Abstract: A fixation system for repairing a pars fracture includes a needle guide configured to be docked on a lamina of the pars, a needle, a guidewire, and a screw assembly. A portion of the needle is configured for insertion through a passage of the needle guide. A portion of the guidewire is configured for insertion through a passage of the needle. The screw assembly includes a collar and an elongated portion, the collar being movable with respect to the elongated portion. A portion of the screw assembly is configured to contact the lamina co-axially with the guidewire.

Abstract: A bone anchoring device includes a receiving part with a recess for receiving a rod and a flexible head receiving portion for pivotably holding a head of a bone anchoring element, a pressure member configured to exert pressure on the head when the head is held in the head receiving portion, and a clamping ring positionable around the head receiving portion and movable from a first position where the head is pivotable relative to the receiving part, to a second position where the clamping ring exerts a radial force on the head receiving portion to lock the head relative to the receiving part. When the clamping ring is at the first position, the clamping ring abuts the receiving part to restrict upward movement, while a surface of the clamping ring that faces upwards is exposed for engaging an instrument to move the clamping ring to the second position.

Abstract: A pivotal bone anchor assembly for securing an elongate rod to patient bone includes a shank having a head and an anchor portion, a receiver having an axial bore and a channel for receiving the elongate rod, a collet insert top loaded into a first position within the axial bore and having a collet pocket for receiving the shank head, and a pressure ring uploadable into the collet pocket prior to the shank head and having an upper surface for engaging the rod. After receiving the shank head within the collet pocket, the collet insert and pressure ring are downwardly deployable with the shank head into a second position to capture the shank head in the assembly, the pressure ring being operable to transfer pressure from the elongate rod in the channel to the shank head to lock an angular position of the shank relative to the receiver.

Abstract: The invention is directed in various aspects to a system including anchors, anchor components, and anchor assemblies and subassemblies that are adapted for attachment to a bony structure of a clinical subject. For example, two or more such anchors in the form of screws may be affixed to bones, for example, vertebral structures such as the pedicle, and each anchor is connected to a stabilizer such as a surgical rod that is inserted between the anchors. The anchors and assemblies are novel in many respects owing to their modular nature, which in contrast to conventional systems, allows the anchors to be provided to a surgeon in modular, subassembly and fully assembled form to enable a broad array of choices in devising the optimal plane for surgical bone fixation.

Abstract: A translating polyaxial bone screw assembly for anchoring a connecting rod to a spinal vertebra comprises a bone screw having a threaded shank and a head coupled to a yoke. The yoke has at one end a rod receiving channel for receiving a connecting rod and an opposite end that is coupled to the bone screw by a coupling assembly. The coupling assembly couples the yoke for polyaxial movement relative to the bone screw and for translational movement of the yoke in a direction transverse to the axis of the bone screw. The coupling assembly comprises a biasing element supported for joint movement with the yoke that provides a manually surmountable tension force between the yoke and bone screw head that is maintained during polyaxial and translational movement. A fastening element is supported by the yoke for securing the connecting rod between the fastening element and the coupling assembly.

Abstract: Open implant closure structures include a helically wound guide and advancement flange form having splay control surfaces. Multi-start closures and closures with inner set screws have splay control contours for interlocking with cooperating flange forms of bone anchor receivers. Flange form heights, thicknesses and other geometry, such as splay control ramp angle may be varied.

Abstract: A fixation unit for a suture-less fixation of tissue at a bone comprises an anchor element that is arranged to be fixed to a bone, and a retaining element that is arranged to be coupled with the anchor element to attach a tissue section to the bone. The anchor element and the retaining element are lockable to one another and form therebetween a retaining zone into which the tissue section is mountable. A handling device comprises a mounting tool that is arranged for inserting the fixation unit.

Abstract: A polyaxial bone screw assembly includes a threaded shank body having an integral upper portion receivable in an integral receiver, the receiver having an upper channel for receiving a longitudinal connecting member and a lower cavity cooperating with a lower opening. The receiver can have crimp tabs, but is devoid of spring tabs and collet-like flexible structures. A down-loadable compression insert (some with lock and release feature), a down-loadable friction fit split retaining ring and an up-loadable shank upper portion cooperate to provide for pop- or snap-on assembly of the shank with the receiver either prior to or after implantation of the shank into a vertebra. The shank and receiver once assembled cannot be disassembled. The receiver and insert include aligned tool receiving apertures for lock and release of the polyaxial mechanism.

