Abstract: A fastener assembly including an existing polyaxial pedicle screw that has been previously installed in a spinal structure, the polyaxial pedicle screw including a polyaxial head to which a prosthetic member is secured, a fastening portion fastened to the polyaxial head over the prosthetic member, and a connector element that extends from the fastening portion, the connector element being connected to another spinal structure.

Abstract: An orthopedic stabilization system of implants that includes a bone attachment means that provides poly-axial fixation of the system to the vertebrae, and a connector means that connects the bone attachment means to the spinal rod in a fashion that allows variable height adjustment of the spinal rod (dorsal in the case of posterior spinal pedicle fixation). The orthopedic stabilization system includes a locking means with a tightenable ball-joint arrangement that locks a post means to the bone attachment means in a desired relative spatial orientation. Several embodiments are disclosed, some using traditional mechanical locking means such as screw fasteners, taper-locking interfaces and collets. Embodiments are described that use the austenitic transformation of shape memory alloy (SMA) material to effect a locking of both the ball-joint arrangement and the connector means.

Abstract: A polyaxial screw assembly includes a pedicle screw, a coupling, an insert, and a housing. The pedicle screw includes a shank having a helical thread formed thereon and a head at one end. The coupling is positioned on top the pedicle screw and releasably engages portions of the head. The coupling and pedicle screw are positioned within a distal portion of the housing. The pedicle screw is slid through an opening in the insert and the insert is thread into the distal portion of the housing to retain the coupling and the pedicle screw within the housing. The pedicle screw is rotatable and pivotable relative to the housing. Compressing the coupling within the housing locks the pedicle screw in a desired orientation.

Abstract: A medical implant assembly includes a polyaxial bone anchor having a shank, a receiver, a lower compression insert with planar surfaces for closely receiving an elongate connecting member with planar surfaces and a one-piece closure structure. The connecting member is made from a polymer. The closure structure engages both the connecting member and the insert with the engagement between the closure structure and the insert securely locking the polyaxial mechanism even if the connecting member exhibits creep.

Abstract: A pedicle screw construct includes a pedicle screw, a coupling, a collet, and a set screw. The pedicle screw includes a shank having a helical thread formed thereon and a head at one end. The collet is positioned atop the head of the pedicle screw. The collet and pedicle screw are inserted into the coupling. The set screw is positioned in the collet such that the set screw contacts a portion of the rod and is releasably secured to the pedicle screw via a gripping tool. The pedicle screw is rotatable and pivotable relative to the collet and coupling assembly.

Abstract: The present invention generally is directed toward a spinal fixation system whereby a coupling element allows the physician to selectively lock or unlock either the connection between the coupling element and a fastener, such as to allow for repositioning of the coupling element, or the connection between the coupling element and an elongate rod. The locking or unlocking of these connections may be made independently and as desired by the physician.

Abstract: A polyaxial bone anchor including a housing and a bone screw. A bottom surface of the housing includes an aperture that defines an angulation limit of the bone screw for each azimuthal angle around a longitudinal axis of the housing. The aperture is V-shaped, with the V-shape having converging side walls that define a low-angulation direction near their intersection and a high-angulation direction opposite the low-angulation direction. In some cases, the angulation limit of the bone screw is generally constant over a range of azimuthal angles centered around the high-angulation direction. The housing may be modular, including tabs on one component that are plastically deformed to engage a lip on another component. During assembly, a mandrel advances longitudinally along a bore in the housing, and forces the tabs radially outward toward the lip to a radially outward plastically deformed state.

Abstract: A polyaxial bone anchor has a locking element shaped and configured to allow an anchoring member (e.g., a screw or hook) to polyaxially rotate at large angles about a central axis of the bone anchor before compression locking the anchoring member within an anchor head.

Abstract: The present invention generally provides a polyaxial fixation device having a shank with a spherical head formed on a proximal end thereof, and a receiver member having an axial passage formed therein that is adapted to polyaxially seat the spherical head of the shank. The polyaxial bone screw further includes an engagement member that is adapted to provide sufficient friction between the spherical head and the receiver member to enable the shank to be maintained in a desired angular orientation before locking the spherical head within the receiver member.

