Structured implants were approved by the FDA and Health Canada in 2014 as a third form of breast implant. Structured implants incorporate both saline and silicone gel implant technology. The filler is only saline solution in case of rupture and has a natural feel like silicone gel implants. The implant uses an internal structure which consists of a series of nested shells that support the upper pole with the two lumen being filled with only saline. The implant is inserted empty and then filled once in place which requires less of an incision than pre-filled implants. If one of the lumen of the structured implant ruptures, it leaks and empties. The other lumen remain intact and the implant only partially deflates, allowing for ease of explant and replacement.
Since experienced surgeons are aware of these issues with saline breast implants and their need for eventual replacement, they opt to place them under the chest muscle. The chest muscle works as an extra layer of tissue over the implant, which makes for a smoother transition from the chest wall to the implant. The finished product is a more seamless transition versus a more visible and abrupt change when the implant is not placed below the pectoral muscle. As for gel breast implants, they can also be safely placed below the pretorial muscle if that is a viable option for the patient since replacement and wrinkling is less common with this type of implant.