Abstract:
Instrumentation systems that facilitate the reproducible deployment and placement of fixation device such as a screw, via an aligned, percutaneous access and approach, designed to relieve lower back pain and possibly improve disc health and prevent progression or transition of disease. Information about methods and equipment for accessing and preparing bone for subsequent delivery of a bone screw such as a facet screw across a facet joint. Some of the many teachings contained herein address a system of visual indicators may be used in connection with a bore cutter that operates around an anchored guide wire to avoid dislodging the anchored guide wire.

Description:
[0001]    This application claims priority and incorporates by reference U.S. Provisional Application No. 60/878,955 filed Jan. 5, 2007 for Method and Apparatus for Spine Stabilization Systems. 
         [0002]    This application may be used in combination with co-pending and commonly assigned U.S. patent application Ser. No. 11/593,445 filed Nov. 6, 2006 for Application of Therapy Aligned to an Internal Target Path and published as Application No. 2007/0112351. The &#39;445 application as published is incorporated by reference herein. 
         [0003]    While one or more applications have been incorporated by reference to provide additional detail it should be noted that these other applications (including any that have subsequently issued as patents) were written at an earlier time and had a different focus from the present application. Thus, to the extent that the teachings or use of terminology differ in any of these incorporated applications from the present application, the present application controls. 
     
    
     BACKGROUND 
     Field of the Disclosure 
       [0004]    This disclosure relates generally to medical procedures and in particular, minimally invasive medical procedures. One application of the present disclosure is in providing therapy to adjacent spinal vertebrae. More specifically, one application uses instrumentation systems that facilitate the reproducible deployment and placement of fixation device such as a screw, via an aligned, percutaneous access and approach, designed to relieve lower back pain and possibly improve disc health and prevent progression or transition of disease. This present disclosure provides information about methods and equipment for accessing and preparing bone for subsequent delivery of a bone screw such as a facet screw across a facet joint, or a pedicle screw (including but not limited to trans facet; translaminar, or transpedicular screws). One use of the instrumentation system of the present disclosure is to allow surgeons to accurately and reproducibly deploy, fixation devices such as translaminar facet screws across the facet joints to affix adjacent vertebrae in via a minimally invasive, percutaneous approach, that is, the placement of screws either directly across the facet joints of adjacent vertebrae across the facet joints through the lamina (translaminar) as both a primary mechanism for spinal fixation and as a secondary mechanism for fixation to augment anterior fusion or pedicle screw fixation instrumentation. In addition to the effective and safe placement of devices such as the delivery of facet screws for fusing adjacent vertebrae in a minimally invasive procedure that saves time during surgery and is less traumatic to the patient, as will be understood by one of skill in the art, these instrumentation systems are also applicable to and may facilitate deployment of a variety of other orthopedic devices or screws in motion segments other than or in addition to L5-S1 (for example as used in multi-level therapies), and in the different parts of the spine (such as, cervical; thoracic, with concomitant adjustments as needed and appropriate to system instrumentation dimensions, such as, lengths; diameters) as well as other bones, such as, appendicular surgery or surgery to the foot or the wrist. 
         [0005]    Terminology 
         [0006]    In the context of the present disclosure anterior refers to in front of the spinal column (ventral); posterior refers to behind the column (dorsal); cephalad means towards the patient&#39;s head (also sometimes “superior,”); caudal refers to the direction or location that is closer to the feet (also sometimes “inferior,”). The terms proximal and distal are defined with respect to the surgeon performing the operation. Thus, with respect to components used by the surgeon, the end of a component that is normally held by or at least closer to the surgeon is proximal and the end of a component that is placed into a patient or is most distant to the surgeon during use is distal. 
         [0007]    Guide Wire and Guide Pin 
         [0008]    While it is common in the medical arts to call items with a diameter of about 1.5 millimeters or less guide wires and items with diameters of about 1.5 millimeters or more guide pins, that distinction is not useful with respect to the present disclosure as the range of diameters that may be used for the guide wires described below may be below or above the approximate 1.5 millimeter cusp. Thus the term guide wire as used herein is not limited to items with a diameter of 1.5 millimeters or less. Sometimes a guide pin is cannulated and sometimes it is not depending on the intended use of the guide pin. As used in herein, the terms guide wire and guide pin may be used interchangeably. 
         [0009]    In the context herein, “biocompatible” refers to an absence of chronic inflammation response when or if physiological tissues are in contact with, or exposed to (e.g., wear debris) the materials and devices of the present disclosure. 
         [0010]    Items made in accordance with the present disclosure will be manufactured. Any manufacturing process is going to have some range for actual values for any given target value. Many processes have looser tolerances for parameters that are not critical and thus the range of values that may occur in the normal course of manufacturing is broader. Unless otherwise explicitly indicated any dimension provided in this disclosure is to be taken in that context and not as an absolute value. To help illustrate this concept, some of the figures provided with this disclosure include examples of dimensions and manufacturing tolerances for various components (dimensions not marked with units are generally in inches). Further, it is frequently true that sizes are for components are actually nominal sizes rather than precise sizes. 
         [0011]    Introduction to Relevant Anatomy and Terms 
         [0012]    The spinal column is a complex system of bone segments (vertebral bodies and other bone segments) which are in most cases separated from one another by discs in the intervertebral spaces (sacral vertebrae are an exception). In the context of the present disclosure, a “motion segment” includes adjacent vertebrae, (an inferior and a superior vertebral body), and the intervertebral disc space separating said two vertebral bodies (discussed below). Unless previously fused, each motion segment contributes to the overall flexibility of the spine. In other words, unless previously fused, each motion segment contributes to the overall ability of the spine to flex to provide support for the movement of the trunk and head. 
         [0013]    The individual motion segments within the spinal columns allow movement within constrained limits and provide protection for the spinal cord. The discs are important to cushion and distribute the large forces that pass through the spinal column as a person walks, bends, lifts, or otherwise moves. Unfortunately, for a number of reasons, for some people, one or more discs in the spinal column will not operate as intended. The reasons for disc problems range from a congenital defect, disease, injury, or degeneration attributable to aging. Often when the discs are not operating properly, the gap between adjacent vertebral bodies is reduced and this causes additional problems including pain. 
         [0014]    Anatomy of a Motion Segment 
         [0015]    Turning to  FIGS. 1 and 2 , the components of the vertebrae are introduced.  FIG. 1  is a top perspective view of a single vertebra  704 . The vertebra has a hard outer shell of cortical bone  784  and an interior of cancellous bone  788 . 
         [0016]    The spinal cord (not shown) is protected in the spinal foramen  792  formed by the two pedicles  712 ,  716  and the two laminae  720 ,  724 . Extending from the pedicles are two transverse processes  728 ,  732 . Extending from the midline of the vertebra where the two laminae meet is the spinous process  736 . These three processes serve as connection points for ligaments and muscle. 
         [0017]    Vertebrae move relative to one other in order to allow the spine to bend forward (flexion), bend backward (extension), bend to the right or left (lateral bending), twist (rotate in the z-axis) and other forms of movement. While the disc  780  plays an important part in this movement in absorbing shocks and distributing loads, there are also joints on the posterior side of the spinal column that allow for movement of a vertebra relative to an adjacent vertebra. 
         [0018]    These joints are called facet joints. Most vertebrae have four facet joints. Two facet joints between a particular vertebra and the adjacent cephalad vertebra and two facet joints between the particular vertebra and the adjacent caudal vertebra. 
         [0019]    The components of the facet joints are the superior articular process  740  and  744  and the inferior articular process  748  and  752 . 
         [0020]      FIG. 2  is a rear perspective view of a motion segment  700  with a lower (more caudal) vertebra  704  and a higher (more cephalad) vertebra  804 . The anterior portion of the vertebra is the vertebral body  708 ,  808 . Between the two vertebral bodies  708  and  808  is a disc  780 . The spinous processes  736  and  836  and the transverse processes  728 ,  732 ,  828 ,  832  are visible in this view. 
