latissimus

Latissimus dorsi, commonly referred to as the latissimus, is a large, flat muscle of the back that forms part of the posterior axillary fold and covers much of the lower back. It extends from the lower thoracic and lumbar region up toward the upper arm, contributing to the contour and movement of the back.

Origin and insertion follow a broad pattern. The muscle originates from the thoracolumbar fascia, spinous processes of typically T7–T12, the lumbar vertebrae (via the fascia), the iliac crest, and the inferior ribs (usually ribs 9–12), with occasional attachments to the inferior angle of the scapula. It inserts into the intertubercular (bicipital) groove of the humerus, on the front surface of the upper arm bone.

Nerve supply comes from the thoracodorsal nerve, a branch of the posterior cord of the brachial plexus, usually carrying fibers from C6–C8. The primary blood supply is from the thoracodorsal artery, a branch of the subscapular artery.

Functionally, the latissimus dorsi acts to extend, adduct, and medially rotate the arm at the shoulder joint. It also assists in drawing the shoulder downward and backward. With the arms fixed, it can aid in movements of the trunk, and it plays a prominent role in activities such as pulling, climbing, and swimming.

Clinical notes include susceptibility to strains in athletes performing repetitive pulling movements. In reconstructive surgery, the latissimus dorsi can be used as a donor flap (latissimus dorsi flap) for soft tissue reconstruction.