp may then be inserted into the channel in the first tong. A rasp of various dimensions (width and height) may be used to remove tissue within the facet joint to facilitate a fusion and to gauge the width and height of the final implant. The rasp is then withdrawn from the channel in the first tong. Next, an inserter having an implant as described above affixed to it is inserted into the channel in the first tong. In an embodiment, the inserter may have a shaft, an axle within the shaft, a handle that turns the axle, and a male-threaded connection at the distal end of the axle that is screwed into the female-threaded engagement feature on the implant, and at least one prong aligned with another engagement feature on the proximal face of the implant. The inserter is inserted into the channel in the first tong, and the implant is placed and secured in the facet joint. The handle is rotated to unscrew the implant and disconnect the implant from the inserter, and the first tong is withdrawn, leaving the implant securely in position. 
     In an embodiment, a second tong may be provided having two prongs at a distal end that are smooth or roughened and a channel in the shaft along the entire length of the second tong, wherein the interior cross-section of the channel matches the uniform cross-sectional profile of the first tong. The chisel nested in the first tong is inserted into the proximal end of the channel on the second tong into a nested position wherein the chisel tip, prongs of the first tong, and prongs of the second tong may be aligned. The chisel nested in the first tong and nested in the second tong may then be inserted into the facet joint. In an embodiment, the chisel and first tong are withdrawn, and a rasp may be inserted into the channel in the second tong. Rasps of various dimensions (width and height) may be manipulated by the surgeon to remove tissue within the facet joint to facilitate a fusion and to gauge the width and height of the final implant. The rasp may then be withdrawn from the channel in the first tong, and an inserter as described above having an implant as described above affixed to it, is inserted into the channel in the second tong, and the implant is placed and secured in the facet joint. The handle may be rotated to disconnect the implant from the inserter, and the second tong is withdrawn, leaving the implant securely in position. 
     In an embodiment, a second decorticator may be provided and the chisel nested in the first tong nested in the second tong are inserted therein to further decorticate the facet joint. In an embodiment, a third tong is provided that the chisel, the first tong and the second tong are inserted within to provide an appropriate space for the implant in a facet joint. 
     In an embodiment, the width of the space decorticated for the implant in the facet joint is controlled by the use of one or more tongs, and the height of the space decorticated for the implant is controlled by the height of the rasp. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  is a perspective view of an embodiment of the inventive implant with a centered nose and without a graft window. 
         FIG.  1 B  is a perspective front view of the inventive implant of  FIG.  1 A . 
         FIG.  1 C  is a side elevation view of the inventive implant of  FIG.  1 A . 
         FIG.  1 D  is a front elevation view of the proximal end of the inventive implant of  FIG.  1 A . 
         FIG.  1 E  is a back-elevation view of the inventive implant of  FIG.  1 A . 
         FIG.  2 A  is a perspective view from the rear and above of an embodiment of the inventive implant with a centered nose and with a graft window. 
         FIG.  2 B  is a perspective front view of the inventive implant of  FIG.  2 A . 
         FIG.  2 C  is a top view of the inventive implant of  FIG.  2 A . 
         FIG.  3 A  is a perspective view from the rear and below of an embodiment of the inventive implant having a nose which is off center and no graft window. 
         FIG.  3 B  is a front perspective view of the implant of  FIG.  3 A . 
         FIG.  4 A  is a perspective back view of an embodiment of the inventive implant with an off-centered nose and a graft window. 
         FIG.  4 B  is a front perspective view of the implant of figure of the inventive implant of  FIG.  4 A . 
         FIG.  5 A ,  FIG.  5 B , and  FIG.  5 C  depict an entry chisel according to an embodiment of this invention. 
         FIG.  6 A ,  FIG.  6 B ,  FIG.  6 C  and  FIG.  6 D  depict a first facet tong according to an embodiment of this invention. 
         FIG.  7 A ,  FIG.  7 B ,  FIG.  7 C  and  FIG.  7 D  depict the entry chisel nested within the first facet tong. 
         FIG.  8 A ,  FIG.  8 B ,  FIG.  8 C  and  FIG.  8 D  depict a first decorticator tool according to an embodiment of this invention. 
         FIG.  9 A ,  FIG.  9 B  and  FIG.  9 C  depict the apparatus as shown in  FIG.  7    nested inside the first decorticator. The decorticator includes a removable handle. 
         FIG.  10 A ,  FIG.  10 B , and  FIG.  10 C  depict a second facet tong. 
         FIG.  11 A ,  FIG.  11 B ,  FIG.  11 C  and  FIG.  11 D  depict the apparatus of  FIG.  7    nested inside the second facet tong. 
         FIG.  12 A  and  FIG.  12 B  depict a second decorticator according to an embodiment of this invention. 
         FIG.  13 A ,  FIG.  13 B , and  FIG.  13 C  depict the apparatus of  FIG.  11    nested inside the second decorticator. 
         FIG.  14 A ,  FIG.  14 B , and  FIG.  14 C  depict a third facet tong according to an embodiment of this invention. 
         FIG.  15 A ,  FIG.  15 B ,  FIG.  15 C  and  FIG.  15 D  depict the apparatus of  FIG.  11    nested inside the third facet tong according to an embodiment of this invention. 
         FIG.  16 A ,  FIG.  16 B  and  FIG.  16 C  depict the apparatus of  FIG.  15    with the entry chisel removed according to an embodiment of this invention. 
         FIG.  17 A  and  FIG.  17 B  depict the apparatus of  FIG.  16    with the first tong removed according to an embodiment of this invention. 
         FIG.  18 A  and  FIG.  18 B  depict the apparatus of  FIG.  17    with the second tong removed. 
         FIG.  19 A ,  FIG.  19 B  and  FIG.  19 C  depict a rasp tool according to an embodiment of this invention. 
         FIGS.  20 A and  20 B  show the rasp apparatus inserted into the third tong according to an embodiment of this invention. 
         FIGS.  21 A and  21 B  show an inserter tool according to an embodiment of this invention. 
         FIGS.  22 A and  22 B  depict the inserter tool with an exemplary implant affixed to the distal end. 
         FIG.  23    is a cutaway view showing an implant according to an embodiment of this invention affixed to the distal end of the inserter tool. 
         FIG.  24 A ,  FIG.  24 B , and  FIG.  24 C  depict a final set up with a rasp nested in the third tong according to an embodiment of this invention. 
     
