Introduction 19 1 Cochlear Baha® (Cochlear Bone Anchored Solutions AG, Mölnlycke, Sweden) processor have decreased in size while simultaneously maintaining maximal power output and increasing the fitting range from 45db SNHL to 55 dB SNHL. The footprint of this processor decreased from 30x21x12mm 11.6g in the Baha® 4 to 26x19x12mm 11.5g in the Baha®6. Audiological benefit Audiological gain is not an ideal parameter when comparing different BCHDs. Some authors prefer to use aided hearing thresholds as a better parameter for comparison. A literature review shows there is little consensus on this topic. In 2019, Snik et al undertook meta-analysis of published data and found that the gain was 10dB higher in the Baha®5 sound processor when compared to the Ponto 3 sound processor [69]. Snik et al concluded that this difference in gain was due to the maximal power output being 9 dB higher in the Baha® 5. Interestingly there was no significant difference between these two processors' word recognition scores presented at 65 dB SPL [70]. Transcutaneous Processors Transcutaneous devices provide sound transmission through intact skin to remove the skin complication created by a skin penetrating abutment. First developed in 1986 by Hough et al [71] these systems are comprised of two components. An implanted fixture which is implanted into the temporal bone to which a magnet is attached. The overlying skin is closed. An external processor with an external magnet is then connected to allow for transmission of either vibration stimuli or digital information. Although Hough’s initial system the Xomed Audiant was eventually withdrawn from the market due to high retention pressures combined with insufficient amplification, the concept remained viable and new systems were brought to market in 2013. In the modern setting, transcutaneous systems are available in two categories; • The vibrating mass transducer is implanted under the skin and signals sent via electromagnetic induction from the external processor to it (active device) • The transducer is placed externally, and the vibration is transmitted through the intact skin and soft tissue (passive device). These options minimise skin complications caused by a skin penetrating abutment. However, the retention forces of the magnets required to stabilise them on the skin surface can cause pain and irritation. Up to 38% of the adult population reported skin numbness, pain or discomfort in the first 6 months after implantation [72] and there are reported cases of skin necrosis from this type of device [73]. A similar rate of skin irritation has been reported in paediatric populations (16%) [74].
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