Abstract:
A device and method for contouring articular processes of a facet joint includes a guide with a spacer extending outward in a longitudinal direction from a distal end of the guide. The spacer includes a width to space apart the articular processes in a widthwise direction. A cutting member that is offset the spacer in the widthwise direction includes a cutting edge oriented to contour one of the articular processes in the longitudinal direction. The cutting member may be fixed or moveable relative to the guide. If the cutting member is moveable relative to the guide, the guide may include a guide edge along which the cutting member moves to control the accuracy of the contouring. A second cutting member may be offset a second side of the spacer in the widthwise direction and include a second cutting edge oriented to contour the second articular process in the longitudinal direction.

Description:
BACKGROUND  
       [0001]    The human spine serves many functions. The vertebral members of the spinal column protect the spinal cord. The spinal column also supports other portions of the human body. Furthermore, moveable facet joints and resilient discs disposed between the vertebral members permit motion between individual vertebral members. Each vertebrae includes an anterior body and a posterior arch. The posterior arch includes two pedicles and two laminae that join together to form the spinous process. A transverse process is laterally positioned at the transition from the pedicles to the laminae. Both the spinous process and transverse process provide for attachment of fibrous tissue, including muscle. Two inferior articular processes extend downward from the junction of the laminae and the transverse process. Further, two superior articular processes extend upward from the junction. The articular processes of adjacent vertebrae form the facet joints. The inferior articular process of one vertebra articulates with the superior articular process of the vertebra below. The facet joints are referred to as gliding joints because the articular surfaces glide over each other. 
         [0002]    Vertebral implants are often used in the surgical treatment of spinal disorders such as degenerative disc disease, disc herniations, curvature abnormalities, and trauma. Many different types of treatments are used. In some cases, spinal fusion is indicated to inhibit relative motion between vertebral bodies. Spinal fusion often involves the removal of the vertebral disc and insertion of an interbody implant to create a fused junction between a pair of vertebral bodies. Furthermore, the facet joints may be fused to complete the fusion between vertebral pairs. Facet fusion may be initiated by decorticating the opposing articulating surfaces and packing bone growth promoting substances into the space between the articular processes. The facet joints are generally small as compared to the intervertebral space. It may be difficult for the surgeon to determine the amount of contouring and shaping required for each of the articular processes. A trial-and-error routine is performed as the surgeon removes a first amount of material from one or both surfaces and determines whether the spacing is adequate for receiving a fusion device. Consequently, a certain amount of precision is desirable in preparing the articulating surfaces to receive a fusion implant and to prevent excessive trauma to the processes. 
       SUMMARY  
       [0003]    Illustrative embodiments disclosed herein are directed to devices and methods for contouring articular processes of a facet joint. The device may include a guide with a spacer extending outward in a longitudinal direction from a distal end of the guide. The spacer may include one or more prongs. The spacer includes a width to space apart the articular processes in a widthwise direction. A cutting member that is offset the spacer in the widthwise direction includes a cutting edge oriented to contour one of the articular processes in the longitudinal direction. The cutting member may be fixed or moveable relative to the guide. In either embodiment, a second cutting member may be offset a second side of the spacer in the widthwise direction and include a second cutting edge oriented to contour the second articular process in the longitudinal direction. 
