# Patent

## Title
Polyaxial bone screw assembly with fixed retaining structure

## Abstract

A polyaxial bone screw assembly includes a threaded shank body having an integral upper portion receivable in a receiver and retained within the receiver by a retaining structure in the form of an open ring. The receiver has a U-shaped channel for receiving a spinal fixation rod. The shank upper portion is designed to directly frictionally engage the spinal fixation rod when a closure structure operably urges the rod toward the upper portion, fixing the bone screw shank body in a selected angular orientation with respect to the receiver.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Application No. 60/699,092 filed Jul. 14, 2005. The present application is a continuation-in-part of U.S. patent application Ser. No. 10/818,554, filed Apr. 5, 2004, now U.S. Pat. No. 7,662,175, which was a continuation of U.S. patent application Ser. No. 10/464,633, filed Jun. 18, 2003, now U.S. Pat. No. 6,716,214 and a continuation-in-part of U.S. patent application Ser. No. 10/651,003, filed Aug. 28, 2003, now U.S. Pat. No. 8,137,386.


BACKGROUND OF THE INVENTION
The present invention is directed to polyaxial bone screws for use in bone surgery, particularly spinal surgery. Such screws have a rod receiver that can swivel about a shank of the bone screw, allowing the receiver to be positioned in any of a number of angular configurations relative to the shank.
Many spinal surgery procedures require securing various implants to bone and especially to vertebrae along the spine. For example, elongate rods are often utilized that extend along the spine to provide support to vertebrae that have been damaged or weakened due to injury or disease. Such rods must be supported by certain vertebrae and support other vertebrae.
The most common mechanism for providing vertebral support is to implant bone screws into certain bones which then in turn support the rod or are supported by the rod. Bone screws of this type may have a fixed head or receiver relative to a shank thereof. In the fixed bone screws, the receiver cannot be moved relative to the shank and the rod must be favorably positioned in order for it to be placed within the receiver. This is sometimes very difficult or impossible to do. Therefore, polyaxial bone screws are commonly preferred.
Polyaxial bone screws allow rotation of the receiver about the shank until a desired rotational position of the receiver is achieved relative to the shank. Thereafter, a rod can be inserted into the receiver and eventually the receiver is locked or fixed in a particular position relative to the shank.
A variety of polyaxial or swivel-head bone screw assemblies are available. One type of bone screw assembly includes an open receiver that allows for placement of a rod within the receiver. A closure top or plug is then used to capture the rod in the receiver of the screw.
Because such implants are for placement within the human body, it is desirable for the implant to have as little effect on the body as possible. Consequently, heavy, bulky implants are undesirable and lighter implants with a relatively small profile both in height and width are more desirable. However, a drawback to smaller, lighter implants is that they may be more difficult to rigidly fix to each other and into a desired angular position. Lack of bulk may also mean lack of strength, resulting in slippage under high loading. Also, more component parts may be required to rigidly fix the implant in a desired position. A further drawback of smaller components is that they may be difficult to handle during surgery because of their small size or fail to provide adequate driving or gripping surfaces for tools used to drive the shank into bone or drive the closure top into the screw head.
SUMMARY OF THE INVENTION
A polyaxial bone screw assembly of the present invention includes a shank having a body for fixation to a bone and an upper portion receivable in a cavity of a receiver. A retaining structure, preferably a collar-like retaining ring is also receivable in the cavity. The retaining structure is resilient and open, including first and second spaced ends being movable toward and away from one another. The shank upper portion and the retaining structure are sized and shaped to be bottom loadable into the receiver, with the retaining structure being compressed during insertion. Upon expanding to an original form, the retaining structure engages the receiver and captures the shank upper portion within a cavity of the receiver.
Another aspect of the invention is a tool engagement formation on the shank upper portion, allowing for non-slip engagement by a tool for driving the bone screw shank into bone. The tool engagement formation may be in the form of an axial projection or an internal drive. The illustrated receiver includes an open channel communicating with the cavity that receives the shank upper portion and the retaining structure. The channel is sized and shaped for receiving a rod or other structural member and includes arms with a discontinuous guide and advancement structure for mating with a guide and advancement structure of a closure structure. The guide and advancement structure is preferably a flange form or other splay resistant guide and advancement structure. The shank upper portion is sized and shaped for frictional contact with a rod seated in the channel. In operation, a closure structure operably urges the rod into direct contact with the upper portion of the bone screw shank which in turn frictionally engages the retaining structure, fixing the bone screw shank body in a selected angular orientation with respect to the receiver.
OBJECTS AND ADVANTAGES OF THE INVENTION
Therefore, objects of the present invention include providing a polyaxial bone screw assembly with features that may be readily, securely fastened to each other and to bone. Furthermore, it is an object of the invention to provide a lightweight, low profile polyaxial bone screw assembly that may be assembled prior to implantation and also assembles in such a manner that the components cooperate to create an overall structure that prevents unintentional disassembly. Another object of the invention is to provide a polyaxial bone screw assembly with a reduced number of components; specifically a bone screw assembly that does not require spacers, compression transfer members or other inserts for placement between a rod and the bone screw shank portion captured within the receiver. A further object of the invention is to provide a polyaxial bone screw assembly that is relatively easy to use, inexpensive to produce and especially well adapted for the intended usage thereof.
Other objects and advantages of the 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 having a shank, a receiver, and a retaining structure, and shown with a rod and a closure structure.
FIG. 2 is an enlarged top plan view of the retaining structure of FIG. 1.
FIG. 3 is a cross-sectional view taken along the line 3-3 of FIG. 2.
FIG. 4 is an enlarged cross-sectional view of the receiver, taken along the line 4-4 of FIG. 1.
FIG. 5 is an enlarged front elevational view of the shank of FIG. 1.
FIG. 6 is a cross-sectional view taken along the line 6-6 of FIG. 5.
FIG. 7 is an enlarged top plan view of the shank of FIG. 5.
FIG. 8 is an enlarged partial front elevational view of the shank of FIG. 1 shown fully assembled with the retaining structure, receiver, rod and closure structure of FIG. 1, with portions broken away to show the detail thereof.
FIG. 9 is a partial front elevational view with portions broken away similar to FIG. 8, showing an articulation of the shank with respect to the receiver.
FIG. 10 is a partial perspective view, showing the shank, receiver, retaining structure, rod and closure structure of FIG. 1 fully assembled and implanted in a vertebra, shown in cross-section.
FIG. 11 is an exploded perspective view of a second embodiment of a polyaxial bone screw assembly according to the present invention having a shank, a receiver, and a retaining structure, and shown with a rod and a closure structure.
FIG. 12 is an enlarged front elevational view of the shank of FIG. 11.
FIG. 13 is a cross-sectional view taken along the line 13-13 of FIG. 12.
FIG. 14 is an enlarged top plan view of the shank of FIG. 12.
FIG. 15 is an enlarged partial front elevational view of the shank of FIG. 11 shown fully assembled with the retaining structure, receiver, rod and closure structure of FIG. 11, with portions broken away to show the detail thereof.
FIG. 16 is a partial front elevational view with portions broken away similar to FIG. 15, showing an articulation of the shank with respect to the receiver.
FIG. 17 is a partial perspective view, showing the shank, receiver, retaining structure, rod and closure structure of FIG. 11 fully assembled and implanted in a vertebra, shown in cross-section.
FIG. 18 is an exploded perspective view of a third embodiment of a polyaxial bone screw assembly according to the present invention having a shank, a receiver, and a retaining structure, and shown with a rod and a closure structure.
FIG. 19 is an enlarged top plan view of the retaining structure of FIG. 18.
FIG. 20 is a cross-sectional view taken along the line 20-20 of FIG. 19.
FIG. 21 is an enlarged cross-sectional view of the receiver, taken along the line 21-21 of FIG. 18.
FIG. 22 is an enlarged front elevational view of the shank of FIG. 18.
FIG. 23 is a cross-sectional view taken along the line 23-23 of FIG. 22.
FIG. 24 is an enlarged top plan view of the shank of FIG. 22.
FIG. 25 is an enlarged partial front elevational view of the shank of FIG. 18 shown fully assembled with the retaining structure, receiver, rod and closure structure of FIG. 18, with portions broken away to show the detail thereof.
FIG. 26 is a partial front elevational view with portions broken away similar to FIG. 25, showing an articulation of the shank with respect to the receiver.
FIG. 27 is a partial perspective view, showing the shank, receiver, retaining structure, rod and closure structure of FIG. 18 fully assembled and implanted in a vertebra, shown in cross-section.
FIG. 28 is an exploded perspective view of a fourth embodiment of a polyaxial bone screw assembly according to the present invention having a shank, a receiver, and a retaining structure, and shown with a rod and a closure structure.
FIG. 29 is an enlarged front elevational view of the shank of FIG. 28.
FIG. 30 is a cross-sectional view taken along the line 30-30 of FIG. 29.
FIG. 31 is an enlarged top plan view of the shank of FIG. 29.
FIG. 32 is an enlarged partial front elevational view of the shank of FIG. 28 shown fully assembled with the retaining structure, receiver, rod and closure structure of FIG. 28, with portions broken away to show the detail thereof.
FIG. 33 is a partial front elevational view with portions broken away similar to FIG. 32, showing an articulation of the shank with respect to the receiver.



