Patent Publication Number: US-2023157730-A1

Title: Pivotal bone anchor assembly with method for insert tool deployment

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 17/581,797, filed Jan. 21, 2022, now U.S. Pat. No. 11,559,335, which is a continuation of U.S. patent application Ser. No. 14/658,721, filed Mar. 16, 2015, now U.S. Pat. No. 11,229,457, which is a continuation of Ser. No. 13/317,387, filed Oct. 19, 2011, now U.S. Pat. No. 8,998,959, which claims the benefit of U.S. Provisional Application No. 61/455,842, filed Oct. 21, 2010, each of which is incorporated by reference in its entirety herein, and for all purposes. 
     U.S. patent application Ser. No. 13/317,387 is also a continuation-in-part of U.S. patent application Ser. No. 12/924,802, filed Oct. 5, 2010, now U.S. Pat. No. 8,556,938, and which application Ser. No. 12/924,802 claims the benefit of the following U.S. Provisional Patent Applications: U.S. Provisional Application No. 61/278,240, filed Oct. 5, 2009; U.S. Provisional Application No. 61/336,911, filed Jan. 28, 2010; U.S. Provisional Application No. 61/343,737, filed May 3, 2010; U.S. Provisional Application No. 61/395,564, filed May 14, 2010; U.S. Provisional Application No. 61/395,752, filed May 17, 2010; U.S. Provisional Application No. 61/396,390, filed May 26, 2010; U.S. Provisional Application No. 61/398,807, filed Jul. 1, 2010; U.S. Provisional Application No. 61/400,504, filed Jul. 29, 2010; U.S. Provisional Application No. 61/402,959, filed Sep. 8, 2010; U.S. Provisional Application No. 61/403,696, filed Sep. 20, 2010; and U.S. Provisional Application No. 61/403,915, filed Sep. 23, 2010. Each of the above applications is incorporated by reference in its entirety herein, and for all purposes. 
     U.S. patent application Ser. No. 14/658,721 is also a continuation-in-part of U.S. patent application Ser. No. 12/802,849, filed Jun. 15, 2010, now abandoned, and which application Ser. No. 12/802,849 claims the benefit of the following U.S. Provisional Patent Applications: U.S. Provisional Application No. 61/268,708, filed Jun. 15, 2009; U.S. Provisional Application No. 61/270,754, filed Jul. 13, 2009; U.S. Provisional Application No. 61/336,911, filed Jan. 28, 2010; U.S. Provisional Application No. 61/395,564, filed May 14, 2010; U.S. Provisional Application No. 61/395,752, filed May 17, 2010; and U.S. Provisional Application No. 61/396,390, filed May 26, 2010. Each of the above applications is incorporated by reference in its entirety herein, and for all purposes. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention is directed to polyaxial bone screw shanks with heads for use in bone surgery, more specifically to spinal surgery and particularly to such screws with receiver member assemblies including compression or pressure inserts and expansion-only split retainers to snap over, capture and retain the bone screw shank head in the receiver member assembly and later fix the bone screw shank with respect to the receiver assembly. 
     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. Generally, the screws must be inserted into the bone as an integral unit along with the head, or as a preassembled unit in the form of a shank and pivotal receiver, such as a polyaxial bone screw assembly. 
     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 similar open ends for receiving rods or portions of other fixation and stabilization structure. 
     A common approach for providing vertebral column 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, or may be of a polyaxial screw nature. 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 typically allow for a loose or floppy rotation of the head or receiver about the shank until a desired rotational position of the receiver is achieved by fixing such position relative to the shank during a final stage of a medical procedure when a rod or other longitudinal connecting member is inserted into the receiver, followed by a locking screw or other closure. This floppy feature can be, in some cases, undesirable and make the procedure more difficult. Also, it is often desirable to insert the bone screw shank separate from the receiver or head due to its bulk which can get in the way of what the surgeon needs to do. Such screws that allow for this capability are sometimes referred to as modular polyaxial screws. 
     With specific reference to modular snap-on or pop-on polyaxial pedicle screw systems having shank receiver assemblies, the prior art has shown and taught the concept of the receiver and certain retainer parts forming an assembly wherein a contractile locking engagement between the parts is created to fix the shank head with respect to the receiver and retainer. The receiver and shank head retainer assemblies in the prior art have included a contractile retainer ring and/or a lower pressure insert with an expansion and contraction collet-type of structure having contractile locking engagement for the shank head due to direct contact between the retainer and/or the collet structure with the receiver resulting in contraction of the retainer ring and/or the collet-type structure of the insert against the shank head. 
     The prior art for modular polyaxial screw assemblies has also shown and taught that the contact surfaces on the outside of the collect and/or retainer and the inside of the receiver can be tapered, conical, radiused, spherical, curvate, multi-curvate, rounded, as well as other configurations to create a contractile type of locking engagement for the shank head with respect to the receiver. 
     In addition, the prior art for modular polyaxial screw assemblies has shown and taught that the shank head can both enter and escape from a collet-like structure on the insert or from the retainer when the insert or retainer is in the up position and within the expansion recess or chamber of the receiver. This is the case unless the insert and/or the retainer are blocked from being able to be pushed back up into receiver bore or cavity. 
     SUMMARY OF THE INVENTION 
     The present invention differentiates from the prior art by not allowing the receiver to be removed from the shank head once the parts are snapped-on and connected. This is true even if the retainer can go back up into the expansion chamber. This approach or design has been found to be more secure and to provide more resistance to pull-out forces compared to the prior art for modular polyaxial screw designs. Collect-like structures extending downwardly from lower pressure inserts, when used in modular polyaxial screw designs, as shown in the prior art, have been found to be somewhat weak with respect to pull-out forces encountered during some spinal reduction procedures. The present invention is designed to solve these problems. 
     The present invention also differentiates from all of the prior art by providing a split retainer ring with a collet-like upper portion or super structure, wherein the collet-like structure having inwardly facing panels or fingers does not participate at all in the locking engagement for the shank head with respect to the receiver. In addition, the retainer ring itself for the present invention is uniquely characterized by a base portion providing expansion to receive and capture the shank head and then having only expansion (not contraction) locking engagement between the shank head and the retainer ring base and between the retainer ring base and horizontal and vertical loading surfaces near a bottom opening of the receiver. 
     The expansion-only retainer ring base in the present invention is positioned entirely below the shank head hemisphere in the receiver and can be a stronger, more substantial structure to resist larger pull out forces on the assembly. The retainer ring base can also be better supported on a generally horizontal loading surface near the lower opening in the bottom of the receiver. This design has been found to be stronger and more secure when compared to that of the prior art which uses some type of contractile locking engagement between the parts, as described above; and, again, once assembled it cannot be disassembled. 
