Middle Ear Prosthesis Research Articles

Safety evaluation of titanium middle ear prostheses at 3.0 tesla

To assess the magnetic resonance imaging (MRI) safety of titanium middle ear prostheses at 3.0 tesla (T). Titanium middle ear prostheses from 3 commercial vendors were examined for magnetic field interactions at 3 T. Initially, ex vivo studies were performed to test for rotational motion and forward displacement (translational motion) of the prostheses in a static magnetic field. If movement was observed during this screening study, then the prosthesis was tested to determine the translational or rotational force acting upon the prosthesis. In addition to testing for prosthesis displacement, temperature changes of the prostheses were measured to assess for radiofrequency heating during imaging. Twenty-one of the 24 titanium prostheses tested revealed no movement when tested in the 3 T static magnetic field. Three prostheses revealed minimal movement during the screening study. A translational force test (string test) was performed upon these 3 prostheses, and the measured angle of displacement was used to determine the force. This calculated force acting upon each prosthesis was essentially zero. Therefore, we conclude that the magnetic field interaction is negligible. A positive control with a ferromagnetic stainless steel prosthesis demonstrated obvious displacement during the screening study, as well as deflection of the prosthesis by 90 degrees in the translational force test. Last, heating of the titanium prostheses did not occur in the 7 models tested. Middle ear prostheses made from titanium are safe, neither deflecting nor heating during magnetic resonance examinations conducted at 3 T. C-1.

Surgical-Handling Properties of the Titanium Prosthesis in Ossiculoplasty

Despite the wide variety of ossiculoplasty techniques that are available, success rates are limited. Current use indicates that surgeons prefer ceramic, autograft bone, and plastic pore prostheses. During the past decade, titanium prostheses have been used with great promise. Although their use is not widespread, satisfaction rates are high. An earlier study of ossiculoplasty showed that titanium prostheses were effective in reducing conductive hearing loss. To date, the surgical-handling attributes of titanium middle ear prostheses have not been assessed. We report the results of our survey of 32 otologic surgeons who used the open Tübingen titanium prosthesis for primary and revision ossiculoplasty during tympanoplasty in 400 patients at 12 academic and nonacademic otolaryngology clinics, most of them in Germany. Because the audiometric efficacy of titanium prostheses has been previously reported, our primary outcomes measures included ease of use with respect to the amount of time required to prepare the implants for placement and the surgeons' overall impression of the intraoperative handling characteristics of the implants, taking into consideration factors such as positioning, length adjustment, visibility, and the stability of the coupling. Surgeons also compared the properties of the titanium implant with those of gold, ceramic, and autograft implants that they had used in the past. Based on the results of 383 of the 400 ossiculoplasties, our survey revealed that the titanium implant was significantly superior to the others in all measured respects.

Malleus relocation in ossicular reconstruction: managing the anteriorly positioned malleus: results in a series of 268 cases.

The objective of this study was to report an original method of malleus relocation allowing for better placement of both partial and total prostheses in ossicular reconstruction. We conducted a retrospective review of clinical and audiometric findings. A tertiary referral center. This is a study of 268 patients who underwent ossiculoplasty surgery from October 1997 to October 2000 for chronic otitis media, noninflammatory disease, and otosclerosis revision. Malleus relocation with total and partial ossicular replacement prostheses was used in all cases. Audiometric assessment included pre- and postoperative audiometric evaluation using conventional audiometry. Air-bone gap, bone-conduction thresholds, and air-conduction thresholds were measured. A postoperative air-bone gap closed to within 10 dB was achieved in 56% of cases. An air-bone gap smaller than 20 dB was obtained in 78% of cases. Postoperative improvement of air-conduction thresholds superior to 20 dB was found in 41.5% of cases. The postoperative bone-conduction thresholds were unchanged in 98% of cases. One case of total postoperative sensorineural hearing loss was seen in this series (0.4%). Extrusion of the protheses was not observed in this series. Follow up ranged from 6 to 36 months (mean, 12.4 months). This study shows that malleus relocation is a safe and efficient technique for ossicular reconstruction. The ideal position of the relocated malleus allows easier and more stable placement of middle ear prostheses.

