Patent Publication Number: US-2012029568-A1

Title: Spinal connecting members with radiused rigid sleeves and tensioned cords

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/400,504 filed Jul. 29, 2010 and U.S. Provisional Patent Application Ser. No. 61/403,915 filed Sep. 23, 2010, both of which are incorporated by reference herein. 
     This application is also a continuation-in-part of U.S. patent application Ser. No. 12/802,849 filed Jun. 15, 2010 that claims the benefit of the following U.S. Provisional Patent Application Serial Nos.: 61/268,708, filed Jun. 15, 2009; 61/270,754, filed Jul. 13, 2009; 61/336,911 filed Jan. 28, 2010; 61/395,564 filed May 14, 2010; 61/395,752 filed May 17, 2010; and 61/396,390 filed May 26, 2010; all of which are incorporated by reference herein. This application is also a continuation-in-part of U.S. patent application Ser. No. 12/924,802 filed Oct. 5, 2010 that is incorporated by reference hereon. This application is also a continuation-in-part of U.S. patent application Ser. No. 12/221,442 filed Aug. 1, 2008 that is a continuation-in-part of U.S. patent application Ser. No. 11/328,481 filed Jan. 9, 2006, both of which are also incorporated by reference herein. This application is also a continuation-in-part of U.S. patent application Ser. No. 12/148,465 filed Apr. 18, 2008 that claims the benefit of U.S. Provisional Patent Application Ser. No. 60/927,111 filed May 1, 2007, both of which are incorporated by reference herein. This application is also a continuation-in-part of U.S. patent application Ser. No. 12/661,042 filed Mar. 10, 2010 that claims the benefit of U.S. Provisional Patent Application Ser. No. 61/210,058 filed Mar. 13, 2009, both of which are incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention is directed to dynamic fixation assemblies for use in bone surgery, particularly spinal surgery, and in particular to longitudinal connecting members and cooperating bone anchors or fasteners for such assemblies, the connecting members being attached to at least two bone anchors. 
     Historically, it has been common to fuse adjacent vertebrae that are placed in fixed relation by the installation therealong of bone screws or other bone anchors and cooperating longitudinal connecting members or other elongate members. Fusion results in the permanent immobilization of one or more of the intervertebral joints. Because the anchoring of bone screws, hooks and other types of anchors directly to a vertebra can result in significant forces being placed on the vertebra, and such forces may ultimately result in the loosening of the bone screw or other anchor from the vertebra, fusion allows for the growth and development of a bone counterpart to the longitudinal connecting member that can maintain the spine in the desired position even if the implants ultimately fail or are removed. Because fusion has been a desired component of spinal stabilization procedures, longitudinal connecting members have been designed that are of a material, size and shape to largely resist bending (flexion, extension and lateral), torsion, shear, distraction and compression, and thus substantially immobilize the portion of the spine that is to be fused. Thus, longitudinal connecting members are typically uniform along an entire length thereof, and usually made from a single or integral piece of material having a uniform diameter or width of a size to provide substantially inelastic rigid support in all planes. 
     An alternative to fusion, which immobilizes at least a portion of the spine, and the use of more rigid longitudinal connecting members or other rigid structure has been a “soft” or “dynamic” stabilization approach in which a flexible loop-, S-, C- or U-shaped member or a coil-like and/or a spring-like member is utilized as an elastic longitudinal connecting member fixed between a pair of pedicle screws in an attempt to create, as much as possible, a normal loading pattern between the vertebrae in flexion, extension, side bending, distraction, compression and torsion. Another type of soft or dynamic system known in the art includes bone anchors connected by flexible cords or strands, typically made from a plastic material. Such a cord or strand may be threaded through cannulated spacers that are disposed between adjacent bone anchors when such a cord or strand is implanted, tensioned and attached to the bone anchors. The spacers typically span the distance between bone anchors, providing limits on the bending movement of the cord or strand and thus strengthening and supporting the overall system. Shear forces are not well resisted by the typical cord and spacer stabilization systems. Such tensioned cord and spacer systems may also cause facet joint compression during spinal movement, especially flexion. 
     The complex dynamic conditions associated with spinal movement create challenges for the design of elongate elastic longitudinal connecting members that exhibit an adequate fatigue strength to provide stabilization and protected motion of the spine, without fusion, and that allow for some natural movement of the portion of the spine being reinforced and supported by the elongate elastic or flexible connecting member. A further challenge are situations in which a portion or length of the spine requires a more rigid stabilization, possibly including fusion, while another portion or length may be better supported by a more dynamic system that allows for protective movement. 
     SUMMARY OF THE INVENTION 
     Longitudinal connecting member assemblies according to the invention for use between at least two bone anchors provide dynamic, protected motion of the spine and may be extended to provide additional dynamic sections or more rigid support along an adjacent length of the spine, with fusion, if desired. A dynamic longitudinal connecting member assembly according to the invention has an inner segment or core made from a cord in the disclosed embodiment, the cord being tensioned and fixed at least at either end of the assembly. The cord is received by at least one hard, rigid, inelastic segment or sleeve, the sleeve attachable to at least one bone anchor. Sleeves of the invention include a surface for direct engagement with a shank of a polyaxial bone screw. Such a surface may be configured as being concave, with a radius the same or similar to an upper convex domed surface of the shank and/or a spherical or otherwise curved surface at or near an upper surface of the shank. In some embodiments, the cord is received by at least a pair of such sleeves, each sleeve attachable to a bone anchor. In some embodiments, the sleeve or sleeves slidingly receive the cord. In other embodiments, the sleeve or sleeves are either fixed or left unfixed to the cord by the surgeon, resulting in a connecting member having variable segmental stiffness along a length thereof. A variety of embodiments according to the invention are possible. Additional sleeves may be attached to additional bone anchors and cooperate with additional cut-to-length spacers to create longer assemblies. Sleeves may also be extended to provide inelastic rod, bar or tube extensions, especially on one end. Spacers with different measures of rigidity may be connected according to embodiments of the invention. Either rigid lengths or cords may be of greater or lesser lengths for attaching to one or a plurality of bone anchors. In some embodiments, longitudinal connecting member assemblies may be dynamically loaded before insertion, or after being operatively attached to at least a pair of bone anchors along a patient&#39;s spine by tensioning the inner cord and at least partially compressing an end bumper and/or at least one spacer located between the bone anchors. Typically, the at least one spacer has some flexibility in bending, with the spacer protecting and limiting flexing movement of the inner core and providing shear resistance. 
