WO2004107959A2

WO2004107959A2 - Stylus for surgical navigation system

Info

Publication number: WO2004107959A2
Application number: PCT/US2004/017266
Authority: WO
Inventors: Udo Warschewske; Karl-Heinz Reinwald
Original assignee: Schaerer Mayfield Usa, Inc.
Priority date: 2003-05-30
Filing date: 2004-06-01
Publication date: 2004-12-16
Also published as: WO2004107959A3

Abstract

A stylus (10) for a tracking device of a surgical navigation system includes a handle (14), a removable tip (12), a rivet (28) adapted to hold a sensor within a fluid-tight compartment, and two opposing pushbuttons (16, 18), one or both of which can activate the sensor. The dual pushbuttons (16) enable a surgeon to simultaneously apply equal but oppositely directed radial forces to both sides of the handle (14) during registration of a fiducial marker, thereby to eliminate and/or reduce undesired movement of the tip during pushbutton depression, and also to provide redundancy in activating the sensor. The tip (12) removably mounts to the handle (14) in a keyed manner, via a guide boss (32) and slot (22), to assure proper connection of the desired tip (12) at a known fixed distance between a distal end of the tip (12) and the handle (14). The stylus (10) enables the handle (14) and rivet to interchangeably connect to one of a number of differently sized or shaped tips, to allow the surgeon to select the tip which best suits a particular need.

Description

STYLUS FOR SURGICAL NAVIGATION SYSTEM

FIELD OF THE INVENTION

The present invention relates to the medical diagnostic and surgical

arts, and more particularly to an operating stylus, or pointer, for a tracking device

in a frameless stereotactic navigation system.

BACKGROUND OF THE INVENTION

Frameless image-guided stereotactic navigation systems typically

use a position-sensed tracking device to input, or "click on," patient fiducial

landmarks in real time in order to correlate the position and orientation of the tracking device to stored data sets obtained from a prior scan of the patient. By

co-registering multiple fiducial landmarks in real time with the same landmarks

that were identified and used during scanning, the surgeon can manipulate the

tracking device in real time to vary the images shown on a display, and obtained from the stored data, in order to plan and select a desired surgical trajectory toward a "target" in the patient. Such tracking devices may be mounted on an articulated arm, with digital encoders to identify the position and orientation, or

they may be sensed optically, or even magnetically. In all cases, the tracking device includes a pointer tip which is position-sensed, and when the tip is placed

by a surgeon on a fiducial marker, an electrical signaling mechanism within the

system generates an electrical signal to indicate that the particular marker has

been identified and located.

In one prior art example of a tracking device for a navigation system

of this type, the handle of the tracking device includes a depressable pushbutton

which generates an electrical signal which is conveyed to the system through a

wire. Such a structure is shown in Fig. 12 of PCT Application No.

PCT/EP99/08602, which is expressly incorporated by reference herein, in its entirety. The tracking device of the '602 PCT Application utilizes magnetic

sensing, and the device assures accuracy via a tip mounting structure which

fixedly and assuredly holds the tracking device tip a known fixed distance from a

magnetic sensor held within a handle. The mounting structure of the sensor

relative to the handle isolates the sensor within a fluid-tight midsection of the

device, thereby protecting it from deformation forces which could adversely affect

sensitivity, such as force from sterilization. To indicate that a fiducial landmark has been located, the surgeon applies a radially directed force to depress the

pushbutton which is located on the handle, thereby "clicking" on a landmark. As the uses for frameless image-guided stereotactic navigation

systems continue to evolve, it becomes increasingly important for tracking devices to adapt to these new and different uses, while at the same time maintaining the same types of advantages as achieved by prior tracking devices, as shown in the

'602 PCT application.

It is an object of the present invention to enhance the versatility of

tracking devices used in an image-guided stereotactic surgical navigation system,

without sacrificing accuracy or durability.

Moreover, it is also believed that, at least in some instances with

some surgeons, the radial depression of a pushbutton on a handle of this type may

inevitably cause some unintended movement of the tip from the desired location

on the marker. It is therefore another object of this invention to eliminate, or at least to significantly reduce, the undesired movement of a tracking device tip

during pushbutton registration of a patient fiducial.

