WO2009132389A1

WO2009132389A1 - Bilateral alignment tool for use on a skull

Info

Publication number: WO2009132389A1
Application number: PCT/AU2009/000533
Authority: WO
Inventors: James William Leith Dalton
Original assignee: Cochlear Ltd
Priority date: 2008-05-01
Filing date: 2009-04-30
Publication date: 2009-11-05

Abstract

A gauging tool for surgery procedures to be performed on a recipient, including a gauge member shaped and sized to over arch the head of the recipient extending from at least one side of the recipient to the other side of the recipient about the mid-sagittal plane of the recipient; two body part locating pieces adapted for placement on the body of the recipient substantially symmetrical about the mid-sagittal plane of the recipient having rota table attachment to the gauge member such that in use the gauge member can rotate about the head of the recipient and wherein the gauge member is useable to gauge the location of surgery on the head of the recipient substantially equidistant from the body part of the recipient associated with the body part locating pieces.

Description

BILATERAL ALIGNMENT TOOL FOR USE ON A SKULL

This invention relates to a tool which can be used to assist surgeons to locate a surgical site on a human skull such as an implant site in a recipient and in particular a cochlear implant.

BACKGROUND

A variety of medical implants apply electrical energy to tissue of a recipient to stimulate that tissue. Examples of such implants include pace makers, auditory brain stem implants (ABI), devices using Functional Electrical Stimulation (FES) techniques as well as Spinal Cord Stimulators, and cochlear implants.

A cochlear implant allows for electrical stimulating signals to be applied directly to the auditory nerve fibres of a recipient, allowing the brain to perceive a hearing sensation approximating the natural hearing sensation. These stimulating signals are applied by an array of electrodes implanted into the recipient's cochlea.

The electrode array is connected to a stimulator unit which generates the electrical signals for delivery to the electrode array. The stimulator unit in turn is operationally connected to a signal processing unit which also contains a microphone for receiving audio signals from the environment, and for processing these signals to generate control signals for the stimulator.

A cochlear stimulation system includes internal components referred to as the implant package including a receiving coil and associated receiver with electronics to both receive signals and generate stimulation currents for providing to an electrode array and the external component which includes the speech processor having at least a microphone, signal transforming electronics and a transmitter coil. This is a very general description of a highly complex system.

Part of the process of implanting the internal components is the implantation of a stimulator unit and an associated receiving coil, which has a number of forms but generally is small enough to be fitted to into the skull wall of the cochlear system recipient most commonly children.

Figure 1 depicts an example of the location of both the internal and external components about and within the skull of a recipient. The external components depicted in this figure include the external processor 10 typically worn over the ear (commonly referred to as Behind The Ear (BTE) unit) and partially visible behind the visible ear lobe 12 and an external signal transmitter unit 14 located just above the ear lobe and over the skull of the cochlear implant recipient which can be partially hidden by the recipient's hair. The external signal transmitter unit 14 is maintained in position over the implanted receiving coil assembly 16 by magnetic attraction between a portion of the transmitter unit (generally a circular coil having a magnet centrally located) and metal portion located in the implanted receiving coil assembly.

The internal components depicted in this figure include the implanted receiving coil 16 and associated stimulator signal processor 18 referred to as a stimulator unit 22 located in the wall of the skull and the electrode array 20 which is located in the scala tympani of the cochlear region of the recipient.

It should be noted that Figure 1 depicts but one of the many configurations of cochlear implant systems.

There exist a variety of shapes and sizes of stimulator units 22 but common to all such devices is the need to accurately locate the unit in the skull of the recipient. The accuracy of location is equally as important when the recipient requires two implants one for each ear, termed a bilateral implant arrangement (a similar term with similar meaning usable in this context is contra-lateral) as each implant_. is preferably located equi-lateral of the mid-sagittal plane of the human body. A stimulator unit 22 should be positioned accurately for all the right reasons including the need to have a clearance between the externally located processor 10 and the implanted stimulator unit 22 as it is not desirable to have contact which otherwise can cause pressure on the skin of the wearer that may lead to tissue damage, infection and discomfort. A further reason for careful location choice of the stimulator unit 22 is that when placing the implanted stimulator unit the future comfort of the recipient is considered, which includes, placement is in a typically flatter portion of the skull and placement that is not too low on the skull that flexing of the head using the head flexors is problematic, nor too low that should the implant recipient wear a hat, cap or glasses there is minimal interference. A Surgeon's Guide (Table 1) has been developed to assist in this placement.

