HSC Section 8_April 2017

efficiency when compared to round window coupling. It

was also hypothesized that regardless of the coupling

technique, patients would attain benefits in regards to

speech perception and quality of life outcomes.

Initial results in our cohort confirmed that ossicular

coupling provides better coupling efficiency than the round

window application. In particular, stapes coupling provides

the most efficient coupling and the least efficient coupling

was when utilizing round window vibroplasty with inter-

posed fascia between the FMT and round window. This

finding held true across the frequencies tested. Therefore,

based on our clinical in vivo data, coupling the FMT to the

ossicular chain or remnants of the chain wherever possible

is the preferred option for sensorineural, mixed, or con-

ductive hearing losses.

As well as providing improved coupling efficiency, an

ossicular attachment point is less surgically challenging.

No drilling of the RW niche is required when using the os-

sicular chain as an attachment point, thus reducing the risk of

iatrogenic sensorineural hearing loss. It also removes the

surgical complexity associated with the high degree of var-

iability evidenced in RW anatomy across individual patients.

From the patients’ perspective, coupling to the ossicular

chain allows immediate postoperative VSB activation.

The ossicular chain attachment also reduces the risk of

the FMT migration encountered in RW vibroplasty. None

of the subjects in this study with stapes or incus place-

ment experienced FMT migration. This is in line with

other published data with only one reported FMT dis-

placement in the classic incus application in a patient who

underwent magnetic resonance imaging and required revi-

sion surgery to re-attach the FMT to the incus (19). In con-

trast, revision surgery has been required because of FMT

displacement in RW vibroplasty. Marino et al. (20) noted

4 of 18 subjects, Skarzynski et al. (13) report 2 of 21 sub-

jects, and Baumgartner et al. (21) report 1 of 12 patients.

Patients who typically require an implantable hearing

solution such as the VSB have an underlying chronic

middle ear pathology which could potentially persist after

device implantation (22). With a more ‘‘secure’’ attachment

point such as the stapes or incus, the risk of a recurring

active middle ear condition affecting FMT placement is

perhaps reduced compared to a RW placement. It is im-

portant, however, to determine that there is a viable ossicular

attachment point and that the round window reflex is present

before using the stapes as the preferred attachment point.

These surgical prerequisites are also reported in other studies

(23

25).

The other question was whether in round window

vibroplasty the use or non-use of interposed tissue would

affect coupling efficiency. Our ongoing results indicate that

coupling efficiency was better without interposed tissue.

These results are in contrast to recommended surgical

protocols which promote the use of interposed fascia or

Tutoplast (7,9,10,12,21,26). However, many of the studies

supporting the use of interposed tissue are using results

from cadavers with results not able to be applied in ‘‘real

life’’ patients. The tissues in cadavers also demonstrate an

altered compliance and elasticity when compared to the

tissue behavior in vivo. Extensive drilling of the round

window niche to optimize FMT positioning is far less risky

in a cadaver where there is no risk of causing additional

hearing loss.

The possibility of scar tissue formation or atrophy in the

interposed fascia and a reduction in long-term coupling

efficiency has been proposed (7). It has also been proposed

that interposed fascia is resorbed after a period of time

thereby reducing coupling and that perichondrium is su-

perior for interposition as it is more robust and consistent

(27). However, it is uncertain how and to what extent the

perichondrium becomes resorbed over time.

The size mismatch between the FMT and RW and the

variation of the RW niche remain an ongoing challenge

rendering direct contact impossible in some cases. There-

fore, in these cases, a soft tissue coupler or commercially

available clip coupler is necessary to establish an RWM-

coupler interface. Though the coupling efficiency is not as

effective with a soft tissue coupler, the FMT properties and

programming of the external processor can compensate for

any coupling inefficiencies, especially in patients with a

conductive hearing loss. It is important, however, to con-

sider that patients with significant mixed hearing losses

require significant gain which can be only achieved through

optimal coupling.

All subjects in this study attained significant hearing

benefits post-VSB surgery regardless of the coupling

technique employed. These benefits encompassed im-

proved speech perception at normal conversational levels

and decreased tinnitus perception in those experiencing

tinnitus preoperatively.

The authors recognize that one of the limitations of this

study is that the small sample size with outliers having the

potential to skew results. Further investigations are being

undertaken to determine if results of a larger group of

patients are consistent with our initial findings.

CONCLUSION

We were able to demonstrate that vibroplasty modalities

using the ossicular chain elements such as the stapes or incus

provide best FMT coupling outcomes. In cases where no

ossicular chain is present, direct placement of the FMT on the

RWmembrane, whether it be complete or partial, is the next

best option. In cases where the RW anatomy negates direct

RW membrane placement, a mechanical interface such as a

soft tissue coupler or a clip coupler is crucial for FMT

functioning and subsequent good hearing outcomes.

Acknowledgments:

The authors thank Iride and Aldo Fabi, and

Ana Mairata for their invaluable support, comments, and feedback.

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