Patent ID: 12185984

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 toFIGS.1-28, the reference numeral1generally designates a polyaxial bone screw assembly according to the present invention. The assembly1includes a shank4that further includes a body6integral with an upwardly extending capture structure8; a head or receiver10; a retaining and articulating structure or ring12; and a side-loading pressure insert14. The shank4, head or receiver10, retaining and articulating structure12and insert14are preferably assembled prior to implantation of the shank body6into a vertebra15, which procedure is shown inFIGS.17and18.

FIGS.19-28further show a closure structure or nested fastener, generally18, of the invention for capturing a longitudinal member such as a rod21within the head or receiver10. The insert14allows for setting an angle of articulation between the shank body6and the head or receiver10prior to insertion of the rod21, if desired. Upon installation, which will be described in detail below, the nested fastener18presses against the rod21that in turn presses against the insert14that presses against the capture structure8which biases the retaining and articulating structure12into fixed frictional contact with the head or receiver10, so as to fix the rod21relative to the vertebra15. The head or receiver10and shank4cooperate in such a manner that the head10and shank4can 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 head10with the shank4until both are locked or fixed relative to each other.

The shank4, best illustrated inFIGS.1and2, is elongate, with the shank body6having a helically wound bone implantable thread24extending from near a neck26located adjacent to the capture structure8to a tip28of the body6and extending radially outward therefrom. During use, the body6utilizing the thread24for gripping and advancement is implanted into the vertebra15leading with the tip28and driven down into the vertebra15with an installation or driving tool31so as to be implanted in the vertebra15to near the neck26, as shown inFIG.24, and as is described more fully in the paragraphs below. The shank4has 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 assembly1in actual use.

The neck26extends axially outward and upward from the shank body6. The neck26may be of reduced radius as compared to an adjacent top32of the body6. Further extending axially and outwardly from the neck26is the capture structure8that provides a connective or capture structure disposed at a distance from the body top32and thus at a distance from the vertebra15when the body6is implanted in the vertebra15.

The capture structure8is configured for connecting the shank4to the head or receiver10and capturing the shank4in the head10. The capture structure8has an outer substantially cylindrical surface34having a helically wound guide and advancement structure thereon which in the illustrated embodiment is a V-shaped thread36extending from near the neck26to adjacent to an annular upper surface38. Although a simple thread36is shown in the drawings, it is foreseen that other structures including other types of threads, such as buttress and reverse angle threads, and non threads, such as helically wound flanges with interlocking surfaces, may be alternatively used in alternative embodiments of the present invention.

Projecting along the axis A upwardly and outwardly from the annular surface38of the capture structure8is a curved or dome-shaped top42. The illustrated top42is radially extending, convex, substantially hemispherical or dome-shaped, preferably having a substantially uniform radius of generation to provide for positive engagement with the insert14at almost any orientation of the shank4, as will be described more fully below. It is foreseen that in certain embodiments the radius may vary depending upon the needs and desires of the particular structure and the domed top42may have a shape that is only partly spherical or some other shape. For example, the domed top could be radiused at the location of greatest projection along the axis A and otherwise feathered along a periphery thereof so as to not have a continuous uniform radius of generation throughout but rather a continually changing radius of generation along at least the length thereof.

The shank4shown in some of the drawings is cannulated, having a small central bore44extending an entire length of the shank4along the axis A. The bore44has a first circular opening46at the shank tip28and a second circular opening48at the top surface42. The bore44is coaxial with the threaded body6and the capture structure outer surface34. The bore44provides a passage through the shank4interior for a length of wire or pin49as shown inFIGS.17and18, inserted into the vertebra15prior to the insertion of the shank body6, the pin49providing a guide for insertion of the shank body6into the vertebra15.

Referring toFIGS.1,2,9-11and14, the head or receiver10has a generally cylindrical outer profile with a substantially cylindrical base50integral with a pair of opposed upstanding arms52that extend from the base50to a top surface54. The arms52form a U-shaped cradle and define a U-shaped channel56between the arms52and include an upper opening57and a lower seat58having substantially the same radius as the rod21for operably snugly receiving the rod21.

Each of the arms52has an interior surface60that defines the inner cylindrical profile and includes a partial helically wound guide and advancement structure62. In the illustrated embodiment, the guide and advancement structure62is a partial helically wound flange form configured to mate under rotation with a similar structure on the nested fastener18, as described more fully below. However, it is foreseen that the guide and advancement structure62could alternatively be a V-shaped thread, a buttress thread, a square thread, a reverse angle thread or other thread like or non-thread like helically wound advancement structures for operably guiding under rotation and advancing the fastener18downward between the arms52.

Tool engaging grooves64are formed on outer substantially cylindrical surfaces65of the arms52which may be used for holding the head10during assembly with the shank4and the retaining and articulating structure12and also during the implantation of the shank body6into vertebra15. The illustrated grooves64are disposed near the top54of the head10and each extend partially circumferentially about a periphery of each arm52and may include an undercut or dovetail feature for engagement with a holding tool. A holding tool (not shown) is equipped with structure sized and shaped to be received in the grooves64. The holding tool and respective grooves64may be configured for either a twist on/twist off engagement with the head, or a flexible snap on/snap off engagement wherein the holding tool has legs which splay outwardly to position the tool for engagement in the grooves64or a combination thereof. It is foreseen that the grooves64and the cooperating holding tool may be configured to be of a variety of sizes and locations along the cylindrical surfaces65. Also disposed centrally on each arm52is an oval through-bore68that allows for manipulation of the insert14as will be described more fully below.

Communicating with the U-shaped channel56and located within the base50of the head or receiver10is a chamber or cavity78substantially defined by an inner surface80of the base50, the cavity78opening upwardly into the U-shaped channel56. The inner surface80is substantially spherical, with at least a portion thereof forming a partial internal spherical seating surface82having a first radius. The surface82is sized and shaped for mating with the retaining and articulating structure12, as described more fully below.

The base50further includes a restrictive neck83defining a bore84communicating with the cavity78and a lower exterior86of the base50. The bore84is coaxially aligned with respect to a rotational axis B of the head10. The bore84may be conically counterbored or beveled in a region85to widen the angular range of the shank4. The neck83and associated bore84are sized and shaped to be smaller than a radial dimension of the retaining and articulating structure12, as will be discussed further below, so as to form a restriction at the location of the neck83relative to the retaining and articulating structure12, to prevent the retaining and articulating structure12from passing from the cavity78and out into the lower exterior86of the head10when the retaining and articulating structure12is seated. However, it is foreseen that the retaining and articulating structure could be compressible (such as where such structure has a missing section) and that the retaining structure could be loaded up through the neck83and then allowed to expand and fully seat in the spherical seating surface.

It is foreseen that the inner surface80may further include an elongate upper loading recess (not shown) for accommodating and loading the retaining and articulating structure12into the cavity78. Such a loading recess would be generally vertically disposed in the head10, extending between and communicating with both the channel56and the cavity78, allowing for ease in top loading the retaining and articulating structure12into the cavity through the upper opening57and otherwise allowing for the spherical wall80of the head10to have a radius allowing for substantial thickness and strength of the head base50.

On each arm52, disposed adjacent to and directly below the guide and advancement structure62is an inner, inset surface87having a width or diameter greater than a distance between the interior surfaces60of the arms52. An inner insert receiving surface88is located between the surface87and the inner substantially spherical surface80. The insert receiving surface88includes a band of ridges or teeth89extending across each arm52and running parallel to the head top surface54. The ridges or teeth89each incline in a downward direction toward the base50and are sized and shaped to cooperate with ratchet teeth disposed on the insert14as will be described more fully below. The inner surface87provides space for insertion of the insert14into the head10with no initial engagement of the teeth89with the head10as illustrated inFIG.10.

