Latissimus Dorsi Muscle Anatomy

The name latissimus dorsi muscle (L. widest of back) was well chosen because this muscle covers a wide area of the back. This large fan-shaped muscle passes from the trunk to the humerus and acts directly on the glenohumeral joint and indirectly on the pectoral girdle (scapulothoracic joint). The latissimus dorsi extends, retracts, and rotates the humerus medially (e.g., when folding your arms behind your back or scratching the skin over the opposite scapula).

Latissimus Dorsi Muscle Anatomy

Origins and Insertions

The latissimus dorsi exhibits a remarkably extensive origin pattern, encompassing multiple vertebral and non-vertebral attachment points. The muscle originates from the spinous processes of vertebrae T7-T12, all lumbar vertebrae, and the posterior third of the external lip of the iliac crest. Additionally, it attaches to the thoracolumbar fascia and the external surfaces of ribs 9-12, forming what clinicians often refer to as a broad, triangular muscle sheet.

The muscle’s insertion point presents a more concentrated arrangement, with muscle fibers converging into a thick, twisted tendon that inserts into the floor of the intertubercular groove of the humerus. This unique insertion pattern creates a distinctive spiral configuration that significantly influences its biomechanical properties.

Neurovascular Supply

The thoracodorsal nerve, originating from the posterior cord of the brachial plexus (C6-C8), provides primary innervation to the latissimus dorsi. Understanding this innervation pattern proves crucial in clinical scenarios involving nerve blocks or evaluating neurological deficits.

The thoracodorsal artery, a branch of the subscapular artery, supplies the muscle’s vascular requirements, making it a reliable option for myocutaneous flap procedures in reconstructive surgery.

See Also: Brachial Plexus Anatomy

Functional Biomechanics

In clinical practice, the latissimus dorsi demonstrates several critical functions that impact upper extremity movement and posture. The muscle serves as a powerful internal rotator and adductor of the shoulder joint, while simultaneously extending and medially rotating the arm. During respiration, it functions as an accessory muscle of expiration, particularly during forceful exhalation such as coughing or sneezing.

The muscle’s extensive attachment points enable it to assist in spinal extension and lateral flexion when the upper extremity is fixed. This functional versatility makes it particularly relevant in both athletic performance and rehabilitation settings.

Clinical Significance and Pathology

Overuse injuries commonly present in athletes involved in swimming, climbing, or throwing sports. The muscle’s involvement in complex shoulder movements makes it susceptible to strains, particularly at the musculotendinous junction.

The latissimus dorsi’s broad anatomical footprint makes it particularly valuable in reconstructive surgery. Its reliable vascular supply and substantial surface area have established it as a preferred donor site for various myocutaneous flap procedures, including breast reconstruction and functional muscle transfer operations.

Clinical examination of the latissimus dorsi requires a systematic approach. The muscle’s function can be assessed through specific manual muscle testing procedures, typically involving shoulder adduction and internal rotation against resistance. Practitioners should note that isolated testing may prove challenging due to synergistic muscle action, particularly from the teres major.

References & More

1. Gray’s Anatomy: The Anatomical Basis of Clinical Practice, 42nd Edition https://www.elsevier.com/books/grays-anatomy/standring/978-0-7020-7710-5
2. Clinically Oriented Anatomy, 8th Edition https://shop.lww.com/Moore-Clinically-Oriented-Anatomy/p/9781496347213