         [0004]    In embodiments where the cutting member is fixed with respect to the guides, the cutting edge may be proximally disposed relative to the guide. Contouring is performed by driving the guide into the facet joint. In embodiments where the cutting member is moveable relative to the guide, the guide may include a guide edge along which the cutting member moves to control the accuracy of the contouring. The cutting member may move laterally and/or in the longitudinal direction relative to the guide. Once the articular processes are prepared accordingly, an implant can be inserted between the processes to promote facet joint fusion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0005]      FIG. 1  is a lateral view of a facet implant according to one embodiment shown relative to vertebral bodies; 
           [0006]      FIG. 2  is an axial section view according to the section lines in  FIG. 1 ; 
           [0007]      FIG. 3  is an axial section view of a facet joint showing a cutting tool used to prepare the articular processes of the facet joint according to one embodiment; 
           [0008]      FIG. 4  is a perspective detail view of a facet joint cutter according to one embodiment; 
           [0009]      FIG. 5  is an axial section view of a facet joint showing a cutting tool preparing one articular process of the facet joint according to one embodiment; 
           [0010]      FIG. 6  is an axial section view of a facet joint showing a cutting tool used to prepare the articular processes of the facet joint according to one embodiment; 
           [0011]      FIG. 7  is a detail view of a facet joint cutter according to one embodiment; 
           [0012]      FIG. 8  is an axial section view of a facet joint showing a cutting tool preparing one articular process of the facet joint according to one embodiment; 
           [0013]      FIG. 9  is a detail view of a facet joint cutter according to one embodiment; 
           [0014]      FIG. 10  is an axial section view of a prepared facet joint showing an implant insertable between the articular processes of the facet joint according to one embodiment; 
           [0015]      FIG. 11  is a lateral view of an exemplary facet fusion implant according to one embodiment; 
           [0016]      FIG. 12  is a top view of an exemplary facet fusion implant according to one embodiment; 
           [0017]      FIG. 13  is an axial section view of a facet joint showing a guide used to prepare the articular processes of the facet joint according to one embodiment; 
           [0018]      FIG. 14  is an axial section view of a facet joint showing a guide and cutting tool used to prepare the articular processes of the facet joint according to one embodiment; 
           [0019]      FIG. 15  is a perspective view of a guide and cutting tool used to prepare the articular processes of a facet joint according to one embodiment; 
           [0020]      FIG. 16  is a perspective view of a guide used to prepare the articular processes of a facet joint according to one embodiment; 
           [0021]      FIG. 17  is a perspective view of a cutting tool used to prepare the articular processes of a facet joint according to one embodiment; 
           [0022]      FIG. 18  is a perspective view of a cutting tool used to prepare the articular processes of a facet joint according to one embodiment; 
           [0023]      FIGS. 19A and 19B  are perspective views of a cutting tool used to prepare the articular processes of a facet joint according to one embodiment; 
           [0024]      FIG. 20  is a perspective view of a guide used to prepare the articular processes of a facet joint according to one embodiment; 
           [0025]      FIG. 21  is a perspective view of a guide used to prepare the articular processes of a facet joint according to one embodiment; 
           [0026]      FIG. 22  is a perspective view of a guide used to prepare the articular processes of a facet joint according to one embodiment; 
           [0027]      FIG. 23  is a perspective view of a guide used to prepare the articular processes of a facet joint according to one embodiment; 
           [0028]      FIG. 24  is a perspective view of a guide used to prepare the articular processes of a facet joint according to one embodiment; and 
           [0029]      FIG. 25  is a perspective view of a guide and cutting tool used to prepare the articular processes of a facet joint according to one embodiment. 
       
    
    
     DETAILED DESCRIPTION  
       [0030]    The various embodiments disclosed herein relate to methods and devices used in the preparation of a facet joint to promote fusion of the facet in spinal fusion surgery.  FIG. 1  illustrates one embodiment of an implant  10  installed according to this approach. Specifically,  FIG. 1  shows a lateral view of two vertebrae V 1 , V 2  and an intervertebral disc D disposed therebetween. During fusion surgery, some or the entire disc D is removed and may be replaced with an implant or graft that ultimately fuses to the vertebrae V 1 , V 2 . In addition, a surgeon may elect to fuse the facet joints J that are formed between the inferior articular process IP of the superior vertebra V 1  and the superior articular process SP of the inferior vertebra V 2 . To that end, the implant  10  may be inserted between the articular processes IP, SP as illustrated and disclosed herein. The section view shown in  FIG. 2  is depicted according to the section line labeled II-II in  FIG. 1 . The exemplary implant  10  illustrated in  FIG. 1  is also presented in  FIG. 2 . In one or more embodiments, the implant  10  may be pinned, screwed, or otherwise secured to the articular processes IP, SP using a fastener  12 . The fastener  12  may be implemented using a pin, a nail, a screw, a staple, a band, or other feature that secures the implant  10  to the facet joint J until fusion occurs. Other embodiments disclosed herein may be implemented without a fastener  12 . 
