SE542086C2

SE542086C2 - Tool for Attachment of Marker of a Surgical Navigation System

Info

Publication number: SE542086C2
Application number: SE1751320A
Authority: SE
Inventors: Anton Lindahl; Morgan Andersson
Original assignee: Ortoma Ab
Priority date: 2017-10-25
Filing date: 2017-10-25
Publication date: 2020-02-25
Also published as: SE1751320A1; WO2019083431A1

Abstract

A tool (1) for use with a surgical navigation system is disclosed. The tool comprises a body (2) having a top surface (3). An attachment interface is provided on the body (2) and configured to attach a marker of the navigation system to the tool (1). The attachment interface comprises a first protrusion (4) or recess and a second protrusion (5) or recess being spaced apart and extending from the top surface (3) of the body (2). Each of the first protrusion (4) or recess and the second protrusion (5) or recess has a first portion (4a, 5a) with a first diameter and a second portion (4b, 5b) with a second diameter. The first diameter is larger than the second diameter. The first portion (4a, 5a) extends from the top surface (3) and the second portion (4b, 5b) extends from the first portion(4).

Description

TOOL FOR ATTACHMENT OF MARKER OF A SURGICAL NAVIGATION SYSTEM Field of the Invention This invention pertains in general to the field of navigation systems, such as surgical navigation systems. More particularly, the invention relates a tool to be used with a surgical navigation system. The tool may be a calibration tool, such as to be used to calibrate the location of other tools, such as surgical instruments, within space such that an end-effector of the instrument can be tracked with high, such as with sub-millimeter, accuracy in space. The tool comprises a body having a top surface. An attachment interface is provided on the body and configured to attach a marker of the navigation system to the tool. The attachment interface comprises a first protrusion or recess and a second protrusion or recess being spaced apart and extending from the top surface of the body. Each of the first protrusion or recess and the second protrusion or recess has a first portion with a first diameter and a second portion with a second diameter. The first diameter is larger than the second diameter. The first portion extends from the top surface and the second portion extends from the first portion. The attachment interface provides for re-positioning accuracy of the marker to the tool, which is particularly useful when the tool is a calibration tool, which has a calibration location located at a predefined position relative the attachment interface.

Background of the Invention Orthopedic replacement systems, such as hip, knee, foot and ankle, shoulder, elbow, and spine replacement systems are commonly available. These systems comprise implants including various components for total replacements of a piece of the patient’s anatomy. Each system comprises a range of components, including various sizes. For example, a hip replacement system can comprise an acetabular component, which includes an acetabular shell, and acetabular insert, and a bearing, and the femoral component, which includes the femoral stem. The systems can be cemented or press-fit. Furthermore, a wide variety of system specific instruments are used with each replacement system. Again taking a hip replacement system as an example, such as system may include instruments including osteotomes, reamers, saws, handles, planars, reamers, stem inserters, stem impactors, head impactors, chisels, broach handles, and trial components. Many times, the instruments are combined in kits, which include the required instrumentation for a particular replacement system. The instruments are to a large extent for multiple use.

Different replacement systems may be available on different markets. On each market, a number of competitive replacement systems are often available. On top of this, different replacement systems are available for the various surgical fields exemplified above. In summary, that means that there are a large number of replacement systems, and an even larger number of implant components and instruments, available on the global market. Providing a generic navigation system that is applicable to all of these replacement systems is challenging.

Surgeons generally select to work with a few replacement systems for a particular surgical intervention, such that a replacement surgery suitable to the individual patient can be provided. This means that the surgeon can have the required instruments available, and have a limited number of implant components in stock to be able to select amongst a few suitable implant components during surgery. Since the surgeon only works with a limited number of replacement systems, the surgeon can master these replacement systems in order to perform a surgery at the best of his/her ability. Yet, there are a large number of surgical interventions where the implant components are positioned in non-optimal positions, with non-optimal surgical outcome for the patient. Hence, there is a need for improvement of the positioning of implant components for orthopedic replacement systems.

However, the surgeon do not want to work with different surgical navigation systems that are each specific for a single replacement system. Instead, the flexibility to select the most appropriate navigation system and at the same time to use the replacement system with which the surgeon is familiar is desired.

Various Computer Assisted Orthopedic Systems (CAOS) exist, which range from active robotic to passive navigation systems. Active robotic systems are capable of performing surgery autonomously without interaction by the surgeon. Semi-automatic robotic systems also exist, which give the surgeon more freedom, but still within certain limitations. Many times, the surgeon wants to be in control of the surgery. In such situations, passive or semi-automatic navigation systems are preferred, which provide additional information during a procedure compared to conventional surgery but do not perform the surgical action. The surgeon controls the intervention but acts on additional patient information obtained from a pre-operative scan. During surgery with a robotic and semiautomatic system, the surgical instrument is not in the hands of the surgeon but carried by a robot, which is only indirectly controlled by the surgeon.

Common to the robotic and surgical navigation systems is that they use some type of passive or active marker, which a receiver or locator, such as a camera using triangulation methods, can follow in real time. Many of these systems use a number of passive geometrical objects, such as spheres or discs, arranged in a particular known pattern. By observing the geometrical objects in space, the instruments’ position and orientation in space can be tracked.

