Impact of Scala Tympani Geometry on Insertion Forces during Implantation

(1) Background: During a cochlear implant insertion, the mechanical trauma can cause residual hearing loss in up to half of implantations. The forces on the cochlea during the insertion can lead to this mechanical trauma but can be highly variable between subjects which is thought to be due to diffe...

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Bibliographic Details
Published in:	Biosensors (Basel) Vol. 12; no. 11; p. 999
Main Authors:	Hrncirik, Filip, Roberts, Iwan V, Swords, Chloe, Christopher, Peter J, Chhabu, Akil, Gee, Andrew H, Bance, Manohar L
Format:	Journal Article
Language:	English
Published:	Switzerland MDPI AG 01-11-2022 MDPI
Subjects:	3D printing Acoustics Care and treatment Cochlea Cochlea - anatomy & histology Cochlea - surgery cochlear implant Cochlear Implantation - methods Cochlear Implants Curvature Data acquisition Depression, Mental Diagnosis Electrodes Geometry Health aspects Hearing loss Humans Insertion insertion forces Mathematical models Mechanical Phenomena micro-CT Parameters Patients Prevention Risk factors scala tympani Scala Tympani - surgery Three dimensional models Three dimensional printing Transplants & implants Trauma United Kingdom cochlear implant micro-CT scala tympani insertion forces 3D printing
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Summary:	(1) Background: During a cochlear implant insertion, the mechanical trauma can cause residual hearing loss in up to half of implantations. The forces on the cochlea during the insertion can lead to this mechanical trauma but can be highly variable between subjects which is thought to be due to differing anatomy, namely of the scala tympani. This study presents a systematic investigation of the influence of different geometrical parameters of the scala tympani on the cochlear implant insertion force. The influence of these parameters on the insertion forces were determined by testing the forces within 3D-printed, optically transparent models of the scala tympani with geometric alterations. (2) Methods: Three-dimensional segmentations of the cochlea were characterised using a custom MATLAB script which parametrised the scala tympani model, procedurally altered the key shape parameters (e.g., the volume, vertical trajectory, curvature, and cross-sectional area), and generated 3D printable models that were printed using a digital light processing 3D printer. The printed models were then attached to a custom insertion setup that measured the insertion forces on the cochlear implant and the scala tympani model during a controlled robotic insertion. (3) Results: It was determined that the insertion force is largely unaffected by the overall size, curvature, vertical trajectory, and cross-sectional area once the forces were normalised to an angular insertion depth. A Capstan-based model of the CI insertion forces was developed and matched well to the data acquired. (4) Conclusion: By using accurate 3D-printed models of the scala tympani with geometrical alterations, it was possible to demonstrate the insensitivity of the insertion forces to the size and shape of the scala tympani, after controlling for the angular insertion depth. This supports the Capstan model of the cochlear implant insertion force which predicts an exponential growth of the frictional force with an angular insertion depth. This concludes that the angular insertion depth, rather than the length of the CI inserted, should be the major consideration when evaluating the insertion force and associated mechanical trauma caused by cochlear implant insertion.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 These authors contributed equally to this work.
ISSN:	2079-6374 2079-6374
DOI:	10.3390/bios12110999