Patent Description:
Bone anchors used in particular in spinal surgery include a shank to be anchored in a bone and a receiving part with two free legs to receive a spinal rod therebetween. In minimally invasive surgery (MIS) only small incisions are made in the skin of a patient. To provide access to the bone anchor, extension members are used that extend the legs of the bone anchor to permit guiding and/or supplying elements of an implant or instruments to the bone anchor. <CIT>, for example, describes such a bone anchor with extension members.

In some cases, the extension members can be compressed towards each other in a direction transverse to their longitudinal extension. This may result in a narrowing of the pathway to the bone anchor which may cause difficulties to advance instruments or elements to the bone anchor. In other cases, the extension members may be spread inadvertently and break-off.

<CIT> describes a collar for extenders which collar is configured to receive the extenders and maintain the extenders in a parallel orientation so as to prevent splaying and premature break-off.

<CIT> discloses a locking sleeve for receiving and locking the legs of a pedicle screw. The locking sleeve includes a stop ring that limits the accommodation depth of the legs in the locking sleeve.

<CIT> discloses a collar for attachment to extenders of an extender system, the body of the collar comprising first and second cavities configured to receive the extenders and an intermediate cavity disposed therebetween and configured to receive instruments and/or implants.

It is an object of the invention to provide an improved connection device for use with extension members of a bone anchor and to a system of such a bone anchor and a connection device which is simple to handle.

The object is solved by a connection device of claim <NUM> and by a system of a system of a bone anchor and a connection device of claim <NUM>.

The present invention is defined in independent claim <NUM> while preferred embodiments are set forth in the dependent claims. Claim <NUM> recites a system of a bone anchoring device and a connection device according to one of claims <NUM> to <NUM>. According to the invention, a connection device for use with extension members of a bone anchor comprises a sleeve defining a longitudinal axis and configured to be placed at least partially around a portion of at least one of the extension members. The extension member comprises a free end and the sleeve comprises a wall portion that is configured to extend at least partially around the extension member; wherein the wall portion comprises at least one opening that is configured to permit the free end of the extension member to extend at least partially therethrough.

Still according to the invention, the connection device for use with extension members of a bone anchoring device comprises a sleeve defining a longitudinal axis and configured to be placed at least partially around a portion of at least one of the extension members. The extension member comprises a free end and the sleeve comprises a contact surface configured to be contacted by at least one of the extension members. The contact surface is shaped and oriented such that when the sleeve is placed around the extension member and moved away from the free end of the extension member towards the bone anchor, a clamping force is generated which at least temporarily maintains the sleeve on the extension member.

In an embodiment, the contact surface of the sleeve and a cooperating surface of the extension member are inclined such that an increasing clamping force is generated when the sleeve is mounted on the extension members.

The extension members preferably comprise a pair of extension members that are open at their free ends, i.e. are separated from each other at least in the region of their free ends, more particularly are separated from each other along substantially their entire length. Such open extension members may have advantages, in particular in MIS, compared to extension members that are closed at their upper end opposite to the bone anchor. Such an advantage may be, for example, an improved visibility of the implantation site.

With the connection device, it is possible to keep the space between the extension members open, if necessary. Further, it is possible to remove the connection device if it is no longer required.

Moreover, the connection device provides stability to the extension members. In particular it can prevent the compression or spreading of the extension members towards each other and away from each other, respectively. Moreover, the connection device may be easily connectable to and removable from the extension members. Also, it has a small size and is robust. In particular the open structure of the sleeve may contribute to a small size.

Since the sleeve comprises a hollow interior, further instruments can be received therein. For example, an auxiliary instrument in the form of a pin can extend therethrough and project out of the sleeve for facilitating orientation and/or centering of the sleeve relative to the extension members. Instead of an auxiliary instrument, instruments for manipulating the bone anchor or components of the bone anchor may be inserted through the sleeve and guided by the extension members to the implantation site.

Still further, the connection device may be implemented in various manners. For example, the connection device may be used in connection with the alignment of the receiving part of a polyaxial bone anchor, in connection with the insertion of a locking member or of the rod or in connection with the insertion and removal of an adapter for example for injecting bone cement or another substance.

