Introduction
Tissue expansion relies on the ability of skin and soft tissues to generate in response to tension. In plastic surgery, tension is generated by implanting a subcutaneous balloon (expander) that is inflated over a period of weeks; new tissue is generated in response to the constant stretch caused by the progressive inflation of this expander. This tissue can be used to reconstruct extirpative or traumatic defects such as those encountered after mastectomy, burn excision, or removal of giant nevi.
Biological Basis of Tissue Expansion
A number of studies support the concept that the increase in skin surface area after expansion is due to the generation of new tissue rather than the stretching of existing skin. In culture, mechanical stress induces fibroblast and epidermal hyperplasia. These cells preserve their phenotype without malignant degeneration. This observation is supported by the fact that there has never been a reported case of skin malignancy secondary to tissue expansion.
From a histological standpoint, adult and pediatric skin responds to expansion in the same manner. Within 1 week of expansion, the epidermis begins to thicken and the dermis thins. The skin appendages do not change. The subcutaneous fat and muscle atrophy. Cellular proliferation reduces the resting tension of the skin over time, enabling another round of expansion to take place. Once the process is complete, the expanded skin eventually returns to its baseline thickness. The vessels of the skin and subcutaneous tissue also resume their pre-expanded size and number; however anecdotally, some flaps demonstrate increased vascularity.
Indications
In general terms, expansion of tissue is used to improve rotation, transposition or advancement of local or regional flaps, or to increase the harvest of full-thickness skin grafts. Recently, tissue expansion has been successfully applied to myocutaneous and free flaps. In adults, aside from their use in breast reconstruction, tissue expanders are used primarily for secondary burn and trauma reconstruction in the head and neck region. In the pediatric population, expanders have been used in a multitude of reconstructive procedures. The most common indication in children is to reconstruct defects left by excision of giant congenital nevi. Tissue expansion is contraindicated in infected skin. Although expansion is possible in radiated or scarred tissue, it is associated with a much higher complication rate and should be avoided whenever possible.
Technique
Expanders come in a variety of shapes and sizes, and there is no absolute ideal expander for a given site or condition. Expanders can have either internal or external filling ports. Most experienced surgeons recommend using remote ports. These should be placed away from the expander. Internal ports have both a higher failure rate and a greater incidence of accidental expander rupture. In children, the use of internal ports is associated with a higher rate of exposure of the expander due to the pressure exerted on the skin by the port. Whenever possible, the incision should be placed within tissue destined to be excised, as in the case of congenital nevi. Straight incisions along the border of the defect should be avoided because this will enlarge the defect and may interfere with flap coverage. An alternative is to use a U- or V-shaped incision that is hidden and remote from the defect. Such incisions should be perpendicular to the direction of expansion in order to maximize skin blood supply. When doing serial expansion, longitudinal blood supply must be preserved. This holds true especially in the trunk and extremities.
The expander should be placed on top of the deep fascia (or subgaleal in the scalp), unless the plan is to incorporate muscle into the expanded flap. The pocket should always be larger than the base diameter of the expander. Blunt dissection in a single fascial plane is safest for preserving blood supply. Most surgeons overinflate tissue expanders beyond the manufacturer’s recommended maximum capacity. Studies have demonstrated that significant overinflation is possible before weakening or rupturing. The rate of inflation is variable and largely based on surgeon preference. Patient comfort and signs of tissue perfusion, such as tension, color, and capillary refill, guide the filling rate. Filling is usually initiated one week after surgery.
Tissue expansion should continue until the expanded area is larger than the defect, because of the length that is lost upon advancement and inset of the flap. The use of rotation and transposition flaps enables the transfer of tension from the tip of the flap more proximally to its base. A single or double back-cut can be performed prior to inset in order to gain extra length. Lastly, the donor site should be closed in layers after the implant capsule is excised. Pre-expansion of distant pedicle- or free-flaps facilitates closure of otherwise tight donor sites.
Intraoperative Expansion
Most surgeons fill the expanders intraoperatively with sufficient saline to eliminate dead space and tamponade raw surfaces to help prevent postoperative bleeding. There is, however, an alternative to traditional prolonged expansion. Immediate intraoperative expansion combined with broad undermining of the defect can help reduce the tension that occurs on the distal parts of a local flap. In rapid expansion, the skin initially expands due to its elasticity and the displacement of interstitial fluid. Within minutes, the alignment of the collagen fibers changes due to the stretch. This process yields up to 20% more tissue for flap coverage. Intraoperative expansion is indicated for relatively small defects, such as in coverage of defects of the ear.
