The present invention relates to a medical marker device for detection by navigation system in a navigated medical procedure which comprises in particular an image-detectable two-dimensional marker pattern for detection by an imaging unit of the navigation system. Furthermore, the invention also relates to a combination of such a marker device and a navigation system for conducting a navigated medical procedure.
In navigated medical procedures such as knee operations it is often desirable to determine the longitudinal axis of the tibia (i.e. its proximodistal axis). Known methods for doing so rely for example on medical image information in order to determine the positions of landmarks on the tibia from which the position and orientation of the mechanical, in particular proximodistal and/or longitudinal, tibia axis can be determined. The position and orientation of the mechanical axis is defined in particular by the positions of the proximal endpoint of the tibia and the distal endpoint of the tibia. The distal endpoint is commonly determined as approximately the three-dimensional centerpoint between the positions of the medial malleolus and the lateral malleolus.
These image-based methods however may not provide information about the in-situ placement of for example a cutting block for cutting the proximal end of the tibia for example in knee total endoprosthesis implantation. For in-situ determination of the orientation of such a cutting block relative to the proximodistal tibia axis, the state of the art relies on detection of a marker device indicating in particular the positions of the medial and lateral malleolus, respectively, by for example a stereotactic camera of a navigation system which does not have a fixed position relative to the cutting block. This approach is cumbersome since detection of such a marker device is only possible within the field of view of the stereotactic camera.
A problem to be solved by the present invention therefore is to provide a marker device which serves to simplify in-situ determination of the mechanical tibia axis. In particular the present invention seeks to solve line-of-sight problems when determining the orientation of the cutting block in particular relative to the mechanical axis of the tibia.
This problem is solved by the subject-matter of any appended independent claim. Advantages, advantageous features, advantageous embodiments and advantageous aspects of the present invention are disclosed in the following and contained in the subject-matter of the dependent claims. Different advantageous features can be combined in accordance with the invention wherever technically expedient and feasible. Specifically, a feature of one embodiment which has the same or a similar function to another feature of another embodiment can be exchanged with said other feature. A feature of one embodiment which adds an additional function to another embodiment can in particular be added to said other embodiment.
In this section, individual aspects of the present invention are described by way of mere example without limiting the invention to the combination of features described in this section.
In order to solve the aforementioned problem, the invention provides a marker device comprising at least one image-detectable two-dimensional marker pattern which is provided for example on a planar carrier surface of a carrier part. The carrier part is connected to a positioning part, wherein the position of the carrier part relative to the positioning part may be fixed or adjustable. The positioning part is preferably formed to fit substantially flush onto an anatomical structure such as for example a malleolus, and the positioning part is preferably connected to a support part for supporting the carrier part and the positioning part (and therefore also the marker pattern) on an anatomical structure such as the ankle joint. The support part can be formed as a strap arrangement, a forceps, or as a fixation system shaped as a splint or a shoe or comprising a plate-shaped positioning part which is fastened to the anatomical structure with an adhesive foil.
In this section, a general description of the preferred features of the invention is given.
The invention preferably provides a medical marker device for detection by a navigation system in a navigated medical procedure. In the context of this invention, a marker device is understood to be a physical structure which can be detected by a detection unit of a navigation system in order to determine the position of the marker device in a navigation coordinate system. The navigation system preferably comprises a computer which conducts the electronic data processing for determining that position, the computer being operatively coupled to a detection unit such as an imaging unit (for example a digital camera which may be at least one of a still image camera and a digital camera) which is configured to detect the marker device. The position of the marker device can then be determined for example by analysis of the resulting image, in particular by a known image segmentation algorithm, in order to determine the distance between the imaging plane of the imaging unit and the marker device and to determine the orientation of the marker device relative to the imaging plane. As a result, the spatial relationship (in particular at least one of the position and the orientation) between the marker device and the imaging unit can be determined.
