WO2015144246A1

WO2015144246A1 - Instrument for creating an artificial landmark on a surface of a bone and medical navigation system

Info

Publication number: WO2015144246A1
Application number: PCT/EP2014/056340
Authority: WO
Inventors: Nadja HEINDL; Uli Mezger; Lennart Stieglitz; Jürgen Beck
Original assignee: Brainlab Ag
Priority date: 2014-03-28
Filing date: 2014-03-28
Publication date: 2015-10-01

Abstract

The present invention relates to a medical artificial landmark creating instrument (1) for creating an artificial landmark on a surface of a bone (7) through skin covering the bone (7), comprising an artificial landmark creation structure (2; 4 a) and an instrument marker device (3) which is in a known spatial relationship with respect to at least a part of the artificial landmark creation structure (2; 4a), wherein the instrument marker device (3) comprises at least three markers (3a, 3b, 3c) in a known geometric arrangement.

Description

INSTRUMENT FOR CREATING AN ARTIFICIAL LANDMARK ON A SURFACE

OF A BONE AND MEDICAL NAVIGATION SYSTEM

The present invention relates to a medical artificial landmark creating instrument for creating an artificial landmark on a surface of a bone through skin covering the bone, a medical navigation system comprising said medical artificial landmark creating instrument and a medical registration method.

Objects such as medical instruments or bones are tracked in modern surgeries using a medical navigation system. This requires the object to be provided with a marker device which is detectable by the medical navigation system. Since the medical navigation system can only detect the position of the marker device, it is essential to know the positional relationship between the object, or at least a part of the object, and the marker device. This positional relationship is generally referred to as registration.

There are many ways for establishing a reliable initial registration between the object, in particular a bone, and a marker device. Approaches known in the art include, among others, to obtain the initial registration from three-dimensional medical image data or to sample points on the surface of the bone using a pointer. The general problem is that the initial registration degrades over time. Exemplary reasons for this degradation are sterile preparation after registration, exchanging the marker device or forces acting on the marker device, such as forces caused by draping sheets. In some cases, the marker device is not directly connected to the bone to be registered. This in particular occurs with craniotomy applications, where the head is typically held in a head holder and the marker device is attached to said head holder. If the head moves within the head holder, the initial registration is degraded or even lost

One solution to this problem is to acquire intraoperative landmarks using the navigation system. When the bone is exposed, intraoperative landmarks can be sampled. Sampling a point, such as a landmark, means to determine the location of the point, in particular relative to the marker device. However, at this time the initial registration can already be degraded, for example by exposing the bone or replacing the marker device used for obtaining the initial registration by a sterile marker device which can be used during surgery. In order to solve this problem, the inventors have discovered an approach that provides the preconditions for verifying the registration or re-establishing the registration at a time as close to the time of the initial registration as possible. This in particular includes creating artificial landmarks on the bone as shortly after the initial registration as possible. The locations of the artificial landmarks relative to the marker device can be stored, such that the stored locations can later be compared to sampled locations of the artificial landmarks.

In this document, the term "position" means the (spatial) location in up to three translational dimensions and/or the alignment (or orientation) in up to three rotational dimensions.

The present invention relates to a medical artificial landmark creating instrument for creating an artificial landmark on a surface of a bone through skin covering the bone. The instrument comprises an artificial landmark creation structure and an instrument marker device which is in a known spatial relationship with respect to at least a part of the artificial landmark creation structure, wherein the instrument marker device comprises at least three markers in a known geometric arrangement.

With this configuration, the medical artificial landmark creating instrument can create the artificial landmark and be tracked by a medical navigation system in order to determine the location of the artificial landmark at the same time. In this document, the expression "at the same time" can mean at exactly the same time, but also within a period of time such as within 0.2, 0.5, 1 or 2 seconds.

Since the artificial landmark can be created through the skin, it is not necessary to expose the bone in order to create the artificial landmark. It is therefore possible to create the artificial landmark immediately after the initial registration between the bone and a corresponding bone marker device is established. The bone marker device is a marker device associated with the bone for tracking the bone by tracking the bone marker device. Hie location of an artificial landmark on the bone is invariant, which means that it does not change over time, at least not during a time required for a surgery. An advantage of an artificial landmark is that it can easily be sampled during surgery. Physiological landmarks in theory are defined, distinct points, while in practical situations it is hard to exactly find and sample such a landmark. This means that if a physiological landmark is sampled several times, even by the same person, then the location of the sampled point may vary in a certain range. An artificial landmark, on the contrary, is a defined, distinct point which can easily be found and be exactly sampled each time.

