Patent Description:
A polyaxial bone anchoring device includes a coupling device and a bone anchoring element with a head that is pivotably received in the coupling device and that can be locked at various angles of the bone anchoring element relative to the coupling device. The coupling device also receives a rod that is configured to connect the polyaxial bone anchoring device to a further bone anchor. For example, <CIT> describes a polyaxial bone anchoring device comprising a receiver member that includes an open bottom, a first locking member and a first sidewall. The open bottom receives a shank having a substantially spherical head. The first sidewall has a first recess which is configured to receive the first locking member. The first locking member is slideable within the first recess and is configured to press-fittingly engage the substantially spherical head. In addition, there is a second press-fit locking mechanism for engaging the rod such that the head of the shank and the rod can be locked independently.

<CIT> describes a bone anchoring device including a receiving part for receiving a rod and an anchoring element having a head positionable within the receiving part. The bone anchoring device further has a locking device that protrudes from an inner wall of the receiving part and engages with a recessed surface portion of the head of the anchoring element, such that the anchoring element is pivotable relative to the receiving part around a single axis of rotation.

<CIT> describes a two-piece closure for polyaxial bone screws including an outer fastener and an inner set screw, the outer fastener having a drive system with pockets that cooperate with a pronged drive tool. The polyaxial screw includes a lower pressure insert engaged with the outer fastener, the insert in some embodiments being made from a cobalt chrome alloy.

<CIT> describes a pedicle screw assembly comprising a screw having a threaded portion and a head portion, a tulip body configured to be positioned on the head portion, a tulip saddle configured to be coupled to the tulip body within the tulip body, and at least one wedge member configured to be inserted between the tulip saddle and the tulip body. The tulip saddle has an upper portion and a lower portion, the lower portion being configured to retain the tulip saddle on the head portion and the upper portion being configured to retain a rod.

It is the object of the invention to provide a coupling device for coupling a bone anchoring element to a rod and a polyaxial bone anchoring device which such a coupling device in which the coupling device is improved and/or is an alternative compared to conventional coupling devices, in particular wherein the coupling device has an easily accessible and/or easily operated locking mechanism for the head.

The object is solved by a coupling device according to claim <NUM>. Further developments are given in the dependent claims.

According to embodiments, the coupling device for coupling a rod to a bone anchoring element, includes a receiving part comprising a first end and a second end, an accommodation space at or close to the second end for pivotably holding a head of the bone anchoring element therein, a recess for receiving the rod, the recess defining a rod channel axis, and a central axis extending through the first end and the second end around which the head is configured to pivot in the accommodation space, the central axis defining an axial direction. The coupling device further includes a pressure member positionable in the receiving part such that the pressure member extends at least partially into the accommodation space for exerting pressure onto an inserted head and a locking member movable relative to the receiving part in the axial direction between a first position in which the head is insertable into the accommodation space and a second position in which the head is at least temporarily locked in the accommodation space by the locking member, wherein the locking member is configured to exert pressure onto the head only from one side in a direction different from the axial direction and wherein the pressure member comprises a recess and wherein the locking member is configured to act onto an inserted head through the recess of the pressure member.

The coupling device permits a provisional locking of the head without a rod being placed in the rod channel of the coupling device. In addition, the head can also be locked with the locking member when the rod is at a higher place than at the bottom of the rod channel. Thus the head can be locked independently from the rod. Moreover, such a provisional locking can be achieved while a position of an inserted rod is still variable. It is not necessary to have a set screw or another fixation member placed to fix the rod. Hence, the coupling device may be particularly applicable to such polyaxial bone anchoring devices that use a set screw or another fixation member to fix the position of the rod and to finally lock the head in the receiving part as a whole.

A polyaxial bone anchoring device includes the coupling device and a bone anchoring element with a head that is pivotably received in the accommodation space.

With the coupling device correction steps during surgery that require a change of the angle of the bone anchoring element relative to the coupling device and/or a change of the position of the rod can be carried out several times.

The locking member may be easily accessible and/or easily operated by an instrument that can engage the locking member from outside.

The polyaxial bone anchoring device may be a bottom-loading polyaxial bone anchoring device in which the head of the bone anchoring element is inserted from the bottom end of the receiving part. Alternatively, the polyaxial bone anchoring device may be a side-loading polyaxial bone anchoring device in which the head of the bone anchoring element is inserted from a side of the receiving part. Lastly, it may be also conceivable that the head of the bone anchoring element is inserted from the top of the receiving part, thus forming a top-loading polyaxial bone anchoring device. Hence, the coupling device may be implemented in various designs.

With the term "rod" an elongate member is that is intended to connect two or more anchoring devices. In one embodiment, the rod may be a straight stiff part that is suitable to be used as a stabilization member. In other embodiments, the rod may have various shapes and/or varying cross-section along its length and/or may be stiff or more flexible and/or may be curved.

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

A polyaxial bone anchoring device according to a first embodiment which is generally shown in <FIG> includes a bone anchoring element <NUM> in the form of a screw member having a shank <NUM> with a threaded portion and a head <NUM>. The head <NUM> may have a spherically-shaped outer surface portion including a greatest outer diameter E. A shank axis S is defined by the longitudinal axis or screw axis of the shank <NUM>. On its free end 3a the head <NUM> may have a recess <NUM> for engagement with an instrument. The bone anchoring device further includes a coupling device for connecting the bone anchoring element <NUM> to an elongate stabilization member, such as a rod <NUM>. The coupling device comprises a receiving part <NUM>, a pressure member <NUM> and a locking member <NUM>. For securing the rod <NUM> in the receiving part <NUM> and for exerting pressure onto the pressure member <NUM>, a fixation device <NUM>, for example a set screw, which cooperates with the receiving part <NUM>, may be provided in addition.