     An object of the invention is to provide lightweight, reduced volume, low profile assemblies for use with at least two bone anchors. Furthermore, it is an object of the invention to provide apparatus and methods that are easy to use and especially adapted for the intended use thereof and wherein the apparatus are comparatively inexpensive to make and suitable for use. 
     Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. 
     The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a set of longitudinal connecting member components according to the invention, in particular a first sleeve, a second sleeve and a sleeve/rod coupler. 
         FIG. 2  is an enlarged perspective view of the first sleeve of  FIG. 1  shown assembled with a polyaxial bone screw assembly, in partial perspective view, cooperating with a slide or slipping closure top. 
         FIG. 2   a  is a partial perspective view, similar to 
         FIG. 2  showing a modified, flangeless sleeve assembled with the polyaxial bone screw assembly of  FIG. 2 . 
         FIG. 3  is a reduced and exploded front elevational view of the entire assembly of  FIG. 2  and further shown with two closure tops: the slide or slipping closure top (on left) of  FIG. 2  and an alternative cord gripping closure top (on right). 
         FIG. 4  is a reduced top plan view of the sleeve shown in  FIG. 2 . 
         FIG. 5  is a bottom plan view of the sleeve of  FIG. 4 . 
         FIG. 6  is a front elevational view of the sleeve of  FIG. 4 . 
         FIG. 7  is a side elevational view of the sleeve of  FIG. 4 . 
         FIG. 8  is an enlarged cross-sectional view taken along the line  8 - 8  of  FIG. 4 . 
         FIG. 9  is an enlarged and partial side elevational view of the assembly shown in  FIG. 2  with portions broken away to show the detail thereof and shown with a cord (in phantom). 
         FIG. 10  is an enlarged and partial side elevational view of the second sleeve illustrated in  FIG. 1  shown with the bone screw assembly of  FIG. 3  in side elevation, and further assembled with the alternative cord gripping closure top of  FIG. 3 , also shown in side elevation. 
         FIG. 11  is a partial side elevational view of the assembly shown in  FIG. 10  with portions broken away to show the detail thereof and further shown with a cord (in phantom). 
         FIG. 12  is a reduced perspective view of the sleeve/rod coupler of  FIG. 1  shown with the bone screw assembly of  FIG. 3  and the alternative cord gripping closure top of  FIG. 3 , also in reduced perspective view. 
         FIG. 13  is an enlarged and partial front elevational view of the assembly of  FIG. 12 . 
         FIG. 14  is an enlarged and partial side elevational view of the assembly of  FIG. 12  with portions broken away to show the detail thereof. 
         FIG. 15  is a partial perspective view of a longitudinal connecting member assembly that includes sleeves of the invention, a cord, an end blocker assembly and compressible spacers and is shown with each sleeve attached to a bone screw of  FIG. 3 , shown in reduced and partial perspective view and partially exploded to show sliding or fixed cooperation of the cord with the closure tops shown in  FIG. 3 . 
         FIG. 16  is a perspective view of another set of longitudinal connecting member components according to the invention, in particular a first sleeve with parallel flanges, a second sleeve with parallel flanges and tubular extensions, a third sleeve with lordotic flanges and tubular extensions and a sleeve/rod coupler. 
         FIG. 17  is a partial perspective view of the first sleeve of  FIG. 16  shown in a stage of assembly with a polyaxial bone screw having portions broken away to show the detail thereof. 
         FIG. 18  is a partial perspective view, with portions broken away, similar to  FIG. 17 , showing the polyaxial bone screw of  FIG. 17  fully assembled with the first sleeve and the slide or slipping closure of  FIGS. 2 and 3 . 
         FIG. 19  is an enlarged and partial side elevational view of the assembly of  FIG. 18  with portions broken away to show the detail thereof and showing the bone screw shank disposed at an angle with respect to the receiver thereof. 
         FIG. 20  is a reduced top plan view of the second sleeve shown in  FIG. 16 . 
         FIG. 21  is a bottom plan view of the sleeve of  FIG. 20 . 
         FIG. 22  is a side elevational view of the sleeve of  FIG. 20 . 
         FIG. 23  is a front elevational view of the sleeve of  FIG. 20 . 
         FIG. 24  is a cross-sectional view taken along the line  24 - 24  of  FIG. 20 . 
         FIG. 25  is an enlarged and partial perspective view of the assembly of  FIG. 18 , but including the second sleeve of  FIG. 20  in lieu of the first sleeve shown in  FIG. 18  and with portions broken away to show the detail thereof. 
         FIG. 26  is a partial perspective view of the assembly of  FIG. 25 , but including the third lordotic sleeve of  FIG. 16  in lieu of the second sleeve shown in  FIG. 25  and with portions broken away to show the detail thereof. 
         FIG. 27  is a reduced and partial side elevational view of the assembly of  FIG. 26  with portions broken away to show the detail thereof. 
         FIG. 28  is an alternative perspective view of the sleeve/rod coupler of  FIG. 16 . 
         FIG. 29  is a side elevational view of the sleeve/rod coupler of  FIG. 28  with portions broken away to show the detail thereof. 
         FIG. 30  is another perspective view of the sleeve/rod coupler of  FIG. 28  shown assembled with the bone screw assembly of  FIG. 18  in lieu of the sleeve shown in  FIG. 18 , the bone screw assembly shown in partial, perspective view and with portions broken away to show the detail thereof. 
         FIG. 31  is a partial perspective view of another longitudinal connecting member assembly that includes sleeves of the invention the same or similar to those shown in  FIG. 16 , a cord, an end blocker assembly and compressible spacers and is shown with each sleeve attached to a bone screw of  FIG. 18 , shown in reduced and partial perspective view and partially exploded to show sliding or fixed cooperation of the cord with the closure tops shown in  FIG. 3 . 
