Should breast implants go over the muscle or under the muscle - which is better?
An implant placed above the muscle is referred to as 'sub-mammary' (or 'sub-glandular'), while an implant placed under the muscle is referred to as 'sub-pectoral' (or 'sub-muscular'). The muscle in question is the pectoralis major. The term 'sub-pectoral' or 'sub-muscular' is somewhat misleading, as implants placed under the pec major are only partially covered by the muscle. The pec major covers the upper/medial half of the breast area, so a 'sub-pectoral' implant is truly subpectoral only in the upper and medial aspect of the augmented breast, while the lower and lateral aspect of the implant is actually in a sub-mammary position. Because sub-pectoral implants are, in reality, both sub-pectoral (upper/medial breast) and sub-mammary (lower/lateral breast), this placement has more recently been referred to as a 'dual plane' approach to breast augmentation.
There is also 'total submuscular' implant placement, in which the implant is positioned behind the pec major and the serratus anterior muscle, so that the entire implant surface is covered by muscle tissue. This is not commonly done for cosmetic breast augmentations, but has been used for breast reconstruction using breast implants.
There are a number of compelling reasons for selecting subpectoral placement over submammary placement. The most significant is that fact that radiologists have indicated that it is easier to image breast tissue by means of mammography when the implant is subpectoral. The pec major also provides an additional layer of tissue to conceal breast implants in the 'social aspect' of the breasts - that part that is easily visible in swimsuits and lower-cut clothing. Additionally, the pec major is quite effective at flattening the upper pole of a breast implant so that a natural slope for the upper aspect of the breast is created.
Implants placed on top of the pec major tend to look very convex in the upper pole. The breast begins quite 'abruptly' in the upper aspect of the chest, and the appearance is therefore distinctly unnatural. Submammary implants are also more likely to have visible implant folds and ripples in the cleavage area. Another consideration is the fact that there is some evidence which suggests that the risk of capsular contracture may be lower with subpectoral implant placement. Even if the risk of contracture is the same, a mild contracture tends to be less noticeable and therefore less of a problem for the patient when the implants are in a subpectoral position.
Submammary placement may produce a reasonable result for fuller figured patients with larger starting breast volumes, as the larger amount of natural subcutaneous fat and breast tissue helps to conceal the implant contours. The problem is that as breasts age, they tend to deflate - especially in the upper pole. So what was adequate implant coverage in the cleavage area at age 27 may be inadequate coverage at age 37, and implant folds and ripples gradually become visible. So subpectoral placement is the best choice for both the short and long term.
'Sub-fascial' breast augmentation is also possible. Fascia is the term for a sheet of connective tissue made of collagen, and the pec major has a fascial covering as most muscles do. Breast implants can be placed behind the pec major fascia only, rather than behind the entire muscle, however this approach is not widely used. The pec major fascia is a relatively thin layer of tissue, so it is not nearly as effective in concealing breast implants as the actual muscle itself. Partial sub-fascial placement can be useful in some breast augmentation revision surgeries, where variations in pec major origin or incorrect release of the pec major has resulted in significant distortion of breast appearance when the muscle contracts.