The most common location for placing the implants in breast augmentation is under the muscle. What this means is that a pocket is made between the thicker outer pectoralis major muscle and the thinner underlying pectoralis minor muscle. When it comes to nerves in breast augmentation the most common concern is about nipple sensation and one of its major sensory contributing nerves coming in from the side of the chest wall which is at some risk of injury as the outer pocket dissection is done. But there is another nerve, known as the medial pectoral nerve, that almost always get injured in the pocket dissection between the two pectoralis muscles. The medial pectoral nerve either comes up from the pectoralis minor muscle to innervate the major muscle from below or does so around the lateral aspect of the minor muscle. When placing a breast implant below the muscle, the pectoralis muscle is therefore partially deinnervated. This causes some muscle atrophy which is actually believed to be advantageous as it allows the breast to project better. As the thicker pectoralis muscle gets a little thinner over the implant, this allows the breast to acquire a more natural shape on the lower pole of the breast. In female bodybuilders, this pectoralis muscle atrophy may cause some weakness in the muscle which can be overcome by weight training.
Dr. Barry Eppley