Bone support apparatus

An apparatus for connecting a bone anchor to a support rod includes a connector body and a cap. The connector body has a channel to receive and locate the support rod relative to the bone anchor. The cap is moveable longitudinally into a partially installed position in the channel, and snaps into non-threaded engagement with the connector body by rotating from the partially installed position to an installed position without moving axially relative to the connector body. In some embodiments, a sleeve fits over a socket portion of the connector body in a temporary position in which the sleeve permits insertion of the bone anchor into the socket. The sleeve engages the connector body so as to be restrained from axial and rotational movement relative to the connector body when in the temporary position. Tools are provided for installing the connector body, sleeve, cap, and support rod.

TECHNICAL FIELD

The claimed invention relates to a device for connecting a bone support member to a bone anchor, and more specifically a bone screw or hook to a support rod.

BACKGROUND

Many methods of treating spinal disorders are known in the art. One known method involves anchoring a screw or a hook to the vertebrae, and fixing the screws or hooks along a spinal rod to position or immobilize the vertebrae with respect to one another. The screws or hooks commonly have heads with channels in which the spinal rod is inserted and subsequently clamped by a set screw or fastener or locking cap. This method may commonly involve multiple screws or hooks, as well as multiple spinal rods. With this method, the spinal rod(s) may be shaped to maintain the vertebrae in such an orientation as to correct the spinal disorder at hand (e.g. to straighten a spine having abnormal curvature). Additionally or alternatively, the screws or hooks my be spaced along the rod(s) to compress or distract adjacent vertebrae.

Surgeons have often encountered considerably difficulty with this method because of trouble aligning the spinal rod(s) with the channels in the heads of the screws or hooks. For example, the heads of the screws or hooks are often out of alignment with one another because of the curvature of the spine or the size and shape of each vertebrae. To facilitate easier insertion of the spinal rods into the channels, and to provide additional flexibility in the positioning of the spinal rods and the screws and hooks, connectors have been developed (which include the support rod channel) which initially pivots with respect to the anchor member (e.g., screw or hook). One example of such a screw assembly is disclosed in U.S. Pat. No. 5,586,984 to Errico et al., which is incorporated herein by reference.

The process of positioning and setting known bone anchors may be tedious and relatively time-consuming, typically requiring more than one surgical tool to clamp the spinal rod and anchor member in desired positions. Even with a high degree of skill and care, the process of positioning a known bone anchor assembly and then manipulating the connector to clamp or re-clamp the spinal rod and bone anchor in place can tale more time than desired during a surgical procedure or even resulting in the rod, anchor member, or both moving out of position before clamping is completed. Furthermore, the preassembled connectors and bone anchors require a large inventory of assemblies to accommodate the various size rods and bone anchors necessary to fit the variety of patient sizes.

Therefore, a need still exists for bone anchors including polyaxial bone anchors that provide an improved mechanism for clamping the spinal rod and anchor member in their desired positions, and can reduce the inventory requirements at the medical facility.

SUMMARY

An apparatus for connecting a bone anchor to a support rod comprises a connector body and a cap. The connector body has a channel, preferably a U-shaped channel, that receives and locates the support rod relative to the bone anchor. The cap secures the support rod in the channel. The cap is movable into a partially installed position in the channel, preferably by moving the cap axially down along the longitudinal axis, and then into attachment with the connector body by rotating from the partially installed position to an installed position without moving axially along the longitudinal axis relative to the connector body. The cap preferably comprises a ring and a set screw. The ring preferably attaches to the connector body but preferably does not lock or clamp the support rod or the bone anchor. More specifically, the ring and set screw assembly moves axially down the longitudinal axis into a partially installed position and the ring alone, or ring and set screw assembly, are preferably rotated about 90° to an installed position where the ring and set screw are attached to the connector body. Preferably at this point, the support rod is retained within the connector body but movable with respect to the connector body. Also, preferably at this point, the bone anchor, if a polyaxial bone anchor assembly, can rotate and angulate within the connector body. Preferably the bone anchor can angulate through a range of angles from about −25° to about +25° relative to the longitudinal axis of the connector body.

In one embodiment, the connector body has a pair of arms preferably shaped as cylindrical segments facing one another across the channel. Each arm preferably has curved opposite edge surfaces, a rim projecting radially inward, and a recess or notch in the rim. The cap is generally circular or disk-like, and preferably has a pair of bosses projecting radially outward. The cap optionally further has a pair of stoppers projecting radially outward and optionally a set of flanges projecting radially outward. In this example, the cap is receivable in the channel in a partially installed position in which the bosses, stoppers, and flanges are located in the space between the arms on the connector body. The cap is rotatable from the partially installed position to an installed position in which the bosses are received in the recesses, each stopper abuts or is in close proximity to a side edge of an arm, and the flanges are located beneath the rim. Preferably, the cap moves from the partially installed position to the installed position by rotating the cap, preferably without further axial movement as it is rotated.

In the case of a polyaxial connector body, which has a socket for insertion, angulation, and removal of the bone anchor, a sleeve may fit over the connector body in a temporary position in which it permits insertion of the bone anchor into the socket. The sleeve can advance from the temporary position to a locking position in which it blocks both angulation and removal of the bone anchor. The sleeve may be restrained from axial and rotational movement relative to the connector body when in the temporary position. The sleeve is preferably placed in the temporary position before the connector device is shipped to and/or handled by a surgeon. A surgeon may place the bone anchor into position on the spine, for example, a bone screw may be inserted into a vertebra, and thereafter the connector body may be snapped onto the bone anchor. The ability to place the bone anchor without the connector body attached may provide better visualization while inserting the bone anchor and it may be easier to insert the bone anchor into the vertebrae.

In one embodiment, the apparatus for connecting a bone anchor to a support rod comprises a connector body having a top opening, two opposed arms and a channel to receive and locate the support rod relative to the bone anchor, the channel communicating with the top opening, and a cap to secure the support rod in the channel. The cap preferably has one or more radial projections and the cap is configured to move axially into the top opening of the connector body into a partially installed position covering the top opening, and configured to thereafter rotate to an installed position without moving axially relative the connector body, whereby the one or more projections contact and deflect one or more of the arms outward to enlarge the top opening as the cap rotates toward the installed position. Preferably, the cap is movable axially into the partially installed position without rotating relative to the connector body. Each connector body arm preferably has at least one recess, and the cap's one or more radial projections are configured to fit or snap into at least one of the recesses when the cap is rotated into the installed position. More preferably the cap has at least two radial projections spaced approximately 180° from each other and the arms preferably are configured to deflect radially outward under the influence of the projections when the cap is rotated toward the installed position, and to snap back inward to capture the projections in the recesses when the cap reaches the installed position.

