Patent Publication Number: US-9833328-B2

Title: System and methods for facet joint treatment

Description:
REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. application Ser. No. 13/678,535, which was filed on Nov. 15, 2012, and which is a continuation-in-part of U.S. application Ser. No. 13/084,104, which was filed on Apr. 11, 2011, which claimed priority to U.S. Provisional Application No. 61/355,140, which was filed on Jun. 15, 2010, the contents of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     An embodiment of the invention relates to a system for treating facet joint pain. More particularly, the invention relates to an implant system for treating facet joint pain. 
     BACKGROUND OF THE INVENTION 
     Within the next ten years, more than seventy million people will join the ranks of seniors. In an aging population, the articular cartilage that allows bones to smoothly move over each other wears down with time and disease, and like many tissues in the body, articular cartilage has a limited ability to heal itself. 
     At this time, options that help to relieve severe degenerative joint pain, or osteoarthritis, include joint replacement or fusion. As examples, approximately 200,000 total knee joint replacement operations and over 300,000 hip joint replacement operations are performed annually. While these operations are generally effective at treating the affected joint, these artificial joint implants typically only last about 10-15 years. 
     Chronic lower back pain also affects both work force productivity and healthcare expense. There are currently over 500,000 surgical procedures performed annually in the United States in an attempt to alleviate lower back pain even though such surgical procedures are typically only performed after the failure of more conservative therapy such as bed rest, pain and muscle relaxant medication, physical therapy or steroid injection. The source of this pain may originate from dysfunction among a plurality of anatomical structures (as described below) that are comprised in the spine, including facet joints. 
     To understand spinal biomechanics, and the impacts of dysfunction in therapy, it is useful to first consider the spinal anatomy. The vertebrae of the spine are conventionally subdivided into several sections. Moving from the head (cephalad) to the tailbone (caudal), the sections are cervical, thoracic, lumbar, sacral, and coccygeal. 
     Regardless of location, each vertebra forms two pedicles and two laminae that combine to define a spinal foramen in which the spinal cord is protected. Extending laterally from the pedicles are two transverse processes. Extending from the mid-line of the vertebra where the two laminae meet is a spinous process. These three processes serve as a connection point for ligaments and muscles. 
     Adjacent vertebrae are separated by an intervertebral disc and surfaces of the adjacent vertebrae form portions of two facet joints by and between the two vertebrae. Relative to a spinal segment consisting of an intermediate vertebra, an immediately adjacent cephalad vertebra, and an immediately adjacent caudal vertebra, the intermediate vertebra forms portions of four facet joints; namely, two facet joints with the cephalad vertebra, and two facet joints with the caudal vertebra. 
     With the above background in mind,  FIGS. 1A and 1B  illustrate a facet joint  20  composed of a superior articular facet  22  and an inferior articular facet  24 . The superior articular facet  22  is formed by the vertebral level below the intervertebral disc (i.e., a superior articular facet projects upward from the junction of the lamina and the pedicle), whereas the inferior articular facet  24  is formed by the vertebral level above the intervertebral disc (i.e., an inferior articular facet projects downward). 
     On the superior articular facet  22  is a superior articular face  26 , and on the inferior articular facet  24  is an inferior articular face  28 . Facet joints are oriented obliquely to the sagittal plane, and the joint space itself is curved from front to back. The more posteriorly located inferior face  28  is convex, whereas the more interiorly located superior face  26  is concave. 
     The facet joint  20  is a synovial joint that is defined by the two opposing bony faces  26 ,  28  with cartilage  30  between them and a capsule  32  around the joint  20 . More specifically, synovial fluid  34  is contained inside the joint  20  by the capsule  32 , that is otherwise a water-tight sac of soft tissue and ligaments that fully surrounds and encloses the joint  20 , and keeps the joint faces  26 ,  28  lubricated. 
     The ends of the bone articular facets  22 ,  24  that make up the synovial facet joint  20  are normally covered with the articular, hyaline cartilage  30  that allows the bony faces  26 ,  28  to glide against one another, providing the flexibility that allows the movement of vertebral bodies relative to one another. 
     As indicated above, there are two facet joints between each pair of vertebrae, one on each side (located posterior and lateral of the vertebral centerline), from the top and bottom of each vertebra. The joints combine with the disc space to create a three joint complex at each vertebral level, and each joint extends and overlaps neighboring vertebral facet joints, linking each other and hence the vertebra together. 
     The assembly of two vertebral bodies, the interposed spinal disc and the attached ligaments, muscles, and facet joints (inferior articulating processes that articulate with the superior articular processes of the next succeeding vertebra in the caudal direction) is referred to as a “spinal motion segment.” Each motion segment contributes to the overall flexibility of the spine and contributes to the overall ability of the spine to provide support for the movement of the trunk and head, and in particular, the facet joints limit torsional (twisting) motion. 
     When the facets of one or more vertebral bodies degenerate or otherwise become damaged such that the vertebrae no longer articulate or properly align with each other, there is a resulting loss of mobility and pain or discomfort. The functional role of the facet joints in a spinal motion segment is thus relevant to an understanding of the operative and functional advantages of the facet joint systems and methods disclosed herein, which achieve dynamic stabilization and mobility preservation without constraining motion in any plane. 
     As indicated above, facet joints are located on the posterior column of the spine. The context of this discussion: “anterior” refers to in front of the spinal column, and “posterior” refers to behind the column; “cephalad” means towards a patient&#39;s head (sometimes referred to as “superior”); and “caudal” (sometimes referred to as “inferior”) refers to the direction or location that is closer to the patient&#39;s feet. 
     Facet joints can be arthritic due to degeneration with aging, trauma, or disease (e.g., pathologies that include inflammatory, metabolic, or synovial, disorders). In addition, fractures, torn ligaments, and disc problems (e.g., dehydration or herniation) can all cause abnormal movement and alignment, putting extra stress on the surfaces of the facet joint. 
     The physiological response to this extra pressure is the development of osteophites, i.e., bone spurs. As the spurs form around the edges of the facet joint, the joint becomes enlarged, a condition called hypertrophy, and eventually the joint surfaces become arthritic. When the articular cartilage degenerates or wears away, the bone underneath is uncovered and rubs against bone. The joint thus becomes inflamed, swollen, and painful. 
     Facet joint arthritis is a significant source of neck and back pain, and is attributable to about 15-30% of persistent lower back pain complaints. Upon failure of conservative treatment for facet joint pain such as intra-articular steroids/local anesthetic injections administered under fluoroscopic guidance, some patients with chronic pain may eventually require surgical intervention for facet joint arthritis including, for example, facet rhizotomy; facet ectomony to remove the facet joint to reduce pressure on the exiting nerve root; total joint replacement or facet arthrodesis (i.e., fixation leading to fusion, where the two articulating surfaces of the joint remain immobile or grow solidly together and form a single, solid piece of bone); etc. 
     While these surgical procedures may alleviate back pain, many joint replacements and all fusions do not restore the normal physiological function and motion attributable to healthy anatomical form. Rather, they often significantly alter spinal biomechanics that can in turn cause or exacerbate co-existing spinal instabilities and degeneration at other spinal levels or in other joints associated with spinal motion. 
     There is a cause-and-effect relationship among intervertebral disc integrity, facet loads, and spinal degeneration. Specifically, the progressive loss of disc height with disc degeneration often also alters the facet joint&#39;s mechanical ability as the facet joints degenerate or dislocate, and ligaments lose elasticity and their load-carrying ability. More specifically, with disc-space narrowing, as frequently occurs with degenerative disc disease, there is an increased load in the facet joints, especially in extension, and concomitant degeneration of the facet joints and capsules. 
     Since the facet joint capsules are primarily loaded in flexion and in rotation, and the facet joints are the primary resistors against rotational or torsional forces (e.g., normally, the facet joints control approximately 30% of axial rotation), facet joint degeneration significantly alters spinal mobility. 
     The need to provide minimally invasive therapies that provide pain relief while restoring and preserving the biomechanical function of the physiological facet joints is paramount to overall spinal mobility, and to date, therapies have not adequately satisfied all of these issues, as noted below. 
     One therapy, facet rhizotomy, involves techniques that sever small nerves that go to the facet joint. The intent of the procedure is to stop the transmission of pain impulses along these nerves. The nerve(s) is identified using a diagnostic injection. Then, the surgeon inserts a large, hollow needle through the tissues in the low back. A radiofrequency probe is inserted through the needle, and a fluoroscope is used to guide the probe toward the nerve. The probe is slowly heated until the nerve is severed. 
     Another technique using pulsed radiofrequency does not actually burn the nerve, rather it is believed to stun the nerve. Yet another technique involves denervation by probe tip freezing, and still another procedure involves carefully controlled injection of botox toxin to treat muscle spasm, a protective reflex that may occur when the facets are inflamed that in turn causes the nearby muscles that parallel the spine to go into spasm. 
     While these procedures may provide pain relief, they do not address ongoing joint degeneration (e.g., wear on articulating surfaces), which leads to kinematic and biomechanical dysfunction that may in turn lead to transition syndrome (i.e., progression of degeneration and pain to other joints) at other levels. 
     While certain clinicians have advocated prosthetic total joint replacement of damaged facet joints, in practice, it is difficult to implement such a prosthesis for a variety of reasons including the variability of facet joint geometry from facet joint to facet joint, and the high level of interaction between the facet joint and the other components in the spinal column. 
     Moreover, joint replacement is a highly invasive and time-consuming procedure, requiring pre-preparation of joint surfaces and removal of bone, and thus there are associated risks, including blood loss and morbidity, increased anesthesia time, and increased convalescence time. 
     A related therapeutic treatment of the facet joint entails the provision of an artificial facet joint where the inferior facet segment, the mating superior facet segment, or both, are covered with a cap (i.e., over all, or substantially all, of the facet). One such device and related method of implantation is described in Fitz, U.S. Pat. No. Re 36,758. 
     While potentially viable, the capping of the facet segments has several potential disadvantages. Clinical concerns are believed to result from the disruption of the periosteum and ligamentum teres femoris, both serving a nutrition delivery role to the femoral head, thereby leading to avascular necrosis of the bony support structure for the cap. 
     Another potential disadvantage of facet capping is that to accommodate the wide variability in anatomical morphology of the facets, not only between individuals, but also between levels within the spinal column, a very wide range of cap sizes and shapes is required. 
     Even further, implantation of the caps, such as those described in U.S. Pat. No. Re 36,758, cannot be performed on a minimally-invasive basis, and entail fairly significant preparatory steps at the implantation site (e.g., removal and/or re-shaping of bone). At least with use of caps over osteoarthritic femoral heads, the capping of articular bone ends has sometimes experienced clinical failure by mechanical loosening. 
     Another therapeutic treatment of the facet joint is to affix the superior articular process to the inferior articular process using a facet screw. Although the fixation therapy may alleviate symptoms associated with a degenerated facet joint, it also sacrifices some of the ability of the motion segment to move and thus sacrifices some of the ability of the spinal column to move in a natural manner. 
     Central and lateral spinal stenosis (joint narrowing), degenerative spondylolisthesis, and degenerative scoliosis may all result from the abnormal mechanical relationship between the anterior and posterior column structures and induce debilitating pain. More recently, a percutaneously-implantable, facet joint stabilization device has been developed, and is described in U.S. application Ser. No. 12/238,196 (filed Sep. 25, 2008 and entitled “Method and Apparatus for Facet Joint Stabilization”), the teaching of which are incorporated herein by reference. The facet joint stabilization device generally entails a superior body and an inferior body that, when combined, form an exteriorly threaded device. 
