Tissue Expansion
Tissue expansion is a technique in which the skin is stretched beyond its usual limits to cover an adjacent bald area of scalp. It is most commonly used in conjunction with scalp reductions or lifts, but may also be used with flaps.
Tissue expansion is a relatively aggressive procedure and many question its appropriateness in treating androgenetic alopecia (common baldness). On the other hand, it is an invaluable technique for repairing burns and other injuries to the scalp when hair loss is associated with scarring.
In order to work, tissue expansion relies on two recently described properties of skin, Mechanical Creep and Biological Creep. Mechanical Creep is the stretching of skin that is due to tension applied over minutes to hours. The stretching is usually performed intra-operatively and is due to collagen re-alignment, displacement of fluids, fragmenting of elastic fibers and recruitment of adjacent skin. In contrast, Biological Creep involves the stretching due to tension over weeks to months. The mechanism of this is new tissue growth as well as recruitment of adjacent skin.
There are two types of tissue expansion, Volumetric and Non-Volumetric. In Volumetric Expansion, a balloon is placed under the scalp and gradually inflated, stretching the skin over weeks to months. This "balloon expansion" is very effective, but is generally too disfiguring for treating male pattern baldness. It's use is usually limited to treating hair loss associated with injuries or congenital defects.
Non-volumetric tissue expansion, also called "scalp extension", can be used in combination with a scalp reduction for treating male pattern baldness. The most popular type is the Frechet Extender which is a thin sheet of bioplastic that is placed under the skin through an incision. As it is stretched, its hooks are attached onto the undersurface of the scalp in two different areas. They are left in place for approximately 4 weeks during which time the skin stretches and buckles up. The redundant bald scalp is then excised in a subsequent surgical procedure. An intermediate type of device, designed by Martin Unger, is the PATE (Prolonged Acute Tissue Expansion) which can be used intra-operatively.
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