The geometrical objects trackable by the locator have a predefined fixed relationship relative the position and orientation of the end effector of the surgical instrument. Therefore, also common to these robotic and surgical navigation systems is that system specific surgical instruments are required for each navigation system to accurately and reproducibly align implant components with the pre-operative plan. That means, in order for a surgeon who wants to use a navigated replacement system in order to improve the accuracy of replacement component positioning, but who currently uses a particular replacement system that is not designed for surgical navigation, the surgeon has to switch to a new unfamiliar replacement system, including new an unfamiliar instruments. Furthermore, if the surgeon currently is using multiple replacement systems that are not navigated, the surgeon may be limited to choose a single navigated surgical replacement system, since it is not economically viable to have multiple navigated replacement systems, it is simply too expensive. The navigated replacement system may provide a better surgical outcome, but still not be optimal. Even an experienced surgeon will be, at least initially, inexperienced with a new surgical navigation system. Therefore, there exists a need for a surgical navigation system that can be used with any orthopedic replacement system, also non-navigated replacement systems, already available on the marked and with which the surgeon is already familiar, such that the surgeon does not need any training on the replacement system, with which he/she is already experienced.

WO2011134083 discloses systems and methods for surgical guidance and image registration, in which three-dimensional image data associated with an object or patient, is registered to topological image data obtained using a surface topology imaging device. The system utilizes fiducial markers attached to system specific surgical instruments that have a fixed relationship relative to an end-effector of the instrument. The position of the end-effector of the surgical instrument is determined and recorded using a 3D model of the surgical instrument, which is imported from computer aided design (CAD) drawings, in which the instrument tip is known.

Alternatively, the surgical instrument including the fiducial markers can be profiled with a structured light scanner to obtain its 3D geometry. Hence, the system becomes complicated, time-consuming to use, and expensive, since system specific surgical instruments with fiducial markers are required, processes for obtaining the positions of the instrument tip relative the fiducial markers, which is undesired during surgical action where time is a scarce resource, not only during the surgical action itself but also in preparation therefore.

US2009234217A1, US2011251607, and US2007238981A1 disclose various aspects of navigation systems. However, utilizing various types of fiducial markers, they all suffer from at least the same issues as the navigation system disclosed in WO2034083, such as in relation to the calibration of the position of the end-effector or tool-tip relative fiducial markers.

US5921992 discloses intraoperative calibration of an arbitrary surgical instrument relative a surgical navigation digitizing system. The system comprises a calibration guide that has markers in known positions relative a guide tube. Hence, the entire calibration guide is pre-calibrated relative a camera system and its position is known in the navigation system. Alternatively, a calibrated guide has a chuck that can be closed on a probe end of an instrument. The instrument is an existing calibrated instrument so that its probe end and tip position are already known in the coordinate system of the cameras. Inserting the pre-calibrated instrument will determine the position of the calibration guide. Then, the pre-calibrated instrument is removed from the chuck, and the position of other instruments having the same shape as the pre-calibrated instrument can be calibrated into the coordinate system of the cameras by inserting its probe into the chuck. An array of light markers can be directly clamped to the instrument before calibration. This system is very inflexible, since it may only be used together with instruments having identical shapes and positions of the probe end. Also, if the calibration instrument is moved, it has to be re-calibrated. Adding a new instrument, or using the system together with a different replacement system, requires multiple calibration guides and/or new calibration probes. In this document, a marker is a single light element; multiple markers/light elements provide a pattern that is trackable. The markers are individually attached to the calibration guide and cannot be removed as a set, which makes the positional accuracy between the markers uncertain.

US7166114 discloses a surgical navigation system that does not require a calibration system to track the axis of an instrument. Instead, a tracker is attached to the instrument using a precalibrated adapter. The adapter has a known relation between the coordinate system of the tracker and the surgical tool or tool axis. This is done by having precise knowledge of location of the adapter relative the tool axis when the adapter is attached to the surgical tool. This requires precharacterisation of each adapter of the system to each surgical tool with which it is used. Utilizing the tracker for different replacement systems, or even surgical tools with different geometrical shapes, requires a database where the location of the surgical tool axis relative the adapter and tracker coordinate system is stored. The adapter and tracker have to be characterised in the same coordinate system. Adopting the navigation system to new replacement systems or surgical instruments is complex, expensive and time-consuming and requires precise characterization of each adapter to achieve the accuracy required in surgical navigation systems.

US2005/0288575 recognizes that adapters such as described in US7166114 are expensive and time-consuming to develop. The solution is to have an adapter that is coupled to a surgical tool in a non-fixed manner, and can be calibrated by moving the adapter along the tool axis. It is only possible to track the tool axis, but not the end-effector of the tool. Also, it is only possible to track position, not orientation. Similar to other adapter based systems, the navigation system knows the identity of the particular adapter and the surgical instrument. The system is queried with regard to the dimensions of the interface and channel configuration of the adapter, and the dimensions of the surgical tool and its effector axis. Hence, the adapter needs to be pre-calibrated, i.e. its shape between an interface for attaching the tracker to the adapter and an interface for coupling the adapter in a non-fixed manner to the surgical tool is known and stored in a database. Again, this system requires pre-characterisation of each adapter of the system to each surgical tool with which it is used, with the same challenges as with regard to the system of US7166114.