         FIG. 32  is partial front elevational view of an alternative bone screw shank for use with longitudinal connecting members and sleeves of the invention, the shank spherical head hemisphere being shown in phantom. 
         FIG. 33  is a perspective view of the shank of  FIG. 32 . 
         FIG. 34  is an enlarged and partial side elevational view of the assembly of  FIG. 18  with portions broken away, similar to  FIG. 19  with the exception that the bone screw shank shown in  FIG. 19  has been replaced with the bone screw shank of  FIGS. 32 and 33 , also with portions broken away to show the detail thereof. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. It is also noted that any reference to the words top, bottom, up and down, and the like, in this application refers to the alignment shown in the various drawings, as well as the normal connotations applied to such devices, and is not intended to restrict positioning of the connecting member assemblies of the application and cooperating bone anchors in actual use. 
     With reference to  FIGS. 1-15 , and particularly to  FIG. 15 , polyaxial bone screws, generally  1  are shown cooperating with longitudinal connecting member assemblies such as the assembly, generally  201  of the present invention, that include sleeves, generally  204  of the present invention, shown in greater detail in  FIGS. 1-14 . It is noted that the particular polyaxial bone screw  1  shown in  FIGS. 1-15  is an example of a bone screw for use with the present invention and other types of bone screws, for example screws having top or bottom loaded shanks and/or different types of structure for capturing the shank within the receiver may be used. The bone screw  1  is described in detail in U.S. patent application Ser. No. 12/924,802 filed Oct. 5, 2010 (U.S. Patent Application Publication No. 2011/0098755 published Apr. 28, 2011, hereafter identified as the &#39;755 publication) that is incorporated by reference herein. Briefly, with particular reference to  FIG. 3 , the bone screw assembly  1  includes a shank  4  having a body  6  for insertion into a vertebra, and an upper portion or head  8 . The bone screw assembly further includes a receiver  10  for the pivotable housing of the shank head  8  with respect to the receiver  10 , and a split ring shank retainer  12  for a pop-on or snap-on capturing of the shank head  8  within the receiver  10 . The receiver is sized and shaped to mate with a closure top  18  fully described in the &#39;755 publication that is utilized in the present invention as a cord slip or sliding closure, or with a cord fixing closure top  18 ′ that will be described in greater detail below. The shank head  8  has an outer partially spherical or curved surface  34  and a radiused, domed or otherwise curved top  40  located on a drive feature  41 , the surface  40  being spaced from the outer spherical surface  34 , the domed top  40  typically being sized and shaped for direct engagement with a rigid rod (not shown). A radius of the top  40  is typically not the same as a radius of the spherical head surface  34 . In some embodiments, the top  40  and the spherical head surface  34  have the same radius. The spherical surface  34  is spaced from the shank drive feature  41 . Sleeves of the present invention include a curved or radiused concave surface or surfaces shaped to advantageously frictionally mate with either the curved top surface  40  or the curved surface  34  to allow for a stable frictional engagement between the sleeve  204  (or the sleeve  1204  described below) and the shank  4  at a variety of articulations of the shank  4  with respect to the receiver  10 . 
     With further reference to  FIG. 15 , the polyaxial bone screws  1  are shown with the dynamic stabilization longitudinal connecting member assembly  201  that includes a plurality of the hard, rigid, inelastic, flanged sleeves, generally  204  through which a tensioned cord  206  ex tends. The cord  206  is shown in phantom in  FIGS. 9 and 11 , and see, for example,  FIG. 15 , that also illustrates a cooperating cord blocker or fixer  210  with a cord fixing set screw  212 , an elastic end bumper  214 , and elastic or inelastic spacers  216  that are each located about the cord  206  and are disposed between each pair of bone anchors  1  of the overall assembly  201 . The tubular bumper  214  and tubular spacers  216  shown in  FIG. 15  are transparent, allowing for viewing of the sleeves, generally  204 , and the tensioned cord  206 . However, it is foreseen that in other embodiments, the spacers  216  may be made of materials that may not be transparent or translucent. Cords, blockers and set screws, elastic bumpers and spacers that are the same or similar to the cord  206 , blocker  210  and set screw  212 , elastic bumper  214  and spacers  216  are described in detail in U.S. patent application Ser. No. 12/802,849 incorporated by reference herein (U.S. Publication No. 2010/0331887 published Dec. 30, 2010). 
     Also as shown in  FIG. 15 , two types of bone screw closures are utilized, either the slide or slipping closure top  18  described in the &#39;755 publication or the cord gripping closure top  18 ′ that is described in detail in U.S. patent application Ser. No. 12/802,849 already incorporated by reference herein. The top  18 ′ only differs from the top  18  in that the top  18 ′ does not include a bottom rim or bottom point, but rather a cord penetrating extension  300  for gripping the cord  206 . The extension structure  300  is illustrated has being integral with the closure, cylindrical in shape and having a planar bottom surface  301 . It is noted that the extension  300  may be made of other geometric shapes and may include a more pointed surface or surfaces. 
     With reference to  FIG. 9 , the slide or slip closure top  18  engages a respective sleeve  204 A but not the cord  206 , allowing the cord to slip or slide within the polyaxial screw  1 . With reference to  FIG. 11 , the gripping structure  300  of the grip closure top  18 ′ extends through the sleeve  204 B and grips and fixes the cord  206  against a surface of the sleeve  204 B and thus fixes the cord  206  in relation to the cooperating polyaxial screw  1 . 
