Flaps

J.M. Sheehan (*)

Northshore Center for Medical Aesthetics, Northbrook, IL, USA

e-mail: Jessicasheehan09@gmail.com

T.E. Rohrer

SkinCare Physicians, Chestnut Hill, MA, USA

Summary: Introduction

•The planning and execution of a flap repair following Mohs surgery vary from case to case. A skilled surgeon evaluates the risks and benefits of various options in each individual patient and maximizes repair success by weighing risks and benefits.

33.1Introduction

While flap design and successful implementation is as much an art form as it is a science, there are many principles to keep in mind when planning the closure.

As with all surgical repairs, wounds should be closed under minimal tension without distorting critical anatomic structures and landmarks (eyelid, eyebrow, nose, lip, hairline, etc.). Scars should be placed within cosmetic units, along cosmetic unit junctions, or along skin tension lines. The flap must be executed such that the mobilized skin and associated adnexal structures are viable, and there is maximal preservation of sensory and motor nerve function.

The planning and execution of a flap repair following Mohs surgery vary from case to case. A skilled surgeon evaluates the risks and benefits of various options in each individual patient and anticipates potential complications. The elements to successfully perform any dermatologic surgery include proper patient selection and preparation, comprehension of risks and necessary precautions, use of sterile or clean technique, informed procedure design and meticulous suture technique, and postoperative wound care and patient education.

Summary: Risks and Precautions

•There are many risks to dermatologic surgery and flap repair, including pain, bleeding, bruising, infection, dehiscence, and undesirable scar. These risks should be explained to the patient and/or family before surgery. Steps should be taken to minimize these risks.

33.2Risks and Precautions

It is important that both the patient and practitioner be aware of the risks of dermatologic surgery. In fact, it is required by law in all 50 states that these risks be documented for proper patient consent [1]. The main risks of dermatologic surgery and flap repair include the following.

Pain from the procedure itself is mitigated by the use of local anesthesia, although the delivery of lidocaine in and of itself is painful. Postoperative pain is typically minimal and controlled with over-the-counter analgesics such as acetaminophen. Meticulous operative technique will also help minimize postoperative pain. More severe pain may require the prescription of narcotics.

Excessive bleeding, subsequent bruising, and possible hematoma formation are also risks. A hematoma is a particularly undesirable complication as it can

interfere with flap viability. Most dermatologic surgeons now recommend that medically necessary anticoagulation, including aspirin, clopidogrel, heparin, and warfarin, be continued perioperatively [2]. Herbal supplements such as ginseng or garlic, vitamin E, aspirin, and nonsteroidal anti-inflammatory agents that are not prescribed by a physician should be discontinued 2 weeks prior to surgery if possible [2]. The consumption of alcohol should also be restricted immediately before and after the procedure. Meticulous hemostasis with electrocautery or coagulation, arterial ligation of larger arteries, and the application of a compression bandage minimize the risk of bleeding.

Risk of infection exists whenever the barrier of the skin is breached. Wound infection is relatively uncommon [3] and occurs more frequently in particular patient populations, such as those who are diabetic, smokers, or immunosuppressed, and at certain surgical sites, such as the ear or lower leg [4]. Sterile technique and atraumatic tissue handling minimize this risk. Prophylactic antibiotics may be administered for highrisk patients or if the wound base or suture perforates into non-sterile areas, such as the nasal or oral cavities.

Wound dehiscence or flap necrosis occurs in wounds with high tension, in poorly vascularized flaps, or in cases of poor wound healing or infection. Tobacco smoking considerably increases this risk. This risk is reduced by proper design of the flap, which includes a broad pedicle, minimal torsion of the tissue, and minimal tension. The use of buried subcutaneous sutures is paramount, and at times fascial plication is required to relieve tension on wound edges. Patients should be advised in minimizing activity and immobilization of the wound edges for 1–2 weeks after surgery.

