RESPONSE TO LETTER TO THE EDITOR REGARDING: HEARING DEVICE COIL PLACEMENT LATERAL TO THE TEMPORALIS: AN ALTERNATIVE TO FLAP THINNING FOR COCHLEAR AND TRANSCUTANEOUS BONE-ANCHORED IMPLANTS

RESPONSE TO LETTER We are grateful to Ozturan et al. for their interest and comments on our study (1). The primary objective in this study was to provide a video illustration of the surgical technique for placing both bone conduction and cochlear implants lateral to the temporalis in patients with thicker scalps who are at risk for poor processor coupling. This issue is increasingly relevant given the growing obesity epidemic, combined with the use of internal diametric device magnets that often have poorer retention (2). Ozturan et al. (3) have previously published on this topic with respect to the placement of cochlear implants lateral to the temporalis fascia, particularly in patients with elevated body mass indices. We agree with this technique, and believe that the surgical video complements the technique put forth by Ozturan et al. We also believe this technique can be applied to bone-anchored implants, as discussed in our study (1). Since the publication of our study, we have longer-term outcomes of this technique that may be relevant to the reader. Since 2017, we have identified four active transcutaneous bone-anchored implant (Cochlear Osia and Med-EL Bonebridge) device failures in three patients, requiring revision surgery and implant replacement. All of these failures were identified within 3 years of initial implantation. Three devices in this group were placed lateral to the temporalis, and one was placed in a traditional subperiosteal pocket. The device failure pattern was similar in all cases; specifically, sound and connectivity intermittency were reported by patients and confirmed on physician and audiology examination. In all cases, manufacturer device testing following explantation demonstrated damage to the internal device wires consistent with “bending stress” or “chronic implant movement.” Notably, in these four cases, there was no significant bend required between the transducer and the coil portions of the internal device for placement. While conjecture, it is possible that the internal device wiring at the implant waist was impacted by movement of the temporalis muscle or a more mobile interfascial pocket; although it is notable that one implant was in a subperiosteal pocket and still encountered a similar issue. While speculative, it is possible that the transcutaneous bone conduction implants are more vulnerable to chronic movement when compared to cochlear implants for two reasons: 1) bone-anchored implants are fixed to bone in one location, putting more stress on the implant waist with movement of the mobile portion of the device; and 2) cochlear implants do not have a narrow waist region and are generally less flexible, which may offer more support for internal wiring. In other words, it is possible that the flexibility of the transcutaneous bone conduction implant systems around the waist region, created to facilitate device placement, introduces susceptibility to wire breakage if exposed to chronic repetitive movement from temporalis muscle contraction, wearing a hat, or other mechanisms. Though these device failures have been uncommon at our institution, we believe it to be important to report these to identify potential patterns and mitigate risks. Of course, further study and trends are required to validate any hypotheses regarding the causality of these device failures. In summary, we agree with Ozturan et al. that placement of cochlear implants and bone conduction implants lateral to the temporalis fascia can address processor retention issues as well as reduce the risks associated with skin flap thinning. There may be device functionality implications related to device placement (e.g., lateral to temporalis) in the long run particularly for current transcutaneous bone conduction implant systems; however, this remains to be determined. Ashley M. Nassiri Department of Otolaryngology–Head and Neck Surgery, University of Colorado School of Medicine, Aurora, COCynthia A. HoganMatthew L. Carlson Department of Otolaryngology–Head and Neck Surgery, Mayo Clinic, Rochester, MN [email protected]