Acoustomechanical properties of open TTP ® titanium middle ear prostheses

Objective: The purpose of the study was to identify acoustcomechanical properties of various biostable and biocompatible materials to create a middle ear prosthesis with the following properties: (i) improved handling including a good view of the head of the stapes or footplate and adjustable length, (ii) improved acoustical characteristics that are adequate for ossiculoplastic. The identified material should serve to build CE and FDA approved prostheses for clinical use in patients. Methods: Test models made of Teflon, polyetheretherketone, polyethylenterephtalate, polysulfone, gold, Al 2O 3 ceramics, carbon and titanium were investigated for their potential to fulfill the requirements. Acoustical properties were investigated by laser Doppler velocimetry (LDV) in mechanical middle ear models (MMM). Measured data were fed in to a recently created computer model of the middle ear (multibody systems approach, MBS). Using computer-aided design (CAD) measured and computed data allowed creation and fine precision of titanium prostheses (Tübingen Titanium Protheses, TTP ®). Their handling was tested in temporal bones. Acoustomechanical properties were investigated using the MBS and mechanical middle ear models. Main outcome measures: Input impedance, mass, stiffness, and geometry of test models and prostheses were determined. Furthermore, their influence on the intraprosthetic transfer functions and on coupling to either tympanic membrane or stapes was investigated. Results: Final results were FDA- and CE-approved filigreed titanium prostheses with an open head that fulfilled the four requirements detailed above. The prostheses (TTP ®) were developed in defined lengths of between 1.75 and 3.5 mm (partial) and 3.0 and 6.5 mm (total) as well as in adjustable lengths (TTP-Vario ®). Conclusions: The results suggest acoustomechanical advantages of TTPs ® because they combine a significantly low mass with high stiffness. In contrast to closed prostheses, the open head and filigreed design allow an excellent view of the prosthesis foot during coupling to the head or footplate of stapes, contributing to an improved intraoperative reliability of prosthesis coupling.

Early Results With Titanium Ossicular Implants

To report the efficacy of titanium middle ear prosthesis for ossicular reconstruction. Retrospective chart reviews were performed for 25 patients who had undergone titanium ossicular implants between January 1, 1999, and June 1, 20001. Tertiary otology referral center. All patients had a minimum of 6 months of postoperative follow-up and no evidence of recurrent otologic disease. All patients had undergone ossiculoplasty using titanium middle ear implants. Comparisons of preoperative and postoperative pure tone averages were performed. Air-bone gap closures and implant extrusion rates were measured. RESULTS Overall mean pure tone averages improved 22.2 dB with air-bone gap improvement at 20.9 dB. Fifty-six percent of patients achieved air-bone gap less than 20 dB postoperatively. The overall extrusion rate was 4%. However, with the placement of cartilage graft interposed between the prosthesis and the tympanic membrane, no extrusion was observed. Titanium implants provide comparable hearing improvement compared with other materials. The extrusion rate seems quite low if cartilage interposition graft is inserted. Its ease of handling, biocompatible properties, and sound conducting properties improve its efficacy as an ossicular implant.

Histopathology of Biocompatible Hydroxylapatite-Polyethylene Composite in Ossiculoplasty

The biocompatibility of hydroxylapatite-polyethylene composite implants (HAPEX, Smith and Nephew) was investigated in this study. Eleven middle ear prostheses, removed during revision surgery, have been examined by light microscopy, transmission electron microscopy and scanning electron microscopy. The results show that the middle ear prostheses become overgrown by fibrous tissue inside a thin epithelial layer. In some cases the prosthesis is covered by fibrous tissue without an outer layer of epithelial cells. No arguments have been found for the accumulation of macrophages and foreign body giant cells associated with a foreign body reaction to the material. Therefore, hydroxylapatite-polyethylene composite implants (HAPEX, Smith and Nephew) would seem to be very suitable for reconstructive middle ear surgery.

Osteoblast-like Cell Cultures from Human Stapes

Objective --In order to develop new middle ear prostheses for ossicular reconstruction it is important to study how the recipient middle ear tissues, especially the stapes footplate and superstructure, react to the implanted biomaterial. In this respect, animal studies and cell cultures using non-specific cells are of limited value. Material and methods --The morphology and growth pattern of cells cultured from human stapes were studied. Cultured cells were examined for the presence of alkaline phosphatase and were processed for immunocytochemistry in order to detect the presence of osteocalcine. Fibroblast cultures served as controls. Results --Cultured stapes cells proliferated in a polygonal-cubic shape and without any regular pattern in the culture. These cells were shown to contain alkaline phosphatase and osteocalcine. Cultured fascia fibroblasts proliferated in a spindle-shaped form and in a pattern resembling a shoal of fish. Cultured fibroblasts did not contain alkaline phosphatase or osteocalcine. Conclusions --It is possible to culture osteoblasts from human stapes. These cells can be characterized as osteoblast-like cells by means of their external shape and the presence of alkaline phosphatase and osteocalcine. Using these cultures, specific in vitro investigations concerning the interaction of biomaterials and middle ear ossicles could be performed.

