## 5 Conclusions  
This multi-center data collection enabled us to compare findings across a large patient cohort in the United Kingdom over a significant time period. This enabled us to understand device reliability, the occurrence of complications, and factors that might affect events for the BB and VSB. This is the largest compiled dataset on these devices. Patient safety and device integrity are essential requirements for lifetime implantation. While advances in surgical practice and device manufacture that occur over time may improve outcomes, they cannot always counteract person-specific complications. These may occur, for example, due to low resistance to infection and inflammatory responses to implantation. We observed high survival rates for BB and VSB devices, with the majority of procedure-related or device-related issues occurring intraoperatively or in the first-month post-implantation and person-specific complications occurring over a longer time frame. The person-specific complications were most apparent for the VSB and are understandable given the complex patient group that cannot use conventional hearing aids. Both medical, audiological, and administrative support are necessary for good patient and device management. Postoperative advice to patients, particularly during the early period of activation of the device, should emphasize wound care and the importance of monitoring contact pressure from the headpiece magnet. This should be adjusted to maintain good adhesion and transmission while avoiding pain and discomfort. Staff and patients should be aware that over time, alterations in magnet strength should be expected. Factors such as postoperative oedema, skin flap thickness, and hair thickness will vary, and magnets may need to be changed accordingly. Empowering the patient to maintain the good function of their device by giving training on self-monitoring of the device can promote both best use and prompt and appropriate requests for clinical support, thus helping to avoid gradual deterioration of performance. Given appropriate support infrastructure from the implanting service, these devices offer a safe and effective treatment for a range of hearing impairments with a low incidence of technical and surgical complications. However, the importance of planning and resourcing for long-term care and the proper counseling of candidates cannot be overemphasized. VSB and BB are safe and effective devices that meet the needs of a group of patients not easily met by conventional hearing aids. Conceptualization, D.V., J.B., R.A., M.B., J.T., S.C., P.S., H.G., T.N., A.A., M.C., A.S., R.G., F.R., T.W. and S.S.; Methodology, D.V., J.B., R.A., M.B., J.T., S.C., P.S., H.G., T.N., A.A., M.C., A.S., R.G., F.R., T.W., L.K. and S.S.; Formal analysis, D.V. and W.L. ; Investigation, R.A., M.B., J.T., S.C., P.S., H.G., T.N., A.A., S.E., M.C., A.S., R.G., F.R., T.W., L.K. and S.S.; Data curation, D.V., J.B. and S.E. ; Writing--original draft, D.V. and J.B.; Writing--review & editing, R.A., M.B., J.T., S.C., P.S., H.G., T.N., A.A., S.E., M.C., A.S., R.G., F.R., T.W., L.K. and S.S.; Visualization, D.V. and W.L. All authors have read and agreed to the published version of the manuscript. [PERSON] would like to acknowledge support from a Medical Research Council (MRC) UK Senior Fellowship (MR/S002537/1), a research grant from MED-EL to support data entry, National Institute of Health Research (NIHR) Program Grant for Applied Research (201608) and Biomedical Research Centre (203312). The views expressed are those of the author(s) and not necessarily those of the MRC, NIHR or the Department of Health and Social Care. **Informed Consent Statement:** Informed consent was obtained for all participants in the prospective arm of the study. For those in the retrospective arm each research and development board at each clinical site determined if patients should be contacted for consent of data in medical notes and where appropriate this was sought prior to data collection.