The cap preferably non-threadingly attaches to the connector body. The connector body preferably has arms shaped as cylindrical segments with radially extending rims, the cap has radially projecting flanges that are located circumferentially between the arms when the cap is in the partially installed position, and the flanges are configured to move circumferentially beneath the rims preferably without camming action when the cap is rotated toward and into the installed position. The cap preferably is rotated about 90° from the partially installed position to the installed position. The radially extending rims preferably contain recesses and the cap has radial projections configured to snap into the recesses when the cap is rotated into the installed position, and the cap preferably further has the radially projecting flanges configured to move circumferentially beneath the rims when the cap is rotated toward and into the installed position.

The cap optionally may include one or more radially projecting stoppers configured to move into abutment with or proximity to the connector body to block continued rotation of the cap beyond the installed position. The cap may comprises a ring and a set screw threadably mounted in the ring. In one embodiment, the connector body may have a bottom opening and is configured to receive at least a portion of the bone anchor through the bottom opening. In other embodiments, the connector body may be integral with the bone anchor. In use, the connector body and cap are interconnected as an assembly with a support rod in the channel, and further includes a plurality of such assemblies that are spaced apart from each other along the length of the support rod.

In yet another embodiment, an apparatus for connecting a bone anchor to a support rod, comprises (i) a connector body having a channel to receive and locate the support rod relative to the bone anchor, the connector body having two arms shaped as cylindrical segments facing across the channel, with each arm having a radially extending rim containing a recess, and (ii) a cap to secure the support rod in the channel, the cap having projections and flanges projecting radially outward from its periphery, the cap being configured to be freely movable axially into the channel to a partially installed position in which the projections and the flanges are located circumferentially between the arms, and the cap being further configured to attach to the arms by rotating from the partially installed position to an installed position in which the projections are located in the recesses and the flanges located beneath the rims. Preferably, each flange comprises a length extending about 90° of the cap. The cap projections preferably are located above a middle portion of the flange.

The connector body preferably is configured for the arms to deflect radially outward under the influence of the projections when the cap is rotated toward the installed position, and to snap back inward to capture the projections in the recesses when the cap reaches the installed position. The arms are located in the rotational path of movement of the flanges when the cap is in the partially installed position, and the projections are configured to deflect the arms radially outward to provide clearance for the flanges to move beneath the rims without interference when the cap is rotated toward and into the installed position. The recesses are optionally located in central portions of the rims.

Optionally, the connector body may include a sleeve surrounding at least a portion of the connector body. The sleeve preferably is configured to fit over the connector body in a temporary position in which the sleeve permits insertion of the bone anchor, preferably the sleeve is movable to a provisional locking position in which the sleeve permits angulation but prevents removal of the bone anchor, and preferably the sleeve is moveable to a locking position in which the sleeve prevents both angulation and removal of the bone anchor.

In yet another embodiment, the device for connecting a bone anchor to a support rod includes a connector body having a channel for receiving and locating the support rod relative to the bone anchor, the connector body having a pair of arms shaped as curved segments facing across the channel, with each arm having opposite side edge surfaces, a rim projecting radially inward, and a recess in the rim, and a generally circular cap to secure the support rod in the channel, the cap having a pair of bosses projecting radially outward, a pair of stoppers projecting radially outward, and a pair of flanges projecting radially outward, the cap being receivable in the channel in a partially installed position in which the bosses, stoppers and flanges are located circumferentially between the arms on the connector body, and being rotatable from the partially installed position to an installed position in which the bosses are received in the recesses, each stopper abuts or is in proximity to the side edge of an arm, and the flanges are located beneath the rims. The bosses preferably project radially outward sufficiently to move against side edges of the arms to deflect the arms radially outward upon rotation of the cap from the partially installed position toward the installed position, and are sized to fit, preferably completely, within the recesses so that the arms will return to their original undeflected conditions when the cap reaches the installed position. The bosses also preferably project radially outward in diametrically opposed positions on the cap, the stoppers project radially outward in diametrically opposed positions on the cap that are circumferentially offset about 45 degrees from the bosses, and the flanges extend about 90 degrees about the periphery of the cap.

The bone connecting device in a further embodiment includes (i) a connector body having a bottom opening, a channel to receive the support rod and a socket for insertion, angulation, and removal of the bone anchor, the socket in communication with the bottom opening, and (ii) a sleeve configured to fit over the connector body in a temporary position in which the sleeve permits insertion of the bone anchor, the sleeve configured to move to a provisional locking position in which the sleeve permits angulation but prevents removal of the bone anchor, and the sleeve configured to move to a locking position in which the sleeve prevents both angulation and removal of the bone anchor. The sleeve is optionally configured to engage the connector body so as to be restrained from axial and rotational movement relative to the connector body when in the temporary position. The sleeve may be configured to engage the connector body in an interference fit in the temporary position. The sleeve may have inner flanges configured to establish the interference fit with the connector body.

The sleeve may be further configured to fit over the connector body in a preliminary position in which the sleeve is freely movable axially and rotationally relative to the connector body, and the sleeve may be configured to be axially moveable to the temporary position. The connector body preferably has a substantially cylindrical outer surface with radially raised step portions, and the sleeve preferably has inner retainer portions that are moveable axially against the step portions of the cylindrical outer surface to establish an interference fit with the connector body upon movement of the sleeve axially from the preliminary position to the temporary position.

The sleeve may be configured (i) to be receivable over the connector body in a first preliminary position upon movement of the sleeve axially over the connector body in a first direction, (ii) to be rotated from the first preliminary position to a second preliminary position, and (iii) to move from the second preliminary position to the temporary position, onward to the provisional locking position, and further to the locking position upon movement of the sleeve axially over the connector body in a second direction opposite the first direction. In use, the connector body and sleeve are interconnected in an assembly mounted on the bone anchor with a support rod in the channel, and further may comprise a plurality of such assemblies that are spaced apart from each other along the length of the support rod.

The sleeve may be receivable over the connector body in a locking position in which the sleeve prevents angulation and removal of the bone anchor from the socket, the sleeve preferably having inwardly projecting retainer flanges receivable against the connector body in an interference fit from which the sleeve is releasable for movement toward the locking position. The connector body may have a substantially cylindrical outer surface with radially raised step portions, and the retainer flanges may be deflectable to enlarged inner diameters to establish the interference fit upon moving axially onto the step portions of the cylindrical outer surface. The step portions of the cylindrical outer surface may be upper step portions and the substantially cylindrical outer surface further may have lower step portions that are raised radially outward from the upper step portions, and the retainer flanges are deflectable to further enlarged inner diameters upon moving axially onto the lower step portions. The substantially cylindrical outer surface may have axially extending grooves located circumferentially between the step portions. The flanges may be configured and arranged so that the flanges may move axially in the grooves without interference with the connector body. The connector body may have a lower section and a middle section, the lower section preferably contains the socket and the middle section preferably contains the substantially cylindrical outer surface, the connector body further may have a concave transition portion between the lower and middle sections, and the projecting retainer flanges may be receivable in the concave transition portion to prevent the sleeve from moving axially and contacting the substantially cylindrical outer surface.

