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Skin Anatomy for the Reconstructive Surgeon

Skin anatomy informs donor selection, graft take, flap perfusion and scar planning in genital and perineal reconstruction. The main considerations are tissue layers, vascular connections and direction-dependent mechanics. This page covers the anatomy; Flaps in GU Reconstruction develops flap classification and design.[1][2]

Layers and Their Surgical Relevance​

Skin proper comprises the epidermis and dermis; the underlying hypodermis (subcutaneous tissue) is considered with them for reconstructive planning. These layers have different structural and vascular roles.[1][3]

Epidermis​

The epidermis is avascular stratified squamous epithelium, nourished by diffusion from the dermis. Its thickness varies substantially with site. The usual strata are basale, spinosum, granulosum and corneum; a distinct stratum lucidum belongs to thick glabrous skin, such as the palm and sole. The 32–42 μm measurements in a 12-cadaver free-flap donor study describe those sampled sites, not the full range of human epidermal thickness.[1][4]

When de-epithelializing tissue that will be buried, remove epidermis while preserving the dermis and its vascular connections. A cadaveric DIEP contrast-perfusion experiment found less perfused territory after dermal removal; this supports the anatomical importance of the dermal network but does not establish a corresponding percentage of clinical flap loss.[5]

Dermis​

The dermis provides much of the skin’s tensile behavior and contains interconnected vascular networks. In the sampled cadaveric donor sites, mean dermal thickness ranged from approximately 950 μm at the radial forearm to 2,150 μm at the thoracodorsal region.[4] It is divided into:

  • Papillary dermis (superficial) — thinner, looser connective tissue with fine capillary loops
  • Reticular dermis (deep) — dense collagen and elastin; the subdermal vascular plexus lies at the dermal–subcutaneous junction[3][6]

The dermis contains fibroblasts, collagen, elastin, glycosaminoglycans, skin adnexa (hair follicles, sebaceous and sweat glands), mechanoreceptors, and the critical cutaneous vascular networks.[7] The anisotropic alignment of its collagen and elastin fibers is the structural origin of the direction-dependent mechanical behavior of skin; relaxed skin tension lines and Langer’s cleavage lines are related but distinct descriptions that help guide incision and flap planning (see Biomechanics below).[8][9]

Hypodermis (Subcutaneous Fat)​

Hypodermal thickness is a major contributor to flap bulk. The cadaveric donor-site study measured approximately 1,900 μm at the radial forearm and 7,100 μm at the DIEP site; individual thickness varies with body habitus and location.[4] This layer holds adipose lobules separated by fibrous septa carrying the larger subcutaneous vessels and perforating arteries. A subcutaneous vascular network, sited between the dense and loose adipose laminae, links the larger subcutaneous vessels, the vertical perforators, and the subdermal plexus.[10] The safe elevation or thinning plane depends on the particular flap and the course of its vessels.

Donor siteDermis (≈ μm)Subcutaneous fat (≈ μm)Reconstructive note
Radial forearm~950~1,900Thinnest sampled dermis and fat; actual suitability also depends on vessels, hair, sensation and donor morbidity
Thoracodorsal~2,150intermediateThickest sampled dermis; thickness alone does not establish mechanical superiority
DIEP / lower abdomenintermediate~7,100Thickest sampled fat; patient-specific bulk must be assessed

Approximate means from a 12-cadaver study of radial forearm, anterolateral thigh, thoracodorsal and DIEP sites. These are anatomical observations, not a donor-selection ranking or an individual patient’s measurements.[4]

Cutaneous Vascular Anatomy​

The blood supply to the skin is organized hierarchically, and that hierarchy is exactly what flap classification is built on.[2]

Plexuses of the skin:

  • Subdermal plexus — at the dermal–subcutaneous junction; the dominant supply for random pattern flaps. Blood enters from the flap base and runs through this interconnected network, which is why a random flap's length-to-width ratio matters: the plexus can only perfuse a finite distance from its pedicle.[11][12]
  • Subcutaneous plexus — within the subcutaneous fat, fed by perforating vessels from the underlying source artery.
  • Fascial plexus — on or within the deep fascia, supplied by septocutaneous and musculocutaneous perforators; the basis of fasciocutaneous flaps.[13]

