Atraumatic surgical approach to the cochlea with a micromanipulator

ORIGINAL ARTICLE

Atraumatic surgical approach to the cochlea with a micromanipulator

MANUEL J. MANRIQUE1, JOAN SAVALL2, FRANCISCO JAVIER CERVERA-PAZ1,

JORGE REY1, CAROLINA DER1, MIKEL ECHEVERRIA2 & MIKEL ARES2

1Department of Otorhinolaryngology, Head & Neck Surgery, Clinica Universitaria, University of Navarra, Pamplona and2CEIT and Tecnun, University of Navarra, San Sebastian, Spain

AbstractConclusions. Our design and preliminary results show that the the micromanipulator could be a great help to the surgeon inthe atraumatic surgical approach to the lateral wall of the cochlea at the promontory. Objectives. Hearing preservation incochlear implant opens new frontiers in the treatment of sensorineural hearing loss. To preserve the membranous labyrinthintact, new surgical tools are needed, either for cochlear implantation or for other applications. The objectives of thisstudy were to design and test a micromanipulator coupled to a drilling tool for the atraumatic exposure of the spiralligament. The micromanipulator is designed to increase precision when drilling the otic capsule bone. Materials andmethods. A group from the University of Navarra worked on the device design � based on a compliant mechanism � and invitro test. The components and functioning of the micromanipulator are described. It was tested in 10 formalinizedtemporal bones after a mastoidectomy, a posterior tympanotomy, and a transcanal tympanotomy were performed. Themicromanipulator was placed over the cranial surface, and used to expose the endostium, anteriorly to the round windowniche. Results. A combined approach through the external auditory canal was feasible, together with a posteriortympanotomy to visually control the work and make complementary manoeuvres. Drilling was easy, and visual controlthrough the posterior tympanotomy was excellent. A high degree of drilling precision was achieved. A little disruption of themembranous labyrinth was found only in the first bone of the series.

Keywords: Inner ear, assisted surgery, surgical instruments, temporal bone, cochleostomy

Introduction

Surgery for the restoration of auditory function has

been basically focused on the treatment of conduc-

tive hearing loss caused by external and middle ear

lesions. It is only since the development of cochlear

implants (CIs) that some types of sensorineural

hearing loss � for example, severe to profound

sensorineural hearing loss originated in the cochlea

� have been treated by means of the surgical

placement of a CI. However, their use has generally

involved the loss of any remaining hearing function.

Cochlear surgery aiming to place implantable

devices or for any other purpose, without generating

relevant damage in its structures, is still an un-

reached objective. However, some clinical experi-

ences suggest the possibility of surgically

approaching the membranous labyrinth of the inter-

nal ear without producing permanent lesions.

A review of the literature indicates that the percen-

tage of lesions that cause a sensorineural auditory

loss after fenestration surgery of the horizontal

semicircular canal is B/1% [1,2], around 1% after

stapedectomy [3,4], 2% after surgery of the endo-

lymphatic sac [5] and B/5% after occlusion of the

posterior semicircular canal in cases of benign

paroxysmal vertigo [6]. On the other hand, some

experiences have been presented recently, showing

that it is possible to preserve hearing in the low-

frequency range after the insertion of a CI. This is

the case for short CI electrode arrays placed into the

scala tympani of the cochlear basal turn [7], or

complete insertions using long perimodiolar arrays

[8]. This sort of implantation has allowed so-called

hybrid stimulation, i.e. simultaneous electric and

acoustic stimulation in the same ear.

Correspondence: Dr F.J. Cervera-Paz, Departamento de Otorrinolaringologıa, Clınica Universitaria de Navarra, Avda Pıo XII no 36, 31008 Pamplona, Spain.

