Patent Publication Number: US-2021186571-A1

Title: Pivotal bone anchor assembly with snap on articulating retainer

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/456,163 filed Nov. 2, 2010 that is 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 claims the benefit of the following U.S. Provisional Patent Application Serial Nos. 61/278,240, filed Oct. 5, 2009; 61/336,911, filed Jan. 28, 2010; 61/343,737 filed May 3, 2010; 61/395,564 filed May 14, 2010; 61/395,752 filed May 17, 2010; 61/396,390 filed May 26, 2010; 61/398,807 filed Jul. 1, 2010; 61/400,504 filed July 28, 2010; 61/402,959 filed Sep. 8, 2010; 61/403,696 filed Sep. 20, 2010; and 61/403,915 filed Sep. 23, 2010, all of which are incorporated by reference herein. This application is also a continuation-in-part of U.S. patent application Ser. No. 12/802,849 filed Jun. 15, 2010 that claims the benefit of U.S. Provisional Patent Application Ser. No. 61/268,708 filed Jun. 15, 2009, both of which are incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention is directed to polyaxial bone screws for use in bone surgery, particularly spinal surgery and particularly to such screws with compression or pressure inserts. 
     Bone screws are utilized in many types of spinal surgery in order to secure various implants to vertebrae along the spinal column for the purpose of stabilizing and/or adjusting spinal alignment. Although both closed-ended and open-ended bone screws are known, open-ended screws are particularly well suited for connections to rods and connector arms, because such rods or arms do not need to be passed through a closed bore, but rather can be laid or urged into an open channel within a receiver or head of such a screw. 
     Typical open-ended bone screws include a threaded shank with a pair of parallel projecting branches or arms which form a yoke with a U-shaped slot or channel to receive a rod. Hooks and other types of connectors, as are used in spinal fixation techniques, may also include open ends for receiving rods or portions of other structure. 
     A common mechanism for providing vertebral support is to implant bone screws into certain bones which then in turn support a longitudinal structure such as a rod, or are supported by such a rod. Bone screws of this type may have a fixed head or receiver relative to a shank thereof. In the fixed bone screws, the rod receiver head cannot be moved relative to the shank and the rod must be favorably positioned in order for it to be placed within the receiver head. This is sometimes very difficult or impossible to do. Therefore, polyaxial bone screws are commonly preferred. 
     Open-ended polyaxial bone screws allow rotation of the head or receiver about the shank until a desired rotational position of the head is achieved relative to the shank. Thereafter, a rod or other longitudinal connecting member can be inserted into the head or receiver and eventually the receiver is locked or fixed in a particular position relative to the shank. During the rod implantation process it is desirable to utilize bone screws or other bone anchors that have components that remain within the bone screw and further remain properly aligned during what is sometimes a very lengthy, difficult procedure. 
     SUMMARY OF THE INVENTION 
     A polyaxial bone screw assembly according to the invention includes a shank having an upper portion and a body for fixation to a bone; a receiver defining an upper open channel, a cavity and a lower opening; a compression insert; and an open ring-like resilient retainer for capturing the shank upper portion in the receiver along a cylindrical, frusto-conical, curvate or combination interface, the upper portion and attached retainer thereafter being pivotable with respect to the receiver prior to locking of the shank into a desired configuration. The compression insert operatively engages the shank upper portion and may be configured to be spaced from the retainer at all angular orientations of the shank with respect to the receiver. According to an aspect of the invention, an outer radius of the shank upper portion is different than an outer radius of the retainer. In some embodiments, the shank and retainer have the same outer radius. In various embodiments of the invention, the compression insert and retainer may or may not be down- or top-loaded through the upper open channel of the receiver while the shank upper portion is always bottom- or up-loadable into the receiver lower cavity at the lower opening. The resilient retainer is sized and shaped to expand about the shank upper portion and then “snap” or “pop” into place about the upper portion within the receiver cavity. Illustrated receivers typically include structure prohibiting the compression insert from moving upwardly out of the receiver channel and the compression insert prohibits movement of the retainer out of the receiver. Thus, after the compression insert and retainer are loaded into the receiver, both the compression insert and the retainer are captured within the receiver. A pre-assembled receiver, compression insert and retainer may be “popped on” or “snapped-on” to the shank upper portion prior to or after implantation of the shank into a vertebra. Such a “popping on” procedure includes the steps of uploading the shank upper portion into the receiver lower opening, the shank upper portion pressing against and expanding the resilient retainer followed by contraction of the retainer to an original or near original shape thereof about the shank upper portion along a cylindrical, curvate or frusto-conical surface thereof. 
     It is an object of the present invention to provide apparatus and methods directed to polyaxial bone screw assemblies with features that may be readily, securely fastened to each other and to bone. 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 tools are comparatively inexpensive to produce. 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 an exploded perspective view of a polyaxial bone screw assembly according to the present invention including a shank, a receiver, an open retainer and a compression insert and also shown with a closure top and a longitudinal connecting member in the form of a hard rod. 
         FIG. 2  is an enlarged top plan view of the shank of  FIG. 1 . 
         FIG. 3  is a cross-sectional view taken along the line  3 - 3  of  FIG. 2 . 
         FIG. 4  is an enlarged side elevational view of the receiver of  FIG. 1  with portions broken away to show the detail thereof. 
         FIG. 5  is an enlarged side elevational view of the retainer of  FIG. 1 . 
         FIG. 6  is a top plan view of the retainer of  FIG. 5 . 
         FIG. 7  is a bottom plan view of the retainer of  FIG. 5 . 
         FIG. 8  is an enlarged front elevational view of the receiver of  FIG. 1  with portions broken away to show the detail thereof and shown in an early stage of assembly with the retainer of  FIG. 5 . 
         FIG. 9  is a top plan view of the receiver and retainer of  FIG. 8 . 
         FIG. 10  is a front elevational view of the receiver, similar to  FIG. 8 , with portions broken away to show the detail thereof, further showing the retainer and also the compression insert of  FIG. 1  in a later stage of assembly, the compression insert shown in side elevation. 
         FIG. 11  is a perspective view, showing the receiver and compression insert of  FIG. 10  in an assembled configuration. 
         FIG. 12  is an enlarged side elevational view with portions broken away to show the detail thereof, showing the receiver, retainer and compression insert of  FIG. 11 . 
         FIG. 13  is an enlarged and partial, partially exploded front elevational view of the shank of  FIG. 1  and the receiver, retainer and compression insert as assembled as in  FIG. 12 , with portions broken away to show the detail thereof, the shank being shown implanted in a vertebra. 
         FIG. 14  is a partial front elevational view, similar to  FIG. 13 , with portions broken away to show the detail thereof and showing the shank in a stage of assembly with the retainer. 
         FIG. 15  is a partial front elevational view, similar to  FIG. 14 , with portions broken away to show the detail thereof and showing the shank in a subsequent stage of assembly with the retainer. 
         FIG. 16  is an enlarged and partial front elevational view, similar to  FIG. 15 , with portions broken away to show the detail thereof, showing the shank fully assembled with the retainer and showing the compression insert in a subsequent rod receiving position. 
         FIG. 17  is an enlarged and partially exploded side elevational view of the shank, retainer, receiver, compression insert, rod and closure of  FIG. 1  with portions broken away to show the detail thereof, shown in a stage of assembly subsequent to that shown in  FIG. 16  and with the shank disposed at an angle with respect to the receiver. 
         FIG. 18  is a reduced and partial perspective view of the assembly of  FIG. 17 , shown fully assembled. 
         FIG. 19  is an enlarged and partial front elevational view of the assembly of  FIG. 17  shown with the shank shown axially aligned with the receiver. 
         FIG. 20  is an enlarged and partial cross-sectional view taken along the line  20 - 20  of  FIG. 19 . 
         FIG. 21  is an exploded perspective view of a second, alternative embodiment of a polyaxial bone screw assembly according to the present invention including a shank, a receiver, a retainer, a compression insert and a closure top, and further shown with a longitudinal connecting member in the form of a rod. 
         FIG. 22  is an enlarged side elevational view of the receiver of  FIG. 21 . 
         FIG. 23  is an enlarged perspective view of the compression insert of  FIG. 21 . 
         FIG. 24  is a cross-sectional view of the receiver taken along the line  24 - 24  of  FIG. 22 , with the compression insert of  FIG. 21  shown in side elevation in an early stage of assembly and further shown with the retainer of  FIG. 21  with portions broken away to show the detail thereof. 
         FIG. 25  is an enlarged front elevational view of the receiver, retainer and compression insert of  FIG. 24  with portions broken away to show the detail thereof, the insert shown in a further stage of assembly. 
         FIG. 26  is a partial front elevational view of the shank, receiver, retainer and compression insert of  FIG. 25  with portions broken away to show the detail thereof and shown in a stage of assembly of the shank with the retainer. 
         FIG. 27  is a partial front elevational view with portions broken away, similar to  FIG. 26 , showing the shank, retainer and compression insert fully assembled within the receiver and positioned for receiving the rod of  FIG. 21 . 
         FIG. 28  is an enlarged and partial side elevational view of the shank, receiver, retainer, compression insert, rod and closure of  FIG. 21  with portions broken away to show the detail thereof and shown fully assembled and with the shank disposed at an angle with respect to the receiver. 
         FIG. 29  is an enlarged and partial cross-sectional view taken along the line  29 - 29  of  FIG. 28 . 
         FIG. 30  is an exploded perspective view of a third, alternative embodiment of a polyaxial bone screw assembly according to the present invention including a shank, a receiver, a retainer, a compression insert and a closure top, and further shown with a longitudinal connecting member in the form of a deformable rod. 
         FIG. 31  is an enlarged perspective view of the receiver of  FIG. 30 . 
         FIG. 32  is an enlarged perspective view of the compression insert of  FIG. 30 . 
         FIG. 33  is an enlarged exploded perspective view of the receiver and compression insert of  FIG. 30  shown in a first stage of assembly. 
         FIG. 34  is a perspective view of the receiver and compression insert of  FIG. 33 , shown assembled. 
         FIG. 35  is a cross-sectional view taken along the line  35 - 35  of  FIG. 34 . 
         FIG. 36  is an enlarged and partial front elevational view of the shank, receiver, retainer and compression insert of  FIG. 30  with portions broken away to show the detail thereof and showing the shank in an initial stage of assembly with the retainer. 
         FIG. 37  is an enlarged and partial and partially exploded front elevational view of the shank, receiver, retainer, compression insert, rod and closure top of  FIG. 30  with portions broken away to show the detail thereof. 
         FIG. 38  is a partial front elevational view with portions broken away, similar to  FIG. 37 , showing all the components of  FIG. 30  fully assembled. 
         FIG. 39  is an enlarged and partial side elevational view of the assembly shown in  FIG. 30  with portions broken away to show the detail thereof and shown fully assembled as in  FIG. 38  but with the shank disposed at an angle with respect to the receiver. 
         FIG. 40  is an exploded perspective view of a fourth, alternative embodiment of a polyaxial bone screw assembly according to the present invention including a shank, a receiver, a retainer, a compression insert and a closure top, and further shown with a longitudinal connecting member in the form of a rod. 
         FIG. 41  is an enlarged top plan view of the shank of  FIG. 40 . 
         FIG. 42  is a cross-sectional view taken along the line  42 - 42  of  FIG. 41 . 
         FIG. 43  is an enlarged top plan view of the retainer of  FIG. 40 . 
         FIG. 44  is an enlarged and partial side elevational view of the assembly of  FIG. 40  with portions broken away to show the detail thereof. 
         FIG. 45  is a reduced and partial cross-sectional view taken along the line  45 - 45  of  FIG. 44 . 
         FIG. 46  is a reduced side elevational view of the assembly of  FIG. 40  shown with the shank disposed at an angle with respect to the receiver. 
         FIG. 47  is an enlarged and partial side elevational view, similar to  FIG. 46 , with portions broken away to show the detail thereof. 
         FIG. 48  is an exploded perspective view of a fifth, alternative embodiment of a polyaxial bone screw assembly according to the present invention including a shank, a receiver, a retainer, a compression insert and a closure top, and further shown with a longitudinal connecting member in the form of a rod. 
         FIG. 49  is an enlarged and partial front elevational view of the assembly of  FIG. 48  with portions broken away to show the detail thereof. 
         FIG. 50  is a side elevational view of the assembly of  FIG. 48  shown with the shank disposed at an angle with respect to the receiver. 
         FIG. 51  is an enlarged and partial side elevational view, similar to  FIG. 50 , with portions broken away to show the detail thereof. 
         FIG. 52  is an exploded perspective view of a sixth, alternative embodiment of a polyaxial bone screw assembly according to the present invention including a shank, a receiver, a retainer, a compression insert and a closure top, and further shown with a longitudinal connecting member in the form of a deformable rod. 
         FIG. 53  is an enlarged and partial front elevational view of the assembly of  FIG. 52  with portions broken away to show the detail thereof. 
         FIG. 54  is an enlarged and partial cross-sectional view taken along the line  54 - 54  of  FIG. 53 . 
         FIG. 55  is a perspective view of an alternative retainer for use with polyaxial bone screw assembles according to the invention. 
         FIG. 56  is a bottom perspective view of the retainer of  FIG. 55 . 
         FIG. 57  is a top plan view of the retainer of  FIG. 55 . 
         FIG. 58  is a bottom plan view of the retainer of  FIG. 55 . 
         FIG. 59  is an exploded perspective view of a seventh alternative embodiment of a polyaxial bone screw assembly according to the present invention including a shank, a receiver, a retainer, a compression insert and a closure top, and further shown with a longitudinal connecting member in the form of a rod. 
         FIG. 60  is an enlarged and partial front elevational view of the assembly of  FIG. 59  with portions broken away to show the detail thereof. 
         FIG. 61  is an exploded perspective view of a eighth alternative embodiment of a polyaxial bone screw assembly according to the present invention including a shank, a receiver, a retainer, a compression insert and a closure top, and further shown with a longitudinal connecting member in the form of a rod. 
         FIG. 62  is an enlarged and partial front elevational view of the assembly of  FIG. 61  with portions broken away to show the detail thereof. 
         FIG. 63  is an exploded perspective view of a ninth alternative embodiment of a polyaxial bone screw assembly according to the present invention including a shank, a receiver, a retainer, a compression insert and a closure top, and further shown with a longitudinal connecting member in the form of a rod. 
         FIG. 64  is an enlarged and partial front elevational view of the assembly of  FIG. 63  with portions broken away to show the detail thereof. 
         FIG. 65  is an exploded perspective view of a tenth alternative embodiment of a polyaxial bone screw assembly according to the present invention including a shank, a receiver, a retainer, a compression insert and a closure top, and further shown with a longitudinal connecting member in the form of a rod. 
         FIG. 66  is an enlarged and partial front elevational view of the assembly of  FIG. 65  with portions broken away to show the detail thereof. 
         FIG. 67  is an exploded perspective view of a eleventh alternative embodiment of a polyaxial bone screw assembly according to the present invention including a shank, a receiver, a retainer, a compression insert and a closure top, and further shown with a longitudinal connecting member in the form of a rod. 
         FIG. 68  is an enlarged and partial front elevational view of the assembly of  FIG. 67  with portions broken away to show the detail thereof. 
         FIG. 69  is an exploded perspective view of a twelfth alternative embodiment of a polyaxial bone screw assembly according to the present invention including a shank, a receiver, a retainer, a compression insert and a closure top, and further shown with a longitudinal connecting member in the form of a rod. 
         FIG. 70  is an enlarged and partial front elevational view of the assembly of  FIG. 69  with portions broken away to show the detail thereof. 
         FIG. 71  is an exploded perspective view of a thirteenth alternative embodiment of a polyaxial bone screw assembly according to the present invention including a shank, a receiver, a retainer, a compression insert and a closure top, and further shown with a longitudinal connecting member in the form of a rod. 
         FIG. 72  is an enlarged and partial front elevational view of the assembly of  FIG. 71  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 bone attachment structures in actual use. 