All of the systems mentioned above comprise active or passive objects that are integrated with or that have structures for attaching the objects one by one to the element to be tracked by the navigation system.

US2017086941 discloses a marker for a navigation system, which comprises a support for light generating elements in a known predetermined pattern. The marker provides for fixing the light generating elements with high accuracy relative each other, facilitation tracking of the marker with high accuracy. The marker can be fixed to on an object (respectively a subject) to be tracked. In a surgical application, the subject is typically the patient to be operated. The marker may be fixed on a bone structure (femur, tibia, pelvis, skull, etc.), a head frame used in neurology, or screwed, glued, fixed on the patient via an elastic band, glasses' frame, etc. The marker could be a planar support that has a mechanism to attach it on an object/subject. The position of the light generating elements with respect to the attachment mechanism is called the geometry and should be well known. The support of the markers is precisely tooled and/or moulded to avoid an individual calibration process of the marker. Hence, by tracking the light generating elements, the attachment mechanism can also be tracked. If this marker is attached to a tool or instrument, and the location of an end effector of the tool or instrument is calibrated relative the attachment mechanism, the location of the end effector can be tracked by tracking the light generating elements. However, this requires precise positioning of the marker to the tool each time it is used. Hence, it is necessary to re-position the marker to the tool with sub-millimetre accuracy or stability in order to avoid a calibration process of the tool to which the marker is used or to avoid that the marker is dislocated after calibration. Positional accuracy without calibration is particularly important when the tool is a calibration tool. It is also important that the marker is stable when attached to an instrument, such that the marker does not move after an end-effector of the instrument has been calibrated relative a calibration tool. Providing the marker and the attachable light generating means facilitates attachment to any instrument, and provides a system where the marker may be sterilizable and for multiple use, and the light generating means may pre-sterilized single use components.

In a surgical navigation system, a marker, such as the marker of US2017086941 may be attached to an instrument. Another marker may be attached to a calibration tool. The calibration tool has at least one predefined location for receiving the end-effector of the surgical instrument carrying the marker, and an attachment mechanism for attaching another marker marker to the calibration tool. If the location of the predefined location for the end-effector and the location of the attachment mechanism for receiving the marker on the calibration tool is known, the position of the end-effector can be calibrated and tracked with high accuracy. However, this requires attaching the marker at least to the calibration tool with high accuracy and in a stable manner such that the marker is attached and maintained at a fixed location, including with sub-millimetre accuracy. Particularly, attaching a marker with a planar surface to a tool or instrument in a stable and accurate position multiple times challenging.

Hence, there exists a need for a tool or instrument, to which a marker carrying a plurality of trackable objects may be positioned with an accuracy defined for the system and/or in a stable manner allowing for improved guidance, precision, increased flexibility, cost-effectiveness, calibration and/or patient safety for use together with any orthopedic replacement system and surgical instruments of arbitrary shape available on the market.

Summary of the Invention Accordingly, embodiments of the present invention preferably seek to mitigate, alleviate or eliminate one or more deficiencies, disadvantages or issues in the art, such as the above-identified, singly or in any combination by providing a tool according to the appended patent claims.

Embodiments comprise a tool for use with a surgical navigation system. The tool comprises a body having a top surface, and an attachment interface provided on the body and configured to attach a marker of the navigation system to the tool. The attachment interface comprises a first protrusion or recess and a second protrusion or recess being spaced apart and extending from the top surface. Each of the first protrusion or recess and the second protrusion or recess has a first portion with a first diameter and a second portion with a second diameter. The first diameter is larger than the second diameter. The first portion extends from the top surface and the second portion extends from the first portion.

Each of the first protrusion or recess and the second protrusion or recess may comprise a ledge between a circumference of the first portion and a circumference of the second portion. The ledge of the first protrusion or recess and the ledge of the second protrusion or recess may be provided in a single plane. In some embodiments, the ledge is planar.

A third protrusion or recess may extend from the top surface and may be located between the first protrusion or recess and the second protrusion or recess. The third protrusion or recess may be spaced apart from a line extending through the first protrusion or recess and the second protrusion or recess. A top surface of the third protrusion may be located in a single plane. The ledge of each of the first protrusion or recess and the second protrusion or recess may be located in the single plane. The single plane may be substantially parallel with a plane defined by at least a portion of the top surface. The third protrusion or recess may be centered between the first protrusion or recess and the second protrusion or recess.

A connection interface may be configured to removably fix the marker to the tool. The connection interface may be spaced apart from the line extending through the first protrusion or recess and the second protrusion or recess. Optionally or additionally, the connection interface may be located between the third protrusion or recess and the line extending through the first protrusion or recess and the second protrusion or recess. The third protrusion or recess and the connection interface may be aligned between the first protrusion or recess and the second protrusion or recess. Preferably, the third protrusion is spaced apart from the line between the first protrusion or recess and the second protrusion or recess. It may be spaced apart a distance substantially equal to or larger than a distance between the first recess or protrusion and the second protrusion or recess.

A height of the first portion of the first protrusion and the height of the first portion of the second protrusion from the top surface may be larger than any portion of the top surface between the first protrusion and the second protrusion.