Abstract: Certain shear bolts described herein provide failure bending resistance when torque is applied to members being connected by the bolts, while maintaining shearability. Certain other shear bolts described herein provide a shear region having different shear limits dependent upon the direction of force being applied to the shear region.

Abstract: Described herein is a pedicle screw for use in the thoracolumbar spine where the height can be adjusted intra-operatively before or after installation member of the longitudinal member. The pedicle screws with adjustable height may be made with a monoaxial or polyaxial configuration. The height of the pedicle screw can be lengthened or shortened.

Abstract: Disclosed is a bone fracture fixation device, such as for reducing and compressing fractures in the proximal femur. The fixation device includes an elongate body with a helical cancellous bone anchor on a distal end. An axially moveable proximal anchor is carried by the proximal end of the fixation device. The device is rotated into position across the fracture or separation between adjacent bones and into the adjacent bone or bone fragment, and the proximal anchor is distally advanced to apply secondary compression and lock the device into place. The device may also be used for soft tissue attachments.

Abstract: A guide assembly includes a spinal screw assembly having a bone screw and a spinal rod holder; and a spinal rod guide having first and second elongated arc portions defining a pair of longitudinal slots extending along the first and second arc portions, each of the first and second arc portions further defining at least one recess extending transversely from each of the longitudinal slots, the at least one recess configured to receive at least a portion of a reduction tool to enable reduction of a spinal rod received within the spinal rod holder.

Abstract: A fusion device includes a screw having a head and a shaft. A hollow bone dowel is disposed about the shaft of the screw. The bone dowel is formed from a bone-like, biocompatible, or allograft material.

Abstract: A prosthesis for the replacement of at least a portion of the bone of a facet located on a mammalian vertebra, comprising: an articulating surface that articulates with another facet; a bone contacting surface that contacts a surface of the vertebra, the articulating surface being connected to the bone contacting surface; and a fixation element that attaches the bone contacting surface to the vertebra, the fixation element being adapted for implantation into an interior bone space of a pedicle of the vertebra; wherein the prosthesis is configured so that no portion of the prosthesis contacts the posterior arch of the vertebra.

Abstract: The percutaneous minimally invasive pedicle fixation system herein comprises a bone screw and a hook-rod, wherein the bone screw includes a positioning casing and a screw body. The positioning casing comprises securing base, an alignment casing and a screw body passage. The securing base includes a through hole at the bottom and two openings arranged opposite to each other in the wall. The alignment casing has a wall portion and a volume reduce portion, wherein the wall portion is configured with an elongate opening and the volume reduced portion is a portion with part of the wall removed to recede from the outer surface of the securing base and a guide opening formed in the volume reduced portion. The positioning casing further includes a first easy breaking portion between the alignment casing and the securing base so that the alignment casing can be removed from the positioning casing.

Abstract: A reversible bone coupling device including a first component having a first elongated stem portion for insertion from a first end longitudinally into a surface of a first bone piece, and a second component having a second elongated stem portion for insertion from a second end longitudinally into a surface of a second bone piece, and a connector extending from a second top for coupling with the first component and reversibly locking therein.

Abstract: An assembly for the fixation of a spinal facet joint, including an outer shank, an inner shank and a tip, such that rotation of the inner shank with respect to the outer shank causes the tip to move into the outer shank. Movement of the tip causes deformation of the distal end of the outer shank such that the distal end of the outer shank is larger in diameter than the hole through which it was inserted, said deformation causing increased compression and reduced chance of device loosening.