The invention further provides tools for installing the connector body, cap, and support rod. The tools may include a tube that provides a passageway that may guide the cap toward and into engagement with the connector body.

Once the connector body has been clicked onto the bone anchor, there are two techniques to install the support rod.

1. Insertion of the support rod into the U-shaped channel of the connector body prior to the installation of the tools used to guide the cap toward and into engagement with the connector body. The tools used to insert the support rod may have means to push the rod into position and restrain movement of the rod relative to the connector prior to the installation of the cap to enhance the insertion of the cap.

2. Insertion of the support rod after installation of the tools used to guide the cap toward and into engagement with the connector body. The tube providing a passageway for the cap may have a slot to receive the support rod transversely through the tube and may have means to restrain movement of the rod relative to the connector body prior to the installation of the cap.

One such tool for connecting a bone anchor assembly to a support rod, wherein the bone anchor assembly has a connector body with a channel to receive the support rod, and has a cap receivable on the connector body in an installed position to secure the support rod in the channel, comprises a tube having a distal end, a proximal end, an opening at each end, and an axial passageway in communication with the openings, the tube configured to guide the cap toward and into engagement with the connector body upon movement of the cap longitudinally through the axial passageway of the tube; the tube further having two collateral recesses at the proximal end to receive the support rod already loosely placed in the channel of the connector body and two collateral projections lateral to the recesses fitting in-between the support rod and the connector body. Rotating the tube, the projections may get engaged with the connector body, thus, a force may be exerted on the rod by the tube pushing the rod into place and restraining movement of the rod relative to the connector body. Depending on the geometry of the collateral recesses, the connector body may actively be pulled up to the support rod allowing corrections of the spine.

Another tool for connecting a bone anchor assembly to a support rod, wherein the bone anchor assembly has a connector body with a channel to receive the support rod, and has a cap receivable on the connector body in an installed position to secure the support rod in the channel, comprises a tube having a distal end, a proximal end, an opening at each end, and an axial passageway in communication with the openings, the tube configured to guide the cap toward and into engagement with the connector body upon movement of the cap longitudinally through the axial passageway of the tube, the tube further having a slot at and transverse to the distal end to receive the support rod, and being further configured to interconnect the support rod with the tube and the connector body prior to installation of the cap. The tube may be receivable over the connector body in a first orientation in which the support rod is movable downward through the slot toward and into the channel, and the tube may be movable relative to the connector body to a second orientation in which the tube blocks movement of the support rod upward within the channel. The tube may be rotatable from the first orientation to the second orientation. The tube may have surfaces that extend transversely from the slot in opposite directions so as to move circumferentially over the support rod upon rotation of the tube from the first orientation to the second orientation. The tube and the connector body together may be configured to block movement of the tube upward relative to the connector body when the tube is in the second orientation. The connector body may have cylindrical segments with downwardly facing blocking portions, and the tube may have cylindrical segments with upwardly facing blocking portions configured to move under the downwardly facing blocking portions upon rotation of the tube from the first orientation to the second orientation.

A system of tools for connecting a bone anchor assembly to a bone support rod wherein the bone anchor assembly has a bone anchor, a connector body and a sleeve, the connector body has a channel to receive the bone support rod and a socket to receive the bone anchor, and the sleeve is movable axially over the connector body into a locking position to secure the bone anchor in the socket is also disclosed, the system may comprise: (i) a tube having a distal end, a proximal end, an opening at each end, and an axial passageway in communication with the openings, the tube receivable over the connector body and having a slot to receive the bone support rod; and (ii) an elongated tool receivable within the axial passageway of the tube and configured to interlock axially with the connector body inside the tube, whereby the elongated tool can apply a force axially against the connector body in reaction to a force urging the sleeve axially toward the locking position. The elongated tool may be configured to interlock axially with the connector body upon rotating relative to the connector body and the tube. The elongated tool may have cylindrical segments that are rotatable into axially interlocked engagement with the connector body. The connector body may have cylindrically contoured arms at which the segments of the elongated tool interlock with the connector body. The system may further comprise a pusher tool movable telescopically within the tube toward and into engagement with the sleeve to apply a force axially downward against the sleeve when the elongated tool is interlocked with the connector body within the tube. The system may further comprise a hand-held actuator operative to apply a force axially upward against the elongated tool and simultaneously to apply a force axially downward against the pusher tool.

A system for connecting a bone anchor assembly to a support rod wherein the bone anchor assembly has a connector body with a channel to receive the support rod, and has a cap configured to fit on the connector body in an installed position to secure the support rod in the channel is also disclosed, the system comprising: (i) a tube having a distal end, a proximal end, an opening at each end, and an axial passageway in communication with the openings, the tube configured to guide the cap toward and into engagement with the connector body upon movement of the cap through the tube; and (ii) a cap holder configured to carry the cap through the axial passageway of the tube and to place the cap in the installed position on the connector body, wherein the cap and the cap holder have screw threads for screwing the cap holder into attachment with the cap outside of the tube and for unscrewing the cap holder from the cap inside the tube. The cap may include a set screw with an external screw thread, and the cap holder may have an internal screw thread for mating with the external screw thread.

An apparatus or system for connecting a bone anchor assembly to a support rod, wherein the bone anchor assembly has a connector body with arms and a channel to receive the support rod between the arms, and further has a cap configured to fit on the connector body in an installed position in which a screw on the cap can be tightened against the support rod in the channel is also disclosed, the apparatus or system may comprise: a counter-torque instrument configured to restrain the cap from moving under the influence of torque transmitted from the set screw to the cap, the counter-torque instrument having segments configured to fit between the flanges of the cap to restrain the cap from rotating. The system may further comprise a guide tube configured to guide the cap toward and into engagement with the connector body upon movement of the cap through the guide tube, and a cap holder configured to carry the cap through the guide tube and to place the cap in the installed position on the connector body, wherein the counter-torque instrument includes an insertion tube receivable within the guide tube and through which the cap is movable by the cap holder. The counter-torque instrument may have a handle projecting laterally from the insertion tube.