The second portion of at least one of the first protrusion or recess and the second protrusion or recess may be cylindrical, such as circular cylindrical or elliptical cylindrical.

In some embodiments, the tool is a calibration tool and the attachment interface is located at a predetermined distance from at least one calibration location or calibration element for a surgical instrument. The predetermined distance is preferably substantially equal to or shorter than a distance between the first protrusion or recess and the second protrusion or recess.

In some embodiments, the tool is an adapter for attaching the marker to a surgical instrument. A system may comprise at least one tool, which is a calibration tool according to the embodiments of the invention, and at least one other tool, which is an adapter according to embodiments of the invention.

The tool may be a calibration tool comprising a calibration location or calibration element, such as to calibrate the location of an end-effector of a surgical instrument. The attachment interface may provide a repositioning accuracy for the marker. The calibration location or calibration element may be located at a distance from the attachment interface. A calibration accuracy of the calibration location may be defined based on the repositioning accuracy of the attachment interface. The location of the calibration location or calibration element relative the attachment interface may also be determined based on a desired calibration accuracy at the calibration location or calibration element.

The embodiments provide for attaching a marker, which may have a production tolerance that does not require calibration, to a tool with a stable attachment interface. The attachment interface provides for stability such that the marker is stable when attached to the tool. Embodiments also provide for a tool having an attachment interface to which such a marker may be repositioned multiple times with an accuracy or tolerance that is sufficient for using the tool as a calibration tool without transferring inaccuracies to a calibration location or calibration element beyond what is acceptable in a surgical navigation system used for tracking the location in space of surgical instruments and/or implants. Hence, the embodiments provide a tool with an attachment interface for a marker that is robust. Also, embodiments provide a tool that has sufficient production tolerance without the need to calibrate the tool before being used for calibration of the location of end-effectors of surgical instruments. Hence, the geometry of each individual tool does not need to be measured before being used as a calibration tool. Thus, each individual tool does not need to be traced in a memory of the surgical navigation system. This reduces the complexity of the surgical navigation system, with which the tool according to embodiments of the invention is used.

It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

Brief Description of the Drawings These and other aspects, features and advantages of which embodiments of the invention are capable of will be apparent and elucidated from the following description of embodiments of the present invention, reference being made to the accompanying drawings, in which: Fig. 1a is a perspective view of the tool with the attachment interface; Fig. 1b is a top view of the tool with the attachment interface; Fig. 1c is a side view of the tool with the attachment interface; Fig. 1d is a front view of the tool with the attachment interface; Figs. 2a-2c is a schematic illustration of tools with the attachment interface exemplified as an adapter and a calibration tool, to which markers are attached; Fig. 3 is a graph illustrating distance ratio relative tolerance ratio; and Fig. 4 is a front view of the tool with a marker attached to the attachment interface.

Description of Embodiments Specific embodiments of the invention will now be described with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The terminology used in the detailed description of the embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, like numbers refer to like elements.

The following description focuses on embodiments of the present invention applicable to a surgical navigation system. However, it will be appreciated that the invention is not limited to this application but may be applied to many other procedures, such as other navigation systems where the position and/or orientation of an object is tracked. The examples given in the below embodiments relate to a hip replacement surgery. Other embodiments include knee surgery, spine surgery, elbow surgery, ankle surgery, and other implant replacement surgeries.

In the below embodiments, reference is made to tracking position and orientation of instruments. In this context, the term instruments, in addition to instruments for the surgical examples given herein, include implant components, such as for replacement of patient anatomy or adding into the patient anatomy, as well as for temporary attachment of components of the replacement system during the surgical intervention. Such temporary components may include threaded screws or unthreaded nails for temporary attaching trackers to the patient anatomy during surgery in the same way as the trackers are attached to the attachment components, as will be described herein.

Furthermore, instruments include surgical guides that may attached to the anatomy or implants for guiding the instrument or checking accuracy of an installed implant, such as checking rotation, position, and/or orientation of an implant.

A surgical navigation system has been disclosed in patent application no.

PCT/SE2013/050952 by the same applicant as the applicant of the present invention, which is incorporated herein in its entirety for all purposes. The surgical navigation system of patent application no. PCT/SE2013/050952 has been further improved by embodiments disclosed in patent application PCT/SE2016/051119 by the same applicant as the applicant of the present invention, and which is incorporated herein in its entirety for all purposes.

The present invention provides a tool with an attachment interface for a marker, to which a plurality fiducials, such as light generating objects, are attached or attachable at predefined locations and in a predefined pattern. The marker may be of the type e.g. disclosed in US2017086941, which is included herein by reference for all purposes, and particularly as an example of such a marker. For example reflective discs or spheres may be attached to the markers in the predefined pattern, such that the marker, and thus a tool or instrument to which the marker is attached, may be tracked in space with the surgical navigation system. The marker is particularly useful for attachment to tools via an adapter, such as described in PCT/SE2016/051118 by the same applicant as the applicant of the present invention, and which is incorporated herein in its entirety for all purposes.