In abdominal DIEP anatomy, important perforator branches occur at two levels: just above Scarpa's fascia (fascial plexus — often larger-caliber branches) and at the subdermal plexus (more numerous, smaller branches).[13] Adjacent perforators communicate through direct linking vessels (true anastomoses running parallel within the subcutaneous tissue) and indirect linking vessels (connections through the subdermal plexus) — the conduits that let one perforator territory recruit its neighbor.[14]

Nakajima's classification divides cutaneous flaps into five vascular types — cutaneous, fasciocutaneous, adipofascial, septocutaneous, and musculocutaneous — with fasciocutaneous flaps further subdivided into six patterns by their input to the fasciocutaneous plexus.[2] The clinical extensions of this vascular map — the angiosome and perforasome concepts and how they set safe flap dimensions — are covered on the flaps page.

Biomechanics​

Skin behaves as a non-linear, viscoelastic, anisotropic material, and that mechanical character is decisive for incision orientation, closure tension, and flap advancement.[8]

  • Relaxed skin tension lines (RSTLs) describe the furrows observed with skin at rest or gently pinched. Langer’s lines were derived from cleavage patterns in cadaveric skin. They should not be used as interchangeable terms.[20]
  • Incision orientation changes retraction and closing tension. Experimental wound studies support considering local tension lines, but living skin movement, the defect shape, scar location and vascular preservation also matter.[15][16]
  • A finite-element study of expanded flaps predicted lower flap stress with certain advancement directions. This is a modeling result, not a universal rule to advance every flap perpendicular to RSTLs.[17]
  • Site, age, collagen orientation and testing method affect measured mechanics.[8][9]

In 56 excised human back-skin specimens, mean ultimate tensile strength was 21.6 ± 8.4 MPa and mean elastic modulus 83.3 ± 34.9 MPa. These laboratory values describe that test population and method; they do not define a safe clinical stretch or closure-tension threshold.[9]

Neurovascular Relationships​

Anatomical studies describe longitudinal vascular networks accompanying many cutaneous nerves, providing the basis for neurocutaneous and neurovascular flap designs. The nerve, arterial pedicle and venous drainage must still be identified for the selected flap; these observations do not guarantee identical anatomy in every patient.[18] Cutaneous veins likewise carry their own accompanying arteries (venocutaneous perforators), which is what makes venoadipofascial pedicled flaps possible.[19] For sensate genital reconstruction, distinguish the donor flap’s sensory nerve from the recipient nerve used for coaptation and from the vascular pedicle. Their identities depend on the named flap and operation.

Reconstructive Relevance​

  • Assess the actual donor. Thickness, hair distribution, vascular anatomy, sensation, available surface area and donor morbidity jointly determine suitability; the small histology study did not compare clinical phalloplasty outcomes.[4]
  • Preserve the vascular network. Dermal removal or thinning can interrupt critical connections. Cadaveric and animal experiments support caution; thinning must follow the anatomy and evidence for the specific flap rather than a blanket prohibition for all flaps.[5][11][12]
  • Assess local tension and motion. Plan incisions with observed skin lines and cosmetic boundaries where possible, and distribute closure tension without compromising perfusion.[15][16][20]
  • Connect anatomy to flap design. Random, axial, fasciocutaneous and perforator terminology describes different aspects of blood supply or tissue composition, not mutually exclusive layers. See flap classification and design.

See also: Flaps in GU Reconstruction · Plastic Surgery Principles · Reconstructive Ladder · Wound Healing · STSG · FTSG

References​

1. Arda O, Göksügür N, Tüzün Y. Basic histological structure and functions of facial skin. Clin Dermatol. 2014;32(1):3–13. doi:10.1016/j.clindermatol.2013.05.021

2. Nakajima H, Fujino T, Adachi S. A new concept of vascular supply to the skin and classification of skin flaps according to their vascularization. Ann Plast Surg. 1986;16(1):1–19. doi:10.1097/00000637-198601000-00001

3. Hamad J, McCormick BJ, Sayed CJ, et al. Multidisciplinary update on genital hidradenitis suppurativa: a review. JAMA Surg. 2020;155(10):970–977. doi:10.1001/jamasurg.2020.2611

