Bone tracking method, bone tracking method, and bone tracker set

Abstract

The invention relates to a bone tracking system (100) for tracking at least two bones relative to one another, comprising: a bone tracker set (1); an optical camera (102) for optically detecting optical reference markers (12) of the bone tracker set (1) for spatial tracking by means of a navigation system (104); and a control unit (108), wherein the control unit (108) is adapted: to carry out a position determination with six degrees of freedom for a first reference marker (12) of the two reference markers (12); to carry out a position determination with at least one degree of freedom for a second reference marker (12) of the two reference markers (12); and to check the position determination of the first reference marker (12) by determining the position of the second reference marker (12). The present invention also relates to a bone tracking method and to a bone tracker set (1) for the bone tracking system

Description

[0001] Bone tracking method, bone tracking method and bone tracker set

[0002] Description

[0003] Technical area

[0004] The present disclosure relates to a bone tracking system, a bone tracking method, and a bone tracker set (having at least two bone trackers) for a / the bone tracking system for tracking, and further preferably for registering, at least two bones (multiple bones) relative to each other, in particular two vertebral (column) bones relative to each other.

[0005] Technical background

[0006] Spinal navigation and spinal robotics are now established methods for surgical interventions on a patient. However, most current navigation systems only allow, if at all, the spatial tracking of a single (spinal) bone at a time. They are too large and too invasive (with associated tissue damage to the patient) to attach reference frames to the bone, which are usually attached to the spinous process. While this allows the individual pedicle screws to be precisely implanted in the spine, it does not allow for monitoring the actual spinal reconstruction to restore the patient's spinal function.

[0007] The use of EM tracking (electromagnetic tracking) has been proposed for multi-level spinal tracking, but EM tracking often suffers from limited accuracy due to EM interference from other devices in the operating room. These electrical devices influence the electromagnetic field due to their material or their own radiation, so the tracking is not robust enough or requires significant calibration effort to obtain even halfway acceptable results.

[0008] Optical reference bodies, such as rigid bodies with markers attached at multiple levels, have also been proposed. However, in order to localize each vertebral body to be tracked with six degrees of freedom (6 DOF / six degrees of freedom) (three degrees of freedom position - approximately x, y, z; three degrees of freedom orientation - approximately three angles), the reference body (e.g., rigid body) as a tracker requires a bulky and large design and, for example, has mechanical clamps or pins with an additional claw for rotational fixation. Due to the large geometric structure, line-of-sight is also difficult, and a (disadvantageous) line-of-sight problem becomes very relevant. In addition, the reference body must have a sufficient three-dimensional (3D) extent to enable precise spatial tracking with six degrees of freedom (6 DOF tracking).However, a bulky tracker increases the invasiveness for the patient, especially in multi-level surgeries, such as three or more levels (3+), and a reference body with a larger extension also carries the risk of collisions between the reference bodies of the individual vertebral bodies as well as collisions between the reference bodies and a surgical instrument.

[0009] US 2022 / 0192752 A1, for example, discloses a registration system with an X-ray device and a visible-light camera. The X-ray device acquires a first X-ray image, and the visible-light camera simultaneously acquires another visible-light image. In addition, a further image is acquired with a set positioning marker, and a computer system provides a navigation interface.

[0010] US 2021 / 0174950 A1 discloses a stereoscopic marking device comprising a polyhedral cube. This cube has at least four flat surfaces, wherein the at least four flat surfaces are used as a primary marker. The primary marker has a primary graphic code, while three secondary markers individually comprise a first secondary graphic code, a second secondary graphic code, and a third secondary graphic code. The primary graphic code is used to provide spatial coordinate information used for calculating six-degree-of-freedom (6-DOF) attitude data. The polyhedral cube is configured to be attached to a vertebral body at a surgical site.

[0011] WO 2021 / 069449 A1 relates to a medical system with multiple adapters and multiple fiducial markers.

[0012] EP 4 104 786 A1 relates to a method for determining poses of tracked vertebral bodies.

[0013] Summary of the present disclosure

[0014] It is therefore the object of the present disclosure to avoid or at least mitigate the disadvantages of the prior art and, in particular, to provide a bone tracking system, a bone tracking method, and a bone tracking set with which bones can be tracked even better relative to one another. One sub-objective can be seen, in particular, in performing registration using optical and X-ray scanning.

[0015] The object of the present disclosure is achieved with regard to a bone tracking system by the features of claim 1, and with regard to a bone tracking method or a bone tracker set by the features of the independent claims. Advantageous further developments are the subject of the dependent claims.

[0016] The present disclosure relates to a bone tracking system for tracking at least two bones relative to each other, comprising: a bone tracker set, wherein the bone tracker set has at least two bone fixations, each with a distal bone anchor, which is provided and adapted to be attached directly to or in a bone of a patient, as well as at least two reference adapters (preferably each rigidly connectable or connected to one of the bone fixations) each with a proximal optical reference marker, an optical camera for optically capturing the optical reference markers of the bone tracker set for spatial tracking by a navigation system, and a control unit, wherein the control unit is adapted to capture and spatially track the at least two optical reference markers via the optical camera, wherein the control unit is adapted toto carry out a position determination with six degrees of freedom (DoF) for a first reference marker of the two reference markers, to carry out a position determination with at least one degree of freedom for a second reference marker of the two reference markers and to check the position determination of the first reference marker by determining the position of the second reference marker.

[0017] This means that a 6 DoF + 1 DoF tracking solution is proposed, in which a first vertebral body or reference marker is tracked with six degrees of freedom and a second, adjacent vertebral body or reference marker is tracked with any number of degrees of freedom, preferably using machine vision. This increases tracking accuracy and, due to redundancy, improves tracking robustness. The optional number of degrees of freedom for the second vertebral body opens up many possibilities for designing the (second) reference marker.

[0018] According to a preferred embodiment, the control unit can be adapted to determine the position of the second reference marker with six degrees of freedom. This means that a 6 DoF + 6 DoF tracking solution is proposed, in which a first vertebral body or reference marker and a second, adjacent vertebral body or reference marker are each tracked with 6 degrees of freedom, preferably using machine vision. This makes it possible to further increase the accuracy of the tracking and, due to the high level of redundancy, to improve the robustness of the tracking. According to a preferred embodiment, the control unit can be adapted to determine the position of the second reference marker with a maximum of four or a maximum of five degrees of freedom. This means that a 6 DoF + 4 DoF / 5 DoF tracking solution is proposed, in which a first vertebral body orA reference marker with six degrees of freedom and a second, adjacent vertebral body or reference marker with (exactly / maximum) four or five degrees of freedom are tracked, preferably using machine vision. This allows for further increasing tracking accuracy and improving tracking robustness due to the higher redundancy. The four or five degrees of freedom for the second vertebral body open up many possibilities for designing the (second) reference marker, such as determining no rotation around a reference marker axis and / or no translation along the reference marker axis.

