Audiological outcome of the pull-back technique in cochlear implantees

The distance of the cochlear implant electrode contacts to the modiolus can be reduced by a surgical technique called "pull-back." This procedure changes the location of the fully inserted electrode array by moving the electrode out of the cochlea until the first silicon ring is visible in the cochleostomy. This leads to a more focused stimulation, which in turn could possibly improve hearing performance. The objective of the present study was to investigate the influence of the pull-back technique on frequency difference limens (FDL) and speech perception.

Double-blind trial.

Twelve pull-back and 12 matched controls (matched by age, gender, duration of deafness, and duration of implant use) were used. Twenty-four patients were implanted with the Nucleus-24 Contour Advance array. In 12 patients the pull-back technique was used and in 12 matched controls a standard insertion technique was applied. Twelve months after the initial stimulation speech perception, spread of neuronal excitation (SOE) at electrodes 5, 10, and 15; and FDLs at 1, 2, and 4 kHz were measured.

There was no significant difference of speech perception performance between the two groups. However, the mean FDL for the 4 kHz reference tone was significantly lower in the pull-back group compared to the controls. The SOE was significantly reduced at basal, middle, and apical electrodes in the electrode pull-back group.

The pull-back technique seems to have its greatest effect on perimodiolar position in the basal regions of the cochlea. Therefore, it is most likely to observe improved FDL in the 4 kHz region. Current speech recognition tests do not reflect the lower FDL.