     When inserted into the joint space, the inferior and superior bodies establish an engaged relationship with the corresponding inferior and superior bony faces of the facet joint anatomy, respectively, and are somewhat slidable relative to one another to facilitate near normal facet joint motion ability. While viable, areas for improvement remain, including retention, long-term functioning, and insertion techniques. 
     As the present disclosure contemplates accessing various vertebral elements and joints through a preferred approach that comes in from a percutaneous posterior approach, “proximal” and “distal” are defined in context of this channel of approach. Consequently, “proximal” is closer to the beginning of the channel and thus closer to the clinician, and “distal” is further from the beginning of the channel and thus more distant from the clinician. 
     When referencing access or delivery tools, “distal” would be the end intended for insertion into the access channel, and “proximal” refers to the opposing end, generally the end closer to the handle of the delivery tool. When referencing implants, generally “distal” would be the leading end first inserted into the joint and “proximal” refers to the trailing end, generally in an engagement with a deployment tool. 
     In light of the above, a need exists for additional therapies applicable to facet joints to stabilize and augment the facet joint in alleviating problems without initial resort to the more radical therapies of replacing the facet joint with a prosthesis and/or fixation of the facet joint and the inherent loss of natural movement of that motion segment. 
     SUMMARY OF THE INVENTION 
     An embodiment of the invention is directed to a method of resurfacing a facet joint with a facet implant system. The facet joint has a superior facet and an inferior facet that are adjacent to each other and movable with respect to each other. 
     A first facet implant component is provided that has a first visualization marker. The first visualization marker includes a first marker section and a second marker section. The first marker section is oriented at an angle with respect to the second marker section. 
     The first facet implant component is implanted between the superior facet and the inferior facet. A location and an orientation of the first facet implant component are determined using an imaging technique that locates the first visualization marker. 
     Another embodiment is directed to a method of resurfacing a facet joint with a facet implant system. The facet joint has a superior facet and an inferior facet that are adjacent to each other and movable with respect to each other. 
     A first facet implant component is provided that has a first visualization marker. The first visualization marker includes a first marker section and a second marker section. The first marker section is oriented at an angle with respect to the second marker section. 
     A second facet implant component is provided that has a second visualization marker with respect to the second articulating surface. The second visualization marker includes a third marker section and a fourth marker section. The third marker section is oriented at an angle with respect to the fourth marker section. 
     The first facet implant component and the second implant component are implanted between the superior facet and the inferior facet so that the first facet implant component is adjacent to the second implant component. A location and an orientation of the first facet implant component and the second facet implant component are determined using an imaging technique that locates the first visualization marker and the second visualization marker. 
     Another embodiment is directed to a method of resurfacing a facet joint with a facet implant system. The facet joint has a superior facet and an inferior facet that are adjacent to each other and movable with respect to each other. 
     A first facet implant component is provided that has a first visualization marker. The first visualization marker includes a first marker section and a second marker section. The first marker section is oriented at an angle with respect to the second marker section. 
     A second facet implant component is provided that has a second visualization marker. The second visualization marker includes a third marker section and a fourth marker section. The third marker section is oriented at an angle with respect to the fourth marker section; 
     The first facet implant component and the second implant component are implanted between the superior facet and the inferior facet so that the first facet implant component is adjacent to the second implant component, at least a portion of the first marker section overlaps the third market section and at least a portion of the second marker section does not overlap the fourth marker section. 
     A location and an orientation of the first facet implant component and the second facet implant component is determined using an imaging technique that locates the first visualization marker and the second visualization marker. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of embodiments and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and together with the description serve to explain principles of embodiments. Other embodiments and many of the intended advantages of embodiments will be readily appreciated as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts. 
         FIG. 1A  is a simplified cross-sectional view of a human spinal segment illustrating anatomy of native facet joints with which the systems and methods of the present disclosure are useful in treating. 
         FIG. 1B  is an enlarged view of one facet joint of the segment of  FIG. 1A . 
         FIG. 2  is a perspective view of a resurfacing body according to an embodiment of the invention. 
         FIG. 3  is a side view of the resurfacing body of  FIG. 2 . 
         FIG. 4  is top view of another configuration of the resurfacing body having a tab extending therefrom. 
         FIG. 5  is a sectional view of the resurfacing body taken along a line A-A in  FIG. 4 . 
         FIG. 6  is a perspective view of the resurfacing body of  FIG. 4 . 
         FIG. 7  is a top view of another configuration of the resurfacing body having a tab extending therefrom. 
         FIG. 8  is a sectional view of the resurfacing body taken along a line A-A in  FIG. 7 . 
         FIG. 9  is a perspective view of the resurfacing body of  FIG. 7 . 
         FIG. 10  is a top view of an alternative embodiment of the implant. 
         FIG. 11  is a side view of two of the implants of  FIG. 10  positioned in an insertion orientation. 
         FIG. 12  is a first perspective view of the implant of  FIG. 10 . 
         FIG. 13  is a second perspective view of the implant of  FIG. 10 . 
         FIG. 14  is a top view of a guide probe assembly according to an embodiment of the invention. 
         FIG. 15  is a sectional view of the guide probe assembly taken along a line A-A in  FIG. 14 . 
         FIG. 16  is an enlarged sectional view of a tip portion of the guide probe assembly. 
         FIG. 17  is a side view of a guide probe assembly according to an alternative embodiment of the invention. 
         FIG. 18  is a perspective view of a guide cannula for use in conjunction with an embodiment of the invention. 
         FIG. 19  is a side view of the guide cannula of  FIG. 18 . 
         FIG. 20  is a side view of a delivery cannula according to an embodiment of the invention. 
         FIG. 21  is a side view of an implant insertion tool according to an embodiment of the invention. 
         FIG. 22  is a side view of an implant insertion tool according to an alternative embodiment of the invention. 
         FIG. 23  is a side view of an implant insertion tool according to another alternative embodiment of the invention. 
         FIG. 24  is a side view of an implant countersink positioner according to an embodiment of the invention. 
         FIG. 25  is a top view of the resurfacing device positioned adjacent to a distal end of the implant insertion tool. 
         FIG. 26  is a perspective view of the resurfacing device in engagement with an extension on the distal end of the implant insertion tool. 
         FIG. 27  is a perspective view of the delivery cannula inserted into the guide cannula. 
         FIG. 28  is a perspective view of the implant insertion tool in an initial position where the resurfacing device is inside of the delivery cannula and where the delivery cannula is inside of the guide cannula. 
         FIG. 29  is a perspective view of the implant insertion tool in an inserted position where the resurfacing device is partially extending beyond the distal end of the delivery cannula. 
         FIG. 30  is a perspective view of the implant insertion tool in a partially retracted position where the resurfacing device is moved beyond the delivery cannula for implanting the resurfacing device in the facet joint. 
         FIG. 31  is a side view of a leaflet retractor tool for use in withdrawing the implant insertion tool from the delivery cannula. 
         FIG. 32  is a perspective view of the guide probe assembly inserted into the facet joint and the guide cannula being inserted over the guide probe assembly. 
         FIG. 33  is a sectional view of the resurfacing device that has been implanted in one of the facet joints. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     One embodiment of an implant system  40  in accordance with principles of the invention and useful for treating a facet joint of a patient is illustrated in  FIG. 2 . The implant system  40  may include a superior resurfacing device  42  and an inferior resurfacing device  44 . 
     As illustrated in  FIG. 2 , the superior resurfacing device  42  may be positioned on top of the inferior resurfacing device  44  so that the superior resurfacing device  42  and the interior resurfacing device  44  are oriented in opposite directions as the superior resurfacing device  42  and the inferior resurfacing device  44  would be oriented during the implantation process. Details on the various components of the resurfacing devices  42 ,  44  are provided below. 
     In certain embodiments, the resurfacing devices  42 ,  44  may be substantially similar to each other where the superior resurfacing device  42  is placed adjacent to a superior facet joint articular face (e.g., the superior articular face  26  of  FIG. 1B ), and the inferior resurfacing device  44  is placed adjacent to an inferior facet joint articular face (e.g., the inferior articular face  28  of  FIG. 1B ). 
     The resurfacing devices  42 ,  44  may be capable of substantially conforming to the naturally-occurring shape or curvature of the facet joint anatomy. The resurfacing devices  42 ,  44  thereby replace the bone-on-bone interface of the natural facet joint in a manner achieving normal or near normal mobility. 
     While not required, the resurfacing devices  42 ,  44  may be substantially similar to each other in some embodiments. As such, the following description of the superior resurfacing device  42  is equally applicable to the inferior resurfacing device  44 . 
     The resurfacing device  42  consists of a resurfacing body  46 . In certain embodiments described below, one or more additional components can be attached to, or extend from, the resurfacing body  46 . In certain embodiments, the resurfacing body  46  may have a disc-like shape, that includes a base web  50  and a plurality of teeth  52  (referenced generally). 
     The base web  50  defines opposing major surfaces  54 ,  56 , as illustrated in  FIG. 3 , with the first major surface  54  providing or serving as an articulating surface (e.g., articulates relative to a corresponding articulating surface of the inferior resurfacing device  44  ( FIG. 2 )) as described below. Thus, the first major surface  54  may also be referenced as the “articulating surface” of the resurfacing body  46 . The plurality of teeth  52  may project from the second major surface  56  in a direction that is generally opposite the first major surface  54 . 
     With specific reference to  FIGS. 2 and 3 , the base web  50  defines an outer perimeter  58  of the resurfacing body  46 . In certain embodiments, the outer perimeter  58  may have a generally circular shape that generally conforms to a shape of the facet joint in which the resurfacing body is to be implanted. In other embodiments, the perimeter may have an oval-like shape (relative to a top or bottom plan view). The resurfacing device  44  may be formed with other shapes, examples of which include square, rectangular, hexagonal and curvilinear. 
     An overall size or footprint of the resurfacing body  46  is defined by the outer perimeter  58  and can vary depending upon a size of the facet joint being treated, but is generally relatively small, especially as compared to conventional facet joint prostheses and/or capping devices. As is noted above, the resurfacing body  46  should be large enough to prevent bone-to-bone contact in the facet joint. 
     In certain embodiments, a diameter of the resurfacing body  46  may be in the range of between about 3 millimeters and about 15 millimeters. In other embodiments, the diameter of the resurfacing body may be in the range of between about 5 millimeters and about 10 millimeters. 
     Facet joint treatment systems in accordance with this invention may be provided to a treating clinician with two or more different superior resurfacing devices  42  (and two or more different inferior resurfacing devices  44 ) each having a differently-sized resurfacing body  46 . 
     Examples of the sizes of the resurfacing bodies include about 5 millimeters, about 8 millimeters, about 10 millimeters and about 12 millimeters. The treating clinician may select the most appropriately sized resurfacing device for implantation based upon an evaluation of the facet joint to be treated. 
     While it is desirable for the resurfacing body  46  to be sufficiently large to prevent bone-to-bone contact within the facet joint, the resurfacing body  46  should not be too large such that the resurfacing body  46  extends beyond the facet joint as such a condition could result in damage to the tissue adjacent to the facet joint where the resurfacing body  46  is implanted. 
     For reasons that are set forth in more detail below, the resurfacing body  46  may incorporate one or more features dictating a preferred insertion orientation and/or direction. For example, the resurfacing body  46  may be more readily inserted into, and subsequently retained within, a facet joint in a particular orientation. 