Fig 2 depicts a typical pre-operative test placement and illustrates the use of the template mentioned in the Surgeon's Guide (Table 1) as well as the positioning of the implant relative to the ear and remainder of the skull. The template shown in Fig. 2 is made wholly of silicon and is usable as a template only, so that the surgeon can make outline marks on the skin covering the skull as deem necessary before performing the surgery to implant an actual stimulator unit.

Having established the position of one implant is it just as problematic to locate a second such implant in a bilateral implant procedure. Visual comparison requires looking at both sides of the head at the same time which is sometimes possible with a child when the recipient is a small but is not possible to do when about to operate on the head of an older recipient. Alternative techniques include the use of measuring tapes and plastic sheets to determine the position and orientation of the second implant based on the position of the first implant and all such techniques take inordinate time and have undesirable inaccuracies.

The arrangement and method disclosed in this specification addresses the difficulties in locating the site of a bilateral surgical procedure and in one particular example the site of the surgical implantation of bilateral cochlear implant stimulator units and associated elements during surgery and provides a method and means that at least provides an alternative to current techniques.

BRIEF DESCRIPTION OF THE INVENTION In one aspect of the invention, there is provided a gauging tool for surgery procedures to be performed on recipient, including a gauge member shaped and sized to over arch the head of the recipient extending from at least one side of the recipient to the other side of the recipient about the mid-sagittal plane of the recipient; two body part locating pieces adapted for placement on the body of the recipient substantially symmetrical about the mid-sagittal plane of the recipient having rotatable attachment to the gauge member such that in use the gauge member can rotate about the head of the recipient and wherein the gauge member is useable to gauge the location of surgery on the head of the recipient substantially equidistant from the body part of the recipient associated with the body part locating pieces.

In one form, the two body part locating pieces are adapted for placement in the external ear canal of the recipient.

In yet another form, the gauge member is elongate and provides a flat surface substantially parallel to the surface of the head of the recipient.

In another form, the gauge member is markable to indicate a position on the gauge member that represents a surgical position on one side of the recipient's head used to gauge a corresponding position on the substantially laterally opposite side of the recipient 's head.

In yet another form, the gauge member includes indicia which are usable to gauge a corresponding position on the substantially laterally opposite side of the recipient's head.

In one form, the gauge member is made of plastic wherein the stiffness of the plastic allows rrύnirnal flexing during use.

In another form, the gauge member includes indicia along a portion of its surface. In yet another form, wherein the gauge member includes spaced lines along at least substantially laterally opposite side portions of its surface.

In another form the gauge member is substantially "U" shaped.

In another form, the surgical location is intended for or is a cochlear implant system component.

According to a second aspect of the invention, there is provided a method of using a gauge tool for surgery procedures to be performed on a recipient, including the step of: gauging the position of a location on the head of the recipient using a gauge member shaped to over arch the head of the recipient extending from at least one side of the recipient to the other side of the recipient about the mid-sagittal plane of the recipient which has been placed on the body of the recipient using two body part locating pieces adapted for placement on the body of the recipient substantially symmetrically about the mid-sagittal plane of the recipient having rotatable attachment to the gauge member such that in use the gauge member can rotate about the head of the recipient and gauging takes place on each side of the mid-sagittal plane based on the position gauged on the opposite side of the head of the recipient.

In a yet further aspect of the invention, there is provided a method of using a gauge tool for surgery procedures to be performed on a recipient, including the steps of: gauging the position of a location on the head of the recipient using a gauge member shaped to over arch the head of the recipient extending from at least one side of the recipient to the other side of the recipient about the mid-sagittal plane of the recipient which has been placed on the body of the recipient using two body part locating pieces adapted for placement on the body of the recipient substantially symmetrically about the mid-sagittal plane of the recipient having rotatable attachment to the gauge member such that in use the gauge member can rotate about the head of the recipient and reversing the location of the two body part locating pieces with respect to the respective body parts so as to gauge the location of surgery on the head of the recipient substantially equidistant from the body part of the recipient associated with the body part locating pieces.

Throughout this specification and the claims that follow unless the context requires otherwise, the words 'comprise' and 'include' and variations such as 'comprising' and 'including' will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that such prior art forms part of the common general knowledge.