    
    
     DETAILED DESCRIPTION 
     This invention provides an implant for the fusion of cervical spinal vertebrae, tools to insert the implant, and surgical procedures. 
     Implants 
     In an embodiment, the implant is a shim  100  with a box-shaped body as shown in  FIGS.  1 A- 1 E . For orientation, the shim has a blunt distal end that would sit anteriorly within the facet joint, also referred to herein as a nose, for insertion in between the cervical facet joints to minimize damage during insertion and reduce the tolerance necessary to insert the implant without unnecessary damage at the implant insertion site. The terminology “distal” and “proximal” are in relation to the surgeon implanting the inventive shim. Thus, the proximal face is closest to the surgeon during implantation, and the distal face is the leading edge inserted into the body of the patient at the implant site. The distal end of the implant, then, would sit more anteriorly within the facet joint, and the proximal end of the implant would sit more posteriorly within the facet joint. 
     In an embodiment, the inventive shim  100  has a proximal side with one or more insertion device engagement features  132  and  134 . In an embodiment, the insertion device engagement features are one or more threaded ( 134 ) and non-threaded ( 130 ) holes or indents adapted to receive appropriate tools used to aid in the implantation of the inventive device. In the embodiment illustrated in the figures, there are three holes in the proximal face of the implant, and the center hole  134  is threaded. In an embodiment, the holes may be drilled into the implant after the body is formed or may be created as the implant is created using additive manufacturing techniques. 
     The inventive implants also have a superior face  140  and an inferior face  142 . In an embodiment, the superior and inferior faces both have a series of parallel grooves or serrations  144  running in a transverse direction. 
       FIGS.  2 ,  3 , and  4    all illustrate variations on the embodiment of  FIG.  1   . In  FIGS.  2 A and  2 B , implant  102  is illustrated. This is similar to implant  100  but also features a graft window  150 , that in an embodiment, is an aperture through the entire thickness of the implant  102  from the inferior surface to the superior surface. 
       FIGS.  3 A and  3 B  show embodiment  104 , that is similar to embodiment  100 , but with an offset blunt nose  112 .  FIGS.  4 A and  4 B  show embodiment  106 , which has the offset nose and the graft window  150 . The blunt nose  112  in embodiments  104  and  106  is biased towards the inferior face of the implant. Put differently, the transverse axis used for the radius defining the curvature of the blunt nose is biased towards the inferior side of the implant. By contrast, the transverse axis used for the radius defining blunt nose  110  in embodiment  100 , where blunt nose  110  is centered between the inferior and superior sides, is centered between the inferior and superior sides. 
     Thus, there are at least four embodiments of the shim of this invention: (1) centered blunt nose, no graft window ( 100 ); (2) centered blunt nose, with the graft window ( 102 ); (3) offset blunt nose, no graft window ( 104 ); (4) offset blunt nose, with the graft window ( 106 ). Other embodiments are possible and within the scope of this invention. 
     The inventive implants are shims that are inserted by distraction of the facet joints and inserted into position with appropriate tools. In an embodiment, the shims are inserted in between the two facets and within the facet joint. In contrast to the prior art devices discussed above, such as the CAVUX®, HONOUR® ORB, Valeo® II C, UNIFLEX® Cervical cages, the inventive implants have a serrated surface, porous structure of the material, features which allow osseous in-growth and better fixation of the implant and consecutively of the joints. An additional embodiment of the instant invention provides a graft window which allows osseous growth and may provide additional osseous integration. 
