While breast implants are the most commonly performed aesthetic body implant, buttock implants are a very distant second to them. Besides being very much lower in the numbers of procedures performed, the silicone implants used to do them are also different.
Silicone breast implants are composed of two layers, an outer solid silicone shell or bag and is filled with an internal cohesive gel material. Because the outer layer and internal filler material are physically different and structurally separate, most breast implants will eventually fail due to a disruption or tear in the containment shell. While the cohesive internal gel is not going to come leaking out like older silicone implants, such shell disruption will still result in the need to replace the implant.
While buttock implants are also composed of a silicone material, they are structurally different. Their silicone composition is solid throughout and do not have an internal gel filling. (this is true for FDA approved buttock implants in the U.S.) While the silicone material is of a very low durometer it is still solid. Thus they do not have the risk of implant failure caused by shell disruption. As a result they would never need to be replaced due to an implant structural problem.
To illustrate this point I took a buttock implant and tore it apart by hand. You can see that it separates into torn pieces. Careful inspection of a torn implant piece shows that it actually has a two solid components. There is the larger internal solid soft gel and a thinner outer layer that surrounds it. The purpose of the thin outer solid layer is help with its insertion to prevent inadvertent tearing of the implant.
Buttocks implants by their silicone structure can not rupture or develop implant failure like silicone breast implants. Once placed buttock implants will never to be replaced due to loss of implant integrity.
Dr. Barry Eppley