The receiving part <NUM> is substantially cylindrical preferably a monolithic part and has a first or top end 5a, a second or bottom end 5b and a passage <NUM> extending from the top end 5a towards the bottom 5b, the passage <NUM> defining a longitudinal central axis C. At the bottom end 5b, the passage <NUM> forms an opening <NUM> which opening <NUM> has a width that is greater than a greatest width of the head <NUM> such that the head <NUM> of the bone anchoring element <NUM> is insertable through the opening <NUM>. Adjacent to the opening <NUM>, the passage <NUM> has a narrowing section 51a which narrows, for example conically, towards the bottom end 5b. The narrowing section 51a is configured to cooperate with a portion of the pressure member <NUM> such that a compressive force can be exerted via the pressure member <NUM> onto an inserted head <NUM>. A widened section 51b follows the narrowing section 51a in the direction of the top end 5a. The widened section 51b is dimensioned such that a portion of the pressure member can expand therein to permit the head <NUM> to enter. Thus, at least the widened section 51b forms an accommodation space that is configured to accommodate the head <NUM> and also a portion of the pressure member <NUM>. Adjacent to the widened section 51b an small narrowing transition section 51c may be formed that narrows towards the remaining sections of the passage <NUM> up to the top end 5a which are sized such that the pressure member <NUM> can move therein in an axial direction. Adjacent to the top end 5a, an internal thread <NUM> is formed that is configured to cooperate with the fixation device <NUM> that comprises a cooperating thread. The threads of the receiving part <NUM> and of the fixation device <NUM>, respectively, may be threads that reduce or eliminate radial forces during tightening of the fixation device <NUM>, such as a square thread, for example.

Moreover, a substantially U-shaped recess <NUM> is formed at the top end 5a and extends to a distance therefrom. The substantially U-shaped recess <NUM> divides the upper portion of the receiving part <NUM> into two free legs <NUM> and forms a channel for receiving the rod <NUM>. A longitudinal axis or rod channel axis L of the substantially U-shaped recess <NUM> is coincident with a longitudinal axis of a straight rod <NUM> when the rod lies in the rod channel. On one side of the channel, a groove or pocket <NUM> is formed in the wall of the receiving part <NUM> that extends from a bottom 54a of the U-shaped recess <NUM> in the direction of the second end 5b up to a distance from the second end 5b. In greater detail, the pocket <NUM> extends substantially up to the lower edge of the widened section 51b as best seen in <FIG>. Preferably, the pocket <NUM> is shaped so as to receive a portion of the locking member <NUM> as described below. More specifically, the pocket <NUM> comprises a broader first section 56a for receiving a broader portion of the locking member <NUM> and a narrower second section 56b that is closer to the second end 5b for receiving a narrower section of the locking member <NUM>. The depth of the pocket <NUM> is such that the locking member <NUM> can reach the head <NUM> to exert pressure onto the head <NUM>. For limiting the path of axial movement of the locking member <NUM>, an elongate hole <NUM> that is elongate in the direction of the central axis C is provided that extends transversely from the pocket <NUM> to the outside of the receiving part <NUM>. The elongate hole <NUM> is configured to receive a pin connected to the locking member <NUM> that is configured to abut against the upper or lower end of the elongate hole <NUM> when the locking member <NUM> is moved.

In addition, the pocket <NUM> is open to the accommodation space by means of an axial recess <NUM> that extends from the bottom 54a of the U-shaped recess <NUM> substantially up to the narrowing section 51a of the passage <NUM>. Through the axial recess <NUM> a head-contacting surface of the locking member <NUM> can extend to contact an inserted head <NUM>. At the side of the pocket <NUM>, a portion <NUM> of the receiving part adjacent to the legs <NUM> has been cut away to provide space for the locking member <NUM>, such that, when the locking member <NUM> is assembled with the receiving part <NUM> an outer contour of the receiving part in the region of the legs <NUM> is not substantially greater on the side of the locking member than on the opposite side.

To secure the pressure member <NUM> against rotation within the receiving part <NUM> a rotation securing device is provided. The rotation securing device may comprise a through-hole <NUM> in the center of each leg <NUM> seen in the circumferential direction which through holes <NUM> are configured to receive pins 500a, respectively. A tool or instrument engagement portion <NUM>, such as a circumferential groove, can be optionally provided at the legs <NUM> to allow engagement of the receiving part <NUM> with an instrument. Lastly, the receiving part may comprise a structure for securing an insertion position of the pressure member <NUM> in the receiving part <NUM> in which the head <NUM> is insertable and a pre-locking position of the pressure member <NUM> in the receiving part <NUM> in which an inserted head <NUM> cannot be removed. The structure may comprise a first stop <NUM>, for example in the form of a circumferential groove below the thread <NUM> at an inner wall of the legs <NUM> to secure the insertion position and a second stop <NUM> below the first stop <NUM> to secure the pre-locking position.

Referring in addition to <FIG>, the pressure member will be explained in greater detail. Preferably, the pressure member <NUM> is a monolithic piece. It has a first or top end 6a and a second or bottom end 6b and may be substantially cylindrical with an outer diameter that allows it to move in the passage <NUM> of the receiving part <NUM>. At the top end 6a, a rod receiving recess <NUM> is formed that provides a rod support surface 61a. The rod support surface may have a substantially V-shaped cross-section with a longitudinal axis extending substantially perpendicular to the cylinder axis of the pressure member <NUM> which coincides with the central axis C of the receiving part <NUM> when the pressure member is in the receiving part <NUM>. A depth of the rod receiving recess <NUM> may be smaller than a diameter of the rod <NUM>. Hence, when the rod <NUM> rests on the support surface 61a, it projects over the top end 6a of the pressure member <NUM> as shown for example in <FIG>. The V-shape of the rod support surface 61a permits to use rods with different diameters.