         [0031]    The implant  10  and fastener  12  may be constructed of biocompatible materials, including metals, such as titanium or stainless steel, non-metals, such as PEEK or UHMWPE. The implant  10  and fastener  12  may be constructed of a graft material, which is interpreted herein to include implants constructed from natural or synthetic bone materials including, but not limited to autograft, allograft, xenograft, or calcium phosphate. In embodiments where the implant  10  is constructed from synthetic or manufactured materials, the implant  10  may be coated or textured to improve the likelihood of bony ingrowth into the implant. Similarly, the implant may be impregnated, packed, or filled with bone growth promoting substances such as Bone Morphogenetic Protein (BMP), demineralized bone matrix (DBM), allograft, autograft, xenograft, or other osteoinductive growth factors. For example, the implant  10  may include a porous structure with open portions of the implant  10  packed with the bone growth promoting substance. In certain implementations, the implant  10  may osseointegrate or become part of the fusion mass at the facet joint J to increase the size and stability of the fusion mass. In one embodiment, the fastener  12  may be constructed from a bioabsorbable material that begins to dissolve after the implant  10  has begun to fuse to the facet joint J. 
         [0032]    The facet joint J may be prepared in advance of receiving the implant  10  by decorticating the articulating surfaces of the joint J.  FIG. 3  illustrates one embodiment of a cutting tool  20 A adapted for this purpose. The cutting tool  20 A includes a handle  26 , elongated shaft  24 , and cutter  22 A disposed at the distal end of the tool  20 A.  FIG. 4  illustrates a detailed perspective view of the cutter  22 A according to the drawing callout in  FIG. 3 . The illustrated embodiment includes a spacer guide  32 A at the distal end of the cutting tool  20 A and a blade  28 A proximally disposed on one side of the guide  32 A. The blade  28 A includes a sharpened leading edge  30 A that is configured to remove cartilage and/or bone from one of the articular processes that form the facet joint J. The guide  32 A includes a width W 1  that enters the facet joint J (as shown in  FIG. 5 ) and keeps the blade  28 A parallel to the joint J. The guide  32 A and blade  28 A include a length L 1  in the transverse direction that is at least as wide as an implant  10  that is inserted into the joint J. The cutting tool  20 A may be driven into the joint J through impact with the handle  26 . Other conventionally known techniques, including manual, electric, and pneumatic drivers, may be used to drive the cutter  22 A through the facet joint J thereby removing bone and cartilage from one of the two processes. Notably,  FIG. 5  shows the inferior process IP of vertebra V 1  being prepared in this manner. 
         [0033]    After one of the two articular processes IP, SP is prepared, a second cutting tool  20 B may be used to prepare the other of the two processes IP, SP. In the embodiment shown in  FIG. 6 , the second cutting tool  20 B is used to remove cartilage and bone from the superior process SP of vertebra V 2 . The second cutting tool  20 B is similar in form to the first cutting tool  20 A in that it includes a handle  26 , elongated shaft  24 , and cutter  22 B disposed at the distal end of the tool  20 B.  FIG. 7  illustrates a detailed view of the cutter  22 B. The illustrated embodiment includes a spacer guide  32 B at the distal end of the cutting tool  20 B and a blade  28 B proximally disposed on one side of the guide  32 B. The blade  28 B includes a sharpened leading edge  30 B that is configured to remove cartilage and/or bone from one of the articular processes that form the facet joint J. The guide  32 B includes a width W 2  that is greater than the width W 1  of the first guide  32 A. The additional width accounts for material that is removed by the first cutting tool  20 A. The second guide  32 B enters the facet joint J (as shown in  FIG. 8 ), moving along the previously prepared surface and keeps the blade  28 B parallel to the joint J. As before, the cutting tool  20 B may be driven into the joint J through impact with the handle  26 , other conventionally known driving techniques. 
         [0034]      FIG. 9  shows an embodiment of a cutter  22 C including blades  28 C that are proximally disposed on opposite sides of the spacer guide  32 C. The guide  32 C includes a width W 1  that is substantially similar to that of the guide  32 A on the first cutting tool  20 A. In the embodiment shown, the blades  28 C are positioned so that the leading cutting edge  30 C of each blade is disposed at substantially the same longitudinal position. In an unillustrated embodiment, the blades  28 C may be staggered slightly so that each initially engages bone at different times. In either case, the illustrated cutter  22 C may permit preparation of both articulating faces of the facet joint J using a single cutting tool. 
