Abstract:
A variable angle connection between a spinal rod (A) and a vertebral anchor (B) with a clevis ( 3 ) to attach to the vertebral anchor, permitting the vertebral anchor to be longitudinally offset from the connecting point on the rod. The connection assembly has a bolt ( 2 ) with an aperture ( 6 ) for receiving a portion of the spinal implant rod at one end. The assembly also has a clevis ( 3 ). The clevis defines a bore ( 7 ) to hold a portion of the vertebral anchor and the ears ( 8, 9 ) of the clevis have holes through which the bolt is located with the bolt rotatably connected to the ears. The assembly also has a rod interface washer ( 4 ) positioned over a portion of the bolt, between the aperture ( 6 ) of the bolt and the inside ear of the clevis. The rod interface washer is partly movable between the aperture of the bolt and the clevis, but the washer is fixed against rotating in relation to the bolt. Finally, the assembly also includes a compression member ( 5 ) that pushes the rod toward the vertebral anchor so that the inside and outside ears of said clevis are pressed together and the clevis is tightened the vertebral anchor.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of priority of provisional patent application Serial No. 60/466,148, filed Apr. 28, 2003, which is incorporated herein by reference. This application is a continuation-in-part of U.S. patent application Ser. No. 09/694,291, filed Oct. 23, 2000, which is a continuation-in-part application of Applicant&#39;s U.S. patent application Ser. No. 09/526,104, filed Mar. 15, 2000, both of which are incorporated herein by reference. These claims for priority are neither admissions nor indications by the Applicant or inventor that the claimed inventions are not entirely supported by the prior application. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to a spinal implant connection between a spinal rod and a vertebral anchor, and more particularly relates to a spinal implant connection with a clevis to attach to the vertebral anchor.  
         BACKGROUND  
         [0003]    Spinal implant systems provide a rod for supporting the spine and for properly positioning components of the spine for various treatment purposes. Bolts, screws, and hooks are typically secured to the vertebrae for connection to the supporting rod. These vertebral anchors must frequently be positioned at various angles due the anatomical structure of the patient, the physiological problem being treated, and the preference of the physician. It is difficult to provide secure connections between the spinal support rod and these vertebral anchors at all the various angles that are required, especially where there are different distances between the rod and bolts and where these components are located at different heights on the patient.  
           [0004]    One solution to this problem is shown in U.S. Pat. Nos. 5,643,263 and 5,885,285 to Simonson, the disclosures of which are specifically incorporated into this specification by reference. These patents describe a connection between a rod and a vertebral anchor, through which a surgeon may vary the angle between a spinal rod and the anchor to which the rod is attached. The connection is equipped with an interlocking set of washers that allow the surgeon to fix the desired angle between the anchor and the rod. In general, this system requires the surgeon in a typical installation to either sacrifice the capsule of the facet joint that may reside next to the connection, or elevate the connection above the facet joint and thereby raise the profile of the entire spinal implant system at that location. Occasionally, however, the surgeon may not wish to exercise either of these options in a particular surgery. Hence, an improvement over the device shown in these earlier patents would be a connection assembly that simultaneously minimizes the profile of the spinal implant system above the patient&#39;s spine without generally requiring the surgeon to sacrifice a facet joint that may reside next to a particular rod-to-vertebral-anchor connection assembly. The following invention is one solution to that need.  
         SUMMARY OF THE INVENTION  
         [0005]    In one aspect, this invention is a connection assembly between a spinal implant rod and a vertebral anchor. The assembly has a bolt with an aperture for receiving a portion of the spinal implant rod at one end. The assembly also has a clevis. The clevis defines a bore to hold a portion of the vertebral anchor and the ears of the clevis have holes through which the bolt is located with the bolt rotably connected to the ears. The assembly also has a rod interface washer positioned over a portion of the bolt, between the aperture of the bolt and the inside ear of the clevis. The rod interface washer is partly movable between the aperture of the bolt and the clevis, but the washer is fixed against rotating in relation to the bolt. Finally, the assembly also includes a compression member, such as a screw, that forceably engages or threads into the side of the bolt and continues into the aperture of the bolt. The screw is used to push the rod toward the vertebral anchor so that the inside and outside ears of the clevis are pressed together and the clevis is tightened around the vertebral anchor.  
