A self-adjusting ossicular prosthesis containing polyurethane sponge.

Hypothesis: Middle ear ossicular replacement prostheses whose length can adjust in vivo to changes in middle ear dimensions following insertion may have acoustic advantages.

Background: Optimal tension is an important factor in the acoustic performance of incus-stapes replacement prostheses. Length is the primary determinant of postinsertion tension with conventional prostheses. Postoperative changes in prosthesis tension may occur leading to a worsening of postoperative hearing.

Methods: Testing of a self-adjusting prosthesis (SAP) containing a polyurethane sponge attached to the head of a titanium partial ossicular replacement prosthesis (PORP) was performed in 5 fresh temporal bones. This SAP was compared with optimal length PORPs at different tensions. Sound input was 80 dB sound pressure level at 0.1 to 10 kHz. Stapes footplate displacement was measured using a laser Doppler vibrometer before and after incus removal and after PORP and SAP insertion between the malleus and stapes. One to 3 glass shims were then inserted between the malleus and optimal length PORP and SAP to change prosthesis tension. Measurement of stapes displacement was repeated with increased prosthesis lengths of 0.15, 0.30, and 0.45 mm.

Results: There was a clear tendency in the optimal length PORPs for a decrease in footplate displacement below 1.0 kHz, in general proportional to the increasing length. The SAP provided equivalent transmission as the optimal length PORP below 4.0 kHz and better transmission below 1.0 kHz at the varying increased lengths.

Conclusion: An SAP seems to decrease the effect of changes in prosthesis length between the malleus and stapes at lower frequencies.