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research-article2014
AORXXX10.1177/0003489414534013Annals of Otology, Rhinology & LaryngologyBeltrame et al
Article
Consensus Statement on Round Window Vibroplasty
Annals of Otology, Rhinology & Laryngology 2014, Vol. 123(10) 734–740 © The Author(s) 2014 Reprints and permissions: sagepub.com/journalsPermissions.nav DOI: 10.1177/0003489414534013 aor.sagepub.com
Achille M. Beltrame, MD1, Ingo Todt, MD2, Georg Sprinzl, MD3, Milan Profant, MD4, and Burkhard Schwab, MD5
Abstract Objective: This study aimed to review current knowledge regarding implantation of the Vibrant Soundbridge floating mass transducer (FMT) at the round window (round window vibroplasty) as well as to form a consensus on steps for a reliable, stable surgical procedure. Data Sources: Review of the literature and experimental observations by the authors. Conclusion: Round window (RW) vibroplasty has been established as a reliable procedure that produces good and stable results for patients with conductive or mixed hearing loss. The experience gained over the past few years of the authors’ more than 200 implantations has led to consensus on several key points: (1) a wide and bloodless access to the middle ear with facial nerve monitoring, (2) the careful and correct identification and exposure of the round window membrane, (3) a good setup for efficient energy transition of the FMT, namely, perpendicular placement of the FMT with no contact to bone and the placement of cartilage behind the FMT to create a preloaded “spring” function, and (4) 4 points of FMT fixation: a rim of the round window bony overhang left intact both anterior and posterior to the FMT, conductor link stabilization, and cartilage behind the FMT. In addition, the FMT should be covered with soft tissue. Keywords Vibrant Soundbridge, round window, vibroplasty, floating mass transducer, conductive hearing loss, mixed hearing loss
Background The Vibrant Soundbridge (VSB; Vibrant MED-EL, Innsbruck, Austria) active middle ear implant has been used since 1996 to treat sensorineural hearing loss. In 2007, the indications were expanded to include conductive and mixed hearing losses. The active floating mass transducer (FMT) was placed in the round window niche in patients with conductive hearing loss or mixed hearing loss, bypassing the middle ear structures and directly stimulating the inner ear. This surgical technique, termed round window (RW) vibroplasty, was first presented in 2005 at the IFOS Meeting in Rome and published in 2006 by Colletti et al.1 Since then, various techniques and styles in regard to different steps of RW vibroplasty have been used, and the array of difficulties that accompany any new surgical technique have surfaced as well. Conditions that could indicate placement of the FMT on the RW include chronic otitis media in dry ears, sequelae of cholesteatoma, an open cavity with missing ossicles, congenital atresia, or other pathological findings that include a mobile stapes footplate. Patients with radical cavities have often had multiple middle ear surgeries with inadequate results and therefore have difficulties wearing hearing aids because of placement loss of the ear mold. RW vibroplasty
provides a viable option for social hearing restoration since it solves both of these problems: there is no need for an ear mold and the inner ear is directly stimulated. Several studies have been published that document the safety and efficacy of implantation with the VSB2-7 as well as RW vibroplasty in particular.1,2,8-16 The authors of this article participated in a scientific roundtable meeting held in Munich, Germany, on February 11, 2011, to discuss and form a consensus on issues regarding RW vibroplasty. Collectively, they have performed 237 RW vibroplasty implantations in adults and children (until July 2013). The learning curve experienced among different surgeons over the years has resulted in a reliable, stable 1
Centro Clinico, Rovereto, Trento, Italy Department of Otolaryngology at UKB, Hospital of the University of Berlin (Charité Medical School), Berlin, Germany 3 Landesklinikum St Poelten, St Poelten, Austria 4 Department of Otorhinolaryngology, Slovak Medical University, Bratislava, Slovak Republic 5 Department of Otorhinolaryngology, Hannover Medical University, Hannover, Germany 2
Corresponding Author: Dr Ingo Todt, Department of Otolaryngology at UKB, Charité Medical School, Warener Str. 7, D-12683 Berlin, Germany. Email: [email protected]
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of the RW niche (tegmen), the anterior lip (postis anterior), the posterior lip (postis posterior), and the mucosal fold (shown in Figure 1). There is a large amount of variability in the size and proximal location of these structures from patient to patient.
Preoperative Radiological Assessment
Figure 1. Cross-section through round window area with relevant structures.
surgical procedure. The objective of this publication is to suggest a standardized surgical procedure for RW vibroplasty, based on the authors’ wealth of experience.
Relevance The Vibrant Soundbridge is an active middle ear implant for people with sensorineural, conductive, and mixed hearing losses and consists of an external audio processor and the implanted vibrating ossicular prosthesis (VORP). The VORP is made up of a receiver/stimulator, a conductor link, and a transducer (the floating mass transducer, or FMT). The FMT is 2.3 mm long and 1.8 mm in diameter, with a weight of about 25 mg. The FMT has a single-point attachment clip, which gives the surgeon the flexibility to use the device based on the patient’s needs and anatomy. With conductive and mixed hearing losses, the FMT is attached either in the RW niche, completely bypassing the ossicular chain, or to remnants of the ossicular chain by using vibroplasty couplers. Vibroplasty couplers are modified middle ear prostheses that are attached to the FMT to facilitate coupling to various middle ear structures. The scientific roundtable discussed and formed consensus on the following 4 points: 1. 2. 3. 4.
