Definition

By: Gregory R. Waryasz, MD

The subclavius of the musculoskeletal system is characterized by protecting the subclavian vessels and superior trunk of the brachial plexus.

It is part of the anterior axioappendicular muscles.  It consists of skeletal muscle fibers.

Its unique structural features include being a small and round muscle under the clavicle.  It overlies the subclavian vessels and brachial plexus.

The origin is at the junction of the 1st rib and the costal cartilage.

The insertion is the inferior surface of the middle third of the clavicle.

The blood supply is from clavicular branch of the thoracoacromial trunk and subclavian arteries.  Venous drainage is from the accompanying veins.

The innervation is from the nerve to the subclavius.

The subclavius muscle as well as all other bones, muscles, and ligaments of the body are derived of mesodermal origin in the embryo.

The function of the subclavius is to anchor and depress the clavicle. It helps to protect the subclavian vessels and brachial plexus during clavicle fractures. The subclavius also helps to resist sternoclavicular joint separation during pulling motions.

Common diseases include injury during clavicle fracture, acromioclavicular (AC) joint separation, or sternoclavicular (SC) joint separation.

Thoracic outlet syndrome is a disorder of compression of the structures at the thoracic outlet.  The structures can be part of the brachial plexus, subclavian artery, or subclavian vein giving different symptoms.  The thoracic outlet space is formed by the clavicle, 1st rib, subclavius muscle, costoclavicular ligament, and the anterior scalene muscle.  Sometimes the first rib is the culprit for the compression or a tumor.

Commonly used diagnostic procedures include clinical history, physical exam, x-ray, CT-scan and MRI.

It is usually treated with either a sling or surgical fixation for a clavicle fracture or for AC or SC joint separations. Thoracic outlet syndrome is treated with physical therapy and possible first rib resection.

References

Lieberman J (ed), AAOS Comprehensive Orthopaedic Review, American Academy of Orthopaedic Surgeons, 2008.

Moore K, Dalley A (eds), Clinically Oriented Anatomy (5th edition), Lippincott Williams & Wilkins, Philadelphia, PA, 2006.

Wheeless’ Textbook of Orthopaedics: Thoracic Outlet Syndrome (http://www.wheelessonline.com/ortho/thoracic_outlet_syndrome)