Patent Description:
A polyaxial bone anchoring device of this type is known, for example, from <CIT>. The polyaxial pedicle screw described is this document includes a receiving head having a transversal U-shaped passage, and a shank having a threaded portion and a bulging end rotatable housed within the receiving head. A locking insert is also housed within the receiving head and is matable with the bulging end. The receiving head includes a lateral aperture, the lateral aperture exposing a contact surface of the locking insert in such a way that an external pressing component can act on the contact surface to maintain the locking insert into its locking position.

In <CIT> a polyaxial bone anchoring device is described that includes a receiving part with two legs defining a recess for receiving a rod and a pressure member for exerting pressure on a head of the bone anchor in the receiving part. The pressure member has an engagement portion that extends at least partially into a leg of the receiving part and is directly engageable from outside the bone anchoring device. With an instrument, for example, the pressure member can be adjusted from a non-locking position where the head is pivotable to a locking position where the head is clamped.

<CIT> discloses an orthopedic apparatus comprising a shaft portion for engaging a bony structure and a body in communication with the shaft portion. The body includes an area for receiving and retaining a connector rod and an engagement mechanism for communication with a rod, and the engagement mechanism is moveable between a first position for receiving the rod and a second position where the rod is secured by a frictional contact in a locking engagement in the body.

<CIT> describes a surgical instrument configured for attachment to a surgical device, such as a bone anchor, the bone anchor comprising a tulip housing to capture the head of a threaded shank, a pressure cap positioned within the tulip housing, and a retaining ring that limits radial expansion of a distal radially expandable portion of the tulip housing. The bone anchor further comprises a compression mechanism for bringing the pressure cap into close contact with head to create a friction fit.

In spinal surgery, often multiple segments of the spinal column have to be corrected and/or stabilized using a spinal rod and polyaxial bone anchors. During such a procedure, repeated adjustments of the bone anchor and the rod relative to the receiving part of a polyaxial bone anchoring device may become necessary. Therefore, there is a need for simple and effective handling of the polyaxial bone anchoring device in terms of locking and unlocking of the head and the rod during the correction steps.

It is the object of the invention to provide an improved coupling device and an improved polyaxial bone anchoring device as well as a system of such a coupling device or such a polyaxial bone anchoring device and an instrument that is convenient to operate and/or effective in terms of locking.

The object is solved by a coupling device of claim <NUM> or by a bone anchoring device of claim <NUM> or by a system of claim <NUM>. Further developments are given in the dependent claims. In addition, further developments of the coupling device can also be implemented as further developments of the bone anchoring device and/or the system and vice versa.

According to an embodiment, a coupling device for coupling a rod to a bone anchor, includes a receiving part configured to receive a head of the bone anchor, the receiving part having a first end and a second end, a central axis extending through the first end and the second end, and two legs defining a recess at the first end for receiving the rod. The coupling device further includes a pressure member movable in the receiving part to exert pressure on an inserted head. And an actuating portion (herein also called actuating member) configured to act on the pressure member is provided on the receiving part. The actuating portion is configured to rotate at least partially around an axis of rotation that extends at an angle or is inclined relative to the central axis to move the pressure member from a non-locking position in which an inserted head is pivotable in the receiving part to a locking position in which the head is clamped. Preferably the axis of rotation is substantially perpendicular to the central axis so that the pressure member is moved downward towards the second end. Further preferably the actuating portion comprises a cam portion and the pressure member follows the movement of the cam portion.

With such a structure, a rotational movement of the actuating portion can be transformed into a linear movement of the pressure member. This permits to move the pressure member only a small distance for locking the head. More specifically, the actuating portion may include rotating shaft and a cam portion that acts on the pressure member. This permits to precisely effect a small movement of the pressure member with a simple construction.

The locking of the head may be temporary as long as the instrument acts on the actuating portion. Hence, the steps of adjusting the angular position of the coupling device relative to the bone anchor can be carried out repeatedly in a quick and easy manner.

According to an embodiment, the actuating portion is rotatable in a first direction to move the pressure member to the locking position and in a second direction, preferably opposite to the first direction, to move the pressure member to the non locking position.

According to an embodiment, the actuating portion is configured to cooperate with the receiving part in a non-threaded manner. According to a further embodiment, the actuating portion is substantially stationary in a direction of the axis of rotation while rotating. According to the invention, the actuating portion is configured to rotate when a force in the direction of the central axis is applied thereto. According to a still further embodiment, the axis of rotation intersects the central axis.

An embodiment of an instrument includes a first instrument portion, preferably an outer tube, the first instrument portion being configured to engage the receiving part, a second instrument portion, preferably an inner portion arranged at least partially in the first instrument portion and being displaceable relative to the first instrument portion, the second instrument portion being configured to engage the actuating portion. When the first instrument portion engages the receiving part and the second instrument portion engages the actuating portion and rotates the actuating portion, the pressure member is movable from a non-locking position in which an inserted head is pivotable in the receiving part to a locking position in which the head is clamped. In a still further embodiment the second instrument portion is configured to rotate the actuating portion in an opposite direction so that the pressure member is moved from the locking position back to a non locking position.

According to a further embodiment, the instrument comprises a first instrument portion that is configured to be attached to the receiving part and a second instrument portion that is configured to act on the actuating portion of the receiving part to rotate the actuating portion in a first direction to move the pressure member to the locking position and to actuate the actuating portion in a second direction, preferably opposite to the first direction, to move the pressure member to the non locking position. The actuating portion of the receiving part may comprise a two-armed lever the pivot axis of which coincides with the axis of rotation of the actuating portion. The second instrument portion may comprise a first pushing member that is configured to act on one arm of the two-armed lever and a second pushing member that is configured to act on
the other arm of the two-armed lever. Since the receiving part may have two actuating portions, a pair of a first and a second pushing member may be provided for each actuating portion. With this embodiment the head can be selectively locked and unlocked with respect to the receiving part.

The instrument may be designed such that the recess of the receiving part that receives the rod can remain unobstructed during the locking of the head of the bone anchor. Hence, it is possible to temporarily lock the head of the bone anchor while a rod and/or a fixation member is not yet placed in the rod channel or in the case that the rod is at a higher position than the bottom of the rod channel. This may increase the possibilities for surgical correction steps.

The bone anchoring device may be a bottom loading bone anchoring device where the head of the bone anchor is insertable from the lower end of the receiving part or a top loading bone anchoring device where the bone anchor is insertable into the receiving part from the upper end.

Further features and advantages of the invention will become apparent from the description of embodiments by means of the accompanying drawings. In the drawings:.

