Anatomy of the Superficial Back Muscles and Spaces

The Latissimus Dorsi

The latissimus dorsi is a large, powerful muscle that originates from the lower thoracic spinous processes, the thoracolumbar fascia, and the posterior iliac crest. It inserts into the intertubercular groove of the humerus. Its primary actions include shoulder extension, medial rotation, and adduction.

Scapular Stabilizers: Levator Scapulae and Rhomboids

Deep to the trapezius lie muscles that are vital for fine-tuning scapular movement:

• Levator Scapulae: Originating from the transverse processes of C1-C4, it elevates the scapula and assists in downward rotation.
• Rhomboid Muscles: The rhomboid minor and major attach to the vertebral border of the scapula. They are responsible for scapular retraction and downward rotation.

Neurovascular Pathways

Understanding the course of nerves is vital for diagnosing motor deficits. In the superficial back, nerves often travel deep to muscle layers to reach their targets.

The Dorsal Scapular Nerve

Originating from the C5 nerve root of the brachial plexus, the dorsal scapular nerve approaches the levator scapulae muscle anteriorly. It then disappears deep to the muscle, traveling along the vertebral border of the scapula, where it provides innervation to the rhomboid muscles.

The Thoracodorsal Nerve

The thoracodorsal nerve provides the motor supply to the latissimus dorsi. It is composed of fibers from the C6, C7, and C8 nerve roots. This nerve travels alongside the thoracodorsal artery (a branch of the axillary artery) to reach the medial border of the latissimus dorsi.

Clinical Note: When assessing a patient with weakness in shoulder adduction or medial rotation, clinicians should consider the integrity of the thoracodorsal nerve and the C6-C8 nerve roots.

Anatomical Spaces

The arrangement of these muscles creates specific "windows" or spaces that are clinically significant.

The Triangle of Auscultation

The triangle of auscultation is a relatively thin area of the back where there is less muscle coverage, making it an ideal location for listening to lung sounds via auscultation. Its boundaries are:

• Medial: Trapezius muscle.
• Inferior: Latissimus dorsi muscle.
• Superior: Rhomboid major muscle.

The Lumbar Triangle

Located in the lower back, the lumbar triangle is a space defined by the following borders:

• Lateral: External abdominal oblique muscle.
• Medial: Latissimus dorsi muscle.
• Inferior: The iliac crest.

Summary Table of Superficial Back Muscles