Abstract: The present invention relates to pedicle screw spinal rod connectors and more specifically, a pedicle screw head extender for use with a pedicle screw to ease connection to a spinal rod. The pedicle screw head extenders provided herein can be used with either fixed head pedicle screws or multi-axial head pedicle screws. The pedicle screw head extenders can either be threaded to or snapped into place within the various pedicle screws. It may also be possible to use the present invention with other types of spinal screws that may be connected to spinal rods without the screw actually being implanted through the pedicle of the spine.

Abstract: The present invention generally is directed toward a spinal fixation system whereby a coupling element allows the physician to selectively lock or unlock either the connection between the coupling element and a fastener, such as to allow for repositioning of the coupling element, or the connection between the coupling element and an elongate rod. The locking or unlocking of these connections may be made independently and as desired by the physician.

Abstract: A method comprising attaching a screw head to a bone fixator component, wherein the screw head comprises a first portion comprising a slot and an inwardly curved bottom portion; and a second portion comprising an outwardly protruding and expandable bulbous end extending from the inwardly curved bottom portion; and wherein the bone fixator component comprises a concave socket adapted to receive the screw head; securing the bone fixator component in a bone; securing a locking pin in the screw head; engaging the locking pin with the bone fixator component; inserting a longitudinal member in the screw head; and inserting a blocker in the screw head.

Abstract: Systems and methods of treating spinal deformity, including one or more intervertebral implants to be introduced laterally into respective intervertebral spaces, a plurality of bone screws introduced generally laterally into vertebral bodies adjacent to the intervertebral implants and/or the intervertebral implants themselves, and a cable dimensioned to be coupled to the bone screws and manipulated to adjust and/or correct the spinal deformity.

Abstract: A spine derotation system includes bone fixation elements, fixture members, clamps and stabilizers. The clamps can collectively lock together multiple proximal ends of bone fixation elements extending from one lateral side of the spine. The stabilizers may include clamp stabilizers that are configured to couple together two or more clamps to each other so as to facilitate derotation and alignment of multiple vertebrae of a patient's spine. The stabilizers may also include fixture stabilizers that are configured to couple together two fixture members on the same vertebra to facilitate derotation.

Abstract: A bone anchoring device includes a bone anchoring element having a shaft to be anchored in the bone and a head, a receiving part for receiving a rod to be connected to the bone anchoring element, and a pressure member acting onto the head to lock the position of the head relative to the receiving part, the receiving part is formed in one piece and includes an open first bore with a first bore axis, a recess shaped and sized to receive a rod having a longitudinal axis, and a second bore having a second bore axis. The second bore is in communication with the first bore and is sized to receive the head with a part of the shaft extending through the second bore. The second bore axis includes an angle of approximately 90° with a plane defined by the first bore axis and the longitudinal axis of the rod.

Abstract: A polyaxial bone screw assembly includes a threaded shank body having an upper capture structure, a head and an open, compressible retainer collar. The capture structure and retainer collar are both threaded for rotatable attachment within a cavity of the head. The head has a U-shaped cradle defining a channel for receiving a spinal fixation rod. The head channel communicates with the cavity and further with a restrictive opening that allows for loading the capture structure into the head but prevents passage of the attached retainer collar out of the head. The open retainer collar may be bottom- or top-loaded by compressing open ends of the ring towards each other, the collar springing back into a rounded shape after insertion in the head. The open collar has an external substantially spherical surface that mates with an internal surface of the head, providing a ball joint, enabling the head to be disposed at an angle relative to the shank body.

Abstract: A polyaxial bone screw assembly includes a threaded shank body member having an upper portion with an internal drive and, alternatively, a laterally extending alignment rib or fin. The bone screw assembly also includes a lockable receiver coupling member, an open retainer ring member having a slit or gap and a compression insert member. An inset conical or cylindrical surface on the shank upper portion frictionally engages a similarly shaped inner surface of the retainer ring. The receiver includes a restrictive lower opening that allows for uploading the shank upper portion and compressed retainer ring into the receiver cavity, but prevents passage of the retainer ring out of the receiver once the ring inner surface engages the conical surface of the shank upper portion.