Specific embodiments of the invention will now be described in some further detail with reference to and as illustrated in the accompanying figures. These embodiments are illustrative, and not meant to be restrictive of the scope of the invention. Suggestions and descriptions of other embodiments may be included within the scope of the invention but they may not be illustrated in the accompanying figures or alternatively features of the invention may be shown in the figures but not described in the specification.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 depicts an example of the location of both internal and external components of an example cochlear implant system about and within the skull of a recipient using a cut-away view of the recipient so as to view both external and internal components;

Figure 2 depicts a perspective view of an example of the pre-operative test location of the external component of the cochlear implant system on the skull of a recipient;

Figure 3 depicts a top view of an example of an implanted cochlear system component being an extra-cochlear stimulator unit of the metal type; Figure 4 depicts a top view of an example of implanted cochlear system component being an extra-cochlear stimulator unit of the ceramic type; Figure 5 depicts a perspective view of a gauging tool for surgery procedures according to an embodiment of the invention; Figure 6 depicts a side view of the gauge tool of Fig. 5 in use upon the head of a recipient;

Figure 7 depicts a side view of the gauge tool of Fig. 5 in use upon the head of a recipient in place for gauging or marking as desired by the user of the tool; Figure 8 depicts a side view of the gauge tool of Fig. 5 in use in a reversed position assisted by viewing Figure 7 from the opposite side of the recipient;

Figure 9 depicts a side view of the gauge tool of Fig.5 on the head of a recipient; Figure 10 depicts a partial perspective view of a gauge tool having indicia representing graduations along a portion of the "U" shaped portion; and Figure 11 depicts a perspective view of a length adjustable version of the gauge tool of Fig. 5.

DETAILED DESCRITION OF AN EMBODIMENT OF THE INVENTION

The invention described by way of example herein uses the locating process for implanting a cochlear system into a recipient. However, the principle of the invention may be applied to any surgical process that has as a desirable outcome the equi-distant spacing of two implant elements or surgical procedures from a point, zone, or plane on or associated with the human skull. The term recipient is used to describe the recipient of the surgical procedure which for the purposes of the example used in this specification is a recipient of a cochlear implant.

Two examples of implanted cochlear implant components are depicted in Figures 3 and 4.

Figure 3 depicts an extra-cochlear stimulator unit 20 having a metal housing 26 (in one example titanium), as is the receiving coil 24 (for receiving signals from the external components) and a magnet 29 which are both located external to the casing 26. The cochlear simulator unit is encased in a bio-compatible elastomeric silicone capsule 28 so that the unit can be moulded to the shape of the skull where possible. In this particular illustration the intra-cochlear electrode array 22 is shown extending out of the encased simulator unit, which itself if covered in biocompatible material.

Figure 4 depicts an extra-cochlear stimulator 30 having a ceramic housing which can encases the receiving coil (not shown) but which still receives energy and communications from an externally located coil and external processing unit (not shown). However, since the ceramic stimulator 30 uses an internal coil the depth of the implantation is greater than that of the metal encased version depicted in Figure 3 which has an external coil located elsewhere on the skull but still under the skin.

Implantation locations for each these types of extra-cochlear stimulator units can be different, and by way of example only, the ceramic encased unit 30 can be located closer to the ear than the metal encased unit 20.

Both housings described and illustrated in Fig's 3 and 4 must be hermetically sealed to protect the delicate electronics housed therein and also protect the implant recipient from any damage that may arise from those same contents. The materials used in an implanted device in contact with the recipient's body are bio- compatible materials.

By way of example, the implanted metal encased stimulator unit can be placed in the mastoid bone in a custom made cavity of approximately 16 mm in diameter and of the required depth to suit the type of implanted unit, in one example that is 2 mm. The internal coil associated with a particular type of stimulator unit is arranged to lie just under the skin so that it can be more readily coupled to the externally located transmitting coil rather than being hindered by an intervening bone structure if otherwise located.

The coil and its silicon housing is shaped, in one example, and in the shaped example has a predetermined curve (for example a 20° bend with respect to the plane of the embedded stimulator unit housing) to assist conforming the coil element to the shape of the recipient's skull and thus make the implant more comfortable, functional and aesthetic.

The location of the stimulator unit is important with respect to the recipient's pinna (a relevant portion of the recipient's ear) and the location of the external coil is importantly located to match the location of a specific version of the large variety of external component configurations. Fig. 2 depicts how a surgeon can use a template to mark the desired location, on the recipient's skull, of the stimulator unit and also know at the same time the desirable location of the receiving coil of that particular type of simulator unit. For all the reasons described previously the placement can be usefully determined pre-operatively along with the help and understanding of the recipient and if not them their family, making the process ultimately better suited to the recipient's individual needs.