     Thus, a polyaxial bone screw assembly according to the invention includes a shank having an integral upper portion or integral spherical head and a body for fixation to a bone; a separate receiver defining an upper open channel, a central bore, a lower cavity and a lower opening; a top drop and turn in place lower compression insert; and a friction fit resilient expansion-only split retainer for capturing the shank head in the receiver lower cavity, the shank head being frictionally engaged with, but still movable in a non-floppy manner with respect to the friction fit retainer and the receiver prior to locking of the shank into a desired configuration. The compression insert operatively engages the shank head and is spaced from the retainer by the head that is snapped into the resilient retainer. The shank is finally locked into a fixed position relative to the receiver by frictional engagement between the insert and a lower split ring-like portion of the retainer base, as described previously, due to a downward force placed on the compression insert by a closure top pressing on a rod, or other longitudinal connecting member, captured within the receiver bore and channel. In the illustrated embodiments, retainers and compression inserts are downloaded into the receiver, but uploaded embodiments are also foreseen. The shank head can be positioned into the receiver lower cavity at the lower opening thereof prior to or after insertion of the shank into bone. Some compression inserts include a lock and release feature for independent locking of the polyaxial mechanism os the screw can be used like a fixed monoaxial screw. The shank can be cannulated for minimally invasive surgery applications. The receiver can have crimp tabs, but is devoid of any type of spring tabs or collet-like structures. The lower pressure insert and/or the retainer are both devoid of any type of receiver-retainer contractile locking engagements with respect to the shank head. The retainer can also have upwardly extending spring tabs which are deployed into openings in the receiver cavity so that the retainer and captured shank head are stabilized and retained in the region of the receiver locking chamber once they enter into this lower portion of the receiver cavity. In this way, the shank head and retainer cannot go back up into the receiver cavity. 
     Again, a pre-assembled receiver, compression insert and friction fit split retainer may be “pushed-on”, “snapped-on” or “popped-on” to the shank head prior to or after implantation of the shank into a vertebra. Such a “snapping on” procedure includes the steps of uploading the shank head into the receiver lower opening, the shank head pressing against the base portion of the split retainer ring and expanding the resilient lower open retainer portion out into an expansion portion or chamber of the receiver cavity followed by an elastic return of the retainer back to an original or nominal shape thereof after the hemisphere of the shank head or upper portion passes through the lower ring-like portion of the retainer. The shank head also enters into the friction fit upper portion or super structure of the retainer, the panels of the friction fit portion of the retainer snapping onto the shank head as the retainer returns to a neutral or close to neutral orientation, providing a non-floppy connection between the retainer and the shank head. The friction fit between the shank head and the retainer is temporary and not part of the final locking mechanism. In the illustrated embodiment, when the shank is ultimately locked between the compression insert and the lower portion of the retainer, the friction fit collet-like panels of the retainer are no longer in a friction fit engagement with the shank head and they are not in contact with the receiver. The final fixation occurs as a result of a locking expansion-type of contact between the shank head and the lower portion of the split retainer and an expansion-type of non-tapered locking engagement between the lower portion of the retainer ring and the locking chamber in the lower portion of the receiver cavity. The retainer can expand more in the upper portion or expansion chamber of the receiver cavity to allow the shank head to pass through, but has restricted expansion to retain the shank head when the retainer lower ring portion is against the locking chamber surfaces in the lower portion of the receiver cavity and the shank head is forced down against the retainer ring during final locking. In some embodiments, when the polyaxial mechanism is locked, the insert is wedged against a surface of the receiver resulting in a tapered locking engagement, allowing for adjustment or removal of the rod or other connecting member without loss of a desired angular relationship between the shank and the receiver. This independent locking feature allows the polyaxial screw to function like a fixed monoaxial screw. 
     It is foreseen that the lower pressure insert could also be configured to be independently locked by a tool or instrument, thereby allowing the pop-on polyaxial screw to be distracted, compressed and/or rotated along and around the rod to provide for improved spinal correction techniques. Such a tool would engage the pop-on receiver from the sides and then engage the insert and wedge or force the insert down into a locked position within the receiver. With the tool still in place and the correction maintained, the rod could then be locked within the receiver channel by a closure top followed by removal of the tool. This process could involve multiple screws all being manipulated simultaneously with multiple tools to achieve the desired correction. 
     It is noted that once the shank head is captured by the retainer ring and the retainer and head are moved down into the locking chamber region of the receiver cavity, retainer spring tabs are deployed outwardly stabilizing the retainer so that the retainer cannot go back up into the receiver cavity. This spring tab deployment also creates good rotational stability between the retainer and receiver and provides for an additional rotational friction fit between the shank head and the receiver itself since the retainer cannot axially rotate in the receiver. 
     Objects of the invention further include providing 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 front elevational view of a polyaxial bone screw assembly according to the present invention including a shank, a receiver without spring tabs, an open friction fit expansion-only retainer and a top drop and turn in place lower compression insert, further shown with a portion of a longitudinal connecting member in the form of a rod and a closure top. 
         FIG.  2    is an enlarged top plan view of the shank of  FIG.  1   . 
         FIG.  3    is reduced 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   . 
         FIG.  5    is a reduced perspective view of the receiver of  FIG.  4   . 
         FIG.  6    is a reduced top plan view of the receiver of  FIG.  4   . 
         FIG.  7    is a reduced bottom plan view of the receiver of  FIG.  4   . 
         FIG.  8    is a reduced cross-sectional view taken along the line  8 - 8  of  FIG.  6   . 
         FIG.  9    is an enlarged cross-sectional view taken along the line  9 - 9  of  FIG.  6   . 
         FIG.  10    is an enlarged perspective view of the retainer of  FIG.  1   . 
         FIG.  11    is an enlarged side elevational view of the retainer of  FIG.  10   . 
         FIG.  12    is an enlarged front elevational view of the retainer of  FIG.  10   . 
         FIG.  13    is an enlarged top plan view of the retainer of  FIG.  10   . 
         FIG.  14    is an enlarged bottom plan view of the retainer of  FIG.  10   . 
         FIG.  15    is a cross-sectional view taken along the line  15 - 15  of  FIG.  13   . 
         FIG.  16    is an enlarged perspective view of the insert of  FIG.  1   . 
         FIG.  17    is an enlarged side elevational view of the insert of  FIG.  16   . 
         FIG.  18    is an enlarged top plan view of the insert of  FIG.  16   . 