     With reference to  FIGS. 1-20  the reference number  1  generally represents a polyaxial bone screw apparatus or assembly according to the present invention. The assembly  1  includes a shank  4 , that further includes a body  6  integral with an upwardly extending upper portion or capture structure  8 ; a receiver  10 ; a retaining structure or retainer  12  and a compression or pressure insert  14 . The receiver  10 , retainer  12  and compression insert  14  are initially assembled and may be further assembled with the shank  4  either prior or subsequent to implantation of the shank body  6  into a vertebra  13 , as will be described in greater detail below.  FIG. 1  further shows a closure structure  18  of the invention for capturing a longitudinal member, for example, a rod  21  which in turn engages the compression insert  14  that presses against the shank upper portion  8  into fixed frictional contact with the retainer  12 , so as to capture, and fix the longitudinal connecting member  21  within the receiver  10  and thus fix the member  21  relative to the vertebra  13 . The illustrated rod  21  is hard, stiff, non-elastic and cylindrical, having an outer cylindrical surface  22 . It is foreseen (and also will be described with respect to other embodiments) that the rod  21  may be elastic, deformable and/or of a different cross-sectional geometry. The receiver  10  and the shank  4  cooperate in such a manner that the receiver  10  and the shank  4  can be secured at any of a plurality of angles, articulations or rotational alignments relative to one another and within a selected range of angles both from side to side and from front to rear, to enable flexible or articulated engagement of the receiver  10  with the shank  4  until both are locked or fixed relative to each other near the end of an implantation procedure. 
     The shank  4 , best illustrated in  FIGS. 1-3 , is elongate, with the shank body  6  having a helically wound bone implantable thread  24  (single or dual lead thread form) extending from near a neck  26  located adjacent to the upper portion or capture structure  8 , to a tip  28  of the body  6  and extending radially outwardly therefrom. During use, the body  6  utilizing the thread  24  for gripping and advancement is implanted into the vertebra  13  leading with the tip  28  and driven down into the vertebra with an installation or driving tool (not shown), so as to be implanted in the vertebra to near the neck  26 , as more fully described in the paragraphs below. The shank  4  has an elongate axis of rotation generally identified by the reference letter A. 
     The neck  26  extends axially upward from the shank body  6 . The neck  26  may be of the same or is typically of a slightly reduced radius as compared to an adjacent upper end or top  32  of the body  6  where the thread  24  terminates. Further extending axially and outwardly from the neck  26  is the shank upper portion  8  that provides a connective or capture apparatus disposed at a distance from the upper end  32  and thus at a distance from the vertebra  13  when the body  6  is implanted in such vertebra. 
     The shank upper portion  8  is configured for a pivotable connection between the shank  4  (with attached retainer  12 ) and the receiver  10  prior to fixing of the shank  4  in a desired position with respect to the receiver  10 . The shank upper portion  8  has an outer, convex and substantially spherical lower surface  34  that extends outwardly and upwardly from the neck  26  and terminates at a substantially planar ledge or shelf  36  that is annular and disposed perpendicular to the shank axis A. The spherical lower surface  34  has an outer radius that is the same or substantially similar to an outer radius of the retainer  12  as will be described in greater detail below, the surface  34  as well as the retainer  12  outer surface participating in the ball and socket joint formed by the shank  4  and attached retainer  12  within the partially spherical surface defining an inner cavity of the receiver  10 . Extending upwardly from the ledge  36  is a cylindrical surface  38 , the surface  38  having a radius that is smaller than the radius of the lower spherical surface  34 . Extending outwardly from the cylindrical surface  38  is another annular surface or upper ledge  40  that faces toward the ledge  36  and is also substantially perpendicular to the axis A. As will be discussed in greater detail below, the lower ledge  36 , cylindrical surface  38  and upper ledge  40  cooperate to capture and fix the resilient open retainer  12  to the shank upper portion  8 , prohibiting movement of the retainer  12  along the axis A once the retainer  12  is located between the ledges  36  and  40 . Extending upwardly from the upper ledge  40  is a cylindrical surface  42  having a radius smaller than the radius of the spherical surface  34  but larger than the radius of the cylindrical surface  38 . Extending upwardly from the surface  42  is an upper partially spherical or domed surface  44 . The spherical surface  44  has an outer radius configured for sliding cooperation and ultimate frictional mating with a substantially spherical concave surface of the compression insert  14  that has the same or substantially similar radius as the surface  44 . The radius of the surface  44  is smaller than the radius of the lower spherical surface  34 . Located near or adjacent to the surface  44  is an annular top surface  46 . In the illustrated embodiment bevel  47  extends about the spherical surface  44  and is located between the spherical surface  44  and the annular planar top surface  46 . 
     A counter sunk substantially planar base or seating surface  49  partially defines an internal drive feature or imprint  50 . The illustrated internal drive feature  50  is an aperture formed in the top surface  46  and has a hex shape designed to receive a hex tool (not shown) of an Allen wrench type, into the aperture for rotating and driving the bone screw shank  4 . 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 multi-lobular or star-shaped aperture, such as those sold under the trademark TORX, or the like. The seat or base  49  of the drive feature  50  is disposed perpendicular to the axis A with the drive feature  50  otherwise being coaxial with the axis A. In operation, a driving tool is received in the internal drive feature  50 , being seated at the base  49  and engaging the six faces of the drive feature  50  for both driving and rotating the shank body  6  into the vertebra  13 , either before the shank  4  is attached to the receiver  10  as shown in  FIG. 13  or after the shank  4  is attached to the receiver  10 , with the shank body  6  being driven into the vertebra  13  with the driving tool extending into the receiver  10 . 
     The shank  4  shown in the drawings is cannulated, having a small central bore  51  extending an entire length of the shank  4  along the axis A. The bore  50  is defined by an inner cylindrical wall of the shank  4  and has a circular opening at the shank tip  28  and an upper opening communicating with the internal drive  50  at the surface  49 . The bore  51  is coaxial with the threaded body  6  and the upper portion  8 . The bore  51  provides a passage through the shank  4  interior for a length of wire (not shown) inserted into the vertebra  13  prior to the insertion of the shank body  6 , the wire providing a guide for insertion of the shank body  6  into the vertebra  13 . 
     To provide a biologically active interface with the bone, the threaded shank body  6  may be coated, perforated, made porous or otherwise treated. The treatment may include, but is not limited to a plasma spray coating or other type of coating of a metal or, for example, a calcium phosphate; or a roughening, perforation or indentation in the shank surface, such as by sputtering, sand blasting or acid etching, that allows for bony ingrowth or ongrowth. Certain metal coatings act as a scaffold for bone ingrowth. Bio-ceramic calcium phosphate coatings include, but are not limited to: alpha-tri-calcium phosphate and beta-tri-calcium phosphate (Ca 3 (PO 4 ) 2 , tetra-calcium phosphate (Ca 4 P 2 O 9 ), amorphous calcium phosphate and hydroxyapatite (Ca 10 (PO 9 ) 6 (OH) 2 ). Coating with hydroxyapatite, for example, is desirable as hydroxyapatite is chemically similar to bone with respect to mineral content and has been identified as being bioactive and thus not only supportive of bone ingrowth, but actively taking part in bone bonding. 
     With particular reference to  FIGS. 1, 4 and 8-11 , the receiver  10  has a generally U-shaped appearance with a partially discontinuous substantially cylindrical inner profile and a partially cylindrical and partially faceted outer profile. The receiver  10  has an axis of rotation B that is shown in  FIG. 1  as being aligned with and the same as the axis of rotation A of the shank  4 , such orientation being desirable, but not required during assembly of the receiver  10  with the shank  4 . After the receiver  10  is pivotally attached to the shank  4 , either before or after the shank  4  is implanted in a vertebra  13 , the axis B is typically disposed at an angle with respect to the axis A, as shown, for example, in  FIGS. 17 and 18 . 
     The receiver  10  includes a substantially cylindrical base  58  integral with a pair of opposed upstanding arms  60  forming a cradle and defining a U-shaped channel  62  between the arms  60  with an upper opening, generally  63 , and a U-shaped lower seat  64 , the channel  62  having a width for operably snugly receiving the rod  21  between the arms  60 . Each of the arms  60  has an interior surface  66  that has a cylindrical profile and further includes a partial helically wound guide and advancement structure  68  extending radially inwardly from the surface  66  and located adjacent top surfaces  69  of each of the arms  60 . In the illustrated embodiment, the guide and advancement structure  68  is a partial helically wound interlocking flangeform configured to mate under rotation with a similar structure on the closure structure  18 , as described more fully below. However, it is foreseen that the guide and advancement structure  68  could alternatively be a square-shaped thread, a buttress thread, a reverse angle thread or other thread-like or non-thread-like helically wound discontinuous advancement structure for operably guiding under rotation and advancing the closure structure  18  downward between the arms  60 , as well as eventual torquing when the closure structure  18  abuts against the rod  21 . 
     An opposed pair of tool receiving and engaging apertures  71  are formed on outer surfaces  72  of the arms  60 . Furthermore, two additional pair of tool receiving and engaging apertures  73  are formed on the arm surfaces  72  between each top surface  69  and the aperture  71 . Some or all of the apertures  71  and  73  may be used for holding the receiver  10  during assembly with the shank  4  and the retainer  12 , during the implantation of the shank body  6  into a vertebra when the shank is pre-assembled with the receiver  10 , and during assembly of the bone anchor assembly  1  with the rod  21  and the closure structure  18 . It is foreseen that tool receiving grooves or apertures may be configured in a variety of shapes and sizes and be disposed at other locations on the receiver arms  62 . As illustrated, the apertures  71  do not extend completely through the arms  60 . At each aperture  71 , a thin wall  75  partially defines the aperture  71 , the wall  75  being pushed or crimped inwardly toward and into a cooperating aperture of the pressure insert  14  during assembly therewith as will be described in greater detail below. Alternatively, and as will be described in greater detail below, the receiver or the pressure insert may be equipped with spring tabs that bias against a respective pressure insert or receiver to prohibit rotational movement of the insert about the receiver axis once the insert is loaded in the receiver and positioned with the rod-receiving channel of the insert in alignment with the U-shaped channel of the receiver. 
     Communicating with and located beneath the U-shaped channel  62  of the receiver  10  at the base portion  58  thereof is a chamber or cavity, generally  76 , defined in part by a lower inner cylindrical surface  78 , a substantially curved or spherical seating surface portion  80 , a lower ledge  82 , a central cylindrical portion  84 , and an upper shelf, generally  86 , further defined by a lower annular surface or stop  87 , a cylindrical surface  88  and an upper frusto-conical surface  89 . An annular surface  90  disposed perpendicular to the axis B spans between the surface  89  and the cylindrical surface  66  that substantially defines each of the receiver inner arms. In the illustrated embodiment, a frusto-conical or beveled surface  91  is located between the spherical seating surface  80  and the lower ledge  82 . Opposed grooves  92  are formed in the shelf  86 , the grooves  92  located near each U-shaped lower seat  64 , the grooves  92  being sized and shaped for receiving the retainer  12  there through during assembly of the retainer  12  with the receiver  10  as will be described in greater detail below. The central cylindrical portion  84  is sized and shaped to allow for expansion of the retainer  12  about the surface  42  of the shank upper portion  8  during assembly while the upper shelf  86  acts as a stop, prohibiting upward movement of the retainer  12  out of the receiver cavity  76 . The seating surface  80  is sized and shaped for slidably mating with the retainer  12  and also the surface  34  of the shank  4  and ultimately frictionally mating with the retainer  12  and or the surface  34  as will be described in greater detail below. The lower cylindrical surface  78  includes a bottom edge or neck  93  that forms a lower opening, generally  95 , that communicates with both the cavity  76  and a receiver lower exterior or bottom  94  of the base  58 . The neck  93  is substantially coaxially aligned with respect to the rotational axis B of the receiver  10 . The lower neck  93  is also sized and shaped to be smaller than an outer radial dimension of the retainer  12  when the retainer  12  is fixed to the shank upper portion  8 , so as to form a restriction to prevent the structure  12  and attached shank portion  8  from passing through the cavity  76  and out the lower exterior  94  of the receiver  10  during operation thereof. 
     With particular reference to  FIGS. 1 and 5-10 , the open retainer  12  that operates to capture the shank upper portion  8  within the receiver  10  has a central axis C that is operationally the same as the axis A associated with the shank  4  when the shank upper portion  8  and the retainer  12  are installed within the receiver  10 . The retainer  12  is made from a resilient material, such as a stainless steel or titanium alloy, so that the retainer  12  may be expanded during assembly as will be described in greater detail below. However, because there is no need to compress the retainer  12  during assembly, the opening or slit that allows for expansion of the retainer  12  is designed to be very narrow, advantageously providing substantial or almost full surface contact between the retainer and the shank upper portion  8  and also between the retainer and the receiver seating surface  80 . The retainer  12  has a central channel or hollow through bore, generally  101 , that passes entirely through the structure  12  from a top surface  102  to a bottom surface  104  thereof. The bore  101  is primarily defined by a discontinuous inner cylindrical surface  105  that runs from the top surface  102  to the bottom surface  104 . In some embodiments of the invention, as will be described in greater detail below, notches or grooves may be formed in the inner and/or bottom surfaces to more evenly distribute stress across the entire retainer during expansion thereof. The retainer  12  further includes an outer substantially spherical surface  107  running between the top surface  102  and the bottom surface  104 , the surface  107  having the same or similar radius as the receiver seating surface  80  and the shank lower spherical surface  34 . The resilient retainer  12  further includes first and second end surfaces,  109  and  110  disposed in spaced relation to one another when the retainer is in a neutral state. Both end surfaces  109  and  110  are disposed substantially perpendicular to the top surface  102  and the bottom surface  104 . The embodiment shown in  FIGS. 1-20  illustrates the surfaces  109  and  110  as substantially parallel, however, it is foreseen that it may be desirable to orient the surfaces obliquely or at a slight angle. 
     With reference to  FIGS. 1 and 10-16 , the compression insert  14  is illustrated that is sized and shaped to be received by and down-loaded into the receiver  10  through the channel  64  and then rotated (see arrow R) as best illustrated in  FIGS. 10 and 11 . The compression insert  14  has an operational central axis that is the same as the central axis B of the receiver  10 . With particular reference to  FIG. 12 , the compression insert  14  has a central channel or through bore substantially defined by an inner cylindrical surface  121  coaxial with an inner partially spherical surface  122 . The compression insert  14  through bore is sized and shaped to receive a driving tool (not shown) therethrough that engages the shank drive feature  50  when the shank body  6  is driven into bone with the receiver  10  attached. The surface  122  is sized and shaped to slidingly receive and ultimately frictionally engage the substantially spherical or domed surface  44  of the shank upper portion  8  such that the surface  44  initially slidingly and pivotally mates with the spherical surface  122  to create a ball-and-socket type joint. The surfaces  44  and/or  122  may include a roughening or surface finish to aid in frictional contact between them once a desired angle of articulation of the shank  4  with respect to the receiver  10  is reached. 
     The compression insert  14  has a substantially cylindrical body  126  integral with a pair of upstanding arms  127 . The bore defined by the inner surface  121  is disposed primarily within and through the body  126  and communicates with a generally U-shaped through channel  131  that is defined by the upstanding arms  127 . The channel  131  has a lower seat  132  sized and shaped to closely, snugly engage the rod  21 . It is foreseen that an alternative embodiment may be configured to include planar holding surfaces that closely hold a square or rectangular bar as well as hold a cylindrical rod-shaped, cord, or sleeved cord longitudinal connecting member. The arms  127  disposed on either side of the channel  131  extend upwardly from the body  126  to top surfaces  133 . The arms  127  are sized and configured for ultimate placement below the receiver guide and advancement structure  68 . It is foreseen that in some embodiments of the invention, the arms may be extended and the closure top configured such the arms ultimately directly engage the closure top  18  for locking of the polyaxial mechanism, for example, when the rod  21  is made from a deformable material. In such embodiments, the insert  14  would include a rotation blocking structure or feature that abuts against cooperating structure located on an inner wall of the receiver  10  (such as the insert shown with the assembly shown in  FIGS. 30-39 , for example), preventing rotation of the insert with respect to the receiver when the closure top is rotated into engagement with the insert. In the present embodiment, the top surfaces  133  of the arms  127  are ultimately positioned in spaced relation with the closure top  18 , so that the closure top  18  frictionally engages the rod  21  only, pressing the rod  21  downwardly against the seating surface  132 , the insert  14  in turn pressing against the shank  4  upper portion  8  that presses against the retainer  12  to lock the polyaxial mechanism of the bone screw assembly  1  at a desired angle. 
     The insert body  126  has a bottom surface  135  that is adjacent to the inner spherical surface  122 . In the illustrated embodiment, the surface  134  is disposed at an angle with respect to the cylindrical surface of the body  126 , providing improved clearance between components of the assembly  1  (as shown, for example, in  FIG. 12 ). In other embodiments, the bottom surface may be substantially perpendicular to the cylindrical body  126  or have more than one curved, conical or annular surfaces. 
     The illustrated insert  14  further includes other features for manipulating and holding the insert  14  within the receiver  10 . Each insert arm  127  includes an outer surface  137  having a substantially vertical groove  138  formed thereon, the grooves  138  cooperate with the receiver crimp wall  75  to aid in alignment of the insert channel  131  with the receiver channel  62 . 
