I. INTRODUCTION
A. Definition
1. An artificial filling device is used to grow and expand local tissue to reconstruct an adjacent soft tissue defect when primary closure is not possible.
2. A silicone elastomer reservoir is placed beneath the donor tissue and slowly filled over time with saline, causing the overlying soft tissue envelope to stretch with a net increase in surface area per unit volume.
B. Advantages
1. Reconstruct “like with like” using donor and recipient tissues that share similarities in color, thickness, texture, and hair-bearing patterns.
2. Larger soft tissue defects that would usually require a local flap for reconstruction can be closed primarily using expanded local tissue, which simultaneously limits donor site morbidity.
3. A robust angiogenic response is achieved histologically within the expanded local tissue resembling an incisional delay phenomenon.
4. Predictable amounts of donor tissue can be gained through the expansion process
5. As a reconstructive technique, it is versatile, reliable, and repeatable and can be applied to many regions of the body.
C. Disadvantages
1. Multiple operations (at least two for placement and removal of the expander) and outpatient visits are required.
2. Definitive reconstruction is delayed secondary to the expansion process.
3. Specific complications related to the presence of foreign material (e.g., infection, exposure, or extrusion).
4. Temporary contour deformity at the donor site that is often difficult to conceal (e.g., scalp and forehead reconstruction).
II. HISTOLOGY
A. Soft tissue
1. Skin
a. *Epidermis
i. Increase in thickness through hyperkeratosis and acanthosis
ii. Increase in mitosis
iii. Narrowing of intracellular spaces
b. Dermis
i. *No change in thickness of papillary dermis, but there is a decrease in thickness of reticular dermis so overall thinning
ii. Fibroblast and myofibroblast increase in number with thickened collagen bundles.
iii. Sweat glands and hair follicles spread out and demonstrate degenerative changes.
iv. Fragmentation and rupture of elastin producing striae
c. Clinically, expanded skin is often dry with pigmentary changes, and there is decreased appreciation of pain, temperature, pressure, and light touch.
d. Changes in thickness of expanded skin are temporary, and return to baseline occurs approximately 2 years after the expansion process.
______________
*Denotes common in-service examination topics
a. *Decrease in mass
b. Decrease in thickness and mass.
c. Myofibril and myofilament disorganization.
d. No loss of function, but muscle injury has been reported during the expansion process (e.g., reduced brow elevation due to frontalis damage).
3. Fat
a. *Decrease in thickness, especially subcutaneous fat.
b. Clinically, this manifests as reduced flap bulk.
c. Atrophic adipocytes are eventually replaced by fibrosis causing fat loss (30% to 50%) which is permanent.
B. Capsule
1. Formed by a foreign body reaction composed of parallel-oriented fibro-blasts intervening with a dense layer of collagen bundles.
2. During removal of the expander, capsulotomy increases surface area and maximizes flap advancement.
3. Capsulectomy should be used judiciously to avoid interrupting the vascular supply to random-pattern flaps.
C. Vascularity
1. Expanded skin is hypervascular
2. Greatest density of blood vessels is found at the interface between the capsule and expanded local tissue.
III. BIOMECHANICS
A. Creep
1. Definition
a. The tendency of tissue to deform permanently under the influence of stress.
b. Can either be an acute (mechanical) or chronic (biological) response to sustained tissue stretch.
2. Mechanical
a. Acute tissue elongation due to reorientation of the collagen bundles in parallel with the applied force vector, and recruitment of adjacent tissue from surrounding zones of skin laxity.
b. Mechanical creep is responsible for the initial gain in tissue length at the time of expander placement as a result of the intraoperative fill volume.
c. Water is displaced out of ground substance and elastic fibers microfragment.
3. Biological
a. Chronic tissue elongation due to new tissue regeneration.
b. Both during and following completion of the expansion process, sustained tissue stretch leads to the addition of new tissue within the expanded field by activating collagenogenesis, angiogenesis, and epidermal proliferation.
