Otosclerosis frequently presents with conductive-hearing-loss (CHL) (1). Hearing-aids (HA) are considered the reference treatment in otosclerosis (2). If technical (i.e., auditory-feedback) or medical problems (i.e., chronic-external-otitis [COE] prevent HA, conventional-stapedotomy [SDT] may be considered instead (2)). SDT may allow closure of the air-bone gap (ABG) in pure CHL. However, also mixed-hearing-loss (MHL) occurs in otosclerosis (1). To address the sensorineural part of the MHL, additional HA after SDT are required (3). If otosclerosis progresses further, or technical or medical problems prevent HA, even this combined treatment may be insufficient for audiologic rehabilitation (4).
For these cases, active-middle-ear-implants (AMEI) have been developed (5–11). Amongst other available AMEIs, the Vibrant Soundbridge® (VSB, MedEl; Innsbruck, Austria) is considered valuable, since various couplers for the floating-mass-transducer (FMT) are available. It was introduced in the 1990s (6) and obtained the indication for sensorineural-hearing-loss (SNHL) in 2002 (8). Originally, the FMT was coupled to the long-incudial-process (LP) (8). Recently, alternative (10), coupling sites were proposed (5,7,9–11). Thus, the indication for VSB expanded to MHL (5). Available coupling sites include the round-window (RW) (5), the oval-window (OW) (7,11), and the short-incudial-process (SP) (9). The latter limits the extent of surgery from a wide posterior-tympanotomy to an extended-antrotomy (9).
Although VSB is considered safe and effective in patients with MHL caused by chronic-otitis-media (COM) (10,12,13), less data are available about its application in MHL caused by otosclerosis (4,14–16). Dumon first describe a VSB implantation together with SDT in one otosclerotic patient. A combined endaural and retroauricular approach was required. A LP-vibroplasty was performed followed by SDT. The FMT clip was fitted over the positioned stapes-piston. A complete closure of the ABG and additional gain via the VSB was achieved. The authors concluded that the gains of both procedures add up (4). Kontorinis performed a similar procedure in two patients with MHL caused by Osteogenesis imperfecta. The mean postoperative air-conductive (AC) pure-tone average (PTA) was 52.5 and 85.0 dB-HL, respectively. The authors referred to this operation as “power-stapes”-surgery (15). Venail implanted two otosclerotic patients using VSB after SDT. The mean postoperative AC-PTA was 27.5 and 38.8 dB-HL, respectively (16). Recently, Coordes et al. (14) VSB-implanted one otosclerotic patient, who underwent bilateral conventional-stapedotomy (SDT) 20 years before. Here, a RW-vibroplasty was performed instead. A postoperative gain of 25 dB-HL was observed.
“Power-stapes”-surgery performed as SDT in conjunction with simultaneous or consecutive LP- or RW-vibroplasty for otosclerotic patients were previously reported in several case reports (4,14–17). All authors concluded the intervention to be safe (4,14–17). However, no case series exploring the significance of “power-stapes”-surgery in otosclerotic patients are available (4,14–16). Moreover, certain limitations apply to the surgical technique previously proposed: all reports share a wide posterior-tympanotomy for FMT coupling. This bears the risk of injury to the Chorda-tympani, the facial-nerve, and the horizontal-semicircular-canal. Moreover, the FMT Clip has to be fitted over the positioned stapes-piston, additionally endangering the open inner-ear.
We propose a “modified-power-stapes” surgery (mPP) in otosclerotic patients, in which disease progressed or technical or medical problems prevent HA. We performed SP-vibroplasties in combination with simultaneous SDT in a larger series. Since the stapes is replaced by a piston and then mechanically driven by an AMEI, the surgery proposed here is referred to as mPP. Patients undergoing mPP were case-matched to patients undergoing SDT. We questioned whether mPP is equally safe and effective as SDT in a matched cohort. Clinical histories, surgical technique, and outcome performance tests are reported.
MATERIALS AND METHODS
This retrospective, matched case-control series exploring whether mPP is equally safe and effective as SDT was conducted at the Departments of Otorhinolaryngology, Medical University of Innsbruck and Klinikum Wels-Grieskirchen. Charts of adult otosclerotic patients with moderate to profound MHL (18) and limited satisfaction with previously worn HA which underwent mPP at either department, were retrospectively reviewed. Inclusion criteria are detailed in Table 1.
After chart review of the study-cohort was completed, a case-matched-cohort was generated from a larger sample of patients undergoing SDT at the Department of Otorhinolaryngology, Medical University of Innsbruck. Inclusion criteria for the case-matched-cohort were the same as for the study-cohort (Table 1) except for availability of postoperative aided pure-tone audiogram and speech-intelligibility test since these tests were not routinely performed in these patients.