     The insert body  126  has an outer diameter slightly smaller than a diameter between crests of the guide and advancement structure  68  of the receiver  10 , allowing for top loading of the compression insert  14  into the receiver opening  63 , with the arms  127  of the insert  14  being located between the receiver arms  60  during insertion of the insert  14  into the receiver  10 . Once the arms  127  of the insert  14  are generally located beneath the guide and advancement structure  68 , the insert  14  is rotated into place about the receiver axis B (see  FIG. 11  and the arrow R) until the insert top surfaces  133  are located directly below the guide and advancement structure  68  of each receiver arm  60  as will be described in greater detail below. 
     With reference to  FIGS. 1 and 17-20 , the illustrated elongate rod or longitudinal connecting member  21  (of which only a portion has been shown) can be any of a variety of implants utilized in reconstructive spinal surgery, but is typically a cylindrical, elongate structure having the outer substantially smooth, cylindrical surface  22  of uniform diameter. The rod  21  may be made from a variety of metals, metal alloys and deformable and less compressible plastics, including, but not limited to rods made of elastomeric, polyetheretherketone (PEEK) and other types of materials, such as polycarbonate urethanes (PCU) and polyethylenes. 
     Longitudinal connecting members for use with the assembly  1  may take a variety of shapes, including but not limited to rods or bars of oval, rectangular or other curved or polygonal cross-section. The shape of the insert  14  may be modified so as to closely hold the particular longitudinal connecting member used in the assembly  1 . Some embodiments of the assembly  1  may also be used with a tensioned cord. Such a cord may be made from a variety of materials, including polyester or other plastic fibers, strands or threads, such as polyethylene-terephthalate. Furthermore, the longitudinal connector may be a component of a longer overall dynamic stabilization connecting member, with cylindrical or bar-shaped portions sized and shaped for being received by the compression insert  14  of the receiver having a U-shaped, rectangular- or other-shaped channel, for closely receiving the longitudinal connecting member. The longitudinal connecting member may be integral or otherwise fixed to a bendable or damping component that is sized and shaped to be located between adjacent pairs of bone screw assemblies  1 , for example. A damping component or bumper may be attached to the longitudinal connecting member at one or both sides of the bone screw assembly  1 . A rod or bar (or rod or bar component) of a longitudinal connecting member may be made of a variety of materials ranging from deformable plastics to hard metals, depending upon the desired application. Thus, bars and rods of the invention may be made of materials including, but not limited to metal and metal alloys including but not limited to stainless steel, titanium, titanium alloys and cobalt chrome; or other suitable materials, including plastic polymers such as polyetheretherketone (PEEK), ultra-high-molecular weight-polyethylene (UHMWP), polyurethanes and composites, including composites containing carbon fiber, natural or synthetic elastomers such as polyisoprene (natural rubber), and synthetic polymers, copolymers, and thermoplastic elastomers, for example, polyurethane elastomers such as polycarbonate-urethane elastomers. 
     With reference to  FIGS. 1 and 17-20 , the closure structure or closure top  18  shown with the assembly  1  is rotatably received between the spaced arms  60  of the receiver  10 . It is noted that the closure  18  top could be a twist-in or slide-in closure structure. The illustrated closure structure  18  is substantially cylindrical and includes an outer helically wound guide and advancement structure  182  in the form of a flange that operably joins with the guide and advancement structure  68  disposed on the arms  60  of the receiver  10 . The flange form utilized in accordance with the present invention may take a variety of forms, including those described in Applicant&#39;s U.S. Pat. No. 6,726,689, which is incorporated herein by reference. Although it is foreseen that the closure structure guide and advancement structure could alternatively be a buttress thread, a square thread, a reverse angle thread or other thread like or non-thread like helically wound advancement structure, for operably guiding under rotation and advancing the closure structure  18  downward between the arms  60  and having such a nature as to resist splaying of the arms  60  when the closure structure  18  is advanced into the channel  62 , the flange form illustrated herein as described more fully in Applicant&#39;s U.S. Pat. No. 6,726,689 is preferred as the added strength provided by such flange form beneficially cooperates with and counters any reduction in strength caused by the any reduced profile of the receiver  10  that may more advantageously engage longitudinal connecting member components. The illustrated closure structure  18  also includes a top surface  184  with an internal drive  186  in the form of an aperture that is illustrated as a star-shaped internal drive such as that sold under the trademark TORX, or may be, for example, a hex drive, or other internal drives such as slotted, tri-wing, spanner, two or more apertures of various shapes, and the like. A driving tool (not shown) sized and shaped for engagement with the internal drive  186  is used for both rotatable engagement and, if needed, disengagement of the closure  18  from the receiver arms  60 . It is also foreseen that the closure structure  18  may alternatively include a break-off head designed to allow such a head to break from a base of the closure at a preselected torque, for example, 70 to 140 inch pounds. Such a closure structure would also include a base having an internal drive to be used for closure removal. A base or bottom surface  188  of the closure is planar and further includes a point  189  and a rim  190  for engagement and penetration into the surface  22  of the rod  21  in certain embodiments of the invention. The closure top  18  may further include a cannulation through bore (not shown) extending along a central axis thereof and through the top and bottom surfaces thereof. Such a through bore provides a passage through the closure  18  interior for a length of wire (not shown) inserted therein to provide a guide for insertion of the closure top into the receiver arms  60 . 
     Preferably, the receiver  10 , the retainer  12  and the compression insert  14  are assembled at a factory setting that includes tooling for holding, alignment and manipulation of the component pieces, as well as crimping a portion of the receiver  10  toward the insert  14 . In some circumstances, the shank  4  is also assembled with the receiver  10 , the retainer  12  and the compression insert  14  at the factory. In other instances, it is desirable to first implant the shank  4 , followed by addition of the pre-assembled receiver, retainer and compression insert at the insertion point (see, e.g.,  FIG. 13 ). In this way, the surgeon may advantageously and more easily implant and manipulate the shanks  4 , distract or compress the vertebrae with the shanks and work around the shank upper portions or heads without the cooperating receivers being in the way. In other instances, it is desirable for the surgical staff to pre-assemble a shank of a desired size and/or variety (e.g., surface treatment of roughening the upper portion  8  and/or hydroxyapatite on the shank  6 ), with the receiver, retainer and compression insert. Allowing the surgeon to choose the appropriately sized or treated shank  4  advantageously reduces inventory requirements, thus reducing overall cost. 
     Pre-assembly of the receiver  10 , retainer  12  and compression insert  14  is shown in  FIGS. 8-12 . With particular reference to  FIGS. 8 and 9 , first the retainer  12  is inserted into the upper receiver opening  63 , leading with the outer surface  107 , the top surface  102  facing one arm  60  and the retainer bottom surface  104  facing the opposing arm  60 . The retainer  12  is then lowered in such sideways manner into the channel  62  and partially into the receiver cavity through the opposed grooves  92 , followed by tilting the retainer  12  such that the top surface  102  is moved into a position within the receiver under the annular surface or ledge  87  as best shown in  FIG. 10 . The retainer  12  is now at least partially seated on the receiver spherical surface  80 . 
     Also with reference to  FIG. 10  and with further reference to  FIGS. 11 and 12 , the compression insert  14  is then downloaded into the receiver  10  through the upper opening  63  with the bottom surface  135  facing the receiver arm top surfaces  69  and the insert arms  127  located between the opposed receiver arms  60 . The insert  14  is then lowered toward the channel seat  64  until the insert  14  arm upper surfaces  133  are adjacent the receiver arm inner surfaces  66  located below the guide and advancement structure  68 . Thereafter, the insert  14  is rotated in a clockwise or counter-clockwise manner (see the arrow R) about the receiver axis B until the upper arm surfaces  133  are directly below the guide and advancement structure  68  of each arm as illustrated in  FIGS. 11 and 12  with the U-shaped channel  131  of the insert  14  aligned with the U-shaped channel  62  of the receiver  10 . In some embodiments, the insert arms  127  may need to be compressed slightly during rotation to clear inner surfaces of the receiver arms  60 . As shown in  FIGS. 12 and 13 , the insert cylindrical base body  126  is received within the cylindrical surface  88  of the shelf  86  that defines an upper portion of the receiver base  58  with lower portions of the arms  127  in contact with the shelf surface  89 . With reference to  FIG. 13 , the receiver thin walls  75  are then crimped inwardly toward the axis B by inserting a tool (not shown) through the receiver apertures  71 , the tool pressing the walls  75  until the inner wall surfaces engage the insert  14  at the grooves  138  formed on the outer surface  137  of each of the insert arms  127  (see, e.g.,  FIG. 16 ). The crimping of the walls  75  into the grooves  138  keeps the insert  14  U-shaped channel  131  aligned with the receiver U-shaped channel  62 . The crimping of the receiver walls  75  prohibits rotation of the insert  14  about the receiver axis B but allows for limited axial movement of the insert  14  with respect to the receiver  10  along the axis B when some force is exerted to slide the insert with respect to the receiver crimped walls up or down along the grooves  138 . The insert  14  is fully captured within the receiver  10  by the guide and advancement structure  68  prohibiting movement of the insert  14  up and out through the receiver opening  63  as well as by retainer  12  located below the insert as shown in  FIG. 12 . Furthermore, as best shown in  FIG. 12 , during shipping and handling, the insert  14  prohibits the retainer  12  from escaping out of the receiver  10  through the opening  63  and also prohibits the retainer from moving out of alignment within the receiver chamber  76 , and, in some embodiments from escaping out of the bottom opening  95 . The receiver  10 , retainer  12  and insert  14  combination is now pre-assembled and ready for assembly with the shank  4  either at the factory, by surgery staff prior to implantation, or directly upon an implanted shank  4  as will be described herein. 
     As illustrated in  FIG. 13 , the bone screw shank  4  or an entire assembly  1  made up of the assembled shank  4 , receiver  10 , retainer  12  and compression insert  14 , is screwed into a bone, such as the vertebra  13 , by rotation of the shank  4  using a suitable driving tool (not shown) that operably drives and rotates the shank body  6  by engagement thereof at the internal drive  50 . Specifically, the vertebra  13  may be pre-drilled to minimize stressing the bone and have a guide wire (not shown) inserted therein to provide a guide for the placement and angle of the shank  4  with respect to the vertebra. A further tap hole may be made using a tap with the guide wire as a guide. Then, the bone screw shank  4  or the entire assembly  1  is threaded onto the guide wire utilizing the cannulation bore  51  by first threading the wire into the opening at the bottom  28  and then out of the top opening at the drive feature  50 . The shank  4  is then driven into the vertebra using the wire as a placement guide. It is foreseen that the shank and other bone screw assembly parts, the rod  21  (also having a central lumen in some embodiments) and the closure top  18  (also with a central bore) can be inserted in a percutaneous or minimally invasive surgical manner, utilizing guide wires. When the shank  4  is driven into the vertebra  13  without the remainder of the assembly  1 , the shank  4  may either be driven to a desired final location or may be driven to a location slightly above or proud to provide for ease in assembly with the pre-assembled receiver, compression insert and retainer. 
     With further reference to  FIG. 13 , the pre-assembled receiver, insert and retainer are placed above the shank upper portion  8  until the shank upper portion is received within the opening  95 . With particular reference to  FIGS. 14 and 15 , as the shank upper portion  8  is moved into the interior  76  of the receiver base, the shank upper portion  8  presses upwardly against the retainer  12  in the recess partially defined by the cylindrical surface  84 . As the portion  8  continues to move upwardly toward the channel  62 , the surface  44  forces outward movement of the retainer  12  towards the cylindrical surface  84  in the receiver expansion chamber or area as the shank  4  presses the retainer  12  against the receiver lower annular ledge surface  87 . The retainer  12  initially expands about the shank upper spherical surface  44  and then slides along the cylindrical surface  42 , snapping or popping into the recessed cylindrical surface  38 , the surface  105  of the retainer  12  fully contacting and frictionally engaging the cylindrical surface  38  between the shank lower ledge  36  and the upper ledge  40 . At this time, the retainer  12  is in a neutral or slightly expanded state, fully snapped onto the shank upper portion  8  with both the retainer  12  and shank upper portion  8  in pivotal relation with the receiver  10 . 
     With reference to  FIG. 16 , the shank  4  and attached retainer  12  are then moved downwardly into a desired position with the retainer seated on the surface  80 . The insert  14  may be pressed downwardly by a tool or by a rod and closure top as shown in  FIG. 20 . In some embodiments, the crimp walls  75  require that some force is used to press the inert  14  downwardly against the shank upper portion  8 . In such embodiments, the insert  14  surface  122  is in frictional engagement with the shank upper portion surface  44  to an extent that the shank is pivotable with respect to the receiver, but in a non-floppy manner. In some embodiments, when the receiver  10  is pre-assembled with the shank  4 , the entire assembly  1  may be implanted at this time by inserting the driving tool (not shown) into the receiver and the shank drive  50  and rotating and driving the shank  4  into a desired location of the vertebra  13 . 
     The rod  21  is eventually positioned in an open or percutaneous manner in cooperation with the at least two bone screw assemblies  1 . The closure structure  18  is then inserted into and advanced between the arms  60  of each of the receivers  10 . The closure structure  18  is rotated, using a tool engaged with the inner drive  186  until a selected pressure is reached at which point the rod  21  engages the U-shaped seating surface  131  of the compression insert  14 , further pressing the insert spherical surface  122  against the shank spherical surface  44 , pressing the shank upper portion  8  and attached retainer  12  into locked frictional engagement with the receiver  10 . With specific reference to  FIGS. 19 and 20 , as the closure structure  18  rotates and moves downwardly into the respective receiver  10 , the point  189  and rim  190  engage and penetrate the rod surface  22 , the closure structure  18  pressing downwardly against and biasing the rod  21  into compressive engagement with the insert  14  that urges the shank upper portion  8  and attached retainer  12  into locking engagement with the receiver, the retainer  12  spherical surface  107  frictionally abutting the spherical seating surface  80  of the receiver  10 . For example, about 80 to about 120 inch pounds of torque on the closure top may be applied for fixing the bone screw shank  6  with respect to the receiver  10 . Also, for example, with reference to  FIGS. 17 and 18 , when the shank  4  is disposed at an angle with respect to the receiver  10 , the lower spherical surface  34  of the shank upper portion  8  may also be in frictional engagement with a portion of the receiver spherical seating surface  80 . The retainer  12  may also expand slightly upon locking, providing a full and secure frictional locking engagement with the receiver at the surface  80 . 
     If removal of the rod  21  from any of the bone screw assemblies  1  is necessary, or if it is desired to release the rod  21  at a particular location, disassembly is accomplished by using the driving tool (not shown) that mates with the internal drive  186  on the closure structure  18  to rotate and remove such closure structure from the cooperating receiver  10 . Disassembly is then accomplished in reverse order to the procedure described previously herein for assembly. 
     With reference to  FIGS. 21-29  the reference number  201  generally represents a polyaxial bone screw apparatus or assembly according to the present invention. The assembly  201  includes a shank  204 , that further includes a body  206  integral with an upwardly extending upper portion or capture structure  208 ; a receiver  210 ; a retainer structure  212  and a compression or pressure insert  214 . The receiver  210 , retainer  212  and compression insert  214  are initially assembled and may be further assembled with the shank  204  either prior or subsequent to implantation of the shank body  206  into a vertebra (not shown), such as the vertebra  13  shown in  FIG. 13  and described with respect to the assembly  1 .  FIGS. 21 and 28-29  further show a closure structure  218  of the invention for capturing a longitudinal connecting member, for example, a rod  221  which in turn engages the compression insert  214  that presses against the shank upper portion  208  and popped-on retainer  212 , so as to capture, and fix the longitudinal connecting member  221  within the receiver  210  and thus fix the member  221  relative to the vertebra (not shown). The illustrated rod  221  is hard, stiff, non-elastic and cylindrical, having an outer cylindrical surface  222 . It is foreseen that in other embodiments, the rod  221  may be elastic, deformable and/or of a different cross-sectional geometry as previously described herein with respect to the rod  21  of the assembly  1 . The receiver  210  and the shank  204  cooperate in such a manner that the receiver  210  and the shank  204  can be secured at any of a plurality of angles, articulations or rotational alignments relative to one another and within a selected range of angles both from side to side and from front to rear, to enable flexible or articulated engagement of the receiver  210  with the shank  204  until both are locked or fixed relative to each other near the end of an implantation procedure. 
