Anatomy Before Surgery
After a mastectomy removes breast tissue, two closely aligned muscles called the pectoralis major and pectoralis minor lie directly beneath the skin on the chest wall Positioned over the ribs, the larger pectoralis major is on top overlapping the smaller pectoralis minor underneath it. The pectoralis major is a thick muscle that originates on the humerus bone of the upper arm and fans out to attach to the collarbone, the breastbone, cartilage at the second through the sixth ribs, and the upper abdominal muscles. The pectoralis minor, a slim, triangular muscle, attaches to the third, fourth, and fifth ribs as well as to the under the surface of the wing bone (scapula) on your back.
Your pectoral muscles have several tasks. The pectoralis major helps you flex and rotate your arm at the shoulder joint and pull it in toward your body. The pectoralis minor helps keep the wing bone flat on your back. The muscles work in concert to help you push or press against resistance, such as when opening a heavy door. Normally the muscles lie flat on the chest wall. During the course of the surgeries performed for implant reconstruction and during tissue expansions, the pectoralis major has actively pushed away from the ribs. The procedures may weaken these muscles, undermine posture, and restrict shoulder motion.
How Is Posture Affected?
Good posture depends on the counterbalancing forces of the pectoral muscles pulling the shoulder forward while back muscles pull it backwards. The pectoralis minor is tasked with helping to keep the wing bone (scapula) flat on your back. Weakness in the chest muscles may cause the shoulder to hunch forward and makes standing up straight difficult. Protective posturing—head tilted forward, shoulder raised and hunched, elbow bent so that your hand rests across your belly, and body bending forward at the waist—can occur because of discomfort after surgery. The discomfort stems from tightness in the area where the incision was closed after surgery and from the tissue expander pressing against pectoral muscles, which may set off muscle spasms. Some of this pain eases as the muscle spasms relax a few days after the tissue expander is placed or after each injection of saline. At that point, the remaining discomfort is due to skin tightness and the process of healing.