Latissimus dorsi

Musculus latissimus dorsi

Also known as: lats, climbing muscle, swimmer muscle

The broadest muscle of the back. It sweeps from the lower spine, thoracolumbar fascia and iliac crest to the floor of the intertubercular groove, and it extends, adducts and medially rotates the humerus.

Overview

Latissimus dorsi ("widest of the back") has an extensive aponeurotic origin. It arises from the spinous processes of T7–T12, the thoracolumbar fascia (and through it the lumbar and sacral spines), the posterior third of the iliac crest and the lower 3–4 ribs, and often from the inferior angle of the scapula. Its fibres converge and twist around the lower border of teres major, forming the posterior axillary fold together with it. They insert by a flat tendon into the floor of the intertubercular sulcus of the humerus, between pectoralis major (lateral lip) and teres major (medial lip).

It is the prime mover for pulling the raised arm down and back: extension, adduction and medial rotation of the humerus. Examples are swimming strokes, chopping wood, rowing, and hauling the trunk upward in climbing or pull-ups. With the arms fixed, it lifts the pelvis (as when walking with crutches) and assists forced expiration and coughing. It is supplied by the thoracodorsal nerve (C6–C8) from the posterior cord, which runs with the thoracodorsal artery on its deep surface.

Location

Lower and lateral back, extending to the axilla.

Anatomy

Origin

Spinous processes of T7–T12, thoracolumbar fascia, posterior third of the iliac crest, inferior 3–4 ribs and (often) the inferior angle of the scapula.

Insertion

Floor of the intertubercular sulcus (bicipital groove) of the humerus.

Action

Extension, adduction and medial rotation of the humerus at the shoulder; elevates the trunk toward the arms when the arms are fixed.

Innervation

Thoracodorsal nerve (posterior cord of the brachial plexus).

Nerve roots

C6–C8

Arterial supply

Thoracodorsal artery (from the subscapular artery); dorsal perforating branches of the 9th–11th posterior intercostal, subcostal and lumbar arteries.

Relations

Forms the posterior axillary fold with teres major. Its upper border forms part of the triangle of auscultation, and its lateral border forms part of the inferior lumbar (Petit) triangle.

Clinical significance

Latissimus dorsi flap

Because of its long pedicle (thoracodorsal vessels) and large size, it is a workhorse flap for breast reconstruction after mastectomy and for covering large defects.

Thoracodorsal nerve injury

The nerve can be injured in axillary surgery. Arm extension and adduction become weak, for example when climbing or using crutches.

Lumbar (Petit) hernia

A rare hernia through the inferior lumbar triangle, bounded by latissimus dorsi, external oblique and the iliac crest.