Anatomical considerations Preoperative radiological assessment Surgical technique (with subsections) Experience with revision surgeries
Evidence/Roundtable Outcomes Anatomical Considerations The following anatomical structures serve as important landmarks for a surgeon attempting implantation of a VSB using RW vibroplasty: the promontory, the superior border
It is recommended that a computed tomography (CT) scan be performed prior to implantation. An axial plane view CT scan, imaging the mastoid portion of the facial nerve, should be included as well as a coronal view, which is especially necessary in patients with malformations. The cone beam CT is also being used as a new and more precise technique to image bony structures.17-23 When evaluating the CT scan, several points need to be considered. A CT is a valuable tool for viewing the bone surrounding the round window. In addition, the facial nerve, the RW niche itself, the jugular bulb, the tegmen (for determining the depth of the RW niche), and the distance between the facial nerve and RW niche should all be visualized. A high jugular bulb could make a perpendicular placement of the FMT on the RW membrane (RWM) difficult. In patients with malformations, there are additional anatomical structures that need to be evaluated. Although a CT scan can serve to inform the surgeon about whether or not the RW vibroplasty technique can be used, the final decision about where to place the FMT must always be made intraoperatively. The authors also recommend performing 1 last magnetic resonance imaging (MRI) scan prior to surgery to rule out any non-ear-related medical issues. This is important because MRI scans are contraindicated for the Vibrant Soundbridge.
Surgical Technique The RW vibroplasty surgical technique aims at providing good coupling to ensure efficient energy transfer of the FMT to the inner ear, as well as stability over time. Depending on the individual patient’s conditions, a facial recess or a transmeatal approach can be performed to gain access to the middle ear. In ears that have had previous operations, a radical cavity or a subtotal petrosectomy may also be used. It is important to ensure a wide and bloodless access to the middle ear. In ears with pathological disorders, the first point of orientation would be the facial nerve, followed by the stapes footplate. Drilling in the RW area. A piece of fascia or perichondrium should be prepared so that if the RW membrane is accidentally punctured, it can be immediately reconstructed. Before beginning to drill in the RW area, a clean, bloodless surgical field should be guaranteed. A 0.8- to 1.5-mm diamond burr
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Figure 2. Floating mass transducer sizer.
(or skeeter) should be used on as low a speed as possible to drill away bone in the RW area as well as to remove granulation. To expose the membrane, drilling should be initiated at the bony overhang of the RW, as this is where the RWM is most likely to be found. Enough bone should be removed so that the RWM can be successfully identified. At the same time, enough bone should be left both anteriorly and posteriorly to allow a stable placement for the FMT. Once the RWM is identified, care must be taken not to open it accidentally. Particular attention should also be given to the possible existence of a false RW membrane (mucosal fold). To maximize the chances of locating the actual RWM, several measures can be taken. The membrane should be visually checked against 3 factors: (1) If the membrane appears light in color and is confined to the RW niche, it is most likely the real RWM. (2) If it is confined to the RW niche but appears dark in color, then the RWM might be thickened, in which case no removal is necessary. (3) If the membrane is not confined to the RW niche, then it is probably a false RWM. In this situation, performing an interplay between the RW and oval window (OW) may help to identify the true RWM. However, this will not work if the footplate is fixed or partially fixed; in addition, this technique carries the risk of harming the inner ear. If the inner ear is accidentally exposed, it is imperative to be careful not to suck out any perilymph. The previously prepared piece of fascia or perichondrium should then be immediately placed on the RWM to close it. In addition, systemic corticosteroids (8-16 mg of dexamethasone) should be administered to the patient. Enough bone should be removed in the hypotympanum, using a 1.4- to 1.8-mm diamond burr, for the axis of the FMT to be perpendicular to the RWM. The FMT sizer (a dummy of the FMT; see Figure 2) should have enough space that the FMT will be in contact with the RWM without touching any bone. Because a perpendicular placement of the FMT is difficult in patients with a high jugular bulb, an alternate approach is recommended in such patients. Fixation of the conductor link. The conductor link should be fixed close to the surrounding structures like the middle fossa dura and sigmoid sinus in the posterior tympanotomy.
This is done with fibrin glue or bone pate before placement of the FMT at the RWM, with the cable left slack close to the FMT. In a transcanal approach as well as with radical cavities, a groove should be drilled inferiorly. This will relieve stress on the conductor link, create more stability, and avoid future contact with the skin of the ear canal or the cavity. The coronal view of the CT scan can be used to make sure there is enough bone in this area to drill a groove. This groove should be 0.5 to 1 mm wide and, if possible, 2 mm deep. It should be drilled at an angle of approximately 45º so that the cable from the conductor link will also be covered by intact bone. After the conductor link is placed in the groove, bone pate is used as a cover. In a transcanal approach, the rest of the conductor link should be positioned in a partially drilled-out mastoidectomy. In a radical cavity, a wider groove should be drilled so that the rest of the cable can also be placed into a groove. Usage of material between the RW and FMT. Experience has shown that it is advantageous to use a thin layer of no more than 0.1 to 0.2 mm of cushioning material between the FMT and the RWM. Different types of material including fascia, perichondrium, and artificial fascia (eg, Tutopatch, which is irradiated bovine pericardium; Brown, Tutogen medical, Neunkirchen, Germany) were employed for this purpose, with the consensus being that perichondrium or artificial fascia has provided the best results over time. Perichondrium from the tragus or concha is denser and smoother than temporalis fascia. Artificial fascia has a welldefined thickness. However, it is expensive, and as it is made from bovine tissue, it cannot be used in some countries. To get the right size for placement on the RWM, a biopsy punch of 2 mm in diameter can be used. Positioning the FMT. The FMT of the Vibrant Soundbridge comes with a clip, which is normally used to attach it to the long process of the incus. In RW vibroplasty, this clip first needs to be cut off with scissors or a scalpel since it is unnecessary for this application. The FMT is then advanced into the middle ear using a needle or nonmagnetic instruments and placed against the RWM with the side where the clip was cut off facing away from the RWM. The FMT’s conductor link should be manually bent just enough so that the FMT is in the right position to be placed on the RWM. As previously mentioned, it is very important that enough bone be left both anteriorly and posteriorly while drilling, so that a bony rim surrounds the RW membrane and provides a stable placement for the FMT. If at all feasible, the FMT should slightly protrude into the RW opening, as this will help to keep the FMT stably in place in the RW niche. After the FMT is in place, the piece of perichondrium or artificial fascia should be eased underneath the FMT against the RWM. At this point, some surgeons choose to gently perform an interplay between the OW and RW to determine
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Figure 3. Cross-section through round window area with floating mass transducer in place.