         FIG.  19    is an enlarged bottom plan view of the insert of  FIG.  16   . 
         FIG.  20    is a cross-sectional view taken along the line  20 - 20  of  FIG.  18   . 
         FIG.  21    is an enlarged front elevational view of an alternative insert according to the invention for use in lieu of the insert shown in  FIG.  1   , with portions broken away to show the detail thereof. 
         FIG.  22    is an enlarged front elevational view of the retainer and receiver of  FIG.  1    with portions of the receiver broken away (as illustrated in  FIG.  27   ) to show the detail thereof, the retainer being shown downloaded into the receiver (in phantom) to a partially inserted stage of assembly. 
         FIG.  23    is a front elevational view of the retainer and receiver with portions broken away, similar to that shown in  FIG.  24   , further showing the retainer seated within the receiver and also showing the insert of  FIG.  1    in side elevation (in phantom) above the receiver and then being downloaded into the receiver to a partially inserted stage of assembly. 
         FIG.  24    is a front elevational view with portions broken away, similar to  FIG.  23   , showing the insert rotated into a position in alignment with the receiver. 
         FIG.  25    is a front elevational view with portions broken away, similar to  FIG.  24    showing arms or upwardly extending spring tabs of the retainer being pinched (with a tool not shown) towards one another and the retainer partially moved upwardly within the receiver. 
         FIG.  26    is a front elevational view similar to  FIG.  25    showing the retainer arms placed in a desired upward position within the receiver and the pinching tool removed so that the retainer pushes outwardly against the receiver and is held against the receiver during shipping. 
         FIG.  27    is a reduced perspective view with portions broken away of the assembly as shown in  FIG.  26   . 
         FIG.  28    is a perspective view with portions broken away, similar to  FIG.  27   , showing a portion of the receiver crimped against the insert. 
         FIG.  29    is an enlarged front elevational view with portions broken away, similar to  FIG.  26   , also including the crimping of  FIG.  28    and further showing an enlarged and partial shank of  FIG.  1    in a first stage of assembly with the retainer, a hemisphere of the shank head and a vertebra portion are both shown in phantom. 
         FIG.  30    is a partial front elevational view with portions broken away, similar to  FIG.  29   , showing the retainer lower portion in an expanded state about a mid-portion of the shank head, the head hemisphere shown in phantom. 
         FIG.  31    is a reduced partial front elevational view with portions broken away, similar to  FIG.  30   , the shank upper portion or head in frictional engagement with an upper portion of the retainer. 
         FIG.  32    is a partial side elevational view with portions broken away of the assembly in a stage as shown in  FIG.  31   . 
         FIG.  33    is a partial front elevational view with portions broken away, similar to  FIG.  31   , the shank upper portion with attached retainer being shown pulled down into a seated position within the lower receiver cavity. 
         FIG.  34    is an enlarged and partial front elevational view with portions broken away of the entire assembly of  FIG.  1   , the assembly shown in a locked position with the insert wedged against surfaces of the receiver. 
         FIG.  35    is an enlarged and partial side elevational view with portions broken away of the entire assembly of  FIG.  1   , shown locked into position with the shank disposed at an angle with respect to the receiver, the rod being shown in phantom. 
         FIG.  36    is a reduced and partial front elevational view with portions broken away, similar to  FIG.  34   , showing the insert retaining the assembly in a locked position when the closure top and the rod are removed. 
         FIG.  37    is an enlarged and partial front elevational view with portion broken away, similar to  FIG.  36   , further showing the assembly with a replacement deformable rod and alternative closure top. 
         FIG.  38    is an enlarged perspective view of an alternative non-locking insert according to the invention. 
         FIG.  39    is an enlarged and partial front elevational view of the assembly of  FIG.  1    shown in a fully assembled locked position with the non-locking insert of  FIG.  38    in lieu of the locking insert shown in  FIG.  1   , 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 - 39    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 head structure  8 ; a receiver  10 ; a friction fit retainer  12 , and a crown-like 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  17 , as will be described in greater detail below.  FIGS.  1  and  34 - 36    further show a closure structure  18  for capturing a longitudinal connecting 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  17 . The illustrated rod  21  is hard, stiff, non-elastic and cylindrical, having an outer cylindrical surface  22 . It is foreseen that in other embodiments, the rod  21  may be elastic, deformable and/or of different materials and cross-sectional geometries. 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 and different thread types) extending from near a neck  26  located adjacent to the upper portion or head  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  17  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 a location at or 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 or head  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  17  when the body  6  is implanted in such vertebra. 
     The shank upper portion  8  is configured for a pivotable connection between the shank  4  and the retainer  12  and 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 surface  34  that extends outwardly and upwardly from the neck  26  that in some embodiments terminates at a substantially planar top or rim surface  38 . In the illustrated embodiment, a frusto-conical surface  39  extends from the spherical surface  34  to the top surface  38 , providing additional clearance during shank angulation as best shown in  FIG.  35   . The spherical surface  34  has an outer radius configured for temporary frictional, non-floppy, sliding cooperation with panels of the retainer  12  having concave or flat surfaces, as well as ultimate frictional engagement with the insert  14  at an inner partially spherical surface thereof, as will be discussed more fully in the paragraphs below. The top surface  38  is substantially perpendicular to the axis A. The spherical surface  34  shown in the present embodiment is substantially smooth, but in some embodiments may include a roughening or other surface treatment and is sized and shaped for cooperation and ultimate frictional engagement with the compression insert  14  as well as ultimate frictional engagement with a lower ring-like portion of the retainer  12 . The shank spherical surface  34  is locked into place exclusively by the insert  14  and the retainer  12  lower portion and not by inner surfaces defining the receiver cavity. 
     A counter sunk substantially planar base or stepped seating surface  45  partially defines an internal drive feature or imprint  46 . The illustrated internal drive feature  46  is an aperture formed in the top surface  38  and has a star shape designed to receive a 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 hex-shaped aperture. The seat or base surfaces  45  of the drive feature  46  are disposed substantially perpendicular to the axis A with the drive feature  46  otherwise being coaxial with the axis A. As illustrated in  FIGS.  2  and  3   , the drive seat  45  may include beveled or stepped surfaces that may further enhance gripping with the driving tool. In operation, a driving tool (not shown) is received in the internal drive feature  46 , being seated at the base  45  and engaging the faces of the drive feature  46  for both driving and rotating the shank body  6  into the vertebra  17 , either before the shank  4  is attached to the receiver  10  or after the shank  4  is attached to the receiver  10 , with the shank body  6  being driven into the vertebra  17  with the driving tool extending into the receiver  10 . 