Moreover, the rod receiving recess <NUM> is shaped such that two free legs <NUM> are formed. that may be separated from the rod support surface 61a on each side by a groove <NUM>. By means of this, the legs <NUM> are slightly flexible in a direction transverse to the longitudinal axis of the rod support surface 61a. A free end of the legs <NUM> may have a radially protruding rim 62a an upper surface of which forms the first end 6a of the pressure member. The rim 62a is configured to engage the grooves <NUM>, <NUM> provided at the inner surface of the legs <NUM> of the receiving part <NUM> to secure the insertion position or the pre-locking position of the pressure member <NUM> in the receiving part <NUM>. At the center of each of the legs <NUM> an axially extending elongate through-hole <NUM> is provided that serves for receiving the pins 500a shown in <FIG>.

Adjacent to the bottom end 6b of the pressure member <NUM> an outer surface portion <NUM> may be tapered, preferably conically-shaped, which is configured to cooperate with the narrowing section 51a of the receiving part <NUM>. Further, a hollow head receiving portion <NUM> is formed in the pressure member <NUM> that defines an opening <NUM> at the second end 6b for inserting the head <NUM>. The head receiving portion <NUM> may have a lower and an upper substantially spherical section 66a, 66b that are shaped so as to matingly receive the spherical head <NUM>. An intermediate section 66c has a greater inner diameter for facilitating the insertion of the head <NUM>. In addition, a plurality of recesses <NUM> are formed that extend completely through the pressure member <NUM> into the widened section 66b and which are open to the second end via substantially axially extending slits 68a. The recesses <NUM> may have an inverted drop shape with the broader portion facing towards the second end 6b. The recesses <NUM> and the slits 61a are configured to spread when the head <NUM> is inserted. A particular recess 68b of the recesses <NUM> is circumferentially aligned with the rod support surface 61a. In general, the number, shape and size of the recesses <NUM> are selected such that a desired flexibility is achieved that allows to insert the head <NUM> through the second end until it is received in the head receiving portion <NUM>. Moreover, the size of the head receiving portion <NUM> may be such that the head <NUM> can be held therein by friction before a locking is effected. When the head <NUM> is inserted into the head receiving portion <NUM>, a part of the surface of the head <NUM> extends slightly through the particular recess 68b that is aligned with the rod support surface 61a as shown, for example, in <FIG>, <FIG>.

Moreover, an axial recess <NUM> is formed in the outer surface of the pressure member <NUM>, which extends from one end of the rod support surface 61a into the particular recess 68b of the recesses <NUM> of the head receiving portion <NUM>. The recess <NUM> is shaped so as to receive and/or guide a head contacting portion of the locking member <NUM> therein such that the head contacting portion of the locking member <NUM> is able to contact an inserted head <NUM>.

Lastly, a coaxial bore <NUM> extending through the rod support surface <NUM> into the head receiving section <NUM> permits access to the head with an instrument.

Referring in addition to <FIG>, the locking member <NUM> is a substantially U-shaped sliding piece. Preferably it is a monolithic piece with a first or upper end 7a and a second or lower end 7b, an outer side and an opposite inner side in relation to the receiving part <NUM> when the locking member <NUM> is mounted thereto. A substantially U-shaped recess <NUM> having a bottom 71a defines two upstanding legs <NUM>. The size of the substantially U-shaped recess <NUM> is such that when the locking member <NUM> is mounted to the receiving part <NUM> and moved to a lowermost position, the free end of the legs <NUM> is substantially flush with the top end 5a of the receiving part and the rod <NUM> fits into the U-shaped recess <NUM> of the locking member <NUM>.

From the bottom 71a a base portion <NUM> extends that is configured to be slidably received in the pocket <NUM> of the receiving part <NUM>. A first or upper portion 73a of the base portion <NUM> is broader and is configured to be received at least partially in the first portion 56a of the pocket <NUM> and a second or lower portion 73b is narrower and is configured to be received in the second portion 56b of the pocket <NUM>. The left and right ends of the pocket <NUM> and the base portion <NUM> may be rounded. In addition, the outer ends of the first portion 56a of the slot and of the first portion 73a of the base portion <NUM> may be conically widening towards the bottom end 5a of the receiving part <NUM> and the bottom end 7a of the locking member <NUM>, respectively. Between the first portion 73a and the second portion 73b of the base portion <NUM> a shoulder <NUM> is formed.

An outer surface <NUM> of the base portion 73a and an opposite inner surface <NUM> may be substantially flat. At the inner surface <NUM> a protrusion <NUM> is formed that projects into the passage <NUM> of the receiving part <NUM> when the locking member <NUM> is mounted to the receiving part <NUM>. The protrusion <NUM> has a substantially rectangular contour that mates an inner contour of the recess <NUM> in the receiving part <NUM>. An upper end 77a of the protrusion <NUM> may be concavely shaped and flush with the bottom 71a of the U-shaped recess <NUM>. The surface 77b of the protrusion forms a head contacting surface of the locking member <NUM>. Hence, the thickness of the protrusion <NUM> is such that when the locking member <NUM> is mounted to the receiving part <NUM> and the protrusion <NUM> has entered the recess <NUM> at the receiving part <NUM> and the recess <NUM> at the pressure member, it can contact the head <NUM> which partially extends through the particular recess 68b of the pressure member <NUM>.

