Can saline be added to a smaller breast implant 2 years after surgery ? It is under the muscle.

Although it can be done, there is a minimal amount that could be added, and not worth doing. The cost of two new implants will probably be less than $800 of the total cost of the procedure.

It is possible to do this but also dependent on the initial surgical approach.  However, it probably voids the warranty and, if you developed a complication, which is possible whenever the cavity is opened, you would be responsible for its replacement.  If you had an axillary approach, this could definitely not be done.

The short answer to your question is yes, additional saline CAN be added to a breast implant, even years after the original augmentation.  There is a limit (usually around 30 ml) on how much can be added before the implant becomes unacceptably firm and there is additional rippling.  So, if you are wanting a significant change in size, you will need to have the pocket enlarged and the implants replaced.  This is a relatively straight-forward procedure in someone who also has implants in place.