Latissimus Dorsi
The muscle that lies on the back over the lateral flank is the latissimus dorsi.
Anatomical Description
The latissimus dorsi is the largest, flat, dorso-lateral muscle on the trunk, positioned posterior to the arm 1. Based on detailed anatomical studies:
Origin: The muscle originates from:
- Spinous processes of thoracic vertebrae T7-T12
- Thoracolumbar fascia
- Iliac crest
- Inferior 3-4 ribs
- Inferior angle of scapula 1
Insertion: Floor of the intertubercular groove of the humerus 1
Location: The latissimus dorsi is partly covered by the trapezius on its median dorsal region and extends over the lateral flank area of the back 1
Functional Characteristics
The latissimus dorsi's primary function is movement of the upper limb, including:
- Extension, adduction, and internal rotation of the shoulder joint
- Transverse extension (horizontal abduction)
- Flexion from an extended position 1
Important caveat: Despite common assertions, biomechanical analysis demonstrates that the latissimus dorsi's contribution to lumbar spine extension is trivial, with a maximum extensor moment of only 6.3 N·m 2. The muscle is designed primarily to move the upper limb or raise the entire trunk during brachiation, not to provide significant mechanical support to the lumbosacral region 2.
Clinical Relevance
The latissimus dorsi is frequently utilized in reconstructive surgery as a pedicle flap for breast reconstruction, rotator cuff repair, and coverage of defects in the face, scalp, and cranium 1. The muscle has a consistent neurovascular pedicle with a mean length of 11 cm, making it reliable for surgical transfer 3.