Vibratory sample magnetometry of middle ear prostheses and manufacturing materials.

To assess the magnetic properties of stapes prostheses and manufacturing materials using a vibratory sample magnetometer (VSM). VSM was performed on 16 samples, including ferromagnetic 420F stainless steel, with an LDJ Model 9600 VSM in accordance with American Society for Testing and Materials standard A894. A VSM measures the magnetic dipole moment of a sample in a magnetic field. The magnetic field is swept over a range of magnetic fields, and the magnetic dipole moment is plotted as a function of field. The prostheses made of 316L stainless steel previously found to be ferromagnetic had the highest specific magnetic moments. The specific magnetic moments ranged from 0.023 electromagnetic units (emu)/g to 156 emu/g. The samples made with 316L stainless steel, which is used in otologic implants, were significantly less magnetic than was the 420F stainless steel. VSM demonstrates that prostheses made with 316L stainless steel are relatively nonferromagnetic compared with 420F stainless steel. However, none of the implants are nonmagnetic. The torque and linear force on the prosthesis is a concern. The safety of performing MRI on patients with these implants needs to be further assessed.

Mass loading on the ossicles and middle ear function.

The middle ear as a levered vibrating system for sound transmission from the external to the inner ear is affected by changes in ossicular chain mass. Mass loading of the ossicles may impair ossicular dynamics and sound transmission to the inner ear. It is incumbent on otologic surgeons and researchers of middle ear mechanics to consider the mass loading effect on middle ear function in clinical and physiological applications. The residual hearing and frequency response can change after surgery or implantation of middle ear prostheses. We conducted experiments on mass loading effects on the middle ear transfer functions by using laser Doppler interferometry and a human temporal bone model. Two implant mass loading conditions were tested on 17 fresh or fresh-frozen temporal bones and compared with the unloaded condition for the frequencies 250 to 8,000 Hz. The results show that the linearity of the middle ear function did not change, although displacement of the stapes footplate decreased after the increased masses were placed on the incudostapedial joint. The greater the mass of the implant, the less displacement was measured at the stapes footplate. We conclude that there is a quantitative limit to increased mass on the ossicular chain above which the mass will remarkably impair hearing thresholds.

Middle ear prosthesis displacement in high-strength magnetic fields.

Middle ear prostheses made from nonmagnetic, magnetic resonance (MR)-compatible metals reportedly displace ex vivo in the presence of high magnetic fields used in MR imaging (MRI). The authors postulate that the prosthesis displacement seen with "nonmagnetic" MR-compatible prostheses ex vivo may not be clinically significant in vivo. Middle ear prostheses made from ferromagnetic (420F stainless steel) and nonmagnetic MR-compatible metals (316L stainless steel and platinum) were examined for magnetic field interactions at 4.7 Tesla (T). Ex vivo testing consisted of measurements of the translational and rotational motion of the prosthesis induced by the static magnetic field. In vivo testing was assessed by implanting prostheses in cadaveric temporal bones and performing clinical MRI sequences. Prosthesis displacement was measured semiquantitatively. Angular deflection was observed in all samples made from nonmagnetic stainless steel. The negative control (platinum) demonstrated no deflection, and the positive controls (ferromagnetic stainless steel) deflected >90 degrees. Torque analysis showed movement in five of five nonmagnetic stainless steel prostheses. Prostheses made from nonmagnetic stainless steel remained in place without appreciable loosening in vivo after MRI. Prostheses made with known ferromagnetic properties were displaced at 4.7 T but not at 1.5 T. Middle ear prostheses made from low-magnetic stainless steel do move in the presence of high magnetic fields ex vivo; however, this does not appear to be clinically or statistically significant in vivo at 4.7 T. Magnetic resonance imaging should be undertaken with caution in individuals with prostheses made from stainless steel with strong ferromagnetic properties.

Evaluation of hydroxyapatite ossicular chain prostheses

Hydroxyapatite (HA) middle ear prostheses have gained popularity as an alternative to human autografts and homografts. This study reports on 3 HA prostheses types: total ossicular chain prostheses, used for grafting the stapes footplate to the tympanic membrane; partial ossicular chain prostheses, used for grafting the stapes superstructure to the tympanic membrane; and Kartush incus struts (Smith & Nephew Richards Inc), used for grafting the stapes superstructure to the undersurface of the malleus. This single-surgeon study of 33 consecutive cases revealed a statistically significant difference in mean postoperative air-bone gap and airbone gap closure between incus struts (14/26 dB) or partial (22/11 dB) or total (25/10 dB) ossicular chain prostheses ( t test: P < 0.05). Prognostic risk factors graded by the Middle Ear Risk Index indicate a tendency for worse postoperative hearing with increasing Middle Ear Risk Index. This study supports the use of HA ossicular prostheses and, in particular, the use of the malleus for ossicular chain construction. (Otolaryngol Head Neck Surg 2000; 123:425-9.)

