Abstract:
Methods of assembling a vertebral anchor to a body shaped to receive a longitudinal member. The methods may include inserting a wear member and a head of an anchor into a cavity through an inlet in a first end of a body. The body may further include a second end with a channel to receive the longitudinal member. The method may include deforming the first end of the body and reducing a width of the inlet measured perpendicular to a longitudinal axis of the body and capturing the wear member and the head in the cavity. The method may also include compressing the wear member against the head of the anchor and increasing an amount of interference between the wear member and the head.

Description:
RELATED APPLICATION 
       [0001]    The present application is a divisional application of U.S. patent application Ser. No. 11/341,188 filed on Jan. 27, 2006, and herein incorporated by reference in its entirety. 
     
    
     BACKGROUND  
       [0002]    Longitudinal members, such as spinal rods, are often used in the surgical treatment of spinal disorders such as degenerative disc disease, disc herniations, scoliosis or other curvature abnormalities, and fractures. Different types of surgical treatments are used. In some cases, spinal fusion is indicated to inhibit relative motion between vertebral bodies. In other cases, dynamic implants are used to preserve motion between vertebral bodies. For either type of surgical treatment, longitudinal members may be attached to the exterior of two or more vertebrae, whether it is at a posterior, anterior, or lateral side of the vertebrae. In other embodiments, longitudinal members are attached to the vertebrae without the use of dynamic implants or spinal fusion. 
         [0003]    Longitudinal members may provide a stable, rigid column that encourages bones to fuse after spinal-fusion surgery. Further, the longitudinal members may redirect stresses over a wider area away from a damaged or defective region. Also, rigid longitudinal members may restore the spine to its proper alignment. In some cases, flexible longitudinal members may be appropriate. Flexible longitudinal members may provide other advantages, such as increasing loading on interbody constructs, decreasing stress transfer to adjacent vertebral elements while bone-graft healing takes place, and generally balancing strength with flexibility. 
         [0004]    Conventionally, longitudinal members are secured to vertebral members using rigid clamping devices. These clamping devices may be multi-axial in the sense that they are adjustable prior to securing. However, once secured, the clamping devices are locked in place. A surgeon may wish to implant a flexible rod system and have more freedom to control pivot points or the nature of the pivoting motion. At present, a surgeon might only have a choice between rigid and flexible longitudinal members, which may not necessarily provide the desired degree of flexibility. 
       SUMMARY  
       [0005]    The present application is directed to methods of assembling a vertebral anchor to a body shaped to receive a longitudinal member. The methods may include inserting a wear member and a head of an anchor into a cavity through an inlet in a first end of a body. The body may further include a second end with a channel to receive the longitudinal member. The method may include deforming the first end of the body and reducing a width of the inlet measured perpendicular to a longitudinal axis of the body and capturing the wear member and the head in the cavity. The method may also include compressing the wear member against the head of the anchor and increasing an amount of interference between the wear member and the head. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIGS. 1A and 1B  are perspective views of a pivoting head assembly according to one or more embodiments comprising a longitudinal member attached to the spine; 
           [0007]      FIGS. 2A and 2B  are perspective views of a pivoting head coupled to an anchor member according to one embodiment; 
           [0008]      FIG. 3  is a side section view of a pivoting head coupled to an anchor member and securing a longitudinal member according to one embodiment; 
           [0009]      FIG. 4  is a perspective view of an anchor member for use with a pivoting head according to one embodiment; 
           [0010]      FIGS. 5A-C  are top section views of a pivoting head with an anchor member and wear member inserted therein according to different embodiments; 
           [0011]      FIG. 6  is a perspective view of a wear member for use with a pivoting head according to one embodiment; 
           [0012]      FIG. 7  is a side view, including a partial section view, of an assembled anchor member and wear member for use with a pivoting head according to one embodiment; 
           [0013]      FIG. 8  is a side section view of a pivoting head with an anchor member and wear member inserted therein according to one embodiment; 
           [0014]      FIG. 9  is a side section view of an assembled pivoting head with an anchor member and wear member constrained therein according to one embodiment; 
           [0015]      FIG. 10  is a detailed section view of the bottom region of a pivoting head according to one embodiment; 
           [0016]      FIG. 11  is a side section view of a pivoting head and various wear members that may be used with the pivoting head according to one embodiment; 