It is still another object of the invention to readily and equally

accommodate surgeons who may desire to use either the right hand or the left

hand to manipulate a tracking device handle of an image-guided stereotactic

surgical navigation system.

SUMMARY OF THE INVENTION

The present invention achieves the above-stated objects via a

tracking device, i.e. a stylus, having a handle and a removable tip, the handle having a sensor mounted in a fluid-tight compartment and two pushbuttons, either

of which can activate the stylus. The tip removably mounts to the handle in a secure manner to assure a known fixed distance between the distal end of the tip and the sensor. According to one aspect of the invention, the handle allows the flexibility of having removable and interchangeable tips for use on a single handle,

such that a variable array of tips can be used by the surgeon during a single operation. If a different tip is desired, the surgeon can simply remove the tip

currently being used and replace it with one of a different size or configuration.

This removability feature enables the surgeon to select from tips of differing size

or shape, including tips with a bayonet or offset distal end, thereby allowing the

surgeon to use the tip which best suits the particular need of the patient or the

medical procedure. Therefore, a single sensor, located within the handle, can

communicate with multiple tips, each tip having a different tolerance which is determined by a predetermined, fixed distance between the tip and the sensor.

The sensor is generally activated by the user upon pressing of the pushbuttons located on the handle of the stylus. Information is then sent to a computer, usually

through a signal lead or wire. Wireless communication, however, is also possible.

Moreover, the present invention achieves these advantages with

enhanced accuracy, via the placement on the handle of oppositely directed

activation pushbuttons. According to a preferred embodiment of the invention, the

stylus handle permits simultaneous pressing of both pushbuttons by a surgeon.

These pushbuttons enable the surgeon to simultaneously apply equal but

oppositely directed radial forces to both sides of the handle during registration of a fiducial marker, thereby to eliminate, or at least to significantly reduce, undesired

movement of the tip during pushbutton depression. This dual pushbutton feature also equally accommodates left-handed or right-handed pushbutton actuation. With a dual pushbutton configuration, the surgeon can be either right-handed or

left-handed, yet still be able to activate the stylus with equal facility. The pushbutton that is pressed first in time will activate the placement of the fiducial. Failure of one

of the pushbuttons will not render the stylus useless, because the system of pushbuttons is redundant, such that when one pushbutton fails the other is

unaffected.

In accordance with another aspect of the invention, the tip, which is preferably bayonet-shaped in order to allow the user more easily view the site of

application of the tip, is removably connected to the handle by way of a rivet which

fits partially into both the tip and the handle. When the tip of the stylus is removed,

one can see, projecting from the top of the handle, the top of the rivet, which is preferably made of titanium. This rivet is what guides the attachment of the tip to

the handle. The projecting top of the rivet fits into the hollow center of a coupling

shaft, located at the proximal end of the tip. The tip's proximal end is made up of a

connecting element and a sealing head. The connecting element has this hollow

center, into which the top part of the rivet fits. The sealing head, located at the

proximal end of the tip, screws onto the handle after the rivet has fit into the

connecting element. The projecting top of the rivet also has a guide boss, which

slidably fits into a slot of the connecting element. The slot ensures that the tip is

properly guided onto the handle.

In accordance with one aspect of the present invention, the tip can fit onto the handle in only one correct position, otherwise the tip will not communicate

with the sensor. The guide boss and slot configuration therefore determines this correct fit. Once the guide boss has fit into position in the slot, then the sealing head screws axially down onto the handle. The sealing head has internal threads,

and the connecting element has external threads. Thus the sealing head screws down over the connecting element and onto the handle, until it reaches a shelf on

the rivet. The rivet, being an insertion of the handle, therefore acts as the attachment point of the tip onto the handle.

Once attached, the removable tip, through the connecting element,

can communicate with the sensor within the handle. When the dual pushbuttons

are pressed, the stylus is activated and the fiducial is placed. The structure of the

stylus described above meets the objectives of the present invention, thereby

affording the surgeon the versatility of having removable, interchangeable tips, better visibility of the tip application site, the elimination of undesired tip distortion

upon pushbutton registration, and either right or left handed use of the tracking

device handle.

