Patent Description:
Bone clamps are used for many purposes. In some cases, bone clamps help to join bone parts. In other cases, bone clamps support an auxiliary device assisting in a surgical intervention. An example of such an auxiliary device is a tracker of a surgical tracking system. Bone clamps can be used to attach the tracker to a bone that is to be tracked during a surgical intervention. Surgical tracking techniques are commonly used for assisting surgeons in a surgical navigation context in which a bone is tracked using a dynamic reference frame.

To provide a high tracking accuracy and, thus, the desired surgical results, the tracker has to be firmly attached to the bone that is to be tracked. One possibility in this regard is to use a bone clamp configured to support the tracker. Conventional bone clamps comprise clamping jaws which are pressed against opposite bone surfaces (see the bone clamp described in <CIT>). Another possibility is the use of bone screws to directly attach the tracker to bone.

Each of these attachment options has its advantages and disadvantages. The use of bone screws generally leads to a more stable fixation of the tracker compared to the use of clamping jaws. Inserting bone screws into bone is, however, an invasive procedure that injures tissue and bone. While the use of conventional bone clamps is generally less invasive than the use of bone screws, the clamping jaws still need to be placed over a significant area on both sides of a bone, and teeth of the jaws must penetrate deep enough into the bone to ensure a stable hold. Larger jaws usually also provide a larger contact area and thus an improved grip. As a result, the jaw surfaces can be of considerable size. On the other hand, the tissue between the clamp and the bone is damaged when the clamp is mounted. Thus, the larger the jaw surfaces, the more invasive is the mounting of the clamp.

Furthermore, conventional bone clamps are largely made of non-radiolucent materials such as stainless steel. Such clamps thus create large artifacts on an intraoperatively acquired image, such as an X-ray image.

<CIT> discloses a medical fastening system for fastening a medical marker device to an anatomical body part. The fastening system comprises a base part comprising a holding unit for holding the marker device and a connecting part for connecting the base part to the anatomical body part. The base part further comprises a fastening unit for fastening the connecting part to the base part so that the base part remains rotatable relative to the connecting part.

<CIT> discloses a surgical registration tool. The tool includes a bone engagement structure comprising a distal condyle abutment structure, at least one posterior condyle abutment structure, a side condyle abutment structure, and an anterior shaft abutment structure. The distal condyle abutment structure includes a distal planar surface. The at least one posterior condyle abutment structure includes at least one planar surface extending distally from the distal planar surface and positioned perpendicular to the distal planar surface. The side condyle abutment structure includes a planar surface extending distally from the distal planar surface and positioned perpendicular to the distal planar surface and the at least one planar surface. The anterior shaft abutment structure extends distally from the distal planar surface and terminates at a distal tip. The registration tool also includes a handle coupled to the engagement structure and extending proximally therefrom, and a tracker array configured to couple to the handle.

<CIT> discloses a device for minimally invasive attachment of a tracker and/or a registration phantom to a patient's bone. The device comprises a base made of a radiotransparent material. The base comprises a support surface intended to face the bone, a plurality of non-parallel through holes for passing a respective percutaneous pin through the base, and at least one slot extending from an edge of the base in a direction transversal to the through holes. Said slot passes throughout the base until the support surface and is intended to engage a percutaneous pin implanted into the patient's bone so as to allow the base to slide along said pin. The base further comprises a reproducible fixation system for attaching the tracker and/or the registration phantom to the base.

<CIT> discloses a registration marker with an anti-rotation base for orthopedic surgical procedures. The anti-rotation base includes a surface configured to rest on and bear against a surface of a glenoid of a patient. The anti-rotation base also includes a plurality of pin receptacles that each define a respective pin axis. The pin axis of a first pin receptacle of the plurality of pin receptacles is not parallel to the pin axis of a second pin receptacle of the plurality of pin receptacles. Additionally, the anti-rotation base includes a mounting receptacle configured to receive the registration marker.

There is a need for a device and a system addressing one or more of the above, or other, problems.

The invention is defined in the independent claim. Additional embodiments are defined by the appended claims.

According to one aspect, a bone clamp comprising two or more clamping members configured to clampingly receive a bone therebetween is provided. The bone clamp further comprises a basis supporting at least two of the clamping members at a first distance to each other. At least one of the at least two clamping members has a body and is rotatably supported by the basis. The at least one rotatably supported clamping member has a bone engaging structure extending helically along at least a part of a length of its body. The bone engaging structure is configured to engage a side surface of the bone upon rotation of the at least one rotatably supported clamping member.