         [0035]    Once the opposing surfaces of the joint J are prepared as shown in  FIG. 10 , the implant  10  may be placed into the facet joint J using an insertion tool  34 . As suggested above, the implant  10  is intended to fuse with the previously articulating processes IP, SP, thereby fusing the vertebrae V 1 , V 2  at the facet joint J. To that end, the implant  10  may include various features to promote fusion.  FIGS. 11 and 12  illustrate one exemplary embodiment of an implant  10  that may be used for facet fusion. The implant  10  includes surface features  36  to promote bone growth and adhesion at the interface between the implant  10  and articulating processes IP, SP. Examples of features used for this purpose include, for example, teeth, scales, keels, knurls, and roughened surfaces. Some of these features  36  may be applied through post-processing techniques such as blasting, chemical etching, and coating, such as with hydroxyapatite. The bone interface surfaces  38  may also include growth-promoting additives such as bone morphogenetic proteins. Alternatively, pores, cavities, or other recesses into which bone may grow may be incorporated via a molding process. Other types of coatings or surface preparation may be used to improve bone growth into or through the bone-contact surfaces  38 .  FIG. 12  further shows that the implant  10  may include one or more apertures  39  that may be packed with bone growth promoting material  100  in an attempt to promote new bone growth that will ultimately fuse the facet joint J. Some non-limiting examples of bone growth promoting substances that may be inserted into the aperture  39  include Bone Morphogenetic Protein (BMP), demineralized bone matrix (DBM), allograft, autograft, xenograft, or other osteoinductive growth factors to facilitate fusion of the facet joint J. Further, the shape of the exemplary implant  10  is substantially rectangular. However, the implant  10  may assume other shapes, including for example, round, square, oval, polygonal, or other shapes that would occur to one skilled in the art. During the insertion procedure, the implant  10  may be adhered to the articular processes IP, SP with a biocompatible adhesive. Suitable adhesives may include protein derived, aldehyde based adhesive materials, albumin/glutaraldehyde materials, and cyanoacrylate-based materials. 
         [0036]    In embodiments described above, the guides  32 A-C and blades  28 A-C formed a part of the same cutter  22 A-C. In other embodiments, the guide and blade may be separated into different bodies.  FIGS. 13 and 14  illustrate one such embodiment where a hand-held guide body  40  is inserted into the facet joint J in a first step. Subsequently, a cutting tool  50 , including one or more blades  58 , is inserted through the guide body  40  to prepare the articulating surfaces of the processes IP, SP. As discussed in greater detail below, motion of the cutting tool  50  is constrained by the guide body  40  to control the joint J preparation. In the embodiment shown, the guide body  40  is formed at a distal end of a guide tool  42  that includes a handle  26  and elongated arm  24  that allow a surgeon to accurately position the guide body  40  relative to the processes IP, SP. 
         [0037]      FIG. 15  depicts a perspective view of the exemplary guide body  40  viewed in the general direction of the arrow labeled XV in  FIG. 13 . The guide body  40  is sized to be mounted between articular processes of a facet joint J and has a pair of edges  42 ,  44  that are spaced for receiving blades  58  of the cutting tool  50 . The pair of edges  42 ,  44  are spaced a distance apart for the first edge  42  to align with a first articular process, and the second edge  44  to align with a second articular process. The cutting tool  50  in the illustrated embodiment includes a pair of blades  58 , with respective cutting edges  62 . The blades  58  are sized to fit between the pair of edges  42 ,  44  respectively. The cutting edges  62  are positioned at a distal end of the blades  58  with a mount  56  at the proximal end. The mount may include apertures  55  for attachment to a driver. Using the cutting tool  50  and guide body  40  comprises inserting the guide body  40  adjacent a facet joint J and inserting the blades  58  through the pair of edges  42 ,  44 . The edges  42 ,  44  are sized for the blades  58  to move within and contour the members. The guide body  40  and cutting tool  50  are constructed of rigid materials, such as stainless steel, though other materials, including other metals or non-metals may be used. 
         [0038]    The guide body  40  is sized such that the first and second edges  42 ,  44  extend through the guide body  40  and position the cutting tool  50  at the proper placement relative to the facet joint J and support the blades  58  during the contouring procedure. The guide body  40  may also act as a spacer to position articular processes IP, SP of the facet joint J an appropriate distance apart for performing the contouring process. Facet joint J spacing may be achieved with a spacer  60 , including one or more prongs  64  as described in greater detail below. In one embodiment, guide body  40  is constructed of a unitary member. In another embodiment, guide body  40  is an assembled part comprising two or more different sections. 
