A Fiducial Marker

Abstract

A fiducial marker and method for use in the navigation of a surgical procedure is described. The fiducial marker includes a means to readily guide a navigation probe and includes an upper surface with a sloped guide surface for guiding the probe, the upper surface further including a substantially centrally positioned well to receive at least part of the probe. The guide surface may alternatively be configured to align with a complementary portion of part of the navigation probe.

Claims

1. A fiducial marker comprising: a head having an upper surface and a lower surface; a shaft extending along a longitudinal axis from the lower surface of the head; the upper surface having a sloped guide surface for guiding a navigation probe, the upper surface further including a substantially centrally positioned well to receive at least part of the navigation probe.

2. The fiducial marker of claim 1 comprising a pedicle screw.

3. The fiducial marker of claim 2, wherein the pedicle screw is registered on a navigation system and wherein probing of the pedicle screw with the navigation re-registers the position of the pedicle screw throughout a surgical procedure.

4. The fiducial marker of any one of the preceding claims, wherein the guide surface slopes towards the shaft from an outer edge of the head, terminating at an inner edge.

5. The fiducial marker of claim 4, wherein the inner edge of the guide surface defines the opening of the well.

6. The fiducial marker of any one of the preceding claims, wherein the well is substantially centrally located on the head.

7. The fiducial marker of any one of the preceding claims, wherein a diameter of the well is less than 30% of the diameter of the head.

8. The fiducial marker of any one of the preceding claims, wherein the upper surface and the lower surface are connected by at least one outer sidewall.

9. The fiducial marker of claim 8, wherein at least part of the outer sidewall is threaded.

10. The fiducial marker of claim 8 or claim 9, comprising a plurality of outer sidewalls.

11. The fiducial marker of claim 10, comprising 6 outer sidewalls.

12. The fiducial marker of any one of the preceding claims, wherein a pitch of the slope of the guide surface is a constant pitch.

13. The fiducial marker of any one of the preceding claims, wherein, the lower surface of the head is substantially curved from a central portion to an outer edge.

14. The fiducial marker of any one of the preceding claims, wherein, the lower surface of the head is substantially planar.

15. The fiducial marker of any one of the preceding claims, wherein the navigation probe comprises an elongate body which terminates in a relatively convex probing tip.

16. A fiducial marker comprising: a head having an upper surface and a lower surface; a shaft extending along a longitudinal axis from the lower surface of the head; the upper surface having a guide surface for receiving a navigation probe, the guide surface configured to align with a complementary portion of at least part of the navigation probe.

17. The fiducial marker of claim 16, wherein the guide surface is a convex surface.

18. The fiducial marker of claim 17, wherein the navigation probe comprises an elongate body which terminates in a relatively concave probing surface, said concave probing surface configured to engage with the convex guide surface.

19. The fiducial marker of any one of claims 16 to 18, further including a screw threaded region on the head to allow the head to be at least partially countersunk in a bone of a patient.

20. The fiducial marker of any one of claims 16 to 18, wherein the lower surface is substantially planar such that the head sits flat on a surface of a bone in which the fiducial marker is inserted.

21. The fiducial marker of any one of claims 16 to 20, further including at least a second guide surface.

22. The fiducial marker of claim 21, wherein the second guide surface comprises a recess or dimple in the upper surface of the head.

23. The fiducial marker of any one of the preceding claims wherein a thread of the shaft has a reduced depth adjacent to the lower surface of the head relative to the remainder of the thread.

24. The fiducial marker of any one of the preceding claims including a region which is reflective of light or other electromagnetic energy.′

25. The fiducial marker of any one of claims 1 to 23, including connection means to connect to a reflective member.

26. The fiducial marker of any one of the preceding claims, further including an identification collar around the shaft and adjacent to the lower surface of the head.

27. The fiducial marker of claim 26, wherein includes a tail extending therefrom.

28. A system for aiding surgery on a patient comprising: one or more fiducial markers each comprising a head having an upper surface and a lower surface; a shaft extending along a longitudinal axis from the lower surface of the head; the upper surface having a sloped guide surface to guide a navigation probe, the upper surface further including a substantially centrally positioned well to receive at least part of the navigation probe; a display device; and a storage device that stores an image of at least a portion of the anatomy of the patient, including, for display on the display device, an analyser adapted to receive positional data of a navigation probe based on positioning of the probe relative to one or more of said fiducial markers on the patient; and wherein, based on said positional data, said analyser outputs correctional data to adjust an alignment of the image on said display device to match locations of said one or more fiducial markers.

