Lip Teh
TISSUE EXPANSION
A) HISTORY
· Codivilla (1905) noted that distraction used for bone lengthening resulted in tissue expansion.
· TE was first used beneficially by Neumann in 1957 (PRS 19:124; 1957). He placed a rubber balloon beneath the temporal skin and serially inflated it to provide local tissue for ear reconstruction. The port was external and the expander was inflated with air. Neumann’s report was treated as anecdotal.
· In 1975 Radovan did clinical trials (met with scepticism) and re-introduced the TE. His expander is the type that is in use today: ie internal, self-sealing port with semi-rigid back plate, expanded with saline.
· In 1982, Austad and Rose develop a self expanding osmotic expander
· Austad independently studied the histological changes of TE in the lab.
B) TYPES OF TISSUE EXPANDERS
- ‘Physiological’ expansion: growth, pregnancy, tumours, festoons, etc.
- Iatrogenic expansion
- Remote port
- Internal port
- Osmotic/hydrophilic expanders
Some expanders are designed to expand asymmetrically due to variations in wall thickness.
Rapid expansion – mechanically assisted delayed primary closure using various commercial devices (Sure-Closure, Wisebands)
C) THE PATHOPHYSIOLOGY AND BIOLOGY OF TISSUE EXPANSION
· TE can be divide up into several phases:
1. Insertion
2. Expansion - wound healing phase, expansion phase,
3. Reconstruction
· The expansion phase may occur at different rates, broadly classified into 4 groups:
1. continuous
2. intra-operative,
3. rapid (eg, daily),
4. slow (eg, weekly).
· TE exerts its effect on tissue aimed at expansion and on adjacent tissue that may not require expansion.
· Expandable tissues are skin (epi and dermis), muscle, fascia,vessels and nerves, hollow muscular organs? other tissues?
· TE is a combination of:
1. Creep - the progressive increase in the skin length that occurs when skin is stretched by a constant force
- Mechanical (70%) - due to collagen fibres adopting parallel orientation, micro fragmentation of elastin fibres, Displacement of water, Recruitment of tissue from adjacent areas
- Biological (30%) – growth of new tissue
2. Stress relaxation - progressive decrease in tension when skin is stretched to a constant length
3. Delay
· Limiting factors to TE include skin elasticity and nutrient blood flow.
Changes that Occur in Different Tissues during Expansion
Generally during the expansion phase, skin gets thinner and the collagen content increases.
1. Epidermis
· Mitotic activity in the epidermis is increased during expansion. The epidermis thickens initially, probably because of postoperative edema, but returns to normal within several weeks.
· With expansion, an increase in melanocytic activity has been noticed. The resulting hyperpigmentation usually disappears spontaneously after reconstruction.
· Histological changes:
1. reduction in inter-cellular distances,
2. flattening of rete ridges,
3. thickening of stratum spinosum (acanthosis)
2. Dermis
· The dermis over the TE thins. This process starts as soon as the TE is placed and continues during expansion.
· Overall, expanded skin has a net accumulation of collagen.
Histological changes (in subcutaneously placed expanders):
1. Thick and compact bundles of collagen are formed and are oriented parallel to the expander surface
2. Active fibroblasts are noted
3. Myo-fibroblasts are seen in the deep dermis near the capsule
4. On EM, elastin fibres become thicker and longer.
5. Accessory skin structures (glands and hair follicles) may show compression but no degeneration.
6. individual follicles hair may be separated by at least a factor of 2 without producing noticeable hair thinning.
3. Subcutaneous Tissue
· Subcutaneous tissue thins as a result of TE, seems to be permanent
· Fat atrophy occurs.
· Fibrous septae thicken.
· Vascular structures increase.
4. Muscle
· Muscle atrophies (whether the implant is placed above or below the muscle)
· Muscle mass is diminished and a ‘bathtub’ depression is seen after removal of the TE.
· It is thought that these changes rapidly reverse and the muscle returns to normal.
· Muscle function usually remains unaffected and atrophy recovers
· Histological changes show only those of pressure atrophy:
1. Reduced mitochondria
2. Abnormally arranged sarcomeres.
· The vasculature in the muscles remain normal.
5. Bone
· Bony erosion occurs under TE (especially in the very young paediatric patient).
· Bony liping and deposition of bone occur at the periphery of the expander.
· Cranial suture lines become effaced and convoluted.
· Serial CT scans reveal decreased bone thickness and volume but unchanged bone density.