           [0017]      FIG. 12  is a side section view of an assembled pivoting head with an anchor member and wear member constrained therein according to one embodiment; 
           [0018]      FIG. 13  is a detailed section view of the bottom region of a pivoting head according to one embodiment; 
           [0019]      FIG. 14  is a detailed section view of the bottom region of a pivoting head according to one embodiment; 
           [0020]      FIG. 15  is a detailed section view of an interference snap ring that may be used with the pivoting head according to one embodiment; 
           [0021]      FIG. 16  is a perspective view of a pivoting head coupled to an anchor member according to one embodiment; 
           [0022]      FIG. 17  is a side section view of an assembled pivoting head with an anchor member and wear member constrained therein according to one embodiment; 
           [0023]      FIG. 18  is a side section view of an assembled pivoting head with an anchor member and wear member constrained therein according to one embodiment; 
           [0024]      FIG. 19  is a perspective view of a wear member for use with a pivoting head according to one embodiment; 
           [0025]      FIG. 20  is a side section view of an assembled pivoting head with an anchor member and wear member constrained therein according to one embodiment; and 
           [0026]      FIG. 21  is a side section view of an assembled pivoting head with an anchor member and wear member constrained therein according to one embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    The various embodiments disclosed herein are directed to pivoting mechanisms and methods for securing longitudinal members in a spinal implant. Various types of longitudinal members are contemplated, including spinal rods that may be secured between multiple vertebral bodies.  FIGS. 1A and 1B  show another type of longitudinal member  15  that is secured between the sacrum S and a vertebral member V (i.e., L5). In one embodiment, the longitudinal member  15  is a flexible member, such as a resin or polymer compound. Some flexible non-metallic longitudinal members  15  are constructed from materials such as PEEK and UHMWPE. Other types of flexible longitudinal members  15  may comprise braided metallic structures. In one embodiment, the longitudinal member  15  is rigid or semi-rigid and may be constructed from metals, including for example stainless steels, cobalt-chrome, titanium, and shape memory alloys. Further, the longitudinal member  15  may be straight, curved, or comprise one or more curved portions along its length. 
         [0028]    In  FIGS. 1A and 1B , the longitudinal member  15  is secured to the vertebral member V with one embodiment of a pivoting head  10  in accordance with the teachings provided herein. In the embodiment shown, the longitudinal member  15  is secured to a saddle  16  within the pivoting head  10  with a securing member  12 . The securing member  12  shown in  FIGS. 1A and 1B  features a snap-off driving member  14 . The driving member  14  is integrally formed with the securing member  12  and allows a surgeon to drive the securing member  12  into contact with the longitudinal member  15  to achieve a certain installation torque. Above that torque, the driving member  14  will snap off, separating from the securing member  12 . In this manner, the securing member  12  may provide the desired clamping force to secure the longitudinal member  15 . 
         [0029]      FIG. 1A  shows a first orientation for the pivoting head  10  identified by the centerline labeled X. By contrast,  FIG. 1B  shows a second position representing a different spatial relationship between the sacrum S and the vertebra V. As compared to  FIG. 1A , the vertebra V in  FIG. 1B  exhibits some amount of angular and torsional displacement relative to the sacrum S. Consequently, the pivoting head  10  is illustrated in a second orientation identified by the centerline labeled Y. The pivoting head  10  may provide some or all of this rotation. The illustrations provided in  FIGS. 1A and 1B  show the pivoting head  10  as part of a spinal implant that is coupled between a vertebral body V and a sacrum S. It should be understood that the pivoting head  10  may be used in constructs that are coupled to vertebral bodies V alone. Further, a vertebral implant may be construed to mean implants that are coupled to any or all portions of a spine, including the sacrum, vertebral bodies, and the skull. 
         [0030]      FIGS. 2A and 2B  illustrate perspective views of the illustrative embodiment of the pivoting head  10  coupled to an anchor member  18 . A head  32  of the anchor member  18  is pivotally coupled to a base portion  34  of the pivoting head  10 . In one embodiment, the anchor member  18  comprises threads for insertion into a vertebral member V as shown in  FIGS. 1A and 1B . In one embodiment, the anchor member  18  is a pedicle screw. The exemplary saddle  16  is comprised of opposed upright portions forming a U-shaped channel within which a longitudinal member  15  is placed. A seating surface  24  forms the bottom of the U-shaped channel. In one embodiment, the seating surface  24  is curved to substantially match the radius of a longitudinal member  15  that is positioned within the saddle  16 . An aperture  26  within the seating surface provides access to a driving feature used to insert the anchor member  18  into a vertebral member V. 