The connection device may be used together with all kinds of bone anchors that have extension members, such as polyaxial bone anchors which comprise a shank pivotably connected to the receiving part or monoaxial bone anchors which comprise a shank fixedly connected to the receiving part.

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

Referring to <FIG>, the connection device is shown together with a polyaxial bone anchor. The polyaxial bone anchor includes an anchoring element <NUM> having a shank <NUM> with a bone engagement structure, such as a thread, and a head <NUM>. The head may have a recess 3a for an instrument (<FIG>). A receiving part <NUM> with a head receiving portion <NUM> is configured to receive the head <NUM> in a pivotable manner. The receiving part <NUM> also comprises a rod receiving portion including a substantially U-shaped recess <NUM> by means of which two upstanding legs <NUM> are formed. The recess <NUM> is configured to receive a rod <NUM> therein. In the embodiment shown, the legs <NUM> are extended in an axial direction and may comprise a circumferentially extending weakened portion 7a for permitting an upper portion of the legs <NUM> to be broken off. Elongate extension members <NUM> are connected to the legs <NUM> that form extensions of the legs <NUM>. A locking ring <NUM> is configured to extend around the head receiving portion <NUM> and to compress the head receiving portion to lock the head <NUM> in a particular angular position of the shank <NUM> relative to the receiving part <NUM>. Between the legs <NUM>, a locking member <NUM> can be inserted for locking the rod <NUM> in the recess <NUM> as shown in <FIG>.

A connection device <NUM> is provided that is configured to be connected to each of the two extension members <NUM>. By means of this, the extension members <NUM> are connected with each other through the connection device <NUM> and can maintain a defined distance relative to each other along substantially their entire length. The connection device <NUM> comprises a sleeve <NUM> and may optionally comprise an auxiliary member <NUM> as depicted in <FIG>.

Referring now in addition to <FIG>, the extension members <NUM> will be described in greater detail. The extension members <NUM> may have a substantially hollow cylinder segment shape with an outer edge <NUM> and a free end 8a, the cylindrical shape defining an axial direction and a circumferential direction. The shape preferably matches a cylinder segment shape of the legs <NUM> of the receiving part <NUM>. Specifically, the circumferential width of each of the extension members <NUM> may be substantially the same as that of the legs <NUM>. Thus, the extension members <NUM> are spaced apart from each other at such a distance that the rod <NUM> can pass therethrough. An inner surface of the extension members <NUM> may be thread-free. This permits to advance the locking member <NUM> and/or further components between the extension members <NUM> in a sliding or non-rotating manner. In a region of an end portion <NUM> adjacent to the free end 8a of each of the extension members <NUM> the outer edge <NUM> comprises an inclined edge portion <NUM> at either side in the circumferential direction. The inclined edge portion <NUM> is substantially flat and configured to cooperate with a corresponding inclined surface on the sleeve <NUM> as described below. The direction of the inclination is such that, as best seen in <FIG>, the distance between points lying on the inclined edge portion <NUM> of one extension member and corresponding points at the same axial position of the other extension member have a continuously increasing distance from each other in the axial direction towards the free end 8a. Edge portions <NUM> between the free end 8a and the inclined edge portion <NUM> may be rounded. By the inclined edge portion <NUM>, the width of the extension members in the circumferential direction decreases towards the free end 8a.

On the outer surface of each of the extension members <NUM> a marking <NUM> may be provided that serves for correctly orienting the sleeve <NUM> relative to the extension members <NUM> prior to connecting it to the extension members. The marking <NUM> may have a circumferentially extending first portion 84a that may be located at a greater distance from the free end 8a in the axial direction than the end of inclined edge portion <NUM> that faces towards the bone anchor. At substantially the center in circumferential direction, the marking <NUM> may comprise a second portion 84b that extends in the axial direction.

