The subclavius muscle is a short, triangular muscle of the thoracic wall that lies underneath the clavicle. It originates from the first rib and courses laterally to insert on the undersurface of the middle third of the clavicle.
The main function of the subclavius is to stabilize the clavicle during movements of the shoulder girdle. In addition, it is significant in preventing injuries to the adjacent neurovascular structures due to fractures of the clavicle.
This article will describe the anatomy and functions of the subclavius muscle.
|Origin||Costal cartilage, sternal end of rib 1|
|Insertion||Anteroinferior surface of middle third of clavicle|
|Innervation||Subclavian nerve (C5-C6)|
|Blood supply||Clavicular branch of thoracoacromial artery, suprascapular artery|
|Function||Sternoclavicular joint: Anchors and depresses clavicle|
Origin and insertion
The subclavius muscle originates by a strong tendon from the sternal end of the 1st rib, near its articulation with the costal cartilage. The tendon spreads superolaterally into a muscle belly that inserts into the lower surface of the middle third of the body of clavicle (groove for subclavius muscle).
The subclavius is enclosed by the clavipectoral fascia, which is a fibrous connective tissue that spans the interval between the clavicle and pectoralis minor muscle. The pectoralis major muscle courses superficial to the subclavius and clavipectoral fascia. The brachial plexus, suprascapular artery, subclavian artery and subclavian vein pass deep to the subclavius muscle.
The subclavius is innervated by the subclavian nerve (C5-6), a small branch that arises from the superior trunk of brachial plexus.
The subclavius muscle receives arterial blood from the clavicular branch of thoracoacromial artery, with contributions from the suprascapular artery.
The main function of the subclavius muscle is the active stabilization of the clavicle at the sternoclavicular joint during movements of the shoulder and arm. Furthermore, its contraction leads to a depression of the sternal end of the clavicle and subsequent elevation of the first rib. This movement is rather insignificant, but still helps to prevent dislocation of the clavicle at the sternoclavicular joint during certain types of activity.
Additionally, the subclavius is important to prevent injury of the adjacent subclavian blood vessels and the superior trunk of the brachial plexus in case of a fractured clavicle.
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The vessels and nerves running behind the subclavius muscle can sometimes become entrapped between the clavicle and the first rib, inside the costoclavicular space. This is referred to as costoclavicular syndrome and marks one of the three types of thoracic outlet syndromes (TOS).
This syndrome can be caused by fractures and thoracic deformities, amongst others. Typical symptoms include irritations of the brachial plexus and circulatory disorders of the arm