As depicted in <FIG>, a bone anchoring device according to an embodiment of the invention includes a bone anchor <NUM> in the form of, for example, a bone screw having a shank <NUM> with a threaded portion and a head <NUM> with a spherically-shaped outer surface portion. The head <NUM> may also have a recess <NUM> for engagement with a drive tool. The bone anchoring device also includes a coupling device that comprises a receiving part <NUM> for receiving a rod (not shown) to be connected to the bone anchor <NUM>. In addition, a pressure member <NUM> forms a part of the coupling device. The pressure member <NUM> is provided in the receiving part <NUM> and is configured to exert pressure on the head <NUM> of the bone anchor <NUM> to clamp and/or finally lock the head <NUM> with respect to the receiving part <NUM>. Two actuating members <NUM> that generally form actuating portions are mounted in opposite walls of the receiving part <NUM> and are configured to actuate the pressure member <NUM> to exert pressure on the head <NUM>. The bone anchoring device may further include a fixation member (not shown), for example an inner screw or set screw for fixing the rod in the receiving part <NUM>.

The receiving part <NUM> will be described in greater detail, referring additionally to <FIG>. The receiving part <NUM> includes a first end 5a forming an upper end and an opposite second end 5b forming a lower end, and a central axis C that passes through the first end 5a and the second end 5b. The overall outer shape of the receiving part may be substantially cylindrical except for structures such as projections and grooves that are formed on or in the cylindrical surface. A passage <NUM> extends through the receiving part <NUM> from the first end 5a to the second end 5b. The passage <NUM> may have several sections having different diameters. In one section that starts at or close to the first end 5a and extends to a distance from the first end 5a, the passage <NUM> is formed as a first coaxial bore 50a that may be provided in at least a portion thereof with an internal thread <NUM>. Between the first coaxial bore 50a and the second end 5b a widened portion in a form of a second coaxial bore 50b may be provided that permits a portion of the pressure member <NUM> to expand therein. Between the second end 5b and the second coaxial bore 50b, a narrowing portion 50c is formed that narrows, for example in a conical shape, towards the second end 5b. By the passage <NUM>, an opening <NUM> is formed at the second end 5b a width of which is greater than a greatest outer diameter E of the head <NUM>. Hence, the receiving part <NUM> is suitable for insertion of the head <NUM> of the bone anchor <NUM> through the opening <NUM> at the second 5b into the receiving part <NUM>.

In a region adjacent to the first end 5a of the receiving part <NUM>, a recess <NUM> that may be substantially U-shaped extends from the first end 5a in the direction of the second end 5b. A width of the recess <NUM> is slightly greater than a diameter of the rod to be inserted, such that the rod can be placed in the recess <NUM> and can be guided therein. By means of this, the recess <NUM> forms a rod receiving recess or a channel for the rod, wherein the sidewalls of the channel define two free legs <NUM>. Each of the legs <NUM> comprises a transverse hole <NUM>. The transverse holes <NUM> extend completely from the outer surface of the receiving part <NUM> into the passage <NUM> and may be substantially cylindrical holes having a cylinder axis R. In the embodiment, the cylinder axis R extends perpendicular to the central axis C and intersects the central axis C. The holes <NUM> may be at an axial height slightly above a bottom 53a of the substantially U-shaped recess <NUM>. Moreover, the cylinder axis R of the holes <NUM> may extend substantially through a center of the legs <NUM> in the circumferential direction. Hence, the holes are substantially symmetrical and with respect to a plane extending through the central axis C and through a center of the legs <NUM> and cylinder axes R of the two holes <NUM> are coincident. An inner diameter of the holes <NUM> is only slightly greater than an outer diameter of the actuating members <NUM> such that the actuating members <NUM> can be inserted in the holes <NUM>, respectively, and are rotatably supported therein. Hence, the cooperation between the actuating member <NUM> and the receiving part is non-threaded.

On each leg <NUM>, above the hole <NUM>, a protrusion <NUM> is formed on the outer wall of the leg <NUM> that serves as an engagement portion for engaging the receiving part <NUM> with an instrument. The protrusions <NUM> are asymmetrical with respect to each other in relation to a plane extending through the central axis and the center of each leg. In greater detail, each protrusion <NUM> is offset from the hole <NUM> in the same circumferential direction and adjoins the border of the recess <NUM>. As can be seen in particular in <FIG> in a top view, one protrusion <NUM> at one leg <NUM> which is on one side of the longitudinal axis of the recess <NUM> is offset towards one border of the recess <NUM> in the direction of the axis L. The other protrusion <NUM> at the other leg <NUM> is at the opposite side of the longitudinal axis L of the recess <NUM> and is offset towards an opposite border of the recess <NUM> in the direction of the axis L. The protrusion <NUM> comprises a four-cornered base 56a with a cylindrical outer surface and a roof-shaped portion 56b that is oriented towards the first end 5a. The roof-shaped portion 56b may have a beveled portion 56c at its tip region. In the example shown, the protrusion <NUM> is on one side flush with the border of the recess <NUM>. It shall be noted, that the protrusion may have other shapes that render it suitable for engagement with an instrument.

In addition, the receiving part <NUM> comprises on each leg <NUM> a groove <NUM> in its outer wall for guiding a portion of an instrument to the actuating member <NUM> when the actuating member <NUM> is placed into the hole <NUM>. The groove <NUM> extends substantially parallel to the central axis C from the first end 5a to a distance from the second end 5b and is located adjacent to the hole <NUM> on a side opposite to the protrusion <NUM> in the circumferential direction. Moreover, the groove <NUM> may be open towards the hole <NUM>. At a distance from the lowermost end of the internal thread <NUM> a circumferentially extending groove <NUM> may be formed in the inner wall of the receiving part, that serves as an abutment for a portion of the pressure member <NUM>.

Referring additionally to <FIG>, the pressure member <NUM> will be described in greater detail. The pressure member <NUM> includes a first end 6a that forms an upper end and a second end 6b that forms a lower end. An upper portion <NUM> of the pressure member includes a rod receiving portion and a lower portion <NUM> of the pressure member includes a head receiving portion. The outer surface of the pressure member <NUM> is substantially cylindrical with such an outer diameter that the pressure member <NUM> can be placed into the passage and can slide in the coaxial bore 50a of the receiving part <NUM>. When the pressure member <NUM> is mounted to the receiving part <NUM> the central axis of the pressure member coincides with the central axis C of the receiving part. In the upper portion <NUM> a rod support surface <NUM> may be provided that is configured to support an inserted rod. A longitudinal axis <NUM> of the rod support surface <NUM> extends transverse to the central axis C. The rod support surface <NUM> may have a V-shaped cross-section in a direction transverse to the central axis C to permit support of rods of different diameters. However, the rod support surface can also be flat or cylindrical or can have any other shape. To the left and to the right of the rod support surface <NUM> upstanding legs <NUM> are formed that have a substantially flat inner surface and a substantially cylindrical outer surface.

Adjacent to the first end 6a a substantially cylindrical rim portion <NUM> is formed on each leg <NUM> that protrudes beyond the outer surface of the cylindrical main portion <NUM> of the pressure member <NUM>. An outermost section of the rim portion <NUM> may be cut away so that a flattened outer end 64a may be formed. At the center of the legs <NUM> in the circumferential direction the flattened end 64a may be flush with the cylindrical outer surface of the pressure member. The rim portion <NUM> is configured to engage the groove <NUM> of the receiving part <NUM> to prevent the escape of the pressure member <NUM> through the first end once it has been placed into the receiving part <NUM> and assumes an insertion position for the head <NUM>. Between the rod support surface <NUM> and the upstanding legs <NUM> grooves <NUM> extending parallel to the rod support surface <NUM> are formed that render the upstanding legs <NUM> slightly flexible.