[0019] According to a further, possibly independently claimable, aspect, the present disclosure relates to a bone tracking system for tracking at least two bones relative to each other, comprising: a bone tracker set, wherein the bone tracker set has at least two bone fixations and at least two reference adapters, wherein the bone fixations each have a distal bone anchor and a proximal end portion with a coupling portion, wherein the bone anchors are provided and adapted to be fastened directly to or in a bone of a patient, wherein the reference adapters each have a proximal optical reference marker and a counter-coupling structure, wherein the counter-coupling structure is attached or attachable to the coupling portion of the bone fixation, in particular can be coupled and uncoupled without tools,an optical camera for optically capturing the optical reference markers of the bone tracker set for spatial tracking by a navigation system, and a control unit, wherein the control unit is adapted to capture the at least two optical reference markers via the optical camera and to spatially track them and to perform a position determination with a maximum of five degrees of freedom for each optical reference marker, wherein the control unit is further adapted to determine at least the remaining sixth degree of freedom based on the at least two optical reference markers. Alternatively, the bone tracker set can comprise at least two bone fixations, each with a distal bone anchor, which is provided and adapted to be attached directly to or in a bone of a patient.and at least two reference adapters (preferably each rigidly connectable or connected to one of the bone fixations), each with a proximal optical reference marker.

[0020] Furthermore, a basic idea of ​​the present disclosure can be seen in providing a system for the (spatial) tracking of several bones in relation to one another, in particular for spinal surgery, in which at least two bones, in particular vertebrae, are tracked by attaching / anchoring or inserting a bone fixation, in particular as or in the form of a pin (as a special embodiment), (for example in the spinous process), without rotational stability being required. The bone fixations, in particular the pins, have a proximal end portion (which is in particular adapted to protrude from the patient's skin) to which a reference adapter, in particular a sleeve, can be coupled, in particular fastened. This reference adapter, in particular the sleeve as a special embodiment of the reference adapter, has or carries an optical reference marker.Each optical reference marker enables pose determination or orientation determination with a maximum of five, in particular four or five, degrees of freedom (at least one rotation is still undetermined). To determine the (at least) missing sixth degree of freedom for unambiguous orientation determination, the optical reference marker of a, in particular adjacent, bone fixation and reference adapter, in particular a pin and sleeve, is used.

[0021] Preferably, the system also enables patient registration when using an intraoperative 3D X-ray scanner by correlating the distal part of the pin in the X-ray image with the optical marker tracked by an optical camera system. In particular, optical reference markers cannot be used for registration, and thus the optical camera system cannot be used either. Registration can be performed solely through the bone fixation and a corresponding determination (e.g., via a software algorithm) that detects the position of the bone fixation in the bone, preferably the pin as the bone fixation, in the spinous process.

[0022] According to a possibly independently claimable aspect, the present disclosure provides a bone tracker set for a bone tracking system, preferably the one described above or below, for tracking, and preferably further for registering, at least two bones (several bones) relative to one another, comprising: at least two bone fixations, in particular pins, which are provided and adapted to be fixed by means of a distal bone anchor directly to or in a bone of a patient (rigid orin constant relation to the bone), wherein in each case a proximal end section of the bone fixation, in particular of the pin, has a coupling section (or fastening section), and at least two reference adapters, in particular sleeves, which each have or carry a proximal optical reference marker and the reference adapters, in particular sleeves, are adapted to be able to be coupled or uncoupled from the coupling section of the respective bone fixation, in particular of the respective pin, without the need for tools.

[0023] The advantage lies in the fact that the relative positions, in particular locations, of the bones, in particular of several vertebral bodies, can be tracked in real time intraoperatively, thereby monitoring the repositioning of the bones, in particular of the spine, to a desired state. The disclosure furthermore makes it possible to register several vertebral bodies at once using a single X-ray scan and also avoids rescanning the patient with, for example, an X-ray scanner if the bones, in particular vertebral bodies, have moved relative to one another. The disclosure makes it possible to remove the reference adapters, in particular sleeves, with the optical reference markers (as trackers) at any time during the operation when navigation is not needed, and to reattach the optical reference markers without losing the registration, thereby enabling, in particular, minimally invasive tracking.In other words, a bone tracker set with at least two bone trackers is proposed, wherein each bone tracker has at least two separate components, namely a bone fixation that is adapted to be fixed to or in a respective bone, and a reference adapter with an optical reference marker that can be coupled and detached from the bone fixation without the need for tools using a coupling interface. This allows an optical reference marker to be quickly attached and removed intraoperatively. The respective bone can be optically tracked (with the help of the second bone tracker) using the optical reference marker. While a single bone tracker is still underdetermined (e.g. 4DOF or 5DOF), two bone trackers can be used to unambiguously track the bone tracker and thus the respective bone.

[0024] In particular, a form-fitting coupling interface is provided between the bone fixation on the one hand and the (separate but connectable and detachable) reference adapter / tracking adapter on the other hand. This form-fitting connection does not necessarily include rotation, thus preventing complete determination with six degrees of freedom (6DOF). For rotatable / rotatable reference adapters, the coordinate system is constructed in particular on the basis of the analysis of two, preferably adjacent, reference adapters (each with the optical reference marker), i.e., based on two times four determinable degrees of freedom (2x 4 DOF) to form a complete set of determined degrees of freedom (1x 6DOF) and thus the tracked position of the respective bone (belonging to the reference adapter).

[0025] Spatial tracking can be provided, with registration as an additional option. However, registration can also be achieved in other ways, such as by tracking a 3D scanner.

[0026] According to an independent aspect, an associated analog method is provided which, based on two (coupled) reference adapters (as trackers), can determine the 6 DOF coordinate system of each individual bone, in particular vertebral body. With the present disclosure, the reference adapters and the optical reference markers can be determined not only via five degrees of freedom (5 DOF), but also via only four degrees of freedom (4 DOF), for example if only the axis in space is known but not a specific point on the axis. By combining two axes, each with 4 DOF, one can then determine a 6 DOF coordinate system (and thus the position). One can also say that each tracker has a maximum of five degrees of freedom (5 DOF), whereby 6 DOF can then always be determined by combination.A key idea is that a single bone fixation with a coupled reference adapter (as a single tracker) does not have six degrees of freedom (6 DOF), so it does not have to be rotationally fixed and can be smaller.

