Characterization of intracochlear rupture forces in fresh human cadaveric cochleae.

ABSTRACT

HYPOTHESIS: To develop a method to measure the forces required for a probe to translocate from the scala tympani (ST) to the scala vestibuli (SV) in fresh human cochleae. BACKGROUND: Translocation of cochlear implant electrodes from the ST to the SV may lead to suboptimal audiologic outcomes. Prior work investigating the rupture forces of human intracochlear membranes comes from a single study conducted on isolated ex vivo cadaveric specimens. METHODS: Fresh (postmortem <120 h), nonfixed, never-frozen human temporal bones underwent preparation consisting of surgical isolation of the cochleae and exposure of the osseous spiral lamina, basilar membrane, and Reissner's membrane complex by removing bone covering the ST and the SV. Each isolated cochlea was mounted to a force sensor using an adjustable mounting platform. A 300-µm-diameter ball-tipped probe was attached to a piezoelectric linear motor and advanced at 1 mm/s from the ST to the SV while recording force from the load cell concurrent with video. RESULTS: Ten specimens were successfully exposed and analyzed. The range of rupture forces was 42 to 122 mN, with a mean of 88 mN. Nine of the 10 specimens failed via simple puncture, whereas one failed by being avulsed from its medial attachment. CONCLUSION: Using a novel technique, we report the forces required to translocate a model of an electrode from the ST to the SV. Correlation to human perceptual ability is necessary to determine if a surgeon can detect such translocation during cochlear implant surgery.