GENERIC DEPTH INDICATOR FOR SURGICAL NAVIGATIONAL TOOLS

Abstract

A depth-indicating device for determining the depth of insertion of a surgical tool comprising a pair of spaced apart end caps, separated by a compressed spring, with the surgical tool passing through axial openings in both end caps, and firmly attached to one of the end caps, but free to slide through the opening in the other. A guide tube is attached to the second endcap, such that the surgical tool can be guided to its operating position on a body part. The second end cap and guide tube are attached to a location having a known position relative to the body part. A tracking marker is attached to the first end cap such that its longitudinal position can be tracked using a remote racking camera. Since the surgical tool is attached to the first end cap, the tool position is also tracked by the tracking system.

Claims

1. A depth-indicating device for determining the depth of insertion of a surgical tool, said system, comprising: a first and a second cap element, each cap having an axial opening adapted for insertion of said surgical tool, said surgical tool being fixed in said axial opening in said first cap element and freely movable through said opening in said second cap element; a compressed spring extending between said first and second cap elements; a tool guide attached to said second cap element; and a first position marker attached to said first cap element, such that the position of said first cap element can be determined in a remote tracking system; wherein said second cap element is disposed at a location whose spatial position is known.

2. A depth-indicating device according to claim 1, wherein said location is the end effector of a robotic arm.

3. A depth-indicating device according to claim 2, wherein the position of said end effector of said robotic is correlated with said remote tracking system, such that said depth indicating device provides a correct indication of the position of said tool taking into account any motion of said end effector.

4. A depth-indicating device according to claim 1, wherein said location is a fixed support in the region of a body part on which said surgical tool is to operate.

5. A depth-indicating device according to any of the previous claims, wherein the spatial location of a body part on which said surgical tool is to operate is known to said remote tracking system.

6. A depth-indicating device according to any of the previous claims, further comprising a second position marker attached to said second cap element or to a component having a known spatial relation to said second cap element, such that the spatial position of said second cap element can be determined in said remote tracking system.

7. A depth-indicating device according to any of the previous claims, wherein said first position marker is attached to said first cap element such that it can freely rotate about the axis of said cap element, such that if the line of sight between said first position marker and said remote tracking system is obstructed, said first position marker can be rotated to a different orientation, and the position of said first cap element can be determined using aid first position marker in said different orientation.

8. A depth-indicating device according to any of the previous claims, wherein said spring has a free length such that it remains compressed when said first and said second cap elements are separated by their maximum intended distance.

9. A depth-indicating device according to any of the previous claims wherein said spatial position of said location is known to said tracking system.

10. A depth-indicating device according to any of the previous claims, wherein the spatial position of said location is known relative to said body part on which said surgical tool is to operate by means of said remote tracking system and a marker element mounted in a known location relative to said anatomical body part.

11. A depth-indicating device according to any of the claims 1 to 9, wherein the spatial position of said location is known relative to said body part on which said surgical tool is to operate by means of a registration procedure involving anatomical comparisons using intraoperative images.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The presently claimed invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which:

[0024] FIG. 1 shows a schematic view of an implementation of the invention using the generic spring depth control navigation device to measure the depth of entry of a surgical drill bit into a vertebral body; and

[0025] FIG. 2 shows details of the depth indicator in operation and its connection to a robotic arm

DETAILED DESCRIPTION

[0026] Reference is now made to FIG. 1, which illustrates schematically one example of the generic depth indicator of the present disclosure. A spring 1 is contained between end caps 3, 4 by each of its ends. The unloaded length of the spring must be greater than the maximum distance between the end caps 3, 4, in order to always maintain the spring in a minimally compressed state end, such that the end caps 3, 4, are always at a clearly defined distance apart, for any normal mutual position of the end caps. The proximal end cap 3, contains an opening 7 into which a surgical tool 9 can be inserted and attached to the end cap 3, such that the cap moves with motion of the tool, or vice versa. The term proximal is used throughout this disclosure to relate to that end of an element closer to the operator, while the term distal relates to the end closer to the subject. To the proximal cap is attached a navigation marker 2, which can optionally rotate around the axis of the device through 360 degrees. The function of this marker will be described hereinbelow. The distal cap 4 also has an opening 17, through which the surgical tool 9 can freely slide, and this cap acts as an anchoring cap in that it is attached or anchored to a position whose location in space is defined relative to the anatomic body part on which the tool is to operate. This position could be either a fixed position, or the end effector of a robotic arm 6, whose position in space relative to the anatomic element is defined by the robotic control. The pose of the end effector of the robotic arm should be known relative to the subject's anatomyin the example shown, a spinal vertebra 10by any of the methods known in the art, whether by means of three dimensional navigation markers, or by using a registration procedure for defining the pose of the robotic arm relative to the bone using intraoperative images.