Audiologic Performance Testing
Preoperative pure-tone audiograms were performed at the day before surgery with an Interacoustics AC40 audiometer (Electrotech Corporation, Chandigarh, India) in sound treated room. Thresholds were measured between 0.125 and 8 kHz, while the contralateral ear was masked with a small-band signal. For postoperative pure-tone audiograms, the latest audiogram performed was used. For postoperative aided pure-tone audiograms, the VSB was active and used. Preoperative word-recognition-scores (WSR) were only routinely measured in patients undergoing mPP at the day before surgery with an Interacoustics AC40 audiometer. WRS was measured using the German “Freiburger” speech-intelligibility test, using 50-word lists of monosyllabic nouns at supratreshold presentation levels between 60 and 110 dB SPL under free-field conditions without masking of the contralateral ear with small-band signal. Also postoperative WRS were only routinely measured in patients undergoing mPP with the VSB active and used.
Surgery was performed by three different surgeons with comparable surgical experience (19). After obtaining written informed consent, a facial-nerve monitoring (Neurosign 100, Neurosign surgical, UK) was installed and checked for functionality. A tympanomeatal-flap was created and the tympanic-membrane was mobilized, via a retroauricular-incision. The Chorda-tympani was spared. The posterior-superior bony auricular canal was drilled out using a 1.8 mm diamond-burr until full visualization of the LP, the incudostapedial-joint, the stapedial-superstructure, the RW, and the OW. The stapes was checked for fixation, confirming the diagnosis of otosclerosis (Fig. 1A). The incudostapedial-joint and the stapedial-tendon were severed, before the stapes-superstructure was removed.
A basic-mastoidectomy and extended-antrotomy were performed over the same retroauricular-incision, widely exposing the SP (Fig. 1B). After preparation of the periosteum pocket and the implant bed, the VSB's FMT (VORP 503, Med-El) was attached to the SP-coupler (Med-El), and implanted in the prepared bed. The SP-coupler was fixed to the SP and checked for sufficient freedom of movement (Fig. 1C). The coupling of the FMT was performed after the removal of the stapes-superstructure and before the stapes-piston implantation, giving maximum safety to the inner-ear.
The stapes-footplate was perforated with a Sharplan C40 carbon dioxide laser (Lumenis Ltd., Yokneam, Israel) resulting in a 0.6 mm perforation. A 0.6 mm Titanium stapes-piston (Heinz-Kurz GmbH, Dusslingen, Germany) was inserted into the stapes’-footplate perforation and cramped to the LP (Fig. 1D). The stapes-footplate and the piston's cramping site were covered with connective tissue. Since the stapes is replaced by a piston and then mechanically driven by and AMEI, the surgery proposed here is referred to as mPP instead of the previously frequently used term “power-stapes” (15), which should be reserved for AMEI-coupling to an intact, complete stapes.
For the SDT, the surgical technique was the similar as for the mPP previously described except for the SP-vibroplasty steps. In contrast to mPP, the SDT was performed over an endaural approach.
Calculation of Outcome Parameters
As recommended by the Committee on Hearing of the American Academy of Otolaryngology–Head and Neck Surgery (20), both, AC-PTA and BC-PTA were calculated by dividing the added thresholds at 0.5-, 1-, 2-, and 3-kHZ by four pre- and postoperatively. ABG-PTA was calculated by subtracting BC-PTA from AC-PTA pre- and postoperatively. WRS were calculated as percentage value at 80 dB SPL pre- and postoperative for patients undergoing mPP only.
Moreover, scattergrams relating pre- and postoperative AC-PTA and WRS for patients undergoing mPP were provided. Since WRS was not routinely measured pre- and postoperatively in patients undergoing SDT, data were not available. Therefore, improvement in WRS between mPP and SDT could not be compared and was not considered as outcome parameter.
A larger sample of patients undergoing SDT at the Department of Otorhinolaryngology, Medical University of Innsbruck, was compared to the study-cohort undergoing mPP via propensity-score-matching plug-in for SPSS24 (IBM, Armonk, NY). The case-matched-cohort was matched to the study-cohort for preoperative 1) AC-PTA, 2) bone-conductive (BC)-PTA, and 3) ABG-PTA. A maximum difference of ≥±10 dB-HL for each matching criterion was defined as acceptable tolerance margin for possible matches.
