HSC Section 8_April 2017

DOES COUPLING & POSITIONING IN VIBROPLASTY MATTER?

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. 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. CONCLUSION

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 Y 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

Acknowledgments: The authors thank Iride and Aldo Fabi, and Ana Mairata for their invaluable support, comments, and feedback.

REFERENCES

1. Snik AF, Mylanus EA, Cremers CW. The bone-anchored hearing aid: a solution for previously unresolved otologic problems. Otolaryngol Clin North Am 2001;34:365 Y 72. 2. Yellon RF. Atresiaplasty versus BAHA for congenital aural atresia. Laryngoscope 2011;121.

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