• Open Access

Vibroplasty in mixed and conductive hearing loss: Comparison of different coupling methods

Authors


  • c.a. and w.g. have received research grants from MED-EL.

  • The authors have no other funding, financial relationships, or conflicts of interest to disclose.

Abstract

Objectives/Hypothesis

To evaluate modified coupling techniques of the Vibrant Soundbridge system in patients with mixed and conductive hearing loss and to compare it with conventional vibroplasty.

Study Design

Retrospective study.

Methods

Two different groups were evaluated: 1) nine cases of conventional incus vibroplasty in comparison with 2) nine patients with modified coupling of the floating mass transducer. In the modified coupling approach, the vibrant floating mass transducer was attached to 1) the stapes/oval window, 2) the round window, or 3) the drilled promontory bone (promontory fenestration window). In three patients, an additional ossiculoplasty was performed. Preoperative and postoperative aided and unaided pure-tone and free-field audiometry and Freiburg monosyllabic word test were used to assess hearing outcome.

Results

Functional hearing gain obtained in patients with mixed and conductive hearing loss who underwent modified coupling was 39 dB. Patients with pure sensorineural hearing loss who received conventional incus coupling showed a functional hearing gain of 25 dB. Average functional gain was 41 dB in the oval window group, 45 dB in the round window group, and 30 dB in the promontory fenestration window group. Word recognition test revealed an average improvement of 51% and 21% in the modified and in the conventional approach, respectively.

Conclusions

Modified vibroplasty is a safe and effective treatment for patients with conductive and mixed hearing loss. Coupling the floating mass transducer to the promontory bone (promontory fenestration window) is a viable option in chronically disabled ears if oval and round window coupling is not possible.

Level of Evidence

4. Laryngoscope, 124:1436–1443, 2014

INTRODUCTION

The Vibrant Soundbridge (VSB) is an active middle ear implant that is currently used in patients with conductive, sensorineural, and mixed hearing loss. It is an effective treatment option in patients with malformed ears, ear canal stenosis, chronic ear disease, tympanosclerosis, or otosclerosis who do not tolerate conventional hearing aids or do not benefit from surgical interventions. Since 2009, the indication for VSB implantation was extended to children suffering from bilateral congenital mixed or conductive hearing loss.[1]

The first implantation in Austria with conventional incus coupling was performed in 1998 in our department.[2] Originally the floating mass transducer (FMT) was crimped to the long process of the incus.[3] Various alternative surgical coupling techniques have been developed in the past years:

Coupling of the FMT to the cochlea via round[4, 5] or oval window vibroplasty[6] showed promising results. A mismatch between the diameter of the FMT and that of the round window membrane may result in insufficient coupling efficacy. Now round window couplers offer good FMT–round window membrane contact, especially in cases of otosclerotic middle ears.[7]

The VSB can be attached to different parts of the stapes such as the stapes head or the footplate using a clip or oval window coupler.[8] Alternatively, the FMT can also be connected to a partial or a total ossicular replacement prosthesis to treat conductive and mixed hearing loss.[9, 10] Although the abovementioned techniques are feasible in most cases, malformed ears or tympanosclerosis can make VSB application difficult.

The aim of the present study is to present different surgical VSB–FMT coupling methods in chronically disabled middle ears. We present data on conventional, oval, and round vibroplasty with and without additional total ossicular replacement prosthesis (TORP)/partial ossicular replacement prosthesis (PORP) ossiculoplasty. Additionally, direct application of the FMT to the promontory bone (promontory fenestration window) was evaluated in cases where neither the round window nor the oval window was accessible for attachment of the FMT.

MATERIALS AND METHODS

Conventional Incus Vibroplasty

Nine patients with sensorineural hearing loss received traditional vibroplasty, where the clip of the FMT is classically fitted to the long process of the incus (Fig. 1). The age ranged between 40 and 72 years (mean = 60 years); 77% were men, and 33% were women. Mean sensorineural hearing loss was 60 dB (standard deviation [SD] = 11).

Figure 1.

Conventional incus vibroplasty. The floating mass transducer is fitted to the long process of the incus.