The accompanying drawings and detailed description help to

illustrate and describe the various advantages of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a stylus for an image-guided surgical

navigation system according to the present invention.

FIG. 2 is a side view in cross-section of one embodiment of the tip

of the stylus.

FIG. 3 is a front view of the connecting element of FIG. 2. FIG. 4 is a top, cross-sectional view of the connecting element of

FIG. 3. FIG. 5 is a side view of the rivet according to one aspect of the

invention.

FIG. 6 is a top view of the rivet in FIG. 5 showing the guide boss as it

comes off of the cage for the sensor .

FIG. 7 is a frontal view of the guide boss of the rivet in FIG. 6.

FIG. 8 is a side view in partial cross-section showing the internal

connections of the rivet within the connecting element of the tip.

FIG. 9 is a side view of the rivet connected to the tip.

FIG. 10 is a partial frontal view of the stylus of FIG. 1.

FIG. 11 is a cross-sectional view of the sealing head according to one embodiment of the present invention.

FIG. 12 is a top, cross-sectional view of the sealing head of FIG. 11.

FIG. 13 is a side view of a housing for the handle.

FIG. 14 is a cross-section through the key portion of the handle of

one embodiment of the invention.

FIG. 15 is a frontal view in cross-section of the handle of FIG. 13.

DETAILED DESCRIPTION

FIG. 1 shows a stylus 10 according to a first embodiment of the present invention, with a tip 12 attached to a handle 14. As shown, the tip 12 is

bayonet-shaped and has a proximal end 13, a distal end 11 , and a middle section 15. This configuration of the tip 12 allows the user to look over the fingers to more conveniently see the site of application of the distal end 11 of the tip 12. The proximal end 13 of tip 12 includes a connecting element 20 and a sealing head

26. The sealing head 26 has internal threads 44 (not shown), which are able to

move axially down external threads 24 (not shown) of the connecting element 20

and onto the handle 14, thereby mounting the tip 12 onto the handle 14 in a

reversible manner. The details of connecting the tip 12 to the handle 14 will be

more fully described herein below. FIG. 1 further shows the handle 14 with a first

pushbutton 16 which is operable to activate the stylus 10. The first pushbutton has a water-tight and vapor-tight cover 17.

FIG. 2 is a side view in cross-section of the tip 12, showing the

connecting element 20 located at the proximal end 13 of the tip 12. As will be

described below, the connecting element is an important part of the tip 12,

because, when the tip is properly connected to the handle, the connecting element

20 allows communication between the tip 12 and the sensor (not shown). The

connecting element has a hollow center 21 , a slot 22, and external threads 24. As

described below (FIG. 8) the hollow center 21 is configured to receive a cage

portion of a rivet (not shown), and the slot 22 is configured to receive a guide boss

(not shown) as the rivet is inserted into the hollow center 21 of the connecting

element 20. The hollow center 21 widens near the proximal end of the connecting

element 20, in order to accommodate a shelf on the cage of the rivet (not shown).

The external threads 24 of the connecting element 20 allow the sealing head 26 (not shown) to screw axially down the connecting element 20. FIG. 3 is a front view of the tip 12 of FIG. 2 showing the slot 22 of the connecting element 20. As noted

above, the slot 22 permits a guide boss (not shown) to slide into the connecting element 20 in only one way. FIG. 4 is top, cross-sectional view through line X of FIG. 3, further illustrating the configuration of the slot 22 and the hollow center 21 within the connecting element 20.

FIG. 5 is a side view of the rivet 28. The rivet structure is an

important aspect of the invention, as it serves to both house the sensor for the

navigation system and to join the handle to the tip. The rivet 28 is an insertion for

the handle (not shown), and is comprised of a cage 30 and a shank 38. The cage 30 houses the sensor (not shown), and therefore is water-tight, vapor-tight, and air¬

tight. The cage 30 portion of the rivet projects from the top of the handle (not shown) and is further comprised of a guide boss 32, a shelf 34, and a stump 36.