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.
With reference to FIGS. 1-10, the reference numeral 1 generally represents a polyaxial bone screw 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; and an independent open retaining structure 12. The shank 4, the receiver 10 and the retaining structure 12 preferably are assembled prior to implantation of the shank body 6 into a vertebra 15.
FIGS. 1 and 8-10 further show a closure structure 18 for compressing and biasing a longitudinal member such as a rod 21 against the shank upper portion 8 biasing the upper portion 8 into fixed frictional contact with the retaining structure 12 installed in the receiver 10, so as to fix the rod 21 relative to the vertebra 15. The receiver 10, the retaining structure 12 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 an end of an implantation procedure.
The shank 4, best illustrated in FIGS. 1 and 5-7, is elongate, with the shank body 6 having a helically wound bone implantable thread 24 extending from near a neck 26 located adjacent to the 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 15 leading with the tip 28 and driven down into the vertebra 15 with an installation or driving tool (not shown), so as to be implanted in the vertebra 15 to near the neck 26, as shown in FIG. 10, and as is described more fully in the paragraphs below. The shank 4 has an elongate axis of rotation generally identified by the reference letter A. It is 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 assembly 1 in actual use.
The neck 26 extends axially outwardly and upwardly from the shank body 6. With particular reference to FIGS. 5 and 6, the illustrated neck 26 is of reduced radius as compared to the shank body 6 and an outer diameter of the thread 24. Further extending axially and outwardly from the neck 26 is the shank upper portion 8 that provides a connective or capture structure disposed at a distance from the thread 24 and thus at a distance from the vertebra 15 when the body 6 is implanted in the vertebra 15.
The shank upper portion 8 is configured for connecting the shank 4 to the receiver 10 and capturing the shank 4 in the receiver 10. With particular reference to FIGS. 1 and 5-7, the upper portion 8 has an outer, convex and partially spherical or hemispherical surface 34 that extends outwardly and upwardly from the neck 26 and terminates at a substantially annular surface 38. The spherical surface 34 has an outer radius configured for sliding cooperation and ultimate frictional mating with a concave surface of the retaining structure 12 and a partially spherical inner surface of the receiver 10, having a substantially similar radius, discussed more fully in the paragraphs below. The flat surface 38 is substantially perpendicular to the axis A. The spherical surface 34 shown in the present embodiment is smooth, but it is foreseen that such surface may include a roughened or textured surface or surface finish, or may be scored, knurled, or the like, for enhancing frictional engagement with the retaining structure 12 and the receiver 10. A counter sunk substantially planar base or seating surface 40 also is disposed perpendicular to the axis A and extends radially from a centrally located tool engagement structure 41. The sunken seating surface 40 is disposed between the tool engagement structure and the surface 38. The structure 41 has a top 42 and six driving faces 43 that form a hexagonal extension head driving structure mateable with a socket driving tool (not shown). The base 40 also includes a hexagonal outer perimeter 44 defined by outer driving faces that are parallel to the axis A and terminate at the surface 38. The tool engagement structure 41 is coaxial with the bone screw body 6 and extends along the axis A. In operation, a driving tool (not shown) fits about and engages the tool engagement structure 41 at the faces 43 for both driving and rotating the shank body 6 into the vertebra 15. A bottom of the driving tool may abut against the base 40 and also the faces defining the outer hexagonal perimeter 44, providing additional surfaces for engagement with the driving tool. It is foreseen that in other embodiments according to the invention, the driving features of the bone screw shank may take a variety of forms, including internal and external drives of different shapes and sized. As will be described with respect to the bone screw assembly 601 below, in smaller embodiments, a curved, concave surface may extend from the tool engagement structure to the outer spherical surface, allowing for the tool engagement structure to be designed with a somewhat longer axial length and thus providing a greater surface area for engagement with a driving tool, but without the planar seating surface 40 and additional planar driving faces because of the limitation of the small size of such a bone screw.
The top end surface 42 of the shank 4 is preferably curved or dome-shaped as shown in the drawings, for simple smooth contact engagement or positive mating engagement with the rod 21, when the bone screw assembly 1 is assembled, as shown in FIGS. 8 and 9 and in any angular arrangement of the shank 4 relative to the receiver 10. In the illustrated embodiment the surface 42 is smooth. While not required in accordance with the practice of the invention, the surface 42 may be scored, knurled or the like to further increase frictional positive mating engagement between the surface 42 and the rod 21.
The shank 4 shown in the drawings is cannulated, having a small central bore 45 extending an entire length of the shank 4 along the axis A, coaxial with the threaded body 6. The bore 45 has a first circular opening 46 at the shank tip 28 and a second circular opening 48 at the top surface 42. The bore 45 provides a passage through the shank 4 interior for a length of wire (not shown) inserted into the vertebra 15 prior to the insertion of the shank body 6, the wire providing a guide for insertion of the shank body 6 into the vertebra 15.
Referring to FIGS. 1 and 4, the receiver 10 has a generally U-shaped appearance with a discontinuous partially cylindrical inner profile and a faceted outer profile. The receiver 10 includes a base 50 integral with a pair of upstanding arms 52 and 54 forming a U-shaped cradle and defining a U-shaped channel 56 between the arms 52 and 54 with an upper opening 57 and a lower seat 58 having substantially the same radius as the rod 21 for operably snugly receiving the rod 21.
Each of the arms 52 and 54 has an interior surface 60 that in part defines the inner cylindrical profile and includes a partial helically wound guide and advancement structure 62 having an axis of rotation B. In the illustrated embodiment, the guide and advancement structure 62 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 62 could alternatively be another type of splay preventing structure such as a buttress thread, a square 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 52 and 54, as well as eventual torquing when the closure structure 18 abuts against the rod 21.
Tool engaging apertures or grip bores 64 are formed within the arms 52 and 54 and may be used for holding the receiver 10 during assembly with the shank 4 and the retaining structure 12 and also during the implantation of the shank body 6 into a vertebra 15. A holding tool (not shown) and the apertures 64 can be configured for a snap on/spring off, snap on/twist off, twist on/twist off, twist on/pry off or other flexible engagement wherein the holding tool has flexible legs which splay outwardly to position the tool for engagement in the apertures 64. It is noted that the apertures 64 the cooperating holding tool may be configured to be of a variety of sizes and locations along any of the surfaces of the arms 52 and 54. In the illustrated embodiment, the apertures 64 communicate with upwardly projecting hidden recesses 66 to further aid in securely holding the receiver 10 to a holding tool.
Communicating with and located beneath the U-shaped channel 56 of the receiver 10 is a chamber or cavity 78 substantially defined by an inner, substantially spherical or partially cylindrical surface 80 of the base 50 and an inner substantially spherical concave surface 82 that communicates with the U-shaped channel 56. The spherical surface 82 is disposed between the channel 56 and the inner surface 80. A circumferential ridge 83 is formed at the intersection of the inner surface 60 and the inner substantially spherical surface 82. The substantially spherical surface 82 is sized and shaped for slidable mating and eventual frictional engagement with the shank upper portion 8, having a radius that is approximately the same as a radius of the convex surface 34 of the shank upper portion 8 as described more fully below. The concave spherical surface 82 opens or widens at the lower surface 80, the surface 80 being sized to receive a shank upper portion 8 bottom loaded at a lower opening 84 of the receiver 10 where the surface 80 opens to an exterior 85 of the base 50. It is foreseen that if desired, some of the lower surface 80 may be cylindrical in nature (similar to the surface 280 of the assembly 201), rather than partially spherical as shown in FIG. 4. The spherical surface 82 provides a stop, upper shoulder or barrier near and at the ridge 83 prohibiting the shank upper portion 8 from being removable through the channel 56. The lower inner surface that opens to the exterior 85 of the base 50 is coaxially aligned with respect to the rotational axis B of the receiver 10 and is sized and shaped to receive the shank upper portion 8 therethrough and also receive the retaining structure 12 when the structure 12 is in a compressed configuration as will be described in greater detail below. Formed in a portion of the surface 80 near the spherical inner surface 82 is a circumferential recess or groove 86 that is sized and shaped to receive the retaining structure 12 when the structure 12 is in an uncompressed position as will also be discussed further below, so as to form a restriction at the location of the groove 86 to prevent the uncompressed retaining structure 12 from passing from the cavity 78 and out the lower opening 84 of the receiver 10 when the retaining structure 12 is loaded and seated in the groove 86, thereby also retaining the shank upper portion 8 within the cavity 78. Between the groove 86 and the opening 84 communicating with the base exterior 85, the receiver includes a chamfer or conical surface 88. As illustrated in FIG. 9, the surface 88 provides additional clearance for an angled or articulated bone screw shank 4 with respect to the receiver 10.
The retaining structure or collar 12 that is used to retain the capture structure 8 of the shank 4 within the receiver 10 is best illustrated by FIGS. 1-3. The structure 12 has a central axis C that is operationally the same as the axis B associated with the receiver 10 when the capture structure 8 and the retaining structure 12 are installed within the receiver 10. The retaining structure 12 has a central channel or hollow 91 that passes entirely through the structure 12 from a top surface 92 to a bottom surface 94 thereof. Surfaces that define the channel 91 include a discontinuous inner spherical surface 95 adjacent the top surface 92; an edge 97 adjacent the surface 95 and coaxial with the axis C; and a discontinuous conical surface, bevel or chamfer 98 sloping away from the axis C, adjacent the edge 97 and terminating at the bottom surface 94. The spherical surface 95 has a radius sized and shaped to cooperate with a radius of the substantially spherical surface 34 of the shank upper portion 8 such that the surface 95 slidingly and pivotally mates with the spherical surface 34 as described more fully below. The surface 95 may include a roughening or surface finish for providing additional frictional contact between the surface 95 and the surface 34, once a desired angle of articulation of the shank 4 with respect to the receiver 10 is reached.
The resilient retaining structure 12 includes first and second end surfaces, 100 and 101 disposed in spaced relation to one another and an outer substantially cylindrical surface 104. Both end surfaces 100 and 101 are disposed substantially perpendicular to the top surface 92 and the bottom surface 94. A width X between the surfaces 100 and 101 is determined by a desired amount of compressibility of the open retaining structure 12 when loaded into the receiver 10. The space X shown in FIG. 2 provides adequate space between the surfaces 100 and 101 for the retaining structure 12 to be pinched, with the surfaces 100 and 101 compressed toward one another to an almost touching or touching configuration, to an extent that the compressed retaining structure 12 is up or bottom loadable through the opening 84. After passing through the opening 84 and along a portion of the lower inner surface, the retaining structure 12 expands or springs back to an original uncompressed, rounded or collar-like configuration of FIG. 2 once in the groove 86. The embodiment shown in FIG. 2 illustrates the surfaces 100 and 101 as substantially parallel and vertical, however, it is foreseen that it may be desirable to orient the surfaces obliquely or at a slight angle depending upon the amount of compression desired during loading of the retaining and articulating structure 12 into the receiver 10.