· Osteoclastic resorption occurs beneath TE’s and a periosteal reaction occurs at the periphery.
· These changes are progressive and significant and can be seen macroscopically and on histology.
· The pathophysiology is a remodelling effect, not just simple pressure deformation.
· The skull is affected more than the long bones.
· After removal of the TE, the bone remodels. Evidence of this remodelling can be seen from day 5. Full healing occurs by about 2 months (PRS 1990)
· The inner table, the intracranial pressure and the brain are generally not affected by cranial TE’s. Isolated case reports of full thickness erosion.
6. The Capsule
· A dense fibrous capsule forms around the TE. (Thickness = 300 to 1200 microns)
Capsule thickness is greatest at 2 to 2½ months.
There are 4 histological zones to the capsule around a prosthesis (some have observed only 3 zones, ie no transitional zone):
1. Inner zone closest to the TE which contains cellular layer with macrophages and fibroblasts, and relatively acellular collagen fiber bundles
2. Central zone formed by fibrous tissue:
a) fibroblasts and myofibroblasts,
b) thick bundles of collagen fibres becoming increasingly more parallel towards the priphery
3. Transitional zone:
a) loose bundles of collagen,
b) few blood vessels.
4. Outer zone - predominantly a vascular layer containing
a) dilated established and new blood vessels,
b) loosely dispersed collagen fibres,
c) thick and elongated elastic fibres,
d) fibroblasts and occasional mast cells.
· With time the capsule becomes less cellular and more fibrous.
· Only if there is infection or extrusion is there a significant inflammatory cell response.
· The capsule is important in providing the increased vascularity seen in an expanded flap
Changes that have NOT been noted to Occur with TE
· Dystrophic calcification.
· Ossification.
· Dysplastic changes.
· Changes in normal cell maturation.
Vascularity of Expanded Tissue
· _Expanded tissue is extremely well vascularised. This has been shown both clinically and histologically.
· New vessels form adjacent to the capsule.
· The mechanism of formation and degree of persistence after expansion is unknown.
· Expanded random pattern flaps can have a greater length and still survive as compared to control flaps and delayed flaps of the same width (Cherry, Austad and Pasyk, PRS 72:680, 1983):
· Similar experiments with microspheres have demonstrated increased flap length survival as well as increased blood flow to expanded tissue.
· Microsphere experiments have also demonstrated that the circulation in the capsule exceeds that of the sub-dermal plexus!
Where Does the Extra Tissue Come From (Dividend or Loan)?
· Tissue surface area is increased by TE.
· Clinical observation, photos and tattoo techniques reveal that expansion occurs maximally in the central area over the TE and least towards the periphery.
· What is the source of the extra tissue gained by TE?
A] Recruitment of tissue from adjacent areas (loan)
B] Increased growth (dividend).
· Brobmann and Huber (PRS 76:731, 1985) showed significant recruitment of tissue from adjacent areas. This has been confirmed by other authors. Recruitment (or loan) of tissue from adjacent areas should result in thinning of skin at the periphery of an area of TE. But no thinning at the periphery has been demonstrated (ie the skin has not stretched and thinned). In fact the periphery usually appears normal and it is postulated that transient thinning stimulates increased mitotic activity and that thus there is a dividend or net gain in tissue.
· Austad, Thomas and Pasyk (PRS 78:63, 1986) demonstrated increased mitotic activity in the epidermis during expansion. There was a threefold increase in epidermal mitotic activity occurring within 24 hours of expansion followed by a gradual return to normal baseline levels over 2 to 5 days. With prosthesis deflation, there was a significant decline in the rate of epidermal mitoses below the normal baseline level.
· Mechanism of action was not postulated. Expansion would therefore appear to result in a net increase in tissue (a dividend).
· But what percentage of the expanded tissue arises from recruitment and what percentage arises from the growth of new tissue is unknown.
After Reconstruction, What Changes can be seen in the Previously Expanded Tissue?
Essentially none!
1. Epidermal, dermal, subcutaneous tissue and muscle thickness return to normal.
2. Blood vessels return to normal size and number.
3. No residual capsule can be seen.
(In specimens taken 2 years after reconstruction).