4. Hwang K, Kim H, Kim DJ. Thickness of skin and subcutaneous tissue of the free flap donor sites: a histologic study. Microsurgery. 2016;36(1):54–8. doi:10.1002/micr.30000

5. Laungani AT, Van Alphen N, Christner JA, et al. Three-dimensional CT angiography assessment of the impact of the dermis and the subdermal plexus in DIEP flap perfusion. J Plast Reconstr Aesthet Surg. 2015;68(4):525–30. doi:10.1016/j.bjps.2014.12.004

6. Kaur A, Midha S, Giri S, Mohanty S. Functional skin grafts: where biomaterials meet stem cells. Stem Cells Int. 2019;2019:1286054. doi:10.1155/2019/1286054

7. Wong R, Geyer S, Weninger W, Guimberteau JC, Wong JK. The dynamic anatomy and patterning of skin. Exp Dermatol. 2016;25(2):92–8. doi:10.1111/exd.12832

8. Ayadh M, Guillermin A, Abellan MA, Bigouret A, Zahouani H. The assessment of natural human skin tension orientation and its variation according to age for two body areas: forearm and thigh. J Mech Behav Biomed Mater. 2023;141:105798. doi:10.1016/j.jmbbm.2023.105798

9. Ní Annaidh A, Bruyère K, Destrade M, Gilchrist MD, Otténio M. Characterization of the anisotropic mechanical properties of excised human skin. J Mech Behav Biomed Mater. 2012;5(1):139–48. doi:10.1016/j.jmbbm.2011.08.016

10. Pearl RM, Johnson D. The vascular supply to the skin: an anatomical and physiological reappraisal — Part I. Ann Plast Surg. 1983;11(2):99–105. doi:10.1097/00000637-198308000-00002

11. Myers B, Donovan W. The location of the blood supply in random flaps. Plast Reconstr Surg. 1976;58(3):314–6. doi:10.1097/00006534-197609000-00010

12. Yazar S, Guzel MZ, Aydin Y, Arslan H, Demir M. Demonstration of circulation haemodynamics in random pattern thinned skin flap (an experimental study). J Plast Reconstr Aesthet Surg. 2008;61(11):1368–77. doi:10.1016/j.bjps.2007.11.045

13. Lee KT, Mun GH. Perfusion of the DIEP flaps: a systematic review with meta-analysis. Microsurgery. 2018;38(1):98–108. doi:10.1002/micr.30024

14. Saint-Cyr M, Wong C, Schaverien M, Mojallal A, Rohrich RJ. The perforasome theory: vascular anatomy and clinical implications. Plast Reconstr Surg. 2009;124(5):1529–1544. doi:10.1097/PRS.0b013e3181b98a6c

15. Ksander GA, Vistnes LM, Rose EH. Excisional wound biomechanics, skin tension lines, and elastic contraction. Plast Reconstr Surg. 1977;59(3):398–406. doi:10.1097/00006534-197703000-00015

16. McGuire MF. Studies of the excisional wound: I. Biomechanical effects of undermining and wound orientation on closing tension and work. Plast Reconstr Surg. 1980;66(3):419–27.

17. Buganza-Tepole A, Steinberg JP, Kuhl E, Gosain AK. Application of finite element modeling to optimize flap design with tissue expansion. Plast Reconstr Surg. 2014;134(4):785–792. doi:10.1097/PRS.0000000000000553

18. Taylor GI, Gianoutsos MP, Morris SF. The neurovascular territories of the skin and muscles: anatomic study and clinical implications. Plast Reconstr Surg. 1994;94(1):1–36. doi:10.1097/00006534-199407000-00001

19. Nakajima H, Imanishi N, Fukuzumi S, et al. Accompanying arteries of the cutaneous veins and cutaneous nerves in the extremities: anatomical study and a concept of the venoadipofascial and/or neuroadipofascial pedicled fasciocutaneous flap. Plast Reconstr Surg. 1998;102(3):779–91. doi:10.1097/00006534-199809030-00024

20. Borges AF. Relaxed skin tension lines (RSTL) versus other skin lines. Plast Reconstr Surg. 1984;73(1):144–150. doi:10.1097/00006534-198401000-00036