         [0031]    In  FIG. 2A , the pivoting head  10  is shown substantially aligned with the anchor member  18  along the centerline labeled X. In  FIG. 2B , the anchor member  18  is shown pivoted relative to the pivoting head  10 . That is, the pivoting head  10  is shown still aligned with the centerline labeled X while the anchor member  18  is shown aligned with the centerline labeled Y. The pivoted displacement of the pivoting head  10  relative to the anchor member  18  achieved in  FIG. 2B  is provided by an articulation mechanism that is more clearly visible in the section view provided in  FIG. 3 . 
         [0032]      FIG. 3  shows a section view of the pivoting head  10  holding a different type of longitudinal member  28 . In this embodiment, the longitudinal member  28  is a spinal rod. The spinal rod  28  is secured within the saddle  16  with a securing member  12 . In the embodiment shown, the securing member  12  is an externally threaded set screw, though other types of securing members such as externally threaded caps and nuts may be used. In the embodiment shown, an articulation mechanism  40  is disposed below the saddle  16  and generally aligned with the central axis X. The articulation mechanism  40  comprises an anchor head  32  of the anchor member  18  that is pivotally coupled to a wear member  30  within the base portion  34  of the pivoting head  10 . Since the anchor head  32  is configured to pivot within the wear member  30 , the wear member  30  and the outer surface of the anchor head  32  may be constructed of a wear resistance material. Some suitable examples may include hardened metals, titanium carbide, cobalt chrome, polymers, and ceramics. 
         [0033]    In other embodiments, a wear resistant layer may be coated onto the anchor head  32  and the wear member  30 . In one embodiment, the wear member  30  may be integrally formed into or form a part of the base portion  34 . In one embodiment, the wear member  30  may be bonded to the base portion  34  using a biocompatible adhesive such as PMMA or other known adhesives. In these alternative embodiments, the part of the base portion  34  in contact with the anchor head  32  may be coated with a wear resistant layer. Coating processes that include, for example, vapor deposition, dip coating, diffusion bonding, and electron beam welding may be used to coat the above indicated materials onto a similar or dissimilar substrate. Diffusion bonding is a solid-state joining process capable of joining a wide range of metal and ceramic combinations. The process may be applied over a variety of durations, applied pressure, bonding temperature, and method of heat application. The bonding is typically formed in the solid phase and may be carried out in vacuum or a protective atmosphere, with heat being applied by radiant, induction, direct or indirect resistance heating. Electron beam welding is a fusion welding process in which a beam of high-velocity electrons is applied to the materials being joined. The workpieces melt as the kinetic energy of the electrons is transformed into heat upon impact. Pressure is not necessarily applied, though the welding is often done in a vacuum to prevent the dispersion of the electron beam. 
         [0034]    The articulation mechanism  40  is spatially and functionally isolated from the clamping forces that are applied between the securing member  12 , the rod  28 , and the seating surface  24  (see  FIGS. 2A ,  2 B). That is, since the compression forces applied by the securing member  12  are not transmitted to the articulation mechanism  40 , the anchor member  18  rotates about the central axis X under the influence of the sliding resistance provided by the various embodiments disclosed herein. In this manner, the articulation mechanism  40  is not only spatially isolated from the securing member  12 , but also physically isolated from the forces provided by the securing member  12 . 
         [0035]      FIG. 4  shows a perspective view of the anchor head  32  of the exemplary anchor member  18 . The anchor head  32  includes a driving feature  42  that allows a surgeon to attach the anchor member  18  to a vertebra V. In the embodiment shown, a hex recess driving feature  42  is shown. Other types of driving features  42  may be appropriate, including for example, slotted, star, Torx, and cross-shaped features. The driving feature  42  may be accessed through the aperture  26  shown in  FIGS. 2A ,  2 B, and  3 . 