In the lower portion <NUM> of the pressure member <NUM> a head receiving recess <NUM> is provided for the head <NUM> of the bone anchor <NUM>. The head receiving recess <NUM> may be substantially spherically-shaped with a radius corresponding to that of the head <NUM> and extends over the region of the head with the greatest outer diameter E. The lower portion also comprises a plurality of slits <NUM> that are open at the second end 6b. The number and dimensions of the slits <NUM> are such that the wall confining the head receiving recess <NUM> is flexible, more specifically that it can expand to snap onto the head <NUM> when the head <NUM> is inserted. To increase the flexibility the closed end portion 68a of the slits <NUM> may be widened. An outer surface portion <NUM> adjacent to the second end 6b of the pressure member <NUM> may be tapered, for example conically tapered. The outer surface portion <NUM> is configured to cooperate with the narrowing portion 50c of the passage of the receiving part <NUM>. A coaxial bore <NUM> in the pressure member <NUM> permits access to the head <NUM> with a drive tool.

In each of the legs <NUM> a recess <NUM> is formed that extends completely through the leg from the outside to inside. The recesses <NUM> are elongate in the circumferential direction and have substantially cylinder segment-shaped ends 600a, connected by two substantially straight portions 600b. Moreover, the recesses <NUM> have such a length in the circumferential direction and such a height in the axial direction of the central axis C, that a protrusion of the actuating member <NUM> is configured to move therein substantially only in the lengthwise direction of the elongate hole <NUM>. More specifically, the recesses <NUM> are arranged asymmetrical with respect to the center of the legs in the circumferential direction as can be seen in particular in <FIG>. One recess <NUM> on the one leg <NUM> is offset from the center of the leg towards one side and the other recess <NUM> is offset from the center of the leg <NUM> towards the opposite side. This follows from the eccentric arrangement of the engagement portions on the actuating members <NUM> as explained below.

As shown in <FIG> and additionally <FIG>, the actuating members <NUM> may be identical and may each be designed as a monolithic piece that is insertable into a hole <NUM> of the receiving part <NUM>. More specifically, each actuating member <NUM> has a cylindrical main portion <NUM> that has an outer diameter such that the actuating member can be placed into the hole <NUM> in the leg <NUM> of the receiving part <NUM> and is rotatably supported in the hole <NUM>. The main portion <NUM> comprises two opposite circular or partially circular end faces, one of which forms an outside face 70a which faces to the outside of the receiving part <NUM> and the opposite one forms an inside face 70b which faces to the inside of the receiving part <NUM> when the actuating member is mounted to the receiving part <NUM>. The thickness of the main portion <NUM> substantially corresponds to the wall thickness of the receiving part around the holes <NUM>.

On the outside face 70a a lever-like protrusion <NUM> that has a rear end 71a and an opposite free forward end 71b is formed. The lever-like protrusion <NUM> has a thickness perpendicular to the outside face that may smoothly increase from the rear end 71a to a distance from the rear end 71a and may then be constant up to the to the free end 71b. The free end 71b may protrude beyond the contour of the outside surface 70a. As shown in particular in <FIG>, the position of the lever-like protrusion <NUM> may be such that it extends over the region with the largest diameter of the outside surface 70a but may be arranged closer to one side of the main portion <NUM> than to an opposite side in a direction perpendicular to the lever axis. An upper side 71c of the lever-like protrusion <NUM> forms an engagement surface that is configured to be engaged by a portion of the instrument. Adjacent to the engagement surface 71c the outside surface 70a has a recess <NUM> where a portion of the main body <NUM> is cut away. The recess <NUM> may provide guidance and space for a portion of the instrument.

When the actuating member <NUM> is inserted into the hole <NUM>, the cylinder axis of the main portion <NUM> is coincident with the cylinder axis R of the hole and forms an axis of rotation R for the actuating member <NUM>. At the inside surface 70b an engagement portion for engaging the pressure member in the form of a cylindrical protrusion <NUM> is provided that has an outer diameter smaller than an outer diameter of the main portion <NUM> of the actuating member <NUM>. The cylindrical protrusion <NUM> is at the inside face 70b at a position opposite to the front region of the lever-like protrusion <NUM> and may extend up to the outer edge of the main portion <NUM>. The cylinder axis z of the cylindrical protrusion <NUM> extends parallel to the cylinder axis R of the main portion <NUM>, hence the cylinder axis z of the cylindrical protrusion <NUM> is offset from the axis of rotation R of the main portion <NUM>. By means of this, the cylindrical protrusion <NUM> serves as an eccentric actuating portion, more specifically as a cam portion. The height of the cylindrical protrusion <NUM> is such that once the actuating member <NUM> is mounted in the hole <NUM>, the cylindrical protrusion <NUM> extends into the recess <NUM> of the leg <NUM> of the pressure member <NUM>. As a result, when the lever-like protrusion <NUM> is engaged by an instrument and pressed down, the actuating member <NUM> is rotated to some extent in the hole <NUM>. While rotating, the actuating member <NUM> may be stationary in the direction of the axis of rotation. The cylindrical protrusion <NUM> is confined in its movement in the recess <NUM> between the ends 600a. As the cylindrical protrusion <NUM> moves on an eccentric path around the axis of rotation R, it moves downward and the pressure member <NUM> follows this movement thereby exerting a downwardly directed force onto an inserted head <NUM>. hence the cylindrical protrusion acts as a cam.

Referring now to <FIG>, an instrument which is suitable for use with the bone anchoring device described above will be explained. The instrument <NUM> includes a first instrument portion in the form of an outer member <NUM> and an inner member <NUM>. The inner member <NUM> is displaceable relative to the outer member <NUM> and a handle and/or actuating device including, for example, a rotating knob <NUM> is provided for displacing the inner member relative to the outer member. Various mechanisms may be implemented to displace the inner member <NUM> relative to the outer member <NUM>. An overall shape of the inner and outer member is tubular although the tubes may have slits so that they are not completely closed. A central longitudinal axis of the tube coincides with the central longitudinal axis C of the receiving part when the instrument is attached thereto. Referring in addition to <FIG> a front portion of the outer member <NUM> is shown in an enlarged view. The outer member <NUM> comprises a front end 110a that in use faces towards the bone anchoring device. Two opposite slits <NUM> that are open at the front end 110a extend over a portion of the outer member so that two arms <NUM> are formed that are flexible at least to such an extent, that they can spread apart to engage the protrusions <NUM> at the receiving part <NUM>. The width of the longitudinal slits <NUM> may be at least as large as the diameter of the rod to be inserted into the receiving part. This permits to use the instrument when a rod is already inserted or when the rod has to be inserted during attachment of the instrument.