     With further reference to  FIG. 15 , tubular extensions of some of the sleeves  204  may extend into and through some or all of the spacers  216 . Such spacer overlap with respect to a respective sleeve provides advantageous anti-shear support for the connecting member  201 . A portion of the cord blocker  210  also extends into a bore of the bumper  214 . The bumper  214  also extends about the cord  206  and is typically made from an elastomer while the outer spacers  216 , although typically elastomeric, may be made from a material with a different durometer, typically (but not always) being tougher and less compressible than the material of the bumper  214 . The sleeves  204  and in some embodiments the spacers  216 , are typically made from a hard, non-elastic material, such as a metal or metal alloy, for example, such as cobalt chromium. Flanged portions of the sleeves  204  are located on either side of the bone screw receivers  10 , the flanges abutting against the spacers  216  or the bumper  214 , the flanges extending radially outwardly to an extent to fully engage ends of adjacent spacers or the bumper, resulting in a stable, secure, substantially full contact between the individual elements of the assembly  201 . Furthermore, the flanges allow for assembly and dynamic setting of the connector  201  prior to implantation, if desired, with the cord  206  being placed in tension and at least the bumper  214  being placed in compression. In some embodiments of the invention, tensioning of the cord  206  and compression of the bumper  214  and optionally the spacers  216  may be performed after the assembly  201  is attached to the bone screws  1 . 
     Sleeves  204  of the invention may be provided with or without tubular extensions, on one or both sides thereof, and with different lengths of tubular extensions, as best shown in  FIG. 15 . With particular reference to  FIG. 1 , three different types of sleeves  204 , shown without tubular extensions, are illustrated. They are a parallel flanged sleeve  204 A, an angled or lordotic sleeve  204 B and a transition sleeve  204 C that includes a rod/cord coupler. 
     With particular reference to  FIGS. 2 ,  3  and  9 , the bone screw assembly  1  is illustrated with the sleeve  204 A. With particular reference to  FIGS. 4-8 , the sleeve  204 A further includes a body portion  234  generally sized and shaped for being received within the polyaxial bone screw  1  receiver  10  and about a cord  206 . A through bore  236  extends centrally through the body portion  234 , the bore  236  being sized and shaped to slidingly receive the cord  206 . The body portion  234  further includes a pair of spaced radially extending flanges  237  and  238  with a partially cylindrical and partially planar body portion being located therebetween, the body portion having a slightly enlarged or protruding portion or portions illustrated as opposed faceted or partially cylindrical and partially planar extensions or body portions  239 , the portions  239  sized and shaped to closely fit within inner arm surfaces of the bone screw receiver  10 . The portions  239  center the sleeve within the bone screw receiver  10  and also advantageously strengthen the sleeve, resulting in better load transfer. The body  234  with centering structure  239  further includes a bottom surface  240  having a curved, concave surface, illustrated as a partially spherical surface  241  configured to closely match in size and shape and thus cooperate and frictionally engage the domed surface  40  of the shank upper portion  8  in a variety of angular configurations, as shown in  FIGS. 9 and 11 , for example. The illustrated surface  241  is smooth, having the same or similar radius as the domed surface  40  of the shank  4 , but it is foreseen that the surface  241  (and/or the surface  40  of the shank) may be roughened or include ridges or points for penetration into the shank surface  40 . 
     In some embodiments of sleeves of the invention, the flanges  237  and  238  may be reduced or eliminated as shown by the modified sleeve  204 A′ shown in  FIG. 2   a  having an outer planar surface  242 ′ being flush or nearly flush to outer surfaces of the receiver  10  that form the receiver U-shaped channel. The sleeve  204 A′ is otherwise identical to the sleeve  204 A shown in the other figures. The centering of the sleeve  204 A′ with respect to the bone screw receiver  10  is performed by the portion or portions  239 . 
     In the embodiment shown in the figures (other than  FIG. 2   a .), the flanges  237  and  238  are substantially cylindrical having opposed inner side surfaces  242  spaced and shaped for closely receiving the bone screw  1  receiver  10 . Each flange also has an outer annular planar surface  242 A. The illustrated flanges  237  and  238  include a lower cut-out, partially defined by the surfaces  242 , allowing for a close fit between inner flange surfaces  242  and the receiver  10  at or near outer surfaces partially defining the receiver U-shaped channel and the receiver base  60 . The body portion  239  as well as flange surfaces  242  may be sized and shaped to be receivable by and frictionally fixed to a variety of monoaxial or polyaxial screw heads or receivers, including the receiver  10 . A bore  243  is formed in the body  234  between the flanges  237  and  238 , the bore  243  being transverse to and communicating with the through bore  236 . The bore  243  is sized and shaped to receive the extension structure  300  of the closure top  18 ′. Curved inner surfaces  244  surrounding and adjacent the bore  243  and partially defining upper portions of the flanges  237  and  238  are sized and shaped to closely receive both the closure tops  18  and  18 ′ as shown in  FIGS. 9 and 11 . The sleeve  204 A is shown with the closure top  18  in  FIGS. 2 and 9 , and thus, as best illustrated in  FIG. 9 , the top  18  engages the surfaces  244  but does not extend down into the through bore  236 , allowing for the cord  206  (shown in phantom) to slide freely there within. As illustrated in  FIG. 11 , the closure top  18 ′ is inserted in the sleeve  204 B with the closure top body engaging surfaces  244 ′ as well as the extension  300  extending into and through the sleeve  204 B with the surface  301  frictionally gripping a cord  206  (shown in phantom) against an internal surface defining the through bore  236 ′, and thus placing such cord  206  in fixed relation with the cooperating bone screw receiver  10 . 
     The sleeves, generally  204 , as well as the cord blocker  210  with set screw  212  may be made from a variety of inelastic materials, including, but not limited to metals, metal alloys, including cobalt chromium, and inelastic plastics including, but not limited to plastic polymers such as polyetheretherketone (PEEK), ultra-high-molecular weight-polyethylene (UHMWP), polyurethanes and composites, including composites containing carbon fiber and layers of different materials. 
     With reference to  FIGS. 1 ,  10  and  11 , the lordosing or lordotic sleeve  204 B is illustrated. The sleeve  204 B is identical to the sleeve  204 A with the exception that flanges  237 ′ and  238 ′ are provided that slope at an angle, inwardly towards the bone screw receiver  10  as best shown in  FIG. 10  and also in the assembly  201  shown in  FIG. 15  that illustrates the use of a plurality of lordotic sleeves similar to the sleeve  204 B, many of which further include tubular extensions on one or both ends thereof. All of the other features and structure of the sleeve  204 B that are identical to the sleeve  204 A are identified with the same reference numbers but with a prime symbol (“′”) located thereafter. For example, the sleeve  204 B includes a body  234 ′, a through bore  236 ′, centering extension portions  239 ′, a bottom radiused surface  241 ′, lower inner flange surfaces  242 ′, a bore  243 ′ and upper inner flange surfaces  244 ′ that are the same or similar in form and function to the respective body  234 , through bore  236 , centering extension portions  239 , radiused surface  241 , lower inner flange surfaces  242 , bore  243  and upper inner flange surfaces  244  of the sleeve  204 A previously described herein. 