The retaining and articulating structure or ring12is used to retain the capture structure8of the shank4within the head10. The retaining and articulating structure12, best illustrated byFIGS.1,14,16and18, has an operational central axis that is the same as the elongate axis A associated with the shank4, but when the retaining and articulating structure12is separated from the shank4, the axis of rotation is identified as an axis C. The retaining and articulating structure12has a central bore90that passes entirely through the retaining and articulating structure12from a top surface92to a bottom surface94thereof. A first inner cylindrical surface96defines a substantial portion of the bore90, the surface96having a helically wound guide and advancement structure thereon as shown by a helical rib or thread98extending from adjacent the top surface92to adjacent the bottom surface94. Although a simple helical rib98is shown in the drawings, it is foreseen that other helical structures including other types of threads, such as buttress and reverse angle threads, and non threads, such as helically wound flanges with interlocking surfaces, may be alternatively used in an alternative embodiment of the present invention. The inner cylindrical surface96with helical rib98are configured to mate under rotation with the capture structure outer surface34and helical advancement structure or thread36, as described more fully below.

The retaining and articulating structure12has a radially outer partially spherically shaped surface104sized and shaped to mate with the partial spherically shaped seating surface82of the head and having a radius approximately equal to the radius associated with the surface82. The retaining and articulating structure radius is larger than the radius of the neck83of the head10. Although not required, it is foreseen that the outer partially spherically shaped surfaced104may be a high friction surface such as a knurled surface or the like.

The retaining and articulating structure top surface92extends from the central bore90to the outer surface104. The top surface92is disposed at an angle with respect to the bottom surface94, with the top surface92sloping in a downward direction toward the bottom surface94as the top surface92extends toward the outer surface104. As illustrated inFIG.11and discussed more fully below, the angle of inclination of the top surface92is configured for contact and frictional engagement with a bottom surface of the insert14.

The retaining and articulating structure12further includes a tool engagement structure in the form of a transverse slot106formed in the top surface92for engagement with the driving tool31shown inFIGS.17and18. As will be described more fully below, the tool31is configured to fit within the transverse slot106on either side of the domed top42of the shank4and utilized for driving the shank body6into the vertebra15.

The elongate rod or longitudinal member21that is utilized with the assembly1can be any of a variety of implants utilized in reconstructive spinal surgery, but is normally a cylindrical elongate structure having a smooth, outer cylindrical surface108of uniform diameter. The rod21is preferably sized and shaped to snugly seat near the bottom of the U-shaped channel56of the head10and, during normal operation, is positioned slightly above the bottom of the channel56at the lower seat58. In the illustrated embodiment, the domed top42of the shank4does not come into direct contact with the rod21, but rather, the side-loading insert44is received within the bone screw head10prior to rod insertion, and ultimately is positioned between the rod21and the top42.

The insert14is best illustrated inFIGS.3-7. The insert14includes a base110integral with a pair of upstanding arms112. The base110and arms112form a generally U-shaped, open, through-channel114having a substantially cylindrical bottom seating surface116configured to operably snugly engage the rod21. Each arm112has a faceted outer profile with a lower facet or face120extending from the base110and integral with a side facet or face122that includes a bar or rack of inclined teeth124for ratcheting the insert14down by degrees into the head10in cooperation with the ridges or teeth89disposed on the insert receiving surface88, as will be described more fully below. Each side facet or face122extends between one of the lower facets120and a top surface126. The ratchet teeth124are disposed near the top surface126and each tooth124runs in a direction parallel to the top surface126. Furthermore, each tooth124includes a surface130inclined in an outward and upward direction toward the top surface126. The teeth124are thus readily movable or ratcheted downwardly toward the cavity78of the bone screw head10when desired, after side insertion of the insert14into the head10as illustrated inFIGS.1and2. Once the teeth124are pressed downwardly into engagement with the teeth89, the insert14resists upward movement toward the opening57of the bone screw head channel56.

Disposed on either side of each side facet122are lateral facets128that terminate at planar outer edge surfaces132. Also extending between the edge surfaces132and the base110are lower facets134. A pair of opposing, squared-off notches136are formed on each lower facet134in a central location where the facet134contacts the edge surfaces132. The notches136are sized and shaped to correspond and cooperate with the transverse slot106of the retaining and articulating structure12to allow for insertion of the driving tool31through the notches136and into the slot106for engagement with the retaining and articulating structure during installation of the shank body6into bone.

Disposed centrally on a bottom surface138of the base110, opposite the seating surface116is a concave, substantially spherical formation140. A cannulation bore142extends through a central portion of the formation140. The formation140is sized and shaped to snugly frictionally fit about the domed top42of the capture structure8. As will be described in greater detail below, as the insert14is ratcheted downwardly into contact with the domed top42and the retaining and articulating structure12, the insert14may be used to set the articulation of the shank body6with respect to the bone screw head10prior to insertion and locking of the rod21into the head10, or by inserting and compressing the rod21with the closure top18and then releasing the closure top18. As illustrated inFIG.23and discussed more fully below, the side bores or apertures68formed in the head10allow for manipulation of the insert14with respect to the dome shaped top42by a tool146that has opposed pinchers or prongs147for extending through the bores68and pressing against the arms112of the insert14to loosen the insert14from the head10. Eventually, the rod21is placed in the U-shaped channel56and/or the rod21which has been placed in the channel directly, abutingly engages or re-engages the insert14that in turn engages the shank capture structure domed top42, as shown, for example, inFIGS.11and22, consequently biasing the shank4downwardly in a direction toward the base50of the head10when the assembly1is fully assembled. The shank4and retaining and articulating structure12are thereby locked in position relative to the head10by the rod21firmly pushing downward on the insert14and the shank domed top surface42.

With reference toFIGS.12-18, the driving tool31according to the invention includes a handle150, an elongate cylindrical stem or shaft154and an engagement structure156. The engagement structure156is configured to operably mate with both the insert14and the retaining and articulating structure12at the transverse slot106thereof. The shaft154with attached engagement structure156is receivable in and passes through the interior of the bone screw head10. The stem or shaft154is rigidly attached to the handle150and coaxial therewith. The handle150includes outer grooves158disposed about an outer cylindrical surface160thereof to aid in gripping and rotating the respective components.

The engagement structure156includes an oblong support162with two opposed arms164extending downwardly from the support162and away from the shaft154at either end of the support162. The oblong support162has a substantially cylindrical lower surface166sized and shaped to fit within the U-shaped channel114of the insert14and operably mate with the bottom seating surface116during turning rotation and driving the of the bone screw shank4into bone. Each arm164further includes an extension168sized and shaped to fit within the transverse slot106of the retaining and articulating structure12. As illustrated inFIG.16, each extension168has a thickness such that the extension168fits snugly between the threaded cylindrical surface34of the capture structure8and the inner surface80of the head10, while a bottom surface170of the extension168seats evenly on a base surface171of the transverse slot106. Each arm164also includes an inner seating surface174disposed parallel to the base surface171. Each inner seating surface174is sized and shape to seat upon and engage the annular top surface38of the capture structure8when the extensions168are seated within the transverse slot106. Thus, the engagement structure156of the driving tool31engages the bone screw assembly1at the lower cylindrical surface166, the extensions168and the inner seating surface174when driving the shank body6into the vertebra15, as will be described more fully below. The driving tool31also includes a centrally located cannulation bore176extending along a length thereof, sized shaped and located to cooperate with the cannulation bore44of the bone screw shank4and the cannulation bore142of the insert14.

With particular reference toFIGS.19-21, the closure structure or nested fastener18can 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 arms52of the head10. The fastener18screws between the spaced arms52. The illustrated fastener18includes an outer fastener204and an uploaded set screw206. The fastener204includes a base208integral or otherwise attached to a break-off head210. The base208cooperates with the head10of the bone screw assembly1, as illustrated inFIGS.22-28, to close the head U-shaped channel56and to clamp the spinal fixation rod21within the bone screw head10. The break-off installation head210includes a faceted outer surface220sized and shaped for engagement with a tool221for installing the fastener204to the bone screw head or receiver10and thereafter separating the break-off head210from a respective base208when installation torque exceeds selected levels.

The base208of the fastener204is substantially cylindrical, having an axis of rotation D and an external surface250having a guide and advancement structure252disposed thereon. The guide and advancement structure252is matingly attachable to the guide and advancement structure62of the bone screw head10. As with the guide and advancement structure62, the guide and advancement structure252can be of any type, including V-type threads, buttress threads, reverse angle threads, or square threads. Preferably the guide and advancement structure252is a helically wound flange form that interlocks with the reciprocal flange form as part of the guide and advancement structure62on the interior of the bone screw arms52. The guide and advancement structures62and252are preferably of a type that do not exert radially outward forces on the arms52and thereby avoid tendencies toward splaying of the arms52of the bone screw head10, when the fastener204is tightly torqued into the head10.

