Creation of a pocket for the tissue expander under the muscle is a safe and effective way to reconstruct the breast mound. Muscle coverage provides a good blood supply to the overlying skin, which decreases healing risks, and also camouflages the implant. This means that there is less risk for seeing rippling of the subsequent permanent implant or seeing the implant edges, which allows the reconstruction to appear more natural. Conversely, because the implant is under the muscle, patients may notice changes in the appearance of the breast when they contract the chest muscle. This can create animation deformity, or change in the appearance at the upper pole of the breast with contraction of the chest muscle. and also pushes the implant down and out towards the armpit.
To avoid this issue, tissue expanders are now being placed above the chest muscle, termed prepectoral tissue expander breast reconstruction. In this approach, a support material, such as Alloderm, may be used to secure the position of the implant on top of the muscle, or the implant will simply be sutured into place using the attached tabs, but the chest muscle is not lifted off of the chest wall. The tissue expander is placed on top of the muscle, secured into place, and then is filled with air (instead of saline).
Expansion with air reduces weight on the skin and, therefore, risk for healing problems. Because the muscle is not lifted, patients who have this type of reconstruction generally will have less pain after surgery. Placement above the muscle also allows patients to avoid animation deformity associated with traditional tissue expander reconstruction approaches. Despite this benefit, there are also downsides to this approach; patients may have slightly higher risk for delayed healing after surgery, and may find that they are more likely to have visible rippling after permanent implant placement. Regardless of the placement of the tissue expander, expansion will continue as planned.