Abstract: The present invention includes a pedicle screw made with a bone fastener and a rod coupling head, the rod coupling head comprising an upper rod coupling: the lower rod coupling having a lateral rod opening adapted to receive a permanent rod; an angled bore extends into the lateral rod opening; and a permanent rod fastener in the angled bore to engage a permanent rod in the lateral rod opening; and a upper rod coupling having an upper rod opening adapted to receive a temporary rod, wherein the upper rod opening is formed to receive a temporary rod fastener; wherein the upper rod coupling is detachable from the lower rod coupling at a transition and a temporary rod is temporarily affixed into the upper rod opening during a bone realignment and a permanent rod is positioned in the lateral rod opening and engaged by the permanent rod fastener upon final bone alignment.

Abstract: A bone anchoring device has an anchoring element, a receiving portion, and a pressure element. The anchoring element includes a shank to be anchored in a bone or a vertebra and a head, the head having an exterior surface with a spherical segment-shaped portion. The shank and the head are separate parts. The receiving portion includes a first end, a second end opposite to the first end, a longitudinal axis passing through the two ends, a bore coaxial with the longitudinal axis, and a first region adjacent to the second end for receiving a spherical segment-shaped section of the head. The pressure element exerts pressure on the head to lock the head in the receiving portion. The head has a hollow inner portion to receive a free end portion of the shank and wherein the head and the end portion are formed such that the end portion can be elastically clamped by the head.

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: An intervertebral implant system is disclosed which includes a spinal spacer for engagement between vertebrae and at least one semi-constrained bone screw assembly. The spinal spacer includes a body extending between first and second end surfaces to define opposing top and bottom vertebral engaging surfaces. The second end surface of the body includes at least one aperture formed therethrough at an angle relative to the centerline axis and a screw opening defined therethrough. The semi-constrained bone screw assembly is adapted for insertion through the screw opening and includes a shank, a head and a rod member. The rod member is fixedly engageable with the shank and moveably coupled to the head such that both the rod member and the shank are moveable with respect to the head.

Abstract: A pedicle screw and rod fixation assembly including a pair of opposing tabs having a proximal end and a distal end, the pair of opposing tabs being coupled to one another about the distal end thereof by a screw head member, a decoupling mechanism for decoupling the pair of opposing tabs from the screw head member, a rod receiving slot between the pair of opposing tabs, and a sliding member configured for coupling to the pair of opposing tabs. The sliding member and the pair of opposing tabs are configured for allowing movement of the sliding member distally along the pair of opposing tabs and preventing movement of the sliding member proximally along the pair of opposing tabs.

Abstract: A receiving part for receiving a rod for coupling the rod to a bone anchoring element includes a receiving part body including: a rod receiving portion with 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 an exterior surface with a curved portion; and a locking ring around the head receiving portion, wherein the locking ring has an interior surface with a curved portion for engagement with the curved portion of the exterior surface of the head receiving portion for locking a position of the head relative to the head receiving portion.

Abstract: In an exemplary embodiment, the present invention provides a fastener assembly that can be used for the fixation or anchoring of orthopedic devices or instruments to bone tissue. In particular, the present invention preferably provides a low profile variable angle or fixed angle fastener assembly that is able to securely connect the orthopedic device to bone tissue. Furthermore, in an exemplary embodiment, the present invention provides a fastener assembly having a locking mechanism that will quickly and easily lock the fastener assembly with respect to the orthopedic device.

Abstract: A translating polyaxial bone anchor for anchoring a connecting rod to a spinal vertebra comprises a fastener having a bone engaging portion and a head, the head defining a socket. An insert is captively retained in the socket and configured for swiveling polyaxial movement therein. The insert includes an elongate connecting element defining an axis, the connecting element projecting outwardly from and through the socket. A yoke having at one end a rod receiving channel for receiving a connecting rod is coupled to the fastener by a coupling member. The coupling member couples the yoke to the insert connecting element for joint polyaxial movement relative to the fastener and for translational movement of the yoke in a direction transverse to the axis of the connecting member. A fastening element is supported by the yoke for securing the connecting rod between the fastening element and the coupling member.

