Can breast implants that were placed under the muscle come out from under that muscle?

Hello,In my experience this is very rare but it would be possible especially for very large implants as less of the implant surface would be covered and secured by the muscle. Talk with your Plastic Surgeon in person if you think that you have an implant issue.All the best

In the case of submuscular implants, only the top of the implant is covered by muscle. The lower aspect of the implant is under gland, fat and skin. In the case of large implants, it is possible for the skin to stretch to the point that the implant comes out from under the muscle entirely. With smooth gel implants this is more likely. The result is rippling, sagging, and a general undesirable breast shape. This can be corrected but usually requires skin reduction and placement of a smaller textured implant. . 

Yes, over time, especially with large heavy implants, your breasts may stretch and sag so that the implants are no longer under the muscle, or much less of the implant remains under the muscle. The pocket may stretch over time to let the implants drop. The pocket could be tightened. If you have large heavy implants, you may need to change to a smaller implant that will not be so heavy on your tissues.