Tel: �/34 948255400. Fax: �/34 948296634. E-mail: [email protected]

Acta Oto-Laryngologica, 2007; 127: 122�131

(Received 1 March 2006; accepted 27 April 2006)

ISSN 0001-6489 print/ISSN 1651-2551 online # 2007 Taylor & Francis

DOI: 10.1080/00016480600827063

We presume that any treatment of sensorineural

hearing loss of cochlear origin requires an atraumatic

approach to such an organ. This would create a new

surgical concept, which could be named in a global

sense ‘cochlear surgery’. Surgical approach to the

cochlea without cochlear or vestibular function loss

for diagnostic procedures, administration of protec-

tive or regenerative drugs, cells or intra-/extra-

cochlear device implantation would be included in

this concept.

Attainment of this goal requires the use of all the

advances in surgical techniques, CI designs and tools

used for their implantation or for the delivery of such

substances. To date, those different atraumatic

approaches to the cochlea have been attempted

using conventional microsurgical tehcniques. In

this paper we describe a new approach to attain the

same goal: the use of a micromanipulator designed

to expose the cochlea without lesions, together with

the surgical technique to handle it. Atraumatic

cochlear surgery is based on an initial concept: to

expose its membranous cover without breaking its

continuity or altering its microvascularization, while

keeping its content intact. Taking into account the

size of the cochlea, its location and fragility, the

surgical approach in the aforementioned terms

requires the use of tools adapted to a micromanipu-

lator to increase the drilling precision. We estimate

that a purely manual approach to the cochlea has

such error margins that could induce damage in a

relevant percentage of cases. Also, a desirable

property of any technique is that most surgeons

can reproduce it. The use of micromanipulators can

help to fulfil this characteristic.

A multidisciplinary group of otolaryngologists and

engineers was created in the University of Navarra

for the design and testing of the micromanipulator

for cochlear surgery.

Materials and methods

Development and description of the micromanipulator

General description. To carry out the approach to the

labyrinth at the level of the lateral wall of the cochlea

the surgeon uses a long, thin-necked milling tool. We

chose a Skeeter otological microdrill system (Med-

tronic Inc., Minneapolis, USA). A diamond bur on

its tip was used to make the small aperture on the

promontory.

Therefore, the main goal to be satisfied by the

micromanipulator is the preparation of a small

groove of 5�/2�/2 mm or less. These dimensions

must be considered as a departure point that varies

according to the requirements of surgery for each

individual patient. To put this new procedure into

practice the concept of a passive-controlled joint

is introduced. The point is to let the surgeon

handle the microdrill directly with a special support

to increase their skill and control of the tool

(Figure 1). Given the importance of the tactile

feedback, the surgeon is encouraged to handle the

tool directly. The enhancement consists of an inter-

mediate element introduced to assist the surgeon

during the operation. Apart from touch, other

advantages are lower costs and simplicity. The latter

characteristic means that the surgeon needs less time

to carry out the operation than when using bulky and

sophisticated devices.

The essential part is the passive-controlled joint

and the most important aspect is its design, as it will

provide the necessary accuracy to perform the

operation. That key element is the compliant me-

chanism, which will be explained in the next section.

A general description of the micromanipulator will

be given before explanation of the compliant me-

chanism. Figure 1A depicts a representation of the

device placed on the temporal bone of a patient and

the drilling tool handled by a surgeon. For clarity’s

sake an orthogonal system of reference XYZ is

established, in which the Z axis is the auditory

tube line, X is the main direction of the groove and

Y is perpendicular to X and Z. We need to

distinguish two positions of the micromanipulator:

coupled (Figure 1A) and decoupled (Figure 1B).

The first one corresponds to the operating condition;

the decoupled position, on the other hand, separates

the micromanipulator into two parts. There is a fixed

assembly, attached to the bone, and a free assembly,

which supports the tool. This is useful when the

surgeon needs to change the diamond bur or just for

visual inspections inside the ear.

The system comprises three subassemblies (see

Figure 2). (1) Compliant mechanism. This provides

direct support to the surgical tool. It gives the finest

movements to the tool tip. (2) Positioning subsys-

tem. This supports the compliant mechanism and

provides regulation of Z and rotations and transla-

tions on planes X and Y. (3) Attachment subsystem.