Abstract: A medical screw system configured to facilitate determination of when the screw system is desirably set in a bone during implantation of the screw at a surgical site. The screw system includes a screw and a washer having a central ring surrounding a head receiving pocket configured for receiving the head of the screw, a plurality of arms spaced around and extending outwardly from the ring, the arms each having a bone contacting surface that engages the bone when the screw is implanted into the bone, and a groove defined between the arms and an exterior of the central ring. The groove is configured to enable the arms to flex when the screw system becomes desirably set into the bone to provide a visual indication that the screw is desirably set in the bone.

Abstract: A receiving part for receiving a rod for coupling the rod to a bone anchoring element includes a receiving part body including a rod receiving portion with 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 so as to allow introduction and clamping of the head, the head receiving portion having an exterior surface with a tapered portion; and a locking ring around the head receiving portion and including an interior surface with a curved portion configured to engage the tapered portion of the exterior surface of the head receiving portion to clamp the head.

Abstract: The present teachings provide one or more surgical implements for repairing damaged tissue, such as in the case of a spinal fixation procedure. A uniplanar bone anchor system for a fixation procedure is provided. The system can include a bone fastener including a head with a bearing surface and a shaft adapted to engage an anatomy. The system can also include a saddle, which can include a first bore formed about a longitudinal axis that receives the bone fastener and a coupling bore defined transverse to the longitudinal axis. The system can also include a coupling system, which can have a second bearing surface. The coupling system can be received through the coupling bore such that the second bearing surface of the coupling system can contact the bearing surface to permit the bone fastener to move in only one plane.

Abstract: A bone screw is created, with a thread section (1) with a tip (6) at a first end and a head (8) for engaging with a screwdriver at the opposite second end, which serves as traction element to connect shattered or split off parts of bones to one another. So that fusion of the screw with the bones can take place, the thread section (1) is constructed as tubular and its wall has a plurality of recesses.

Abstract: A screw implant a shaft and a threaded area for anchoring in the bone, a head having engagement surfaces or openings for the application of an insertion tool, wherein the shaft and the head are formed in one piece, wherein there is associated with the shaft between the thread and the head at least one separation area where the head with an upper part of the shaft is separated, and a replacement head, which can be fixed to the remaining lower part of the shaft. The replacement head may have an inner drill hole, which is from the size designated to fit a cross section of the shaft and into which the shaft is inserted.

Abstract: A bone screw extension assembly for use in placing a connecting rod percutaneously into tissue of a patient comprises a multi-axial bone screw and a screw extension releasably coupled to yoke of the bone screw. The screw extension includes coaxially disposed outer sleeve and inner sleeves that are rotatable relative to each other. A screw engaging member projects radially from the distal end of the inner sleeve and is configured to engage an extension coupling surface on the outer sleeve upon relative rotation of the inner and outer sleeves. A securement member including cooperative surfaces is defined adjacent the distal end of the inner and outer sleeves that is operable upon relative rotation of the inner sleeve and outer sleeve to radially secure the sleeves together to thereby maintain the engagement of the screw engaging member and the bone screw.

Abstract: An apparatus is designed to attach an implant to bone in a manner that permits rotational adjustment of the implant about multiple axes prior to securement via the apparatus. The apparatus includes separate rotational and translational fasteners that can be individually locked to independently restrict rotation and translation of the implant relative to the bone. The rotational fastener includes an interpositional member, an expandable engagement member, and a rotational locking member that urges the expandable engagement member to advance along the interpositional member. The resulting expansion of the engagement member causes it to engage the implant. The rotational fastener is slidable along a fixation member implanted in the bone until the translational fastener is applied to restrict relative translation between the rotational fastener and the bone.

Abstract: Coupling assemblies and systems and methods are provided with an anchor member movably coupled with a receiver member extending along a receiver axis. A seat member is movable in the receiver member to assume any one of a plurality of orientations corresponding to an orientation of a connecting element extending through the receiver member transversely to the receiver axis.

Abstract: The screw assembly includes a screw, an insert, and a body member. The screw includes a longitudinal axis and a proximal end with a head portion and a distal end with a threaded portion. The insert operably couples with the head portion and is configured to rotate relative to the head portion about the longitudinal axis. The body member operably couples with the insert and is configured to pivot relative to the insert in a single plane parallel to the longtudinal axis. In other features, the body member operably couples with the insert and is configured to pivot relative to the insert about a transverse axis normal to a plane parallel to the longtudinal axis.

