Hearing Preservation as a Function of Angular Insertion Depth With Manual Versus Robotic-Assisted Insertion Techniques

OBJECTIVE: This study reviewed the early shifts in low-frequency hearing for cochlear implant (CI) hearing preservation candidates who underwent cochlear implantation using either manual or robotic-assisted insertion of the electrode array and evaluated possible contributing factors such as angular insertion depth (AID), preoperative hearing, and age. PATIENTS: Adult CI hearing preservation candidates (≥18 yr, ≤70 dB HL at 250 Hz) who underwent cochlear implantation with a straight electrode array through a manual or robotic-assisted insertion. MAIN OUTCOME MEASURES: A low-frequency pure tone average (125, 250, and 500 Hz) was calculated from the unaided thresholds obtained preoperatively and within the initial weeks following surgery. Queried data included impedance values measured intraoperatively and at CI activation, and the AID of the most apical electrode contact. RESULTS: Of 120 cases (66 females), 92 underwent manual insertion (median age = 69.0 yrs, interquartile range = 63.5 to 79.0) and 28 underwent robotic-assisted insertion (median age = 67.0 yrs, interquartile range = 60.9 to 76.3). Patients received either a 23, 24, 26, 28, or 31.5 mm electrode array. Significantly less low-frequency pure tone average shift was observed for robotic-assisted insertions (P = 0.028), shallower AIDs (P = 0.010), and younger patients (P = 0.001). There was a significant interaction between insertion group and AID (P = 0.010), with robotic-assisted insertion demonstrating better hearing preservation at AIDs exceeding 490°. Impedance values did not differ significantly between insertion groups intraoperatively or at CI activation. CONCLUSIONS: Robotic-assisted electrode array insertion may support better early hearing preservation compared with manual insertions, particularly for patients with electrode arrays placed at deeper AIDs. LEVEL OF EVIDENCE: Level IV; retrospective cohort study.