           [0006]    Optionally, the inside ear of the clevis and the rod interface washer have mating male protrusions and female cavities on their surfaces such that, when pressed together, the protrusions and cavities engage to further prevent rotation of the clevis in relation to the rod interface washer. In this alternative design, the protrusions and cavities have multiple interlocking orientations so that the rod interface washer and the clevis can be interlocked in a plurality of fixed angles in relation to each other.  
           [0007]    An object of this invention is to reduce the physical mass that is typically required to attach a spinal rod to a vertebral anchor.  
           [0008]    An advantage of this invention is that the clevis allows a vertebral anchor to be placed closer to the spinal rod than prior art designs that also use a single means to allow the surgeon to secure both the anchor and the rod to the connection assembly in one tightening step.  
           [0009]    A feature of this invention is that it allows the surgeon the option of lowering the profile of a spinal attachment system closer to the spine without requiring the surgeon to sacrifice the capsule of a facet joint that may reside next to the connection assembly. In other words, this invention allows the connection assembly to be placed in a position that is medial to the facet joint.  
           [0010]    As used in this specification the term “clevis” is used in its ordinary and accustomed meaning that being—“(1): a fitting for attaching or suspending parts (as a cable to another structural member of a bridge or a hanger for supporting pipe) that consists usu. of a U-shaped piece of metal with the ends drilled to receive a pin or bolt (2): any of various connections in which one part is fitted between the forked ends of another and fastened by means of a bolt or pin passing through the forked ends.”  Webster&#39;s Third New International Dictionary, Unabridged.    
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a perspective view of a connection assembly constructed pursuant to this invention.  
         [0012]    [0012]FIGS. 2 and 2A are end views of a connection assembly constructed pursuant to this invention.  
         [0013]    [0013]FIGS. 3 and 3A are top views of a connection assembly constructed pursuant to this invention.  
         [0014]    [0014]FIG. 4 is a top view of a bolt constructed pursuant to this invention.  
         [0015]    [0015]FIG. 5 is a side view of a bolt constructed pursuant to this invention.  
         [0016]    [0016]FIG. 6 is an end view of a bolt constructed pursuant to this invention.  
         [0017]    [0017]FIG. 7 is a cross-sectional view of a bolt constructed pursuant to this invention.  
         [0018]    [0018]FIGS. 8 &amp; 9 respectfully depict a stop in plan and elevational views constructed pursuant to this invention.  
         [0019]    [0019]FIG. 10 is a cross-sectional view of clevis constructed pursuant to this invention.  
         [0020]    [0020]FIG. 11 is an end view of a clevis constructed pursuant to this invention.  
         [0021]    [0021]FIG. 12 is a side view of a clevis constructed pursuant to this invention.  
         [0022]    [0022]FIG. 13 is a side view of one alternative embodiment of a clevis constructed pursuant to this invention.  
         [0023]    [0023]FIG. 14 is a side view of a second alternative embodiment of a clevis constructed pursuant to this invention.  
         [0024]    [0024]FIGS. 15, 16 &amp;  17  are respectively top, side, and cross-sectional views of a connection assembly constructed pursuant to this invention.  
         [0025]    [0025]FIGS. 18, 19 &amp;  20  are respectively end, side, and top views of a rod interface washer constructed pursuant to this invention.  
         [0026]    [0026]FIGS. 21, 22 &amp;  23  are respectively top, side, and cross-sectional views of an embodiment of this invention.  
         [0027]    [0027]FIGS. 24, 25 &amp;  26  are respectively side, cross-sectional, and top views of a bolt used in one embodiment of this invention.  
         [0028]    [0028]FIGS. 27, 28 &amp;  29  are respectively cross-sectional, side, and front views of a clevis used in one embodiment of this invention.  
         [0029]    [0029]FIG. 30 is a cross-sectional view of a clevis used in one embodiment of this invention.  
         [0030]    [0030]FIGS. 31, 32 &amp;  33  are respectively front, a side and a second side views of one embodiment of a rod interface washer used in one embodiment of this invention.  
         [0031]    [0031]FIG. 34 is a top plan view of a connection assembly according to another embodiment of the present invention.  
         [0032]    [0032]FIG. 35 is a view of the apparatus of FIG. 34 as taken along lines  35 - 35  of FIG. 34.  
         [0033]    [0033]FIG. 36 is a cross sectional view of the apparatus of FIG. 34 as taken along line  36 - 36  of FIG. 34.  
         [0034]    [0034]FIG. 37 is a side elevational view of a bolt according to another embodiment of the present invention.  
