Wound around knee where exposed bone require a flap and rest can be managed by split skin graft
26.2 Split Skin Graft
For below-knee defect, ipsilateral thigh is the preferred donor site as the patient can use the other limb for routine work during the immediate postoperative period. If only one sheet of graft is necessary, it should be harvested from the posterior aspect of the thigh. This will avoid any scar in the future on the more visible areas of the thigh. After cleaning and draping, the SSG is first harvested if the size of the wound is known. A chronic wound is thoroughly scraped by the back of the knife till punctate bleeding appears. Long-standing ulcers should be excised judiciously till the healthy tissue all around to ensure proper “take” of the graft. A hot swab is kept to maintain hemostasis. After few minutes it is removed using normal saline sprinkle. Multiple perforations are made on the graft with No. 15 surgical blade to prevent hematoma underneath. The wound is finally washed with normal saline. The graft is secured over the wound by catgut/Vicryl stitches or stapler. In contoured defect it is preferred to apply several quilting stitches through the graft to the bed to obliterate the dead space and to avoid tenting of the graft. Through the perforations, saline is pushed with a syringe to remove micro clots. A nonadhesive firm dressing is applied for proper contact between the graft and the bed. The first dressing is opened after 2–3 days. A pink graft without hematoma and infection confirms the “take” of the graft. The donor site is opened around 3 weeks once it has epithelialized.
The indications for resurfacing a wound with a flap are as follows: exposed (a) vital structures, e.g., bone and joint, tendon, neurovascular bundle, etc., (b) exposed hardware following orthopedic surgery for fracture fixation, and (c) contour defect. There could be two types of flaps, locoregional flap and free flap through microvascular transfer. This chapter deals with the former procedures. The choice of nature and constituent of the flap also depend upon the abovementioned types of defect and the availability of healthy adjacent tissue .
The available flaps are fasciocutaneous, adipofascial, fascial, muscle, musculocutaneous, and a combination of them . Fasciocutaneous flap is the commonest choice as it is reliable and stable. It consists of skin, subcutaneous tissue, and deep fascia. The adipofascial flap consists of adipose tissue and deep fascia . The fascial flap has only deep fascia. As the flap becomes thinner, the incorporation of vascular arcades is reduced. Therefore, their safe dimension is also reduced. Hence, the planning of the flap prior to surgery is of utmost importance. The planning includes decision regarding the constituent, vascular basis, plane of dissection, mode of transfer, donor site morbidity, and postoperative care.
For the choice of flap, the non-weightbearing areas of the limb and weightbearing areas of the heel and sole should be considered separately because the requirements are different. For defects over the non-weightbearing areas from the knee to foot, fasciocutaneous flap is preferred as larger dimension of tissue can be transferred and it is most stable. The donor site usually needs skin graft. For noncontoured defects and exposed Achilles tendon, adipofascial flap provides good result. The donor area is sutured primarily. For defects over the areas where subcutaneous tissue is less, e.g., shin of tibia, malleoli, etc., fascial flap is considered so that the flap does not look bulky. Both the adipofascial and fascial flaps require SSG over them, and the donor site is sutured primarily. The gastrocnemius muscle flap is useful for contour defects of upper third of the leg and knee. Sometimes a split muscle flap is a choice to reduce the bulk and to preserve the functional unit in an already traumatized leg. Soleus muscle is also used for upper and middle third defects. These muscle flaps require SSG to cover them. Myocutaneous flaps can also be designed based on either head of gastrocnemius; however, they are bulky and not aesthetic. Any flap which proves to be bulky can be debulked in a secondary procedure after few months.
