Long-term results using a piezoelectric semi-implantable middle ear hearing device

IMPLANTABLE ELECTRONIC OTOLOGIC DEVICES: STATE OF THE ART

0030-6665/01 $15.00

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LONG-TERM RESULTS USING A PIEZOELECTRIC SEMI-IMPLANTABLE MIDDLE EAR HEARING DEVICE The Rion Device E-type Naoaki Yanagihara, MD, Hidemitu Sato, MD, Yasuyuki Hinohira, MD, Kiyohumi Gyo, MD, a n d Kiyoharu Hori, B Eng

In recent years, enthusiasm for implantable hearing devices has been growing worldwide. Several devices with different functional principles have been developed, and some have been applied to patients with varying degree of success.’ Since 1978, the authors and co-workers at Ehime University have collaborated with the group led by J. Suzuki at Teikyo University and with the Rion and Sanyo Electric Companies to develop an implantable hearing aid, using an ossicular vibrator composed of a piezoelectric ceramic bimorph. In 1983, prototypes of totally and partially implantable hearing aids were ~ompleted.~, l1 The team at Ehime University designed an Ehime (E)-typeossicular vibrator that is suitable for a transmastoid implant operation. The following year, they first successfully used the partially implantable hearing aid, the Ron Device E-type (RDE) in a patient with intractable deafness caused by chronic otitis media.7 Since then they have implanted the devices in 39 patients. Careful follow-up studies of all patients have been conducted to determine the advantages and disadvantages of the device, and the investigators have directed their efforts to improving the efficacy and reliability of treatment with the device. This article reviews these technical and surgicalimprovements and reports the results of long-term follow-up studies. From the Department of Otolaryngology, Ehime University Medical School, Ehime (NY, HS, YH, KG); Takanoko Hospital, Matsuyama (NY); and the Department of Hearing Aid Technology, Rion Company, Kokubunji City, Tokyo (KH), Japan

OTOLARYNGOLOGIC CLINICS OF NORTH AMERICA VOLUME 34 NUMBER 2 APRIL 2001

389

390

YANAGIHARA et a1

RION DEVICE E-TYPE

The RDE involves a three-step process. First, a microphone transforms sound waves into electrical signals. Second, the electrical signals are amplified and processed in an electronic circuit. Third, the amplified electrical impulses are transformed into mechanical vibrations by a piezoelectric ceramic bimorph attached to the stapes. With its excellent electroacousticproperties, the piezoelectric ossicular vibrator efficientlytransmits high-fidelity sound signals to the inner ear. The vibrator element is small enough (1.4mm wide, 0.6 mm thick, and 7 mm long) to allow implantation in the middle ear. The piezoelectricbimorph element has a bracket for anchoring it at an appropriate site in the middle ear. This E-type ossicular vibrator is designed to be implanted using a transmastoid approach. As shown in Figure 1, the RDE is a partially implantable device. The E-type ossicular vibrator is implanted together with an internal coil and a connecting wire. The microphone, amplifier, external coil, and battery are housed in an ear-level container,which hangs behind the auricle. The electret microphone converts sound signals into electrical signals that are fed into the amplifier.After amplification, the signals are fed into the external link coil. Electromagneticsignals from the external linkcoil excite the internal link coil under the retroauricularskinby electromagnetic induction to supply electroacoustic signals to the vibrator element. Finally, the vibrator element of the piezoelectric bimorph is activated to vibrate the stapes. Figure 2 shows the outer and inner units. Figure 3 shows the outer unit in use. Because there is neither an earphone nor a wire, most of the unit is invisible; it is hidden by hair, and the external ear canal remains open. INDICATIONS

The maximum output power of the vibrator element compensates for a 50-dB loss of bone conduction at 1 kHz. Therefore, the authors implanted the device

Figure 1. Functional principle of RDE. A microphone, amplifier, battery, and magnetic coil are housed in an ear level container. Sound signals received by the microphoneare amplified and transmittedto the ossicular vibrator by means of magnetic induction.

LONG-TERM RESULTS USING A PIEZOELECTRIC HEARING DEVICE

391

Figure 2. A, Internal component. 13,External component.

into patients with a mixed hearing loss that was caused by a severely damaged middle ear that could not be rehabilitated by ordinary middle ear surgery. Such middle ear damage results from adhesive otitis media, fibrosis of the tympanic cavity, tympanosclerosis, or total loss of the sound conductive mechanism. Before implantation, any middle ear inflammation must be controlled with a preparatory operation. Application of the device is limited to patients with bilateral deafness.The device is implanted in the ear with the greater hearing loss. The audiologiccriteria for selecting candidates were (1)an average bone conduction hearing level for speech frequencies not exceeding 50 dB, and (2) a speech discrimination score better than 70%. In addition, (3) an intraoperative vibratory hearing test proved that there was sufficient sensitivity to the ossicular vibrator.8

N

W

w

Figure 3. The outer unit is worn behind the auricle. The patient has been using the RDE for 11 years. Note there is no visible wire and earphone.