[0027] According to one embodiment, at least one bone fixation, preferably all bone fixations, in particular a pin or the pins, can have a screw shaft with an external (screw) thread as a distal bone anchor for screwing into the bone. In particular, the screw shaft can be designed similarly to a screw shaft of a pedicle screw, for example with different thread pitches and / or a hollow shaft and / or sharp cutting edges. The screw shaft extends distally and preferably coaxially to the remaining section of the bone fixation, in particular the pin. In particular, the bone fixation, in particular the pin (as a special embodiment of the bone fixation), has two opposite "end" sections, on the one hand the distal screw shaft and on the other hand the proximal coupling section. In particular, bone fixations, in particular the pins, can therefore have a screw-shaped distal end.Alternatively, the bone fixation, in particular the pin, can have a pin as a distal bone anchor in order to be fixed in the bone, preferably in a spinous process. Such fixation by means of a pin can be carried out simply and efficiently, in particular since the fixation of the degree of freedom around the rotation axis by the (bone) tracker, which has, for example, five degrees of freedom (5-DOF), is not required. Rotation around the longitudinal axis of the pin is freely possible and is not necessarily required for tracking. In one embodiment, the bone tracker set can also have a set with two bone fixations, wherein a first bone fixation has a screw shaft and the second bone fixation has a pin as a bone anchor.For example, in a large bone, the first bone fixation can be screwed in using the screw shaft, which sits particularly firmly and stably, and in a smaller bone, the second bone fixation can be fixed using the pin, which is preferably in the form of a nail.

[0028] Preferably, the bone fixations, in particular pins, have a (radially protruding) collar as a stop on the proximal end section. In particular, the collar is the closure or end stop of the coupling section, so that reference adapters, in particular sleeves, in particular the optical reference marker, coupled to the bone fixation, in particular the pin, always have a fixed geometric relationship to the bone fixation, in particular the pin, and the distal bone anchor. As a result, by detecting the optical reference pattern, conclusions can be drawn directly about the distal bone anchor and thus about the bone via the static, fixed relationship. In particular, only rotation remains as a degree of freedom, i.e. the sleeve with the optical reference markers can be rotated about its own axis on the pin.In particular, the pins have a collar at or near the proximal end, so that the coupled sleeve has a fixed geometric relationship to the pin and the distal bone anchor. With the stop, five degrees of freedom (5 DOF) can be determined, whereas without the stop, only four degrees of freedom can be determined (4 DOF). In both cases, the rotation is open, so two trackers or bone fixators with reference adapters are always required to determine the complete position with six degrees of freedom (6 DOF position).

[0029] According to a further embodiment, the pins can have a cylindrical outer contour as a coupling section and the sleeve can have a hollow cylindrical counter-coupling section, which is adapted to be plugged or pluggable over the cylindrical outer contour without tools, in particular by means of a clearance fit of approximately d"7 8or d )for easy coupling and uncoupling (with sliding on and off) or a transition fit for stable coupling (approximately d6 7, wherein an external thread is preferably provided in the area of ​​the front side of the cylindrical outer contour of the coupling section and a complementary internal thread is provided in the hollow cylindrical counter-coupling structure in order to ensure secure coupling and uncoupling without the need for tools. In particular in combination with a thread, the sleeve can first be pushed on and secured by means of approximately half a turn or a full turn. By means of the cylindrical outer contour (of the coupling section) of the pin, in particular with a collar at a distal end of the coupling section, and the hollow cylindrical sleeve, which can be easily pushed on, an efficient and secure system or set can be provided. In particular, a diameter of the coupling section is a minimum of 2 mm, preferably 4 mm and / or a maximum of 10 mm, preferably a maximum of 5 mm.The sleeve can thus be easily coupled (mounted) and uncoupled (dismounted) during the procedure without tools, so that the sleeve is only coupled when navigation is required.

[0030] In particular, the coupling section (as or with the coupling structure) and the counter-coupling structure can form a magnetic connection / coupling when coupled, preferably at least one of the two coupling structures has a magnet that forms the magnetic connection. With two magnets, these must have opposite polarity; with one magnet, a metallic (magnetically attractive) structure on the opposite side is sufficient. Thus, the risk of relative movement in the axial direction can be prevented or at least minimized by means of the magnetic attachment. In other words, a magnetic coupling is provided which is independent of the shape of the coupling section and the counter-coupling structure (as a form-fitting interface). The magnetic coupling allows for a stable connection without tools. One could also say that a type of locking device is provided by means of the magnetic coupling.

[0031] Preferably, a dimension of the cylindrical coupling structure in the axial direction is at least 15 mm, preferably at least 30 mm, so that the coupling structure provides a sufficient length for a coupling.

[0032] According to another embodiment, the bone fixation can also have a proximal sleeve and the reference adapter can be designed as a pin, with the optical reference marker preferably being attached to a proximal head. In this embodiment, the pin and sleeve are thus reversed from the (special) embodiment described above.

[0033] Preferably, a dimension of the end portion of the bone fixation, in particular of the pin, is at least 30 mm in order to protrude from a skin of the patient in the implanted state.

[0034] According to one embodiment, at least one of the reference adapters or the at least two reference adapters may have a proximal head with the optical reference marker.

[0035] According to one embodiment, the proximal head can be rotationally symmetrical.

[0036] According to one embodiment, the proximal head may be designed as a rotational body.

[0037] According to one embodiment, the sleeve can have a proximal sleeve head, in particular a conically shaped sleeve head (similar to an umbrella), with an optical reference marker, on whose outer surface (of the sleeve head) an optical pattern, in particular a circumferential QR code, is incorporated or applied as an optical reference marker, for example, printed or engraved. The optical reference body can thus be an optical pattern with characteristic visual features.

[0038] According to a further embodiment, the reference adapter, in particular the sleeve, can have a proximal head, in particular a sleeve head, in the form of a flat disc (flat disc) with the optical reference marker, on whose (proximal) outer surface (proximal to the flat disc) an optical pattern, in particular a circumferential QR code, is incorporated or applied as an optical reference marker, for example printed or engraved. A flat disc is cost-effective to produce and offers a good view of the optical reference marker from the proximal direction. The flat disc is arranged concentrically to the longitudinal axis and in particular symmetrically about the longitudinal axis. In one embodiment, the flat disc has a circular contour. Alternatively, the flat disc can also have an oval circumferential contour.

[0039] In particular, the reference adapter can have a proximal head with two spaced-apart marker spheres arranged coaxially with a longitudinal axis of the reference adapter, which together form the proximal optical reference marker. Two marker spheres located on the longitudinal axis of the reference adapter are used as the optical reference marker. These marker spheres can be used to determine a straight line in space through a reference point (i.e., 4DOF), or preferably even with a reference point (5DOF).

[0040] According to a further embodiment, the reference adapter, in particular the sleeve, can have a proximal head, in particular a sleeve head, with at least two concentric rings, in particular precisely two rings, which are spaced apart from one another and arranged both concentrically to one another and to a longitudinal axis of the sleeve, so that when the reference adapter is coupled to the bone fixation, in particular the sleeve to the pin, the rings also have their center point in the axis of the bone fixation, in particular the pin. The optical reference body can therefore in particular have or consist of two rings, wherein both rings ultimately have their center point in the axis (in particular of the pin) in the coupled state.In order to better track the rings, it is sufficient if only one position of the ring can be captured by the optical camera so that the ring can be extrapolated (using the adapted control unit) and the center of the ring can be determined.