         [0021]    The facet joint portion of the superior articular processes  740  and  744  for vertebra  704  are engaged by the inferior articular processes  848  and  852  of vertebra  804  to as part of facet joints  742  and  746 . The superior articular processes  840 ,  844  for the vertebra  808  are visible as they would engage with the inferior articular processes from the next more cephalad vertebra. Likewise the inferior articular processes  748 ,  752  of vertebra  704  would engage with the superior articular processes of the next more caudal vertebra. A neuralforamen  856  (sometimes neural foramen) is partially visible in  FIG. 2 . There is another neuralforamen on the opposite side. The neuralforamina provide a passage for the nerves connecting to the spinal cord. If this passage way is constricted, the constriction called stenosis of the neuralforamina can cause pain or other neural symptoms. 
         [0022]    With respect to motion, vertebrae move relative to one other in order to allow the spine to bend forward (flexion), bend backward (extension), bend to the right or left (lateral bending), twist (rotate in the z-axis) and other forms of movement. While the disc plays an important part in this movement in absorbing shocks and distributing loads, there are also joints on the posterior side of the spinal column that allow for movement of a vertebra relative to an adjacent vertebra. 
         [0023]    These joints are called facet joints. Most vertebrae have four facet joints. Two facet joints between a particular vertebra and the adjacent cephalad vertebra and two facet joints between the particular vertebra and the adjacent caudal vertebra. The components of the facet joints are the superior articular process the inferior articular process. The facet joints are positioned between each pair of adjacent vertebrae, share and support with the respective intervertebral disc included in that motion segment, compressive axial loads on the spine. Spinal mobility intricately involves movement of the motion segment and the loss of normal movement of the motion segment resulting from the loss of disc hydration. Specifically, fluidity, elasticity and thickness of the disc are important for mobility. With the loss of disc hydration, the discs lose some of their ability to act as a cushion. The structures comprising the motion segments of the spine undergo a deformative process, since with the loss of hydrostatic pressure within the disc; the disc loses its viscoelastic capacity to attenuate shock and can no longer uniformly distribute loads. As the nucleus pulposus loses its water content, the disc collapses, resulting in a narrowing of the intervertebral disc space and causing the two vertebrae above and below to move closer to one another. As this shift occurs, the facet joints located on the posterior column of the spine are forced to shift. This loss of disc height often also alters the facet joint&#39;s mechanical ability. (Those with an interest in additional drawings of the anatomy of facet joints are directed to  FIGS. 1   a - 1   d  of the provisional 60/878,955 referenced above and available through Public PAIR at www.uspto.gov after this application is published). 
         [0024]    Thus, it is also known to place fixation devices such as screws, either directly across the facet joints of adjacent vertebrae or indirectly across the facet joints through the lamina (i.e., translaminar) as a primary mechanism for spinal fixation and also as an ancillary mechanism for fixation to augment anterior fusion or pedicle screw fixation instrumentation, and as such, both direct and translaminar facet screws are often being implanted. More specifically, translaminar, transarticular, transpedicular, and/or transfacetpedicular bone fasteners (e.g., screws, pins, wires) inserted contralaterally or ipsilaterally are sometimes used alone or in combination/adjunct with other devices in order to create an anterior/posterior fixation construct as a mechanical, load-sharing aid to fracture healing or interbody (e.g., L 5 -S 1 ) stabilization and fusion of the lumbar spine. 
         [0025]    The fixation devices and their deployment by means of the instrumentation system of the present disclosure enable an effective adjunct therapy to procedures such as anterior lumbar interbody fusion (ALIF); transforaminal lumbar interbody fusion (TLIF); laminectomy; laminotomy; foraminotomy; discectomy, including anterior cervical discectomy and fusion (ACD; ACDF). More specifically, yet another advantage of the system of the present disclosure is the biomechanical “balance” derived from an ability to deploy the posterior stabilizing devices in conjunction with an anterior supporting structures, e.g., axially deployed implants such as those described in commonly assigned U.S. Pat. No. 6,921,403 issued Jul. 26, 2005 and U.S. application Ser. No. 11/202,655 filed Aug. 13, 2005, deployed by means of instrumentation such as described in co-pending and commonly assigned U.S. patent application Ser. Nos. 10/971,779; 10/971,781; 10/971,731; 10/972,077; 10/971,765; 10/972,065; 10/971,775; 10/972,299; 10/971,780 each filed on Oct. 22, 2004 and 11/501,351 filed Aug. 9, 2006, the contents of each of the aforementioned U.S. patent applications are hereby incorporated into this disclosure by reference. (These earlier applications are available through the USPTO and may be accessed through Public PAIR at www.uspto.gov). 
         [0026]    Thus, the teachings of the present disclosure may be used as an adjunct to, for example, anterior column disc or nucleus pulposus replacement (procedures which involve the removal of tissue and which destabilize the spine) as part of a fusion procedure, in addition to primary stand-alone treatment for patients with isolated posterior column disease as noted above to maintain the mechanical relationship between the anterior and posterior column structures. 
         [0027]    The facets are true articulating joints in the lumbosacral spine, and play an important role in guiding segmental motion and in limiting their maximal range, so it is logical to fix these directly (i.e., one therapeutic treatment of the facet joint is to affix the superior articular process to the inferior articular process using a facet screw) to achieve spine fixation. Facet screws may be inserted bilaterally through the superior side of the facet, across the facet joint, and into the pedicle. Alternatively, the facet screws may be inserted from the base of the spinous process into the opposite lamina and across the facet joint and into the base of the lower vertebral transverse process. Lower lumbar spinal fusion in patients by techniques involving screw fixation of the facet joints often achieves stability comparable to that of pedicle screw fixation even after long-term repetitive cycling, although pedicle screw systems are generally used in lieu of facet screws when there is degenerative disease of the facets with instability. Bone quality may dictate the fixation method. 
         [0028]    Such therapies may be indicated to treat pseudoarthrosis, spinal stenosis, spondylolisthesis, segmental degenerative disease, or degenerative disc disease, and supplementation of posteriolateral fusion by means of such screws may significantly improve time to fusion, fusion rate, and clinical outcomes. 
         [0029]    Orthopaedic Drill Bits 
         [0030]    Of relevance to evaluation of the novel cutting tool disclosed below is the extent to which the prior art teaches away from the teachings of the present disclosure. Thus, it is useful to review the features of standard orthopedic devices in the prior art. Such devices, or drill bits, are typically constructed with a cutting end and a shaft characterized with a spiral, or helix. As depicted in  FIG. 3 , the cutting end (distal end) of a generic cutting tool  104  has a cutting edge  108  moving in a direction of cutting  112 . The cutting edge  108  may be characterized by a rake angle  116  and the clearance angle  124 . The wedge angle  120  is that between the cutting face  128  and the flank  132 , while the rake angle  116  is the angle at which the cutting face  128  is presented to the material. The clearance angle  124  is the angle by which the flank  132  of the drill clears the material that has been cut. These terms for all cutting tools apply generally to drill bits. 
         [0031]    Moving to  FIG. 4   a - 4   c , the tip of a drill bit  152  is shown in  FIG. 4   a  in profile, from a front view in  FIG. 4   b , and a portion of a drill bit is shown to illustrate the helix, wedge, and clearance angels. The drill bit  152  can be further described in terms of a point angle  136 , the flank  132  and the chisel edge  144 . The point angle  136  is that angle between the two cutting edges measured in a sagittal plane and in standard orthopedic drill bits is typically about 90 degrees. 
         [0032]    With reference to prior art drills, the flank  132  is the flat part of the drill bit when viewed end-on ( FIG. 4   b ); this flank surface is not totally in contact with the bone surface, but separated from it by the clearance angle  124  ( FIG. 4   c ). The flank  132  of the drill bit  152  represents a large surface area for friction and the generation of heat. The term chisel edge  144  refers to the tip of the drill bit  152  at the apex of the point angle  136 . The helix of a drill bit  152  is measured as the helix angle  148  ( FIG. 4   c ) and is often defined as slow, standard or quick, representing small, standard and large helix angles, respectively. A quick helix has more turns per unit length than a slow helix. Traditionally, a slow helix is used to drill material from which debris clears easily, such as brass or cast iron, in conjunction with a large point angle, while fast helix would be preferable for materials which must be cleared quickly to avoid blocking the flutes  140 , and attempts have been made to pattern flutes (e.g., parabolic) or alter helix lengths to improve clearance of debris from deep holes, such as cortices of a femur, and allow higher feed rates of drill bit advancement. 