Figs. 1a-1d illustrate a tool 1 for use with a surgical navigation system. In the illustrated embodiments, the tool is a calibration tool, which may be used to calibrate the location in space of an end-effector of a surgical instrument, such as is illustrated in Figs. 2a-2d. Flowever, the tool 1 may comprise an adapter 110, (Figs. 2a-2c) as an intermediate element for attachment of the marker to any type of surgical instrument. Surgical instruments may comprise system specific instruments, such as discussed in the Background of the Invention section, to which the adapter 110 is attached. Furthermore, embodiments of the tool 1 may comprise a surgical instrument having an integrated attachment interface to which the marker may be attached. In the following, the embodiments will be described relative a calibration tool, but the described embodiments are not limited to a calibration tool unless specific reference is made to embodiments specific for a calibration tool.

The tool has a body 2. The body may comprise at least one top surface 3.

An attachment interface is provided on the body 2 and configured to attach a marker of the navigation system to the tool 1. The attachment interface may be configured to attach the marker substantially non-rotationally relative the body 2, such that the position of the marker relative the body is fixed and/or stable. Non-rotationally means that the marker should not be allowed to rotate beyond what is possible due to production tolerances. Such rotation could be in a first plane illustrated by arrow a1 in Fig. 1b, and/or in a second plane illustrated by arrow a2 in Fig. 1c.

The attachment interface comprises a first protrusion or recess 4 and a second protrusion or recess 5, which may be spaced apart and may extend from the top surface 3 of the body 2. Each of the first protrusion or recess 4 and the second protrusion or recess 5 may have a first portion 4a with a first diameter. At least one of the first protrusion or recess 4 and second protrusion or recess 5 may have a second portion 4b, 5b with a second diameter. The first diameter and the second diameter may be different. The first diameter may be larger than the second diameter, i.e. the diameter of the first portion 4a, 5a may be larger than the diameter of the second portion 4b, 5b. The first portion 4a, 5a, may extend from the top surface 3 and the second portion 4b, 5b may extend from the first portion 4a, 5a. Hence, a marker having a recess with a maximum diameter smaller than the outer or maximum diameter of the first portion 4a, 5a and larger than the outer or maximum diameter of the second portion 4b, 5b may be supported on an end surface 4c, 5c of the first portion 4a, 5a. Hence, since the end surface 4c, 5c is spaced apart from the top surface 3, the surface of the marker may be spaced apart from the top surface 3, and contact area between marker and the tool is reduced to the end surface 4c, 5c. Hence, the stability of the marker when attached to the tool 1 is improved compared to a situation where a larger portion of the marker abuts the top surface 3. This is particularly useful for markers that are made of a monolithic material or as a monolithic component and that have a planar surface facing the top surface when attached to the tool 1. Recesses or protrusions may be provided in the planar surface of the marker and arranged to mate with the protrusion or recess 4, 5. Without the first portion 4a, 5a, the planar surface of the marker would abut the top surface. Hence, if the top surface 2 is not completely planar, the marker could rotate or tilt around an axis extending through the first protrusion or recess 4 and the second protrusion or recess 5, as is illustrated with arrow a2 in Fig. 1c. Hence, embodiments provides for a stable attachment of a marker to the tool.

In the embodiments of Figs. 1a-1c, the attachment interface of the tool 1 is a protrusion, configured to fit within a recess of the marker. In other embodiments, the attachment interface of the tool 1 is a recess configured to receive a protrusion at the marker. Such a protrusion at the marker may have the same configuration as the protrusion 4, 5 described with regard to the embodiments of Figs. 1a-1c. In the following, reference will only be made to a protrusion 4, 5, with the understanding that the protrusion 4, 5 of the tool equally be a recess and the marker may have mating protrusions.

Furthermore, if both the first protrusion 4 and the second protrusion 5 have a second portion 4b, 5b, the attachment interface provides for rotationally locking of the marker to the tool 1, such as in a plane parallel to the top surface, as is illustrated with arrow a1 in Fig. 1b. Rotationally locking means that the marker may not rotate other than what is possible due to production tolerances.

As is illustrated in Figs. 1a-1c, each of the first protrusion 4 and the second protrusion 5 may comprise a ledge, such as formed by the end surface 4c, 5c of the first portion 4a, 5a. The ledge may be provided between an outer circumference of the first portion 4a, 5a and an outer circumference of the second portion 4b, 4c. The ledge of the first protrusion 4 and the ledge of the second protrusion 5 may be provided in a single plane. Thus, each ledge may be planar. This provides for stability of the marker when supported by the ledges. Alternatively, the ledge may be sloping from the outer circumference of the first portion 4a, 5a and towards the outer circumference of the second portion 4b, 5b and towards the top surface 3 of the tool 1. Hence, the marker will be supported by the outer circumference of the ledge, wherein the contact area between the marker and the tool 1 is further reduced, which even further enhances the stability. A combination of a planar ledge and a sloping ledge may also be envisaged, such as at one or both of the protrusions 4, 5.

A third protrusion 6 may extend from the top surface 3. In the following, reference will be made to the third protrusion 6, but this could equally be a recess. The third protrusion 6 may be located between the first protrusion 4 and the second protrusion 5. The third protrusion 6 provides additional support for the marker, such that three spaced apart support areas on the tool is provided. This enhances stability. The third protrusion 6 may be located on an imaginary line 8a extending between the first protrusion 4 and the second protrusion 5. In other embodiments, the third protrusion 6 is spaced apart from the imaginary line 8a, such as illustrated in Figs. 1a-1c. Still, the third protrusion 6 may be located between the first protrusion 4 and the second protrusion 5. This also contributes to the stability of the marker, such as in a plane parallel to the top surface 3.