FIGS. 8 and 9 illustrate the structure 12 installed in the groove 86 of the receiver 10 and in engagement with the shank upper portion 8. FIG. 8 illustrates the shank 4, receiver 10 and retaining structure 12 in co-axial alignment. In other words, axes A, B and C are aligned. FIG. 9 illustrates an articulating or swiveling relationship between the upper portion 8 and the installed retaining structure 12 wherein the bone screw upper portion 8 is slidable with respect to the retaining structure 12 at the surface 95, resulting in an orientation wherein the axis A of the shank 4 is not axially aligned with, but rather disposed at an angle with respect to the axes B and C of the receiver 10 and the retaining structure 12 respectively.
The elongate rod or longitudinal member 21 that is utilized with the assembly 1 can be any of a variety of implants utilized in reconstructive spinal surgery, but is normally a cylindrical elongate structure having a smooth cylindrical surface 116 of uniform diameter. The rod 21 is preferably sized and shaped to snugly seat near the bottom of the U-shaped channel 56 of the receiver 10 and, during normal operation, is positioned slightly above the bottom of the channel 56 at the lower seat 58. In particular, the rod 21 normally directly or abutingly engages the shank top surface 42, as shown in FIGS. 8 and 9 and is biased against the domed shank top surface 42, consequently biasing the shank 4 downwardly in a direction toward the base 50 of the receiver 10 when the assembly 1 is fully assembled. For this to occur, the shank top surface 42 must extend at least slightly into the space of the channel 56 when engaging the retaining structure 12. The shank 4 is thereby locked or held in position relative to the receiver 10 by the rod 21 firmly pushing downward on the shank top surface 42.
With reference to FIGS. 1 and 8-10, the closure structure or closure top 18 can be any of a variety of different types of closure structures for use in conjunction with the present invention with suitable mating structure on the upstanding arms 52 and 54. In the embodiment shown, the closure top 18 is rotatably received between the spaced arms 52 and 54. It is foreseen that a mating and advancement structure could be located on the external surfaces of the arms 52 and 54 for mating with a closure top.
The illustrated closure top 18 has a generally cylindrical shaped base 128 with an upwardly extending break-off head 130. The base 128 includes a helically wound guide and advancement structure 131 that is sized, shaped and positioned so as to engage the guide and advancement structure 62 on the arms 52 and 54 to provide for rotating advancement of the closure structure 18 into the receiver 10 when rotated clockwise and, in particular, to cover the top or upwardly open portion 57 of the U-shaped channel 56 to capture the rod 21, preferably without splaying of the arms 52 and 54. The base 128 has a lower or bottom surface 132 with a centrally located pointed projection 133 for engaging and penetrating the rod 21 at the rod surface 116. In certain embodiments according to the invention, a circumferential rim (not shown) may also extend from the bottom surface 132, the rim providing additional engagement points with the rod surface 116. The closure structure 18 operably biases against the rod 21 by advancement and applies pressure to the rod 21 under torquing, so that the rod 21 is urged downwardly against the shank top end surface 42 that extends into the channel 56. Downward biasing of the shank top surface 42 operably produces a frictional engagement between the rod 21 and the surface 42 and also urges the shank upper portion 8 toward the retaining structure 12 that has been loaded into the receiver 10 and expanded into the groove 86, so as to frictionally engage the spherical surface 34 of the shank upper portion 8 with the spherical surface 95 of the retaining structure 12 fixing the shank 4 in a selected, rigid position relative to the receiver 10.
The closure structure break-off head 130 is secured to the base 128 at a neck 134 that is sized and shaped so as to break away at a preselected torque that is designed to properly seat the shank upper portion 8 in the receiver 10. The break-off head 130 includes an external faceted surface 135 that is sized and shaped to receive a conventional mating socket type head of a driving tool (not shown) to rotate and torque the closure structure 18. The break-off head 130 also includes a central bore 137 and one or more grooves 138 for operably receiving manipulating tools. Alternatively, a closure structure for use with the assembly 1 may not include a break-off head, but rather simply have a cylindrical body with a guide and advancement structure thereon and a top surface with an internal tool engagement structure formed therein, such as a hex aperture or a variety of internal tool-engaging forms of various shapes, such as a multi-lobular aperture sold under the trademark TORX, or the like.
The illustrated closure structure 18 also includes an internal drive removal tool engagement structure 140 in the form of an axially aligned aperture having a hex shape, disposed in the base 128. The internal drive or aperture 140 is accessible after the break-off head 130 breaks away from the base 128. The drive 140 is designed to receive a hex tool, of an Allen wrench type, for rotating the closure structure base 128 subsequent to installation so as to provide for removal thereof, if necessary. Such a 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 left hand threaded bore, or an easyout engageable step down bore, or a multi-lobular aperture, such as those sold under the trademark TORX, or the like.
Prior to the polyaxial bone screw assembly 1 being placed in use according to the invention, the retaining structure 12 is preferably first inserted about the bone screw shaft 6. This may be accomplished by either placing the structure 12 over the tip 28 and moving the structure 12 toward the upper portion 8 with the shaft 6 extending through the central channel 91 or inserting the structure 12 on the bone screw 4 at the neck 26 of the shank body 6, with the end surfaces 100 and 101 being pulled away from one another and pressed against and about the neck 26 until the surfaces 100 and 101 expand around the neck 26 and then spring back into a first position with the inner surface 95 facing the surface 34 of the shank upper portion 8. The shank upper portion 8 and the connected structure 12 are then simultaneously up or bottom-loaded into the receiver through the opening 84 with the upper portion 8 being placed into the cavity 78. The structure 12 is manually compressed by pinching the surfaces 100 and 101 toward one another as the neck 26 is placed into the opening 84 until the structure 12 is aligned with the groove 86. The compressive force is then removed and the structure 12 resiliently springs back and returns to the original ring-like or collar-like orientation. Then, as illustrated in FIGS. 8 and 9, the top surface 92, bottom surface 94 and outer cylindrical surface 104 of the structure 12 frictionally engage the groove 86, fixing the retaining structure 12 in the receiver 10 and capturing the shank upper portion 8 within the receiver and in sliding, pivotal relationship with the spherical surface 95 of the retaining structure 12, and in certain angular orientations or articulations, with the spherical surface 82 of the receiver 10.
In an alternative method of installation, the bone screw shank upper portion 8 is first placed in the receiver 10 by inserting the upper portion 8 through the opening 84 and into the cavity 78. The retaining structure 12 may then be placed over the shank body 6 at the tip 28 and moved toward the shank upper portion 8. As with the previously described installation method, the structure 12 is manually compressed by pinching the surfaces 100 and 101 toward one another as the structure 12 is placed in the opening 84 until the structure 12 is aligned with the groove 86. The compressive force is then removed and the structure 12 resiliently springs back and returns to the original ring-like or collar-like orientation, fixing the structure 12 in the receiver 10 and capturing the shank upper portion 8 within the receiver cavity 78.
The capture structure 8 may then be manipulated into a position substantially coaxial with the receiver 10 in readiness for bone implantation. The assembly 1 is typically screwed into a bone, such as the vertebra 15, by rotation of the shank 4 using a driving tool (not shown) that operably drives and rotates the shank 4 by engagement thereof with the faces 43 of the hexagonally shaped tool engagement structure 41 of the shank 4. Preferably, when the driving tool engages the structure 41, a bottom or end portion thereof abuts the countersunk planar seating surface 40 and outer surfaces of the driving tool engage the walls that define the outer perimeter 44, providing an additional driving interface.
Typically, the receiver 10 and the retaining structure 12 are assembled on the shank 4 before inserting the shank body 6 into the vertebra 15 as previously described hereon. However, it is foreseen that in certain circumstances, the shank body 6 can be first partially implanted with the capture structure 8 extending proud to allow placement of the retaining structure 12 about the neck 26, followed by assembly with the receiver 10. Then the shank body 6 can be further driven into the vertebra 15.
The vertebra 15 may be pre-drilled to minimize stressing the bone and have a guide wire (not shown) inserted to provide a guide for the placement and angle of the shank 4 with respect to the vertebra 15. A further tap hole may be made using a tap with the guide wire as a guide. Then, the assembly 1 or the solitary shank 4, is threaded onto the guide wire utilizing the cannulation bore 45 by first threading the wire into the bottom opening 46 and then out of the top opening 48. The shank 4 is then driven into the vertebra 15, using the wire as a placement guide.
With reference to FIGS. 8 and 9, the rod 21 is eventually positioned within the receiver U-shaped channel 56, and the closure structure or top 18 is then inserted into and advanced between the arms 52 and 54 so as to bias or push against the rod 21. The break-off head 130 of the closure structure 18 is twisted to a preselected torque, for example 90 to 120 inch pounds, to urge the rod 21 downwardly. The shank top end surface 42, because it is rounded to approximately equally extend upward into the channel 56 approximately the same amount no matter what degree of rotation exists between the shank 4 and receiver 10 and because the surface 42 is sized to extend upwardly into the U-shaped channel 56, the surface 42 is engaged by the rod 21 and pushed downwardly toward the base 50 of the receiver 10 when the closure structure 18 biases downwardly toward and onto the rod 21. The downward pressure on the shank 4 urges the shank top portion 8 downward toward the retaining structure 12 and possibly against the receiver seating surface 82. As the closure structure 18 presses against the rod 21, the rod 21 presses against the shank upper portion 8 that becomes frictionally, rigidly attached to the receiver 10 at the retaining structure 12.
As previously described, FIG. 8 illustrates the polyaxial bone screw assembly 1 and including the rod 21 and the closure structure 18 positioned at a level or extent of articulation in which the axis A of the bone screw shank and the axis B of the receiver are coaxial. FIGS. 9 and 10 illustrate the assembly 1 with the axis A of the bone shank 4 at an angle with respect to the axis B of the receiver 10, and with the shank 4 being fixed in such angular locked configuration and implanted in the vertebra 15.
If removal of the assembly 1 and the associated rod 21 and the closure structure 18 is necessary, disassembly is accomplished by using a driving tool (not shown) mating with driving surfaces of the aperture 140 on the closure structure 18 to rotate the base 138 and reverse the advancement thereof in the receiver 10. Then, disassembly of the assembly 1 is accomplished in reverse order to the procedure described previously herein for assembly.
With reference to FIGS. 11-17, the reference numeral 201 generally represents a second or alternative embodiment of a bone screw 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; and an independent open retaining structure 212. The shank 204, the receiver 210 and the retaining structure 212 preferably are assembled prior to implantation of the shank body 206 into a vertebra 215.
FIGS. 11 and 15-17 further show a closure structure 218 for compressing and biasing a longitudinal member such as a rod 221 against the shank upper portion 208 biasing the upper portion 208 into fixed frictional contact with the retaining structure 212 installed in the receiver 210, so as to fix the rod 221 relative to the vertebra 215. The receiver 210, the retaining structure 212 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 an end of an implantation procedure.
The shank 204, best illustrated in FIGS. 11-14, is elongate, with the shank body 206 having a helically wound bone implantable thread 224 extending from near a neck 226 located adjacent to the shank upper portion 208 to a tip 228 of the body 206 and extending radially outwardly therefrom. During use, the body 206 utilizing the thread 224 for gripping and advancement is implanted into the vertebra 215 leading with the tip 228 and driven down into the vertebra 215 with an installation or driving tool (not shown), so as to be implanted in the vertebra 215 to near the neck 226, as shown in FIG. 17, and as is described more fully in the paragraphs below. The shank 204 has an elongate axis of rotation generally identified by the reference letter D.