         [0033]    Moreover, there are studies in the literature which appear to suggest that for orthopedic drill bits, substantially large point angles are both needed and preferred for optimum performance (e.g., Saha et al., [1982] and Natali, et al., [1996] recommend 118° while Fuchsberger [1987] recommends 70° to 75°. 
         [0034]    References may be found at: 1) Bonfield W, and C H Li. The temperature dependence of the deformation of bone.  J Biomechanics  1968; 1:323-9. 2) Fuchsberger A. Optimization of the spiral drill for use in medicine.  Z Orthop  1987; 125:290-7. 3) Natali C., Ingle, P., and J. Dowell. The Journal of Bone and Joint Surgery VOL. 78-B, No. 3, MAY 1996 p. 357-362. 4) Saha S., Pal S., and J A Albright. Surgical drilling: design and performance of an improved drill.  J Biomech Eng  1982; 104:245-52. 
       SUMMARY 
       [0035]    Aspects of the teachings contained within this disclosure are addressed in the claims submitted with this application upon filing. Rather than adding redundant restatements of the contents of the claims, these claims should be considered incorporated by reference into this summary. 
         [0036]    This summary is meant to provide an introduction to the concepts that are disclosed within the specification without being an exhaustive list of the many teachings and variations upon those teachings that are provided in the extended discussion within this disclosure. Thus, the contents of this summary should not be used to limit the scope of the claims that follow. Other systems, methods, features and advantages of the disclosed teachings will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within the scope of and be protected by the accompanying claims. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0037]    The disclosure can be better understood with reference to the following figures. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the disclosure. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views. 
           [0038]      FIG. 1  is a top perspective view of a single vertebra  704 . 
           [0039]      FIG. 2  shows a pair of vertebrae from a rear perspective view. 
           [0040]      FIG. 3  shows concepts for generic cutting tools. 
           [0041]      FIG. 4   a - 4   c  shows concepts of prior art drill bits. 
           [0042]      FIG. 5  is a flow chart showing one method of deploying facet screws. 
           [0043]      FIG. 6  introduces a set of instruments for use in the method described in  FIG. 5 . 
           [0044]      FIG. 7  illustrates a rear view of the lower spine with a trajectory for placement of a facet screw across a L5/S1 facet joint. 
           [0045]      FIG. 8  provides an enlarged view of the distal end of the guide pin assembly at the facet joint. 
           [0046]      FIG. 9  shows an enlarged view of the visual indicia section  2052  of the guide wire  2040 . 
           [0047]      FIG. 10  is a side view of a fully threaded facet screw. 
           [0048]      FIG. 11  is a side view of a lag facet screw. 
           [0049]      FIG. 12  shows a longitudinal cross section of a fully threaded facet screw  2400 . 
           [0050]      FIG. 13  provides an enlarged view of detail C from  FIG. 12 . 
           [0051]      FIG. 14  shows a front view of the distal end  2404  of the fully threaded facet screw. 
           [0052]      FIG. 15  shows a side view of the cannulated guide pin  2008 . 
           [0053]      FIG. 16  shows the details of the distal end  2024  of the cannulated guide pin  2008 . 
           [0054]      FIG. 17  shows details of the proximal end  2020  of the cannulated guide pin  2008 . 
           [0055]      FIG. 18  shows a side view of the guide pin with grip  2016 . 
           [0056]      FIG. 19  provides detail on the grip  2150 . 
           [0057]      FIG. 20  shows a side view of the subassembly of the cannulated guide pin  2008  with inserted guide pin with grip  2016 . 
           [0058]      FIG. 21  is a cross section of the complete guide pin assembly. 
           [0059]      FIG. 22  is an enlarged detail of  FIG. 21 . 
           [0060]      FIG. 23  shows the first grind which puts a point angle of about 30 degrees on the guide wire 
           [0061]      FIG. 24  shows the second grind at about 15 degrees to form a cutting point on the guide wire. 
           [0062]      FIG. 25  is a cross section of the dilator sheath  2084 . 
           [0063]      FIG. 26  provides details of the proximal end  2096  of the dilator sheath  2084 . 
           [0064]      FIG. 27  provides details of the distal end  2092  of the dilator sheath  2084 . 
           [0065]      FIG. 28  provides a perspective view of the distal end  2204  of the bore cutter  2200 . 
           [0066]      FIG. 29  provides a side view of details of the bore cutter. 
           [0067]      FIG. 30  shows a front view of the bore cutter  2200  from  FIG. 28 . 
           [0068]      FIG. 31  is a cross section of the bore cutter taken to show the clearance angle  2240 . 
           [0069]      FIG. 32  provides a top view of a bore cutter  2200 . 
           [0070]      FIG. 33  is a perspective view of the distal end of bore cutter  2200  with the distal end  2044  of the guide wire  2040 . 
           [0071]      FIG. 34  shows a top view of a facet screw tap  2110 . 
           [0072]      FIG. 35  is an enlarged perspective view of the distal end of the facet screw tap. 
           [0073]      FIG. 36  shows a L5/S1 motion segment with an implanted fusion rod and one of the two facet screws across one of the two facet joints. 
       
    
    
     DETAILED DESCRIPTION 
       [0074]    In order to provide context for the various pieces of equipment to be described in detail below, it is useful to start with a description of one exemplary method for delivering a facet screw across a facet joint as set forth in the flow chart in  FIG. 5 . This particular sequence is adapted for L5/S1 facet joint. This sequence of steps references a set of instruments introduced in  FIG. 6 . To avoid interruptions in the description of the process, the instruments are described in greater detail in subsequent sections. 
         [0075]    To provide context for the process, it is useful to note that the operating room may be set up as follows. 
         [0076]    The patient may have received preparation for spine surgery as known in the art. Biplanar fluoroscopy, known in the art, may be used to allow for visualization of instruments that are inserted into the patient. (Biplanar fluoroscopy includes AP (anterior/posterior) and lateral fluoroscopy.) Note that a surgeon may opt to use one fluoroscope and have it moved from the one plane to another or alternatively the surgeon may have two fluoroscopes set up, one in each plane. Having two scopes set up saves the time involved in moving the scopes back and forth but some surgeons prefer to have less equipment as the equipment takes up space. 
         [0077]    The patient may be placed in a prone position. The patient&#39;s lumbar spine will be in flexion and hips will be in flexion. Often, the placement of facet screws will follow the insertion of a fusion rod in accordance with teachings in the various applications cited and incorporated by reference into this application. 
         [0078]    The AP fluoroscopy may be oriented so that the vertebral endplate of L5 may be viewed from the Ferguson angle. Before proceeding, the surgeon may wish to note the landmarks of the L5/S1 facets and the L3 spinous process. 
         [0079]    Step  1004  Create incision. As shown in  FIG. 7 , make a midline incision at the L3 spinous process  204 . The midline incision is first made in the skin between the L 2   208  and L 3   212 , or at the L3 spinous process  204 . The location of the incision may vary, dependent on individual patient anatomy.  FIG. 7  shows the general trajectory  2002  desired for placing a facet screw into one of the facet joints  228  between the L 5   216  and S 1   220  vertebrae. As it is relevant to the trajectory, the L 4   224  vertebrae are also identified in  FIG. 7 . 
         [0080]    Step  1008  Extend incision. Continue the incision through the dorsal facia on either side of the L3 spinous process (the exact position of the incision may vary due to patient anatomy). 
         [0081]    Step  1012  Create the guide pin assembly. Turning to  FIG. 6  and  FIG. 8 , create the guide pin assembly  2004  by inserting the distal end  2028  of the guide pin with grip  2016  into the proximal end  2020  of the cannulated guide pin  2008 . Place the distal end  2010  of the guide pin handle  2012  over the grip  2150  of the guide pin with grip  2016  and the proximal end  2020  of the cannulated guide pin  2008 . Tighten the enlarged set screw  2126  to capture both the proximal end  2020  of the cannulated guide pin  2008  and the grip  2150  of the guide pin with grip  2016 . 
