Subpectoral (under-the-muscle) implants
In both breast augmentation and breast reconstruction, breast implants are commonly placed under the pectoralis muscle. The advantage of placing implants underneath the pectoralis muscle is that it provides additional soft tissue coverage over the implant, which can be important when someone has very little or no breast tissue. The additional soft tissue coverage can soften the implant edges that might otherwise be visible and palpable. In addition, the action of the muscle on top of the implant can help shape the top portion of the implant so that it does not look artificially full. Finally, the squeezing action of the muscle on the implant can reduce the incidence of capsular contracture.
The action of the pectoralis muscle flexing over a breast implant can lead to hypermobility. When the muscle presses down on the implant, it can temporarily deform and change the shape of the implant and move it upward or to the side. In addition, since the pectoralis muscle is normally flat against the chest wall, the presence of an implant underneath the pectoralis muscle can feel tight or even painful. For most women, the discomfort usually improves over time, but some women never become accustomed to the tight feeling of an implant underneath the pectoralis muscle.