Abstract: A polyaxial bone anchoring device is provided including a bone anchoring element (1) comprising a head (3) and a shank (2); a receiving part (4, 4?) for receiving a rod (100) for coupling the rod to the bone anchoring element, the receiving part comprising a first end (4a), an opposite second end (4b) and a central axis (C) extending through the first end and the second end, and a channel (9) for receiving the rod and an accommodation space (11) for receiving the head; a pressure element (6, 6?) arranged in the receiving part and configured to exert pressure onto the head; wherein the pressure element (6) comprises flexible sections (66a, 66b) facing away from the head (3), characterized in that the flexible sections (66a, 66b) comprise a free end portion (69a, 69b) with respect to the central axis (C) that cooperates with an inclined surface portion (15a, 15b) of the receiving part (4) such as to hold the pressure element (6) in a position in which it exerts a pre-load onto the head before the head is lo

Abstract: A polyaxial bone screw assembly includes a threaded shank body having an upper portion, a receiver member or head, a retaining and articulating structure, and a pressure insert disposed between the shank upper portion and a rod. The receiver has a U-shaped cradle defining a channel for receiving a spinal fixation rod and a receiver cavity. The retaining and articulating structure attaches to the shank and rotates with the shank in the cavity during positioning. The pressure insert presses upon the shank upper portion and not the retaining and articulating structure.

Abstract: The present invention generally is directed toward a spinal fixation system whereby a coupling element allows the physician to selectively lock or unlock either the connection between the coupling element and a fastener, such as to allow for repositioning of the coupling element, or the connection between the coupling element and an elongate rod. The locking or unlocking of these connections may be made independently and as desired by the physician.

Abstract: An orthopedic stabilization system of implants that includes a bone attachment means that provides poly-axial fixation of the system to the vertebrae, and a connector means that connects the bone attachment means to the spinal rod in a fashion that allows variable height adjustment of the spinal rod (dorsal in the case of posterior spinal pedicle fixation). The orthopedic stabilization system includes a locking means with a tightenable ball-joint arrangement that locks a post means to the bone attachment means in a desired relative spatial orientation. Several embodiments are disclosed, some using traditional mechanical locking means such as screw fasteners, taper-locking interfaces and collets. Embodiments are described that use the austenitic transformation of shape memory alloy (SMA) material to effect a locking of both the ball-joint arrangement and the connector means.

Abstract: The bottom loading fastening system that consists of the polyaxial ball and socket joint used in conjunction with a bone screw having threads on one end for use in anchoring to the spine and a spherical connector on the other end operating as a pivot point about which a connecting assembly moves in a polyaxial fashion. A substantially U-shaped connecting assembly has a lower receptacle having a retainer ring within a retaining ring groove for use in securing the spherical connector to the connecting assembly.

Abstract: A poly-axial bone fastener assembly having a collar and a bone fastener can be coaxially locked to prevent poly-axial movements of the collar relative to the bone fastener while permitting the collar to rotate about an axis of the bone fastener, thereby combining the functions and advantages of a poly-axial bone screw and a fixed angle bone screw. Some embodiments of a coaxial locking mechanism may include a c-clip with a locking pin, a c-clip with hooks, a split ring with square corners, a pin that spins inside the collar, pins that travel about a neck of the bone fastener, a coaxially locking top that screws into the collar over a head of the bone fastener, and a top nut that threads onto the head of the bone fastener inside the collar to trap a flange of the collar between a shoulder of the bone fastener and the top nut.

Abstract: A pedicle screw fixation system and method for use of the same are disclosed. In one embodiment, a tulip is provided for holding a head of a pedicle screw substantially along a longitudinal axis. The tulip includes opposing first and second U-shaped receiving slots aligned along a transverse axis. A rod is received by the opposing first and second U-shaped receiving slots. A coupling collar includes a plurality of resilient fingers circumferentially disposed therearound such that a snap fit engagement with the head of the pedicle screw formed. The coupling collar includes a first deformable face operable for contact with the rod. A set screw is adapted for driving engagement through the tulip along the longitudinal axis such that a second deformable face is positioned for contact with the rod. The first and second deformable faces conform to the shape of the rod in response to forceful engagement therewith.

Abstract: A dynamic stabilization, motion preservation spinal implant system includes an anchor system, a horizontal rod system and a vertical rod system. The systems are modular so that various constructs and configurations can be created and customized to a patient.

Abstract: A dynamic anchoring device is described. An element with a shank for anchoring in a bone or a vertebra and with a head connected to the shank is provided with a receiving part for the head and with an elastomeric pressure element acting on the head. The pressure element is formed and located in such a way that, upon a movement of the element from a first angular position of the shank relative to the receiving part into a second angular position, it exerts a return force on the head. Further, a dynamic stabilization device, in particular for vertebrae, is provided. In such a stabilization device, a rod is connected two anchoring devices. At least one of the anchoring devices is constructed as dynamic anchoring element.