29. A system for aiding surgery on a patient comprising: one or a fiducial markers comprising: a head having an upper surface and a lower surface; a shaft extending along a longitudinal axis from the lower surface of the head; the upper surface having a guide surface for receiving a navigation probe, the guide surface configured to align with a complementary portion of at least part of the navigation probe; a display device; and a storage device that stores an image of at least a portion of the anatomy of the patient, including, for display on the display device, an analyser adapted to receive positional data of a navigation probe based on positioning of the probe relative to one or more of said fiducial markers on the patient; and wherein, based on said positional data, said analyser outputs correctional data to adjust an alignment of the image on said display device to match locations of said one or more fiducial markers.

30. The system of claim 28 or claim 29, wherein the system further includes an input device to receive data from the navigation probe which is positionable relative to said one or more fiducial markers and to deliver said data to the analyser.

31. The system of any one of claims 28 to 30, further comprising a display.

32. The system of any one of claims 28 to 31 for use in a spinal surgery.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0101] FIG. 1 is a side view of an embodiment of a fiducial marker;

[0102] FIG. 2 is a side view of an embodiment of a fiducial marker with a probe touched against the well of the marker;

[0103] FIG. 3 is a side view of the embodiment of FIG. 2 with the probe orientated differently;

[0104] FIG. 4 is a side elevational view of the head of an embodiment of a fiducial marker;

[0105] FIG. 5 is a side view of the head of FIG. 4;

[0106] FIG. 6 is a flow chart illustrating a navigation system using the fiducial markers herein disclosed;

[0107] FIG. 7 is a schematic representation of use of a probe and the fiducial markers as herein disclosed in a navigation system;

[0108] FIGS. 8a and 8b are representations of images taken during a procedure.

[0109] FIG. 9 is a cross sectional view of a fiducial marker and navigation probe according to a further embodiment;

[0110] FIG. 10a is a cross sectional view through A-A of FIG. 10b showing a further embodiment; and

[0111] FIG. 10b is a top plan view of the embodiment of FIG. 10a.

DESCRIPTION OF EMBODIMENTS

[0112] One embodiment of the fiducial marker is generally shown as 10 in the accompanying drawings. Fiducial marker 10 has a head 11 which has an upper surface 12 and a lower surface 13. Shaft 14 extends along a longitudinal axis from lower surface 13 of head 11.

[0113] Upper surface 12 has a sloped guide surface 15 to receive and guide a navigation probe 100. Well 16 is centrally positioned in the head 11 and configured to receive the end 101 of navigation probe 100.

[0114] Guide surface 15 extends from an outer edge 17 of head 11, inwardly and downwardly towards shaft 14. Guide surface 15 terminates at an inner edge 18 which defines the opening of well 16. Well 16 is positioned in a central part of head 11 and its upper opening is defined by the inner edge 18 of guide surface 15. Sidewall 20 extends from inner edge 18 to a closed well base 21.

[0115] The diameter of the well can be seen in the Figures to be significantly less than the diameter of head 11. The diameter should, however, be sufficient to receive the end 101 of probe 100.

[0116] In FIGS. 1 to 3, the well is substantially hemispherical in shape. However, other shapes are envisaged. Further, the slope of the sidewall 20 of well 16 may vary and may be more or less sloped than depicted. However, it is envisaged that the slope is sufficient to prevent end 101 of probe 100 slipping out of the well in use.

[0117] The sidewall 20 of the well as shown in FIGS. 1 to 3 and FIG. 6 has a steeper pitched slope relative to the pitch of the slope of guide surface 15. The pitch is taken to be the angle of the slope relative to an axis which is normal to the longitudinal axis of the shaft and as shown as line x-x in FIG. 2.

[0118] The pitch of guide surface 15 as depicted is constant along a length of the guide surface from outer edge 17 to the inner edge 18.

[0119] As depicted in FIGS. 4 and 6, head 11 has at a plurality of outer sidewalls 23. As shown in FIG. 4, the head has six identical sidewalls 23 to form a hex nut structure. The six outer sidewalls 23 form a driver feature for marker 10 by which a complementary socket driver grips the sidewall and allows a surgeon to insert the marker into a bone, or remove the marker from the bone.