In accordance with the invention, the marker device preferably comprises an image-detectable two-dimensional marker pattern which is detected by the imaging unit. The marker pattern is for example a graphical feature, the specific dimensions of which are preferably known to a position-determination algorithm used by the navigation system in order to determine the spatial relationship between the imaging unit and the marker pattern. In particular, the marker pattern is a graphical feature which is capable of producing an image appearance when imaged by the imaging unit which depends on the spatial relationship between the imaging unit and the marker pattern. For example, the size of the image appearance of the marker pattern can be used to determine the distance between the marker pattern and the imaging plane of the imaging unit, and a difference in shape of the image appearance of the marker pattern compared to its known shape (in particular when viewed in a direction perpendicular to a plane in which the marker pattern is arranged, in particular perpendicular to a carrier surface of the carrier part) may be used to determine the orientation of the marker pattern relative to the imaging plane. For example, the marker pattern is embodied by a moiré pattern which changes its visual appearance depending on the perspective from which it is being looked at. Preferably, the marker pattern is designed such that it has a distinguishable appearance for detection in at least one of a video image and a still image taken by the imaging unit.
Preferably, the marker device comprises a carrier part for carrying the marker pattern, in particular the marker pattern is attached to the carrier part. For example, the carrier part is provided with a planar carrier surface which is provided with a marker pattern (for example, the marker pattern may be printed or stuck onto the planar carrier surface). In an alternative embodiment, the carrier part may be embodied by a rod, to the end of which a planar member representing the marker pattern is attached.
Preferably, the marker device comprises a positioning part for positioning the marker device on an anatomical structure. The positioning part is preferably connected to the carrier part in preferably a predetermined (in particular known) and advantageously fixed spatial relationship (in particular fixed position and orientation) relative to the carrier part. Therefore, the spatial relationship (in particular at least one of the position and the orientation) of the marker pattern relative to the positioning part is also predetermined (in particular known) and advantageously fixed. The positioning part is preferably shaped to be positioned substantially flush with the anatomical structure, in particular with a malleolus (in particular of the skin covering a malleolus). For example, the positioning part is cup-shaped so as to fit onto the exterior surface of a malleolus. By positioning the positioning part on a malleolus, the position of the malleolus and therefore a landmark required to determine the distal endpoint of the tibia axis can be determined based on determining the position of the marker pattern.
Preferably, the marker device comprises a support part for supporting the carrier part and the positioning part. In particular, the support part is connected to at least one of the carrier part and the positioning part. Preferably, the spatial relationship (in particular at least one of the position and the orientation) of the positioning part relative to the support part is adjustable. For example, the support part is forceps-shaped (in particular comprises a forceps) wherein a positioning part is provided preferably at the end of each forceps arm and wherein two of the aforementioned two-dimensional marker patterns are provided on the forceps arms in a predetermined and in particular known spatial relationship relative to the positioning parts. In this case, the orientation of the positioning parts and the forceps arms to which the respectively other part is attached is adjustable by changing the opening angle of the forceps. Alternatively, the support part may comprise an arrangement comprising at least one of the set of straps, a shoe and a splint, each one of which is preferably suitable to fasten the marker device to an anatomical structure such as in particular an ankle joint. If the support part is embodied by a shoe-like structure, this shoe-like structure is preferably designed to form-fit to the anatomical structure, in particular to form-fit to a lower thigh, in particular to an ankle joint.
If the support part is embodied by a set of straps, these straps may be at least partly led through for example the positioning part while allowing the straps to move relative to the positioning part. If the support part is shoe-shaped, the carrier part and the positioning part may be designed so that they can slide in a slot formed in the shoe-shaped support part in at least one dimension. Preferably, a second slot is provided in the shoe-shaped structure which allows to move the arrangement of marker pattern, carrier parts and positioning parts in two degrees of freedom (in particular in two translational directions) relative to the support part. Alternatively, the positioning parts may be attached to the shoe-shaped structure via forceps-shaped connecting arms which are attached to the shoe-shaped structure via a ball joint which allows to position two positioning parts and therefore two marker patterns at each end of the forceps-shaped connecting arms on the anatomical structure, in particular on the malleoli.