     Relative to the configuration of  FIGS. 2 and 3 , the outer perimeter  58  can be described as generally defining a leading or distal end  70 , a trailing or proximal end  72 , and opposing sides  74 ,  76 . During an insertion procedure, the resurfacing body  46  may be oriented such that the leading end  70  is initially inserted into the facet joint, followed by the trailing end  72 . 
     In addition to the teeth  52  having a structure corresponding with these designations (and thus the intended insertion direction and orientation described below), the trailing end  72  can form or define an engagement feature  80 , as illustrated in  FIG. 2 , that promotes desired interaction with a separately-provided insertion tool, which is discussed in more detail below. 
     In certain embodiments, the engagement feature  80  is an aperture that includes at least two aperture regions  81   a ,  81   b . The first aperture region  81   a  may intersect the outer perimeter  58  or edge proximate the trailing end  72 . The second aperture region  81   b  is in communication with the first aperture region  81   a  and is oriented on a side of the first aperture region  81   a  that is opposite the outer perimeter  58 . 
     The first aperture region  81   a  may have a width that is smaller than a width of the second aperture region  81   b . The shape of the engagement feature  80  thereby provides a partially enclosed aperture to facilitate attachment of the resurfacing body  46  to the implant insertion tool during the insertion process. 
     A force to separate the resurfacing body  46  from the implant insertion tool should be sufficiently large so that the resurfacing body  46  does not inadvertently separate from the implant insertion tool  312 . In certain embodiments, the force to separate the resurfacing body  46  from the implant insertion tool  312  is at least 1 Newton. In other embodiments, the force to separate the resurfacing body  46  from the implant insertion tool  312  is between about 1 Newton and about 10 Newtons. In still other embodiments, the separation force is about 5 Newtons. 
     The separation force may be affected by a difference in the sizes of the widths of the first aperture region  81   a  and the second aperture region  81   b  and the width of the extension. The separation force may also be affected by other factors such as the rigidity of the resurfacing body  46  and the extension on the implant insertion tool  312 . For example, if the resurfacing body  46  or the extension is fabricated from a flexible material, the separation force may be lower if the resurfacing body  46  or the extension is fabricated from a relatively rigid material. 
     The engagement feature  80  may be formed at the same time the other portions of the resurfacing body  46  are formed such as by molding. Alternatively, the engagement feature  80  may be formed after the resurfacing body  46  is formed such as by stamping out the region that defines the first aperture region  81   a  and the second aperture region  81   b.    
     It is possible to use other techniques for maintaining the resurfacing device  46  in engagement with the implant insertion tool  312  during the process of inserting the resurfacing device  46  into the facet joint. An example of one such alternative attachment technique is attaching the resurfacing device  46  and the implant insertion tool  312  with a frangible connection. When a force that is greater than a threshold force, the frangible connection may be severed to thereby allow the implant insertion tool  312  to be removed while leaving the resurfacing body  46  in the facet joint. In certain embodiments, the force to sever the frangible connection is at least 1 Newton. In other embodiments, the force to sever the frangible connection is between about 1 Newton and about 10 Newtons. In still other embodiments, the separation force is about 5 Newtons. 
     In certain embodiments, the base web  50  has, in some constructions, a relatively uniform thickness (e.g., nominal thickness variation of +/−0.05 mm), as illustrated in  FIG. 3 . The base web  50  forms the articulating surface  54  to be relatively smooth. This smoothness attribute is, at least in part, a function of the material employed for the resurfacing body  46  as described below. 
     In other embodiments, the articulating surface  54  of the base web  50  may be coated with a separate layer that provides enhanced frictional (i.e., lower coefficient of friction) and wear characteristics. An example of one such material have a low coefficient of friction is polytetrafluoroethylene (PTFE), which is available under the designation TEFLON. 
     The plurality of teeth  52  project from the second major surface  56  of the base web  50 . These teeth  52  may have a variety of forms. In some embodiments, the teeth  52  are arranged to form or define discrete zones or teeth sets, such as the first, second and third teeth sets  90 ,  92 ,  94  generally identified in  FIG. 2 . 
     The first teeth set  90  may be centrally located along the base web  50  extending between the leading and trailing ends  70 ,  72 . Individual teeth of the first teeth set  90  may be generally identical. More particularly, each of the teeth may include a leading face  98  and a trailing face  100  that extends from the second major surface  56  and intersect at a tip  102 . The leading face  98  may be oriented more proximate the leading end  70  (as compared to the trailing face  100 ), whereas the trailing face  100  may be oriented more proximate the trailing end  72 . 
     With these designations in mind, the teeth may be constructed to define an insertion direction whereby an angle α formed by the leading face  98  relative to the second major surface  56  is smaller than an angle β formed by the trailing face  100  relative to the second major surface  56 . 
     In these configurations, the leading face  98  may have a more gradual slope relative to the leading end  70  as compared to a slope of the trailing face  100  relative to the trailing end  72  such that the tooth  96   a  more overtly engages a separate structure, such as the facet joint superior face (not shown) at and along the trailing face  100  as compared to the leading face  98 . 
     In some configurations, the angle α defined by the leading face  98  may be in the range of 20°-60°, whereas the angle β defined by the trailing face  100  is approximately 90°. Suitable angles may be affected by a variety of factors such as the material from which the resurfacing body  46  is fabricated. Regardless, and returning to  FIG. 2 , the remaining teeth of the first teeth set  90  may be aligned with one another in two or more rows as shown. 
     The second teeth set  92  and the third teeth set  94  may be formed at or along the opposing sides  74 ,  76 , respectively, as illustrated in  FIG. 2 . In this regard, while the individual teeth of the second and third sets  92 ,  94  may have the non-symmetrical relationship described above with respect to the tooth discussed above, an exterior face  103  associated with each tooth of the second and third teeth sets  92 ,  94  establish an angle of extension relative to the second major surface  56  that approaches 90°. 
     With this but one acceptable construction, the second and third teeth sets  92 ,  94  overtly resist side-to-side displacement of the resurfacing body  46  relative to a corresponding facet joint face following insertion. For example, the second teeth set  92  may resist leftward displacement of the resurfacing body  46 , whereas the third teeth set  94  may resist rightward displacement. 
     In certain embodiments, each tooth of the plurality of teeth  52  may have an identical, or nearly identical, height (or extension from the second major surface  56 ), as illustrated in  FIG. 3 . In other embodiments, the teeth of the first teeth set  90  may have an elevated height as compared to teeth of the second and third teeth sets  92 ,  94 , and combine to define a tapering height of the resurfacing body  46  from the leading end  70  to the trailing end  72 . 
     Stated otherwise, and relative to the illustrated embodiment in which the first major surface  54  is planar, a height of the leading tooth  96   a  is greater than a height of a trailing tooth  96   b . For example, the tips  102  associated with the teeth of the first teeth set  90  combine to define a hypothetical plane P. The plane P is, in some embodiments, non-perpendicular relative to a plane of the first major surface  54 , combining with the first major surface  54  to define an included angle Δ in the range of between about 1° and about 5°. 
     In other embodiment, other angles are also contemplated where the teeth  52  have substantially similar heights. In certain embodiments, the tallest tooth  96   a  may be provided at the leading end  70  that ultimately is located opposite the point of insertion into the facet joint. As a result, the leading tooth  96   a  may establish a more rigid engagement with the corresponding facet joint face to thereby overtly resist displacement upon final insertion. 
     The base web  50  and the teeth  52  combine to define an overall thickness T of the resurfacing body  46 . For example, a lateral distance between the first major surface  54  and the tip  102  of the “tallest” tooth  96   a . As described in greater detail below, a desired conformability characteristic of the resurfacing body  46  is influenced by the overall thickness T and the base web thickness t, and thus the overall thickness T is selected, along with other parameters, to effectuate the desired degree of conformability. 
     In some constructions, the overall thickness T of the resurfacing body  46  is between about 0.25 millimeters and about 4 millimeters, although other dimensions are also contemplated. As a point of reference, the overall thickness T associated with the resurfacing body  46  selected by the treating clinician for insertion into a particular facet joint may vary as a function of other procedures associated with the insertion. 
     For example, where the resurfacing body  46  is inserted into a facet joint without any overt tissue removal prior to insertion, the overall thickness T can be between about 0.5 millimeters and about 2.5 millimeters. If the insertion procedure entails first removing cartilage (or other tissue) from the facet joint, a larger version of the resurfacing body  46  can be inserted, such that the overall thickness T of the resurfacing body  46  is between about 0.5 millimeters and about 3 millimeters. 
     The resurfacing devices  42 ,  44 , and thus the corresponding resurfacing bodies  46 , may be integrally formed of a robust material that achieves desired conformability. The resurfacing body  46  in accordance with this invention maintains its structural integrity (i.e., little or no wear) without adhesive or cohesive damage when subjected to typical articulation of the facet joint with movement of the patient. 
     In some constructions, the resurfacing devices  42 ,  44  may be formed of an implantable-grade plastic, although other materials such as metal are also available. For example, the resurfacing devices  42 ,  44  may be made from the polyetherketone (PEK) family of plastics, which have strength, wear, flexibility, and biocompatibility properties appropriate for insertion into, and long-term functioning within, the facet joint. 
     Polyetheretherketone (PEEK) has been found to provide not only the conformability attributes described below, but also long-term mechanical strength and resistance to wear. Additional materials may be incorporated, such as those exhibiting radio-opacity properties. For example, the resurfacing devices  42 ,  44  may be formed from a radio-opaque mineral (e.g., barium)-loaded PEK composition. 
     Visualization may also be provided via one or more radio-opaque marker bands (e.g., platinum marker band). The marker band(s) can be embedded within the resurfacing device  42 ,  44 . For example, a radio-opaque rod may be inserted into a hole formed in the resurfacing device  42 ,  44 , as illustrated in  FIG. 5 . Alternatively, the radio-opaque material may be inserted around a perimeter of the resurfacing device  42 ,  44 . 
     The selected materials, shapes, and dimensions associated with the resurfacing body  46  of each of the resurfacing devices  42 ,  44  impart or create a conformability property to the resurfacing body  46  sufficient to allow the resurfacing body  46  to “match” the multi-planar concavity associated with a native facet joint articular face anatomy. 
     With the resurfacing device  42 ,  44  embodiment of  FIG. 2 , the resurfacing body  46  forms an entirety of the corresponding resurfacing device  42 ,  44 . In other embodiments described below, one or more additional components may be included with the resurfacing body  46 , such that the following explanation of conformability is specifically applicable to the resurfacing body  46 , but may also apply equally to the resurfacing devices  42 ,  44  as a whole. 
     In general terms, “conformability” may be inversely proportional to bending stiffness of the resurfacing body  46  during insertion, and may be increased as the resurfacing body  46  heats to body temperature and is allowed to creep. From a clinical perspective, “conformability” of the resurfacing body  46  entails the resurfacing body  46  conforming to a radius of curvature of the C-shaped or J-shaped portions of the articular joint such as the concave-shaped superior articular face  26  of  FIG. 1B  or the convex-shaped inferior articular face  28  of  FIG. 1B . 
     As a point of reference, the minimum radius of curvature of the human facet joint in the transverse plane is on the order of 20 millimeters, with a lower bound (10th percentile) on the order of 7 millimeters. The radius of curvature will vary with the vertebral level and the patient&#39;s specific anatomy and disease state. Preparation of the facet joint prior to insertion of the resurfacing devices  42 ,  44  may also change the radius of curvature. 
     A range of curvature radii of 7 millimeters to infinity (i.e., flat facet anatomy) can be accommodated by the resurfacing devices  42 ,  44  of the present disclosure. There also may be curvature in the sagittal plane; the conformable nature of the resurfacing body  46  of the present disclosure is capable of substantially “matching” any sagittal plane curvature as well. 