     The shank  4  shown in the drawings is cannulated, having a small central bore  50  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 external drive  46  at the driving seat  45 . The bore  50  is coaxial with the threaded body  6  and the upper portion  8 . The bore  50  provides a passage through the shank  4  interior for a length of wire (not shown) inserted into the vertebra  17  prior to the insertion of the shank body  6 , the wire providing a guide for insertion of the shank body  6  into the vertebra  17 . It is foreseen that the shank could be solid and made of different materials, including metal and non-metals. 
     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 4 ) 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  and  4 - 9   , the receiver  10  has a generally U-shaped appearance with partially discontinuous and partially cylindrical inner and outer profiles. 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  17 , the axis B is typically disposed at an angle with respect to the axis A, as shown, for example, in  FIG.  35   . 
     The receiver  10  includes a substantially cylindrical base  60  defining a bore or inner cavity, generally  61 , the base  60  being integral with a pair of opposed upstanding arms  62  forming a cradle and defining a channel  64  between the arms  62  with an upper opening, generally  66 , and a U-shaped lower channel portion or seat  68 , the channel  64  having a width for operably snugly receiving the rod  21  or portion of another longitudinal connector between the arms  62 , the channel  64  communicating with the base cavity  61 . Inner opposed substantially planar arm surfaces  69  partially define the channel  64  directly above the seat  68  and are located on either side of each arm interior surface generally  70 , that includes various inner cylindrical profiles, an upper one of which is a partial helically wound guide and advancement structure  72  located adjacent top surfaces  73  of each of the arms  62 . In the illustrated embodiment, the guide and advancement structure  72  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 for certain embodiments of the invention, the guide and advancement structure  72  could alternatively be a square-shaped thread, a buttress thread, a reverse angle thread or other thread-like or non-threadlike helically wound discontinuous advancement structures, for operably guiding under rotation and advancing the closure structure  18  downward between the arms  62 , as well as eventual torquing when the closure structure  18  abuts against the rod  21  or other longitudinal connecting member. It is foreseen that the arms  62  could have break-off extensions. 
     An opposed pair of key-hole like tool receiving and engaging grooves or apertures, generally  74 , each having an upper arched through bore  75 , are formed on outer surfaces  76  of the arms  62 . Each through bore  75  extends between the outer surface  76  and the inner surface  70  and is located above a rectangular shaped shallow recessed arm portion or crimp wall  77  that defines the portion of the aperture  74  that does not extend completely through the respective arm  62 . The thin walled portion  77  is pressed or crimped into the insert  14  to prohibit rotation and misalignment of the insert  14  with respect to the receiver  10  as will be described in greater detail below. In other embodiments of the invention, other surfaces forming the groove or aperture  74  may be inwardly crimped. The receiver  10  is an integral structure and devoid of any spring tabs or collet-like structures. Preferably the insert and/or receiver are configured with structure for blocking rotation of the insert with respect to the receiver, such as crimp tabs  77 , but allowing some up and down movement of the insert with respect to the receiver during the assembly and implant procedure. Two additional rectangular shaped through bores  78  are also formed in the arms  62  and located directly below the apertures  74 . It is foreseen that the opening  78  could assume almost any shape. The through bores  78  are sized and shaped for receiving portions of the retainer  12  during top loading of the retainer  12  into the receiver  10  as will be described more fully below and as shown, for example, in  FIG.  22   . An upper surface  79  defining each bore  78  functions as an upper stop for a portion of the retainer  12 , during shipping and during assembly, as shown, for example, in  FIG.  28   , and as will be described in greater detail below. Also formed in each outer arm surface  76  near the top surface  73  is an undercut tool receiving and engaging groove  81 . Some or all of the apertures  74  and  78  and the groove  81  may be used for holding the receiver  10  during assembly with the insert  14 , the retainer  12  and the shank  4 ; during the implantation of the shank body  6  into a vertebra when the shank is pre-assembled with the receiver  10 ; during assembly of the bone anchor assembly  1  with the rod  21  and the closure structure  18 ; and during lock and release adjustment of the insert  14  with respect to the receiver  10 , either into or out of frictional engagement with the inner surfaces of the receiver  10  as will be described in greater detail below. 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 . 
     Returning to the interior surface  70  of the receiver arms  62 , located below the guide and advancement structure  72  is a discontinuous cylindrical surface  82  partially defining a run-out feature for the guide and advancement structure  72 . The cylindrical surface  82  has a diameter equal to or slightly greater than a greater diameter of the guide and advancement structure  72 . Moving downwardly, in a direction toward the base  60 , following the cylindrical surface  82  of each arm is a cylindrical or tapered surface  84  partially defined by a run-out seat or surface  85  that extends inwardly toward the axis B and runs perpendicular or somewhat obliquely towards the axis B. The surface  84  has a diameter smaller than the diameter of the surface  82 . The surface  84  is sized and shaped to initially closely receive a lower portion of the insert  14  and later frictionally engage a tapered or frusto-conical upper portion of the insert  14 , providing a lock and release function that will be described in greater detail below. A discontinuous annular surface  86  is located below and adjacent to the surface  84 . The surface  86  is substantially perpendicular to the axis B, but could also be somewhat oblique. Another discontinuous cylindrical surface  88  is located below and adjacent to the surface  86 . The surface  88  has a diameter slightly larger than the diameter of the surface  84 . A discontinuous annular surface or narrow ledge  89  is located below the surface  88  and is substantially perpendicular to the axis B. A partially discontinuous cylindrical surface  90  is located on each arm below and adjacent to the surface  89 . The surface  90  also defines an upper cylindrical surface of the base cavity  61 . The surface  90  has a diameter slightly smaller than the diameter of the surface  88  but larger than the diameter of the surface  84 . It is noted that in some embodiments of the invention, the surfaces  88  and  90  are combined and form a single smooth cylindrical surface. 
     The through bores  75  each extend through the arms at the surfaces  82 ,  84  and  88 . The crimping wall  77  is located in an inner recessed surface area  92  that is formed in both the surfaces  88  and  90 . In the illustrated embodiment, the crimping wall  77  has an inner surface  93  that is primarily located at the portion of the area  92  that is formed in the cylindrical surface  88 . Each through bore  78  is located directly below the area  92 . It is foreseen that the crimp wall  77  could be in the form of a deformable crimp tab. 
