Sternocleidomastoid Muscle and Musculocutaneous Flap

EDITORIAL COMMENT

The designs and clinical applications are anatomically possible but have limited use with intraoral cancer, particularly if they have been irradiated. Even if a neck dissection is not necessary, the space of potential spread of intraoral cancer would be violated. The sternocleidomastoid muscle alone is quite helpful in covering the traumatically exposed or infected mandible. The limiting factor for its arc of rotation is the eleventh nerve that innervates it.

The sternocleidomastoid muscle and musculocutaneous flap can be used for reconstruction of the tongue, floor of the mouth, tonsillar fossa, and cheek (1, 2, 3, 4, 5, 6, 7). It also can be used for pharyngoesophageal defects (see Chapter 223). There are several advantages to the sternocleidomastoid flap. It uses local tissue for one-stage reconstruction of oropharyngeal defects of moderate size, with donor sites that may be closed primarily without the necessity of skin grafts. The flap can be
used successfully in patients who have had previous radiation to the neck if the skin is soft and supple over the muscle and there is no clinical evidence of radiation fibrosis or induration.

ANATOMY

The sternocleidomastoid muscle is a round muscle that arises by two tendinous fascicles from the sternum and the medial third of the clavicle, passes obliquely across the side of the neck, and inserts on the lateral surface of the mastoid process. Fresh and preserved cadaver dissections have demonstrated that the sternocleidomastoid has three blood supplies (7, 8) (Fig. 194.1). These vessels enter the muscle at various sites as nutrient vessels to circulate within the muscle and provide musculocutaneous branches to the overlying skin. Although sonic small branches may travel for a centimeter or two along the undersurface of the muscle, there is no axial distribution of vessels along the length of the undersurface of the muscle.

The blood supply to the superior portion of the sternocleidomastoid is a branch from the occipital artery that enters the muscle just below the mastoid region (Fig. 194.1). The blood supply to the inferior portion is from a branch of the thyrocervical trunk. Midway between its origin and insertion, the sternocleidomastoid is supplied by a branch of the superior thyroid artery as well as by smaller vessels from the adjacent strap muscles.

FLAP DESIGN AND DIMENSIONS

Flaps can be designed with only a “paddle” of skin attached over one end of a pedicle of the sternocleidomastoid muscle, which then is used to transport this skin (7, 9). The muscle pedicle may be based on either the superior or inferior blood supply (Fig. 194.2), the choice being made according to the ease with which the flap may be transported to the defect. In each case, the donor site can be closed either by local advancement of the neck skin or by local transposition flaps.

FIGURE 194.1 The three blood supplies to the sternocleidomastoid are the occipital artery superiorly, superior thyroid artery midway, and thyrocervical trunk inferiorly. (From Ariyan, ref. 7, with permission.)

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