     The shank  204 , best illustrated in  FIGS. 21 and 26-29  is substantially similar to the shank  4  previously described herein with respect to the assembly  1 . Thus, the shank  204  includes the shank body  206 , upper portion or head  208 , a shank thread  224 , a neck  226 , a tip  228 , a top of thread  232 , an upper portion lower spherical surface  234  a shelf or ledge  236 , a cylindrical surface  238 , and upper ledge  240  and upper spherical surface  244 , a top surface  246 , an internal drive  250  and a cannulation bore  251  the same or substantially similar to the respective body  6 , upper portion or head  8 , shank thread  24 , neck  26 , tip  28 , top of thread  32 , lower spherical surface  34 , shelf  36 , cylindrical surface  38 , upper ledge  40 , upper spherical surface  44 , top surface  46 , internal drive  50  and cannulation bore  51 , as well as other features previously described herein with respect to the shank  4  of the assembly  1 . 
     With particular reference to  FIGS. 21, 22 and 24-29 , the receiver  210  is substantially similar to the receiver  10  with the exception of opposed resilient spring tabs  275  that are provided in lieu of the thin walls  75  of the receiver  10 . As shown in  FIG. 25 , for example, and discussed in greater detail below, the spring tabs  275  advantageously resiliently hold the insert  214  in an upper portion of the receiver until the insert  214  is pressed down by the user into a friction fit working position wherein the insert  214  is in frictional contact with the shank upper portion  208 , the shank still movable with respect to the insert,  214 , but not in a loose or floppy manner. 
     The receiver  210  includes a base  258  with integral upstanding arms  260 , a U-shaped channel  262  having an upper opening  263  and a lower seat  264 , an arm interior substantially cylindrical surface  266 , a guide and advancement structure  268 , arm top surfaces  269 , an inner base cavity or chamber generally  276 , a lower cylindrical surface  278 , a spherical seating surface  280 , a lower ledge  282 , a central cylindrical portion  284 , an upper shelf, generally  286  further defined by a lower annular surface  287 , a cylindrical surface  288 , and an upper frusto-conical surface  289 , a pair of opposed grooves  292 , a neck  293 , a bottom surface  294  and a lower opening, generally  295 , the same or substantially similar to the respective base  58  with integral upstanding arms  60 , U-shaped channel  62 , channel upper opening  63  and lower seat  64 , arm interior substantially cylindrical surface  66 , guide and advancement structure  68 , arm top surfaces  69 , inner base cavity or chamber generally  76 , lower cylindrical surface  78 , spherical seating surface  80 , lower ledge  82 , central cylindrical portion  84 , upper shelf, generally  86  further defined by the lower annular surface  87 , the cylindrical surface  88 , and the upper frusto-conical surface  89 , opposed grooves  92 , neck  93 , bottom surface  94  and lower opening  95  of the receiver  10 , and other features previously described herein with respect to the assembly  1 . 
     Extending through each receiver arm  260  is an aperture  271  formed in an arm outer surface  272  and extending through each arm to the inner cylindrical surface  266 . Each aperture  271  is in the form of a squared-off U-shape, thus forming each of the spring tabs  275  that are substantially rectangular in profile. Each tab  275  is integral with the respective receiver arm  260  at a location below and near the guide and advancement structure  268 . Each tab  275  has an inner surface  273  that is an extension of the inner cylindrical surface  266  and is initially aligned with the surface  266  as shown, for example, in FIG.  24 . A bottom surface  274  of each tab  275  is spaced from a remainder of the inner cylindrical surface  266  that extends downwardly to the shelf  286 . As shown, for example, in  FIG. 25 , each spring tab  275  is bent inwardly toward a center axis of the receiver  210  either before or after the insert  214  is mounted within the receiver  210 . In the illustrated embodiment, the tabs  275  are pressed inwardly toward grooves in the insert  214  after the insert  214  is located within the receiver as shown in  FIG. 25  and as will be described in greater detail below. 
     With reference to  FIGS. 21 and 24-29 , the retainer  212  is the same or substantially similar in form and function to the retainer  12  previously described herein with respect to the assembly  1 . Therefore, the retainer  212  includes a central through bore  301 , a top surface  302 , a bottom surface  304 , an inner cylindrical surface  305 , a spherical surface  307  and end surfaces  309  and  310  that are the same or similar to the respective central through bore  101 , top surface  102 , bottom surface  104 , inner cylindrical surface  105 , spherical surface  107  and end surfaces  109  and  110  previously described herein with respect to the retainer  12 . 
     With reference to  FIGS. 21 and 23-29 , the compression insert  214  is substantially similar in form and function to the insert  14  previously described herein with respect to the assembly  1 . The insert  214  differs from the insert  14  only in a groove or flat  338  that has a different geometry than the groove  138  of the insert  14 . Therefore, the insert  214  includes an inner cylindrical surface  321 , an inner spherical surface  322 , a cylindrical body  326 , a pair of upstanding arms  327 , a U-shaped channel  331  having a lower seat  332 , arm top surfaces  333 , a bottom surface  335  and arm outer surfaces  337  that are the same or substantially similar to the respective inner cylindrical surface  121 , inner spherical surface  122 , cylindrical body  126 , upstanding arms  127 , U-shaped channel  131  with lower seat  132 , arm top surfaces  133 , the bottom surface  135  and arm outer surfaces  137  of the insert  14  previously described herein. 
     The flat  338  formed in each arm outer surface  337  runs from the top surface  333  to a lower ledge  340 . As shown, for example, in  FIG. 26 , the flat  338  and the flat lower ledge  340  are sized and shaped to allow the insert  214  to be moved upwardly adjacent to the guide and advancement structure  268  during the “popping-on” of the shank  204  into the retainer  212  located within the receiver expansion chamber formed within the inner cylindrical surface  284 . The receiver spring tabs  275  are in sliding frictional engagement with the flats  338  during all of the assembly steps with the shank  204  as well as when the shank  204  is manipulated with respect to the receiver  210 , the insert surface  322  in frictional but movable engagement with the shank surface  244 , providing non-floppy pivoting of the shank  204  with respect to the receiver  210  until the shank and receiver are locked together by action of the closure top  218  pressing against the rod  221  that in turn presses against the insert  214 . 
     With reference to  FIGS. 21 and 28-29 , the closure top  218  is identical or substantially similar to the closure top  18  previously described herein with respect to the assembly  1 , having a flange form guide and advancement structure  382 , a top surface  384 , an internal drive  386 , a base or bottom surface  388 , a point  389  and a rim  390  the same or substantially similar to the respective guide and advancement structure  182 , top surface  184 , internal drive  186 , base or bottom surface  188 , point  189  and rim  190  of the closure top  18 . 
     Preferably, the receiver  210 , the retainer  212  and the compression insert  214  are assembled at a factory setting that includes tooling for holding, alignment and manipulation of the component pieces, as well as pressing the receiver  210  spring tabs  275  toward the insert  214 . In some circumstances, the shank  204  is also assembled with the receiver  210 , the retainer  212  and the compression insert  214  at the factory. In other instances, it is desirable to first implant the shank  204 , followed by addition of the pre-assembled receiver, retainer and compression insert at the insertion point, similar to what is shown with respect to assembly  1  at  FIG. 13 . In this way, the surgeon may advantageously and more easily implant and manipulate the shanks  204 , distract or compress the vertebrae with the shanks and work around the shank upper portions or heads without the cooperating receivers being in the way. In other instances, it is desirable for the surgical staff to pre-assemble a shank of a desired size and/or variety (e.g., surface treatment of roughening the upper portion  208  and/or hydroxyapatite on the shank  206 ), with the receiver, retainer and compression insert. Allowing the surgeon to choose the appropriately sized or treated shank  204  advantageously reduces inventory requirements, thus reducing overall cost. 
     Pre-assembly of the compression insert  214  with the receiver  210  and retainer  212  is shown  FIGS. 24-25 . First, however, the retainer  212  is inserted into the upper receiver opening  263 , leading with the outer surface  307 , the top surface  302  facing one arm  260  and the retainer bottom surface  304  facing the opposing arm  260 . The retainer  212  is then lowered in such sideways manner into the channel  262  and partially into the receiver cavity through the opposed grooves  292 , followed by tilting the retainer  212  such that the top surface  302  is moved into a position within the receiver under the annular surface or ledge  287  and the retainer is at least partially seated on the receiver spherical surface  280 . Reference is made herein to  FIGS. 8-10  showing the insertion of the retainer  12  into the receiver  10  which is accomplished in an identical manner to the insertion of the retainer  212  into the receiver  210 . 
     With reference to  FIGS. 24 and 25 , the compression insert  214  is then downloaded into the receiver  210  through the upper opening  263  with the bottom surface  335  facing the receiver arm top surfaces  269  and the insert arms  327  located between the opposed receiver arms  260 . The insert  214  is then lowered toward the channel seat  264  until the insert  214  arm upper surfaces  333  are adjacent the receiver arm inner surfaces  266  located below the guide and advancement structure  268 . Thereafter, the insert  214  is rotated in a clockwise or counter-clockwise manner about the receiver axis until the upper arm surfaces  333  are directly below the guide and advancement structure  268  of each arm as illustrated in  FIG. 25  with the U-shaped channel  331  of the insert  214  aligned with the U-shaped channel  262  of the receiver  210 . At this time, the receiver spring tabs  275  are pressed and bent inwardly until the spring tab surfaces  273  frictionally engage the insert flat surfaces  338 . At this time, in some embodiments of the invention, frictional engagement between the tabs  275  and the insert surfaces  338  may be used to hold the insert  214  in an upper portion of the receiver  210 , for example as shown in  FIG. 26 . In other embodiments, the spring tabs  275  function only to hold the insert  214  U-shaped channel  331  in alignment with the receiver U-shaped channel  262 . Also, in other embodiments, the spring tabs  275  are bent inwardly before the insert  214  is loaded into the receiver, the tabs  275  being resilient enough to be pushed outwardly during rotation of the insert  214  and then snapping onto the flat surfaces  338  once the insert  214  is rotated into a desired aligned position. In other embodiments of the invention, the spring tabs  275  may be originally formed or machined to be directed inwardly and then are sprung outwardly during rotation of the insert  214 , springing back to a neutral inwardly directed position once the flats  338  engage the inner surfaces  273  of the spring tabs  275 . As shown in  FIG. 24-27 , the receiver spring tabs  275  prohibit rotation of the insert  214  about the receiver central axis but allow for limited up and down movement of the insert  214  with respect to the receiver  210  along the central axis thereof when some force is exerted to slide the insert with respect to the receiver spring tab surfaces  273  up or down along the flats  338 . The insert  214  is fully captured within the receiver  210  by the guide and advancement structure  268  prohibiting movement of the insert  214  up and out through the receiver opening  263  as well as by the spring tabs  275  abutting against the ledge  340  of the flats  338 . Furthermore, similar to what is shown with respect to the assembly  1  in  FIG. 12 , during shipping and handling, the insert  214  prohibits the retainer  212  from escaping out of the receiver  210  through the opening  263  and also prohibits the retainer from moving out of alignment within the receiver chamber  276 , and, in some embodiments from escaping out of the bottom opening  295 . The receiver  210 , retainer  212  and insert  214  combination is now pre-assembled and ready for assembly with the shank  204  either at the factory, by surgery staff prior to implantation, or directly upon an implanted shank  204  as will be described herein. 
     Similar to the description herein with respect to the assembly  1 , the bone screw shank  204  or an entire assembly  201  made up of the assembled shank  204 , receiver  210 , retainer  212  and compression insert  214 , is screwed into a bone, such as the vertebra  13 , by rotation of the shank  204  using a suitable driving tool (not shown) that operably drives and rotates the shank body  206  by engagement thereof at the internal drive  250  and in a percutaneous or minimally invasive surgical manner. When the shank  204  is driven into the vertebra without the remainder of the assembly  201 , the shank  204  may either be driven to a desired final location or may be driven to a location slightly above or proud to provide for ease in assembly with the pre-assembled receiver, compression insert and retainer. 
     With reference to  FIGS. 13-15  (directed to identical or substantially similar assembly steps for the assembly  1 ) and with reference to  FIG. 26 , the pre-assembled receiver, insert and retainer are placed above the shank upper portion  208  until the shank upper portion is received within the opening  295 . As the shank upper portion  208  is moved into the interior  276  of the receiver base, the shank upper portion  208  presses upwardly against the retainer  212  in the recess partially defined by the cylindrical surface  284 . As the portion  208  continues to move upwardly toward the channel  262 , the surface  244  forces outward movement of the retainer  212  towards the cylindrical surface  284  in the receiver expansion chamber or area as the shank  204  presses the retainer  212  against the receiver lower annular ledge surface  287 . The retainer  212  initially expands about the shank upper spherical surface  244  and then slides along the cylindrical surface  242 , snapping or popping into the recessed cylindrical surface  238 , the surface  305  of the retainer  212  fully contacting and frictionally engaging the cylindrical surface  238  between the shank lower ledge  236  and the upper ledge  240 . At this time, the retainer  212  is in a neutral or slightly expanded state, fully snapped onto the shank upper portion  208  with both the retainer  212  and shank upper portion  208  in pivotal relation with the receiver  210 . 
     With reference to  FIG. 27 , the shank  204  and attached retainer  212  are then moved downwardly into a desired position with the retainer seated on the surface  280 . The insert  214  may slide downwardly with the retainer  212 , or in some embodiments, remain in an upper part of the receiver  210  retained by the spring tabs  275  until the insert  214  is pressed downwardly by a tool or by a rod and closure top as shown in  FIG. 29 . In such embodiments, the insert  214  surface  322  is in frictional engagement with the shank upper portion surface  244  to an extent that the shank is pivotable with respect to the receiver, but in a non-floppy manner. In some embodiments, when the receiver  210  is pre-assembled with the shank  204 , the entire assembly  201  may be implanted at this time by inserting the driving tool (not shown) into the receiver and the shank drive  250  and rotating and driving the shank  204  into a desired location of the vertebra, such as the previously illustrated vertebra  13 . 
     The rod  221  is eventually positioned in an open or percutaneous manner in cooperation with the at least two bone screw assemblies  201 . The closure structure  218  is then inserted into and advanced between the arms  260  of each of the receivers  210 . The closure structure  218  is rotated, using a tool engaged with the inner drive  386  until a selected pressure is reached at which point the rod  221  engages the U-shaped seating surface  331  of the compression insert  214 , further pressing the insert spherical surface  322  against the shank spherical surface  244 , pressing the retainer  212  that is attached to the shank upper portion  208  into locked frictional engagement with the receiver  210 . As the closure structure  218  rotates and moves downwardly into the respective receiver  210 , the point  389  and rim  390  engage and penetrate the rod surface  222 , the closure structure  218  pressing downwardly against and biasing the rod  221  into compressive engagement with the insert  214  that urges the shank upper portion  208  and attached retainer  212  into locking engagement with the receiver, the retainer  212  spherical surface  307  frictionally abutting the spherical seating surface  280  of the receiver  210 . For example, about 80 to about 120 inch pounds of torque on the closure top may be applied for fixing the bone screw shank  206  with respect to the receiver  210 . Also, for example, with reference to  FIGS. 28 and 29 , when the shank  204  is disposed at an angle with respect to the receiver  210 , the lower spherical surface  234  of the shank upper portion  208  may also be in frictional engagement with a portion of the receiver spherical seating surface  280 . The retainer  212  may also expand slightly upon locking, providing a full and secure frictional locking engagement with the receiver at the surface  280 . 
     If removal of the rod  221  from any of the bone screw assemblies  201  is necessary, or if it is desired to release the rod  221  at a particular location, disassembly is accomplished by using the driving tool (not shown) that mates with the internal drive  386  on the closure structure  218  to rotate and remove such closure structure from the cooperating receiver  210 . Disassembly is then accomplished in reverse order to the procedure described previously herein for assembly. 
     With reference to  FIGS. 30-39  the reference number  401  generally represents a polyaxial bone screw apparatus or assembly according to the present invention. The assembly  401  includes a shank  404 , that further includes a body  406  integral with an upwardly extending upper portion or capture structure  408 ; a receiver  410 ; an open retainer structure  412  and a compression or pressure insert  414 .  FIGS. 30 and 37-39  further show a closure structure  418  of the invention for capturing a longitudinal connecting member, for example, a deformable rod  421  within the receiver  410 . The rod  421  may be elastic or inelastic, and is illustrated as a deformable PEEK rod. The assembly  401  is substantially identical to the assembly  1  with a few exceptions. The exceptions are a stop block or blocks  540  located on the insert  414 , each cooperating with a receiver recess having a curved or planar stop wall  470  that prohibits rotation of the insert  414  with respect to the receiver  410  in a clock-wise manner, providing for secure and sturdy alignment between the insert  414  and the receiver  410  when the closure top  418  is rotated in a clock-wise manner to press down, not only upon the deformable rod  421 , but also on the insert  414  as shown in  FIG. 38 , for example. Thus, even if the PEEK or other deformable rod  421  shifts or deforms with respect to the closure top  418 , the polyaxial mechanism of the assembly  401  will remain locked in place because of the locking force of the closure top  418  on the insert  414  that in turns presses directly against the shank as will be described in greater detail below. 