The length of the elongate extension members <NUM> may be such that they protrude a sufficient distance out of the skin of a patient when the bone anchor has been implanted into a bone part or a vertebra. The extension members <NUM> may be fixedly connected to the legs <NUM>, e.g. by welding. Alternatively, the extension members <NUM> may be monolithically formed with the receiving part <NUM> and may have a break-off section that permits to break them off. Still further alternatively, the extension members <NUM> may be removably connected to the legs, e.g. by a plug-in, clip-on or a similar connection.

Referring additionally to <FIG>, the sleeve <NUM> will be described in greater detail. The sleeve <NUM> may be substantially cylindrical and has a first end 20a and an opposite second end 20b. By the cylinder axis of the sleeve, a central longitudinal axis L is defined. When the sleeve <NUM> is mounted to the extension members <NUM>, the first end 20a is facing towards the bone anchor. Adjacent to the first end 20a a first portion <NUM> of the sleeve <NUM> may be a substantially cylindrical ring with a wall thickness that is greater than the thickness of the wall of the extension members <NUM> in a direction transverse to the longitudinal axis L. In the first portion <NUM>, two opposite cylinder segment-shaped guiding recesses <NUM> are formed for guiding through at least the end portion <NUM> of the extension members <NUM>, respectively. Hence, the inner contour of the guiding recesses <NUM> substantially matches the outer contour of the extension members <NUM> in a cross-section perpendicular to the longitudinal axis L. The guiding recesses <NUM> are offset by <NUM>° so that each of the guiding recesses <NUM> can guide one extension member <NUM> therethrough. A height of the first portion <NUM> in the axial direction may be such that when the inclined edge portion <NUM> of the extension member <NUM> has passed through the guiding recess <NUM>, the first portion 84a of the marking is visible above the guiding recess <NUM> as illustrated, for example, in <FIG>. Approximately at the center of each guiding recess <NUM> in the circumferential direction an axially extending marking <NUM> is provided on the outer surface of the first portion <NUM>. The marking <NUM> serves for orienting the sleeve <NUM> properly with respect to the extension members <NUM>.

Between the second end 20b and the first portion <NUM>, the sleeve has a second portion <NUM> which may be also cylindrical with a slightly greater inner diameter than the first portion <NUM>. By means of this, a step 24a may be formed between the first portion <NUM> and the second portion <NUM>. In the axial direction above the guiding recesses <NUM>, two recesses <NUM> offset by <NUM>° are formed in the cylindrical surface of the second portion <NUM>. The recesses <NUM> each have a base 25a that is provided by the upper edge of the first portion <NUM> and that has a width in the circumferential direction that substantially corresponds to the circumferential width of the guiding recesses <NUM> or is slightly greater. A top edge 25b of the recesses <NUM> also extends in the circumferential direction and is shorter than the base 25a. Hence, the circumferential width of the recesses <NUM> is smaller at the top edge 25b than at the base 25a corresponding to the decreasing width of the end portions <NUM> of the extension members <NUM>. The edges between the top edge 25b and the base 25a of the recesses <NUM>, respectively, are formed as substantially flat inclined surfaces 25c that are oriented outwards. The size of the recesses <NUM> in the axial direction is such that the end portions <NUM> of the extension members <NUM> can extend therein to such an extent that the first marking 84a of the extension members <NUM> is visible within the recess <NUM> above the base 25a. The inclined surface 25c forms with at least a portion thereof a contact surface that is configured to cooperate with the inclined edge portion <NUM> of the extension members <NUM>, respectively. Hence, each recess <NUM> has two inclined surfaces 25c facing in the same outward direction. The inclination of the inclined surface 25c is such that points on the same axial height on the inclined surfaces of opposite recesses <NUM> have an increasing distance from the base 25a towards the top edge 25b. More specifically, the inclination of the inclined surface 25c is such that when the end portion <NUM> of the extension member <NUM> enters the recess <NUM> but is not yet at an uppermost position, there is still a clearance between the inclined edge portion <NUM> and the inclined surface 25c as depicted in <FIG>. When the end portion <NUM> of the extension member <NUM> is further moved into the recess <NUM> and contacts the inclined surface 25c as shown in <FIG>, the friction force generated thereby increases and clamps the sleeve <NUM> on the extension members <NUM>. The angle of inclination of the inclined surface 25c relative to the central longitudinal axis L may be, depending on the friction between the surfaces, between around <NUM>° and <NUM>°, more preferably around <NUM>° to <NUM>°. Preferably the angle of inclination is greater than an angle that would produce a self-locking effect.

