Like every other decision about breast implant surgery, the question of whether to place the implant under the muscle or over is the subject of much debate, with confusion and misinformation in every direction. Suffice it to say that there is no single best method that applies to every patient; the key is to establish priorities based upon individual anatomy, implant type, and several other factors.
First we need to define some terms. When the implant is placed in front of (above) the muscle, that is usually called subglandular, since the breast is a gland. Beneath the breast tissue is a layer of muscle, most of which is the pectoralis major. This muscle is shaped like an oriental fan, with the gathered part attaching to the upper arm bone and the outer edge attaching to the sternum, or breast bone, and the ribs. Since it is only attached to the chest wall around the edge, there is a potential space beneath it where an implant can be placed. When the implant is below (behind) the pectoral muscle, it may be called subpectoral or submuscular.
The term total submuscular is used when other muscles on the chest wall are raised in order to cover the sections of the implant that the pectoral muscle doesn’t. Specifically these areas are on the outside (lateral) and the lower portion. Typically, the pectoral muscle covers about the upper two thirds of an implant. There are potential advantages to having total submuscular coverage but no agreement among plastic surgeons as to whether or not it is practical to do this in every case.
Why go under the muscle? There are several reasons why this is the most common approach for breast augmentation. (When implants are used for breast reconstruction, they are almost always placed total submuscular.) One important long-term consideration is that implants under the muscle seem to interfere less with mammograms. Implants may, however, still obscure some of the breast tissue. In theory, this could mean that an early breast cancer could be missed, or diagnosis delayed until the tumor is larger, though studies have shown no indication that this occurs in clinical practice. Special mammographic techniques called Eklund views are recommended for women with implants, and having implants does not mean that mammograms should be avoided.
Other benefits of submuscular placement are aesthetic; often times, the implants appear more natural. This is because the transition from the upper chest into the top of the breast is smoother, and the outline of the implant is less visible. This becomes much more important in thin women. The implants may be less apparent to touch when they are under the muscle as well. Historically, submuscular implants have been shown to be less prone to capsular contracture, which is a thickening and hardening of the natural scar layer that is formed around implants. There are other aspects that are probably more important in capsular contracture, however, so this isn’t usually the deciding factor.
There are of course disadvantages to submuscular placement of breast implants as well, otherwise they would all be placed in that plane. Activity of the muscle, whether with normal use or with athletic activity, can affect the implant in several ways. Some believe that muscle activity “massages” the implant and that capsular contracture is less likely for that reason; there is little hard evidence to support that theory, however. Muscle activity can also push the implant out of position either during healing or over time. This can be seen as loss of cleavage, with implants being too far apart, or implants too low, called “bottoming out”. These problems can be minimized by certain surgical techniques.