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Flaps — classification, blood supply and tissue expansion
A flap is tissue moved together with its blood supply, so it covers beds on which a graft would fail; the key exam classification is by blood supply — random versus axial flaps, and the Mathes-Nahai classification of muscles by the number and importance of their pedicles.
Why it matters in the exam
A random flap is nourished by the subdermal plexus without a defined vessel, so its length is limited relative to its width (more is possible on the face, where supply is rich); an axial flap is based on a named vessel running along it. Mathes-Nahai: type 1 — one pedicle (tensor fasciae latae, gastrocnemius); type 2 — a dominant pedicle and minor pedicles (gracilis, soleus, trapezius); type 3 — two dominant pedicles (gluteus maximus, rectus abdominis, serratus anterior); type 4 — segmental pedicles (sartorius, tibialis anterior, the long toe extensors) — so the whole muscle cannot be raised on one pedicle; type 5 — a dominant pedicle and secondary segmental pedicles (latissimus dorsi, pectoralis major), which can be raised on either. Fasciocutaneous flaps are classified by Cormack-Lamberty from A to D.
The angiosome concept (Taylor) describes the skin as a mosaic of territories, each fed by a source artery, with "choke vessels" between them; dilating them by "delay" — dividing part of the supply a few days to two weeks before transfer — increases the area that survives. Perforator flaps (such as DIEP and ALT) take skin and fat on a vessel that passes through muscle or septum, sparing the muscle. A flap's arc of rotation is limited by the pedicle's entry point: a pedicle close to the end of the muscle allows a wide arc. Tissue expansion grows local skin of the same colour and texture: the epidermis thickens, the dermis thins, muscle atrophies, a capsule forms around the expander and vessel numbers rise — which makes expanded skin a flap with a good blood supply. The reconstructive ladder starts with primary closure and climbs to a free flap, but today the step chosen is the one that gives the best result, not necessarily the simplest.
Key points
- Random — subdermal plexus; axial — a named vessel.
- Mathes-Nahai 1 to 5 by pedicles.
- Type 4 — segmental (sartorius).
- Angiosome and choke vessels; delay increases survival.
- Tissue expansion: epidermis thickens, dermis thins, more vessels.
Summary table
| Mathes-Nahai type | Pedicles | Examples |
|---|---|---|
| 1 | One pedicle | Tensor fasciae latae, gastrocnemius |
| 2 | Dominant and minor | Gracilis, soleus, trapezius |
| 3 | Two dominant | Gluteus maximus, rectus abdominis, serratus anterior |
| 4 | Segmental | Sartorius, tibialis anterior, long extensors |
| 5 | Dominant and secondary segmental | Latissimus dorsi, pectoralis major |
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Sources
- Mathes and Nahai classification of muscle flaps, 1981 — Patterns of vascular anatomy
- Cormack and Lamberty classification of fasciocutaneous flaps, 1984 — Types A to D
- Taylor and Palmer, the angiosome concept, 1987 — Vascular territories of the body
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.