Prepectoral Versus Retropectoral Implant-Based Breast Reconstruction—Considerations Regarding the Implant Pocket

Background/Objectives: Prepectoral implant positioning has become an established option for implant-based breast reconstruction (IBBR) following a mastectomy. The impact of the implant position on the selected implant pocket thickness and the presence of residual fibroglandular breast tissue (RFGT) has yet to be determined. Methods: Patients following an IBBR between 2013 and 2017 at the Department of Obstetrics and Gynecology, Medical University of Vienna, Austria, and with an available archived breast MRI were identified through a retrospective chart review. Breast MRIs were reevaluated using Osirix. Results: A total of 14 patients (23 breasts) with prepectoral and 30 patients (45 breasts) with retropectoral breast implants were included. A reduction in the postoperative skin and subcutaneous tissue thickness compared to preoperative measurements was found in both cohorts, reaching statistical significance in the prepectoral subgroup (medially p = 0.001, laterally p = 0.044). Significantly higher RFGT volumes were present in the prepectoral compared to the retropectoral cohort (p = 0.026). This difference remained significant after accounting for unevenly distributed subgroup characteristics. In the retropectoral cohort, a significant reduction in the postoperative compared to preoperative thickness of the pectoralis major muscle (PMM) was observed (p < 0.001). The PMM only accounted for 30% of the implant pocket covering the breast implant. Conclusions: Prepectoral IBBR was associated with higher volumes of RFGT and a significant reduction in postoperative skin and subcutaneous tissue thickness compared with retropectoral reconstruction. These findings suggest that implant position may influence the quality of the implant pocket and underscore the importance of careful surgical planning and meticulous dissection. Further studies are warranted to determine the clinical significance of these findings with regard to oncologic and reconstructive outcomes. In retropectoral reconstruction, marked postoperative atrophy of the PMM was observed, raising questions about the long-term advantages of this reconstructive approach.