Bilateral implantation can occur in either of two ways; the first being when the surgery includes two implants at essentially the same time (simultaneous implantation) and when the surgery to implant a second cochlear system occurs some days, months or years, after an earlier implantation (sequential implantation).

Bilateral implantation takes the desirable location of a first implant and uses it to more easily locate a second implant providing the convenience and ultimately a positive aesthetic as the implants are symmetrical with respect to the ears and skull features of the recipient and likely symmetrical with respect to the mid- sagittal plane of the recipient.

The tool 40 depicted in Fig. 5 described herein provides an instrument to assist a surgeon to determine an implant location (when implanting the internal cochlear components) with respect to an already implanted coil and/ or stimulator unit of a cochlear implant that is to be implanted bilaterally (whether simultaneously or sequentially) so that each of the components are equidistant from the pinna, in distance as well as angle with respect to the mid-sagittal plane and the vertical. The largest portion of the tool is a generally "U" shaped portion 42 (preferably the shape of a child's skull) having ear locating pieces 44 and 46 at each end of the "U" shaped tool, each facing inward with respect to the ends of the "U" shape. These ear locating pieces 44 and 46 are to be placed in the recipient's two external ear canals (auditory canals) or other locations on the pinna or head that are symmetrical about the mid-sagittal plane of the recipient.

The "U" shaped portion 42 is rotatable with respect to the ear locating pieces 44 and 46, and once the ear locating pieces are in place, the "U" shaped portion 42 is moveable about the head of the recipient 50 as depicted in Fig. 6 using phantom lines to depict various locations.

In preference the "U" shaped portion 42 of the tool 40 is moveable from a position behind and below the ears (52R) as shown in phantom on the side of the recipient 50 of the recipient to directly above (52A) the head 54 of the recipient, and if need be in front (52F) of the head 54 of the recipient as may be needed in a surgery involving facial procedures.

The movement is preferably smooth and predicable while the ear locating pieces are stationary in the external ear canals of the recipient of the surgery and the axis of rotation (coming out of the page at the centre portion of the ears) of the "U" shaped portion is maintained with respect to the remainder of the head of the recipient.

The embodiment described in some detail herein involves the use of the ears as the interface location of the body part locating pieces generally because the location of the surgically implanted elements is importantly located with respect to that part of the body. However, it is possible for there to be other interface locations of the body part locating pieces. In a further example, the interface could be a part of the jaw of the person and the placement could be achieved by the recipient bitting down on a mouth piece and the gauge member being rotatable with respect to the mouth piece. The tool 40 is preferably non-sterile and disposable as it will be used prior to medical preparation of the eventual surgical site. It may be used in pre-operative or intra-operative procedures (again, prior to medical preparation of the site(s)). However, it is a matter of selection of materials, packaging and procedures as to whether it is made suitable for aseptic use during a surgery.

For simultaneous implantations where a first side of the recipient needs to be fitted with an implant and then the other side, a first site is determined by the skill of the surgeon sometimes in consultation with the recipient or the recipient's family. The surgeon may also use the Surgeon's Guide (Table 1) to assist them to locate the first site. Part of the process is using a template as depicted in Fig. 2 to locate a first surgical placement mark to be drawn on the skin of the recipient prior to surgery. For sequential implantations the surgeon would use the previously implanted recipient's coil location as a guide for determining the bilateral location of a second implant, noting that if the first location is not ideal then an offset distance may be part of the determination process of the second location.

As depicted in Fig. 7 which shows a side view of the recipient's head and the tool in use, the two body part locating pieces 44 and (46 not shown) of the tool 40 are placed in the ears of the recipient. The tool is then rotated so that a portion of the tool, being in this embodiment a portion of the "U" shaped portion 42, lies above or below or over the predetermined location (as identified previously by the surgeon or the already implanted component (either the coil or the stimulator)). The surgeon can then gauge the position of the surgery with respect to the tool and in one example a mark 60 is made on the tool.

Either way (for simultaneous or sequential implantation) this first mark on the tool becomes a mark that enables the use of the tool to determine the location on the recipient's skull of the bilaterally positioned surgical site for the equivalent element of the implanted unit. In an embodiment, to be described in greater detail later in the specification, indicia (lines and possibly numbers) on the tool, equidistant on each side of the tool from the body part locating pieces are used to gauge the location of elements on the head of the recipient. It is assumed that the body part locating pieces are located symmetrically of the mid-sagittal plane; otherwise an offset can be used as required.

In the embodiment illustrated in Figures 8 and 9, the tool is then removed from the head of the recipient and reversed so that the ear locating pieces are in opposite ears, as depicted in Fig. 8.