     In an embodiment, the entire implant is fabricated from medically compatible tantalum, titanium, tantalum alloy, or titanium alloy. For example, an appropriate titanium alloy may be titanium 6AL4V and 6AL4V ELI (ASTM Standard F1472, https://www.astm.org/Standards/F1472.htm (see also https://en.wikipedia.org/wiki/Ti-6AI-4V)), which are alloys made with about 6% aluminum and 4% vanadium. An appropriate tantalum alloy may be tantalum alloyed with 2.5% to 10% tungsten, or 40% niobium. These materials are known to have good biocompatibility and match the modulus of elasticity of bone. In an embodiment, the implant may be manufactured from a titanium alloy in accordance with ASTM F136, or where exterior surfaces are coated with medical-grade commercially pure titanium (CP Ti) per ASTM F1580. 
     In an embodiment, all surfaces of the implant may be roughened with macro surface roughness or nano-coating. This may be accomplished with a technique such as grit blasting, acid etching, or plasma spray coating (also called thermal spray coating). 
     In an embodiment, all surfaces of the implant are coated with hydroxyapatite (HA) and/or tricalcium phosphate (TCP), with a coating thickness of approximately 35 µm. HA and TCP are well known as osteoconductive materials that encourage bone growth. 
     In an embodiment, the implant may be fabricated from a porous material known to enhance bone in-growth, for example with pore sizes ranging in 200 to 900 µm to facilitate in-growth and have a porosity of 60-65% to mimic cancellous bone. The combination of surface roughness, HA or TCP coating, and porosity will facilitate in growth which is desirable for fusion. 
     The inventive shim implants of this invention may be implanted by known minimally invasive methods. For example, prior to inserting the shim implant, the patent may be positioned prone with face down and the adequate intra-operative imaging of the desired facet joint(s) is assessed. Then a paracentral stab incision is made in line with and caudal to the facet joint on the anterior-posterior projection, and a blunt entry dilator or chisel is guided through the soft tissues and is placed in between the facet joint. A subsequent dilator or series of dilators is then placed over the initial dilator and into the facet joint to access the joint space, and the blunt entry chisel or dilator is removed while the outer most dilator is kept in place. Subsequently, the extra-articular portion of the facet joint is decorticated with a decortication tool used first over and/or around the dilator, and a rasp next within the dilator to decorticate the intra-articular portion of the facet joint. Once decortication is complete, the shim implant is inserted under image guidance with a shim inserter device. After the shim implant is in position the shim inserter device is removed. Graft material can optionally be packaged posterior to and around the implant through the distractor tool. The dilator tool is then removed, and soft tissue closure and dressing are performed. In the detailed description below, the subsequent dilators are labeled as tongs. 
     Tools 
     In an embodiment, the implants herein may be implanted into a cervical facet joint in a posterior approach. 
     In an embodiment a series of nestable tools are provided to place the implants of this invention. 
     In an embodiment, an entry chisel  210  is provided as depicted in  FIGS.  5 A,  5 B, and  5 C , comprising a shaft having a distal and proximal end. The distal end is the tip of the chisel  211 , with smooth inferior and superior surfaces. The proximal end  212  has a roughened surface. The device may have dual cannulation channels  214 . The channels  214  may accept a guidewire to guide the placement of the apparatus as discussed herein. The device shaft may have rounded superior and inferior surfaces  218  and flat sides  219 . The chisel has a uniform cross-sectional profile because in the next step, the first tong is inserted using the chisel as a guide ( FIG.  7   ). The rounded superior and inferior surfaces and flat sides prevent the first tong from rotating out of plane from the chisel at the next step of the procedure. The chisel further has a series of transfer perforations (holes)  216  that serve as navigational landmarks for intra-operative imaging to evaluate the position of the tool during the implantation procedure. 
     Operationally, chisel  210  can be placed with the assistance of guide wires that fit within cannulation channels  214 . This feature assists the accurate placement of the tool during surgery. The chisel position can also be modified with the use of such guide wires. 