         [0082]    Step  1016  Advance guide pin assembly. The guide pin assembly  2004  is inserted and advanced until the distal end  2032  contacts the inferior articular process of L5 (superior portion of the L5/S1 facet on this side), as shown in  FIGS. 7 and 8 . One possible technique is to advance the guide pin assembly  2004  down the lamina of L 3   212 , L 4   224 , and L 5   216  (See  FIG. 7 ). Another alternative is to advance the guide pin assembly  2004  directly to the facet joint. Percutaneous insertion of the guide pin assembly  2004  may be performed by the surgeon while using radiographic visualization, such as fluoroscopic guidance by means of both anteroposterior (AP) and lateral fluoroscopy to safely enable advancement of the guide pin assembly  2004  through the soft tissue of the posterior access track up to the target site on a spinal vertebra and to locate the facet joint. On the lateral fluoroscope view, a good initial bony landmark to aim at is the midpoint of the inferior process of L 5  angling the distal end  2032  of the guide pin assembly  2004  towards the neck of the S1 pedicle. The surgeon moves the guide pin assembly  2004  to laterally angle and advance the distal end  2032  of the guide pin assembly  2004  towards the facet joint  228 , so that its distal end  2032  is directly above the center of the facet joint  228  and not into the spinal canal (as best seen in the fluoroscopic AP view). Once the facet joint  228  is located, adjustments are made to the guide pin assembly  2004  via the guide pin handle  2012  to achieve the desired trajectory  2002  towards the pedicle, which is again verified in both AP and Lateral planes using the fluoroscope. 
         [0083]    Step  1022  Verify the trajectory in both AP and Lateral Planes using the fluoroscope. 
         [0084]    Step  1026  Dock guide pin assembly  2004  into inferior articular process of L 5  at facet joint  228  (See  FIG. 2  elements  848  and  852  for examples of inferior articular processes). A mallet or other impact delivery tool such as a slap hammer ( FIG. 6  element  2036 ) is then used to dock the cannulated guide pin  2008  into the inferior articular process of L 5 . The process of lightly docking may move the distal end  2024  of the cannulated guide pin  2008  a few millimeters into the facet joint. 
         [0085]    Step  1030  Remove the guide pin handle  2012  from the Guide Pin Assembly removed while leaving in place the cannulated guide pin  2008  and the guide pin with grip  2016  Step  1034  Remove the guide pin with grip  2016  from the cannulated guide pin  2008 . This may be done by using a Kelly clamp to twist and remove the guide pin with grip  2016 . 
         [0086]    Step  1038  Insert the distal end  2044  of the guide wire  2040  into the proximal end  2020  of the cannulated guide pin  2008 . 
         [0087]    Step  1042  Drive the distal end  2044  of the guide wire  2040  to the desired position. Using a wire driver, the distal end  2044  of the guide wire  2040  is advanced across the facet joint so that it is securely engaged in the facet, while fluoroscopically verifying proper placement and trajectory, and repositioning as needed. The wire driver may actually be the same device that is used to drive the boring cutter. The distal end  2044  of the guide wire  2040  may be ground to provide a drilling tip to allow the guide wire  2040  to be driven rather than a conventional tip at the axial centerline of the guide wire (not shown). 
         [0088]    Step  1046  Look at depth markers on guide wire and adjust guide wire if necessary. Once the surgeon has achieved the desired placement, trajectory and depth, the guide wire  2040  is examined to determine the appropriate nominal size of facet screw to use.  FIG. 9  show guide wire  2040  with distal end  2044  that is driven across the facet joint and proximal end  2048  that extends beyond the cannulated guide pin  2008 .  FIG. 9  shows an enlarged view of the visual indicia section  2052  of the guide wire  2040 . While the visual indicators could be arranged in any of a number of ways, in this example there are two laser marked bands  2056  and  2060 . As the guide wire  2040  is much narrower than the diameter of the bore cutter or tap discussed below, it is thought that using bands rather than individual strips for each landmark makes the visual indicators easier to see. 
         [0089]    These bands are placed on the guide wire  2040  so that the surgeon receives an indication of the appropriate nominal screw length to use based on the inserted depth of the distal end  2044  of the guide wire  2040  beyond the distal end  2024  of the cannulated guide pin  2008  (See  FIG. 6 ). For example, when the distal end  2044  of the guide wire  2040  extends a distance of approximately 30 millimeters beyond the distal end  2024  of the cannulated guide pin  2008 , the distal edge of the more distal band will be approximately at the proximal end  2020  of the cannulated guide pin  2008 . This landmark  2064  will indicate that a nominal length of 25 millimeters will be appropriate as a 25 millimeter bore may be prepared while leaving a suitable length  2068  of the distal end  2044  of the guide wire  2040  anchored so that the process of preparing a bore does not dislodge the guide wire  2040 . While other distances may be used, an offset of 5 millimeters between the actual extension of the distal end of the guide wire  2040  and the length of screw suggested by the landmark provides a suitable length  2068  of guide wire  2040  that remains anchored after boring. The width of the bands and the gap between bands provides three other landmarks  2072 ,  2076 , and  2080  to indicate that three other nominal screw lengths are appropriate. 
         [0090]    If at the start of step  1046  all of the landmarks for the visual indicia section  2052  are within the cannulated guide pin  2008 , then the surgeon may choose the longest nominal screw length (such as 40 millimeters in the present example) and simply have more guide pin anchored after the boring step. 
         [0091]    If at the start of step  1046  all of the landmarks for the visual indicia section  2052  are visible and the landmark for the shortest suggested nominal screw length (in this case landmark  2064 ) are close to the proximal end  2020  of the cannulated guide pin  2008 , then the surgeon may drive the guide wire  2040  further into the patient to ensure an adequate insertion depth to allow the guide wire  2040  to remain anchored after preparing a bore for the shortest nominal screw length (25 millimeters in this example). 
         [0092]    Step  1050  Place the dilator sheath  2084  over the dilator  2100  if it is not already in place. See  FIG. 6  for these components. More specifically, the proximal end  2096  of the dilator sheath  2084  is placed initially over the distal end  2104  of the dilator  2100 . This example uses a 6 millimeter dilator. 
         [0093]    Step  1054  Advance the sheathed dilator. Advance the distal ends of the Dilator and Dilator Sheath to the facet joint. More specifically, hold the handle  2108  of the dilator  2100  and advance the distal end  2104  of the sheathed dilator  2100  over the proximal end  2048  of the guide wire  2040  and the proximal end  2020  of the cannulated guide pin  2008  and advance the sheathed dilator  2100  to the facet joint. 
         [0094]    Step  1058  Remove the dilator  2100  while leaving the inserted dilator sheath  2084  in place. The proximal end  2096  of the dilator sheath  2084  extends out of the patient. 
         [0095]    Step  1062  Remove the cannulated guide pin  2008 . More specifically, the proximal end  2020  of the cannulated guide pin  2008  extends beyond the proximal end  2096  of the dilator sheath  2084 . Thus, the cannulated guide pin  2008  may be grasped and removed from the dilator sheath  2084  while leaving the anchored guide pin  2016 . Some may choose to twist the docked cannulated guide pin  2008  while holding the dilator sheath  2084  in place in order to free the docked distal end  2024  of the cannulated guide pin  2008 . Alternatively, the guide pin handle  2012  may be re-attached to the cannulated guide pin  2008  so that the guide pin handle  2012  may be used to assist in releasing the docked distal end  2024  of the cannulated guide pin  2008  such as by tapping on the guide pin handle  2012  to move the guide pin handle  2012  away from the facet joint. 
         [0096]    Step  1064  Insert the proximal end  2208  of the bore cutter  2200  into a power driver (not shown). 