D) BASIC PRINCIPLES OF TISSUE EXPANSION
I. Advantages:
1. Local tissue: Better colour, texture, thickness and sensation
2. Minor donor site morbidity (primary closure usually possible)
3. Improved flap vascularity due to delay effect and capsular neovascularisation
4. Generally good aesthetic results
II. Disadvantages:
1. 2 operations
2. Prolonged treatment course
3. Multiple visits and injections
4. Temporary cosmetic and functional impairment
5. Expense
6. Complications
III. Indications:
1. For shortage of tissue
2. For obtaining skin with special desirable qualities
3. Creation of a flap otherwise not possible
4. Avoiding donor site problems
Where is tissue expansion useful:
1. for tissue shortage: eg, for breast reconstruction,
2. for obtaining skin with special desirable properties: eg, for correction of alopecia,
3. for creation of a flap otherwise not possible: eg, pre-expanded forehead flap for nasal reconstruction allows the creation of a broader longer flap than would otherwise be possible,
4. for creation of flaps of skin and functioning muscle: eg, flaps for H+N reconstruction and for facial re-animation,
5. for avoiding problem donor sites: eg, lower leg defects reconstruction.
But, where the lesion can be removed by 3 serial excisions, this is done in preference to TE.
IV. Technique
1. Planning
· Plan the procedure in reverse so that the type of local flap that will be used for reconstruction can be visualised. This allows appropriate selection of expander (size and shape) as well as correct placement of incision and expander pocket. Select stable tissue for expansion.
· Depending on the area – plan for subcutaneous or subfascial/muscular placement
o scalp – place subgaleal (subcutaneous placement associated with ischeamia)
o face – place above SMAS (below SMAS associated with abnormal facial gesturing).
· incisions should not compromise blood supply or later flap movement.
· Place incisions so that they may be incorporated into the incisions necessary for the ultimate reconstruction and so that they are concealed along the borders of facial aesthetic units. Radial incisions are preferred by some to minimize tension on the suture lines, but these may be difficult to accomplish without creating additional scars and perhaps compromising the blood supply to the expanded flap. Radial incisions lie perpendicular to the forces of expansion. This allows inflation of the expander to begin immediately with a lower risk of wound separation. An alternative is to make a small incision at the margin of the defect, roughly parallel to the defect. This tangential incision is at increased risk for wound separation once expansion begins, and no expansion should be attempted initially.
· The expander should be slightly larger than the defect to be repaired. After measuring the defect, select an expander with a slightly larger base diameter. Some authors recommend expanders with a base 2.5 times the diameter of the defect to be closed, although this is not always possible within the confines of the head and neck region.
2. First Stage (Insertion of the TE)
· Peri-operative cephalosporin is used (Iconomou, Michelow, Zuker - Toronto Hosp for Sick Children: Annals 31(2):135, 1993). Cloxacillin at RXH.
· Make a large (usually subcutaneous) pocket - larger than the expander selected to allow the base of the TE to lie flat and to allow closure after placement.
· Some advocate making the pocket prior to choosing the TE. The pocket is made as big as is necessary and then the largest, comfortably-fitting expander is selected afterwards.
· Some recommend that the long axis of the TE be perpendicular to the skin incision so that the suture line is not stressed during expansion.
· Obtain good haemostasis.
· Minimal handling of the TE.
· Check the function and integrity of the TE prior to placement.
· Place the filler port in a separate subcutaneous pocket.
· Place a small volume of saline (10-20% of the volume of the TE) in the TE to reduce folds and to improve haemostasis by the pressure effect.
· Drains are used by us but not in Toronto (ref. above).
· Closure in at least 2 layers: 1 layer to close the pocket with the TE inside; 1 (or more) layers to the skin and subcut tissue.
3. Expansion
· Begin expansion only after the incision has completely healed, usually after + 3 wks.
· Expansion should be done under sterile conditions injecting saline via a small (usually 23 gauge) needle. Inject + 10 to 20% of the total TE volume (rough guide).
· Sedation / EMLA cream are useful adjuncts, especially in the child.
· The end points of expansion are determined by:
a) patient comfort / pain
b) skin tension and blanching.
· Continue expansion until enough soft tissue to cover approximately twice the area of the defect has been achieved. Over-expansion is better than under-expansion.
· Measurement over the dome(height) of the expander minus the base width of the expander provides a rough estimate of the additional tissue available for reconstruction
· Usually wait about 3 weeks before the reconstruction is done.
4. Reconstruction
· Reconstruction is done with the local expanded flap (advanced, transposed or rotated) or the expanded tissue can be used as a free graft. Check that the expanded tissue is large enough before excising any lesion.
· Evidence exists that the increased vascularity of expanded flaps may be exquisitely sensitive to the vasoconstrictive effects of adrenaline; therefore, it should not be used