Above the base <NUM> in the direction to the top end 7a the legs <NUM> each comprise a thickened portion <NUM> with a substantially a cylindrical outer surface portion and a chamfered portion 78a towards the top end 7a. The size of the thickened portion <NUM> and the chamfered portion 78a is such that when the locking member <NUM> is mounted to the receiving part and is in the lowermost position, the outer surface of the thickened portion <NUM> is substantially flush with the outer surface of the legs <NUM> of the receiving part <NUM>. On the outer side each leg <NUM> comprises an engagement portion <NUM> that protrudes in a mounted state of the locking member in the longitudinal direction of the recess <NUM>. The engagement portion <NUM> may be located in the region of the thickened portion <NUM> of the legs <NUM>. In the example shown, the engagement portions <NUM> have a substantially square shaped cross-section that may sloghtly increase towards the free end. However, any other shape that is suitable for engagement with an instrument may be contemplated.

Lastly, at a distance from the bottom end 7b, a hole <NUM> may be provided in the outer surface of the second portion 73b of the base portion <NUM> which is configured to receive a pin 700a. The pin 700a is configured to protrude into the elongate hole <NUM> of the receiving part <NUM>.

The parts and portions of the bone anchoring device may be made of any material, preferably however of titanium or stainless steel or any bio-compatible metal or metal alloy or plastic material. As 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, polyether ether ketone (PEEK) or poly-L-lactide acid (PLLA). The parts can be made of the same or of different materials from another.

In operation, the locking member <NUM> is configured to assume at least a first position which may be a non locking position, for example an insertion position, and a second position which may be a locking position. In the insertion position the locking member is in an uppermost position where the pin 700a abuts against the upper end of the elongate recess <NUM> of the receiving part <NUM>. In this case, the protrusion <NUM> of the locking member <NUM> does not lock an inserted head <NUM>. In the locking position, the locking member <NUM> is in a lowermost axial position in which the head contacting surface 77b of the protrusion <NUM> is configured to contact an inserted head <NUM> such that it exerts pressure onto an inserted head <NUM> that locks the head <NUM> in the accommodation space. In the locking position, the pin 700a may abut against the lower end of the elongate recess <NUM> of the receiving part <NUM> or may be close to the lower end of the recess <NUM>. The locking member <NUM> may assume a plurality of further axial positions with increasing pressure onto an inserted head <NUM> when the locking member <NUM> is moved from the insertion position to the locking position.

Referring to <FIG> the operation and function of the coupling device will be explained. It shall be noted that the rod is not inserted, i.e. all locking and unlocking steps where the locking member <NUM> is actuated can be carried out without a rod being present in the rod channel. In use, the bone anchoring element <NUM> may be inserted first into a prepared hole in bone or in a vertebra and the receiving part <NUM> with the pre-assembled pressure member <NUM> and the pre-assembled locking member <NUM> is mounted to the head <NUM> as shown in <FIG>. Alternatively, the polyaxial bone anchoring device is pre-assembled in such a manner that the receiving part with the pressure member <NUM> and the locking member <NUM> is already mounted onto the head <NUM>.

For assembling the polyaxial bone anchoring device, the head <NUM> is inserted from the lower end 5a of the receiving part <NUM> while the pressure member <NUM> is at an uppermost insertion position where the upper rim 62a abuts against the upper edge of the groove <NUM> as shown in <FIG>. When the head <NUM> enters through the lower opening <NUM> into the receiving part and further into the head receiving portion <NUM> of the pressure member <NUM>, the lower portion of the pressure member <NUM> is expanded in the widening section 51c of the accommodation space of the receiving part <NUM> and the pressure member <NUM> snaps onto the head <NUM> as shown in <FIG>. During this step, the locking member <NUM> is in the uppermost position in which the pins 700a abut against the upper end of the elongate hole <NUM> of the receiving part <NUM>.

As shown in <FIG>, the pressure member is then moved downward, i.e. towards the bottom end 5b of the receiving part <NUM> until the tapered external surface portion <NUM> of the pressure member <NUM> engages the narrowing portion 51a of the receiving part <NUM>. Thereby, the lower opening <NUM> of the receiving part <NUM> is reduced by the pressure member <NUM>, so that the head <NUM> cannot be removed from the receiving part. When the upper rim 62a of the pressure member engages the groove <NUM> of the receiving part <NUM> and abuts against the upper edge thereof, this pre-locking position of the pressure member <NUM> is secured. The locking member <NUM> is still in the insertion position.

Next, as shown in <FIG>, the locking member <NUM> is moved downward, for example by engaging the engagement portion <NUM> with an instrument (not shown) while the protrusion <NUM> of the locking member <NUM> is guided in the recess <NUM> of the pressure member <NUM>. The head contacting surface 77b of the protrusion <NUM> contacts the head <NUM> a portion of which extends through the particular recess 68b of the pressure member <NUM> and exerts pressure from one side onto the head <NUM>. When the head contacting surface 77b is configured to press onto the head <NUM> from the side at a position that may be approximately the region with the greatest outer diameter E of the head <NUM>, the head <NUM> is locked in the pressure member <NUM> and consequently in the receiving part <NUM>.

As depicted in <FIG>, when the pin 700a does not yet abut against the lower end of the elongate recess <NUM> of the receiving part <NUM>, the head <NUM> may already be contacted by the head contacting surface 77b of the locking member <NUM> but is still pivotable. As depicted in <FIG>, further downward movement of the locking member <NUM> until the pin 700a abuts against the lower end <NUM> of the receiving part <NUM>, increases the force upon the head <NUM> such that the head <NUM> is locked in this position. By moving the locking member <NUM> in the opposite direction, i.e. upwards in this embodiment, the head <NUM> can be unlocked. While only a position is shown in which the shank axis S is coincident with the central axis C, it shall be understood that the head <NUM> can be locked at a variety of angles relative to the receiving part <NUM>.