The bone clamp may be used for various purposes, such as joining bone parts.

Additionally, or in the alternative, the bone clamp may be used as a support structure for an auxiliary device used during a surgical intervention. The bone clamp may be configured to be detachably mounted to bone.

The basis may be substantially be made of a solid material. The base may be substantially made of a radiolucent material (e.g., from a polymeric material). The body of one or more of the clamping members may be substantially cylindrical (possibly including a certain tapering in a direction towards the bone, wherein the tapering is less than <NUM>°, in particular less than <NUM>° relative to a longitudinal axis of the body). One or more of the clamping members may be integrally formed with the basis.

The bone engaging structure may be a continuous thread or a thread-like structure. The thread-like structure may comprise discontinuous, spaced-apart protrusions arranged along a helical path. The thread or thread-like structure may have a self-tapping configuration. The at least one rotatably supported clamping member may be a self-tapping bone screw. The thread or thread-like structure may be configured to cut into a side surface of a bone upon rotation of the at least one rotatably supported clamping member. The thread or thread-like structure may have at least one of a diameter between <NUM> and <NUM>, in particular between <NUM> and <NUM>, a height between <NUM> to <NUM>, in particular between <NUM> and <NUM>, and a pitch between <NUM> and <NUM>, in particular between <NUM> and <NUM>.

In the case of three or more clamping members, at least one of the three or more clamping members may have a body without any bone engaging structure and, for example, form a pin. Additionally or alternatively, at least one of the three or more clamping members may be formed as a planar or curved plate (with or without any bone penetrating structures on a surface facing a side surface of the bone received by the bone clamp). Such a clamping member without any bone engaging structure may be configured immovable relative to the base (e.g., integral with the base). In some versions, such a clamping member may comprise teeth on a bone contacting surface thereof.

The at least two clamping members each have a body that is rotatably supported by the basis and has a bone engaging structure extending helically along at least a part of a length of its body. The at least two rotatably supported clamping members are supported at the first from each other. In the case of three or more clamping members, a first and a second rotatably supported clamping member may be supported at the first distance and the first and at least one third (e.g., non-rotatable) clamping member may be supported at a second distance. The first and the second clamping members may be arranged on a first side of the bone and the at least one third clamping member may be arranged on a second side of the bone opposite to the first side. At least one of the first distance and the second distance may be predefined. At least one of the first distance and the second distance may be fixed. The first distance may be smaller or larger than the second distance.

The first distance may be selected such that the at least two clamping members can be brought into a clamping engagement with a bone from at least a first side and a second side of the bone. The second side may be opposite to the first side. For example, the bone clamp may comprise three, four or more clamping members configured to be brought into a clamping engagement with a bone from two, three or four sides. The size of the bone may be previously known or determined. For example, the bone clamp may be dimensioned to be clamped to a vertebra, in particular a spinous or transverse process of the vertebra. In another example, the bone clamp may be dimensioned to be clamped to a bone of a pelvis or a collar bone or another bone.

The second distance may be selected based on a side length of the bone, in particular of the first or the second side of the bone. Two clamping members arranged on the same side of the bone may be spaced apart by the second distance.

In one variant, at least one of the rotatably supported clamping members may be located on the first side of the bone and at least another rotatably supported clamping members may be located on the second side of the bone. The bone engaging structures of the rotatably supported clamping members located on the first and second sides of the bone may be configured to engage the respective one of the first and second sides of the bone upon rotation of the respective rotatably supported clamping member. In some implementations, the bone clamp comprises at least three or four rotatable clamping members, with at least one or two rotatable clamping member being located on the first side and at least two rotatable clamping members being located on the second side.

In one variant, each of the at least two clamping members has a longitudinal axis, with the longitudinal axes of the at least two clamping members extending substantially parallel to each other. A substantially parallel extension may, for example, be given if the axes (or their extensions) enclose an angle of less than +/-<NUM>°.

In one variant, the bone clamp may be configured to move in a direction parallel to the longitudinal axes of the at least two rotatably supported clamping members upon simultaneous rotation thereof. In this variant, upon rotation of the rotatably supported clamping members, the clamping members may not individually move relative to the basis along the longitudinal axes towards the bone. Instead, the whole bone clamp moves in a direction parallel to the longitudinal axes. In such a variant, the rotatably supported clamping members may be infinitely rotatable in the basis without advancing relative to the basis.