The shank 38 portion of the rivet 28 is generally affixed within the housing of the

handle (not shown) and is comprised of three sections, namely a knurled surface

section 40, a center post 41 , and a face 42. The knurled surface section 40 has

beveled ridges 39 which operate to firmly affix the rivet 28 within the handle (not

shown). FIG. 6 is a top view through the letter X in FIG. 5 showing the guide boss

32 as it projects off of the cage 30. The diameter of the shelf 34 is larger than the

diameter of the top portion of the cage 30, and therefore can be seen from this

angle. FIG. 7 is a frontal view along the guide boss 32, as it projects radially from

the sensor cage.

Referring now to FIG. 8, the rivet 28 of FIG. 5 is shown inserted

within the tip 12. The cage 30 portion of the rivet 28 is properly fitted within the hollow center 21 of the connecting element 20 of the tip 12. The sealing head 26

seals the cage 30 within the connecting element 20 after the guide boss 32 has properly slid into position within the slot 22. Generally, the guide boss 32 initially

slidably enters the slot 22 of the connecting element 20, thereby guiding the sensor cage 30 into the correct position within the hollow center 21 of the

connecting element 20. Once the guide boss 32 has slid into place in the slot 22,

then internal threads 44 of the sealing head 26, which communicate with external threads 24 of the connecting element 20, allow the sealing head 26 to be axially

screwed down the connecting element 20 and over the shelf 34 of the rivet 28, until

the lip 46 of the sealing head 26 sits beneath the shelf 34 and adjacent the stump

36 of the cage 30. Thus, it can be appreciated that the connecting element 20 and

the sealing head 26 are separate, but inter-related, portions of the tip 12. Also, it

can be appreciated that the slot 22 allows the sensor cage 30 to fit into the connecting element 20 in only one way, such that the tip 12 fits onto the handle 14

(not shown) in only one way. As will be explained further below, the shank 38 of the

rivet 28, in the assembled form of the stylus 10, is located within the handle 14.

Once in this position, with the tip 12 properly fitted onto the cage 30, and the shank

properly affixed within the handle, the stylus is functional. That is, the sensor (not

shown), located within the cage 30, is now able to communicate with the tip 12

through the connecting element 20.

FIG. 9 is a smaller, side view of the structure of FIG. 8, showing the

rivet 28 connected to the tip 12. The sensor cage 30 (not shown) portion of the rivet 28 has slidably fit into the hollow center 21 of the connecting element 20 and

can no longer be seen. The shank 38 portion of the rivet can be seen projecting out of the sealing head 26. As noted above, the connecting element 20 operates

to aid in the communication of the tip 12 with the sensor located within the cage 30 when the cage 30 is properly located within the tip 12. FIG. 10 is a partial frontal view of the stylus 10 of FIG. 1. The handle

14 is cylindrical in shape. The guide boss 32 fits the connecting element 20 onto

the handle 14. The slot 22 (not shown) for the guide boss 32 is completely covered

by the sealing head 26. The stylus 10 will not function unless the guide boss 32 has been slid completely into the slot (not shown) and the sealing head 26 has

screwed onto the handle 14. The sealing head 26 is screwed down the connecting element 20 and onto the handle 14 after the guide boss 32 has been fit into the slot. As more fully explained above, generally the user first slides the guide boss

32 into the slot of the connecting element 20, and then screws on the sealing head

26 to complete the assembly of the tip onto the handle. The tip 12 does not rotate,

nor does the connecting element 20. Only the sealing head 26 rotates as it is

screwed on to the handle 14.

FIG. 11 is a side, cross-sectional view of the sealing head 26

showing the internal screw threads 44 and the lip 46. The sealing head 26 has

internal threads 44 which are screwed onto the external threads 24 of the

connecting element 20 (not shown). FIG. 12 is a top, cross-sectional view of the

sealing head of FIG. 11. The lip 46 of the sealing head 26 is smaller in diameter

than the top of the sealing head 26, such that the lip 46 will seal the connection

between the tip 12 and the handle 14 when it is seated adjacent the stump 36 of

the cage 30 (see FIG. 8).