     With the above understandings in mind, the conformability characteristic of the resurfacing body  46  is sufficient such that the resurfacing body  46  readily transition from the relatively flat state illustrated in  FIG. 2  to an inserted state (not shown but reflected, for example, in  FIG. 30 ) in which the resurfacing body  46  substantially matches or mimics the naturally-occurring shape (e.g., radius of curvature of curved portions) of the facet joint face to which the resurfacing body  46  is secured. In this regard, the facet joint  20  ( FIG. 1B ) is subject to, or experiences, various loads that effectuate compressive forces at the region of interface between the superior and inferior articular faces  26 ,  28  ( FIG. 1B ). 
     These physiologic forces across the facet joint  20  will vary with activity, posture, body loads, and muscle forces, and tend to be between about 7% and about 14% of body load when standing. However, in the prone, slightly flexed position during surgery/implantation, these loads may be as little as zero. The intrinsic forces will be generated as the resurfacing device  42 ,  44  (and thus the corresponding resurfacing body  46 ) are inserted and the capsule  32  ( FIG. 1B ) is tensioned. Compression of the underlying cartilage and subchondral bone, slight flexion, or laminar strains may result and would accommodate some thickness of the devices  42 ,  44 . However, separation/posterior translation of the superior facets would be required to accommodate a large portion of a collective thickness of the devices  42 ,  44 . 
     Compressive loads normal to and across the articular faces  26 ,  28  will be generated upon separation/posterior translation of the superior facets due to joint capsule tensioning. The conformable nature of the resurfacing body  46  is such that in the presence of these typical compressive forces, the resurfacing body  46  will transition from the relatively flat state to the inserted state in which the resurfacing body  46  substantially matches the geometry of the facet joint surface to which the resurfacing body  46  is secured. 
     For example, the resurfacing body  46  will flex to conform with a macroscopic shape/contour of the native articular face to which the resurfacing body  46  is applied, but may not conform to the microscopic variations in the native articular face because of small deviations due to cartilage defects, bony fissures, or small voids during preparation of the joint (typically between about 0.05 millimeters and about 0.5 millimeters in width). 
     This process will occur as the compressive forces applied by the ends of the hypothetical concave region of one facet articular surface (e.g., the superior articular surface  26 ) and the center of the corresponding convex surface on the opposing articular facet (e.g., the inferior articular surface  28 ) generate a bending moment on the resurfacing body  46  that produces strain to conform the resurfacing body  46  to the native anatomy. 
     As used through this specification, a resurfacing body that conforms to the minimum radius of curvature of an adult human facet joint under normal physiologic forces (e.g., between about 180 and about 450 Newtons/millimeter per segment assuming a net 1 millimeter posterior shear translation) without deviations from the articular surface to which the resurfacing body is applied of greater than 1 millimeter is defined as being “conformable” and “substantially matching” the multi-planar curvatures of a facet joint. 
     Alternatively, a resurfacing body sized for placement within an adult human facet joint and exhibiting a Conformability Factor (described below) of not more than 100 Newtons is also defined as being “conformable” and “substantially matching” the multi-planar curvatures of a facet joint in accordance with the present disclosure. In some embodiments, resurfacing bodies in accordance with the present disclosure exhibit a Conformability Factor of not more than 50 Newtons, and in other embodiments not more than 25 Newtons. 
     It has surprisingly been found that forming the resurfacing body  46  (and thus either of the resurfacing devices  42 ,  44  of the one embodiment of  FIG. 2 ) of PEEK and with the footprint size and thickness dimensions described above achieves the desired conformability characteristics, long-term resistance to wear, and facet joint stabilization following insertion. 
     Another embodiment of the resurfacing body  46  is illustrated in  FIGS. 4-6 . The resurfacing body  46  may have a similar over shape and a similar tooth pattern to the resurfacing body illustrated in  FIGS. 2-3  except as noted below. 
     The resurfacing body  46  may include a radio opaque marker  82  placed therein. The radio opaque marker  82  may be utilized to monitor the location of the resurfacing body  46  is implanted in a non-invasive manner as the radio opaque marker  82  may be viewed using many different types of imaging conventionally used in the medical field. 
     The radio opaque marker  82  should be sufficiently large to facilitate viewing the radio opaque marker using conventional medical imaging techniques. However, the radio opaque marker  82  should be sufficiently small such that the radio opaque marker  82  does not impede the flexibility of the resurfacing body  46  after implantation. Alternatively or additionally, the radio opaque marker  82  may be fabricated from a flexible material that does not impede the ability of the resurfacing body  46  to flex after implantation. 
     While it is possible to incorporate the radio opaque marker  82  during the process used to fabricate the resurfacing body  46 , it is also possible to insert the radio opaque marker  82  into the resurfacing body  46  after fabrication. 
     One such suitable technique for inserting the radio opaque marker  82  into the resurfacing device includes forming an aperture in the resurfacing body  46 . In certain embodiments, the aperture may be formed using a drill. 
     In certain embodiments, the radio opaque marker  82  may be placed into the resurfacing body  46  from a trailing end  72  thereof proximate a center line of the resurfacing body  46 . Using such a configuration provides the resurfacing body  46  with symmetry to assist in evaluating the position of the resurfacing body  46  based upon medical imaging of the radio opaque marker  82 . 
     The placement of the radio opaque marker  82  in the resurfacing body  46  should be relatively accurate such that the radio opaque marker  82  does not extend through one of the surfaces of the resurfacing body  46 . Such an occurrence could lead to degradation of the resurfacing body  46  or could cause damage to the tissue in the facet joint that is adjacent to the resurfacing body  46 . 
     To ensure that the radio opaque marker  82  does not extend through the upper surface of the resurfacing body  46 , an additional material region  84  may be provided in the region adjacent to the radio opaque marker  82 , as illustrated in  FIGS. 4 and 5 . The radio opaque marker  82  may be placed at an approximately equal distance between the upper and lower surfaces of the resurfacing body in the additional material region  84 . 
     An elongated tab  86  may extend from the trailing end  72  of the resurfacing body  46 . The elongated tab  86  could be used in the manufacturing process and then be severed from the other portions of the resurfacing body  46  once manufacturing is completed. Alternatively, the elongated tab  86  may be used in conjunction with the insertion of the resurfacing body  46  into the facet joint as opposed to the implantation system described herein. In such instances, a line of weakening may be provided where the elongated tab  84  intersects the resurfacing body  46 . 
     Another embodiment of the resurfacing body  46  is illustrated in  FIGS. 7-9 . The resurfacing body  46  may have a similar over shape and a similar tooth pattern to the resurfacing body illustrated in  FIGS. 2-3  except as noted below. 
     The resurfacing body  46  may include a radio opaque marker  82  placed therein. The radio opaque marker  82  may be utilized to monitor the location of the resurfacing body  46  is implanted in a non-invasive manner as the radio opaque marker  82  may be viewed using many different types of imaging conventionally used in the medical field. The features and placement of the radio opaque marker  82  are similar to the features and placement of the radio opaque marker  82  in the embodiment of the resurfacing body  46  illustrated in  FIGS. 4-6   
     An elongated tab  86  may extend from the trailing end  72  of the resurfacing body  46 . The structure and function of the elongated tab  86  may be to the structure and function of the elongated tab  86  in the embodiment of the resurfacing body  46  illustrated in  FIGS. 4-6 . 
     The resurfacing body  46 , and thus the system  40 , may be delivered to, and inserted within, a facet joint in a variety of manners via various instrumentations sets or systems. Components of one useful insertion tooling set are discussed below. 
     One of the important aspects of accurately delivering the resurfacing body  46  is to not only accurately locate the desired facet joint but also to accurately position the resurfacing body delivery system with respect to the facet joint to permit the resurfacing body  46  to be accurately inserted into the facet joint. 
     Another embodiment of the invention is directed to an implant system  101 , as illustrated in  FIGS. 10-13 . In certain embodiments, the implant system  101  includes a superior resurfacing device  106  and an inferior resurfacing device  108 , as illustrated in  FIG. 11 . 
     The superior resurfacing device  106  serves as a liner for a superior facet and the inferior resurfacing device  108  serves as a liner for an inferior facet. In certain embodiments, the resurfacing devices  106 ,  108  are capable of conforming to the naturally-occurring shape or curvature of the facet joint anatomy. 
     The resurfacing devices  106 ,  108  thereby replace a bone-on-bone interface caused by degradation of the natural joint in a manner achieving normal or near normal mobility of the vertebrae. It is also possible to use the concepts of the invention in conjunction with other articular joints. 
     The superior resurfacing device  106  and the inferior resurfacing device  108  may each have a substantially similar shape. As such, the description herein is provided with respect to the superior resurfacing device  106 . 
     While  FIGS. 10, 12 and 13  illustrate that the superior resurfacing device  106  has a disc-like shape, it is possible for the superior resurfacing device  106  to have other shapes using the concepts of this invention. 
     The superior resurfacing device  106  may be defined as having a leading edge  110 , a trailing edge  112 , a first opposing side  114  and a second opposing side  116 . The leading edge  110  is on the end of the superior resurfacing device  106  that is intended to be inserted first during the implantation process. 
     The trailing edge  112  may be oriented generally opposite from the leading edge  110 . As such, the trailing edge  112  is the end of the superior resurfacing device  106  that enters a bodily space last during the implantation process. 
     The first opposing side  114  and the second opposing  116  are located on opposite edges of the superior resurfacing device  106 . The first opposing side  114  and the second opposing side  116  extend between the leading edge  110  and the trailing edge  112 . 
     The superior resurfacing device  106  may include a base web  120  and a plurality of teeth  122  that extend from the base web  120 . The base web  120  defines opposing major surfaces that include a first major surface  124  and a second major surface  126 . 
     In certain embodiments, the base web  120  may be formed with a relatively uniform thickness. In other embodiments, the base web  120  is tapered such that proximate the leading edge  110 , the base web  120  is thicker than proximate the trailing edge  112 . In certain embodiments, the angle of the taper is up to about 4 degrees. In other embodiments, the angle of the taper is about 2 degrees. 
     The first major surface  124  may be generally smooth to serve as an articulating surface, which articulates relative to a corresponding articulating surface of the inferior resurfacing device  108  when the first major surfaces  124  on the superior resurfacing device  106  and the inferior resurfacing device  108  are positioned adjacent to each other as illustrated in  FIG. 11 . 
     As such, the first major surface  124  can be referred to as the “articulating surface” of the superior resurfacing device  106 . In certain embodiments, the articulating surface  124  may be coated with a separate layer that provides enhanced frictional (i.e., lower coefficient of friction) and/or wear characteristics. 
     The plurality of teeth  122  project from the second major surface  126  in a direction generally opposite the first major surface  124 . In certain embodiments, the plurality of teeth  122  may include at least two groups of teeth. The teeth in each group of teeth may be shaped differently, oriented in a different direction and/or aligned differently than the teeth in the other groups of teeth. 
     While the description below is provided with respect to a particular configuration of teeth that is illustrated in the figures, a person of skill in the art will appreciate that various other configurations of teeth may be used that incorporate the concepts discussed below to reduce the potential of the superior and inferior resurfacing devices  106 ,  108  moving after implantation. 
     An important aspect of the teeth  122  is that they minimize the movement of the superior and inferior resurfacing devices  106 ,  108  with respect to the adjacent tissue. Such movement can include sliding out of the joint in which the superior and inferior resurfacing devices  106 ,  108  are implanted. Such movement can also include rotation of one of more of the superior and inferior resurfacing devices  106 ,  108  in the joint where the superior and inferior resurfacing devices  106 ,  108  implanted. 