A system for connecting a bone anchor assembly to a support rod wherein the bone anchor assembly has a bone anchor, a connector body, a sleeve and a cap, the connector body has a channel to receive the support rod and a socket for angulation of the bone anchor, the sleeve is configured to fit over the connector body in a locking position in which the sleeve blocks angulation of the bone anchor, and the cap is receivable on the connector body in an installed position securing the bone support rod in the channel is also disclosed, the system may comprise: (i) a tube configured to guide the cap toward and into engagement with the connector body upon movement of the cap longitudinally through the tube, the tube having a slot to receive the bone support rod through the tube, and being further configured to interlock the bone support rod with the connector body prior to installation of the cap; and (ii) an elongated tool receivable within the tube and configured to interlock axially with the connector body inside the tube, whereby the elongated tool can apply a force axially against the connector body in reaction to a force urging the sleeve axially toward the locking position. The system may further comprise a cap holder configured to carry the cap through the tube and to place the cap in the installed position on the connector body, wherein the cap and the cap holder have screw threads for screwing the cap holder into attachment with the cap outside of the tube and for unscrewing the cap holder from the cap inside the tube. The system may further comprise a counter-torque instrument configured to restrain the cap from moving under the influence of torque transmitted from the set screw to the cap, the counter-torque instrument having cylindrically contoured segments configured to fit between the flanges of the cap to restrain the cap from rotating.

Another tool may actuate the sleeve on the connector body. This other tool may fit within the tube to interlock axially with the connector body inside the tube. When interlocked with the connector body, the elongated tool can apply a force upward against the connector body in reaction to a force urging the sleeve downward toward the locking position.

Additional installation tools may include a holder that carries the cap through the tube to place the cap in the installed position on the connector body, and a counter-torque instrument that restrains the connector body from rotating under the influence of torque transmitted from the cap. It should be recognized that one or more of the tools may be included in a kit.

DETAILED DESCRIPTION

The drawings include examples of a bone fixation system and tools and instruments to assist in the implantation of the system. The drawings and description are merely exemplary to illustrate features, parts and tools that may be used singularly or in combination with other features, and the present invention should not be limited to the embodiments shown. The parts shown in the drawings include examples of how a person of ordinary skill in the art can make and use the claimed invention and are provided and described herein for enablement and best mode purposes and should not be used to impose limitations that are not recited in the claims.

A connector device10is shown inFIGS. 1 and 2. The connector device10is an assembly of parts for interconnecting a bone anchor12with a bone support device14. In this particular example, the support device14is a spinal rod, and the anchor12may be one of several pedicle screws implanted in vertebrae preferably in a row extending along the length of the spine. The connector device10may thus be one in a corresponding row of connector devices that rigidly interconnect the pedicle screws12with the rod14.

The device10shown inFIGS. 1 and 2includes a connector body20that is mounted on the head22of the bone anchor12. While the bone anchor12is illustrated as a bone screw, it may also be a hook, pin, or other fastener. When the body20is first mounted on the head22it may rotate or pivot polyaxially relative to the screw12. This type of movement, which is known as angulation, enables the body20to be adjusted into alignment with the other bodies20in the other devices10that are spaced apart along the length of the spine.FIGS. 1 and 2illustrate a top loading connector body20but other connector bodies such as side loading or closed connector bodies also may be used. The rod14may be restrained by or attached to the row of aligned bodies20. Although the illustrated bone anchor12is a separate part upon which the connector body20is mounted for polyaxial movement, alternative embodiments may include a monoaxial bone anchor which, as known in the art, is a bone anchor that has a connector body integral with and monolithic with the bone anchor.

Other parts of the device10may include a cap30and a sleeve32. The cap30retains the rod14within the body20. Specifically, the cap30is installed in the body20over the rod14, and preferably includes a locking ring that attaches to the connector body and a set screw34that is tightened downward against the rod14. The locking ring preferably attaches to the connector body but preferably does not lock the rod or bone anchor relative to the connector body. Preferably, when the set screw34is tightened against the rod14, it clamps the rod14firmly between the locking cap30and the sleeve32. This restrains the rod14from moving relative to the body20. Tightening the set screw also pushes the sleeve32downward to a locking position which prevents further angulation of the body20on the pedicle screw12.

As shown separately inFIGS. 3-5, the connector body20is a vertically elongated part with upper, middle, and lower sections36,38and40centered on a longitudinal axis41. The lower section40of the body20preferably has inner and outer surfaces42and44preferably with spherical contours. Preferably, the exterior surface44of the lower section40is at least part spherical. The inner surface42has a chamfered edge46, and defines a socket or chamber47for receiving the head22of the pedicle screw12(FIG. 2). A bottom opening48communicates with the socket47.

While the inner surface42of the socket47preferably has spherical contours to mate with the partially spherical contour of the illustrated pedicle screw12, the inner surface42may have conical contours or other shapes, and the head of the bone anchor12may also have a conical contour or other shape. Slots49extend axially upward to separate the lower section40into segments50. In the illustrated example the slots49are spaced apart at 60° intervals about the axis41, as are the corresponding segments50. Preferably, six slots are equidistantly spaced around the circumference of the loser section40. The slots49may be evenly or unevenly spaced, and may be spaced at different angular intervals. The slots49enable the segments50to deflect radially outward when the chamfered edge46is pressed forcefully downward over the bone anchor head22, and to shift radially back inward to capture the screw head22in the socket47. The lower section40preferably forms an open ended chamber that is part spherical in shape and which is expandable and compressible to receive the preferably geometrically complementary head of a bone anchor. When the segments are in their unbiased natural state, the bottom opening48at the edges46is smaller than the largest diameter of the head of the bone anchor.

As best shown inFIG. 3, the outer surface44is interrupted by recessed flats54that preferably traverse the slots49. As best shown inFIG. 5, the outer surface44has a concave portion56defining a transition between the lower and middle sections40and38of the body20. The middle section38has a cylindrical outer surface60that is similarly interrupted by recessed flats62in alignment with the flats54in the lower section40. Upper and lower step portions64and66of the cylindrical outer surface60are raised radially and extend circumferentially between the flats62.

The middle and upper sections38and36of the body20together define a generally U-shaped channel71for receiving the spinal fixation device14and the cap30. The axis of the channel71is generally perpendicular to the longitudinal axis41of the connector body20. The axis of the channel71preferably intersects the axis41of the connector body, but may be offset or eccentric thereto. A trough-shaped inner surface72extends across the bottom of the channel71. A pair of arms74at the upper section36define a top opening75communicating with the channel71. The arms74preferably are configured as diametrically opposed curved or cylindrical segments facing each other across the channel71.