where to best place the FMT, although this is possible only if the stapes footplate is mobile. Once the FMT is positioned, a small piece of tangentially cut cartilage should be placed behind the FMT to help create a preloaded “spring” function, driving the FMT against the RWM (see Figure 3). In addition, the FMT should be covered with soft tissue and cartilage placed over the FMT to prevent extrusion in case of the development of an atelectatic membrane. Fibrin glue may also be used over this layer. Bone dust should not be used close to the FMT, since it might lead to ossification. Stability over time is guaranteed by a 4-point fixation: the anterior and posterior rim of the RW, cartilage behind the FMT, and a fixed conductor link, as described above. In addition, the FMT should be covered with soft tissue. Techniques using the RW coupler. The vibroplasty-RW-coupler (see Figure 4) was introduced in 2010 to provide a better connection between the FMT and RWM in difficult cases. Since then, 2 of the authors have collected limited experience using this coupler. The technique is identical to that of RW vibroplasty without the coupler, with a few small exceptions. Drilling in the lip region can be slightly less extensive, whereas drilling in the hypotympanum should be increased to accommodate the legs of the RW coupler that hold the FMT. Connecting the FMT to the RW coupler is a challenging process that should be done before insertion into the middle ear. The coupler should first be placed on a wet cloth on the surgical table with its legs facing upward before placing the FMT into the coupler.
Experiences With Revision Surgeries Revision surgeries were carried out on patients who experienced poor coupling that led to insufficient gain and poor hearing results. The causes for the poor results included dislocation of the FMT and a conductor link that did not have
Figure 4. Round window coupler.
enough slack cable. It was noted that in 5 cases where autologous fascia was used as a material between the FMT and RW membrane, the fascia was not seen during the revision and appeared to have been resorbed. Conversely, no perichondrium or artificial fascia was noted to have been resorbed. Patients who had originally been supplied with autologous fascia were therefore given artificial fascia between the FMT and RW membrane during the revision surgery. Extrusion of the conductor link can be another cause for revision surgeries. However, with the recommended deep groove for the conductor link in place, this risk should be minimized. It is important to evaluate the bone conduction thresholds to make sure that patients have not moved out of the indication range for a Vibrant Soundbridge. If the implant is working, the revision can often be done under local anesthesia via the transcanal technique, which carries with it the advantage of not harming the conductor link. The benefit of using local anesthesia is that the patient is able to give feedback during the operation.
Considerations/Issues Adequate surgical training is of the utmost importance for successful RW vibroplasty. Pennings et al24 observed the presence of a significant learning curve in RW vibroplasty. In their temporal bone study, they noticed that this learning curve occurred over a substantial period of time, and therefore, they recommend that surgeons practice with temporal
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bone work before attempting the actual surgery. Our authors have also noticed this learning curve phenomenon.25 The removal of bone in the RW area is tricky, necessitating a skilled surgeon. To achieve good results with RW vibroplasty, it is important to identify the real RWM. This involves the precise removal of bone in the RW niche26,27 and hypotympanum as well as taking extreme care not to open the RWM. To have good energy transmission to the inner ear as well as an implantation that will be stable over a long period of time, the following points are important: (1) the FMT should be placed perpendicularly to the RWM, avoiding all contact with bone10,26,28; (2) the stapes footplate should be checked for mobility; (3) perichondrium or artificial fascia should be placed between the FMT and the RWM; and (4) cartilage should be placed behind the FMT. A soft tissue material is placed between the FMT and RWM for 2 reasons: (1) to minimize the risk of perforating the RW membrane and (2) to avoid the FMT coming into contact with bone. There also remains the question of whether or not the usage of soft tissue material may help to achieve better transmission of vibrations from the FMT. Holland et al29 compared the transfer functions using different materials (2-mm discs of human temporalis fascia [thin], fibro-fatty fascia [thick], Permacol [xenograft] and Tutoplast [allograft], as well as cartilage and soft silastic) between the RW and an active middle ear implant (AMEI) in temporal bones, concluding that artificial fascia was superior to the other materials, with temporalis fascia achieving the second-best results. Nakajima et al30 also concluded in their temporal bone study that efficient coupling of the FMT to the inner ear fluid (using fascia from neck muscle) is crucial for RW vibroplasty to have a good outcome. Arnold et al31 went further to state that since some patients have a very narrow RW niche or a high facial nerve that could prevent enough drilling to sufficiently expose the RWM, placing fascia on the RWM can improve sound transmission if the FMT otherwise does not fit in the optimal, perpendicular fashion. Although many authors have reported on the usage of soft tissue material in RW implantations—mainly as a cushion2,6,10,16,20,24,26,30,32-38—there has been some controversy regarding the effectiveness of this material in sound transfer. Rajan et al39 showed that using a soft tissue coupler between the FMT and RWM resulted in less efficient coupling than when putting the FMT in direct (full or partial) contact with the RW membrane. However, Pennings et al24 performed an extensive comparison of cushioning materials used in different combinations (between the FMT and RWM, covering the FMT, etc) in temporal bone studies, concluding that fascia used either between the FMT and the RWM or to cover the FMT resulted in better coupling than no fascia at all, although no significant additional benefit was seen when using the fascia in both places. Precisely for
