Surface area and tissue volume increases with differential expansion.

Increasing sophistication in generating soft tissue by tissue expansion has resulted in the evolution of differential expanders. These prostheses attempt to asymmetrically generate tissue for specific reconstruction, most commonly the breast. Using the pig model, differential expanders were placed in the rib area. A square grid was marked over the area, and the expander inflated. For each grid subunit, the surface area was calculated, the thickness measured, and the volume calculated. Subunits in the area of preferential expansion exhibited the greatest increase in surface area, however, these same subunits exhibited pronounced thinning of the tissue. The corresponding volume of these subunits was greater than that of nonexpanded subunits, but the increase was less than when comparing subunit surface area. All expanders were displaced superiorly during the course of inflation. These findings are of clinical significance in that the mastectomy scar and nipple reconstruction both are situated in the area of minimal thickness. Displacement of differential expanders must be anticipated so that the resultant inframammary fold will ultimately be symmetrical with the opposite side.