Some further characteristics of expanded tissue.

It has been shown that during expansion there is a component of migration of surrounding tissue that probably contributes to the available tissue in local reconstructive procedures. Although there is a 63 per cent increase through expansion of a given flap with a particular expander, this results in only a 30 per cent increase after elevation and inset. This increase is basically maintained for a 3- or 4-month period. The 56 per cent decrease in area probably results from contraction of the extensible skin. The 30 per cent that remains probably results from a combination of stretch evidenced by reorientation, along with an increase in the cellular and extracellular components of expanded tissue. Therefore, there are components of both loan and dividend in tissue expansion. This further understanding should be helpful in the planning of tissue expansion. (Editors' note: Although there may be some element of "loan" initially, from peripheral regions, no thinning of the periphery has been observed. To the contrary, the periphery appears normal. It is likely that transient thinning of the periphery causes increased mitotic activity, and that this area is also made to produce a "dividend" ultimately. Unless permanent thinning can be documented, the "dividend hypothesis" remains valid.