Referring to Fig. 8 depicting the opposite (and new) side of the head 54, the surgeon can place a mark 70 on the skin gauged from the first mark 60 on the tools' "U" shaped portion 42. The angle of the tool is repeated by ensuring that the tool on the first side lines up with the first site in the same manner as it was when the mark or other gauging was performed.

The new mark on the head of the recipient provides the location for the implant placement which may be the only implant for that surgery or the second planned implant of the surgery.

The surgeon may make two marks on the tool (they of course can make as many as they think are required), one for the coil and the other for the stimulator, or one for the magnet location or the outer dimensions of any of the implantable elements.

The mark 60 on the tool can thus be used to provide symmetry of the location of an implant on the head of the recipient with respect to the prior or other surgically determined location. The symmetry can be with respect to the body part used for anchoring the tool during its use, and ideally as stated previously, that will provide symmetry about the mid-sagittal plane of the implant recipient. Fig. 9 depicts a side view of a gauge tool on the head of a recipient and the surgeons mark on the second site for a bilateral implant.

Fig. 10 depicts a side view of a further embodiment of the gauge tool having indicia along at least a portion of the tool extending along from the rotating ends towards the mid-sagittal plane. The indicia depicted on the tool include centimetre and millimetre spaced markings. The indicia need not be numbered and does not necessarily need to be equidistant. The indicia are made on one side of the tool or if they are on both sides of the tool, they are the same on both sides of the gauge tool relative to the axis of rotation of the rotating portions of the gauge tool. The tool is reversed, by reversing the location of the two body part locating pieces with respect to the respective body parts.

Clearly, the accuracy of the symmetry of the gauging process is dependant primarily on the repeatability of the rotational motion of the tool but also to some degree on the proper fitment of the ear locating pieces and the adequate stiffness of the "U" shaped portion.

Anticipating or being aware of the assumptions and possible reasons for miss- alignment will assist the skilled person to select appropriate materials for each of the pieces of the tool and for the surgeon to check on the symmetry of the ears of the recipient and make adjustments if required.

For example, the ear locating pieces 44 and 46 can be mouldable foam so that they can be moulded to the shape of both inner ear canals (location of the pinna of the ear) to provide a stable base for the rotating elements of the tool.

The rotation assembly of the ear locating and "U" shaped portion may simply include an interference fitting spindle portion on the ends of the "U" shaped portion. The spindle is shaped to fit into the foam of the ear locating pieces and adapted to rotate with sufficient stability and repeatability (at least the one to a dozen times the single use tool will be moved) during its use. An alternative rotation assembly may include an annular element located in the foam of the ear locating pieces into which a spindle protruding from the base of the "U" shaped portion of the tool can be fitted and be smoothly rotatable within, thereby providing a repeatable rotational movement better than the arrangement described in the preceding paragraph.

The "U" shaped portion can be made of a stiff material, for example, plastic of suitable stiffness for its purpose wherein for example the stiffness of the plastic allows minimal flexing during use.

Once the surgeon is satisfied with the marking of the recipient's skull the tool is removed and discarded.

A new aseptic tool may also be used during surgery to double check locations or if the implantation of one unit has not been possible in the planned location and a new symmetrical location for the simultaneously implanted unit needs to be determined.

Fig. 11 depicts a perspective view of a length adjustable version of the gauge tool 100 similar in primary function to that depicted in Figure 4 but being adjustable in length to accommodate a variety of head sizes. In the embodiment depicted in Fig. 10, the "U" shaped portion is formed from two parts 102 and 104 that slidably engage, either a separate portion 106 or one of the parts 102 or 104 extends into the other. Either frictionally or otherwise the relative position of the two parts can be fixed to suit the use of the tool.

The need for a length adjustable version of the invention may be limited as it is possible to manufacture single use items such as a tool in a variety of sizes to suit a range of recipient head sizes. Most likely there being an infant, child and adult version of predetermined size and associated configurations (such as various ear bud sizes to match the tool size).

It will be appreciated by those skilled in the art that the invention is not restricted in its use to the particular application described. Neither is the present invention restricted in its preferred embodiment with regard to the particular elements and/ or features described or depicted herein. It will be appreciated that various modifications can be made without departing from the principles of the invention. Therefore, the invention should be understood to include all such modifications within its scope.