The fastener204includes an internal, centrally located through-bore254. At the base208, the bore254is substantially defined by a guide and advancement structure, shown inFIGS.20and21as an internal V-shaped thread256. The thread256is sized and shaped to receive the threaded set screw206therein as will be discussed in more detail below. Although a traditional V-shaped thread256is shown, it is foreseen that other types of helical guide and advancement structures may be used. Near a substantially annular planar top surface258of the base208, an abutment shoulder260, extends uniformly radially inwardly. The abutment shoulder260is spaced from the V-shaped thread256and sized and shaped to be a stop for the set screw206, prohibiting the set screw206from advancing out of the top258of the base208. It is foreseen that alternatively, the set screw206may be equipped with an outwardly extending abutment feature near a base thereof, with complimentary alterations made in the base208, such that the set screw206would be prohibited from advancing out of the top258of the base208due to abutment of such outwardly extending feature against a surface of the base208.

An inner cylindrical wall262separates the abutment shoulder260from the thread256. The cylindrical wall262has a diameter slightly greater than a root or major diameter of the internal thread256. The wall262partially defines a cylindrical space or passage264for axial adjustable placement of the screw206with respect to the rod21as will be discussed in more detail below.

The fastener204further includes the break-off head210that is integral or otherwise attached to the fastener204at a neck or weakened region266. The neck266is dimensioned in thickness to control the torque at which the break-off head210separates from the fastener204. The preselected separation torque of the neck266is designed to provide secure clamping of the rod21by the fastener204before the head210separates. For example, 120 inch pounds of force may be a selected break-off torque. The illustrated, hexagonal faceted surfaces220of the break-off head210enables positive, non-slip engagement of the head210by the installation and torquing tool221illustrated inFIG.25. Separation of the break-off head210leaves only the more compact base208of the fastener204installed in the bone screw head or receiver10, so that the installed fastener204has a low profile.

The base208of the fastener204may include structure to provide clamping engagement between the base208and the rod21. In the embodiment disclosed inFIGS.19-28, a bottom surface268of the base208has an interference structure in the form of a “cup point” or V-shaped ridge or ring270. The V-ring270operably cuts into the outer surface108of the rod21during assembly, when the fastener204is threaded into the screw head10, so that the fastener more positively secures the rod21against rotational and translational movement of the rod21relative to the bone screw head10. As the rod21may be bent or skewed with respect to the head10at a location of engagement between the rod21and the fastener204, only a portion or a side of the V-ring270may engage with and cut into the rod21. It is also foreseen that in some embodiments, clamp enhancing structure on the fastener204, such as the V-ring270, or surface finish such as knurling, may or may not be necessary or desirable.

The uploadable set screw206has a substantially planar top276and a bottom277. The set screw206is substantially cylindrical in shape, having an axis of rotation E, and includes an outer cylindrical surface278with a V-shaped thread280extending from the top276to the bottom277thereof. The surface278and thread280are sized and shaped to be received by and mated with the inner thread256of the fastener base208in a nested relationship. Thus, in operation, the axis of rotation E is the same as the axis of rotation D of the fastener204.

The embodiment of the set screw206best illustrated inFIGS.19-21includes interference structure for enhancing clamping or setting engagement with the surface108of the rod21. The bottom277of the illustrated set screw206has a centrally located set point282and a peripherally located cup point or V-shaped set ring284projecting therefrom. The set point282and the set ring284are designed to cut into the surface108of the rod21when the set screw206is tightly fastened into the fastener base208. The set point282projects outwardly from the bottom277to a location beyond the outermost surface of the set ring284. Thus, the set point282is an initial and primary source of engagement with the rod21, directly pressing against the rod18along the central axis of rotation D of the set screw206. As with the V-ring270of the fastener204, the V-ring284may contact and press against the rod21only along a portion thereof if the rod21is bent or otherwise disposed in a skewed relationship with the bone screw head10. It is foreseen that a domed shape projection (not shown) may be utilized in lieu of the set point282. Such a projection may be a radially extending convex, curved, partially spherical or dome-shaped interference or compressive structure, having a substantially uniform radius to provide for positive engagement with the rod21at the surface108. Such a domed structure may extend a greatest distance along the central axis E. It is also foreseen that other structures for enhancing clamping, such as knurling or the like may be used in some embodiments or none in others.

The set screw206includes a central aperture286formed in the top276and defined by faceted side walls288and a hexagonal bottom seating surface289, forming a hex-shaped internal drive for positive, non-slip engagement by a set screw installment and removal tool such as an Allen-type wrench290as depicted inFIGS.20,26and28. With reference toFIG.20, the central aperture286cooperates with the central internal bore254of the fastener204for accessing and uploading the set screw206into the fastener204prior to engagement with the bone screw head10. After the nested fastener18engages the bone screw head10, and the break-off head210is broken off, the tool290is used to set and lock the set screw206against the rod21as illustrated inFIG.26.

There are circumstances under which it is desirable or necessary to release the rod21from the bone screw head10. For example, it might be necessary for a surgeon to re-adjust components of a spinal fixation system, including the rod21, during an implant procedure, following an injury to a person with such a system implanted. In such circumstances, the tool290may be used to remove both the set screw206and attached fastener base208as a single unit, with the set screw206contacting and contained within the base208by the abutment shoulder260. Thus, as illustrated inFIG.28, rotation of the tool290engaged with the set screw206backs both the set screw206and the fastener base208out of the guide and advancement structure252in the arms52of the bone screw head10, thereby releasing the rod21for removal from the bone screw head10or repositioning of the rod21. It is foreseen that other removal structures such as side slots or other screw receiving and engagement structures may be used to engage the set screw206that is nested in the fastener base208.

With reference toFIGS.1and2, prior to the polyaxial bone screw assembly1being implanted in the vertebra15, the retaining and articulating structure12is typically first inserted or top-loaded, into the head U-shaped channel56, and then into the cavity78to dispose the structure12within the inner surface80of the head10. The structure12is typically turned or rotated such that the axis C is perpendicular to the axis B of the head10during insertion of the structure12into the head10. Then, after the retaining and articulating structure12is within the cavity78, the retaining and articulating structure12is rotated approximately 90 degrees such that the axis C is coaxial with the axis B of the head10, and then the structure12is seated in sliding engagement with the seating surface82of the head10.

The shank capture structure8is preloaded, inserted or bottom-loaded into the head10through the bore84defined by the neck83. In other embodiments according to the invention (not shown), the shank4may be sized and configured to be top-loaded, if desired in which case it must be inserted prior to the retaining and articulating structure12. The retaining and articulating structure12, now disposed in the head10is coaxially aligned with the shank capture structure8so that the helical v-shaped thread36rotatingly mates with the thread98of the retaining and articulating structure12.

The shank4and/or the retaining and articulating structure12are rotated to fully mate the structures36and98along the respective cylindrical surfaces34and96, fixing the capture structure8to the retaining and articulating structure12, until the annular top surface38of the capture structure8and the retaining and articulating structure top surface92are contiguous. Permanent, rigid engagement of the capture structure8to the retaining and articulating structure12may be further ensured and supported by the use of adhesive, a spot weld, a one-way thread or deforming one or both of the threads36and98with a punch or the like.

With reference toFIG.9, at this time the shank4is in slidable and rotatable engagement with respect to the head10, while the capture structure8and the lower aperture or neck83of the head10cooperate to maintain the shank body6in rotational relation with the head10. According to the embodiment of the invention shown inFIGS.1-28, only the retaining and articulating structure12is in slidable engagement with the head spherical seating surface82. Both the capture structure8and threaded portion of the shank body6are in spaced relation with the head10. The shank body6can be rotated through a substantial angular rotation relative to the head10, both from side to side and from front to rear so as to substantially provide a universal or ball joint wherein the angle of rotation is only restricted by engagement of the neck26of the shank body6with the neck or lower aperture83of the head10. It is foreseen that in some embodiments that the retaining structure could simply keep the shank upper portion in the receiver and not articulate with the shank upper portion. In such embodiments, the shank upper portion could have a spherical enlargement that articulates with the head spherical seating surface, the insert and the retaining structure itself.