Furthermore, a substantially rectangular cutout <NUM> is formed on each of the arms <NUM> adjacent to the recess <NUM> and to the front 110a. The width of the recesses <NUM> in the circumferential direction is such that a portion of the inner member <NUM> can extend therein. Moreover, the cutouts <NUM> are at positions that are asymmetric with respect to the substantially U-shaped recess <NUM> of the receiving part <NUM> when the instrument is attached thereto. Specifically, the cutouts <NUM> are provided at different sides of the U-shaped recess <NUM> and at different ends of the U-shaped recess <NUM> in the direction of longitudinal axis L of the U-shaped recess <NUM>. Furthermore, at a distance from the front end 110a an engagement recess <NUM> is provided on each arm <NUM>. The engagement recess <NUM> is located on each arm <NUM> at a position that it can engage the protrusion <NUM> on the receiving part <NUM> when the outer member <NUM> is placed onto the receiving part <NUM>. Moreover, the contour of the engagement recesses <NUM> is such that it substantially matches the contour of the engagement protrusions so that a form-fit engagement can be achieved.

At substantially a center of each of the arms <NUM> in the circumferential direction an axially elongate guiding recess <NUM> is formed that is sized and shaped to provide guidance for protrusions of the inner member <NUM>. In greater detail, each recess <NUM> has an upper region 115a and a lower region 115b that is narrowed with respect to the upper region 115a. This is achieved by two wings 115c that extend from the longitudinal sides of the recess <NUM> towards the middle in the circumferential direction. The wings 115c have a distance from the outer surface of the front portion <NUM> so that, as depicted in <FIG> a portion of the inner member <NUM> that extends between the wings 115c is still within the recess <NUM> or in other words does not protrude substantially to the outside.

A front portion of the inner member <NUM> is illustrated in greater detail in <FIG>. The inner member <NUM> has an outer diameter that permits it to extend through the outer member <NUM>. In a circumferential direction opposite elongate slits <NUM> extend from the front end 120a of the inner member over a length so that two arms <NUM> are formed. The width of the slits <NUM> is at least as large as the diameter of a rod to be inserted into the receiving part. Adjacent to the slits <NUM> two extensions <NUM> are formed that start at a distance above the free end 120a and extend beyond the free end 120a in the axial direction. The extensions <NUM> may have a cylindrical inner surface that matches with the cylindrical outer surface of the receiving part <NUM>. In addition, the extensions <NUM> may have a cylindrical outer surface corresponding to the outer surface of the outer member <NUM>. The radial positions of the extensions <NUM> are such that when the inner member <NUM> is in the outer member <NUM> and the slits <NUM> of the inner member and <NUM> of the outer member overlap, the extensions fill in the cutouts <NUM>.

At the center of each of the arms <NUM> in the circumferential direction two axially spaced apart protrusions <NUM>, <NUM> are formed that are configured to engage the elongate recesses <NUM> on the arms <NUM> of the outer member <NUM>. The first protrusion <NUM> may be substantially cuboid-shaped and is configured to be received in the upper portion 115a of the recess <NUM> of the outer member <NUM>. The second protrusion <NUM> is spaced apart from the first protrusion <NUM> towards the front end 120a and comprises a narrower neck portion 125a and a substantially plate-shaped head 125b. The neck portion 125a is configured to be guided between the wings 115c and the head portion 125b is configured to extend over the wings 115c. When the inner member <NUM> is in the outer member <NUM> and the extensions <NUM> extend into the recesses <NUM>, an axial movement of the inner member <NUM> relative to the outer member <NUM> is limited by the axial movement of the first protrusion <NUM> in the upper region 115a of the elongate recess <NUM>. The extensions <NUM> can be moved beyond the front end 110a of the outer member <NUM> until the first protrusion <NUM> abuts against the wings 115c. It shall be noted that along the arms of the inner member and the outer member further protrusions and recesses may be formed as depicted in <FIG>. The displacement of the inner member relative to the outer member can be effected using the rotating knob or handle <NUM>.

The parts and portions of the bone anchoring device and the instrument may be made of any material, preferably however, of titanium or stainless steel or of any bio-compatible metal or metal alloy or plastic material. As a bio-compatible alloy, a NiTi alloy, for example Nitinol, may be used. Other materials can be magnesium or magnesium alloys. Bio-compatible plastic materials for use may be, for example, be polyether ether ketone (PEEK) or poly-L-lactide acid (PLLA). The parts can be made of the same or of different materials from another.

The actuating members <NUM> may preferably be preassembled with the receiving part. Once they have been inserted into the holes a portion 57a of the outer edge of the holes <NUM> may be slightly deformed so that it provides an obstacle for the inserted actuating member in the outward direction (<FIG>). With this, the actuating member may be prevented from being inadvertently pushed out of the hole <NUM> to the outside. The deformed portion 57a may be preferably at the bottom of the hole <NUM> in the direction towards the second end 5b of the receiving part <NUM>. The orientation of the actuating members <NUM> in the holes is such that the lever-like protrusions <NUM> are on the outside and the cylindrical protrusions <NUM> extend into the recesses <NUM> of the pressure member <NUM>, respectively. As the two actuating members <NUM> are identical, the free ends 71b of the lever-like protrusions <NUM> show in opposite directions when seen along the rod channel. Correspondingly, the cylindrical protrusions <NUM> are located at opposite ends 600a of the associated recesses <NUM> of the pressure member <NUM>, respectively. When the actuating members <NUM> are actuated, they rotate in opposite directions.

The pressure member <NUM> may also be pre-assembled with the receiving part <NUM>. For mounting, the pressure member <NUM> may be inserted through the first end 5a into the passage <NUM> of the receiving part <NUM> until the head receiving recess <NUM> extends into the accommodation space 50b. As the legs <NUM> of the pressure member <NUM> are slightly flexible, the outwardly extending rim <NUM> can slide along the inner wall of the threaded region in the receiving part until it snaps into the groove <NUM> when the pressure member <NUM> has reached a position in which the recesses <NUM> overlap the holes <NUM>, respectively. The rod support surface <NUM> is aligned with the substantially U-shaped recess <NUM> of the receiving part <NUM>.

The coupling device preassembled in this way can be mounted to the bone anchor <NUM> either outside a patient's body or in-situ after the bone anchor <NUM> has been inserted into bone or a vertebra.

Assembly of the coupling device and the bone anchor will be described referring to <FIG> and the corresponding cross-sectional illustrations <FIG>. First, as depicted in <FIG> and <FIG>, the pressure member is in an insertion position which the head receiving recess <NUM> is at least partially within the widened portion 50b of the passage <NUM> of the receiving part <NUM>. The coupling device is oriented with the second end 5b of the receiving part towards the head <NUM> of the bone anchor. The cylindrical protrusions <NUM> of the actuating members <NUM> extend into the recesses <NUM> in which they can move to some extent. Moreover, the protrusions substantially prevent rotation of the pressure member <NUM> within the receiving part <NUM>.

Next, as depicted in <FIG> and <FIG>, the head <NUM> is inserted through the opening <NUM> at the second end 5b into the receiving part <NUM> and more particularly into the head receiving recess <NUM> of the pressure member <NUM>. As the outwardly extending rim <NUM> abuts against an upper surface of the groove <NUM> in the receiving part, pressure member <NUM> cannot be pushed out through the first end 5a of the receiving part <NUM> in this insertion position.

