Auris atresia (AA) is a congenital pathology characterized by middle ear malformation together with outer ear aplasia or hypoplasia. AA has a different severity, and the severe form of the disorder does not indicate an absence or significant underdevelopment of an identifiable ear canal (complete atresia) and middle ear structures. AA is sometimes associated with a malformation in the ear called “microtia”.
Changes in the outer ear canal and middle ear structures are responsible for conductive hearing loss affecting patients. Hearing restoration procedures can recreate a normal outer and middle ear anatomy to support recovery of hearing function, or the surgeon can simply restore hearing capacity by bypassing defective structures with bone anchored hearing implants (BAHIs). Restoring normal anatomy is often associated with narrowing of the external ear canal due to bone regrowth.
The formulation of a therapeutic strategy can be supplemented using the Jahrsdoerfer classification to determine the severity of the malformation. This article contains information about the various bone fixation prostheses currently used (Baha, Ponto, Alpha2 by Sophono, Bonebridge) and the results that can be obtained with the use of these implants.
Bone Anchored Hearing Implant (BAHI)
Congenital aural atresia (CAA) is a congenital malformation of the ear that causes both aesthetic and functional impairments. Malformation shows different degrees of deterioration; CAA may be the only malformation in the body or may be associated with other malformations as observed in syndromic patients. CAA is a failure in ear development that occurs during the first weeks of gestation; the failure may be completed by affecting the outer and middle ear, or it may be partial, such as a stenotic outer canal with normal middle ear structures.
In all cases, hearing function is impaired despite having different hearing thresholds. Regardless of the severity of the hearing impairment, it shows a decrease in memory function and cognitive abilities of children with hearing loss, so restoration of hearing function should ultimately be considered the first goal pursued in the CAA. (Considering the adolescent age with the aesthetic reconstruction of the outer ear)
They proposed a CT grading system for CAA, which has been shown to correlate with postoperative hearing outcomes, as a supportive method in the decision-making process of CCA malformation; The author’s suggestion is that the high scoring malformation should be treated with external canal bone reconstruction and eventually ossiculoplasty, while in the case of lower scores, bone anchored hearing implants (BAHIs) are the most appropriate treatment.
Other more recent scoring systems have been proposed, such as the Lübeck score; this system is based on powerful analysis in high resolution CT scanning. The proposed method is researcher Jahrsdoerfer et al. It used a 16-point rating to address the best ear implant with the same effectiveness as.
Hearing restoration with bone stimulation was not immediately successful; In fact, in 1920 the first electronic implantable device was the preferred method, and bone stimulation prostheses were considered the last alternative. Moreover, after the Second World War, with the advent of the transistor, the electronic prosthesis became smaller and more manageable, similar to real hearing aids. Anyway, the system has been widely used in recent years, thanks to new discoveries that better explain physiological stimulation of the interior with bone stimulation and advanced technologies (which miniaturize the systems and make the system implantable. (Treatment of hearing impairments). It solved the old problems with external bone stimulation as the correct pressure and also reduced bone stimulation due to skin impedance.
In the light of numerous observations and experiments, it has been concluded that the bone conduit is a kind of natural sound conduction and that the sound properties are normal and quite similar to that made by air. BAHI explains the problems of traditional retro-auricular stimulation, such as poor performance due to insufficient contact between the vibrator and the skin, pain at the contact site, or aesthetically unacceptable decubitus and arch prostheses, temporal bone with an external transducer; The vibration of the transducer on the bone consequently causes stimulation of the inner ear cells by sound perception.
The connection between the pin and the transducer determines the type of BAHI: percutaneous or subcutaneous. Both implant methods require surgery. The difference between subcutaneous and percutaneous system is the way the titanium screw is placed according to the skin plan; in the first, the skin is opened surgically and the abutment is placed directly over the mastoid; The surgical opening is then closed by suturing the skin. Instead, the percutaneous system consists of a titanium implant placed by “piercing” the skin. All BAHI systems consist of three main components:
An internal titanium fixture surgically attached to the temporal bone behind the ear
An external abutment that connects to the implant during surgery
An external sound processor attached to the abutment
All systems currently on the market offer the following features: high amplification power, operating independently in the presence – absence of the ear canal and middle ear, direct bone conduction with clear sound can be tested before surgery, and all systems are quite similar. (in terms of comfort)
Temporal Bone Anatomy and BAHI
Surgeons should keep in mind the normal anatomy of the temporal bone, as it helps to remember anatomical landmarks when severe malformations occur in the patient that needs to be implanted. When CAA is associated with microtia, the main anatomical landmarks are the zygomatic process (image 7 sagittal plane view); In fact, this structure is generally well preserved in the case of craniofacial malformation. In the absence of the zygomatic process, the squamous suture should be identified as alternative signs.