     With particular reference to  FIGS. 30 and 36-39 , the shank  404  is substantially similar in form and function to the shank  4  previously described herein with respect to the assembly  1 . Thus, the shank  404  includes the shank body  406 , upper portion or head  408 , a lower spherical surface  434 , a cylindrical surface  438 , an upper cylindrical surface  442 , an upper spherical surface  444  and an internal drive  250  that are the same or substantially similar in form and function to the respective body  6 , upper portion or head  8 , lower spherical surface  34 , cylindrical surface  38 , upper cylindrical surface  42 , upper spherical surface  44 , internal drive  50 , and all the other features previously described herein with respect to the shank  4  of the assembly  1 . 
     With particular reference to  FIGS. 30, 31 and 33-39 , the receiver  410  is substantially similar to the receiver  10  previously described herein with the exception of the addition of the recessed stop wall  470  mentioned above. Thus, the receiver  410  includes a base  458  with integral upstanding arms  460 , a U-shaped channel  462 , arm interior substantially cylindrical surfaces  466 , a guide and advancement structure  468 , a pair of opposed tool apertures  471  each partially defined by a thin crimp wall  475 , an inner base cavity or chamber generally  476 , a lower cylindrical surface  478 , a spherical seating surface  480 , a central cylindrical expansion portion  484  and an upper shelf, generally  486 , the same or substantially similar in form and function to the respective base  58  with integral upstanding arms  60 , U-shaped channel  62 , arm interior substantially cylindrical surfaces  66 , guide and advancement structure  68 , tool apertures  71 , crimp walls  75 , inner base cavity or chamber generally  76 , lower cylindrical surface  78 , spherical seating surface  80 , central cylindrical expansion portion  84  and upper shelf, generally  86 , and other features previously described herein with respect to the receiver  10  of the assembly  1 . 
     With particular reference to  FIG. 31 , the recess in the receiver that is partially defined by the blocking wall  470  is formed in each cylindrical inner surface  466  located below the guide and advancement structure  468 . The recesses with blocking walls  470  are located opposite one another such that the insert  414  may only be rotated into place in a clock-wise manner as will be described in more detail below. 
     With reference to  FIGS. 30 and 36-39 , the open, expandable retainer  412  is the same or substantially similar in form and function to the retainer  12  previously described herein with respect to the assembly  1 . Therefore, the retainer  212  includes a top surface  502 , a bottom surface  504 , an inner cylindrical surface  505 , an outer spherical surface  507  and a through slit  508  that are the same or similar in form and function to the respective top surface  102 , bottom surface  104 , inner cylindrical surface  105 , outer spherical surface  107  and slit formed by end surfaces  109  and  110  previously described herein with respect to the retainer  12 . 
     With reference to  FIGS. 30 and 32-39 , the compression insert  414  is substantially similar in form and function to the insert  14  previously described herein with respect to the assembly  1  with the exception of the addition of the block or stop  540 . Therefore, the insert  414  includes an inner cylindrical surface  521 , an inner spherical surface  522 , a cylindrical body  526 , a pair of upstanding arms  527 , a U-shaped channel  531  having a lower seat  532 , arm top surfaces  533 , a bottom surface  535  and arm outer surfaces  537 , each with a groove  538  formed therein that are the same or substantially similar in form and function to the respective inner cylindrical surface  121 , inner spherical surface  122 , cylindrical body  126 , upstanding arms  127 , U-shaped channel  131  with lower seat  132 , arm top surfaces  133 , the bottom surface  135  and arm outer surfaces  137  with grooves  138  of the insert  14  previously described herein. The illustrated embodiment includes two stop blocks  540 , each formed on the outside surface  537  of each arm  527  and located near the arm top surface  533 . 
     With reference to  FIGS. 30 and 37-39 , the closure top  418  is substantially similar to the closure top  18  previously described herein with respect to the assembly  1  with the exception of the lower rod contacting surfaces thereof. The closure top  418  has a flange form guide and advancement structure  582 , a top surface  584  and an internal drive  586  that is the same of substantially similar in form and function to the respective guide and advancement structure  182 , top surface  184  and internal drive  186  of the closure top  18  previously described herein. The closure top  418  further includes an annular outer base rim  588  and a central point or nub  589 . The nub  589  is located centrally on a domed or spherical surface  590  that is surrounded by and extends from the base rim  588  downwardly away from the closure  418 . 
     The receiver  410  and the retainer  412  are assembled in a manner identical to what has been described herein with respect to the assembly of the receiver  10  and the retainer  12 . As with the assembly  1 , preferably, the receiver  410 , the retainer  412  and the compression insert  414  are assembled at a factory setting that includes tooling for holding, alignment and manipulation of the component pieces, as well as crimping the receiver thin walls  475  into the insert grooves  538 . 
     Pre-assembly of the compression insert  414  with the receiver  410  and retainer  412  is shown  FIGS. 33-36 . The compression insert  414  is downloaded (see arrow W) into the receiver  410  with the insert arms  527  located between the opposed receiver arms  460 , the insert  414  being lowered toward the receiver base  458  until the insert  414  arm upper surfaces  533  are adjacent the receiver arm inner surfaces  466  located below the guide and advancement structures  468 . Thereafter, the insert  414  is rotated in a clockwise direction shown by the arrow X about the receiver axis until the insert stop blocks  540  abut against each of the receiver recess stop walls  470 . Such occurs when the upper arm surfaces  533  are directly below the guide and advancement structure  468  of each arm as illustrated in  FIG. 34  with the U-shaped channel  531  of the insert  414  aligned with the U-shaped channel  462  of the receiver  410 . At this time, the receiver thin crimp walls  475  are pressed inwardly into the insert grooves  538  as shown in  FIGS. 35 and 36 . At this time, in some embodiments of the invention, frictional engagement between the crimp walls  475  and the insert surfaces grooves  538  may be used to hold the insert  414  in an upper portion of the receiver  410 , for example as shown in  FIG. 36 . In addition to holding the insert  414  in a desired axial position within the receiver  410 , the crimping of the walls  475  in the grooves  538  prohibits counter-clockwise rotation of the insert  414  with respect to the receiver  410 . 
     Similar to the description herein with respect to the assembly  1 , the bone screw shank  404  or an entire assembly  401  made up of the assembled shank  404 , receiver  410 , retainer  412  and compression insert  414 , is screwed into a bone, such as the vertebra  13 , by rotation of the shank  404  using a suitable driving tool (not shown) that operably drives and rotates the shank body  406  by engagement thereof at the internal drive  450  and in a percutaneous or minimally invasive surgical manner, or otherwise as desired. When the shank  404  is driven into the vertebra without the remainder of the assembly  401 , the shank  404  may either be driven to a desired final location or may be driven to a location slightly above or proud to provide for ease in assembly with the pre-assembled receiver, compression insert and retainer. 
     With reference to  FIGS. 36-37  (and the discussion previously provided herein with respect to the assembly  1 ), the pre-assembled receiver, insert and retainer are placed above the shank upper portion  408  and as the shank upper portion  408  is moved into the interior  476  of the receiver base, the shank upper portion  408  presses upwardly against the retainer  412  in the expansion recess partially defined by the cylindrical surface  484 . As the portion  408  continues to move upwardly toward the channel  462 , the surface  444  forces outward movement of the retainer  412  towards the cylindrical surface  484  in the receiver expansion chamber or area as the shank  404  presses the retainer  412  against the receiver lower annular ledge surface  487 . The retainer  412  initially expands about the shank upper spherical surface  444  and then slides along the cylindrical surface  442 , snapping or popping into the recessed cylindrical surface  438 , the surface  505  of the retainer  412  fully contacting and frictionally engaging the cylindrical surface  438  between the surfaces  434  and  442 . At this time, the retainer  412  is in a neutral or slightly expanded state, fully snapped onto the shank upper portion  408  with both the retainer  412  and shank upper portion  408  in pivotal relation with the receiver  410 . 
     With reference to  FIG. 37 , the shank  404  and attached retainer  412  are then moved downwardly into a desired position with the retainer seated on the surface  480 . The insert  414  may slide downwardly with the retainer  412 , or in some embodiments, remain in an upper part of the receiver  410  retained by the crimp walls  475  until the insert  414  is pressed downwardly by a tool or by a rod and closure top. In such embodiments, the insert  414  surface  522  is in frictional engagement with the shank upper portion surface  444  to an extent that the shank is pivotable with respect to the receiver, but in a non-floppy manner. In some embodiments, when the receiver  410  is pre-assembled with the shank  404 , the entire assembly  401  may be implanted at this time by inserting the driving tool (not shown) into the receiver and the shank drive  450  and rotating and driving the shank  404  into a desired location of the vertebra, such as the previously illustrated vertebra  13 . 
     The rod  421  is eventually positioned in an open or percutaneous manner in cooperation with the at least two bone screw assemblies  401 . The closure structure  418  is then inserted into and advanced between the arms  460  of each of the receivers  410 . The closure structure  418  is rotated, using a tool engaged with the inner drive  586  until a selected pressure is reached at which point the rod  421  engages the U-shaped seating surface  531  of the compression insert  414 . Also, as shown in  FIG. 38 , the closure top annular base rim  588  engages and presses down upon top surfaces  533  of the insert  414  arms  527 , pressing the insert spherical surface  522  against the shank spherical surface  444 , that in turn presses the shank upper portion  408  with attached retainer  412  into locked frictional engagement with the receiver  410  independently of any locking pressure placed by the rod  421  onto the insert  414 . As the closure structure  418  rotates and moves downwardly into the respective receiver  410 , the point or nub  589  and dome  590  engage and penetrate or deform the rod surface  422 , the closure structure  418  pressing downwardly against and biasing the rod  421  into compressive engagement with the insert  414  that also urges the shank upper portion  408  and attached retainer  412  into locking engagement with the receiver, the retainer  412  spherical surface  507  frictionally abutting the spherical seating surface  480  of the receiver  410 . For example, about 80 to about 120 inch pounds of torque on the closure top may be applied for fixing the bone screw shank  406  with respect to the receiver  410  by direct locking engagement between the closure top  418 , the insert  414 , the shank upper portion  408  and attached retainer  412  with the receiver seating surface  480 . Over- or undue deformation of the deformable rod  421  therefore does not occur because of the direct cooperation between the closure top  418  and the compression insert  414 . Also, for example, with reference to  FIG. 39 , when the shank  404  is disposed at an angle with respect to the receiver  410 , the lower spherical surface  434  of the shank upper portion  408  may also be in frictional engagement with a portion of the receiver spherical seating surface  480 . The retainer  412  may also expand slightly upon locking, providing a full and secure frictional locking engagement with the receiver at the surface  480 . 
     If removal of the rod  421  from any of the bone screw assemblies  401  is necessary, or if it is desired to release the rod  421  at a particular location, disassembly is accomplished by using the driving tool (not shown) that mates with the internal drive  586  on the closure structure  418  to rotate and remove such closure structure from the cooperating receiver  410 . Disassembly is then accomplished in reverse order to the procedure described previously herein for assembly. 
     With reference to  FIGS. 40-47  the reference number  601  generally represents a polyaxial bone screw apparatus or assembly according to the present invention. The assembly  601  includes a shank  604 , that further includes a body  606  integral with an upwardly extending upper portion or capture structure  608 ; a receiver  610 ; an open retainer structure  612  and a compression or pressure insert  614 .  FIGS. 40 and 44-47  further show a closure structure  618  of the invention for capturing a longitudinal connecting member, for example, a rod  621  within the receiver  610 . The rod  621  having an outer cylindrical surface  622  may be the same or substantially similar to the rod  21  or other longitudinal connecting members previously described herein with respect to the assembly  1 . The assembly  601  is substantially identical to the assembly  1  with the exception of a feature of the shank  604  and a feature of the retainer  612 . Specifically, the shank  604  does not include a lower spherical surface such as the surface  34  of the shank  4  and the retainer  612  inner cylindrical surface further includes inner vertical grooves. 
     With particular reference to  FIGS. 40-42 , the shank  604  is substantially similar in form and function to the shank  4  previously described herein with respect to the assembly  1 , and thus includes the shank body  606 , upper portion or head  608 , a lower cylindrical surface  638 , a ledge  640 , an upper cylindrical surface  642 , an upper spherical surface  644  and an internal drive  650  that are the same or substantially similar in form and function to the respective body  6 , upper portion or head  8 , cylindrical surface  38 , ledge  40 , upper cylindrical surface  42 , upper spherical surface  44 , internal drive  50 , and all the other features previously described herein with respect to the shank  4  of the assembly  1  with the exception of the lower spherical surface  34 . The shank cylindrical surface  638  extends from the lower ledge  640  to adjacent a neck  626  that joins the shank upper portion  608  with the shank body  606 . 
     With particular reference to  FIGS. 40 and 44-47 , the receiver  610  is substantially similar to the receiver  10  previously described herein and thus includes a base  658  with integral upstanding arms  660 , a U-shaped channel  662 , an arm interior substantially cylindrical surface  666 , a guide and advancement structure  668 , a tool aperture  671  partially defined by a thin crimp wall  675 , an inner base cavity or chamber generally  676 , a lower cylindrical surface  678 , a spherical seating surface  680 , a central cylindrical expansion portion  684  and an upper shelf, generally  686 , the same or substantially similar in form and function to the respective base  58  with integral upstanding arms  60 , U-shaped channel  62 , arm interior substantially cylindrical surface  66 , guide and advancement structure  68 , tool aperture  71 , crimp wall  75 , inner base cavity or chamber generally  76 , lower cylindrical surface  78 , spherical seating surface  80 , central cylindrical expansion portion  84  and upper shelf, generally  86 , and other features previously described herein with respect to the receiver  10  of the assembly  1 . 
     With particular reference to  FIGS. 40, 43 and 44 , the open, expandable retainer  612  is the same or substantially similar in form and function to the retainer  12  previously described herein with respect to the assembly  1 , with the addition of inner grooves. Therefore, the retainer  612  includes a top surface  702 , a bottom surface  704 , an inner cylindrical surface  705 , an outer spherical surface  707  and a through slit  708  that are the same or similar in form and function to the respective top surface  102 , bottom surface  104 , inner cylindrical surface  105 , outer spherical surface  107  and slit formed by end surfaces  109  and  110  previously described herein with respect to the retainer  12 . Formed in the inner surface  705  are four equally spaced grooves  715 . The grooves  715  aid during the expansion of the retainer  612  and furthermore in resiliency and gripping of the retainer  612  on the shank surface  638 . As compared to the retainer  12 , the spaced grooves  715  of the retainer  612  provide for a more even expansion during assembly with the shank upper portion  608 , resulting in less stress in the area directly opposite the slit  708 . The retainer  612  also requires less space for expansion about the upper portion  608  since not all of the expansion is occurring opposite the slit  708 , but rather at each of the grooves  715 . Less stress during expansion results in a stronger retainer  12  post-expansion. 
     With reference to  FIGS. 40, 44, 45 and 47 , the compression insert  614  is substantially similar in form and function to the insert  14  previously described herein with respect to the assembly  1 . Therefore, the insert  614  includes an inner cylindrical surface  721 , an inner spherical surface  722 , a cylindrical body  726 , a pair of upstanding arms  727 , a U-shaped channel  731  having a lower seat  732 , arm top surfaces  733 , a bottom surface  735  and arm outer surfaces  737 , each with a groove  738  formed therein that are the same or substantially similar in form and function to the respective inner cylindrical surface  121 , inner spherical surface  122 , cylindrical body  126 , upstanding arms  127 , U-shaped channel  131  with lower seat  132 , arm top surfaces  133 , the bottom surface  135  and arm outer surfaces  137  with grooves  138  of the insert  14  previously described herein. 
     With reference to  FIGS. 40 and 44-47 , the closure top  618  is identical to the closure top  18  previously described herein with respect to the assembly  1  with the exception of the lower rod contacting surfaces thereof. The closure top  618  has a flange form guide and advancement structure  782 , a top surface  784 , an internal drive  786 , a bottom surface  788 , a point  789  and a rim  790  that is the same in form and function to the respective guide and advancement structure  182 , top surface  184 , internal drive  186 , base  188 , point  189  and rim  190  of the closure top  18  previously described herein. 
