TITLE: TISSUE
EXPANDERS
SOURCE:
UTMB Dept. of Otolaryngology Grand Rounds
DATE: October
15, 1997
RESIDENT PHYSICIAN:
Stephanie Cordes, M.D.
FACULTY: Karen
H. Calhoun, M.D., F.A.C.S.
SERIES EDITOR:
Francis B. Quinn, Jr., M.D., F.A.C.S.
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Tissue expansion is being used much more in reconstructive surgery for the treatment of a variety of problems in both children and adults. It is used in reconstruction in instances where there is not enough adjacent tissue to close a defect primarily or to repair with a local flap. Expansion is also indicated when repair of a defect by an alternative method such as a local, regional, or distant flap will result in an unacceptable donor or recipient site deformity.
The simplest example of tissue expansion is the abdominal wall of a pregnant woman in response to a growing uterus. The overlying skin accommodates the expansion while maintaining normal appendages and thickness. The concept of tissue expansion has opened a whole new frontier in reconstructive surgery. The tissue expansion technique is advantageous in facial reconstruction because it makes it possible to resurface wider defects with neighboring skin that is similar in color and texture.
The custom of soft-tissue expansion of the ears, nose, lips, and other body parts has been practiced by primitive cultures for aesthetic or religious purposes. African women of certain tribes place large plates in the lower lip to enlarge this structure. Women in Burma place rings around the neck to enhance linear growth.
Tissue expansion for medical purposes was first reported in 1905 by Codvilla, who attempted to lengthen the femur. Neuman (1957) was the first to expand skin by using an inflatable balloon. He reconstructed a subtotally avulsed auricle by using expanded skin from above the ear to cover a cartilage graft. It was not until 1976 that another study concerning tissue expansion surfaced, when Radovan successfully expanded an arm flap using a temporary tissue expander. The flap was used to resurface an adjacent defect of the arm following removal of a lesion. Radovan later refined and popularized this technique for postmastectomy breast reconstruction. More recent reports have described the use of tissue expansion for a variety of congenital and acquired deformities.
Tissue expanders are Silastic balloons. The shape of the expander depends primarily on the site of expansion and the reconstruction needs. The standard shapes are round, rectangular, or crescent. Use of the rectangular expander provides the most effective surface area gained when compared to the round or crescent. Rectangular expanders gain 38% in tissue area of the calculated surface increase of the expander, where as round expanders gain 25% and crescent expanders gain 32% of calculated surface increase.
Expanders are available in various volumes ranging from a few cubic centimeters to several thousand cubic centimeters. In the head, face, and neck, most expanders used are in the 1 to 250-ml volumetric range. There is a considerable margin of safety in selecting the proper volume since expanders can be overinflated at least 15 times the vendors stated maximum volume. A disadvantage of overinflation is increased leakage from the dome of the injection port. Nordstrom etal. found that the average pressure necessary for leakage from the injection port of an expander was 32 mmHg (range 8- 110 mmHg). Thus, overinflation will predispose to leakage. To circumvent the potential problem of leakage, it is best to select the largest expander that can reasonable be inserted beneath the region of expansion or to consider the use of two or more expanders to gain the needed tissue. In any event, the proven safety of limited overinflation allows a margin of error in the initial choice of implant volume, and later permits continued expansion if more tissue is needed.
The size of the expander must be large enough to provide the required expansive forces necessary to achieve the desired tissue augmentation. One method of selecting the appropriate expander is based on the size of the base of the expander. Van Rappard etal. studied surface area increases of a number of expanders of different size and shape. They recommended that when using a rectangular or crescentric expander the appropriate size expander would be one in which the surface area of the expander base is 2.5 times as large as the defect to be closed. In the case of round expanders, the diameter of the expander base rather than the area of the base should be 2.5 times a large as the defect. Another method of selecting an expander is based on the circumference of the balloon portion of the expander. The expander must be of sufficient volume so that the apical circumference of the dome of skin overlying the fully inflated expander is two to three times the width of the defect. Even if the chosen expander creates excessive skin, suturing the expanded flap of tissue without tension will keep widening of the postoperative scar to a minimum.
