Scalar position characteristics and translocation rates of different lateral wall electrodes within the cochlear basal turn: a cone beam computed tomography study

Abstract

PURPOSE: This retrospective study systematically compared scalar position characteristics and translocation (STL) rates within the cochlear basal turn (CBT) across three different lateral wall (LW) electrodes. METHODS: The study included 148 morphologically normal cochleae implanted with Advanced Bionics SlimJ (ABSJ, n = 51), Cochlear Slim Straight (CSS, n = 51), or MED-EL FLEX (MFX, n = 46). Cochlear dimensions (distances A and B) and angular insertion depth (AID) were measured by two observers. Scalar position was assessed on postoperative cone-beam CT at 90°, 180°, 270°, and 360° by three observers using a five-point scale (1-2 = scala vestibuli (SV), 3 = central, 4-5 = scala tympani (ST)). RESULTS: Distances A and B were comparable across groups (p > .05). Mean AID was significantly greater for MFX (p < .001). MFX had higher median scalar scores than CSS at every angle (all Bonferroni-adjusted p < .001) and than ABSJ at 180°, 270°, and 360° (adjusted p < .001). ST retention (all four median scores ≥ 3) was observed in 92.2% of ABSJ, 78.4% of CSS, and 100% of MFX cases, while STL (median score decreased to 1-2 and remained ≤ 3) occurred in 7.8%, 15.7%, and 0%, respectively. MFX demonstrated significantly lower STL and higher ST retention rates than CSS (adjusted p = .018 and p < .003, respectively). No independent associations of distance A, distance B, or AID with either STL or ST retention were identified (all p ≥ .54). CONCLUSION: Significant differences in scalar position and STL rates were observed among LW electrodes, with MFX showing the most stable ST placement.