Flaps, Classification

A flap is a unit of tissue that is transferred from one site (donor site) to another (recipient site) while maintaining its own blood supply.

Flaps come in many different shapes and forms. They range from simple advancements of skin to composites of many different types of tissue. These composites need not consist only of soft tissue. They may include skin, muscle, bone, fat, or fascia.

How does a flap differ from a graft? A flap is transferred with its blood supply intact, and a graft is a transfer of tissue without its own blood supply. Therefore, survival of the graft depends entirely on the blood supply from the recipient site.

History of flap surgery

The term flap originated in the 16th century from the Dutch word flappe, meaning something that hung broad and loose, fastened only by one side. The history of flap surgery dates as far back as 600 BC, when Sushruta Samita described nasal reconstruction using a cheek flap. The origins of forehead rhinoplasty may be traced back to approximately 1440 AD in India. Some reports suggest flap surgeries were being performed before the birth of Christ.

The surgical procedures described during the early years involved the use of pivotal flaps, which transport skin to an adjacent area while rotating the skin about its pedicle (blood supply). The French were the first to describe advancement flaps, which transfer skin from an adjacent area without rotation. Distant pedicle flaps, which transfer tissue to a remote site, also were reported in Italian literature during the Renaissance period.

Subsequent surgical flap evolution occurred in phases. During the First and Second World Wars, pedicled flaps were used extensively. The next period occurred in the 1950s and 1960s, when surgeons reported using axial pattern flaps (flaps with named blood supplies). In the 1970s, a distinction was made between axial and random flaps (unnamed blood supply) and muscle and musculocutaneous (muscle and skin) flaps. This was a breakthrough in the understanding of flap surgery that eventually led to the birth of free tissue transfer.

In the 1980s, the number of different tissue types used increased significantly with the development of fasciocutaneous (fascia and skin) flaps (which are less bulky than muscle flaps), osseous (bone) flaps, and osseocutaneous (bone and skin) flaps.

The most recent advancement in flap surgery came in the 1990s with the introduction of perforator flaps. These flaps are supplied by small vessels (previously thought too small to sustain a flap) that typically arise from a named blood supply and penetrate muscle, muscle septae, or both to supply the overlying tissue. An example of this is the deep inferior epigastric perforator (DIEP) flap, which has now become the criterion standard in breast reconstruction.

Classification of flaps

Most classification systems have been designed for the sole purpose of aiding communication with peers by being familiar with the correct vocabulary to use. However, the crucial point for any physician to remember is that communication with the patient is of foremost importance. The patient must be able to picture, with the surgeon's guidance, what the surgeon is planning.

Many different methods have been used to classify flaps. Furthermore, these classification systems are often complex and varied in principle.

To improve the reader's understanding of flap classification, the author has summarized the most commonly used classifications into 3 simplified categories: type of blood supply, type of tissue to be transferred, and location of donor site.

• Blood supply
• • Like any living tissue, flaps must receive adequate blood flow to survive. A flap can maintain its blood supply in 2 main ways.
  • If the blood supply is not derived from a recognized artery but, rather, comes from many little unnamed vessels, the flap is referred to as a random flap. Many local cutaneous (skin) flaps fall into this category. If the blood supply comes from a recognized artery or group of arteries, it is referred to as an axial flap. Most muscle flaps have axial blood supplies.
  • Because of the complexity and variation observed in axial blood supply, a further subclassification (axial types I-V) was made by Mathes and Nahai and is readily used in plastic and reconstructive surgery literature to describe different types of muscle flaps (see Image 1).¹
  • The classification of flaps based on blood supply, including the Mathes and Nahai subclassification, can be summarized as follows:
  • • Random (no named blood vessel)
    • Axial (named blood vessel) Mathes and Nahai classification
    • • One vascular pedicle (eg, tensor fascia lata)
      • Dominant pedicle(s) and minor pedicle(s) (eg, gracilis)
      • Two dominant pedicles (eg, gluteus maximus)
      • Segmental vascular pedicles (eg, sartorius)
      • One dominant pedicle and secondary segmental pedicles (eg, latissimus dorsi)
• Tissue to be transferred
• • In general, flaps may comprise in part or in whole almost any component of the human body, as long as an adequate blood supply to the flap can be ensured once the tissue has been transferred.
  • Flaps may be composed of just one type of tissue or several different types of tissue. Flaps composed of one type of tissue include skin (cutaneous), fascia, muscle, bone, and visceral (eg, colon, small intestine, omentum) flaps. Composite flaps include fasciocutaneous (eg, radial forearm flap), myocutaneous (eg, transverse rectus abdominis muscle [TRAM] flap), osseocutaneous (eg, fibula flap), tendocutaneous (eg, dorsalis pedis flap), and sensory/innervated flaps (eg, dorsalis pedis flap with deep peroneal nerve).
  • Therefore, another way of classifying flaps is by describing the different types of tissue that are being used in the flap.
• Location of donor site
• • Tissue may be transferred from an area adjacent to the defect. This is known as a local flap. It may be described based on its geometric design, be advanced, or both. Pivotal (geometric) flaps include rotation, transposition, and interpolation. Advancement flaps include single pedicle, bipedicle, and V-Y flaps.
  • Tissue transferred from an noncontiguous anatomic site (ie, from a different part of the body) is referred to as a distant flap.
  • Distant flaps may be either pedicled (transferred while still attached to their original blood supply) or free. Free flaps are physically detached from their native blood supply and then reattached to vessels at the recipient site. This anastomosis typically is performed using a microscope, thus is known as a microsurgical anastomosis.

Principles of flap surgery

Now that the main ways of classifying flaps have been introduced, the remaining sections of this article are devoted to the most important principles to remember before performing flap surgery. Like any surgical procedure, flap surgery is not devoid of risk. Complications such as complete flap loss can be catastrophic. Considering the following basic principles before any flap surgery serves patients well by optimizing outcome and decreasing operative morbidity.