this reason, they suggest using fascia both between the FMT and RWM and as a cover for the FMT in case the piece of fascia should become dislodged from one of the positions. Conversely, in a retrospective study of 21 patients followed over a 3-year period, Skarzynski et al40 asserted that there is no fascia necessary between the FMT and RW, as long as the RW niche has been properly drilled off and there is fascia placed over the FMT to hold it in place. The authors of this article reached the consensus that in their experience, the benefits of using soft tissue as a buffer and cushion between the FMT and RWM outweigh the open issues concerning sound transfer. There have been difficulties with fascia resorption reported,41 and the experiences gained from revision surgeries have led to the preferred usage of artificial fascia or perichondrium. In addition, if there is soft tissue in place between the RW and FMT, the danger of harming the inner ear during revision surgery is minimized. Stable fixation of the FMT is another crucial point for success with RW vibroplasty. For good, long-term results, it is very important to make sure that the FMT is sitting securely in the RW niche. To promote this, 4 points of fixation should be used. Some bone should be left when drilling the overhang, so that it can help anchor the FMT anteriorly and posteriorly. In addition, the conductor link should be well fixed. If it is appropriately stabilized, its stiff internal wire will help to hold the FMT in place.36 The groove described previously constitutes an adequate fixation technique for the transcanal approach.32,33,35 Such a groove is also recommended for radical cavities. The last point of fixation is the cartilage placed behind the FMT, which prevents the FMT from migrating out of the RW niche by holding it in the bony ring that consists of the postis anterior, postis posterior, and tegmen. It also pushes the FMT toward the RWM, acting as a slight “spring,” so that free movement of the FMT is guaranteed. In addition, the whole FMT is covered with fascia. If we consider what has been learned from revision surgeries, there seem to be 2 main ways that RW vibroplasty can fail: (1) dislocation of the FMT and (2) extrusion of the conductor link. With the surgical technique described in this article, these 2 modes of failure should be minimized. The RW-coupler has been used successfully in patients with subtotal petrosectomy42 and tympanosclerosis.43 The experiences gathered from revision surgeries on RW vibroplasty patients have provided invaluable contributions to the previously described learning curve. This has resulted in the authors’ consensus concerning standardizing important aspects of this procedure. Most notably, issues involving fascia or perichondrium resorption41 as well as FMT migration away from the RW39 have been documented and corrected. The risk for FMT migration seems to be higher in patients who have undergone multiple middle ear surgeries, which prompts some surgeons to treat such patients with
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Summary Round window vibroplasty has been established as a reliable procedure that produces good and stable results for patients with conductive or mixed hearing loss. The experience gained over the past few years of the authors’ 237 implantations has led to consensus on several key points and the attempt to standardize the procedure. This includes (1) a wide and bloodless access to the middle ear with facial nerve monitoring, (2) the careful and correct identification and exposure of the RWM, (3) a good setup for efficient energy transition of the FMT, namely, perpendicular FMT placement with no contact with bone and the use of cartilage behind the FMT, and (4) 4 points of FMT fixation: a rim of the round window bony overhang left intact both anterior and posterior to the FMT, conductor link stabilization, and cartilage behind the FMT to create a preloaded spring function. In addition, the FMT should be covered with soft tissue. Declaration of Conflicting Interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding The author(s) received no financial support for the research, authorship, and/or publication of this article.
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5 years of imaging experience. Radiol Med. 2012;117(3): 488-499. 23. Cerini R, Faccioli N, Barillari M, et al. Bionic ear imaging. Radiol Med. 2008;113(2):265-277. 24. Pennings RJ, Ho A, Brown J, van Wijhe RG, Bance M. Analysis of Vibrant Soundbridge placement against the round window membrane in a human cadaveric temporal bone model. Otol Neurotol. 2010;31(6):998-1003. 25. Todt I, Rademacher G, Wagner J, Mittmann P, Basta D, Ernst A. Radiological control of the floating mass transducer attached to the round window. ScientificWorldJournal. 2013;2013:902945. 26. Colletti V, Mandala M, Colletti L. Electrocochleography in round window Vibrant Soundbridge implantation. Otolaryngol Head Neck Surg. 2012;146(4):633-640. 27. Roland PS, Wright CG, Isaacson B. Cochlear implant electrode insertion: the round window revisited. Laryngoscope. 2007;117(8):1397-1402. 28. Shimizu Y, Puria S, Goode RL. The floating mass transducer on the round window versus attachment to an ossicular replacement prosthesis. Otol Neurotol. 2011;32(1):98-103. 29. Holland NJ, Koka K, Lupo JE, Jenkins HA, Tollin DJ. Optimization of round window drive with the MET-V transducer with different interposed collagen materials. Hear Res. 2010;263(1-2):239. 30. Nakajima HH, Dong W, Olson ES, Rosowski JJ, Ravicz ME, Merchant SN. Evaluation of round window stimulation using the floating mass transducer by intracochlear sound pressure measurements in human temporal bones. Otol Neurotol. 2010;31(3):506-511. 31. Arnold A, Stieger C, Candreia C, Pfiffner F, Kompis M. Factors improving the vibration transfer of the floating mass transducer at the round window. Otol Neurotol. 2010;31(1):122-128. 32. Bruschini L, Forli F, Giannarelli M, Bruschini P, Berrettini S. Exclusive transcanal surgical approach for Vibrant Soundbridge implantation: surgical and functional results. Otol Neurotol. 2009;30(7):950-955. 33. Colletti L, Carner M, Mandala M, Veronese S, Colletti V. The floating mass transducer for external auditory canal and middle ear malformations. Otol Neurotol. 2011;32(1): 108-115.
