Clinical evaluation of piezoelectric ear surgery.

Abstract

We evaluated the use of piezoelectric surgery (Piezosurgery; Mectron Medical Technology; Carasco, Genoa, Italy) as a means of avoiding some complications of osteotomy and osteoplasty in otologic surgery, particularly in classic canal-wall-up mastoidectomy. Piezoelectric surgery is a recently developed system for cutting bone with microvibrations created by the piezoelectric effect. This effect occurs when an electric current is passed through certain ceramics and crystals, causing them to oscillate at ultrasonic frequencies. Our study population was made up of 20 adults with unilateral chronic otitis media. In all patients, piezoelectric surgery allowed for effective, precise, safe, easy, and rapid intraoperative management. In particular, the instrument's precision allowed surgeons to make exact, clean, and smooth cuts without causing any injury to adjacent soft tissue. No complications were noted. We conclude that the piezoelectric device is superior to conventionally rotating instruments for performing classic canal-wall-up mastoidectomy.

Introduction

In otologic surgery, bone has traditionally been cut with either manual or motorized instruments. Obviously, these instruments have their drawbacks. Manual instruments are difficult to control in cortical bone, especially when a precise cut is required. Motorized instruments generate a significant amount of heat at the cutting site, and overheating of nearby tissues can alter the healing response. The production of heat can be limited by reducing rotational velocity, but this hinders the cutting action. A low rotation speed is usually compensated for with an increase in manual pressure, but this can cause macrovibrations and reduce surgical sensitivity.

A desire to overcome these limitations stimulated the development of a new instrument--the piezoelectric surgery device--that is able to cut bone cleanly and quickly without causing necrosis or damage to nonmineralized tissue. (1-4) Bone is cut by microvibrations created by the piezoelectric effect, which occurs when an electric current is passed through certain ceramics and crystals, causing them to oscillate at ultrasonic frequencies. Piezoelectric surgery is already used in various types of surgery, including endodontal and maxillofacial surgery. (1-8) In this article, we describe our evaluation of the applicability and effectiveness of piezoelectric surgery in mastoidectomy.

Patients and methods

For this study, we enrolled 20 patients--12 men and 8 women, aged 44 to 58 years (mean: 51.4)--who were affected by chronic otitis media. Eleven patients had left-sided disease and 9 were affected on the right.

Before surgery, all patients underwent otomicroscopic evaluation of the external and middle ear, liminal tonal audiometry, tympanometry, and auditory brainstem response (ABR) testing. Also, patients underwent rotatory vestibular stimulation by stop test from a constant angular velocity of 90[degrees]/sec, and their induced nystagmus was recorded by electronystagmography (ENG).

Under general anesthesia and with orotracheal intubation, all patients underwent classic intact canal-wall-up mastoidectomy. An incision was made in the retroauricular skin, and the entire mastoid plane was exposed. Then the bone of the mastoid was removed with a piezoelectric surgery device (Piezosurgery; Mectron Medical Technology; Carasco, Genoa, Italy). The equipment consists of two handpieces, two inserts, four insert tips of various diameters, and two peristaltic pumps that provide cooling during surgery by discharging a jet of physiologic saline solution (figure). The device's ultrasonic frequency ranges from 24.7 to 29.5 kHz, and the amount of applied power ranges from 2.8 to 16 W. The cutting force can be programmed according to the density of the bone cut. The microvibrations created in the piezoelectric handpiece cause the inserts to vibrate linearly between 60 and 210 [micro]m.

One day after surgery, all patients underwent liminal tonal audiometry. At 15 days postoperatively, they underwent otomicroscopic evaluation for the removal of remnants of unabsorbed Gelfoam and for evaluation of the tympanic membrane. At 1 month and 6 months, all patients underwent repeat liminal tonal audiometry, ABR testing, and ENG.

The subjective parameters o four assessment of piezoelectric surgery were its reliability, precision, safety in soft tissues, ease of use, and speed.

Results

Piezoelectric surgery proved to be effective and efficient in both sclerotic and pneumatized mastoids. In all patients, precise, clean, and smooth cuts were achieved quickly, easily, and safely, even in difficult-to-reach anatomic sites. No complications were noted in soft tissues such as the facial nerves and vascular formations. With respect to the inserts, the variety of angles and diameters greatly facilitated the procedure. The presence of the two peristaltic pumps and the two handpieces allowed us to perform surgery without stopping to change tips. Particularly useful was the action of the saline solution, which kept the operating site blood-free and provided for excellent intraoperative visibility.

At 1 and 6 months postoperatively, findings on liminal tonal audiometry, ABR testing, and ENG revealed that the preoperative values had not changed in any patient.

Discussion

The results of the first experimental attempts to cut bone with ultrasonic instruments were poor. A standard ultrasonic instrument cannot be used for osteotomy unless the tip is very sharp. Even then, the low amount of power generated by these instruments does not allow for osteotomy when the bone is highly mineralized or thick because macrovibrations and an increase in temperature can lead to bony necrosis. (9-11)

Because piezoelectricity is 3 times more powerful than standard ultrasound, it can cut highly mineralized bone. (1-4) In fact, the low vibration frequency generated by the piezoelectric surgery device is optimal for mineralized tissue, and it will not damage adjacent soft tissue. Finally, the ability to make precise cuts in difficult anatomic situations is an important factor in rating this device as superior to conventional instruments. (1-4)

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Extensive preliminary testing of the Piezosurgery device was performed on laboratory materials. The first step in this process was to determine whether the handpieces and inserts used for other types of surgery could be used for otologic surgery. We found that they could not be used in ear procedures because the surgical field is so restricted. Therefore, new handpieces and inserts customized specifically for otologic surgery were created. The width, thickness, and angles of the inserts were all dependent on the amount of applied power, the density of the bone, and indication for surgery. The tips of the inserts were coated with various grades of diamond. The preliminary tests revealed that piezoelectric surgery is feasible for several otologic procedures. With regard to safety, no damage to the nerve structures and soft tissues occurred when these structures were deliberately put into contact with the device.

Histologic comparisons of piezoelectric surgery with saw and bur procedures in animals demonstrated the superiority of piezoelectric surgery in terms of safety, cutting precision, and protection of anatomic structures. (12,13) The presence of live osteocytes of normal dimensions and morphology on the cut surfaces confirmed the lesser degree of trauma induced by the piezoelectric cut.

Our findings indicate that the piezoelectric surgery device provides better cutting efficacy than ultrasonic devices that involve magnetostrictive technology, which converts most of the generated energy into heat. (9-11) Piezoelectric ceramics convert only 30% of energy into heat, so 70% is delivered for cutting power.

We conclude that the piezoelectric device is superior to conventional instruments for performing classic intact canal-wall-up mastoidectomy.

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From the Department of Otorhinolaryngology, University of Genoa (Dr. Dellepiane, Dr. Mora, and Prof. Salami), and the Department of Otorhinolaryngology, University of Palermo (Prof. Salzano), Italy.

Corresponding author: Renzo Mora, MD, Via dei Mille 11/9, 16132, Genoa, Italy. Phone: [phone]; fax: [phone]; e-mail: [e-mail]

Financial disclosure: None of the authors has any financial arrangement with the manufacturer or distributor of the device discussed in this article.