Clinical data of patients including sex, age, type of surgery, number of previous ear surgeries, site of surgery, and department at which surgery was performed was recorded (Table 2). Outcome parameters were mean postoperative 1) AC-PTA, 2) BC-PTA, 3) ABG-PTA and the corresponding pre- to postoperative changes within cohorts and between cohorts for patients undergoing either a) mPP or b) SDT. We questioned whether mPP is equally safe and effective as SDT in a case-matched-cohort. The change between mean pre- and postoperative BC-PTA served as safety outcome parameter. No change or a change towards a lower mean postoperative BC-PTA (negative values) was considered as positive outcome. The change between mean pre- and postoperative AC-PTA, the ABG-PTA and the percentage rate of complete ABG-closures achieved, served as effectiveness outcome parameter. A change towards a lower mean postoperative AC-PTA and/or a lower mean postoperative ABG-PTA (negative values) was considered as positive outcome. Additionally, 4) postoperative aided pure tone PTAs and 5) postoperative WRS only for a) mPP were provided.
Frequency data were presented in tabular form. For patients undergoing mPP only, pre- and postoperative AC-PTA in relation to WRS presented as scattergram as recommended was provided (20). For continuous data means and standard deviations (SD) as well as minimums and maximums were provided. Chi-square and Fisher's exact tests were used to test for statistical significance defined as p < 0.05. Additionally repeated measure analysis of variance analysis and Cohen effect size calculations were performed. All calculations were performed with SPSS24 and its corresponding plug-ins.
A total of 160 otosclerotic patients with moderate to profound MHL (18) were included in this retrospective study. Of these, 14 patients underwent mPP for limited satisfaction with previously worn HA. Reasons for limited satisfaction with previously worn HA include auditory-feedback and COE (eight and six patients, respectively). Of the 14 patients, which underwent mPP, five were operated at the Department of Otorhinolaryngology, Medical University of Innsbruck and nine at the Department of Otorhinolaryngology, Klinikum Wels-Grieskirchen. Of these, seven patients were women. The mean (±SD) age was 54 (±9) years, ranging from 40 to 69 years (Table 2).
The remaining 146 patients underwent SDT followed by HA fitting, if required. Of these, 14 patients were matched to the study-cohort undergoing mPP for preoperative AC-PTA, BC-PTA, and ABG-PTA. Of these, eight patients were women. The mean (±SD) age was 56 (±11) years, ranging from 37 to 78 years (Table 2). Detailed data of all 28 patients included in the statistical analysis is presented in Table 2.
For mPP patients, mean preoperative AC-PTA, BC-PTA, and ABG-PTA was 66.8, 38.0, and 28.8 dB-HL, respectively. A representative preoperative pure-tone audiogram and tympanometry of the right ear of a 55-year-old female patient undergoing mPP for moderate to profound MHL and limited satisfaction with previously worn HA for 5 years because of COE is depicted in Figure 2.
For SDT patients, mean AC-PTA, BC-PTA, and ABG-PTA was 67.1, 37.5, and 29.6 dB-HL, respectively. Neither of this preoperative audiologic findings significantly differed between the study-cohort and the case-matched-cohort (p = 0.939, p = 0.849, and p = 0.777, respectively). Additional SD, minimums and maximums are provided in Table 3.
For mPP patients only, WRS was available for 13 of 14 patients. Mean preoperative WRS at 80 dB SPL was 32.0%. Preoperative scattergrams for patients undergoing mPP as recommended (20) are depicted in Figure 3A.
For mPP patients, mean preoperative BC-PTA was 38.0 compared with 36.7 dB-HL postoperatively, which was not significant (p = 0.450; Table 3). A representative postoperative pure-tone audiogram and additional aided threshold using VSB® (MedEl, Innsbruck, Austria) of the right ear of the same 55-year-old female patient as presented in Figure 2 after mPP is depicted in Figure 4.
For SDT patients, mean preoperative BC-PTA was 37.1 compared with 36.9 dB-HL postoperatively, which was not significant (p = 0.540; Table 3). Postoperative change in mean BC-PTA for mPP patients was better with –1.3 compared with –0.2 dB HL for SDT, but this difference was not significant (p = 0.077). No significant difference in mean postoperative BC-PTA between mPP and SDT was observed (p = 0.450; Table 3)
For mPP patients, mean preoperative AC-PTA was 66.8 compared with 47.1 dB-HL postoperatively, which was significant (p < 0.001; Table 3). For SDT patients, mean preoperative AC-PTA was 66.3 compared with 46.5 dB-HL postoperatively, which was significant (p < 0.001; Table 3). Postoperative change in mean AC-PTA for mPP was –19.6 compared with –19.7 dB-HL for SDT, which was not significant (p = 0.991). No significant difference in mean postoperative AC-PTA between mPP and SDT was observed (p = 0.550; Table 3).