Scalp
Although tissue expansion does not increase the number of hair follicles, the size of the hair-bearing region can be doubled without a noticeable decrease in hair density. As such, tissue expansion may be used a means of treating male pattern baldness in addition to reconstructing the scalp. Expanders are most commonly placed in the occipital or posterior parietal regions. They should be placed under the galea, superficial to the periosteum. It usually requires 6-8 weeks to complete the expansion in adults, and up to 12 weeks in children. Radial scoring of the galea at the time of surgery can speed the process. Once the expansion is complete, flaps are advanced or transposed, ideally based on named arteries of the scalp. It is important to orient flaps so that the correct direction of hair growth is maintained. Although galeal scoring or capuslotomy incisions can be useful, wide undermining is a safer method of recruiting tissue.
Forehead
The brow position is the most important structure to preserve during forehead expansion. When possible, two or more expanders are used with incisions hidden within the hairline. For mid-forehead lesions, bilateral, temporal expanders are used, and the skin is advanced medially based on the superficial temporal arteries. Expanders should be placed deep to the frontalis muscle. Expansion can usually begin 7-10 days postoperatively. When a large forehead flap is required for nasal reconstruction, the forehead skin can be pre-expanded prior to flap transfer.
Face and Neck
The skin of the neck and face is relatively thin. Therefore, multiple expanders with smaller volumes are preferable to a single large expander. In general, however, a single larger expander is preferable to several smaller expanders. Careful planning is essential in determining where to place the expanders, and where incisions should be located. Considerations such as preserving aesthetic units, matching skin color, avoiding distortion of the eyelids and oral commissure, and facial symmetry are all essential. The expander is usually placed above the platysma muscle in order to avoid risk of facial nerve injury and to keep the flap from being excessively bulky. The expanded flaps can be advanced, rotated, or transposed. Incisions should be placed in skin creases such as the nasolabial fold. Expanding the hairless skin adjacent to the mastoid region can increase the available tissue for reconstructive procedures of the ear. The skin above the clavicle can be expanded to provide full-thickness skin grafts to the face.
Trunk
Unlike the head and neck, there are very few critical landmarks on the trunk that must be preserved. Aside from the breast and nipple-areola complex, distortion of the skin and soft tissues of the trunk is well-tolerated. For defects requiring excision, multiple expanders surrounding the defect are often employed. Many myocutaneous flaps of the trunk, such as the latissimus dorsi, TRAM and pectoralis flaps, can be pre-expanded in order to increase their size and facilitate donor site closure. Expanders can also be used to expand the skin of the abdomen for use as a donor site of full-thickness skin grafts.
Extremities
Tissue expansion in the extremities has been reported to have a higher complication rate in comparison to other regions and therefore should not be a first choice among the reconstructive options. The blood supply and drainage of the extremities is inferior to that of the trunk and head. This predisposes limbs, especially below the knee, to an increased rate of infection and wound complications. Multiple expanders are usually required in the extremites.
Complications
Proper placement and filling of tissue expanders has a steep learning curve. With experience, the complication rate drops dramatically. Among all patients, the major complication rate is about 10% and includes implant exposure, deflation, and wound dehiscence. Minor complications also occur in about 10% of patients. These include filling port problems, seroma, hematoma, infection and delayed healing.
Patients under the age of 7 have the highest risk of complications. One explanation for this is that young children are more prone to expander rupture due to external pressure on the expanded skin. Expansion in the extremities caries twice the risk of complication compared to other regions. The use of tissue expansion in burn reconstruction and soft tissue loss has a 15-20% major complication rate, whereas for congenital nevi it is 5-7%. Finally, tissue that has undergone serial expansion (two or more prior expansions) is at a higher risk for a major complication.
Pearls and Pitfalls
Tissue expansion should be avoided in infected fields, in close proximity to a malignancy, in skin-grafted regions, and in skin that has been previously radiated.
Every effort should be made to place the incision as far as possible from the region to be expanded, unless the incision can be incorporated into the tissue that is destined to be excised. If the incision is subject to the tension of expansion, it becomes at risk for dehiscence and hypertrophic scarring.
A key point in tissue expansion is the development of an adequately sized pocket. If the pocket is too small, expansion will likely fail. If the pocket is overly large, the expander can shift positions, resulting in expansion of the wrong tissue. Textured expanders are less likely to shift after placement.
The rate of expansion is variable and depends both on the body site as well as patient factors. Some skin is more amenable to expansion, and some patients can tolerate the discomfort better than others. It is possible to be overly aggressive with the rate of expansion, resulting in overlying skin ischemia, necrosis and ultimately implant extrusion.
