1. A flap is a piece of living composite tissue which carries with it its own blood supply and is used to close a defect or address a deficiency. When such tissue is shifted locally it is called a ‘local flap’. A flap can be transferred to a distant site, remaining attached at its base (or pedicle), which is the source of its blood supply. Its transferred part is allowed to establish vascular connections from the recipient area over a period of time (usually two to three weeks) after which the pedicle is divided. This is a staged distant flap. In the third category, the whole of the flap is lifted off its moorings with only specific blood vessels which supply it and then these blood vessels are anastomosed to blood vessels in the recipient site to restore its circulation these are called ‘free flaps’. Because these vessels might be small and require a microscope for their anastomosis, these flaps are frequently referred to as ‘free microvascular flaps’. The restoration of the circulation of these flaps needs to be established quickly in a matter of hours.
Prabha Yadav and her group from TMH Mumbai pertinently point out that an island pedicled flap with its own source vessel in its base is neither a free flap nor a distant staged flap or classically a local flap and forms a separate subset which Visweswar Bhattacharya rightly calls a single stage regional flap.
2. The words “composite tissue” imply more than one layer and traditionally the tissues so moved as a flap consisted of the whole of the skin and at least a part if not the whole of the subcutaneous tissue. In the last four decades the composite nature of the flaps has changed and a flap can now include in addition to skin and subcutaneous tissue deeper structures such as fascia, muscle and bone. Exceptionally it may also carry tendons and nerves. A flap of adipofascial tissue without skin and a flap of fascia alone have also been described. A muscle flap without its cover such as fascia and skin is now a fairly common procedure. A part of the colon transferred to reconstruct the vaginal passage or a segment of a small bowel used to reconstruct the oesophagus are also flaps because they are composite in nature and their circulation is either maintained through their pedicles or restored by microvascular anastomosis.
Visweswar Bhattacharya from Varanasi adds there can be combination of flaps e.g. Adepofascial or fascial extension of fasciocutaneous flap to fill up the contour defects. There could be also fasciocutaneous extension of myocutaneous flap.
Samir Kumta from Mumbai suggests that the word ‘flap’ should be used only when the transferred tissue contains skin.
3. Because of its composite nature and its intact blood supply the flap is a net addition to the area where it is transferred. In other words the flap is a living thing and adds value within hours after its transfer. This is in contrast to a skin graft which must borrow from the recipient site for its survival.
4. What flow from the above are the indications for flaps.
a. To re-establish the anatomical and physiological integrity of a part (e.g. en bloc reconstruction of a head and neck defect created after surgery for a malignant tumour).
b. To cover, protect and nourish vital parts of the body for e.g. bones, joints, tendons or major vessels or nerves which are exposed.
c. To cover and protect vital organs of the body for e.g. the brain, viscera or the eye.
Also see photographs in the chapter on Burns Part 4 : Electrical Burns for a similar indication.
d. To improve function for e.g. as in a flap which carries a sensory nerve or a transfer of a muscle to improve the results of a facial palsy or create a sphincter for e.g. anal sphincter via a Gracilis muscle flap.
e. To improve appearance by substituting the exact tissue that is missing in a defect.
f. To replace a dense adherent scar where several layers of the integument have healed by secondary intention leading to deformities or loss of function or instability.
g. To achieve cover in this manner which will allow a later surgical access to a part which needs repair or reconstruction.
Please see photographs of a case of Electrical Burns in the chapter ‘Burns Chapter 18, Part 4’.
h. To create living, durable, tubular structures e.g. reconstruction of oesophagus or a vaginal passage.
i. To heal wounds with major net tissue loss across joints or vital parts where mere epithelialisation is likely to undergo repeated breakdowns and affect function. This indication also includes areas which have been irradiated or where extravasation of a toxic chemotherapeutic agent has caused multi-layered necrosis.
j. In contractures of whatever etiology where a skin graft might succeed yet a flap will give better aesthetic or long term results.
k. To plug holes in vital structures which cannot heal by themselves for e.g. a broncho-pleural fistula or a sizeable fistula after repair of a hypospadias (a hypospadias cripple) or a fistula in the hard palate or a vesico-vaginal fistula.
l. All flaps also improve the local immunological status of the area to which they are transferred and infected cavities are frequently controlled and cured by filling them with flaps. This is a concurrent indication in many situations.
5. Every incision that a surgeon makes is a step towards the creation of a flap. When the incision is deepened and then undermined for example with a C-shaped retractor in a right para median incision on the abdomen, the incised undermined flap anterior to the C-shaped retractor loses some of its blood supply which enters it from its bed (in this case the perforators from the anterior rectus sheath which envelopes the rectus muscle). However such a flap will survive even if it is undermined extensively because it receives blood supply from the inter-costal, sub-costal and lumbar vessels from its lateral side. Contrast this with a vertical incision in the lower-one third of the leg over the tendo-Achilles. If in order to get access to the tendon to repair it, the skin is undermined even for three or four centimeters the likelihood that it might necrose after closure of the incision is much higher than for the abdominal incision described above. What necroses is an undermined flap of skin because its loss of blood supply from its bed was not compensated from its other three sides.