B. Stress relaxation
1. Stress is defined as the average force per unit surface area within the tissue.
2. Strain is defined as the amount of tissue deformation that occurs in response to stress.
3. Stress relaxation refers to the gradual decline in stress over time at constant strain in biological tissues. Clinically, this is important because the acutely stretched tissue can relax before the next expansion, thereby preventing ischemia-related complications of the overlying soft tissue envelope.
IV. PRINCIPLES OF TISSUE EXPANDER PLACEMENT
A. Fundamental design
1. Shape
a. Rectangular expanders are useful on the trunk and extremities, and result in the greatest amount of actual tissue gain (approximately 40% of theoretical tissue gain).
b. Round expanders are most commonly used in breast reconstruction and result in the least amount of actual tissue gain (approximately 25% of theoretical tissue gain).
c. Crescent expanders are useful in scalp reconstruction and gain more tissue centrally than peripherally.
d. Anatomic expanders differentially expand the overlying soft tissue envelope to more accurately recreate the body part of interest (e.g., teardrop-shaped expanders used in breast reconstruction).
e. Custom expanders are designed for irregular defects, but may be more expensive.
2. Filling port
a. *Remote filling ports are connected to the tissue expander via silastic tubing and can either be placed subcutaneously (most common) for percutaneous access or externalized for direct access. Crucial not to make tunnel too wide or port will fall down back next to the expander making it difficult to fill.
b. Integrated filling ports are located within the expander, although this design may increase the risk of inadvertent puncture of the outer shell.
c. Self-filling osmotic expanders do not have a filling port, but instead rely upon an osmotically active hypertonic saline or hydrogel-based solution to gradually absorb fluid from the surrounding soft tissues over a 4- to 8-week time period.
3. Permanence
a. Most tissue expanders are temporarily placed, and either later exchanged for a permanent saline or silicone prosthesis, or removed completely to allow for rearrangement of the expanded local tissue.
b. A few permanent expanders are less commonly used in breast reconstruction, consisting of an empty inner core designed to be remotely filled with saline, surrounded by an outer compartment filled with silicone gel.
B. Geometry of tissue expansion
1. Use the largest expander possible with a base diameter approximately two to three times that of the diameter of the soft tissue defect to be reconstructed.
2. If the expander contains a base plate or rigid backing, this side should be placed along the floor of the pocket to guide the direction of expansion outwards.
3. Multiple expanders are sometimes needed to reconstruct a single defect, depending on the availability of donor tissue.
C. Donor site
1. The expander is usually placed adjacent and parallel to the long axis of the soft tissue defect; if placed in the extremities, the expander should not cross any joints or impinge on joint motion.
2. Donor tissue must be well vascularized and free of unstable scar and must display no evidence of infection or contamination.
3. Use cautiously in irradiated tissue or patients with poorly controlled diabetes mellitus, vascular disease, or connective tissue disorders.
D. Expander pocket
1. The expander pocket can be developed in the subcutaneous, submuscular, or subgaleal planes depending on the location of the soft tissue defect.
2. The size of the expander pocket should be individually tailored to allow the expander to lie completely flat with minimal wrinkling.
3. Excessive dissection should be limited to prevent expander migration postoperatively, and meticulous hemostasis is important to minimize hematoma formation.
E. Incision placement
1. *Incisions are placed radial to the expander pocket and perpendicular to the direction of expansion to minimize tension on the incision during the expansion process; undue tension placed on the incision during expansion can cause dehiscence and exposure of the expander.
2. Consider future reconstructive options when planning incision placement such that the incisions can easily be incorporated into planned flaps or the tissue to be resected.
3. Endoscopic-assisted expander placement (refer to Chapter 6, “Endoscopic Plastic Surgery”) utilizes smaller incisions and allows more direct visualization of the expander pocket, but at the expense of a steep learning curve and altered depth perception.
1. Insert a 23G butterfly needle or Huber (noncutting) needle into the filling port perpendicularly; bigger needles should be avoided because they can cause valve leak due to increased back pressure.
2. At the time of expander placement, an initial volume is infused intraoperatively to gently fill the expander pocket to prevent seroma formation, and in the case of breast reconstruction patients, to maintain the shape of the overlying soft tissue envelope.