The insert14is then loaded into the head10as illustrated inFIGS.1and2and further operationally shown inFIGS.9-11. With particular reference toFIG.10, the insert U-shaped channel114is aligned with the head10U-shaped channel56and the insert14is initially side-loaded into the head10with the ratchet teeth124disposed adjacent to the surfaces87and directly above the ratchet teeth89of the insert receiving surface88. Such placement allows for unrestricted angular rotation of the shank body6with respect to the head10. As illustrated inFIG.11, the insert14may be pushed downward into contact with the domed top42, frictionally engaging the top42with the insert14and thus setting the angle of orientation of the shank body6with respect to the head10at any desired angle. Because of the orientation of the insert ratchet teeth124and the bone screw head ratchet teeth89, the insert14is readily and easily pushed downward into the head and toward the domed top42, setting or fixing the desired angle of orientation between the shank body6and the head10. Again, this can be done directly with a tool or by compression through the rod21. Furthermore, the cooperating ratchet teeth124and89resist any upward, loosening forces, as will be described more fully below. As shown inFIG.11, a full range of articulation is possible utilizing the insert14, also due to the cooperation of the sloped, faceted surfaces120,134, of the insert14and also the inclined top surface92of the retaining and articulating structure12.

With reference toFIG.10, and alsoFIGS.12-18, the assembly1is typically screwed into a bone, such as the vertebra15, by rotation of the shank4using the driving tool31that operably drives and rotates the shank4by engagement thereof with the insert14and the transverse slot106of the retaining and articulating structure12. Specifically with reference toFIGS.14-16, the tool31shown inFIGS.12and13is inserted into the head10of the bone screw fitted with an insert that has been loosely placed in the head10as shown inFIG.10. The surface166of the driving tool31comes into contact with the bottom seating surface116of the insert14and the tool arms164extend through the insert notches136, pushing the insert down into the head10until the tool extensions168seat within the transverse slot106with the tool bottom surface170frictionally engaging the base171defining the transverse slot106. As illustrated inFIG.16, some frictional engagement between the tool surface174and the top surface38of the capture structure8may also be achievable during rotation of the driving tool31. It is foreseen that in other embodiments according to the invention, the transverse slot106may be replaced by other types of tool engaging recesses.

Preferably prior to implantation of the bone screw assembly1into the vertebra15, the set screw206is assembled with the fastener204. With particular reference toFIGS.19-21, the Allen-type tool290is inserted through the bore254of the fastener204and into the aperture286of the set screw206until seated on the bottom surface289, with faceted outer surfaces292of the tool290engaging the inner faceted walls288of the set screw206. The set screw206is then uploaded into the fastener204by rotation of the set screw206with respect to the fastener204to mate the set screw thread280with the fastener inner thread256until the set screw top surface276abuts the abutment shoulder260, resulting in the nested arrangement of the fastener18shown inFIG.21, with the set screw206completely enveloped in the fastener base208. The nested assembly18shown inFIG.21is now pre-assembled and ready for use with a bone screw head10and cooperating rod21. As illustrated inFIG.21, in such a pre-assembly arrangement, the V-ring270preferably projects beyond the point282and the V-ring284of the set screw206, such that the base208will seat fully within the bone screw arms52prior to engagement of the set screw206with the rod21.

Typically at least two and up to a plurality of bone screw assemblies1are implanted into vertebrae for use with the rod21. With reference toFIGS.17and18, each vertebra15may be pre-drilled to minimize stressing the bone and have the guide wire or pin49inserted therein that is shaped for the cannula44of the bone screw shank6and provides a guide for the placement and angle of the shank4with respect to the vertebra15. A further tap hole may be made using a tap with the guide wire49as a guide. Then, the assembly1and the driving tool31are threaded onto the guide wire by first threading the wire into the bottom opening46of the shank body6. The wire49is then threaded out of the top opening48and through the bore142of the insert14and then into the bore176of the driving tool31. The shank body6is then driven into the vertebra15, by rotation of the driving tool31, using the wire49as a placement guide.

With reference toFIG.22, the rod21is eventually positioned within the head U-shaped channel56, and the nested fastener18is then inserted into and advanced between the arms52. With reference toFIG.23, before or after rod insertion, it may be desirable to move the insert14to a position disengaged from the shank domed top42to allow for rotation of the shank body6with respect to the head10to a desired angle of articulation. As illustrated inFIG.23, the manipulation tool146may be utilized for such purpose by inserting the prongs147of the tool146into the opposing bores68and pinching or squeezing the insert arms112toward one another to release the insert ratchet teeth124from the ratchet teeth89disposed on the head10, and then move the insert14up and away from the domed top42. The tool146may also be used to lower the insert14into position against the domed top42. The bores68are preferably configured with an oblong orientation such that the insert14may be accessed for upward and downward positioning. Thus, utilizing the insert14, a bone screw assembly1may be set and fixed at a desired angle of articulation prior to implantation of the rod21, or after the rod21is placed in the head10. Furthermore, if it is desired for the bone screw shank to remain rotatable with respect to the head10during part or all of a procedure until the rod21and bone screw assembly1are clamped into final position with the fastener18, the insert14may be manipulated as shown inFIG.23to provide for such freedom of articulation.

With reference toFIG.24, the insert14is pressed downwardly into engagement with the shank domed top surface42to set the angle of articulation of the shank body6with respect to the head10at the position shown. The rod21is seated on the insert14and the fastener18is initially placed between the arms52and rotated using the installation tool221engaged with the surfaces220of the break-off head210until the fastener guide and advancement structure252is fully mated with the head guide and advancement structure62, but with the set screw206in position within the fastener base208such that the point282and the ring284are not engaged with the rod21. With reference toFIG.25, the break-off head210is then twisted to a preselected torque, for example 90 to 120 inch pounds, also utilizing the tool221in engagement with the faceted outer surface220of the break-off head210, with or without bending of the rod21in order to achieve and maintain a desired alignment of the spine.

With reference toFIGS.26and27, thereafter, the set screws206are tightened, preferably in a selected order, by inserting the Allen-type tool290into the aperture286and rotating the tool290to thread the set screw206downwardly toward the rod21. As each set screw206is torqued tightly using the tool290, first the point282and then portions of the V-ring284preferably come into contact and abrade or dig into the rod surface108.

As previously discussed herein, because the rod21may be bent, not all projected portions of the fastener base208and the set screw206may come into contact with the rod21. The availability of multiple locations of engagement of the fastener base208and the set screw206with the rod21increases the probability that the rod21will be engaged securely by the nested fastener assembly18. It is noted that the fastener base208may only seat at the bottom of the bone screw head opening57so as to close the opening57and capture the rod21therein without the V-ring270or the base268contacting the rod surface108. The set screw206is then turned and tightened against the rod21, the point284engaging the rod surface108and thereby securing the rod21in place.

FIG.27illustrates the polyaxial bone screw assembly1and including the rod21and the nested fastener18positioned in a vertebra15. The axis A of the bone shank4is illustrated as not being coaxial with the axis B of the head10and the shank4is fixed in this angular locked configuration. Other angular configurations can be achieved, as required during installation surgery due to positioning of the rod21or the like. It is noted that in the illustrated embodiment, the shank domed top42is rounded to approximately equally extend upward into the channel56approximately the same amount no matter what degree of rotation exists between the shank4and head10and the surface42is sized to extend slightly upwardly into the U-shaped channel56. Thus, the surface42is engaged by the insert14that is in turn engaged by the rod21and pushed downwardly toward the base50of the head10when the nested fastener18biases downwardly toward and onto the rod21. However, it is foreseen that the thickness of the insert14may be increased to allow for a shank top that does not extend into the U-shaped channel56.

The downward pressure on the shank4pressed upon by the insert14in turn urges the retaining and articulating structure12downward toward the head seating surface82, with the retaining and articulating structure outer surface104in frictional engagement with the head seating surface82. As the nested fastener18presses against the rod21, the rod21presses against the shank and the retaining and articulating structure12that is now rigidly attached to the shank4which in turn becomes frictionally and rigidly attached to the head10, fixing the shank body6in a desired angular configuration with respect to the head10and the rod21.