6. The etymology of the word ‘flap’ has antecedents in the wing of a bird (because it flaps when it moves, flapping of a wing). That gives a good picture of what a standard flap is; a base and three free sides. In fact a local or distant staged flap is usually cut on three sides and lifted off its bed and will certainly be jeopardized if its fourth side is unable to perfuse it adequately. Bearing this in mind, by a general rule, a flap was considered safe in most parts of the body if the base of the flap was equal to the length of the flap. This rule did not actually investigate the ability of the base to perfuse but was arrived at by experience and assumed that the random (not specific) blood supply from the base was enough to perfuse the flap and allow it to survive. But a flap of such a dimension had limitations in moving locally and in a staged flap, not much of its surface area could be conveniently attached to the prospective recipient area.
7. It is on this background that we need to view the history of making of flaps. As it happens the two crucial events in this regard happened nearly 2,600 years apart. According to tradition, when Sushruta (600 BC) placed a broad leaf, with a very narrow stalk on the forehead (as a pattern), the stalk near the medial end of the eyebrow and over the nose and cut his flap and rotated it through 180°, to repair a ‘cut nose’, according to literature, he had said in Sanskrit, “it (the flap) survives by continuity”. Sanskrit aphorisms are too brief for us to be able to fathom what Sushruta thought or meant to convey but the word continuity obviously meant continuity with the rest of the body. This flap’s dimensions were outrageous by modern standards of only 60 or 70 years ago. Then came Milton who in 1970 showed by cutting flaps of varying lengths and also of varying breadths on the backs of pigs, that what mattered was what was contained in the base of the flap and not how broad or long it was. If the base included a segmental vessel, the flap could be cut to a considerable length even if the base was very narrow, as long as the flap included the vessel. Milton, who shared his name with the well known poet, was a poet himself in that according to an old Indian tradition the word ‘poet’ in Sanskrit is ‘kavi’ who is supposed to be a visionary and it is said of a poet that “what the sun (‘Ravi’ in Sanskrit) does not show, a ‘Kavi’ will see”. Milton saw things on the back of a pig.
8. Milton’s work explained how the delto-pectoral flap had been successful. It contained numerous blood vessels that ran across the chest to the shoulder having emerged from the inter-costal spaces. Soon the groin flap based on the superficial, circumflex, iliac artery was described and a successful transfer of muscle with its blood supply intact was published to obliterate and close a bony cavity.
9. While all this appears reasonable on hindsight, in the world of science, there is many an offshoot pursued by very talented and industrious individuals which fall by the way side as momentum gathers in one particular direction. The tube pedicle was one such effort, in which a random area of skin and subcutaneous tissue of a sizeable dimension was cut only on two sides instead of three and tubed on itself to allow blood vessels to orient along the axis of the tube. Then after a certain interval one end of the tube was cut, sometimes after slow strangulation to modify and to allow the blood to flow only from the other end, then the flap was cut and the cut end was put on the desired recipient part and reconstruction was achieved in further stages. Several variations of this maneuver are now a part of the history of plastic surgery but in their time some very elegant results for mutilating injuries particularly during the wars became possible through these flaps. As happens frequently in the world of science, ideas occur to scientific workers at about the same time and the idea of a tube pedicle in fact has two fathers – Gillies in England and Filatov in Russia.
10. All this was part of what was collectively called a ‘delay’ (phenomenon) in order to improve the vascularity of the flap which was beyond the one-to-one ratio. The basic delay procedure involved cutting a flap on three sides with its base intact but which was not lifted off its bed which also supplied it with blood. Later in a matter of couple of weeks the flap was lifted from its bed, leaving the base intact and sutured back to ensure that it survived only by way of blood vessels in its base. If the flap survived it was transferred. If only a small part of the flap died, the necrosed part was trimmed and the rest of the flap was transferred. Journals and books published prior to 1970 are filled with papers dealing with the delay procedure on a variety of animals and in some instances on patients. An additional feature of these papers was a variety of drugs used to improve the vascularity of the flaps (pharmacological intervention). Interestingly there is very little evidence that any pharmacological intervention really improves the flaps length-breadth ratio or can save a dying flap. Flaps die because they are improperly planned or poorly executed and then are not closely observed in the post-operative period for tell-tale signs that point to a remedial measure. Nature is robust and efficient. We need to understand her and she is not kind when her rules are broken.
Phil Sykes from England, the archivist of these short notes adds:
Stuart H Milton was a surgical research assistant with Tom Patterson in the Oxford Plastic Surgery Unit in the late 1960s. He was awarded the Kay- Kilner Prize by the BAPS in 1967 for his essay on “The Tubed Pedicle Flap”. His seminal work using a pig model between 1969 and 1972 was to debunk the rigid “length-breadth” teaching of flap survival by showing that as long as a vascular pedicle was included in the narrow base of a flap it could be extended for the full length of the territory supplied by that vascular system. Like much good research this simple observation opened up whole new areas. Axial pattern flaps, free flaps, muscle amd myocutaneous flaps followed. Sadly he died in America without the recognition he deserved. Had he lived longer he would have seen the results of his work when the rapid growth of safe reconstructive flap surgery took off in the mid 1970s.