Posterior Tibial Artery Perforator Flap

Introduction

In the field of reconstructive surgery, not a day goes by without a skin flap being used. The earliest description of skin flaps was by Sushruta in 600 bc and this was, in fact, a local flap, of axial type. The flap described by Tagliacozzi in 1597 was a random pattern flap from the medial aspect of the upper arm. These two flaps, being a local flap and distant flap, respectively, were both used for reconstruction of the nose. Despite extensive studies of the blood supply to the skin by Manchot in 1889 and Salmon in 1936, most of the reconstructions during the First and Second World Wars were by tube pedicles. In 1973, McGregor and Morgan classified skin flaps into axial and random pattern flaps. Ponten highlighted the value of fascia in augmenting the blood supply to the skin. In 1995, Batchelor and Moss reported that the fascia acts like a scaffold for the sub-, intra-, and suprafascial vascular plexus. Taylor and Palmer in 1987, proposed the concept of “angiosomes” (vascular territories) and choke vessels. With this knowledge, the floodgates were opened for various types of fasciocutaneous flaps.

The skin plays an important role in protecting the body and thermoregulation. It is separated from the underlying structures by connective tissue called fascia. The skin, in order to regulate the temperature of the body, needs a rich blood supply; hence there is a regular connection between the vessels within the tissue compartment and the skin via various perforations in the deep fascia. Taylor identified an average of 374 cutaneous perforators in the body. Fujino, in 1967, demonstrated the importance of perforators in the circulation of skin flaps. He also reported that the perforators and the axial vein are important for interstitial fluid turnover.

There are different types of perforators. Our own clinical observations have identified two distinct vessels: the perforating vessels, which penetrate the deep fascia and have an artery and venae comitantes, and the fascial feeder vessels, which do not penetrate the deep fascia but terminate under it. The latter are mainly arterial without any venae comitantes. Both the perforators and the fascial feeders take part in the formation of the subfascial, intrafascial, and suprafascial plexi. These in turn communicate and form a rich plexus under the skin.

We now have various types of skin flaps based on perforating vessels and this has led to some confusion. To alleviate this, Wei et al. in 2001 defined perforators as those vessels that penetrate muscle on their path toward skin. But, anatomically, the blood vessels that supply the muscles, bone, and large tendons also penetrate the deep fascia to supply the skin. In addition to these vessels, there are blood vessels called “septocutaneous direct perforators” that also perforate the deep fascia and these travel between muscles and compartments. Linton published a detailed study of the septocutaneous vessels of the leg and used the term “perforator”. He described the communicating veins between the superficial and deep systems and the accompanying artery. In 2009, Saint-Cyr et al. introduced the term “perforasome.” Each perforator holds a unique vascular territory and by direct and indirect linking vessels they form a network and play a critical part in perforator flap perfusion.

Numerous anatomic cadaveric studies have established the number, location, and type of perforators of the posterior tibial artery. For practical purposes, the leg has been divided in many ways: into an upper concealed part and a lowed exposed part ; into five 7 cm parts ; into four zones ; three zones ; and 10 equal parts . Most recently, Shaverian and Saint-Cyr found that there were three constant clusters of perforators at 4–9 cm, 13–18 cm, and 21–26 cm from the medial malleollus.

There are a greater number of longer and larger-caliber, muscle-type perforators in the upper half, while the perforators of the lower half, or lower third, of the leg are the shorter, direct cutaneous type. My own clinical observation is that there are three direct septocutaneous perforators in the lower third, which correspond to Linton's venous connection between the superficial and deep vein system. These perforators communicate with each other as well as with the anterior tibial and perineal artery perforators, to form a suprafascial level network.

There is also a rich vascular network forming a circle of anastomoses around the ankle joint. This knowledge will help reconstructive surgeons to use various perforating flaps based proximally or distally around the knee and ankle joints ( Table 61.1 ).

The posterior tibial artery perforator has septocutaneous, musculocutaneous, and periosteocutaneous perforators as described by Koshima et al. in 1992. We also noticed that, apart from these perforators, there are vessels that supply the Achilles tendon and also perforate to supply the skin. These are called “tendinocutaneous.” Based on these perforating vessels, it is possible to raise small cutaneous flaps as local flaps to cover the exposed bone and tendon over the leg.

The perforator concept has become a method of choice in reconstruction both as free and local pedicle flap. This requires two basic understandings: the knowledge of blood supply of the skin and the surface anatomy of muscles and compartments. This will help in locating perforators and planning a flap for reconstruction.

A Doppler is a useful tool to use prior to raising per­forator flaps, especially pedicled perforator flaps. CT angiography is a useful but not essential form of imaging, as most perforator-based flaps do not require intramuscular dissection.

Flap Anatomy ( Fig. 61.1 and see Ch. 13 and Fig 13.6 , Fig 13.7 , Fig 13.10 , Fig 13.11 , Fig 13.12 , Fig 13.13 , Fig 13.19 )

The fasciocutaneous or adipofascial flaps, based on perforating vessels of the posterior tibial artery, can be proximally or distally based. For defects over the foot, reverse posterior tibial artery flaps can be used, incorporating all the perforators of the posterior tibial artery.

Flap Components

The flaps based on perforators of the posterior tibial artery are mostly fasciocutaneous or adipofascial type. As the perforators of the posterior artery anastomose with other perforators, it is possible to incorporate a small amount of muscle, bone, and tendon. These structures are transported in part with the flap and this part is vascularized by the flap in a reverse manner.

Preoperative Preparation

In this section the reconstructive surgeon should consider three factors: the patient, the wound, and the leg.

Assess the patient regarding fitness for surgery, age (posterior artery perforator flaps can be used with any age), and sex (one has to bear in mind the resulting donor site morbidity, especially in young female patients). Assess other medical conditions, i.e., diabetes mellitus, arteriosclerosis, and conditions such as pyoderma gangrenosum. Take the necessary steps to optimize the patient's medical condition prior to surgery.

The wound should be assessed as to whether it is clean with healthy granulation tissue and for the presence of infection, while exposure of underlying structures such as bone and tendons should also be assessed. The extent of disease process or traumatized field surrounding the wound should be assessed. An absolute contraindication to a perforator flap is a degloving injury, as generally, the perforators are severed. Relative contraindications include patients who are obese, diabetic, chronic smokers, and sufferers of pyoderma gangrenosum.

The vascularity of the leg should be assessed before the operation by the presence of peripheral pulsations of the three major vessels of the leg. An arteriogram is helpful but not essential. In approximately 6% of patients, the posterior tibial artery is weak or absent.

Before the operation, the leg is shaved and cleaned with antiseptic solution. Prophylaxis against deep vein thrombosis is given perioperatively.

Flap Design