Modified Vibroplasty

Five patients with mixed hearing loss including four patients with congenital aural atresia received a VSB (MedEl, Innsbruck, Austria). Reasons for implantation were sensorineural, conductive, or mixed hearing loss, no adequate benefit from a conventional hearing aid, and recurrent infections of the external ear canal induced by hearing aids. High-resolution computed tomography was performed preoperatively in all patients. Modified coupling was performed when there was no option for conventional attachment of the FMT. The patients were between 3 and 73 years of age (mean = 45 years); 56% were men, and 44% were women.

Children included in the study presented with atresia of the external ear canal with middle ear anomalies. Patients 2 and 3 had congenital microtia. Patient 9 suffered from Franceschetti syndrome. None of these malformations were associated with a sensorineural hearing loss.

All procedures were in accordance with the Declaration of Helsinki of 1975. The Medical University of Vienna Ethics Committees approved the study (ethical commission number 522/2005).

Surgical Procedure

The experienced senior author (w.g.) performed all operations except one (patient 9 was operated on by w.-d.b.). Depending on the intraoperative findings, the surgeon decided which coupling technique was most suitable for the individual patient. A mastoidectomy and posterior tympanotomy was performed in patients where the posterior wall had been preserved. An implant bed was drilled into the occipitotemporal bone to fix the implant housing with bone-anchored sutures. Each patient's specific anatomic situation required an individual surgical procedure. The individual data of patients who received modified coupling, including age, surgical history, type of hearing loss, intraoperative status, and type of previous surgery, are listed in Table 1.

Table 1. Patient Characteristics: Individual Data for Patients Who Received Modified Coupling.
PatientSexAge, yrDiagnosis, Surgical HistoryIntraoperative FindingsSurgical Procedure
  1. EAC = external auditory canal; F = female; FMT = floating mass transducer; HA = hearing aid; M = male; OW = oval window; PORP = partial ossicular replacement prosthesis; RW = round window; TORP = total ossicular replacement prosthesis; VSB = Vibrant Soundbridge.

1F67Mixed hearing loss, tympanoplasty in alio loco (cholesteatoma)Fenestra probe negativeFMT clip fixation on stapes crura (+ fibrin glue), PORP on stapes head, Tutoplast
2M17Stapes malformation, atresia of the EAC with dysplasia of the middle ear, ear canal reconstruction, no sensorineural hearing lossStapes malformation, RW not visibleFMT clip fixation on stapes crura, Tutoplast
3M6Congenital atresia aurisMalformed incusFMT coupler on stapes head
4M73Mixed hearing loss, 2× tympanoplasty with radical cavity, conventional HA refusedErosion of incusFMT coupler on stapes head
5M58Mixed hearing loss, radical cavity, cholesteatoma, did not tolerate conventional HAIncus and malleus already removed, hypermobile stapesFMT clip fixation on stapes head
6M72Mixed hearing loss, 7× tympanoplasty, radical cavity, chronic discharge problems with conventional HAPartial ossification of RW, round window test negative, old TORP removedRW vibroplasty with Tutoplast and fibrin glue, additional TORP (7 mm) in OW; complication: after 6 months, cable break, then good hearing, could play instrument after 10 years
7F70Mixed hearing loss, 2× tympanoplasty (cholesteatoma)Radical cavity inflammation, granulation, facial nerve overhanging OW, no bony coveringRemoval of old cartilage and TORP, partial ossification (Skeeter), RW vibroplasty with Tutoplast and fibrin glue, additional TORP (7 mm) in OW; complication: severe candida infection 1 year after surgery with TORP extrusion, VSB function preserved
8F3Atresia of the EAC with dysplasia of the middle earRW covered by facial nervePromontory fenestration
9F37Franceschetti syndromeMissing EAC with dysplasia of the middle ear, no bony covering of facial nerve, RW and OW covered by facial nervePromontory fenestration

Stapes

Depending on the intraoperative status, different attachment techniques for the FMT were used. When the incus was missing and the stapes was present (n = 5), the clip was crimped on the stapes crura (in two cases) or on the stapes head (in one case). Alternatively a clip coupler for fixation to the stapes head was used in two cases (Fig. 2). In one of the patients with crimping to the stapes crura, an additional partial prosthesis (Titan-PORP) was fixed to the stapes head (Fig. 3).

Figure 2.

Clip coupler fixation on stapes head. (A) The floating mass transducer is connected to the clip coupler. (B) Finally, the clip coupler is crimped to the stapes head.