At least a portion of a top surface 6a of the third protrusion 6 may be located in a single plane. The top surface 6a may be planar or slanted, as discussed above with regard to the ledge of the first protrusion 4 and the second protrusion 5. The ledge of each of the first protrusion 4 and the second protrusion 5, discussed above, may be located in the same plane as the top surface 6a. This provides for stability of the marker.

The third protrusion 6 may be centered between the first protrusion 4 and the second protrusion 5. This also contributes to the stability of the marker.

A connection interface 7 may be configured to removably fix the marker to the tool 1. The connection interface 7 may be spaced apart from the imaginary line 8a extending through the first protrusion 4 and the second protrusion 5. Alternatively or additionally, the connection interface 7 may be located between the third protrusion 6 and the imaginary line 8a ending through the first protrusion 4 and the second protrusion 5. Hence, connection interface 7 may be located within a triangle formed by the imaginary line 8a extending through the first protrusion 4 and the second protrusion 5, a second imaginary line 8b extending through the first protrusion 4 and the third protrusion 6, and a third imaginary line 8c extending through the second protrusion 5 and the third protrusion 6. The connection interface may be a threaded connection, wherein a threaded hole or a threaded pin extends into or from the body 2, and a screw or nut engages the threaded hole or pin and abuts a top surface of the marker. Hence a pressure may be applied to the marker by a head of the screw such that the marker is fixedly attached to the tool. In other embodiments the connection interface is a snap-fit connection sized to apply a pressure from the marker to the support surfaces of the tool. Positioning the connection interface 7 with the tringle formed by the imaginary lines 8a-8c provides for an even distribution of the pressure to the support surfaces provided by the first protrusion 4, the second protrusion 5 and the third protrusion 6.

The third protrusion 6 and the connection interface 7 may be aligned between the first protrusion 4 and the second protrusion 5. Hence, the distance d1, d2, measured parallel to the first imaginary line 8a, from the first protrusion 4 and the second protrusion d2 may be substantially equivalent. Furthermore, third protrusion 6 and the connection interface 7 may be the spaced apart from the first imaginary line 8a. The protrusion 6 may be spaced apart a distance d3, and the connection interface 7 may be spaced apart a distance d4 measured perpendicular to the first imaginary line 8a. The distance d4 may be substantially equal to or larger than a distance d5 between the first protrusion 4 and the second protrusion 5. This also contributes to the stability of the marker when attached to the tool, as will be further explained below. The distances are defined relative the center of each structure, or lines extending through the center of each structure.

A height of the first portion 4a of the first protrusion 4 and the height of the first portion 5a of the second protrusion 5 from the top surface 3 of the tool 1 may be larger than any portion of the top surface 3 between the first protrusion 4 and the second protrusion 5. Hence, it the marker has a substantially planar surface facing the top surface 3 of the tool, no portion of the marker may abut the top surface, wherein stability of the marker when attached to the tool 1 is facilitated for.

The second portion 4b, 5b of at least one of the first protrusion 4 and the second protrusion 5 may be cylindrical, such as circular cylindrical or elliptical cylindrical. A circular cylindrical shape of the second portion 4b, 5b may be snugly received in both a circular cylindrical and an elliptical cylindrical recess. Hence, a cylindrical shape facilitates flexibility of the tool 1 while the stability of the marker may be achieved, since it may operate with markers having circular cylindrical or elliptical cylindrical, or a combination thereof, recesses for attachment to the tool 1.

Figs. 1a-1d illustrates a tool 1 in the form of a calibration tool. The calibration tool may comprise one or several calibration elements or locations 10a, 10b, 10c. When calibrating various tools, the location, i.e. the position and/or the orientation of the tool, such as an end-effector of the tool, may be calibrated. Calibration in this context is to register the location of the object being calibrated using the navigation system such that the object can be tracked in space. Within a surgical navigation system, the tracking of the end-effector should be performed with accuracy in the millimeter range, preferably in the sub-millimeter range. For some surgical instruments and components, tracking with accuracy of 1-2 mm may be acceptable even if sub-millimeter accuracy is preferred, such as for hip or knee surgery. For other types of surgery, such as spine surgery, the accuracy should be in the sub-millimeter range, such as in the range of 20-40 ?m range.

A first calibration element 10a may be provided to calibrate the location of a pointer tool, such as the location of the tip of the pointer tool. The first calibration element may provide a calibration location in the form of a conical recess in the body 3. A second calibration element 10b may be provided to calibrate the location of a cup inserter for a hip surgery. The second calibration element 10b may comprise a calibration location in the form of planar surface having recesses extending from the planar surface. A planar surface of the cup inserter may abut the planar surface of the tool 1, and be rotated such that projections of the cup inserter extend into the recesses of the tool 1. Hence, the location of the cup inserter may be calibrated, such that also the implant, in this case a cup of a hip implant, also can be tracked in space by the navigation system when attached to the cup inserter. A third calibration element 10c may be to calibrate the location of a reamer within the navigation system. The third calibration element 10c may comprise a cross made of pins extending from a center post as the calibration location. The pins may be caught by hooks at a shaft or chuck of a reamer tool. The location and rotation of the reamer may be tracked in space. Tracking of surgical tools, such as the pointer, the cup inserter, and the reamer, may be made by attaching a marker to these surgical tools, and calibrate their end-effectors relative the calibration tool. The marker should be attached with a stable attachment interface, such as described herein, such that the marker does not move after calibration and during use of the surgical tools.

