A modified prosthesis head for middle ear titanium implants--experimental and first clinical results.

OBJECTIVE: An ossicular chain defect represents a challenging situation for otosurgeons. Despite modern reconstruction techniques, unsatisfying postoperative hearing results regularly occur. These are commonly caused by prosthesis dislocation. Whereas the reasons for prosthesis dysfunction occurring months or years after implantation are related to independent chronic conditions, early events of dislocations are more related to the technical fixation of the prosthesis inside the middle ear cavity. Consequently, a safe coupling between prosthesis head and tympanic membrane is essential for a successful type III tympanoplasty. Our study evaluated the use of a new prosthesis design with the aim to reduce short-term postoperative prosthesis dislocation in mind.

STUDY DESIGN: Prospective experimental and clinical study.

METHODS: A modified titanium total ossicular replacement prosthesis (TORP), whose head had spikes that extend into the cartilaginous neotympanic membrane, was designed and tested experimentally and then clinically. The lateral holding force of the new prosthesis head against lateral shift was measured and compared with common prosthesis heads without spikes. After proving this design experimentally, the prostheses were used intraoperatively in 35 tympanoplasty type III operations. Results were analyzed prospectively and compared with 35 retrospectively analyzed controls with conventional TORP prostheses.

RESULTS: The lateral holding forces for the spike prosthesis heads were significantly higher (134 mN) than those for common prosthesis heads (92 mN) at a contact pressure of 100 mN. Postoperatively, pure-tone audiometry revealed satisfying hearing results. Spiked and conventional titanium TORPs yielded postoperative air-bone gaps (ABGs) of 20.9 and 18.6 dB with 54% and 57% ABG closure, within 20 dB, respectively. The air-bone gap was reduced by an average of 14 and 15 dB, respectively. However, these differences were not statistically significant. Both in the study and in the control group, no signs of prosthesis dislocation were discovered.

CONCLUSION: The experimental data show that the new modified prosthesis head has an increased lateral holding force and thus reduces the risk of dislocation at the coupling side of the tympanic membrane. The postoperative hearing results are comparable to those of conventional prostheses. To confirm the advantage of the modified prosthesis plates over conventional prostheses, future studies with larger study populations are necessary.