Abstract: A spinal stabilization apparatus and method according to which an anchor element is engaged with a bone structure of a spinal system. The anchor element defines a reservoir adapted to contain a bone-growth promoting material and the reservoir is in fluid communication with the bone structure via at least one aperture defined in the anchor element. A rod-connecting element extend from the anchor element and is adapted to extend outward from the bone structure to engage at least a portion of a rod when the rod extends within a vicinity of the spinal system and the bone structure.

Abstract: A polyaxial bone screw assembly includes a threaded shank body having an integral upper portion receivable in a receiver, the receiver having an upper channel for receiving a longitudinal connecting member and a lower cavity cooperating with a lower opening. The upper portion expands a retaining member in the receiver cavity to capture the shank upper portion in the receiver. In some embodiment either the retaining member or an insert provide for a friction fit of the shank upper portion in the receiver resulting in non-floppy placement of the shank with respect to the receiver. Some retainers and inserts have a lock-and-release feature. Final locking of the polyaxial mechanism is provided by frictional engagement between the shank upper portion and the retaining member. A pre-assembled receiver, retaining member and optional insert may be popped-on or snapped-on to the shank upper portion prior to or after implantation of the shank into a vertebra.

Abstract: Exemplary spinal fixation devices, systems, and method are provided for stabilizing vertebrae in a patient's spine. In one exemplary embodiment, methods and devices are provided for coupling one or more bone anchors, such as hooks, screws, etc., and/or one or more spinal fixation elements, such as spinal rods, cables, plates, etc. In certain exemplary embodiments, a cross connector is provided for connecting and stabilizing two bone anchors, a bone anchor and a spinal fixation element, or a bone anchor and bone.

Abstract: A bone stabilizer assembly includes a fixation element, a coupling element, and a compression nut. The fixation element is adapted to engage a bone and having a head portion and shank portion. The coupling element has an internal bore sized to receive the shank portion of the fixation element and a pyramid-shaped seat for supporting the head portion of the fixation element. The coupling element is adapted to receive a stabilizer rod. The compression nut is engagable with the coupling element and is adapted to rotatingly move distally into the coupling element to translate a force to the head portion through the rod and the saddle such that the head portion is forced against the seat of the coupling element to prevent relative movement between the fixation element and the coupling element.

Abstract: Methods, systems, devices and tools for placing bone stabilization components in a patient are provided. The systems and devices have a reduced number of discrete components that allow placement through small incisions and tubes. More particularly, the present invention is directed to screws for use in systems and methods of treating the spine, which eliminate pain and enable spinal motion, which effectively mimics that of a normally functioning spine. Methods are also provided for installation of the screw and other subject systems.

Abstract: Within a given spinal segment, the stable vertebral level is identified. Within the lower lumbar spine, that level is most commonly at the sacrum. A bone fastener is rigidly affixed to the stable spinal segment and an interconnecting member is rigidly affixed to the bone fastener so as to form a cantilever construct. Vertebral bodies that exhibit aberrant spinal motion and/or mal-alignment relative to the stable segment are then attached to the interconnecting member using non-rigid bone fastener(s). The motion profile of the dynamic fastener can be varied and may be selected to provide the desired vertebral motion characteristics. The interconnecting member may be rigid or it may be alternatively made rigid parallel to the direction of greatest instability and non-rigid in the other planes.

Abstract: A polyaxial bone screw assembly includes a threaded shank body integral with an upper capture structure and a head having an inner cavity for receiving the capture structure. The capture structure is threaded and the head includes a threaded opening for rotatable assembly with the capture structure and eventual locking frictional engagement between the capture structure and the head.

Abstract: A spinal alignment system for interconnecting vertebral bodies is disclosed. The system includes a bone screw polyaxially connected to a seat. The seat includes a top opening, a first rod receiving portion and a second rod receiving portion, a first rod channel and a second rod channel. The system is implanted into a first vertebral body. A first rod is introduced to the seat through the top opening in a first orientation and connected to the first rod receiving portion. A second rod is introduced to the seat through the top opening in a first orientation and connected to the second rod receiving portion. The first and second rods are each moved into a second orientation such that the rods project through the first and second rod channels, respectively. The rods are capable of polyaxial movement with respect to the seat for landing the opposite ends of the rods in adjacent seats of screw systems implanted in other vertebral bodies.