LONG-TERM RESULTS USING A PIEZOELECTRIC HEARING DEVICE

393

IMPLANTATION OF THE FIRST VERSION OF THE RlON DEVICE E-TYPE

Between 1984 and 1989, the authors implanted the first version of the RDE in 28 patients. All but 1patient regained socially useful hearing using the device. In the one exception, hearing did not result because of the insufficient sensitivity of the vibrator. Two months later the device was removed. The remaining 27 patients were able to hear high-fidelity sound of natural quality through the device postoperatively. The authors have learned that the device compensates for conduction loss and an additional 10-dB sensory loss. The patients can hear without feedback, oppressivesensationsin the ear, or the discomfort that can be caused by tight occlusion of the external ear canal. The authors have demonstrated that the high-fidelity sound afforded by the device is much better than that afforded by a conventional hearing aid.'r3 As indicated in Table 1, the authors experienced postoperative complications in 17 patients: 1. In eight patients with eustachian tube dysfunction, the eardrum retracted toward the vibrator element, and keratin debris accumulated in the pocket around the vibrator element. Although the function of the internal unit was undisturbed, the debris had to be removed every 3 or 4 months. In two patients, the device kept functioning; in three patients, the device kept functioning following a revision operation; and in three patients, the device was finally removed because the vibrator became exposed and connection between the vibrator tip and the stapes was interrupted. 2. Because of the thickness of the internal coil, the retroauricular skin bulged at the postero-inferior corner of the coil. The skin gradually atrophied, and finally a retroauricular fistula formed. In four patients, this fistula necessitated removal of the device. 3. In four patients, hearing through the device disappeared because of lack of sensitivity of the vibrator. In one patient, bilateral sensorineural hearing loss suddenly advanced beyond the sensitivity of the vibrator. In two patients, the hydroxyapatite tube between the tip of the vibrator and the stapes was disrupted. In one patient, the sensitivity of the vibrator element deteriorated with age. 4. In one patient, the device stopped functioning when the wire became disconnected following head trauma.

The remaining 10 patients have used the devices without any trouble for at least 10 years, as indicated in Table 1. The surgically removed devices were examined to check for deterioration of vibrator function with time. Three vibrators were removed without disturbing the insulation.In two, all the specificationswere unchanged, but in one a slight decrease within the allowable sensitivity limit was noted.

THE SECOND VERSION OF THE RlON DEVICE E-TYPE

To eliminate these problems, technologic improvements were made to the internal components: 1. The thickness of the internal coil was reduced by two thirds.

bra

w a

1988 1988

1989 1989 1989 1989

1989 1989

F M

F F M M

M F

52 42

49 59 46 65

38 47

13 14 15 16 17 18 19 20

21 22

23 24 25 26

27 28

F M F M F F F F F

F

I = canal-up operation;II = canal-down operation.

11

5 6 7 8 9 10

4

M M M M F F F

1984 1985 1985 1986 1986 1986 1986 1987 1987 1987 1987 1987 1988 1988 1988 1988 1988 1988 1988

1 2 3

M

Year Implanted

M

Sex

60

Age

45 45 48 59 56 28 39 43 48 20 56 37 71 37 49 38 60 43

Patient Number

125 108

86 19 31 126

104 116

144 104 141 118 117 135 95

54

137 88 171 12 70 110 56 156 130 68 34

Months of Use

11 11

I I I

I

I I

n

I I I I I1 I I I I I

I

II

I I I I I I

Type Operation Problem

decrease of sensitivity decrease of sensitivity pocket

pocket

pocket

pocket

decrease of sensitivity fistula fistula pocket

pocket pocket pocket disconnection decrease of sensitivity fistula fistula

Table 1. CLINICAL DATA OF THE PATIENTS USING THE FIRST VERSION OF RlON DEVICE E-TYPE

removed removed functioning removed stopped functioning removed removed functioning removed removed removed removed functioning functioning functioning functioning functioning functioning revision surgery, functioning functioning revision surgery, functioning functioning removed stopped functioning revision surgery, functioning functioning functioning

Outcome

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2. The toughness of the wire was increased. The bending strength of the wire exceeded 10,000 bends, and that of the covering insulation exceeded 40 bends. 3. A sharper screw and a driver that facilitated tightening of the fixing plate to the temporal bone were used. An intraoperative check of the internal components was developed to ensure functioning of the components just before implantation. At surgery, two sets of the internal components are available. If there is mechanical damage to the vibrator during surgery, a second one is available. To cope with deterioration in the sensitivity of the vibrator because of device age, the method of insulation was improved, and stricter selection standards were adopted for the product. Consequently, the reliability of the vibrator was enhanced. To compensate for progressive sensory loss as the patient ages, a more powerful external unit with an average 10-dB increment in output power was developed.

