Interobserver agreement of coiling of Med-El cochlear implant: plain x-ray studies

The objective of this study was to describe the interobserver agreement of otologists in judging the extent of cochlear electrode insertion as depicted in plain radiographs done in various projections relative to that of Stenvers (45 degrees from midline).

Ten experienced U.S. MED-EL cochlear implant surgeons, unaware of the image history, judged depths of electrode coiling in 12 images.

In a bequeathed cranial base specimen, a standard MED-EL Combi 40+ electrode was inserted 3 mm less than fully and stabilized. With a custom cephalostat, the specimen was positioned in the Frankfort horizontal plane. Plain radiographs were made in six projections in 15 degrees increments, from posterior-anterior to near lateral. After the electrode array was withdrawn 5 mm and stabilized, six additional radiographs were similarly taken.

Greater variability of assessed coiling was associated with projections other than Stenvers. The coefficient of variation for the Stenvers projection was significantly less than half that of the anterior-posterior and the other projections studied.

In plain radiographic assessment of the degree of coiling of the MED-EL electrode, interobserver agreement was best for the Stenvers view.