Further, as depicted in <FIG> and <FIG>, the head <NUM> has fully entered the head receiving recess <NUM> of the pressure member. Due to the flexibility of the pressure member <NUM> in the region of the head receiving recess <NUM>, the pressure member snaps onto the head <NUM>. The widened portion 50b of the passage provides space for expansion of the pressure member therein when the head <NUM> is inserted. Depending on the size of the head receiving recess <NUM> relative to the head, the head <NUM> may be held by friction in the head receiving recess.

Finally, as shown in <FIG> and <FIG>, the pressure member <NUM> is moved downward towards the second end 5b of the receiving part <NUM>. Alternatively, when the bone anchor <NUM> has been inserted already into bone, the receiving part is pulled upwards relative to the bone anchor <NUM>. By means of this, the outer surface portion <NUM> of the pressure member <NUM> enters the narrowing portion 50c of the passage <NUM> whereby the size of the opening <NUM> in the receiving part <NUM> is reduced and the head <NUM> is prevented from being removed through the opening <NUM>. This constitutes a pre-locking configuration. Preferably, in the pre-locking configuration, the head <NUM> is additionally clamped by friction and temporarily held in an angular position prior to final locking. The downward movement of the pressure member <NUM> into the pre-locking configuration causes the cylindrical protrusions <NUM> to move slightly within the recesses <NUM>, respectively, which rotates the actuating members <NUM>. As a result thereof, the lever-like protrusions <NUM> assume an inclined position.

In the clinical use, usually two bone anchors may be anchored in bone or in vertebrae which bone anchors shall be connected through a rod. <FIG> show use of the bone anchoring device with the instrument described in <FIG>. The bone anchoring device is in the assembled and preferably in the pre-locked state as depicted in <FIG> and <FIG>. In a first configuration of the instrument, the inner member <NUM> is in a retracted position, which means that the extensions <NUM> are substantially completely within the recesses <NUM>. Preferably, in the first configuration, the front end 110a and the free ends of the extensions <NUM> are substantially flush with each other. The recesses <NUM>, <NUM> of the instrument <NUM> are substantially aligned with the U-shaped recess <NUM> of receiving part <NUM>. As shown in <FIG>, the instrument is moved towards the bone anchoring device.

Next, as shown in <FIG>, the instrument <NUM> is placed onto the receiving part and the outer member <NUM> is attached to the receiving part by engaging the engagement recesses <NUM> at the outer member <NUM> with the protrusions <NUM> of the receiving part. The beveled portion 56c at the roof of the protrusion <NUM> facilitates the engagement.

Finally, as shown in <FIG>, the inner member <NUM> is pushed downward so that the extensions <NUM> move in the axial direction out of the recesses <NUM> and press with their free ends on the engagement surface 71c of the lever-like protrusion <NUM> of the actuating members <NUM>. When the lever-like protrusions <NUM> are pushed downward, the actuating members <NUM> are rotated to a small extent in the holes <NUM>, respectively, which results in the pressure member <NUM> being moved further axially into the narrowing portion 50c which locks the head <NUM>.

<FIG> show two configurations of the instrument and the bone anchoring device. In <FIG> the bone anchoring device is in the pre-locking configuration of <FIG> and <FIG> and the lever-like protrusion <NUM> is only touched by the free end surface of the extension <NUM>. In <FIG> the extension <NUM> has been pushed further downward to rotate the actuating member <NUM> by pressing onto the lever-like protrusion <NUM>. In this configuration the head is temporarily locked by the instrument. As soon as the inner member <NUM> is retracted, the pressure is relieved and the head <NUM> is pivotable again within the head receiving recess <NUM> of the pressure member <NUM>. It shall be noted that it may be possible by adjusting the force applied by the instrument to adjust the locking force on the head.

A second embodiment of the instrument together with the polyaxial bone anchoring device of the first embodiment is shown in <FIG>. The description of parts and portions of the instrument that are identical or highly similar to those of the first embodiment shall not be repeated and such parts or portions shall have the same reference numerals as in the first embodiment. The instrument <NUM>' has an inner member <NUM>' that includes two bar-shaped pushing members <NUM>' configured to press onto the lever-like protrusion <NUM> of the actuating member <NUM>. As can be seen in <FIG>, the outer member <NUM>' comprises at each arm <NUM>' an axially extending compartment <NUM>' for guiding through the bar-shaped pushing member <NUM>'. As additionally shown in <FIG>, the outer member <NUM>' is a substantially tubular part with a front end 110a and which has two slits 111a', 111b' separated by a bridging portion 111c'. The slits divide the outer member into two arms <NUM>' which are free at the front end <NUM>. Each arm comprises at a distance from the front end 110a a recess <NUM>' for engagement with the protrusion <NUM> of the receiving part. More specifically, the recesses <NUM>' are arranged asymmetrical at positions corresponding to positions of the protrusions <NUM> at the receiving part, when the outer member is attached to the receiving part and the slits 111a, 111b and the substantially U-shaped recess <NUM> are aligned.

Each arm comprises an elongate compartment <NUM>'. for the pushing member <NUM>'. The elongate compartment <NUM>' extends from a distance from the rear end (not shown) of the outer member <NUM>' up to the front end 110a and is open towards the inside of the outer member <NUM>'. An inner contour of the compartment <NUM>' may substantially match an outer contour of the pushing member <NUM>' so that the pushing member <NUM>' is guided in the compartment <NUM>'. The compartment <NUM>' is at such a position in the circumferential direction that when the pushing member <NUM>' extends through the compartment <NUM>' it is configured to touch a forward region of the engagement surface 71c of the lever-like protrusion <NUM>. Hence, the compartment <NUM>' is offset from a center of the arm <NUM>' in a circumferential direction and the two compartments <NUM>' are arranged asymmetrically with respect to each other in the same manner as the lever-like protrusions <NUM> of the actuating members <NUM> are.

The pushing members <NUM>' may have a square-shaped cross-section with rounded or flattened corners. The front end 120a may be convexly rounded. The pushing members <NUM>' are connected in such a manner to the outer member <NUM>' that rotating a handle or actuating member <NUM>' displaces the pushing members <NUM>' relative to the outer member <NUM>'. It shall be noted that in the rearward portion of the outer member a stabilization sleeve <NUM> may be provided that gives stability to the outer member <NUM>'.

In use, as shown in <FIG>, the polyaxial bone anchoring device is in the pre-locking condition as shown in <FIG> and <FIG> when the instrument <NUM>' is attached to the receiving part <NUM>. The arms <NUM>' are slightly spread apart so that the recesses <NUM>' of the outer member <NUM>' can engage the protrusions <NUM> of the receiving part <NUM>. The pushing members <NUM>' are moved out of the compartment <NUM>' until they press with their front surface 120a onto the engagement surface 71c of the lever-like protrusion <NUM>. Since the front surface 120a of the pushing member is rounded, a sufficient contact between the end surface 120a and the engagement surface 71a can be achieved. Each pushing member <NUM>' presses the lever-like protrusion <NUM> downward whereby the corresponding actuating member <NUM> rotates within the hole. As in the first embodiment, the cylindrical protrusion <NUM> moves downward and pushes the pressure member <NUM> deeper into the narrowing portion 50c of the receiving part. As a result thereof, the head <NUM> is temporarily locked as long as the pushing member <NUM>' presses onto the lever-like protrusion <NUM>. When the pushing members are retracted, the pressure exerted onto the pressure member by the actuating member <NUM> is relieved and the head is pivotable again.

