Risk Factors for Step-off Deformity of the Donor Site Following Abdominal Flap-based Breast Reconstruction

Background: Step-off deformity is a suboptimal aesthetic outcome at the donor site following abdominal flap harvesting for breast reconstruction. This study assessed the prevalence of step-off deformities post-autologous breast reconstruction and explored the associated risk factors. Methods: This retrospective study evaluated step-off deformities among consecutive patients who had undergone autologous abdominal flap-based breast reconstruction between January 2019 and December 2022. The postoperative evaluation utilized medical records and photos, defining step-off deformity as a thickness discrepancy in the upper and lower abdominal tissue with reference to the scar line and angles <165°. Moreover, we explored potential risk factors, including abdominal subcutaneous tissue thickness based on computed tomography. Results: In total, 187 patients underwent abdominal flap-based breast reconstruction; 38 exhibited step-off deformity. The case group exhibited significantly higher body mass index (BMI) and greater subcutaneous layer thickness in both the upper and lower abdomen compared to those of the control group. The groups did not differ significantly in postoperative complications, including abdominal bulging or hernia. Multivariable analysis revealed notable risk factors for step-off deformity development: BMI (p=0.026), presence of preoperative abdominal fold (p=0.028) and thickness differences between the upper and lower abdomen (p=0.011). The cut-off values were 26.1 kg/m 2 for BMI and 9.5 mm for thickness differences. Conclusions: Higher BMI, presence of abdominal fold, and significant upper-lower abdomen tissue thickness differences may be associated with an increased risk of donor step-off deformity after abdominal flap harvest. Our findings may inform patient counseling and warrant attention when closing donor wounds in high-risk individuals.