Tissue Expansion

Background

The process of tissue expansion in reconstructive surgery was first reported by Charles Neumann, who described its application for auricular soft tissue reconstruction in 1957. Neumann simply applied concepts found in both normal physiological as well as pathological processes of the human body. Examples of this phenomenon include pregnancy, where the abdomen increases in size to accommodate the enlarging fetus, and rapid neoplastic growth, which may result in soft tissue expansion, deformity, and eventual skin breakdown. African tribes have also adopted tissue expansion as part of their cultural background, enlarging facial structures such as the lip or the ear.

Nearly half a century later, tissue expansion was repopularized by Radovan for use in postmastectomy breast reconstruction, although its applicability soon became evident in other branches of plastic surgery. Tissue expansion enables soft tissue coverage of large defects secondary to burns, trauma, congenital malformations and cancer excision. It involves the insertion of an implant adjacent to a wound or defect that needs to be resurfaced. The implant is then incrementally enlarged by injection of isotonic saline, resulting in stretching of the overlying soft tissue. The expanded skin can then be used to resurface a defect or incorporate permanent prostheses, including those used for postmastectomy breast reconstructions. Tissue expansion exploits the principles of controlled mechanical skin overstretch in order to generate new tissues with ideal compliance and almost perfect skin color, texture match, and sensibility to the resurfaced defect.

However, this useful tool on the reconstructive ladder does not come without its complications. In this chapter, we review the effects of tissue expansion on soft tissues and explore the tenets that govern its safe and effective use in the patient. We also discuss recent developments in tissue expansion such as external volume expansion and needleless expansion techniques with carbon dioxide.

Viscoelastic Properties of Skin

The structural components of skin can be altered by expansion as demonstrated by several biomechanical studies. Its viscoelasticity means that the mechanical response to loading involves both a viscous (time-dependent) and an elastic (time-independent) component. Skin is mainly composed of dermis and epidermis. The predominant proteins in the dermal layer are collagen types I and III, which are produced by fibroblasts. In the relaxed state, their triple helical structure results in a wavy and convoluted alignment. Upon stretching, the collagen fibers straighten and realign parallel to each other. The skin’s elasticity, essential for joint movements, is due mainly to superficial thin bundles of microfibrils associated with progressively larger amounts of amorphous elastin to form elastic fibers. Once strain is released, elastin fibers return collagen to its relaxed coiled posture. If stretched excessively, elastin is prone to fragmentation, resulting in a loss of recoil. Viscoelastic properties change with age and repeated mechanical forces, resulting in skin laxity.

Skin is a dynamic organ and acclimatizes to constant mechanical forces applied to it due to its viscoelastic properties ( Box 6.1 ). On a tissular and cellular level, constant mechanical stress induces changes termed mechanical creep and biological creep . These phenomena interact to restore resting tension of stretched tissues to baseline – stress relaxation ( Fig. 6.1 ). For example, a wound that was under tension intraoperatively but relaxed at outpatient follow-up is an example of stress relaxation.