         [0036]    In the embodiment illustrated in  FIG. 4 , the anchor head  32  is substantially spherical to allow multi-axial pivoting of the anchor member  18  relative to the pivoting head  10 . In other embodiments, the anchor head  32  has other shapes to allow motion in fewer directions. For instance, a disc-shaped anchor head  32  may provide motion within a desired plane.  FIGS. 5A ,  5 B, and  5 C illustrate some of these alternative embodiments. Specifically,  FIGS. 5A-5C  are top section views according to the section line X-X shown in  FIG. 3 .  FIG. 5A  shows one embodiment where the anchor head  32  and wear member  30  are substantially spherical as previously described. With this configuration, the pivoting head  10  may pivot about a plurality of axes, including axes A, B, C, and D as shown in  FIG. 5A .  FIG. 5B  shows an alternative embodiment where the anchor head  132  and wear member  130  are substantially disc-shaped. As disclosed above, this configuration may allow pivoting motion about axis B, but not other axes, including axis A.  FIG. 5C  depicts another embodiment that is characterized by at least two different spherical radii R 1 , R 2 . This configuration may provide a different resistance to rotation about axes A and B. A somewhat pronounced difference in radii R 1 , R 2  is shown in  FIG. 5C , though in practice, a fairly small difference may produce the desired result. 
         [0037]      FIG. 6  shows a perspective view of a wear member  30  according to one embodiment. As depicted, the wear member  30  is cylindrically shaped and includes an outer surface  44  and an inner surface  46  extending between a top surface  50  and a bottom surface  52 . Generally, the inner surface  46  is constructed to match the shape of the anchor head  32  of the threaded anchor member  18 . The outer surface  44  may be configured as desired to fit within the base portion  34  of the pivoting head  10  as shown in  FIG. 3 . In one embodiment, the outer surface  44  is substantially cylindrical. The exemplary wear member  30  also includes a gap  48 . The gap  48  in the present embodiment may be used to spread open the wear member  30  by an amount sufficient to slip the wear member  30  over the anchor head  32  of the anchor member  18 . 
         [0038]    The wear member  30  is shown installed on the anchor head  32  in  FIG. 7 .  FIG. 7  also shows relevant dimensions of the wear member  30  and the anchor head  32 . Dimension L represents a width of the anchor head  32  at its widest point. The width may comprise a diameter, a spherical diameter, or other linear dimension. Dimensions M and N respectively represent an interior width at the top  50  and bottom  52  of the wear member  30 . Notably, dimension L is larger than both M and N. Thus, the gap  48  allows the anchor head  32  to fit within the wear member  30  as shown in  FIG. 7 . 
         [0039]      FIG. 8  shows the assembled wear member  30  and anchor member  18  inserted into the base portion  34  of the pivoting head  10 . The anchor member  18  and wear member  30  are retained within the base portion  34  by deforming the lower lip  56  in the direction of the arrow labeled F. The deforming step may be performed using a variety of techniques, including but not limited to mechanical pressing, swaging, and orbital forming. Orbital forming (or orbital forging) is a cold metal forming process during which the workpiece (the base portion  34  in this case) is transformed between upper and lower dies. The process features one or the other of these dies orbiting relative to the other with a compression force applied therebetween. Due to this orbiting motion over the workpiece, the resultant localized forces can achieve a high degree of deformation at a relatively low compression force level. The fully assembled pivoting head  10  is illustrated in  FIG. 9 . In this Figure, the lower lip  56  of the base portion  34  is formed to constrain the wear member  30  and the anchor member  18 . 
         [0040]      FIG. 10  shows a detail view of the lower lip  56  of the base portion  34 . The forming technique used to form the lower lip  56  under and around the wear member  30  may be controlled to produce a pivoting head  10  with a desired, predetermined resistance to motion. The dashed lines labeled INT 1  and INT 2  depict this ability to control the amount of interference between the parts, and hence the amount of resistance to motion. If a greater amount of resistance to motion is desired, the lower lip  56  may be deformed a greater amount as indicated by the dashed line labeled INT 2 . A lesser amount of deformation indicated by the dashed line INT 1  may produce less resistance to motion. In one embodiment, the lower lip  56  is formed to produce a very large resistance to motion such that the pivoting head  10  is, for all practical purposes, fixed. At the opposite end of the spectrum, the lower lip  56  is formed to merely place the relevant parts (base portion  34 , wear member  30 , and anchor head  32 ) in contact with one another or in close proximity to one another. In this embodiment, the pivoting head  10  is free to rotate with very little or no resistance to motion. At points between these extremes (indicated by dashed line INT 1 ), a desired amount of interference may produce a desirable resistance to motion. 
         [0041]    The resistance to motion may be measured in standard torque units, such as inch-ounces or other units of measure. As the parts are formed, the measurable resistance to motion may be marked on the exterior of the pivoting head  10  to provide surgeons an indication of the relative flexibility of the pivoting head  10 . This marking may be provided as an alphanumeric indication as represented by the letter T in  FIGS. 2A and 2B . The marking may be stamped, whether by ink or metal deformation, engraved, or otherwise displayed on the pivoting head  10 . 