A third embodiment of the instrument and a modified embodiment of the receiving part will be described referring to <FIG>. Parts and portions of the polyaxial bone anchoring device that are identical or highly similar to the polyaxial bone anchoring device of the previous embodiments have the same reference numerals and the description thereof will not be repeated.

The polyaxial bone anchoring device comprises the bone anchor <NUM> as in the previous embodiments and a modified receiving part <NUM>', a modified pressure member <NUM>' and modified actuating members <NUM>'. Referring more in detail to <FIG>, the passage <NUM> in the receiving part <NUM>' comprises a substantially conically tapering section 50c' that extends from the second end 5b over a region of the head receiving recess of the pressure member that includes the greatest diameter of the head and that is configured to cooperate with a corresponding conically tapering outer surface of the pressure member <NUM>' as described below. The conically tapering section 50c' is interrupted in the axial direction by a widened portion 50b' that has an enlarged inner diameter for permitting the pressure member <NUM>' to expand therein during insertion of the head <NUM>. The holes <NUM> for receiving the actuating members <NUM> are as in the first embodiment located in the middle of each leg <NUM> in the circumferential direction and extend in the axial direction above the bottom 53a of the substantially U-shaped recess <NUM>. Between an upper edge of each hole <NUM> in the direction of the first end 5a an engagement protrusion <NUM>' is provided that is symmetrical to the center of each leg <NUM> in the circumferential direction. The engagement protrusion <NUM>' may have the same or a similar shape as in the previous embodiments, i.e. it has a base and a roof-shaped upper portion. The groove in the outer surface of the receiving part may be omitted.

The pressure member <NUM>' has an upper portion <NUM> that is identical to the upper portion of the previous embodiments. The lower portion <NUM>' comprises a conically-shaped outer surface <NUM>' that extends over an axial height such that it includes the portion with the greatest diameter of the head when the head is inserted. When the pressure member <NUM>' is in the receiving part <NUM>', the outer conical surface portion <NUM>' contacts the conically tapered portion 50c' above and below the widened portion 50b'.

The actuating members <NUM>' in this embodiment comprise the cylindrical main portion <NUM> and the cylindrical eccentric protrusion <NUM> protruding from the inside face 70b as in the first embodiment. On the outside face 70a, an engagement portion for the instrument is formed as a cylindrical protrusion <NUM>' which may be also arranged eccentrically relative to the main portion <NUM> and arranged at the same position as the cylindrical protrusion <NUM> but on the opposite side of the main portion <NUM>. The cylinder axis z' of the cylindrical protrusion <NUM>' is offset from the axis of rotation R of the main portion <NUM>. The size of the cylindrical protrusion <NUM>' may be the same as that of the cylindrical protrusion <NUM>. Moreover, the cylinder axes of the cylindrical protrusions <NUM>', <NUM> may be coincident. On the outside face 70a, a cutaway portion <NUM> or other marking may be provided for orienting the actuating member properly in the hole <NUM>. More specifically, referring in particular to <FIG>, the actuating members <NUM>' are mounted to the receiving part <NUM>' in such a manner that the cylinder axis z' is offset from the center of the leg <NUM> in the circumferential direction. In this way, the protrusion <NUM>' functions similar to the lever <NUM> of the previous embodiments.

As depicted in Fig. 47a, the instrument <NUM>" comprises an outer member <NUM>" that is substantially tube-shaped and an inner member <NUM>", also substantially tube-shaped and guided in the outer member <NUM>". The outer member <NUM>" comprises at its front end 110a a substantially rectangular recess <NUM>" that divides the front portion into two arms <NUM>". A width of the recess <NUM>" is such that the arms <NUM>" are spaced apart from each other so as to permit the front portion to be placed over the receiving part <NUM>'. The axial length of the recess <NUM>" is such that when the front portion has been placed onto the receiving part, there is still a space in the axial direction that permits to insert the rod. The inner wall of the arms <NUM>" each comprise at a distance from the front end 110a a recessed portion <NUM>' that serves for receiving a front portion of the inner member <NUM>" therein. On an inner wall of the arms <NUM>" at a distance from the front end 110a an engagement recess <NUM>" is formed that has the contour of substantially an U rotated by <NUM>° so that it is open in the circumferential direction to one edge of the arm <NUM>". The engagement recess <NUM>" at the opposite arm <NUM>" is open in the same direction. The contour of the recess <NUM>" is such that the cylindrical protrusion <NUM>' of the actuating member <NUM>' can be received and guided therein. When the instrument is placed on the receiving part <NUM>' at a lateral position relative to the engagement protrusions <NUM>' of the actuating members <NUM>', rotation of the instrument towards the protrusions <NUM>' causes the engagement recesses <NUM>" to engage the corresponding engagement protrusions <NUM>'.

The inner member <NUM>" is displaceable with respect to the outer member <NUM>" by a mechanism <NUM>" that may comprise a lever <NUM>", for example (<FIG>). Various mechanisms may be used to displace the inner member relative to the outer member. The front portion of the inner member <NUM>" comprises at the front end 120a two arms <NUM>". The arms <NUM>" may be guided within the arms <NUM>" of the outer member <NUM>". At the inner wall of each of the arms <NUM>" an engagement recess <NUM>" is formed that has on one side a shape matching the shape of the protrusion <NUM>' of the receiving part and that is open in the circumferential direction on the other side. The engagement recesses <NUM>" on the inner member are positioned and shaped so as to permit engagement with the engagement protrusions <NUM>' of the receiving part <NUM>' when the instrument is placed onto the receiving part and rotated in one direction.

In use, as depicted in <FIG>, the arms of the instrument are placed over the receiving part <NUM>' laterally from the engagement protrusions <NUM>'. A rod <NUM> may be inserted already into the recess <NUM>.

Next, as shown in <FIG>, the instrument is rotated until the engagement recesses <NUM>" of the inner member <NUM>" engage the engagement protrusions <NUM>' of the receiving part <NUM> and simultaneously the engagement recesses <NUM>" of the outer member <NUM>" engage the engagement protrusions <NUM>' of the actuating members <NUM>'.

Thereafter, as shown in <FIG>, the outer member <NUM>" is displaced relative to the inner member <NUM>" downward in a direction towards the second end 5b of the receiving part <NUM>'. The inner member exerts a force onto the engagement protrusions <NUM>' so that the actuating members <NUM>' rotate around the axis of rotation R. Simultaneously, the eccentric protrusions <NUM> move downward and as a result, the pressure member <NUM>' is pressed into the conical section 50c" of the passage to lock the head <NUM>.