For weightbearing areas of heel and sole, the requirement is different. The adipofascial and fascial flaps are not suitable as they do not withstand the wear and tear of daily life. The flap is decided on the location of the defect, its dimension, and condition of the adjacent tissue. If it is around 2–4 cm, a local flap of similar tissue is ideal with primary closure of the donor site. It can be rotation, transposition, V–Y advancement, or bilobed flap. If it is a deep posttraumatic or trophic ulcer at the heel up to 4 cm, muscle flaps of the first layer of the sole can be turned over and SSG is applied. These muscles are abductor digiti minimi, flexor digitorum brevis, and abductor hallucis. The donor site of muscle exposure is closed primarily. If the defect is larger, more than one muscle can be transferred. If the defect over the heel involves whole of the heel, an inferiorly based fasciocutaneous flap is designed from the proximal calf area and rotated 180° to cover the defect. Large inferiorly based fasciocutaneous flap can resurface almost two third of the sole or dorsum of foot. The sural neurocutaneous flap is the other choice for the heel and other adjacent defects. If ipsilateral calf tissue is not available, a cross-leg flap can be designed.
26.4 Vascular Basis of the Flaps
It has two aspects: (a) vascular arcades within the different constituents of flap and (b) perfusing vessels through which blood reaches to the tissue from the main vascular trunk. Earlier main vascular trunk used to be sacrificed to transfer the tissue to the defect. Now with better understanding of vascularity, the tissue is transferred based on the small vessels arising from the main vessel called “perforators.” These perforators are of two types: (a) musculocutaneous, when it courses through the muscle, e.g., gastrocnemius, and then enters the subfascial surface of the deep fascia, and (b) septocutaneous, when it traverses through the septum in between the muscle bellies before entering the deep fascia . The third type of vessel is the (c) direct cutaneous artery which arises from the main vascular trunk and directly enters the subcutaneous tissue. The perforators then arborizes into the rich vascular network on the subfascial surface of the deep fascia which subsequently passes through the deep fascia in the intrafascial course to form the suprafascial plexus . Further it communicates with the subcutaneous plexus and then with the subdermal and dermal network . Thus, it is a continuous rich arcade through different layers of tissue. This is the vascular basis of different constituent of flap .
26.5 Hemodynamics of Flaps
It is of utmost importance to understand the hemodynamic of flap for the successful tissue transfer. Vascular plexuses of different layers of tissue play important part in the success of flap transfer. Earlier the deep fascia was supposed to be an avascular structure with only function of covering the muscle underneath to prevent herniation. Now the vascular anastomosis of the deep fascia in one of the dominant systems is well established. The musculocutaneous and septocutaneous perforators first make rich plexus at the level of deep fascia as they perforate on their way to the superficial layers of anastomotic channels. That is why incorporation of deep fascia provides significant enhancement to vascularity. Each perforator has a territory of anastomotic network called “angiosome.” The perforators of different dimensions are present at regular interval of 3–4 cm . Their angiosomes communicate freely to form a continuous vascular arcade throughout the limb . The amount of blood flowing through a perforator is directly proportional to the internal diameter . Depending upon the perfusion pressure of a perforator, blood is pushed in to the vascular network. Thus, several adjacent angiosomes will be perfused by a single perforator. It is important to understand this mechanism because while dissecting a flap, several perforators are severed and the flap gets its blood supply through one or two perforators those have been incorporated in the pedicle of the flap.
26.6 Vascular Axis
There are three major vascular axes in the lower limb, namely, anterior tibial, posterior tibial, and peroneal. Several perforators arise from them. With the advancement of technology in the form of audio Doppler, color Doppler, two-dimensional and three-dimensional CT angiography, etc., these perforators can be precisely identified and measured from fixed bony landmarks. Their internal diameter can be gauged based on which they are classified into three categories: group-1, up to 1 mm; group 2, 1.1–2 mm; and group 3, more than 2 mm. The constituent of the flap decides which vascular networks have been incorporated. For example, fasciocutaneous flap contains subfascial, suprafascial, subcutaneous, subdermal, and dermal plexus . In adipofascial flap, subdermal and dermal network are not included. In fascial flap, only the subfascial and suprafascial network remains. Therefore, the fasciocutaneous flap has larger safe dimension followed by adipofascial flap and then fascial flap. In myocutaneous flap, the underlying muscle is also incorporated and the overruling fasciocutaneous unit receives the blood supply through the musculocutaneous perforators. Muscle flap is used based on the blood supply of a particular muscle. Regarding mobility of the flap, it is necessary to understand that the thicker the flap, the less is the mobility. Accordingly transfer of tissue has to be calculated. Therefore, it has bearing on the measurement of flap while planning. Similarly flap with broader base will have less mobility. With advanced knowledge of the perforators, the base can be substantially narrowed with much greater mobility. This allows increased reach of the flap to reconstruct distant defects.