A second embodiment of the polyaxial bone anchoring device with a second embodiment of the coupling device and the use thereof is shown in <FIG>. Parts and portions of the second embodiment that are identical or highly similar to the parts and portions of the first embodiment are designated with the same reference numerals and the description thereof is not repeated. The receiving part <NUM>' and the locking member <NUM>' form together a receiving part consisting of two parts. In particular, the locking member <NUM>' forms a part of the wall defining the accommodation space for the head <NUM> inside the receiving part. In this manner, the coupling device may be a side-loading coupling device in which the head <NUM> of the bone anchoring element can be inserted from the side into the accommodation space, that means the insertion direction is transverse to the central axis C. Alternatively, the coupling device may be a top-loading coupling device in which the head <NUM> of the bone anchoring element may be inserted through the top end 5a. The receiving part <NUM>' forms a seat for the head and the pressure element <NUM>' is configured to exert pressure only from above onto the head <NUM>.

Referring to <FIG>, the receiving part <NUM>' comprises a widening portion 51a' that widens towards the bottom end 5b. This allows the shank <NUM> to pivot to a sufficiently large angle. Following the widening section 51a', a spherical portion 51b' is formed that has a smaller diameter than the greatest diameter of the head at the junction to the widening portion 51a'. By means of this, the spherically-shaped portion 51b' forms a seat for the head <NUM> in which the head <NUM> is configured to pivot. It shall be noted that any other shape of the seat may be contemplated that allows the head to pivot therein. The spherically-shaped portion 51b' is followed in the direction of the top end 5a by a first substantially cylindrical section 51c' with a greater inner diameter than an outer diameter of the head <NUM>. More specifically, the substantially cylindrical section 51c' serves for accommodating a part of the pressure member <NUM>' when the pressure member is mounted to the receiving part <NUM>'. Between the first substantially cylindrical section 51c' and the region of the internal thread <NUM>, the passage comprises a second substantially cylindrical section 51d' that has a slightly smaller inner diameter than the first substantially cylindrical section 51c' such that a step 51e' is formed there-between. The step may serve as a stop for the pressure member <NUM>' to secure the pre-locking position. The two substantially cylindrical sections 51c' and 51d' serve for receiving the pressure member <NUM>' in such a manner that a portion of the pressure member <NUM>' can slightly expand in the greater section 51c'.

In addition, the receiving part <NUM>' a portion of the receiving part <NUM>' is cut away in a plane extending parallel to the central axis C and perpendicular to the rod channel axis L. As a result thereof, an opening <NUM>' is provided which extends transverse to the rod channel axis L at a distance from the central axis C. The opening <NUM>' extends in an axial direction through the accommodation space comprising the spherical section 51b' and the two cylindrical sections 51c' and 51d' until it joins the U-shaped recess <NUM>. Moreover, at the side of the legs <NUM>' that faces towards the opening <NUM>' each leg has a cut away portion <NUM>' that extends from the top end 5a towards the bottom end 5b that forms an acute angle undercut or a V-shaped groove <NUM>' with the remaining outer surface <NUM>' that faces in the rod channel direction. The undercut <NUM>' serves as a guiding structure for the locking element <NUM>'. At a distance from the second end 5b the outer surface <NUM>' ends so that a step <NUM>' is formed. This may facilitate placement of the locking member <NUM>' onto the receiving part <NUM>'.

At a distance from the step 51e' that is exposed to the outside at the edge of the opening <NUM>', towards the top end 5a, there may be a recess <NUM>' at the edge of the opening <NUM>'. The recess <NUM>' serves for securing an insertion position of the pressure member <NUM>'. Moreover, at the outer surface of the legs <NUM>', an instrument engagement recess <NUM>' may be formed in each leg that may be open to the cut away portion <NUM> and may have a rounded end in the circumferential direction towards the opposite side of each leg <NUM>'.

Referring further to <FIG>, the pressure member <NUM>' is a substantially cylindrical part, preferably a monolithic part, with a top end 6a and an opposite bottom end 6b and a recess <NUM>' at the top end that provides a rod support surface 61a'. In this embodiment, the pressure member <NUM>' lacks the legs that extend to the right and the left of an inserted rod. In other words, the rod support surface 61a' extends to a position well below the greatest outer diameter of a rod <NUM> placed on the rod support surface 61a'. From the bottom end 6b a substantially spherically-shaped recess <NUM>' extends in the direction of the top end 6a. The recess <NUM>' is configured to contact an inserted head <NUM> to exert pressure onto the head <NUM> only from above a region with the greatest outer diameter.

At one side of the rod support surface 61a', an axially and circumferentially extending recess <NUM>' is formed that allows a portion of the locking member <NUM>' to slide there along. The circumferential width of the recess <NUM>' may substantially correspond to the circumferential width of the rod support surface 61a' or may be slightly larger as shown in <FIG>. At the position of the recess <NUM>', a portion of the pressure member <NUM>' is cut away between the bottom end 6b and a lower edge 69a' of the recess <NUM>' such that, in this region, the pressure member <NUM>' is shorter in the axial direction to permit the locking member <NUM>' to contact the head <NUM>. At both sides of the recess <NUM>' a horizontal i.e. a circumferentially extending slit <NUM> is formed that extends from the axial edges 69a' of the recess <NUM>' in a circumferential direction to such an extent that two free arms <NUM> are formed the lower edge of which defines the second end 6b of the pressure member 6b. Hence, the free arms <NUM> have the shape of substantially a cylinder shell section. The arms <NUM> may have an outwardly directed end portion 611a. By means of the recess <NUM>, the arms <NUM> are slightly flexible in a direction away and towards the central axis C. For example, when the pressure member <NUM>' is inserted into the receiving part <NUM>', the arms <NUM> may be compressed for the purpose of insertion, such that the end portions 611a are at least partially moved into the recesses <NUM>, respectively. When the arms <NUM> spread, the can create a tension that holds the pressure member in position. The pressure member <NUM>' also comprises a coaxial bore <NUM> that permits access to an inserted head <NUM>.

