Latissimus dorsi

The latissimus dorsi is a large, flat muscle of the back that plays a crucial role in upper limb movement and trunk stabilization. It is significant in both functional anatomy and clinical practice due to its involvement in motion, injury, and surgical applications. Understanding its structure and function is essential for medical and rehabilitation professionals.

Anatomy

Origin

• Spinous processes of the lower thoracic vertebrae (T7-T12)
• Thoracolumbar fascia
• Iliac crest
• Inferior angle of the scapula
• Lower three to four ribs

Insertion

• Floor of the intertubercular sulcus of the humerus

Innervation

• Thoracodorsal nerve, arising from the posterior cord of the brachial plexus (C6-C8)

Blood Supply

• Thoracodorsal artery, a branch of the subscapular artery
• Segmental perforators from posterior intercostal and lumbar arteries

Function

• Extension, adduction, and medial rotation of the humerus
• Assists in upper limb movements such as climbing, swimming, and rowing
• Acts as an accessory muscle in respiration during forced expiration
• Contributes to stabilization of the trunk and posture during upper limb activities

Biomechanics

• Interaction with Shoulder Girdle Muscles: The latissimus dorsi works synergistically with the teres major, pectoralis major, and rotator cuff muscles to facilitate coordinated shoulder movements.
• Contribution to Posture and Trunk Stabilization: By anchoring the humerus and connecting to the thoracolumbar fascia, it helps maintain upright posture and stabilizes the spine during upper limb activities.
• Role in Complex Upper Limb Movements: Essential in activities requiring powerful extension, adduction, and internal rotation of the arm, such as rowing, swimming, and climbing.

Clinical Significance

Injuries and Disorders

• Muscle strain or tear from overuse or sudden heavy lifting
• Tendinopathy, particularly at the humeral insertion
• Latissimus dorsi rupture, though rare, can occur in athletes performing forceful upper limb movements

Surgical Applications

• Use as a flap in reconstructive surgery, especially for breast reconstruction and coverage of soft tissue defects
• Tendon transfer procedures to restore function in cases of rotator cuff or shoulder girdle deficiencies

Rehabilitation

• Physical therapy exercises to strengthen the muscle and improve flexibility
• Post-surgical rehabilitation protocols to restore range of motion and prevent adhesions or contractures

Imaging

• MRI: Provides detailed visualization of the latissimus dorsi muscle, its tendinous insertion, and surrounding soft tissues, useful for detecting tears, strains, or tumors.
• Ultrasound: Allows real-time assessment of muscle integrity, dynamic movement, and tendon pathology, often used in sports medicine and rehabilitation.
• CT Scan: Useful in anatomical assessment prior to surgical procedures or flap reconstruction, especially when bony landmarks need evaluation.

Variants and Anatomical Considerations

• Accessory slips or additional fascicles may arise from the scapula, ribs, or vertebrae, potentially affecting muscle function and surgical planning.
• Variations in tendon insertion can influence strength and risk of injury, particularly in athletes or manual laborers.
• Awareness of these anatomical variations is critical during surgical flap harvest to avoid inadvertent injury to neurovascular structures.

References

1. Standring S. Gray’s Anatomy: The Anatomical Basis of Clinical Practice. 42nd edition. London: Elsevier; 2020.
2. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. 9th edition. Philadelphia: Wolters Kluwer; 2020.
3. Netter FH. Atlas of Human Anatomy. 7th edition. Philadelphia: Elsevier; 2018.
4. Beebe AC, et al. Surgical anatomy and clinical applications of the latissimus dorsi muscle flap. Ann Plast Surg. 2015;75(5):536-542.
5. Huang JJ, et al. Latissimus dorsi muscle: anatomical variations and implications for reconstructive surgery. Clin Anat. 2014;27(8):1190-1197.
6. Schaverien MV, Saint-Cyr M. Flaps of the back. Semin Plast Surg. 2008;22(2):86-97.
7. Karakasis D, et al. Latissimus dorsi injuries in athletes: review of anatomy, function, and treatment. J Sports Med Phys Fitness. 2016;56(9):1120-1128.
8. Eladoumikdachi F, et al. Anatomy and clinical applications of the latissimus dorsi muscle. Semin Plast Surg. 2009;23(3):165-172.