     With reference to  FIG. 1  and  FIGS. 12-14 , the sleeve and rod/cord coupler  204 C includes sleeve body  234 ″, a partial through bore  236 ″, a single flange  238 ″, centering extension portions  239 ″, a bottom radiused surface  241 ″, lower inner flange surfaces  242 ″, a bore  243 ″ and upper inner flange surfaces  244 ″ that are substantially similar in form and function to the respective sleeve body  234 , bore  236 , flange  238 , centering portions  239 , radiused surface  241 , lower inner flange surfaces  242 , bore  243  and upper inner flange surfaces  244  of the sleeve  204 A previously described herein. At an end opposed to the flange  238 ″, the body portion  234 ″ is integral with an elongate solid rod portion  250 . Also, formed in the body portion  234 ″ is an aperture or through bore  251  transverse to and communicating with the bore  236 ″, the through bore  251  being sized and shaped to closely receive a cord holding pin  252 . The pin  252 , if used, extends completely through the cord  206 , independently fixing the cord  206  to the sleeve  204 C. Alternatively, in some embodiments of the invention, the pin  252  is not used and the closure top  18 ′ is inserted within a bore  243 ″ of the sleeve/coupler  204 C to fix the cord  206  to the sleeve  204 C. Although  FIG. 14  illustrates using both the closure top  18 ′ and the pin  252 , this is for the purpose of illustration and is not necessary for the practice of the invention. In the illustrated embodiment, the bores  243 ″ and 251 are substantially parallel to one another. The rod portion  250  may be provided in a variety of lengths (or cut to length) to cooperate with one or more bone screws to provide a rigid support end to a dynamic assembly, such as the assembly  201  shown in  FIG. 15 . 
     The assembly  201  may be assembled as follows: First, after the bone screws  1  are implanted, the distance between the screws is measured. Thereafter, the spacers  216  are cut to a desired length based upon the measurement made between the bone screws. Because the sleeves  204  are made from a hard material, typically a metal or metal alloy, if it is desired to use sleeves with tubular extensions as shown in  FIG. 15 , it is not practical to cut the tubular portions to a desired length during the surgical procedure. Therefore, a variety of sleeves  204  are typically provided to end users having at least three different tube portion lengths. 
     With particular reference to  FIG. 15 , sleeves  204 , spacers  216 , cord blockers  210  and, if desired, a rod/sleeve coupler  204 C are fed onto a cord  206  in a desired order to result in the assembly of  FIG. 15  and in a manner as described in greater detail in the patent application Ser. No. 12/802,849 incorporated by reference herein. It is noted that the cord  206  is typically much longer than shown in the drawing figures and then cut to length near an end thereof after being fully assembled with the remaining elements of the assembly  201 , tensioned and fixed to the blocker  210 . In some embodiments of the invention, single blockers, bumper/blocker combinations or rod/cord couplers (or various different combinations thereof) may be placed on either end of the assembly and the cord pre-tensioned before the assembly is implanted in and between the already implanted bone screws  1 . In other embodiments, such as the assembly shown in  FIG. 15 , a loosely assembled connector may be placed in contact with and between the implanted bone screws  25 , with the set screw  212  engaged with the cord  206  enough to prevent the elements from slipping off one end of the cord  206 . But, unlike the illustration of  FIG. 15 , the cord  206  would not yet be tensioned and thus the individual elements would most likely be more spread apart along the cord more than is illustrated in the drawing figure. Also, the cord  206  would be much longer at this time so that the cord may be grasped and tensioned after the assembly is fixed to the bone screws  1 . 
     The assembly  201  is implanted by inserting each sleeves  204  into to one of the bone screws  1 . Closure tops  18  or  18 ′ are then inserted into and advanced between the arms of the bone screw receiver  10  so as to bias or push against the respective sleeves  204 . A driving tool (not shown) is inserted into each closure drive to rotate and drive the respective closure top  18  or  18 ′ into the respective receiver  10 . Each shank dome surface  40  is engaged by the cooperating sleeve surface  241 ,  241 ′ or  241 ″ and pushed downwardly when the closure top  18  or  18 ′ pushes downwardly on the sleeve  204 A, B or C. The downward pressure on the shank  4  in turn urges the shank spherical surface  34  into locking engagement with the retainer  12  that in turn expands into locking engagement with the receiver  10 . A tensioning tool (not shown) known in the art may then be used to pull upon and put tension on the cord  206 . It is noted that in the particular embodiment shown in  FIG. 15 , two gripping closures  18 ′ are shown. Thus, it may be desirable to lock only one of the closure  18 ′ initially and thereafter lock the other after tensioning, or alternatively perform more than one tensioning step. The cord  206  is preferably tensioned until the bumper compresses and then the set screw  212  is rotated and driven into the blocker  210  and up against the cord  206  using a driving tool (not shown) engaged with an inner drive of the screw  212 . The blocker  210  advantageously includes opposed planar sides allowing for the placement of a counter-torque tool for holding the blocker during tensioning and fixing of the cord  206  within the blocker. As explained in U.S. patent application Ser. No. 12/802,849, the set screw  212  and blocker  210  combination includes a limited travel feature such that the set screw is locked into place at a location that firmly holds but does not damage the cord  206 . The cord  206  is ultimately trimmed to a desired length close to each end of the connector  201 . 