IMPLANTATION OF THE SECOND VERSION OF THE DEVICE

Two operations were developed to increase the safety of implantation and to prevent delayed problems.

Operation 1: Canal-up Operation

To prevent delayed problems caused by eustachian tube dysfunction,the canalup operation creates a laterally positioned hard wall instead of using the ear drum to separate a large middle ear cavity from the external ear canal (Fig. 4). A retroauricular skin incision is made posterior to the internal coil, and a thick retroauricular skin flap is elevated from the mastoid process. Then a transcortical mastoidectomy is made, and a large posterior hypotympanotomy opening is created by drilling the posterior bony ridge of the tympanic membrane and about one third of the bony posterior wall of the external ear canal. The tympanic membrane is removed, and the canal skin is elevated laterally. A piece of cartilage flap resected from the posterior aspect of the auricle is attached to the ridge of the bony external ear canal using fibrin glue. To strengthen the cartilage flap, it is backed with bone paste, and its lateral surface is lined with the elevated canal skin. Next, the fixing plate of the vibrator element is firmly fixed to the squamous portion of the temporal bone with a titanium screw so that the vibrator element is anchored at an appropriate position to connect the tip of the vibrator element to the stapes. A hydroxyapatite tube is then interposed between the tip of the vibrator and the head of the stapes. If the superstructure of the stapes is missing, a column of the same material is interposed between the tip and the footplate.The base of the bracket is firmly fixed with bone paste. The internal coil is implanted just beneath the external coil in the bony hollow created in the cortical bone of the mastoid process. After the retroauricular wound is closed, the hearing afforded by the device is tested by connecting the outer unit to an audiometer. From the given threshold values, the postoperative hearing level afforded by the device can be accurately assessed.

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Figure 4. Operation 1 (canal-upoperation).A, Principleof the implant operation 1. B, Surgical view. The internal component is implanted in the middle ear cavity created by the enlarged posterior tympanotomy opening.

Operation 2: Canal-down Operation6

If the ear has previously been operated on using a canal-down method, all the skin covering the cavity should be removed. The vibrator unit is then fixed as shown in Figure 4. A bulky pedicle temporalis muscle flap is created to protect the vibrator, and the orifice of the external ear canal is sutured closed. Before the wound is closed, the internal coil is placed in the bony hollow created in the cortical bone of the mastoid process, and the function of the implanted unit is checked as in the canal-up operation.

LONG-TERM RESULTS USING A PIEZOELECTRIC HEARING DEVICE

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LONG-TERM RESULTS As described previously, the authors experienced trouble caused by technologic or medical failure in 17 of the 27 patients in whom the first version of the device was implanted. The remaining 10 patients continue to use the device without any trouble at least 10years after it was implanted (Table 1).Table 2 presents the clinical data for the 11patients in whom the second version of the device was implanted. In one patient, the device was removed because of a retroauricular fistula. In two patients, revision surgery was necessary to remove cholesteatoma arising after the canal-down operation. Since revision surgery, these patients have used the device without trouble. In all nine patients who underwent surgery after 1990, the device is functioning quite well. The reliability of the treatment has greatly improved. Table 3 shows the audiologic data for the two groups of patients. One group has used the device for more than 10years and the other for less than 10 years. There were no marked differences in any of the parameters examined. In both groups, a hearing level improvement of 36 dB was obtained 3 months postoperatively, and at the most recent examination the improvement decreased to 21 dB. Nevertheless, the hearing level afforded by the device has remained stable, at a socially adequate level. The decreased hearing level is attributed to a decrease in the sensitivity of the ossicular vibrator caused by aging and to tissue reaction around the vibrator element impeding vibrator function. Deterioration of bone conduction caused by use of the device was not noted in any of the patients. Once patients became accustomed to using the device, their satisfaction level was high. Patients could hear clear, natural sounds without interference noise or howling caused by acoustic feedback. Even in noisy environments, patients could easily hear speech. Wearing discomfort was negligible. None of the patients complained of fatigue or headache, even after long use. Once the patients began to use the device, they all preferred it to a conventional hearing aid.9, 1612 Clinical trials at two other university hospitals in Japan are in progress, and the same successful results were reported recently5