[0041] Preferably, the at least two concentric rings can each have a unique optical pattern and / or a different diameter to improve optical tracking. This allows a distal and proximal ring to be directly identified, whereby the position can be determined unambiguously to within approximately one degree of rotation. In particular, each ring can have a unique optical pattern to facilitate localization of the ring with the optical camera.

[0042] The present disclosure also relates to a bone tracking system for tracking, and further preferably for registering, at least two bones (several bones) relative to one another, in particular at least two spinal bones, said system comprising: a bone tracker set according to the present disclosure, an optical camera for optically capturing the optical reference markers of the bone tracker set and for spatial tracking by a navigation system, a visual display device, in particular a surgical monitor, and a control unit which is specially adapted to capture the at least two optical reference markers via the optical camera and to spatially track them and for each optical reference marker (the reference adapter coupled to the bone fixation, in particular the sleeve coupled to the pin) a position determination with a maximum of five, in particular four or five,degrees of freedom (5DOF), and the control unit is adapted to determine the remaining sixth degree of freedom (for 5 DOF) or also the fifth and sixth degrees of freedom (for 4 DOF) based on two, in particular adjacent, optical reference markers, and to visually output the position of the bones relative to each other via the display device in a live tracking mode, in particular with superimposed anatomical parameters, such as preferably a sagittal plane or balance. This disclosure thus proposes a bone tracking system that enables the tracking of multiple bones using minimally invasive bone anchors and (optical) reference bodies with a small profile.

[0043] A bone anchor, in particular a pin-shaped one (pin with a distal bone anchor as an embodiment of bone fixation), is inserted into the bone, for example a spinous process, until sufficient longitudinal stability is achieved. While the distal section of the pin (as bone fixation) is anchored to or in the bone, in particular sits within the bone, the proximal section of the pin protrudes outside the patient's skin when implanted. Rotational stability is not required here. In this case, at least two bones (for example vertebral bodies) are anchored. The proximal section of the pin is designed or configured such that it can be coupled to a separate sleeve, in particular fits into a separate sleeve that is inserted over the proximal part of the pin with a fixed geometric relationship to the distal part of the pin. The sleeve, in turn, carries an optical reference marker orA reference body that enables tracking with an optical camera. This allows the pin, in particular, to be screwed into the bone without requiring a specific final rotation of the pin, increasing flexibility and handling on the operating table.

[0044] However, only (a maximum of) five degrees of freedom (5 DOF) can be determined per bone, in particular four or five degrees of freedom (4 DOF or 5 DOF), because the bone tracking system or bone tracking set has a rotational symmetry around a pin axis or can rotate around the axis. More precisely, one axis in particular is localized in space, with a reference point, i.e., with five degrees of freedom (5 DOF). The optical reference marker, in particular the optical pattern, can therefore be symmetrical around the pin axis and have a low profile relative to the pin axis. To determine all six degrees of freedom (i.e., the full 6 DOF), a pin and a sleeve (as a reference body) of a bone, especially an adjacent bone, are used to determine (at least) the missing rotational degree of freedom, i.e., to include the missing rotational degree of freedom (rotational DOF).Therefore, the tracking of the position and the two rotation parameters of the first bone is not influenced by the position of the second bone. Since the rotation of the first bone around the axis of the pin is very unlikely, i.e. very small, within the given spine, errors from such a movement can be neglected. To further reduce the error of the sixth degree of freedom (6 DOF), which is determined by another, particularly adjacent, bone, several, particularly adjacent, bones can be consulted or used to determine the missing sixth degree of freedom of the first bone. The bones do not necessarily have to be directly adjacent. For example, the next but one bone, in particular the next but one vertebral body, can also be used to determine the missing degree of freedom (using the optical reference marker).Preferably, the bone tracking system can comprise an intraoperative 3D X-ray scanner, and the control unit can be adapted to spatially capture (and optionally preferably also track) the pin, in particular a distal portion thereof, in a 3D X-ray image and to correlate the pin in the X-ray image with the optical reference marker of an optical image of the optical camera, in particular to perform registration, preferably of the patient. Thus, the bone tracking system is also capable of registering a patient using an intraoperative 3D X-ray scanner. For example, the pins are first inserted into all vertebral bodies to be treated. Then, a 3D X-ray scan / 3D X-ray image is taken. The position of the distal end of the pins is then determined using the 3D X-ray dataset or the 3D X-ray image.In the 3D dataset, the vertebral bodies must be segmented and registered separately. The correlation between the distal end of the pins and the attached sleeve is known by design. The sleeves are located using the optical camera with the optical reference marker (or body). With each pin, five degrees of freedom (5 DOF) can be determined (only rotation around the pin is missing). Using two pins, the full six degrees of freedom (6 DOF) can be determined, enabling complete spatial tracking. Thus, two pins and sleeves are required for the spatial tracking of at least two bones. Furthermore, registration can be achieved if necessary using additional features on the pin(s) visible in the 3D X-ray scan. However, even in the 3D X-ray scan, the sleeve can only be detected with five degrees of freedom (5 DOF).

[0045] In particular, registration can be performed with two bone fixations, particularly pins, in a 3D X-ray scan ("X-ray image"). In this case, the bone fixations, particularly pins, initially provide only four degrees of freedom (4 DOF) (a straight line in space). By evaluating two bone fixations, particularly two pins, a 6 DOF registration can then be determined from 2x 4 DOF (two skew lines spanning a coordinate system). However, this only works if the lines are not parallel. Otherwise, a point on the line must be determined for at least one of the lines – this can be the distal end, in particular. This determines five degrees of freedom (5 DOF), and registration can be performed unambiguously even with parallel lines.

[0046] In one embodiment, the control unit can be adapted to detect the position, in particular the location, of each ring using the optical camera in the case of optical reference markers in the form of at least two rings and to determine the first center point of the first ring and the second center point of the second ring by means of calculation, in particular extrapolation, in order to determine the location of the pin (and thus the location of the associated bone) by means of the determination of the two center points.

[0047] According to one embodiment, the optical camera may be a white light camera or an infrared camera.

[0048] In particular, the bone tracking system may comprise a mobile medical cart carrying the optical camera, which is particularly adapted to be placed next to an operating table. Thus, the optical camera may be mounted on a cart that can be positioned next to the operating table.

[0049] Preferably, the position of the optical reference markers can also be recorded with a microscope during the X-ray image acquisition, and the position of the 3D X-ray scanner / X-ray system can also be recorded with the microscope, with the X-ray system or X-ray machine calibrated. In this way, the position of the reference markers can be determined using two acquisition modes.

[0050] Preferably, the bone tracking system may comprise a medical robot, and the optical camera may be attached to a robot arm of the robot, wherein the camera is positionable over a patient by means of the robot arm to avoid or minimize line-of-sight problems. In other words, the optical camera may be mounted on a robot arm that is positionable over the patient, thereby minimizing line-of-sight problems.