     The assembly and disassembly, if desired, and implantation and operation of the assembly  601  is performed in a manner identical to what has been described herein with respect to the assembly  1 . In operation, the retainer  612  inner surface  705  grips the shank surface  638  with the retainer top surface  702  abutting against the shank ledge  640  as shown, for example, in  FIGS. 44-47 . The downward force applied on the shank upper spherical surface  644  by the compression insert surface  722  maintains the retainer  612  in engagement with the ledge  640  as the retainer spherical surface  707  is pressed against the receiver seating surface  680  at all desired angles of articulation between the shank  604  and the receiver  610  as shown, for example, in  FIG. 47 . 
     With reference to  FIGS. 48-51  the reference number  801  generally represents a polyaxial bone screw apparatus or assembly according to the present invention. The assembly  801  includes a shank  804 , that further includes a body  806  integral with an upwardly extending upper portion or capture structure  808 ; a receiver  810 ; an open retainer structure  812  and a compression or pressure insert  814 .  FIGS. 48, 49 and 51  further show a closure structure  818  of the invention for capturing a longitudinal connecting member, for example, a rod  821  within the receiver  810 . The rod  821  is the same or substantially similar to the rod  21  or other longitudinal connecting members previously described herein with respect to the assembly  1 . The assembly  801  is a combination of the assembly  201  and the assembly  601 , both previously described herein. Specifically, the shank  804 , the retainer  812  and the closure top  818  are identical or substantially similar to the respective shank  604 , retainer  612  and closure top  618  of the assembly  601  while the receiver  810  and the compression insert  814  are identical or substantially similar to the respective receiver  210  and insert  214  of the assembly  201 . In other words, the assembly  801  is identical to the previously described assembly  601  with the exception that receiver spring tabs  275  and insert flat surface portions  338  of the assembly  201  have replaced the receiver crimp walls  678  and insert grooves  738  of the assembly  601 . The assembly  801  has designated spring tabs  875  and cooperating insert flat surface portions  838 . The assembly and disassembly, if desired, and implantation and operation of the assembly  801  is performed in a manner identical to what has been described herein with respect to the assembly  201 . 
     With reference to  FIGS. 52-54  the reference number  901  generally represents a polyaxial bone screw apparatus or assembly according to the present invention. The assembly  901  includes a shank  904 , that further includes a body  906  integral with an upwardly extending upper portion or capture structure  908 ; a receiver  910 ; an open retainer structure  912  and a compression or pressure insert  914 .  FIGS. 52-54  further show a closure structure  918  of the invention for capturing a longitudinal connecting member, for example, a deformable rod  921  within the receiver  910 . The rod  921  is the same or substantially similar to the rod  421  previously described herein with respect to the assembly  401 . The assembly  901  is a combination of the assembly  401  and the assembly  601 . Specifically, the shank  904  and the retainer  912  are identical or substantially similar to the respective shank  604  and retainer  612  of the assembly  601  while the receiver  910 , the compression insert  914  and the closure top  918  are identical or substantially similar to the respective receiver  410 , insert  414  and closure top  418  of the assembly  401 . The assembly and disassembly, if desired, and implantation and operation of the assembly  901  is performed in a manner identical to what has been described herein with respect to the assembly  401 . 
     With reference to  FIGS. 55-58 , an alternative open retainer  12 ′ for use with any of the other assemblies described herein is substantially similar to the open retainer  12  previously described herein with the exception of grooves formed in the retainer  12 ′. Specifically, the retainer  12 ′ includes a top surface  102 ′, a bottom surface  104 ′, an inner cylindrical surface  105 ′, an outer spherical surface  107 ′ and end surfaces  109 ′ and  110 ′ that are the same or similar in form and function to the respective top surface  102 , bottom surface  104 , inner cylindrical surface  105 , outer spherical surface  107  and slit formed by end surfaces  109  and  110  previously described herein with respect to the retainer  12 . Furthermore, four evenly spaced grooves  115 ′ are formed in the bottom surface  104 ′ and extend through the inner surface  105 ′ and the outer spherical surface  107 ′ about halfway toward the top surface  102 ′. It is foreseen that there may be more or fewer groves  115 ′. The grooves  115 ′ advantageously even out the stress on the retainer  12 ′ during expansion thereof over a shank upper portion  8 ,  208 ,  408 ,  608 ,  808  or  908  previously described herein. Thus, the grooves  115 ′ aid in making the retainer  12 ′ more strong and resilient, deforming outwardly during expansion in a more even or uniform fashion at the grooves  115 ′, resulting in less stress at the portion of the retainer located directly opposite the slit formed by the end surfaces  109 ′ and  110 ′. 
     With reference to  FIGS. 59-60  the reference number  1001  generally represents a polyaxial bone screw apparatus or assembly according to the present invention. The assembly  1001  includes a shank  1004 , that further includes a body  1006  integral with an upwardly extending upper portion or capture structure  1008 ; a receiver  1010 ; an open retainer structure  1012  and a compression or pressure insert  1014 .  FIGS. 59 and 60  further show a closure structure  1018  of the invention for capturing a longitudinal connecting member, for example, a rod  1021  within the receiver  1010 . The rod  1021  is the same or substantially similar to the rod  21  or other longitudinal connecting members previously described herein with respect to the assembly  1 . The receiver  1010 , the insert  1014 , the closure top  1018  and the rod  1021  are identical or substantially similar to the respective receiver  210 , insert  214 , closure top  218  and rod  221  previously described herein with respect to the assembly  201  shown in  FIGS. 21-29  and previously described herein. The shank  1004  and the retainer  1012  are similar to the respective shank  204  and retainer  212  of the assembly  201 , but there are some differences. Primarily, the shank and retainer have been modified to have a frusto-conical interface as compared to the cylindrical interface shown between the shank  204  and the retainer  212 . 
     Specifically, the shank  1004 , having the shank body  1006  includes a helically wound bone implantable thread  1024  (single or dual lead thread form) extending from near a neck  1026  located adjacent to the upper portion or capture structure  1008 , to a tip  1028  of the body  1006  and extending radially outwardly therefrom. The neck  1026  extends axially upward from the shank body  1006 . The neck  1026  may be of the same or is typically of a slightly reduced radius as compared to an adjacent upper end or top  1032  of the body  1006  where the thread  1024  terminates. Further extending axially and outwardly from the neck  1026  is the shank upper portion  1008  that provides a connective or capture apparatus disposed at a distance from the upper end  1032  and thus at a distance from a vertebra, such as the vertebra  13  when the body  1006  is implanted in such vertebra. 
     The shank upper portion  1008  is configured for a pivotable connection between the shank  1004  (with attached retainer  1012 ) and the receiver  1010  prior to fixing of the shank  1004  in a desired position with respect to the receiver  1010 . The shank upper portion  1008  has an outer, convex and substantially spherical lower surface  1034  that extends outwardly and upwardly from the neck  1026  and terminates at a frusto-conical surface  1038 . In some embodiments of the invention, the spherical lower surface  1034  has an outer radius that is the same or substantially similar to an outer radius of the retainer  1012  so that the surface  1034  as well as the retainer  1012  outer surface participating in the ball and socket joint formed by the shank  1004  and attached retainer  1012  within the partially spherical surface defining an inner cavity of the receiver  1010 . However, in other embodiments, the radius of the shank portion  1034  may be different than a radius of the retainer  1012 . Adjacent the spherical surface  1034  is the upwardly and inwardly extending frusto-conical surface  1038 . Extending outwardly from the frusto-conical surface  1038  is an annular surface or upper ledge  1040  that faces downwardly toward the frusto-conical surface  1038  and is substantially perpendicular to a central axis of the shank  1004 . The frusto-conical surface  1038  and the upper ledge  1040  cooperate to capture and fix the resilient open retainer  1012  to the shank upper portion  1008 , prohibiting movement of the retainer  1012  along the shank axis once the retainer  1012  is located beneath ledge  1040 . The illustrated frusto-conical surface  1038  is narrower at a top thereof. In other words, a diameter of the surface  1038  near the upper ledge  1040  is smaller than a diameter of the surface  1038  near the lower spherical surface  1034 . Extending upwardly from the upper ledge  1040  is a spherical or domed surface  1044 . The spherical surface  1044  has an outer radius configured for sliding cooperation and ultimate frictional mating with a substantially spherical concave surface of the compression insert  1014  that has the same or substantially similar radius as the surface  1044 . The radius of the surface  1044  is smaller than the radius of the lower spherical surface  1034 . Located near or adjacent to the surface  1044  is an annular top surface  1046 . A counter sunk internal drive feature  1050  is formed in the top surface  1046  and has a hex shape designed to receive a hex tool (not shown) of an Allen wrench type, into the aperture for rotating and driving the bone screw shank  1004 . 
     The open retainer  1012  that operates to capture the shank upper portion  1008  within the receiver  1010  is made from a resilient material, such as a stainless steel or titanium alloy, so that the retainer  1012  may be expanded during assembly. However, because there is no need to compress the retainer  1012  during assembly, an opening or slit, generally  1108  that allows for expansion of the retainer  1012  is designed to be very narrow, advantageously providing substantial or almost full surface contact between the retainer and the shank upper portion  1008  and also between the retainer and the receiver  1010  seating surface. The retainer  1012  has a central channel or hollow through bore that passes entirely through the structure  1012  from a top surface  1102  to a bottom surface  1104  thereof. The bore is primarily defined by a discontinuous inner frusto-conical surface  1105  that runs from the top surface  1102  to the bottom surface  1104 . The retainer  1012  further includes an outer substantially spherical surface  1107  running between the top surface  1102  and the bottom surface  1104 , the surface  1107  having the same or similar radius (when the resilient retainer  1012  is in a non-expanded, neutral or near neutral state) as the receiver  1010  seating surface and the shank lower spherical surface  1034  and thus larger than the radius of the dome  1044  of the shank  1004  that engages the similarly radiused lower surface of the insert  1014 . The resilient retainer  1012  further includes first and second end surfaces disposed in spaced relation to one another forming the slit  1108  when the retainer is in a neutral or near neutral state. 
     The assembly  1001  is assembled in a manner similar to the assembly  1 ,  201  and  601 , for example, as previously described herein, with the shank upper portion  1008  being snapped or popped into the receiver  1010  by pushing the shank spherical surface  1044  through the retainer  1012  already located within the receiver inner cavity. As shown in  FIG. 60 , once assembled, the frusto-conical surface  1038  of the shank  1004  contacts the frusto-conical surface  1105  of the retainer  1012  with the retainer top surface  1102  abutting against the shank ledge surface  1040 , providing a secure fit between the shank  1004  and the retainer  1012 , the retainer  1012  thus capturing the shank head  1008  within the receiver  1010 . Further assembly and disassembly, if desired, and implantation and operation of the assembly  1001  is performed in a manner identical to what has been described herein with respect to the assemblies  1 ,  201 ,  601  and  801 , for example. 
     With reference to  FIGS. 61-62  the reference number  2001  generally represents another polyaxial bone screw apparatus or assembly according to the present invention. The assembly  2001  includes a shank  2004 , that further includes a body  2006  integral with an upwardly extending upper portion or capture structure  2008 ; a receiver  2010 ; an open retainer structure  2012  and a compression or pressure insert  2014 .  FIGS. 61 and 62  further show a closure structure  2018  of the invention for capturing a longitudinal connecting member, for example, a rod  2021  within the receiver  2010 . The rod  2021  is the same or substantially similar to the rod  21  or other longitudinal connecting members previously described herein with respect to the assembly  1 . The receiver  2010 , the insert  2014 , the closure top  2018  and the rod  2021  are identical or substantially similar to the respective receiver  10 , insert  14 , closure top  18  and rod  21  previously described herein with respect to the assembly  1  shown in  FIGS. 1-20  and previously described herein. The shank  2004  and the retainer  2012  are similar to the respective shank  4  and retainer  12  of the assembly  1 , but there are some differences. Primarily, the shank and retainer have been modified to have a frusto-conical interface as compared to the cylindrical interface shown between the shank  4  and the retainer  12 . 
     Specifically, the shank  2004 , having the shank body  2006  includes a helically wound bone implantable thread  2024  (single or dual lead thread form) extending from near a neck  2026  located adjacent to the upper portion or capture structure  2008 , to a tip  2028  of the body  2006  and extending radially outwardly therefrom. The neck  2026  extends axially upward from the shank body  2006 . The neck  2026  may be of the same or is typically of a slightly reduced radius as compared to an adjacent upper end or top  2032  of the body  2006  where the thread  2024  terminates. Further extending axially and outwardly from the neck  2026  is the shank upper portion  2008  that provides a connective or capture apparatus disposed at a distance from the upper end  2032  and thus at a distance from a vertebra, such as the vertebra  13  when the body  2006  is implanted in such vertebra. 
     The shank upper portion  2008  is configured for a pivotable connection between the shank  2004  (with attached retainer  2012 ) and the receiver  2010  prior to fixing of the shank  2004  in a desired position with respect to the receiver  2010 . The shank upper portion  2008  has an outer, convex and substantially spherical lower surface  2034  that. extends outwardly and upwardly from the neck  2026  and terminates at a lower ledge  2036 . The spherical lower surface  2034  has an outer radius that is the same or substantially similar to an outer radius of the retainer  2012 , the surface  2034  as well as the retainer  2012  outer surface participating in the ball and socket joint formed by the shank  2004  and attached retainer  2012  within the partially spherical surface defining an inner cavity of the receiver  2010 . Adjacent the surface  2034  is the annular, planar lower ledge surface  2036  positioned perpendicular to a central axis of the shank  2004 . Extending outwardly and upwardly from the lower ledge  2036  is a frusto-conical surface  2038 . Extending from the frusto-conical surface  2038  is an annular surface or upper ledge  2040  that is opposite the lower ledge  2036 , and faces downwardly toward the frusto-conical surface  2038 , the upper ledge  2040  also being substantially perpendicular to the central axis of the shank  2004 . The frusto-conical surface  2038  and the upper and lower ledges  2036  and  2040  cooperate to capture and fix the resilient open retainer  2012  to the shank upper portion  2008 , prohibiting movement of the retainer  2012  along the shank axis once the retainer  2012  is located between the ledges  2036  and  2040 . The illustrated frusto-conical surface  2038  is narrower at a bottom thereof. In other words, a diameter of the surface  2038  near the upper ledge  2040  is larger than a diameter of the surface  2038  near the bottom ledge  2036 . Extending upwardly from the upper ledge  2040  is a spherical or domed surface  2044 . The spherical surface  2044  has an outer radius configured for sliding cooperation and ultimate frictional mating with a substantially spherical concave surface of the compression insert  2014  that has the same or substantially similar radius as the surface  2044 . The radius of the surface  2044  is smaller than the radius of the lower spherical surface  2034 . Located near or adjacent to the surface  2044  is an annular top surface  2046 . A counter sunk internal drive feature  2050  is formed in the top surface  2046  and has a hex shape designed to receive a hex tool (not shown) of an Allen wrench type, into the aperture for rotating and driving the bone screw shank  2004 . 
     The open retainer  2012  that operates to capture the shank upper portion  2008  within the receiver  2010  is made from a resilient material, such as a stainless steel or titanium alloy, so that the retainer  2012  may be expanded during assembly. However, because there is no need to compress the retainer  2012  during assembly, an opening or slit, generally  2108  that allows for expansion of the retainer  2012  is designed to be very narrow, advantageously providing substantial or almost full surface contact between the retainer and the shank upper portion  2008  and also between the retainer and the receiver  2010  seating surface. The retainer  2012  has a central channel or hollow through bore that passes entirely through the structure  2012  from a top surface  2102  to a bottom surface  2104  thereof. The bore is primarily defined by a discontinuous inner frusto-conical surface  2105  that runs from the top surface  2102  to the bottom surface  2104 . The retainer  2012  further includes an outer substantially spherical surface  2107  running between the top surface  2102  and the bottom surface  2104 , the surface  2107  having the same or similar radius (when in a neutral or near neutral state) as the receiver  2010  seating surface and the shank lower spherical surface  2034  and thus larger than the radius of the dome  2044  of the shank  2004  that engages the similarly radiused lower surface of the insert  2014 . The resilient retainer  2012  further includes first and second end surfaces disposed in spaced relation to one another forming the slit  2108  when the retainer is in a neutral or near neutral state. 