     The assembly  201  is thus substantially dynamically loaded and oriented relative to the cooperating vertebra, providing relief (e.g., shock absorption) and protected movement with respect to flexion, extension, distraction and compressive forces placed on the assembly  201  and the connected bone screws  1 . In some embodiments of a connecting member according to the invention, the sleeve and rod combination  204 C may be used at one end (or both ends) of the assembly to provide a hard, non-elastic elongate portion for attachment to an additional bone screw or screws, if needed, to provide a connecting member with both dynamic, elastic segments as well as a longer rigid inelastic segment. 
     If removal of the assembly  201  from any of the bone screw assemblies  1  is necessary, or if it is desired to release the assembly at a particular location, disassembly is accomplished by using the driving tool (not shown) with a driving formation cooperating with the closure structure  18  or  18 ′ internal drive to rotate and remove the closure structure from the respective receiver  10 . Disassembly is then accomplished in reverse order to the procedure described previously herein for assembly. 
     Eventually, if the spine requires more rigid support, the connecting member assembly  201  according to the invention may be removed and replaced with another longitudinal connecting member, such as a solid rod or bar, having the same width or diameter as body portions of the sleeves  204 , utilizing the same receivers  10  and the same or similar closure structures  18 . Alternatively, if less support is eventually required, a less rigid, more flexible assembly, for example, an assembly having spacers  216  and a bumper or bumpers  214  made of a softer more compressible material than the spacer and bumper being replaced thereby, also utilizing the same bone screws  1  and the closures  18 ′ as well as the closure  18 . 
     With reference to  FIGS. 16-34 , another embodiment of connecting member sleeves according to the invention, generally  1204 , is shown. The sleeves  1204  are substantially similar to the sleeves  204  previously described herein and with the exception of the size and placement of a radiused lower surface that engages a larger spherical surface of a cooperating bone anchor shank (e.g., the spherical surface  34  of the shank  4  or surface  34 ′ of a shank  1 ′) than the domed surface  40  previously described herein with respect to the bone screw assembly  1 . With particular reference to  FIG. 31 , polyaxial bone screws, generally  1 ′ are shown cooperating with a longitudinal connecting member assembly of the invention, generally  1201 , that includes the sleeves, generally  1204  of the present invention that are shown in greater detail in  FIGS. 16-30  and  34 . The polyaxial bone screw  1 ′ shown in  FIGS. 16-31  is similar, but not identical to the bone screw  1  previously described herein. The screw  1 ′ is also described in detail in U.S. patent application Ser. No. 12/924,802, already incorporated by reference herein. Briefly, with particular reference to  FIGS. 17 ,  18  and  19 , the bone screw assembly  1 ′ includes a shank  4 ′ having a body  6 ′ for insertion into a vertebra, and an upper portion or head  8 ′. The bone screw assembly further includes a receiver  10 ′ for pivotable housing the shank head  8 ′ with respect to the receiver  10 ′ and a split ring shank retainer  12 ′ for capturing the shank head  8 ′ within the receiver  10 ′. The receiver is sized and shaped to mate with the slip closure top  18  or the grip closure top  18 ′ fully described in the &#39;755 publication and previously described hereon with respect to the bone screw  1 . The shank head  8 ′ has an outer partially radiused or spherical surface  34 ′ and a radiused, domed or otherwise curved top  40 ′ located on a drive feature  41 ′, the same or substantially similar to the respective head outer surface  34 , domed top  40  and drive feature  41  previously described herein with respect to the bone screw  1 . 
     With further reference to  FIG. 31 , the polyaxial bone screws  1 ′ are shown with the dynamic stabilization longitudinal connecting member assembly  1201  that includes a plurality of the hard, inelastic, flanged sleeves, generally  1204  through which a tensioned cord  1206  extends. The cord  1206  is substantially the same or similar to the cord  206  previously described herein. The assembly further includes a cord blocker  1210  with set screw  1212 , a bumper  1214  and spacers  1216  substantially the same or similar in form and function to the respective blocker  210 , set screw  212 , bumper  214  and spacers  216  previously described herein with respect to the assembly  201 . Tubular extensions of some of the sleeves  1204  are shown extending into and through some of the spacers  1216 . Flanged portions of the sleeves  1204  are located on either side of the bone screw receivers  10 ′, the flanges abutting against the spacers  1216  or the bumper  1214 , the flanges extending radially outwardly to an extent to fully engage ends of adjacent spacers or the bumper, resulting in a stable, secure, substantially full contact between the individual elements of the assembly  1201 . Furthermore, the flanges allow for assembly and dynamic setting of the connector  1201  prior to implantation, if desired, with the cord  1206  being placed in tension and at least the bumper  1214  being placed in compression, such arrangements having blockers, rod/cord couplers or other fixing structure attached to the cord at either end of the assembly. In some embodiments of the invention, tensioning of the cord  1216  and compression of the bumper  1214 , if used and optionally the spacers  1216  may be performed after the assembly  1201  is attached to the bone screws  1 ′. 
     Sleeves  1204  of the invention may be provided with or without tubular extensions, on one or both sides thereof, and with different lengths of tubular extensions, as best shown in  FIG. 31 . With particular reference to  FIG. 16 , three different types of sleeves  1204  are shown. They are a parallel flanged sleeve  1204 A, as well as a parallel flanged sleeve  1204 A′ having tubular extensions  1230 , an angled or lordotic sleeve  1204 B, shown with tubular extensions  1230  and a transition sleeve  1204 C that includes a rod/cord coupler. 