34. Colletti V, Carner M, Colletti L. TORP vs round window implant for hearing restoration of patients with extensive ossicular chain defect. Acta Otolaryngol. 2009;129(4):449-452. 35. Kiefer J, Arnold W, Staudenmaier R. Round window stimulation with an implantable hearing aid (Soundbridge) combined with autogenous reconstruction of the auricle— a new approach. ORL J Otorhinolaryngol Relat Spec. 2006;68(6):378-385. 36. Mlynski R, Mueller J, Hagen R. Surgical approaches to position the Vibrant Soundbridge in conductive and mixed hearing loss. Operative Techniques in Otolaryngology–Head and Neck Surgery. 2010;21(4):272-277. 37. Streitberger C, Perotti M, Beltrame MA, Giarbini N. Vibrant Soundbridge for hearing restoration after chronic ear surgery. Rev Laryngol Otol Rhinol (Bord). 2009;130(2):83-88. 38. Verhaegen VJ, Mulder JJ, Noten JF, Luijten BM, Cremers CW, Snik AF. Intraoperative auditory steady state response measurements during Vibrant Soundbridge middle ear implantation in patients with mixed hearing loss: preliminary results. Otol Neurotol. 2010;31(9):1365-1368. 39. Rajan GP, Lampacher P, Ambett R, et al. Impact of floating mass transducer coupling and positioning in round window vibroplasty. Otol Neurotol. 2011;32(2):271-277. 40. Skarzynski H, Olszewski L, Skarzynski PH, et al. Direct round window stimulation with the Med-El Vibrant Soundbridge: 5 years of experience using a technique without interposed fascia. Eur Arch Otorhinolaryngol. 2014;271(3):477-482. 41. Buckingham RA. Fascia and perichondrium atrophy in tympanoplasty and recurrent middle ear atelectasis. Ann Otol Rhinol Laryngol. 1992;101(9):755-758. 42. Verhaert N, Mojallal H, Schwab B. Indications and outcome of subtotal petrosectomy for active middle ear implants. Eur Arch Otorhinolaryngol. 2013;270(4):1243-1248. 43. Iwasaki S, Suzuki H, Moteki H, Miyagawa M, Takumi Y, Usami S. Experience with the Vibrant Soundbridge RW-Coupler for round window vibroplasty with tympanosclerosis. Acta Otolaryngol. 2012;132(6):676-682. 44. Linder T, Schlegel C, DeMin N, van der Westhuizen S. Active middle ear implants in patients undergoing subtotal petrosectomy: new application for the Vibrant Soundbridge device and its implication for lateral cranium base surgery. Otol Neurotol. 2009;30(1):41-47.
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research-article2014
AORXXX10.1177/0003489414534013Annals of Otology, Rhinology & LaryngologyBeltrame et al
Article
Consensus Statement on Round Window Vibroplasty
Annals of Otology, Rhinology & Laryngology 2014, Vol. 123(10) 734–740 © The Author(s) 2014 Reprints and permissions: sagepub.com/journalsPermissions.nav DOI: 10.1177/0003489414534013 aor.sagepub.com
Achille M. Beltrame, MD1, Ingo Todt, MD2, Georg Sprinzl, MD3, Milan Profant, MD4, and Burkhard Schwab, MD5
Abstract Objective: This study aimed to review current knowledge regarding implantation of the Vibrant Soundbridge floating mass transducer (FMT) at the round window (round window vibroplasty) as well as to form a consensus on steps for a reliable, stable surgical procedure. Data Sources: Review of the literature and experimental observations by the authors. Conclusion: Round window (RW) vibroplasty has been established as a reliable procedure that produces good and stable results for patients with conductive or mixed hearing loss. The experience gained over the past few years of the authors’ more than 200 implantations has led to consensus on several key points: (1) a wide and bloodless access to the middle ear with facial nerve monitoring, (2) the careful and correct identification and exposure of the round window membrane, (3) a good setup for efficient energy transition of the FMT, namely, perpendicular placement of the FMT with no contact to bone and the placement of cartilage behind the FMT to create a preloaded “spring” function, and (4) 4 points of FMT fixation: a rim of the round window bony overhang left intact both anterior and posterior to the FMT, conductor link stabilization, and cartilage behind the FMT. In addition, the FMT should be covered with soft tissue. Keywords Vibrant Soundbridge, round window, vibroplasty, floating mass transducer, conductive hearing loss, mixed hearing loss
Background The Vibrant Soundbridge (VSB; Vibrant MED-EL, Innsbruck, Austria) active middle ear implant has been used since 1996 to treat sensorineural hearing loss. In 2007, the indications were expanded to include conductive and mixed hearing losses. The active floating mass transducer (FMT) was placed in the round window niche in patients with conductive hearing loss or mixed hearing loss, bypassing the middle ear structures and directly stimulating the inner ear. This surgical technique, termed round window (RW) vibroplasty, was first presented in 2005 at the IFOS Meeting in Rome and published in 2006 by Colletti et al.1 Since then, various techniques and styles in regard to different steps of RW vibroplasty have been used, and the array of difficulties that accompany any new surgical technique have surfaced as well. Conditions that could indicate placement of the FMT on the RW include chronic otitis media in dry ears, sequelae of cholesteatoma, an open cavity with missing ossicles, congenital atresia, or other pathological findings that include a mobile stapes footplate. Patients with radical cavities have often had multiple middle ear surgeries with inadequate results and therefore have difficulties wearing hearing aids because of placement loss of the ear mold. RW vibroplasty
provides a viable option for social hearing restoration since it solves both of these problems: there is no need for an ear mold and the inner ear is directly stimulated. Several studies have been published that document the safety and efficacy of implantation with the VSB2-7 as well as RW vibroplasty in particular.1,2,8-16 The authors of this article participated in a scientific roundtable meeting held in Munich, Germany, on February 11, 2011, to discuss and form a consensus on issues regarding RW vibroplasty. Collectively, they have performed 237 RW vibroplasty implantations in adults and children (until July 2013). The learning curve experienced among different surgeons over the years has resulted in a reliable, stable 1
Centro Clinico, Rovereto, Trento, Italy Department of Otolaryngology at UKB, Hospital of the University of Berlin (Charité Medical School), Berlin, Germany 3 Landesklinikum St Poelten, St Poelten, Austria 4 Department of Otorhinolaryngology, Slovak Medical University, Bratislava, Slovak Republic 5 Department of Otorhinolaryngology, Hannover Medical University, Hannover, Germany 2
Corresponding Author: Dr Ingo Todt, Department of Otolaryngology at UKB, Charité Medical School, Warener Str. 7, D-12683 Berlin, Germany. Email: [email protected]
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of the RW niche (tegmen), the anterior lip (postis anterior), the posterior lip (postis posterior), and the mucosal fold (shown in Figure 1). There is a large amount of variability in the size and proximal location of these structures from patient to patient.
