The subclavius is a small muscle running parallel to the clavicle from the first costochondral junction to the inferior clavicle. Its primary mechanical role is modest, but its anatomical significance is considerable because it lies directly over the subclavian vessels and brachial plexus, physically protecting them from inferior clavicle fracture fragments. Its nerve supply originates from the upper trunk of the brachial plexus and subclavius integrity testing can help localise brachial plexus injuries.
| Origin | Junction of the first rib and its costal cartilage |
|---|---|
| Insertion | Inferior surface of the middle third of the clavicle |
| Nerve Supply | Nerve to subclavius (C5, C6) |
| Blood Supply | Clavicular branch of the thoracoacromial artery |
| Actions | Depression and stabilisation of the clavicle during shoulder movement; Protects the subclavian vessels from fracture fragments of the clavicle |
|---|
It depresses and stabilises the clavicle at the sternoclavicular joint during shoulder girdle elevation and protraction movements, serving more as a joint stabiliser than a prime mover.
Subclavius hypertrophy or spasm can contribute to costoclavicular syndrome, a form of thoracic outlet syndrome where the space between the clavicle and first rib is narrowed and the neurovascular structures are compressed. An enlarged subclavius is seen on MRI in some patients with thoracic outlet syndrome. The muscle is routinely protected or retracted during clavicle fracture repair surgery to protect the underlying vessels.
The subclavius is not directly palpable through the overlying pectoralis major, but tenderness in the subclavicular groove can be elicited with deep pressure in the infraclavicular fossa during thoracic outlet syndrome assessment.
Compression of the neurovascular bundle between a hypertrophied subclavius and the first rib producing thoracic outlet symptoms reproduced by bracing the shoulders back and downward in the military posture position.
