Chapter 6: Tissue Expansion

Creep refers to a permanent elongation in tissues subjected to an external force. There are two types of creep: mechanical and biologic. Mechanical creep occurs where tissue is acutely stretched and results in collagen realignment, elastic fiber microfragmentation, water displacement, and recruitment of adjacent tissue. In contrast, biologic creep occurs where tissues are stretched for a prolonged period and cellular ingrowth is initiated. Changes include an increase in collagen production, angiogenesis, and epidermal proliferation.1–5

There are a number of changes that occur in the skin and subcutaneous tissue during tissue expansion. A key factor is an increase in vascularity within expanded soft tissue because of an increased size and number of vessels secondary to angiogenesis. The highest vessel density is found at the junction of the capsule and host tissue, and this was demonstrated by Pasyk et al1 who analyzed the capsule, identifying four distinct layers. The outermost layer had a high density of collagen and blood vessels. This has clinical relevance in that the capsule itself can increase skin flap viability and should be left in situ following expansion where possible. The dermis thins, not thickens, fibroblasts and myofibroblasts increase in number, and sweat glands and hair follicles become less dense. Thickness does not return to normal until approximately 2 years after expansion. The epidermis thickens secondary to hyperkeratosis and normalizes after 6 months. Muscle tends to decrease in thickness and mass due to either compression or stretch from the expander (depending on which level the expander is placed). In this scenario muscle function is not usually significantly reduced by the expansion process itself, although the medial release and muscle undermining may do so. Fat is extremely sensitive to mechanical force and aggressive expansion is likely to cause fat necrosis. In general, the subcutaneous layer thins and some permanent loss of fat occurs.2

Internal tissue expanders are formed with a silicone elastomer shell surrounding an internal reservoir. They may be classified by shape, permanence, inflation mechanism, or filling portal type. Shapes include round, crescentic, and rectangular. Implants are commonly temporary but may be permanent such as some breast prostheses with a second inner compartment filled with silicone. Inflation is usually manual but can be self-filling as a result of osmosis when hypertonic expanders are used. The filling portal can be integrated or placed externally.1

Breast implant associated anaplastic large cell lymphoma (BIA-ALCL) is a rare type of non-Hodgkin’s lymphoma, with more than 500 cases worldwide. In most reported cases, it has been identified within the breast capsule and seroma fluid surrounding the implant at a range of time points following primary implantation. It may also be found as a solid tumor mass within the breast parenchyma. This condition has been most often associated with specific brands of textured breast implants and at present there are no cases of BIA-ALCL identified with smooth surfaced implants worldwide. The FDA has recommended that certain textured implant types are no longer used, and a number of these have now been removed from the market. The use of an integrated port, placement beneath the pectoralis muscle, nor a rapid expansion process have been associated with a reduced risk of BIA-ALCL. There may well be a link between infection, biofilms, and development of capsular contracture, but there is currently no strong evidence to substantiate that BIA-ALCL is caused by infection. Nonetheless, meticulous care must be taken to minimize infection with any breast implants and a single dose of antibiotics (rather than a 1-week course) is accepted to represent best practice in most centers. Overall, the use of a tissue expander in the breast presents a low risk for patients for development of BIA-ALCL. However, the use of a smooth shelled device may be a factor in minimizing overall risk for the patient. The downside is that smooth devices are more likely to migrate in the early postoperative phase, and in the longer term, may be more likely to develop capsular contracture.1,2

5. Johnson TM, Lowe L, Brown MD, Sullivan MJ, Nelson BR. Histology and physiology of tissue expansion. J Dermatol Surg Oncol 1993;19(12):1074–1078

The use of permanent expanders is popular in breast reconstruction and they can be shaped with differential expansion of the upper/lower poles. This can help recreate a more natural breast contour with ptosis. They are comprised of a more highly projecting lower pole and a more modestly projecting upper pole. Expanders can have integrated or remote ports. Remote ports are either placed externally or subcutaneously and are palpable and therefore do not require a magnetic locator, which is reserved for integrated ports.1 Expander geometry affects the amount of surface area gained. Expanders that are rectangular (not crescentic) achieve the greatest percentage of their calculated expansion at 38%. Crescentic expanders usually achieve values of approximately 32%, and round expanders typically achieve values of approximately 25%. Osmotic, self-inflating expanders contain hypertonic sodium chloride crystals and fill by osmosis. The rate of expansion cannot be altered after insertion. Although commercially available, they are not commonly used in clinical practice. They tend to be occasionally used in pediatric patients with scalp or periorbital defects and are otherwise largely experimental.2