The medical artificial landmark creating instrument comprises a distal end which penetrates through the skin and comprises the artificial landmark creation structure. The distal end may be cone-shaped such that it can be inserted through the skin or at least one blade for creating an incision which is large enough for penetrating the skin with the distal end there through.

In one embodiment, the artificial landmark creation structure comprises a tip which is adapted to create a cavity in the surface of the bone. The cavity men is the artificial landmark or a part of the artificial landmark. The tip is made of a material which is hard enough to create the cavity. The tip may comprise a blade which cuts out a part of the surface of the bone, in particular caused by a rotational movement of the tip about a longitudinal axis of the medical artificial landmark creating instrument. The cavity can also be referred to as a dent, an indentation or a mechanical artificial landmark.

In one implementation of this embodiment, the tip comprises a rotatable blade or a drill. The blade or drill is preferably rotatable about the longitudinal axis of the medical artificial landmark creating instrument. The landmark creation structure comprises an energy storage such as a pre-loaded spring which is adapted to rotate the blade or drill, for example by 720 degrees, when the energy is released from the energy storage. The rotating blade or drill then creates the artificial landmark.

The energy storage might comprise a force detector which is adapted to detect whether or not a force with which the tip of the artificial landmark creation structure is pushed against the bone exceeds a predetermined threshold and releases the energy if mis is the case. The force detector might comprise a spring-biased retention member which locks the pre-loaded spring until the threshold is exceeded. In an alternative, the energy might be released upon manual operation of a push-button.

In another embodiment, the artificial landmark creation structure comprises a liquid- dispensing mechanism. The liquid-dispensing mechanism in particular includes a liquid outlet for ejecting the liquid. The liquid outlet is preferably located at the distal end of the medical artificial landmark creating instrument, in particular at the tip of the medical artificial landmark creating instrument. The liquid creates an optical artificial landmark, for example caused by colorants comprised in the liquid. The liquid preferably is a biocompatible liquid. The liquid preferably automatically dissipates after a predetermined amount of time. The liquid preferably is an ink.

Preferably, the tip of the medical artificial landmark creating instrument can act both as the liquid outlet to create an optical artificial landmark and to create a cavity. The medical artificial landmark creating instrument can thus create a hybrid artificial landmark.

In one embodiment, the medical artificial landmark creating instrument further comprises an infrared LED. The infrared LED emits infrared light, in particular a flash or burst of infrared light, once the artificial landmark was created. The medical navigation system can then detect the infrared light emitted by the infrared LED and, when or once the infrared light is or was detected, determines the position of the instrument marker device, and therefore the location of the artificial landmark. In other words, the infrared light emitted by the infrared LED triggers the determination of the position of the instrument marker device, and therefore of the location of the artificial landmark.

In one embodiment, the medical artificial landmark creating instrument comprises an infrared LED activation button. Upon operation of the infrared LED activation button, the infrared LED emits the infrared light. In an alternative embodiment, the medical artificial landmark creating instrument comprises a force detector which is adapted to detect a force exerted on the artificial landmark creation structure. If this force exceeds a predetermined threshold which indicates mat the artificial landmark creation structure is pushed against the surface of the bone, then the infrared LED is caused to emit the infrared light. The force detector might be the same one as the force detector described above with reference to the rotatable blade or drill.

In one embodiment, the medical artificial landmark creating instrument comprises an infrared reflective region, a movable cover which covers the infrared reflective region and a cover removal button which is connected to the cover such that operating the cover removal button moves the movable cover in order to expose the infrared reflective region. The cover removal button is preferably operated when the artificial landmark creation structure creates or has created the artificial landmark. When the infrared reflective region is exposed, infrared light emitted from the medical navigation system is reflected back to a camera of the medical navigation system. When the medical navigation system detects the infrared light reflected by the infrared reflective region, it determines the position of the instrument marker device and therefore the location of the artificial landmark as described above with regard to the infrared LED.