         [0039]    In the embodiment illustrated in  FIGS. 14 and 15 , the first and second edges  42 ,  44  are part of an interior aperture  46  that is sized to receive the cutting tool  50 . Lateral walls  45  define the overall width of the aperture  46  and edges  42 ,  44 . In some embodiments, the aperture  46  and lateral walls  45  extend between the first and second edges  42 ,  44 . The aperture  46  is sized for the surgeon to visually observe the contouring process. The aperture  46  further allows for access to the facet joint J for irrigation and bone removal during the contouring process. Aperture  46  may include a variety of sizes and shapes depending upon the application. Thus, in addition to the rectangular shape shown, the aperture may include, for example, oval, hourglass, or I-beam shapes. For example,  FIG. 25  illustrates a guide body  40  with the aforementioned spacer  60  and an inner aperture  46  that is rounded. A corresponding cutting tool  50  includes a rounded shape with a circular leading edge  62 . The leading edge  62  may be serrated. The cutting tool  50  may be impacted in the direction of arrow C. Alternatively, the cutting tool  50  may be used to contour the articular processes IP, SP by rotating the cutting tool  50  in the direction of arrow R. Other types of rotary cutting tools known in the art, including broaches, drilling bits, reamers, and other fluted or non-fluted boring tools, may be used in conjunction with the guide body in  FIG. 25 . 
         [0040]    Referring again to  FIG. 15 , the edges  42 ,  44  include a width greater than the blades  58  to provide room for the cutting tool  50  to pass during the contouring process. In one embodiment, the edges  42 ,  44  may be sized for the blades  58  to pass through the guide body  40  with motion substantially constrained in the direction of arrow C. In one embodiment, the edges  42 ,  44  may be sized for the blades  58  to pass through in the direction of arrow C as well as reciprocate back and forth in the direction of arrow S. The edges  42 ,  44  may be sharpened to remove bone material from the articular processes IP, SP as the cutting tool  50  is driven or impacted in the direction of arrow C. Further, cutting tool  50  movement may be oscillating, reciprocating, vibratory, and other known manners. The first and second edges  42 ,  44  may include a variety of shapes depending upon the specific application. In the embodiment illustrated, the first and second edges  42 ,  44  are straight and parallel to contour parallel surfaces of the adjacent articular processes IP, SP. However, depending upon the application, other embodiments may be included such as curved edges and jagged edges. In one embodiment, the blades  58  are shaped to conform to the shape of the edges  42 ,  44 . 
         [0041]    In the illustrated embodiment, a spacer  60  extends from a distal face  61  of the guide body  40  for spacing the articular processes IP, SP. Spacer  60  may include a variety of shapes to fit between the articular processes IP, SP and space them a predetermined distance apart. In one embodiment, spacer  60  includes two prongs  64  that extend outward from the guide body  40 . Spacer  60  is spaced between the first and second edges  42 ,  44  to not interfere with access to the articular processes IP, SP during the contouring. Worded in another manner, the distance between the first and second edges  42 ,  44  is about equal to or greater than the width of the spacer  60 . In one embodiment, the distance between the first and second edges  42 ,  44  is about the same as the width of the spacer  60  such that the reference edges  42 ,  44  align with the edges of the articular processes IP, SP to contour only a small amount. In another embodiment, the distance between the first and second edges  42 ,  44  is greater than the width of the spacer  60  such that reference edges  42 ,  44  align further on the vertebral members to contour a larger amount. 
         [0042]    In the embodiment shown in  FIGS. 14 and 15 , the guide body  40  is attached to a handle  26  for positioning within the facet joint J. In other embodiments, such as the guide body  40 A shown in  FIG. 16 , apertures  48  may be positioned for attaching the guide body  40 A to the articular processes IP, SP. Note that in each of the various embodiments disclosed herein, the guide body  40  may include one or both of the mounting apertures  18  and the elongated arm  24  and handle  26 . Apertures  48  may be spaced at a variety of locations about the guide body  40 A. The apertures  48  may be formed within a tab  49  that extends from the guide body  40 A. In one embodiment, the apertures  48  are located on opposite sides of the guide body  40 A such that a first aperture  48  is aligned with a first articular process IP, SP and a second aperture (not visible in  FIG. 16 ) is aligned with a second articular process IP, SP. Each aperture  48  is sized to receive a fastener (not shown) such as a bone screw, nail, or staple for at least temporary connection to the articular processes IP, SP. Further, in one or more embodiments, the distal face  61  of the guide body  40 ,  40 A may include surface features  65  such as teeth, spikes, scales, knurls, or roughened surfaces to penetrate the bone adjacent to the facet joint J to further secure the guide relative to the facet joint J while cutting tool  50  contours the articular processes IP, SP. 
