Development of patient-specific drug-releasing round window implants for the treatment of inner ear diseases

Motivation The modern therapy of inner ear disorders is increasingly being determined by pharmacological therapies. Local drug delivery to the inner ear is very challenging but superior to systemic treatment due to reduction of side effects. Access to the inner ear is usually found via the round window membrane (RWM). The RWM is located in the bony round window niche (RWN), which allows local deposition of drugs. For safe and controlled drug delivery via the RWN optimal fitted implants with optimally drug loading designed for the individual shape of the niche have to be developed.

Material/Methods Cone beam computed tomography (CBCT) images of 50 patients were analyzed. Based on the reconstructed 3D volumes, the individual anatomical structures of the RWN of the patients were determined by segmentation using 3D slicer^TM. A custom build plug-in was used, which allows the determination of the midmodiolar axis by fitting a mean model of the scala tympani and the scala vestibuli in the CBCT-data. This allowed defining a coordinate system relative to the cochlear. The segmentation-data were transformed into voxel data and the diameter and volume of the individual RWN as well as the RWM area and the bony overhang length were measured.

Results A large individual anatomical variability of the RWN with a mean volume of 4.54 mm³ (min 2.28mm³, max 6.64mm³) was detected. The area of the RWM ranged from 1.30mm² to 4.39mm² (mean: 2.93mm²). The bony overhang had a mean length of 0.56mm (min 0.04mm, max 1.24mm). No sex specific or age related differences were observed and no intra-individual variances were detected.

Conclusion Our data prove that there is a need for individually shaped RWN implants due to clinically relevant differences in the volume and shape of the niche.

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Publication History

Article published online:
10 June 2020