For mPP patients, mean preoperative ABG-PTA was 28.8 compared with 10.4 dB-HL postoperatively, which was significant (p < 0.001; Table 3). For SDT patients, mean preoperative ABG-PTA was 29.1 compared with 9.6 dB-HL, which was significant (p < 0.001; Table 3). Postoperative change in mean ABG-PTA for mPP was –18.3 compared with –19.5 dB-HL for SDT, which was not significant (p = 0.771). No significant difference in mean postoperative ABG-PTA between mPP and SDT was observed (p = 0.450; Table 3).
In mPP patients, complete closure of the ABG was achieved in 43% (6/14), compared with 30% (4/14) in SDT patients. Although the rate of postoperative complete closures for mPP was higher than for SDT, this difference was not significant (p = 0.695).
Postoperative aided PTA were available for mPP patients only, since aided pure-tone audiograms were not routinely measured in patients undergoing SDT in the two departments.
For mPP patients, the mean postoperative aided PTA was 35.5 compared with 47.1 dB-HL postoperatively, which was significant (p < 0.001). The additional improvement between mean postoperative aided PTA and mean postoperative AC-PTA for mPP patients was 11.6 dB-HL, which was significant (p < 0.001). Also the aided postoperative PTA for mPP patients was significantly better than the postoperative AC-PTA for patients SDT (35.5 versus 46.5 dB-HL; p < 0.001).
For mPP patients only, WRS was available for 14 of 14 patients. Mean preoperative WRS at 80 dB SPL was 85.0%. Postoperative scattergrams for patients undergoing mPP as recommended (20) are depicted in Figure 3B.
If otosclerosis progresses or technical or medical problems prevent HA, SDT alone may be insufficient for audiologic rehabilitation (4). AMEIs may be considered instead in otosclerotic patients with moderate to profound MHL and limited satisfaction with previously worn HA (5). Currently, the VSB (6) is preferably implanted at our departments. While initially LP-vibroplasties (8) were performed, surgical technique evolved and different coupling sites (5,7,9–11) and new indications (5,8) were proposed. Available data regarding mPP in otosclerotic patients is case report based (4,14–16). Most previous reports performed a LP-vibroplasty via a wide posterior-tympanotomy coupling the FMT clip over the positioned stapes-piston (4,15,16). This may endangers vital anatomical structures and the open inner ear. We propose mPP as SP-vibroplasty in combination with simultaneous SDT (Fig. 1). This mPP was performed in a larger series. We explored this modified intervention for safety and efficacy compared with matched SDT patients.
Charts of otosclerotic patients with moderate to profound MHL (18) and limited satisfaction with previously worn HA, which underwent mPP at either of two tertiary otologic referral centers between were retrospectively reviewed (Table 1). Complete data sets for mPP patients, consisting of clinical data (Table 2), pre- and postoperative pure-tone audiograms, pre- and postoperative speech-intelligibility test and postoperative aided pure-tone audiograms, were available for 13 patients (Table 3). One preoperative speech-intelligibility test was missing in one patient. They were matched for preoperative bone-conduction (BC-PTA), air-conduction (AC-PTA), and air-bone gaps (ABG-PTAs) with SDT patients. Finally, complete data sets for 28 patients were available, of which clinical data (Table 2) and preoperative audiologic findings (Table 3) did not significantly differ (all p < 0.777; Table 3), which suggests successful matching. Since the limited satisfaction with previously worn HA and not acoustical indications were the reason for undergoing mPP rather than SDT for all patients included, a possible selection bias may be negligible.
The change between mean pre- and postoperative BC-PTA served as safety outcome parameter. We assumed the intervention as safe, if no change or a change towards the better occurred. For both interventions the pre- and postoperative mean BC-PTA changed towards slightly better values with 38.0 to 36.7 and 37.1 to 36.9 dB-HL for mPP and SDT, respectively. Although, the numeric change in postoperative mean BC-PTA for mPP was slightly better with –1.3 compared with –0.2 dB-HL, this difference did not reach significance (p = 0.077). However, a trend might be suggested. Since no deterioration of postoperative mean BC-PTA was observed in mPP patients, the present data suggest that both interventions might be comparably safe (Table 3).
The change between mean pre- and postoperative AC-PTA and ABG-PTA served as safety outcome parameter. Changes towards lower values were considered as positive outcome. For both interventions a significant change between pre- and postoperative mean AC-PTA was observed from 66.8 to 47.1 and from 66.3 to 46.5 dB-HL for mPP and SDT, respectively (both p < 0.001; Table 3). The postoperative change in mean AC-PTA was almost identical with –19.6 for mPP and –19.7 dB-HL for SDT. Consequently, no significant difference was observed (p = 0.991).