SUMMARY

From the long-term follow-up studies, the authors derived the following conclusions:

1. The device can function safely in the ear for more than 10 years. 2. The device provides a natural sound quality without feedback and wearing discomfort. The quality of hearing afforded by the device is very close to that perceived by physiologic hearing. 3. Sensorineural hearing loss attributable to long-term use of the device was not recognized in any of the patients. 4. The implant operation could be repeated safely and provided the patient with high levels of satisfaction. The studies indicate that the E o n Device E-type can be used to rehabilitate mixed deafness that cannot be satisfactorily rehabilitated by either surgical means or a conventionalhearing aid.

w

42

60 42 48 58 67 53

48 53 48 20

29

30 31 32 33 34 35

36 37 38 39

M F

F

F

M

F

M F

F

F

F

Sex

I1 = canal-down operation; I = canal-up operation

Ane

Patient Number

1995 1996 1996 1997

1990 1990 1990 1990 1990 1990

1990

Year ImDlanted

38 38 39 36

119 76 109 113 24 109

120

Months of Use

I1 I1 I1 I

I I1 I1 I I1 I1

I1

Type of ODeration

Table 2. CLINICAL DATA OF THE PATIENTS USING THE SECOND VERSION OF RlON DEVICE E-TYPE

revision surgery, functioning functioning functioning functioning functioning removed revision surgery, functioning functioning functioning functioning functioning

cholesteatoma

fistula cholesteatoma

pocket

Outcome

Problem

17 8

Period of Use

Shorter than 10 years Longer than 10 years

91 f 30 140 f 17

Period of Use (in Months)

42-71 42-65

Age Range (in Years)

62.1 f 11.2 58.1 f 8.2

Preop AC (dB)

Preop = preoperative; AC = air-conduction; BC = bone conduction; RDE-HL = Rion device E-type.

Number of Patients

Table 3.AUDIOLOGIC DATA AND PERIOD OF USE, MEAN f SD

*

39.4 f 9.9 35.2 6.8

Preop BC (dB)

RDE-HL: Most Recent (dB)

37.6 & 13.9 38.8 & 6.8

RDE-HL: 3 Months Postop (dB)

26.0 f 9.8 22.4 f 6.7

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YANAGIHARA et a1

References 1. Gyo K, Yanagihara N, Saiki T, et al: Present status and outlook of the implantable hearing aid. Am J Otol 11:250-253,1990 2. Huttenbrink K-B: Current status and clinical reflection on implantable hearing aids. Am J Otol20:409-415,1999 3. Saiki T, Gyo K, Yanagihara N: Audiological evaluation of the middle ear implantTemporal auditory acuity. Journal of Otolaryngology Japan 93:413-419,1990 4. Suzuki J, Kodera K, Yanagihara N. Middle ear implant for humans. Acta Otolaryngol (Stockh) 99:313-317,1985 5. Tono T, Inaba J, Takenaka M, et al: Clinical experiences and postoperative results with partially implantable middle ear implant. Journal of Otolaryngology Japan 102:835-845, 1999 6. Yanagihara N: Surgical aspects of the partially implantable hearing aid of the Ehime type. Operative techniques. Otolaryngol Head Neck Surg 3:32-38,1992 7. Yanagihara N, Aritomo H, Yamanaka N, et al: Implantable hearing aid: Report of the first human application. Arch Otolaryngol Head Neck Surg 1135369-872,1987 8. Yanagihara N, Aritomo H, Yamanaka E, et al: Intraoperative assessment of vibratorinduced hearing. Advances in Audiology 43124-133,1988 9. Yanagihara N, Gyo K, Hinohira Y: Partially implantable hearing aid using piezoelectric ceramic ossicular vibrator: Results of the implant operation and assessment of the hearing afforded by the device. Otolaryngol Clin North Am 28:85-97,1995 10. Yanagihara N, Hinihira Y, Gyo K Surgical rehabilitation of deafness with partially implantable hearing aid using piezoelectric ceramic ossicular vibrator. Auris Nasus Larynx 24:91-98,1997 11. Yanagihara N, Suzuki JI, Gyo K, et al: Development of an implantable hearing aid using a piezoelectric vibrator of bimorph design: State of the art. Otolaryngol Head Neck Surg 92:706-712,1984 12. Yanagihara N, Yamanaka E, Gyo K: Implantable hearing aid using an ossicular vibrator composed of a piezoelectric ceramic bimorph Application of four patients. Am J Otol 8:213-219,1987

Address reprint requests to Naoaki Yanagihara, MD Takanoko Hospital 525-1 Takanoko-cho Matsuyama-city 79043925 Japan e-mail: yanagiha8m.ehime-u.ac.jp