[0051] In particular, the optical camera can be a surgical visualization system, in particular an exoscope, or be present in such a system, which performs two functions: surgical visualization and optical tracking, or the optical camera can be a separate optical camera from a surgical visualization system, such as an exoscope, which can be positioned in particular next to an exoscope. In other words, the optical camera can simultaneously be a surgical visualization system, such as an exoscope, or a separate camera that can be positioned next to the exoscope.

[0052] In one embodiment, in addition to the live tracking mode, the bone tracking system can also be operated in a scanning mode, in which the control unit is adapted to move the optical camera by means of a robot arm such that the camera scans the optical patterns and visually outputs the positions, in particular the locations, of the vertebral bodies in relation to one another in a static display via the display device. In other words, in addition to the live tracking mode, a scanning mode can also be provided, in which the optical camera moves along and scans the optical reference markers, in particular the optical patterns, and displays the locations of the vertebral bodies in relation to one another in a static display. Such a process can be repeated each time the bones, in particular the spine, are repositioned.

[0053] In particular, the pin has dimensions such that it protrudes from the patient's skin by at least 1 cm, preferably at least 3 cm, when anchored in the bone.

[0054] In particular, when mounted on a robotic arm, the optical camera can be easily positioned to avoid compromising ergonomics for the surgeons while still allowing good tracking. Preferably, pre-operative planning software can be provided in a storage unit, allowing the navigation system to plan the desired positions between the bones, especially the vertebral bodies, in advance.

[0055] In particular, the control unit can be adapted to display the positions of the vertebral bodies relative to each other intraoperatively in a live tracking mode, whereby in particular anatomical parameters such as the sagittal balance are calculated and additionally displayed.

[0056] In particular, the bone tracking system can also be used to track surgical instruments as patient trackers, either using the same optical camera to track the optical reference bodies of the instruments, or tracking the instruments with a separate optical (instrument) camera, whereby both cameras must be calibrated or tracked to each other.

[0057] The present disclosure also relates to a bone tracking method for tracking at least two bones relative to one another, in particular at least two spinal bones, comprising the steps of: tracking, by means of a bone tracking system, in particular a bone tracking system according to the present disclosure, two bone trackers of a bone tracker set, each having a bone fixation and a reference adapter, in particular a bone tracker set according to the present disclosure, wherein the reference adapter each has a proximal optical reference marker;

[0058] Determining an axis of the first bone fixation, in particular a unit vector of a first pin, which coincides with the main axis of the bone fixation;

[0059] Determining a coordinate origin of the first bone fixation;

[0060] Determining a second line or axis lying in the plane spanned by the first optical reference pattern that intersects the axis of the second bone fixation;

[0061] Determining the third axis by the vector product of the first axis and the second axis;

[0062] Determine a Cartesian coordinate system of the first bone fixation and thus of the first bone with the coordinate origin and the three axes for tracking the bone fixation and thus of the bone.

[0063] Another aspect of the present disclosure relates to a computer-readable storage medium and a computer program, each comprising instructions which, when executed by a computer, cause the computer to carry out the method steps of the bone tracking method.

[0064] In particular, the control unit (analog) of the bone tracking system can be adapted to carry out the corresponding steps of the

[0065] bone tracking procedure.

[0066] Short description of the characters

[0067] The present disclosure is explained below using preferred embodiments with reference to the accompanying figures. They show:

[0068] Fig. 1 is a schematic view of a bone tracking system of a preferred embodiment of the present disclosure including a bone tracker set according to a first preferred embodiment of the present disclosure;

[0069] Fig. 2 is a detailed view of the bone tracker set from Fig. 1;

[0070] Fig. 3 is a schematic view of a bone tracker set according to another preferred embodiment;

[0071] Fig. 4 is a schematic view of a pin of the bone tracker set in an X-ray image; Fig. 5 is another schematic view of pins of the bone tracker set;

[0072] Fig. 6 is a schematic view of a bone tracking set to explain the calculations and relationships between the pins and sleeves of individual bones;

[0073] Fig. 7 is a schematic view of a bone tracker set according to another preferred embodiment with marker spheres;

[0074] Fig. 8 is a schematic view of a bone tracker set according to another preferred embodiment with a flat disc; and

[0075] Fig. 9 is a flowchart of a bone tracking method according to a preferred embodiment.

[0076] The figures are schematic in nature and are intended only to aid understanding of the invention. Identical elements are provided with the same reference numerals. The features of the various embodiments can be interchanged.

[0077] Detailed description of preferred embodiments

[0078] Fig. 1 shows a bone tracker set 1 according to a first preferred embodiment of the present disclosure and a bone tracking system 100 according to a first preferred embodiment of the present disclosure, wherein Fig. 2 shows a detailed view of the bone tracker set 1.

[0079] Specifically, Fig. 1 (and Fig. 2) shows a bone tracker set 1 for the bone tracking system 100 for tracking and registering at least three vertebral (column) bones (as bones) relative to one another. The bone tracker set 1 has three pins 2 (as an embodiment of a bone fixation), each adapted to be fastened directly into a vertebral bone of a patient P by means of a distal bone anchor 4. Except for the bone anchor 4, the pins 2 are designed to be essentially rotationally symmetrical. Each pin 2 has a proximal end section 6 with a coupling section 8 for coupling a respective sleeve 10 (as an embodiment of a reference adapter). Specifically, three separate sleeves 10 are provided, each carrying a proximal optical reference marker 12 for optical (spatial) tracking.The sleeves 10 are adapted to be coupled or uncoupled from the coupling section 8 of the pin 2 without the use of tools. The sleeves 10 have a counter-coupling structure 14, which will be described in more detail below.

[0080] The bone tracking system 100 (hereinafter referred to as system 100) for tracking and registering the three vertebral (column) bones relative to one another is designed in the form of a robot-guided surgical microscope and, in turn, has an optical camera 102 for optically capturing the optical reference markers 12 of the bone tracker set 1 for spatial tracking by a navigation system 104. The microscope head itself is used as the optical camera 102, so that the camera 102 is used for both surgical visualization and optical tracking. The system 100 further has a visual display device 106 in the form of a surgical monitor, which can optionally be supplemented with a head-mounted display.In addition, a control unit 108 of the system 100 is specially adapted to detect and spatially track the at least three optical reference markers 12 via the optical camera 102 and to carry out a position determination with five degrees of freedom (5DOF) for each optical reference marker 12. For this purpose, the control unit 108 is further adapted to determine the remaining sixth degree of freedom based on two adjacent optical reference markers 12 and, in a live tracking mode, to visually output the position of the bones relative to one another via the display device 106, in particular with superimposed anatomical parameters, such as preferably a sagittal plane or balance. In particular, the control unit 108 is adapted to carry out such a determination as described for Fig. 6. In addition to the optical camera 102, the system 100 also has a (separate) navigation camera 118, which, among other things,The optical camera 102 is tracked using a rigid body with four markers. The system 100 as a whole is arranged on a medical cart 112, allowing it to be placed in a mobile manner in the operating room.