         [0035]    [0035]FIG. 38 is a view of the apparatus of FIG. 37 as taken along line  38 - 38  of FIG. 37.  
         [0036]    [0036]FIG. 39 is a cross sectional view of the apparatus of FIG. 38 as taken along line  39 - 39  of FIG. 38.  
         [0037]    [0037]FIG. 40 is a side elevational view of a clevis according to another embodiment of the present invention.  
         [0038]    [0038]FIG. 41 is a view of the apparatus of FIG. 40 as taken along line  41 - 41  of FIG. 40.  
         [0039]    [0039]FIG. 42 is a cross sectional view of the apparatus of FIG. 41 as taken along line  42 - 42  of FIG. 41.  
         [0040]    [0040]FIG. 43 is a front elevational view of a rod interface washer according to another embodiment of the present invention.  
         [0041]    [0041]FIG. 44 is a view of the apparatus of FIG. 43 as taken along line  44 - 44  of FIG. 43, with the view being rotated.  
         [0042]    [0042]FIG. 45 is a view of the apparatus of FIG. 43 as taken along line  45 - 45  of FIG. 43, with the view being rotated.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0043]    Specific language is used in the following description to publicly disclose the invention and to convey its principles to others. No limits on the breadth of the patent rights based simply on using specific language are intended. Also included are any alterations and modifications to the description that should normally occur to one of average skill in this technology.  
         [0044]    A connection assembly  1  according to the invention is shown in FIGS.  1 - 3 . Connection assembly  1  is shown attaching a spinal implant rod “A” with a longitudinal axis L 1  to the shaft of a vertebral anchor “B” with the longitudinal axis L 2 . Connection assembly  1  includes a bolt  2 , a clevis  3 , a rod interface washer  4 , and a set screw  5 . Bolt  2  has an aperture  6  for receiving a rod in a spinal implant system. While a closed aperture is shown, it will nevertheless be understood that an open-sided aperture may also be used to permit top-loading of the connector rod. Set screw  5  is forceably inserted through a threaded opening  15  in bolt  5  and into aperture  6  so as to allow set screw  5  to push against rod A. Clevis  3  has a bore  7  for receiving a vertebral anchor in a spinal implant system. Clevis  3  wraps around the shaft of vertebral anchor B and is simultaneously tightened when set screw  5  is tightened against rod A. It is contemplated that the shaft of B may be roughened and the interior of clevis  3  may be correspondingly roughened to increase friction between them. As set screw  5  pushes against rod A, rod A pushes against rod interface washer  4 . This force pinches the ends  8  and  9  of clevis  3  together between rod interface washer  4  and stop  10 , which tightens clevis  3  around vertebral anchor B. In this manner, set screw  5  acts as a compression member to tighten the connection assembly and achieve substantial fixation.  
         [0045]    Details of bolt  2  are shown in FIGS.  4 - 7 . Bolt  2  can be subdivided into bolt head portion  11 , bolt shaft portion  12 , washer seat portion  13  and washer stop portion  14 . Threaded openings  15   a  &amp;  15   b , and aperture  6  reside in bolt head portion  11 . Threaded openings  15   a  &amp;  15   b  open into aperture  6  at an oblique angle A 4  with respect to longitudinal axis L 3  to allow set screw  5  (FIGS.  1 - 3 ) to force spinal rod A toward the distal end  16  of aperture  6 . Bolt  2  is substantially symmetrical about longitudinal axis L 3  such that threaded openings  15   a  and  15   b  are substantially mirror images. Bolt shaft portion  12  is generally cylindrical in shape and is sized to accept the eyes (items  17  and  18 , FIG. 10) of clevis  3 . Clevis  3  is then held on shaft portion  12  by attaching stop  10  (shown in isolation in FIGS. 8 &amp; 9) to the end  19  of shaft portion  12 , either by welding or some other suitable means. As an alternative, shaft portion  12  may include threads and stop  10  may be correspondingly threaded to be held in position. In this alternative design, stop  10  may be the compressive member utilized to tighten connection assembly  1 .  
         [0046]    Bolt  2  also preferably includes washer seat portion  13  and washer stop portion  14 . A seat portion  13  that is substantially rectangular in cross-section is currently preferred, but washer seat portion  13  can be of any suitable shape that may interlock with a complementary shape in rod interface washer  4  (FIGS.  1 - 3 ) to prevent rod interface washer  4  from rotating in relation to bolt  2 . As shown, washer stop  14  is generally provided by placing a raised edge in bolt head portion  11 . Washer stop  14  prevents rod interface washer  4  from being inadvertently removed from connector assembly  1  during installation.  