     The first set of teeth  130  may resist movement of the superior resurfacing device  106  towards the trailing edge  112  such that the superior resurfacing device  106  moves out of the implant region in a direction that is opposite of the direction in which the superior resurfacing device  106  moved during the implantation process. 
     The first set of teeth  130  may be positioned at an intermediate location on the base web  120 . As used herein, intermediate location means that the first set of teeth  130  is not located proximate the first opposing side  114  and the second opposing side  116 . The first set of teeth  130  may also not be located proximate to the trailing edge  112 . In certain embodiments, the first set of teeth  130  are positioned proximate the leading edge  110 . 
     Alternatively, the first set of teeth  130  may be positioned to substantially cover the second major surface  126  such that the first set of teeth  130  are located proximate to the first opposing side  114  and the second opposing side  116 . 
     The first set of teeth  130  may be positioned in a plurality of rows. These rows may be oriented generally transverse to a direction in which the superior resurfacing device  106  moves during the insertion process. 
     The teeth in adjacent rows of the first set of teeth  130  may be offset, as most clearly illustrated in  FIG. 13 . In certain embodiments, the teeth in a first row are placed so that the edges of the teeth in the first row are approximately aligned with a center of the teeth in a second row. 
     Using such a configuration of teeth enhances the ability of the superior resurfacing device  106  to resist movement after implantation because if the teeth in the first row cut a path through the tissue into which the teeth extend, the teeth in the second row will not also pass through the same path in the tissue. Rather, the teeth in the second row will have to cut a separate path through the tissue into which the teeth extend. Such a process requires more force than if the teeth in the second row move through the path formed in the tissue by the first row of teeth. 
     Alternatively or additionally, at least a portion of the teeth in the first set of teeth  130  may have a greater width. As used herein, width of the teeth is a direction that is generally perpendicular to the direction between the leading edge  110  and the trailing edge  112 . 
     The teeth  130  having the greater width may also enhance the ability of the superior resurfacing device  106  to resist movement after implantation because the teeth  130  having the greater width engage the tissue over a larger area than the other teeth having a smaller width. In one such configuration, the teeth  130  with a greater width have a width that is about twice as large as the width of the teeth in the other portion of the first set of teeth  130 . 
     The wider teeth  130  may also exhibit a greater resistance to deformation when subjected to a load placed thereon such as when it is attempted to slide the superior resurfacing device  106  with respect to the tissue into which the teeth  130  are implanted. Such greater resistance to deformation reduces the potential that the teeth  130  will deform to an extent where the teeth fail and/or that the superior resurfacing device  106  is permitted to move with respect to the tissue into which the teeth  130  are implanted. 
     In certain embodiments, the teeth  130  with the greater width may be positioned closer to the leading edge  110  than the other teeth in the first set of teeth  130  that have a smaller width. The teeth  130  with the greater width may be provided in more than one row. In certain embodiments, there are at least two rows of teeth  130  having a greater width. 
     The teeth in the different rows of the first set of teeth  130  may be formed so that the teeth in the rows proximate the leading edge  110  have a depth that is greater than a depth of the teeth in the rows proximate the trailing edge  112 , as illustrated in  FIG. 11 . As used herein, depth of the teeth is a direction that is generally perpendicular second major surface  126 . 
     In certain embodiments, the teeth in the rows proximate the leading edge  110  have a depth that is between about 80 percent and about 120 percent greater than a depth of the teeth in the rows proximate the trailing edge  112 . 
     There may also be at least one intermediate row of teeth having a depth that is less than the depth of the teeth in the rows proximate the leading edge  110  and having a depth that is greater than the depth of the teeth in the rows proximate the trailing edge  112 . 
     The teeth in the first set of teeth  130  may each have a leading face  133  and a trailing face  135 . The leading face  133  is oriented towards the leading edge  110  while the trailing face  135  is oriented towards the trailing edge  112 . An angle formed between the trailing face  135  and the base web  120  is less than an angle formed between the leading face  133  and the base web  120 . 
     In certain embodiments, the angle formed between the leading face  133  and the base web  120  may be between about 20° and about 60°. In other embodiments, the angle formed between the leading face  133  and the base web  120  may be between about 30° and about 50°. 
     In certain embodiments, the angle formed between the trailing face  135  and the base web  120  may be between about 75° and about 105°. In other embodiments, the angle formed between the trailing face  135  and the base web  120  may be about 90°. 
     The teeth may also include a first side surface  136  and a second side surface  138 . An angle formed between the first side surface  136  and the base web  120  may be between about 40° and about 80°. In other embodiments, the angle formed between the first side surface  136  and the base web  120  may be between about 60° and about 80°. The second side surface  138  may be oriented at an angle with respect to the base web  120  that is about the same as the angle between the first side surface  136  and the base web  120 . 
     In other embodiments, the trailing face  135  may include an upper tooth section  137  and a lower tooth section  139  that are oriented in a non-collinear orientation with respect to each other, as illustrated in  FIG. 13 . In certain embodiments, an obtuse angle is formed between the upper tooth section  137  and the lower tooth section  139 . In other embodiments, the angle between the upper tooth section  137  and the lower tooth section  139  is between about 135° and 170°. 
     As a result of this configuration, the upper tooth section  137  may be oriented at an angle with respect to the base web  120  that is greater than an angle between the lower tooth section  139  and the base web  120 . 
     The first set of teeth  130  may include a plurality of leading edge teeth  141  that are positioned along the leading edge  110 , as illustrated in  FIGS. 10, 12 and 13 . The teeth in the plurality of leading edge teeth  141  may have a width and a depth that is similar to the teeth positioned proximate to a center of the superior resurfacing device  106 . 
     First and second side surfaces of the leading edge teeth  141  may be oriented at a smaller angle than the teeth positioned proximate to the center of the superior resurfacing device  106 . This configuration provides the teeth in the leading edge teeth  141  with a pointer configuration than the other teeth in the first set of teeth  130 . 
     Because the leading edge teeth  141  are positioned along the leading edge  110  and because of the curvature of the leading edge  110 , the teeth in the leading edge teeth  141  may not all have the same depth, as most clearly illustrated in  FIG. 10 . 
     The second set of teeth  132  and the third set of teeth  134  enhance the ability of the superior resurfacing device  106  to resist being displaced side-to-side after implantation. Such movement may be in a direction that is angularly offset with respect to a direction in which the superior resurfacing device  106  moves during the implantation process. 
     While it is possible for the movement to be generally perpendicular to the direction in which the superior resurfacing device  106  moves during the implantation process, the second set of teeth  132  and the third set of teeth  134  may also prevent movement of the superior resurfacing device  106  in other directions that are not perpendicular to the direction in which the superior resurfacing device  106  moves during the implantation process. 
     The second set of teeth  132  are formed at or along the first opposing side  114 . The individual teeth  140  in the second set of teeth  132  may be formed with a non-symmetrical relationship with respect to the teeth in the first set of teeth  130 . 
     The second set of teeth  132  may be arranged in a plurality of rows. In certain embodiments, the second set of teeth  132  includes a first row of teeth  132   a  and a second row of teeth  132   b . The first row of teeth  132   a  is positioned along the first opposing side  114 . The second row of teeth  132   b  may be positioned between the first row of teeth  132   a  and the first set of teeth  130 . 
     While it is illustrated that the teeth in the second set of teeth  132   b  are generally aligned with the teeth in the first set of teeth  132   a , in certain embodiments, the teeth in the second set of teeth  132   b  may be offset from the teeth in the first set of teeth  132   a  similar to the manner in which adjacent rows of teeth in the first set of teeth  130  are offset from each other. 
     The second teeth  140  in the first row of teeth  132   a  may each have an exterior face  142   a  and an interior face  144   a . The exterior face  142   a  faces the first opposing side  114  while the interior face  144   a  faces the second opposing side  116 . An angle formed between the interior face  144   a  and the base web  120  is less than an angle formed between the exterior face  142   a  and the base web  120 . 
     In certain embodiments, the angle formed between the exterior face  142   a  and the base web  120  may be between about 75° and about 105°. In other embodiments, the angle formed between the exterior face  142   a  and the base web  120  may be about 90°. 
     In certain embodiments, the angle formed between the interior face  144  and the base web  120  may be between about 20° and about 60°. In other embodiments, the angle formed between the interior face  144  and the base web  120  may be between about 30° and about 50°. 
     The second teeth  140  may also include a first side surface  146  and a second side surface  148 . An angle formed between the first side surface  146  and the base web  120  may be between about 40° and about 80°. In other embodiments, the angle formed between the first side surface  146  and the base web  120  may be between about 60° and about 80°. The second side surface  148  may be oriented at an angle with respect to the base web  120  that is about the same as the angle between the first side surface  146  and the base web  120 . 
     The teeth in the second row of teeth  132   b  may be shaped similarly to the teeth in the first row of teeth  132   a  in most respects. In one configuration, an angle between the exterior face  142   b  of the teeth in the second row of teeth  132   b  and the base web  120  may be less than an angle between the exterior face  142   a  of the teeth in the first row of teeth  132   a  and the base web  120 . 
     In certain embodiments, the angle formed between the exterior face  142   b  of the teeth in the second row of teeth  132   b  and the base web  120  may be between about 60° and about 80°. 
     In other embodiments, the exterior face  142   b  of the teeth in the second row of teeth  132   b  includes an upper tooth section  147  and a lower tooth section  149  that are oriented in a non-collinear orientation with respect to each other. In certain embodiments, an obtuse angle is formed between the upper tooth section  147  and the lower tooth section  149 . 
     As a result of this configuration, the upper tooth section  147  may be oriented at an angle with respect to the base web  120  that is greater than an angle between the lower tooth section  149  and the base web  120 . 
     The third set of teeth  134  are formed at or along the second opposing side  116 . The individual teeth  150  in the third set of teeth  134  may be formed with a non-symmetrical relationship with respect to the teeth in the first set of teeth  130 . 
     The third set of teeth  134  may be arranged in a plurality of rows. In certain embodiments, the third set of teeth  134  includes a first row of teeth  134   a  and a second row of teeth  134   b . The first row of teeth  134   a  is positioned along the second opposing side  116 . The second row of teeth  134   b  may be positioned between the first row of teeth  134   a  and the first set of teeth  130 . 
     While it is illustrated that the teeth in the second row of teeth  134   b  are generally aligned with the teeth in the first row of teeth  134   a , in certain embodiments, the teeth in the second row of teeth  134   b  may be offset from the teeth in the first row of teeth  134   a  similar to the manner in which adjacent rows of teeth in the first set of teeth  130  are offset from each other. 
     The third teeth  150  in the first row of teeth  134   a  each have an exterior face  152  and an interior face  154 . The exterior face  152  face the second opposing side  116  while the interior face  154  faces the first opposing side  114 . An angle formed between the interior face  154  and the base web  120  is less than an angle formed between the exterior face  152  and the base web  120 . 
     In certain embodiments, the angle formed between the exterior face  152  and the base web  120  may be between about 75° and about 105°. In other embodiments, the angle formed between the exterior face  152  and the base web  120  may be about 90°. 
     In certain embodiments, the angle formed between the interior face  154  and the base web  120  may be between about 20° and about 60°. In other embodiments, the angle formed between the interior face  154  and the base web  120  may be between about 30° and about 50°. 