3. The expansion process usually begins 2 to 3 weeks postoperatively and continues on a weekly basis thereafter.
4. Approximately 50 to 100 cc can be infused during each expansion, but regardless of the volume infused, the expander is filled until the patient expresses discomfort or the overlying skin blanches.
5. The expansion process is complete based on surgeon preference when he/she deems there is enough donor tissue available to reconstruct the soft tissue defect; however, this is often a difficult decision and additional “over” expansion is often recommended to ensure adequate soft tissue coverage.
V. CLINICAL APPLICATIONS
A. Scalp and forehead reconstruction
1. Indications include traumatic, congenital, and oncologic soft tissue defects, as well as androgenic and burn alopecia; *approximately 50% of the scalp can be reconstructed using tissue expansion without causing noticeable thinning of the remaining hair.
2. The expander is usually placed in either the subcutaneous or subgaleal (more common) planes.
3. Incisions are camouflaged in either the frontotemporal hairline, brow line, vertical midline, or within relaxed skin tension lines.
4. Following completion of the expansion process, the soft tissue defect is often reconstructed with a large rotation-advancement flap; however, it is not uncommon for multiple rounds of tissue expansion to be required in a serially staged process.
5. Caution should be observed when expanding near the temporal branch of the facial nerve to avoid stretching or iatrogenic transection.
B. Facial defects
1. Indications are identical to scalp and forehead reconstruction.
2. The expander is placed in the subcutaneous plane centrally or over the parotidomasseteric fascia laterally.
3. Following completion of the expansion process, the soft tissue defect is often reconstructed with a local flap.
4. Caution should be observed when expanding near the zygomatic and buccal branches of the facial nerve and Stenson’s duct.
C. Nasal reconstruction
1. Small soft tissue defects can be reconstructed using tissue expansion; most useful in the thin, mobile skin over the root or dorsum of the nose.
2. When using a forehead flap, intraoperative tissue expansion of the forehead skin may allow for primary closure of the donor site via mechanical creep.
D. Auricular defects
1. Indications include both congenital (e.g., microtia) and acquired causes (e.g., traumatic amputation, burns, or skin malignancy).
2. The expander is placed in the subcutaneous plane.
3. The incision is placed along the postauricular hairline.
4. Following completion of the expansion process, thin, well-vascularized, non- hair-bearing skin can be easily draped over the inserted neocartilaginous framework.
E. Neck reconstruction
1. The expander is usually placed above the platysma.
2. Caution should be observed when expanding near the marginal mandibular and cervical branches of the facial nerve.
F. Breast reconstruction (refer to Chapter 37, “Breast Reconstruction”)
1. Indications include both immediate and delayed reconstruction after acquired mastectomy defects.
2. Usually a two-stage procedure, in which the expander is later exchanged for a permanent saline or silicone prosthesis once the expansion process is complete and tissue equilibration has been achieved, although a second procedure can sometimes be avoided if the expander behaves as a permanent implant.
3. The expander is placed beneath the pectoralis major, and the inferolateral pole is covered by either serratus anterior fascia or processed acellular dermal matrix scaffold.
4. Caution should be observed in irradiated tissue given increased postoperative expander-related complications including infection, exposure, and extrusion.
G. Abdominal wall reconstruction
1. Similar to scalp reconstruction, approximately 50% of the abdominal wall can be reconstructed using a components separation technique after the expansion process is complete.
2. The expander is placed either in the subcutaneous plane or between the external and internal obliques for myofascial defects.
3. Due to the segmental innervation pattern of the abdominal wall, damage to any motor or sensory nerves is less likely to have long-standing, debilitating consequences compared to the use of tissue expansion in the extremities.
H. Upper and lower extremity reconstruction
1. *Classically, the use of tissue expansion in the extremities is associated with higher complication rates, especially in the lower limb.
2. The expander is placed above the deep investing fascia of the muscles.
3. Caution should be observed when expanding near named sensory nerves and superficial vessels due to the lack of a segmental innervation pattern in the extremities.
4. There is an increased propensity to form keloids in the deltoid region.
5. The expander should not cross any joints or impinge on joint motion.
I. Flap pre-expansion
1. Pre-expansion of axial fasciocutaneous flaps facilitates coverage of larger soft tissue defects using expanded local tissue and simultaneously limits donor site morbidity by allowing primary closure.