In another variant, each of the at least one rotatably supported clamping member is configured to move relative to the basis in a direction parallel to the longitudinal axis of its body, when rotated. Upon rotation, the at least one rotatably supported clamping member may thus advance relative to the base. In this variant, multiple rotatably supported clamping members, if present, may be rotated non-simultaneously.

In some implementations, the bone clamp may comprise a combination of one or more rotatably supported clamping members that are configured to move along their respective longitudinal axes relative to the basis when rotated, and one or more rotatably supported clamping members that are configured not to move along their respective longitudinal axes relative to the basis when rotated.

The body of the at least one rotatably supported clamping member may comprise a distal portion configured to receive at least a part of an actuation member configured to rotate the at least one rotatably supported clamping member. The distal portion may comprise a torque-receiving structure (e.g., it may be formed like a screwhead). In particular, the distal portion may comprise a slot, a cross-slot, a hexagonal socket or a socket having any other geometrical form suited to receive an actuation member capable of generating or transmitting a torque. The basis may be formed to support the rotatably supported clamping member in such a way that the distal portion does not extend beyond the basis.

The body of the at least one rotatably supported clamping member may comprise a tapering proximal portion. The tapering portion may form a pointed or a rounded tip. The body of the at least one rotatably supported clamping member may further comprise a substantially cylindrical portion adjacent to the tapering proximal portion. In some implementations, the bone engaging structure extends over at least a portion of the tapering proximal portion and (e.g., an adjacent) portion the substantially cylindrical portion.

In one variant, the basis may be made of radiolucent material (e.g., a polymer). In this variant, only the clamping members of the bone clamp may be radiopaque (e.g., the clamping members may be made from metal). As a result, the size of artifacts in an interoperative scan (e.g., an x-ray image) of a patient anatomy with the bone clamp mounted thereon may be reduced in comparison to common bone clamps.

The bone clamp comprises one of a gear unit and an interface configured for releasably engaging the gear unit or vice versa. The gear unit may have a single torque input structure and a torque output structure for each of two or more of the rotatably supported clamping members to simultaneously rotate each of the rotatably supported clamping members in response to an input torque. Each torque output structure may comprise an actuation member for actuating a rotatably supported clamping member. The single torque input structure and the torque output structures may be connected via an epicyclic gear train, such as a planetary gearset. The gear unit may thus enable a comfortable way to simultaneously actuate multiple rotatably supported clamping members. Simultaneously actuating multiple rotatably supported clamping members may result in a faster way of mounting and dismounting the bone clamp compared to an individual actuation of each rotatably supported clamping member.

The interface may comprise at least one fastening member configured to releasably engage at least one complementary fastening member of the gear unit (or vice versa). For example, the fastening members may comprise at least one of complementary snap fit connections, screws and complementary threads.

The bone clamp may comprise a guiding member or an interface for receiving the guiding member. The interface may be configured to releasably receive the guiding member. The guiding member may comprise a guiding tube for each of the at least one rotatably supported clamping members, each guiding tube being configured for guiding an actuation member (such as a screw driver) to the respective rotatably supported clamping member.

The bone clamp may support, or may be configured to support, an auxiliary device. The auxiliary device may be a tracker of a surgical tracking system. The tracker may comprise one or more trackable elements. The configuration of the trackable elements depends on the nature of the tracking system, so that the tracker may be an optic tracker or an electromagnetic tracker. As such, the trackable elements may take the form of passive or active optical markers (e.g., light emitting diodes, LEDs, emitting in the visible or infrared spectrum), electromagnetic field sensors (e.g., coils), and so on. In some variants, the bone clamp comprises an interface configured to support the tracker. The interface may be configured to releasably receive the tracker. The interface may be configured to generate a clamping force (see, e.g., <CIT>) or to be based on a form fit (e.g., when the interface is provided by the guiding member).

According to another aspect, a surgical tracking system is provided. The surgical tracking system comprises the bone clamp as described herein. The surgical tracking system further comprises a tracker (e.g., detachably) supported by the bone clamp and a sensor system configured to detect the tracker supported by the bone clamp. The tracker may be an optical tracker and the sensor system may comprise an optical camera.

Further features and advantages of the bone clamp and the surgical tracking system presented herein are described below with reference to the accompanying drawings, in which:.

