Latissimus Dorsi
The latissimus dorsi is the widest muscle in the human body, covering the lower back. It is a powerful extensor, adductor, and medial rotator of the arm, and is crucial for swimming, climbing, and pulling movements.
Origin, Insertion, Action, Innervation
OOrigin
Spinous processes of T7-L5 vertebrae, thoracolumbar fascia, iliac crest, inferior angle of scapula, and lower 3-4 ribs.
IInsertion
Floor of intertubercular (bicipital) groove of humerus
AAction
- • Extension of the arm
- • Adduction of the arm
- • Medial rotation of the arm
- • Depression of the shoulder (pulls shoulder down)
- • Assists with forced expiration
NInnervation
Thoracodorsal nerve (C6, C7, C8)
Blood Supply
Thoracodorsal artery
Clinical Relevance
The latissimus dorsi is used in muscle flap surgery for breast reconstruction and other procedures. Weakness indicates thoracodorsal nerve damage. The muscle is tested by having the patient cough with hands on hips - it should contract.
Palpation
Palpate on the posterior axillary fold. Have the patient adduct the arm against resistance or cough with hands on hips to feel the muscle contract.
Study Tips
- ✓Widest muscle in the body - extensive origin, narrow insertion
- ✓Thoracodorsal nerve (C6, C7, C8) - 'thoraco' for thorax, 'dorsal' for back
- ✓Same insertion as pec major and teres major (bicipital groove)
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Common questions about the latissimus dorsi
The latissimus dorsi extends, adducts, and medially rotates the arm. It is powerful in pulling movements like climbing and swimming. It also depresses the shoulder and assists with forced expiration.
The latissimus dorsi is innervated by the thoracodorsal nerve, which carries fibers from the C6, C7, and C8 nerve roots. This nerve arises from the posterior cord of the brachial plexus.
Latissimus dorsi means 'widest muscle of the back' in Latin. Athletes and fitness enthusiasts commonly call it the 'lats' for short. It is indeed the widest muscle in the human body.
The latissimus dorsi can be used as a pedicled or free flap for breast reconstruction, chest wall reconstruction, and other reconstructive procedures. Its large size and reliable blood supply make it valuable for surgeons.