The arms74are alike, and each has a length extending approximately 90° about the axis41between a pair of circumferentially opposite edge surfaces76. Each arm74further has a planar shoulder surface78facing axially upward within the channel71, and has a rim80projecting inward at its upper end. Each rim80preferably has a rounded inside corner defining a groove81that extends across the arm74between the opposite edge surfaces76. Each rim80also has a notch or recess83preferably mid-way between the opposite edge surfaces76.

The connector device preferably has a locking means for clamping the bone anchor relative to the connector body. The locking means preferably is axially moveable relative to the lower section of the connector such that in a temporary position the socket or chamber can expand resiliently to receive the head of the bone anchor preferably in a click-on or snap-on action, but in a provisional locking position, the chamber can no longer expand. The locking means preferably is moveable into a further position where it bears against the outside surface of the lower section defining the socket to compress segments50around the head of the bone anchor to prevent movement between the bone anchor and the connector.

The locking means preferably comprises a sleeve at least partially located around and moveable over the lower section40of the connector. As shown separately inFIGS. 6-8, the sleeve32may be a short cylindrical part with a longitudinal central axis89and is preferably configured to operate in a two-stage locking operation. The sleeve32assists with locking the position of the bone anchor12relative to the connector body20. Preferably, a pair of recessed surfaces90at the open upper end91of the sleeve32are aligned as seats for the rod14(FIGS. 1 and 2). Guide flanges92and retainer flanges94at the interior of the sleeve32are configured for the manner in which the sleeve32fits over the connector body20. The guide flanges92project radially inward at the upper end91of the sleeve32, and are arranged in diametrically opposed pairs. As with the slots49in the body20(FIG. 3), there are preferably six guide flanges92preferably spaced apart at 60° intervals.

The guide flanges92have a common inner diameter that preferably is slightly greater than the outer diameter of the body20at the cylindrical surface66. The retainer flanges94project radially inward at locations directly beneath the guide flanges92, and also have a common inner diameter. The inner diameter of the retainer flanges94preferably is slightly greater than outer diameter at the flats62in the cylindrical surface60slightly less than the inner diameter of the guide flanges92, and slightly less than the outer diameter of the cylindrical surface64. To provide enough space for the retainer flanges94during the installation of sleeve32, the distance between two collateral flats54is slightly less than the inner diameter of the retainer flanges94.

In addition to the flanges92and94for engaging the middle section38of the body20, the sleeve32has inner surfaces100and102for engaging the lower section40of the body20. The first inner surface100has a cylindrical contour centered on the axis89. The second inner surface102extends axially upward from the first inner surface100with a conical contour that tapers radially inward. The conical inner surface102is slidable over the outer surface of the lower section40to compress the chamber47to lock the bone anchor relative to the connector body20. Preferably, contact between the spherical outer surface of the lower section of the connector body and the conical inner wall of the sleeve is tangential to the spherical outer surface of the lower section40.

To attach the sleeve to the body connector, the sleeve32is placed over the body20by aligning the flanges92and94of the sleeve32with the flats54and62and moving the upper end91of the sleeve upward over the lower section40of the body20from beneath into the first preliminary position (FIG. 9a), thereby temporarily compressing the segments50. The flats54and62on the body20guide the sleeve32by providing grooves, pathways or space along which the flanges92and94are axially movable over the body20. When the sleeve32reaches a first preliminary position, as shown inFIG. 9a, the flanges92and94are located at the flats62on the cylindrical surface60. The sleeve32is next rotated, preferably 30°, from the first preliminary position until the collateral recesses90on top of the sleeve32are aligned with the U-shaped channel71of the body20(FIG. 9b), and then pushing the sleeve32down into the second preliminary position. This moves the flanges92and94to a position in which they are located between the flats62and above the step portions64and66, as shown inFIG. 10(oblique view). The flanges92and94preferably do not yet engage the cylindrical surface60tightly enough to restrain axial or rotational movement of the sleeve32relative to the body20.

The sleeve32is next moved downward from the second preliminary position until the retainer flanges94move axially onto the upper step portions64of the cylindrical surface60. This causes the retainer flanges94to bear against upper step portions64and deflect to enlarged inner diameters at which they establish an interference fit with the upper step portions64, as shown inFIGS. 10 and 11. The interference fit restrains the sleeve32from moving axially or rotationally relative to the body20. In this manner the sleeve32is conveniently retained on the body20in a temporary position for later advancement to the locking position in which it prevents angulation of the body20relative to the bone anchor. The lower step portion66of the cylindrical surface60, which is raised radially from the upper step portion64, blocks the sleeve from being inadvertently moved further downward. Preferably, the sleeve32is placed in the temporary position before the connector device10is shipped to and/or handled by a surgeon. While the sleeve32is retained in the temporary position ofFIG. 11, the inner surfaces100and102are spaced from the outer surface44of the body20and the segments50of the body20are free to deflect radially outward for insertion of the pedicle screw head22into the socket47. With the sleeve in the temporary position, the bone anchor can also be dislodged from the socket47.

When the sleeve32is moved further downward, the retainer flanges94on the sleeve32are deflected to further enlarged inner diameters as they move onto the lower step portions66of the cylindrical surface, and then snap back toward their original inner diameters as they move axially over and downward past the lower step portions66. In this position, the retainer flanges no longer bear against the step portions64or66but occupy the gap created by the transition56. The transition56captures the retainer flanges94to block the sleeve32from moving back upward. When the sleeve32is in the position shown inFIG. 12, with the bottom inner surface100of the sleeve32closely surrounding the outer surface44of the body20, it is in a provisional locking position. In the provisional locking position, the upper annular surface95of the sleeve preferably is adjacent the step portions64,66and in loose contact with the cylindrical surface60. In the provisional locking position, the sleeve32prevents removal of the screw head22from the socket47by blocking the segments50from deflecting radially outward. However, the sleeve32does not yet engage or bear against the segments50tightly enough to prevent continued angulation of the body20on the screw head22. Angulation is not prevented until the sleeve32is later pushed downward from the provisional locking position to the locking position, at which time the tapered contour of the second inner surface102causes the sleeve32to press radially inward against the segments50tightly enough to clamp the screw head22firmly within the socket47.

The cap30preferably includes set screw34and a locking ring120(shown separately inFIGS. 13-15). The inner periphery of the ring120defines a bore121with a central axis123and an internal screw thread124for receiving the set screw34. The outer periphery131of the ring120is configured to mate with the arms74of the connector body20. The outer periphery131preferably includes a pair of projections (also referred to as bosses)126projecting radially outward in diametrically opposed positions to fit into the notches or recesses83in the arms74. The projections or bosses126preferably have a curved surface129. A pair of stoppers128project radially outward in positions that are circumferentially offset from the bosses126approximately 45° about the axis123. The stoppers preferably have curved leading edges129.

