19. Tissue Expansion
- The word ‘expand’ means to increase in size and bulk and expansion is one of the principle characteristics of living tissue during growth and is genetically encoded. This encoding allows the skull to remain in an unfused state to accommodate the rapid growth of the brain in the first two years and the skull continues to remain malleable for several years later to accommodate the deposition of non-neuronal tissue. The increase in blood supply as development occurs is proportionate to growth. This happens steadily with the exception of some spurts for e.g. adolescence. The uterus expands very rapidly during pregnancy (from the size of a pear to a football) and the increase in blood supply in this instance occurs via neo-angiogenesis. This tissue expansion has been known to the human race probably ever since it came into existence. However the recorded use of this principle of expansion of tissue in the form of a surgical treatment has been very recent (less than 70 years).
- In the little known anecdote narrated by Ilizarov the well known Siberian surgeon, a patient accidentally turned the screws the other way round on his ring fixator for several weeks causing distraction of bone ends instead of bringing them together which was what Ilizarov was attempting to do.What was revealed in that case was to lay the foundation for stretching and expanding tissue because new bone had been deposited in between the distracted fragments leading to a net gain in length. Ilizarov postulated that this had resulted from a chronic anoxic stimulus because of the stretching of blood vessels which lead to increase in vascularity and deposition of new bone.Tony Watson, the editor, adds that Ilizarov was born in Poland, went to school in Azerbaijan and to a medical school in the Crimea before being sent by his Soviet masters to Siberia.
- Over the last three or four decades expansion mainly of skin and subcutaneous tissue has been used to create and recruit more tissue which can be used as flaps in adjacent areas (classically in the head and neck) or to create space to accommodate an implant (as in the breast). The expanders are made of derivatives of silicon in the form of bags of varying shapes and sizes and usually have a less expandable and a more expandable surface. Modern tissue expanders have a filling system in the nature of a tube, continuous with the main expander and a soldered port at the end of the tube in which saline can be instilled by injection with a fine needle of less than 24 gauge. Expansion is done over several weeks. Normally about 10% of the total expander volume is injected at a time, generally once a week. The process of expansion is time consuming, maybe painful and, when expanders are used in exposed parts, they can produce an unacceptable, unnatural appearance over several weeks/months. The recipient of the expander needs to be told of every detail of the procedure and must be psychologically stable, which may not be the case because of the deformation that the patient has already suffered. He or she must be warned of complications such as a leak, more often from the port which normally has a sealing quality and might be minor, and rarely from the main bag of the expander. The latter will invariably mean removal of the expander and the process will have to be started again with a new expander. Pain during the process of expansion can be severe in some cases, is unpredictable and might force the procedure to be abandoned. Because modern expanders have a buried port, infection is uncommon but because expansion is done as an out-patient procedure, strict aseptic precautions must be ensured at the time of the procedure. Occasionally an expander can get exposed if expansion is done too rapidly and overlying skin might give way. In the life of an average plastic surgeon tissue expansion does not constitute a frequent procedure and the learning curve can be slow. All the more reason why the patients must be made aware of all untoward possibilities.
- Placement of expanders must follow proper planning. The defect to be created after excision of the lesion must be measured accurately and about 10% must be added to the figure to allow for retraction of surrounding tissue after the excision. The availability of surrounding tissue must then be measured. The amount to be obtained by expansion is added to this measurement to judge if the expanded tissue will suffice to cover the defect. The expandability of the tissue varies. Roughly the forehead and the scalp will expand optimally up to twice its size. The neck, the breast and the abdominal wall will expand more, in an ascending order but each individual case has to be judged independently. The undersurface, where the expander rests is important and the firmer it is the better the overlying expansion.
- Tissue expanders create consequences on the tissue on which they rest, though this underlying part is usually less expandable. Be that as may, the process of expansion can produce atrophy of muscles or render a bone thinner (a scalloped appearance of the bone is visible to the naked eye when the expander is removed). Fortunately both effects are short lived and a reversal to normalcy occurs within months.
- Effects of expansion on the tissues:
– Expansion leads to addition of bulk in the expanded tissue by way of formation of well differentiated cells through mitosis as well as recruitment from the surrounding skin.
– The process of expansion induces deposition of collagen fibres which appear to be laid parallel to the expanding agent and is also accompanied by creation of myofibroblasts in large numbers.
– The expander gets surrounded by a thick fibrous capsule; the extent of this capsule is proportionate to the amount of expansion.
– The area under expansion increases its vascularity greatly through active neo-angiogenesis.