[0120] Lower surface 13 of head 11 includes a central portion 24 substantially aligned longitudinally with well 16. This central portion 24 comprises the lowest point on lower surface 13. Further, shaft 14 extends from central portion 24 of the lower surface 13.

[0121] Lower surface 13 curves outwardly from central portion 24 to a junction 25 with outer sidewall 23. The rate of curvature of the lower surface is relatively constant.

[0122] Base 21 of well 16 aligns with junction 25. Outer sidewalls 23 are visible to a CT or other scanner, the sidewall being distinct from the lower curved surface 13. Base 20 aligns with junction 25 to provide visual comparison of the location of navigation probe 100 in relation to fiducial marker 10 on the navigation system's imaging screens. If the probe is accurately shown on a screen it will appear to be centrally positioned on the head and at the same depth as junction 25.

[0123] Shaft 14 is threaded along its length from a first end 26 to a second bone cutting end 27.

[0124] When used in a broader navigation system, the markers as mentioned may provide a check of the accuracy of the imaging.

[0125] The depicted, system 200 in FIG. 6 is designed to aid a surgeon or surgical team performing corrective spinal surgery. The system 200 comprises a computer monitor 211 that serves to display CT images taken of a patient's spine by a CT imager 212. The images displayed on display 211 are stored in a suitable data storage device 213.

[0126] The system further comprises an analyser 214 in the form of a computer processor. The analyser 214 is designed to compare the CT image provided by the imager 212 with the position of one or more fiducial markers 10 positioned on the patient. The position of the one or more markers 10 is determined using a surgical navigation probe 100 which is brought into contact with the one or more markers 10. The positional data from the probe 100 is provided through an input device 216 to the analyser 214 which in turn provides an output of said comparison to the display device 211. The use of the probe allows the analyser 214 to generate correctional data so allowing for correctional alignment of the displayed CT image to match with the actual position of the one or more markers 10 on the patient.

[0127] To position the one or more fiducial markers 10, the surgeon first exposes bony anatomy of the spine 240, posteriorly, laterally, obliquely, or anteriorly, at the desired levels. FIG. 8 provides an illustrative depiction of this. A fiducial marker 10 can then be mounted to a piece of bone away from the area to be resected or operated thereon, usually the next vertebra up or down the spine 240 and usually on the spinous process in a posterior approach.

[0128] One or more markers 10 and/or probe 100 can include reflective components, such as reflective balls 220. The reflective components can be designed to reflect light of a particular frequency, for example infrared (IR), with a navigation device, such as IR camera 202, having a capability to remotely detect the position of the markers, probe and other instruments being then part of the system. In use, the IR camera is pointed at the whole operative site, including the surgical marker(s) clamped or mounted to bone.

[0129] The position of a first marker 10 may be determined using the reflective components 220 and/or through being probed, and initial registration of the displayed image may therefore be made using the first marker 10. A CT scan can then be taken. This can be achieved through use of a mobile CT scanner that is brought into the operating theatre. In taking the CT scan, the aim is to show all of the desired operative levels as well as the fiducial markers.

[0130] The CT scanner can be connected or viewed by the IR camera and subsequent CT images obtained in all three planes can be looked at simultaneously on three separate regions or windows of the display 11. These images typically show the patient as they are lying on the operating table and as depicted in FIG. 8, fiducial marker 10 can be seen in the bone. Furthermore, probe 100 may have one or more reflective markers 220 as described herein and can be used by the surgeon such that it effectively points at various parts of the anatomy. Using the IR camera, the location of probe 100 relative to the patient may be monitored and superimposed over the CT images of the patient's anatomy.

[0131] An illustration of a surgeon manipulating probe 100, in order to probe the position of a fiducial marker 10a located in the spine 240 of a patient's body, in the field of view of an IR camera 202, is provided in FIG. 7.

[0132] The system can be used to identify the correct placement point for one or more pedicle screws 300, as well as the correct angle, and depth, to drill for them. As the pedicles of the vertebra are drilled, probe 100 can also be inserted into the drill hole to check its location and orientation. The planned screw size can also be superimposed, rather than just the line of the probe, to ensure the screw diameter and length do not exceed the available space.

