Modified sutureless recess/tunnel technique for fixation of the internal receiver-stimulator in cochlear implantation

Abstract

Background

Fixation of receiver-stimulator (RS) in cochlear implantation is an important step of surgery, while the technique used is still debatable.

Aim of study

The aim of our study is to evaluate the applicability of our modified recess/tunnel (R/T) fixation technique.

Materials and methods

De novo cases between august 2018 and December 2020 were included. A bony recess was drilled deep to the full thickness of RS. A tunnel was fashioned for the fantail and electrode lead with a groove to slide it without trauma. No tie-down sutures were used. The length between the RS magnet and tragus was measured during follow-up visits.

Results

Seventy-eight patients received the new R/T; 37 (47.4%) were females. Children were 50 (64.1%) with an average age of 4.3 ± 2 years, while adults were 28 (35.9%) with an average age of 36.4 ± 10 years. Right implants were 69 implants while left ones were only 9. The average total operative time was 86 ± 13 min, while the average R/T preparation time was 11 ± 4 min which represents 12.8% of the total operative time. No RS migration, hard. or soft failures were detected. One case had postoperative haematoma originating from the skin, while other minor complications were not related to fixation and were treated medically.

Conclusion

The R/T fixation technique provides good fixation to RS, fantail, and electrode lead protection and fixation. The disadvantages of wide exposure especially longer operative time can be avoided with this technique.

Background

Cochlear implants (CI) have gained expanded indications currently. The revolutionary advance in both the hard and software of the device made it a more reliable solution for severe and profound hearing loss. But still being a demanding solution both financially and technically, it is crucial to reduce the odds of failures and revision interventions to the minimum.

Among the supposedly preventable causes of failure is receiver-stimulator (RS) migration. It forms around 5% of postoperative complications of CI in the paediatric population [1]. RS migration is linked to electrode damage and wound complications and may subsequently lead to extrusion of the device [2].

There are many RS fixation techniques described in the literature. These techniques fall mainly into one of two categories: bony recess techniques (opted by most surgeons) and tight periosteal pocket techniques (opted by a minority but increasing). Each category has its advantages and disadvantages among the variations described in both [3]. Although there is no consensus in the literature about an ultimate technique, it is worth noting that most of the manufacturers go with the bony recess techniques as stated in their manuals [4,5,6].

Our CI team in the National Hearing and Speech Institute adopts the bony recess technique as being the sound surgical practice in such a valuable and demanding procedure. We perform many variations of this technique with and without tie-down sutures. In this study, the authors evaluate a new variation of the recess/tunnel (R/T) technique considering gaining from its advantages and reducing the disadvantages to the minimum.

Methods

The study was compliant with local laws and the principles of the Declaration of Helsinki and was approved by the local ethics committee. Subjects were selected from CI candidates who attended the National Hearing and Speech Institute in the period between August 2018 and December 2020. Only De novo cases were included; revision cases were excluded from this study. All cases were operated on and followed up by the authors.

The full routine preoperative preparations were done in all cases. On the day of surgery, the operated site was marked, and hair was shaved in the inpatient ward. To speed up performance the operation was divided into two sections: The surgical steps without a microscope (flap preparation, cortical mastoidectomy and preparation of R/T) which were done first, followed by microscopic steps (posterior tympanotomy, the opening of the cochlear duct and insertion the electrode array).

The procedure was started with a lazy S incision and raising anterior and posterior skin flaps. Then the periosteal flap was fashioned in a 90° tilted T-shape incision. Cortical mastoidectomy was done exposing the fossa incudis with the short process of incus within. The cavity edges are fashioned in undermined shape to harbour the lead without the need for further compression. The sinodural angle was deepened posterosuperiorly for 1–1.5 cm creating a pocket under the cortex of the parietotemporal plate and thinning it as anterior preparation of the fantail and electrode lead tunnel (Fig. 1A).

Fig. 1

A Pocket being created in the sinodural angle via coarse diamond burr (black outlined arrow). B Recess drilled (yellow star) to accommodate RS thickness, pocket formed in sinodural angle leaving 2.5–3 cm bridge (yellow outlined arrow)

A bony recess for the RS was drilled posterosuperior to the mastoid cavity starting by using the specific template for each device to mark the limits and leaving a 2–2.5-cm-wide ridge between the recess and the mastoid cavity. The recess was deepened to accommodate the whole thickness of the used RS (Fig. 1B) exposure of the dura was to be avoided as much as possible unless it was inevitable. Then using diamond and coarse diamond burrs with sizes 3.5 down to 2.3 or less, the anterior ridge was undermined anteroinferiorly to meet the preformed sinodural pocket until the two cavities coalesce forming a tunnel connecting the recess with the mastoid cavity covered with a thin cortical bone bridge (Fig. 2A).

Fig. 2

A A tunnel is formed between sinodural angle and the recess (black arrow). B An instrument introduced inro the tunnel showing the slope towards the mastoid and the notch for the fantail of the wire. C A groove being drilled in the superior buttress of the bony bridge (black arrow)

The tunnel was widened and polished, a notch was created in the edge of the bridge (recess side) to accommodate the fantail of the electrode lead as it emerges from the RS and a slope was created in the floor of the tunnel towards the anterior side to receive the lead with ease as it is rested in the mastoid cavity. The net distance between the sinodural angle and the edge of the recess is to be 1–1.5 cm as recommended by the manufacturing companies to keep the RS away from the external device behind the ear (Fig. 2B).

A groove was drilled in either the anterosuperior or the posteroinferior buttress of the cortical bridge over the tunnel according to the position and exposure of the dura and sigmoid sinus together with the orientation of fantail exit from the RS (Fig. 2C). This groove was used to slide the fantail and electrode lead smoothly into the tunnel. No tie-down sutures were used in any of the included cases. This modification allows the surgeon to avoid passing the electrode array through the tunnel preventing unnecessary trauma and contamination with remnant bone dust before its introduction into the cochlear duct.

