Individual difference in pectoralis major muscle thickness and its effect on single-stage breast reconstruction using a tissue expander

In breast reconstruction using a tissue expander (TE), sufficient coverage of the TE with the pectoralis major (PM) muscle, particularly with a musculofascial flap, is highly important for avoiding postoperative complications. In patients in whom the PM is thin, intraoperative trauma often occurs, leading to troublesome repair. The present study aimed to investigate the usefulness of preoperative measurement of PM thickness in planning of breast reconstruction using a TE. In this case-control study, we identified 68 patients (70 breasts) with mammary carcinoma treated with simple mastectomy and TE insertion from April 2014 to December 2016. We measured average PM thickness at two specific points, sternocostal PM distance on the long axis and sternocostal PM area preoperatively using magnetic resonance imaging. Then, we analyzed the difference in PM thickness among individuals and its relationship to intraoperative trauma to the PM or surgical difficulty creating a muscular pocket (delicate PM). Average PM thickness was significantly larger in younger patients (p = 0.046) and those with larger breasts (p < 0.01). In addition, average PM thickness on the affected side was significantly smaller in patients with delicate PM (12 breasts) (p < 0.01). PM thickness had a significant influence on delicate or firm PM (odds ratio 27.40; 95% confidence interval 2.01-372.00; p = 0.013). These findings demonstrate the usefulness of preoperative measurement of PM thickness in planning of breast reconstruction using a TE. Dissection should be performed more carefully in patients with average PM thickness less than 2.9 mm.