Preoperative Radiological Assessment
Figure 1. Cross-section through round window area with relevant structures.
surgical procedure. The objective of this publication is to suggest a standardized surgical procedure for RW vibroplasty, based on the authors’ wealth of experience.
Relevance The Vibrant Soundbridge is an active middle ear implant for people with sensorineural, conductive, and mixed hearing losses and consists of an external audio processor and the implanted vibrating ossicular prosthesis (VORP). The VORP is made up of a receiver/stimulator, a conductor link, and a transducer (the floating mass transducer, or FMT). The FMT is 2.3 mm long and 1.8 mm in diameter, with a weight of about 25 mg. The FMT has a single-point attachment clip, which gives the surgeon the flexibility to use the device based on the patient’s needs and anatomy. With conductive and mixed hearing losses, the FMT is attached either in the RW niche, completely bypassing the ossicular chain, or to remnants of the ossicular chain by using vibroplasty couplers. Vibroplasty couplers are modified middle ear prostheses that are attached to the FMT to facilitate coupling to various middle ear structures. The scientific roundtable discussed and formed consensus on the following 4 points: 1. 2. 3. 4.
Anatomical considerations Preoperative radiological assessment Surgical technique (with subsections) Experience with revision surgeries
Evidence/Roundtable Outcomes Anatomical Considerations The following anatomical structures serve as important landmarks for a surgeon attempting implantation of a VSB using RW vibroplasty: the promontory, the superior border
It is recommended that a computed tomography (CT) scan be performed prior to implantation. An axial plane view CT scan, imaging the mastoid portion of the facial nerve, should be included as well as a coronal view, which is especially necessary in patients with malformations. The cone beam CT is also being used as a new and more precise technique to image bony structures.17-23 When evaluating the CT scan, several points need to be considered. A CT is a valuable tool for viewing the bone surrounding the round window. In addition, the facial nerve, the RW niche itself, the jugular bulb, the tegmen (for determining the depth of the RW niche), and the distance between the facial nerve and RW niche should all be visualized. A high jugular bulb could make a perpendicular placement of the FMT on the RW membrane (RWM) difficult. In patients with malformations, there are additional anatomical structures that need to be evaluated. Although a CT scan can serve to inform the surgeon about whether or not the RW vibroplasty technique can be used, the final decision about where to place the FMT must always be made intraoperatively. The authors also recommend performing 1 last magnetic resonance imaging (MRI) scan prior to surgery to rule out any non-ear-related medical issues. This is important because MRI scans are contraindicated for the Vibrant Soundbridge.
Surgical Technique The RW vibroplasty surgical technique aims at providing good coupling to ensure efficient energy transfer of the FMT to the inner ear, as well as stability over time. Depending on the individual patient’s conditions, a facial recess or a transmeatal approach can be performed to gain access to the middle ear. In ears that have had previous operations, a radical cavity or a subtotal petrosectomy may also be used. It is important to ensure a wide and bloodless access to the middle ear. In ears with pathological disorders, the first point of orientation would be the facial nerve, followed by the stapes footplate. Drilling in the RW area. A piece of fascia or perichondrium should be prepared so that if the RW membrane is accidentally punctured, it can be immediately reconstructed. Before beginning to drill in the RW area, a clean, bloodless surgical field should be guaranteed. A 0.8- to 1.5-mm diamond burr
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Figure 2. Floating mass transducer sizer.
(or skeeter) should be used on as low a speed as possible to drill away bone in the RW area as well as to remove granulation. To expose the membrane, drilling should be initiated at the bony overhang of the RW, as this is where the RWM is most likely to be found. Enough bone should be removed so that the RWM can be successfully identified. At the same time, enough bone should be left both anteriorly and posteriorly to allow a stable placement for the FMT. Once the RWM is identified, care must be taken not to open it accidentally. Particular attention should also be given to the possible existence of a false RW membrane (mucosal fold). To maximize the chances of locating the actual RWM, several measures can be taken. The membrane should be visually checked against 3 factors: (1) If the membrane appears light in color and is confined to the RW niche, it is most likely the real RWM. (2) If it is confined to the RW niche but appears dark in color, then the RWM might be thickened, in which case no removal is necessary. (3) If the membrane is not confined to the RW niche, then it is probably a false RWM. In this situation, performing an interplay between the RW and oval window (OW) may help to identify the true RWM. However, this will not work if the footplate is fixed or partially fixed; in addition, this technique carries the risk of harming the inner ear. If the inner ear is accidentally exposed, it is imperative to be careful not to suck out any perilymph. The previously prepared piece of fascia or perichondrium should then be immediately placed on the RWM to close it. In addition, systemic corticosteroids (8-16 mg of dexamethasone) should be administered to the patient. Enough bone should be removed in the hypotympanum, using a 1.4- to 1.8-mm diamond burr, for the axis of the FMT to be perpendicular to the RWM. The FMT sizer (a dummy of the FMT; see Figure 2) should have enough space that the FMT will be in contact with the RWM without touching any bone. Because a perpendicular placement of the FMT is difficult in patients with a high jugular bulb, an alternate approach is recommended in such patients. Fixation of the conductor link. The conductor link should be fixed close to the surrounding structures like the middle fossa dura and sigmoid sinus in the posterior tympanotomy.