- While all of these effects enable a surgeon to use this expanded skin in adjacent areas which have a similar texture, colour and other properties (such as in hair bearing skin), the formation of the capsule means extraction of the expander after its purpose is served is easy and angiogenesis means that the flaps created by expansion are very safe for local transfer. The deposition of collagen and elastic tissue means that the elasticity of the transferred tissue is maintained. However the presence of a large number of myofibroblasts while ensuring that healing around the transferred flaps will remain robust;scars (sometimes hypertrophic) can be a problem. The capsule gives an added advantage when cover is obtained over uneven defects.
- While planning the expander and later while advancing flaps or transferring them the surgeon must make sure that the blood supply (axial) of the flap is kept in mind. In fact at the time of planning itself the blood vessels on which the flap is or will be based should be clearly included in the design of the flap that will ultimately move to an adjacent location.
- Indications:After a period of initial enthusiasm where tissue expansion was used for a variety of indications, the use of tissue expanders has become somewhat circumscribed. Successful transfer of hair follicles as free grafts, in large numbers, in a single sitting under local anaesthesia by trichologists from different disciplines, has meant that patients (!) with male pattern baldness would rather not undergo a prolonged and sometimes painful and obviously ugly looking process of tissue expansion followed by surgery under general anaesthesiafortransfer of expanded flaps.
Post-burn or post-traumatic alopecia however still remains an indication for flap cover after tissue expansion but here as well, if the scar is restricted to the dermis and the subcutaneous tissue is spared, successful follicular transfer in several sittings remains a viable option for the patient. Excellent modern wigs are now available and many of them will opt for them for severe (grade IV or V) alopecia where all surgical modalities have very limited applications.
In the breast as well, with the advent of large free soft tissue transfers together with skin from the lower abdomen, based on perforators, immediate adequate full reconstruction of the breast can be undertaken, particularly because modern oncological practices for early malignant lesions of the breast do not involve extensive excision and spares adequate skin. However in such cases tissue expansion is still sometimes employed; the scar of the mastectomy is allowed to settle and the expander is introduced through the same area. After the expander has reached a desirable size an implant is introduced by an axillary approach. The areolar reconstruction in either of the above methods is done secondarily. Immediate expander placement is also possible, at the time of the mastectomy, if there is not enough skin for an adequate sized implant to be inserted.
Tissue expansion in the breast is ideal for asymmetry, severe unilateral hypoplasia, amazia and Poland’s syndrome in which the pectoralis major muscle is also missing. A breast implant of an appropriate size after an adequate expansion once the pubertal spurt is completed gives excellent results. The expander can be introduced during the time of breast development and gradually filled to keep pace with the other breast. In the case of Poland’s syndrome a breast expander can be used under the latissimus dorsi which is transferred to the chest wall to start with and allowed to settle. Once the expansion is complete an implant is then introduced. In all of the above, the incisions employed will be in and around the axillary region and are somewhat hidden.
The other indications where tissue expanders help greatly is around the face, the neck and the nose, for example, large nevi, very broad scars or mutilating injuries of the nose. These may require not only skin cover but also a skeletal reconstruction. The skin in the neck can be expanded to be used over the face or across the other part of the neck and the skin over the lateral part of the face after expansion can be transposed, advanced or rotated over its central part. A broad defect on the nose can be covered with an expanded forehead flap where the residual defect can be closed easily even though the flap was quite broad. In all the above examples the texture, the colour and the quality of the skin is maintained.
An unusual indication for tissue expansion is to allow the harvest of a full thickness graft. Expanded neck skin is an excellent source for such full thickness grafts because the residual defect can be closed transversely within one of the creases. Photographs wherein a large full thickness graft was harvested from expanded abdominal skin are included here because this is an unusual application.
- The use of tissue expanders in the extremities particularly below the elbow or the knee is not very rewarding.
- Tissue expanders in children below five years are usually avoided because the children are not cooperative and it is difficult to control their activities.
- While it is possible to employ sub-muscular expanders particularly in the back to create large musculo-cutaneous flaps (latissimus dorsi) they are rarely employed because subcutaneous expansion is adequate to create large flaps to effect local transfers. However such expanded musculocutaneous flaps are occasionally used as free flaps for very large defects in other parts of the body.
- In reconstruction of the breast with or without tissue transfers, the use of expanders is safe if radiotherapy is in progress. Exchange of the expander with an implant is generally delayed to 3 months after radiotherapy is complete.
- Expanders which expand by themselves by incorporating hygroscopic substances, though an extremely attractive proposition, have not been popular because the rate of expansion so far has not been controllable. This causes problems.
- While introducing a standard expander it is beneficial if some saline is injected at that time to prevent any dead space that might occur and to reduce the time of the expansion process.