Definition
By: Gregory R. Waryasz, MD
The subscapularis muscle of the musculoskeletal system is characterized by being located on the anterior face of the scapula.
It is part of the scapulohumeral muscles and rotator cuff. It consists of skeletal muscle fibers.
Its unique structural features include its thick and triangular shape. It forms a part of the posterior wall of the axilla. The muscle crosses the anterior scapulohumeral joint on its way to insert into the humerus.
The origin is the subscapular fossa on the anterior scapula.
The insertion is the lesser tubercle of the humerus.
The blood supply is from the transverse cervical and subscapular arteries and venous drainage is from the accompanying veins.
The innervation is from the upper and lower subscapular nerve.
The subscapularis 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 subscapularis muscle is to medially rotate and adduct the humerus. The subscapularis also helps to hold the humeral head into the glenoid cavity.
The rotator cuff tendons blend with the joint capsule to help reinforce it. Rotator cuff muscle contraction helps to hold the larger humeral head into the glenoid.
Common diseases include rotator cuff tendinitis, tears, and impingement syndrome. These injuries more commonly affect the supraspinatus component of the rotator cuff. Recurrent subluxations or dislocations of the shoulder are often treated with surgery on the subscapularis.
Impingement syndrome refers to a microtrauma to the rotator cuff due to decreased space between the humeral head and the structures above the rotator cuff. The trauma leads to inflammation, swelling, pain, and decreased rotator cuff function.
Rotator cuff tendinitis is a condition of overuse associated with irritation and swelling of the cuff tendons. It most commonly is the supraspinatus tendon. Patients have pain with moving the shoulder and the pain may awaken them at night.
Rotator cuff tears can be asymptomatic or symptomatic. The prevalence increases with age. The tear can be partial or complete. Pain is worse at night and with overhead activities.
Rotator cuff tear arthropathy is a condition of shoulder arthritis with a rotator cuff tear. Patients may have pain, decreased shoulder range of motion, and significant arthritic changes and damage to the glenohumeral joint.
Commonly used diagnostic procedures include clinical history, physical exam, and MRI.
It is usually treated with physical therapy and NSAIDs for impingement syndrome and tendinitis. Rotator cuff tears may require arthroscopic repair by a surgeon. Rotator cuff tear arthropathy may require a shoulder joint replacement.
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: Subscapularis Muscle (http://www.wheelessonline.com/ortho/subscapularis_muscle)