Surgical Implant Method and Timing
The FDA recommends that the device be used in children not younger than 5 years old. The researchers say the ideal age to implant a BAHI is between 2 and 4 years, as the thickness of the retromastoid bone (2.5-3 mm) at this age allows for a completely safe surgery without risk of damaging the dura. In addition, with regard to the age of the implant, it should be taken into account that children must have sufficient dexterity to maintain the device and a good psychological disposition to follow the recommendations of parents and caregivers. Hearing aids are usually corrected before 5 years using an elastic band (Softband).
The Tjellström et al. The technique proposed in 1977 suggests the creation of a thin muscle-cutaneous flap. The main disadvantage is an altered vascularization that can lead to infection and wound healing problems, retro-ear dysesthesia and alopecia. To solve these problems, a less invasive technique using a linear retro-ear incision has been proposed and is currently most used.
The main benefit of this new technique is the good protection of vascularization in the surgical area, which allows avoiding all the problems of the musculoskeletal flap (infection, recovery problems, dysesthesia, etc.). Another low invasive technique proposed is based on removing a very small piece of skin from the area where the titanium implant should be placed. The removed skin is the same size as the biopsy.
Alpha 2 by Sophono is a prosthesis attached to another bone without percutaneous screw and consists of a processor implanted subcutaneously and subcutaneously connected by a titanium component containing two magnets. Magnetic attraction allows to hold the processor in place and transmit acoustic energy. The limitations of such a device are represented by possible discomfort and complications due to loss of energy from the skin layer and soft tissue pressure.
Bonebridge by MED-EL is a semi-implantable bone conduction hearing system containing a processor attached subcutaneously to a titanium component and implanted subcutaneously with silicone. The transducer placed in the mastoid bone transmits mechanical vibrations directly to the inner ear, which jumps to the middle and outer ear. The delivery system is lightweight (10g) and has an area of 8.7mm (height) × 15.8mm (diameter). The two titanium screws responsible for the vibrations transmitted to the system are placed at a distance of approximately 24 mm between them.
Bonebridge is the unique BAHI with active mechanism; The information analyzed by the sound processor is sent to the antenna and transmitted to the system through the skin. It converts the received signals into mechanical vibrations transmitted to the inner ear by bone conduction. The transducer is surgically positioned at a seno-dural angle. However, due to its light bulky internal implant, the most suitable location to place the BB implant should be carefully selected preoperatively using 3D reconstruction software.
Compared to the percutaneous BCI, Bonebridge’s transcutaneous technology provides prevention of various complications, including skin reaction, skin growth on the abutment, implant extrusion, and wound infection. BB offers the same risks as other BAHIs (skin infection and skin necrosis) and currently no one has identified serious complications using this implant. It is recommended to use double flaps to minimize skin trauma and improve results.
We widely use BAHIs both in the case of aural atresia (single or bilateral form) and as a treatment for unilateral deafness, and our results are supported by observations from other authors. It has been observed that AHI improves not only the hearing abilities of children in noise situations, but also their dictation capacity during school activity. We compared children wearing BAHI immediately after implant and 3 months later we were implanted and 3 months later it was observed that their speech perception abilities increased over time, reaching the same scores observed in healthy children.
In addition, we analyzed short and working memory abilities in children with BAHI before and after implantation and determined that both of these memory functions were improved by restoring hearing with BAHIs. The memory abilities increased over time as the speech perception was made, coinciding with the scores obtained by the healthy children in the same age range. Finally, it was observed that children improved their school scores and increased their relationships with friends and environment after BAHI was implanted.
Reported complications are mild skin problems such as local irritation around the titanium implant and hypertrophic fear. Skin inflammation can be explained as an immune response against an external body (screw). In the literature, rates for skin regrowth range from 5% to 7.5% and for extrusion of the abutment from 1.3% to 10%.
Author: Ozlem Guvenc Agaoglu