The same reference numerals are used to denote the same or similar components.

<FIG> illustrates a schematic representation of a bone clamp <NUM> clamped to a bone <NUM>. In the example of <FIG>, the bone <NUM> is a transverse process of a vertebra. The bone clamp <NUM> comprises a basis <NUM> and three clamping members <NUM>, each rotatably supported by the basis <NUM>. The basis <NUM> is made from a solid, polymeric and radiolucent material.

Each of the rotatably supported clamping members <NUM> comprises a substantially cylindrical body <NUM> extending along a longitudinal axis thereof. Each of the clamping members <NUM> further comprises a bone engaging structure <NUM> extending helically along at least a part of a length of its substantially cylindrical body <NUM>. The bone engaging structures <NUM> shown in <FIG> form a thread extending along a part of the length of the substantially cylindrical bodies <NUM>. The thread may have a self-tapping configuration. The clamping member bodies <NUM> may be derived from bone screws.

In some implementations, the clamping members <NUM> are infinitely rotatable in the basis <NUM> (i.e., without being advanced relative to the basis <NUM>). In such implementations, one or more (e.g., all) of the clamping members <NUM> may comprise a non-threaded portion between its head and its threaded portions. This non-threaded portion may then be rotatably supported in the basis <NUM>. In other implementations, the basis <NUM> may comprise a counter-thread (not shown) for at least one of the bone engaging structures <NUM> (or for another thread type provided between a head of the clamping member <NUM> and the corresponding bone engaging structure). The counter-thread enables the corresponding at least one clamping member <NUM> to move relative to the basis <NUM> in a direction parallel to the longitudinal axis of its body <NUM> upon rotation thereof. Each clamping member <NUM> may be actuated, i.e., rotated individually.

As further shown in <FIG>, one of the rotatably supported clamping members <NUM> is located at a first side of the transverse process (i.e., the back side of the transverse process in the view of <FIG>). The other two rotatably supported clamping members <NUM> are located at an opposite second side of the transverse process, i.e., the front side of the transverse process.

The rotatably supported clamping members <NUM> located on the first and second sides of the transverse process are spaced apart from each other in such a way that the respective bone engaging structure <NUM> engages the respective surfaces of the first and second sides of the transverse process (e.g., for about <NUM>,<NUM> to <NUM>). As a result, the transverse process is clampingly engaged by the bone clamp <NUM>.

Utilizing rotatably supported clamping members <NUM> reduces the invasiveness compared to common bone clamps or bone screws that are fully (i.e., over <NUM>° of their circumference) screwed into bone. Further, the basis <NUM> may be made of translucent material. As a result, the size of artifacts in surgical image data will be reduced.

<FIG> illustrates a schematic representation of an interaction between clamping members <NUM> of a bone clamp <NUM> with bone <NUM>. A first clamping member <NUM> shown on the right side of the bone <NUM> is a rotatably supported clamping member 120A as described with reference to <FIG>. Upon rotation of the rotatably supported clamping member 120A, the bone engaging structure <NUM> engages a surface of a side of the bone <NUM>. Depending on the direction of the rotation, the rotatably supported clamping member 120A advances along the surface of the bone <NUM> either in a downward direction for mounting the bone clamp <NUM> or in an upward direction for dismounting the bone clamp <NUM>.

A second clamping member 120B shown on the left side of the bone <NUM> does not comprise a bone engaging structure <NUM> in the example illustrated in <FIG>. The clamping member 120B may form a rod or a plate-like structure and may be integral with the basis.

The clamping member 120B may comprise one or more bone piercing structures such as teeth (not shown) configured to pierce the left side of the bone, e.g., prior to or upon advancing of the first clamping member <NUM> along the right side of the bone. In some variants, the clamping member 120B is first brought into firm abutment with one side of the bone <NUM>. Then, the rotatably supported clamping member 120A is actuated and advances relative to the basis in a downward direction (as illustrated by the straight arrow in <FIG>).

<FIG> illustrates a schematic representation of a bone clamp <NUM> comprising three rotatably supported clamping members <NUM> and a guiding member <NUM>. The longitudinal axes of the bodies <NUM> of the clamping members <NUM> extend substantially in parallel directions (with angular deviation of +/- <NUM>° or less). The guiding member <NUM> comprises three guiding tubes <NUM>, i.e., one guiding tube <NUM> for each of the rotatably supported clamping members <NUM>. Each guiding tube <NUM> is associated with a different one of the rotatably supported clamping members <NUM> in that the guiding tube <NUM> is formed as a substantially hollow-cylindric sleeve extending co-axially relative to the body <NUM> of the associated clamping member <NUM>.