With reference toFIG.28, if removal of the assembly1is necessary, or if it is desired to release the rod21at a particular location, disassembly is accomplished by using the Allen-type driving tool290, mated with the set screw206at the aperture286and turned in a direction to rotate the set screw206up and out of the base208. The set screw top276then backs into and abuts the abutment shoulder260, transferring rotational torque exerted from the tool290from the set screw206to the fastener base208. The base208then rotates with the guide and advancement structure252threading out of the guide and advancement structure62of the head10. Thus, both the set screw206and the fastener base208are removed from the bone screw head10at the same time. If desired, the manipulation tool146may be used as shown inFIG.23and previously described herein to disengage the insert14from the shank domed top42. Finally, disassembly of the assembly1is accomplished in reverse order to the procedure described previously herein for assembly.

With reference toFIGS.29-42, the reference number301generally represents a second or alternative embodiment of an assembly according to the present invention. The assembly301includes a bone screw shank304, having a capture structure306and a shank body308with a thread310for threadably implanting into a bone, such as a vertebra313, and a head or receiver314which connects with the shank304to engage and secure a structural member, such as a spinal fixation rod316, relative to the vertebra313. The assembly301also includes a retaining and articulating structure or ring320operably positioned within the head or receiver314and engaging the capture structure306on the upper portion of the shank304. The capture structure306is retained within the head or receiver314by the retaining and articulating structure320as will be described more fully below. The assembly301further includes a pressure insert324, engageable with the upper portion of the capture structure306and the rod316as will be described more fully below. The shank304, head or receiver314, retaining and articulating structure320and the insert324are preferably assembled prior to implantation of the shank body308into the vertebra313.

With reference toFIG.42, the assembly301further includes a closure top326for fixing the rod316within the head or receiver314. The insert324allows for setting an angle of articulation between the shank body308and the head or receiver314prior to insertion of the rod316, if desired. Upon installation, which will be described in detail below, the closure top326presses against the rod316that in turn presses against the insert324that presses against the upper end of the capture structure306which biases the retaining and articulating structure320into fixed frictional contact with the head or receiver314, so as to fix the rod316relative to the vertebra313. The head or receiver314and shank304cooperate in such a manner that the head or receiver314and shank304can 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 head or receiver314with the shank304until both are locked or fixed relative to each other.

Referring toFIGS.29,36-38and40, the shank304is elongated and sized and shaped to be screwed into one of the vertebra313. The shank body308includes the external helically wound thread310that extends from an outer tip330to a neck332disposed adjacent the capture structure306.

On the illustrated shank304, the capture structure306includes a region334that is frusto-conical in shape, diverging in diameter in a direction away from the outer tip330and that is coaxially aligned with an axis of rotation of the shank body308. The region334terminates at an annular seating surface335. The illustrated capture structure306has a maximum radius that is less than a radius associated with the shank thread310and further, preferably less than the radius of the shank body308whereupon the thread8is located.

The capture structure306has a plurality of tool engageable grooves, apertures or the like336to enable positive engagement by an appropriately shaped installation tool338to thread and drive the shank body308into the vertebra313as will be discussed in greater detail below. The illustrated shank capture structure306includes four evenly spaced tool engageable grooves336, but it is foreseen that the driving structure may include fewer grooves, an alternative configuration of grooves or other driver receiving structure. An upper end surface340of the capture structure306opposite the tip330is provided with a formation or dome342to be positively and interferingly engaged by the insert324, which in turn is positively engaged by the rod316when the assembly301is assembled into place. The illustrated dome342is radiused, knurled and centered on the upper end surface340so as to be coaxial with the remainder of the shank304. The scoring or knurling of the dome342operably frictionally abuts against the insert324when the insert324is rotated into engagement with the head or receiver314, as described more fully below, to provide for a selected setting of a desired angle of articulation between the shank body308and the head314prior to insertion and locking down of the rod315. It is foreseen that in certain embodiments, the purpose of the dome342is simply to be engaged by the insert324that is in turn engaged by the rod316, pushing the shank304in such a manner as to frictionally engage the retaining and articulating structure320with the head314as described below. Preferably, the dome342is radiused so that the dome342engages the insert324at approximately the same location regardless of the angle of articulation of the shank body308with respect to the head314. However, it is foreseen that in certain embodiments shapes other than the dome342could be utilized.

Referring toFIGS.29-31, and36-42, the head or receiver314is generally cylindrical in external profile and has a central and axially aligned shank receiving bore346ending at an inner and lower neck347. The neck347is radiused to receive the shank capture structure306and preferably smaller than a radius of the shank body308and thread310. The bore346is also preferably sized larger than the capture structure306of the shank304to enable the shank394to be oriented through a range of angular dispositions relative to the head or receiver314. The bore346may be conically counterbored or beveled in a region348to widen the angular range of the shank304.

The head or receiver314is provided with a U-shaped rod cradle350sized to receive the rod316therethrough. The illustrated cradle350is rounded and radiused at an inner or lower portion or seat352to snugly mate with a cylindrical outer surface354of the rod316and open at an outer end or top356, with spaced apart side surfaces358so as to form upstanding and spaced apart arms360. The side surfaces358have guide and advancement structures362formed thereon that are complementary to guide and advancement structures364of the closure top326(FIG.42). The illustrated structures362and364are helically wound flanges or threads that advance the closure top326into the head314, as the closure top326is rotated about a central axis thereof. It is foreseen that the structures362and364may be interlocking helical flange forms similar to the structures62and252previously described herein with respect to the assembly1, V-shaped threads, buttress threads, square threads, reverse angle threads, or other types of threads or flange forms. Preferably, the structures362and364are of such a nature as to resist splaying of the arms360when the closure top326is advanced into the U-shaped cradle350.

Furthermore the head or receiver314includes an assembly cavity366formed therein that opens into the cradle350. A partially spherical socket or seat368defines the assembly cavity366. The seat368is disposed between the arm inner surfaces358and the neck347defining the shank bore346and as illustrated has a radius that is slightly less than a radius of the assembly cavity366. The seat368has a substantially spherical shape and extends upward coaxially through the head314from the neck347to the cavity366. The cavity366and the seat368will be detailed further below.

Each arm inner surface358further includes a recessed portion370disposed between the guide and advancement structure362and the seat368. The portion370is defined by an upper shoulder372, a lower shoulder374and a wall376disposed between the upper and lower shoulders372,374. The wall376is parallel to an axis of rotation of the head314that is operably coaxial with the shank304. As will be described in greater detail below, the insert324may be operably disposed in the recessed portion370and include a setting position wherein the insert324abuts against the upper shoulder372and presses against the shank capture structure dome342, allowing for the setting of a desired angle of articulation of the bone screw shank body308with respect to the head314during surgery, prior to lock down of the rod316by the closure top326. The head or receiver314may further include external, closed end grip bores378for positive engagement by a holding tool (not shown) to facilitate secure gripping of the head314during assembly, installation and/or manipulation of the assembly301.

The retaining and articulating structure320, best illustrated inFIGS.29-31and36is used to retain the capture structure306within the head or receiver314. The retaining and articulating structure320is in the form of a discontinuous ring that resiliently expands and contracts to enable the structure320to be snapped over and seated on the capture structure306. The retaining and articulating structure320, similar to a remainder of the assembly301, is preferably formed of a material such as a spring stainless steel, tantalum, titanium or other resilient implantable material. The illustrated retaining and articulating structure320forms a gap or radial split380extending from a top surface382to a bottom surface384thereof, that allows the structure320to expand in circumference to fit over the capture structure306. The retaining and articulating structure320includes an inner surface382formed by a through-bore sized and shaped to be compatible with the conical shape of the capture structure306. The retaining and articulating structure320has an outer surface that is frusto-spherical, partially spherical, or a segment of a sphere, with a spherical radius approximately equivalent to the spherical radius of the spherical seat368within the head314and smaller than a radius of the cavity366. As will be described more fully below, the bottom surface384seats upon the annular seating surface335of the shank capture structure306when the retaining and articulating structure320is fully installed on the capture structure306.

The closure top326is generally cylindrical in shape and is provided with a break-off head390that is connected to the closure top326by a weakened area or neck392such that the break-off head390separates from the closure top326at a predetermined torque applied to the break-off head390during assembly. The illustrated break-off head390has a hexagonal cross section for engagement by a tool (not shown) of a complementary shape. The closure top326further includes a central point394for abrading and/or penetrating the rod316when fully installed on the head314. Furthermore, the closure top326includes a driving formation, such as a hex aperture (not shown) for removal of the closure top, if desired, after the break-off head390is broken off.