     With particular reference to  FIGS. 17-19 , the bone screw assembly  1 ′ is illustrated with the sleeve  1204 A. Because the sleeves  1204 A and  1204 A′ are identical with the exception that the sleeve  1204 A′ further includes the cylindrical tubes  1230  on either side thereof, the same reference numerals are otherwise used for the sleeves  1204 A and  1204 A′. With further reference to  FIGS. 19-25 , the sleeves  1204 A and  1204 A′ further each include a body portion  1234  generally sized and shaped for being received within the polyaxial bone screw receiver  10 ′ and about a cord  1206 . A through bore  1236  extends centrally through the body portion  1234 , the bore  1236  being sized and shaped to slidingly receive the cord  1206 . The body portion  1234  further includes a pair of spaced radially extending flanges  1237  and  1238  with a partially cylindrical and partially planar body portion being located therebetween, the body portion having a slightly enlarged or protruding portion or portions illustrated as partially cylindrical surface portions  1239  sized and shaped to closely fit and thus center the sleeve at a desired location within the inner arm surfaces of the bone screw receiver  10 ′. In addition to generally centering the sleeve within a bone screw receiver or other bone anchor, the portions  1239  advantageously strengthen the sleeve, resulting in better load transfer. The body  1234  with centering structure  1239  further includes a bottom surface  1240  having a curved, concave surface, illustrated as a spherical surface  1241  configured to closely cooperate and frictionally engage the spherical surface  34 ′ of the shank upper portion  8  at a variety of angles or articulations of the shank with respect to the sleeve, one of which is shown, for example, in  FIG. 19 . The illustrated surface  1241  has the same or substantially similar radius as the shank surface  34 ′ and is smooth. It is foreseen that the surface  1241  may be roughened or include ridges or points for penetration into the shank surface  34 ′. 
     Similar to what is shown in  FIG. 2   a  with respect to the sleeve  204 A′, in some embodiments, the flanges  1237  and  1238  may be reduced or eliminated as the centering of the sleeve with respect to the bone screw receiver  10 ′ may be performed solely by the portion or portions  1239 . In the illustrated embodiment, the flanges  1237  and  1238  are substantially cylindrical having opposed lower curved inner side surfaces  1242  spaced for closely receiving outer surfaces of the bone screw receiver  10 ′ near the base  60 ′ thereof. The illustrated flanges  1237  and  1238  each include a lower cut-out, partially formed by the inner side surfaces  1242  that allows for a close fit between the inner flange surfaces  1242  and the receiver  10 ′ surfaces. The body portion  1239  as well as flange surfaces  1242  may be sized and shaped to be receivable by and frictionally mated to a variety of monoaxial or polyaxial screw heads or receivers, including, but not limited to the receiver  10 ′ as well as the receiver  10  previously discussed herein. A bore  1243  is formed in the body  1234  between the flanges  1237  and  1238 , the bore  1243  being transverse to and communicating with the through bore  1236 . Upper curved surfaces  1244  surrounding and adjacent the bore  1243  and partially defining inner upper portions of the flanges  1237  and  1238  are sized and shaped to closely receive both the closure tops  18  and  18 ′ as shown, for example, in  FIG. 19 . With specific reference to  FIG. 19 , the non-gripping closure top  18  engages the surfaces  1244  but does not extend through the bore  1243  and thus does not extend down into the through bore  1236 , allowing for the cord  1206  (shown in phantom) to slide freely within the bore  1236 . Similar to what is shown with respect to the sleeves  204 , as illustrated in  FIG. 11 , when the closure top  18 ′ is inserted into any of the sleeves  1204  with the extension  300  extending into and through the sleeve, the surface  301  frictionally grips the cord  1206  against an internal surface defining the through bore  1236 , and thus places such cord  1206  in fixed relation with the cooperating bone screw receiver  10 ′. 
     The sleeves, generally  1204 , as well as the cord blocker  1210  with set screw  1212  may be made from a variety of inelastic materials, including, but not limited to metals, metal alloys, including cobalt chromium, and inelastic plastics including, but not limited to plastic polymers such as polyetheretherketone (PEEK), ultra-high-molecular weight-polyethylene (UHMWP), polyurethanes and composites, including composites containing carbon fiber and layers of different materials. 
     With reference to  FIGS. 26 and 27 , the lordosing or lordotic sleeve  1204 B is illustrated. The sleeve  1204 B is identical to the sleeve  1204 A′ with the exception that flanges  1237 ′ and  1238 ′ are provided that slope at an angle, inwardly towards the bone screw receiver  10 ′ as best shown in  FIG. 27  and also in the assembly  1201  shown in  FIG. 31  that illustrates the use of a plurality of lordotic sleeves similar to the sleeve  1204 B, some of which further include tubular extensions  1230 ,  1230 ′, no extensions, and/or longer sleeve extensions or combinations of short, long and/or no extensions on the ends thereof. Unlike the sleeves  1204 A and  1204 A′ that have the inner bore  1236  extending along a single central longitudinal axis, as best shown in  FIG. 27 , the sleeves  1204 B form an inner bore  1236 ′ that is defined by an intersection of two axes A′ and B′, the intersection located centrally within the sleeve. 
     With reference to  FIG. 16  and  FIGS. 28-30 , the sleeve and rod/cord coupler  1204 C includes a sleeve body  1234 ″, a partial through bore  1236 ″, a single flange  1238 ″, centering extension portions  1239 ″, a bottom radiused surface  1241 ″, lower inner flange surfaces  1242 ″, a bore  1243 ″ and upper inner flange surfaces  1244 ″ that are substantially similar in form and function to the respective sleeve body  1234 , bore  1236 , flange  1238 , centering portions  1239 , radiused surface  1241 , lower inner flange surfaces  1242 , bore  1243  and upper inner flange surfaces  1244  of the sleeves  1204 A and  1204 A′ previously described herein. At an end opposed to the flange  1238 ″, the body portion  1234 ″ is integral with an elongate solid rod portion  1250 . Also, formed in the body portion  1234 ″ is an aperture or through bore  1251  disposed transverse to and communicating with the bore  1236 ″, the through bore  1251  sized and shaped to closely receive a cord holding pin (not shown) the same or similar to the pin  252  illustrated in  FIGS. 13 and 14 . The pin, if used, extends completely through the cord  1206 , independently fixing the cord  1206  to the sleeve  1204 C. Alternatively, in some embodiments of the invention, the pin  1252  is not used and a closure top  18 ′ may be inserted within the bore  1243 ″ of the sleeve/coupler  1204 C to fix the cord  1206  to the sleeve  1204 C. In the illustrated embodiment, the bores  1243 ″ and  1251  are substantially parallel to one another. The rod portion  1250  may be provided in a variety of lengths (or cut to length) to cooperate with one or more bone screws to provide a rigid support end to a dynamic assembly, such as the assembly  1201  shown in  FIG. 31 . 