The neck 226 extends axially outwardly and upwardly from the shank body 206. With particular reference to FIG. 12-13, the illustrated neck 226 is of reduced radius as compared to the shank body 206 and an outer diameter of the thread 224. Further extending axially and outwardly from the neck 226 is the shank upper portion 208 that provides a connective or capture structure disposed at a distance from the thread 224 and thus at a distance from the vertebra 215 when the body 206 is implanted in the vertebra 215.
The shank upper portion 208 is configured for connecting the shank 204 to the receiver 210 and capturing the shank 204 in the receiver 210. With particular reference to FIGS. 12-14, the upper portion 208 has an outer, convex and substantially spherical surface 234 that extends outwardly and upwardly from the neck 226 and terminates at a substantially planar top surface 238. The spherical surface 234 has an outer radius configured for sliding cooperation and ultimate frictional mating with a concave surface of the retaining structure 212 and a substantially spherical inner surface of the receiver 210, having a substantially similar radius, discussed more fully in the paragraphs below. The flat surface 238 is substantially perpendicular to the axis D. The spherical surface 234 shown in the present embodiment is smooth, but it is foreseen that the surface 234 may include a roughened or textured surface or surface finish, or may be scored, knurled, or the like, for enhancing frictional engagement with the retaining structure 212 and the receiver 210. A counter sunk substantially planar base or seating surface 240 partially defines an internal drive feature or imprint 241. The illustrated internal drive feature 241 is an aperture formed in the top 238 and has a hex shape designed to receive a hex tool of an Allen wrench type, into the aperture for rotating and driving the bone screw shank 204. 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 aperture, such as those sold under the trademark TORX, or the like. The seat or base 240 of the drive feature 241 is disposed perpendicular to the axis D with the drive feature 241 otherwise being coaxial with the axis D. Six driving faces or walls 242, each disposed parallel to the axis D also define the feature 241. The planar top surface 238 extends from a hexagonal outer perimeter 244 defined by the driving faces 242 and terminates at a circular edge 243. The circular edge 243 also defines a top or terminating upper edge of the spherical outer surface 234. In operation, a driving tool (not shown) is received in the internal drive feature 241, being seated at the base 240 and engaging the faces 242 for both driving and rotating the shank body 206 into the vertebra 215.
The shank 204 shown in the drawings is cannulated, having a small central bore 245 extending an entire length of the shank 204 along the axis D, coaxial with the threaded body 206. The bore 245 has a first circular opening 246 at the shank tip 228 and a second circular opening 248 at the driving feature seating surface 240. The bore 245 provides a passage through the shank 204 interior for a length of wire (not shown) inserted into the vertebra 215 prior to the insertion of the shank body 206, the wire providing a guide for insertion of the shank body 206 into the vertebra 215.
Referring to FIGS. 11 and 15-16, the receiver 210 has an axis of rotation E and is substantially similar to the receiver 10 previously described herein. Thus, the description of the receiver 10 is incorporated by reference with respect to the receiver 210. Specifically, the receiver 210 includes a receiver base 250, arms 252 and 254, a U-shaped channel 256 with an upper opening 257, a lower seat 258, an interior surface 260, guide and advancement structure 262, grip bores 264, recesses 266, a chamber or cavity 278, a lower inner surface 280, an inner spherical surface 282, a ridge 283, a lower opening 284, a base exterior 285 and a groove 286 the same or substantially similar to the respective base 50, arms 52 and 54, U-shaped channel 56 with upper opening 57, lower seat 58, interior surface 60, guide and advancement structure 62, grip bores 64, recesses 66, cavity 78, lower inner surface 80, inner spherical surface 82, ridge 83, lower opening 84, base exterior 85 and groove 86 previously described herein with respect to the receiver 10 of the assembly 1. As discussed earlier with respect to the assembly 1, as compared to the receiver 10, the receiver 210 lower surface 280 is substantially cylindrical while the lower surface 80 is mostly spherical.
The retaining structure or collar 212 that is used to retain the capture structure 208 of the shank 204 within the receiver 210 is best illustrated in FIGS. 11 and 15-16. The structure 212 has a central axis F that is operationally the same as the axis E associated with the receiver 210 when the capture structure 208 and the retaining structure 212 are installed within the receiver 210. The retaining structure 212 is the same or substantially similar to the retaining structure 12 previously described herein and thus the description of the structure 12 is incorporated by reference herein with respect to the structure 212. Specifically, the structure 212 includes a central channel 291, a top 292, a bottom 294, a partially spherical inner surface 295, a conical surface or chamfer 298, end surfaces 300 and 301 and an outer cylindrical surface 304, the same or substantially similar to respective central channel 91, top 92, bottom 94, spherical inner surface 95, conical surface 98, end surfaces 100 and 101 and outer cylindrical surface 104 of the retaining structure 12.
A width or space between the surfaces 300 and 301 is determined by a desired amount of compressibility of the open retaining structure 212 when loaded into the receiver 210. The space shown in FIG. 11 between the surfaces 300 and 301 provides an adequate distance between the surfaces 300 and 301 for the retaining structure 212 to be pinched, with the surfaces 300 and 301 compressed toward one another to an almost touching or touching configuration, to an extent that the compressed retaining structure 212 is up or bottom loadable through the opening 284. As illustrated in FIG. 11, the surfaces 300 and 301 are substantially parallel and vertical, however, it is foreseen that it may be desirable to orient the surfaces obliquely or at a slight angle depending upon the amount of compression desired during loading of the retaining and articulating structure 212 into the receiver 210. After passing through the opening 284 and along a portion of the cylindrical inner surface 280, the retaining structure 212 expands or springs back to an original uncompressed, rounded or collar-like configuration once in the groove 286. FIGS. 15 and 16 illustrate the structure 212 in a fully installed position in the receiver 210 and having an articulating or swiveling relationship with the upper portion 208 of the bone screw shank 204 wherein the bone screw upper portion 208 is slidable with respect to the retaining structure 212 at the surface 295.
The elongate rod or longitudinal member 221 that is utilized with the assembly 201 can be any of a variety of implants utilized in reconstructive spinal surgery, but is normally a cylindrical elongate structure having a smooth cylindrical surface 316 of uniform diameter. The rod 221 is preferably sized and shaped to snugly seat near the bottom of the U-shaped channel 256 of the receiver 210 and, during normal operation, is positioned slightly above the bottom of the channel 256 at the lower seat 258. In particular, the rod 221 directly or abutingly engages the upper portion 208 of the shank 204 either at the top 238, the circular edge 243 or the spherical surface 234, as shown in FIGS. 15 and 16, and is biased against the upper portion 208, consequently biasing the shank 204 downwardly in a direction toward the base 250 of the receiver 210 when the assembly 201 is fully assembled. For this to occur, the shank upper portion 208 must extend at least slightly into the space of the channel 256 when engaging the retaining structure 212. The shank 204 is thereby locked or held in position relative to the receiver 210 by the rod 221 firmly pushing downward on the shank upper portion 208.
With reference to FIGS. 11 and 15-17, the closure structure or closure top 218 can be any of a variety of different types of closure structures for use in conjunction with the present invention with suitable mating structure on the upstanding arms 252 and 254. In the embodiment shown, the closure top 218 is rotatably received between the spaced arms 252 and 254. It is foreseen that a mating and advancement structure could be located on the external surfaces of the arms 252 and 254 for mating with a closure top.
The illustrated closure structure 218 is substantially cylindrical, having a top 328 and a bottom 329. The closure structure 218 further includes a helically wound guide and advancement structure 331 that is sized, shaped and positioned so as to engage the guide and advancement structure 262 on the arms 252 and 254 to provide for rotating advancement of the closure structure 218 into the receiver 210 when rotated clockwise and, in particular, to cover the top or upwardly open portion 257 of the U-shaped channel 256 to capture the rod 221, preferably without splaying of the arms 252 and 254. The closure structure bottom 329 includes a centrally located pointed projection 333 for engaging and penetrating the rod 221 at the rod surface 316. In certain embodiments according to the invention, a circumferential rim (not shown) may also extend from the bottom surface 329, the rim providing additional engagement points with the rod surface 316. The closure structure 218 operably biases against the rod 221 by advancement and applies pressure to the rod 221, so that the rod 221 is urged downwardly against the shank upper portion 208 that extends into the channel 256. Downward biasing of the shank upper portion 208 operably produces a frictional engagement between the rod 221 and the upper portion 208 and also urges the shank upper portion 208 toward the retaining structure 212 that has been loaded into the receiver 210 and expanded into the groove 286, so as to frictionally engage the spherical surface 234 of the shank upper portion 208 with the spherical surface 295 of the retaining structure 212 fixing the shank 204 in a selected, rigid position relative to the receiver 210. It is noted that because the illustrated shank upper portion 208 includes the flat surface 238, circular edge 243 and spherical surface 234 and the rod 221 may engage any of such surfaces, the rod 221 may be seated at a distance from the receiver lower seat 258 and the closure structure 218 may not be disposed flush to a top of the receiver 210 when fully engaged with the rod 221 biasing the rod 221 into locking engagement with the shank 204. Such placement of the closure structure 218 and the rod 221 does not hinder the closure structure 218 from seating in the receiver 210 and fixing the rod 221 in a locked position within the receiver 210.
Formed in the closure structure 218 top surface 328 is an internal drive feature 336 sized and shaped to receive a mating driving tool (not shown) to rotate and torque the closure structure 218 against the rod 221. The illustrated drive feature 336 is multi-lobular, but it is foreseen that the internal drive feature may be a hex aperture or a variety of internal tool-engaging forms of various shapes. The drive feature 336 may also be used to remove the closure structure 218 from the receiver 210 subsequent to installation, if desired or necessary.
Prior to the polyaxial bone screw assembly 201 being placed in use according to the invention, the retaining structure 212 is preferably first inserted about the bone screw shaft 206. This may be accomplished by either placing the structure 212 over the tip 228 and moving the structure 212 toward the upper portion 208 with the shaft 206 extending through the central channel 291 or inserting the structure 212 on the bone screw 204 at the neck 226 of the shank body 206, with the end surfaces 300 and 301 being pulled away from one another and pressed against and about the neck 226 until the surfaces 300 and 301 expand around the neck 226 and then spring back into a first position with the inner surface 295 facing the surface 234 of the shank upper portion 208. The shank upper portion 208 and the connected structure 212 are then simultaneously up or bottom-loaded into the receiver through the opening 284 with the upper portion 208 being placed into the cavity 278. The structure 212 is manually compressed by pinching the surfaces 300 and 301 toward one another as the neck 226 is placed into the opening 284 until the structure 212 is aligned with the groove 286. The compressive force is then removed and the structure 212 resiliently springs back and returns to the original ring-like or collar-like orientation. Then, as illustrated in FIG. 15, the top surface 292, bottom surface 294 and outer cylindrical surface 304 of the structure 212 frictionally engage the groove 286, fixing the retaining structure 212 in the receiver 210 and capturing the shank upper portion 208 within the receiver and in sliding, pivotal relationship with the spherical surface 295 of the retaining structure 212 and with the spherical surface 282 of the receiver 210.
In an alternative method of installation, the bone screw shank upper portion 208 is first placed in the receiver 210 by inserting the upper portion 208 through the opening 284 and into the cavity 278. The retaining structure 212 may then be placed over the shank body 206 at the tip 228 and moved toward the shank upper portion 208. As with the previously described installation method, the structure 212 is manually compressed by pinching the surfaces 300 and 301 toward one another as the structure 212 is placed in the opening 284 until the structure 212 is aligned with the groove 286. The compressive force is then removed and the structure 212 resiliently springs back and returns to the original ring-like or collar-like orientation, fixing the structure 212 in the receiver 210 and capturing the shank upper portion 208 within the receiver cavity 278.