As a general rule, the diameter of the expanded flap should be 2-3 times the diameter of the skin that is to be excised
Tissue expansion relies on the ability of skin and soft tissues to generate in response to tension. In plastic surgery, tension is generated by implanting a subcutaneous balloon (expander) that is inflated over a period of weeks; new tissue is generated in response to the constant stretch caused by the progressive inflation of this expander. This tissue can be used to reconstruct extirpative or traumatic defects such as those encountered after mastectomy, burn excision, or removal of giant nevi.
Biological Basis of Tissue Expansion
A number of studies support the concept that the increase in skin surface area after expansion is due to the generation of new tissue rather than the stretching of existing skin. In culture, mechanical stress induces fibroblast and epidermal hyperplasia. These cells preserve their phenotype without malignant degeneration. This observation is supported by the fact that there has never been a reported case of skin malignancy secondary to tissue expansion.
From a histological standpoint, adult and pediatric skin responds to expansion in the same manner. Within 1 week of expansion, the epidermis begins to thicken and the dermis thins. The skin appendages do not change. The subcutaneous fat and muscle atrophy. Cellular proliferation reduces the resting tension of the skin over time, enabling another round of expansion to take place. Once the process is complete, the expanded skin eventually returns to its baseline thickness. The vessels of the skin and subcutaneous tissue also resume their pre-expanded size and number; however anecdotally, some flaps demonstrate increased vascularity.
Indications
In general terms, expansion of tissue is used to improve rotation, transposition or advancement of local or regional flaps, or to increase the harvest of full-thickness skin grafts. Recently, tissue expansion has been successfully applied to myocutaneous and free flaps. In adults, aside from their use in breast reconstruction, tissue expanders are used primarily for secondary burn and trauma reconstruction in the head and neck region. In the pediatric population, expanders have been used in a multitude of reconstructive procedures. The most common indication in children is to reconstruct defects left by excision of giant congenital nevi. Tissue expansion is contraindicated in infected skin. Although expansion is possible in radiated or scarred tissue, it is associated with a much higher complication rate and should be avoided whenever possible.
Technique
Expanders come in a variety of shapes and sizes, and there is no absolute ideal expander for a given site or condition. Expanders can have either internal or external filling ports. Most experienced surgeons recommend using remote ports. These should be placed away from the expander. Internal ports have both a higher failure rate and a greater incidence of accidental expander rupture. In children, the use of internal ports is associated with a higher rate of exposure of the expander due to the pressure exerted on the skin by the port. Whenever possible, the incision should be placed within tissue destined to be excised, as in the case of congenital nevi. Straight incisions along the border of the defect should be avoided because this will enlarge the defect and may interfere with flap coverage. An alternative is to use a U- or V-shaped incision that is hidden and remote from the defect. Such incisions should be perpendicular to the direction of expansion in order to maximize skin blood supply. When doing serial expansion, longitudinal blood supply must be preserved. This holds true especially in the trunk and extremities.
The expander should be placed on top of the deep fascia (or subgaleal in the scalp), unless the plan is to incorporate muscle into the expanded flap. The pocket should always be larger than the base diameter of the expander. Blunt dissection in a single fascial plane is safest for preserving blood supply. Most surgeons overinflate tissue expanders beyond the manufacturer’s recommended maximum capacity. Studies have demonstrated that significant overinflation is possible before weakening or rupturing. The rate of inflation is variable and largely based on surgeon preference. Patient comfort and signs of tissue perfusion, such as tension, color, and capillary refill, guide the filling rate. Filling is usually initiated one week after surgery.
Tissue expansion should continue until the expanded area is larger than the defect, because of the length that is lost upon advancement and inset of the flap. The use of rotation and transposition flaps enables the transfer of tension from the tip of the flap more proximally to its base. A single or double back-cut can be performed prior to inset in order to gain extra length. Lastly, the donor site should be closed in layers after the implant capsule is excised. Pre-expansion of distant pedicle- or free-flaps facilitates closure of otherwise tight donor sites.
Intraoperative Expansion
Most surgeons fill the expanders intraoperatively with sufficient saline to eliminate dead space and tamponade raw surfaces to help prevent postoperative bleeding. There is, however, an alternative to traditional prolonged expansion. Immediate intraoperative expansion combined with broad undermining of the defect can help reduce the tension that occurs on the distal parts of a local flap. In rapid expansion, the skin initially expands due to its elasticity and the displacement of interstitial fluid. Within minutes, the alignment of the collagen fibers changes due to the stretch. This process yields up to 20% more tissue for flap coverage. Intraoperative expansion is indicated for relatively small defects, such as in coverage of defects of the ear.
