Continuing Education Activity

Trauma and resection of tumors often leave large defects requiring coverage, which have historically meant multi-stage procedures. However, axial pattern flaps, which rely on an anatomically named direct cutaneous blood supply, have presented a single-stage procedure that provides a reliable, cosmetically appealing option. This activity reviews the indications, complications, and contraindications regarding axial flaps and highlights the role of the interprofessional team in evaluating and caring for axial flaps preoperative, intraoperatively, and postoperatively.

Objectives:

• Identify the indications for use of axial flaps.
• Describe the anatomy and physiology of axial flaps.
• Summarize the most common complications associated with axial flaps.
• Explain the importance of post-operative monitoring for axial flaps.

Introduction

An axial pattern flap incorporates an anatomically named vascular pedicle.[1] Due to the direct cutaneous blood supply, a large skin area can be transferred acutely rather than in a delayed fashion that has previously been the gold standard. Historically, random pattern flaps were harvested in a delayed manner to foster better circulation to the flap. There are several advantages when using an axial pattern flap, which includes no need for delay procedures, full-thickness, durable skin, and excellent cosmetic results.[2] Furthermore, it has been shown that the area of survival in axial pattern flaps is significantly better versus flaps which do not incorporate a direct cutaneous blood supply. Studies have shown the difference in 95% survival for axial pattern flaps versus 53% survival in flaps without a direct cutaneous supply.[3] Some examples of axial pattern flaps include: 

• Nasolabial flap off of the angular vessels 
• Paramedian forehead flap off of the supratrochlear vessels 
• Facial artery musculomucosal flap 
• Melolabial flap

Anatomy and Physiology

Understanding basic skin anatomy is crucial to understanding the anatomy and physiology of flaps. The deep and superficial vascular plexus supply the skin. The deep vascular plexus is also known as the subdermal plexus. This vascular supply serves two main functions- nutritional support and thermoregulation. All flaps rely on the skin's plexuses for survival.[4]

There are four basic types of cutaneous flaps- random, axial, reverse flow axial pattern flaps, and island flaps. Random flaps rely on blood supply from the subdermal plexus, which is supplied by unnamed musculocutaneous perforators.[5] Axial pattern flaps derive their blood supply directly from an anatomically named fasciocutaneous artery that runs beneath the flap's longitudinal axis.[6] These arteries ensure blood supply to the subdermal plexus and guarantee blood supply to the flap. Outside of the territory that is immediately supplied by the artery, the flap behaves like a random flap because the more distal regions rely on the deep and superficial vascular plexus for survival.[7] 

Reverse flow axial pattern flaps are axial flaps in which the main blood supply is divided proximally. The blood flows in a retrograde manner through the distal vessel, which is accomplished via venae comitantes, bypass vessels, and valvular incompetence. Finally, island flaps also represent a type of axial pattern flap raised on a pedicle that lacks skin to facilitate transfer to a distant site.[4]

Indications

Axial flaps are indicated for one-stage reconstruction of wounds when a large amount of skin is needed to fill a defect following trauma or mass resection. There are various areas from which axial flaps can be taken. The recipient site must be healthy and without any infection indications; however, granulation tissue does not have to be present. Unlike grafts, the flap carries its own blood supply and does not require a vascular bed. Advantages of axial flaps include a greater width to length ratio versus random pattern flaps, full-thickness coverage, durable skin, and excellent cosmetic results. Due to these flaps' predictable vascular supply, they can provide durable full-thickness skin, which can result in minimal scar tissue and near-normal hair growth.[2]

Contraindications

The use of axial flaps is contraindicated in patients who present with an active infection at the recipient site, or if there is any compromise to the flap pedicle or inadequate debridement of the wound bed. Relative contraindications, including smoking, are common to all flap surgery as it increases the risk of flap necrosis. Furthermore, avoiding radiated skin areas as the donor site is recommended to reduce the risk of flap failure.

Equipment

Axial flaps do not require any specialized equipment and are less technically demanding compared to microvascular free transfer. The equipment required is generally the same for other regional and local flap surgery.[8][9] Doppler can be useful for axial vessel and perforator mapping.

Personnel

Axial flaps can be performed efficiently with one surgical assistant to assist with retraction, suturing, cutting, and achieving hemostasis.

Preparation

Before surgery, the physical examination is crucial to assess any prior hypertrophic, hyper/hypopigmented scars, or any keloids and appropriately caution the patient. Additionally, a manual pinch test at the donor site will confirm the ability to close the donor site primarily. If needed pre-operatively, vessel position and patency can be confirmed with a handheld doppler. As is the case with any surgical intervention, it is crucial to have an informed discussion with the patient pre-operatively in which all the risks, benefits, and alternatives are discussed regarding axial flaps. When discussing with elderly patients, they should be cautioned that the flap is at a greater risk of necrosis as dermal blood vessels tend to collapse, become disorganized or absent with age.[4]

Technique or Treatment

When considering where to make the initial incision, it is important to consider skin tension and understand that the greatest tension exists along the relaxed skin tension lines, and the least tension exists along the lines of maximum extensibility. Keeping this in mind, incisions should be placed parallel to the relaxed skin tension lines to minimize tension.[10] 

Generally, axial flaps are typically raised from the trunk, neck, or proximal limbs in areas where there is sufficient loose skin to facilitate the donor site's closure with minimal morbidity. There are a variety of different axial flaps which can be raised; however, the basic operative technique is as follows:[4]

• Measure the dimensions of the defect 
• Design a skin paddle which is centered over the axial course of the vascular pedicle, taking care to ensure that the plan of dissection includes the fasciocutaneous vessel within the subcutaneous fat 
• It is useful to leave a cuff of fascia and subcutaneous fat around the pedicle to avoid injuring. It is unnecessary to visualize the pedicle, but if there is evidence of arterial insufficiency in the flap, you may need to skeletonize the vessels. 
• Transfer the flap into the defect 
• Inset the flap into the defect 
• Close the donor site either primarily or with skin grafts depending on the size of the defect

Complications

Potential complications regarding axial flap include:

• Seroma formation
• Wound drainage
• Donor site dehiscence
• Distal flap necrosis[9]
• There is also the potential for delayed or incomplete wound healing, venous congestion requiring suture release or placement back to original positions for the delay to augment axial supply

Clinical Significance

Axial flaps can provide a low complexity, one-step method for reconstruction for defects which are larger in area. They can obviate the need for multistep procedures and provide patients with durable skin and a better cosmetic result. They offer an efficient, less complicated means to repair defects that would otherwise be difficult or impossible to repair.

Enhancing Healthcare Team Outcomes

As with all flap surgery, it is of the utmost importance to have cooperation and understanding of the flap's success. Postoperative bleeding and flap complications typically occur in the first 24-72 hours postoperatively. Intraoperatively, the surgeon needs to achieve appropriate hemostasis and protect the pedicle and prevent any postoperative complications. Postoperatively the nursing staff must be appropriately trained to understand the early signs of flap compromise.