The capture structure 208 may then be manipulated into a position substantially coaxial with the receiver 210 in readiness for bone implantation. The assembly 201 is typically screwed into a bone, such as the vertebra 215, by rotation of the shank 204 using a driving tool (not shown) that operably drives and rotates the shank 204 by engagement thereof with the base 240 and the faces 242 of the internal drive feature 241.
Typically, the receiver 210 and the retaining structure 212 are assembled on the shank 204 before inserting the shank body 206 into the vertebra 215 as previously described hereon. However, it is foreseen that in certain circumstances, the shank body 206 can be first partially implanted with the capture structure 208 extending proud to allow placement of the retaining structure 212 about the neck 226, followed by assembly with the receiver 210. Then the shank body 206 can be further driven into the vertebra 215.
The vertebra 215 may be pre-drilled to minimize stressing the bone and have a guide wire (not shown) inserted to provide a guide for the placement and angle of the shank 204 with respect to the vertebra 215. A further tap hole may be made using a tap with the guide wire as a guide. Then, the assembly 201 or the solitary shank 204, is threaded onto the guide wire utilizing the cannulation bore 245 by first threading the wire into the bottom opening 246, then out of the top opening 248 and then through and out of the driving feature 241. The shank 204 is then driven into the vertebra 215, using the wire as a placement guide.
With reference to FIGS. 15-17, the rod 221 is eventually positioned within the receiver U-shaped channel 256, and the closure structure or top 218 is then inserted into and advanced between the arms 252 and 254 so as to bias or push against the rod 221 and urge the rod 221 downwardly. Depending on a desired amount of articulation between the shank body 206 and the receiver 210, the rod 221 comes into contacted with the planar top surface 238 (shown in FIG. 15), the circular edge 243 (shown in FIG. 16) or the spherical surface 234 of the shank upper portion 208 and such surface is engaged by the rod 221 and pushed downwardly toward the base 250 of the receiver 210 when the closure structure 218 biases downwardly toward and onto the rod 221. The downward pressure on the shank 204 urges the shank top portion 208 downward toward the retaining structure 212 and typically against the receiver seating surface 282. As the closure structure 218 presses against the rod 221, the rod 221 presses against the shank upper portion 208 that becomes frictionally, rigidly attached to the receiver 210 at the retaining structure 212.
FIGS. 15-17 illustrates the polyaxial bone screw assembly 201 and including the rod 221 and the closure structure 218 positioned at various articulations or locked angular orientations in which the axis D of the bone screw shank and the axis E of the receiver are not coaxial. FIG. 17 also shows the shank 204 implanted in the vertebra 15. As previously described, full locking installation is obtainable when the rod 221 engages the rim 243 or the spherical surface 234, even though such engagement places the rod 221 higher in the channel 256 and therefore the closure structure 218 does not seat in a manner that is flush with the top surface of the receiver 210.
If removal of the assembly 201 and the associated rod 221 and the closure structure 218 is necessary, disassembly is accomplished by using a driving tool (not shown) mating with the internal drive 336 on the closure structure 218 to rotate the structure 218 and reverse the advancement thereof in the receiver 210. Then, disassembly of the assembly 201 is accomplished in reverse order to the procedure described previously herein for assembly.
With reference to FIGS. 18-27, the reference numeral 401 generally represents a third or alternative embodiment of a bone screw 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; and an independent open retaining structure 412. The shank 404, the receiver 410 and the retaining structure 412 preferably are assembled prior to implantation of the shank body 406 into a vertebra 415.
FIGS. 18 and 25-27 further show a closure structure 418 for compressing and biasing a longitudinal member such as a rod 421 against the shank upper portion 408 biasing the upper portion 408 into fixed frictional contact with the retaining structure 412 installed in the receiver 410, so as to fix the rod 421 relative to the vertebra 415. The receiver 410, the retaining structure 412 and the shank 404 cooperate in such a manner that the receiver 410 and the shank 404 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 410 with the shank 404 until both are locked or fixed relative to each other near an end of an implantation procedure.
The shank 404, best illustrated in FIGS. 18 and 22-24, is elongate, with the shank body 406 having a helically wound bone implantable thread 424 extending from near a neck 426 located adjacent to the shank upper portion 408 to a tip 428 of the body 406 and extending radially outwardly therefrom. During use, the body 406 utilizing the thread 424 for gripping and advancement is implanted into the vertebra 415 leading with the tip 428 and driven down into the vertebra 415 with an installation or driving tool (not shown), so as to be implanted in the vertebra 415 to near the neck 426, as shown in FIG. 27, and similar to what has been described previously with respect to the similar bone screw assemblies 1 and 201. The shank 404 has an elongate axis of rotation generally identified by the reference letter G.
The neck 426 extends axially outwardly and upwardly from the shank body 406. With particular reference to FIGS. 22-23, the illustrated neck 426 is of reduced radius as compared to the shank body 406 and an outer diameter of the thread 424. Further extending axially and outwardly from the neck 426 is the shank upper portion 408 that provides a connective or capture structure disposed at a distance from the thread 424 and thus at a distance from the vertebra 415 when the body 406 is implanted in the vertebra 415.
The shank upper portion 408 is configured for connecting the shank 404 to the receiver 410 and capturing the shank 404 in the receiver 410. The upper portion 408 has an outer, lower, convex and partially spherical surface 434 that extends outwardly and upwardly from the neck 426 and terminates at a substantially planar annular surface 436. A second, upper convex partially spherical surface 437 extends from the planar surface 436 to a planar and annular top surface 438.
The lower spherical surface 434 is substantially hemispherical and has an outer radius configured for sliding cooperation and ultimate frictional mating with a concave surface of the retaining structure 412 and a substantially spherical inner surface of the receiver 410, having a substantially similar radius, discussed more fully below. The planar or flat surfaces 436 and 438 are both substantially perpendicular to the shank axis G. The partially spherical surface 434 shown in the present embodiment is smooth, but it is foreseen that the surface 434 may include a roughened or textured surface or surface finish, or may be scored, knurled, or the like, for enhancing frictional engagement with the retaining structure 412 and the receiver 410.
The upper, partially spherical surface 437 has a radius that is smaller than the radius of the lower spherical surface 434. A compared to the assembly 201 that has the shank 204 with the substantially spherical surface 234, the pair of spherical surfaces 434 and 437 of the shank upper portion 408 cooperate with the smaller upper spherical surface 437 providing a more compact structure with greater clearance between the upper spherical surface 437 and the inner walls of the receiver 410 than available to the single spherical surface 234, allowing for ease in articulation and a slightly greater degree of angulation of the shank 408 with respect to the receiver 410 than provided by the assembly 201.
A counter sunk substantially planar base or seating surface 440 partially defines an internal drive feature or imprint 441. The illustrated internal drive feature 441 is an aperture formed in the top 438 and has a hex shape designed to receive a hex tool of an Allen wrench type, into the aperture for rotating and driving the bone screw shank 404. 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 aperture, such as those sold under the trademark TORX, or the like. The seat or base 440 of the drive feature 441 is disposed perpendicular to the axis G with the drive feature 441 otherwise being coaxial with the axis G. Six driving faces or walls 442, each disposed parallel to the axis G also define the feature 441. The planar top surface 438 extends from a hexagonal outer perimeter 444 defined by the driving faces 442 and terminates at a circular edge 443. The circular edge 443 also defines a top or terminating upper edge of the upper spherical outer surface 437. In operation, a driving tool (not shown) is received in the internal drive feature 441, being seated at the base 440 and engaging the faces 442 for both driving and rotating the shank body 406 into the vertebra 415.
The shank 404 shown in the drawings is cannulated, having a small central bore 445 extending an entire length of the shank 404 along the axis G, coaxial with the threaded body 406. The bore 445 has a first circular opening 446 at the shank tip 428 and a second circular opening 448 at the driving feature seating surface 440. The bore 445 provides a passage through the shank 404 interior for a length of wire (not shown) inserted into the vertebra 415 prior to the insertion of the shank body 406, the wire providing a guide for insertion of the shank body 406 into the vertebra 415.
Referring to FIGS. 21 and 25-26, the receiver 410 is substantially similar to the receivers 10 and 210 previously described herein and thus those descriptions are incorporated by reference herein with respect to the receiver 410. The receiver 410 has an axis of rotation H and further includes a receiver base 450, arms 452 and 454, a U-shaped channel 456 with an upper opening 457, a lower seat 458, an interior surface 460, guide and advancement structure 462, grip bores 464, a chamber or cavity 478, a lower inner surface 480, an upper inner spherical surface 482, a ridge 483, a lower opening 484, a base exterior 485 and a groove 486 the same or substantially similar to the respective base 50, arms 52 and 54, U-shaped channel 56 with upper opening 57, lower seat 58, interior surface 60, guide and advancement structure 62, grip bores 64, cavity 78, lower inner surface 80, upper inner spherical surface 82, ridge 83, lower opening 84, base exterior 85 and groove 86 previously described herein with respect to the receiver 10 of the assembly 1.
Although not shown, the grip bores 464 may include recesses similar to the recesses 66 described herein with respect to the assembly 1. Also at the opening 484, the surface is substantially cylindrical, having a radius sufficient to allow for the uploading of the shank upper portion 408 through the opening 484 and beyond the groove 486 and into the chamber 478 in slidable engagement with the surfaces 480 and 482, with the ridge 483 providing a stop so that the upper portion 408 is prohibited from passing through the U-shaped channel 456. As with the previously described embodiments, the lower inner surface 480 disposed above and adjacent the groove 486 may be a continuation of the spherical surface 482 as shown in FIG. 21 or in some embodiments, the lower inner surface 480 may be substantially cylindrical in form as illustrated in FIGS. 15 and 16 with respect to the assembly 201.
The receiver 410 also differs slightly from the previously described receivers 10 and 210 in outward configuration or form. For example, the base 450 is substantially cylindrical in outer form and the arms 452 and 454 include added outwardly extending material or thickness, providing the same basic functions as the bases and arms of the receivers 10 and 210, but advantageously reducing bulk where not necessary at the base, and adding bulk, and thus strength, at the arms 452 and 454.
The retaining structure or collar 412 that is used to retain the capture structure 408 of the shank 404 within the receiver 410 is best illustrated in FIGS. 18-20. The structure 412 has a central axis I that is operationally the same as the axis H associated with the receiver 410 when the capture structure 408 and the retaining structure 412 are installed within the receiver 410. The retaining structure 412 is the same or substantially similar to the retaining structure 12 previously described herein and thus the description of the structure 12 is incorporated by reference herein with respect to the structure 412. Specifically, the structure 412 includes a central channel 491, a top 492, a bottom 494, a substantially spherical inner surface 495, end surfaces 500 and 501 and an outer cylindrical surface 504, the same or substantially similar to respective central channel 91, top 92, bottom 94, spherical inner surface 95, end surfaces 100 and 101 and outer cylindrical surface 104 of the retaining structure 12. Unlike the structure 12, the structure 412 does not include a lower inner chamfer. The entire inner surface of the structure 412 is substantially spherical. However, it is foreseen that the structure 412 may include such a sloping or conical chamfer or bevel.