     The third teeth  150  may also include a first side surface  156  and a second side surface  158 . An angle formed between the first side surface  156  and the base web  120  may be between about 40° and about 80°. In other embodiments, the angle formed between the first side surface  156  and the base web  120  may be between about 60° and about 80°. The second side surface  158  may be oriented at an angle with respect to the base web  120  that is about the same as the angle between the first side surface  156  and the base web  120 . 
     The teeth in the second row of teeth  134   b  may be shaped similarly to the teeth in the first row of teeth  134   a  in most respects. In one configuration, an angle between the exterior face  152   b  of the teeth in the second row of teeth  134   b  and the base web  120  may be less than an angle between the exterior face  152   a  of the teeth in the first group of teeth  134   a  and the base web  120 . 
     In certain embodiments, the angle formed between the exterior face  152   b  of the teeth in the second row of teeth  142   b  and the base web  120  may be between about 60° and about 80°. 
     In other embodiments, the exterior face  152   b  of the teeth in the second row of teeth  134   b  includes an upper tooth section  157  and a lower tooth section  159  that are oriented in a non-collinear orientation with respect to each other. In certain embodiments, an obtuse angle is formed between the upper tooth section  157  and the lower tooth section  159 . 
     As a result of this configuration, the upper tooth section  157  may be oriented at an angle with respect to the base web  120  that is greater than an angle between the lower tooth section  159  and the base web  120 . 
     In some constructions, each tooth of the plurality of teeth can have an identical, or nearly identical, height. In other embodiments, the teeth can be formed with a tapered height such that the teeth proximate the leading edge  110  have a height that is greater than a height of the teeth proximate the trailing edge  112 . 
     The height of the teeth may be tapered at an angle of up to about 4 degrees. In certain embodiments, the height of the teeth may be tapered at an angle of about 2 degrees. As a result of this configuration, the teeth proximate the leading edge  110  can establish a more rigid engagement with the corresponding tissue face to thereby resist displacement after insertion. 
     As described in greater detail below, a desired conformability characteristic of the superior resurfacing device  106  may be influenced by the overall thickness and the base web  120  to effectuate the desired degree of conformability. The overall thickness of the superior resurfacing device  106  may be selected by the treating clinician for insertion into a particular joint may vary as a function of other procedures associated with the insertion. 
     The conformability of the superior resurfacing device  106  may be enhanced by the layout of the teeth. In certain embodiments, the orientation of the first group of teeth  132  so that the teeth in adjacent rows are offset from each other may enhance the ability of the superior resurfacing device  106  to bend as compared to teeth configurations where teeth in adjacent rows are aligned with each other. 
     For example, the arrangement of the teeth in the offset configuration may provide the superior resurfacing device  106  with a greater number of folding axes than the configuration where teeth in adjacent rows are aligned with each other. 
     For example, where the superior resurfacing device  106  is inserted into a joint without any overt tissue removal prior to insertion, the overall thickness can be in the range of 0.5-2.5 mm. If, however, the insertion procedure entails first removing cartilage (or other tissue) from the joint, a thicker version of the superior resurfacing device  106  can be inserted, such that the overall thickness of the superior resurfacing device  106  is in the range of 0.5-3 mm. 
     The superior and inferior resurfacing devices  106 ,  108  may be integrally formed of a robust material that achieves desired conformability. The resurfacing body  46  in accordance with the present disclosure maintains its structural integrity (i.e., little or no wear) without adhesive or cohesive damage when subjected to typical articulation of the joint with movement of the patient. 
     In some constructions, the superior and inferior resurfacing devices  106 ,  108  are formed of an implantable-grade plastic, although other materials such as metal are also available. For example, the superior and inferior resurfacing devices  106 ,  108  can be made from the polyetherketone (PEK) family of plastics, which have strength, wear, flexibility, and biocompatibility properties appropriate for insertion into, and long-term functioning within, the joint. 
     Polyetheretherketone (PEEK) has surprisingly been found to provide not only the conformability attributes described below, but also long-term mechanical strength and resistance to wear. Additional material(s) can be incorporated, such as those exhibiting radio-opacity properties. For example, the superior and inferior resurfacing devices  106 ,  108  can be formed from a radio-opaque mineral (e.g., barium)-loaded PEK composition. 
     Visualization can also be provided via one or more radio-opaque marker bands (e.g., platinum marker band). The visualization marker  170  can be embedded within at least one of the superior and inferior resurfacing device  106 ,  108  (e.g., a radio-opaque rod inserted into a hole formed in the superior and inferior resurfacing device  106 ,  108 ). In another configuration, the radio-opaque material may be inserted along a portion of a perimeter of the superior and inferior resurfacing device  106 ,  108 . 
     In another configuration of the visualization marker  170  indicates not only the location of the superior and inferior resurfacing device  106 ,  108  but also the orientation of the superior and inferior resurfacing device  106 ,  108  with respect to each other. 
     One such configuration of the visualization marker  170  includes two marker portions  172 ,  174  that are oriented at an angle with respect to each other. A first marker portion  172  may be oriented at an angle with respect to the second marker portion  174  that is between about 60 degrees and about 100 degrees. In certain embodiments, the angle between the first marker portion  172  and the second marker portion  174  is between about 70 degrees and about 80 degrees. 
     The first marker portion  172  may be positioned proximate to a central axis of the superior resurfacing device  106  that is intermediate the first opposing side  114  and the second opposing side  116 . 
     An aperture  180  may be formed from the trailing edge  112  of the superior resurfacing device  106  that has a depth that is greater than a length of the first marker portion  172 . The aperture  180  has a diameter that is slightly larger than the diameter of the first marker portion  172 . 
     Adjacent to and intersecting with the aperture  180  is a channel  182  that has a length that is slightly larger than a length of the second marker portion  174 . The channel  182  has a width that is slightly larger than the width of the second marker portion  174 . 
     Forming the aperture  180  and the channel  182  with the preceding dimensions enables the visualization marker  170  to be recessed beneath the side of the superior resurfacing device  106  after insertion of the first marker portion  172  into the aperture  180  and the second marker portion  174  into the channel  182 . 
     A sealant (not shown) may be placed over the visualization marker  170  to retain the visualization marker  170  in a stationary position with respect to the superior resurfacing device  106 . The sealant should resist degradation after the superior and inferior resurfacing devices  106 ,  108  are implanted. The sealant should also be selected to minimize the potential of adverse interactions after the superior and inferior resurfacing devices  106 ,  108  are implanted. 
     Since the superior and inferior resurfacing devices  106 ,  108  are formed substantially similar to each other and the superior and inferior resurfacing devices  106 ,  108  are implanted with the articulating surfaces facing each other, the first marker portion in the superior and inferior resurfacing devices  106 ,  108  are aligned with each other during the insertion process. 
     In view of the preceding comments, if during evaluation of the position of the superior and inferior resurfacing devices  106 ,  108  using the visualization marker  170  indicates that the first marker portions  172  in the superior and inferior resurfacing device  106 ,  108  are not aligned with each other, it will be possible to determine that at least one of the superior and inferior resurfacing devices  106 ,  108  are not correctly oriented. 
     When the superior and inferior resurfacing devices  106 ,  108  are inserted correctly, the second marker portions  174  will be directed opposite from each other. The two visualization markers  170  thereby provide a generally T-shape. If the second marker portions  174  do not form the top of the T-shape using a radio-opaque detection technique, it can be determined that the superior and inferior resurfacing devices  106 ,  108  are not correctly inserted. For example, if the visualization markers  170  in the superior and inferior resurfacing devices  106 ,  108  form an L-shape, it can be determines that the articulating surface on the superior resurfacing device  106  is not facing the articulating surface on the inferior resurfacing device  108 . 
     Depending on a thickness of the superior resurfacing device  106  proximate the trailing edge  112 , there may not be teeth positioned on the superior resurfacing device  106  proximate the trailing edge  112 , such as illustrated in  FIGS. 13-16 . For example, to accommodate the visualization marker  170 , the base web  120  may need to be formed with a thickness proximate the trailing edge  112  than in the other portions of the superior resurfacing device  106  where the visualization marker  170  is not implanted therein. 
     The selected materials, shapes, and dimensions associated with the superior and inferior resurfacing devices  106 ,  108  impart or create a conformability property that allows the superior and inferior resurfacing devices  106 ,  108  to “match” the multi-planar concavity associated with a native joint articular face anatomy. 
     In general terms, “conformability” is inversely proportional to bending stiffness of the superior and inferior resurfacing device  106 ,  108  during insertion, and may be increased as the superior resurfacing device  106 ,  108  heats to body temperature and is allowed to creep. 
     With the above understandings in mind, the conformability characteristic of the superior and inferior resurfacing devices  106 ,  108  is sufficient such that the superior and inferior resurfacing devices  106 ,  108  readily transition from the relatively flat state illustrated in  FIGS. 13-16  to an inserted state (not shown) in which the superior and inferior resurfacing devices  106 ,  108  substantially matches or mimics the naturally-occurring shape (e.g., radius of curvature of curved portions) of the joint face to which the superior and inferior resurfacing devices  106 ,  108  are secured. In this regard, the joint is subject to, or experiences, various loads that effectuate compressive forces at the region of interface between the superior and inferior articular faces. 
     Compressive loads normal to and across the articular faces will be generated upon separation/posterior translation of the superior articulating joint due to joint capsule tensioning. The conformable nature of the superior and inferior resurfacing devices  106 ,  108  is such that in the presence of these typical compressive forces, the superior and information resurfacing devices  106 ,  108  will transition from the relatively flat state to the inserted state in which the superior and inferior resurfacing devices  106 ,  108  substantially matches the geometry of the joint surface to which the superior and inferior resurfacing devices  106 ,  108  are secured (i.e., the superior and inferior resurfacing devices  106 ,  108  will flex to conform with a macroscopic shape/contour of the native articular face to which the superior and inferior resurfacing device  106 ,  108  are applied, but may not conform to the microscopic variations in the native articular face, for example small deviations due to cartilage defects, bony fissures, or small voids during preparation of the joint (typically 0.05-0.5 mm in width)). 
     This process will occur as the compressive forces applied by the ends of the hypothetical concave region of one articular surface (e.g., the superior articular surface) and the center of the corresponding convex surface on the opposing articular (e.g., the inferior articular surface) generate a bending moment on the superior and inferior resurfacing device  106 ,  108  that produces strain to conform the superior and inferior resurfacing devices  106 ,  108  to the native anatomy. 
     In certain embodiments, a guide probe assembly  200 , as illustrated in  FIGS. 14 and 15 , may be initially used to locate the region in the facet joint where the resurfacing device  46  is to be inserted. The guide probe assembly  200  may include a guide probe shaft  202  and a guide probe tip  204  that extends from a distal end of the guide probe shaft  202 . 
     The guide probe shaft  202  may have a substantially rectangular profile, as illustrated in  FIGS. 14 and 15 . Forming the guide probe shaft  202  with the substantially rectangular profile enables the guide cannula  260  to slide over the guide probe assembly  200  after the guide probe assembly  200  is positioned with the guide probe tip  204  at least partially in the facet joint, as is discussed in more detail herein. This process reduces the time associated with implanting the resurfacing body  46  when compared to an implantation system that does not utilize this insertion process. 
     To minimize the size of the incision that is formed in the patient, the guide probe shaft  202  may be formed with a width and a height that is approximately equal to a width and a height of the resurfacing body  46 . 
     In certain embodiments, the guide probe shaft  202  has a width of between about 5 millimeters and about 20 millimeters. In other embodiments, the guide probe shaft  202  has a width of about 12 millimeters. 
     In certain embodiments, the guide probe shaft  202  has a thickness of between about 0.20 millimeters and about 10 millimeters. In other embodiments, the guide probe shaft  202  has a thickness of about 2 millimeters. 
