Definition

By: Gregory R. Waryasz, MD

The latissimus dorsi of the musculoskeletal system is characterized by covering a large area on the back. Its name means “widest of the back”.

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

Its unique structural features its large, fan shape.  It spans from the spine to the humerus.  The insertion into the humerus is a flat tendon that twists on itself.  The origin on the spinous process is a broad aponeurosis.

The origin is at the spinous processes of the inferior 6 thoracic vertebrae, thoracolumbar fascia, iliac crest, and inferior 3 or 4 ribs.

The insertion is the floor of the intertubercular groove of the humerus.

The blood supply is from the dorsal scapular and subscapular artery and venous drainage is from the accompanying veins.

The innervation is from the thoracodorsal nerve.

The latissimus dorsi 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 latissimus dorsi is to extend, adduct, and medially rotate the humerus.  It is involved in the climbing motion for pull-ups or rock-climbing.  The synergists are the rhomboids, pectoralis major, and teres major.

Common diseases include muscle strain and paralysis.

Paralysis of the latissimus dorsi can occur if there is surgical injury to the thoracodorsal nerve. Patients are unable to raise the trunk with the upper limbs for activities such as climbing.

The latissimus dorsi muscle can be transferred to other locations to provide tissue coverage or to improve function.

Cardiomyoplasty is a procedure for patients with low cardiac output that cannot have a heart transplant.  The latissimus dorsi is wrapped around the heart and is stimulated electrically to work synchronously with ventricle function.

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

It is usually treated with physical therapy and NSAIDs for latissimus dorsi strain.

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: Latissimus Dorsi (http://www.wheelessonline.com/ortho/latissimus_dorsi)