     The assembly  2001  is assembled in a manner similar to the assembly  1 , for example, as previously described herein, with the shank upper portion  2008  being snapped or popped into the receiver  2010  by pushing the shank spherical surface  2044  through the retainer  2012  already located within the receiver inner cavity. As shown in  FIG. 62 , once assembled, the frusto-conical surface  2038  of the shank  2004  contacts the frusto-conical surface  2105  of the retainer  2012  with the retainer bottom surface  2104  seated on the shank lower ledge surface  2036  and a portion of the retainer top surface  2102  abutting against the shank upper ledge surface  2040 , providing a secure fit between the shank  2004  and the retainer  2012 , the retainer  2012  thus capturing the shank head  2008  within the receiver  2010 . Further assembly and disassembly, if desired, and implantation and operation of the assembly  2001  is performed in a manner identical to what has been described herein with respect to the assemblies  1 ,  201 ,  601  and  801 , for example. 
     With reference to  FIGS. 63-64  the reference number  3001  generally represents another polyaxial bone screw apparatus or assembly according to the present invention. The assembly  3001  includes a shank  3004 , that further includes a body  3006  integral with an upwardly extending upper portion or capture structure  3008 ; a receiver  3010 ; an open retainer structure  3012  and a compression or pressure insert  3014 .  FIGS. 63 and 64  further show a closure structure  3018  of the invention for capturing a longitudinal connecting member, for example, a rod  3021  within the receiver  3010 . The rod  3021  is the same or substantially similar to the rod  21  or other longitudinal connecting members previously described herein with respect to the assembly  1 . The receiver  3010 , the insert  3014 , the closure top  3018  and the rod  3021  are identical or substantially similar to the respective receiver  210 , insert  214 , closure top  218  and rod  221  previously described herein with respect to the assembly  201  shown in  FIGS. 21-29  and previously described herein. The shank  3004  and the retainer  3012  are similar to the respective shank  204  and retainer  212  of the assembly  201 , but there are some differences. Primarily, the shank and retainer have been modified to have a sloping and curved interface as compared to the cylindrical interface shown between the shank  204  and the retainer  212 . 
     Specifically, the shank  3004 , having the shank body  3006  includes a helically wound bone implantable thread  3024  (single or dual lead thread form) extending from near a neck  3026  located adjacent to the upper portion or capture structure  3008 , to a tip  3028  of the body  3006  and extending radially outwardly therefrom. The neck  1026  extends axially upward from the shank body  1006 . The neck  3026  may be of the same or is typically of a slightly reduced radius as compared to an adjacent upper end or top  3032  of the body  3006  where the thread  3024  terminates. Further extending axially and outwardly from the neck  3026  is the shank upper portion  3008  that provides a connective or capture apparatus disposed at a distance from the upper end  3032  and thus at a distance from a vertebra, such as the vertebra  13  when the body  3006  is implanted in such vertebra. 
     The shank upper portion  3008  is configured for a pivotable connection between the shank  31004  (with attached retainer  3012 ) and the receiver  3010  prior to fixing of the shank  3004  in a desired position with respect to the receiver  3010 . The shank upper portion  3008  has an outer, convex and substantially spherical lower surface  3034  that extends outwardly and upwardly from the neck  3026  and terminates at a curved surface  3038 . The spherical lower surface  3034  has an outer radius that is the same or substantially similar to an outer radius of the retainer  3012  so that the surface  3034  as well as the retainer  3012  outer surface participating in the ball and socket joint formed by the shank  3004  and attached retainer  3012  within the partially spherical surface defining an inner cavity of the receiver  3010 . Adjacent the spherical surface  3034  the an upwardly and inwardly extending curved surface of revolution  3038  formed about a central axis of the shank  3004 , the illustrated surface  3038  being somewhat trumpet-like in form, having at least one and up to a plurality a radii. Extending outwardly from the surface  3038  is an annular surface or upper ledge  3040  that faces downwardly toward the curved surface  3038  and is substantially perpendicular to the central axis of the shank  3004 . The curved surface  3038  and the upper ledge  3040  cooperate to capture and fix the resilient open retainer  3012  to the shank upper portion  3008 , prohibiting movement of the retainer  3012  along the shank axis once the retainer  3012  is located beneath ledge  3040 . The illustrated curved surface  3038  is narrower at a top thereof. In other words, a diameter of the surface  3038  near the upper ledge  3040  is smaller than a diameter of the surface  3038  near the lower spherical surface  3034 . Extending upwardly from the upper ledge  3040  is a spherical or domed surface  3044 . The spherical surface  3044  has an outer radius configured for sliding cooperation and ultimate frictional mating with a substantially spherical concave surface of the compression insert  3014  that has the same or substantially similar radius as the surface  3044 . The radius of the surface  3044  is smaller than the radius of the lower spherical surface  3034 . Located near or adjacent to the surface  3044  is an annular top surface  3046 . A counter sunk internal drive feature  3050  is formed in the top surface  3046  and has a hex shape designed to receive a hex tool (not shown) of an Allen wrench type, into the aperture for rotating and driving the bone screw shank  3004 . 
     The open retainer  3012  that operates to capture the shank upper portion  3008  within the receiver  3010  is made from a resilient material, such as a stainless steel or titanium alloy, so that the retainer  3012  may be expanded during assembly. However, because there is no need to compress the retainer  3012  during assembly, an opening or slit, generally  3108  that allows for expansion of the retainer  3012  is designed to be very narrow, advantageously providing substantial or almost full surface contact between the retainer and the shank upper portion  3008  and also between the retainer and the receiver  3010  seating surface. The retainer  3012  has a central channel or hollow through bore that passes entirely through the structure  3012  from a top surface  3102  to a bottom surface  3104  thereof. The bore is primarily defined by a discontinuous inner curved surface of rotation  3105  that runs from the top surface  3102  to the bottom surface  3104 . The retainer  3012  further includes an outer substantially spherical surface  3107  running between the top surface  3102  and the bottom surface  3104 , the surface  3107  having the same or similar radius (when the resilient retainer  3012  is in a non-expanded, neutral or near neutral state) as the receiver  3010  seating surface and the shank lower spherical surface  3034  and thus larger than the radius of the dome  3044  of the shank  3004  that engages the similarly radiused lower surface of the insert  3014 . The resilient retainer  3012  further includes first and second end surfaces disposed in spaced relation to one another forming the slit  3108  when the retainer is in a neutral or near neutral state. 
     The assembly  3001  is assembled in a manner similar to the assembly  1 ,  201  and  601 , for example, as previously described herein, with the shank upper portion  3008  being snapped or popped into the receiver  3010  by pushing the shank spherical surface  3044  through the retainer  3012  already located within the receiver inner cavity. As shown in  FIG. 64 , once assembled, the curved surface  3038  of the shank  3004  matches and is in mating contact with the curved surface  3105  of the retainer  3012  with a portion of the retainer top surface  3102  abutting against the shank ledge surface  3040 , providing a secure fit between the shank  3004  and the retainer  3012 , the retainer  3012  thus capturing the shank head  3008  within the receiver  3010 . Further assembly and disassembly, if desired, and implantation and operation of the assembly  3001  is performed in a manner identical to what has been described herein with respect to the assemblies  1 ,  201 ,  601  and  801 , for example. 
     With reference to  FIGS. 65-66  the reference number  4001  generally represents another polyaxial bone screw apparatus or assembly according to the present invention. The assembly  4001  includes a shank  4004 , that further includes a body  4006  integral with an upwardly extending upper portion or capture structure  4008 ; a receiver  4010 ; an open retainer structure  4012  and a compression or pressure insert  4014 .  FIGS. 65 and 66  further show a closure structure  4018  of the invention for capturing a longitudinal connecting member, for example, a rod  4021  within the receiver  4010 . The rod  4021  is the same or substantially similar to the rod  21  or other longitudinal connecting members previously described herein with respect to the assembly  1 . The receiver  4010 , the insert  4014 , the closure top  4018  and the rod  4021  are identical or substantially similar to the respective receiver  10 , insert  14 , closure top  18  and rod  21  previously described herein with respect to the assembly  1  shown in  FIGS. 1-20  and previously described herein. The shank  4004  and the retainer  4012  are similar to the respective shank  4  and retainer  12  of the assembly  1 , but there are some differences. Primarily, the shank and retainer have been modified to have a curved, surface of rotation interface as compared to the cylindrical interface shown between the shank  4  and the retainer  12 . 
     Specifically, the shank  4004 , having the shank body  4006  includes a helically wound bone implantable thread  4024  (single or dual lead thread form) extending from near a neck  4026  located adjacent to the upper portion or capture structure  4008 , to a tip  4028  of the body  4006  and extending radially outwardly therefrom. The neck  4026  extends axially upward from the shank body  4006 . The neck  4026  may be of the same or of a slightly reduced radius as compared to an adjacent upper end or top  4032  of the body  4006  where the thread  4024  terminates. Further extending axially and outwardly from the neck  4026  is the shank upper portion  4008  that provides a connective or capture apparatus disposed at a distance from the upper end  4032  and thus at a distance from a vertebra, such as the vertebra  13  when the body  4006  is implanted in such vertebra. 
     The shank upper portion  4008  is configured for a pivotable connection between the shank  4004  (with attached retainer  4012 ) and the receiver  4010  prior to fixing of the shank  4004  in a desired position with respect to the receiver  4010 . The shank upper portion  4008  has an outer, convex and substantially spherical lower surface  4034  that extends outwardly and upwardly from the neck  4026  and terminates at an annular surface  4036 . The spherical lower surface  4034  has an outer radius that is the same or substantially similar to an outer radius of the retainer  4012 , the surface  4034  as well as the retainer  4012  outer surface participating in the ball and socket joint formed by the shank  4004  and attached retainer  4012  within the partially spherical surface defining an inner cavity of the receiver  4010 . Adjacent the surface  4034  is the annular, planar lower ledge surface  4036  positioned perpendicular to a central axis of the shank  4004 . Extending outwardly and upwardly from the lower ledge  4036  is a curved surface of rotation  4038  formed about the shank central axis. Unlike the trumpet like surface  3038  previously described with respect to the assembly  3001 , the surface  4038  is uniform, defined by a curve with a single radius. Extending from the curved surface  4038  is an annular surface or upper ledge  4040  that is opposite the lower ledge  4036 , and faces downwardly toward the curved surface  4038 , the upper ledge  4040  also being substantially perpendicular to the central axis of the shank  4004 . The curved surface  4038  and the upper and lower ledges  4036  and  4040  cooperate to capture and fix the resilient open retainer  4012  to the shank upper portion  4008 , prohibiting movement of the retainer  4012  along the shank axis once the retainer  4012  is located between the ledges  4036  and  4040 . Extending upwardly from the upper ledge  4040  is a spherical or domed surface  4044 . The spherical surface  4044  has an outer radius configured for sliding cooperation and ultimate frictional mating with a substantially spherical concave surface of the compression insert  4014  that has the same or substantially similar radius as the surface  4044 . The radius of the surface  4044  is smaller than the radius of the lower spherical surface  4034  and the outer radius of the retainer  4012 . Located near or adjacent to the surface  4044  is an annular top surface  4046 . A counter sunk internal drive feature  4050  is formed in the top surface  4046  and has a hex shape designed to receive a hex tool (not shown) of an Allen wrench type, into the aperture for rotating and driving the bone screw shank  4004 . 
     The open retainer  4012  that operates to capture the shank upper portion  4008  within the receiver  4010  is made from a resilient material, such as a stainless steel or titanium alloy, so that the retainer  4012  may be expanded during assembly. However, because there is no need to compress the retainer  4012  during assembly, an opening or slit, generally  4108  that allows for expansion of the retainer  4012  is designed to be very narrow, advantageously providing substantial or almost full surface contact between the retainer and the shank upper portion  4008  and also between the retainer and the receiver  4010  seating surface. The retainer  4012  has a central channel or hollow through bore that passes entirely through the structure  4012  from a top surface  4102  to a bottom surface  4104  thereof. The bore is primarily defined by a discontinuous inner curved surface  4105  that runs from the top surface  4102  to the bottom surface  4104 . The retainer  4012  further includes an outer substantially spherical surface  4107  running between the top surface  4102  and the bottom surface  4104 , the surface  4107  having the same or similar radius (when in a neutral or near neutral state) as the receiver  4010  seating surface and the shank lower spherical surface  4034  and thus larger than the radius of the dome  4044  of the shank  4004  that engages the insert  4014 . The resilient retainer  4012  further includes first and second end surfaces disposed in spaced relation to one another forming the slit  4108  when the retainer is in a neutral or near neutral state. 
     The assembly  4001  is assembled in a manner similar to the assembly  1 , for example, as previously described herein, with the shank upper portion  4008  being snapped or popped into the receiver  4010  by pushing the shank spherical surface  4044  through the retainer  4012  already located within the receiver inner cavity. As shown in  FIG. 66 , once assembled, the curved surface  4038  of the shank  4004  aligns and closely contacts the curved surface  4105  the retainer  4012  with the retainer bottom surface  4104  seated on the shank lower ledge surface  4036  and a portion of the retainer top surface  4102  abutting against the shank upper ledge surface  4040 , providing a secure fit between the shank  4004  and the retainer  4012 , the retainer  4012  thus capturing the shank head  4008  within the receiver  4010 . Further assembly and disassembly, if desired, and implantation and operation of the assembly  4001  is performed in a manner identical to what has been described herein with respect to the assemblies  1 ,  201 ,  601  and  801 , for example. 
     With reference to  FIGS. 67-68  the reference number  5001  generally represents another polyaxial bone screw apparatus or assembly according to the present invention. The assembly  5001  includes a shank  5004 , that further includes a body  5006  integral with an upwardly extending upper portion or capture structure  5008 ; a receiver  5010 ; an open retainer structure  5012  and a compression or pressure insert  5014 .  FIGS. 67 and 68  further show a closure structure  5018  of the invention for capturing a longitudinal connecting member, for example, a rod  5021  within the receiver  5010 . The rod  5021  is the same or substantially similar to the rod  21  or other longitudinal connecting members previously described herein with respect to the assembly  1 . The receiver  5010 , the insert  5014 , the closure top  5018  and the rod  5021  are substantially similar to the respective receiver  10 , insert  14 , closure top  18  and rod  21  previously described herein with respect to the assembly  1  shown in  FIGS. 1-20  and previously described herein. It is noted that to accommodate the slightly taller retainer  5012 , the receiver  5010  interior has also been slightly modified to create a slightly taller inner expansion chamber for the expansion of the retainer  5012  about the shank head  5008  within such chamber. The shank  5004  and the retainer  5012  are similar to the respective shank  4  and retainer  12  of the assembly  1 , but there are some differences. Primarily, the shank and retainer have been modified to provide an assembly wherein the retainer  5012  has an outer radius that is the same as an upper outer radius of the shank  5010  that in turn engages the insert  5014  at a lower concave surface thereof, also having the same radius. 
     Specifically, the shank  5004 , having the shank body  5006  includes a helically wound bone implantable thread  5024  (single or dual lead thread form) extending from near a neck  5026  located adjacent to the upper portion or capture structure  5008 , to a tip  5028  of the body  5006  and extending radially outwardly therefrom. The neck  5026  extends axially upward from the shank body  5006 . The neck  5026  may be of the same or of a slightly reduced radius as compared to an adjacent upper end or top  5032  of the body  5006  where the thread  5024  terminates. Further extending axially and outwardly from the neck  5026  is the shank upper portion  5008  that provides a connective or capture apparatus disposed at a distance from the upper end  5032  and thus at a distance from a vertebra, such as the vertebra  13  when the body  5006  is implanted in such vertebra. 
     The shank upper portion  5008  is configured for a pivotable connection between the shank  5004  (with attached retainer  5012 ) and the receiver  5010  prior to fixing of the shank  5004  in a desired position with respect to the receiver  5010 . The shank upper portion  5008  has an outer, convex and substantially spherical lower surface  5034  that extends outwardly and upwardly from the neck  5026  and terminates at an annular surface  5036 . The spherical lower surface  5034  has an outer radius that is the same or substantially similar to an outer radius of the retainer  5012 , the surface  5034  as well as the retainer  5012  outer surface participating in the ball and socket joint formed by the shank  5004  and attached retainer  5012  within the partially spherical surface defining an inner cavity of the receiver  5010 . Adjacent the surface  5034  is the annular, planar lower ledge surface  5036  positioned perpendicular to a central axis of the shank  5004 . Extending upwardly from the lower ledge  5036  is a cylindrical surface  5038  formed about the shank central axis. Extending from the cylindrical surface  5038  is an annular surface or upper ledge  5040  that is opposite the lower ledge  5036 , the upper ledge  5040  also being substantially perpendicular to the central axis of the shank  5004 . The cylindrical surface  5038  and the upper and lower ledges  5036  and  5040  cooperate to capture and fix the resilient open retainer  5012  to the shank upper portion  5008 , prohibiting movement of the retainer  5012  along the shank axis once the retainer  5012  is located between the ledges  5036  and  5040 . Extending upwardly from the upper ledge  5040  is a spherical or domed surface  5044 . The spherical surface  5044  has an outer radius configured for sliding cooperation and ultimate frictional mating with a substantially spherical concave surface of the compression insert  5014  that has the same or substantially similar radius as the surface  5044 . The radius of the surface  5044  is the same or substantially the same as the radius of the lower spherical surface  5034  and the outer radius of the retainer  5012 . Located near or adjacent to the surface  5044  is an annular top surface  5046 . A counter sunk internal drive feature  5050  is formed in the top surface  5046  and has a hex shape designed to receive a hex tool (not shown) of an Allen wrench type, into the aperture for rotating and driving the bone screw shank  5004 . 
