Guiding Cochlear Implant Electrode Insertion Using Impedance Measurements: A Computational Simulation Study

Intraoperative tissue trauma during cochlear implant (CI) insertion remains a primary cause of residual hearing loss. Because insertion currently relies largely on clinician experience without direct visualization within the optically obscured inner ear, real-time guidance is critical for minimizing mechanical contact with delicate anatomical structures. This study evaluates multi-channel electrical impedance for real-time trajectory tracking and boundary proximity detection during automated electrode insertion. A computational finite-element model of the human cochlea was used to analyze complex impedance profiles across eight bipolar configurations (E1–E2 to E15–E16) and 25 insertion models (M1–M25), yielding 2592 evaluations across central, medial, and lateral trajectories under varying bulk tissue conductivities. At 1kHz, reactive contributions were negligible (X<25 Ω, ϕ≤0.27°), confirming an overwhelmingly resistive response (R>2400 Ω, >99.5% of total impedance). Bulk conductivity scaled baseline impedance magnitudes without substantially altering the spatial profile geometry. Across the three insertion trajectories, impedance exhibited a characteristic U-shaped evolution, initially decreasing as the electrode array (EA) advanced toward the scala tympani (ST) center before increasing near the terminal insertion region. Boundary proximity further increased impedance variation, with mean impedance values increasing by 24–38% for the medial trajectory and 25–35% for the lateral trajectory relative to the middle baseline. Localized impedance increases were observed for the medial pair E3–E4 (65% at M20) and the lateral pair E1–E2 (88% at M23). The differential impedance profiles indicate that boundary-induced proximity effects substantially exceed baseline spatial variations, demonstrating the sensitivity of multi-channel impedance measurements to electrode–wall proximity. These findings support the potential use of impedance signatures as a real-time feedback signal for boundary proximity detection, clinician guidance, and closed-loop trajectory adjustment during automated CI insertion. Recognizing the characteristic U-shaped impedance profile and its sensitivity to boundary proximity may provide valuable intraoperative feedback for monitoring electrode-array position and reducing the risk of boundary contact and associated mechanical trauma.