Referring in addition to <FIG>, the locking member <NUM>" is a substantially U-shaped sliding piece or slider. Preferably it is a monolithic piece with a first or upper end 7a and a second or lower end 7b, an outer side and an opposite inner side in relation to the receiving part <NUM>' when the locking member <NUM>' is mounted thereto. From the top end 7a a substantially U-shaped recess <NUM>' extends to a distance from the second end 7b. The substantially U-shaped recess has a width and a depth such that when the locking member <NUM>' is mounted to the receiving part <NUM>' and is in a locking position the bottom 71a of the U-shaped recess is located slightly below an inserted rod <NUM> as shown in <FIG>. Hence, by means of the U-shaped recess <NUM>' two free legs <NUM>' are formed. A outer surface <NUM>' that faces towards the outside of the receiving part <NUM>' may be substantially flat. Side surfaces <NUM>' to the left and to the right of the outer surface <NUM>' may be substantially cylindrical to correspond to the cylindrical outer surface of the receiving part <NUM>'.

The inner surface <NUM>' that faces towards the receiving part <NUM>' when the locking member <NUM>' is mounted is substantially flat. In the inner surface <NUM>', a recess <NUM>' extends from the top end 7a towards the bottom end 7b which leaves two axially extending flat portions 76a' in the inner surface adjacent to the sidewalls <NUM>', respectively. The flat portions 76a' are configured to abut against the cut away portions <NUM>' of the receiving part. The recess <NUM>' forms at the left and the right axial edge acute angle undercut portions or axially extending V-shaped grooves 77a' that are configured to engage the undercut portions <NUM>' of the receiving part. By means of this, the locking member <NUM>' is guided axially when mounted to the receiving part <NUM>'. From the bottom 71a' of the substantially U-shaped recess <NUM>' a shallow depression or groove <NUM>' extends up to the bottom end 7b which widens in the axial direction towards the bottom end 7b. The groove <NUM>' has a decreasing depth in the direction from the bottom end 7b towards the top end 7a as particularly depicted in <FIG>. When the locking member <NUM>' is mounted to the receiving part <NUM>' the groove <NUM>' forms a head contacting surface. Hence, with the decreasing depth, the groove <NUM>' forms a wedge with respect to exerting pressure onto the head. Also in this embodiment, like in the first embodiment, the pressure is exerted by the locking member <NUM>' onto an inserted head from one side.

Between the bottom end 7b and the groove <NUM>' a chamfered section 78a' may be formed that facilitates engagement with the head <NUM>. At each of the legs <NUM>' at a distance from the top end 7a a tool or instrument engagement recess <NUM>' may be formed, for example in the form of an axial recess or cutout. The tool engagement recess <NUM>' may be substantially at the same axial position as the tool engagement recess <NUM>' of the receiving part <NUM>, when when the locking member <NUM>' is mounted to the receiving part <NUM>' and when it is in the locking position.

Referring to <FIG>, the assembly of the polyaxial bone anchoring device will be explained. As shown in <FIG>, the pressure member <NUM>' is inserted from the top end 5a into the receiving part <NUM>'. Then, as shown in <FIG>, the pressure member <NUM>' is moved downward until the free ends 611a of the arms <NUM> snap in the recess <NUM>' of the receiving part <NUM>' to secure an insertion position for the head <NUM>. In this position of the pressure member <NUM>' relative to the receiving part <NUM>', the locking member <NUM>' is mounted from the top end 5a of the receiving part <NUM>' as shown in <FIG>. To mount the locking member <NUM>', the undercut portions 77a' of the locking member <NUM>' engage the undercut portions <NUM>' of the receiving part <NUM>' such that the locking member <NUM>' can slide downward in a guided manner. As shown in <FIG>, when the locking member <NUM>' is moved only to such a distance from the bottom end 5b of the receiving part <NUM>' that the head <NUM> can be inserted from the side through the opening <NUM>' into the accommodation space.

Next, once the head <NUM> has been inserted as shown in <FIG> and <FIG>, the pressure member <NUM>' is moved downward until the free ends 611a of the arms <NUM> snap under the step 51e' as shown in.

In this position of the pressure member <NUM>' relative to the receiving part <NUM>', the head can no longer be removed through the opening <NUM>'. Thus, the position shown in <FIG> shows a pre-locking position of the pressure member <NUM>'. For locking the head <NUM>, the locking member <NUM>' is then moved further downward as shown in <FIG>. Thereby, the shallow depression <NUM>' in the locking member <NUM>' engages the head <NUM> as shown in <FIG>. Due to the decreasing depth of the groove <NUM>', the pressure onto an inserted head <NUM> increases. In the lowermost position of the locking member <NUM>' as shown in <FIG> and <FIG>, the compression force of the locking member <NUM>' is such that the head <NUM> is locked.

<FIG> show a third embodiment of a polyaxial bone anchoring device and a third embodiment of the coupling device. Parts and portions that are identical or highly similar are indicated with the same reference numerals as the previous embodiments and the description thereof will not be repeated.

The third embodiment of the coupling device differs from the second embodiment by the locking member <NUM>" that is configured to be mounted from the bottom end of the receiving part. In addition, the head of the bone anchoring element can be inserted from the bottom end into the accommodation space of the receiving part.

