Synmastia ( or symmastia) is when the implants have been placed to close together initially, or the tissues have weakened over time enough to alow the implants to come together underneath the skin. This can lead to raising of the tissues over the sternum and the appearance of no cleavage and even one breast instead of two. The causes are variable, but are usually due to overdissection in the sternal area or implant placement that is too large for the pocket, creating inordinate amount of medial pressure on the tissues.
Repairing synmastia can be a very difficult challenge, and a patient has to be willing to undergo not only an extensive surgery, but also a strict post-op recovery period. Repair can include a number of variables, from changing the implant pocket, changing the size and profile of the implant, reinforcing the medial areas with their own tissue or some sort of biological material( Alloderm or Strattice), etc.
Recovery involves a strict period of wearing a thong bra 24/7 to help keep pressure on the sternal area between the breasts, and no vigorous activities/ exercise for at least 1 month (and often times up to 3 months).