After careful consideration of the above variables, one must choose the type of expander to use. The first expander has a distant filling valve where the injection port that receives the needle during inflation is attached by a stem of varying lengths to the expander. This expander has a self-sealing inflation reservoir that is inserted subcutaneously away from the expander. The sizes range from 1-1000 cc and shapes include round, crescent, u-shaped, hemisphere, and rectangular. This Radovan expander is the most frequently used system. Filling is safe because the port is easy to localize. Placement of the reservoir dome must be considered carefully to avoid kinking of the connecting tubing and pressure necrosis leading to exposure of the implant. There is a dense fibrous capsule that forms along the connecting tubing to the port that must be incised before tissue mobilization to gain maximal extensibility.
The second available design is one in which the expander and injection port are a single unit (incorporated filling valve). This port has a self-sealing membrane and is lined with a metal or a thick polymer to prevent accidental puncture of the dome during injection of saline. A silicone palpation ring surrounds the injection site that usually allows for adequate localization under thin skin, however, it may require dye tattooing or a metallic locating device under thicker tissue. The sizes range from 50cc to 1000 cc and shapes include hemispheric, rectangular, crescent, and teardrop. Unfortunately, this type of expander does not come in miniexpanders and the stiffness of the injection port causes an increased risk of skin erosion, especially if placed over bone.
A third type of tissue expander obtains more expansion at one end than the other by using different physiomechanical properties within the envelope. These directional or differential expanders are mostly used in breast reconstruction to obtain a more normal looking breast. More recently there use has been advocated in treating male pattern baldness.
The last type of expander is somewhat experimental. This is a self inflating expander consisting of a semi-permeable membrane that surrounds a substance such as sodium chloride, which is present in adequate concentrations to create an osmotic gradient across the wall of the expander. The interior of the expander is hypertonic relative to the extracellular water, thereby causing a net influx of water into the expander.
There are three basic properties of skin that are important to tissue expansion. These include: 1) skin tension, 2) skin extensibility, and, 3) viscoelasticity. Skin tension is the amount of tension that naturally occurs in all tissues. It is the function of the elastic fiber network and varies with location in the body and age of the subject. Skin tension is visible by the contraction of wound margins when incisions are made. This property causes some shrinkage of flap size when it is incised and elevated.
Skin extensibility is the response of skin to mechanical forces. It allows skin stretching with joint motion or rib cage movement and brings the skin back to a fully relaxed state. This property also causes some decrease in the area of an expanded flap after elevation. Some portion of tissue expansion involves extensibility of overlying tissue.
Viscoelasticity includes creep and stress relaxation. Creep is seen when the force applied to continue stretching the skin, gradually increases the length. The stress- relaxation behavior of a tissue is seen when a specimen of skin containing collagen is stretched and then held constant. The applied force is first seen to rise as the tissue is stretched and then to fall in the period during which the deformation is held constant. During the deformation phase, the work done in deforming the tissue increases the strain energy stored, and the applied force consequently increases. From the point at which the deformation is held constant, the decreasing force indicates a reduction in the amount of strain energy stored within the tissues.
Two types of expansion are recognized and used clinically today: prolonged tissue expansion (PTE), in which expansion occurs over 1-6 weeks, and rapid intraoperative tissue expansion (RITE), in which the expansion is performed cyclically in the operating room. Prolonged tissue expansion allows resurfacing of even wider defects with neighboring skin similar in color, texture, sensation, and retained adnexal structures. Expanded skin can simply be advanced into the defect for primary closure or in instances requiring the use of a flap, the secondary defect can be easily closed without tension. Flaps harvested from expanded skin have an increased vascularity and tissue can be expanded a second or third time if necessary. The major disadvantage is that it requires two separate surgical procedures: one to place the expander (outpatient, local anesthesia) and the other to remove the expander and perform the reconstruction. This type of tissue expansion is also labor-intensive in that frequent visits to the office are necessary for inflation of the implanted expander. It takes several weeks to gain adequate tissue by expansion and is therefore limited for the most part, to elective reconstructive problems. Another disadvantage in the head and neck area is the visible deformity caused by the expansions, particularly toward the end of the expansion process. There are also inherent risks of infection and exposure of the expander or inflation reservoir.