2. Pre-expansion of myocutaneous flaps improves safe flap transfer due to a robust angiogenic response within the expanded local tissue resembling an incisional delay phenomenon.
VI. COMPLICATIONS AND TREATMENT
A. Major
1. Cellulitis and periprosthetic infection
a. Requires early and aggressive treatment with intravenous antibiotics.
b. If caught early, salvage of the expander may be possible with intravenous antibiotics alone; however, removal of the expander is often needed due to decreased clearance of bacteria from around the expander.
c. If the infection becomes periprosthetic, removal of the expander is absolutely mandated.
d. Port site infections can sometimes be managed by externalizing the remote filling port.
2. Hematoma
a. Evacuation of the hematoma is necessary to prevent ischemia of the overlying skin flaps and bacterial superinfection.
b. Removal of the expander is often not necessary.
3. Expander exposure or extrusion
a. Requires removal of the expander if bacterial colonization is suspected.
b. Most commonly due to inadequate pocket creation.
c. Treat infection, if present.
4. Expander deflation
a. Usually presents clinically as a “flat tire,” and most often the result of iatrogenic puncture during insertion of the filling needle.
b. Requires removal and replacement with a new expander.
a. Avoid aggressive dissection during expander placement to prevent devascularization of the overlying skin flaps.
b. Avoid expanding too much during an individual session. If the overlying skin turns white, remove some fluid from the expander.
c. Partial thickness necrosis can usually be managed with local wound care.
d. Full-thickness necrosis requires debridement of all devitalized tissue and reclosure to ensure adequate soft tissue coverage of the expander.
e. Treat infection, if present.
B. Minor
1. Incorrect valve placement or valve turnover.
2. Inadequate expansion.
3. Pain during expansion.
4. Temporary contour deformity at the donor site.
5. Widening of surgical scars.
6. Transient neuropraxia of both motor and sensory nerves.
PEARLS
1. An exposed expander can sometimes be further expanded if not infected.
2. Methylene blue can be used to color the contents of the expander to help identify the valve correctly when filling and to detect leakage more easily.
3. Expanded local tissue can be reexpanded 3 to 6 months later.
4. The epidermis is the only layer of skin that increases in thickness during tissue expansion.
5. The base diameter of the expander should be approximately two to three times that of the diameter of the soft tissue defect to be reconstructed.
6. Approximately 50% of the scalp and abdominal wall can be reconstructed using tissue expansion.
QUESTIONS YOU WILL BE ASKED
1. Describe the phenomena of creep as it relates to tissue expansion.
Creep describes the biological response of cells which proliferate in response to continued mechanical stress.
2. Describe the histological changes seen with tissue expansion.
Gap junctions become disrupted, epidermis thickens, dermis becomes thinner.
3. Describe the contraindications to tissue expansion.
No absolute contraindications, but irradiated bed, infection, extremities in children are all relative contraindications.
4. What is the effect of tissue expander on overlying skin?
Blood flow increases, causing tissue expansion to mimic the delay phenomenon.
Recommended Readings
Austad ED, Pasyk KA, McClatchey KD, Cherry GW. Histomorphologic evaluation of guinea pig skin and soft tissue after controlled tissue expansion. Plast Reconstr Surg. 1982;70(6):704–710. PMID: 7146153.
Cherry GW, Austad E, Pasyk K, McClatchey K, Rohrich RJ. Increased survival and vascularity of random-pattern skin flaps elevated in controlled, expanded skin. Plast Reconstr Surg. 1983;72(5): 680–687. PMID: 6194539.
Huang X, Qu X, Li Q. Risk factors for complications of tissue expansion: a 20-year systematic review and meta-analysis. Plast Reconstr Surg. 2011;128(3):787–797. PMID: 21572375.
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. PMID: 8282904.
Wilhelmi BJ, Blackwell SJ, Mancoll JS, Phillips LG. Creep vs. stretch: a review of the viscoelastic properties of skin. Ann Plast Surg. 1998;41(2):215–219. PMID: 9718160.
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