         [0047]    Referring to FIGS. 2A and 3A, additional characteristics of the preferred embodiment may be seen by contrasting several of connector assembly 1&#39;s relative dimensions. Dimension D 1  is the overall width of connection assembly  1 , measured from the most medial point  50  of connector assembly  1  to its most lateral point  51 . Dimension D 2  is the distance from the inside edge of rod A to the outside edge of vertebral anchor B, measured perpendicularly to L 1 . Dimension D 3  is the distance from the inside edge of rod A to the most lateral end  52  of bolt  2 , measured perpendicularly to L 1 . Dimension D 4  is the distance from the inside edge of rod A to the inside edge of vertebral anchor B, measured perpendicularly to L 1 . Dimension D 5  is the distance from the outside edge of vertebral anchor B to the most lateral point  51  of connector assembly  1 . And dimension D 6  is the distance from L 2  to L 3 , measured parallel to L 1 .  
         [0048]    Contrasting several of these dimensions, most notably D 3  can be less than D 2  in the present invention. In other words the outside edge  52  of bolt  2  does not need to extend beyond the outside edge of vertebral anchor B. Typically, most connectors place the bore to hold a vertebral anchor at the end of a bolt that typically holds the vertebral anchor to the rod, necessarily leaving a portion of the bolt extending past the vertebral anchor. An example of such a design is shown in U.S. Pat. Nos. 5,643,263 and 5,885,285 to Simonson. But here, bolt  2  does not need to extend beyond anchor B, which would allow bolt  2  of connection  1  to be placed in more narrow passageways than connections of prior art designs.  
         [0049]    Next it should be noted that the present invention allows dimension D 4  to be shortened as the surgeon may desire, reducing the overall width D 1  of the connector assembly. In other words and referring also to FIGS. 13 &amp; 14, the present design allows D 4  to be shortened by placing the bore  7  of clevis  3  in a position that is closer to rod A. For example, clevis  3  shown in FIG. 14 could conceivably place vertebral anchor B so close to rod A that only the width of clevis  3  around bore  7  would separate vertebral anchor B from rod A.  
         [0050]    Finally, the present design also allows vertebral anchor B to be laterally offset a distance D 6  from the longitudinal axis L 3  of bolt  2 , allowing bolt  2  and its connection to rod A to lie in a different transverse plane on the patient than vertebral anchor B would lie. Most designs such as U.S. Pat. Nos. 5,643,263 and 5,885,285 to Simonson place the bore to hold vertebral anchor B in the same transverse plane as the connection to rod A. In other words, vertebral anchor B is usually situated in line with the longitudinal axis of the structure, usually a bolt, that holds the vertebral anchor B and rod A together. Here, however, the present invention allows bolt  2  to be placed in one transverse plane (in one longitudinal location along rod A) and vertebral anchor B to be placed in another transverse plane (or another longitudinal location along rod A). Thusly situated, bolt  2  is separated from vertebral anchor B by a distance D 6 , measured longitudinally along rod A. Moreover, D 6  can be larger than D 4 , readily allowing bolt  2  to be placed in one longitudinal position on the spine and vertebral anchor B to be placed in another position, above or below bolt  2 . Located in this fashion, the surgeon can place the connector assembly of the present invention in a location that avoids interfering with the facet joints of the patient&#39;s spine.  
         [0051]    Details of clevis  3  are shown in FIGS.  10 - 12 . Clevis  3  includes a bore  7 , a proximal ear  8  or end  8  and a distal ear  9  or end  9 . Proximal ear  8  has an eye  18  and distal ear  9  has an eye  17 . As previously presented, bolt  5  attaches to clevis  3  by placing the shaft portion of bolt  5  through eyes  17  and  18  and then attaching end  10  (FIG. 15). The proximal ear  8  also includes a connection surface  20 . Connection surface  20  preferably includes structure for facilitating the engagement of clevis  3  against rotational movement relative to rod interface washer  4 . This engagement structure is preferably a plurality of variable angle ridges  21  that radiate from the rotational center of clevis  3 . In other words, the structure is a set of interlocking teeth that can generally be characterized as male protrusions and complementary female cavities.  
