What is the blood supply to the sternocleidomastoid muscle (SCM)?

Blood Supply of the Sternocleidomastoid Muscle

The sternocleidomastoid muscle receives its arterial blood supply from three distinct regional sources: the occipital artery supplying the upper third, branches from the superior thyroid or external carotid artery supplying the middle third, and the suprascapular artery (in over 80% of cases) supplying the lower third. 1

Upper Third Blood Supply

• The upper third of the SCM is constantly supplied by branches of the occipital artery in all individuals, making this the most reliable vascular pedicle 2, 1
• These branches can be categorized into types 1, 2a, 2b, and 3 based on their anatomical courses 1
• The occipital artery supply extends throughout the entire upper portion of the muscle 2

Middle Third Blood Supply

The middle third demonstrates the most anatomical variability:

• Superior thyroid artery branches supply this region in 42-53% of cases 1, 3
• External carotid artery branches provide supply in 20-27% of cases 1, 3
• Both vessels contribute in 20-27% of cases 1, 3
• This middle pedicle is critical for composite flap viability and must be preserved along with the inferior pedicle to ensure full muscle vascularization 3

Lower Third Blood Supply

• The suprascapular artery provides the dominant blood supply to the lower third in over 73-80% of cases, which represents a more consistent pattern than previously described 1, 3
• Alternative sources include the transverse cervical artery (7-13%), thyrocervical trunk (13%), or superficial cervical artery (0-7%) 3
• The first minor pedicle originating from the superior thyroid artery specifically supplies the clavicular head 2

Clinical Implications for Surgical Flaps

When harvesting SCM flaps, the inferior pedicle alone cannot ensure complete muscle vascularization—both the middle and inferior pedicles must be preserved for safe composite flap elevation. 3

• For split SCM flaps using the clavicular head, the muscle can be divided cranially up to the level of the first minor pedicle, and preservation of this pedicle ensures flap reliability 2
• The sternal head can be safely used up to the occipital artery level while leaving the minor pedicle and clavicular head intact 2
• Inferiorly based rotated SCM flaps pedicled on the sternal origin receive optimal vascularization from the superior thyroid/external carotid artery and accessory supply from the suprascapular artery 4
• Injection studies demonstrate that the lower pedicle alone reaches only the four lower levels of the muscle, while combined middle and inferior pedicle preservation achieves 100% vascularization of all six muscle levels 3

Anatomical Landmarks

• The internal carotid artery can be identified by dissection along the anterior border of the sternocleidomastoid muscle 5
• The carotid pulse is palpable just medial to the sternocleidomastoid muscle 5
• For carotid sinus massage, compression is applied at the anterior margin of the sternocleidomastoid muscle between the angle of the jaw and cricoid cartilage 5

Common Pitfalls

• Do not assume the lower third is supplied by the inferior thyroid artery—this is outdated information; the suprascapular artery is the dominant source 1
• Never harvest an SCM flap based solely on the inferior pedicle without preserving the middle pedicle, as this risks flap necrosis 3
• When splitting the SCM muscle, do not extend the division cranial to the first minor pedicle without ensuring adequate vascular supply to both heads 2