The guiding tubes <NUM> are configured for guiding an actuation member (not shown) to the head of each of the rotatably supported clamping members <NUM>. Each head comprises a torque-receiving structure to be driven by the actuation member. Since the rotatably supported clamping members <NUM> extend in parallel directions, simultaneous actuation (i.e., simultaneous rotation) of the clamping members <NUM> is facilitated. In case of simultaneous actuation, the bone clamp <NUM> is configured to move in a direction parallel to the longitudinal axes of the bodies <NUM> of the clamping members <NUM>. In other words, no relative translational movement between the basis <NUM> and the clamping members <NUM> takes place upon simultaneous actuation of the clamping members <NUM>.

In another example, the bone clamp <NUM> comprises an interface (not shown) for removably receiving the guiding member <NUM>. A removable guiding member <NUM> may lead to a less obstructed surgical area, which results in better view and less obstructions for a surgeon. Further, cleaning of the bone clamp <NUM> and the guiding member <NUM> may be facilitated and reusability may be improved.

<FIG> illustrates a schematic representation of the bone clamp <NUM> of <FIG> with an optical tracker <NUM> attached to the guiding member <NUM>. The optical tracker <NUM> comprises four passive markers <NUM> in the form of reflective spheres and is releasably attached to the guiding member <NUM>. For attachment to the guiding member <NUM>, the tracker <NUM> comprises three cylindrical protrusions <NUM> configured to be received by the guiding member <NUM> in a form-fitting manner.

<FIG> illustrates a schematic representation of multiple bone clamps <NUM>, each mounted to a different vertebra and comprising an interface <NUM> configured to releasably support an associated optical tracker <NUM>. In this configuration, multiple vertebrae can be tracked during a surgical intervention.

The interface <NUM> of each tracker <NUM> is located on a side surface of the basis <NUM> and extends longitudinally in a direction parallel to longitudinal axes of the bodies <NUM> of the rotatably supported clamping members <NUM>. The interface <NUM> may be releasably attachable to the basis <NUM>. Each tracker <NUM> comprise four passive optical markers <NUM>. Further, each tracker <NUM> is configured to removably receive a distal portion of the interface <NUM> of the bone clamp <NUM>.

Removably attaching the interface <NUM> to the base <NUM> and the tracker <NUM> to the interface <NUM> increases adaptability of each individual bone clamp <NUM> to the needs of a surgeon. Further, tracker registration may be facilitated. In particular, a registration of a first tracker <NUM> may be used for registration of a second tracker <NUM>. After registration of the second tracker <NUM>, the first tracker <NUM> may be removed to provide a less obstructive surgical space.

<FIG> illustrates a schematic representation of a bone clamp <NUM> comprising multiple rotatably supported clamping members <NUM> and a gear unit <NUM> for simultaneously actuating the rotatably supported clamping members <NUM>. The gear unit <NUM> comprises a single torque input structure <NUM> with a central sun gear <NUM> and multiple torque output structures <NUM> with associated planetary gears <NUM>. The gear unit <NUM> comprises one torque output structure <NUM> for each of the rotatably supported clamping members <NUM>. Each of the planetary gears <NUM> of the torque output structures is configured to mesh with the sun gear <NUM> of the torque input structure <NUM> to enable simultaneous rotation of the torque output structures <NUM> in response to an input torque. Each of the torque output structures <NUM> is further configured to engage one of the rotatably supported clamping members <NUM> in a torque-transmitting manner. Therefore, simultaneous rotation of the torque output structures <NUM> in response to an input torque results in a simultaneous rotation of the rotatably supported clamping members <NUM> when the torque output structures <NUM> engage the rotatably supported clamping members <NUM>.

The gear unit <NUM> further comprises a housing <NUM> with an upper housing part <NUM> and a lower housing part <NUM>. The upper and lower housing parts <NUM>, <NUM> are shown spaced apart from each other to allow a better view of the gears <NUM>, <NUM> of the torque input structure <NUM> and the torque output structures <NUM>, respectively. In an assembled state, the upper and lower housing parts <NUM>, <NUM> are removably attached to each other and abut each other (see <FIG>). The housing <NUM> is configured to rotatably support the torque input and output structures <NUM>, <NUM>.

