Abstract:
A connector pivotally connects an anchor to a longitudinal member in a spinal implant. The connector body may include an oppositely disposed channel and cavity that are aligned on a common axis of the body, but isolated from each other. The channel receives the longitudinal member and the cavity receives the anchor. The anchor may include a shaft and an enlarged head that fits within the cavity. The cavity may include a narrow opening that is sized to retain the head within the cavity. The head may pivot within a wear member. The anchor may freely pivot within the cavity when a fastener mates with the receiver to maintain the longitudinal member within the channel.

Description:
BACKGROUND  
       [0001]     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.  
         [0002]     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, a flexible longitudinal member 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.  
         [0003]     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  
       [0004]     Illustrative embodiments disclosed herein are directed to a connector that pivotally connects a vertebral anchor to a longitudinal member. The connector body may be directly or indirectly attached to the anchor. The connector body may include a channel and a cavity that are aligned along a common axis. The channel is generally sized to receive the longitudinal member. The connector may have an associated fastener that mates with the channel to maintain the longitudinal member in the channel. The cavity may be positioned on an opposite side of the body from the channel while being aligned with the channel. Further, the cavity may include a narrow opening that extends into an enlarged receiving area. The receiving area may be isolated from the channel. In one embodiment, an intermediate section defines a boundary between the receiving area and the channel. The receiving area may be sized to accommodate an enlarged head of the anchor. The narrow opening may be sized to retain the head within the receiving area. The receiving area may be further sized to allow the anchor to freely pivot about the common axis, even when the fastener mates with the receiver. The connector may also include a wear member positioned within the cavity. The wear member may form its own receiving area that is isolated from the channel and sized to accommodate the head of the anchor. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]      FIGS. 1A and 1B  are perspective views of an assembly according to one or more embodiments comprising a longitudinal member attached to the spine;  
         [0006]      FIGS. 2A and 2B  are perspective views of a pivoting head coupled to an anchor member according to one embodiment;  
         [0007]      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;  
         [0008]      FIG. 4  is a perspective view of an anchor member for use with a pivoting head according to one embodiment;  
         [0009]      FIG. 5  is a perspective view of a wear member for use with a pivoting head according to one embodiment;  
         [0010]      FIG. 6  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;  
         [0011]      FIG. 7  is a side section view of a pivoting head with an anchor member and wear member inserted therein according to one embodiment;  
         [0012]      FIG. 8  is a side section view of an assembled pivoting head with an anchor member and wear member constrained therein according to one embodiment;  
         [0013]      FIGS. 9A and 9B  are top section views of a pivoting head with an anchor member and wear member inserted therein according to different embodiments;  
         [0014]      FIG. 10  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. 11  is a perspective view of a wear member for use with a pivoting head according to one embodiment;  
         [0016]      FIG. 12  is a side section view of an unassembled anchor member and wear member for use with a pivoting head according to one embodiment;  
         [0017]      FIGS. 13A and 13B  are side section views of an assembled anchor member and wear member for use with a pivoting head according to one embodiment;  
         [0018]      FIGS. 14A and 14B  are side section views showing a technique for assembling a pivoting head with an anchor member and wear member constrained therein according to one embodiment;  
         [0019]      FIG. 15  is a side section view of an assembled pivoting head with an anchor member and wear member constrained therein according to one embodiment; and  
         [0020]      FIG. 16  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  
       [0021]     The various embodiments disclosed herein are directed to non-locking, multi-axial clamping mechanisms for securing longitudinal members. 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 (e.g., L 5 ). 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.  
         [0022]     In  FIGS. 1A and 1B , the longitudinal member  15  is secured to the vertebral member V with one embodiment of a non-locking, 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 .  
         [0023]      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.  
         [0024]      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  FIG. 1 . 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.  
         [0025]     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 .  
         [0026]      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 enlarged 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 enlarged head  32  is configured to pivot within the wear member  30 , the wear member  30  and the outer surface of the enlarged head  32  may be constructed of a wear resistant material. Some suitable examples may include hardened metals, titanium carbide, cobalt chrome, polymers, and ceramics.  
         [0027]     In other embodiments, a wear resistant layer may be coated onto the enlarged 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 enlarged 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.  