         [0052]    Referring to FIGS. 10, 13 and  14 ; bore  7  of clevis  3  may assume various orientations in relation to the centerline  22  of clevis  3 . FIG. 10 depicts bore  7  offset from centerline  22  toward the stop (not shown) of bolt  2 . Optionally, bore  7  can be offset from centerline  22  toward the aperture (not shown) of bolt  2 , as shown in FIG. 14, or bore  7  can be placed in the same plane as centerline  22 , as shown in FIG. 13. It being understood that the alternative clevis designs may permit even smaller total width of connection assembly by bringing the vertebral anchor closer to the rod.  
         [0053]    Details of rod interface washer  4  are shown in FIGS.  18 - 20 . Rod interface washer  4  can be any of several suitable shapes, including the circle that is depicted. One surface  23  of the rod interface washer  4  has an engagement surface, which preferably includes an engagement groove  24  that accepts a cylindrical spinal implant rod (such as rod A in FIGS.  1 - 3 ). Engagement groove  24  preferably runs across the entire face of surface  23 . Rod interface washer  4  also has a central opening  25  that corresponds to the cross-sectional shape of previously presented washer seat portion  13  in bolt  2 . In the currently preferred embodiment, both washer seat portion  13  and opening  25  are substantially square. Although, this shape could vary from many possible shapes that would similarly prevent rod interface washer from rotating in respect to bolt  2 . To assist in this regard, it is also preferable that rod interface washer have a guide groove  26  to accept bolt head portion  11  of bolt  2  to further lock bolt  2  and rod interface washer  4  together. In this regard it should be noted that guide groove  26  and engagement groove  24  are preferably placed in such a manner that orients aperture  6  substantially parallel to groove  24 . This placement helps insure that a spinal rod (item A in FIGS.  1 - 3 ) will be held in the connector assembly in a direction that is substantially perpendicular to bolt  2 , and in turn, also substantially perpendicular to set screw  5 .  
         [0054]    Rod interface washer  4  also includes connection surface  27 . Connection surface  27  preferably includes structure for facilitating the engagement of rod interface washer against rotational movement relative to clevis  3 . This engagement structure is preferably a plurality of variable angle ridges  28  that radiate from the rotational center of rod engagement washer  4  as that previously described on clevis  3 . Variable angle ridges  28  are sized to mate with the similar variable angle ridges  21  on clevis  3 . Referring to FIGS. 11 and 18, both sets of ridges consist of alternating male protrusions and female cavities. Hence, once placed together, these interlocking ridges prevent rod engagement washer  4  from rotating in respect to clevis  3 . And although radiating ridges are shown to facilitate the fixation of these two parts, it is also contemplated that other structures could serve this function. For example, it is also contemplated that one could use any number of interlocking male and female structures such as rounded bumps or knurling and mating cavities. The locking engagement of connection surface  20  with connection surface  27  may occur at any of a plurality of angles. More specifically, the angle between longitudinal axis LI of the vertebral anchor and longitudinal axis L 2  of the rod may be adjusted to meet the requirements of the patient&#39;s anatomy.  
         [0055]    The rotatable connection assembly of this invention is again depicted in FIGS.  15 - 17 , less set screw  5 , which has been removed for clarity along with rod A and vertebral anchor B. The device is used by placing a spinal rod through aperture  6  in bolt  2 . The post of a vertebral anchor is then located in bore  7  of clevis  3  and the variable angle ridges  20  on the rod interface washer are interlocked with the variable angle ridges  28  on clevis  3  as the surgeon desires. Thusly situated, the assembly is then tightened by threading set screw  5  into either of the threaded openings  15  of bolt  2 . Upon entering aperture  6 , set screw  5  contacts the spinal rod and forces the spinal rod toward interface washer  4 . The spinal rod then contacts rod interface washer  4 , and preferably engages groove  24 . As one continues turning set screw  5 , rod interface washer presses ears  8  and  9  of clevis  3  against stop  10 . This action forces ears  8  and  9  together, which in turn, tighten clevis  3  around the post of the vertebral anchor. The variable angle surfaces, item  20  on clevis  3  and item  27  on rod interface washer  4 , engage each other and prevent rod interface washer  4  from rotating in relation to clevis  3 , which further locks clevis  3  in relation to bolt  2  because rod interface washer  4  cannot rotate in relation to bolt  2 . Adjustments can be made by loosening set screw  5  then re-tightening the set screw when the preferred position has been located.  