FIG. 13 is a side view of a housing 50 for the handle, with a cover 17

for pushbutton 16. The cover 17 can be made of silicon or some other material capable of making a water-tight seal with the housing 50 for the handle. FIG. 14 is

a cross-section through the handle at the level of the pushbuttons 16 and 18. Pushbuttons 16 and 18 are operable, when pushed by the user, to contact the

center post 41 , which is a part of the shank 38 portion of the rivet 28. The two

pushbuttons 16, 18 on the handle 14 allow the user to press both pushbuttons at

the same time, or only a single pushbutton, depending on preference and/or

handedness. Chronologically, the first pushbutton to make contact with the center post 41 will activate the stylus. Upon activation by a pushbutton, the sensor will

send a signal indicating the position of the tip 12 to the computer (not shown). By allowing the user to press both pushbuttons at the same time, the tip of the stylus is

less likely to move, thereby enabling minimal distortion at the distal end of the tip

during usage.

FIG. 15 is a frontal view in cross-section of the housing 50 of FIG.

13. In accordance with one aspect of the invention, the housing 50 contains a first

pushbutton aperture 56 and a second pushbutton aperture 58. A rivet aperture 54

is configured to accept the rivet 28 (not shown). The internal portion of the housing

50 is configured to house the shank portion 38 of the rivet 28, the pushbuttons 16

and 18, and a lead wire (not shown).

Generally, the tip 12 is operated by the user to touch a part of the

site that is to be identified during the surgical procedure. There is a sensor housed

in the water-tight cage 30. The cage 30 communicates with the tip 12 through the connecting element 20. When the stylus 10 has the tip 12 and the handle 14

properly connected, the sensor transmits the position of the tip 12, and thus also

the orientation and direction of the tip 12, to the navigation system. The navigation

system then enables a computer (not shown) to mark a fiducial, and display a representation thereof based on the position of the tip 12 and the specified orientation in space at the time of the marking. The stylus 10 thus serves to

operate an entire navigational system wherein a distinction is made between an

operational field and a control field, as more completely described in the '602

PCT, which, as noted above, is fully incorporated herein in its entirety.

The tip 12 is made of a rigid material, preferably stainless steel or

titanium. The advantage of having a first pushbutton 16 and second pushbutton 18 is that the failure rate of the stylus 10 is reduced. That is, if a first pushbutton 16

should fail during operation of the stylus 10, the second pushbutton 18 is still

functional such that the procedure or surgical operation can continue. The novel

two pushbutton system is thus a redundant system, so that failure of one

pushbutton will not render the entire stylus 10 useless. The advantage of this is that

a single sensor can communicate with multiple tips having different tolerances, the

tolerances determined by a predetermined, fixed distance between the tip and the

sensor. When connected to the handle 14, the tip 12 communicates with the

sensor located inside the cage 30. The sensor is generally activated by the user

upon pressing of the pushbuttons 16, 18. When activated, the sensor is able to

receive information regarding the tip 12 through the connecting element 20. Information about the location and orientation of the tip 12 is then sent to a

computer, usually through a signal lead or wire. Wireless communication,

however, is also possible.

In accordance with one aspect of the invention, the tip is bayonet- shaped, such the distal end 11 of the tip 12 is offset at an angle from the handle

14. The bayonet shape of the tip 12 improves visibility of the surgical field. That is,

the operator is able to view his target in the surgical field as he looks over his or her fingers, while still being able to view the tip 12. The tip 12 of the stylus 10 can be shorter than other tips known in the prior art. Therefore, the stylus 10 of the

present invention is better suited for working under a microscope. The handle 14

of the stylus 10 is cylindrical in shape and is constructed of PEEK, or a plastic material. The tip 12 is preferably made of titanium, and the pushbuttons 16, 18

have covers 17, 19 that can be made of silicone. When the tip 12 of the stylus 10 is removed, one can see, projecting from the top of the handle, the top of the cage

