In very rare instances, Symmastia can occur as a defect of breast augmentation surgery. When implants are inserted too close to the midline of the body, it causes a lifting of the skin away from the chest, creating an 
unattractive connected appearance sometimes referred to as “breadloafing.”
Symmastia can also occur as a rare congenital defect in which soft tissue connects, or webs, both breasts together at the sternum (breast bone). Symmastia seems to be more prevalent among thin women, mostly due to the minimal tissue and/or fat covering the sternum.
In our experience, Symmastia generally occurs due to aggressively cutting open the chest muscle during an implant operation. In the early years of breast augmentation, surgeons would attempt to release some of the chest tissue in order to get the implants closer together, which can cause the defect as well.
I must give a kind word of caution to everyone reading this and having second thoughts about getting a breast procedure done. Symmastia is the least common of all cosmetic breast augmentation complications.
Today we take a much less invasive approach to altering the body. Our goal is to nip and tuck, not cut and stretch.
Symmastia can be due to malposision of the breast implant alone. In these cases one or both implants migrate across the midline lifting up the skin of the sternum. Or it can be a lifting of the skin only. Or symmastia can be both a lifting of the skin and shifting of the implant. After carefully examining the patient to determine the caus eof the symmastia a plan is developed specific for that patient. These days I often use either Belladerm or Strattice for repair of implant malposition or symmastia.
In the following video, Dr. Moliver walks you through a procedure to fix a Symmastia case.
WARNING: The following video contains graphic surgical footage, and may not be suitable for all audiences. Viewer discretion is advised.