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BIOANATOMY AND BIOMECHANICS
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In a normal individual, the scalp is defined by the extent of dense terminal hair overlying the calvarium. In youth, the scalp is generously covered with hair. With age, thinning or outright hair loss is common. Without adequate photoprotection, the scalp is frequently burned and skin cancer of the scalp is common.
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The scalp is supplied by an anastomosing series of moderate-sized arteries, which derive from the supraorbital and supratrochlear systems, the superficial temporal vessels, the postauricular arteries, and the occipital arteries. Most of the larger vessels run just above the galeal fascia and provide smaller extensions that supply the subcutis and dermis.
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The structure of the scalp is defined by a layered system (Fig. 14.1). The dermis of the scalp is relatively thin and punctuated by numerous terminal hair follicles. The subdermal and subcutaneous plexi are richly supplied by innumerable vessels. The layer of adipose is highly variable from individual to individual and may be either very well developed or almost nonexistent. The first fascial layer is the galea, which envelopes the scalp and extends from the occipital musculature over the head and down to the superior orbital rim. Beneath the galea is a layer of loose areolar tissue, and finally, above the bone is an adherent layer of periosteum.
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Mobility on the scalp is extremely variable and depends on multiple factors, ultimately being restrained by the rigidity and adherence of the galea. Some individuals have a scalp that is drum-tight and almost impossible to move. Others have a loose scalp that mimics the easily mobile skin of a Shar Pei dog (Fig. 14.2). Mobility can be divided into two zones, one being the ability to move the galea and the other being the mobility of the tissues above the galea. The loose, areolar tissue beneath the galea can be widely undermined in a relatively bloodless plane, and in some individuals, the galea may be closed over a reasonable distance. In many individuals, however, the galea is tight, and little to no additional mobility will be achieved by undermining. Galeotomies can be performed and do lead to some tension release, but they are challenging on direct side-to-side closures and risk transecting large-caliber vessels.1 Mobility above fascia is similarly variable and depends on multiple factors including the thickness of the adipose layer and the fibrous adherence of the overlying tissues to the galea.
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