[0133] During this procedure, fiducial markers 10 can be used, from time to time, to check the accuracy of the navigation. Because the markers are in situ when the CT scan is taken, they show on the CT images. Probe 100 as superimposed on the displayed images should then be shown touching exactly onto the heads of the scanned markers 10 when the probe 100 is touched onto the heads of the actual screws by the surgeon. However, this is often not the case with the screws appearing to be 1 or more millimetres away from the position of the probe when viewed on the display, despite the fact the probe is placed exactly in head 11, or as exactly as the head 11 design allows, as shown in FIG. 8a. This “offset” could require the surgeon to estimate a correction for the image shown for the other areas of anatomic interest, such as the pedicle of the vertebra.

[0134] The system as described herein provides the surgeon or surgical team with a means of correcting for such offsets when they occur. Although not depicted, at least three fiducial markers 10 can be positioned to the patient, each on a different plane to that of the others. The use of at least three fiducial markers 10 can ensure that the CT image can be realigned in at least three axes/planes, so ensuring an appropriate three dimensional image of the anatomy of the patient. At least three fiduciary screws may be positioned on each segment (e.g., on each vertebra). As the spine consists of multiple intercalated segments with intrinsic abilities for movement in any plane at any time point, the use of three fiduciary markers per segment may allow ultimate control of subsequent image manipulation and hence navigation.

[0135] In one embodiment, the analyser 214 of the system 200 can make an initial determination of the position of the three fiducial markers 10 and so form a three dimensional image. For example, the analyser can in effect create a three dimensional solid based on the initial determination of the three fiduciary screws. The surgeon can then use 100 to physically touch the actual fiducial markers 10 to generate positional data. The analyser 214 can then use the positional data provided by this action to form a corrected three dimensional solid and then manipulate or align the CT image on the display to the actual location of the body, thus providing a form of registration or re-registration of the image and the patient's body. The corrected image is shown in FIG. 8b.

[0136] The features of the fiducial markers 10 having a guide surface 15 and a well 16 allow a surgeon to easily and reliably contact the marker with probe 100. The slope of the guide surface 15 guides the tip of probe 100 towards and into well 16. The dimensions of well 16 are such that the tip of probe 100 sits within the well and is not easily dislodged.

[0137] FIG. 9 depicts a further embodiment of a fiducial marker 300 which has a head 301 with an upper surface 302 and a lower surface 303. Upper surface 302 includes a guide surface 304 for receiving a navigation probe 400. As shown, guide surface 304 comprises a convex surface which engages with a complementary concave surface 401 of navigation probe 400. Specifically, in this embodiment, through monitoring using a navigation system the positioning of the concave surface 401 of the navigation probe 400 and the orientation of the probe 400 axis, the axis in free space along which the spherical centre 305 of the fiducial marker 300 lies can be determined. Moreover, through knowledge of the constant distance between the concave surface 401 and the spherical centre 305 of the fiducial marker 300 (which is the substantially same as the radius of the spherical top surface of the fiducial marker 300 when the concave surface 401 is engaged with the guide surface 304), the location of the spherical centre 305 can be identified.

[0138] As may be appreciated from the embodiment shown in FIG. 9, for example, the concave surface 401 may be positioned to align with other parts of the upper surface 302 which would therein comprise the guide surface for the probe 400.

[0139] Fiducial marker 300 also includes a hex drive recess 306 to allow the marker to be driven into a bone of a patient.

[0140] FIG. 10a shows an embodiment of a fiducial marker 500 wherein upper surface 501 includes dimple 502. This marker 500 may be used with either of the probe types depicted as 100 and 400. That is, dimple 502 may act as a guide surface to guide probe 100. Further, the hemispherical nature of at least part of the upper surface 501 allows a probe having a concave tip such as shown in FIG. 9a to be brought into abutment with the upper surface 501.

[0141] A region of the upper surface adjacent to its join with lower surface 503 includes a screw thread 504. This allows the head to be screwed into a bone. An imaginary upper bony surface is shown in FIG. 9b as dashed line 510 which depicts the positioning of the marker 500 once positioned in the bone.

[0142] A top plan view of marker 500 is shown in FIG. 10b. In this embodiment, cross screws 505 are provided on upper surface 501 to receive a driver to allow the marker 500 to be implanted in a bone.

[0143] It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive

[0144] Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.