Ossiculoplasty Efficacy Monitored by ECoG-Laser-Doppler Technique

Abstract

Objective: 1) Understand changes in the acoustic conductivity of the ossicular chain reconstruction during ossiculoplasty. 2) Assess the need to change shape and positioning of the prosthesis during surgery.

Method: Six patients underwent a “second look” procedure 12 months after closed tympanoplasty. A prosthesis was positioned between the stapes plate and graft. Laser Doppler Vibrometer (LDV) was used to assess prosthesis moveability. Simultaneously round window electrocochleography (RW-ECoG) was recorded to evaluate hearing threshold. LDV and RW-ECoG were recorded following acoustic stimulation.

Results: The average value of LDV-speed at 500 Hz is 0.29 m/s (SD 0,19), at 1000 Hz is 0.16 m/s (SD 0.084), at 2000 Hz is 0.043 m/s (SD 0.026), at 4000 Hzis 0.047 m/s (SD 0.0093) and at 8000 Hz is 0.018 m/s (SD 0.0093). The prosthesis revealed a significantly higher mobility at 500 to 1000 Hz than at 2000 Hz. Ossicular movability measured on the prosthesis compared to intraoperatively measured hearing thresholds. Both techniques showed its utility in assessment of efficacy of acoustic energy transfer after ossiculoplasty, though in patients with affected bone curve, discrepancies between hearing thresholds and LDV results were observed.

Conclusion: Intraoperative assessment of amplitudes and thresholds of ossicular chain movability informs the surgeon about efficiency of the acoustic energy transfer through the reconstructed ossicular chain. LDV technique with RW-ECoG led to achievement of the optimal position and tension of reconstructed ossicles.