Abstract: A percutaneous access device includes an inner tube and an outer tube disposed about at least a portion of the inner tube. The outer tube may be sized to span from a skin incision in a patient to a site proximate the spine of the patient. The distal end of the outer tube may be adapted to releasably engage a bone anchor. The inner tube may be adjustable relative to the outer tube between a first position and a second position in which the distal end of the inner tube contacts the bone anchor. A bone anchor assembly includes a bone anchor having a distal bone engaging portion and a receiving member having a recess for receiving a spinal fixation element. The proximal end of the receiving member may have an arcuate groove formed on an exterior surface thereof to facilitate connection of an instrument to the receiving member.

Abstract: Methods and devices that utilize segmental fixation between several adjacent vertebrae, thus allowing each vertebrae to be adjusted independently, are provided. In general, the device includes a spinal anchoring element that is adapted to seat at least one spinal fixation element, and a closure mechanism that is adapted to mate to the spinal anchoring element to lock the at least one spinal fixation element in a fixed position relative to the spinal anchoring element.

Abstract: A receiving part for coupling a rod to a bone anchoring element includes a receiving part body including a rod receiving portion having a channel for receiving a rod, and a head receiving portion for accommodating a head of a bone anchoring element, the head receiving portion having an open end and being flexible for inserting and clamping of the head; and a locking ring around the head receiving portion, wherein in a pre-locking position, a spring portion on one of the locking ring or the receiving part body engages a corresponding portion on the other one of the locking ring or the receiving part body, and the locking ring exerts a first force onto the head receiving portion, and wherein in a locking position, the locking ring exerts a second force greater than the first force onto the head receiving portion to lock the head therein.

Abstract: A coupling device for securing an elongate member to the spine is provided. The coupling device comprises a compressible inner member that secures an anchor member therein when the inner member is axially shifted within an outer member. The elongate member is retained within the device by an axially inserted locking member, and may be secured independently of the anchor member. The coupling device and anchor may be configured to provide increased angulation of the anchor with respect to the coupling device. For instance, anchor member may have an offset head portion in order to provide normal pivoting of the coupling device when the anchor is attached to bone at an angle.

Abstract: A bone anchoring device includes a receiving part for receiving a rod, the receiving part has a first bore coaxial with a longitudinal axis and a second bore, and an anchoring element having a first end for insertion into the bone and a second end positionable within a second bore, the anchoring element being movable relative to the receiving part in limited angular range about the longitudinal axis, the angles lying in a single plane. The bone anchoring device further includes a fixation element cooperating with the receiving part to lock the anchoring element relative to the receiving part. The anchoring element is pivotable relative to the receiving part around one rotational axis transverse to the longitudinal axis.

Abstract: A method of stabilizing bone, such as a spine, includes providing a coupling element having first and second sections that are angled relative to one another, the coupling element having rod receiving openings for securing an elongated member such as an orthopedic rod, and assembling the coupling element with an anchoring element. The method includes securing the anchoring element in bone, moving the coupling element relative to the anchoring element to align the rod receiving openings with the orthopedic rod, securing the orthopedic rod in the rod receiving openings, and after the securing step, locking the coupling element from further movement relative to the anchoring element.

Abstract: A method of providing spinal stabilization is provided herein. More specifically, the method includes positioning a plurality of fixation assemblies within a plurality of vertebrae in a trans-lamina orientation wherein each fixation assembly includes a proximal portion configured to securely receive a stabilization element (e.g., a stabilization rod). The proximal portions of the various fixation assemblies can be aligned so as to secure at least one stabilization element in a desired position (e.g., along and above a midline of the patient's spine, adjacent and parallel to the midline). A system for providing spinal stabilization is also provided which utilizes trans-lamina delivery and positioning of fixation assemblies within target vertebrae thereby providing stronger fixation and a significant reduction in associated tissue damage.

Abstract: The present invention may include a pedicle screw with a multifunctional adaptor, a strain reliever, and a dual-surface cap. The multifunctional adaptor may include a convex pivot ring for improving multi-axial movement and locking stability, an integrated locking mechanism for improving maneuverability, and an integrated compression member for improving the assembly process. The strain reliever may be formed along a neck of the pedicle screw for relieving mechanical stress asserted thereto, and thereby preventing a breakage thereof. The dual-surface cap may provide a slightly sloped surface for reducing the tension of the stabilizing rod. The present invention may also provide for a dynamic adaptor for flexibly connecting two stabilizing rods, which may be versatilely adapted to various pedicle screw configurations.