Although the extension member may not reach up to the upper edge 25a of the recess <NUM>, the upper edge 25a may serve as a stop for limiting a downward movement of the sleeve when the sleeve is <NUM> mounted to the extension members <NUM>. Between the inclined surfaces 25c and the base 25a an additional recess or groove <NUM> may be formed on either end to provide more space when the end portion <NUM> of the extension member enters into the recess <NUM>. An outer surface of the second portion <NUM> of the sleeve <NUM> may have a gripping structure for facilitating gripping, such as plurality of circumferentially extending flutes or corrugations.

Referring now to <FIG>, the auxiliary member <NUM> will be described in greater detail. The auxiliary member <NUM> comprises a substantially cylindrical pin <NUM> with a bevelled front end portion <NUM>. An outer diameter of the cylindrical pin <NUM> corresponds substantially to an inner diameter of the second portion <NUM> of the sleeve <NUM> so that the pin <NUM> can be inserted into the sleeve <NUM> and guided therein, and preferably can be held by friction therein. The length of the pin <NUM> is such that in the inserted state at least the bevelled front end portion <NUM> and preferably a still further portion of the pin <NUM> protrude out of the first end 20a of the sleeve <NUM>. At the side opposite to the bevelled front end portion <NUM>, a head <NUM>, for example a cylindrical head, is formed that has a greater diameter than the pin <NUM> so that a step 33a is formed at the transition. The step 33a functions as a stop for the insertion of the auxiliary member <NUM> into the sleeve <NUM>.

The auxiliary member <NUM> serves for facilitating the connection of the sleeve <NUM> to the extension members <NUM>. This may be achieved by the centering function of the bevelled front portion <NUM>. In addition, the pin <NUM> is configured to keep the end portions <NUM> of the extension members at such a distance that they can be aligned with the guiding recesses <NUM> and inserted therein.

The parts and portions of the bone anchor and of the connection device including the sleeve and the auxiliary member may be made of any material, preferably however, of titanium or stainless steel or of any biocompatible metal or metal alloy or plastic material. As biocompatible alloy, a NiTi alloy, for example Nitinol, may be used. Other materials can be also magnesium or magnesium alloys. Biocompatible 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 the clinical use, first, the bone anchor is inserted into bone or into a vertebra. For example, the bone anchor can be of the type of a polyaxial pedicle screw the shank <NUM> of which is inserted into the pedicle of a vertebra. In a first way of use, the receiving part <NUM> is preassembled with the anchoring element <NUM>. Then, the shank <NUM> is inserted into the bone or vertebra. In a second way of use, the shank <NUM> is first inserted into the bone or vertebra and thereafter the receiving part <NUM> is mounted onto the head <NUM> of the anchoring element <NUM>. In any case, the extension members <NUM> protrude from the skin of the patient.

The two extension members <NUM> are then connected by the sleeve <NUM>. In a first way of use, the sleeve <NUM> is placed on the extension members without using the auxiliary member <NUM>. In order to mount the sleeve <NUM> on the extension members <NUM> in the correct orientation, the the marking <NUM> on the first portion <NUM> of the sleeve <NUM> is aligned with the second marking portion 84b of the extension members <NUM>, respectively. The sleeve <NUM> is then slid onto the end portion <NUM> of the extension members <NUM> such that the end portions <NUM> pass through the guiding recesses <NUM>, respectively, and enter the recesses <NUM> as shown in <FIG>. When the inclined edge portions <NUM> of the extension members <NUM> and the inclined surfaces 25c of the sleeve <NUM> engage, as shown in <FIG>, a friction force is generated that holds the sleeve <NUM> and the extension members <NUM> together. The complete visibility of the first marking portion 84a of the extension members <NUM> may be used as indication that the sleeve <NUM> is substantially fixed to the extension members <NUM>.