This supports the positioning subsystem. It offers

the possibility of attaching the micromanipulator at

different points on the bone.

The complete system, with its three subassem-

blies, will be denominated micromanipulator as a

generic name. This utility model has been patented

(ES 2004022721). Initially, as a first approach, the

attachment subsystem is placed on the bone. The

positioning subsystem will provide a sufficient range

of regulation to create the groove. Finally, once the

positioning subsystem is locked, the compliant

mechanism will give the most accurate movements

of the drilling tool.

Micromanipulator for cochlear surgery 123

Compliant mechanism [9�11]. As noted above, an

articulation capable of restricting the desirable range

of movements and stability of the tool is wanted. To

put this into practice the idea of a compliant

mechanism has been applied. Force and movement

in compliant mechanisms are transmitted between

different elements according to their relative flex-

ibility. Figure 3A shows an example of how a

conventional four bar mechanism, with rigid bars

and pins, can be implemented as a compliant

mechanism using the flexibility of the material.

This kind of mechanism provides us with highly

accurate movements and there is no friction, back-

lash or wear. Besides, minimizing assembly opera-

tions can lower production costs. Some drawbacks of

these elements are the limited range of motion, the

minimal off-axis stiffness and poor fatigue life due

to high stress concentrations. Besides, the design

is often complex and might take some time to carry

it out.

The compliant mechanism controls and passively

limits the tool movement direction and range. Its

design must have the necessary degrees of freedom

to create the groove on the promontory. Therefore,

these movements have to be permitted in some

directions and limited in the rest. These degrees of

freedom of the tip tool are: translation on X and Z

and rotation on Y. Translation on Z is obligatory for

drilling the groove in depth, translation on X is

needed for drilling the groove longitudinally and

rotation on Y is needed to control the incidence

angle of the tool and to adapt it to the narrow ear

canal at any position. The compliant mechanism is

not flexible in any other direction. The mechanism is

topologically equivalent to a six bar rigid-body

mechanism in which the pin joints are flexure hinges.

This mechanism provides the three degrees of free-

dom of a rigid solid in the plane: two translations

and one rotation.

On the one hand, the performance of the mechan-

ism depends on the general geometry: the length of

the bars and the angles between them. These factors

will determine the range of movements to perform

the groove. On the other hand, the radius and the

thickness of the flexure hinges will determine the

stiffness of the mechanism in each direction. To

accomplish this kind of flexible mechanism, special

manufacturing techniques and a specific material are

needed. The compliant mechanism is made of

aluminium 7075, chosen because of its high elastic

limit/elastic modulus ratio, and it has been manu-

factured in a wire electro discharge machine

(WEDM), a highly accurate manufacturing technol-

ogy which can produce very thin pieces, required

when the material itself must transmit movement.

Figure 1. (A) Representation of the micromanipulator placed on the temporal bone of a patient, and the drill tool handled by a surgeon.

(B) Micromanipulator decoupled: microdrill�/compliant mechanism�/positioning subsystem�/attachment subsystem.

124 M.J. Manrique et al.

An analytic model has been developed for the

correct dimensioning of the compliant mechanism

and understanding of its behaviour. It is a quick way

to determine the displacements and the stresses

in the material. Besides, a finite element model

(FEM) analysis has been carried out, which assures

the precedent results. In this way, mechanisms

were manufactured with different geometric char-

acteristics to enable validation at the laboratory

(Figure 3B). This procedure permits manufacture

of several types of compliant mechanisms so that

they can be matched with the requirements of the

surgeon: for example, the level of stiffness needed to

perform one type of groove or the other (Figure 3C).

Positioning and attaching mechanisms. The compliant

mechanism is the key element of the design. How-

ever, additional systems are needed to permit an easy

performance positioning of the compliant mechan-

ism. As noted earlier, there is an attaching subsystem

and a positioning subsystem. They contribute to

initiate the drilling of the groove with the correct

orientations. Once the positioning subsystem is

locked, the micromanipulator is ready to perform

the operation and the sole movements come from

the compliant mechanism and the fine pitch screw

for vertical displacement (see Figure 4A).