[0081] In this embodiment, the system 100 has a medical robot 114 as a robot-guided surgical microscope, wherein the optical camera 102 is connected to a multi-jointed robot arm 116 of the robot 114, so that the camera 102 can be positioned over the patient P by means of the robot arm 116, as shown in Fig. 1, in order to avoid line-of-sight problems and to ensure precise tracking.

[0082] The bone tracker set 1 shown in Figs. 1 and 2 will now be described in detail. Specifically, in this embodiment shown in Figs. 1 and 2, each pin 2 has a distal screw shaft 16 with an external thread 18 as a distal bone anchor 4, which is screwed into a spinous process of the vertebral bone. Thus, the pin 2 is securely fixed in the respective bone.

[0083] Furthermore, the pins 2 have a collar 18 on the proximal end section 6 as an axial stop, here as the end stop of the coupling section 8, so that the sleeves 10 coupled to the pin 2 and its optical reference marker 12 always have a fixed geometric relationship to the pin 2 and the distal bone anchor 4. In particular, a tip of the bone screw or screw shaft is relevant as a reference. For example, the distance between the center of one ring and the screw tip is 60 mm, and from the center of the proximal ring, 65 mm. In this way, the navigation system 104 can directly determine the respective bone by detecting the optical reference marker 12, particularly if an image with implanted pins 2 (and possibly a registration with 3D data of the patient) has already been taken using a 3D X-ray device 110.The pins 2 each have a cylindrical outer contour 20 as the coupling section 8, and the sleeve 10 has a hollow-cylindrical counter-coupling section 14, which is adapted to be manually attached without tools over the cylindrical outer contour 20 by a medical professional such as a surgeon. This allows the optical reference marker 12 to be easily and safely attached and detached. Therefore, if navigation is required, the sleeves 10 can be quickly attached and removed again for a subsequent procedure, for example, to enlarge the field of view or to enable better handling by the surgeon in the spinal region.

[0084] In this embodiment, the sleeve 10 has a proximal sleeve head 24 with exactly two concentric rings 30, which are spaced apart from one another and arranged both concentrically to one another and to a longitudinal axis 32 of the sleeve 10, so that the rings 30, when the sleeve 10 is coupled to the pin 2, also have their center point in the axis of the pin 2. The rings 30 can, as in the present case, have a different color marking or a special optical pattern and / or a different diameter; for example, the distal ring 30 can have a larger diameter than the other ring 30. For example, the rings 30 can be attached to the sleeve 10 by means of radial struts, for example three struts.

[0085] The control unit 108 of the system 100 is adapted accordingly to detect the position of each ring 30 of the three optical reference markers 12 in the form of exactly two rings 30 each by the optical camera 102 and to determine the first center point of the first ring and the second center point of the second ring by means of calculation, in particular extrapolation, in order to determine the position of the pin 2 and thus of the associated vertebrae by means of the determination of the two center points and the known reference to a tip of the pin 2.

[0086] With the system 100, spatial tracking of the three vertebrae (relative to one another) of the patient P can be carried out, each with a minimally invasive bone anchor 4 in the form of a screw shaft 16 and connectable and detachable optical reference markers 12 of a small design. The pin 2 with distal bone anchor 4 is therefore initially screwed into the spinous process until sufficient longitudinal stability is achieved. Due to the geometric adaptation, as shown in Figs. 1 and 2, the proximal section of the pin 2 protrudes from the skin of the patient P in order to provide the coupling section 8 outside the patient P. Each proximal section of the pin 2 can be coupled to the separate sleeve 10, which in turn carries the optical reference marker 12.

[0087] For each vertebral bone, only five degrees of freedom can be determined using the optical camera 102 of the control unit 108 and the navigation system 104, since the system 100 or the bone tracking set 1 each exhibits rotational symmetry about an axis of the pin 2 or longitudinal axis 32. The system 100 uses the optical reference marker 12 to locate an axis in space for each pin 2 with a reference point, in particular the screw shaft tip, thus with five degrees of freedom.

[0088] To determine all six degrees of freedom for a unique position (6DOF), pin 2 and sleeve 10 of the adjacent vertebra are used to determine the missing rotational degree of freedom. Since the rotation of the first vertebra around the axis of pin 2 within the spine is very small, errors due to such movement are neglected, as a sufficiently high spatial tracking precision can still be achieved with system 100. In this way, the spine and its bones can be easily and precisely tracked intraoperatively with system 100.

[0089] Fig. 3 shows a further embodiment of the bone tracker set 1 according to the present disclosure. The bone tracker set 1 is essentially identical to the bone tracker set 1 of the first preferred embodiment shown in Figs. 1 and 2, but differs from the first preferred embodiment in that the optical reference marker 12 is not designed in the form of two rings, but in the form of a sleeve 10 with a proximal, conically shaped sleeve head 24, on the outer surface 26 of which an optical pattern 28 in the form of a symmetrical, circumferential QR code is applied as the optical reference marker 12. In this way, an optical pattern 28 can be detected with a flat profile. The bone tracker set 1 can be used alternatively or in addition to that shown in Fig. 1 in the system 100 shown in Fig. 1.Accordingly, the control unit 108 is adapted to carry out a position determination for spatial tracking by means of the optical pattern 28 in addition to the rings.

[0090] In particular, this bone tracker set 1 of Fig. 3 can have a magnet in the reference adapter (which is inserted approximately inside the sleeve on a proximal side), so that a force-fitting, magnetic, tool-free connection (and thus also securing) is provided.

[0091] Fig. 4 shows a schematic view of a pin 2 in an X-ray image. The screw shaft 16 is screwed into the spinous process and (except for the thread) the pin 2 is designed to be rotationally symmetrical about its longitudinal axis. In the X-ray image, the patient can even be registered using the pin 2, which in particular is made of metal so that it can be easily recognized in the X-ray image. The control unit is adapted to locate the pins 2 in the X-ray image and to correlate them with the pins in the optical image taken by the optical camera 102, thus tracking them and, in particular, registering the patient. After the pins have been identified and the vertebral bodies have been segmented, registration is performed by matching the intraoperative X-ray images with the existing CT and MRI scans.

[0092] If, as shown in Fig. 5, several pins 2 are screwed into the vertebral bodies, which can usually be done, the system 100 can reduce the error of the sixth degree of freedom (6 DOF) to be determined, which is determined by an adjacent bone, by using several adjacent bones to determine the missing sixth degree of freedom of the first bone, as explained below with reference to Fig. 6.