In an alternative, the cover removal button is displaced by a cover removal mechanism which moves the movable cover in order to expose the infrared reflective region if the artificial landmark creation structure is pressed against the bone with a force larger than a predetermined threshold. The medical artificial landmark creating instrument then automatically indicates to the medical navigation system that the location of the artificial landmark shall be determined. The cover removal mechanism might act as the force detector described above with reference to the rotatable blade or drill.

The infrared LED and/or the infrared reflective region is preferably provided at a known location relative to the instrument marker device. The medical navigation system therefore can detect the location at which the infrared light is emitted or reflected such that it only determines the location of the artificial landmark if the location of the emitted or reflected infrared light matches the predetermined location relative to the instrument marker device. Infrared light originating from another location, for example infrared light reflected by other objects within the field of view of the camera of the medical navigation system, does not trigger the determination of the location of the artificial landmark.

In a preferred embodiment, the LED activation button or the cover removal button is a liquid- ejecting button of the liquid-dispensing mechanism as described above. When the liquid- ejecting button is operated, the liquid is ejected from the liquid outlet. The same operation that ejects the liquid then also causes the infrared LED to emit infrared light or the movable cover to expose the infrared reflective region. Creating the artificial landmark and indicating to the medical navigation system that the location of the artificial landmark shall be determined can thus be performed by a single action. In addition or as an alternative, the LED activation button or the cover removal button is the push-button which releases the energy from the energy storage as described above with reference to the rotatable blade or drill.

One particular embodiment combines the rotatable blade or drill at the tip of the artificial landmark creating instrument with a liquid dispensing mechanism and an infrared LED or an infrared reflective region. In this particular embodiment, the artificial landmark creating instrument is preferably adapted to first create the mechanical artificial landmark and to then create the optical artificial landmark and to activate the infrared LED or expose the infrared reflective region.

The present invention also relates to a medical navigation system comprising a medical artificial landmark creating instrument as explained above, a marker detection device and a processor. The general structure of the medical navigation system is known in the art. The marker detection device in particular is an infrared stereoscopic camera which can capture a stereoscopic infrared image. The processor can analyze the stereoscopic infrared image in order to determine the location of an infrared tight source, which may be a reflective marker which reflects infrared light, such as light emitted by the marker detection device.

The processor is configured to acquire initial registration data which represent an initial registration between a bone marker device and a bone at a first point in time. The bone marker device is a marker device which is associated with the bone. The bone marker device may be attached to the bone, but it may also be attached to a structure which in turn is attached to the bone. An example of such a structure is a holder or clamp which clamps a bone, in particular the cranium. The bone marker device is preferably rigidly attached to the clamp. A registration between the cranium and the bone marker device attached to the clamp can be determined and used as long as there is no (or only a minor) relative movement between the clamp and the cranium. As explained above, a registration represents the relative position between the bone, and in particular of points, such as landmarks, on the surface of the bone, and the bone marker device.

The processor is further configured to determine an initial artificial landmark location of at least one artificial landmark created on the surface of the bone using the medical artificial landmark creating instrument, wherein an initial artificial landmark location is defined relative to the bone marker device. In other words, the location(s) of the artificial landmark(s) is/are determined relative to the bone marker device while the initial registration between the bone and the bone marker device is still valid. The processor is further configured to then store the determined initial artificial landmark location(s) such mat it/they can be re-used at a later point in time.

The processor is further configured to acquire artificial landmark sample data at a second point in time, wherein the artificial landmark sample data represent the locations) of the artificial landmark(s) relative to the bone marker device at the second point in time. The second point in time is later than the first point in time. If the relative position between the bone and the bone marker device has changed between the first and second points in time, men the locations of the artificial landmarks represented by the artificial landmark sample data no longer equal the initial landmark locations. This information can be used for further actions.

In one embodiment, the processor is also configured to compare at least one artificial landmark location within the artificial landmark sample data with a corresponding stored initial artificial landmark location. An artificial landmark location within the artificial landmark sample data is also referred to as a sampled artificial landmark location. The comparison determines whether or not the sampled artificial landmark location differs from the initial artificial landmark location, which means that the relative position between the bone and the bone marker device has changed.