Similar to what has been previously described herein with respect to the width X of the structure 12 and the width between surfaces 300 and 301 of the structure 212, a width or space between the surfaces 500 and 501 is determined by a desired amount of compressibility of the open retaining structure 512 when loaded into the receiver 510. The space or distance between the surfaces 500 and 501 shown in FIG. 19 provides adequate space between the surfaces 500 and 501 for the retaining structure 412 to be pinched, with the surfaces 500 and 501 compressed toward one another to an almost touching or touching configuration, to an extent that the compressed retaining structure 412 is up or bottom loadable through the opening 484. After passing through the opening 484 and along a portion of the cylindrical inner surface, the retaining structure 412 expands or springs back to an original uncompressed, rounded or collar-like configuration once in the groove 486. FIGS. 25 and 26 illustrate the structure 412 in a fully installed position in the receiver 410 and having an articulating or swiveling relationship with the lower spherical portion 434 of the bone screw shank 404.
The elongate rod or longitudinal member 421 that is utilized with the assembly 401 can be any of a variety of implants utilized in reconstructive spinal surgery, but is normally a cylindrical elongate structure having a smooth cylindrical surface 516 of uniform diameter. The rod 421 is the same or substantially similar to the rods 21 and 221 previously described herein. With reference to FIGS. 25 and 26, the rod 421 directly or abutingly engages the upper portion 408 of the shank 404 either at the top 438, the circular edge 443 or the upper spherical surface 437, and is biased against the upper portion 408, consequently biasing the shank 404 downwardly in a direction toward the base 450 of the receiver 410 when the assembly 401 is fully assembled. For this to occur, the shank upper portion 408 must extend at least slightly into the space of the channel 456 when engaging the retaining structure 412. The shank 404 is thereby locked or held in position relative to the receiver 410 by the rod 421 firmly pushing downward on the shank upper portion 408.
With reference to FIGS. 18 and 25-27, the closure structure or closure top 418 can be any of a variety of different types of closure structures for use in conjunction with the present invention with suitable mating structure on the upstanding arms 452 and 454. In the embodiment shown, the closure top 418 is rotatably received between the spaced arms 452 and 454. It is foreseen that a mating and advancement structure could be located on the external surfaces of the arms 452 and 454 for mating with a closure top.
The illustrated closure structure 418 is substantially similar to the break-off closure structure 18 previously described herein. The structure 418 includes a base 528, a break-off head 530, a guide and advancement structure 531, a bottom surface 532 having a projection or point 533, a neck 534, and external faceted surface 535, a central bore 537 and an internal drive 540 in the base 528 substantially similar to the respective base 128, break-off head 130, guide and advancement structure 131, bottom surface 132, point 133, neck 134, external faceted surface 135, central bore 137 and internal drive 140 in the base 128 of the closure structure 18. When installed, the closure structure 418 operably biases against the rod 421 by advancement and applies pressure to the rod 421, so that the rod 421 is urged downwardly against the shank upper portion 408 that extends into the channel 456. Downward biasing of the shank upper portion 408 operably produces a frictional engagement between the rod 421 and the shank upper portion 408 and also urges the shank upper portion 408 toward the retaining structure 412 that has been loaded into the receiver 410 and expanded into the groove 486, so as to frictionally engage the lower spherical surface 434 of the shank upper portion 408 with the spherical surface 495 of the retaining structure 412 fixing the shank 404 in a selected, rigid position relative to the receiver 410. Similar to the assembly 201 previously described herein, it is noted that because the illustrated shank upper portion 408 includes the flat surface 438, circular edge 443 and spherical surface 437 and the rod 421 may engage any of such surfaces, the rod 421 may be seated at a distance from the receiver lower seat 458 and the closure structure base 528 may not be disposed flush to a top of the receiver 410 when the break-off head 530 has been broken off and the base 528 is fully engaged with the rod 421 biasing the rod 421 into locking engagement with the shank 404. Such placement of the closure structure 418 and the rod 421 does not hinder the closure structure 418 from seating in the receiver 410 and fixing the rod 421 in a locked position within the receiver 410.
In use, the assembly 401 is assembled, implanted, utilized, disassembled and removed identically or substantially similarly to what has been previously described herein with respect to the assembly 1. Therefore such discussion is incorporated by reference herein with respect to the assembly 401.
FIGS. 25 and 26 illustrate the polyaxial bone screw assembly 401 and including the rod 421 and the closure structure 418 positioned at various articulations or locked angular orientations: one in which the axis G of the bone screw shank is coaxial with the axis H of the receiver (FIG. 25); and one in which the axis G of the bone screw shank and the axis H of the receiver are not coaxial (FIG. 26). FIG. 27 also shows the shank 404 implanted in the vertebra 415. As previously described, full locking installation is obtainable when the rod 421 engages the top surface 438, the rim 443 or the upper spherical surface 437, even though such engagement places the rod 421 higher in the channel 456 and therefore the closure structure 418 does not seat in a manner that is flush with the top surface of the receiver 410.
With reference to FIGS. 28-33, the reference numeral 601 generally represents a fourth embodiment of a bone screw assembly according to the present invention. The assembly 601 includes a shank 604 having an axis of rotation J that further includes a body 606 integral with an upwardly extending upper portion or capture structure 608; a receiver 610 having an axis of rotation K; and an independent open retaining structure 612 having an axis of rotation L. The shank 604, the receiver 610 and the retaining structure 612 preferably are assembled prior to implantation of the shank body 606 into a vertebra. FIGS. 28, 32 and 33 further show a closure structure 618 for compressing and biasing a longitudinal member such as a rod 621 against the shank upper portion 608 biasing the upper portion 608 into fixed frictional contact with the retaining structure 612 installed in the receiver 610, so as to fix the rod 621 relative to the vertebra 615. The receiver 610, the retaining structure 612 and the shank 604 cooperate in such a manner that the receiver 610 and the shank 604 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 610 with the shank 604 until both are locked or fixed relative to each other near an end of an implantation procedure.
The shank 604, best illustrated in FIGS. 29-31, is elongate, with the shank body 606 and the upper portion 608 being substantially similar to the shank body 6 and upper portion 8 of the shank 4 previously described herein. Furthermore, the shank 605 includes a thread 624, a neck 626, a tip 628, an upper portion partially spherical surface 634, seating surface 640, a tool engagement structure 641, a top 642 and a cannulation bore 645 identical or substantially similar to the thread 24, neck 26, tip 28, upper portion spherical surface 34, seating surface 40, tool engagement structure 41, top 42 and cannulation bore 45 of the shank 4. Therefore a description of these features will not be repeated here with the exception of the seating surface 640. The shank upper portion 608 does not include an annular surface 38 cooperating with the recessed seating surface 40 described herein with respect to the shank upper portion 8. Rather, the seating surface 640 of the shank upper portion 608 extends or slopes outwardly and upwardly from the tool engagement structure 641 to the substantially spherical surface 634 as best illustrated in FIG. 30. It is noted that in smaller embodiments of bone screws according to the invention, it may be difficult to machine or otherwise form the recessed surface 38 into the bone screw upper portion 8 (illustrated in FIGS. 6 and 7). In such embodiments, the more easily formable sloping seating surface 640 provides adequate seating surface about the tool engagement structure 641 and a slightly elongated tool engagement structure 641 for rotating and implantation of the bone screw shank body 606 into a vertebra.
Referring to FIGS. 28, 32 and 33, the receiver 610 is substantially similar to the receiver 410 previously described herein with one exception, the type of helically wound guide and advancement structure for use in cooperation with the closure structure 618. Specifically, the receiver 610 includes a receiver base 650, arms 652 and 654, a U-shaped channel 656 with an upper opening 657, a lower seat 658, and an interior surface 660 identical or substantially similar to the receiver base 450, arms 452 and 454, U-shaped channel 456 with an upper opening 457, lower seat 458, and the interior surface 460 of the receiver 410. The receiver 610 includes a guide and advancement structure 662 that is located within the receiver 610 similarly to the guide and advancement structure 462 of the receiver 410. However, the guide and advancement structure 462 is a flange form while the guide and advancement structure 662 is a reverse angle form, best illustrated in FIGS. 32 and 33. The receiver 610 further includes grip bores 664, an inner chamber or cavity 678 having a spherical surface and a groove 686 that is identical or substantially similar to the respective grip bores 464, and inner chamber 678 features, including the groove 486 of the receiver 410 of the assembly 401.
The retaining structure or collar 612 that is used to retain the capture structure 608 of the shank 604 within the receiver 610 is best illustrated in FIGS. 28 and 32-33. The structure 612 is identical or substantially similar to the retaining structure 412 previously described herein.
The elongate rod or longitudinal member 621 that is utilized with the assembly 601 can be any of a variety of implants utilized in reconstructive spinal surgery, but is normally a cylindrical elongate structure having a smooth cylindrical surface 687 of uniform diameter. The rod 621 is substantially similar in form and function to the rods 21, 221 and 421 previously described herein.
With reference to FIGS. 28 and 32-33, the closure structure or closure top 618 can be any of a variety of different types of closure structures for use in conjunction with the present invention with suitable mating structure on the upstanding arms 652 and 654. In the embodiment shown, the closure top 618 is rotatably received between the spaced arms 652 and 654. It is foreseen that a mating and advancement structure could be located on the external surfaces of the arms 652 and 654 for mating with a closure top.
The illustrated closure structure 618 is substantially similar to the break-off closure structure 418 previously described herein with the exception that the structure 618 has a reverse angle helical form guide and advancement structure 691, rather than the flange form guide and advancement structure 531 of the closure structure 418.
Specifically, the structure 618 includes a base 688, a break-off head 690, a bottom surface 692 having a projection or point 693, a neck 694, and external faceted surface 695, a central bore 697 and an internal drive 698 in the base 688 substantially similar to the respective base 528, break-off head 530, bottom surface 532, point 533, neck 534, external faceted surface 535, central bore 537 and internal drive 540 in the base 528 of the closure structure 418.
When installed, the closure structure 618 operably biases against the rod 621 by advancement and applies pressure to the rod 621, so that the rod 621 is urged downwardly against the shank upper portion 608 that extends into the channel 656. Downward biasing of the shank upper portion 608 operably produces a frictional engagement between the rod 621 and the shank upper portion 608 and also urges the shank upper portion 608 toward the retaining structure 612 that has been loaded into the receiver 610 and expanded into the groove 686, so as to frictionally engage the spherical surface 634 of the shank upper portion 608 with the inner spherical surface of the retaining structure 612 fixing the shank 604 in a selected, rigid position relative to the receiver 610.
In use, the assembly 601 is assembled, implanted, utilized, disassembled and removed identically or substantially similarly to what has been previously described herein with respect to the assembly 1. Therefore such discussion is incorporated by reference herein with respect to the assembly 601.
FIGS. 32 and 33 illustrate the polyaxial bone screw assembly 601 and including the rod 621 and the closure structure 618 positioned at various articulations or locked angular orientations: one in which the axis J of the bone screw shank is coaxial with the axis K of the receiver (FIG. 32); and one in which the axis J of the bone screw shank and the axis K of the receiver are not coaxial (FIG. 33).
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.