         [0097]    Step  1068  Insert the distal end  2208  of the bore cutter  2200  over the proximal end  2048  of the anchored guide wire  2040  as the guide wire diameter is slightly less than the inner diameter of a cannula that runs through the bore cutter  2200 . Advance the distal end  2208  of the bore cutter  2200  into the proximal end  2096  of the dilator sheath  2084  and to the distal end  2092  of the dilator sheath  2084 . 
         [0098]    Step  1072  Create a pilot hole of appropriate depth. Use the power driver to rotate the bore cutter  2200  to advance the distal end  2204  of the bore cutter  2200  until the appropriate landmark from the set of visual indicators  2212  on the shaft of the bore cutter  2200  approaches the proximal end  2096  of the dilator sheath  2084 . The surgeon may wish to view the distal end  2204  of the bore cutter  2200  while it is being advanced using fluoroscopy. The use of fluoroscopy alone may be sufficient to prevent a surgeon from advancing the distal end  2204  of the bore cutter  2200  too deep and thus dislodging the anchored distal tip  2044  of the guide wire  2040 . However, the use of the landmarks will allow more precise depth control and facilitate the maintenance of a standardized suitable length  2068  of anchored guide wire  2040 . 
         [0099]    For example, if at step  1046 , the landmark on the guide wire  2040  indicated a 25 millimeter screw was appropriate, advance the bore cutter  2200  to create a bore until the 25 millimeter screw landmark approaches the proximal end  2096  of the dilator sheath  2084 . This landmark for a 25 millimeter screw may be established so that the bore cutter  2200  extends approximately 25 millimeters beyond the distal end  2092  of the dilator sheath  2084  to create a pilot bore of approximately 25 millimeters while leaving approximately 5 millimeters of the guide wire  2040  anchored in the pedicle. (5 millimeters being the selected suitable length  2068  of guide wire to be left anchored in this example). Keeping the distal end  2092  of the dilator sheath  2084  abutting the facet joint leads to predictable pilot hole depth. Actually, there is another small amount of bias that helps promote a difference in insertion depth between the distal end of the pilot hole and the distal end of the guide wire  2040  as the guide wire  2040  was inserted a distance beyond the distal end  2024  of the cannulated guide pin  2008  which was itself partially inserted into the facet joint when it was docked. As the distal end  2092  of the dilator sheath  2084  rests against the facet joint and is not docked, the bore cutter  2200  starts its measured extension from the outer surface of the facet joint rather than partially in the facet joint. 
         [0100]    The landmarks on the shaft of the bore cutter  2200  may be presented as shown above for the guide wire  2040  (a pair of laser marked bands). Alternatively, there may be a series of landmark rings, one ring for each nominal screw length. 
         [0101]    Step  1076  Remove the bore cutter  2200  from the guide wire  2040  while leaving the anchored guide wire  2040  in place and leaving the dilator sheath  2084  in place. Note that it is typical for the pilot hole to have a smaller diameter than the minor diameter of the screw to be used. 
         [0102]    Step  1080  Prepare to tap the pilot hole. To tap the pilot hole created by the cutting bore, the facet screw tap  2110  is examined to locate a landmark within a set of visual indicators  2122  near the handle  2118  on the facet screw tap  2110 . More specifically, the landmark corresponding to the previously selected nominal screw length is located. 
         [0103]    Step  1084  Place the distal end of the tap in position. More specifically, place the distal end  2114  of the facet screw tap  2110  (See  FIG. 6 ) over the proximal end  2048  of the guide wire  2040  and move the distal end  2114  of the facet screw tap  2110  through the dilator sheath  2084  to the start of the pilot hole. 
         [0104]    Step  1088  Tap the pilot hole. Using the proximal end  2096  of the dilator sheath  2084  as a guide, advance the tap by rotating the handle  2118  until the appropriate landmark for the selected nominal screw length approaches the dilator sheath  2084 . (In this example the tap is operated by rotating the handle  2118  in a clockwise direction to advance it and counterclockwise to remove it but this would be reversed if the handedness of the facet screws was reversed.) The surgeon may occasionally monitor the advancement of the distal end  2114  of the facet screw tap  2110  using fluoroscopy. 
         [0105]    If a 25 millimeter nominal screw length was indicated back in step  1046 , then the pilot hole would have a depth of approximately 25 millimeters but the distal end  2044  of the anchored guide wire  2040  would extend beyond the distal end  2092  of the dilator sheath  2084  approximately 30 millimeters so that the creation of the pilot hole and the subsequent tapping did not disturb approximately 5 millimeters of guide wire  2040  anchored in the pedicle. The tap may be selected so as to tap threads that correspond to a major diameter that is less than the major diameter to be found on the selected facet screw. This is known as under-tapping and allows the facet screw to cut it own thread path while benefiting from the previously tapped pilot hole. 
         [0106]    Step  1092  Remove the tap. Rotate the handle  2118  the opposite direction from that used to advance the facet screw tap  2110  to remove the facet screw tap  2110  and then pull the facet screw tap clear of the dilator sheath  2084  and guide wire  2040 . 
         [0107]    Step  1096  Place the facet screw onto the guide wire. Surgeons may select a fully threaded facet screw  2400  ( FIG. 10 ) or a lag facet screw  2450  ( FIG. 11 ). These screws will be described in more detail below. The screws are available in a set of nominal lengths corresponding the landmarks on the guide wire  2040 , bore cutter  2200 , and facet screw tap  2110 . With either screw, place the distal end  2404  or  2454  of the cannulated facet screw  2400  or  2450  over the proximal end  2048  of the guide wire  2040  and advance the screw onto the guide wire  2040 . 
         [0108]    Step  1100  Engage the driver with the screw. Place the cannulated distal end  2134  of the driver  2130  ( FIG. 6 ) over the proximal end  2048  of the guide wire  2040  and engage the distal end  2134  of the driver  2130  with a corresponding section in the proximal end  2408  of fully threaded facet screw  2400  or proximal end  2458  of lag facet screw  2450 . Typically, the driver would have a hex tip (for example a 3 millimeter hex tip) to fit into a corresponding hex opening but one of skill in the art could use a square driver, Phillips head driver or some other driver. While a T-handle similar to that used with the facet screw tap  2110  could be used at the proximate end  2138  of the driver  2130 , a screw driver type handle as shown in  FIG. 6  may be preferred as in some instances there may be insufficient clearance between a T handle and the exterior of the patient. 
         [0109]    Step  1104  Advance the screw in the pilot hole. Rotate the driver  2130  the appropriate direction for the thread handedness, to advance the facet screw ( 2400  or  2450 ) and engage the threads of the screw with the walls of the pilot hole. After the screw ( 2400  or  2450 ) is partially engaged, fluoroscopy may be used to monitor the advancement of the facet screw to avoid over driving the facet screw into the pedicle. As the distal end  2404  or  2454  of the facet screw  2400  or  2450  approaches the distal end of the pilot hole, partially retract the dilator sheath  2084  so that the head at the proximal end  2408  or  2458  of the facet screw  2400  or  2450  is visible via fluoroscopy. It is recommended that the surgeon use the “two finger tight rule” to hold the driver with only two fingers to avoid over tightening the facet screw. 
         [0110]    Step  1108  Remove the instrumentation. Once the facet screw  2400  or  2450  is in place, remove the driver  2130 . Next remove the anchored guide wire  2040 . Finally, remove the dilator sheath  2084 . 
         [0111]    Step  1112  Insert second facet screw. Use the midline incision created at step  1004  and repeat subsequent steps to create a tapped pilot hole and deliver the second facet screw. 
         [0112]    The results of the final process are represented in  FIG. 36 .  FIG. 36  shows a L5/S1 motion segment ( 216 / 220 ) with an implanted fusion rod  2080  and one of the two facet screws  2400  across one of the two facet joints. (Other facet screw across other facet joint not visible in this view). 