         [0043]    In one embodiment, cutting tool  50  comprises first and second blades  58  extending a distance apart by a span  57 . A mount  56  is positioned opposite the blades  58  for attachment to a drive source. In one embodiment, blades  58  are the same length such that cutting edges  62  at the distal end are aligned and contour the articular processes IP, SP to the same depth. As suggested above, the blades  58  are spaced a distance apart to align respectively with the first and second edges  42 ,  44 . In one embodiment, blades  58  are parallel and span  57  is substantially perpendicular. The height of the cutting tool  50  is the distance extending between the edges  62  and the span  57 . 
         [0044]    The cutting tool  50  may assume a variety of shapes and configurations. In the embodiment shown in  FIG. 15 , the cutting edges  62  are sharpened and substantially rigid to effectively chisel cartilage and bone matter from the articular processes IP, SP. In an embodiment illustrated in  FIG. 17 , the cutting tool  50 A includes a boxed configuration in which a rectangular hollow body  58 A terminates at a rectangular cutting edge  62 A. The interior  59  of the body  58 A is substantially empty or may include structural reinforcement (not shown) to strengthen the cutting tool  50 A. The cutting tool  50 A further includes an elongated mount  56 A for attachment to a driver. In one embodiment shown in  FIG. 18 , the cutting tool  50 B includes blades  58 B with cutting edges  62 A that are serrated and include a plurality of individual teeth that contact the articular processes IP, SP. Other types of cutting edges  62 A with different teeth sizes and orientations are known and may be used. 
         [0045]      FIG. 19A  illustrates another embodiment of a cutting tool  50 C that comprises a single blade  58 B with an associated cutting edge  62 B. The cutting tool  50 C may include a guide arm  63  serving as a guide to contact a first or second edge  42 ,  44  to position the single blade  58 B. Guide arm  63  does not include a cutting edge  62 . The guide arm  63  is sized to contact one of the reference edges  42 ,  44  and may include a number of different shapes and sizes. The guide arm  63  may include a variety of lengths, provided it is not of such a length to contact the articular processes IP, SP and interfere with the contouring process. In the illustrated embodiment, the span  57  may be narrower or wider than the distance between the reference edges  42 ,  44 .  FIG. 19B  illustrates a similar embodiment of a cutting tool  50 C that comprises a single blade  58 B with an associated cutting edge  62 B, but without a guide arm  63 . In one unillustrated embodiment, the cutting device  50  can include a single or double wheel cutter that passes through the guide body  40  to contour the articular processes IP, SP. 
         [0046]    In each of the above cutting tool embodiments, the mounts  56 ,  56 A,  56 B provide for attaching the cutting tool  50  to a driving device. Other mounts may include a variety of shapes and sizes suitable for a particular driving device and/or application. The mounts  56 ,  56 A,  56 B may be attached to a handle that is impacted to drive the cutting tools  50 ,  50 A-C into the articular processes IP, SP. In certain embodiments, apertures  55  may be positioned for attaching the cutting tools  50 ,  50 B to a driving device. The cutting tools  50 ,  50 A-C may be attached to a power device, such as a reciprocating saw (not shown). A variety of different power sources may drive the cutting tools  50 ,  50 A-C. Embodiments include a rechargeable battery, pneumatic mechanism, and any standard electrical source, such as 110 volt, 60 cycle power sources, with or without a transformer to reduce the voltage as necessary. In one embodiment, the cutting tool  50 ,  50 A-C is oscillated back and forth in a direction parallel with or aligned with the first and second edges  42 ,  44 . In another embodiment, cutting tool  50 ,  50 A-C is oscillated in an in-and-out direction substantially perpendicular to the first and second edges  42 ,  44 . 
         [0047]      FIG. 20  illustrates an embodiment of a guide body  40  featuring a spacer  60  including a single prong  64  extending outward from a distal face of the guide body  40 . The spacer  60  is positioned between the first and second edges  42 ,  44 . Each of the first and second edges  42 ,  44  is respectively associated with an aperture  46 A,  46 B that extends through the guide body  40  and through which the blades  58  of a corresponding cutting tool  50  passes. An intermediate wall  47  is disposed between the apertures  46 A,  46 B. The prong  64  extends from the intermediate wall  47 . The intermediate wall  47  may serve to limit the depth to which the blades  58  pass through the apertures  46 A,  46 B. The prong  64  has a smooth tapered edge that narrows to a rounded end  66 . The rounded end  36  eases the insertion between the vertebral members. The spacer  60  is aligned parallel with the first and second edges  42 ,  44 . The spacer  60  has a width W sized to space the articular processes IP, SP a distance apart to align the first edge  42  with a first of the articular processes IP, SP and the second edge  44  with the second of the articular processes IP, SP. In the illustrated embodiment, the spacer  60  includes a substantially constant thickness W. In other embodiments, the spacer  60  may be wedged, rounded, or chamfered resulting in an varying thickness W. 