In one embodiment, the processor is also configured to modify the initial registration data on the basis of the artificial landmark sample data in order to obtain re-registration data which represent a registration between the bone marker device and the bone at the second point in time. The difference between the sampled artificial landmark locations and the initial artificial landmark locations relative to the bone marker device describes the change of the relative position between the bone and the bone marker device. This means that a transformation can be calculated which describes the change in the relative position between the bone and the bone marker device between the first point in time and the second point in time. This transformation can then be applied to the initial registration data in order to obtain the re- registration data. The re-registration data then represents the correct current registration between the bone and the bone marker device.

In a preferred implementation, the processor is configured to issue an alarm signal if the difference between the sampled artificial landmark location(s) and the initial artificial landmark location(s) exceed(s) a predetermined threshold. This means that an alarm is provided if the initial registration is degraded such that the bone can no longer be reliably tracked.

The present invention also relates to a medical registration method comprising the steps of acquiring initial registration data which represent an initial registration between a bone marker device and a bone at a first point in time, creating at least one artificial landmark on the surface of the bone, preferably using the medical artificial landmark creating instrument as explained above, determining an artificial landmark location of the at least one artificial landmark, wherein an initial artificial landmark location is defined relative to the bone marker device, and storing the determined initial artificial landmark location(s). As explained above, the initial artificial landmark locations represent the locations of the artificial landmarks relative to the bone marker device when the initial registration between the bone marker device and the bone is (still) valid.

In one embodiment, the method further comprises the steps of acquiring artificial landmark sample data at a second point in time, wherein the artificial landmark sample data represent the location(s) of at least one artificial landmark relative to a bone marker device at a second point in time, and comparing at least one artificial landmark location within the artificial landmark sample data with a corresponding stored initial artificial landmark location. An artificial landmark location within the artificial landmark sample data is also referred to as a sampled artificial landmark location. As explained above, an alarm can be issued depending on the result of the comparison to indicate that the initial registration is no longer valid. In one embodiment, the method further comprises the steps of acquiring artificial landmark sample data at a second point in time, wherein the artificial landmark sample data represent the locations of at least three artificial landmarks relative to the bone marker device at the second point in time, and modifying the initial registration data on the basis of the artificial landmark sample data in order to obtain re-registration data which represent a registration between the bone marker device and the bone at the second point in time. An artificial landmark location within the artificial landmark sample data is also referred to as a sampled artificial landmark location. As explained above, the registration between the bone and a bone marker device can be re-established by calculating a transformation which describes the relocation of the initial artificial landmark locations to the sampled artificial landmark locations and applying this transformation to the initial registration.

In one embodiment, the method further comprises the steps of acquiring working space data which represent an area of the bone which is to be exposed during a surgical procedure and calculating target locations of the artificial landmarks from the working space data, wherein the step of creating an artificial landmark involves navigating a medical artificial landmark creating instrument in such a way that the artificial landmarks are created at the target locations. The working space data may be input by a surgeon or may be obtained from a database depending on the surgical procedure to be performed.

Calculating the target locations of the artificial landmarks preferably involves calculating the target locations such that the target locations are located on the area of the bone which will be exposed during the surgical procedure. This ensures that the artificial landmarks are exposed and can be sampled during the surgical procedure. Since the medial artificial landmark creating instrument carries an instrument marker device, it is possible to navigate the medical artificial landmark creating instrument such that the artificial landmarks are created at the target locations.

In one embodiment, the artificial landmark is automatically created when the artificial landmark creation structure of the medical artificial landmark creating instrument is located at the target location. An optical artificial landmark may men be created by automatically ejecting a drop of liquid through the liquid outlet A mechanical artificial landmark may then be created but automatically activating a cutting blade or a drill for creating a cavity.

It lies within the scope of the present invention to combine one or more features of two or more embodiments to form a new embodiment as long as technically feasible. In particular, the method may involve steps performed by the processor and vice versa. Further, the method may utilize hardware components described in connection with the medical artificial landmark creating instrument.

It is the function of a marker to be detected by a marker detection device (for example, a camera or an ultrasound receiver or analytical devices such as CT or MRI devices) in such a way that its spatial position (i.e. its spatial location and or alignment) can be ascertained. The detection device is in particular part of a navigation system. The markers can be active markers. An active marker can for example emit electromagnetic radiation and/or waves which can be in the infrared, visible and/or ultraviolet spectral range. A marker can also however be passive, i.e. can for example reflect electromagnetic radiation in the infrared, visible and/or ultraviolet spectral range or can block x-ray radiation. To this end, the marker can be provided with a surface which has corresponding reflective properties or can be made of metal in order to block the x-ray radiation. It is also possible for a marker to reflect and/or emit electromagnetic radiation and/or waves in the radio frequency range or at ultrasound wavelengths. A marker preferably has a spherical and or spheroid shape and can therefore be referred to as a marker sphere; markers can however also exhibit a cornered, for example cubic, shape.