The micromanipulator is fixed to the squama

temporalis at one point with a bolt (Figure 4). The

finger makes possible a good adaptation of the

system to the bone surface and provides a few holes

through which the bolt can be threaded to the bone.

Two long screws travel down the collar to lean on

the temporal bone (Figure 4). This guarantees more

stability and stiffness, as well as height regulation

through the threaded holes.

Figure 2. Three different stages of the degrees of freedom for the positioning of the compliant mechanism. (a) The compliant coupling in

the lower body provides two orientations. (b) Two displacements and one rotation are achieved by sliding the holder on the washer. (c) The

left-hand fine pitch nut provides precise vertical displacement.


The micromanipulator can be oriented in the X

and Y axes. For this purpose, a coupling mechanism

was manufactured; it is another kind of compliant

mechanism, so the said movements are permitted

and the displacements on X and Y and rotation on Z

are restricted (all movements possible are shown in

Figure 2). The orientation control is carried out with

set screws through three threaded holes and sup-

ported on the collar. The appropriate orientation is

achieved when the clamp guide axis is parallel to the

external auditory canal. The displacement on Z

must be very accurate. Regulation is implemented

with a fine pitch screw, so that a complete turn of the

screw equals 1 mm of vertical displacement of the

compliant mechanism.

Finally, it can be useful to translate the tool on

planes X and Y and to rotate on Z as well. For this,

the holder, where the compliant mechanism is

attached, is sandwiched between two washers and

locked with two bolts.

Surgical technique

Traditionally, in the field of cochlear implant sur-

gery, cochleostomy and electrode insertion are

performed through a posterior tympanotomy. The

use of the micromanipulator, described above, and

the exposure of the membranous cover of the spiral

ligament are not compatible with an approach

exclusively through the posterior tympanotomy.

There are two possible approaches. First, through

the external auditory canal together with a classical

exploratory tympanotomy to make the drilling work

with the manipulator and the visual control through

Figure 3. (A) Similitude of the compliant mechanism to a four bar compliant mechanism, and its corresponding rigid bodies scheme.

(B) Finite element model (FEM) analysis. (C) Several types of compliant mechanisms.


an endoscope adapted to the micromanipulator

(Figure 4). Second, a combined approach through

the external auditory canal together with a posterior

tympanotomy to visually control the work done and

make complementary manoeuvres (irrigation, ex-

traction of small fragments, insertion of electrodes,

deliverance of drugs, etc.) (Figure 4).

If the last approach was performed, the surgical

steps in the atraumatic surgery approach of the

cochlea for some of the mentioned applications

would be, roughly, the following:

. Incision in the retroauricular region and build

up of a cutaneous flap.

. Aperture of the external auditory canal from the

retroauricular region by means of a horizontal

incision in its soft portion, following the plane

of the mastoid cortical.

. Placement of a retractor.

. Development of a tympanomeatal flap and

aperture of the tympanic cavity. Given the

stiffness of the soft tissues in formalin-preserved

temporal bones, the lower half of the tympanic

membrane was cut off.

. Simple mastoidectomy preserving the walls of

the external auditory canal intact.

. Posterior tympanotomy.

. Placement of the attachment subsystem of the

micromanipulator over the surface of the cra-

nial cortical.

. Adaptation of the positioning subsystem and

compliant mechanism to the drilling system,

and drilling of the promontorial region exposing

the membranous labyrinth at the level of the

spiral ligament. The location of the spiral

ligament can be based on the knowledge of

the anatomical topography of the cochlea. In

the future it could be located with an advanced

navigation system.

. Extra- or intra-luminar manoeuvres carried out

in the cochlea.

. Protection of the promontorial region with a

free graft of temporal muscle fascia.