       FIGS.  6 A- 6 D  depict a first tong  230  that entry chisel  210  nestles within. The distal end of the first tong  230  has two prongs  234  that may be smooth or roughened. The proximal end has roughened surface  235  for ease of manual manipulation by the surgeon. A central channel  232  runs the entire length of the tong  230 . The profile (i.e., cross section) of channel  232  matches the cross section of entry chisel  210 . The rounded superior and inferior surfaces  218  along the shaft, and flattened sides  219  of the chisel shaft ensure rotational stability when the chisel is inserted into channel  232 . The tong includes holes  236  for intraoperative imaging of the position of the tool. Because first tong  230  may nestle within a second tong ( FIG.  11   ), tong  230  has a uniform cross-sectional profile with rounded top and bottom  238  and flattened sides  239 . Tong  230  may also be equipped with attachment point  237  providing a firm connection handle  270  ( FIG.  9   ). 
     The embedding of chisel  210  within tong  230  is shown in  FIGS.  7 A- 7 D .  FIGS.  7 A and  7 B  are two perspective views of the entire tool, viewed from the distal end ( FIG.  7 A ) and proximal end ( FIG.  7 B ). Details of the distal end  242  are shown in  FIG.  7 C  and proximal end  244  are shown in  FIG.  7 D . In the distal end  242 , chisel tip  211  is flush with prongs  234 . Proximal end  244  shows the proximal end  212  of entry chisel  210  nested within the channel of tong  230 . Proximal end  212  juts beyond the roughened proximal end  235  of tong  230 . 
     The next step in the procedure relies on a first decorticator  250  ( FIGS.  8 A- 8 D ).  FIG.  8 A  is a perspective view from the distal end, and  FIG.  8 B  is a perspective of the entire tool from the proximal end.  FIG.  8 C  is a close up of the distal end  255  of decorticator  250  showing additional detail.  FIG.  8 D  is a close-up of proximal end  253  of decorticator  250  showing additional detail. Decorticator  250  is a round hollow shaft ( 251 ) running the length of the tool except for the proximal region  258 . Shaft  251  defines channel  252  that runs the length of the tool. The distal end  255  has a diagonal cut forming an ellipsis  254  around the distal end of channel  252 . The inferior edge of the distal end of decorticator  250  is jagged with teeth  256 . The proximal end is depicted with octagonal cross section  258 . Other shapes (besides octagonal) for  258  are possible, such as hexagonal or others. The proximal terminus of channel  252  is shown in  FIG.  8 D . Also shown are anchor points  259  for connection to handle  270  ( FIG.  9   ). 
     As shown in  FIGS.  9 A- 9 C , the chisel nested in tong  230  depicted in  FIG.  7    is inserted into channel  252  of decorticator  250 . Handle  270  may be placed over decorticator  250  to provide a firm grip for the surgeon to manipulate decorticator or other instruments into position. In the illustrated embodiment, handle  270  includes features such as protuberance  271  to improve the grip of the surgeon. Also shown is collar  272  to assist in securing handle  270  to decorticator  250 . The handle may nest over octagonal section  258  on the decorticator. There may also be a mechanism that interacts with holes  259  and  237  to secure handle  270  on decorticator  250 . 
     The decortication procedure involves removal of superficial bone and other tissue to prepare a site for bone grafting for the purpose of fusing of the vertebrae or facet joint. When the degree of desired tissue removal is achieved, the decorticator is removed. If additional decortication is needed additional tongs can be layered over the first tong as discussed in the following paragraphs. 
     As shown in  FIGS.  10 A- 10 C , a second facet tong  280  may be provided, having a distal end with two prongs  284  that may be smooth or roughened and a proximal end with roughened surface  285 . Tong  280  has shaft  281  running the entire length of the tool. Within shaft  281  is channel  282 , adapted to accept tong  230  within it. Accordingly, the upper and lower surfaces of channel  282  are rounded and the sides are flat, to accommodate the cross-sectional profile of tong  230 . On tong  280 , the superior and inferior surfaces  288  are rounded, and sides  289  are flat. Also provided is handle attachment point  287  and a series of transverse perforations  286  for intraoperative imaging of the position of the tool. 