A marker device can for example be a reference star or a pointer or a single marker or a plurality of (individual) markers which are then preferably in a predetermined spatial relationship. A marker device comprises one, two, three or more markers, wherein two or more such markers are in a predetermined spatial relationship. This predetermined spatial relationship is in particular known to a navigation system and is for example stored in a computer of the navigation system.

A navigation system, in particular a surgical navigation system, is understood to mean a system which can comprise: at least one marker device; a transmitter which emits electromagnetic waves and/or radiation and/or ultrasound waves; a receiver which receives electromagnetic waves and/or radiation and/or ultrasound waves; and an electronic data processing device which is connected to the receiver and/or the transmitter, wherein the data processing device (for example, a computer) in particular comprises a processor (CPU) and a working memory and advantageously an indicating device for issuing an indication signal (for example, a visual indicating device such as a monitor and/or an audio indicating device such as a loudspeaker and or a tactile indicating device such as a vibrator) and a permanent data memory, wherein the data processing device processes navigation data forwarded to it by the receiver and can advantageously output guidance information to a user via the indicating device. The navigation data can be stored in the permanent data memory and for example compared with data stored in said memory beforehand.

A landmark is a defined element of an anatomical body part which is always identical or recurs with a high degree of similarity in the same anatomical body part of multiple patients. Typical landmarks are for example the epicondyles of a femoral bone or the tips of the transverse processes and/or dorsal process of a vertebra. The points (main points or auxiliary points) can represent such landmarks. A landmark which lies on (in particular on the surface of) a characteristic anatomical structure of the body part can also represent said structure. The landmark can represent the anatomical structure as a whole or only a point or part of it. A landmark can also for example lie on the anatomical structure, which is in particular a prominent structure. An example of such an anatomical structure is the posterior aspect of the iliac crest. Another example of a landmark is one defined by the rim of the acetabulum, for instance by the centre of said rim. In another example, a landmark represents the bottom or deepest point of an acetabulum, which is derived from a multitude of detection points.

The expression "acquiring data" in particular encompasses (within the framework of a data processing method) the scenario in which the data are determined by the data processing method or program. Determining data in particular encompasses measuring physical quantities and transforming the measured values into data, in particular digital data, and/or computing the data by means of a computer and in particular within the framework of the method in accordance with the invention. The meaning of "acquiring data" also in particular encompasses the scenario in which the data are received or retrieved by the data processing method or program, for example from another program, a previous method step or a data storage medium, in particular for further processing by the data processing method or program. The expression "acquiring data" can therefore also for example mean waiting to receive data and/or receiving the data. The received data can for example be inputted via an interface. The expression "acquiring data" can also mean that the data processing method or program performs steps in order to (actively) receive or retrieve the data from a data source, for instance a data storage medium (such as for example a ROM, RAM, database, hard drive, etc.), or via the interface (for instance, from another computer or a network). The data can be made "ready for use" by performing an additional step before the acquiring step. In accordance with this additional step, the data are generated in order to be acquired. The data are in particular detected or captured (for example by an analytical device). Alternatively or additionally, the data are inputted in accordance with the additional step, for instance via interfaces. The data generated can in particular be inputted (for instance into the computer). In accordance with the additional step (which precedes the acquiring step), the data can also be provided by performing the additional step of storing the data in a data storage medium (such as for example a ROM, RAM, CD and/or hard drive), such that they are ready for use within the framework of the method or program in accordance with the invention. The step of "acquiring data" can therefore also involve commanding a device to obtain and/or provide the data to be acquired. In particular, the acquiring step does not involve an invasive step which would represent a substantial physical interference with the body, requiring professional medical expertise to be carried out and entailing a substantial health risk even when carried out with the required professional care and expertise. In particular, the step of acquiring data, in particular determining data, does not involve a surgical step and in particular does not involve a step of treating a human or animal body using surgery or therapy. In order to distinguish the different data used by the present method, the data are denoted (i.e. referred to) as "XY data" and the like and are defined in terms of the information which they describe, which is then preferably referred to as "XY information" and the like.

