Definition

By: Gregory R. Waryasz, MD

The triceps brachii muscle of the musculoskeletal system is characterized by being the main extensor of the elbow.  It has three heads.

It is part of the arm.  It consists of skeletal muscle fibers.

Its unique structural features include its three heads; long, medial, and lateral. The triceps brachii help to form the triangular space and the quadrangular space.  The triceps brachii provides over 60% of the upper arm mass.

The origin of the long head is the infraglenoid tubercle of the scapula.  The origin of the lateral head is the posterior surface of the humerus, superior to the radial groove.  The origin of the medial head is the posterior surface of the humerus inferior to the radial groove.

The insertion is the proximal end of the olecranon of the ulna and forearm fascia.

The blood supply is from the deep brachial artery and venous drainage is from the accompanying veins.

The innervation is from the radial nerve.

The triceps brachii 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 triceps brachii is to extend the forearm.  The long head helps to resist humeral dislocation specifically inferior dislocation.  The long head also plays a role in extension and adduction of the arm, but it is the least active of the three heads of the triceps.  The medial head is the main workhorse for forearm extension at all speeds of contraction and either with or without resistance.  The lateral head is the strongest and usually only recruited to work against resistance.   The anconeus is the primary synergist to the triceps brachii.

Common diseases include tendinitis, tendinopathy, tears, rupture, and bursitis.

Tendinitis is inflammation of the tendon usually due to overuse.

Tears can occur at any point in the tendons or muscle belly.

Tendon rupture can occur proximally or distally.

Bursitis is a condition that occurs from overuse. The subtendinous olecranon bursa can become inflammed with overuse at the distal insertion of the triceps tendon.

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

It is usually treated with physical therapy and NSAIDs for bursitis and tendinitis.  Triceps tendon tears and rupture may or may not require surgery.   Injury to the triceps usually does not require surgery because gravity will extend the elbow, however surgery may be necessary if the patient has to use crutches.  The brachioradialis muscle can be transferred to help with extension of the elbow.

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: Triceps Brachii (http://www.wheelessonline.com/ortho/triceps_brachii)