Scalp
Although tissue expansion does not increase the number of hair follicles, the size of the hair-bearing region can be doubled without a noticeable decrease in hair density. As such, tissue expansion may be used a means of treating male pattern baldness in addition to reconstructing the scalp. Expanders are most commonly placed in the occipital or posterior parietal regions. They should be placed under the galea, superficial to the periosteum. It usually requires 6-8 weeks to complete the expansion in adults, and up to 12 weeks in children. Radial scoring of the galea at the time of surgery can speed the process. Once the expansion is complete, flaps are advanced or transposed, ideally based on named arteries of the scalp. It is important to orient flaps so that the correct direction of hair growth is maintained. Although galeal scoring or capuslotomy incisions can be useful, wide undermining is a safer method of recruiting tissue.
Forehead
The brow position is the most important structure to preserve during forehead expansion. When possible, two or more expanders are used with incisions hidden within the hairline. For mid-forehead lesions, bilateral, temporal expanders are used, and the skin is advanced medially based on the superficial temporal arteries. Expanders should be placed deep to the frontalis muscle. Expansion can usually begin 7-10 days postoperatively. When a large forehead flap is required for nasal reconstruction, the forehead skin can be pre-expanded prior to flap transfer.
Face and Neck
The skin of the neck and face is relatively thin. Therefore, multiple expanders with smaller volumes are preferable to a single large expander. In general, however, a single larger expander is preferable to several smaller expanders. Careful planning is essential in determining where to place the expanders, and where incisions should be located. Considerations such as preserving aesthetic units, matching skin color, avoiding distortion of the eyelids and oral commissure, and facial symmetry are all essential. The expander is usually placed above the platysma muscle in order to avoid risk of facial nerve injury and to keep the flap from being excessively bulky. The expanded flaps can be advanced, rotated, or transposed. Incisions should be placed in skin creases such as the nasolabial fold. Expanding the hairless skin adjacent to the mastoid region can increase the available tissue for reconstructive procedures of the ear. The skin above the clavicle can be expanded to provide full-thickness skin grafts to the face.
Trunk
Unlike the head and neck, there are very few critical landmarks on the trunk that must be preserved. Aside from the breast and nipple-areola complex, distortion of the skin and soft tissues of the trunk is well-tolerated. For defects requiring excision, multiple expanders surrounding the defect are often employed. Many myocutaneous flaps of the trunk, such as the latissimus dorsi, TRAM and pectoralis flaps, can be pre-expanded in order to increase their size and facilitate donor site closure. Expanders can also be used to expand the skin of the abdomen for use as a donor site of full-thickness skin grafts.
Extremities
Tissue expansion in the extremities has been reported to have a higher complication rate in comparison to other regions and therefore should not be a first choice among the reconstructive options. The blood supply and drainage of the extremities is inferior to that of the trunk and head. This predisposes limbs, especially below the knee, to an increased rate of infection and wound complications. Multiple expanders are usually required in the extremites.
Complications
Proper placement and filling of tissue expanders has a steep learning curve. With experience, the complication rate drops dramatically. Among all patients, the major complication rate is about 10% and includes implant exposure, deflation, and wound dehiscence. Minor complications also occur in about 10% of patients. These include filling port problems, seroma, hematoma, infection and delayed healing.
Patients under the age of 7 have the highest risk of complications. One explanation for this is that young children are more prone to expander rupture due to external pressure on the expanded skin. Expansion in the extremities caries twice the risk of complication compared to other regions. The use of tissue expansion in burn reconstruction and soft tissue loss has a 15-20% major complication rate, whereas for congenital nevi it is 5-7%. Finally, tissue that has undergone serial expansion (two or more prior expansions) is at a higher risk for a major complication.
Pearls and Pitfalls
Tissue expansion should be avoided in infected fields, in close proximity to a malignancy, in skin-grafted regions, and in skin that has been previously radiated.
Every effort should be made to place the incision as far as possible from the region to be expanded, unless the incision can be incorporated into the tissue that is destined to be excised. If the incision is subject to the tension of expansion, it becomes at risk for dehiscence and hypertrophic scarring.
A key point in tissue expansion is the development of an adequately sized pocket. If the pocket is too small, expansion will likely fail. If the pocket is overly large, the expander can shift positions, resulting in expansion of the wrong tissue. Textured expanders are less likely to shift after placement.
The rate of expansion is variable and depends both on the body site as well as patient factors. Some skin is more amenable to expansion, and some patients can tolerate the discomfort better than others. It is possible to be overly aggressive with the rate of expansion, resulting in overlying skin ischemia, necrosis and ultimately implant extrusion.
As a general rule, the diameter of the expanded flap should be 2-3 times the diameter of the skin that is to be excised
