Definition

By: Gregory R. Waryasz, MD

The pectoralis minor of the musculoskeletal system is characterized by being located deep to the pectoralis major.

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

Its unique structural features include having many different anatomic variations to the costal attachments.  The muscle belly is triangular in shape.  The base is from the “fleshy slips” attached to ribs 3 to 5 near the costal cartilages. There are many variations of how these “fleshy slips” attach.  The vessels and nerves to the arm pass under the bridge that is formed by the pectoralis minor and the coracoids process.

The origin is the 3rd to 5th ribs near the costal cartilage attachments.

The insertion is the medial border and the superior surface of the coracoids process of the scapula.

The blood supply is from the pectoral branch of the thoracoacromial trunk and venous drainage is from the accompanying veins.

The innervation is from the medial pectoral nerves.

The pectoralis minor 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 pectoralis minor is to stabilize the scapula by drawing it anteriorly and inferiorly against the thoracic wall.  It is used to help stretch to reach something that is just out of reach. During deep inspiration, the pectoralis minor also elevates the ribs.

Common diseases include congenital absence.

Poland syndrome is a rare birth defect with under development or absence of the pectoralis and webbing/syndactyly of the fingers. It is usually unilateral.  In females the breast tissue can be abnormal.

Commonly used diagnostic procedures include clinical history, physical exam, and MRI.

It is usually treated with observation for the pectoralis minor component of Poland syndrome. Poland syndrome can be treated with a transfer of the latissimus dorsi muscle to regain pectoralis major function.  Poland syndrome may require its other components to be treated as well such as the syndactyly.

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.