Variance in the origin of the pectoralis major muscle: implications for implant-based breast reconstruction

The pectoralis major muscle plays a crucial role in implant-based breast reconstruction. The goal of this study is to document variations of the origin of the pectoralis major muscle (PM). We hope to understand how many women have anatomy allowing for total submuscular coverage of an implant with the PM alone in immediate breast reconstruction.

Fifty patients undergoing mastectomy were recruited. Breast width and the costal origin of the natural inframammary fold (IMF) were measured preoperatively and intraoperatively. The PM width at its origin and the rib origin of the PM were measured intraoperatively. A ratio of the PM origin width to breast width was calculated.

Forty-four percent of breasts studied had the IMF at the level of the seventh rib, 53% at the sixth rib, and 3% at the fifth rib. Twenty percent of PM muscles originated from the seventh rib, 68% from the sixth rib, and 12% from the fifth rib. Thirty-six percent of chests showed a PM originating one rib level above the IMF, 61% at the same level, and 3% one level below the IMF. Seventy-seven percent of chests showed a PM origin width to breast width ratio of <0.8.

Overall, 72% of chests had either a high origin of the PM, a narrow PM relative to the breast width, or both. This anatomy is suboptimal for implant coverage using the PM alone. Surgeons performing implant-based breast reconstruction should be prepared to utilize wide dissection, alternative muscle recruitment, or supplemental acellular dermal matrix.