The Pectoralis Major
The pectoralis major is the large triangular chest muscle running from the sternum and clavicle to the proximal humerus. It has two heads: the larger sternal head (arising from the sternum and upper 6 costal cartilages) and the smaller clavicular head. In breast surgery, submuscular implant placement elevates the pectoralis major off the chest wall to create a pocket beneath it. This requires partial release of the lower and medial muscular attachments to adequately cover the implant.
Fascial Layers
Multiple fascial layers cover the chest wall and are relevant to implant placement. The superficial fascia lies within the breast and contains Cooper's ligaments. The deep fascia (pectoralis fascia) covers the pectoralis major. Some surgeons place implants in the subfascial plane — between the pectoralis fascia and the muscle — as an alternative that may provide better coverage than subglandular while avoiding muscle division. The fascia provides both anatomical planes and structural support.
Serratus Anterior and the Axillary Pocket
For transaxillary (armpit) breast augmentation, the approach passes lateral to the pectoralis, through the axillary fat pad to the breast pocket. Understanding the relationship between pectoralis lateral border, serratus anterior, and the axillary contents is essential for surgeons using this approach.
Implications for Large Implants
Large implants create greater demands on the chest wall. Submuscular placement with very large implants progressively stretches the pectoralis, which over time can become thin, displaced, and functionally weakened. Patients pursuing extreme volumes often move to subglandular or subfascial placement for later staged procedures when the pectoralis cannot accommodate further volume. Understanding these limits informs surgical planning for high-volume cases.
