76 Chapter 5 intervention was nipple necrosis (65.6%). Nipple necrosis occurred significantly more often in the implant loss group compared with the group without implant loss, supporting that a nipple-preserving procedure is a significant risk factor. A risk model for implant loss was created based on four of the risk factors found in this study (obesity, active smoking, a nipple-preserving procedure, and a DTI approach). This risk model showed the direct relationship between the number of risk factors present and the predicted risk of implant loss. The predicted risk in the presence of one risk factor was 8.4%–13.0%, which increased to 21.9%–32.5% in the presence of two risk factors. In the case of three risk factors, the predicted risk was 47.5%–59.3%, which increased to more than 78.2% in the presence of four risk factors. For example, the calculated predicted risk of implant loss was 21.9%–32.5% in a patient with obesity and active smoking status. Based on our risk model, a nipple-preserving mastectomy or a DTI approach is not recommended in this patient because of the increased risk of implant loss of 47.5% to over 78.2% if both procedures were to be performed. Our recommendation would be to not exceed these two risk factors if they are already present in a patient; rather, to choose a safer skin-sparing mastectomy technique with a two-stage reconstruction. These findings would help patients to make informed decisions and could be used to decrease the risk of implant extrusion through personalized therapy. A total of nine oncological surgeons were included in this study, and their contribution to the number of surgical procedures varied widely. A significantly higher risk of implant loss was observed when the surgeon had performed fewer than 50 procedures in four years. It is hypothesized that this may be caused by the quality of the mastectomy flaps, which may be affected by the expertise of the surgeon. However, information on the quality of the skin flaps is absent in this study. Radiotherapy is commonly described in the literature as a risk factor for implant loss.8, 14 However, the risk of radiotherapy on implant loss was not observed in this study. A reason for this might be the retrospective design of the study, thereby lacking accurate data on the amount and timing of radiotherapy. Therefore, the correlation between the exact timing of radiotherapy and implant loss could not be examined. Furthermore, diabetes mellitus and hypertension were found to be predictors for implant loss, but due to the small number of patients (<10% of the total), they could not be interpreted as significant risk factors even though hypertension is a risk factor supported by the literature.16 This study has several limitations. The first limitation is that the data were obtained from only two medical centers with overlapping plastic surgeons and may therefore not be generalizable to the reconstructive population at large. The
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