         [0048]      FIG. 21  illustrates a handle  26  and elongated arm  24  attached to the guide body  40 . The handle  26  allows the surgeon to position and hold the guide body  40  relative to the articular processes IP, SP. The handle  26  allows the surgeon to use tactile senses to position the guide body  40 . In one embodiment, handle  26  is off-center from the guide body  40  such that the surgeon can visually see the guide body  40  when holding the handle  26 . The elongated arm  24  may include a variety of sizes and configurations. In one embodiment as illustrated in  FIG. 21 , a distal end of the elongated arm  24  attaches to a side wall of the guide body  40  to minimize interference with a cutting tool  50 . 
         [0049]    In the guide body  40  shown in  FIGS. 20 and 21 , the first and second edges  42 ,  44  are formed as part of separate apertures  46 A,  46 B. In another embodiment of a guide body  40  shown in  FIG. 22 , the first and second edges  42 ,  44  are formed as a portion of narrow slots  70 ,  72  that form a part of a contiguous aperture  46 . In the illustrated embodiment, the guide body  40  includes a spacer  60  comprising two prongs  64  that extend outward from the guide body  40 . Each prong  64  includes jagged edges  74  to reduce the likelihood of the guide body  40  inadvertently moving from between the articular processes IP, SP. In this embodiment, the jagged edges  74  are angled towards the guide body  40  such that insertion of the prongs  64  is not made more difficult or troublesome than with smooth edges (e.g.,  FIGS. 15 ,  16 ). The angled edges  74  catch on the articular processes IP, SP to prevent inadvertent removal. 
         [0050]      FIG. 23  illustrates an embodiment of the guide  40  that includes first and second edges  42 ,  44  separated a distance apart by a solid guide body. The slots  46 A,  46 B including the first and second edges  42 ,  44  may include a variety of widths depending upon the application. The guide body  40  further includes a spacer  60  including a pair of prongs  64  that extend outward from a distal face of the guide body  40 . The prongs  64  are spaced at points directly between the first and second edges  42 ,  44 . 
         [0051]      FIG. 24  illustrates another embodiment of the guide body  40  including exposed first and second edges  42 ,  44 . The first and second edges  42 ,  44  are spaced a desired distance apart to support and guide the cutting tool  50 . In one embodiment, shoulders  76  are positioned on one or both lateral ends of the edges  42 ,  44  to control the extent of blade  58  movement. Shoulders  76  prevent the blade  58  from inadvertently contacting sections of the articular processes IP, SP that are not to be contoured. In another embodiment, there are no shoulders  76 . An elongated arm  24  may be attached to the guide body  40  to position the edges  42 ,  44 . A spacer  60  comprised of one or more prongs  64  extends outward from one side of the guide body  40 . The spacer  60  may include a variety of widths, including a first and second edge that align substantially with edges  42 ,  44 . In another embodiment (not illustrated), there is no spacer  60 . 
         [0052]    Spatially relative terms such as “under”, “below”, “lower”, “over”, “upper”, and the like, are used for ease of description to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the device in addition to different orientations than those depicted in the figures. Further, terms such as “first”, “second”, and the like, are also used to describe various elements, regions, sections, etc and are also not intended to be limiting. Like terms refer to like elements throughout the description. 
         [0053]    As used herein, the terms “having”, “containing”, “including”, “comprising” and the like are open ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features. The articles “a”, “an” and “the” are intended to include the plural as well as the singular, unless the context clearly indicates otherwise. 
         [0054]    The present invention may be carried out in other specific ways than those herein set forth without departing from the scope and essential characteristics of the invention. For instance, while the various Figures illustrate facet joint preparation for only one of the two facet joints, a similar configuration may exist at the facet joint located on the opposite lateral side of the spine. The descriptions disclosed herein are not intended to be limited to facet joints on a single side of the spine. Those skilled in the art will comprehend the symmetry and applicability of the various embodiments disclosed herein. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.