<FIG> illustrates a schematic representation of a bone clamp <NUM> with a guiding member <NUM> and a gear unit <NUM> as described herein, and a tracker <NUM>. The guiding member <NUM> is releasably attached to the bone clamp <NUM> and has a longitudinal axis extending parallel to the longitudinal axes of the rotatably supported clamping members <NUM> of the bone clamp <NUM>. The guiding member <NUM> is configured for receiving the torque output structures <NUM> of the gear unit <NUM> and guiding them to the rotatably supported clamping members <NUM> of the bone clamp <NUM>.

The tracker <NUM> comprises a first end <NUM> supporting four markers <NUM> and a second end <NUM> that is releasably or non-releasably attached to the guiding member <NUM>. The second end <NUM> of the tracker <NUM> extends in a non-parallel manner relative to the longitudinal axes of the guiding member <NUM> to provide sufficient space for the gear unit <NUM>. The gear unit <NUM> is shown with its housing <NUM> in the assembled state, i.e., with the upper and lower housing parts <NUM>, <NUM> abutting each other and being releasably attached to each other.

<FIG> illustrates a schematic representation of another realization of a bone clamp <NUM> integrally comprising a gear unit <NUM>. Further, an interface <NUM> for receiving a tracker <NUM>, <NUM>, <NUM> is releasably attached to the basis <NUM>.

The bone clamp <NUM> of <FIG> comprises a basis <NUM> with an upper part, i.e., a top, and lower part, i.e., a bottom (the upper part of the basis <NUM> is not shown in <FIG>). The gear unit <NUM> comprises a single torque input structure <NUM> with a sun gear <NUM> and multiple torque output structures <NUM> with planetary gears <NUM>. The gears <NUM>, <NUM> are located within the basis <NUM> of the bone clamp <NUM>. The torque input structure <NUM> extends through the upper part of the basis <NUM>. The basis <NUM> may releasably receive the torque input structure <NUM>. In one example, the rotatably supported clamping members <NUM> may integrally comprise the planetary gears <NUM>.

The bone clamp <NUM> comprising the gear unit <NUM> as shown in <FIG> provides a compact design that can be easily mounted to and dismounted from bone without the need of an external gear unit <NUM> for simultaneous actuation of the rotatably supported clamping members <NUM>.

<FIG> illustrates a schematic representation of a surgical tracking system comprising the bone clamp <NUM> with the optical tracker <NUM> of <FIG> and a camera system <NUM>. The camera system <NUM> may be a camera system <NUM> commonly used for optical tracking. The camera system <NUM> shown in <FIG> comprises a stereo camera <NUM> and a processor <NUM> configured to receive and analyze image data from the stereo camera <NUM> to track the tacker <NUM> in a dynamic reference system. In other examples, the camera system <NUM> may comprise a mono camera or a combination of mono and stereo cameras. The camera system <NUM> may be sensitive in an infrared spectrum. In the case of passive markers, the tracking system <NUM> may further comprise a light source (e.g., an infrared light source).

Claim 1:
A bone clamp (<NUM>) comprising:
two or more clamping members (<NUM>) configured to clampingly receive a bone therebetween;
a basis (<NUM>) supporting at least two of the clamping members (<NUM>) at a first distance to each other, wherein
the at least two clamping members (<NUM>) each have a body (<NUM>) that is rotatably supported by the basis (<NUM>) and a bone engaging structure (<NUM>) extending helically along at least a part of a length of its body (<NUM>), wherein the bone engaging structure (<NUM>) is configured to engage a surface of the bone upon rotation of the respective rotatably supported clamping member (<NUM>), wherein, depending on the direction of the rotation, the rotatably supported clamping member (<NUM>) advances along the surface of the bone either in a downward direction for mounting the bone clamp (<NUM>) or in an upward direction for dismounting the bone clamp (<NUM>);
characterised in that the bone clamp further comprises one of:
a gear unit (<NUM>, <NUM>) having a single torque input structure (<NUM>, <NUM>) and a torque output structure (<NUM>, <NUM>) for each of the rotatably supported clamping members (<NUM>) to simultaneously rotate each of the rotatably supported clamping members (<NUM>) in response to an input torque, and
an interface configured for releasably engaging the gear unit (<NUM>, <NUM>).