This is done with fibrin glue or bone pate before placement of the FMT at the RWM, with the cable left slack close to the FMT. In a transcanal approach as well as with radical cavities, a groove should be drilled inferiorly. This will relieve stress on the conductor link, create more stability, and avoid future contact with the skin of the ear canal or the cavity. The coronal view of the CT scan can be used to make sure there is enough bone in this area to drill a groove. This groove should be 0.5 to 1 mm wide and, if possible, 2 mm deep. It should be drilled at an angle of approximately 45º so that the cable from the conductor link will also be covered by intact bone. After the conductor link is placed in the groove, bone pate is used as a cover. In a transcanal approach, the rest of the conductor link should be positioned in a partially drilled-out mastoidectomy. In a radical cavity, a wider groove should be drilled so that the rest of the cable can also be placed into a groove. Usage of material between the RW and FMT. Experience has shown that it is advantageous to use a thin layer of no more than 0.1 to 0.2 mm of cushioning material between the FMT and the RWM. Different types of material including fascia, perichondrium, and artificial fascia (eg, Tutopatch, which is irradiated bovine pericardium; Brown, Tutogen medical, Neunkirchen, Germany) were employed for this purpose, with the consensus being that perichondrium or artificial fascia has provided the best results over time. Perichondrium from the tragus or concha is denser and smoother than temporalis fascia. Artificial fascia has a welldefined thickness. However, it is expensive, and as it is made from bovine tissue, it cannot be used in some countries. To get the right size for placement on the RWM, a biopsy punch of 2 mm in diameter can be used. Positioning the FMT. The FMT of the Vibrant Soundbridge comes with a clip, which is normally used to attach it to the long process of the incus. In RW vibroplasty, this clip first needs to be cut off with scissors or a scalpel since it is unnecessary for this application. The FMT is then advanced into the middle ear using a needle or nonmagnetic instruments and placed against the RWM with the side where the clip was cut off facing away from the RWM. The FMT’s conductor link should be manually bent just enough so that the FMT is in the right position to be placed on the RWM. As previously mentioned, it is very important that enough bone be left both anteriorly and posteriorly while drilling, so that a bony rim surrounds the RW membrane and provides a stable placement for the FMT. If at all feasible, the FMT should slightly protrude into the RW opening, as this will help to keep the FMT stably in place in the RW niche. After the FMT is in place, the piece of perichondrium or artificial fascia should be eased underneath the FMT against the RWM. At this point, some surgeons choose to gently perform an interplay between the OW and RW to determine
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Figure 3. Cross-section through round window area with floating mass transducer in place.
where to best place the FMT, although this is possible only if the stapes footplate is mobile. Once the FMT is positioned, a small piece of tangentially cut cartilage should be placed behind the FMT to help create a preloaded “spring” function, driving the FMT against the RWM (see Figure 3). In addition, the FMT should be covered with soft tissue and cartilage placed over the FMT to prevent extrusion in case of the development of an atelectatic membrane. Fibrin glue may also be used over this layer. Bone dust should not be used close to the FMT, since it might lead to ossification. Stability over time is guaranteed by a 4-point fixation: the anterior and posterior rim of the RW, cartilage behind the FMT, and a fixed conductor link, as described above. In addition, the FMT should be covered with soft tissue. Techniques using the RW coupler. The vibroplasty-RW-coupler (see Figure 4) was introduced in 2010 to provide a better connection between the FMT and RWM in difficult cases. Since then, 2 of the authors have collected limited experience using this coupler. The technique is identical to that of RW vibroplasty without the coupler, with a few small exceptions. Drilling in the lip region can be slightly less extensive, whereas drilling in the hypotympanum should be increased to accommodate the legs of the RW coupler that hold the FMT. Connecting the FMT to the RW coupler is a challenging process that should be done before insertion into the middle ear. The coupler should first be placed on a wet cloth on the surgical table with its legs facing upward before placing the FMT into the coupler.
Experiences With Revision Surgeries Revision surgeries were carried out on patients who experienced poor coupling that led to insufficient gain and poor hearing results. The causes for the poor results included dislocation of the FMT and a conductor link that did not have
Figure 4. Round window coupler.
enough slack cable. It was noted that in 5 cases where autologous fascia was used as a material between the FMT and RW membrane, the fascia was not seen during the revision and appeared to have been resorbed. Conversely, no perichondrium or artificial fascia was noted to have been resorbed. Patients who had originally been supplied with autologous fascia were therefore given artificial fascia between the FMT and RW membrane during the revision surgery. Extrusion of the conductor link can be another cause for revision surgeries. However, with the recommended deep groove for the conductor link in place, this risk should be minimized. It is important to evaluate the bone conduction thresholds to make sure that patients have not moved out of the indication range for a Vibrant Soundbridge. If the implant is working, the revision can often be done under local anesthesia via the transcanal technique, which carries with it the advantage of not harming the conductor link. The benefit of using local anesthesia is that the patient is able to give feedback during the operation.