         [0056]    Another alternative embodiment of the invention is shown in FIGS.  21  to  33 . Where possible, like identification numerals have been used to identify like structures from previous embodiments. Details of bolt  2  in this embodiment are depicted in FIGS.  24 - 26 , details of clevis  4  are depicted in FIGS.  27 - 29 , and details of rod interface washer are depicted in FIGS.  31 - 33 .  
         [0057]    This embodiment is largely the same as the previous embodiment with two notable exceptions. The first exception is that this embodiment omits end  10 . Referring to FIG. 23, bolt  2  (FIG. 24) is still rotably connected to eye  17  of ear  9  (FIG. 27). In this embodiment, however, bolt  2  has a threaded portion  70  and ear  9  has a matching set of threads  71 . When these two structures are operably engaged, bolt  2  is free to turn about its axis just as bolt  2  is free to turn about its axis in the earlier-described embodiments, but end  10  is no longer required. The second exception is depicted in FIG. 30. Bore  7  does not have a generally round cross-section. Instead, the cross section has been flattened or raised at two locations  60  and  61 . These surfaces force bolt B against the side of bore  7  at surface  62  when clevis  3  is tightened around bolt B, effectively gripping bolt B at three points of contact over the length of bolt B. Optionally, one may also wish to provide a third raised surface at location  62  to contact bolt B.  
         [0058]    [0058]FIGS. 34 through 45 depict a connection assembly  101  according to another embodiment of the present invention. The use of a one-hundred prefix (1XX) before an element number (XX) refers to an element that is the same as the non-prefixed element number, except for the differences shown and described.  
         [0059]    This embodiment is similar to the connection assemblies shown previously. Connection assembly  101  includes a bolt  102 , a clevis  103 , and a rod interface washer  104 . Bolt  102  includes an aperture  106  for receiving a rod in a spinal implant system. Clevis  103  includes a bore  107  for receiving a vertebral anchor in a spinal implant system.  
         [0060]    Clevis  103  wraps around the shafts of vertebral anchor B and is tightened around anchor B when threads  82  of screw  80  are threadably received by internally threaded bore  115   c  of bolt  102  (as best shown in FIG. 36). Screw  80  is one example of a separable threaded member engageable to the threaded end  115   c  of bolt  102 .  
         [0061]    Screw  80  includes a head  84  having a curved shoulder  86 . Shoulder  86  is received within at least a portion of pocket  90  defined in outer face  103 . 3  of ear  109  of clevis  103 . Tightening of screw  80  results in curved shoulder  86  bearing against pocket  90 . Subsequent tightening of bolt  80  results in a bending of ears  108  and  109  towards each other, which tightens bore  107  into three point contact with vertebral anchor B. In one embodiment, shoulder  86  is a convex surface having a radius of about 0.8 mm. In that same embodiment, pocket  90  is a concave surface having a radius of about 7 mm. However, the present invention is not constrained to these particular selections of curvature, and also encompasses other radii of curvature, as well non-spherical, curved surfaces and chamfers. Preferably, the mating surfaces of shoulder  86  and pocket  90  are adapted and configured to be in line contact.  
         [0062]    Referring now to FIG. 42, clevis  103  includes a proximal ear  108  or end  108  and a distal ear  109  or end  109 . Ears  108  and  109  each define eyes  118  and  117 , respectively. Eyes  118  and  117  are preferably circular in cross section and smooth and unthreaded. As can be seen best in FIG. 36, the end of bolt  102 , which includes internal thread  115   c , passes smoothly through eye  118 . The shank of bolt  80  passes smoothly through eye  117 .  
         [0063]    Referring again to FIG. 42, ear  108  includes an internal face  103 . 2  that is generally opposite of an internal face  103 . 1  of ear  109 . These opposing internal faces  103 . 1  and  103 . 2  are drawn closer to one another by tightening of screw  80 . Referring to FIG. 42, these opposing faces are non-parallel to each other when clevis  103  is in a free, unassembled state. In one embodiment of the present invention, the included angle E between faces  103 . 1  and  103 . 2  is about three degrees, although the invention is not limited to this angle.  
         [0064]    While the invention has been illustrated and described in detail, this is to be considered as illustrative and not restrictive of the patent rights. The reader should understand that only the preferred embodiments have been presented and all changes and modifications that come within the spirit of the invention are included if the following claims or the legal equivalent of these claims describes them.