     In use, sleeves generally  1204 , of the invention are assembled into a longitudinal connecting member, such as the member  1201  illustrated in  FIG. 31  in a manner identical or substantially similar to what has been previously described herein with respect to the assembly  201  shown in  FIG. 15 . Disassembly and replacement with a harder, stiffer connector or a softer connector is also accomplished in a manner the same or similar to what has already been described herein with respect to the assembly  201 . Briefly, the assembly  1201  is implanted by inserting each of the sleeves  1204  into to one of the bone screws  1 ′ (or the bone screws  1  or other cooperating bone anchors). Closure tops  18  or  18 ′ are then inserted into and advanced between the arms of the bone screw receiver  10 ′ so as to bias or push against the respective sleeves  1204 . A driving tool (not shown) is inserted into each bone screw closure drive to rotate and drive the respective closure top  18  or  18 ′ into the respective receiver  10 ′. Each shank head partially spherical surface  34 ′ is engaged by the cooperating sleeve surface  241 ,  241 ′ or  241 ″ and pushed downwardly when the closure top  18  or  18 ′ pushes downwardly on the sleeve  1204 A,  1204 A′,  1204 B or  1204 C. The downward pressure on the shank  4 ′ in turn urges the shank spherical surface  34 ′ into locking engagement with the retainer  12 ′ that in turn expands into locking engagement with the receiver  10 ′. A tensioning tool (not shown) known in the art may then be used to pull upon and put tension on the cord  1206  for the first time, or may be used to place additional tension on an already pre-tensioned connecting member assembly that includes a blocker  1210  or blocker/bumper  1214  combination at either end thereof, or a blocker or blocker/bumper at one end thereof and a rod/cord coupler  1204 C at an opposite end thereof. 
     With reference to  FIGS. 32-34 , an alternative bone screw shank  4 ″ is illustrated that includes an internal drive feature  41 ″ in lieu of the domed drive  41 ′ shown in  FIGS. 19 and 27 . The shank  4 ″ otherwise includes a body  6 ″ and an upper portion or head  8 ″ with an outer spherical surface  34 ″ that is the same or substantially similar in form and function to the respective body  6 ′, head  8 ′ and spherical surface  34 ′ previously described herein with respect to shank  4 ′ of the bone screw assembly  1 ′. The shank  4 ″ further includes a rim or frusto-conical surface  40 ″ sized and shaped to allow for adequate clearance between the shank head  8 ″ and the sleeve, generally  1204  during pivoting of the shank  4 ″ with respect to the receiver  10 . 
     In other embodiments, the surface  34 ″ may extend to the drive feature  41 ″ and the concave spherical lower surface  1241  of the sleeve may be extended in a direction toward the bore  1236  to provide greater clearance for the spherical bone shank head during pivoting thereof. In  FIG. 34 , the shank  4 ″ is shown attached to and cooperating with the receiver  10 ′ and the retainer  12 ′ of the bone screw  1 ′ and also with a slightly modified version of the sleeve  1204 A, as well as the closure top  18  in a manner the same or substantially similar to what is shown in  FIG. 19  and described previously herein with respect to the sleeve  1204 A and the bone screw assembly  1 ′. Because the sleeve  1204 A includes the radiused surface  1241  that engages the head spherical surface  34 ″ (or the surface  34 ′ of the bone screw assembly  1 ′ or the surface  34  of the bone screw assembly  1 ), a variety of bone screws having shanks with different driving and bone screw shank capturing and securing features may be used with sleeves of the invention. Thus the bone screw assembly shown in  FIG. 34  that has the shank  4 ″ that includes the internal drive feature  41 ″ should not be considered limiting, but rather as an additional embodiment of a cooperating bone screw of which there is a wide variety. 
     The illustrated drive feature or imprint  41 ″ is counter sunk and includes a stepped or graduated annular seating surface or base. The base surface could be substantially planar. The illustrated internal drive feature  41 ″ is a star shaped or multi-lobular aperture designed to receive a tool (not shown) of an Allen wrench type, into the aperture  41 ″ for rotating and driving the bone screw shank  4 ″ into the vertebra. It is foreseen that such an internal tool engagement structure may take a variety of tool-engaging forms and may include one or more apertures of various shapes, such as a pair of spaced apart apertures or a hex shaped aperture. 
     The sleeve  1204 A illustrated in  FIG. 34  is modified slightly to provide a lower aperture  1260  being sized and shaped to be large enough to receive the driving tool for the shank drive feature  41 ″. The upper aperture  1243  is also large enough to receive the shank driving tool. In operation, the driving tool (not shown) may therefore be received through both apertures  1243  and  1260  of the sleeve  1204 A, followed by being received in the internal drive feature  41 ″ and being seated at the base thereof, engaging the faces of the drive feature  41 ″ for both driving and rotating the shank body  6 ″ into a vertebra. The receiver  10 ′ already equipped with the retainer and the sleeve  1204 A, or for example, the sleeve  294 A′ shown in  FIG. 2   a  having the surfaces  242 ′ that are flush with surfaces of the receiver  10 , may be advantageously provided to a user as a pre-assembled unit. The receiver with sleeve may therefore be mounted on the shank head  8 ″ before or after the shank  4 ″ is driven into the vertebra. In the illustrated embodiment, the driving tool can readily extend through the sleeve at the apertures  1243  and  1260 , for example and then into the drive feature  41 ″ axially aligned with the receiver axis, when the shank  4 ″, retainer  12 ′, sleeve ( 204 A′ or  1204 A, modified with a wide enough aperture  1260  shown in  FIG. 34 ) and receiver  10 ′ combination is driven into the vertebra. The cord  1206  may thereafter be threaded through the aperture  1236  and either a sliding closure  18  or a gripping closure  18 ′ may be used. If a gripping closure  18 ′ is used, some of the cord may be pressed into the aperture  1260  which is not problematic as the cord is adequately gripped and held at edges defining the aperture  1260  as well as by other surfaces defining the closure  18 ′ and the bore  1236 . 
     It is to be understood that while certain forms of the present invention have been illustrated and described herein, it is not to be limited to the specific forms or arrangement of parts described and shown.