         [0113]    One of skill in the art will be able to look at the steps set forth in  FIG. 5  and make minor modifications within the scope of the teachings of the present disclosure. For example, the act of creating the guide pin assembly in step  1012  could be done before creating the incision in step  1004  but it aids the presentation of the material to teach those of skill in the art to discuss the guide pin assembly creation immediately before the use. The text providing explanation of the various steps and providing detailed information on a way to achieve particular steps should not be misinterpreted as an indication that all of the details provided are necessary in order to practice the method taught by this disclosure. One of skill in the art may make modifications to adjust to personal preferences, patient anatomy, or other factors. 
         [0114]    Process Variations and Details. 
         [0115]    Some surgeons may opt to not tap the pilot hole so the steps associated with tapping may be considered optional. 
         [0116]    In implementations that provide the surgeon a choice of two different facet screw diameters in addition to a set of nominal facet screw lengths, the instrument set may be adapted to have a bore cutter  2200  and facet screw tap  2110  that may be used with both screw diameters by being adequately small to be used with the smaller of the two diameters. This eliminates the risk that the large bore cutter  2200  and facet screw tap  2110  will be used to prepare a pilot hole for a small diameter screw and thus lead to a situation where the facet screw does not achieve a high strength installation. 
         [0117]    Details of Components 
         [0118]    Facet Screws 
         [0119]      FIG. 12  shows a longitudinal cross section of a fully threaded facet screw  2400 . Visible at the proximal end  2408  is the hexagonal shaped opening  2412  to receive a corresponding driver. The fully threaded facet screw  2400  has a cannula  2416  that runs the length of the screw so the screw may be used in connection with a guide wire.  FIG. 13  provides an enlarged view of detail C from  FIG. 12  to provide details of a thread pattern that may be used for threads  2420  on the fully threaded facet screw  2400 .  FIG. 14  shows a front view of the distal end  2404  of the fully threaded facet screw. 
         [0120]    For both fully threaded facet screws  2400  and lag facet screws  2450 , representative dimensions for the example given above are about 25 mm to about 65 mm, often between 25 mm to 40 mm in length, and with major diameters of between about 0.120″ (3 mm) to about 0.196″ (5.0 mm) and often about 4 millimeters to 5 millimeters of major diameter. For example, the surgeons may be provided with a set of pairs of screws in the full range of screw lengths (25, 30, 35, and 40 millimeters) in both 4 millimeter and 5 millimeter major diameters for fully threaded facet screws and another complete set for facet lag screws. 
         [0121]    The range of nominal screw lengths may be broader than four nominal sizes and may be longer than 40 millimeters. Some applications may occasionally use screws that are 60 millimeters and even larger. Thus, instrumentation may have more than four distinct landmarks for use with more than four different nominal lengths. While it is likely that an instrument set that is frequently using a screw of a particular nominal length will have visual indicators (landmarks) for use with that nominal length, there may be situations where an unusual screw length may be used that does not have a set of landmarks for that screw length. 
         [0122]    Facet screws, as implantable components, may be fabricated from biocompatible orthopedic implant materials that are common medical grade materials with substantial clinical history across a wide variety of orthopedic utilities that present no biocompatibility issues. For example, screws may be formed, machined, preferably from among high strength (high tensile strength, high fatigue strength), wear and abrasion resistant metal alloys (for example, MP35N; Elgiloy,™ a super alloy of cobalt chrome; Co—Cr alloy such as Stellite™; Ti6Al4V alloy, and nitride coated Ti alloys) according to the desired biomechanical properties. 
         [0123]    Optionally, the head end of the facet screw may be configured for threaded engagement with a set of external threads from a retention rod included as part of the driver so that the fixation screw can be selectively engaged with the retention rod before insertion into the body and then disengaged from the retention rod after the fixation screw is at least partially inserted in to the bore in the vertebra. 
         [0124]    Facet Guide Pin Assembly 
         [0125]    As discussed above, the cannulated guide pin  2008 , guide pin with grip  2016 , and guide pin handle  2012  are formed into an assembly. Details of these components and subassemblies are provided in  FIGS. 15-22 .  FIG. 15  shows a side view of the cannulated guide pin  2008 .  FIG. 16  shows the details of the distal end  2024  of the cannulated guide pin  2008 .  FIG. 17  shows details of the proximal end  2020  of the cannulated guide pin  2008 . 
         [0126]      FIG. 18  shows a side view of the guide pin with grip  2016 .  FIG. 19  provides detail on the grip  2150  at the proximal end of the guide pin with grip  2016 . The grip may be affixed to the guide pin with grip  2016  by a press fit and tested by an appropriate pull test. For example the press fit may be tested to ensure that the grip  2150  remains attached while subjected to a five pound pull test. 
         [0127]      FIG. 20  shows a side view of the subassembly of the cannulated guide pin  2008  with inserted guide pin with grip  2016  visible here only by the distal end  2028  extending beyond the distal end  2024  of the cannulated guide pin  2008  and the grip  2150  extending beyond the proximal end  2020  of the cannulated guide pin  2008 . 
         [0128]      FIG. 21  is a cross section of the complete guide pin assembly  2004  including the guide pin handle  2012  attached via an enlarged set screw  2126 . As shown in detail in  FIG. 22 , the enlarged set screw  2126  engages the proximal end  2020  of the cannulated guide pin  2008  and a portion of the grip  2150  of the guide pin with grip  2016 . Also visible in  FIGS. 21 and 22  is a female hex fitting  2154  open to the proximal end  2158  of the guide pin handle  2012 . The guide pin handle  2012  is used with other instrumentation for other purposes where the female hex fitting  2154  has other uses. The hex fitting is sometimes used to torque the guide pin assembly  2004  to dislodge a cannulated guide pin  2008  from the bone as part of removing the cannulated guide pin. 
         [0129]    Guide Wire 
         [0130]      FIGS. 23-24  show two views of the distal end  2044  of the guide wire  2040 . (See  FIG. 9  for an overall view of the guide wire  2040 ).  FIG. 23  shows the first grind which puts a point angle of about 30 degrees.  FIG. 24  shows the second grind at about 15 degrees to form a cutting point (as opposed to a cutting edge). The distal end  2044  of the guide wire  2040  must advance through the facet joint and remain anchored in the pedicle during the creation of the pilot hole and delivery of the selected facet screw. Thus, a drilling type end may be used as shown rather than a tip with an apex at the axial centerline of the guide wire (not shown). Note that just as the bore cutter  2200  needs the guide wire  2040  to maintain the trajectory of the bore cutter  2200  and keep if from moving radially away from the intended trajectory, the guide wire  2040  needs the cannulated guide pin  2008  to keep the guide wire  2040  aligned with the intended trajectory and prevent the guide wire  2040  from moving along the surface of the facet joint away from the intended place of entry. After the guide wire  2040  is extended beyond the cannulated guide pin  2008  and into the facet joint, the cannulated guide pin  2008  provides support to the guide wire  2040  to keep the portion not in the facet joint from bending. 
         [0131]    The guide wire  2040  may be in the range of 1 millimeter of diameter and 19.75 inches long. While the same guide wire  2040  may be reused to deliver the second facet screw, a kit of single use components for delivery of a pair of facet screws is likely to have a pair of guide wires so that a spare guide wire is available. 
         [0132]    Dilator Sheath 
         [0133]      FIG. 25  is a cross section of the dilator sheath  2084 .  FIG. 26  provides details of the proximal end  2096  of the dilator sheath  2084 .  FIG. 27  provides details of the distal end  2092  of the dilator sheath  2084 . 
         [0134]    Bore Cutter 
         [0135]      FIG. 28  provides a perspective view of the distal end  2204  of the bore cutter  2200 . The bore cutter  2200  is adapted for use with a guide wire  2040  and thus is a tube with outer diameter D and inner diameter d. A first grind called the point grind, creates a first face  2216 . The point angle  2220  is show in  FIG. 29  as 30 degrees but may be made in the range of about 20 degrees to about 45 degrees. Point angles of less than about 20 degrees would result in a leading “tooth” which was too thin, while a 30 degree bevel results in a sharper tip than a 45 degree bevel. 