     The open retainer  5012  that operates to capture the shank upper portion  5008  within the receiver  5010  is made from a resilient material, such as a stainless steel or titanium alloy, so that the retainer  5012  may be expanded during assembly. However, because there is no need to compress the retainer  5012  during assembly, an opening or slit, generally  5108  that allows for expansion of the retainer  5012  is designed to be very narrow, advantageously providing substantial or almost full surface contact between the retainer and the shank upper portion  5008  and also between the retainer and the receiver  5010  seating surface. The retainer  5012  has a central channel or hollow through bore that passes entirely through the structure  5012  from a top surface  5102  to a bottom surface  5104  thereof. The bore is primarily defined by a discontinuous inner cylindrical surface  5105  that runs from the top surface  5102  to the bottom surface  5104 . The retainer  5012  further includes an outer substantially spherical surface  5107  running between the top surface  5102  and the bottom surface  5104 , the surface  5107  having the same or similar radius (when in a neutral or near neutral state) as the receiver  5010  seating surface and the shank lower spherical surface  5034  and thus the same radius as the dome  5044  of the shank  5004  that engages the insert  5014 . The resilient retainer  5012  further includes first and second end surfaces disposed in spaced relation to one another forming the slit  5108  when the retainer is in a neutral or near neutral state. 
     The assembly  5001  is assembled in a manner similar to the assembly  1 , for example, as previously described herein, with the shank upper portion  5008  being snapped or popped into the receiver  5010  by pushing the shank spherical surface  5044  through the retainer  5012  already located within the receiver inner cavity. As shown in  FIG. 68 , once assembled, the cylindrical surface  5038  of the shank  5004  aligns and closely contacts the cylindrical surface  5105  the retainer  5012  with the retainer bottom surface  5104  seated on the shank lower ledge surface  5036  and the retainer top surface  5102  abutting against the shank upper ledge surface  5040 , providing a secure fit between the shank  5004  and the retainer  5012 , the retainer  5012  thus capturing the shank head  5008  within the receiver  5010 . Further assembly and disassembly, if desired, and implantation and operation of the assembly  5001  is performed in a manner identical to what has been described herein with respect to the assemblies  1 ,  201 ,  601  and  801 , for example. 
     With reference to  FIGS. 69-70  the reference number  6001  generally represents a polyaxial bone screw apparatus or assembly according to the present invention. The assembly  6001  includes a shank  6004 , that further includes a body  6006  integral with an upwardly extending upper portion or capture structure  6008 ; a receiver  6010 ; an open retainer structure  6012  and a compression or pressure insert  6014 .  FIGS. 69 and 70  further show a closure structure  6018  of the invention for capturing a longitudinal connecting member, for example, a rod  6021  within the receiver  6010 . The rod  6021  is the same or substantially similar to the rod  21  or other longitudinal connecting members previously described herein with respect to the assembly  1 . The receiver  6010 , the insert  6014 , the closure top  6018  and the rod  6021  are identical or substantially similar to the respective receiver  210 , insert  214 , closure top  218  and rod  221  previously described herein with respect to the assembly  201  shown in  FIGS. 21-29  and previously described herein. It is noted that the receiver  6010  has been slightly modified to accommodate the retainer  6012  that is taller than the retainer  212 . The shank  6004  and the retainer  6012  are similar to the respective shank  204  and retainer  212  of the assembly  201 , but there are some differences. Primarily, the shank and retainer have been modified to have a frusto-conical interface as compared to the cylindrical interface shown between the shank  204  and the retainer  212 . Furthermore, the shank and retainer have been modified to provide an assembly wherein the retainer  6012  has an outer radius that is the same as an upper outer radius of the shank  6010  that in turn engages the insert  6014  at a lower concave surface thereof, also having the same radius. 
     Specifically, the shank  6004 , having the shank body  6006  includes a helically wound bone implantable thread  6024  (single or dual lead thread form) extending from near a neck  6026  located adjacent to the upper portion or capture structure  6008 , to a tip  6028  of the body  6006  and extending radially outwardly therefrom. The neck  6026  extends axially upward from the shank body  6006 . The neck  6026  may be of the same or is typically of a slightly reduced radius as compared to an adjacent upper end or top  6032  of the body  6006  where the thread  6024  terminates. Further extending axially and outwardly from the neck  6026  is the shank upper portion  6008  that provides a connective or capture apparatus disposed at a distance from the upper end  6032  and thus at a distance from a vertebra, such as the vertebra  13  when the body  6006  is implanted in such vertebra. 
     The shank upper portion  6008  is configured for a pivotable connection between the shank  6004  (with attached retainer  6012 ) and the receiver  6010  prior to fixing of the shank  6004  in a desired position with respect to the receiver  6010 . The shank upper portion  6008  has an outer, convex and substantially spherical lower surface  6034  that extends outwardly and upwardly from the neck  6026  and terminates at a cylindrical surface  6036 . The spherical lower surface  6034  has an outer radius that is the same or substantially similar to an outer radius of the retainer  6012  so that the surface  6034  as well as the retainer  6012  outer surface participating in the ball and socket joint formed by the shank  004  and attached retainer  6012  within the partially spherical surface defining an inner cavity of the receiver  6010 . However, in other embodiments, the radius of the shank portion  6034  may be different than a radius of the retainer  6012 . Adjacent the cylindrical surface  6036  is an upwardly and inwardly extending frusto-conical surface  6038 . Extending outwardly from the frusto-conical surface  6038  is an annular surface or upper ledge  6040  that faces downwardly toward the frusto-conical surface  6038  and is substantially perpendicular to a central axis of the shank  6004 . The frusto-conical surface  6038  and the upper ledge  6040  cooperate to capture and fix the resilient open retainer  6012  to the shank upper portion  6008 , prohibiting movement of the retainer  6012  along the shank axis once the retainer  6012  is located beneath ledge  6040 . The illustrated frusto-conical surface  6038  is narrower at a top thereof. In other words, a diameter of the surface  6038  near the upper ledge  6040  is smaller than a diameter of the surface  6038  near the lower spherical surface  6034 . Extending upwardly from the upper ledge  6040  is a cylindrical surface  6042  followed by a spherical or domed surface  6044 . The spherical surface  6044  has an outer radius configured for sliding cooperation and ultimate frictional mating with a substantially spherical concave surface of the compression insert  6014  that has the same or substantially similar radius as the surface  6044 . The radius of the surface  6044  is the same or substantially similar to the radius of the lower spherical surface  6034  and the outer spherical surface of the retainer  6012 . Located near or adjacent to the surface  6044  is an annular top surface  6046 . A counter sunk internal drive feature  6050  is formed in the top surface  6046  and has a hex shape designed to receive a hex tool (not shown) of an Allen wrench type, into the aperture for rotating and driving the bone screw shank  6004 . 
     The open retainer  6012  that operates to capture the shank upper portion  6008  within the receiver  6010  is made from a resilient material, such as a stainless steel or titanium alloy, so that the retainer  6012  may be expanded during assembly. However, because there is no need to compress the retainer  6012  during assembly, an opening or slit, generally  6108  that allows for expansion of the retainer  6012  is designed to be very narrow, advantageously providing substantial or almost full surface contact between the retainer and the shank upper portion  6008  and also between the retainer and the receiver  6010  seating surface. The retainer  6012  has a central channel or hollow through bore that passes entirely through the structure  6012  from a top surface  6102  to a bottom surface  6104  thereof. The bore is primarily defined by a discontinuous inner frusto-conical surface  6105  that runs from the top surface  6102  to the bottom surface  6104 . The retainer  6012  further includes an outer substantially spherical surface  6107  running between the top surface  6102  and the bottom surface  6104 , the surface  6107  having the same or similar radius (when the resilient retainer  6012  is in a non-expanded, neutral or near neutral state) as the receiver  6010  seating surface, the shank lower spherical surface  6034  and the dome  6044  of the shank  6004  that engages the similarly radiused lower surface of the insert  6014 . The resilient retainer  6012  further includes first and second end surfaces disposed in spaced relation to one another forming the slit  6108  when the retainer is in a neutral or near neutral state. 
     The assembly  6001  is assembled in a manner similar to the assembly  1 ,  201  and  601 , for example, as previously described herein, with the shank upper portion  6008  being snapped or popped into the receiver  6010  by pushing the shank spherical surface  6044  through the retainer  6012  already located within the receiver inner cavity. As shown in  FIG. 70 , once assembled, the frusto-conical surface  6038  of the shank  6004  closely contacts the frusto-conical surface  6105  of the retainer  6012  along an entire surface thereof with a portion of the retainer top surface  6102  abutting against the shank ledge surface  6040 , providing a secure fit between the shank  6004  and the retainer  6012 , the retainer  6012  thus capturing the shank head  6008  within the receiver  6010 . Further assembly and disassembly, if desired, and implantation and operation of the assembly  6001  is performed in a manner identical to what has been described herein with respect to the assemblies  1 ,  201 ,  601  and  801 , for example. 
     With reference to  FIGS. 71-72  the reference number  7001  generally represents a polyaxial bone screw apparatus or assembly according to the present invention. The assembly  7001  includes a shank  7004 , that further includes a body  7006  integral with an upwardly extending upper portion or capture structure  7008 ; a receiver  7010 ; an open retainer structure  7012  and a compression or pressure insert  7014 .  FIGS. 71 and 72  further show a closure structure  7018  of the invention for capturing a longitudinal connecting member, for example, a rod  7021  within the receiver  7010 . The rod  7021  is the same or substantially similar to the rod  21  or other longitudinal connecting members previously described herein with respect to the assembly  1 . The receiver  7010 , the insert  7014 , the closure top  7018  and the rod  7021  are identical or substantially similar to the respective receiver  210 , insert  214 , closure top  218  and rod  221  previously described herein with respect to the assembly  201  shown in  FIGS. 21-29 . It is noted that the receiver  7010  has been slightly modified to accommodate the retainer  7012  that is taller than the retainer  212 . The shank  7004  and the retainer  7012  are similar to the respective shank  204  and retainer  212  of the assembly  201 , but there are some differences. Primarily, the shank and retainer have been modified to have a combination frusto-conical and cylindrical interface as compared to the cylindrical interface shown between the shank  204  and the retainer  212 . Furthermore, the shank and retainer have been modified to provide an assembly wherein the retainer  7012  has an outer radius that is the same as an upper outer radius of the shank  7010  that in turn engages the insert  7014  at a lower concave surface thereof, also having the same radius. 
     Specifically, the shank  7004 , having the shank body  7006  includes a helically wound bone implantable thread  7024  (single or dual lead thread form) extending from near a neck  7026  located adjacent to the upper portion or capture structure  7008 , to a tip  7028  of the body  7006  and extending radially outwardly therefrom. The neck  7026  extends axially upward from the shank body  7006 . The neck  7026  may be of the same or slightly reduced radius as compared to an adjacent upper end or top  7032  of the body  7006  where the thread  7024  terminates. Further extending axially and outwardly from the neck  7026  is the shank upper portion  7008  that provides a connective or capture apparatus disposed at a distance from the upper end  7032  and thus at a distance from a vertebra, such as the vertebra  13  when the body  7006  is implanted in such vertebra. 
     The shank upper portion  7008  is configured for a pivotable connection between the shank  7004  (with attached retainer  7012 ) and the receiver  7010  prior to fixing of the shank  7004  in a desired position with respect to the receiver  7010 . The shank upper portion  7008  has an outer, convex and substantially spherical lower surface  7034  that extends outwardly and upwardly from the neck  7026  and terminates at a cylindrical surface  7035 . The spherical lower surface  7034  has an outer radius that is the same or substantially similar to an outer radius of the retainer  7012  so that the surface  7034  as well as the retainer  7012  outer surface participating in the ball and socket joint formed by the shank  7004  and attached retainer  7012  within the partially spherical surface defining an inner cavity of the receiver  7010 . However, in other embodiments, the radius of the shank portion  7034  may be different than a radius of the retainer  7012 . Adjacent the cylindrical surface  7035  is an annular surface  7036  disposed perpendicular to a central axis of the shank  7004 . The surface  7036  is in turn adjacent to an upwardly and inwardly extending frusto-conical surface  7038 . Extending outwardly from the frusto-conical surface  7038  is an annular surface or upper ledge  7040  that faces downwardly toward the frusto-conical surface  7038  and is substantially perpendicular to the central axis of the shank  7004 . The cylindrical surface  7035 , lower ledge  7036 , frusto-conical surface  7038  and upper ledge  7040  cooperate to capture and fix the resilient open retainer  7012  to the shank upper portion  7008 , prohibiting movement of the retainer  7012  along the shank axis once the retainer  7012  is located beneath ledge  7040 . The illustrated frusto-conical surface  7038  is narrower at a top thereof. In other words, a diameter of the surface  7038  near the upper ledge  7040  is smaller than a diameter of the surface  7038  near the cylindrical surface  7035 . Extending upwardly from the upper ledge  7040  is a cylindrical surface  7042  followed by a spherical or domed surface  7044 . The spherical surface  7044  has an outer radius configured for sliding cooperation and ultimate frictional mating with a substantially spherical concave surface of the compression insert  7014  that has the same or substantially similar radius as the surface  7044 . The radius of the surface  7044  is the same or substantially similar to the radius of the lower spherical surface  7034  and the outer spherical surface of the retainer  7012 . Located near or adjacent to the surface  7044  is an annular top surface  7046 . A counter sunk internal drive feature  7050  is formed in the top surface  7046  and has a hex shape designed to receive a hex tool (not shown) of an Allen wrench type, into the aperture for rotating and driving the bone screw shank  7004 . 
     The open retainer  7012  that operates to capture the shank upper portion  7008  within the receiver  7010  is made from a resilient material, such as a stainless steel or titanium alloy, so that the retainer  7012  may be expanded during assembly. However, because there is no need to compress the retainer  7012  during assembly, an opening or slit, generally  7108  that allows for expansion of the retainer  7012  is designed to be very narrow, advantageously providing substantial or almost full surface contact between the retainer and the shank upper portion  7008  and also between the retainer and the receiver  7010  seating surface. The retainer  7012  has a central channel or hollow through bore that passes entirely through the structure  7012  from a top surface  7102  to a bottom surface  7104  thereof. The bore is primarily defined by a discontinuous inner frusto-conical surface  7105  that runs from the top surface  7102  to a cylindrical surface  7106  that in turn is adjacent to the bottom surface  7104 . The retainer  7012  further includes an outer substantially spherical surface  7107  running between the top surface  7102  and the bottom surface  7104 , the surface  7107  having the same or similar radius (when the resilient retainer  7012  is in a non-expanded, neutral or near neutral state) as the receiver  7010  seating surface, the shank lower spherical surface  7034  and the dome  7044  of the shank  7004  that engages the similarly radiused lower surface of the insert  7014 . The resilient retainer  7012  further includes first and second end surfaces disposed in spaced relation to one another forming the slit  7108  when the retainer is in a neutral or near neutral state. 
     The assembly  7001  is assembled in a manner similar to the assembly  1 ,  201  and  601 , for example, as previously described herein, with the shank upper portion  7008  being snapped or popped into the receiver  7010  by pushing the shank spherical surface  7044  through the retainer  7012  already located within the receiver inner cavity. As shown in  FIG. 72 , once assembled, the frusto-conical surface  7038  of the shank  7004  closely contacts the frusto-conical surface  7105  of the retainer  7012  along an entire surface thereof with a portion of the retainer top surface  7102  abutting against the shank ledge surface  7040 . Also, the retainer inner cylindrical surface  7106  closely mates with the shank outer cylindrical surface  7035 , with a portion of the retainer being seated on the ledge surface  7036 . Such a plurality of closely contacting surfaces provides a secure fit between the shank  7004  and the retainer  7012 , the retainer  7012  thus capturing the shank head  7008  within the receiver  7010 . Further assembly and disassembly, if desired, and implantation and operation of the assembly  7001  is performed in a manner identical to what has been described herein with respect to the assemblies  1 ,  201 ,  601  and  801 , for example. 
     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.