Dr. Kevin Yip

Dr Kevin Yip
Orthopaedic Surgeon
MBBS(UK), FRCS(EDIN), FAM(SING), FHKCOS(ORTHO)

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Anatomy

The anatomy of the pectoralis major muscle demonstrates two distinctively different parts—the clavicular head and the sternal head . We feel that when evaluating injuries to the pectoralis it is important to understand the anatomy of the pectoralis major muscle complex.

Unfortunately, many of the published reports never comment on this difference, or describe it incompletely and do not distinguish if a ‘complete’ tear involves one or both heads of the pectoralis. Only a small number of reports specifically address the anatomy of the pectoralis and the relation of the two heads. Wolfe et al.

It suggested the human pectoralis major to be evolved from two distinctly separate muscles in lower mammals. The sternal head of the pectoralis muscle arises from the sternum, upper six ribs, and the aponeurosis of the external oblique muscle. The sternal head is supplied by the medial pectoral nerve (C8-T1) off of the medial cord, and specific pectoral artery.

The clavicular head of the pectoralis major arises from the medial clavicle, and upper sternum. The clavicular head is supplied by the lateral pectoral nerve (C5-C7) off of the lateral cord, and the deltoid branch of the thoraco-acromial artery. The sternal head primarily performs adduction and internal rotation; the clavicular head assists with forward elevation.

The two portions of the muscle form a bi-laminar tendon that inserts lateral to the long head biceps tendon. The clavicular head tendon inserts anterior and slightly distal; the sternal head folds posterior and extends superiorly. To further suggest that these are distinctly different muscles, Poland’s

Syndrome involves the absence of only the sternal portion of the pectoralis muscle , although the clavicular head is present. The primary deformity and associated weakness seen in pectoralis ruptures is related to loss of the sternal head tendon

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