Referring to <FIG>, the passage <NUM>" receiving part <NUM>" comprises a narrowing portion 51a" similar to the receiving part <NUM> of the first embodiment which is adjacent to the second end 5b. Following the narrowing portion 51a" a widened portion 51b" is present that receives a portion of the pressure member <NUM>" with the head therein. The widened portion 51b" forms an accommodation space for the head <NUM> and the pressure member <NUM>". The passage <NUM>" then narrows to a substantially cylindrical portion 51c" that is configured to accommodate an upper part of the pressure member <NUM>". Similar to the second embodiment, a portion of the receiving part <NUM>" is cut away in a plane parallel to the central axis and perpendicular to the longitudinal axis of the rod channel defined by the U-shaped recess <NUM>". By means of this, an opening <NUM>" is formed that extends from the second end 5b up to the rod channel. A front surface <NUM>" adjacent to the opening <NUM>" is substantially flat and configured to abut against a corresponding surface at the locking member <NUM>". To the left and to the right of the front surface <NUM>" seen in the direction of the rod channel, a cutout <NUM>" is formed that comprises an acute angle undercut or groove <NUM>" at both sides of the front surface <NUM>". The undercut <NUM>" is configured to be engaged by a corresponding portion of the locking member <NUM>" and thus forms a guiding structure for guiding the locking member <NUM>" relative to the receiving part <NUM>". The cutout <NUM>" ends at a distance from the top end 5a such that a roof <NUM>" with a downwardly facing surface is formed at the receiving part at both sides from the U-shaped recess. The roof <NUM>" may also act as a stop for an upward movement of the locking member <NUM>". Above the roof <NUM>" a slanted surface portion <NUM>" may be formed is configured to cooperate with a corresponding slanted surface portion of the locking member <NUM>" in a wedge manner to provide a holding structure that holds the locking member in an upper position. Moreover, a further cutout <NUM>" may be formed below the roof <NUM>" and the outer surface portion <NUM>" to provide space for the locking member.

In the center of the legs <NUM>" seen in a circumferential direction, elongate holes <NUM>" are formed that are configured to receive the pins 500a, respectively, for securing the inserted pressure member <NUM>" against rotation and for limiting an axial movement of the pressure member.

Referring to <FIG>, the pressure member <NUM>" is preferably a monolithic piece that is configured to be accommodated in the receiving part <NUM>" to exert pressure onto an inserted head. It comprises a shallow rod support surface 61a" adjacent to the top end 6a of the pressure member. As in the previous embodiments, the rod support surface 61a" may have a V-shaped cross-section. The outer contour of the pressure member <NUM>" may be cylindrical in a small axial region <NUM>" adjacent to the top end 6a followed by a tapered outer surface <NUM>", specifically a conically tapered outer surface, up to the bottom end 6b. Adjacent to the bottom end 6b, a head receiving portion <NUM>" is formed that is open at the bottom end 6b to allow the insertion of the head <NUM>. The head receiving portion <NUM>" includes two substantially spherically-shaped portions 66a", 66b" and an intermediate widened substantially conical portion 66c" that narrows towards the lower spherical portion 66a". A plurality of recesses <NUM>" that are open via slits 68a" towards the bottom end 6b are provided that render the lower portion of the pressure member <NUM>" flexible. The recesses <NUM>" may have an inverted drop shape where the narrow portion faces towards the top end 6a and may extend up to the upper edge of the intermediate portion 66c".

At one side of the rod support surface 61a" and circumferentially aligned with the rod support surface 61a", a substantially rectangular recess <NUM>" is formed that is open to the second end 6b and to the inside of the head receiving portion <NUM>". The axial extension of the recess <NUM>" may be about the same as the axial extension of the recesses <NUM>". When the pressure member <NUM>" is inserted into the receiving part <NUM>" and the locking member <NUM>" is mounted to the receiving part <NUM>", a head contacting surface of the locking member can contact an inserted head <NUM> through the recess <NUM>".

To the left and to the right of the rod support surface the outer wall of the pressure member <NUM>" comprises a through-hole <NUM>" for receiving the pins 500a. Lastly, a coaxial bore <NUM> is provided that extends from the rod support surface to the head receiving portion <NUM>" for permitting access with a tool to the head <NUM>.

Referring to <FIG>, the locking member <NUM>" has an overall shape that, when the locking member <NUM>" is mounted to the receiving part <NUM>" and is in the locking position, complements the cut away portion of the receiving part <NUM>" such that the outer contour of the receiving part <NUM>" and the locking member <NUM>" substantially merge together. In greater detail, the locking member <NUM>" has a top end 7a and an opposite bottom end 7b and a substantially U-shaped recess <NUM>" extending from the top end 7a to a distance from the bottom end 7b. An outer surface portion <NUM>" that is below a bottom 71a" of the U-shaped recess <NUM>" may be substantially flat but can also be rounded or have another shape. Sidewall portions <NUM>" to the left and to the right and also below the outer front surface <NUM>" may be substantially cylindrical to match the outer contour of the receiving part <NUM>".

The inner surface <NUM>" opposite to the outer surface <NUM>" comprises at the outer ends of the locking member seen in a direction of the rod channel to substantially flat surface portions <NUM>" that are configured to abut against the cut out surfaces <NUM>" of the receiving part. A recess <NUM>" that provides axially extending and parallel acute angle undercut portions or grooves 77a" with respect to the substantially flat surface portions <NUM>" which are shaped and sized so as to engage the undercut portions <NUM>" of the receiving part <NUM>". Below the bottom 71a" of a U-shaped recess <NUM>" a further recess <NUM>" with substantially axially extending parallel sidewalls is formed that extends to a small distance apart from the lower end 7b. At the bottom of the recess <NUM>" a protrusion <NUM>" is provided that may have a substantially rectangular contour. The protrusion <NUM>" has a surface 78a" that is tapered in such a manner that the protrusion becomes thicker in a direction from the bottom end 7b towards the top end 7a. In other words, the protrusion forms a wedge when it moves relative to the head <NUM>. The surface 78a" forms a head contacting surface that is configured to contact the head <NUM> when the head <NUM> is in the head receiving portion <NUM>" of the pressure member. To achieve this, the protrusion 78a" can extend through the recess <NUM>" in the pressure member <NUM>". A shallow cylindrical recess <NUM>" with the cylinder axis parallel to the central axis C when the locking member <NUM>" is mounted to the receiving part <NUM>" is formed below the protrusion <NUM>" and permits a portion of the head <NUM> to extend therethrough so that the protrusion <NUM>" can contact the head <NUM>.

