Anatomy and supply
The subclavius muscle is a short muscle of the shoulder girdle. It originates at the first rib (border between the bone and cartilage) and inserts at the lower surface of the lateral clavicle. Thereby it lies behind the pectoralis major. The brachial plexus and both the subclavian artery and vein pass under the subclavius muscle. Due to its location and relatively small size the muscle is hardly palpable. The innervation is carried by the subclavian nerve (C5-6), a branch of the brachial plexus.
The main task of the subclavius muscle is the active stabilization of the clavicle in the sternoclavicular joint during movements of the shoulder and arm. Furthermore its contraction leads to a depression of the clavicle and elevation of the first rib respectively. These movements however play a rather subordinate role.
The vessels and nerves running behind the subclavius muscle can sometimes get entrapped in the room between the clavicle and the first rib (costoclavicular space). This is referred to as the costoclavicular syndrome and marks one of the three types of the thoracic outlet syndrome (TOS). Causes can be fractures and thoracic deformities amongst others. Typical symptoms are irritations of the brachial plexus and circulatory disorders of the arm.