In the following, the invention is described with reference to the enclosed figures which represent preferred embodiments of the invention. The scope of the invention is not however limited to the specific features disclosed in the figures. The figures show:

Figure 1 a medical artificial landmark creating instrument;

Figure 2 a bone with a bone marker device; Figure 3 a medical navigation system and

Figure 4 a medical navigation workflow.

Figure 1 shows a schematic, partial sectional view of a medical artificial landmark creating instrument 1. The instrument 1 comprises a longitudinal shaft as an instrument body, wherein the distal end of the longitudinal shaft is sharpened to form a tip 2. At the proximal end of the longitudinal shaft, a marker device 3 comprising three marker spheres 3a, 3b and 3c arranged in a fixed and known positional relationship is provided. Further provided at the proximal end of the instrument 1 are an infrared LED 6 and a button 5. The infrared LED 6 is arranged in a known location relative to the marker spheres 3a, 3b and 3c.

Within the longitudinal shaft of the instrument 1, a liquid reservoir 4 is provided. The liquid reservoir 4 has a liquid outlet 4a at or close to the tip 2. Details of the liquid-dispensing mechanism which, upon operation of the button S, ejects a drop of liquid from the liquid outlet 4a are not shown in Figure 1.

The distal end of the instrument 1 is shaped such that it can penetrate through skin covering a bone. The shaft, and in particular the tip 2, is made of a material hard enough to create a cavity in the surface of a bone. This cavity is an artificial landmark which can be detected once the bone is at least partly exposed.

When the tip 2 is located on the surface of the bone in order to create an artificial landmark, the button S is operated such that the infrared LED 6 emits infrared light, in particular a burst of flash of infrared light. The button 5 therefore is an infrared LED activation button.

In addition, operation of the button 5 ejects a drop of liquid stored in the liquid reservoir 4 through the liquid outlet 4a such that the drop of liquid is deposited on the surface of the bone, thus creating an optical artificial landmark. The button S therefore also is a liquid- ejecting button.

The location of the tip 2 and the liquid outlet 4a relative to the instrument marker device 3 is known, such that the location of the artificial landmark, which is an optical and/or mechanical artificial landmark, can be determined from the position of the instrument marker device 3 and the known location of the tip 2 or the liquid outlet 4a relative to the instrument marker device 3.

Preferably, the longitudinal shaft of the instrument 1, comprising the liquid reservoir 4 and the tip 2, is disposable, while the rest of the instrument 1, in particular the instrument marker device 3, the button 5, the infrared LED 6 and any liquid-dispensing mechanism or electrical circuit for driving the infrared LED 6, is re-usable.

The longitudinal shaft, and in particular the tip 2, is for example made of steel or nickel titanium. The shaft preferably has a diameter between 0.7 mm and 1.6 mm. The length of the cone-shaped distal end of the longitudinal shaft preferably is between 5 mm and 15 mm.

Figure 2 shows a bone 7, in the present example a cranium, held by a head clamp 8, wherein the head clamp 8 carries a bone marker device 9. The bone marker device comprises three or more marker spheres arranged in a known geometric arrangement. It is rigidly attached to the head clamp 8. In another example, the bone marker device 9 might be directly attached to the bone. As long as a registration between the cranium 7 and the bone marker device 9 is known, objects can be navigated relative to the cranium 7. It is therefore essential to have a reliable registration between the bone 7 and the bone marker device 9.

The instrument 1 may further comprise a handle which enables to securely grasp the instrument 1. In one implementation, the handle can be part of the instrument marker device 3 or vice versa.

Figure 3 schematically shows a medical navigation system 10 comprising a medical artificial landmark creating instrument 1, a navigation computer 11 and a stereoscopic camera 15 as a marker detection device. The navigation computer 11 comprises a central processing unit 12, a memory 13 and an interface 14 for receiving and transmitting data. The stereoscopic camera 15 captures a stereoscopic infrared image from which the central processing unit 12 can determine the location of a marker sphere which is within the field of view of the stereoscopic camera 15. In an alternative, the location of a marker sphere is calculated within the stereoscopic camera 15 and transmitted to the central processing unit 12. The stereoscopic camera 15 preferably comprises an infrared light source which emits infrared light which is reflected back to the stereoscopic camera 15 by a marker sphere.