The insert324is best illustrated inFIGS.32-35. The insert324includes a substantially conical base portion401integral with a body portion404. The base portion401extends outwardly from an annular, flat bottom surface402to the body portion404. The body portion404is oblong, having a width W that is smaller than a length L thereof. The width W is bounded by two substantially flat surfaces405. The width W is slightly smaller than a distance between the inner surfaces of the arms358of the head314. The length L, taken along a center line406is slightly smaller than a diameter of the recessed portion370measured between the surfaces376. A U-shaped cradle or channel407running parallel to the width W extends through the body portion404, and is sized and shaped to receive the rod316thereon as will be described more fully below. Arms408disposed on either side of the cradle406each included a top surface410that is parallel to the bottom surface402and a sloped surface412, starting at the top surface410and sloping downwardly toward the base portion401. The arms408also include rounded, substantially cylindrical side surfaces414, each having a radius slightly smaller than a radius of the wall376that partially defines the recessed portion370of the head314. The sloped surfaces412are disposed opposite one another and the top surfaces410are disposed opposite one another. The sloped surfaces412also slope in opposite directions, each starting at the center line or axis406and running outwardly and downwardly away therefrom to provide for a cam action when the insert324is placed in the head314as shown inFIG.37, and then rotated, the sloped surfaces412engaging the upper shoulder372of the recessed portion370of the head314and thus transforming the circular motion of rotating the insert324in the recessed portion370of the head314into linear motion, pressing the insert324against the shank dome342as will be described more fully below.

Each arm408of the body portion404includes a substantially flat bottom surface416extending from the conical base portion401to the cylindrical surface414. The base portion401further includes a centrally located concave, substantially spherical bottom formation418contiguous to the annular bottom surface402. The spherical bottom formation418is sized and shaped to cooperate and engage with the dome342of the shank capture structure306, providing a snug, frictional fit. Apertures420extend through the U-shaped cradle407and are sized and shaped to cooperate and align with the apertures336of the capture structure306. Thus, in the illustrated embodiment, four evenly spaced apertures420extend through the insert324and axially align with the apertures336as illustrated inFIGS.39and40, both when the insert324is initially placed in the head314and when the insert324is rotated within the head314such that the top surfaces410are adjacent the upper shoulder371. Alignment of the apertures420and the apertures336allow for engagement between the capture structure306, the insert324and the driving tool338as will be described more fully below.

The driver338illustrated atFIG.40includes a handle (not shown), a drive shaft426and an engagement portion428. The engagement portion426includes an oblong support430sized and shaped to fit within the U-shaped cradle407of the insert324. Four prongs432extending from the oblong support430are sized and shaped to extend through the apertures420of the insert324and into the apertures336in the capture structure306, thus operably engaging both the bone screw shank304and the insert324when rotating and driving the shank body308into the vertebra313.

FIGS.30,31and36illustrate the assembly of the bone screw head314, shank304and retaining and articulating structure320. InFIG.30, the retaining and articulating structure320is inserted into the head314through an interior of the U-shaped cradle350. The retaining and articulating structure320is first oriented with a central axis thereof at a right angle to a central axis of the bore346. Then, the retaining and articulating structure is oriented as illustrated inFIG.31with the central axis of the retaining and articulating structure320being parallel or coincident with the axis of the bore346and the neck347, by rotating the retaining and articulating structure320within the assembly cavity366. With reference toFIG.36, the capture structure306of the shank304is then inserted through the head bore346and then adjacent to the retaining and articulating structure inner surface386by expanding the retaining and articulating structure320at the radial split380so as to snap the retaining and articulating structure320over and around the capture structure306at the frusto-conical surface334. The relative resistance encountered by the retaining and articulating structure320allows the capture structure306to expand the circumference of the retaining and articulating structure320, by expansion of the split380, so that the capture structure306enters the retaining and articulating structure320. As illustrated inFIG.37, when fully seated, the surface334frictionally engages the retaining and articulating structure inner surface386and the bottom surface384of the retaining and articulating structure320abuts against the annular seating surface335of the capture structure306thereby limiting penetration of the capture structure306into the retaining and articulating ring structure320.

FIG.37shows the assembly301with the retaining and articulating structure320lowered from the assembly position and positioned in the spherical seat368with the central axis of the shank304coaxial with the central axis of the head314. However, similar to the assembly1, the relevant discussion of which is incorporated by reference herein, the curved or spherical seat368and the curved or spherical outer surface388of the retaining and articulating structure320, allows universal angular positioning of the shank304relative to the head314. The retaining and articulating structure320, thus performs the functions of preventing the capture structure306of the shank304from slipping through the neck347and, in conjunction with the seat368, forms a ball joint for relative orientation of the shank304and the head314.

The insert324is then loaded into the head314as illustrated inFIGS.37and39, with the width dimension W being oriented as shown with respect to the arms360to allow top loading of the insert324. The insert324is lowered into the head314until the concave bottom formation418is seated on the dome342.

For driving the bone screw shank body308into bone, such as the vertebra313, the insert324is first rotated axially as illustrated inFIGS.40and41, with the sloping surfaces412of the insert324contacting the upper shoulder372defining the head recessed portion370, thereby pushing the capture structure306and attached retaining and articulating structure320downwardly against the seat368. As the insert is rotated approximately 90 degrees until the flat surfaces410fully engage the upper shoulder372, the insert324functions as a cam, providing a mechanical linkage that converts rotary motion to linear motion. Frictional engagement between the retaining and articulating structure320and the seat368sets the bone shank304in an angular position with respect to the head314, but does not lock such into position. Thus, the insert324may be used at any time during a procedure to set the shank body308at a desired angle with respect to the head314, but that position is not rigidly fixed until the rod316presses down upon the insert324. When the insert flat surfaces410engage the upper shoulder372, the apertures420of the insert324are aligned with the apertures336of the capture structure306and the insert cradle407is oriented in a position to receive the oblong support430of the driving tool engagement portion428.

With particular reference toFIG.40, the assembly301is typically screwed into a bone, such as the vertebra313, by rotation of the shank304using the driving tool338that operably drives and rotates the shank304by engagement thereof with the insert324and the apertures336of the capture structure306. The driving tool338is inserted into the head314of the bone screw with the prongs432first inserted into the apertures420and then the apertures336until the oblong support430is seated on the insert cradle407.

Typically at least two and up to a plurality of bone screw assemblies301are implanted into vertebrae for use with the rod316. As described with respect to the assembly1, and incorporated by reference herein, each vertebra313may be pre-drilled to minimize stressing the bone. Although not shown, the assembly301may be cannulated in a manner as described with respect to the assembly1so that a guide wire or pin may be used as a guide for the placement and angle of the assembly301. The shank body308is then driven into the vertebra313, by rotation of the driving tool338.

With reference toFIG.42, the rod316is eventually positioned within the head U-shaped rod cradle350, and the closure top326is then inserted into and advanced between the arms360. Before rod insertion, it may be desirable to rotate the insert324to a position disengaged from the shank domed top342as shown inFIG.37, to allow for a loose angular connection of the shank body308with respect to the head314until a desired angle of articulation is decided upon. The driving tool338may be utilized to rotate the insert324by inserting the prongs432in the apertures420. Then, the insert324may be rotated to the position shown inFIG.41, setting, but not locking such desired angular orientation between the shank body308and the head314. In other words, when the insert324is in contact with the upper shoulder372, the insert324presses down on the shank304, providing sufficient frictional engagement between the retaining and articulating structure320and the head seat368that the shank304resists angular movement. However, it may not be desirable to rotate the insert324in order to change the angular orientation of the shank304with respect to the head314. The shank304may simply be moved, using some force, to a desired position, which will then be the set position.

With reference toFIG.24, the rod316is seated on the insert324and the closure top326is initially placed between the arms360and rotated using an installation tool (not shown) engaged with surfaces of the break-off head390until the guide and advancement structure364is fully mated with the head guide and advancement structure262, with the point394penetrating the rod316. The break-off head390is then twisted to a preselected torque, for example 90 to 120 inch pounds, until broken off.