Abstract: A bone attachment device comprises an attachment collar having a hinged lid is disclosed. The bone attachment device may also comprise a bone fastener (such as a bone screw). A bone attachment device including an attachment collar and a spinal rod locking device is disclosed. A bone attachment device as described herein may be used together with a spinal stabilization rod and one or more additional bone attachment devices. Such devices are adapted to clamp and hold a spinal stabilization rod. Methods for implanting a spinal stabilizer having a bone attachment device including a hinged lid are disclosed.

Abstract: Pedicle screws that can include a pedicle screw body, housing, plurality of clamps, rod, and set screw are disclosed herein. The clamps may be positioned side by side inside the lower portion of the housing. When the rod and set screw are provided in the housing, the set screw applies a force on the rod and the rod engages the plurality of clamps, causing the clamps to frictionally engage a head of the pedicle screw between the clamps.

Abstract: Presented herein is a bone screw system that comprises a fixation element, a receiving element, coupling element, and a compression element. The fixation element can be a screw. The receiving element defines an internal bore sized to receive the shank portion of the fixation element and a seat adapted to support the head portion of the fixation element. The seat of the receiving element is shaped to substantially conform to an exterior portion of the head portion of the fixation element. A breakaway groove is positioned externally on each leg or leg extension. The breakaway groove extends inwardly at least partially through the wall of each leg or leg extension. This creates an aperture or slit in the wall leaving the wall with at least on, preferably a pair of leg attachments on each leg or leg extension adjacent the aperture.

Abstract: A spinal bone screw has a receiver with upstanding arms forming a channel for receiving a longitudinal connecting member, such as a rod, the receiver being integral with a threaded shank. The receiver further includes inner surfaces in sliding engagement with an insert, the insert having a seating surface for the rod. The insert and rod being pivotable with respect to the bone screw in a single plane.

Abstract: A receiving part for receiving a rod for coupling the rod to a bone anchoring element includes a receiving part body including a rod receiving portion with 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 so as to allow introduction and clamping of the head, the head receiving portion having an exterior surface with a tapered portion; and a locking ring around the head receiving portion and including an interior surface with a curved portion configured to engage the tapered portion of the exterior surface of the head receiving portion to clamp the head.

Abstract: Techniques are generally described related to a method and system for treating an injury with a bone screw. One example bone screw may be configured to fracture at a pre-selected frangible location so that the point of failure is not in an inaccessible location, e.g., deeply embedded below the surface of a treated bone. The bone screw may further include a material disposed over the frangible location that is designed to temporarily strengthen the screw and selected to be absorbed by the body over a period of time after installation of the screw in the bone. One example bone screw may include an unthreaded portion that is configured to facilitate removal of an embedded screw fragment from a bone in the event that the screw fails in vivo.

Abstract: Bone anchor assemblies and methods are provided having a multi-component bone anchor that is configured to allow the shank of the bone anchor to be bottom loaded into a receiver member. In one embodiment, a bone anchor assembly is provided having a shank with a distal threaded portion and a proximal head portion, a receiver member having an aperture formed in a distal end thereof through which the head portion of the shank can be received, the receiver member defining a polyaxial seat, a non-expandable outer ring configured to be polyaxially disposed within the polyaxial seat of the receiver member and defining a central opening through which the head portion of the shank can be received, and an expandable inner ring having an inner surface configured to mate with the head portion of the shank and an outer surface configured to mate with an inner surface of the outer ring to thereby lock the outer ring in a fixed position relative to the shank.

Abstract: A method for mounting a polyaxial screw into a bone includes rotating a drive cap so that a screw mounted to the drive cap is screwed into a bone, the drive cap having a socket in which a portion of the screw is pivotably disposed, at least a portion of a collet being disposed within the socket between the screw and the drive cap. A stabilizing structure and a fastener are positioned onto a shaft projecting from the drive cap. The fastener is advanced along the shaft so as to push a portion of a compression cap against the collet which in turn wedges the collet within the socket of the drive cap and causes the collet to bias against a portion of the screw, thereby locking the position of the screw, the collet, and the drive cap relative to each other.

