Insertion Depth and Cochlear Implant Speech Recognition Outcomes: A Comparative Study of 28- and 31.5-mm Lateral Wall Arrays.

Objectives: 1) To compare speech recognition outcomes between cochlear implant (CI) recipients of 28- and 31.5-mm lateral wall electrode arrays, and 2) to characterize the relationship between angular insertion depth (AID) and speech recognition.

Study Design: Retrospective review.

Setting: Tertiary academic referral center.

Patients: Seventy-five adult CI recipients of fully inserted 28-mm (n = 28) or 31.5-mm (n = 47) lateral wall arrays listening with a CI-alone device.

Interventions: Cochlear implantation with postoperative computed tomography.

Main Outcome Measures: Consonant-nucleus-consonant (CNC) word recognition assessed with the CI-alone at 12 months postactivation.

Results: The mean AID of the most apical electrode contact for the 31.5-mm array recipients was significantly deeper than the 28-mm array recipients (628° vs 571°, p < 0.001). Following 12 months of listening experience, mean CNC word scores were significantly better for recipients of 31.5-mm arrays compared with those implanted with 28-mm arrays (59.5% vs 48.3%, p = 0.004; Cohen's d = 0.70; 95% CI [0.22, 1.18]). There was a significant positive correlation between AID and CNC word scores (r = 0.372, p = 0.001), with a plateau in performance observed around 600°.

Conclusions: Cochlear implant recipients implanted with a 31.5-mm array experienced better speech recognition than those with a 28-mm array at 12 months postactivation. Deeper insertion of a lateral wall array appears to confer speech recognition benefit up to ∼600°, with a plateau in performance observed thereafter. These data provide preliminary evidence of the insertion depth necessary to optimize speech recognition outcomes for lateral wall electrode arrays among CI-alone users.