         [0028]     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, 2B ). That is, since the compression forces applied by the securing member  12  are not transmitted to the articulation mechanism  40 , the anchor member  18  freely rotates about the central axis X. In one embodiment, there is no interference between the enlarged head  32  and the wear member  30 . This type of fit may minimize the sliding friction that impedes the motion of the anchor member  18  relative to the wear member  30 .  
         [0029]      FIG. 4  shows a perspective view of the enlarged head  32  of the exemplary anchor member  18 . In this illustrated embodiment, the enlarged 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 enlarged head  32  has other shapes to allow motion in fewer directions. For instance, a disc-shaped enlarged head  32  may provide motion within a desired plane. The enlarged head  32  may also include 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, 2B , and  3 .  
         [0030]      FIG. 5  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 enlarged 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.  
         [0031]     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 enlarged head  32  of the anchor member  18 . The wear member  30  is shown installed on the enlarged head  32  in  FIG. 6 .  FIG. 6  also shows relevant dimensions of the wear member  30  and the enlarged head  32 . Dimension L represents a width of the enlarged head  32  at its widest point. 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 enlarged head  32  to fit within the wear member  30  as shown in  FIG. 6 .  
         [0032]      FIG. 7  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. 8 . 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 .  
         [0033]      FIGS. 9A and 9B  show section views according to the section line IX-IX shown in  FIG. 8 .  FIG. 9A  shows one embodiment where the enlarged 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. 9A .  FIG. 9B  shows an alternative embodiment where the enlarged 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.  
         [0034]      FIG. 10  shows an alternative embodiment of the pivoting head  10   a . The section view shown in  FIG. 10  is similar to  FIG. 8  and 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.    
         [0035]      FIG. 11  shows an alternative configuration of the wear member  30   a . The outer and inner surfaces  44   a ,  46   a  may be as described above. The wear member  30   a  also includes a gap  48   a  as with the previous embodiment shown in  FIG. 5 . However, gap  48   a  does 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. The gap  48   a  is illustrated as an arc, though other shapes may be used. The gap  48   a  is sized to be wider than at least a top portion of the anchor member  18 , just beneath the enlarged head  32 , so that the anchor member  18  may be installed into the wear member  30   a  as shown in  FIGS. 12, 13A , and  13 B.  
         [0036]      FIG. 12  shows a side cross-section view of the exemplary anchor member  18  and wear member  30   a . In  FIG. 12 , the anchor member  18  and the wear member  30   a  are unassembled. To insert the anchor member  18  into the wear member  30   a , the anchor member  18  is rotated (relative to the wear member  30   a ) in the direction of the arrow labeled R. Then, as shown in  FIG. 13A , the enlarged head  32  of the rotated anchor member  18  is inserted into the wear member  30   a . Also, with the anchor member  18  rotated as shown, a stem portion  54  of the anchor member  18  just beneath the enlarged head  32  is inserted into the gap  48   a . The enlarged head  32  is inserted past the bottom surface  52   a  at point T. Once inserted in this manner, the anchor member  18  can be rotated back in the direction of the arrow labeled U and towards the orientation shown in  FIG. 13B .  
         [0037]      FIGS. 14A and 14B  show an alternative embodiment of the pivoting head  10   b  where the anchor member  18  is inserted into the base portion  34   b  and wear member  30   a  in a manner similar to that depicted in  FIGS. 13A and 13B . That is, to insert the anchor member  18  into the base portion  34   b , the anchor member  18  is rotated approximately to the position shown in  FIG. 14A . Then, the enlarged head  32  of the rotated anchor member  18  is inserted into the wear member  30   a . At the same time, the stem portion  54  is inserted into the gap  48   a  and a gap  148   a  in the base portion  34   b . Once inserted in this manner, the anchor member  18  can be rotated back in the direction of the arrow labeled U and towards the orientation shown in  FIG. 14B .  
         [0038]     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. 15 and 16 , the pivoting head  10  may be implemented on other types of anchoring members. For example,  FIG. 15  shows a pivoting head  10  incorporated onto a hook-type anchor member  118 . In another embodiment shown in  FIG. 16 , 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.  
         [0039]     Spatially relative terms such as “under”, “below”, “lower”, “over”, “upper”, and the like, are used for ease of description to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the device in addition to different orientations than those depicted in the figures. Further, terms such as “first”, “second”, and the like, are also used to describe various elements, regions, sections, etc and are also not intended to be limiting. Like terms refer to like elements throughout the description.  
         [0040]     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.  
         [0041]     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.