[0027] In addition, a tool guide 8 is also attached to the fixed reference position, or the end effector of the robotic arm 6, together with the anchor cap 4, such that the surgical tool 9 passes through the opening 17 in the anchoring cap 4, and down the tool guide 8, as is known in the art. The tool guide may have a serrated distal end (not shown) for gripping a bone onto which it is aligned, to prevent skiving. The end caps 3, 4, and the spring 1 together comprise a depth indicator 14. The surgical tool 9 is inserted through the depth indicator 14, which is attached to the fixed reference positon or to the robotic arm 6 from above, and through the tool guide 8 which is also attached to the fixed reference positon or the robotic arm 6.

[0028] Actuation of the depth indicator occurs when the surgical tool 9, a bone drill in the exemplary implementation shown in FIG. 1, is advanced by the surgeon. Since the surgical tool is firmly clamped to the end cap 3, longitudinal motion of the surgical tool 9 results in corresponding longitudinal motion of the end cap 3, thereby compressing the spring 1 of the depth indicator 14 between the proximal end cap 3 and the distal end cap 4, which is held in the robotic arm. The spring may be physically connected to the end caps 3, 4, or simply retained therebetween by the compression of the spring. The position of the proximal end cap 3 is monitored by means of a navigation system, which can determine the position of a marker element 2 attached to the end cap. A navigational tracking camera 13 is shown remotely positioned in a location where it can surveille the operating region, and determine the three dimensional position and orientation of any navigation markers in the surveillance region. The displacement of the marker element 2 relative to the fixed location of the distal end cap 4, is measured by the navigation system. That displacement can alternatively be determined by means of one or more additional marker elements 5 attached in a fixed position relative to the distal end cap 4, whose position can be determined by the same navigation system 13 as that used to determine the position of the proximal, moving end cap 3. The depth indicator is thus able to determine the linear longitudinal displacement of the surgical tool 9 affixed to the proximal ends cap 3, and hence, from a knowledge of the starting point of the end tip of the tool, the displacement of that end tip as the surgeon proceeds with the insertion procedure.

[0029] Reference is now made to FIG. 2, which is a schematic close-up view of the depth indicator 14. A surgical tool 9 is shown inserted through the opening 7 in the distal cap 3 of the device, to which it is firmly attached. The surgical tool 9 extends through the spring 1, the opening 7 in the proximal cap 4, and the tool guide 8, which is attached to the fixed reference position, or to the robotic arm 6. The fixed reference position, or the position of the robotic arm used for holding the depth indicator at its distal end cap, may be equipped with navigational markers 5, such that their location is known to the navigation system. As the surgical tool 9 is advanced by the surgeon into the bone, the proximal end cap 3 also moves distally with the drill, thus compressing the spring in a linear direction 12, and this distal linear movement of the markers 2 attached to the end cap is detected by the navigation system, which can thus provide a measure of the distal movement of the tool tip.

[0030] Since navigation markers 2 may be obscured by the device as the linear longitudinal motion 12 proceeds, or as the surgeon moves his hands, the marker may be attached to the proximal endcap in a manner that allows it to rotate 11 around the axis of the device, such that if one particular position shields the navigational line of sight, the marker may be rotated until visual line of sight contact is again made with the navigation system detector camera 13. In the example shown in FIG. 2, the marker element 2 is attached by means of an arm 14 to a rotary bearing (not shown) attached to the axis of the device at the end plate 3, such that the marker element can rotate freely around the device axis, and at a known distance D therefrom. The marker 2, has a three-dimensional layout, whose configuration is known. That configuration defines a known axis, and a known plane of the marker. In the example marker shown in FIG. 2, the marker element has a linear form whose length axis is perpendicular to the plane of rotation of the marker element around the axis of the depth indicator, and hence is parallel to the axis of the tool, and a fixed distance D away therefrom. The navigational system to able to determine, from the three dimensional configuration of the marker element, its angular rotational position relative to the alignment of the depth indicator, and its distance from the axis is known, such that the longitudinal position of the tool can be determined regardless of the rotational position of the marker. Thus, the marker can be freely rotated to avoid obstruction of the line of sight, and still is able to track the longitudinal insertion of the tool.

[0031] When use is made of a tool not having angular symmetry, there is a need to relate the rotational position of the tool with the depth indicator, such that the orientational detection mode of the navigation system can relate to the correct orientation of the tool as the marker is swung around the tool axis. This can be achieved by providing a directional indication in the end plate or another part of the depth indicator, such as a longitudinal slot, which interfaces with a matching feature on the tool, such that the tool orientation is known to the navigational system and to the angular position of the rotating marker.

[0032] The described device has advantages over prior art devices. First, having its own navigation markers operable through 360 degrees, enables it to be fully functional for depth detection in any position. Further, as the device is independent of need for calibration, it saves time and eliminates the error range incumbent in human-dependent procedures. It can be used with any robotic arm or navigation system. The device is designed to be used in combination with a fixed tool guide and does not need to be removed or exchanged with the tool guide in order to operate the tool.

[0033] It is appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and subcombinations of various features described hereinabove as well as variations and modifications thereto which would occur to a person of skill in the art upon reading the above description and which are not in the prior art.