     An annular surface  98  partially defining the base cavity  61  is located below and adjacent to the cylindrical surface  90 . The surface  98  is disposed substantially perpendicular to the axis B, but could be oblique. Another cylindrical surface  99  is located below and adjacent to the surface  98 . The cylindrical surface  99  is oriented substantially parallel to the axis B and is sized and shaped to receive an expanded portion of retainer  12 . The surfaces  98  and  99  define a circumferential recess that is sized and shaped to receive the retainer  12  as it expands around the shank upper portion  8  as the shank  8  moves upwardly toward the channel  64  during assembly. It is foreseen that the recess could be tapered or conical in configuration. A cylindrical surface  101  located below the cylindrical surface  99  is sized and shaped to closely receive and surround a lower portion of the retainer  12  when the retainer is in a substantially neutral position as shown in  FIG.  23   , for example. Thus, the cylindrical surface  101  has a diameter smaller than the diameter of the cylindrical surface  99  that defines the expansion area or expansion chamber for the retainer  12 . The surface  101  is joined or connected to the surface  99  by one or more beveled, curved or conical surfaces  102 . The surfaces  102  allow for sliding and neutral or nominal positioning of the retainer  12  into the space defined by the surface  101  and ultimate seating of the retainer  12  on a lower substantially horizontal annular surface  104  located below and adjacent to the cylindrical surface  101 . 
     Located below and adjacent to the annular seating surface  104  is another substantially cylindrical surface  106  that communicates with a beveled or flared bottom opening surface  107 , the surface  107  communicating with an exterior base surface  108  of the base  60 , defining a lower opening, generally  110 , into the base cavity  61  of the receiver  10 . 
     With particular reference to  FIGS.  1  and  10 - 15   , the lower open or split friction fit retainer  12 , that operates to capture the shank upper portion  8  within the receiver  10 , has a central axis that is operationally the same as the axis B associated with the receiver  10  when the shank upper portion  8  and the retainer  12  are installed within the receiver  10 . The retainer  12  includes a substantially cylindrical discontinuous lower body  116 , a plurality of flex fingers or panels,  117  extending upwardly from the body  116  and a pair of opposed spring arms or tabs  118 , also extending upwardly from the body  116 . The retainer ring  12  is made from a resilient material, such as a stainless steel or titanium alloy, so that the retainer  12  body  116  may be expanded and the panels and tabs ( 117  and  118 ) of the retainer may be manipulated during various steps of assembly as will be described in greater detail below. The retainer  12  has a central channel or hollow through bore, generally  121 , that passes entirely through the retainer  12  from tab  118  top surfaces  122  to a bottom surface  124  of the retainer body  116 . Surfaces that define the channel or bore  121  include an inner lower frusto-conical surface  128  adjacent to the retainer body bottom surface  124 , a substantially cylindrical surface  130  adjacent the frusto-conical surface  128 , a narrow frusto-conical or beveled surface  131  adjacent the cylindrical surface  130  and a partially continuous partially discontinuous substantially spherical surface  132  adjacent the surface  131 , the surface  132  being substantially continuous near the cylindrical surface  130  with the exception of the opposed spring tabs  118  and a through slot or slit, generally  134 . It is foreseen that the surface  131  could also be cylindrical. The surface  132  is in a plurality of segments or pieces at the flex fingers or panels  117  wherein a plurality of substantially evenly spaced slots  136  running outwardly and upwardly through an upper surface  137  separate the surface  132  into the individual flex fingers or panels  117 . In the illustrated embodiment, the slots  136  and the through slit  134  form the six substantially uniform flex fingers or panels  117  as well as partially define the two spring tabs  118 , each panel having the inner spherical surface  132 . It is foreseen that more or fewer flex fingers, tabs or panels may be made by the forming of more or fewer slots  136  and that the surface  132  could be planar or tapered. The discontinuous spherical surface  132  is sized and shaped to closely fit about and snap onto the shank surface  34  during assembly as will be described in greater detail below. Preferably the surface  132  has a radius the same, slightly smaller or slightly larger than the radius of the spherical shank surface  34 . The surface  132  could be bent or deformed inwardly or outwardly to better cooperate with the shank head. In operation, the discontinuous surface  132  advantageously frictionally engages the bone screw shank upper portion or head  8 , allowing for un-locked but non-floppy placement of the angle of the shank  4  with respect to the receiver  10  during surgery prior to locking of the shank  4  with respect to the receiver  10  near the end of the procedure. At the time of locking engagement, as shown in  FIG.  34   , for example, downward and outward force placed on the retainer  12  by the shank upper portion  8  expands the retainer body  116  at the slit  134  and the individual flex fingers or panels  117  no longer frictionally grip the spherical head surface  34  of the upper portion  8 . To aid in bending flexibility and resiliency, certain flex fingers  117  may have sloping outer surfaces or other geometry to gain the level of resiliency desired for expansion and gripping of the fingers  117  about the shank upper portion  8 . The spherical surfaces  132  may include a surface treatment or roughening to provide a desired friction fit. Again, it is noted that the surfaces  132  need not be spherical and may be planar or faceted or include other surface geometries that resiliently grip the shank upper portion or head  8 . Again, in some embodiments, the flexible panels or tabs  117  may be bent or deformed to further enhance frictional engagement. It is noted that the fingers  117  that are directed generally upwardly toward the receiver channel  64  advantageously sufficiently snap about and then grip the shank surface  34  to an extent to provide the friction fit desired for non-floppy placement of the shank body  6  at a desired angle with respect to the receiver  10  during manipulation of the bone screws  1  and the rod  21  or other longitudinal connecting member during surgery. However, as compared to bone screw inserts such as collets known in the art that include downwardly directed portions or panels that are ultimately wedged between a receiver surface and a shank surface upon final locking of the shank to the receiver, the thin upwardly directed fingers or panels  117  that extend away from the shank locking surface that are not as strong as the retainer body  116  or the insert  114 , do not participate or cooperate with the final locking of the insert  114  to the shank upper portion  8 , the shank upper portion  8  to the retainer  12 , and the retainer  12  to the receiver inner and substantially planar surfaces  101  and  104 . For such purpose, the more substantial retainer body  116  having only the very narrow slit  134 , used for expansion purposes only, is the component that locks the shank upper portion  8  between the receiver  10 , the insert  114  and the rod  21  or other longitudinal connecting member. In addition, the surface  131  can be cylindrical and provide a sharp edge for the shank head to lock against. 