Dynamics of Middle Ear Prostheses – Simulations and Measurements

The efficient and systematic development of a middle ear prosthesis necessitates the use of computer models for the prosthesis itself and the reconstructed middle ear. The structure and parameters of the computer model have to be verified by specific measurements of the implant and the reconstructed ear. To obtain a realistic model of a reconstructed ear, three steps of modeling and measurements have been carried out. To get a first approach of the coupling elements a mechanical test rig representing a simplified reconstructed middle ear was built. The velocity of the stapedial footplate was measured with a laser Doppler vibrometer. The corresponding computer model was formulated, and the respective parameters were determined using the measured dynamical transfer functions. In the second step, a prosthesis was implanted into a human temporal bone without inner ear. Exciting this system with noise, the velocity of the stapes footplate was measured with the laser Doppler vibrometer. Based on the multibody system approach, a mechanical computer model was generated to describe the spatial motions of the reconstructed ossicular chain. Varying some significant parameters, simulations have been carried out. To describe the dynamical behavior of the system consisting of middle and inner ear, the computer model used in the second step has been enlarged by adding a simplified structure of the inner ear. The results were compared with in situ measurements taken from living humans.

Standardized measurements of the sound transmission of middle ear implants using a mechanical middle ear model.

Several ways to evaluate the sound transmission properties of middle ear implants are now established. Besides computer-based simulations using acoustic and electrical analog circuits or finite element analysis, measurements can be performed with temporal bone preparations. Experiments with these preparations consider various anatomical properties, but a large number of parameters influence the outcome of measurements. To facilitate standardized measurements, a mechanical middle ear model was developed that allows comparison of the transfer function of middle ear implants on defined conditions. The model approximates the impedances of the tympanic membrane and inner ear with the aid of thin, flexible membranes. The implants are fit between the membranes, and displacement at an artificial stapes foot-plate is measured with an optical probe. Fundamental influences on the sound transmission properties of nine different middle ear implants (total ossicular replacement prostheses) were examined. Although the material and shape were different, some of the prostheses revealed very similar transfer functions. The mass of the implant showed the largest influence on sound conduction. With a higher mass, the frequency area above approximately 1 kHz was found to be significantly deteriorated. The lightest implant used was 4 mg and showed the best overall results. These findings show that middle ear prostheses should be as light as possible for optimum high-frequency transmission.

Titanium as a biomaterial for ossicular replacement: results after implantation in the middle ear of the rabbit.

The middle ear poses unique challenges when finding suitable materials for ossicular reconstruction, primarily because of its link to the external environment via the eustachian tube and, hence, its greater exposure to infectious agents. In this study, the biocompatability of titanium was examined in the middle ear of rabbits by using light and scanning electron microscopy. Implants were placed as middle ear prostheses or as free implants. These were inspected at 28 days, 84 days, 168 days, 336 days and 504 days following implantation for mucosal coverage, percent epithelization and any sign of foreign-body reaction. After 28 days, the prostheses were covered by regular mucosa. Although a majority of the free implants took up to 336 days for complete epithelialization, some of the free implants were not epithelialized even at day 504. There were no inflammatory cells observed on the surface of the material, nor were unusual amounts of fibrous tissue seen. In addition, the titanium material exhibited an affinity toward bone. The results of this animal experiment indicate that titanium is a favorable material for ossicular replacement prostheses.

Epithelialization of titanium prostheses in the middle ear of the rabbit. Possible model of mucosa development

The epithelialization of middle ear implants is regarded as a sign of biocompatibility of the implant material. The mucosal coverage of titanium was studied in the middle ear of rabbits in light microscopy. Implants were used as middle ear prostheses or as a free implants. Studies were performed after 28, 84, 168, 336, and 504 days. The prostheses were seen to be covered by regular mucosa after 28 days. The free implants were not seen to be totally epithelialized even after 504 days. There were no inflammation cells on the surface of the material, nor were unusual amounts of fibrous tissue observed. The middle ear mucosa was initially thickened, but soon returned to normal values. The results of this animal experiment show that titanium is a suitable material for ossicular replacement.