In a second manner of use as shown in <FIG>, the auxiliary member <NUM> is used for placing the sleeve <NUM> on the extension members <NUM>. First, the auxiliary member <NUM> is inserted with the pin portion <NUM> into the sleeve <NUM>. Then, as shown in <FIG> the preassembled connection device comprising the sleeve <NUM> and the auxiliary member <NUM> is oriented with respect to the extension members <NUM> such that the marking <NUM> on the sleeve is aligned with the second marking portion 84b on the extension members <NUM>. In <FIG>, the bevelled end portion <NUM> of the auxiliary member <NUM> and a portion of the pin <NUM> has entered the space between the extension members <NUM>. The bevelled end portion <NUM> facilitates centering of the sleeve with respect to the extension members. The connection device is then further moved in the direction towards the bone anchor and can still be rotated until the markings <NUM> and 84b are exactly aligned.

As shown in <FIG> the end portions <NUM> of the extension members <NUM> have passed through the guiding recesses <NUM> until the free end 8a has entered the recess <NUM> of the sleeve. The inclined surfaces of the sleeve <NUM> and the extension members <NUM> contact each other and a friction force is generated. As shown in <FIG>, the extension members <NUM> can be moved into the recesses <NUM> at least until the first marking 84a on the extension member is fully visible within the recess <NUM>. The friction force is then sufficiently high to prevent sliding-off of the sleeve from the extension members. Finally, as shown in <FIG>, the auxiliary member can be removed.

With the sleeve <NUM> placed onto the extension members <NUM>, the extension members are prevented from being compressed towards each other and/or spread apart from each other. Hence, the extension members can maintain a substantially constant distance or parallel configuration with respect to each other.

As depicted in <FIG>, usually a plurality of bone anchors has been inserted into bone or in the specific example into the pedicles of adjacent vertebrae <NUM> and the rod <NUM> is inserted into the recesses <NUM> of the receiving parts <NUM> of the bone anchors. The sleeve <NUM> is connected to the extension members <NUM> of one of the bone anchors and the locking member <NUM> is inserted or manipulations are made through the sleeve with an instrument <NUM>. The sleeve <NUM> can then be removed and placed onto the neighboring extension members. Alternatively, each of the bone anchors may be provided with a separate sleeve. After the surgical steps have been completed, the extension members <NUM> and the portion of the legs <NUM> above the weakened portion 7a are broken-off and removed.

Modifications of the embodiment of the connection device are possible. For example, it may be sufficient, if one of the cooperating surfaces of the sleeve and the extension members is inclined, the other one may be straight. The recesses <NUM> do not need to be closed towards to the inside of the sleeve. It may be sufficient to provide only a lateral guidance for the extension members. Hence, the guiding recesses <NUM> may be at least partially or fully open towards the inside.

Also, it is possible to prevent falling off of the sleeve by other means, for example resilient engagement of detent portions in recesses or similar means.

Claim 1:
A connection device for use with extension members of a bone anchor, comprising
a sleeve (<NUM>) defining a longitudinal axis (L) and configured to be placed at least partially around a portion of at least one of the extension members (<NUM>), the extension member (<NUM>) comprising a free end (8a) and the sleeve comprising a wall portion that extends at least partially around the portion of the at least one extension member (<NUM>);
wherein the wall portion comprises at least one opening (<NUM>) that is configured to permit the free end (8a) of the at least one extension member (<NUM>) to extend at least partially therethrough; and
wherein the sleeve (<NUM>) comprises a contact surface (25c) configured to be contacted by the extension member (<NUM>); characterized in that
the contact surface (25c) is shaped and oriented such that when the sleeve (<NUM>) is placed around the extension member (<NUM>) and moved away from the free end (8a) of the extension member (<NUM>) towards the bone anchor, a clamping force is generated which maintains the sleeve (<NUM>) at least temporarily on the extension member (<NUM>).