Function, Applicability, and Properties of a Novel Flexible Total Ossicular Replacement Prosthesis With a Silicone Coated Ball and Socket Joint

Partial Ossicular Reconstruction With a Novel Ball Joint Prosthesis: The mCLIP ARC Partial Prosthesis

OBJECTIVE

Middle ear surgery involves reconstruction of the ossicular chain, predominately using rigid implants. New middle ear prostheses strive to mimic the physiologic micromovements of the ossicular chain and prevent dislocation, protrusion, and preloading of the annular ligament due to pressure fluctuations.

METHODS

Thirty-five patients were included in a monocentric, prospective observational study. Patients received tympanoplasty with ossicular reconstruction using the mCLIP ARC partial prosthesis. This titanium prosthesis is equipped with a clip mechanism for coupling at the stapes and a ball joint connecting headplate and shaft. At short-term (ST) and mid-term (MT) follow-up, pure-tone audiometry was performed and the pure tone average of 0.5, 1, 2, and 3 kHz (PTA4) was calculated. The audiological outcome was compared with retrospective data of the Dresden titanium clip prosthesis.

RESULTS

The new prosthesis shows favorable clinical results. Pure-tone audiometry showed satisfactory results in ST and MT follow-up, with the PTA4 air-bone gap (ABG) decreasing from 24.5 (±11) dB to 17.4 (±7.9) dB at the ST follow-up at 27 days to 15.6 (±10.3) dB at MT follow-up at 196 days (n = 32). A PTA4-ABG value of less than 20 dB was achieved by 63% of patients at ST follow-up and by 77% at MT follow-up. There was no significant difference in PTA4 ABG compared to the Dresden titanium clip prosthesis during ST follow-up (p = 0.18).

CONCLUSION

The mCLIP ARC partial prosthesis, a new middle ear prosthesis with a balanced ball joint, shows promising audiological results and is a safe and effective choice for patients with chronic ear disease.

LEVEL OF EVIDENCE

3 Laryngoscope, 134:3323-3328, 2024.

Effects of preloads on middle-ear transfer function and acoustic reflex in ossiculoplasty with PORP

INTRODUCTION

Surgical outcomes in ossiculoplasty with partial ossicular replacement prostheses (PORPs) are greatly influenced by the amount of preload imposed on the PORP. In this study, the attenuation of the middle-ear transfer function (METF) was experimentally investigated for prosthesis-related preloads in different directions, with and without concurrent application of stapedial muscle tension. Different PORP designs were assessed to determine functional benefits of specific design features under preload conditions.

METHODS

The experiments were performed on fresh-frozen human cadaveric temporal bones. The effect of preloads along different directions were experimentally assessed by simulating anatomical variance and postoperative position changes in a controlled setup. The assessments were performed for three different PORP designs featuring either a fixed shaft or ball joint and a Bell-type or Clip-interface. Further, the combined effect of the preloads towards the medial direction with tensional forces of the stapedial muscle was assessed. The METF was obtained via laser-Doppler vibrometry for each measurement condition.

RESULTS

The preloads as well as the stapedial muscle tension primarily attenuated the METF between 0.5 and 4 kHz. The largest attenuations resulted from the preload towards the medial direction. The attenuation of the METF with stapedial muscle tension was reduced with concurrent PORP preloads. PORPs with a ball joint resulted in reduced attenuation only for preloads along the long axis of the stapes footplate. In contrast to the clip interface, the Bell-type interface was prone to lose coupling with the stapes head for preloads in the medial direction.

CONCLUSIONS

The experimental study of the preload effects indicates a direction-dependent attenuation of the METF, with the most pronounced effects resulting from preloads towards the medial direction. Based on the obtained results, the ball joint offers tolerance for angular positioning while the clip interface prevents PORP dislocations for preloads in lateral direction. At high preloads, the attenuation of the METF with stapedial muscle tension is reduced, which should be considered for the interpretation of postoperative acoustic reflex tests.

A Partial Ossicular Replacement Prosthesis With a Concentric Ball Joint in the Headplate

OBJECTIVE

In passive middle ear prosthetics, rigid implants have proven successful in reconstructing the ossicular chain. However, these cannot fully replicate the physiology of the ossicular chain. Pressure fluctuations cause high stresses in rigid passive prostheses, which can result in dislocation, protrusion, and pre-tension in the annular ligament resulting in unsatisfactory hearing results.

METHODS

In collaboration with MED-EL, we developed a new passive middle ear prosthesis that features a balanced, centered ball joint between the headplate and shaft of the prosthesis. We compared the sound transmission properties of this new prosthesis with those of a standard rigid prosthesis. Using Laser-Doppler-Vibrometry, we measured the sound-induced velocity of the stapes footplate relative to a given acoustic stimulus.

RESULTS

The new prosthesis showed equivalent sound transmission characteristics compared to the rigid prosthesis, whereas retaining the ability to compensate for pressure fluctuations due to its ball joint. This ensures good transmission properties even during displacements of the tympanic membrane.

CONCLUSION

This development is a further step toward a physiological reconstruction of the ossicular chain.

LEVEL OF EVIDENCE

N/A Laryngoscope, 2022.