In this embodiment, the outer member <NUM>" can be retracted with respect to the inner member <NUM>". The bottom edge of the recess <NUM>" moves the protrusion <NUM>' upward and the pressure member follows the upward movement so that the temporary locking of the head <NUM> can be released.

The locking and releasing of the head <NUM> can be performed several times until a correct position of the bone anchor <NUM> relative to the receiving part <NUM>' can be found. Generally, the rod <NUM> may be already inserted into the recess <NUM> of the receiving part as shown in the Figures or the recess <NUM> may remain unobstructed and/or the rod <NUM> may be inserted during the correction steps. The instrument can be released by rotating it in the opposite direction to effect the disengagement of the protrusion <NUM>' from the recess <NUM>' and the protrusion <NUM>' from the recess <NUM>'.

As depicted in <FIG>, once the correct angular position of the bone anchor <NUM> relative to the receiving part <NUM>' has been found and the rod has been inserted, a fixation member <NUM>, in this embodiment a set screw, can be inserted between the legs and tightened to fix the rod and the head. The rod or the fixation member can also be inserted before correction or locking of the polyaxial angle takes place.

A still further embodiment of the polyaxial bone anchoring device and an instrument for use with such a polyaxial bone anchoring device is shown in <FIG>. Parts and portions that are identical or highly similar to the parts and portions of the previous embodiments are marked with the same reference numerals. Referring to <FIG>, the receiving part <NUM>" is similar to the receiving part <NUM>' of <FIG> with some details being different. The accommodation space for accommodating a portion of the pressure member comprises a conically tapering lower section 50c" close to the second end 5b that is configured to cooperate with a conical outer surface of the pressure member. Adjacent to the conical section 50c", a cylindrical widened portion 50b" for permitting the pressure member to expand during insertion of the head <NUM>. Above the widened portion 50b" an upper portion 50d" provides space for an upper region of a conical portion of the pressure member. Around the holes <NUM>" that are located in the center of the legs <NUM> in a circumferential direction, a plurality of, preferably shallow, recesses <NUM> are formed in the outer wall of the receiving part <NUM>". The recesses <NUM> are shaped and sized so as to accommodate a portion of the actuating member <NUM>" therein. In greater detail, the recesses <NUM> may be oblong and slightly drop shaped with a narrow end 501a and an opposite broad end 501b. In the embodiment, four such recesses <NUM> are provided that are arranged close to the corners of a virtual square around the hole <NUM>" such that the narrow ends 501a facing each other, respectively. The protrusions <NUM>" for engagement with the instrument are located in the middle of the legs <NUM> in the circumferential direction above the holes <NUM>', respectively. In this embodiment, the protrusions <NUM>" have a substantially rectangular-contoured base and a low roof-shaped portion in the direction of the first end 5a. The protrusion <NUM>" may be framed by two axial grooves <NUM>" for guiding the instrument.

Lastly, the receiving part <NUM>" has two extensions <NUM>, that extend from the legs <NUM> above the first end 5a and which have a length such that they are configured to protrude out of a patient's skin when the polyaxial bone anchoring device is inserted into bone or a vertebra. The extensions <NUM> may have at least in a portion thereof an internal thread <NUM>" that continues into the internal thread <NUM> on the legs <NUM>. The purpose of the extensions <NUM> is to allow the guidance of the instruments and parts, such as for example a fixation screw, from outside to the receiving part <NUM>". Adjacent to the first end 5a which in this case is the outer end of the legs <NUM>, a weakened section <NUM> is formed on each leg <NUM> that has a reduced thickness in the radial direction and permits to break-off the extensions <NUM> from the receiving part <NUM>". The extensions <NUM> can be removed once the polyaxial bone anchoring device has been inserted and once the extensions are no longer needed, preferably after locking of the head and fixation of the rod.

The pressure member <NUM>" has an upper substantially cylindrical portion <NUM>" and a lower conical portion <NUM>". It differs from the pressure member <NUM>' of <FIG> in that the lower portion <NUM>" comprises a conical outer surface portion <NUM>" that extends in the axial direction up to about the middle of the recesses <NUM> for the actuating portions <NUM>". As in the previous embodiments, the recesses <NUM> are located offset from the center of the legs <NUM> of the pressure member <NUM>" to opposite sides. As can be seen in particular in <FIG>, the head receiving recess <NUM>" may comprise at a distance from the second end 6b an enlarged conical section <NUM> that widens towards the second end 6b. This may facilitate pivoting of an inserted head in the head receiving recess <NUM>' to greater angles.

Referring to <FIG>, the actuating portion <NUM>" comprises the cylindrical main portion <NUM> and the cylindrical eccentric protrusion <NUM> protruding from the inside face 70b of the main portion <NUM> as in the embodiment according to <FIG>. The cylinder axis z of the cylindrical protrusion <NUM> is offset from the axis of rotation R of the main portion <NUM>. On the outside face 70a of the main portion <NUM> a bar <NUM>" is formed that is configured to be engaged by an instrument. The bar <NUM>" preferably extends with its free end portions 71a", 71b" beyond the outside contour of the main portion <NUM>. It functions like a two-armed lever with the pivot axis of the lever being coaxial with the axis of rotation R of the main portion <NUM>. In greater detail, one lever arm 75a extends from the pivot axis to one free end 71a" and the other lever arm 75b extends from the pivot axis to the opposite free end 71b". The bar <NUM>" is oriented such with respect to the eccentric protrusion <NUM> that the longitudinal axis l of the bar <NUM>" is substantially parallel to a line that connects the axis of rotation R of the main portion <NUM> and and the axis of rotation z of the eccentric portion <NUM> in a top view as shown in <FIG>. Hence, the bar <NUM>" is substantially aligned with the eccentric protrusion <NUM>. Moreover, the bar <NUM>" may have a convex outer surface 76a that faces away from the cylindrical main portion <NUM> and a concave inner surface 76b that faces towards the main portion <NUM>. The end portions 71a", 71b" may be somewhat thicker in the direction of the main portion <NUM> to provide more stability to the bar <NUM>". When the actuating portions <NUM>" are inserted in the respective holes <NUM>" of the receiving part <NUM>" and oriented such that the longitudinal axis l of the bar <NUM>" extends substantially perpendicular to the central axis C of the receiving part <NUM>", the end portions 71a", 71b" of the bar <NUM>" touch the outer surface of the receiving part <NUM>" between two recesses <NUM>. When the lever is pivoted, the thickened end portions 71a", 71b" move into the recesses <NUM>. This allows to design the receiving part with the actuating portions more compact. The bar <NUM>" has a first lever surface 71c" and an opposite second lever surface 71d" that are oriented substantially parallel to the axis of rotation R of the main portion <NUM> and that can be engaged by an instrument depending on which one of the surfaces is oriented towards the instrument. The two actuating portions <NUM>" are arranged in the holes <NUM>" of the receiving part <NUM>" such that for one of the actuating portions <NUM>" the first lever surface 71c" faces in the direction of the top end 5a of the receiving part <NUM>" and for the other actuating portion <NUM>" the second lever surface 71d" faces towards the upper end 5a of the receiving part <NUM>".