The microscopic stage went routinely, starting with posterior tympanotomy, followed by the opening of the cochlear duct, then after sliding the RS in the prepared bed (Fig. 3A–C); insertion of the electrode array into the cochlear duct was done and sealed with a muscle plug.

Fig. 3

A HiRes ultra RS in place with superior groove. B Concerto RS with mid-oriented wire lead with inferior groove. C Concerto RS with side-oriented wire lead with superior groove. D Bone dust being used to obliterate the tunnel and groove (black outined arrow)

After securing the lead in the mastoid cavity, bone dust is used to obliterate the groove and fill the tunnel (Fig. 3D) as to regain the full coverage of the tunnel to the fantail adding extra protection against trauma. Gel foam was used to fill the mastoid cavity. The closure was done in layers ensuring full coverage of the RS and electrode lead with the periosteal flap (Fig. 4). The skin was closed via interrupted sutures.

Fig. 4

Periosteal flap fully covering the RS

The time of R/T preparation was recorded as a separate entity while recording the total operative time for each case.

Cases were charged the next day with a prescription form of intravenous then oral antibiotic, analgesics, and anti-inflammatory medications. CT imaging was done on the 2nd day of operation to confirm the position of the RS and the insertion of the electrode inside the cochlea.

Programming started 3–4 weeks postoperatively. Follow-up visits were scheduled on monthly basis for 6 months postoperatively and then every 3 months for 2–3 years. The migration of the device was assessed in each visit by the measurement between the RS magnet and the tragus.

The categorical data collected were represented as percentages and numerical ones were represented as mean ± SD. Statistical analysis was performed via SPSS version 24 (SPSS Inc., Chicago, IL, USA).

Results

Seventy-eight patients received the new R/T technique to fix the RS from August 2018 till December 2020; 37 (47.4%) were females. Children number was 50 (64.1%) with an average age of 4.3 ± 2 years, the youngest was 2.6 years old, while adults were 28 (35.9%) with an average age of 36.4 ± 10 years.

Sixty-nine included cases received right implants while only 9 cases received left implants. Two cases had anterior displaced sigmoid sinus which was repositioned posteriorly before preparing the RS recess and 2 cases had subtotal petrosectomy. The average total operative time was 86 ± 13 min, while the average R/T preparation time was 11 ± 4 min which represents 12.8% of the total operative time. The average R/T preparation time decreased through the period of study (Table 1).

Table 1 Distribution of numbers, gender, side, implant, and electrode used through the study period

The follow-up period ranged between 11 and 29 months. No RS migration was detected in any of the included cases, no hard or soft failures were detected also. No wound problems were encountered postoperatively except for one case of postauricular haematoma which was evacuated in the operating theatre the day after the surgery. It was completely subcutaneous and separated from the RS with a sound periosteal flap. Other minor complications were encountered not related to the RS fixation technique; 3 cases had transient partial facial palsy, 2 adults had persistent postoperative vertigo, 2 had chorda tympani injury. All these complications were treated with conservative measures.

Discussion

The technique of the CI procedure is “largely standardized” as stated by Lenarz T [7]. This is true except maybe for RS fixation. There is a variety in the fixation technique, with no scientific evidence favouring any of them until now.

To achieve a hidden seat and more permanent fixation for the RS a larger skin incision, a larger flap and sometimes exposure of dura is needed. But unfortunately, these steps can cause longer operative time, longer healing time and a higher risk of dural and intracranial complications [3]. These disadvantages are the cause for some surgeons to opt for a less invasive approach with a tight periosteal pocket and a shallower recess if any to be drilled [8, 9].

But although being less invasive, the risk of migration is assumably higher with the subperiosteal pocket technique. In one study, there was 20–25% objective RS migration in early and late follow-ups of patients who had tight periosteal pockets [10]. In another study, in a small number of adult patients, migration was detected radiologically after 1 year postoperatively in 50% of the subperiosteal group, while there was no migration in the bone well fixation group [11]. Both studies claimed that was no clinical problems that could be related to these findings.

In another study linking revision surgery with the type of fixation, the revision rate was triple in the subperiosteal tight pocket group (7.18%) versus the bony recess group (2.37%). The most common cause of revision was device failure in both groups but still, the rate of failure was triple in the tight periosteal pocket group (6.88%) versus the bone recess group (2.11%) [2].

In our study, 78 patients had the R/T technique with no migration recorded. The average total operative time was 86 ± 13 min which is comparable to our own operative time in a previous study (85 ± 24 min) [12]. The average R/T preparation time was 11 ± 4 min, not more than 12.8% of total operative time. As shown in Table 1, the time needed to prepare the R/T was decreasing by time due to the improvement of the learning curve. Our average total operative time was less than even the average time of minimal invasive periosteal pocket technique in some studies [13, 14]. Thus, we can state that the disadvantage of lengthy operation was avoided in our study.

In two patients we were challenged by bilateral anteriorly displaced sigmoid sinus. We approached the problem by rerouting the sinus posteriorly to open the access for posterior tympanotomy [15]. Exposure of the sinus served as a landmark for a safe R/T approach away from the displaced structure.

Tie-down sutures were abandoned in this study as the tunnel offered adequate restriction to RS thus avoiding blind drilling of suture holes which may jeopardize dural integrity. The aim of this study was to introduce the modified technique and to evaluate its safety and efficiency, further studies are planned in the future to compare this technique with other established ones.

Conclusion

The R/T fixation technique proved to be a good variant for RS, fantail and electrode lead protection and fixation. Respecting the learning curve can reduce the disadvantages of wide exposure especially longer operative time.