The navigation computer 11 is connected to an output device 17, such as a monitor, and to an input device 16, such as a keyboard, a mouse or a touch sensitive surface of the output device 17. The output device 17 can output data obtained or calculated by the navigation computer 11. The input device 16 is capable of inputting information or data into the navigation computer 11.

Figure 4 shows the steps of a medial workflow. Step S01 involves acquiring initial registration data which represents an initial registration between the bone marker device 9 and the bone 7 at a first point in time. The initial registration data is for example obtained using the stereoscopic camera 15 and a pointer or is received via the interface 14. The initial registration data is stored in the memory 13.

Step S02 involves creating at least one artificial landmark on the surface of the bone using the medical artificial landmark creating instrument 1. As explained above, an artificial landmark can be a mechanical artificial landmark and/or an optical artificial landmark. This step might optionally involve navigating the medical artificial landmark creation instrument 1 such that the artificial landmark(s) are created at predetermined target location(s) on the bone 7.

Step S03 involves determining an initial artificial landmark location for at least one artificial landmark created in step S02. An initial artificial landmark location is determined by determining the position of the instrument marker device 3 and calculating the location of the artificial landmark from the known location of the tip 2 and/or the liquid outlet 4a relative to the instrument marker device 3. The initial artificial landmark location is preferably determined when the medical navigation system 10 detects that the infrared LED emits infrared light. As explained above, emitting infrared light by the infrared LED 6 is triggered by an operation of the button 5. When the surgeon has moved the instrument 1 in order to create a cavity, or indentation, in the surface of the bone 7, in particular by a rotational movement of the instrument 1, he operates the button 5 such that the infrared LED 6 emits infrared light, which is detected by the medical navigation system 10 in order to trigger to determine the initial artificial landmark location. Preferably, the medical navigation system 10 is configured to determine the initial artificial landmark location only if it detects infrared light emitted from the known location of the infrared LED 6 relative to the instrument marker device 3. Infrared light reflected or emitted by any other object, which is at a different location relative to the instrument marker device 3 than the infrared LED 6, does not trigger the determination of the initial artificial landmark location.

If the button 5 acts as a liquid-ejecting button, then the infrared LED 6 automatically emits infrared light when the liquid is ejected from the liquid outlet 4a. In this case, steps S02 and S03 are performed at exactly the same time.

Step S04 involves storing the initial artificial landmark locations determined in step S03, for example in the memory 13. Step S05 involves acquiring artificial landmark sample data at a second point in time, wherein the artificial landmark sample data represent the locations of the artificial landmarks relative to the bone marker device 9 at the second point in time. These locations are also referred to as sampled artificial landmark locations. They are preferably determined using a pointer which is tracked by a medical navigation system 10.

Step S06 involves comparing the sampled artificial landmark locations with the initial artificial landmark locations. A deviation of the sampled artificial landmark locations from the initial artificial landmark locations indicates that the bone marker device 9 has moved relative to the bone 7, which means that the initial registration is degraded or even became invalid. Step S07 involves to output an alarm if this is the case.

Step S08 involves calculating a transformation which transforms the initial artificial landmark locations into the sampled artificial landmark locations. This transformation represents the change in the relative position between the bone 7 and the bone marker device 9 from the first point in time to the second point in time.

Step S09 involves calculating re-registration data which represents the registration between the bone 7 and the bone marker device 9 at the second point in time. The re-registration is calculated by applying the transformation calculated in step S08 to the initial registration data acquired in step S01. A relative movement between the bone 7 and the bone marker device 9 between the first point in time and the second point in time is thus compensated.

Step S10 involves navigating a trackable object relative to the bone 7. Based on the re- registration data, which is valid for the second point in time, a reliable navigation can be performed.

Different medical registration methods may comprise different steps of the workflow shown in Figure 4. A verification method may comprise steps S01 to S07. This registration verification method determines whether or not the registration is still valid.

A re-registration method comprises at least steps S01 to S05, S08 and S09. This re- registration method calculates a new registration for the second point in time. If the re- registration method further comprises the optional step S06, then steps S08 and S09 are only performed if the initial registration is no longer valid. The re-registration method then optionally also includes step S07.

