Implant position: over the muscle, under the muscle, and dual plane

What layers can implants be placed in?

In breast augmentation, the layer in which the implant is placed is a key choice in surgical planning, along with the incision site and the type of implant. A 2010 review described breast augmentation as the most commonly performed cosmetic procedure among women in the United States and named the dual plane beneath the pectoralis major muscle (subpectoral dual-plane) and the space under the breast gland as common implant positions ^[1].

Placement under the breast gland is often called placement over the muscle, and the implant sits between the breast gland tissue and the pectoralis major muscle. Placement under the muscle puts the implant beneath the pectoralis major. In the dual plane, the lower attachment of the muscle is adjusted so that the upper part of the implant lies under the muscle and the lower part lies under the breast gland.

There is also a subfascial position, in which the implant is placed under the thin layer of connective tissue (fascia) that covers the pectoralis major. A 2015 publication described a method of placing the upper part of an anatomically shaped implant under the superficial fascia of the pectoralis major through an armpit incision, and noted that reports on the subfascial position are still few ^[4].

What differs depending on the position?

A 2010 review named capsular contracture as the most common complication of implants ^[1]. For this reason, how implant position and surface type relate to capsular contracture has long been a subject of interest.

A 2019 review of silicone gel implants placed under the muscle identified 98 relevant publications, but stated that only a few studies had evidence strong enough to assess treatment effects ^[2]. Among these, 6 of the 8 studies that reported the risk of capsular contracture with placement under the muscle found similar rates of capsular contracture with smooth and textured implants ^[2].

In the same review, local complications such as rippling (visible wrinkling), late seroma (fluid that collects long after surgery), and double capsule were associated with textured implants, and every case of breast implant-associated lymphoma (BIA-ALCL) was associated with textured implants, with none reported with smooth implants ^[2]. The authors concluded that with placement beneath the pectoralis major, neither surface had a clear advantage, but the level of evidence was rated low, at level V ^[2].

Armpit incision and the dual plane

A 2023 publication explained that breast augmentation with implants is becoming increasingly accepted in Asia, and that Asian women still prefer an armpit (transaxillary) incision ^[3]. The publication considered that using an endoscope with an armpit incision improves control during surgery and reduces complications, and it described an endoscope-assisted method for creating a high dual plane ^[3].

However, this is the view of a publication introducing a specific technique, not a study that compared results in numbers with other positions or incisions. Because it addresses Asian women, it is a useful reference, but the right position can vary depending on your tissue thickness and breast shape.

Rare complications: milk discharge and milk cysts

Rarely, after breast augmentation, milk may come out of the breast (galactorrhea) or collect in a pocket (galactocele). A 2021 systematic review gathered 38 cases from 19 publications, and the implant had been placed under the breast gland in 57% and under the muscle in 37% ^[5].

The authors stated that the number of cases was too small to draw a firm conclusion, but weakly suggested that an incision around the areola, implants under the breast gland, a history of taking hormonal birth control pills, a history of pregnancy, and recent breastfeeding within the past year may be risk factors ^[5]. Symptoms usually began within 3 months ^[5].

Advances in technique and remaining questions

A 2021 review stated that over the nearly 70 years since implant surgery began, technology and techniques have advanced to improve results and reduce complications, but that it remains to be seen whether new tools and techniques will stand the test of time ^[6].

A 2010 review summarized that breast augmentation does not appear to increase the risk of breast cancer ^[1]. However, when you have a breast screening exam, it is a good idea to tell the staff in advance that you have implants and where they are placed.

Most of the sources reviewed here are reviews and descriptions of techniques, and few studies compared results by position under the same conditions. It is therefore difficult to say that any one position is better for everyone.

What to check during your consultation

Implant position is decided by looking at several factors together, such as the thickness of your breast tissue, the elasticity of your skin, and the shape you want. It is a good idea to check the following during your examination.

• The implant position that suits the thickness of your breast tissue
• How the chosen position and incision method work together
• The chance of capsular contracture and changes in shape depending on the position
• The type of implant surface and the risks that come with it
• If you plan to breastfeed, what needs to be considered