Figure 3.

Oval window vibroplasty with additional partial ossicular replacement prosthesis (PORP). (A) The clip coupler is crimped to the stapes crura. (B) Additionally, a partial prosthesis (Titan-PORP) was fixed to the stapes head.

Round Window

Round window vibroplasty was performed in two patients. The facial recess was enlarged inferiorly, and removing granulation identified the round window niche. Then the lip of the round window was drilled to expose the round window membrane. After positioning of the FMT in the round window, Neuro-Patch (B. Braun Melsungen, Melsungen, Germany) and fibrin glue were used to improve contact to the round window membrane. In some cases, small pieces of cartilage and Tutoplast (Tutogen Medical, Neunkirchen am Brand, Germany) with fibrin glue were used to optimize stabilization of the FMT. In two cases, an additional TORP was placed on the oval window.

Promontory Fenestration Window

In two patients, the FMT was coupled via a promontory fenestration to the membranous inner ear structures. Patient 8 showed a congenital atresia of the external ear canal with dysplasia of the middle ear where the round window niche was not accessible because it was covered by the facial nerve (Fig. 4A, B). Patient 9 suffered from Franceschetti syndrome and showed a missing external auditory canal with dysplasia of the middleear. The round and oval windows were covered by the facial nerve. The cochlear endosteum was exposed by gently drilling the promontorium (Fig. 4B) without opening the scala tympani. Reduced drilling speed was used to fenestrate the cochlea. The procedure was stopped when the membranous endosteum became visible under a thin bony layer, which was gently removed with a Rosen needle. The drilling procedure was performed with a Skeeter drilling system (Medtronic, Jacksonville, FL).

Figure 4.

(A) Promontory bone. Patient 8 had an atresia of the external auditory canal with dysplasia of the middle ear. The round window was covered by the facial nerve. The black arrow shows the promontory bone where the cochlear endosteum was exposed to attach the floating mass transducer. (B) Patient 8 showed a congenital atresia of the external ear canal with dysplasia of the middle ear. The round window (dashed white arrow) is covered by the facial nerve (black arrow). The white arrow shows the promontory bone were the fenestration was performed.

A small piece of Neuro-Patch was put on the exposed membrane. After the titanium clip was removed, the FMT was placed on the Neuro-Patch–covered membrane and wrapped in it. Additionally, it was covered with cartilage and fibrin glue (Fig. 5).

Figure 5.

Schematic illustration of the promontory fenestration window. Drilling of the promontory bone was performed until the membranous endosteum became visible. After the titanium clip was removed, the floating mass transducer (FMT) was attached to the Neuro-Patch-covered membrane and additionally covered with cartilage and fibrin glue.

Audiologic Assessment

Pure-tone audiograms and speech perception measurements (Freiburg monosyllabic word test in quiet at 65 and 80 dB) were recorded prior to surgery.

Patients were followed up at 2, 3, and 6 month after the surgery. For the present study, the assessments after 6 months were used, which consisted of free-field pure-tone audiograms (0.25, 0.5, 1, 2, 3, and 4 kHz) and speech audiometry (Freiburg monosyllabic word test). Postoperative bone conduction was obtained in all patients. Functional hearing gain (FHG) was determined as the difference between unaided and aided free-field audiometry.

RESULTS

Preoperative and unaided postoperative air and bone conduction thresholds within a range of 5 dB are displayed in Figures 6 and 7. The mean change in bone conduction value was <5 dB in both coupling groups. In both groups, surgical intervention did not cause any significant difference in preoperative and postoperative air and bone conduction thresholds (P = .91; P = .93). The average FHG in all implanted patients (n = 18) was 33.1 (SD = ±14.3).

Figure 6.

Audiometric results in patients with atypical coupling. Preoperative (Preop) and postoperative (Postop) air conduction (AC) and bone conduction (BC) in patients with mixed hearing loss (n = 6) or congenital aural atresia (n = 3).

Figure 7.

Audiometric results in patients with conventional incus coupling. Preoperative (Preop) and postoperative (Postop) air conduction (AC) and bone conduction (BC) in patients (n = 9) with sensorineural hearing loss.

