Percutaneous vs. transcutaneous transducers for hearing by direct bone conduction.

There is a substantial need for improvement of the hearing situation for patients, with chronic middle ear or ear canal disorders. To improve hearing for these patients, two different bone conduction hearing systems have been developed. The Nobelpharma Auditory System HC 200-the bone-anchored hearing aid we present here-uses a percutaneous transducer; whereas the Audiant device, developed by Dr. Jack Hough, uses a transcutaneous transducer. In percutaneous transmission, the transducer is directly coupled to the bone by means of a permanent skin penetration, whereas in transcutaneous transmission one part of the transducer is implanted and the other part is kept outside the intact skin and soft tissue. Comprehensive audiologic assessments indicate great differences in performance between the two systems. These differences probably originate in differences in length of gap and in different suspension properties of the two transducer systems. This article will demonstrate that large gaps, such as in the transcutaneous transducer, can be devastating for power consumption, maximum output capability, and second harmonic distortion. Since the properties of the suspension in the transcutaneous transducer are not under adequate control and the complication risk of permanent skin penetration is low, we continue to concentrate our efforts on percutaneous transducer systems.