         [0136]    The rake grind creates face  2224  with cutting edge  2228  located on the outer perimeter of the tube (a distance of V2 D from the axial centerline of the bore cutter  2200 ). While the rake angle could potentially be negative or positive, the range of rake grinds for this bore cutter may range from zero degrees to about twenty-five degrees, in most cases from about 1 degree to 25 degrees.  FIG. 30  shows a front view of the bore cutter  2200  from  FIG. 28  which has a rake angle  2232  of about 5 degrees. Rake angles less than about 5 degrees yield cutting edges which are less sharp, while angles which are in excess of about 30 degrees approach being blunt on a different plane. The rake grind imparts a leading blade edge on the device. 
         [0137]    The clearance grind creates face  2236 .  FIG. 31  is a cross section taken to show the clearance angle  2240 . The clearance angle may range from between about 30 degrees to about 70 degrees, and often is about 60 degrees as is shown in  FIG. 31 . The clearance angle  2240  helps move cut material towards the outer periphery and away from the cannula of the bore cutter  2200 . This reduces backfil. Backfill of bone debris into the cannulated drill is undesirable because “packing” of such debris in the cannula of the bore cutter and against the guide wire  2040  may result in the dislodging or unwanted concomitant removal of the guide wire  2040  (over which the bore cutter  2200  is inserted) during removal of the bore cutter  2200  from the surgical site. The guide wire  2040  needs to remain in place in order to enable the accurate placement of the cannulated facet screws. 
         [0138]    While it is thought that a bore cutter  2200  could be used that did not have material removed with a grind for clearance angle, it is currently thought that having this clearance grind is beneficial to the performance of the bore cutter  2200 . 
         [0139]    The bore cutter described above is unusual in that it may be created from a tube with just two grinds: a first grind to add the point angle to the distal end of the tube followed by a grind to put a cutting edge on the tube by grinding substantially parallel to the axial centerline of the tube to create the cutting edge  2228   
         [0140]      FIG. 32  provides a top view of a bore cutter  2200 . 
         [0141]    The combination of geometry shown in  FIGS. 28 to 32  produces a bore cutter that needs an anchored guide wire to restrict the lateral movement of the bore cutter. When restrained by an anchored guide wire having a diameter close to but less than the inner diameter of the bore cutter the combination of angles for the bore cutter minimizes the force required for cortical penetration. 
         [0142]    The bore cutter  2200  may be fabricated from a 300 series stainless steel (e.g., medical grade 304 or 316; full hard temper) and is sized to create a pilot hole slightly under the minor diameter and to a depth about equal to the length of the screw (less the head) or device to be implanted. 
         [0143]      FIG. 33  shows the distal end of bore cutter  2200  with the distal end  2044  of the guide wire  2040 . The combination of these two components forms a bore cutter assembly  2250  as the bore cutter  2200  needs the anchored guide wire  2040  for proper operation. The anchored guide wire  2040  serves to limit the radial movement of the bore cutter  2200  and thus center the rotation of the cutting edge (or edges) of the bore cutter  2200  to operation centered in the vicinity of the axial centerline of the guide wire  2040 . Note that while the diameter of the guide wire  2040  substantially fills the inner diameter of the bore cutter  2200 , there is some clearance. This allows the bore cutter  2200  to rotate relative to an anchored guide wire  2040  without binding against the guide wire  2040 . In general, the clearance may be even less than shown here but needs to be positive so that the bore cutter  2200  may move freely relative to the anchored guide wire  2040 . 
         [0144]    The combination of the guide wire  2040  and the bore cutter  2200  needs to be stiff enough to maintain the intended trajectory of the boring cutter  2200 . The teachings of the present disclosure show a way to maintain depth control of the boring cutter  2200  so as to avoid dislodging the anchored guide pin  2040  while creating a pilot hole of an appropriate depth for a screw of an appropriate length. 
         [0145]    Typical dimensions for a bore cutter in accordance with the above example are as follows. For example, in drilling a pilot hole about 2 millimeters to 3 millimeters diameter for a screw delivered over a guide wire about 1 millimeter in diameter, a bore cutter is used which (depending on technique used and operative target site) ranges from about 6 inches (152 millimeters) to about 15 inches (380 millimeters) in length, and often about 9.5 inches (240 mm). The outer diameter of the bore cutter may be between about 0.080 inches (2 millimeters) to about 0.180 inches (4.5 millimeters) and often between about 0.087 inches (2.2 millimeters) and about 0.092 inches (2.33 millimeters); and inner diameter of between about 0.040 inches (1 millimeter) and about 0.065 inches (1.5 millimeter) and often between about 0.042 inches (1.1 millimeters) and about 0.058 inches (1.4 millimeters); and with a tube wall thickness of between about 0.014 inches (0.35 millimeters) to about 0.025 inches (0.62 millimeters) and often about 0.020 inches (0.5 millimeters). 
         [0146]    One could add another grind to move the cutting edge back from the perimeter of the bore cutter  2200  so that the cutting edge is somewhere between ½ d from the axial centerline to ½ D from the axial centerline of the bore cutter  2200 . 
         [0147]    While the bore cutter  2200  described within this disclosure has a single cutting edge  2228 , nothing in this disclosure should be interpreted as limiting the teachings of the present disclosure to only those bore cutters that have just one cutting edge. One of skill in the art will appreciate that a second or possibly more cutting edges could be cut into the distal end of the bore cutter  2200 . It is likely that any additional cutting edge would have an array of characteristics (distance from axial centerline of the bore cutter, point angle, rake angle) that are the same as the first cutting edge, it would be possible to have a first cutting edge as described above and a second cutting edge that has a different array of characteristics so the teachings of the present disclosure do not require that any second cutting edge be the same as the first cutting edge. 
         [0148]    Tap 
         [0149]      FIG. 34  shows a top view of a facet screw tap  2110  with a set of visual indicators  2122  near the handle  2118  on the facet screw tap  2110 . The dimensions in inches are provided as measured from the distal end  2114 . As best seen in  FIG. 35  showing an enlarged perspective view of the distal end  2114 , the tap is cannulated for use over a guide wire. Also visible in  FIG. 35  is the cutting section  2146 . The tap  2110  is typically fabricated from a hardened stainless steel (such as medical grade 17-4 alloy) with titanium-nitride (Ti—Ni) coated threads and flutes  2142  in the cutting section  2146 . The tap  2110  is generally sized to tap the pilot hole to slightly less than the thread (minor) diameter and to a depth about equal to the length of the screw (less the head). 
         [0150]    For example, in tapping a pilot hole of about 2 mm-3 mm diameter for a screw delivered over a guide wire about 1 mm in diameter in the lumbrosacral spine, a cannulated tap is used which is between about 7.5 inches (190 millimeters) to about 14 inches (355 millimeters) in length and often about 10.25 inches (260 millimeters) (dependent upon the length of the dilator sheath  2084  ( FIG. 6 ); an outer diameter of the tap between about 0.10 inches (2.5 millimeters) to about 0.375 inches (9.5 millimeters) and often about 0.187 inches (4.75 millimeters); and an inner diameter of between about 0.025 inches (0.63 millimeters) and about 0.135 inches (3.4 millimeters) and often about 0.049 inches (1.2 millimeters). Frequently the tap will be chosen to create a tapped thread major diameter to be smaller than the major diameter of the threads on the facet screw. The major diameter of the thread created by the tap may ranges from between about 0.075 inches (1.9 millimeters) and about 0.30 inches (7.6 millimeters), and is often about 0.130 inches (3.3 millimeters), while the thread minor diameter for the tap is smaller than the drilled pilot hole and ranges from between about 0.050 inches (1.25 millimeters) and about 0.295 inches (7.5 millimeters), and is often about 0.090 inches (2.3 millimeters). The core diameter of the tap is smaller than the thread minor diameter, and ranges from between about 0.045 inches (1.2 millimeters) and about 0.290 inches (7.4 millimeters), and is often about 0.080 inches (2.0 millimeters). The thread length may range from between about 0.20 inches (5 millimeters) and about 2 inches (50 millimeters), and is often about 0.85 inches (22 millimeters). Typically, the tap has between 2 and 4 flutes  2142 , often  3 , and the flute length extends beyond the cutting section  2146  to facilitate chip removal, ranging from between about 0.25 inches (6 millimeters) to about 2.1 inches (51 millimeters), and is often about 1 inch (25 millimeters). 