. Extraction of the micromanipulator and repla-

cement of the tympanomeatal flap.

. Suture by planes of the surgical wound.

Experimental procedure: evaluation of the

micromanipulator

The micromanipulator was tested in the ENT

Laboratory of the University of Navarra Medical

School in 10 formalin-preserved human temporal

bones. Before the promontorial drilling to expose the

spiral ligament, a mastoidectomy, a posterior tym-

panotomy, and a transcanal exploratory tympanot-

omy were performed, and the micromanipulator was

placed over the cranial surface. The Skeeter micro-

drill system (Medtronic Inc.) was mounted onto the

micromanipulator, using 0.7�1 mm round diamond

burs. Drilling work over the promontory was in-

tentionally performed with different sizes, to test

precision in preservation of the layrinth regardless of

the cochleostomy size.

After the drilling process, the spiral ligament in the

lateral wall of the cochlea was visually inspected with

a surgical microscope to evaluate its integrity. The

drilled area of the cochleostomy was measured.

For this we used a Wild Heerbrugg M37 dissecting

microscope with a digital camera mounted (Sony

XC-003P). Digital images of the partially decalcified

temporal bones were taken, and then processed

Figure 4. (A) Diagram showing the fixation of the attachment subsystem of the micromanipulator to the squama temporalis. (B) View of

the micromanipulator mounted on a temporal bone.


using a Leica Q500 MC image analyser system

(Leica, Cambridge, UK). This software makes it

possible to obtain several semi-automatic morpho-

metric measurements, by manual selection of the

target area (Figure 5). We obtained a variable

number of measurements in longitudinal and trans-

verse direction of each cochleostomy. These data

were statistically analysed with SPSS 9.0 statistical

package (Chicago, IL, USA) for Windows.

Results

The handling of the attachment subsystem did not

cause serious complications in any of the temporal

bones utilized. The finger suitably adapted to the

temporal squama in all of them and the whole system

was acceptably fixed with a screw applied to one of

the holes. The two long screws provided stability and

stillness, which proved very helpful. The central axis

of the attachment subsystem was parallel to the

external auditory canal in all the bones. In addition,

its position on the temporal bone after the mastoi-

dectomy did not change the vision of the tympanic

cavity through the external auditory canal or the

posterior tympanotomy. It was all placed in B/5 min.

The positioning and the attachment subsystems

were easily assembled. By manipulating the transla-

tion system on X and Y, the device was parallel to the

external auditory canal axis, thus allowing the bur of

the micro-drill to easily reach the promontorial

region. The ossicular chain and the rest of the

tympanic membrane were not damaged during the

positioning manoeuvres of the micro-drill. No pro-

blems arose regarding the walls of the external

auditory canal and the correct positioning of the

tip of the micro-drill in the temporal bones studied.

Figure 5. Image analysis process. The microscopic image is captured, at a known magnification, and digitized. The margins of

cochleostomy area are then manually marked on the digital image (top, white line). Different distances and area of the selected area are

automatically measured (bottom).


The drilling was performed accurately thanks to

the in-depth control provided by the fine pitch screw

(rotation in Z) and to the limited range of movement

on X and Y provided by the compliant mechanism.

Thus, the instrument assists and provides more

precision to the surgeon’s hand movements, preser-

ving tactile feedback. Everything contributed to the

execution of very accurate movements during the

drilling of the promontory. It was especially useful to

be able to control the depth of the drill by moving

the drill back and forth thanks to the fine pitch

screw.

The visual control through the posterior tympa-

notomy was even better than that obtained during

the drilling of the cochleostomy in conventional CI

surgery. It was better because the tip of the drill was

introduced through the external auditory canal and

not through the posterior tympanotomy, and there-

fore did not compete with the surgeon’s visual axis.

Also, the drilling area was cleaner because irrigation

and cleaning were easier and more efficient, which

also enhanced visual control. This is essential to

maintain the membranous labyrinth.

