Influence of the thickness of the skin and subcutaneous tissue covering the mastoid on bone-conduction thresholds obtained transcutaneously versus percutaneously.

Percutaneous and transcutaneous bone-conduction thresholds were obtained at 0.25, 0.5, 1, 2, and 4 kHz in 57 patients who were fitted with the Bone Anchored Hearing Aid (BAHA). Additionally, the thickness of the skin and subcutaneous tissue covering the mastoid was determined. No relation was found between the thickness of the skin and subcutaneous tissue, and the improvement in bone-conduction thresholds at any of the frequencies, i.e. thresholds obtained percutaneously minus transcutaneously. The improvement (or deterioration) in speech recognition with the BAHA in a subgroup of patients who had previously used a (conventional) transcutaneous bone-conduction hearing aid was not related to the thickness of the skin and subcutaneous tissue layers. Therefore, the thickness of the skin and subcutaneous tissue layers measured pre-operatively cannot be used as a predictor of successful fitting with a BAHA.