Located below the bosses126and stoppers128are two flanges130that are sized and shaped to fit beneath the rims80on the arms74. Each flange130on the ring120has a length extending approximately 90° about the axis123from a leading end132to a trailing end134. An upper edge136of each flange130has a rounded contour preferably substantially matching the rounded contours of the grooves, pathways or space81in the arms74. A lower portion138of each flange130projects downward next to the leading end132. The lower portions138of the flanges130preferably have planar bottom surfaces140to sit on the planar shoulder surfaces78of the arms74. The lower portions138form a part cylindrical profile on the underside of the ring120preferably to match the profile of the support rod to be retained by the connector. The lower portions are intended to reinforce the cap.

The cap30is installed on the connector body20by first placing it in the partially installed position shown inFIG. 16. The cap is operatively associated with the upper section36of the connector body20. The projecting parts126,128and130of the ring120are received in channel71, and more specifically the spaces extending circumferentially between the arms74. The bottom surfaces140preferably land on the shoulder surfaces78. The ring120is freely movable coaxially downward between the arms74to take the partially installed position ofFIG. 16without rotating relative to the body20, and is unattached to the body20in that position.

As viewed inFIGS. 16-18, the cap30preferably snaps into attachment with the connector body20when rotated approximately 90° clockwise from the partially installed position without moving axially relative to the body20. Preferably, the arms74initially obstruct the rotational paths of movement of the bosses126, and preferably flanges130on the ring120. As the ring120rotates into and past the position ofFIG. 17, the bosses126, and more specifically, the preferred curved surface of the bosses126move against the adjacent edge surfaces76of the arms74to deflect the arms74radially outward, and, preferably, thereby provide clearance for the flanges130to move beneath the rims80as the bosses126slide along the rims80and the bottom surfaces140slide over the shoulder surfaces78. The bosses126are sized to fit within the notches83so that the arms74will snap back inward to their original undeflected conditions to capture the bosses126in the notches83when the ring120reaches the installed position ofFIG. 18. Further clockwise rotation of the ring120is blocked by the stoppers128in abutment with the side edge surfaces76. The contours of the edges136(FIGS. 13-14) preferably are complementary to the contours in the grooves81(FIG. 5) to ensure a firm fit of the cap30in the body20. At this point, the rod can be retained in the connector body but can still be moveable relative to the connector body, and the connector body can still be moved relative to the bone anchor. In this manner, a physician can still manipulate the bone fixation system since the bone anchor can move relative to the connector and the support rod has not been clamped in position.

Final locking of the connector and bone fixation system can be accomplished by using set screw34. The support rod is moveable within the channel71by the set screw and is clamped therein by the set screw. The set screw34can be tightened downward against the spinal rod14to interlock the connector device10with the pedicle screw12and the rod14. More specifically, the set screw urges the spinal rod against the sleeve to cause the sleeve to move down the connector body. As the sleeve moves down the body, the sleeve inner surface causes the sleeve to press radially inward against the segments50tightly enough to clamp the bone anchor in position. The set screw also clamps the rod tightly enough against the sleeve to hold the support rod in position.

The bone anchor also may be locked in the body22without or before insertion of the spinal rod in the body. For example, the sleeve may be pushed downward to the position shown inFIG. 12without the spinal rod placed in the connector body. Before, or after insertion of the spinal rod, the sleeve may be moved down to press radially against segments50tightly enough to lock the position of the bone anchor. The support rod may also be used to move the sleeve down the connector body into the locked position without the cap being positioned on the connector body.

FIGS. 19-23illustrate a side loading connector device1000. Connector device1000comprises a body1002defining a first section1003for connection to the head1004of a bone anchor1005. The first section1003is substantially similar to lower section40in connector body20. The connector body1002also includes a second section1006adapted for connection to the support rod1007(show in cross-section inFIGS. 21-23). The second section1006is similar to upper and middle sections36,38of the connector body20except as described herein. The connector1000in addition comprises sleeve1008(which is substantially similar to or the same as sleeve32), a cap1009and a retaining member1010.

The second section1006of the body1002defines a laterally open channel1019for receiving the support rod1007. It should be appreciated that in other embodiments of the connector, the longitudinal axes of the first and second sections of the connector may not be coincident. However, in this embodiment, the channel1019is oriented transversely and eccentrically with respect to the longitudinal axis1012of the body1002and the longitudinal axis of the second section1006is coincident with the longitudinal axis of the first section1003. An outer thread1020is formed on an upper portion1021of the body1002which has a reduced diameter. The retaining member1010is adapted to be concentrically mounted around second section1006of the body1002between the sleeve1008and the cap1009. The cap1009in this case is a tightening nut which is threaded on the screw thread1020and comprises a head1022that bears on the end of the retaining member and a depending retaining member portion1023that screws down the thread1020between the retaining member1010and the body1002owing to the reduced diameter of the body1002in this region.

Support rod1007becomes retained in place by the retainer member1010which closes off the channel1019. When the locking cap1009is tightened to lock the connector into its final position, the head1022of the cap1009bears down on the retainer member1010. The retainer member1010again is pressing down on the sleeve1008through the support rod1007. The length of the depending portion1023is short enough that it will not interfere with the support rod1007.

Being forced down by the retainer member1010and the support rod1007, the sleeve1008moves down along the section1003of the body1002simultaneously compressing the chamber1011over the head1004of the bone anchor1005, locking it in position, and clamping the support rod1007. Preferably, the sleeve1008moves down until the support rod1007is stopped by the bottom of the channel1019.

It can be seen inFIGS. 21-23that the sides of the retaining member1010on either side of the channel1019are of different heights such that when the connector1000has been locked using the locking cap1009, a small gap1024of around 0.3 nm is left between the face of the first annular portion of the sleeve1008and the lower edge of one side of the retaining member1010. The different heights on the two side of the retaining member1010are dimensioned such that when cap1009is tightened, only the support rod1007and the longer side of the retaining member1010press against sleeve1008. Hence, the clamping force exerted by cap1009is distributed to three contact zones on the sleeve1008, which are arranged such that they apply uniform pressure to the sleeve1008in a plane substantially perpendicular to the axis1012. As a result, the sleeve1008is maintained coaxially aligned over the spherical outer surface of the section1003of the body1000and therefore uniformly compresses the chamber1011. Also, the contact between the spherical outer surface of the section1003and the conical inside wall1016ais tangential to the spherical outer surface of the section1003. Hence, contact between the section1003and the wall1016aoccurs around an annulus defining a circular contact zone. This circular contact zone provides uniform compression of the chamber1011by the sleeve1008to ensure that the head1004of bone anchor1005is firmly clamped with the chamber1011. The clamping power of the chamber can be increased by roughening or structuring the contact surface of the chamber1011and or the contact surface of the head1004of the bone anchor1005.