       FIGS.  11 A- 11 D  show the apparatus of  FIG.  7    inserted into second tong  280 . Thus,  294  ( FIG.  11 C ) shows the distal end of this arrangement, with entry chisel  210  nested within first tong  230  and nested within second tong  280 .  FIG.  11 C  shows flattened chisel tip  211  flush with prongs  234  (from tong  230 ) and  284  (from tong  280 ). The proximal end of this arrangement is shown in  FIG.  11 D , which depicts chisel proximal end  212  nested within first tong proximal end  236  and nested within second tong proximal end  285 . 
       FIGS.  12 A and  12 B  show a second decorticator  310  that is similar to decorticator  250  only larger to accommodate the apparatus as depicted in  FIG.  11    within it.  FIG.  12 A  is a perspective view from the distal end, and  FIG.  12 B  is a perspective of the entire tool from the proximal end. Decorticator  311  comprises a hollow round (in cross-section) shaft  311  that runs the entire length of the tool. This shaft is designed to fit entry chisel  210  nested within first tong  230  and nested within second tong  280  shown in  FIG.  11    within it (shown in  FIG.  13   ). Distal end  313  of decorticator  310  has an inferior edge  316  with jagged teeth for decorticating bone. Also depicted is a diagonal cut at the distal end to make ellipsis  314 . The proximal end  318  of decorticator  310  is depicted with an octagonal cross section. Other shapes (besides octagonal) for  318  are possible, such as hexagonal or others. The proximal terminus of channel  312  is shown in  FIG.  12 B . Also shown are anchor points  319  for connection to handle  330  ( FIG.  13 A ). 
     The apparatus of  FIG.  11    is nested within  312  as shown in  FIGS.  13 A - 13 C .  FIG.  13 C  is a detail view of distal end of decorticator  310  with entry chisel  210  nested within first tong  230  and nested within second tong  280  (294) inserted within channel  312  in the operational position. Handle  330  is than affixed to the proximal end of decorticator  310  as shown. A mechanism is provided to securely affix handle  330  to the decorticator without allowing the nested chisel and tongs  294  to move. Also shown is collar  332  to assist in securing handle  330  to decorticator  310 . 
     Operationally, the apparatus of  FIG.  13    is used to decorticate and roughen the bone surfaces on the joint as discussed above (paragraph [0068]). Decorticator 2 is then removed, leaving apparatus  294  in the joint. If additional distraction or access to a larger surface area is desired, a third tong  340  may be employed, shown in  FIGS.  14 A- 14 C . Tong  340  is similar to tongs  280  and  230  but is larger to accommodate the apparatus of  FIG.  11    within. Thus, tong  340  has shaft  341  and channel  342  running the entire length of the tool. The distal end of tong  340  has two prongs  344  that may be smooth or roughened. The proximal end has a roughened outer surface  345 . It can be seen is  FIG.  14 C  showing detail of the proximal end, that channel  342  has an interior cross-section matching the cross-section of the exterior of second prong  280 . Also shown is anchor point  347  for a handle, and series of transverse perforations  346  for intra-operative imaging to evaluate position of the tool. 
       FIG.  15    shows the apparatus of  FIG.  11    inserted into channel  342 .  FIG.  15 A  is a perspective view of the entire tool from the distal end.  FIG.  15 B  is a perspective view of the entire tool from the proximal end.  FIG.  15 C  is a detail view of distal end., showing the entry chisel  210 , first tong  230 , second tong  280 , and third tong  340  nested together, with each of prongs  234 ,  284 , and  344  flush with chisel tip  211 . The proximal end of this arrangement is shown in  FIG.  15 D , with each of  212 ,  235  and  285  nested together and within channel  342 . 
     Operational, the apparatus of  FIG.  15    is now wedged within the facet joint at the desired position. At this stage the chisel, first tong, and second tong are removed as follows. 
     First, as depicted in  FIGS.  16 A- 16 C , chisel  210  is withdrawn from the apparatus of  FIG.  15   . This can be seen clearly in the detail of  FIG.  16 C , showing distal end  353  with channel  232  in facet tong  230  empty. This can also be seen at the proximal end  354  in  FIG.  16 B , where the proximal end  212  of chisel  210  is absent. Next, first facet tong  230  is withdrawn to give the apparatus shown in  FIGS.  17 A and  17 B . Finally, second facet tong  280  is withdrawn to give the appearance shown in  FIGS.  18 A and  18 B . At this stage prongs  344  are embedded in the facet joint. 
