Evaluation of a bone groove geometry for fixation of a cochlear implant electrode.

Electrode migration is a rare, but relevant complication in cochlear implant (CI) surgery. An effective countermeasure is to create a bone groove in the facial recess to secure the electrode lead. We use this method routinely since 2013, but still experienced sporadic electrode migration events most likely due to an improper surgical execution. The aim of this study was to determine the optimum groove geometry. Grooves of defined geometry were created in specimens of fresh porcine femur compacta by use of a CNC milling machine. Electrode dummies were fixed in the groove and then exposed to tensile stress. Force measurements were carried out to examine the effect of groove diameter and opening width on the holding force. The mechanical impact on the electrode cable during insertion into the groove was recorded and the electrode lead was examined under microscopic magnification to assess potential structural damage. Optimum groove geometry (diameter 1.10 mm, opening width 0.90 mm) ensured an average holding force of 830 mN which is equivalent to the established fixation by use of a titanium clip. None of the microscopic inspections revealed any morphological deterioration of the electrode lead. The fixation of a CI electrode in a bone groove in the facial recess appears to be effective and safe. Furthermore, this method does not require additional costs or foreign material. The optimum geometry defined in this study helped us to refine our surgical standard produce and to generate more consistent results.