In addition to the provision of top loading, in situ click-on, click off connectors10as shown inFIGS. 1 to 2or side loading, in situ click-on, click-off connectors1000shown inFIGS. 19-23, the set may also comprise a variety of closed, in-situ click-on, click-off connectors1026, an example of which is shown inFIG. 24. The structure of these connectors1026will now be described but it should be appreciated that it includes a first section1003for connection to a head1004of a bone anchor1005as described above. This section1003is identical to those of the connector1000, in both construction and size and will not be described again.

With reference toFIG. 24, the embodiment of closed in situ click-on, click-off connector1026shown therein comprises the body portion1002with adjacent annular step portions1018, as described above. Adjacent the step portions1018, the connector1026comprises a substantially cylindrical body portion1028that is provided with a bore1029therethrough. The bore1029is provided to accommodate a support rod of circular cross-section but the bore1029preferably has a substantially oval profile to permit enough play for the support rod1007, that connector1026can be threaded onto the support rod1007prior to the click-on of the connector1026to the bone anchor1025. The feature of threading the connector1026on to the support rod1007prior to the click-on of the connector1026to a bone anchor, yields the benefit that support rod1007and connectors1026can be assembled into a construct outside of the patient. The construct can then be implanted and clicked onto the bone anchors and secured in a single step, thereby saving the practitioner valuable time during a surgical procedure. To prevent the support rod from slipping out of the connectors during the implantation, one or more stoppers can be installed on either side of the rod after the connectors1026have been threaded onto it.

The closed connector1026has no need for a member1010. However, a locking fastener (not shown) can be screwed down into the body1026in a threaded aperture1030provided at the opposite end of the connector1026to the section1003.

In some embodiments of the invention, locking the connector1026is a two-stage operation. Once the connector1026has been provisionally locked by movement of the sleeve1008partially over the section1003, the locking cap is screwed down into the aperture1030. In a similar fashion to the locking of the connector1001, the cap bears down on the support rod1007inserted through the bore1029so that it pushes down on the sleeve1008forcing it further over the section1003of the connector1026. As the cap is tightened, the support rod1007becomes clamped into the bore1029by the cap and the sleeve1008adopts a similar final position similar to that shown inFIGS. 21 to 23.

In a spinal fixation implant set, a plurality of connectors10,1000,1026and bone anchors12,1005are provided that can be used interchangeably with one another. To this end, a variety of top-loading, side-loading and closed, in situ click-on, click off connectors as described above may be supplied for use with a variety of differently sized support rods.FIGS. 21 to 23show three different embodiments of connector1000which are all constructionally similar to one another but adapted to accommodate support rods1007with diameters of 6 mm, 5 mm and 3.5 mm respectively. It can be seen that the height of the section1006of the connector1000and therefore the height of the retaining member1010vary dependent on the size of the support rod but in all three cases, the dimensions of the section1003of connector1000, the size of the chamber1011and the size of sleeve1008are all identical. It is contemplated that the rod sizes and types of connectors are not limited to those described herein.

Likewise, the bone anchor can take the form of a screw, such as a pedicle screw, or a hook and a range of different types of anchors of varying dimensions, materials and construction may be provided in the spinal fixation implant set in accordance with the invention. However, in all cases, the part spherical heads of the anchors may always be the same shape and size so that any of the connectors in the set can be clicked onto any anchor. If the anchor is a screw, then the head can be provided, in addition with a socket for engagement with a screwdriver to allow fixation of the screw into the patient's bone. Normally, the anchor will be secured to the patient before being clicked into the connector. However, the connector preferably is provided with an aperture such as the aperture1013to permit access to the head to allow adjustments to be made after the connector has been clicked onto the connector but before final locking has taken place.

Tools are provided for installing the connector devices10on the pedicle screws12. These include an implant holder160, as shown inFIG. 25. The implant holder160is a generally cylindrical two-piece device including a guide tube162and an implant extender164within the guide tube162. Although a single implant holder160is shown in the drawings preferably it is one of a number of identical implant holders that preferably correspond to the number of connector devices10on the pedicle screws12.

As shown in the side view ofFIG. 26, the guide tube162has a pair of diametrically opposed slots165extending axially upward from its lower end166nearly to its upper end168. The slots165divide the tube160into segments170. Lower end portions172of the segments170have configurations that are the same as each other, with one having an orientation rotated 180° from the other about the central axis173of the tube162.

As shown inFIGS. 27-30, each lower end portion170of the guide tube162has a notch177, a projection178, and a flange180. The length of the notch177extends upward from the lower end166of the tube162. The width of the notch177begins at one of the slots165and extends partly around the tube162. The notch177thus adjoins one of the slots165and is spaced laterally from the other slot165. A short horizontal edge surface182extends partly across the upper end of the notch177.

The projection178is located inside the tube160at a location spaced laterally from the notch178. More specifically, the projection178extends radially inward at a location adjacent to the slot165that is spaced laterally from the notch177. A surface184of the projection178faces axially upward within the tube160. The flange180also is located inside the tube160, and projects radially inward above the notch177.

The implant extender164(FIGS. 31-33) also is a vertically elongated tool with a pair of cylindrical segments190separated by diametrically opposed slots191. A short generally cylindrical cap192at the upper end of the extender164has a notch193extending downward from the top at one side. A slot195extends partially across the cap192at the other side. Like the lower end portions172of the tube162, the lower end portions196of the extender164are alike and are oriented opposite relative to each other. Each has a horizontally extending groove197preferably intersecting a vertically extending groove199.

FIG. 34shows a pusher200with an actuator202. The pusher200is an elongated member with a hand grip204at its upper end and a pusher bar206at its lower end. As shown inFIG. 35, the pusher bar206has a pair of parallel shoulder surfaces208. Upper and lower claws210and212on the actuator202move toward each other when the actuator handles214are squeezed together. The upper claw210is pivotally connected at pivot225to the pusher200so that the actuator202can swing into and out of the position ofFIG. 34, as indicated by the arrow shown in the drawing.