     The retainer body  116 , the flex fingers  117  and a portion of each of the spring tabs  118  have an outer substantially cylindrical profile, sized and shaped to closely and slidingly fit within the receiver cavity  61  with the exception of outward extensions or wings, generally  140 , of the spring tabs  118  that are located adjacent to the upper surfaces  122 , each wing extending outwardly away from the respective tab body  118  and having a projected outward surface  142  spaced from each top surface  122  that is sized and shaped to closely cooperate and frictionally engage upper surfaces  79  defining the through bores  78 . Outer surfaces  143  located directly beneath each upper surface  122  and above the surfaces  142  are sized and shaped to cooperate with and frictionally engage the cylindrical surface  90  during assembly and shipping as shown, for example, in  FIG.  26   . The tab wings  140  may include more or fewer projections or notches as needed for tooling to resiliently hold the retainer in an upper portion of the cavity  61  when desired, but readily release the retainer  12  into a lower portion of the receiver cavity  61  once the retainer flex tabs  117  engage the shank head  8 . The illustrated spring tabs  118  each includes one or more planar or curved inner surfaces  144  running from the top surface  122  to a tab base surface or seat  145  located adjacent and lateral to the surface  131 . The surfaces  144  extend both outwardly and upward from the base surface  145 . It is foreseen that in other embodiments of the invention, fewer or greater number of planar or other surfaces with other geometries may extend between the top surface  122  and the inner surfaces defining the body  116  of the retainer  12 . Again, the surface  131  can be parallel with the surface  130  and provide a sharp locking edge for the shank head to engage. 
     The through slit  134  of the resilient retainer  12  is defined by first and second end surfaces,  146  and  147  disposed in spaced relation to one another (they may also be touching) when the retainer is in a neutral state. Both end surfaces  146  and  147  are disposed substantially perpendicular to the bottom surface  124 . A width X between the surfaces  146  and  147  is very narrow (slit may be made by EDM process) to provide stability to the retainer  12  during operation. Because the retainer  12  is top loadable in a neutral state and the retainer  12  does not need to be compressed to fit within the receiver cavity  61 , the width X may be much smaller than might be required for a bottom loaded compressible retainer ring. The gap X functions only in expansion to allow the retainer  12  to expand about the shank upper portion  8 . This results in a stronger retainer that provides more surface contact with the shank upper portion  8  upon locking, resulting in a sturdier connection with less likelihood of failure than a retainer ring having a greater gap. Furthermore, because the retainer  12  body  116  is only expanded and never compressed inwardly, the retainer  12  does not undergo the mechanical stress that typically is placed on spring ring type retainers known in the prior art that are both compressed inwardly and expanded outwardly during assembly. 
     It is foreseen that in some embodiments of the invention, the retainer  12  inner surfaces may include a roughening or additional material to increase the friction fit against the shank upper portion  8  prior to lock down by the rod  21  or other longitudinal connecting member. Also, the embodiment shown in  FIGS.  10 - 15    illustrates the surfaces  146  and  147  as substantially parallel, however, it is foreseen that it may be desirable to orient the surfaces obliquely or at a slight angle. 
     With particular reference to  FIGS.  1  and  16 - 21   , the lock and release crown compression insert  14  is illustrated that is sized and shaped to be received by and down-loaded into the receiver  10  at the upper opening  66 . The compression insert  14  has an operational central axis that is the same as the central axis B of the receiver  10 . In operation, the insert advantageously frictionally engages the bone screw shank upper portion  8 . Furthermore, as will be described more fully below, an insert  14  that has locked the shank  4  in a desired angular position with respect to the receiver  10 , by, for example, compression from the rod  21  and closure top  18 , is also wedged into engagement with the receiver  10  at the inner surface  84  and thus retains the shank  6  in a locked position even if the rod  21  and closure top  18  are removed as shown in  FIG.  36   . Such locked position may also be released by the surgeon if desired. The insert  14  is thus preferably made from a solid resilient material, such as a stainless steel or titanium alloy, so that portions of the insert may be pinched and un-wedged from the receiver  10  with a release tool (not shown). 
     The lock-and-release compression insert  14  includes a substantially cylindrical body  156  integral with a pair of upstanding arms  157 . A bore, generally  160 , is disposed primarily within and through the body  156  and communicates with a generally U-shaped through channel  161  that is defined by the upstanding arms  157 . The channel  161  has a lower seat  162  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  157  disposed on either side of the channel  141  extend upwardly from the body  156 . The arms  157  are sized and configured for ultimate placement beneath the cylindrical run-out surface  82  located below the receiver guide and advancement structure  72 . It is foreseen that in some embodiments of the invention, for example, when the insert is non-locking as the insert  14 ″ shown in  FIGS.  38  and  39   , the arms may be extended and the closure top configured such that the arms and, more specifically, the surfaces  164  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 , 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 arms  157  include outer upper flared or frusto-conical surfaces  163  and top surfaces  164  that 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  162 , 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. As will be discussed in greater detail below, frictional engagement between the insert  14  and the receiver  10 , more particularly, the wedging of the tapered surfaces  163  into the cylindrical surfaces  84 , provides independent locking of the polyaxial mechanism of the assembly  1 , maintaining the upper shank portion  8  in locked engagement by and between the retainer  12  and the insert  14  even if the closure top  18  and/or rod  21  are thereafter removed from the receiver  10 . 
     The bore, generally  160 , is substantially defined at the body  156  by an inner cylindrical surface  166  that communicates with the seat  162  and a lower concave substantially spherical surface  168  having a radius the same or substantially similar to a radius of the surface  34  of the shank upper portion  8 . The surface  168  terminates at an annular and substantially planar base surface  169  of the body  156 . In some embodiments of the invention, located between the cylindrical surface  166  and the spherical surface  168  or located along the spherical surface  168  is a shank gripping surface portion, generally  170 , illustrated in  FIG.  21    on an alternative insert  14 ′ that is otherwise identical to the insert  14 . The gripping surface portion  170  includes one or more stepped surfaces or ridges sized and shaped to grip and penetrate into the shank head  8  when the insert  14 ′ is locked against the head surface  34 . It is foreseen that the stepped surface portion  170  may include greater or fewer number of stepped surfaces. It is foreseen that the shank gripping surface portion  170  and also the spherical surface  168  may additionally or alternatively include a roughened or textured surface or surface finish, or may be scored, knurled, or the like, for enhancing frictional engagement with the shank upper portion  8 . 
     The compression insert  14  through bore  160  is sized and shaped to receive the driving tool (not shown) therethrough that engages the shank drive feature  46  when the shank body  6  is driven into bone with the receiver  10  attached. Also, the bore  160  receives a manipulation tool (not shown) used for releasing the insert  14  from a locked position with the receiver, the tool pressing down on the shank and also gripping the insert  14  at through bores  172  located in the arms  157  or with other tool engaging features. A manipulation tool for un-wedging and releasing the insert  14  from the receiver  10  may also access the bores  172  from the receiver through bores  75  in the receiver. Thereby, tools can be configured to release the insert  14  from the inside and outside of the receiver  10 . 