Considerations/Issues Adequate surgical training is of the utmost importance for successful RW vibroplasty. Pennings et al24 observed the presence of a significant learning curve in RW vibroplasty. In their temporal bone study, they noticed that this learning curve occurred over a substantial period of time, and therefore, they recommend that surgeons practice with temporal
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bone work before attempting the actual surgery. Our authors have also noticed this learning curve phenomenon.25 The removal of bone in the RW area is tricky, necessitating a skilled surgeon. To achieve good results with RW vibroplasty, it is important to identify the real RWM. This involves the precise removal of bone in the RW niche26,27 and hypotympanum as well as taking extreme care not to open the RWM. To have good energy transmission to the inner ear as well as an implantation that will be stable over a long period of time, the following points are important: (1) the FMT should be placed perpendicularly to the RWM, avoiding all contact with bone10,26,28; (2) the stapes footplate should be checked for mobility; (3) perichondrium or artificial fascia should be placed between the FMT and the RWM; and (4) cartilage should be placed behind the FMT. A soft tissue material is placed between the FMT and RWM for 2 reasons: (1) to minimize the risk of perforating the RW membrane and (2) to avoid the FMT coming into contact with bone. There also remains the question of whether or not the usage of soft tissue material may help to achieve better transmission of vibrations from the FMT. Holland et al29 compared the transfer functions using different materials (2-mm discs of human temporalis fascia [thin], fibro-fatty fascia [thick], Permacol [xenograft] and Tutoplast [allograft], as well as cartilage and soft silastic) between the RW and an active middle ear implant (AMEI) in temporal bones, concluding that artificial fascia was superior to the other materials, with temporalis fascia achieving the second-best results. Nakajima et al30 also concluded in their temporal bone study that efficient coupling of the FMT to the inner ear fluid (using fascia from neck muscle) is crucial for RW vibroplasty to have a good outcome. Arnold et al31 went further to state that since some patients have a very narrow RW niche or a high facial nerve that could prevent enough drilling to sufficiently expose the RWM, placing fascia on the RWM can improve sound transmission if the FMT otherwise does not fit in the optimal, perpendicular fashion. Although many authors have reported on the usage of soft tissue material in RW implantations—mainly as a cushion2,6,10,16,20,24,26,30,32-38—there has been some controversy regarding the effectiveness of this material in sound transfer. Rajan et al39 showed that using a soft tissue coupler between the FMT and RWM resulted in less efficient coupling than when putting the FMT in direct (full or partial) contact with the RW membrane. However, Pennings et al24 performed an extensive comparison of cushioning materials used in different combinations (between the FMT and RWM, covering the FMT, etc) in temporal bone studies, concluding that fascia used either between the FMT and the RWM or to cover the FMT resulted in better coupling than no fascia at all, although no significant additional benefit was seen when using the fascia in both places. Precisely for
this reason, they suggest using fascia both between the FMT and RWM and as a cover for the FMT in case the piece of fascia should become dislodged from one of the positions. Conversely, in a retrospective study of 21 patients followed over a 3-year period, Skarzynski et al40 asserted that there is no fascia necessary between the FMT and RW, as long as the RW niche has been properly drilled off and there is fascia placed over the FMT to hold it in place. The authors of this article reached the consensus that in their experience, the benefits of using soft tissue as a buffer and cushion between the FMT and RWM outweigh the open issues concerning sound transfer. There have been difficulties with fascia resorption reported,41 and the experiences gained from revision surgeries have led to the preferred usage of artificial fascia or perichondrium. In addition, if there is soft tissue in place between the RW and FMT, the danger of harming the inner ear during revision surgery is minimized. Stable fixation of the FMT is another crucial point for success with RW vibroplasty. For good, long-term results, it is very important to make sure that the FMT is sitting securely in the RW niche. To promote this, 4 points of fixation should be used. Some bone should be left when drilling the overhang, so that it can help anchor the FMT anteriorly and posteriorly. In addition, the conductor link should be well fixed. If it is appropriately stabilized, its stiff internal wire will help to hold the FMT in place.36 The groove described previously constitutes an adequate fixation technique for the transcanal approach.32,33,35 Such a groove is also recommended for radical cavities. The last point of fixation is the cartilage placed behind the FMT, which prevents the FMT from migrating out of the RW niche by holding it in the bony ring that consists of the postis anterior, postis posterior, and tegmen. It also pushes the FMT toward the RWM, acting as a slight “spring,” so that free movement of the FMT is guaranteed. In addition, the whole FMT is covered with fascia. If we consider what has been learned from revision surgeries, there seem to be 2 main ways that RW vibroplasty can fail: (1) dislocation of the FMT and (2) extrusion of the conductor link. With the surgical technique described in this article, these 2 modes of failure should be minimized. The RW-coupler has been used successfully in patients with subtotal petrosectomy42 and tympanosclerosis.43 The experiences gathered from revision surgeries on RW vibroplasty patients have provided invaluable contributions to the previously described learning curve. This has resulted in the authors’ consensus concerning standardizing important aspects of this procedure. Most notably, issues involving fascia or perichondrium resorption41 as well as FMT migration away from the RW39 have been documented and corrected. The risk for FMT migration seems to be higher in patients who have undergone multiple middle ear surgeries, which prompts some surgeons to treat such patients with
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Summary Round window vibroplasty has been established as a reliable procedure that produces good and stable results for patients with conductive or mixed hearing loss. The experience gained over the past few years of the authors’ 237 implantations has led to consensus on several key points and the attempt to standardize the procedure. This includes (1) a wide and bloodless access to the middle ear with facial nerve monitoring, (2) the careful and correct identification and exposure of the RWM, (3) a good setup for efficient energy transition of the FMT, namely, perpendicular FMT placement with no contact with bone and the use of cartilage behind the FMT, and (4) 4 points of FMT fixation: a rim of the round window bony overhang left intact both anterior and posterior to the FMT, conductor link stabilization, and cartilage behind the FMT to create a preloaded spring function. In addition, the FMT should be covered with soft tissue. Declaration of Conflicting Interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding The author(s) received no financial support for the research, authorship, and/or publication of this article.
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