     The guide probe shaft  202  is formed with a length that enables a proximal end of the guide probe shaft  202  to be positioned outside of the patient&#39;s body when the distal end of the guide probe shaft  202  is adjacent the facet joint. Such a configuration facilitates the surgeon or other person who is using the guide probe assembly  200  to accurately position the guide probe assembly  200  with respect to the facet joint. 
     In certain embodiments, the guide probe shaft  202  has a length of between about 10 centimeters and about 30 centimeters. In other embodiments, the guide probe shaft  202  has a length of about 23 centimeters. 
     The distal end of the guide probe shaft  202  may include a tapered region  206 , as illustrated in  FIGS. 14 and 15 , to provide a transition between the guide probe shaft  202  and the guide probe tip  204 . The length of the tapered region  206  may depend on a variety of factors such as a difference in the width and the height of the guide probe shaft  202  and the guide probe tip  204 . 
     The guide probe shaft  202  may be fabricated from a relatively rigid material to facilitate the use of the guide probe shaft  202  to locate the facet joint using the guide probe tip  204 . In certain embodiments, the guide probe shaft  202  may be fabricated from stainless steel. In other embodiments, it is possible to fabricate the guide probe shaft  202  from a non-metallic material such as plastic. 
     An important criterion is that the guide probe shaft  202  be fabricated from a material that is biocompatible. If it is desired to reuse the guide probe shaft  202  for multiple surgical procedures, the guide probe shaft  202  should be capable of withstanding repeated sterilization processes such as by using an autoclave. 
     The guide probe tip  204  is operably connected to the proximal end of the guide probe shaft  202 . In certain embodiments, the guide probe shaft  202  has an aperture  210  formed in the distal end thereof. This aperture  210  is adapted to receive a portion of the guide probe tip  204 . 
     The portion of the guide probe tip  204  that extends into the aperture  210  may have a length that is greater than a length of the guide probe tip  204  that extends beyond the proximal end of the guide probe shaft  202  to enhance the ability of the guide probe tip  204  when attempting to locate a desire location in the facet joint. 
     Forming the guide probe tip  204  separate from the other portions of the guide probe assembly  200  enables guide probe tips  202  having different widths and/or lengths to be used depending on the size, shape and location of the facet joint in which the resurfacing device is being inserted. 
     The guide probe tip  204  may have a thickness and a width that are both smaller than a thickness and a width of the guide probe shaft  202 . In certain embodiments, the guide probe tip  104  has a width of between about 5 millimeters and about 20 millimeters. In other embodiments, the guide probe tip  104  may have a width that is about 9 millimeters. 
     In certain embodiments, the guide probe tip  204  may have a thickness of between about 0.10 millimeters and about 0.50 millimeters. In other embodiments, the guide probe tip  204  may have a thickness of about 0.20 millimeters. 
     The guide probe tip  204  may be formed with a proximal end that is not pointed. Forming the guide probe tip  204  with this configuration at the proximal end minimizes the potential that the guide probe tip  204  will damage or other negatively impact the tissue in the facet joint or surrounding the facet joint. 
     In certain embodiments, it is possible for the proximal end of the guide probe tip  204  to be sharpened such that the guide probe tip  204  may be used to cut tissue when attempting to access the facet joint. 
     The guide probe tip  204  may be fabricated from a material that is rigid but which is flexible. Forming the guide probe tip  204  from a flexible material enhances the ability of the guide probe tip  204  to be positioned at least partially in the facet joint as an initial step in implanting the resurfacing body  46 . 
     In certain embodiments, the guide probe tip  204  is fabricated from a metallic material such as stainless steel. It is also possible to fabricate the guide probe tip  204  from a non-metallic material using the concepts of the invention. 
     An important criterion is selecting the material that is used to fabricate the guide probe tip  204  is that the material be biocompatible. If it is desired to reuse the guide probe tip  204  for multiple surgical procedures, the guide probe tip  204  should be capable of withstanding repeated sterilization processes such as by using an autoclave. 
     The guide probe tip  204  may be attached to the guide probe shaft  202  using at least one fastening device  212 . In certain embodiment at least two of the fastening devices  212  are used to attached the guide probe tip  204  to the guide probe shaft  202 . 
     The fastening device  212  may have a variety of different configurations. In one configuration, the fastening device  212  frictionally engages the guide probe shaft  202  through the aperture formed therein. Alternatively, the fastening device  212  may have a threaded side surface that enables the fastening device  212  to be screwed into the guide probe shaft  202  having an aperture with a complementary shape. 
     As an alternative to the configuration of the guide probe assembly  200  configuration illustrated in  FIGS. 14-16 , alternative configurations of the guide probe assembly  200  may be utilized in conjunction with the concepts of the invention. One such alternative configuration of the guide probe assembly is illustrated at  240  in  FIG. 17 . The guide probe assembly  240  includes an elongated main portion  242  and a handle portion  244  that is attached to a proximal end of the main portion  242 . 
     The main portion  242  may have a configuration that is similar to the guide probe shaft  202  illustrated in  FIGS. 14 and 15 . While  FIG. 17  illustrates that the main portion  242  does not have a separate tip portion, it is possible to adapt the concepts of this embodiments to encompass a separate tip portion so that the tip portion may possess different physical characteristics that the main portion  242  from which the tip portion extends. Even when a separate tip portion is not provided, a proximal end of the main portion  242  may be tapered to facilitate guiding the guide probe assembly  240  to a desired location in the facet joint. 
     The handle portion  244  enhances the ability to grasp the guide probe assembly  240  during the insertion process. In certain embodiments, the handle portion  244  may have a width that is greater than a width of the main portion  242 . The handle portion  244  may also have a thickness that is greater than a thickness of the main portion  242 . 
     The guide probe assembly  240  may be used in conjunction with the guide probe assembly  200 . In such a configuration, the main portion  242  may be placed adjacent to the guide probe assembly  200 . When used in this configuration, the main portion  242  and the guide probe assembly  200  may be thinner than with the separately used configuration so that the main portion  242  and the guide probe assembly  200  may both fit inside of the guide cannula  260 . 
     This configuration may utilize the handle portion  244  for guiding the distal end of the guide probe assembly  200  into a position within the facet joint. Thereafter, the guide probe assembly  240  may be withdrawn. Next, the guide cannula  260  may be placed over the guide probe assembly  200 . 
     The delivery system may include a guide cannula  260 , as illustrated in  FIGS. 18 and 15 . The guide cannula  260  has an internal passage  262  that extends from a proximal end to a distal end thereof. In certain embodiments, the passage  262  may have a generally rectangular configuration. 
     A width of the passage  262  is smaller than a width of the delivery cannula  280 . In certain embodiments, the width of the passage  262  may be between about 3 millimeters and about 15 millimeters. In other embodiments, the width of the passage  262  is between about 5 millimeters and about 10 millimeters. 
     A height of the passage  262  is smaller than a height of the delivery cannula  280 . In certain embodiments, the height of the passage  262  may be between about 0.50 millimeters and about 5 millimeters. In other embodiments, the height of the passage  262  is about 2 millimeters. 
     To facilitate accurately positioning the guide cannula  260  with respect to the facet joint, the proximal end of the guide cannula  260  may have a concave surface  266 . The concave surface  266  may at least partially receive a convex surface of the facet joint to thereby prevent the guide cannula  260  from moving laterally with respect to the facet joint and thereby enhance the ability to accurately insert the resurfacing device into the facet joint. 
     The guide cannula  260  may include a first stop mechanism  270  proximate a distal end thereof. The first stop mechanism  270  limits a distance the delivery cannula  280  may be inserted into the guide cannula  260 . In certain embodiments, the first stop mechanism  270  engages a stop surface  286  that extends from an outer surface of the delivery cannula  280  proximate a distal end thereof. 
     The guide cannula  260  may also include a second stop mechanism  272  extending from the proximal end thereof. The second stop mechanism  272  limits a distance the implant insertion tool  300  may be inserted into the guide cannula  260  to thereby prevent over-insertion of the resurfacing device  46  into the facet joint. The second stop mechanism  272  may engage a shoulder  320  on the implant insertion tool  310  when the implant insertion tool  310  has been extended a desired distance into the guide cannula  260 . 
     To enhance the ability to use the different components of the system, the second stop mechanism  272  may be positioned in a spaced-apart relationship with respect to the first stop mechanism  270 . In certain embodiments, a spacing between the first stop mechanism  270  and the second stop mechanism  272  is between about 1 centimeter and about 5 centimeters. 
     The guide cannula  260  thereby facilitates extending the guide probe shaft  202  into the proximal end of the rectangular passage  262  until the proximal end of the guide cannula  260  is adjacent to the facet joint. Thereafter, the guide probe assembly  200  may be withdrawn from the guide cannula  260  by pulling the distal end of the guide probe assembly  200 . 
     The guide cannula  260  may be fabricated with a length that enables the distal end to be positioned proximate to the facet joint where the implant is to be inserted while the proximal end is positioned outside of the person&#39;s body. In certain embodiments, the guide cannula  260  may have a length of between about 10 centimeters and about 30 centimeters. 
     The delivery cannula  280  may have a generally rectangular profile with a width and a height that are both slightly smaller than the width and the height of the guide cannula  260 . This configuration enables the delivery cannula  280  to be inserted into the guide cannula  260  after the guide stop assembly  200  has been removed from the guide cannula  260 . 
     The delivery cannula  280  has an internal passage  282  that extends from a proximal end to a distal end thereof. In certain embodiments, the passage  282  may have a generally rectangular configuration. 
     A width of the passage  282  is smaller than a width of the main portion  312  of the implant insertion tool  310 . In certain embodiments, the width of the passage  282  may be between about 3 millimeters and about 15 millimeters. In other embodiments, the width of the passage  282  is between about 5 millimeters and about 10 millimeters. 
     A height of the passage  282  is smaller than a height of the main portion  312  of the implant insertion tool  310 . In certain embodiments, the height of the passage  282  may be between about 0.5 millimeters and about 5 millimeters. In other embodiments, the height of the passage  282  is about 2 millimeters. 
     Proximate the proximal end of the delivery cannula  280 , the sides of the passage  282  may be removed so that an upper face and a lower face of the delivery cannula  280  define a pair of arms. When the implant insertion tool  310  is inserted into the delivery cannula  280 , at least a part of the shoulder portion  320  may have a width that is greater than the width of the delivery cannula  280 , as illustrated in  FIG. 19 . This configuration thereby limits the distance that the implant insertion tool  310  may be inserted into the delivery cannula  280 . 
     The delivery cannula  280  may include a pair of leaflets  284  that extend from a distal end thereof. The leaflets  284  may be fabricated from a resilient material. The leaflets  284  may be initially positioned adjacent each other. 
     The leaflets  284  may have a width that is approximately the same as a width of the resurfacing body  46 . A distal end of the leaflets  284  may be curved. The curved distal end of the leaflets  284  thereby minimizes damage to the superior articular face and the inferior articular face of the facet joint as the leaflets are moved into a position at least partially within the facet joint to provide an opening in the facet joint that is adapted to receive the resurfacing body  46 . 
     The leaflets  284  may deflect away from each other as the resurfacing body  46  and the distal end of the implant insertion tool  310  extend therebetween. The leaflets  284  thereby enable maintaining the resurfacing body  46  in engagement with the implant insertion tool  310 . 
     The force required to separate the leaflets  284  should be sufficiently large so that the leaflets  284  are retained in the closed configuration. However, the force should not be too great such that it is difficult for the resurfacing body  46  to be urged between the leaflets  284  during the implantation process or that the leaflets  46  damage the resurfacing body  46  when passing between the leaflets  284 . 