     Thus, the entry chisel  210  and first, second, and third tongs decorticate and establish the appropriate width for the implants as described herein. As discussed in the following paragraphs, the height of the distraction for the implant is established with one or more rasps. 
     Accordingly, as shown in  FIGS.  19 A- 19 C  and  FIG.  20 - 20 A , rasp  400  is inserted into facet tong  340 . Rasps of various sizes, as discussed herein, are used to further decorticate the facet joint in preparation of placement of implant. Rasp  400  is illustrated with several views in  FIGS.  19 A- 19 C . The rasp has a shank  402  running the length from the rasp head at the distal end to the handle at the proximal end. As illustrated, the shank as a rectangular cross-sectional profile. The rasp head has a roughened superior surface  412  and a roughened inferior surface  414 , a distal tip  410  and an angled leading edge  416 . The proximal end of rasp  400  is a handle  418  to aid in insertion and removal. 
     Rasp  400  is inserted into fact tong  340  as shown in  FIGS.  20 A and  20 B . The head of the rasp (i.e.,  416 ) is flush with fork prongs  344 . Shank  402  is sized to that handle  418  fits over the proximal end of facet tong  340 . 
     The rasp head may be made available in a variety of heights and widths. In terms of width, this rasp can be sized to fit into facet tong  230  or  280  or  340 . The height of the rasp head is function of the requirements of the surgery to adjust the facet joint for the desired height of the implant. 
     This procedure may only need a smaller size and can rely on a rasp inserted into facet tong  230  or  280 . Similarly, this procedure may only need a smaller implant that would match the rasp. For illustrative purposes, the remainder of the procedure is illustrated with facet tong  340 . Rasps intended for tongs  230  or  280  must have a length appropriate to the tong tool. 
     The next step is insertion of an implant into facet tong  340 . The implant is attached to implant inserter  430  ( FIGS.  21 A and  21 B ). Inserter  430  has shaft  432  running the length of the tool. Head  433  is at the distal end. In the illustrated embodiment, the distal end has dual prongs  434  to match the implants ( FIGS.  1 - 4   ) and a central threaded head  436  to firmly affix the implant to the tool. The threaded head has male threads and is rotated by handle  438  on the proximal end of inserter  430 . An internal axle  435  (not shown) links handle  438  to threaded head  436  to screw the implant onto or off the tool. Also shown in  FIG.  21 A  is marker  437  near the proximal end to indicate the implant is flush with facet tongs distally. Only one such marking is shown but multiple markings may be employed to match various facet tongs. 
     In an embodiment, the implant affixed to inserter tool  430  is shown in  FIGS.  22 A,  22 B and  23   . Implant  106  is illustrated. To affix the implant to the inserter, male threads  436  are inserted into female threads  134  ( FIGS.  1 - 4   ) and screwed into place by rotating knob  438 . Prongs  434  are aligned with indents  132  on the implant and male thread  436  are turned all the way to affix implant  106  to inserter  430 .  FIG.  23    is a cutaway view of an embodiment of the implant affixed to the inserter tool with male threads  436  and dual prongs  434 . 
     The implant affixed to the inserter tool is then inserted into facet tong  340  as shown in  FIGS.  24 A- 24 C . The implant is inserted into position and inserter tool  430  is removed by unscrewing the tool from the implant by turning knob  438 . Additional graft material may be placed through facet tong to aid in fusion. The facet tong  340  is removed leaving the implant in position and the surgery is completed. 
     Thus, the nested series of tongs adjusts the width of the space in the facet joint for the implant such as  100 ,  102 ,  104 , or  106 , and rasps  400  can be produced in various heights to establish the height of the space for the implant. For example, if a narrower width is sufficient, the surgeon may only require the first and second tongs and omit the third tong. Similarly, if the anatomical requirements are for an even wider implant, a fourth or even fifth tong can be employed.  
     