Similar observations were made for the change between mean pre- and postoperative ABG-PTA. For both interventions a significant improvement in mean postoperative ABG-PTA was observed with 28.8 to 10.4 and 29.1 to 9.6 dB-HL for mPP and SDT, respectively (both p < 0.001). Although the change in mean postoperative ABG-PTA for mPP with –18.3 was slightly less than for SDT with –19.5 dB-HL, this difference was not significant (p = 0.771). In contrast, the rate of postoperatively achieved complete closures was 13% higher for mPP. Although this difference was not significant, various levels of expertise of the surgeons involved may be discussed as reason. However, since all surgeons had comparable experience (19) the sample size is considered a more likely cause. Postoperative aided PTA were available for patients mPP only, since aided pure-tone audiograms were not routinely measured in patients undergoing SDT in the two departments. Due to the retrospective study design, this data could also not be reproduced. The VSB SP-vibroplasty in addition to the simultaneously performed SDT resulted in an additional mean postoperative gain of 11.6 dB-HL resulting in a postoperative aided PTA of 35.5 dB-HL, which was significant (p < 0.001). This aided PTA for mPP patients almost reaches the 30 dB-HL margin, where additional hearing aids for adequate audiologic rehabilitation may be considered unnecessary (21) (Fig. 4). The reasons for patients to choose mPP instead of SDT were limited satisfaction with previously worn HA due to auditory-feedback and COE. Since HA after mPP were not required, this lack of disadvantages of HA may be considered as benefit for patients choosing mPP.
The postoperative results observed in the present cohort were comparable to previous case reports (14–17). Kontorinis reported a postoperative mean AC-PTA for two patients of 52.5 and 85.0 dB-HL. However, these patients were suffering from otosclerosis caused by osteogenesis imperfecta and a LP-vibroplasty was performed instead of the SP-vibroplasty described here (15). Venail reported postoperative mean AC-PTA of 27.5 and 38.8 dB-HL in two patients. However, the SDT was not performed simultaneously in this study (16). Coordes reported a mean functional gain of 25 dB-HL after a RW-vibroplasty. Again, the SDT was performed approximately 20 years before the RW-vibroplasty (14). Most recently, Powell et al. (17) performed a comparable SP-vibroplasty as described in the present study, in one otosclerotic patient, who was no longer able to wear HA because of COE. SP-vibroplasty was followed by a SDT 6 weeks after. A postoperative ABG-PTA reduction from 55 to 20 dB-HL was reported.
Several limitations need to be addressed. Generally, the level of evidence of retrospective studies is limited, especially if the sample size is small (22). We aimed at improving the level of evidence by collecting data from two tertiary otologic referral centers and by creating a matched case-controlled series. Despite these efforts, the present study design remains inferior to any prospective, controlled, or even randomized-controlled trial (22) and therefore studies with superior design should be performed in future.
Additionally, two major postoperative findings were missing for the present analysis due to its retrospective nature. Firstly, no aided postoperative PTA for patients undergoing SDT were available. Since, these patients were matched to the patients undergoing mPP mainly because of moderate to profound MHL, it appears likely that patients with comparable preoperative audiologic findings require additional HA after SDT for adequate rehabilitation. Secondly, both, the indication for SDT as well as the postoperative follow up at both our institution was based purely on pure-tone audiograms. No WRS were raised for these patients. Since retrospective chart reviews were performed, this data could not be reproduced. The change in WRS between the mPP and SDT could not be explored. Therefore it was excluded as outcome parameter. Thus, currently no conclusions can be drawn, whether mPP could be a possible standard procedure for patients with otosclerosis. Better-designed trials (22) should raise these two postoperative audiologic findings for patients undergoing SDT (20). To compensate for this lack of vital data, pre- and postoperative scattergrams for patients undergoing mPP were provided as recommended by the Committee on Hearing of the American Academy of Otolaryngology–Head and Neck Surgery (20) (Fig. 3). Since no WRS for patients undergoing SDT were available, no scattergrams could be provided.
mPP as combination of a short-incudial-process-vibroplasty with simultaneous conventional-stapedotomy limits surgery to an extended antrotomy, possibly sparing vital anatomical structures and coupling the FMT over the positioned stapes-piston (4,15,16). In otosclerotic patients with moderate to profound mixed-hearing-loss (18) or if technical or medical problems prevent hearing-aids, mPP may considered a treatment alternative to conventional-stapedotomy.