Referring to <FIG>, an instrument that is suitable for use with the bone anchoring device according to <FIG> will be explained. The instrument comprises a first instrument portion or outer member <NUM> in the form of a substantially tubular part with a front end 1100a and two slits <NUM> each bridged by a bridging portion <NUM>. The slits <NUM> divide the first instrument portion <NUM> into two arms <NUM> which may be slightly flexible such that they can be clipped on the receiving part <NUM>". Each arm <NUM> comprises at the distance from the front end 1100a a recess <NUM> for engagement with the protrusions <NUM>" of the receiving part <NUM>". More specifically, the recesses <NUM> are arranged in the middle of each of the arms <NUM> in the circumferential direction at positions corresponding to positions of the protrusions <NUM>" of the receiving part <NUM>". Hence, when the first instrument part <NUM> is attached to the receiving part <NUM>" and the slits <NUM> are aligned with the substantially U-shaped recess <NUM>, the protrusions <NUM>" can engage the recesses <NUM> to fix the first instrument portion <NUM> to the receiving part <NUM>".

The instrument <NUM> further comprises a second instrument portion or inner member in the form of a pair of rod-shaped pushing members 1230a, 1230b housed in corresponding axially elongate compartments <NUM> to the left and to the right of the recess <NUM> in each of the arms <NUM>. Each pushing member 1230a, 1230b of one arm <NUM> is configured to press onto one of the lever arms 75a, 75b of the actuating portion <NUM>". The compartments <NUM> may be open to the inside and to the outside of the arms <NUM> in the radial direction and the pushing members are guided in the compartments <NUM>. Moreover, the compartments <NUM> are at such a position that the pushing members 1230a, 1230b are configured to press onto the respective lever arm 75a, 75b at a region close to the corresponding end portion 71a", 71b" of the bar <NUM>", respectively. An end portion <NUM> of each of the pushing members may have a convex outer surface to ensure contact with the lever surface 71c", 71d" in various pivot positions of the bar <NUM>". Each pushing member 1230a, 1230b on each arm <NUM> is movable in the axial direction from a first position in which it does not touch the bar <NUM>" of the actuating portion <NUM>" to a second position in which the end portion <NUM> touches one of the lever arms 75a, 75b of the bar <NUM>". In addition, the each pushing members 1230a, 1230b is movable from the second position to the first position by the action of the other lever arm that pushes back the pushing member.

As shown in <FIG>, the instrument <NUM> comprises a mechanism <NUM> for selectively actuating one of the pushing members 1230a, 1230b on each arm <NUM> from the first position downward in the axial direction to press onto the lever arm 75a, 75b associated with that pushing member. At the same time, the other pushing member on this arm is moved upward by the pressure exerted by the respective other lever arm. Specifically, the mechanism <NUM> may include a lever <NUM> which has two positions associated with the first and second positions of the pushing members.

<FIG> shows the pressure member <NUM>" in the locking position of the head <NUM> in which the conical outer surface <NUM>" of the pressure member <NUM>" engages the tapering inner surface 50c" of the receiving part <NUM>" whereby the pressure member <NUM>" is compressed around the head <NUM>. The pushing member 1230a on the left side is pushed down and simultaneously the corresponding pushing member 1230a on the right side of the other arm (which is not shown in the cross- sectional view) is pushed down to press on the respective lever arms 75a. It shall be noted that due to the relatively small overlap of the conical outer surface <NUM>" of the pressure member with the tapering inner surface 50c" of the receiving part <NUM>", a relatively small force for unlocking is necessary.

As shown in <FIG>, when one of the pushing members 1230a of one arm <NUM> is pushed down to press on the corresponding lever arm 75a, the actuating portion <NUM>" rotates in the clockwise direction and the eccentric protrusion <NUM> moves the pressure member <NUM>" downward, i. towards the second end 5b of the receiving part which results in locking of an inserted head. Thereby, the other one of the pushing members 1230b is moved upwards by the other lever arm 75b. As depicted in <FIG>, when the other one of the pushing members 1230b is moved downward, it presses on the other lever arm 75b to rotate the actuating member <NUM>" in the counterclockwise direction which results in moving the pressure member <NUM>" upward. As a result, an inserted head can be unlocked. It shall be noted that, due to the inverted mounting of the other actuating portion <NUM>" in the other hole <NUM>" of the receiving part <NUM>", the actuating portion provided on the other leg <NUM> of the receiving part <NUM>" rotates in each case in the opposite direction.

Hence, the locking and unlocking can be associated with a specific configuration of the actuating mechanism <NUM> of the instrument. Preferably, pressing the lever arm <NUM> may be associated with locking of the head <NUM> and releasing the pressing of the lever arm <NUM> may be associated with unlocking of the head. In use, the instrument can be snapped onto the receiving part until the protrusions <NUM>" engage the corresponding recesses <NUM> provided on the arm <NUM>. Thereafter, the pushing members can be actuated to lock an inserted head <NUM> and to unlock an inserted head <NUM>. This procedure can be carried out several times.

Modifications of the embodiments described are possible. The features of one embodiment can also be combined with those of another embodiment to produce a variety of still further embodiments. The parts are not limited to their detailed shape as depicted in the embodiments.

For example, the bone anchoring device is shown to be a bottom-loading bone anchoring device where the head <NUM> is inserted from the second or lower end into the receiving part. The bone anchoring device may, however, be a top-loading bone anchoring device where the bone anchor is inserted from the first end or top end into the receiving part. In such a case, the pressure member may have a slightly different design in that it covers the upper portion of the head and presses the head against a seat provided in the receiving part. In a further modification, only one actuating portion is present.

For the bone anchor all kinds of bone anchors such as screws, nails, hooks, etc. may be used.

Claim 1:
A coupling device for coupling a rod to a bone anchor (<NUM>), the coupling device comprising:
a receiving part (<NUM>, <NUM>', <NUM>") configured to receive a head (<NUM>) of the bone anchor (<NUM>), the receiving part (<NUM>,<NUM>', <NUM>") having a first end (5a) and a second end (5b), a central axis (C) extending through the first end (5a) and the second end (5b), and two legs (<NUM>) defining a recess (<NUM>) at the first end for receiving the rod; and
a pressure member (<NUM>, <NUM>', <NUM>") arranged in the receiving part (<NUM>, <NUM>', <NUM>") to exert pressure on the inserted head (<NUM>) of the bone anchor (<NUM>),
an actuating portion (<NUM>, <NUM>', <NUM>") configured to act on the pressure member (<NUM>, <NUM>', <NUM>"),
wherein the actuating portion (<NUM>, <NUM>', <NUM>") is configured to rotate at least partially around an axis of rotation (R) that extends at an angle relative to the central axis (C) to move the pressure member (<NUM>, <NUM>', <NUM>") from a non-locking position in which the inserted head (<NUM>) is pivotable in the receiving part (<NUM>, <NUM>', <NUM>") to a locking position in which the inserted head (<NUM>) is clamped,
characterized in that the actuating portion is configured to rotate when a force in the direction of the central axis (C) is applied thereto.