Institutional review board approval and patients’ written consent were obtained.

Description of the technique (video)Operation planning

In our department, the operation usually is performed under general anesthesia. In preparation for the surgery, a CT-scan with measurement of the bone thickness and implant site planning as well as BAHA-headband trial and audiometry tests are performed.

A template is used to outline the implant on the skin at the desired site. The incision is planned 10–15 mm away from the device. Ultracain local anaestethic with adrenalin is injected into the surgical site. Single shot antibiotics are given only perioperatively.

Retroauricular flap J-shaped incision inferior extended at the hair line

We adopted the retroauricular J-incision anterior to the implant position at the hair line. The first incision cuts through skin und underlying fibrous layers, leaving the temporalis muscle and the posterior auricular muscle intact. This layer is followed posteriorly as far as the posterior implant border.

Relevant surgical anatomy: anteriorly based muscle periosteal flap (Fig. 2)Fig. 2

Anteriorly based muscle periosteal flap

The next incision is far posterior, at the planned posterior implant border up to the scull bone, cutting through the muscular and periosteal layer. Two more incisions are cut: superiorly at the inferior border of the temporalis muscle, and inferiorly at the inferior border of the implant site. Further dissection with bone contact anteriorly is widely exposing the bone for implant placement. Thus, an anterior based muscular periosteal flap is created.

We propose this flap for two reasons. Firstly, it allows more anterior repositioning of the implant if necessary, and secondly, no sutures will be placed above the implant.

Implant placement (Fig. 3)Fig. 3

A flat part of the skull is identified for the placement of the actuator. With the anterior based flap described above, we are able to safely move the position of the implant a little bit anterior if necessary despite reducing the distance to the skin incision, not having to fear skin issues at a later point.

It is necessary to start drilling perpendicularly using the guide with the conical 3 mm guide drill with spacer at 2000 RPM. The initial conical drilling site is enlarged with the suited widening drill.

Using the guiding drill indicator, the implant is inserted at a perpendicular angle to the bone, applying torque forces of 40–50 Ncm for normal compact bone. To avoid bone heating and osteonecrosis at the implant site, constant and abundant irrigation is important.

Before applying the OSI300, the clearance indicator mounted on the BI300 is used to check the smooth, flat bony region. In patients with more edged skull surface and curved mastoid tips, we place the device more superiorly such, that the screw fixation site is 1–2 cm above the level of the external auditory canal. A less cosmetic bump with skin tension over the inferior implant edge can be prevented by this procedure that is also described by Deep et al. [7]. If the temporal line or temporoparietal sutures are prominent, polishing the bone with a diamond drill is helpful to ensure a flat surface and flush contour with the device in place. After the BI implant is positioned, the vibrating part OSI300 is fixed and thightened with a torque key at 25 Ncm. The actuator is flat, rigid and quite big (31.4 × 22 × 4.9 mm). If a bony bump cannot be avoided, a recess well like described by Arndt et al. [7] should be performed.

Closure (Fig. 4) and postoperative careFig. 4

A three layer suture with 3.0 Vicryl for the muscular and subcutaneos layer and Ethilon 4.0 for the skin layer is performed. A light-pressure head bandage is applied for 2 days. Stitches are removed 10 days after the operation and the external sound processor first fitting takes place 4 weeks after surgery (Fig. 5).

Fig. 5

Postoperative appearance and speech processor position