The physiology of expansion by prolonged tissue expansion is not just a matter of stretching skin, but the actual formation of additional new skin which has all the attributes of the original tissue. Austad etal. postulates that tissue expansion causes a decrease in cell density in the basal layer of the skin and that cell density may regulate skin mitotic activity. A lower cell density results in a greater cell proliferation, resulting in growth of additional skin. Inflation of the tissue expander was found to cause a threefold elevation of epidermal mitotic activity within 24 hours, followed by a gradual return to normal baseline over 2 to 5 days. Conversely, deflation of the expander caused a transient decrease in epidermal mitotic activity. The increase in mitosis returns to normal 4 weeks after expansion. On histologic studies, the epidermis has an increase in its thickness and the rete pegs become flattened when compared to nonexpanded skin.
The dermis and subcutaneous tissues are thinned as a result of tissue expansion. This thinning is associated with an overall decrease in tensile strength of the expanded skin. Dermal thinning persisted 36 week after expansion. The subcutaneous layer of fat is intolerant to stretching causing significant thinning. With faster expansion, fat necrosis can be seen. The muscle layer in pigs, which is similar to the platysmal layer in humans, tends to atrophy with maximal expansion. The distance between hair follicles becomes greater with tissue expansion, but there is no new appendages formed.
A capsule forms around the expander as with most foreign body reactions. These capsules are thickest after 2 to 2.5 months of expansion. Within 7 days there is a 2 layer capsule consisting of an inner layer of macrophages and an outer layer of fibroblasts and some lymphocytes. Over time the outer layer becomes more rich in collagen fibers. The bordering layer around the capsule becomes richly vascularized. As expansion proceeds, there is an increase in the number and size of the vessels within flaps supplied by random-pattern vessels and, if present, axial vessels. These changes correspond to the demonstrated increase in blood flow to expanded flaps. In the study by Saxby, this lead to surviving lengths after expansion being 50 percent greater than the delayed controls and nearly 150 percent greater than comparable flaps raised acutely.
The other type of expansion used clinically is rapid intraoperative tissue expansion (RITE) which has been pioneered by Sasaki. It can be used at a moment's notice and permits the stretching of skin beyond its noninherent limits within minutes. It is indicated in situations in which primary closure of a skin defect may be problematic due to limited availability of donor skin or difficulty in the mobilization of donor skin because of tethering or tightness over underlying skeletal or cartilaginous frameworks. Another reason for its use may be to enhance donor skin in regions where distortion of important anatomical structures is likely, such as the lower eyelid, the nostril, or the oral commissure. The tissue for reconstruction is obtained in a matter of minutes via stretching and recruitment. This type of expansion will gain an additional 1-3 cm of tissue depending on site, patients, and local skin factors. This involves a single procedure without the cosmetic deformity outside of the operating room. When this method is combined with PTE, patients have less pain with expansion and the ultimate expansion time is decreased. RITE may be used to stretch unyielding tissue that restricts placement of alloplastic implant in aesthetic procedures. RITE does not give any true tissue gain and has not been found to provide any great advantage over undermining as tissue obtained is mostly by recruitment. Other disadvantages include bruising and a slight degree of ecchymosis. Skin edge ischemia is more common than with prolonged expansion, as is retraction of the wound edges.
There is minimal information available concerning the physiologic changes that take place during rapid skin expansion. Mechanical stretching changes the elasticity of skin by the phenomenon called creep. The physiological changes coinciding with mechanical creep are:
Cyclic loading, that is stretching followed by relaxation as opposed to continual stretching, appears to be the most effective method of recruiting extra tissue. No significant histologic changes in the epidermis, dermis, dermal appendages, adipose tissue, or muscle were observed.