Abstract: An orthopedic fastener is designed to attach an implant to bone in such a manner that, until the fastener is tightened, the implant may be rotationally adjusted against the bone. The implant may have a semispherical bone apposition surface that permits polyaxial rotation of the implant against the bone. The orthopedic fastener has an interpositional member and a compression member. The interpositional member may be a split ring with a conical exterior surface that mates with a conical surface of the implant. The compressing member has a threaded bore that engages a proximal end of a fixation member implanted in the bone such that, in response to rotation of the compression member, the interpositional member is sandwiched securely between the implant and the compression member. The conical surface of the implant compresses the interpositional member about a semispherical surface of the compression member, thereby restricting rotation of the implant.

Abstract: An elongated modular implant is provided which has a distal part and a proximal part both having a leading end and a trailing end, respectively. The trailing end of the distal part includes a tool engagement portion and the leading end of the proximal part includes a distal part engagement portion for an engagement with the tool engagement portion of the distal part. The implant further includes an assembly element for firmly coupling the distal part and the proximal part when the first tool engagement portion of the distal part engages the distal part engagement portion of the proximal part. The proximal part trailing end may also have a tool engagement portion identical to the trailing end of the distal part.

Abstract: A bone anchoring device includes an anchoring element having a shaft and a head; a receiving part for receiving the head and a rod, the receiving part being formed in one piece and having a top end and a bottom end, a bore extending from the top end to the bottom end, an inner wall defined by the bore, a substantially U-shaped channel adjacent to the top end for receiving the rod and a seat adjacent to the bottom end for accommodating the head; a pressure element; and a spring element having a spring force. The anchoring element is inserted from the top end and is pivotable with respect to the receiving part. The pressure element is movable in the bore so as to be able to fix the anchoring element at an angle with respect to the receiving part by exerting pressure onto the head. The spring element acts between the pressure element and the receiving part and allows the pressure element to be introduced from the top end but withstands against removal of the pressure element through the top end.

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: Techniques are generally described related to a method and system for treating an injury with a bone screw. One example bone screw may be configured to fracture at a pre-selected frangible location so that the point of failure is not in an inaccessible location, e.g., deeply embedded below the surface of a treated bone. The bone screw may further include a material disposed over the frangible location that is designed to temporarily strengthen the screw and selected to be absorbed by the body over a period of time after installation of the screw in the bone. One example bone screw may include an unthreaded portion that is configured to facilitate removal of an embedded screw fragment from a bone in the event that the screw fails in vivo.

Abstract: An enclosure device connecting a pedicle fixation device with an elongated spinal fixation member. The enclosure device can include an enclosure member and an elongated guide member affixed to the enclosure member and defining a fracture region for breaking off the guide member from the enclosure member. The enclosure member can have a spherical outer surface rotatably received within a receiver portion of the pedicle fixation device. The enclosure member can include an internal bore capable of slidably receiving the fixation member.

Abstract: A locking and lagging bone screw. The screw includes a head having an outer surface which is at least partially threaded and a shaft which is at least partially threaded having a first end coupled to the head and a second end adapted to be fastened to bone. The head of the screw is able to rotate independently of the shaft. Thus, the head of the screw can be locked to a bone plate by using a first driver (e.g., a torx driver) and the plate can be lagged to the bone by using a second driver (e.g., a hex driver).

Abstract: A bone anchoring device has an anchoring element, a receiving portion, and a pressure element. The anchoring element includes a shank to be anchored in a bone or a vertebra and a head, the head having an exterior surface with a spherical segment-shaped portion. The shank and the head are separate parts. The receiving portion includes a first end, a second end opposite to the first end, a longitudinal axis passing through the two ends, a bore coaxial with the longitudinal axis, and a first region adjacent to the second end for receiving a spherical segment-shaped section of the head. The pressure element exerts pressure on the head to lock the head in the receiving portion. The head has a hollow inner portion to receive a free end portion of the shank and wherein the head and the end portion are formed such that the end portion can be elastically clamped by the head.