Definition
By: Gregory R. Waryasz, MD
The infraspinatus muscle of the musculoskeletal system is characterized by being a powerful lateral rotator of the humerus.
It is part of the scapulohumeral muscles and rotator cuff. It consists of skeletal muscle fibers.
Its unique structural features include it covering the medial three quarters of the infraspinous fossa of the scapula. It is partially covered by the deltoid and the trapezius.
The origin is the infraspinatus fossa of the scapula.
The insertion is the middle facet of the greater tubercle of the humerus.
The blood supply is from the suprascapular artery and circumflex scapular arteries and venous drainage is from the accompanying veins.
The innervation is from the suprascapular nerve.
The infraspinatus 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 infraspinatus is to stabilize the glenohumeral joint and to laterally rotate the humerus. The infraspinatus works synergistically with the teres minor, subscapularis, and deltoid. Another function of the infraspinatus is to help with extension of the humerus.
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.
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.
Injury the suprascapular nerve leading to loss of function of the infraspinatus muscle.
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: Infraspinatus (http://www.wheelessonline.com/ortho/infraspinatus)