     The illustrated insert  14  further includes other features for manipulating and holding the insert  14  within the receiver  10 . Each insert arm  157  includes an outer surface  174  having a substantially vertical groove  175  formed thereon, the groove  175  located below the through bore  172 . The grooves  175  cooperate with the receiver crimp wall  77  to aid in alignment of the insert channel  161  with the receiver channel  64 . Located beneath each groove  175  is a recessed area or portion  178  sized and shaped to receive and allow clearance for the upper surface  122  of the retainer wings  140 , as shown, for example, in  FIG.  26   , during assembly and shipping of the pre-assembled receiver  10 , retainer  12  and insert  14 . 
     The insert body  156  has an outer diameter slightly smaller than a diameter between crests of the guide and advancement structure  72  of the receiver  10 , allowing for top loading of the compression insert  14  into the receiver opening  66 , with the arms  157  of the insert  14  being located between the receiver arms  62  during insertion of the insert  14  into the receiver  10 . Once the arms  157  of the insert  14  are generally located beneath the guide and advancement structure  72 , the insert  14  is rotated into place about the receiver axis B until the top surfaces  164  are located directly below the guide and advancement structure  72  as will be described in greater detail below. 
     With reference to  FIGS.  38  and  39   , an alternative non-locking insert  14 ″ is identical or substantially similar to the insert  14  with the exception of outer arm surfaces  174 ″ that are substantially cylindrical and extend from a top surface  164 ″ to near a bottom surface  169 ″ of the insert  14 ″. In other words, the insert  14 ″ does not include the tapered surfaces  163  of the insert  14 . The arm surfaces  174 ″ are fully and slidingly received by the receiver surfaces  84  as well as the other receiver  10  inner arm surfaces and thus the insert  14 ″ cannot be wedged into the receiver  10  to independently lock the polyaxial mechanism of the assembly  1 . In all other respects, the insert  14 ″ functions the same as the insert  14 . 
     With reference to  FIGS.  1  and  34 - 36   , 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, non-metals 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 polyethelenes. 
     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  34 - 36   , the closure structure or closure top  18  shown with the assembly  1  is rotatably received between the spaced arms  62  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 a an outer helically wound guide and advancement structure  182  in the form of a flange that operably joins with the guide and advancement structure  72  disposed on the arms  62  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  62  and having such a nature as to resist splaying of the arms  62  when the closure structure  18  is advanced into the channel  64 , 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  62 . 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  62 . 
     An alternative closure top  18 ′ for use with a deformable rod  21 ′, such as a PEEK rod, is shown in  FIG.  37   . The top  18 ′ is identical to the top  18  with the exception that a point  189 ′ is located on a domed surface  190 ′ in lieu of the planar bottom with point and rim of the closure top  18 . 
     Preferably, the receiver  10 , the retainer  12  and the compression insert  14  are assembled at a factory setting that includes tooling for holding and alignment of the component pieces and pinching or compressing of the retainer  12  spring tabs  118  and rotating and otherwise manipulating the insert  14  arms, 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. 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 and improving logistics and distribution. 
     Pre-assembly of the receiver  10 , retainer  12  and compression insert  14  is shown in  FIGS.  22 - 28   . With particular reference to  FIG.  22   , first the retainer  12  is inserted into the upper receiver opening  66 , leading with one of the spring tabs  118  with both of the spring tab top surfaces  122  facing one arm  62  and the retainer bottom surface  124  facing the opposing arm  62  (shown in phantom). The retainer  12  is then lowered in such sideways manner into the channel  64  and partially into the receiver cavity  61 , followed by tilting the retainer  212  such that the top surface  122  and thereafter the outer tab or wing  140  of the leading spring tab  118  is moved into a nearby receiver arm through bore  78 . With reference to  FIG.  23   , the retainer  12  is then further tilted or turned and manipulated within the receiver to a position within the cavity until the retainer  12  bottom surface  124  is directed toward the receiver cavity  61  and the spring tab upper surfaces  122  are facing upwardly toward the receiver channel opening  66 . To accomplish such tilting and turning of the retainer  12 , the spring tab arm  118  located within the receiver bore  78  is manipulated downwardly and then upwardly within the bore  78  and finally shifted out of the bore  78  when the opposed spring tab arm  118  outer tab or wing  140  moves past and clears the cylindrical surface  84  of the receiver  10 . Once the retainer bottom surface  124  seats on the receiver surface  104 , both of the spring tab wings  140  are partially located in opposed receiver bores  78 . 
     With reference to  FIGS.  23  and  24   , the compression insert  14  is then downloaded into the receiver  10  through the upper opening  66  with the bottom surface  169  facing the receiver arm top surfaces  73  and the insert arms  157  located between the opposed receiver arms  62 . The insert  14  is then lowered toward the channel seat  68  until the insert  14  arm upper surfaces  164  are adjacent the run-out area below the guide and advancement structure  72  defined in part by the cylindrical surface  82 . Thereafter, the insert  14  is rotated in a clockwise or counter-clockwise manner about the receiver axis B until the upper arm surfaces  164  are directly below the guide and advancement structure  72  as illustrated in  FIG.  24    with the U-shaped channel  161  of the insert  14  aligned with the U-shaped channel  64  of the receiver  10 . In some embodiments, the insert arms  157  may need to be compressed slightly during rotation to clear inner surfaces of the receiver arms  62 . As shown in  FIGS.  24  and  25   , the outer lower cylindrical surface  174  of the insert  14  is received within the cylindrical surface  90  of the receiver. 
     With further reference to  FIGS.  24  and  25   , a tool (not shown) is then used to grip the retainer spring tab arms  118  at outer surfaces thereof and squeeze or press the tabs  118  toward one another while moving the retainer  12  in an upward direction away from the surface  104 . With reference to  FIG.  26   , when the spring tab wing surface projections  142  abut against the surface  79 , the tool (not shown) is released and a portion or portions  143  of each spring tab  118  spring out to engage the surface portion  92  formed in the receiver cylindrical surface  90 . With reference to  FIGS.  26 - 28   , the retainer  12  is now in a desired position for shipping as an assembly along with the separate shank  4 . The insert  14  recessed areas  178  are now located adjacent to the retainer spring tab top surfaces  122 . 