child? Tissue expansion is useful because it can facilitate closure of defects that otherwise require importation of distant tissue, but it has several disadvantages. It is staged and requires at least two surgical procedures; multiple surgical outpatient appointments are needed for expansion; completion of reconstruction is delayed; and appearance and function may be unacceptable for the patient and/or family during the expansion process. Placement of an expander also carries a risk of infection. Should this occur, the expander would need to be removed. A further risk of tissue expansion is implant extrusion and this is a particular risk in high-risk areas of the body where skin blood supply is reduced and following other treatments such as radiation.1–3

Shape selection of the expander depends on location and crescent shapes are often used in the scalp. These are normally placed subgaleally. Precise expander volume is not usually a concern because most can be safely overinflated beyond their recommended maximum volume. The base diameter of the expander should be 2 to 2.5 times the defect diameter (not 5 times). The access incision for initial expander placement should ideally be perpendicular to the main axis of expansion (long axis of the expander), not parallel, to reduce tension across the scar. It should be placed at the edge of the defect so that it can be removed at the time of reconstruction.1–3

Expansion typically begins 2–3 weeks after surgery to allow time for the wound to heal sufficiently without tension. Expansion is best performed with a small needle (23 gauge or smaller). It is performed using sterile saline, which has a similar osmolarity to tissue fluids. Patient discomfort and blanching are both indicators that expansion for that appointment is complete. Tissue expansion is normally safely repeated weekly or every 2 weeks until final fill volume is achieved. Rapid expansion is associated with a greater risk of extrusion. Rapid or early expansion can lead to a greater risk of implant extrusion so a conservative approach to expansion is warranted.1–3

The amount of extra tissue available can be estimated by measuring the dome length and subtracting the base diameter (Fig. 6.1).

The scalp is well suited to reconstruction using tissue expansion providing patients are motivated and willing to tolerate a prolonged period with a deformed appearance of the head. Applications include tumor excision as in this case, burn alopecia, and other traumatic defects (such as delayed procedures). Reconstruction outcomes will be specific to each individual patient and hair thinning will be dependent on both the site and size of the defect as well as the density of the patient’s hair; however, 50% is considered to be the maximum defect size that can be reconstructed in postburn patients without causing significant hair thinning.1

Forehead tissue expanders can be placed before raising a forehead flap with the intended benefit of facilitating direct closure of the donor defect. In practice this is not commonly performed because, in most cases, the caudal part of the donor site is closed directly and the residual defect on the scalp heals well by secondary intention. The forehead skin does expand well and has a relatively low rate of extrusion. A general anesthetic is standard practice for nasal reconstruction when using a forehead flap.1

In general, extremity tissue is associated with the highest complication rate when using tissue expansion techniques. The main complications are poor wound healing, implant extrusion, and infection. Of the extremities, the lower limb has the highest complication rate, especially when used below the knee. This does not mean tissue expansion cannot be used successfully in these locations, rather that patients and clinicians must be aware of the increased risks and these are taken into account. Other contributory risk factors such as diabetes, peripheral vascular disease, previous burn surgery, and previous radiation therapy must also be factored into the decision-making process.1–4 Fig. 6.1 Amount of tissue available equals circumference minus base diameter. Circumference Base diameter Expander Circumference – Base diameter = Tissue available

The most likely reason for an expander not to retain volume following injection of fluid is damage to the outer shell, which allows fluid to leak out of the expander into the subcutaneous tissues. With modern implants, spontaneous volume loss is very unlikely to be due to faulty manufacture and is most likely due to the surgical team causing damage to the shell either during placement of the expander or during the expansion process itself. A risk of using an expander with an integrated port is that the shell can fold over on itself when underfilled, so that when the injecting needle is passed into the valve it also passes through the shell. This is most likely to have occurred in this scenario. The expander is also at risk of damage during wound closure as the suture needle may inadvertently be passed through the silicone shell. If implants or expanders are returned to the manufacturer to assess deflation, the manufacturer is able to identify whether needle damage has occurred. However, in most cases it is immediately obvious if the implant has been punctured, once it is removed. It is unlikely that the fluid has not been injected into the expander providing that the magnetic finder has been used and the backing plate palpated during expansion, but this could potentially occur.1–3