It lies within the scope of the present invention to re-iterate the workflow, or any method comprising workflow steps, starting with step S05, wherein the re-registration data calculated in step S09 are used as the initial registration data in the next iteration. In other words, the registration data is updated several times.

Claims

Claims 1.

A medical artificial landmark creating instrument (1) far creating an artificial landmark on a surface of a bone (7) through skin covering the bone (7), comprising an artificial landmark creation structure (2; 4a) and an instrument marker device (3) which is in a known spatial relationship with respect to at least a part of the artificial landmark creation structure (2; 4a), wherein the instrument marker device (3) comprises at least three markers (3a, 3b, 3c) in a known geometric arrangement

2.

The instrument (1) according to claim 1, wherein the artificial landmark creation structure comprises a tip (2) which is adapted to create a cavity in the surface of the bone (7).

3.

The instrument (1) according to claim 2, wherein the tip (2) comprises a rotatable blade or a drill.

4.

The instrument (1) according to any one of claims 1 to 3, wherein the artificial landmark creation structure comprises a liquid-dispensing mechanism.

5.

The instrument (1) according to any one of claims 1 to 4, further comprising an infrared LED (6).

6.

The instrument (1) according to claim 5, further comprising an infrared LED activation button (5).

7.

The instrument (1) according to any one of claims 1 to 6, further comprising an infrared reflective region, a movable cover which covers the infrared reflective region, and a cover removal button which is connected to the cover such that operating the cover removal button moves the movable cover in order to expose the infrared reflective region.

8.

The instrument (1) according to claim 6 or 7, wherein the LED activation button (5) or the cover removal button is a liquid-ejecting button of a liquid-dispensing mechanism as claimed in claim 3.

9.

A medical navigation system (10) comprising a medical artificial landmark creating instrument (1) according to any one of claims 1 to 7, a marker detection device (15) and a processor (12), wherein the processor (12) is configured to: acquire initial registration data which represent an initial registration between a bone marker device (9) and a bone (7) at a first point in time; determine an initial artificial landmark location of at least one artificial landmark created on the surface of the bone (7) using the medical artificial landmark creating instrument (1), wherein an initial artificial landmark location is defined relative to the bone marker device (9); store the determined initial artificial landmark locations); and acquire artificial landmark sample data at a second point in time, wherein the artificial landmark sample data represent sampled location(s) of the artificial landmark(s) relative to the bone marker device (9) at the second point in time.

10.

The medical navigation system (10) according to claim 9, wherein the processor (12) is also configured to compare at least one sampled artificial landmark location with a corresponding stored initial artificial landmark location.

11.

The medical navigation system (10) according to claim 9 or 10, wherein the processor (12) is also configured to modify the initial registration data on the basis of the artificial landmark sample data in order to obtain re-registration data which represent a registration between the bone marker device (9) and the bone (7) at the second point in time. A medical registration method comprising the steps of: acquiring initial registration data which represent an initial registration between a bone marker device (9) and a bone (7) at a first point in time; creating at least one artificial landmark on the surface of the bone (7), preferably using the medical artificial landmark creating instrument (1) according to any one of claims 1 to 8; determining an initial artificial landmark location of the at least one artificial landmark, wherein an initial artificial landmark location is defined relative to the bone marker device (9); and storing the determined initial artificial landmark location(s). 13.

The method according to claim 10, further comprising the steps of: acquiring artificial landmark sample data at a second point in time, wherein the artificial landmark sample data represent sampled location(s) of at least one artificial landmark relative to the bone marker device (9) at the second point in time; and comparing at least one sampled artificial landmark location with a corresponding stored initial artificial landmark location. 14.

The method according to claim 12 or 13, further comprising the steps of: acquiring artificial landmark sample data at a second point in time, wherein the artificial landmark sample data represent sampled locations of at least three artificial landmarks relative to the bone marker device (9) at the second point in time; and modifying the initial registration data on the basis of the artificial landmark sample data in order to obtain re-registration data which represent a registration between the bone marker device (9) and the bone (7) at the second point in time. 15.

The method according to any one of claims 12 to 14, further comprising the steps of:

acquiring working space data which represent an area of the bone (7) which is to be exposed during a surgical procedure; and calculating target locations of the artificial landmarks from the working space data, wherein the step of creating an artificial landmark involves navigating a medical artificial landmark creating instrument (1) in such a way that the artificial landmarks are created at the target locations.