After deciding the blood supply, the dimension of the flap is calculated depending upon the defect. For small to moderate size defect, a single flap may be sufficient. For larger defect, two or three flaps can be designed perfused by different perforators of the same vessel or different vessels. All these decisions are based on accurate planning and measurement of the defect and flap; otherwise, the flap may fall short. If the calculation is compromised, then the surgeon dissects toward the base of the flap, endangering the vascularity due to probable damage to the perforator and sutures under tension. It may also cause acute kinking at the base. Thus, the vascularity may be compromised leading to part or complete necrosis of the flap.
26.7 Practical Techniques for Flaps
The following steps need to be followed in every type of tissue transfer:
If it is a perforator-based flap, then the location of the perforators should be identified preoperatively which is most commonly done by audio Doppler.
A meticulous “planning in reverse” is done so that the transferred tissue does not fall short of defect in every dimension. It is done with the help of a piece of lint prior to surgery. The lint is kept as if the flap has been transferred over the defect. The pedicle is held by the assistant, and the lint representing the flap is moved to the donor site. The outline of the flap is marked on the donor site one centimeter beyond on the three sides of the proposed flap. This is to take into account the tissue contractility. The transfer is then rechecked holding the pedicle fixed. This certainly ensures correct planning.
The incision is beveled outward specially where multiple tissue constituents are incorporated. Following such incision, all the layers come to the margin at the same level. Then they are secured by 3/0 chromic catgut interrupted stitches as one unit. For example, in fasciocutaneous flap, the deep fascia is sutured to the dermis. This prevents shearing movement between individual planes during dissection and transfer of the flap. Thus, the composite vascular network within the flap is preserved allowing free flow of blood without interruption.
The plane of dissection needs to be identified in the initial phase of dissection which should be maintained throughout.
Several perforators will be encountered as the flap is raised. They need to be severed. While doing so, low coutary may be used toward the main vascular trunk but the end toward the flap should be ligated using 4/0 chromic catgut/Vicryl. Even apparently small looking charring on the flap surface due to cautery may prove to be detrimental for a small segment of flap.
Whenever a flap is moved more than 90° over a pivot point, acute twist should be prevented. This can be achieved by narrowing the pedicle or by raising little longer flap or skeletonizing the perforator.
Avoid suturing under tension. It is preferred to keep a drain under the flap to avoid hematoma.
Low molecular weight dextran is infused during flap elevation and continued for 2 days to enhance microcirculation.
The limb is kept elevated by 30° for better venous drainage.
26.8 Few Common Flaps
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26.8.1 Fasciocutaneous Flap
Constituent wise it consists of skin, subcutaneous tissue, and deep fascia. Majority of moderate-sized defects from knee to foot can be resurfaced by these procedures. For simple understanding of the reconstructive options, the lower limb is divided into upper, middle, and lower third. For upper and middle third, superiorly based (antegrade) flaps based on the perforators of the posterior tibial artery (on medial side) or from the anterolateral aspect based on the perforators of the peroneal artery are used. These flaps are transferred to the defect by rotation or transposition or combination of both. Inferiorly based flaps (retrograde) perfused by the distal perforators of the abovementioned vascular trunks are used for distal third leg (Fig. 26.2), ankle (Fig. 26.3), heel (Fig. 26.4), midsole, and dorsum of foot defects . It is essential to incorporate at least two sizable perforators in the pedicle to ensure adequate blood supply, irrespective of the nature of the flap, that is, how a flap of nonconventional dimension can be transferred with safety. Sometimes there may be intervening normal tissue, and the flap has to reach the defect crossing over this bridge of tissue. It is called “interpolation flap.” In such situation, the pedicle is detached after 3 weeks under local anesthesia, and proximal insetting of the flap is done.
(a) Mid and distal third defect with exposed tibia. (b) and (c) Flap dissected on distal posterior tibial perforatord. (d) Flap transfered to the defect. (e) Followup of healed flap at 3 months