         [0042]    Interference between the base portion  34 , the wear member  30 , and the anchor head  32  will generally contribute to greater amounts of resistance to motion. Accordingly, the parts may be selected according to size to provide the desired resistance to motion. For instance,  FIG. 11  shows a pivoting head  10 , including a base portion  34  that is defined in part by a dimension D 1 . This dimension D 1  corresponds approximately to the outer dimension of the wear members  30   b,    30   c,  and  30   d  that are also shown in  FIG. 10 . However, each wear member  30   b - d  has a slightly different outer dimension D 2 -D 4 . As an example, wear member  30   b  is characterized by the largest outer dimension D 2 . Wear member  30   c  is characterized by the smallest outer diameter D 3  and wear member  30   d  is somewhere between, with an outer diameter D 4 . It is assumed for the sake of this discussion, that the inner surface  46  is the same for all three wear members  30   b - d.  In an alternative embodiment, the inner surface  46  may be constructed with different sizes to create different amounts of interference with the anchor head  32  of the anchor member  18 . In an alternative embodiment, both the inner  46  and outer  44  surfaces may vary between wear members  30 . That is, different wear members  30  may have different thicknesses. In an alternative embodiment, the resistance to pivoting motion of the head  32  may be provided by materials having different coefficients of friction. 
         [0043]    For the embodiments shown in  FIG. 11 , wear member  30   c  will result in the least amount of interference when used in the pivoting head  10 . Conversely, wear member  30   b  will result in the greatest amount of interference when used in the pivoting head  10 . A measurable resistance to motion of the pivoting head  10  can be determined once the parts are assembled. As indicated above, this measured resistance to motion may be marked on the exterior of the pivoting head  10  to provide surgeons an indication of the relative flexibility of the pivoting head  10 . 
         [0044]      FIG. 12  shows an alternative embodiment of the pivoting head  10   a.  The section view shows an alternative technique for retaining the wear member  30  and anchor member  18  within the base portion  34   a.  In this embodiment, a snap ring  58  is inserted into the bottom of the base portion  34   a  beneath the wear member  30 . The snap ring  58  may effectively retain the wear member  30  and anchor member  18  within the pivoting head  10   a.  A detailed view of the area around the snap ring  58  is shown in  FIG. 13 . Notably, in this embodiment, the snap ring  58  acts as a barrier to prevent the wear member  30  from escaping but does not contribute to any interference between the other parts ( 30 ,  32 ,  34 ). 
         [0045]    In an alternative embodiment shown in  FIG. 14 , a snap ring  158  may contribute to the overall resistance to motion of the pivoting head  10   b.  As with the embodiment shown in  FIGS. 12 and 13 , the snap ring  158  is configured to fit within the interior of the base portion  34   b.  However, the interior portion of the snap ring  158  is modified slightly to create an interference with the wear member  30   e.  In this embodiment, the wear member  30   e  is slightly modified to include a rounded lower outside corner  60  to facilitate insertion of the snap ring  158 . A detailed view of a cross section of the snap ring  158  is shown in  FIG. 15 . 
         [0046]    The exemplary snap ring  158  comprises a bottom surface  64 , a top surface  66 , and an outer surface  62 , each of which are configured to fit within the body portion  34   b  of the pivoting head  10   b.  A retaining surface  68  further acts to keep the wear member  30   e  within the pivoting head  10   b.  This snap ring  158  also includes an interference surface  70  that contacts the wear member  30   e  to create a force G (shown in  FIG. 14 ) that compresses the wear member  158  towards the anchor head  32 . The compression force G creates an interference that resists pivoting motion of the anchor head  32  relative to the wear member  30   e.  Snap rings  158  including different interference surfaces  72 ,  74  may be selected to create more or less interference as desired. Once the snap ring  158  is assembled to retain and compress the wear member  30   e,  a measurable resistance to motion of the pivoting head  10   b  can be determined. As indicated above, this measured resistance to motion may be marked on the exterior of the pivoting head  10   b  to provide surgeons an indication of the relative flexibility of the pivoting head  10   b.    
