Contrary to what many patients think, the pectoral muscle often does not cover all of the breast implant when it is placed in the submuscular position.
If the implant is placed at about the level of the nipple, about a third to half of the pectoral muscle covers the implant. The remainder of the implant is covered by a thinner layer called fascia. This is a continuation of the outer covering of the pectoral muscle and is much thinner than muscle
Beneath the implant are the ribs. These are covered with a thin layer of muscle called the serratus muscle and an extension of the covering of the abdominal rectus muscle. Sometimes it is possible to cover all of the implant with a thick layer of muscle but this is unusual.
This suggests that the benefits of the submuscular position such as less palpability of the implant and wrinkling may not be as great as some suggest.
As silicone gel implants return to more general use in the United States, it seems likely that the use of the submuscular pocket may become less popular.