Flap classification: blood supply, tissue and movement

Three questions classify any flap

Every flap is classified by answering three questions: how is it perfused, what is it made of, and how does it reach the defect. A flap is tissue moved with a blood supply of its own — the property that separates it from a graft — which is why circulation dominates every scheme. Cormack and Lamberty's ‘five Cs’ (circulation, composition, contiguity, contour and conditioning) is a tidy checklist, but in the exam and in theatre the first three carry the weight.

Contiguity describes where the tissue comes from: local (adjacent to the defect), regional, distant pedicled (a groin flap to the hand, a cross-leg flap) or free, where the pedicle is divided and re-anastomosed at the recipient site.

Random versus axial supply

A random-pattern flap has no named vessel and survives on the dermal and subdermal plexus fed by unnamed perforators at its base; an axial-pattern flap carries a named artery and vein running along its long axis. McGregor and Morgan's distinction explains why a groin flap on the superficial circumflex iliac vessels can be raised far longer than a random flap of the same width.

The traditional length-to-breadth ratios for random flaps — about 1:1 on the trunk and limbs, more generous on the well-perfused face — are proxies for perfusion pressure, not laws. Milton's experiments showed that widening a random flap does not let you lengthen it: survival length is set by the pressure in the feeding vessels, and a wider base simply recruits more vessels at the same pressure.

Axial flaps can be peninsular, with a skin bridge left at the base, or islanded on the vessels alone, which frees them to rotate further. Classic examples are the paramedian forehead flap (supratrochlear vessels), the groin flap and the deltopectoral flap (internal mammary perforators).

Muscle flaps: Mathes–Nahai types I–V

Mathes and Nahai classify muscles by the number and dominance of their vascular pedicles, and the type predicts how much muscle survives on any one pedicle. A dominant pedicle can carry the whole muscle; a minor pedicle keeps only part of it alive; segmental pedicles each supply their own slice.

Fasciocutaneous flaps: Cormack–Lamberty A–D

Cormack and Lamberty grouped fasciocutaneous flaps by how their perforators reach the deep fascial plexus. Including the deep fascia captures the plexuses above and below it, which is why Pontén's lower-leg ‘superflaps’ survived at lengths that would kill a skin-only flap.

Nakajima extended the idea by describing six routes a deep fascial perforator can take from source vessel to skin — direct cutaneous, direct septocutaneous, direct cutaneous branch of a muscular vessel, perforating cutaneous branch of a muscular vessel, septocutaneous perforator and musculocutaneous perforator — and matching flap types to each. Its value is conceptual: it links the fasciocutaneous schemes to modern perforator flaps.

Composition and movement

Composition is what the flap carries: skin alone, fasciocutaneous, adipofascial, fascial, muscle, musculocutaneous, bone or osteocutaneous, or chimeric — several independent components, each on its own branch of a common pedicle. Add a sensory nerve and the flap is sensate; add a motor nerve to muscle and it becomes a functional transfer.

Movement describes how a local or pedicled flap reaches the defect; the geometry of each design is covered in Local flap geometry.

Perforator flaps and the Gent consensus

A perforator flap is skin and/or fat supplied by a perforator — a vessel that leaves its source artery and passes through or between deep tissues to reach the skin. The Gent consensus (Blondeel and colleagues, 2003) fixed the vocabulary: muscle perforators traverse muscle, septal perforators run only through an intermuscular septum.

• Name by vessel, not muscle. The flap takes the name of its nutrient artery — DIEAP (deep inferior epigastric artery perforator), TDAP (thoracodorsal), SGAP and IGAP (superior and inferior gluteal). Where more than one source vessel could supply a region, the region names the flap.
• Leave the muscle behind. Dissecting the perforator through the muscle spares the muscle and its motor nerve — the central argument for a DIEP over a TRAM.
• Free-style flaps are designed around any Doppler-located perforator rather than a pre-named template.
• The price is a longer, less forgiving dissection on variable anatomy, which is why CT angiography is widely used before a DIEP.

Delay, in brief

Surgical delay increases the area a flap can carry by dividing part of its supply and leaving the tissue in place before transfer. Choke vessels at the edge of the territory dilate and the tissue becomes more tolerant of ischaemia; the effect is near-maximal at about two weeks, which is when delayed transfers are usually scheduled. The mechanisms are covered in Angiosomes, perforasomes and delay.