Anatomical Variations of the Pectoralis Muscle and Its Importance for Breast Implant Surgery

Abstract

In breast augmentation, during submuscular or dual plane dissection, anatomical variations of the inferior and costal origin of the pectoralis major muscle (PMM) play a key role to ensure optimal implant coverage. Especially, a short and narrow muscle or surgical release along the sternum increases the risk of irregularities and animation deformities of the implant.

Methods: In 84 consecutive aesthetic breast augmentations intraoperatively, measurement of PMM dimensions was performed bilaterally. These PMM measurements were then correlated with the preoperative breast width, the inframammary fold, and the placement of the implant's lower pole.

Results: One hundred sixty-eight PMMs of 84 patients were dissected with a dual plane II or III technique for primary aesthetic breast augmentation. In 88% of breasts, the calculated implants' lower pole was below the inferiomedial origin of the pectoralis muscle. In 10% of patients, a separation (more than 1 cm wide and 2 cm wide) in the inferior-medial origin of the PMM was noted. An asymmetry more than 0.5 cm in length between the left and right pectoralis major was noted in 36% of patients.

Conclusions: In this series, the anatomy of the PMM demonstrates a substantial variability in width and length and a considerable asymmetry in its dimensions. These findings emphasize the importance of good access and visualization of the origin of the PMM fibers before its division.

Fig. 1.

Schematic drawing of breast implant and pectoralis major muscle dimensions. A, Elevation of the NS line after augmentation. The NS line is preoperatively marked with hands on top of the head, and the ILP line (ILP) is drawn parallel to this from a midline point at half the implant height (for anatomical implants) distal to the NS line. The PM muscle is divided 2–3 cm above the ILP line and 2–3 cm distal to the NS line in the midline, permitting retraction of the lateral part of the muscle and minimized postoperative animation. B, Intraoperative measuring points before implantation: (a) width of the PMM in relation to the breast meridian halfway between the NS and ILP lines; (b) the (vertical) distance between the inferiomedial origin of PMM and the ILP line; and (c) distance between sternal PMM origin and ILP line. The darker area illustrates the supramuscular dissection in dual plane II-III dissection.

Fig. 2.

Intraoperative view of anatomical PMM variations after the breast implant inset. A, Asymmetry of PMM between left and right side, with ILP line below PMM origin on right side and above on left side. B, Medial split of PMM fibers on both sides. Red bar indicates ILP line. Blue arrows indicate PMM fibers.