Only 1 of the 10 temporal bones studied suffered a

small fracture in the lateral wall of the cochlea. It was

broken in an area close to the membrane of the

round window, next to the crista fenestrae of

the cochlea (bone shown in Figure 5). Apparently,

the spiral ligament in this area is thinner and more

fragile. No continuity solutions were observed for

the other nine cases after carrying out a visual

inspection through the microscope (Figure 6).

The drilling was always performed in the promon-

torial region, encompassing the upper and lower

limits of the round window’s niche. The mean of all

cochleostomies was 1363.66 mm (SD: 436,39) in a

longitudinal direction and 782.59 mm (SD: 230,59)

in a transverse direction. The data collected for each

temporal bone are shown in Table I.

Discussion

Micromanipulators have been used in different

procedures related to the ear. Lescanne et al. [12]

described their use to guide a laser beam in stapes

surgery by a conventional lens-based micromanipu-

lator. Curthoys et al. [13] and Flock et al. [14] used

them in the experimental field to manipulate cellular

structures located in the utricular and saccular

maculae of the guinea pig and in the crista ampul-

laris of the semicircular canal in the frog. Pfister et al.

[15] applied this type of tool to introduce cochleo-

scopes, under micromanipulator control, through

the round window membrane. Massen et al. [16]

and Lenher et al. [17] also described the use of a

micromanipulator to couple the rod tip of a piezo-

electric malleus vibration audiometer through the

external auditory canal toward the umbo of the

tympanic membrane.

Nevertheless, we have not found reports on the

use of these devices to facilitate the precise work of a

drilling system during a surgical procedure on the

cochlea in the medical literature. In an initial

exposition, several possibilities for the manufacture

Figure 6. Drilling work performed in the promontorial region by the use of the micromanipulator, encompassing the upper and lower limits

of the round window’s niche. Note the integrity of the spiral ligament of the cochlea.


of a micromanipulator destined for this objective

were suggested. The use of a teleoperated work-

system [18], although it provides high accuracy and

force-feedback possibility, was discarded because it

incurred high costs, was too sophisticated and

required excessive learning/training time. On the

other hand, the use of existing micromanipulators

already on the market [19,20] would provide greater

precision but they would not facilitate tactile feed-

back during the drilling work, although this system is

quite slow and has little adaptability. The final

decision as regards a micromanipulator based on a

passive-controlled joint has several advantages: the

surgeon retains tactile feedback; the system is simple

and easy to handle; cost is relatively low; and, finally,

it increases the effectiveness of the surgeon.

The microscopic evaluation of the bones shows a

high degree of precision in the use of the micro-

manipulator coupled to the drilling system. We only

found a little disruption of the membranous labyr-

inth in the first bone of the series. We have used

formalin-preserved temporal bones for the initial

tests, although these tissues are stiffer than fresh

ones, and this may impact on the outcome. To assess

the validity of results we are going to use it in a

similar procedure on fresh temporal bones. Thus, in

order to become skilled in the use of the micro-

manipulator, and before using the system in surgery,

we recommend some training on the temporal bone.

The site of the disruption was close to the round

window area, the region of least thickness of the

spiral ligament. This observation, regardless of the

use of the micromanipulator, supports the proposi-

tion that the optimum area for the cochleostomy is at

least 1 mm anterior to the anterior-inferior lip of the

round window niche.

The drilling work was easy to perform, and visual

control through the posterior tympanotomy was

excellent, even better than that obtained when the

drill was introduced via the posterior tympanotomy.

The explanation for this advantageous fact is that the

drilling system does not compete with the visual axis

through the posterior tympanotomy. And secondly,

when introduced via the external auditory canal the

angle of attack formed by the drill with the promon-

tory is approximately 908. This last issue improved

the visual control of the tip of the drill through the

posterior tympanotomy even more.

The area we drilled was more ample than that

usually needed for a regular cochleostomy during a

CI procedure because our goal was not only to assess

the cochleostomy itself, but also other potential

applications of the method designed and tested.

