Tissue expansion

Tissue expansion
Intervention
MeSH	D015626

Skin and tissue expander with inflatable balloon device

Tissue expansion is a technique used by plastic and restorative surgeons to cause the body to grow additional skin, bone or other tissues.

Skin expansion

Skin expansion using a subcutaneous inflatable balloon

Skin expansion is a common surgical procedure to grow extra skin through controlled mechanical overstretch.It creates skin that matches the color, texture, and thickness of the surrounding tissue, while minimizing scars and risk of rejection.

When skin is stretched beyond its physiological limit mechanotransduction pathways are activated. This leads to cell growth as well as to the formation of new cells. In some cases, this may be accomplished by the implantation of inflatable balloons under the skin (see figure). By far the most common method, the surgeon inserts the inflatable expander beneath the skin and periodically, over weeks or months, injects a saline solution to slowly stretch the overlaying skin. The growth of tissue is permanent, but will retract to some degree when the expander is removed. Topically applied tissue expansion devices also exist. These have the benefit of being inexpensive and do not require a surgical procedure to implant them under the skin.

Breast reconstruction surgery, for example, can use this technique when the mammary gland was removed by surgery (mastectomy). Later, a more permanent breast implant filled with saline or silicone gel is inserted under the expanded skin pocket.^{[citation needed]}

In other applications, excess skin is grown purposely by expansion on the back or the buttocks, so that it can be harvested later for transplantation to another site where skin was lost due to trauma, extensive wounds, surgery, burns, etc.

Tissue expansion has also been used for the technique of foreskin restoration, which is usually non-surgical and applies tension externally using specialized devices to replace circumcised tissues with new cells.

Mechanics of skin expansion

Stretching the skin beyond normal expansion invokes several mechanotransduction pathways which increase mitotic activity and promote collagen synthesis. As a result, the skin surface area increases. Continuum mechanics approaches can be used to model skin growth during tissue expansion and non-linear finite element methods can me used to computationally simulate different tissue growth scenarios.

Tissue growth due to skin expansion can be modeled as anisotropic surface area growth as described by the following equations:

$F = F^e \cdot F^g\,$

where $F^e$ is elastic area stretch that is reversible and $F^g$ is irreversible area growth described by:

$F^g = \sqrt{\theta^{g}}\mathbb{I}+[1-\sqrt{\theta^{g}}]n_{0}\otimes n_{0} \,$

where $n_{0}$ is a vector in the direction of skin thickness. We assume that the skin does not grow in the thickness direction for area growth is equal to volume growth or $\theta^{g} = det(F^{g}) = J^{g}$. We also assume that the newly created skin will have the same density, stiffness, and microstructure as the original, non-expanded skin.

Radial Forearm Free Flaps

Recent studies have demonstrated that using topical tissue expansion can reduce the need for a split thickness skin graft after harvesting a forearm free flap. The authors noted that this results in less pain as well as reduced healing time. This method has also been shown to be cost effective as well as improve cosmetics.^{[citation needed]}

For Foreskin Restoration

Circumcised men can use non-surgical tissue expansion techniques to expand their surviving penile skin, making it a longer tube so it can function like a foreskin. Methods may involve securing a tension strap or weight to the skin with tape, or gripping the skin with a tapeless foreskin restoration device that uses straps, or weights, or tension derived from internal expansion of the device. Some men succeed by tugging on the penile skin regularly with their fingers. The total time commitment to go from circumcised to an uncircumcised man's appearance and function might be 2 to 4 years (or more, depending on the severity of the circumcision) while tugging up to 12 hours per day. A foreskin restorer does not usually involve his doctor in the process.^{[citation needed]}

In scalp reconstruction

Tissue expansion has been used on the scalp for treating scalp scarring, in lieu of hair transplation when there is insufficient donor hair to transplant on the scar or the scar tissue is not vascularized to support hair growth. For instance, in a patient who had melanomas removed from the scalp resulting in alopecia defects (hair loss), even one of the most ancient stories of hair loss alopecia is told in the Bible. tissue expansion can be used to allow for the removal of scars and complete hair coverage. The two main indications for choosing tissue expansion over hair grafting are the size and shape of the defect relative to potential supply of donor hair, and the quality and thickness of the scar tissue. Areas of significant scarring and/or tissue atrophy, which is likely to make hair grafting unsuccessful, are best excised and replaced by normal expanded scalp skin. Theoretically, there is no limit to the amount of tissue that can be created with tissue expansion, provided the process is conducted gradually.

Bone expansion

Main article: Distraction osteogenesis

Bone is another tissue that can be expanded relatively easily, by using external devices which are slowly separated using mechanical contraptions, so that bone grows in response to elongation (bone distractor). Other techniques and external devices have been studied and have shown some success, such as in the fitbone surgery. This technique was pioneered in 1951 by the Russian physician Ilizarov, and is called the Ilizarov apparatus. It is capable of lengthening limbs in cases of pathological loss of bone, asymmetry of limbs, dwarfism, short stature, etc. In reconstructive and cosmetic surgery, bone expanders have been used to elongate the mandibula in cases of congenital disorders, trauma, tumors, etc. Other newer devices such as the orthofix and intramedullary skeletal kinetic distractor (ISKD) are also used for limb lengthening. It can add over 6 inches per bone, but is expensive, painful, and time-consuming (each procedure lasts around 8–12 months).^{[citation needed]}

Breast tissue expansion

Tissue expansion is a common technique used for breast reconstruction. This essentially involves expansion of the breast skin and muscle using a temporary tissue expander. After three to four weeks of the mastectomy , a salted solution will be injected into the expander to gradually fill it. This process is supported by a tiny valve mechanism located inside the expander and it will continue until its size is slightly larger than the other breast. Typically it can take several weeks to months to complete the process. This tissue expander is removed after a few months and microvascular flap reconstruction or the insertion of a permanent breast implant is done at the time. Chemotherapy or radiation is sometimes be recommended to by surgical oncologist following after mastectomy. These treatments delays the tissue expansion process by approximately four to eight weeks.Tissue expanders have silicone outer shells and either an internal valve or external port to allow for saline fluid injections.

External links

• Ilizarov apparatus.
• About Faces: Skin. NICDR National Institutes of Health on-line exhibit. Source of the images used.
• Foundation for Hair Restoration