As can be seen from the above, the marker device preferably comprises two-image-detectable two-dimensional marker patterns and an individual carrier part for each of the marker patterns (i.e. one carrier part per marker pattern) and an individual positioning part for positioning each carrier part (i.e. one positioning part per carrier part). One example for such configuration is the aforementioned marker device in which the support part is embodied by a set of straps or a shoe-shaped structure. Two further embodiments with two marker patterns are described in the following. For example, the carrier part can be embodied by a carrying plate which is placed on the anatomical structure such as a malleolus (in particular, one such plate is positioned on each malleolus of an ankle joint) and fastened to the ankle joint with a support part comprising an adhesive foil which is wound over the ankle joint and the carrying plate. If the marker device comprises two marker patterns, two such carrier plates may be used (one for each marker pattern). A marker pattern is then screwed or pushed into an attachment structure of each of the plate (or plates, respectively) through the adhesive foil. In that case, the carrier part is preferably embodied by a male screw thread or a pin which is located in the attachment part of the plate. Alternatively, the support part may be formed as a splint for the ankle joint having a slot in the proximodistal direction which covers the potential proximodistal positions on the malleoli on each lateral side of the splint, and a carrier part and a positioning part with each a marker pattern attached to the carrier part may be provided in each of the slots so as to be movable in the proximodistal direction.
It is clear from the above that it is preferred that if the marker device comprises two marker patterns (and therefore correspondingly two carrier parts and positioning parts), each one of the positioning parts is adjustable relative to the support part so as to be positioned at different positions. In particular, the position parts can be positioned at each a different position so as to be located at the correct proximal distal position of the medial and lateral malleolus, respectively, which in general are not located in the same horizontal plane of the patient's body. In particular in the embodiment having a support part comprising an adhesive foil and a carrier part being embodied by a carrier plate, the marker pattern, the carrier part, the positioning part and the support part are detachably connectable (in particular connected) to each other.
In a further preferred embodiment, the marker device comprises only one marker pattern. In this embodiment, the support part is embodied by for example a strap to which the positioning part is attached preferably such that it is adjustable with regard to the support part (i.e. the strap, for example along the in particular longitudinal direction of the strap). The carrier part is connected to the support part with a connecting part so that the carrier part is movable in particular in the lateral direction when the support part is fixed to the anatomical structure (in particular to the ankle). The position of the marker pattern is then preferably adjusted by user interaction to define approximately the centre between the positions of the two malleoli on that ankle and therefore to define the distal endpoint of the corresponding tibia. Further preferably, the marker device (in particular the carrier part and/or the connecting part) is brought into predetermined orientation relative to the patient's sagittal or coronal plane.
In a further preferred aspect, the invention is also directed to a combination of a navigation system (which is described above) and the above-described marker device.
In an even further preferred aspect of the invention, the invention also relates to a method of determining a position of the distal endpoint of the mechanical, in particular proximodistal and/or longitudinal, tibia axis based on acquiring information about the position of the marker pattern based on using the above-described marker device. If the marker device comprises two marker patterns, the distal endpoint of the mechanical axis is preferably determined based on acquiring information about the positions of both marker patterns, in particular by determining the position of the distal endpoint to be approximately the three-dimensional centre between the positions of the marker patterns. The invention is then preferably also directed to a program, which when executed on a computer, causes the computer to execute the steps of such a method, and to a computer running such a program.
In this section, the invention is described with reference to the appended Figures, wherein the invention shall not be limited to those features described in relation to and illustrated in the Figures.
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The present invention provides for example the following advantages:
Filing Document | Filing Date | Country | Kind |
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PCT/EP2013/066867 | 8/13/2013 | WO | 00 |