Round window insertion of precurved perimodiolar electrode arrays: how successful is it?

Hypothesis: The goal of this human temporal bone study was to assess the safety and efficacy of round window insertion of the Cochlear Contour Advance electrode and identify any anatomic obstacles that may affect its insertion.
Background: Minimizing intracochlear trauma during electrode insertion reduces the risk of losing residual hearing. The Contour Advance electrode is designed for insertion via an anteroinferior cochleostomy, in which drilling causes a degree of inner ear trauma. If consistently successful round window insertions are possible with this electrode, it would allow for better perimodiolar positioning in the basal turn and greater likelihood of hearing preservation.
Methods: A total of 16 human temporal bone round window insertions with the Contour Advance electrode were performed at the University of Melbourne and Southwestern Medical Center, Dallas. Surgeons' observations, fluoroscopy, histology and anatomic dissections were analyzed.
Results: Successful full insertions of the electrode with minimal resistance and good perimodiolar placement were achieved in less that 50% of cases in the Melbourne series and in two-thirds of cases in the Dallas series. A common finding by both centers was obstruction of electrode entry at the anteroinferior margin of the round window, which prevented optimal scala tympani positioning and often resulted in intracochlear trauma.
Conclusion: The anteroinferior region of the round window bony margin influences the trajectory of insertion of the relatively large Contour Advance electrode as well as physically obstructing and distorting the array. A pure round window insertion is not predictable and reliable enough to be a recommended approach for this electrode.