If removal of the assembly301is necessary, or if it is desired to release the rod316at a particular location, disassembly is accomplished by using a tool (not shown) with a driving formation (not shown) located on the closure top326to rotate and remove the closure top326from the head314. Disassembly of the assembly301is accomplished in reverse order to the procedure described previously herein for assembly.

With reference toFIGS.43-54, the reference number501generally represents a third embodiment of an assembly according to the present invention. The assembly401includes a bone screw shank504, having a capture structure506and a shank body508with a thread510for threadably implanting into a bone, such as a vertebra513, and a head or receiver514which connects with the shank504to engage and secure a structural member, such as a spinal fixation rod516, relative to the vertebra513. The assembly501also includes a retaining and articulating structure or ring520operably positioned within the head or receiver514and engaging the capture structure506of the shank504. The capture structure506is retained within the head or receiver514by the retaining and articulating structure520as will be described more fully below. The assembly501further includes a pressure insert524, engageable with the capture structure506and the rod516as will be described more fully below. The shank504, head or receiver514, retaining and articulating structure520and the insert524are preferably assembled prior to implantation of the shank body508into the vertebra513.

With reference toFIG.54, the assembly501further includes a closure top526for fixing the rod516within the head or receiver514. The insert524allows for setting an angle of articulation between the shank body508and the head or receiver514prior to insertion of the rod516, if desired. Upon installation, which will be described in detail below, the closure top526presses against the rod516that in turn presses against the insert524that presses against the capture structure506which biases the retaining and articulating structure520into fixed frictional contact with the head or receiver514, so as to fix the rod516relative to the vertebra513. The head or receiver514and shank504cooperate in such a manner that the head or receiver514and shank504can 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 head or receiver514with the shank504until both are locked or fixed relative to each other.

Referring toFIGS.43,46-48and52, the shank504is elongated and sized and shaped to be screwed into one of the vertebra513. The shank body508includes the external helically wound thread510that extends from an outer tip530to a neck532disposed adjacent the capture structure506.

On the illustrated shank504, the capture Structure506includes a substantially cylindrical threaded region534that is coaxially aligned with an axis of rotation of the shank body508. The region534terminates at an annular seating surface535. The illustrated capture structure506has a maximum radius that is less than a radius associated with the shank thread510.

The capture structure506has a plurality of tool engageable grooves, apertures or the like536to enable positive engagement by an appropriately shaped installation tool538to thread and drive the shank body508into the vertebra513as will be discussed in greater detail below. The illustrated shank capture structure506includes four evenly spaced tool engageable grooves536, but it is foreseen that the driving structure may include fewer grooves, an alternative configuration of grooves or other driver receiving structure. An upper end surface540of the capture structure506opposite the tip530is provided with a formation or dome542to be positively and interferingly engaged by the insert524, which in turn is positively engaged by the rod516when the assembly501is assembled into place. The illustrated dome542is radiused, knurled and centered on the upper end surface540so as to be coaxial with the remainder of the shank504. The scoring or knurling of the dome542operably frictionally abuts against the insert524when the insert524is rotated into engagement with the head or receiver514, as described more fully below, to provide for a selected setting of a desired angle of articulation between the shank body508and the head or receiver514prior to insertion and locking down of the rod515. It is foreseen that in certain embodiments, the purpose of the dome542is simply to be engaged by the insert524that is in turn engaged by the rod516, pushing the shank504in such a manner as to frictionally engage the retaining and articulating structure520with the head or receiver514as described below. Preferably, the dome542is radiused so that the dome542engages the insert524at approximately the same location regardless of the angle of articulation of the shank body508with respect to the head or receiver514. However, it is foreseen that in certain embodiments shapes other than the dome542could be utilized. In the embodiment shown inFIGS.4354, the upper end540supporting the dome542has a hex-shaped profile with side surfaces543configured to mate with an assembly or driving tool (not shown).

Referring toFIGS.43-48, the head or receiver514is generally cylindrical in external profile and has a central and axially aligned shank receiving bore546ending at an inner and lower neck547. The neck547is radiused to receive the shank capture structure506and preferably smaller than a radius of the shank body508and thread510. The bore546is also preferably sized larger than the capture structure506of the shank504to enable the shank594to be oriented through a range of angular dispositions relative to the head or receiver514. The bore546may be conically counterbored or beveled in a region548to widen the angular range of the shank504.

The head or receiver514is provided with a U-shaped rod cradle550sized to receive the rod516therethrough. The illustrated cradle550is rounded and radiused at an inner or lower portion or seat552to snugly mate with a cylindrical outer surface554of the rod516and open at an outer end or top556, with spaced apart side surfaces558so as to form upstanding and spaced apart arms560. The side surfaces558have guide and advancement structures562formed thereon that are complementary to guide and advancement structures564of the closure top526(FIG.54). The illustrated structures562and564are helically wound flanges or threads that advance the closure top526into the head or receiver514, as the closure top526is rotated about a central axis thereof. It is foreseen that the structures562and564may be interlocking helical flange forms similar to the structures62and252previously described herein with respect to the assembly1, V-shaped threads, buttress threads, reverse angle threads, or other types of threads or flange forms. Preferably, the structures562and564are of such a nature as to resist splaying of the arms560when the closure top526is advanced into the U-shaped cradle550.

Furthermore the head or receiver514includes an assembly cavity566formed therein that opens into the cradle550. A partially spherical socket or seat568defines the assembly cavity566. The seat568is disposed between the arm inner surfaces558and the neck547defining the shank bore546and as illustrated has a radius that is slightly less than a radius of the assembly cavity566. The seat568has a substantially spherical shape and extends upward coaxially through the head or receiver514from the neck547to the cavity566. The cavity566and the seat568will be detailed further below.

Each arm inner surface558further includes a recessed portion570disposed between the guide and advancement structure562and the seat568. The portion570is defined by an upper shoulder572, a lower shoulder574and a wall576disposed between the upper and lower shoulders572,574. The wall576is parallel to an axis of rotation of the head or receiver514that is operably coaxial with the shank504. As will be described in greater detail below, the insert524may be operably disposed in the recessed portion570and include a setting position wherein the insert524abuts against the upper shoulder572and presses against the shank capture structure dome542, allowing for the setting of a desired angle of articulation of the bone screw shank body508with respect to the head514during surgery, prior to lock down of the rod516by the closure top526. The head or receiver514may further include external, closed end grip bores578for positive engagement by a holding tool (not shown) to facilitate secure gripping of the head514during assembly, installation and/or manipulation of the assembly501.

The retaining and articulating structure520, best illustrated inFIGS.43-48and54is used to retain the capture structure506within the head or receiver514. The retaining and articulating structure520is in the form of a ring. The retaining and articulating structure520includes a top surface582, a bottom surface584, an inner surface586having a thread587and an outer surface588. The thread587is sized and shaped to mate with the threaded region534of the capture structure506. The retaining and articulating structure520, similar to a remainder of the assembly501, is preferably formed of a material such as a spring stainless steel, tantalum, titanium or other resilient implantable material.

The retaining and articulating structure outer surface588is frusto-spherical, partially spherical, or a segment of a sphere, with a spherical radius approximately equivalent to the spherical radius of the spherical seat568within the head or receiver514and smaller than a radius of the cavity566. As will be described more fully below, the bottom surface584seats upon the annular seating surface535of the shank capture structure506when the retaining and articulating structure520is fully installed on the capture structure506.

The closure top526is generally cylindrical in shape and is provided with a break-off head590that is connected to the closure top526by a weakened area or neck592such that the break-off head590separates from the closure top526at a predetermined torque applied to the break-off head590during assembly. The illustrated break-off head590has a hexagonal cross section for engagement by a tool (not shown) of a complementary shape. The closure top526further includes a central point594for abrading and/or penetrating the rod516when fully installed on the head514. Furthermore, the closure top526includes a driving formation, such as a hex aperture (not shown) for removal of the closure top, if desired, after the break-off head590is broken off.