Conventional Incus Vibroplasty

Average unaided air conduction threshold was 70.5 dB (SD = ±11.7) and 45.2 dB (SD = ± 6.2) in the conventional coupling group (Fig. 8A, B). In the conventional incus coupling group, preoperative and postoperative values at 65 dB HL were 8.8% and 30.7%, which reflects a mean improvement of 20.7 dB (SD = ±13.7; P = .04).

Figure 8.

Unaided and Vibrant Soundbridge (VSB)-aided audiometry results. Mean preoperative unaided and postoperative VSB-aided thresholds of (A) patients with conductive and mixed hearing loss, where modified coupling was used, and (B) patients with sensorineural hearing loss, where conventional coupling to the long process of the incus was performed.

Modified Vibroplasty

Average unaided air conduction threshold in the modified coupling group was 74.6 dB (SD = ±9.0); VSB-aided postoperatively it was 33.8 dB (SD = ±10.9).

Average FHG showed a statistically significant difference of conventional incus coupling technique (25.4 dB; SD = ±13.9) compared to all modified approaches (40.8 dB; SD = ±10.6; P = .001, Fig. 9). Average functional gain was 40.1 dB (SD = ±12.8) in the oval window group, 45.4 dB (SD = ±11.2) in the round window group, and 35.0 dB (SD = ±14.1) in the promontory fenestration window group. The greatest FHG values were detected between 1,000 and 4,000 Hz (Figs. 9 and 10).

Figure 9.

Average functional hearing gain for different coupling modalities at 250 to 4,000 Hz. INCUS = conventional incus coupling; OW = oval window; PFW = promontory fenestration window; RW = round window; TORP = total ossicular replacement prosthesis.

Figure 10.

The average functional hearing gains (FHG) at frequencies between 250 and 4,000 Hz in patients with modified coupling. OW = oval window; PFW = promontory fenestration window; RW = round window; TORP = total ossicular replacement prosthesis.

Mean preoperative and postoperative percentage of speech understanding at 65 dB HL was 3.8% vs. 55.0% in the modified coupling approach resulting in an average improvement of 51.4 (±27.1 SD; P = .002). Values including results for 80 dB SPL are displayed in Figure 11. Analyses revealed a mean difference of speech understanding of 29.6% between conventional and modified coupling (P = .001) across different presentation levels (65 or 80 dB).

Figure 11.

Speach test results. Mean preoperative and postoperative percentage of speech understanding (Freiburg monosyllabic word test [FMWT]) at 65 and 80 dB in patients with modified and conventional incus coupling of the floating mass transducer. VSB = Vibrant Soundbridge.

DISCUSSION

This study provides insight into modified vibroplasty as an alternative treatment option in patients with chronically disabled middle ears where conventional vibroplasty is not an option. The VSB system was developed for conventional incus coupling. However, in patients with previous surgeries, fibrosis, granulation, and ossification of the middle ear, modified coupling approaches are required.

The presented surgical concepts show that coupling of the FMT to 1) different parts of the stapes, 2) the round window, or 3) the promontory bone results in good FHGs in cases of mixed and conductive hearing loss. Data show that coupling of the FMT to the promontory bone (promontory fenestration window vibroplasty) results in aided hearing thresholds between 12.5 and 50.0 dB. Moreover, our findings indicate that an additional oval window TORP in combination with round window vibroplasty could be a useful surgical option when the footplate is still mobile. Results are similar to the outcome in patients with sensorineural hearing loss where the FMT is conventionally attached at the long process of the incus.

The mean aided postoperative air conduction threshold was 33.8 dB, whereas the unaided threshold was 74.6 dB (Fig. 8A), indicating an average FHG of 40.8 dB. Figure 9 displays the FHG curves for the different coupling modalities. Results are in accordance with 14 studies,[11] where the FHG ranged between 30 and 58 dB in conductive and mixed hearing loss and between 23 and 30 dB in pure sensorineural hearing loss. The difference in FHG between conventional and modified coupling is mainly due to the closure of the air–bone gap. Therefore, VSB provides an increased benefit in FHG in cases of conductive hearing loss.

In patients of the modified coupling group, the FMT was attached at different structures of the middle ear, depending on the individual anatomical needs of the patients. Comparison between the three different modified coupling groups showed that round window, oval window, and promontory fenestration vibroplasty resulted in comparable FHGs (Figs. 9 and 10). Only at 4,000 Hz was promontory fenestration vibroplasty not as effective (P = .001). The results of the Freiburg monosyllabic word test revealed good improvement in both groups.