Universal middle ear prosthesis

A middle ear prosthesis 10 is provided having a first portion 12 including a head 16 for engaging the tympanic membrane and a cannulated shaft 20 extending from head 16. The first portion of 12 is operable alone as a partial ossicular prosthesis. A second portion 14 is provided including a shaft having a distal portion 26 insertable in the cannulated shaft 20 of first portion 12. Second portion 14 when in combination with first portion 12 provides a total ossicular prosthesis.

Replacement of ear ossicles with titanium prostheses

Titanium has been a well established implant material for many years. New material processing techniques now permit the manufacture of small implants for ossicular chain reconstruction. Between November 1994 and September 1995, 100 titanium middle ear implants (55 PORP, 45 TORP) were used for reconstruction of the ossicular chain. A range of five different sizes for partial and total protheses suits all implantation needs. The shape of the implants can be altered by bending. Time consuming intraoperative shaping and trimming is avoided. At a follow-up time of three months (33 patients) and six months (17 patients), no adverse reactions or extrusions occurred. Biologic fixation between the foot of the partial prothesis and the head of the stapes was found eight months after implantation. A hearing result of 0-20 dB residual air-bone gap was achieved in 79%. Titanium middle ear implants show good bio-compatibility and are readily integrated into the ossicular chain. Although delicate in shape, they offer excellent mechanical properties in respect to sound conduction and implantation. Initial results show Titanium to be a perfect implant material for middle ear prostheses, although long-term results are not yet available.

Biomaterials in the reconstruction of the human middle ear

The use of biomaterials for reconstruction of the ossicular chain in middle ear involves a different approach from that associated with other regions of the organism. The features of the implantation site and the composition of the prosthesis are responsible for functional failures that result from deterioration or extrusion of the implant. Since the fifties, different types of materials, both biological and synthetic, have been employed in the attempt to achieve the ideal middle ear prosthesis. We present a reprospective study of 166 patients who underwent ossicular chain reconstruction involving autografts and homografts of cartilage or auditory ossicle (n=104) or synthetic prostheses (n=62). We compare prostheses of different compositions on the basis of the cases of extrusion and the histological deterioration encountered with each. In our experience, polymers are associated with frequent extrusion and deterioration of the biomaterial, while the results are better with biological implants and those made of hydroxyapatite.

Ossiculoplasty with polymaleinate ionomeric prosthesis

With the continued concern over the possible transmission of viral infections through homologous middle ear implants, there is increasing pressure to develop a truly biocompatible alloplastic middle ear prosthesis. The polymaleinate ionomer, which has been used in dentistry as a filling and luting material for more than 15 years, has recently been used to construct total and partial ossicular replacement prostheses. In an attempt to evaluate these new implants, a multicenter prospective clinical trial was initiated. To date, 92 patients have undergone implantation. The follow-up interval ranged from 3 months to 22 months. Although it is premature to discuss the long-term results, the preliminary surgical experience and audiometric data with these implants are reviewed. From a surgical perspective, the ionomeric prostheses were easily contoured with a diamond burr and were not prone to shattering. Preliminary follow-up audiometric data were available on 80 patients (59 partial ossicular replacement prostheses and 21 total ossicular replacement prostheses). Of the 59 partial ossicular replacement prostheses the air-bone gaps (average of 500 Hz, 1 kHz, 2 kHz and 3 kHz) were as follows: 0 dB to 10 dB, 15 (25%) of 59; 11 dB to 20 dB, 20 (34%) of 59; 21 dB to 30 dB, 11 (19%) of 59; and greater than 30 dB, 13 (22%) of 59. Of the 21 total ossicular replacement prostheses the air-bone gaps were as follows: 0 dB to 10 dB, 6 (29%) of 21; 11 dB to 20 dB, 6 (29%) of 21; 21 dB to 30 dB, 5 (24%) of 21; and greater than 30 dB, 4 (19%) of 21. (OTOLARYNGOL HEAD NECK SURG 1995;113:420-6.)

Method of implanting a middle ear prosthesis

The middle ear prosthesis includes an elongated link member having an eyelet portion at one end for connection to one of the auditory ossicles and an opposite posting end connectable to part of another auditory ossicle. A hitching member joined to the link member provides a vehicle for attaching the stapedial tendon to the link member to restore the beneficial effects of the stapedial reflex. Movement of the prosthesis and other remaining portions of the auditory ossicles is thus influenced by the stapedial tendon. The hitching member can be formed of a flexible filament or a relatively inflexible material.