In the embodiments illustrated in Figs. 1a-1c, the attachment interface is located at a predetermined distance d6, d7, such as measured perpendicularly from the first imaginary line 8a, from the at least one calibration element or location 10a, 10b, 10c. The distance d6, d7 affects the accuracy of the calibration process, as will be described below. In some embodiments, the distance d6, d7 is substantially equal to or shorter than the distance d5 between the first protrusion 4 and the second protrusion 5.

Figs. 2a-2b schematically illustrates embodiments wherein the tool is an adapter 110 for attaching the marker 102a to a surgical instrument 103. In these figures, the marker is an active marker, but may equally be a passive marker with light reflecting elements.

Figs. 2c-2d schematically illustrates that the tool is a calibration tool 101 comprising a calibration element or location 108. The attachment interface, as described in detail above, provides for positioning a marker 102b to the calibration tool 101 with a repositioning accuracy for the marker relative the calibration tool 101.

Any deviation between the marker and the attachment interface may propagate to an inaccuracy at the calibration element or location 10a, 10b, 10c, 108. The positioning and repositioning accuracy is partly determined by the production accuracy of the marker and the calibration tool 1, 101. However, the effect of the repositioning accuracy or in-accuracy in the production may be controlled by the design of the attachment interface. The positioning accuracy may be controlled by providing the distance d5 between the first protrusion 4 and the second protrusion 5 relative the distance d6, d7 to the calibration element or location 10a, 10b, 10c. For example, the diameter of the second part 4b, 5b, of the first and/or the second protrusion may be 2 mm and produced according to a mechanical components tolerance, such as the International Tolerance grade (IT Grade). This is a standardized measure of the maximum difference in size between the component and the basic size. For example, H7 and h7 or h6 of the IT grade is a very common standard tolerance which gives a tight fit, where the recess of a hole is produced with H7 and the shaft or protrusion is produced with h7 or h6. The tolerance or positioning accuracy should preferably not increase, or not increase too much, from the attachment interface to the calibration element or location 10a, 10b, 10c. This provides for providing a calibration tool that does not need to be pre-calibrated, i.e. the location of the calibration location or element 10a, 10b, 10c relative the attachment interface does not need to be measured after the calibration tool 1, 101 has been produced. This facilitates using the calibration tool 1, 101 with a marker that also does not need to be calibrated before use. Hence, the entire calibration process of the navigation system is enhanced.

Fig. 3 is graph illustrating controlling the tolerance or accuracy at the calibration element 10a, 10b, 10c. The x-axis of the graph is a distance ratio DR calculated as ratio between the distance between the elements providing non-rotational fixation, such as the distance d5 between the second part 4b, 5b of the first protrusion 4 and the second protrusion 5, or the distance d3 between the first and second protrusion 4, 5 and the third protrusion 6, and the distance d6, d7 to the calibration location 10a, 10b, 10c. Hence, the distance ratio DR at the x-axis may be (d5 OR d3)/(d6 OR D7). The y-axis is a tolerance ratio TR, which is the tolerance at the attachment interface relative the tolerance at the calibration element or location 10a, 10b, 10c. The tolerance at the attachment interface is known and defined for the production equipment for the producing the tool. The distances d3, d5, d6, and d7 are also known. This means that the contribution to the tolerance at the calibration element or location 10a, 10b , 10c from the positioning tolerance or accuracy at the attachment interface may be determined. For example, if the distance ratio DR is 1, and the tolerance at the attachment interface is 20 ?m, the marker may repositioned at the attachment interface with a tolerance or accuracy of 20 ?m. this means that the contribution to the tolerance at the calibration element or location 10a, 10b, 10c is maximally 20 ?m. However, it may be allowed to have a contribution to the tolerance at the calibration element or location 10a, 10b, 10c of 40 ?m. This gives a tolerance ratio TR of 2, and a distance ratio DR of 0.5, wherein the distance d6 or D7 may be twice the distance d3 or d5.

Hence, when the calibration element or location 10a, 10b, 10c is located at a distance d6, d7 from the attachment interface, a calibration accuracy of the calibration element or location 10a, 10b, 10c may be defined based on the positioning accuracy at the attachment interface. Hence, the distance between the first protrusion 4 and the second protrusion 5 may be set by an acceptable accuracy at the calibration location and the distance to the calibration location 10, 10b, 10c. This accuracy at the calibration location may be in the low millimeter, such as 1-2 millimeter, to submillimeter, such as 0.2-0.8, range. The attachment interface may be produced with a tolerance according to the examples of the IT Grade standard given above.