An experimental form of tissue expansion is continual tissue expansion by using a pressure-dependent continuous infusion device. Studies show that continuous tissue expansion achieves significant amounts of additional tissue when compared to intraoperative expansion. Schmidt etal. found that continuous tissue expansion using a device that infuses saline at a constant infusing pressure less than capillary filling pressure will expand in 3 days to amounts similar to a model of conventional expansion. It is believed that much of the skin achieved in true tissue expansion represents stretch and reorganization of dermal collagen fibers rather than new skin created by mitosis.
The patient who is selected for the use of a tissue expander is usually one who has a difficult reconstructive challenge, or a person for whom the previously used regional flaps were inappropriate. The same criteria that are used to select a suitable patient for a regional skin flap are applicable to selecting a patient for tissue expanded skin reconstruction. The patient must be willing to subject themselves to a protracted treatment course with potentially embarrassing temporary physical deformity. The patient should have no serious medical problems (diabetes, hypertension) and should not be a heavy smoker. A complete history, physical examination, and survey of pertinent hematologic and biochemical parameters should be taken. The patient must be able to emotionally handle the extreme deformity.
After the patient has been selected as a candidate for tissue expansion, the expander must be selected. It is important to match the expander to the geometry of the expansion site and the geometry of the planned flap. The donor site is selected where tissues are most like those to be replaced, and in close proximity to the defect. The incision for placement should be in a site well hidden and/or incorporated into the incisions planned for reconstruction, and if possible, perpendicular to the long axis of the expander. The incision should not compromise the viability of advancement flaps planned for reconstruction after the expanders are removed. Perioperative antibiotics are given to the patient. The placement of the expander is usually beneath the subcutaneous fat in the face and neck, although it can be placed under the platysma in the neck. In the scalp, expander placement is underneath the galea. The expander should not be placed under previously irradiated skin. A large enough pocket needs to be dissected so that the expander fits without any folding. The reservoir is placed in a separable pocket about 4-6 cm away from the expander. Most surgeons place a drain to drain the wound. The wound is closed and enough saline is instilled into the expander so that the dead space is obliterated and to aid with hemostasis. Expansion is begun 2 weeks postoperatively by instilling saline into the reservoir with a 23 gauge or smaller needle. Enough saline is instilled so that the overlying skin becomes tense or the patient complains of significant discomfort. The skin should blanch with pressure from the expander, but capillary refill should return to normal after adequate pressure is withdrawn. Injections are continued on a weekly basis until the desired amount of skin needed is obtained (usually 6-8 weeks). Upon removal of the expander, it is generally recommended to remove the inner layers of the capsule to allow for further lengthening of the flap of expanded tissue. It is a good idea to leave the superficial layers of the capsule to prevent the flap from becoming too thin. In RITE, expansion takes place by progressively increasing volumes of saline in repetitive cycles of 3 minutes of expansion and 3 minutes of relaxation. It usually requires 3 -4 cycles.
Tissue expansion promises to be one of the most innovative procedures for management of post-traumatic alopecia, male pattern baldness, and the repair of large scalp defects. During scalp expansion, the structure of hair follicles remains unchanged, although they are separated from one another. Hair loss does not occur, and the pattern of hair growth remains the same, however, because the number of hair follicles remains unchanged, hair density is reduced with expansion. Reduction in hair density is not usually noticeable until density has decreased more than 50 percent. Thus, given normal hair density, the scalp can be expanded to two to three times its original surface area before a change is evident. Tissue expansion provides more hair-bearing scalp enabling the removal of more bald scalp during reduction surgery while reducing wound edge tension. In addition, tissue expansion promotes increased vascularity in the area of expansion. These advantages have stimulated the use of expansion in conjunction with pedicled hair-bearing flap surgery for male pattern baldness. Scalp flaps such as temporoparieto-occipital or Juri flap, occipital-based flaps, and temporoparietal flaps have been pre-expanded before their transfer to provide larger and more predictable flaps.