The insert524is best illustrated inFIGS.43,47and49-54. The insert524includes a substantially conical base portion601integral with a body portion604. The base portion601extends outwardly from an annular, flat bottom surface602to the body portion604. The body portion604is oblong, having a width W′ that is smaller than a length L′ thereof. The width W′ is bounded by two substantially flat surfaces605. The width W′ is slightly smaller than a distance between the inner surfaces of the arms558of the head514. The length L′, taken along a center line606is slightly smaller than a diameter of the recessed portion570measured between the surfaces576. A U-shaped cradle or channel607running parallel to the width W extends through the body portion604, and is sized and shaped to receive the rod516thereon as will be described more fully below. Arms608disposed on either side of the cradle606each included a top surface610that is parallel to the bottom surface602and a sloped surface612, starting at the top surface610and sloping downwardly toward the base portion601. The arms608also include rounded, substantially cylindrical side surfaces614, each having a radius slightly smaller than a radius of the wall576that partially defines the recessed portion570of the head514. The sloped surfaces612are disposed opposite one another and the top surfaces610are disposed opposite one another. The sloped surfaces612also slope in opposite directions, each starting at the center line or axis606and running outwardly and downwardly away therefrom to provide for a cam action when the insert524is placed in the head514as shown inFIG.49, and then rotated, the sloped surfaces612engaging the upper shoulder572of the recessed portion570of the head514and thus transforming the circular motion of rotating the insert524in the recessed portion570of the head514into linear motion, pressing the insert524against the shank dome542as will be described more fully below.

Each arm608of the body portion604includes a substantially flat bottom surface616extending from the conical base portion601to the cylindrical surface614. The base portion601further includes a centrally located concave, substantially spherical bottom formation618contiguous to the annular bottom surface602. The spherical bottom formation618is sized and shaped to cooperate and engage with the dome642of the shank capture structure606, providing a snug, frictional fit. Apertures620extend through the U-shaped cradle607and are sized and shaped to cooperate and align with the apertures536of the capture structure506.

Thus, in the illustrated embodiment, four evenly spaced apertures620extend through the insert524and axially align with the apertures536as illustrated inFIGS.49and53, both when the insert524is initially placed in the head514and when the insert524is rotated within the head514such that the top surfaces610are adjacent the upper shoulder571. The alignment of the apertures620and the apertures536as shown inFIG.53allow for engagement between the capture structure506, the insert524and the driving tool538as will be described more fully below.

A pair of points622are disposed in the U-shaped cradle607and project therefrom. The points622are disposed along the center line606and near the surfaces610and612, but could be placed in other areas. The points622are sized and shaped to abrade and penetrate the rod516as will be described more fully below. One to six or more points could be utilized.

The driver538illustrated atFIG.52includes a handle (not shown), a drive shaft626and an engagement portion628. The engagement portion626includes four prongs632extending therefrom sized and shaped to extend through the apertures620of the insert524and into the apertures536in the capture structure506, thus operably engaging both the bone screw shank504and the insert524when rotating and driving the shank body508into the vertebra513.

FIGS.43-47illustrate the assembly of the bone screw head514, shank504and retaining and articulating structure520. InFIG.44, the retaining and articulating structure520is inserted into the head514through an interior of the U-shaped cradle550. The retaining and articulating structure520is first oriented with a central axis thereof at a right angle to a central axis of the bore546. Then, the retaining and articulating structure is oriented as illustrated inFIG.45with the central axis of the retaining and articulating structure520being parallel or coincident with the axis of the bore546and the neck547, by rotating the retaining and articulating structure520within the assembly cavity566. With reference toFIG.56, the capture structure506of the shank504is then inserted through the head bore546and then rotated with respect to the retaining and articulating structure520, mating the threaded region534with thread587disposed on the inner surface586of the retaining and articulating structure520. As illustrated inFIG.47, when fully seated, the bottom surface584of the retaining and articulating structure520abuts against the annular seating surface535of the capture structure506.

FIGS.47and48show the assembly501with the retaining and articulating structure520lowered from the assembly position and positioned in the spherical seat568with the central axis of the shank504coaxial with the central axis of the head514. However, similar to the assembly1, the relevant discussion of which is incorporated by reference herein, the curved or spherical seat568and the curved or spherical outer surface588of the retaining and articulating structure520, allows universal angular positioning of the shank504relative to the head514. The retaining and articulating structure520, thus performs the functions of preventing the capture structure506of the shank504from slipping through the neck547and, in conjunction with the seat568, forms a ball joint for relative orientation of the shank504and the head514.

The insert524is then loaded into the head514as illustrated inFIGS.47and49, with the width dimension W′ being oriented as shown with respect to the arms560to allow top loading of the insert524. The insert524is lowered into the head514until the concave bottom formation618is seated on the dome542.

For driving the bone screw shank body508into bone, such as the vertebra513, the insert524is first rotated axially as illustrated inFIGS.52and53, with the sloping surfaces612of the insert524contacting the upper shoulder572defining the head recessed portion570, thereby pushing the capture structure506and attached retaining and articulating structure520downwardly against the seat568. As the insert is rotated approximately 90 degrees until the flat surfaces610fully engage the upper shoulder572, the insert524functions as a cam, providing a mechanical linkage that converts rotary motion to linear motion. Frictional engagement between the retaining and articulating structure520and the seat568sets the bone shank504in an angular position with respect to the head514, but does not lock such into position. Thus, the insert524may be used at any time during a procedure to set the shank body508at a desired angle with respect to the head514, but that position is not rigidly fixed until the rod516presses down upon the insert524. When the insert flat surfaces610engage the upper shoulder572, the apertures620of the insert524are aligned with the apertures536of the capture structure506and the insert cradle607is oriented in a position to receive the oblong support630of the driving tool engagement portion628.

With particular reference toFIG.52, the assembly501is screwed into a bone, such as the vertebra513, by rotation of the shank504using the driving tool538that operably drives and rotates the shank504by engagement thereof with the apertures620of the insert524and the apertures536of the capture structure506. The driving tool538is inserted into the head514of the bone screw with the prongs632first inserted into the apertures620and then the apertures536, and then driven and rotated into bone.

Alternatively, the assembly501may be driven into bone prior to placement of the insert524in the head514. A hex driving tool (not shown) sized and shaped to mate with the surfaces543of the capture structure506may be used to rotate and drive the shank body508into the vertebra513. Thereafter, the insert524may be placed in the bone screw head514as shown inFIG.47.

Typically at least two and up to a plurality of bone screw assemblies501are implanted into vertebrae for use with the rod516. As described with respect to the assembly1, and incorporated by reference herein, each vertebra513may be pre-drilled to minimize stressing the bone. Although not shown, the assembly501may be cannulated in a manner as described with respect to the assembly1so that a guide wire or pin may be used as a guide for the placement and angle of the assembly501. The shank body508is then driven into the vertebra513, by rotation of the driving tool538.

With reference toFIG.54, the rod516is eventually positioned within the head U-shaped rod cradle550, and the closure top526is then inserted into and advanced between the arms560. Before rod insertion, it may be desirable to rotate the insert524to a position disengaged from the shank domed top542as shown inFIG.47, to allow for a loose angular connection of the shank body508with respect to the head514until a desired angle of articulation is decided upon. The driving tool538may be utilized to rotate the insert524by inserting the prongs632in the apertures620. Then, the insert524may be rotated to the position shown inFIG.53, setting, but not locking such desired angular orientation between the shank body508and the head514. In other words, when the insert5324is in contact with the upper shoulder572, the insert524presses down on the shank504, providing sufficient frictional engagement between the retaining and articulating structure520and the head seat568that the shank504resists angular movement. However, it may not be desirable to rotate the insert524in order to change the angular orientation of the shank504with respect to the head514. The shank504may simply be moved, using some force, to a desired position, which will then be the set position.

With reference toFIG.54, the rod516is seated on the insert524and the closure top526is initially placed between the arms560and rotated using an installation tool (not shown) engaged with surfaces of the break-off head590until the guide and advancement structure564is fully mated with the head guide and advancement structure562, with the point594penetrating the rod516and also the points622penetrating the rod516. The break-off head590is then twisted to a preselected torque, for example 90 to 120 inch pounds, until broken off.

If removal of the assembly501is necessary, or if it is desired to release the rod516at a particular location, disassembly is accomplished by using a tool (not shown) with a driving formation (not shown) located on or in the closure top526to rotate and remove the closure top526from the head514. Disassembly of the assembly501is accomplished in reverse order to the procedure described previously herein for assembly.

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.