Several steps are taken in the process of installing a connector device10with the tools160,200and202to a bone anchor. The process begins with a connector body20that has a sleeve32in the temporary position (FIG. 11). In a preferred sequence of steps, implant holder160is first attached to the connector body20. To do this, implant holder160preferably is first arranged as shown inFIG. 25with the segments190of the extender164offset 90° from the segments170of the guide tube162. The implant holder160is moved downward over the connector body20until the flanges180inside the guide tube162(FIGS. 27 and 30) move downward into abutment with the arms74on the body20. The extender164is then rotated approximately 90° clockwise relative to the guide tube162and the body20. This moves the slots191in the extender164into alignment with the slots165in the guide tube162. This also moves the lower end portions196of the extender164across the arms74of the body20so that the rims80on the arms74are received in the horizontal grooves197(FIG. 33) on the extender164, as shown inFIG. 36. The vertical grooves199on the extender164(FIG. 33) move against the adjacent side edges76of the arms74to stop the extender164from rotating beyond the position shown inFIG. 37. When the rims80are located within the grooves197in this manner, the extender164is axially interlocked with the body20.

In the next step, the pusher200is inserted downward through the extender164and the surrounding guide tube162, as shown inFIG. 38. The actuator202is moved pivotally so that the lower claw212is moved into and through the notch193and slot195in the cap192at the top of the extender164. With the bone anchor preferably implanted in a vertebrae, the surgeon then presses the entire assembly of tools downward against the pedicle screw12to snap the bone anchor into the socket47of the connector body20. The connector body20at this point is now connected to the bone anchor, but removable from the bone anchor because the sleeve32has not moved into the provisional locking position to prevent outward flexing of the segments50.

The surgeon next squeezes the actuator handles214. As the claws210and212move toward each other, the upper claw210drives the pusher200downward through the extender164, as indicated by the arrow shown inFIG. 39. An axially upward reaction force is transmitted to the connector body20by the extender164because the extender164is axially interlocked with the body20. This enables the pusher bar206to move forcefully against the sleeve32to snap the sleeve32downward from the temporary position to the provisional locking position (FIG. 12). Downward movement of the sleeve32is stopped when the shoulder surfaces208of the pusher bar206land on the shoulder surfaces78of the body20.

Having placed the sleeve32in the provisional locking position in the foregoing manner, the surgeon withdraws the pusher200and the actuator202from the implant holder160. This is accomplished by pivoting the actuator202upward to move the lower claw212out of engagement with the extender164at the cap194, and by lifting the actuator202and pusher200upward together. The implant holder160is left in place on the connector body20. This portion of the process is repeated until connector bodies20with sleeves32and implant holders160are mounted on all of the pedicle screws12. Other ways of connecting the connector body onto the bone anchor and moving the sleeve32to the provisional locking position are contemplated.

The provisional locking positions of the sleeves32permit the connector bodies20to angulate into alignment on the row of pedicle screws12. Corresponding angulation of the implant holders160enables the spinal fixation rod14to be inserted longitudinally through the aligned slots165and191in the implant holders160. The rod14is next moved downward along the slots165/191and into the channels71in the connector bodies20.

An alternate pusher220with a wider pusher bar222(FIG. 40) may be used to press the rod14firmly downward to a location beside the notches177in each guide tube162. The surgeon then rotates each guide tube162approximately 45° to move the notches177over the rod14, as shown inFIG. 41. The edge surfaces182at the upper ends of the notches177block the rod14from moving back upward. The projections178inside the guide tube162simultaneously slide beneath the rim of the connector body20to block the guide tube162from moving upward. Rotating the guide tube162into the position ofFIG. 35in this manner temporarily interconnects the rod14with the guide tube162and the connector body20by clamping the rod14between the guide tube162and the connector body20. This restrains the rod14from moving relative to the connector body20prior to installation of the locking cap30. The surgeon then swings the actuator202sideways to rotate the extender164out of axially interlocked engagement with the arms74of the connector body20, and lifts the actuator202to withdraw both the extender164and the pusher220from the guide tube162. These steps are repeated at all of the implant holders160so that all of the guide tubes162(with the extender164removed) are temporarily interconnected with the rod14and the connector bodies20above the pedicle screws12in readiness to receive the locking caps30.

The tool240shown inFIGS. 42 and 43is a counter-torque instrument with an insertion tube242that fits inside the guide tube162. A pair of cylindrically contoured segments244are located at the bottom of the insertion tube242. A handle246projects laterally from the top of the insertion tube242. The tool250shown inFIG. 44is a cap holder with a shaft252for reaching downward through the insertion tube242. An internal screw thread254at the bottom of the shaft252matches the external screw thread on the set screw34at the top of the locking cap30(FIG. 1). The shaft252is placed downward through the insertion tube242before the shaft is screwed into attachment with the set screw34. As shown inFIG. 45, the segments244of the insertion tube242fit closely between the flanges130on the cap30to block the cap30from rotating while the shaft252is being screwed onto the set screw34. When the shaft252has been screwed onto the set screw34as shown inFIG. 45, the shaft252can be extended further downward through the insertion tube242to move the cap30out from between the segments244of the insertion tube242, as shown inFIG. 46.

The interconnected parts shown inFIG. 46are moved downward through the guide tube162to place the locking cap30on the connector body20in the partially installed position ofFIG. 16. A hand grip258at the top of the cap holder250enables the surgeon to rotate the shaft252, and thereby to rotate the attached cap30into the installed position ofFIG. 18. After rotation of the locking cap, the insertion tube242is pushed down fitting the segments244in-between the flanges130on the cap30to prevent the cap30from rotating while loosening the shaft252counter-clockwise.

The next step may be to tighten the set screw34downward against the rod14. A screwdriver (not shown) is inserted downward through the insertion tube242to tighten the set screw34. The segments244of the insertion tube242are still positioned in-between the flanges130on the cap30. The surgeon then holds the handle246firmly to transmit a counter-torque to the arms74while tightening the set screw34. The counter-torque restrains the cap30from rotating under the influence of torque transmitted to the cap30as the set screw34is being tightened.

When the set screw34is being tightened downward against the rod14, it presses the rod14downward against the upper end91(FIG. 2) of the sleeve32. The rod14presses the sleeve32downward from the provisional locking position to the locking position in which the sleeve32prevents further angulation of the connector body20on the bone anchor12. Tightening the set screw also clamps the spinal rod in the channel of the connector body to prevent movement of the spinal rod. As discussed earlier, the surgeon may lock angulation of the bone anchor relative to the connector body independently of locking the spinal rod relative to the connector body by moving the sleeve32down so that it compresses the lower section40of the connector body.

The counter-torque instrument240can also be used to prevent the cap30from being accidentally rotated backwards when loosening of the set screw34is required for parallel distraction or compression with locked screw head22, respectively.

This written description sets forth the best mode of carrying out the invention, and describes the invention in a manner to enable a person of ordinary skill in the art to make and use the invention, by presenting examples of the structural elements recited in the claims. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples, which may be available either before or after the application filing date, are intended to be within the scope of the claims.