         [0047]      FIGS. 16 and 17  illustrate an alternative embodiment of the pivoting head  10   c.  In this embodiment, the resistance to motion may be set intra-operatively. The base portion  34   c  of the pivoting head  10   c  includes one or more adjustment members  76  that allow a surgeon to adjust the amount of interference between the wear member  30  and the anchor head  32 . Further, a surgeon may be able to adjust this amount of interference differently about different axes depending upon how many adjustment members  76  are provided. In the embodiments illustrated, there are four total adjustment members  76 , disposed approximately  90  degrees apart from one another. More or fewer adjustment members  76  may be provided. Also, in one embodiment, one of the adjustment members  76  is substantially aligned with the orientation in which a longitudinal member  15  lies. For example, in the embodiment shown, one adjustment member  76  is substantially parallel to the seating surface  24 . In one embodiment, an adjustment member  76  is substantially transverse to this seating surface. In the embodiment shown, the adjustment members  76  are setscrews that may be screwed in to create a compressive force H that is shown in  FIG. 17 . In another embodiment, the adjustment member  76  may be a pin. The compressive force H may create an increased amount of interference that also creates more resistance to motion. 
         [0048]      FIG. 18  shows an alternative embodiment of the pivoting head  10   d  that includes a threaded region  78  disposed towards a bottom of the base portion  34   d.  An adjustment member  80  having substantially matching threads  84  is threaded onto the threads  78  on the base portion  34   d  and rotated until the desired resistance to motion is obtained. This procedure may be performed intra-operatively. In one embodiment, the threads  78 ,  84  are tapered threads to create an increasing amount of inward compression J and corresponding interference. In one embodiment, a lower opening  82  of the adjustment member  80  is smaller than a width of the threaded portion  78  of the base portion  34   d.  Consequently, the more the adjustment member  80  is threaded onto the base portion  34   d,  the base portion  34   d  is compressed an increasing amount. 
         [0049]      FIG. 19  shows an alternative embodiment of the wear member  30   a  that may be used in one or more embodiments disclosed herein. The wear member  30   a  also includes a series of gaps  48   a  as with the previous embodiment shown in  FIG. 6 . However, gaps  48   a  do not extend from the bottom surface  52   a  to the top surface  50   a.  In this embodiment, the top surface  50   a  of the wear member  30   a  is substantially continuous. In one embodiment, the wear member  30   a  comprises four gaps  48   a  separated by approximately 90 degrees. In other embodiments, more or fewer numbers of gaps  48   a  are used. Since the gaps  48   a  originate at the bottom surface  52   a  of the wear member  30   a,  inward deflection of the wear member  30   a,  particularly near the bottom surface  52   a,  is possible. This feature may be appropriate for one or more embodiments where inward deflection of the wear member  30   a  is used to create a desired resistance to motion. 
         [0050]    Embodiments described above have contemplated an anchor member  18  that comprises threads for insertion into a vertebral member V. Certainly, the pivoting head  10  may be incorporated on other types of bone screws. For example, different types of screws may be used to attach longitudinal members  15  to the sacrum S or to other parts of a vertebral member V. These include, for example, anterior and lateral portions of a vertebral body. In other embodiments, such as those shown in  FIGS. 20 and 21 , the pivoting head  10  may be implemented on other types of anchoring members. For example,  FIG. 20  shows a pivoting head  10  incorporated onto a hook-type anchor member  118 . In another embodiment shown in  FIG. 21 , the pivoting head  10  is incorporated onto another type of threaded anchor member  218  that is inserted into a plate  220  instead of a bony member. 
         [0051]    Spatially relative terms such as “under”, “below”, “lower”, “over”, “upper”, and the like, are used for ease of description to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the device in addition to different orientations than those depicted in the figures. Further, terms such as such as “first”, “second”, and the like, are also used to describe various elements, regions, sections, etc and are also not intended to be limiting. Like terms refer to like elements throughout the description. 
         [0052]    As used herein, the terms “having”, “containing”, “including”, “comprising” and the like are open ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features. The articles “a”, “an” and “the” are intended to include the plural as well as the singular, unless the context clearly indicates otherwise. 
         [0053]    The present invention may be carried out in other specific ways than those herein set forth without departing from the scope and essential characteristics of the invention. For example, embodiments described above have contemplated a pivoting head  10  having a substantially U-shaped recess in which to hold a longitudinal member  15 . Certainly other types of configurations may incorporate the articulation mechanism  40  described herein. For example, alternative embodiments of the pivoting head may have circular apertures, C-shaped clamps, and multi-piece clamps as are known to secure a longitudinal member. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.