Open Access

David OestreicherORCiD, Simon Tobias Winkler, Biru Zhang, Thomas Effertz, Marc Albert Hüser, Tim Meyer, Benjamin Sackmann, Michael Lauxmann, Dirk Beutner, Nicholas Bevis

• Purpose Cartilage is widely used for tympanic membrane (TM) reconstruction, but the impact of graft position relative to the bony ear canal on middle ear mechanics remains unclear. This study examined how cartilage placement affects the middle ear transfer function (METF) and TM vibration. Methods Single‑point Laser Doppler Vibrometry (LDV) was performed on five fresh frozen human temporal bones before and after creating a 2.5 mm perforation in the posterior inferior TM quadrant and after reconstruction with a round-shaped cartilage graft of 4 mm diameter and 0.5 mm thickness placed either on (on‑bony) or separated from (off‑bony) the bony ear canal. TM motion was further assessed using a scanning LDV in a technical membrane model. A validated finite element (FE) model of the middle ear was used to replicate temporal bone measurements and the effect of an experimentally opened versus closed tympanic cavity, representing the in-vivo condition in patients, was evaluated by FE modelling. Results After TM perforation, the METF significantly decreased between 562 – 2094 Hz, and 2951 – 3194 Hz, while showing increased measurement variability below 500 Hz. When performing reconstruction with either the on-bony or the off-bony technique, the METFs partially recover, but show a significant difference in METF compared to the intact TM in the frequency range of 146 – 195, 200 – 217, 739 – 933 Hz (on-bony) and 146 – 295, 718 – 930, 722 – 930 and 1332 – 1719 Hz (off-bony). No significant difference in METF between the on-bony and off-bony reconstruction were found (p > 0.05). Scanning LDV analysis of a technical membrane model showed similar membrane peak velocities between the two graft positions, although the off‑bony configuration shifted the best frequency to lower values. FE simulations of the middle ear confirmed the findings of the temporal bone measurements. Additionally, the model work showed that middle ear transmission with an experimentally opened tympanic cavity differed by 2 dB after on- or off-bony reconstruction compared to a closed tympanic cavity. This was different for the perforated TM: While the transmission loss was nearly constant with an experimentally opened tympanic cavity, a closed tympanic cavity produced frequency‑dependent transmission loss exceeding 40 dB. Conclusion In this temporal bone study, placing the cartilage on the bony ear canal wall did not have an impact on the METF. FE modeling supported the temporal bone findings and suggested that similar behavior could be expected in vivo with a closed tympanic cavity. However, the FE-model suggests that perforation‑induced losses were substantially underestimated in the temporal bone measurements with an experimentally opened tympanic cavity. Positioning of the cartilage graft on the bony ear canal can be advantageous in patients with chronic middle-ear disease to reduce the risk of medialization and formation of retraction pockets without compromising the patients hearing outcome.