## Claims

1. A polyaxial bone screw assembly comprising:
a) a bone screw shank having an upper portion with a capture structure having a lower convex partially spherically shaped first surface;
b) a receiver having a pair of arms forming a channel, the receiver also having a cavity with a concave partially spherically shaped second surface adapted to receive and allow pivotal movement of the shank first surface during positioning and an opening to an exterior of the receiver opposite the pair of arms, the cavity communicating with the channel, the bone screw upper portion being uploaded and received in the cavity through the opening; the receiver having a lower groove within the cavity;
c) a retaining structure being receivable in the cavity and securable to the receiver in fixed relation thereto when the shank upper portion is in the receiver, the retaining structure being outwardly biased and received in the receiver lower groove; the retaining structure having a third surface sized and shaped to receive a portion of the shank first surface, the retaining structure being sized and shaped to retain the shank upper portion within the receiver cavity, the shank upper portion sized and shaped to extend above the retaining structure and receive direct downward force from direct forceful engaging contact between the rod and the shank when the shank upper portion is retained in the cavity by the retaining structure such that all downward force from the rod is applied directly to the shank and so as to lock the angular position of the receiver relative to the shank in a locked position due to the direct forceful contact between the rod and the shank, the assembly having an unlocked position wherein the shank upper portion is in sliding, pivotable relation with the retaining structure and a locked position wherein the shank first surface is in direct frictional engagement with the receiver second surface and the retaining structure third surface; and
d) the second surface of the receiver and the third surface of the retainer cooperating to receive the first surface of the shank capture structure to allow polyaxial rotation of the shank relative to the receiver in the unlocked configuration during assembly.

2. The assembly of claim 1 wherein the shank upper portion has an upper curved dome surface that extends into a rod-receiving channel in the receiver to directly engage a rod in the rod-receiving channel.

3. The assembly of claim 1 wherein the first surface of the shank upper portion slidably matingly engages the second surface of the receiver cavity in the unlocked position.

4. The assembly of claim 1 wherein the shank upper portion has a top rounded surface for engagement with a rod.

5. The assembly of claim 4 wherein the shank upper portion further includes a substantially flat upper surface and an edge disposed between the flat upper surface and the rounded surface, each of the rounded surface, the flat surface and the edge sized and shaped for engagement with the rod.

6. The assembly of claim 1 wherein the shank upper portion has a tool engagement formation disposed thereon adapted for non-slip engagement by a tool for driving the bone screw shank into bone.

7. The assembly of claim 6 wherein the tool engagement formation is an axial projection having a hexagonal profile.

8. The assembly of claim 6 wherein the tool engagement formation is an internal driving feature.

9. The assembly of claim 8 wherein the driving feature has a hexagonal profile.

10. The assembly of claim 1 wherein the retaining structure further comprises first and second spaced ends, the retaining structure being compressible and expandible with the first and second ends being movable toward and away from one another.

11. The assembly of claim 1 wherein the retaining structure is bottom-loadable into the receiver.

12. The assembly of claim 1 wherein the bone screw shank has a body for fixation to bone, the shank body being integral with the shank upper portion.

13. The assembly of claim 1 wherein the bone screw shank is cannulated.

14. The assembly of claim 1 further comprising a closure structure with a lower end and that is insertable into the receiver so as to engage the rod and apply a downward force to the rod, the closure structure for operably urging the bone screw shank through the rod in a direction to frictionally lock the position of the shank upper portion with respect to the retaining structure and the receiver, thereby locking the shank in a selected angle with respect to the receiver.

15. The assembly of claim 14 wherein:
(a) the receiver arms each have a guide and advancement structure on inside surfaces thereof; and
(b) the closure structure is sized and shaped to be positionable between the arms for closing the channel, the closure structure having a splay-resistant guide and advancement structure for rotatably mating with the guide and advancement structures on the arms, biasing the closure structure upon advancement rotation against a rod disposed in the channel.

16. The assembly of claim 14 wherein the closure structure is adapted to operably urge the rod against the shank upper portion upon the closure structure being positioned in the receiver.

17. The assembly of claim 1 wherein the receiver defines a recess for receiving and retaining the retaining structure within the receiver cavity.