For male pattern baldness, tissue expanders are placed under normal hair bearing scalp, usually in the temporoparieto-occipital regions. The expander is placed well away from the hairline to avoid expanding non-hair bearing scalp. Incisions for expander placement are usually made at the edges of the area of alopecia in the case of scalp reduction surgery, or in the proposed line of incision in the case of pedicled scalp flap surgery.
Multiple expanders (volumes 200-400 cc) with distant injection ports are recommended. Expanders should be placed beneath the galea aponeurotica. Inflation of the expander begins 2 weeks postoperatively and continues on a weekly basis. There is an initial 2 to 3 week lag in which expansion proceeds slowly, probably due to the resistance of the galea, however, adequate expansion can usually be accomplished in 6 to 8 weeks. This expansion can be quickened by performing galeotomies at the time the expander is implanted. Expansion continues until the distance across the expanded scalp is equal to the starting distance, plus the width of the scalp segment to be replaced.
The second stage of scalp expansion involves incision at the margin of the alopecia and removal of the expanders. The bald scalp is excised only after advancing or transposing the expanded scalp to be sure sufficient tissue is available to close the proposed resection. If there is insufficient tissue to allow removal of the alopecia, the tissue expanders can be replaced for further expansion. If there is adequate tissue, the capsule surrounding the expander is not usually excised. The wounds are closed in two layers, and suction drains are used.
Scalp expansion has also been quite useful in a two staged reconstruction of scalp deformities resulting from traumatic alopecia, burn scars, hemangiomas, giant nevi, and various neoplasms.
Auricular reconstruction has been constrained by the lack of adequate tissue in the adjacent area, especially non-hair bearing skin. With the use of a crescent- shaped or custom-fitted prosthesis, the remaining periauricular skin can be expanded for reconstruction. The incision for the implant is usually made in the hair bearing scalp. Inflation begins 2 weeks after placement and injections are initially biweekly. The average inflation period is 8 weeks. Once adequate soft tissue is available, the cartilage framework can be placed and reconstruction performed. The capsule needs to be excised to allow for adequate thinning of skin and definition of framework. One of the goals in using expansions for microtia repair is the formation of an auriculocephalic sulcus from the expanded tissue in the same procedure as the placement of the cartilage. A potential complication is the necrosis at the pressure points of the postauricular skin because it is somewhat thinner than the scalp and situated over a bony prominence. To prevent this, the expander should be inspected for folds in its membrane and the injection port connection tubing should be routed away from the bony mastoid tip.
The skin of the eyelids is best replaced by adjacent eyelid tissue rather than skin grafts or cheek flaps. The implant that is used is a cigar-shaped, 1.2cc silicone expander with a rigid back wall to prevent expansion and pressure on the globe and an expansible anterior portion. An oblique skin incision is made in the crow's feet lateral to the lateral canthus. The implant is placed in a subcutaneous pocket that extends from the medial to lateral canthus. The reservoir dome is placed in a remote pocket over the temporal region.
For nasal reconstruction an expanded midline forehead flap is used. A pre-expanded forehead flap facilitates total or near total nasal reconstruction including formation of the vestibular lining and columella. A rectangular expander of 100 to 250 cc volume is used depending on the amount of expanded tissue needed. The prosthesis is placed through an incision behind the hairline in a subgaleal plane. Inflation occurs weekly over 6 to 8 weeks. The flap required for total nasal reconstruction must be 8 cm in vertical dimension and 7 cm in greatest horizontal dimension. Expansion of the forehead skin additionally causes thinning of the tissue allowing for better contouring to create ala. Capsulotomies are often needed for adequate lengthening of the expanded tissue flap.
The expanded forehead flap is also used for the resurfacing of forehead defects. The simultaneous expansion of skin and frontalis muscle generates a sensate cutaneous cover and innervated striated muscle for the restoration of forehead expression.