A further cutout <NUM>" is made at the sidewalls from the top end 7a of the locking member <NUM>" so that a shoulder 703a" is formed that may abut against the roof <NUM>" of the receiving part. From the shoulder 703a" a slanted surface portion <NUM>" extends up to the top end 7a that is configured to engage the slanted surface portion <NUM>" of the receiving part <NUM>". The friction force between the slanted surfaces <NUM>", <NUM>" holds the locking member in position, so that the locking member cannot slide down by itself. Lastly, on each side of the locking member <NUM>" tool or instrument engagement protrusions <NUM>" project from the outer wall to allow engagement with a tool to move the locking member <NUM>". The tool engagement protrusions <NUM>" are shown with a rectangular contour, but any other contour may be contemplated that allows engagement with a tool.

Referring to <FIG> and <FIG>, the assembly of the polyaxial bone anchoring device will be explained. As shown in <FIG>, the pressure member is inserted into the receiving part through the top end 5a and secured by the pins 500a in such a position that the recess <NUM>" of the pressure member <NUM>" is aligned with the middle of the opening <NUM>" of the receiving part <NUM>".

As shown in <FIG> and <FIG>, the locking member <NUM>" is mounted from the bottom end 5b of the receiving part onto the receiving part <NUM>". For mounting, the undercut portions 77a" of the locking member <NUM>" engage the undercut portions <NUM>" of the receiving part <NUM>" so that the locking member <NUM>" can be moved upward in a guided manner. During upward movement, the protrusion <NUM>" engages the recess <NUM>" of the pressure member <NUM>" and moves the pressure member <NUM>" upwards until the pins 500a abut against the upper end of the elongate holes <NUM>" as depicted in <FIG>. The pressure member is in the insertion position. The locking member <NUM>" is moved upwards until the slanted surface <NUM>" engages the slanted surface <NUM>" of the receiving part <NUM>" and the shoulder 703a" abuts against the roof <NUM>".

As further shown in <FIG> and <FIG>, the head <NUM> can then be inserted through the lower opening <NUM>" of the receiving part <NUM>". When entering the accommodation space of the receiving part and the head receiving portion of the pressure member, the pressure member <NUM>" snaps onto the head as shown in <FIG>.

Next, as depicted in <FIG> and <FIG> as well as 65e, the pressure member <NUM>" is moved slightly downwards so that its outer surface at the lower end engages the conically narrowing surface 51a" at the receiving part. In this pre-locking position, the head <NUM> cannot be removed from the accommodation space while it is still pivotable. As shown in <FIG>, the head contacting surface 700a" does not exert sufficient pressure onto the head to lock the head <NUM>.

Finally, locking via the locking member <NUM>" is shown with respect to <FIG>. Moving the locking member <NUM>" downward generates an increasing pressure from the tapered surface 78a" of the protrusion <NUM>" onto the head <NUM> which locks the head.

Finally, with respect to all described embodiments, the rod <NUM> can be inserted and the whole polyaxial bone anchoring device can be locked with the fixation device <NUM> that fixes the rod and also the head via the pressure member. As can be seen easily, by actuating the locking member <NUM>, <NUM>' and <NUM>" a provisional locking of the head can be achieved independently of the presence and/or the fixation of the rod <NUM>. A provisional locking can be released or in other words the head can be unlocked by moving the locking member in the opposite direction.

Claim 1:
A coupling device for coupling a rod to a bone anchoring element, the coupling device including
a receiving part (<NUM>, <NUM>', <NUM>") comprising a first end (5a) and a second end (5b), an accommodation space (51b, 51c; 51b', 51c'; 51b", 51c") at or close to the second end (5b) for pivotably holding a head (<NUM>) of the bone anchoring element (<NUM>) therein, and a recess (<NUM>, <NUM>', <NUM>") for receiving the rod (<NUM>), a central axis (C) extending through the first end (5a) and the second end (5b) around which the head (<NUM>) is configured to pivot in the accommodation space (51b, 51c; 51b', 51c'; 51b", 51c"), the central axis (C) defining an axial direction and wherein the recess for receiving the rod defines a rod channel axis (L);
a pressure member (<NUM>, <NUM>', <NUM>") positionable in the receiving part such that the pressure member extends at least partially into the accommodation space for exerting pressure onto an inserted head; and
a locking member (<NUM>, <NUM>', <NUM>") movable relative to the receiving part (<NUM>, <NUM>', <NUM>") in the axial direction between a first position in which the head (<NUM>) is insertable into the accommodation space (51b, 51c; 51b', 51c'; 51b", 51c") and a second position in which the head (<NUM>) is at least temporarily locked in the accommodation space (51b, 51c; 51b', 51c'; 51b", 51c") by the locking member (<NUM>, <NUM>', <NUM>");
wherein the locking member (<NUM>, <NUM>', <NUM>") is configured to exert pressure onto the head (<NUM>) from one side in a direction different from the axial direction and
wherein the pressure member (<NUM>, <NUM>', <NUM>") comprises a recess (<NUM>, 68b", <NUM>") and wherein the locking member (<NUM>, <NUM>', <NUM>") is configured to act onto an inserted head (<NUM>) through the recess (<NUM>, 68b", <NUM>") of the pressure member (<NUM>, <NUM>', <NUM>").