Undesirable scars are always a possibility. While many steps can be taken to minimize the appearance of the final scar, it is important for the patient to understand that all dermatologic surgery will result in the formation of a scar. Free margins must be respected and never distorted. Closures are best hidden when they are placed on along cosmetic unit junctions and contained in as few cosmetic units as possible. The long axis of the excision and/or design of a repair should be placed in the direction of rhytides or relaxed skin tension lines. Remove standing cones of redundant tissue. Buried vertical mattress sutures should be placed to attain good wound eversion and minimize the tension on the wound edges as it heals. Wounds heal best under the optimal conditions of a clean, occluded environment.

Summary: Flap Design and Execution

•The design and execution of a cutaneous flap require attention to multiple factors. These include functional and cosmetic surgical outcomes and the comprehension of tissue perfusion forces affecting the viability of transferred tissue. Flaps are either based on a large, named artery or on unnamed arterioles and capillaries of the subdermal vascular plexus. They are commonly classified by their primary movement.

33.3Flap Design and Execution

When simple primary closure is not the ideal repair (i.e., because a wound is too large, there is too much tension on the wound edges, or an unacceptable functional or cosmetic result would ensue), a tissue-move- ment procedure, such as a flap, should be considered. A local skin flap is a portion of full-thickness skin and variable subcutaneous tissue transferred from an adjacent donor site into the surgical defect. The flap maintains its blood supply via a vascular pedicle that remains connected to the donor site.

The vascular perfusion pressure, the force of blood flow through a vessel, is greatest at the proximal end of a vessel and decreases steadily as it travels more distal into the flap. To ensure flap survival, the perfusion pressure must be great enough to keep the distal capillaries of the flap patent. If the pressure falls below a certain critical level, the capillaries close leading to an insufficient blood supply to the distal end of the flap.

For years, it was believed that the viable length of a flap was directly proportional to the width of the pedicle. In 1970, Milton discovered that axial flaps in a pig model under the same conditions of blood supply only survive to a finite length regardless of width [5]. Daniel and Williams, as well as Stell, confirmed Milton’s findings and concluded that there was an upper limit of flap length that cannot be increased by increasing the pedicle width [6, 7]. The maximal flap length is determined by vascular supply, not simply pedicle width. The greater the perfusion pressure in the flap pedicle, the longer the flap can be without undergoing necrosis [8]. In addition, the greater the perfusion pressure in the pedicle, the narrower the pedicle may be.

Random pattern flaps, the most widely used in dermatologic surgery, are supported by the small arterioles and capillaries of the subdermal vascular plexus found in the mid to superficial fat. Therefore, undermining and flap mobilization must be performed at or below this level to ensure adequate blood supply. If undermining occurs too superficially, the intradermal vasculature alone will often not be able to support a flap. In general, random pattern flaps on the face should have a maximal length to width ratio of 3:1 [9, 10]. This is however only a rough guideline, and individual patient characteristics such as tobacco use, sebaceous nature of skin, prior radiation or surgical procedures, and precise location all affect vascular perfusion. To help ensure flap survival, the pedicle length to width ratios should not exceed 2:1 on the trunk and extremities.

Axial pattern flaps, with few exceptions, are supported by a large, named artery. They have the highest perfusion pressure at the base and therefore can support very narrow, long flaps (generally greater than 4:1 length to width ratio). Musculocutaneous flaps have the next greatest vascular perfusion pressure, followed by fasciocutaneous flaps, and finally random pattern flaps. Stell discovered that the greatest length of a viable axial flap was 60% greater than that of a random pattern flap [7].

The two movements involved in repairing a defect with a flap are the primary movement, which is the action of placing the flap into the defect, and the secondary movement of tissue in the donor area, which closes the secondary defect and facilitates primary flap movement. Both movements are important in terms of distributing tension in the proper direction and over a larger area so as to minimize tension on the flap itself which might compromise its survival [11]. Flaps are commonly classified according to their primary movement – advancement flaps, rotation flaps, transposition flaps, and interpolation flaps. This classification underplays the reality that many flaps have more than one primary movement, e.g., a rotation flap usually has a component of advancement to fill the distal portion of a wound. Therefore another way to classify flaps is by whether the primary movement is “sliding,” which displaces tissue redundancy at a site distant from the defect (advancement and rotation) or “lifting,” where a flap is moved over intact skin, reorienting wound tension (transposition and interpolation).