Abstract: Implant for stabilizing a spinal column including a pedicle screw, an elongated member, and a retainer for a stabilizing rod. The elongated member can be polyaxially movably connected to the pedicle screw, and have external threads over a longitudinal periphery thereof. The retainer can be one piece, or can include an upper retainer portion and a lower retainer portion. The retainer, or the upper and lower retainer portions, can each have an opening therethrough to receive a stabilization rod to fix one implant to another. In one aspect, the upper retainer portion is internally threaded to engage external threads of the elongated member, the upper retainer portion threadably translating longitudinally along the elongated member by rotation of the elongated member about a longitudinal axis thereof. The upper retainer portion translates toward the lower retainer portion to secure and retain the rod therebetween.

Abstract: A capless multiaxial screw fixation assembly, including: a screw having a threaded portion and a screw head portion positioned at one end thereof; and, a retainer having a first end, a second end opposite the first end, and a bore for receiving the screw threaded portion so that the screw head portion is seated therein. At least one of the screw and the retainer is configured such that the retainer is able to pivot about the screw head portion in a non-symmetrical manner.

Abstract: A spinal fixation system includes a rod and anchor devices that include a bone engaging fastener having a head defining a spherical socket. A ball insert is placed within the socket and rotated so that the ball insert is juxtaposed with the socket. The anchor device further includes a yoke defining a yoke channel for receiving the rod and a stem engaged to the ball insert captured within the socket. A sleeve disposed between the yoke channel and the fastener head supports the rod. A set screw is operable to clamp the rod against the sleeve and draw the insert into engagement within the socket. A releasable detent defined between the yoke and the fastener head is configured to releasably retain the yoke in at least one discrete position relative to the fastener. Portions of the releasable detent may also exert a frictional retention force against the fastener head.

Abstract: A bone-anchoring device is provided. The bone-anchoring device may comprise a screw including a threaded shaft portion configured to engage bone tissue, and a head portion having a cup-shaped cavity. The device may further include a rod connector and a linking member, wherein the linking member includes a spherical head portion configured to engage the cup-shaped cavity of the head of the screw, a widened flange s configured to engage the linking member, and an elongate body extending from the widened flange portion and configured to extend through an opening in the rod connector.

Abstract: A polyaxial ball and socket joint that can be locked into a fixed position. The fastening system consists of the polyaxial ball and socket joint used in conjunction with a bone screw having threads on one end for use in anchoring to the spine and a spherical connector on the other end operating as a pivot point about which a connecting assembly moves in a polyaxial fashion. A substantially U-shaped connecting assembly has a lower receptacle that operates as a socket for housing an upper retainer ring and a lower split retaining ring. The socket is receptive to the spherical connector which is inserted through the lower split retainer ring causing a momentary displacement thereof which allows for the positioning of the spherical connector between the upper and lower retainer rings.

Abstract: A polyaxial bone screw assembly includes a threaded shank body having an upper capture structure, a head, a retaining ring and a nut. The external capture structure surface includes a threaded portion and a smooth portion; the smooth portion for slidably mating with the retaining ring and the threaded portion for rotatable attachment to the nut within a cavity of the head. The nut fixes the retaining ring to the shank and also provides a tool engagement formation for driving the shank body into bone.

Abstract: A polyaxial screw assembly includes an internal load dampening mechanism for sharing and dampening loads between at least one screw member and at least one rod member interconnected by the assembly. A method of interconnecting the orthopedic screw with the rod includes dampening with a body member interconnecting the screw to the rod.

Abstract: An assembly for connecting a support element to a bone. The assembly comprises: a bone screw having a head at one end of a threaded shaft; and a clamp comprising: a base at a first end of the clamp delimiting an opening for receiving the head of the bone screw; and at least two side members extending from the base towards a second end of the clamp. The head of the bone screw and the clamp are configured to allow the head of the bone screw to be inserted into the base from the direction of the first end at a first orientation of the base to the bone screw, and to retain an inserted bone screw within the base at a second orientation of the base relative to the bone screw. This allows the screw to be inserted into the bone without requiring prior assembly of the screw and clamp. It also allows later revision whereby the clamp can be removed from the screw without requiring an implanted screw to be removed from the bone.