[0093] In Fig. 6 the relations to each other are shown and the steps are shown or indicated how the coordinate systems for each vertebrae (for tracking) are constructed or determined: Here O x the (coordinate) center of the optical reference marker 12 of the first pin 2 screwed into the vertebral bone. The unit vector e zrepresents the main axis of the optical reference marker 12 (which coincides with the axis of the pen 2). Specifically, the unit vector in the y-direction e y fixed to the line which is in the plane defined by the first optical reference marker 12 (or its optical pattern; of the first pin 2) (C^, normal to the unit vector in the z-direction e z ) and the (second) axis ( O2, e z2 ) of the adjacent second pin 2. The remaining (and to be determined) unit vector in the x-direction e x is then uniquely determined by the vector product of e z and e y This means that O lf e x , e y , e z a Cartesian coordinate system and the position of the optical reference marker 12 and thus also of the corresponding vertebral bone (due to the screwing into it, a statically determinable transformation is always present).

[0094] If the system 100 now determines the “local” KOS of the pin for each optical reference marker 12, the pins and thus the respective vertebrae can be tracked intraoperatively.

[0095] The procedure for determining this can also be summarized in the following formulas: e zl = axis of the (first) pin

[0096] (1 )

[0097] OJL = coordinate origin of the first pin

[0098] (2) e x = Intersection Level e z2 , OiO2) f plane (O lf e z )

[0099] (4) Accordingly, the control unit 108 of the system 100 is adapted to determine the coordinate systems (KOS) in order to perform tracking and even registration of the patient.

[0100] Fig. 7 shows another embodiment of a bone tracker set 1 of the present disclosure. In contrast to the above optical patterns as a machine vision pattern, two passive marker spheres 34 are now provided on the proximal head. This embodiment also allows for simple, efficient tracking as well as cost-effective manufacturing. In this embodiment, a magnet (not shown) is provided in the reference adapter (inside the sleeve), thus providing a force-fit, magnetic connection.

[0101] Fig. 8 also shows a further embodiment of a bone tracker set 1 of the present disclosure, with the difference that a flat disc 36 is arranged on the proximal head, on the (proximal) upper side of which an optical pattern 28 is introduced (not shown here since the view is onto the underside of the flat disc 36).

[0102] As an alternative to bone fixation in the form of a pin 2 with a screw shaft 16 with an external thread 18, a pin can also be provided as a bone anchor, which is fixed in the bone. For example, the pin can be designed in the form of a nail, which is pressed or driven into the bone.

[0103] Fig. 9 shows a bone tracking method according to a preferred embodiment. The bone tracking method serves to track at least two bones relative to each other, in particular at least two spinal bones.

[0104] In a first step S1, tracking is performed by means of a bone tracking system 100 according to the present disclosure, of two bone trackers of a bone tracker set, each having a bone fixation and a reference adapter of a bone tracker set 1 according to the present disclosure, wherein the reference adapter each has a proximal optical reference marker. In step S2, an axis e is determined. zl the first bone fixation, in particular a unit vector e zl a first pin which coincides with the main axis of bone fixation;

[0105] In step S3, a coordinate origin is determined the first bone fixation and in step S4 determining a line or second axis e yl , which is determined by the first optical reference pattern O lf Normal e zl The plane spanned by the axis e lies z2the second bone fixation.

[0106] In step S5, a third axis e is determined xl by the vector product of the first axis e zl and the second axis e yl ; and finally, determining a Cartesian coordinate system of the first bone fixation and thus of the first bone with the coordinate origin and the three axes e xl , e yl , e zl for tracking bone fixation and thus the bone.

[0107] List of reference symbols

[0108] 1 bone t racker set

[0109] 2 pens

[0110] 4 bone anchors

[0111] 6 Proximal end section

[0112] 8 coupling section

[0113] 10 sleeves

[0114] 12 optical reference markers

[0115] 14 Counter-coupling structure

[0116] 16 screw shaft

[0117] 18 collars

[0118] 20 Cylindrical outer contour

[0119] 22 external threads

[0120] 24 sleeve head

[0121] 26 Exterior area

[0122] 28 optical pattern

[0123] 30 rings

[0124] 32 Longitudinal axis

[0125] 34 marker balls

[0126] 36 flat disc

[0127] 100 Bone Tracking System

[0128] 102 optical camera

[0129] 104 Navigation system

[0130] 106 Display device

[0131] 108 Control unit

[0132] 110 3D X-ray scanners / 3D X-ray machines

[0133] 112 Medical Cart

[0134] 114 Medical Robot

[0135] 116 Robot arm

[0136] 118 Navigation camera

[0137] P Patient

Claims

Claims 1. A bone tracking system (100) for tracking at least two bones relative to one another, comprising: a bone tracker set (1), wherein the bone tracker set (1) has at least two bone fixations (2), each with a distal bone anchor (4) which is provided and adapted to be attached directly to or in a bone of a patient (P), as well as at least two reference adapters (10), each with a proximal optical reference marker (12), an optical camera (102) for optically capturing the optical reference markers (12) of the bone tracker set (1) for spatial tracking by a navigation system (104), and a control unit (108), wherein the control unit (108) is adapted to capture and spatially track the at least two optical reference markers (12) via the optical camera (102), wherein the control unit (108) is adapted toto carry out a position determination with six degrees of freedom for a first reference marker (12) of the two reference markers (12), to carry out a position determination with at least one degree of freedom for a second reference marker (12) of the two reference markers (12), and to check the position determination of the first reference marker (12) by the position determination of the second reference marker (12).

2. Bone tracking system (100) according to claim 1, characterized in that the control unit (108) is adapted to carry out the position determination for the second reference marker (12) with six degrees of freedom.

3. Bone tracking system (100) according to claim 1, characterized in that the control unit (108) is adapted to carry out the position determination for the second reference marker (12) with a maximum of four or a maximum of five degrees of freedom.

4. Bone tracking system (100) for tracking at least two bones relative to one another, comprising: a bone tracker set (1), wherein the bone tracker set (1) has at least two bone fixations (2), each with a distal bone anchor (4), which is provided and adapted to be attached directly to or in a bone of a patient (P), as well as at least two reference adapters (10), each with a proximal optical reference marker (12), an optical camera (102) for optically capturing the optical reference markers (12) of the bone tracker set (1) for spatial tracking by a navigation system (104), and a control unit (108), wherein the control unit (108) is adapted to capture and spatially track the at least two optical reference markers (12) via the optical camera (102), wherein the control unit (108) is adapted toto detect and spatially track the at least two optical reference markers (12) via the optical camera (102) and to carry out a position determination with a maximum of five degrees of freedom for each optical reference marker (12), wherein the control unit (108) is further adapted to determine at least the remaining sixth degree of freedom on the basis of the at least two optical reference markers (12).

5. Bone tracking system (100) according to one of claims 1 to 4, characterized in that the bone tracking system (100) has a visual display device (106), in particular a surgical monitor or a head-mounted display, wherein the control unit (108) is adapted to visually output the position of the bones relative to one another via the display device (106) in a live tracking mode.

6. Bone tracking system (100) according to one of claims 1 to 5, characterized in that the bone tracking system (100) comprises an intraoperative 3D X-ray scanner (110), and the control unit (108) is adapted to the bone fixation (2), in particular a distal portion thereof, to spatially capture and track in a 3D X-ray image and to correlate the bone fixation (2) in the X-ray image with the optical reference marker (12) of an optical image of the optical camera (102) in order to carry out a registration.