     With reference to  FIGS.  27  and  28   , prior to shipping the receiver thin walls  77  are then crimped inwardly toward the axis B by inserting a tool (not shown) through the receiver apertures  74 , the tool pressing the walls  77  until the wall surface  87  engages the insert  14  at the shallow central grooves  175  formed on the outer surface  174  of each of the insert arms  157 . The crimping of the wall surface  93  into the groove  175  keeps the insert  14  U-shaped channel  161  aligned with the receiver U-shaped channel  64  and also helps retain the insert  14  at the upward location shown in  FIG.  26    with the insert arm top surfaces  164  adjacent the guide and advancement structure  72  until the insert  14  is pushed downwardly toward the receiver base  60  after assembly with the shank  4 . Thus, the crimping of the receiver walls  77  helps hold the insert  14  in position and 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 crimped surface  93  up or down along the groove  175 . The insert  14  is fully captured within the receiver  10  by the guide and advancement structure  72  prohibiting movement of the insert  14  up and out through the receiver opening  66  as well as by retainer  12  located below the insert. 
     Typically, the receiver and retainer combination are shipped or otherwise provided to the end user with the spring tab outer wings  140  wedged against the receiver as shown in  FIG.  26   . 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.  29   , 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  17  (shown in phantom), 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  46 . Specifically, the vertebra  17  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  50  by first threading the wire into the opening at the bottom  28  and then out of the top opening at the drive feature  46 . 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 and attachable tower tools mating with the receiver. When the shank  4  is driven into the vertebra  17  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.  29   , 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  110 . With particular reference to  FIGS.  30  and  31   , as the shank upper portion  8  is moved into the interior  61  of the receiver base, the shank upper portion  8  presses upwardly against the retainer  12  in the recess partially defined by the cylindrical surface  99 . As the portion  8  continues to move upwardly toward the channel  64 , the surface  34  forces outward movement of the retainer  12  towards the cylindrical surface  99  defining the receiver expansion recess or chamber. The retainer  12  begins to return to its neutral state as the center of the sphere (shown in dotted lines) passes beyond the center of the retainer expansion recess. At this time also, the spherical surface  34  moves into engagement with the surfaces  132  of the retainer flex tabs or panels  117 , the panels  117  expanding slightly outwardly to receive the surface  34 . With reference to  FIG.  32   , the spherical surface  34  then enters into full frictional engagement with the panel inner surfaces  132 . At this time, the retainer  12  panels and the surface  34  are in a fairly tight friction fit, the surface  34  being pivotable with respect to the retainer  12  with some force. Thus, a tight, non-floppy ball and socket joint is now created between the retainer  12  and the shank upper portion  8 . 
     With reference to  FIG.  33   , the receiver is then pulled upwardly or the shank  4  and attached retainer  12  are then moved downwardly into a desired position with the retainer seated on the surface  104 . Again, this may be accomplished by either an upward pull on the receiver  10  or, in some cases, by driving the shank  4  further into the vertebra  17 . The insert  14  may be pressed downwardly by a tool or by a rod and closure top as shown in  FIG.  34   . Also, 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  46  and rotating and driving the shank  4  into a desired location of the vertebra  17 . Also, when the retainer  12  moves down into the locking chamber, the spring tabs are deployed out into the openings  78  and the shank and retainer cannot move back up again within the receiver. 
     Also with reference to  FIGS.  33  and  34   , prior to assembly with the rod  21  and the closure top  18 , the compression insert  14  frusto-conical surface  163  is near the surface  84 . The insert  14  is prohibited from moving any further downwardly at the beginning of the surface  84  unless forced downwardly by a locking tool or by the closure top pressing downwardly on the rod that in turn presses downwardly on the insert  14  as shown in  FIG.  34   . With further reference to  FIG.  33    and also to  FIG.  35   , at this time, the receiver  10  may be articulated to a desired angular position with respect to the shank  4 , such as that shown in  FIG.  35   , that will be held, but not locked, by the frictional engagement between the retainer  12  and the shank upper portion  8 . 
     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  62  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  162  of the compression insert  14 , further pressing the insert spherical surface  168  (or stepped shank gripping surfaces  170  of the insert  14 ′) against the shank spherical surface  34 , (the edges of the stepped surfaces  170  penetrating into the spherical surface  34 ), pressing the shank upper portion  8  into locked frictional engagement with the retainer  12 . Specifically, 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  toward the retainer  12  and into locking engagement therewith, the retainer  12  frictionally abutting the surface  104  and expanding outwardly against the cylindrical surface  101 . 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, as the closure structure  18  and the rod  21  press the insert  14  downwardly toward the base of the receiver  10 , the insert frusto-conical surface  163  is forced into the receiver cylindrical surface  84 , wedging the insert  14  into fixed frictional engagement with the receiver surface  84 . With reference to  FIG.  36   , at this time, the closure top  18  may be loosened or removed and/or the rod  21  may be adjusted and/or removed and the frictional engagement between the insert  14  and the receiver  10  at the receiver surface  84  will remain locked in place, advantageously maintaining a locked angular position of the shank  4  with respect to the receiver  10 . If the user wishes to release the insert  14  from the receiver  10  and unlock the polyaxial mechanism, a tool (not shown) may be used that includes extensions or prongs that are received by and through the opposed through bores  75  of the receiver  10  and received into the through bores  172  of the insert  14 . Such tool is then pulled upwardly in a direction along the axis B away from the receiver base  60 , thereby pulling the insert slightly upwardly and away from the receiver base  60  and releasing the frusto-conical surface  163  from the cylindrical surface  84 . Alternatively, if both the closure top  18  and the rod  21  are already removed from the receiver  10 , another manipulation tool (not shown) may be used that is inserted into the receiver at the opening  66  and into the insert channel  161 , with prongs or extensions thereof extending outwardly into the insert through bores  172 ; a piston-like portion of the tool thereafter pushing directly on the shank upper portion  8 , thereby pulling the insert  14  surface  163  away from the receiver surface  84  and thus releasing the polyaxial mechanism. At such time, the shank  4  may be articulated with respect to the receiver  10 , and the desired friction fit returns between the retainer  12  and the shank surface  34 , so that an adjustable, but non-floppy relationship still exists between the shank  4  and the receiver  10 . If further disassembly if the assembly  1  is desired, such is accomplished in reverse order to the procedure described previously herein for assembly. 
     With reference to  FIG.  37   , an alternative assembly  1 ′ is shown in which the rod  21  and closure top  18  of the assembly  1  of  FIG.  36    are replaced with a deformable rod  18 ′ and alternative closure top  18 ′. Because of the lock between the insert  14  and the receiver  10 , any loosening of the rod  21 ′ from the receiver  10  that may occur due to rod deformation does not compromise the locked polyaxial mechanism formed by the wedged in insert  14 , the shank upper portion  8 , the retainer  12  and the receiver  10 . 
     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.