Fig. 4 illustrates an example of a marker 200 having a planar surface facing the top surface 3 of the tool 1. As can be seen, the marker 200 is supported by the first part 4a, 5a of the first protrusion 4 and the second protrusion 5, and by the third protrusion. The second part 4b, 5b of the first and the second protrusion 4, 5, respectively, are received within recesses of the marker. In other embodiments, the second part 4b, 5b may extend only partly through the marker. As can also be seen, the marker is spaced apart from the top surface 3. The marker may have light generating elements 201a, 201b, 201c, such as reflective discs, which are illustrated by phantom lines and visible from a top surface of the marker.

Conditional language used herein, such as, among others, “can,” “could,” “might,” “may,” “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or states are included or are to be performed in any particular embodiment.

It should be emphasized that many variations and modifications may be made to the above-described embodiments, the elements of which are to be understood as being among other acceptable examples. All such modifications and variations are intended to be included herein within the scope of this disclosure and covered by the following claims.

The present invention has been described above with reference to specific embodiments. However, other embodiments than the above described are equally possible within the scope of the invention. Different method steps than those described above may be provided within the scope of the invention. The different features and steps of the invention may be combined in other combinations than those described. The scope of the invention is only limited by the appended patent claims.

Claims

1. A tool (1, 101, 110) for use with a surgical navigation system, comprising a body (2) having a top surface (3), an attachment interface provided on the body (2) and configured to attach a marker (102a, 102b) of the navigation system to the tool (1, 101, 110), wherein the attachment interface comprises a first protrusion (4) or recess and a second protrusion (5) or recess being spaced apart and extending from the top surface (3), wherein the each of the first protrusion (4) or recess and the second protrusion (5) or recess has a first portion (4a, 5a) with a first diameter and a second portion (4b, 5b) with a second diameter, the first diameter is larger than the second diameter, and the first portion (4a, 5a) extends from the top surface (3) and the second portion (4b, 5b) extends from the first portion (4a, 5a).

2. The tool according to claim 1, wherein each of the first protrusion (4) or recess and the second protrusion (5) or recess comprises a ledge between a circumference of the first portion (4) and a circumference of the second portion (5), wherein the ledge of the first protrusion (4) or recess and the ledge of the second protrusion (5) or recess are provided in a single plane.

3. The tool according to claim 2, wherein the ledge is planar.

4. The tool according to any of claims 1 -3, comprising a third protrusion (6) or recess extending from the top surface (3) and being located between the first protrusion (4) or recess and the second protrusion (5) or recess.

5. The tool according to claim 4, wherein the third protrusion (6) or recess is spaced apart from a line extending (8a) through the first protrusion (4) or recess and the second protrusion (5) or recess.

6. The tool according to any of claims 4-5, wherein a top surface (6a) of the third protrusion (6) is located in a single plane, and wherein a ledge of each of the first protrusion (4) or recess and the second protrusion (5) or recess are located in said single plane.

7. The tool according to any of claims 4-6, wherein the third protrusion (6) or recess is centered between the first protrusion (4) or recess and the second protrusion (5) or recess.

8. The tool according to any of claims 5-7, comprising a connection interface (7) configured to removably fix the marker (102a, 102b) to the tool (1, 101,110), wherein the connection interface (7) is spaced apart from the line (8) extending through the first protrusion (4) or recess and the second protrusion (5) or recess and is located between the third protrusion (6) or recess and said line (8).

9. The tool according to claim 8, wherein the third protrusion (6) or recess and the connection interface (7) are aligned between the first protrusion (4) or recess and the second protrusion (5) or recess, and preferably spaced apart from said line (8) between said first protrusion (4) or recess and said second protrusion (5) or recess a distance substantially equal to or larger than a distance between the first recess (4) or protrusion and the second protrusion (5) or recess.

10. The tool according to any of the previous claims, wherein a height of the first portion (4a) of the first protrusion (4) and the second protrusion (5) from the top surface (3) is larger than any portion of the top surface (3) between the first protrusion (4) or recess and the second protrusion (5) or recess.

11. The tool according to any of the previous claims, wherein the second portion (4a, 5a) of at least one of the first protrusion (4) or recess and the second protrusion (5) or recess is circular cylindrical.

12. The tool according to any of the previous claims, wherein the tool (1) is a calibration tool (1, 101) and the attachment interface is located at a predetermined distance from at least one calibration location (10a, 10b, 10c, 108) for a surgical instrument (103), wherein the distance preferably is substantially equal to or shorter than a distance between the first protrusion (4) or recess and the second protrusion (5) or recess.

13. The tool according to any of the previous claims, wherein the tool is an adapter (110) for attaching the marker (102a) to a surgical instrument (103).

14. The tool according to any of the previous claims, wherein the tool is a calibration tool (1, 101) comprising a calibration location (10a, 10b, 10c, 108) or calibration element, and the attachment interface provides a positioning accuracy for the marker (102a), wherein the calibration location (10a, 10b, 10c, 108) is located at a distance from the attachment interface, and wherein a calibration accuracy at the calibration location (10a, 10b, 10c, 108) is defined based on the positioning accuracy of the attachment interface.

15. The tool according to claim 14, wherein the calibration accuracy at the calibration location (10a, 10b, 10c, 108) is defined based on the distance between the attachment interface and the calibration location (10a, 10b, 10c, 108) or the calibration element.