Mimicking the Human Tympanic Membrane: The Significance of Scaffold Geometry

The human tympanic membrane (TM) captures sound waves from the environment and transforms them into mechanical motion. The successful transmission of these acoustic vibrations is attributed to the unique architecture of the TM. However, a limited knowledge is available on the contribution of its discrete anatomical features, which is important for fabricating functional TM replacements. This work synergizes theoretical and experimental approaches toward understanding the significance of geometry in tissue-engineered TM scaffolds. Three test designs along with a plain control are chosen to decouple some of the dominant structural elements, such as the radial and circumferential alignment of the collagen fibrils. In silico models suggest a geometrical dependency of their mechanical and acoustical responses, where the presence of radially aligned fibers is observed to have a more prominent effect compared to their circumferential counterparts. Following which, a hybrid fabrication strategy combining electrospinning and additive manufacturing has been optimized to manufacture biomimetic scaffolds within the dimensions of the native TM. The experimental characterizations conducted using macroindentation and laser Doppler vibrometry corroborate the computational findings. Finally, biological studies with human dermal fibroblasts and human mesenchymal stromal cells reveal a favorable influence of scaffold hierarchy on cellular alignment and subsequent collagen deposition.

Contribution of the flexible incudo-malleal joint to middle-ear sound transmission under static pressure loads

The incudo-malleal joint (IMJ) in the human middle ear is a true diarthrodial joint and it has been known that the flexibility of this joint does not contribute to better middle-ear sound transmission. Previous studies have proposed that a gliding motion between the malleus and the incus at this joint prevents the transmission of large displacements of the malleus to the incus and stapes and thus contributes to the protection of the inner ear as an immediate response against large static pressure changes. However, dynamic behavior of this joint under static pressure changes has not been fully revealed. In this study, effects of the flexibility of the IMJ on middle-ear sound transmission under static pressure difference between the middle-ear cavity and the environment were investigated. Experiments were performed in human cadaveric temporal bones with static pressures in the range of +/- 2 kPa being applied to the ear canal (relative to middle-ear cavity). Vibrational motions of the umbo and the stapes footplate center in response to acoustic stimulation (0.2-8 kHz) were measured using a 3D-Laser Doppler vibrometer for (1) the natural IMJ and (2) the IMJ with experimentally-reduced flexibility. With the natural condition of the IMJ, vibrations of the umbo and the stapes footplate center under static pressure loads were attenuated at low frequencies below the middle-ear resonance frequency as observed in previous studies. After the flexibility of the IMJ was reduced, additional attenuations of vibrational motion were observed for the umbo under positive static pressures in the ear canal (EC) and the stapes footplate center under both positive and negative static EC pressures. The additional attenuation of vibration reached 4~7 dB for the umbo under positive static EC pressures and the stapes footplate center under negative EC pressures, and 7~11 dB for the stapes footplate center under positive EC pressures. The results of this study indicate an adaptive mechanism of the flexible IMJ in the human middle ear to changes of static EC pressure by reducing the attenuation of the middle-ear sound transmission. Such results are expected to be used for diagnosis of the IMJ stiffening and to be applied to design of middle-ear prostheses.

[Coupling of active middle ear implants-biomechanical aspects]

Active middle ear implants or implantable hearing aids are used to treat sensorineural or combined hearing loss. Their coupling to the middle ear structures has a large impact on the success of rehabilitation. Practical issues such as the coupling site, influence of middle ear status, and forward and backward excitation of the inner ear are discussed in the context of biomechanics. For this purpose, experimental studies, model simulations, and current literature data are evaluated. The explanations are intended to contribute to a better understanding of certain procedures in hearing rehabilitation with active implants.

Static and dynamic forces in the incudostapedial joint gap

Dynamic pressure at the tympanic membrane is transformed and subsequently transferred through the ossicular chain in the form of forces and moments. The forces are primarily transferred to the inner ear. They are transferred partly to the stapedial annular ligament which exhibits non-linear behavior and stiffens for larger static forces. In unventilated middle ears, static pressure is additionally transferred to the ossicles. The purpose of this study was to measure the force inside the ossicular chain as a physiological parameter. We determined the forces which act for dynamic sound transmission and for static load on the ossicular chain. The study is the first one which introduces these forces. The static forces have direct impact on clinically relevant questions for middle ear reconstructions with passive or active prosthesis. The dynamic forces have an impact on the development of middle ear sensors. Quasi-static forces in the incudostapedial joint (ISJ) gap were measured with two different sensor types in 17 temporal bones. The sensing elements, a single crystal piezo and a strain gauge element for validation, were bonded to a thin flexible titanium plate and encapsulated in a titanium housing to allow the acquisition of the applied force signal inside the ossicular chain. Dynamic forces were measured in 11 temporal bones with the piezo sensor. We measured a static force of 23 mN in the ISJ after sensor insertion. The mean force for dynamic physiological acoustic excitation from 250 Hz to 6 kHz was 26 μN/Pa. If the tympanic membrane is loaded with a static pressure, the static force in the ISJ increases up to 1 N for a maximum static pressure load scenario of 30 kPa.