Table 1

CI24RE (CA) Surgeon's Guide

Surgical Procedure

General surgical issues

The routine use of a facial nerve monitor Is advised, and is particularly important for cases of congenital temporal bone anomalies,, revision surgeries, and other cases in which the facial nerve may be at greater risk,

Broad-spectrum antibiotic coverage for the operation is important Coverage should be determined fay the surgeon, to be consistent with best practice,

1. Pre-incision: non-sterile field

I. Place the BTE Template in position on the ear. Ensure there will be sufficient clearance between the coil and an ear level speech processor so that the speech processor will not rest on the receiver/stimulator.

2 Place the Silicone implant Template on the skin so that the anteroinferior edge is at least I0 mm behind the edge of the pinna and above the canthomeatal line. Angle the template 30 to 45 degrees posteno- superiorly, to lie on a flat portion of the skull, Mark its position on the scafp.

3, Mark the incision with a marking pen. At leart 15 mm must be allowed between the implant and the incision.

The incision must be large enough to accommodate the implant The flap may be inferiorly- or anteriorly-based, but must allow the surgeon to secure the implant to the bone.

4, Hark the centre of the proposed well for the implant bed with a drop of methylene blue on the bone. To do this, insert an 18-gauga needle through the hole in the template and through the skin.

5, Prior to incision, the incision fine may be infiltrated with I :100 000 or

1:200 000 adrenaline/epinephrine unless contraindicated.

2. Incision

1. Make the incision down to the avascular plane of the periosteum and temporalis fascia, and form a flap (a monopolar cutting current may be used), Stabilize the flap using retraction as necessary.

2 Use the Implant Template to check the posrtion of the implant I0

Claims

1. A gauging tool for surgery procedures to be performed on a recipient, including a gauge member shaped and sized to over arch the head of the recipient extending from at least one side of the recipient to the other side of the recipient about the mid-sagittal plane of the recipient; two body part locating pieces adapted for placement on the body of the recipient substantially symmetrical about the mid-sagittal plane of the recipient having rotatable attachment to the gauge member such that in use the gauge member can rotate about the head of the recipient and wherein the gauge member is useable to gauge the location of surgery on the head of the recipient substantially equidistant from the body part of the recipient associated with the body part locating pieces.

2. A tool according to claim 1 wherein the two body part locating pieces are adapted for placement in the external ear canal of the recipient.

3. A tool according to claim 1 wherein the gauge member is substantially "U" shaped.

4. A tool according to claim 1 wherein the gauge member is elongate and provides a flat surface substantially parallel to the surface of the head of the recipient.

5. A tool according to claim 1 wherein the gauge member is markable to indicate a position on the gauge member that represents a surgical position on one side of the recipient's head used to gauge a corresponding position on the substantially laterally opposite side of the recipient's head.

6. A tool according to claim 1 wherein the gauge member includes indicia which are usable to gauge a corresponding position on the substantially laterally opposite side of the recipient's head.

7. A tool according to claim 1 wherein the gauge member is made of plastic wherein the stiffness of the plastic allows rninirnal flexing during use.

8. A tool according to claim 1 wherein the gauge member includes spaced indicia along a portion of its surface.

9. A tool according to claim 1 wherein the gauge member includes spaced lines along a portion of its surface.

10. A tool according to claim 1 wherein the surgical location is intended for or is a cochlear implant system component.

11. A method of using a gauge tool for surgery procedures to be performed on a recipient, including the step of: gauging the position of a location on the head of the recipient using a gauge member shaped to over arch the head of the recipient extending from at least one side of the recipient to the other side of the recipient about the mid-sagittal plane of the recipient which has been placed on the body of the recipient using two body part locating pieces adapted for placement on the body of the recipient substantially symmetrically about the mid-sagittal plane of the recipient having rotatable attachment to the gauge member such that in use the gauge member can rotate about the head of the recipient and gauging takes place on each side of the mid-sagittal plane based on the position gauged on the opposite side of the head of the recipient.

12. A method of using a gauge tool for surgery procedures to be performed on a recipient, including the steps of: gauging the position of a location on the head of the recipient using a gauge member shaped to over arch the head of the recipient extending from at least one side of the recipient to the other side of the recipient about the mid-sagittal plane of the recipient which has been placed on the body of the recipient using two body part locating pieces adapted for placement on the body of the recipient substantially symmetrically about the mid-sagittal plane of the recipient having rotatable attachment to the gauge member such that in use the gauge member can rotate about the head of the recipient and reversing the location of the two body part locating pieces with respect to the respective body parts so as to gauge the location of surgery on the head of the recipient substantially equidistant from the body part of the recipient associated with the body part locating pieces.