The cheek and neck can be considered a single anatomic unit from the standpoint of tissue expansion because skin vascularity, texture, and thickness are similar. Expansion of the cheek and neck is primarily indicated in the reconstruction of defects of the neck and lower two thirds of the face. The expander is placed subcutaneously in the cheek and deep to the platysma muscle in the neck through a small incision considerably removed from the area to be expanded. It is preferable to place the expander over as rigid a foundation as possible to maximize the vector forces of expansion outward toward the overlying skin.
Gravitational forces are more influential in migration of expanders placed in the cheek and neck. To retard inferior migration, secure the base of the expander to underlying structures with permanent sutures. Tissue expansion proceeds with weekly saline injections. Once adequate tissue is obtained, the expander is removed. It may be necessary to score the fibrous capsule surrounding the expander to permit optimal mobilization and draping of the expanded skin. For total resurfacing of the neck, the expanded trapezius fasciocutaneous flap is excellent and can be re-expanded to better resurface the lower face.
Expansion in this area has a particularly high rate of complications. Most common is exposure of the balloon or injection port. But pooling of injected saline, disproportionate expansion of tissue, and gravitational descent of the implant also occur.
Expanded full thickness skin grafts are used for facial resurfacing. These allow the donor site to be closed primarily. The best results occur when facial aesthetic subunits are covered separately.
Any musculocutaneous flap can be considered for premobilization expansion to gain greater length or width for the flap or to thin out the muscular component of the flap. The trapezius, pectoralis, and latissimus musculocutaneous flaps are amenable to expansion. The expander is placed beneath the muscle and expanded for 6-8 weeks prior to flap elevation and transfer. To use this method in the reconstruction of defects secondary to tumors, it often requires that the tumor be excised and initially be covered by a less cosmetic means. It is not possible to wait 6 weeks after a diagnosis of cancer to prepare the flap.
The overall complication rate of tissue expansion is 5 to 7 percent. The rate can be reduced by appropriate patient selection and surgical experience. The most serious complications are overlying skin necrosis, implant exposure, and extrusion. This may occur secondary to infection, trauma, erosion of flap due to folds in the expander, overly aggressive expansion, or placement of the valve over a bony prominence. If the situation is noticed early and thought to be caused by a fold in the expander, the surgeon can attempt to salvage the implant by deflating it and observing the skin. If skin viability returns, the device can be slowly re-inflated. If skin necrosis or expander extrusion occurs, the implant should be surgically removed, the wound cultured and debrided, and the area managed conservatively. Broad-spectrum antibiotics are initiated and frequent wound care and dressing changes are important.
Infection can occur within the expander pocket. In some cases, the infection responds to antibiotics, warm compresses, and partial implant deflation to minimize vascular compromise. If medical therapy fails to clear the infection, the implant should be removed, the pocket irrigated, drained and allowed to heal.
Mechanical failure of the device is unusual. The surgeon should make sure the implant is intact and functioning before placement. When failure and leakage occur, the surgeon has no choice but to remove and replace the expander. The failed implant should be sent back to the manufacturer for analysis of the failure.
Flap ischemia is usually secondary to overfilling of the expander. Pain and blanching are the key indicators that overfilling has occurred. If the flap appears compromised due to decreased capillary perfusion, then the implant should be partially deflated.
It is not always possible to differentiate an expander leak from the development of a wound seroma. Careful aspiration of the fluid collection, as far away from the implant as possible, can be performed for laboratory analysis. If it is a seroma, it can be lightly aspirated and a light compressive dressing applied. During this time the expander should not be inflated.
Remodeling of the skull or facial bones and functional compromise of neurovascular structures should be evaluated. If these complications occur, the implant should be deflated and allow the problem to correct. If there is any doubt about the severity of the compromise, the implant should be removed.
The major emergency in tissue expansion is the development of hematoma after surgery or external trauma. The wound should be reopened, the hematoma evacuated, hemostasis obtained, and the wound copiously irrigated. The key to prevention is careful and meticulous hemostasis at the initial procedure
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