     Proximate the proximal end of the delivery cannula  280 , a stop mechanism  286  may extend from at least one outer surface of the delivery cannula  280 . The stop mechanism  286  may be an elevated region that is oriented generally transverse to an axis of the delivery cannula  280 . 
     In certain embodiments, the stop mechanism  286  may comprise two elevated regions that are mounted in a spaced-apart configuration, as illustrated in  FIG. 20 . The two elevated regions thereby define a channel  288  that extends therebetween. The channel  288  is adapted to receive a portion of a leaflet retractor tool  360 , which may be used to withdraw the delivery cannula  280  from the guide cannula  260 . 
     The stop mechanism  286  engages the first stop mechanism  270  on the guide cannula  260 . The stop mechanism  286  thereby limits a distance to which the delivery cannula  280  may be inserted into the guide cannula  260 . 
     An embodiment of the invention may also include an implant insertion tool  310 , as illustrated in  FIG. 21 . The implant insertion tool  310  may include a main portion  312  and a handle portion  314  that is attached to a proximal end of the main portion  312 . 
     The main portion  312  may have a width and a height that are slightly smaller than the width and the height of the delivery cannula  280 . This configuration enables the main portion  312  to be placed inside of and slide with respect to the delivery cannula  280  during the process of inserting the resurfacing body  46 . 
     In certain embodiments, the width of the main portion  312  may be between about 3 millimeters and about 15 millimeters. In other embodiments, the width of the main portion  312  is between about 1 millimeter and about 5 millimeters. 
     In certain embodiments, the height of the main portion  312  may be between about 0.5 millimeters and about 5 millimeters. In other embodiments, the width of the main portion  312  is about 2 millimeters. 
     Proximate the intersection with the handle portion  314 , the main portion  312  may include a shoulder  320  extending from at least one side thereof. The shoulder  320  may be used to limit a distance to which the implant insertion tool  310  may be inserted into the delivery cannula by engaging the second stop mechanism  272  on the guide cannula  260 . 
     The handle portion  314  may be oriented generally perpendicular to the main portion  312 . The handle portion  314  thereby provides an enlarged surface that may be used to grasp the implant insertion tool  310  and thereby facilitates manipulating the implant insertion tool  310 . In certain embodiments, the length of the handle portion  314  may be between about 5 centimeters and about 15 centimeters. 
     A distal end  322  of the main portion  312  may include a concave surface  323  that is curved to at least partially conform to a surface of the resurfacing body  46 . The concave surface thereby enhances the ability to retain the resurfacing body  46  in a desired position with respect to the implant insertion tool  310   
     To further enhance the ability to maintain the resurfacing body  46  in a desired location with respect to the implant insertion tool  310 , an extension  324  may extend from the distal end  322 . The extension  324  is adapted to engage the engagement feature  80  that is provided in the resurfacing body  46 . 
     The extension  324  may have a shape that is similar to but slightly smaller than the engagement feature  80 . In particular, the extension  324  may include a first extension region  326   a  and a second extension region  326   b.    
     The first extension region  326   a  has a width that is smaller than the width of the first aperture region  81   a . The second extension region  326   b  has a width that is larger than the width of the first aperture region  81   a  and smaller than the width of the second aperture region  81   b . This configuration enables the extension  324  to be retained in the engagement feature  80  to prevent the resurfacing body  46  from being separated from the implant insertion tool  310 . More details on the relative size of the engagement feature  80  and the extension  324  are discussed above. 
       FIGS. 25 and 26  illustrate the relationship between the resurfacing body  46  and the implant insertion tool  310 . In  FIG. 25 , the resurfacing body  46  is placed adjacent to but spaced-apart from the implant insertion tool  310 . In  FIG. 26 , the resurfacing body  46  is in engagement with the implant insertion tool  310  such that the extension  324  extends into and engages the engagement feature  80 . The shape of the engagement feature  80  may be approximately the same as the shape of the extension  324 . 
     Since the accurate placement of the resurfacing body  46  within the facet joint plays an important role in successfully treating the patient, the implant insertion tool  310  is configured to be inserted into the delivery cannula  280  and the guide cannula  260  until the handle portion  314  engages the second stop mechanism  272  on the guide cannula  260 . This configuration protects against inadvertent over insertion of the resurfacing body  46 . 
     In certain situations depending on the shape of the facet joint where the resurfacing body  46  is being implanted, it may be desired to insert the resurfacing body  46  to different distances in the facet joint. To facilitate accurately inserting the resurfacing body  46  to a desired depth, embodiments of the invention utilize implant insertion tools  330  and  340 , as illustrated in  FIGS. 22 and 23 . These implant insertion tools  330 ,  340  provide for selected countersinking of the resurfacing body  46  in the facet joint. 
     Other than the features set forth below, the implant insertion tools  330 ,  340  have a similar configuration to the implant insertion tool  310  illustrated in  FIG. 17 . The implant insertion tool  330  in  FIG. 18  includes a countersink extension  332  that extends from the distal end thereof. The countersink extension  332  may have a concave end surface  334  that with a curvature that is similar to a curvature of the resurfacing body  46 . 
     Similar to the embodiment in  FIG. 21 , an extension  336  is provided on the countersink extension  332  that facilitates attachment of the resurfacing implant  46  to the implant insertion tool  330 . 
     The end surface  334  is spaced apart from the concave surface  322 . In certain embodiments, the distance between the end surfaces may be between about 1 millimeter and about 10 millimeters. In other embodiments, the distance between the end surfaces may be about 3 millimeters. 
     The countersink extension  332  may have a width and a height that are smaller than the width and the height of the main portion  312 . Such a configuration minimizes the potential of contact between the countersink extension  332  and the tissue within the facet joint, as such contact could cause undesirable side effects. 
     The implant insertion tool  340  in  FIG. 23  is similar to the implant insertion tool  330  in  FIG. 22  except that the countersink extension  342  is slightly longer. In certain embodiments, the countersink extension  342  may have a length of about 5 millimeters. 
     It is also possible to utilize a countersink positioner  350 , as illustrated in  FIG. 24  in conjunction with positioning the resurfacing body  46  at a desired location within the facet joint. The countersink positioner  350  is similar to the implant insertion tool  330  illustrated in  FIG. 22  except that the countersink positioned  350  does not include an extension extending from a distal end thereof. 
     The countersink positioner  350  may thereby be utilized after the resurfacing body  46  has been inserted into the facet joint when it is recognized that the resurfacing body  46  is not inserted far enough into the facet joint. After removing the implant insertion tool  310  from the delivery cannula  280 , the countersink positioner  350  is inserted into the delivery cannula  280 . 
     Similar to the handle portion  314  on the implant insertion tool  310  limiting a distance that the implant insertion tool  310  may be inserted into the delivery cannula  280 , the handle portion  352  on the countersink positioner  350  limits the distance that the countersink positioner  350  may be inserted into the delivery cannula  280  so that the resurfacing body  46  may be accurately positioned within the facet joint. 
     In operation, an incision is made in the patient proximate to the facet joint where it is desired to implant the resurfacing body  46 . The guide probe assembly  200  is inserted into the patient so that the guide probe tip  204  can be used to identify the joint line in the facet joint. 
     Next, the guide cannula  260  is slid over the guide probe assembly  200 , as illustrated in  FIG. 27 , until the distal end of the guide cannula  260  is adjacent to the facet joint. The guide probe assembly  200  thereby enables the guide cannula  260  to be accurately and quickly placed in the location for the implanting process. 
     The guide probe assembly  200  is then withdrawn from the guide cannula  260  with care being exercised to maintain the guide cannula  260  in a stationary position with respect to the facet joint. Thereafter, the delivery cannula  280  is inserted into the guide cannula  260  until a rib  281  on the delivery cannula  280  engages the first stop mechanism  270 , as illustrated in  FIG. 28 . The first stop mechanism  270  thereby limits the distance to which the delivery cannula  280  may be inserted into the guide cannula  260 . 
     In this configuration, the leaflets  284  extend from the distal end of the guide cannula  260 . As the distal end of the guide cannula  260  is adjacent to the facet joint, the leaflets  284  extend into the facet joint to cause a region to be formed where the resurfacing body  46  may be inserted in subsequent operations. 
     Next, the resurfacing body  46  is positioned adjacent to the distal end of the implant insertion tool  310  so that the extension  324  extends into the engagement feature  80 , as illustrated in  FIG. 26 . The implant insertion tool  310  is then inserted into the proximal end of the delivery cannula  280 . 
     When the implant insertion tool  310  is almost completely inserted into the delivery cannula  280 , the resurfacing body  46  is recessed in the delivery cannula  280 , as illustrated in  FIG. 29 . 
     In some embodiments, it may be desirable to use a leaflet spreader (not shown) that maintains the leaflets  284  in a spaced apart configuration such that the resurfacing body  46  may be positioned between the leaflets  284 . If it is desired to use the leaflet spreader, the loading process may be changed slightly so that the resurfacing body  46  is attached to the implant insertion tool  310  and then the implant insertion tool  310  is inserted into the delivery cannula  280 . 
     The insertion of the implant insertion tool  310  is continued until the resurfacing body  46  begins to extend from the distal end of the delivery cannula  280 , as illustrated in  FIG. 30 . At this time, the shoulder  320  engages the second stop mechanism  272  to limit the distance to which the implant insertion tool  310  may be inserted into the delivery cannula  280 . As noted above, the leaflets  284  are deflectable to provide a space for the resurfacing body  46  to be inserted into the facet joint. 
     Next, the delivery cannula  280  is urged away from the facet joint, as illustrated in  FIG. 30 . This motion causes the leaflets  284  to be refracted to within the delivery cannula  280 . The facet joint returns to its initial position, which causes the resurfacing body  46  to fill the space between the bones. 
     In certain circumstances, it may be desirable to use a leaflet retractor tool  360  such as is illustrated in  FIG. 31  to cause the delivery cannula  280  to be urged away from the facet joint. The leaflet refractor tool  360  includes a first handle section  362  and a second handle section  364  that are pivotally mounted with respect to each other. 
     The first handle section  362  engages the handle portion  314  on the implant insertion tool  310 . In certain embodiments, the handle portion  314  may have an aperture that extends therethrough and the first handle section  362  may be extended through the aperture to secure the leaflet retractor tool  360  with respect to the implant insertion tool  310 . 
     Thereafter, an end of the second handle section  364  engages a lip  366  extending from the delivery cannula  280  proximate a proximal end thereof. The second handle section  364  is pivoted with respect to the first handle section  362  as indicated by arrow  368 . This pivoting motion causes the delivery cannula  280  to be urged away from the facet joint so that the leaflets  284  are retracted to within the guide cannula  260 . This motion is towards the facet joint to reduce the potential that the guide cannula  260  is moved from its desired position against the facet joint during the implanting process. 
     Thereafter, the implant insertion tool  310  may be separated from the resurfacing body  46  using a gentle pull away from the resurfacing body  46  to leave the resurfacing devices  42 ,  44  in the facet joint as illustrated in  FIG. 33 . The implantation process is thereby complete. Medical imaging may be used to evaluate whether the resurfacing body has been accurately implanted prior to removing the guide cannula  260  from adjacent to the facet joint. 
     In the preceding detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The preceding detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. 
     It is contemplated that features disclosed in this application, as well as those described in the above applications incorporated by reference, can be mixed and matched to suit particular circumstances. Various other modifications and changes will be apparent to those of ordinary skill.