       
         
           
               
               
             
               
                 Drawings Legend 
               
               
                 No. 
                 Description 
               
             
            
               
                 
                   100 
                 
                 Inventive implant, centered blunt nose, no graft window 
               
               
                 
                   102 
                 
                 Inventive implant, centered blunt nose, with graft window 
               
               
                 
                   104 
                 
                 Inventive implant, offset blunt nose, no graft window 
               
               
                 
                   106 
                 
                 Inventive implant, offset blunt nose, with graft window 
               
               
                 
                   110 
                 
                 Centered Blunt nose 
               
               
                 
                   112 
                 
                 Offset blunt nose 
               
               
                 
                   120 
                 
                 Side face 
               
               
                 
                   130 
                 
                 Proximal face 
               
               
                 
                   132 
                 
                 insertion device engagement indent 
               
               
                 
                   134 
                 
                 insertion device engagement indent with threads 
               
               
                 
                   140 
                 
                 Superior face 
               
               
                 
                   142 
                 
                 Inferior face 
               
               
                 
                   144 
                 
                 Serrations in superior and inferior faces 
               
               
                 
                   146 
                 
                 Pores in surface 
               
               
                 
                   150 
                 
                 Graft window 
               
               
                 
                   200 
                 
                 Tool system 
               
               
                 
                   210 
                 
                 Entry chisel 
               
               
                 
                   211 
                 
                 Flattened smooth Chisel tip, distal end 
               
               
                 
                   212 
                 
                 Roughened proximal end 
               
               
                 
                   214 
                 
                 Cannulations for guidewires (dual) 
               
               
                 
                   216 
                 
                 Holes in chisel (markers) for intra-operative imaging to evaluate position of the tool 
               
               
                 
                   218 
                 
                 Rounded top and bottom 
               
               
                 
                   219 
                 
                 Flattened sides 
               
               
                 
                   230 
                 
                 Facet tong 1 
               
               
                 
                   231 
                 
                 Facet tong 1 shaft 
               
               
                 
                   232 
                 
                 Hollow channel in tong 
               
               
                 
                   234 
                 
                 Fork prong (dual) 
               
               
                 
                   235 
                 
                 Roughened proximal end 
               
               
                 
                   236 
                 
                 Holes in shaft for intra-operative imaging to evaluate position of the tool 
               
               
                 
                   237 
                 
                 removable handle attachment point 
               
               
                 
                   238 
                 
                 Rounded top and bottom 
               
               
                 
                   239 
                 
                 Flattened sides 
               
               
                 
                   240 
                 
                 Entry chisel nested inside facet tong 1 
               
               
                 
                   242 
                 
                 Distal end of Entry chisel nested inside facet tong 1 
               
               
                 
                   244 
                 
                 Proximal end of Entry chisel nested inside facet tong 1 
               
               
                 
                   250 
                 
                 Decorticator 1 
               
               
                 
                   251 
                 
                 Decorticator hollow shaft 
               
               
                 
                   252 
                 
                 Central hollow channel, cannulation to fit over tong 1 
               
               
                 
                   253 
                 
                 Decorticator proximal end 
               
               
                 
                   254 
                 
                 distal end elliptical shape 
               
               
                 
                   255 
                 
                 Decorticator distal end 
               
               
                 
                   256 
                 
                 Distal end with jagged teeth 
               
               
                 
                   258 
                 
                 Proximal end with octagonal cross section 
               
               
                 
                   259 
                 
                 Holes in proximal end for anchoring with tool  270 
 
               
               
                 
                   270 
                 
                 Handle 
               
               
                 
                   271 
                 
                 Grip protuberance 
               
               
                 
                   272 
                 
                 Handle collar 
               
               
                 
                   274 
                 
                 Chisel and tong 1 nested inside decorticator 
               
               
                 
                   280 
                 
                 Facet tong 2 
               
               
                 
                   281 
                 
                 Facet tong 2 shaft 
               
               
                 
                   282 
                 
                 Channel to fit over facet tong 1 
               
               
                 
                   284 
                 
                 Fork prong in tong 2 (dual) 
               
               
                 
                   285 
                 
                 Roughened proximal end 
               
               
                 