30 portion of the rivet 28, which can be made of titanium. The shank 38 portion of

the rivet 28 fits tightly in the aperture 54 for the shank 36; the cage 30, with its

protruding guide boss 32, guides the tip 12 on to the handle. The cage 30 of the

rivet 28 fits into the hollow center 21 of the connecting element 20, which is located

at the tip's proximal end 13. The guide boss 32 slidably fits into the slot 22 located

in the connecting element 20. The slot 22 ensures that the tip 12 is properly guided

onto the handle 14. In accordance with another aspect of the present invention, the tip

12 can fit onto the handle 14 in only one correct position, otherwise the stylus 10

will not function. The guide boss 32 and slot 22 configuration determines this

correct fit. Once the guide boss 32 has fit into position in the slot 22, then the

sealing head 26 screws axially down the connecting element 20, covering the slot 22 and reaching a final position adjacent to the stump 36 of the cage 30. The

sealing head 26 has internal threads 44, which interconnect with external threads

24 on the connecting element 20. Only when the slot 22 is completely covered can the tip 12 communicate with the sensor.

While the present invention has been illustrated by a description of various embodiments and while these embodiments have been described in

considerable detail, it is not the intention of the, applicants to restrict or in any way

limit the scope of the appended claims to such detail. Indeed, additional

advantages and modifications will be readily apparent to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details,

representative apparatus, and illustrative examples shown and described.

Accordingly, departures may be made from such details without departing from

the spirit or scope of applicant's general inventive concept.

We claim:

Claims

1. A stylus for a tracking device of a surgical navigation system, comprising:

a hollow cylindrical handle having two pushbuttons mounted thereon and

oriented radially opposite each other, the pushbuttons being configured so as to

be capable of being simultaneously depressed by oppositely directed radially

applied forces; a rivet residing within the handle, the rivet having a cage and a shank, the

shank residing within and configured to be held securely within the handle and the

cage projecting beyond the handle and configured to house a sensor mounted in a

fluid-tight and vapor-tight compartment; and a tip releasably connectable to the handle and the rivet, the tip having a

distal end and a proximal end, the proximal end having a connecting element and

a sealing head, wherein the sealing head cooperates with the cage to removably

mount the tip to the handle in a secure manner which assures a known fixed

distance between the distal end of the tip and the cage, whereby the opposing

pushbuttons minimize undesired movement of the stylus during simultaneous

depression thereof.

2. The stylus of claim 1 wherein the connecting element further comprises a

slot and the cage further comprises a guide boss, the guide boss being slidably

received within the slot in an axial direction, when the tip is mounted to the handle.

3. The stylus of any of the previous claims, wherein the connecting element further comprises a hollow center which receivably houses the cage when the tip is

mounted to the handle.

4. A stylus of any previous claim wherein the rivet is keyed to the tip so as to permit the mounting thereof only in a radially and axially aligned manner.

5. The stylus of any previous claim wherein the connecting element and the

sealing head are threadably connected.

6. The stylus of claim 5 wherein the threadable connection of the connecting

element and the sealing head captures therebetween the cage of the rivet, thereby

to hold the rivet and the tip in a desired axial and radial relationship.

7. A handheld tracking device of a surgical navigation system comprising:

a hollow cylindrical housing; a rivet received within the housing, a cage thereof extending outwardly

therefrom and sized to receivably hold a concealed sensor;

a stylus tip removably mounted to the housing and the rivet along a

longitudinal axis thereof, to achieve a predetermined fixed relationship between

the cage and a distal end of the stylus tip; and

a pair of radially oriented and radially opposed pushbuttons arranged on

opposite sides of the housing, the pushbuttons operatively connected to the cage

so as to be able to activate the sensor when held therein, whereby the oppositely directed pushbuttons enable a surgeon to apply substantially equal but opposite radial forces simultaneously thereto, to actuate the sensor with zero composite radial force applied to the housing, and also to achieve redundancy in sensor

activation.

8. The handheld tracking device of claim 7 wherein any one of a number of differently sized and shaped stylus tips may be removably connected to the

housing and the rivet, each of the stylus tips being keyed to the housing and the

rivet so as to connect axially and radially in only one orientation, thereby to assure

proper connection.