This study reveals that the range of work achievable

with the micromanipulator is wide, and that the

approach through the external auditory canal allows

an extended approach to the promontory if required.

These aspects should be taken into account when

considering potential applications of the microma-

nipulator in the cochlea or vestibule. Among others,

this device may be used in the opening of the cochlea

to take samples for diagnosis, for drug delivery and

stem-cell work, or in other otological procedures

Table I. Data obtained from the microscopic analysis of the cochleostomies in the temporal bones.

Bone no. Direction N Min Max Total Mean SD

1 Long 22 12.766 2285.107 26974.472 1226.112 728.541

1 Trans 7 734.043 734.043 5138.301 734.043 0.000

2 Long 6 325.532 1174.468 4863.830 810.638 406.270

2 Trans 31 44.681 842.553 10353.188 333.974 165.297

3 Long 17 721.277 1940.426 25563.835 1503.755 391.969

3 Trans 28 357.447 1040.426 24874.476 888.374 196.046

4 Long 8 2297.873 2374.469 18817.026 2352.128 25.984

4 Trans 32 312.766 1014.894 27689.155 865.286 199.171

5 Long 29 210.638 2342.554 39836.174 1373.661 673.333

5 Trans 39 223.404 1295.745 46544.690 1193.454 233.860

6 Long 24 145.532 1927.660 28537.031 1189.043 562.131

6 Trans 1 827.9 827.9 827.9 827.9 0.000

7 Long 21 357.447 1621.277 25487.237 1213.678 462.862

7 Trans 11 255.319 1046.809 8693.619 790.329 235.268

8 Long 11 57.447 1321.277 9734.044 884.913 383.045

8 Trans 19 478.723 702.128 12057.449 634.603 63.628

9 Long 26 12.766 2789.362 36178.731 1391.490 1050.807

9 Trans 24 600.000 600.000 14400.000 600.000 0.000

10 Long 21 204.255 2993.618 35585.115 1694.529 1101.543

10 Trans 22 580.851 1021.277 21076.602 958.027 106.077

Direction, direction of the measurement; N, number of lines analysed in this direction plane; Min, minimal data in measurement (in mm);

Max, maximal data in measurement (in mm); Total, addition of all lines in each measurement (in mm); SD, standard deviation (in mm);

Long, longitudinal; Trans, transverse.


such as a platinotomy in stapes surgery or the

implantation of middle ear implants.

The use of the micromanipulator coupled to the

drilling system requires an approach to the lateral

wall of the cochlea through the external auditory

canal. However, along with the earlier mentioned

advantages, this approach may also have some

disadvantages. The anatomy of the external canal

may be unfavourable in such a way that it would not

be posible to reach the middle ear. This happens in

5.26% of patients [19]. Secondly, the technique

requires development of a tympanomeatal flap to

enter the tympanic cavity. This manoeuvre �although routine in otological procedures � may

account for potential complications, such as ear-

drum perforations, or ossicular chain lesions.

It is worth making a final comment on the time

required for device placement. With proper training

the time for the application of the micromanipulator

is around 10 min. In our opinion, the potential

benefits of its use are worth these minutes.

Conclusions

This article describes the successful design of a

micromanipulator device, based on a passive-con-

trolled joint, to be adapted to a commercially

existing drilling system. The device has been tested

in formalinized temporal bones, showing that it can

be of great help in the surgical approach to the lateral

wall of the cochlea at the promontory. The use of the

micromanipulator increases the chance to expose the

endostium while keeping the spiral ligament intact.

This issue is of importance when aiming to achieve

atraumatic surgery for hearing preservation, or other

future diagnostic or therapeutic developments.

Acknowledgements

The experimental element of this paper was sup-

ported by grants from the Fondo de Investigaciones

Sanitarias of Spain (FIS 98/1177) and funding from

Cochlear AG-Ltd.

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Atraumatic surgical approach to the cochlea with a micromanipulator

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