18. The assembly of claim 17 wherein the recess is a circumferential groove.

19. In a polyaxial bone screw assembly for surgical implantation, the assembly including a rod receiver and a shank swivelable with respect to the receiver, the improvement wherein:
a) the shank is bottom-loadable into the receiver and has an integral upper portion with a first convex surface with a first radius that is sized and shaped for direct contact with the rod to receive direct downward force from direct engagement with the rod; the shank having a second lower convex surface for polyaxial contact with the receiver and having a second radius that is larger than the first radius; and further comprising
b) the receiver having a lower groove and a retaining structure that is outwardly biased and received within the receiver groove for retaining the shank upper portion in a cavity in the receiver, the cavity being sized and shaped to allow polvaxial movement of the shank relative to the receiver during positioning of the shank, wherein when assembled the retaining structure is located at a lower end of the shank upper portion so as to directly engage the shank and the rod frictionally engageable therewith when a rod is positioned above the shank upper portion and applies a direct downward locking force to the shank upper portion and not to the retaining structure, so as to frictionally engage the retaining structure and the shank.

20. The assembly according to claim 19 wherein:
a) the shank upper portion having a lower convex partially spherically shaped surface that is sized and positioned such that, when the shank is assembled in the receiver, the shank upper portion pivots within the retaining structure when the assembly is in a positioning configuration and frictionally engages the retaining structure when the assembly is in a locking configuration.

21. The assembly according to claim 20 wherein:
a) when the assembly is in a locking configuration the shank receives a downward force from the rod.

22. A medical implant comprising:
a) a receiver having a cavity, a lower portion with a lower opening, a lower groove near the lower opening within the cavity and an upper portion with a rod-receiving channel;
b) a bone screw shank having an upper portion structured for up-loading through the receiver lower opening into the cavity; the upper portion including a lower convex surface that is sized and shaped to polyaxially rotate relative to the receiver during positioning and that has a first radius; the upper portion having a second convex surface that is adapted to engage a rod in the channel and that has a second radius smaller than the first radius;
c) a retaining member securable to the receiver at a lower end of the shank upper portion by positioning in the groove, the retaining member being sized and shaped for preventing the shank upper portion from passing out of the receiver through the lower opening; and
d) a rod positionable within the rod receiving channel, the rod directly contacting and applying a direct downward force only on the shank upper portion for operably locking the shank in a position relative to the receiver.

23. The assembly according to claim 22 wherein:
a) the shank extends into a rod-receiving channel in the receiver so as to receive downward force directly from the rod.

24. A polyaxial bone screw assembly comprising:
a) a bone screw shank having an upper portion;
b) a receiver having a an upper rod channel adapted to receive a rod lower cavity with an inner spherical surface and a lower groove; the cavity being sized and shaped to allow polyaxial movement of the shank relative to the receiver during positioning of the shank;
c) a retainer positioned within the groove in said receiver cavity and having an inner spherical surface complimentary to that of the receiver cavity spherical surface, such that said spherical surfaces are substantially continuous and contiguous when said retainer is coupled to said receiver, so as to hold said shank upper portion within said cavity and thereby allow polyaxial motion between said shank and said cooperating receiver and retainer during positioning; and
d) the shank being uploaded into the receiver cavity and extending into the channel after the assembly is assembled so as to be adapted to receive all downward locking force from the rod to frictionally lock the position of the shank relative to the receiver during use.

25. A polyaxial bone screw assembly comprising:
a) a bone screw shank having an upper portion with a capture structure having a lower convex partially spherically shaped surface with a first radius and a second upper convex surface having a second radius smaller than the first radius;
b) a receiver having a pair of arms forming a channel, the receiver also having a cavity with an interior surface and an opening to an exterior of the receiver opposite the pair of arms, the cavity communicating with the channel, the bone screw upper portion being received in the cavity through the opening; and
c) a retaining structure being receivable in the cavity and positionable within a recess in the cavity surface and held there by outward biasing of the retainer structure when the shank upper portion is in the receiver, the retaining structure being sized and shaped to retain the shank upper portion within the receiver cavity and hold the upper portion in spaced relation from the cavity surface; the shank upper portion being sized and shaped to extend above the retaining structure and receive direct downward force from direct forceful contact between the rod and the shank when the shank upper portion is retained in the cavity by the retaining structure so that the shank receives all downward force from the rod directly so as to lock the angular position of the receiver relative to the shank in a locked position due to the direct forceful contact between the rod and the shank, the assembly having an unlocked position wherein the shank upper portion is in sliding, pivotable relation with the retaining structure and a locked position wherein the shank capture structure is in direct frictional engagement with the retaining structure.

26. A polyaxial bone screw assembly comprising:
a) a bone screw shank having an upper portion with a capture structure having a lower convex partially spherically shaped first surface with a first radius and a top convex surface with a second radius smaller than the first radius;
b) a receiver having a pair of arms forming a channel, the receiver also having a cavity adapted to receive and allow pivotal movement of the shank first surface during positioning and an opening to an exterior of the receiver opposite the pair of arms, the cavity communicating with the channel, the bone screw upper portion being received in the cavity through the opening;
c) a retaining structure being receivable in a lower end of the cavity and held therein by outward spring biasing of the retainer structure, the retaining structure being sized and shaped to retain the shank upper portion within the receiver cavity, the shank upper portion being sized and shaped to extend above the retaining structure and receive all downward force from the rod by direct forceful contact between the rod and the shank when the shank upper portion is retained in the cavity by the retaining structure so as to lock the angular position of the receiver relative to the shank in a locked position due to the direct forceful contact between the rod and the shank, the assembly having an unlocked position wherein the shank upper portion is in sliding, pivotable relation with the retaining structure and a locked position wherein the shank is in direct frictional locking engagement with the retaining structure.

27. A polyaxial bone screw assembly comprising:
a) a bone screw shank having an upper portion with a capture structure having a lower convex partially spherically shaped surface with a first radius and an upper convex surface with a second radius smaller than the first radius;
b) a receiver having a pair of arms forming a channel, the receiver also having a cavity with an interior surface and an opening to an exterior of the receiver opposite the pair of arms, the cavity communicating with the channel, the bone screw upper portion being received in the cavity through the opening; and
c) a retaining structure being receivable in a lower end of the cavity and secured therein by outward spring biasing of the retaining structure, the retaining structure being positioned within a recess in the cavity surface and having a non-pivotal relation with respect to the receiver, the retaining structure being sized and shaped to retain the shank upper portion within the receiver cavity and hold the upper portion in spaced relation from the cavity surface; the shank upper portion being sized and shaped to extend above the retaining structure and receive direct downward force from direct forceful contact between a rod positioned in the channel and the shank when the shank upper portion is retained in the cavity by the retaining structure and the retaining structure being spaced from the rod so that the downward force from the rod to the shank locks the angular position of the receiver relative to the shank in a locked position due to the direct forceful contact between the rod and the shank, the assembly having an unlocked position wherein the shank upper portion is in sliding, pivotable relation with the retaining structure and a locked position wherein the shank capture structure is in direct frictional engagement with the retaining structure.

28. A polyaxial bone screw assembly comprising:
a) a bone screw shank having an upper portion with a capture structure having a lower convex partially spherically shaped first surface with a first radius and a top convex surface with a second radius smaller than the first radius;
b) a receiver having a pair of arms forming a channel, the receiver also having a cavity adapted to receive and allow pivotal movement of the shank first surface during positioning and an opening to an exterior of the receiver opposite the pair of arms, the cavity communicating with the channel, the bone screw upper portion being uploaded and received in the cavity through the opening;
c) a retaining structure being receivable in a lower part of the cavity and held in position by an outward biasing of the retaining structure, the retaining structure being sized and shaped to retain the shank upper portion within the receiver cavity and to have a non-pivotal relation with respect to the receiver, the shank upper portion being sized and shaped to extend above the retaining structure and receive direct downward force from direct forceful contact between a rod positioned in the channel and the shank and the retaining structure being spaced from the rod when the shank upper portion is retained in the cavity by the retaining structure so as to lock the angular position of the receiver relative to the shank in a locked position due to the direct forceful contact between the rod and the shank, the assembly having an unlocked position wherein the shank upper portion is in sliding, pivotable relation with the retaining structure and a locked position wherein the shank is in direct frictional locking engagement with the retaining structure.

29. A polyaxial bone screw assembly comprising:
a) a bone screw shank having an upper portion with a capture structure having a lower convex partially spherically shaped surface with a first radius and an upper convex surface with a second radius;
b) a receiver having a pair of arms forming a channel, the receiver also having a cavity with an interior surface and an opening to an exterior of the receiver opposite the pair of arms, the cavity communicating with the channel, the bone screw upper portion being received in the cavity through the opening; and
c) a retaining structure being receivable in a lower portion of the cavity, positionable within a recess in the cavity surface and having a non-pivotal relation with respect to the receiver, the retaining structure being sized and shaped to retain the shank upper portion within the receiver cavity and hold the upper portion in spaced relation from the cavity surface; the shank upper portion being sized and shaped to extend above the retaining structure and only receive a direct downward force when the shank upper portion is retained in the cavity by the retaining structure so as to lock the angular position of the receiver relative to the shank in a locked position and so that the retaining structure receives the locking force only through the shank, the assembly having an unlocked position wherein the shank upper portion is in sliding, pivotable relation with the retaining structure and a locked position wherein the shank capture structure is in direct frictional engagement with the retaining structure; wherein the first and second radii are different.

30. A polyaxial bone screw assembly comprising:
a) a bone screw shank having an upper portion with a capture structure having a lower convex partially spherically shaped first surface with a first radius and a top convex surface with a second radius;
b) a receiver having a pair of arms forming a channel, the receiver also having a cavity adapted to receive and allow pivotal movement of the shank first surface during positioning and an opening to an exterior of the receiver opposite the pair of arms, the cavity communicating with the channel, the bone screw upper portion being received in the cavity through the opening;
c) a retaining structure being receivable and secured in a lower portion of the cavity, the retaining structure being sized and shaped to retain the shank upper portion within the receiver cavity and to have a non-pivotal relation with respect to the receiver, the shank upper portion being sized and shaped to extend above the retaining structure so that only the shank upper portion receives a direct downward force when the shank upper portion is retained in the cavity by the retaining structure so as to lock the angular position of the receiver relative to the shank in a locked position, the assembly having an unlocked position wherein the shank upper portion is in sliding, pivotable relation with the retaining structure and a locked position wherein the shank is in direct frictional locking engagement with the retaining structure; wherein the first radius is larger than the second radius.