Complex anatomy of the middle ear as a consequence of multiple surgeries, congenital aural atresia, otosclerosis, tympanosclerosis, and chronic otitis media confronts the surgeon with a difficult decision regarding the restoration of hearing function in patients suffering from conductive and mixed hearing loss. Dependent on the individual intraoperative finding, different surgical strategies are applicable. If there is an intact tympanic membrane with a mobile stapes footplate, a functioning Eustachian tube, and a closed, air-filled, and mucosa-lined middle ear, either a PORP/TORP or a combination with the FMT is an eligible option to restore hearing function.[8, 12-15] In contrast to this, round window vibroplasty showed promising results[4, 16-19] in chronically disabled middle ears where conventional surgical concepts failed.

However, in rare pathologic conditions neither the round window nor the oval window is accessible for vibroplasty.[20] Fixation of the footplate due to extensive cholesteatoma or otosclerosis,[21] malformation,[22] or an unfavorable anatomic course of the facial nerve might require an alternative surgical solution.

Promontory Fenestration Vibroplasty

Our data demonstrate the feasibility of a third promontory window approach as an alternative in such cases. Good FHG was found, although efficacy decreases at higher frequencies compared to oval window and round window vibroplasty (Fig. 10). However, hearing gain in one patient treated with promontory fenestration window vibroplasty was sufficient to provide aided hearing threshold in the speech frequency range of approximately 20 to 35 dB, which is recommended to achieve good speech recognition performance.[9] In the patients supplied with promontory fenestration window vibroplasty, speech tests revealed an improvement of 18% at 65 dB and 53% at 80 dB.

Our clinical results confirm the findings of Lupo et al.[23] that mechanical stimulation by active middle ear implants through a third window into the scala tympani produces physiologic responses nearly identical to acoustic stimulation.

Round Window Vibroplasty and Oval Window TORP

In the present study, we combine the well-established reconstruction of the ossicular chain by a TORP or PORP with the VSB system. The combination of vibroplasty with coupling elements similar to a PORP or TORP has been described in various studies.[24] In this study, we combine round window vibroplasty with a TORP at the oval window as an attempt to improve natural unaided hearing. It might be considered as a kind of “worst case insurance.” In one patient who was implanted with a TORP as well as treated with round window vibroplasty, a wire breakage occurred after 6 months. Nevertheless, this patient reported a satisfying level of hearing and therefore declined a revision surgery.

VSB in Malformation of the Outer and Middle Ear

Reconstruction of the middle ear to restore hearing effectively in patients with atresia remains challenging. Frenzel et al.[25] show that the VSB provides good FHG by closing the air–bone gap. Our data confirm these results. Four patients with congenital atresia of the external ear canal with middle ear anomalies were included in the present study. FHG (Fig. 12) was between 20 and 60 dB, and word recognition improvement was 32% at 65 dB. Patient 2 had a stapes malformation, and the round window was not visible. Thus, the FMT was attached on the anterior crus of the stapes by clip fixation. Patient 3 showed a malformed incus, and the FMT coupler was attached on the stapes head. Patient 8 had an atresia of the auditory canal with dysplasia of the middle ear. As the round window was covered by the facial nerve (Fig. 4B), the promontory fenestration approach (Fig. 5) was chosen for placement of the FMT. FHG for this patient was between 10 and 55 dB. Patient 9 had Franceschetti syndrome, with a missing external auditory canal and dysplasia of the middle ear. The round and oval windows were covered by facial nerve. The coupling of the FMT to the promontory fenestration window resulted in an FHG between 5 and 45 dB.

Figure 12.

Functional hearing gains (FHGs) in patients with middle ear anomalies. Patients 8 and 9 received promontory fenestration window vibroplasty.

CONCLUSION

In this study, modified vibroplasty in previously operated and malformed ears shows good hearing outcomes in patients with conductive and mixed hearing loss. The present data confirm that the VSB provides a safe and effective option for atresia patients. Moreover, results indicate that promontory fenestration window vibroplasty may be considered as an alternative treatment option in cases of mixed or conductive hearing loss, where other surgical approaches are not possible.

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