7. Bone tracking system (100) according to one of claims 4 to 6, characterized in that the bone tracking system (100) is further adapted to register at least two bones relative to each other, wherein the control unit is adapted to detect the bone fixations (2) in the 3D X-ray image, to determine four or five degrees of freedom for each of these bone fixations, in order to determine the six degrees of freedom based thereon.

8. Bone tracking system (100) according to one of claims 4 to 7, characterized in that the control unit (108) is adapted to detect the position, in particular the location, of each ring (30) using the optical camera (102) for optical reference markers (12) in the form of at least two rings (30) and to determine the first center point of the first ring and the second center point of the second ring by means of calculation, in particular extrapolation, in order to determine the location of the bone fixation (2) by means of the determination of the two center points.

9. Bone tracking system (100) according to one of claims 1 to 8, characterized in that the optical camera (102) is a white light camera or an infrared camera.

10. Bone tracking system (100) according to one of claims 1 to 9, characterized in that the bone tracking system (100) comprises a medical mobile cart (112) which carries the optical camera (102) and which is in particular adapted to be placeable next to an operating table.

11. Bone tracking system (100) according to one of claims 1 to 10, characterized in that the bone tracking system (100) comprises a medical robot (114) and the optical camera (102) is mounted on a multi-jointed robot arm (116) of the robot (114), wherein the camera (102) can be positioned over a patient (P) by means of the robot arm (116) in order to avoid or minimize line of sight problems.

12. Bone tracking system (1) according to one of claims 1 to 11, characterized in that the optical camera (102) is a surgical visualization system which performs two functions of optical visualization and spatial tracking, or the optical camera is an optical camera separate from a surgical visualization system.

13. Bone tracking system (100) according to one of claims 11 or 12 in conjunction with claim 5, characterized in that in addition to the live tracking mode, the bone tracking system (100) can also be operated in a scanning mode, in which the control unit (108) is adapted to move the optical camera (102) by means of a robot arm (116) in such a way that it scans the optical reference markers (12), in particular the optical patterns (28), and visually outputs the positions of the bones, in particular vertebral bodies, in relation to one another in a static display via the display device (106).

14. Bone tracking method for tracking at least two bones relative to each other, using a bone tracking system (100) according to one of claims 4 to 13, characterized by the steps: Tracking (S1 ) of the bone tracker set (1 ); Determine (S2) an axis (e zl) a first bone fixation (2) of the two bone fixations (2); Determining (S3) a coordinate origin (O x ) the first bone fixation; Determining (S4) a line or second axis (e yl ), which is in the direction indicated by the first optical reference pattern (O lf Normal e zl ) spanning the axis (e z2 ) a second bone fixation (2) which intersects two bone fixations (2); Determining (S5) a third axis (e xl ) by the vector product of the first axis (e zl ) and the second axis (e yl ); Determine a Cartesian coordinate system of the first bone fixation and thus of the first bone with the coordinate origin (O x ) and the three axes (e xl , e yl , e zl ) for tracking bone fixation and thus the bone.

15. Bone tracker set (1) for a bone tracking system (100) according to one of claims 1 to 13, for tracking, preferably further for registering, at least two bones relative to one another, comprising: at least two bone fixations (2), each having a distal bone anchor (4) and a proximal end section (6) with a coupling section (8), wherein the bone anchor (4) is provided and adapted to be fastened directly to or in a bone of a patient (P), and at least two reference adapters (10), each having a proximal optical reference marker (12) and a counter-coupling structure (14), wherein the counter-coupling structure (14) can be coupled to and uncoupled from the coupling section (8) of the bone fixation (2) without the need for tools.

16. Bone tracker set (1) according to claim 15, characterized in that the bone fixation (2) has a screw shaft (16) with an external thread (18) as a distal bone anchor (4) to be screwed into the bone, or the bone fixation (2) has a pin as a distal bone anchor (4) to be fixed in the bone, preferably in a spinous process.

17. Bone tracker set (1) according to claim 15 or 16, characterized in that the bone fixation (2) has a collar (18) as an axial stop on the proximal end section (6), so that the reference adapter (10) coupled to the bone fixation (2), in particular the optical reference marker (12), always has a fixed geometric relationship to the bone fixation (2) and the distal bone anchor (4).

18. Bone tracker set (1) according to one of claims 15 to 17, characterized in that the bone fixation (2) has a cylindrical outer contour (20) as the coupling section (8) and the reference adapter (10) has a hollow cylindrical section as the counter-coupling section (14), which is adapted to be plugged over the cylindrical outer contour (20) without tools, wherein an external thread (22) is preferably provided in the region of the end face of the cylindrical outer contour (20) of the coupling section (8) and a complementary internal thread is provided in the hollow cylindrical counter-coupling structure (14) in order to provide a tool-free, secure coupling and / or uncoupling by means of screwing.

19. Bone tracker set (1) according to one of claims 15 to 18, characterized in that at least one of the reference adapters (10) or the at least two reference adapters (10) has a proximal head with the optical reference marker (12), wherein the proximal head is rotationally symmetrical.

20. Bone tracker set (1) according to claim 19, characterized in that the proximal head is designed as a rotation body.

21. Bone tracker set (1) according to claim 19 or 20, characterized in that the proximal head (24), in particular a conically shaped sleeve head (24), has an outer surface (26) with an optical pattern (28), in particular a circumferential QR code, as an optical reference marker (12).

22. Bone tracker set (1) according to claim 19 or 20, characterized in that the proximal head (24) has at least two concentric rings (30) which are spaced apart from one another and arranged both concentrically to one another and to a longitudinal axis (32) of the reference adapter (10), so that the rings (30) also have their center point in the axis of the bone fixation (2) when the reference adapter (10) is coupled to the bone fixation (2).

23. Bone tracker set (1) according to claim 22, characterized in that the at least two concentric rings (30) each have a unique optical pattern and / or have a different diameter in order to improve the optical tracking.

24. Bone tracker set (1) according to claim 19 or 20, characterized in that the proximal head is designed in the form of a flat disc (36), on the outer surface of which an optical pattern, in particular a circumferential QR code, is incorporated or applied as an optical reference marker.

25. Bone tracker set (1) according to claim 19 or 20, characterized in that the proximal head has two marker spheres spaced apart from one another and arranged coaxially to a longitudinal axis of the reference adapter, which together form the proximal optical reference marker (12).

26. Bone tracker set (1) according to one of claims 15 to 25, characterized in that the coupling section (8) of the bone fixation and the counter-coupling structure (14) of the reference adapter (10) are adapted to form a magnetic connection as a magnetic coupling with one another in the coupled state, in particular the coupling section (8) and / or the counter-coupling structure (14) has a magnet for the magnetic connection in order to provide tool-free, secure coupling and uncoupling.

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