HSC Section 8_April 2017

ongoing debate among the experts. Different variables

such as the type of vibroplasty, the level of FMT-RW

contact, and the use of soft tissue or titanium couplers all

affect the efficiency and outcomes. It is unclear whether

better results are achieved by placing the FMT in direct

contact with the RW membrane or using an interposed

material such as fascia or Tutoplast. It is also unknown

whether stapes or incus vibroplasty is comparable to RW

vibroplasty with regard to coupling and outcomes espe-

cially in cases such as atresia or chronic ear disease where

frequently both vibroplasty options can be implemented.

This study aims to provide more insight into these aspects.

RW vibroplasty poses surgical challenges that are as-

sociated with the anatomy of the round window. There is

a clear mismatch between the size of the round window

membrane (RWM) with a mean diameter of 0.92 mm (6)

and the size of the FMT with a diameter of 1.8 mm and a

length of 2.3 mm. Furthermore, the shape of the RW

niche and the actual location of the RW membrane

present additional challenges. Frequently, the RW niche

is funnel-shaped with the RWmembrane sitting at the deep

narrow end away from the rim of the niche, thus making

direct placement impossible, even with the available cou-

plers. Pennings et al. (7) noted that the size of the RW niche

and the angle and exposure of the RW membrane were

highly variable in 10 cadaveric temporal bones. In addi-

tion, many patients who would benefit from the RW ap-

plication of the VSB have already undergone multiple

middle ear surgeries making placement of the FMT chal-

lenging due to fibrosis of the middle ear or fibrous oblit-

eration of the RW niche. Rajan et al. (8) demonstrated that

whereas the FMT needed to be in contact with the RW to

attain good coupling efficiency, the degree of contact re-

quired was not a factor in patient outcomes. Therefore,

even in cases of partial contact, good hearing outcomes

were attained for these subjects. This would potentially be

in contrast to patients with a mixed hearing loss who rely

on best possible coupling to maximize the amplifying gain

and minimize loss of sound transfer energy caused by in-

efficient FMT coupling.

The role of couplers or soft tissue interposition is

controversial. The literature is divided into cadaveric and

in vivo patient studies. The latter is more pertinent for

making clinical decisions given we are dealing with

‘‘living tissue’’ in which there are healing processes and

scar tissue formation.

There are human temporal bone studies that demon-

strate the improved coupling efficiency of the use of in-

terposed fascia between the FMT and the RWM (7,9

11),

and in addition, some clinicians recommend the addi-

tional use of a cartilage or soft tissue cap behind the FMT

to create some pretension on the FMT which improves the

coupling to the RW membrane (7,9,10).

Colletti et al. (12) recommend the use of interposed

fascia with ECoG (electrocochleography) measurements

guiding optimal placement of the FMT intraoperatively.

Conversely, Skarzynski et al. (13) report better coupling

with direct FMT to RW contact. Mandala et al. (14)

examined positioning of the FMT in 14 children with

congenital aural atresia and conductive or mixed hearing

loss, and their results found that fascia overlying the FMT

and cartilage packing gave the best ECoG recordings.

Rajan et al. (8) investigated the coupling efficiency in

seven patients with mixed HL and one with conductive

hearing loss. It was demonstrated that all patients had a

significant improvement on speech in quiet and in noise

scores postoperatively compared with preoperative out-

comes. It was also found that coupling efficiency was

higher with partial or complete direct contact of the FMT

with the RWM and reduced when soft tissue coupling

was used. This was one of the first studies that used ob-

jective coupling efficiency measurements to demonstrate

whether partial or full contact with the RW is essential

and whether use of interposed fascia gave better coupling

in the RW-FMT application.

This study expands the work of Rajan et al. (8) by

examining the coupling efficiency when the FMT has

been in contact with the RW either directly or with fascial

underlay or crimped to the stapes or the incus.

MATERIALS AND METHODS

Patients

Ethics approval was obtained for this prospective study from

the local ethics committee and was in accordance with the

Helsinki Declaration. Sixteen patients (nine female, seven male)

are involved to date. The average age at implantation was 56.3

years (range 19

78). Nine patients presented with a conductive

hearing loss, six had a mixed hearing loss, and one patient a

sensorineural hearing loss. All subjects could not benefit from

conventional hearing aids because of chronic otitis externa

(Subjects 9, 12), chronic suppurative otitis media (Subjects 1, 3,

4, 5, 6, 7, 8, 10, 11, 13, 14, 16), severe to profound mixed

hearing loss (Subject 2), and a non-healing external auditory

canal resulting from carcinoma removal (Subject 15). The co-

chlear (bone conduction hearing threshold) of all patients met

the manufacturer’s specifications and all patients had speech

perception results above 50% in the ear considered for im-

plantation. All patients, except Subject 15 who had an open

wound in the external auditory canal, trialed a behind-the-ear

hearing aid before consideration for the VSB. All surgeries were

conducted by an experienced middle ear and implantable device

surgeon. See Table 1 for patient demographics and the surgical

procedure employed.

The mean hearing loss in the implanted ear using the four-

frequency average of air conduction thresholds was 60.4 dB HL

(SD = 24.3 dB) and the mean bone conduction threshold was

25.9 dB HL (SD = 10.1 dB). In the non-implanted ear, the mean air

conduction four-frequency average was 40.7 dBHL (SD = 25.5 dB)

and the bone conduction average was 23.0 dB HL (SD = 10.1 dB).

Materials

All patients received the Vibrant Soundbridge (Vibrant Med-EL,

Innsbruck, Austria). Eight patients wore the 404 Audio processor

and eight patients wore the Amade´ processor. Patients with bone

conduction thresholds less than or equal to 25 dB in one frequency

were fitted with the Amade´ Lo external processor and patients

with worse bone conduction thresholds were fitted with the

Amade´ Hi processor.

R. MARINO ET AL.

Otology & Neurotology, Vol. 36, No. 7, 2015

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