Intra-operative measurements of the stapedius reflex via EMG – A feasibility clinical study

Introduction The potential development of a smart autonomous cochlear implant (CI) would greatly depend on a reliable and objective fitting methodology. One promising approach is the intra-muscular recording of electromyographic (EMG) signals within the stapedius muscle (SM) for detecting the stapedius reflex (SR).

Material & Methods A clinical study was set up in Jena and Tübingen, to assess SR-related EMG responses in 7 single-sided CI-patients. During standard CI implantation surgery an EMG electrode is placed on the stapedius muscle (SM) belly. Elicitation of the reflex is done via both contralateral acoustic stimulation (via tympanometer) and ipsilateral electrical stimulation (via the CI). The contraction of the SM is assessed to determine whether a SR is detectable visually and/or via EMG recordings. Electrodes are placed in the SM using either a retrofacial approach, or from the pyramidal eminence, according to individual anatomy and pre-operative planning.

Results The muscle was accessed via retrofacial approach on 5/7 and via anterior approach on 3/7 patients (on 1/7 both approaches were performed).SR EMG was successfully recorded in 5/7. Offline signal processing was used to remove stimulation artefacts. Data analysis showed a correlation between the SR EMG signal and the visual detection of the SR at the level of the stapedius tendon of 0.95. The EMG signal was detected even before the visual confirmation in 33% of the assessed cases.

Conclusion Our results confirmed that it is possible to reliably record SR-related EMG signals intraoperatively. The methodology for accessing the SM and subsequent electrode placement was found safe and effective, following an imaging-based pre-operative evaluation.

Publication History

Article published online:
24 May 2022