                   286 
                 
                 Holes in shaft 
               
               
                 
                   287 
                 
                 removable handle attachment point 
               
               
                 
                   288 
                 
                 Rounded superior and inferior surfaces 
               
               
                 
                   289 
                 
                 Flat sides 
               
               
                 
                   294 
                 
                 Chisel nested in tonq 1 nested in tonq 2 distal end 
               
               
                 
                   296 
                 
                 Chisel nested in tong 1 nested in tong 2 proximal end 
               
               
                 
                   310 
                 
                 Decorticator 2 
               
               
                 
                   311 
                 
                 Decorticator 2 shaft 
               
               
                 
                   312 
                 
                 Central hollow channel, cannulation to fit over tonq 2 
               
               
                 
                   313 
                 
                 Distal end of decorticator 2 
               
               
                 
                   314 
                 
                 distal end elliptical shape Decorticator 2 
               
               
                 
                   316 
                 
                 Distal end with jagged teeth Decorticator 2 
               
               
                 
                   318 
                 
                 Proximal end with octagonal cross section Decorticator 2 
               
               
                 
                   319 
                 
                 Holes in proximal end for anchoring with tool  270  Decorticator 2 
               
               
                 
                   330 
                 
                 Handle for decorticator 2 
               
               
                 
                   332 
                 
                 Collar for Handle for decorticator 2 
               
               
                 
                   334 
                 
                 Chisel, tong 1, decorticator 1, tong 2 nested in decorticator 2 
               
               
                 
                   340 
                 
                 Facet tong 3 
               
               
                 
                   341 
                 
                 Facet tong 3 shaft 
               
               
                 
                   342 
                 
                 Channel to fit over facet tong 2 
               
               
                 
                   344 
                 
                 Fork prong in tonq 3 (dual) 
               
               
                 
                   345 
                 
                 Roughened distal end tonq 3 
               
               
                 
                   346 
                 
                 Holes in tong 3 shaft 
               
               
                 
                   347 
                 
                 Holes in distal end 
               
               
                 
                   348 
                 
                 Flat internal sides of tong 3 channel 
               
               
                 
                   349 
                 
                 Rounded top and bottom interior surfaces of tong 3 channel 
               
               
                 
                   351 
                 
                 Chisel, tong 1, tong 2 tong 3 nested together distal tip 
               
               
                 
                   353 
                 
                 Distal tip of  351  but with chisel removed. tong 1, tong 2 tong 3 nested together 
               
               
                 
                   354 
                 
                 Proximal end of tong 1, tong 2, tong 3 nested together 
               
               
                 
                   355 
                 
                 Distal tip of  351  with chisel and tong 1 removed, tong 2, tong 3 nested together 
               
               
                 
                   356 
                 
                 Proximal end of tong 2, tong 3 nested together 
               
               
                 
                   400 
                 
                 rasp 
               
               
                 
                   402 
                 
                 Rasp shank 
               
               
                 
                   410 
                 
                 Rasp distal end 
               
               
                 
                   412 
                 
                 Rasp roughened superior end surface 
               
               
                 
                   414 
                 
                 Rasp roughened inferior end surface 
               
               
                 
                   416 
                 
                 Rasp angled leading edge 
               
               
                 
                   418 
                 
                 Rasp handle 
               
               
                 
                   420 
                 
                 Rasp nested in tong 3 
               
               
                 
                   430 
                 
                 Implant inserter 
               
               
                 
                   432 
                 
                 Implant inserter shaft 
               
               
                 
                   433 
                 
                 Implant inserter distal end 
               
               
                 
                   434 
                 
                 Outer Implant prong (dual) 
               
               
                 
                   435 
                 
                 Implant inner shaft (not shown) 
               
               
                 
                   436 
                 
                 Central implant prong threaded 
               
               
                 
                   437 
                 
                 Markings on shaft proximally to indicate the implant is flush with facet tongs distally (only one such marking is drawn but multiple markings would be employed to match various facet tongs) 
               
               
                 
                   438 
                 
                 Handle to unscrew central prong 
               
               
                 
                   439 
                 
                 Roughened distal end 
               
               
                 
                   440 
                 
                 Implant inserter nested in tong 3 
               
               
                 
                   442 
                 
                 Distal end of Implant inserter nested in tong 3 
               
               
                 
                   444 
                 
                 Proximal end of Implant inserter nested in tong 3