         [0151]    The tap is advanced by turning the proximal end so that the flutes and threads at the distal end of the tap progressively cut a thread path into the pilot hole bored into the bone to pre-thread a path to facilitate the subsequent insertion of self-tapping (versus self-drilling) facet screws. Note, that since the threads on a partially threaded facet lag screw  2450  must first travel through the proximal end of the pilot hole, the tapping process is the same for both fully threaded facet screws  2400  and lag facet screws  2450 . Taps are generally expensive to manufacture given the material that is used to create a tap. Thus, taps are generally not disposable parts and are instead cleaned and sterilized for reuse. 
         [0152]    Driver Details 
         [0153]    The facet screw driver generally include elongate bodies (or shafts) and handles fabricated from stainless steel alloys, such as those described in ASTM F899-02 Standard Specifications for Stainless Steels for Surgical Instruments or, for example, 17-4 alloy where torque is a consideration, such as when driving components into bone. Similarly, for this reason, as well as to prevent transfer of dissimilar metallic elements to the implant which may contribute to electrochemical corrosion in-situ some driver tips may be fabricated from the same materials as the implantable translaminar facet screws (such as a titanium alloy). As mentioned above, the handle could be a T-handle or a lower profile handle (as shown in  FIG. 6 ) such as normally found on screw drivers. 
         [0154]    Scale 
         [0155]    The guide wire, boring cutter, tap, and other components are selected based on the range of diameters of facet screw used (in the example above, the facet screw choices were a 4 millimeter major diameter or a 5 millimeter major diameter). If the smallest facet screw to be used was a 5 millimeter screw, then some implementations of the teachings of the present disclosure might be made using a guide wire diameter of more than 1 millimeter. For example if the smallest screw diameter was 5 millimeters rather than 4 millimeters, the system could be set up to use a guide wire with a diameter of 1/16 of an inch. This diameter would be slightly under 1.6 millimeters. As mentioned above, this disclosure does not set an upper limit on the use of guide wire (as opposed to guide pin) at 1.5 millimeters. 
         [0156]    Other Motion Segments 
         [0157]    The example provided above addressed the placement of facet screws across the L5/S1 facet joints. One of ordinary skill in the art could adjust the example provided above to apply these teachings to deploy a facet screw to another motion segment including other motion segments in the lumbar region of the spine. The adjustments may include changing the scale of the facet screws to match the dimensions of the anatomy and potentially adjusting the dimensions of the various components shown in  FIG. 6 . 
         [0158]    Deployment of Other Fixation Screws 
         [0159]    While the example given above was for the deployment of a facet screw across a facet joint, one of ordinary skill in the art could adjust process in accordance with teachings of this disclosure to deliver a bone fixation screw such as a pedicle screw. The dimensions of the screw and of the components in  FIG. 6  would be adjusted as appropriate for the specific use. 
         [0160]    Use of Specialized Boring Cutters and Taps 
         [0161]    While one of skill in the art will appreciate the cost savings in having a series of landmarks on a boring cutter  2200  and on a tap  2110  (if a tap is used in a particular process) so that the boring cutter  2200  and the tap  2110  may be used with a variety of screw lengths, it is not essential that it be done this way. One could enjoy some of the benefits of the present disclosure by having one guide wire  2040  with a series of landmarks  2052  to help identify the appropriate screw length to use so as to leave an adequate amount of the guide wire  2040  anchored in the patient but using a specialized boring cutter (not shown) that has only one landmark and thus is best used with only one particular screw length. Thus, a surgeon would need access to a series of specialized boring cutters (not shown), one for each nominal screw length that is commonly used. 
         [0162]    Likewise, instead of having one tap  2110  with a series of landmarks  2122  so that the tap  2110  may be used with confidence for a variety of different pilot hole depths, a surgeon could have access to a series of taps (not shown), with each tap having just one landmark for use with just one screw length. 
         [0163]    Finally, since the risk of a tap dislodging the anchored section of the guide wire is less than the risk posed by use of a boring cutter, one could imagine a system where the boring cutter had one or more visual landmarks but the tap did not and the surgeon simply tapped until feeling resistance at the bottom of the pilot hole. The relative position of the distal end of the tap relative to the distal end of the guide wire could also be periodically reviewed via fluoroscopy. 
         [0164]    Kits 
         [0165]    Various combinations of the tools and devices described above may be provided in the form of kits, so that all of the tools desirable for performing a particular procedure will be available in a single package. 
         [0166]    The components described above may be divided into three categories (facet screws, single use components, re-usable components). Kits may be arranged by these three categories. For facet screws, there may be a started kit with a full range of screws (at least two screws of each type) representing all combinations of screw type (full or lag), each of the nominal screw lengths, and repeating the set for each of the available screw diameters. Subsequent replacement sets of screws may be available in sets of two screws. 
         [0167]    The reusable components may come in a kit that would include a facet screw tap  2110 , a mallet or other impact tool such as a slap hammer  2036 , a driver for the facet screws, and a dilator  2100  ( FIG. 6 ) that works with the dilator sheath  2084  provided with the disposable kit. The dilator  2100  may not be provided with a kit if the same dilator  2100  was used in a process to deploy a fusion rod through a trans-sacral access channel in a process that would immediately precede the deployment of the facet screws. 
         [0168]    The kit of reusable items might exclude a slap hammer  2036  or mallet as these items may be standard items in the hospital and not need to be in a special kit. The wire driver and power driver used with the bore cutter  2200  are likely to be sold separately from the various instruments shown in  FIG. 6 . As noted above, the wire driver and the power driver may be the same component and used for both tasks. 
         [0169]    The single use components that may be combined together for convenience in a kit. The single use kit may include the cannulated guide pin  2008 . The single use kit may include the guide wire  2040  and most likely a second guide wire  2040  so that a second guide wire  2040  is available for deployment of the second facet screw into the second facet joint in the event that the first guide wire  2040  picks up a small bend or other issue from the use deploying the first facet screw. The single use kit may include a dilator sheath  2084  that fits over the dilator  2100  (it is likely that the dilator  2100  which may be a fair amount of metal would be part of the reusable components). The single use kit may include the boring cutter  2200  (some may call this a cannulated bone drill). The single use kit may include the guide pin with grip  2016  and the guide pin handle  2010 . 
         [0170]    While the initial training of surgeons in this technique may be quite detailed, it is likely that each kit of single use components will include at least some instructions pertaining on the use of the components in the kit in keeping with the intended method of use (such as the method set forth in  FIG. 5 ). The instructions are apt to be written instructions tangible media such as paper but could use or include instructions on other tangible media of any type that allows the instructions to be played or displayed on a device. Examples of other types of tangible media include flash drives and DVD discs but include any tangible media that can be used to convey instructions on a method of use. 
         [0171]    One of skill in the art will appreciate that the choice of what parts are single use and what parts are reusable is made partially on the costs to manufacture a single use part versus the cost to manufacture that same part to sustain multiple sterilization cycles and the cost to sterilize the part. Thus, one could decide that a part such as the guide pin handle  2010  which may be made primarily from a polymer and thus be sufficiently inexpensive to be a single use part may be redesigned to be a re-usable part. 
         [0172]    Teachings May be Used in Isolation or Combined 
         [0173]    One of skill in the art will recognize that some of the alternative implementations set forth above are not universally mutually exclusive and that in some cases additional implementations can be created that employ aspects of two or more of the variations described above. Likewise, the present disclosure is not limited to the specific examples or particular embodiments provided to promote understanding of the various teachings of the present disclosure. Moreover, the scope of the claims which follow covers the range of variations, modifications, and substitutes for the components described herein as would be known to those of skill in the art. 
         [0174]    The legal limitations of the scope of the claimed invention are set forth in the claims that follow and extend to cover their legal equivalents. Those unfamiliar with the legal tests for equivalency should consult a person registered to practice before the patent authority which granted this patent such as the United States Patent and Trademark Office or its counterpart.