Topographical division of the back
To systematize anatomical structures, the posterior surface of the trunk is divided into five key areas. Some of these are located strictly along the midline, while others are symmetrically duplicated on the sides.
- Vertebral region (regio vertebralis). This is an unpaired zone located in the center of the back. Its contours correspond entirely to the shape of the vertebral column.
- Scapular region (regio scapularis). A paired region symmetrically located on the right and left sides. Its boundaries are defined by the contours of the scapula itself. The most important topographical markers here are the angles of the scapula: the superior angle projects at the level of the 2nd rib, while the inferior angle reaches the 7th rib. Visually, the bone contours and muscular ridges (specifically, the erector spinae muscles) are clearly defined in this zone.
- Infrascapular region (regio infrascapularis). Also a paired zone. It occupies the area directly below the scapula and forms the posteroinferior part of the thoracic cage.
- Lumbar region (regio lumbalis). Represented by the right and left halves. Superiorly, it is clearly bounded by the line of the 12th rib, and inferiorly it extends to the iliac crest. A characteristic relief feature here is the lumbar groove, which runs along the lateral edge of the erector spinae muscle.
- Sacral region (regio sacralis). The lowest unpaired region of the back, whose contours are formed by the relief of the sacrum.
External inspection and palpation
The inspection of the posterior trunk relies on a number of reliable visual and palpation markers that allow a physician or student to orient themselves quickly.
- Strictly along the midline of the back, the spinous processes of the vertebrae are easily palpable.
- Lateral to the midline, a prominent muscular relief protrudes—these are the contours of the erector spinae muscle.
- In the upper segment of the trunk, the main visual landmarks are the overall contours of the scapulae and, specifically, the spine of the scapula.
- In the lower section of the back, the iliac crest serves as the basic reference point.
Principles of back muscle organization
The entire muscle mass of the posterior trunk (mm. dorsi) is functionally and topographically divided into two major categories, separated by a fascia:
- Superficial muscles. They lie superficial to the fascial layer. Their biomechanical function is to move and fix the upper limb.
- Deep muscles. These are the so-called "true" back muscles. They lie deep beneath the fascia and are responsible for posture (statics) and all movements of the vertebral column itself.
Briefly: answers to topical questions
Which specific muscles are included in the superficial back muscle group?
The superficial back muscle group includes muscles that lie above the fascia and move the upper limb. These include:
- Trapezius muscle (m. trapezius) — provides scapular movements and neck extension.
- Latissimus dorsi muscle (m. latissimus dorsi) — is responsible for arm adduction and extension.
- Rhomboid muscles (mm. rhomboidei major et minor) — perform adduction of the scapula.
- Levator scapulae muscle — elevates the scapula.
- Serratus posterior muscles — participate in the act of breathing (inspiration and expiration).
Which muscles make up the deep (autochthonous) back muscle group?
The deep (autochthonous) group consists of the true back muscles, which provide movements of the spine. This group includes:
- Erector spinae muscle (m. erector spinae) — provides extension and stabilization.
- Semispinalis muscle — participates in extension, rotation, and stabilization.
- Multifidus muscles (mm. multifidi) — deep muscles innervated by the medial branch.
- Rotator muscles (mm. rotatores) — the deepest back muscles (long and short), which rotate the vertebrae and participate in proprioception.
What is the name of the fascia that separates the superficial and deep back muscles?
The fascia separating these muscle groups is called the thoracolumbar fascia (fascia thoracolumbalis), or thoracolumbar fascia (fascia thoracolumbaris). Superficial muscles lie above this fascia, whereas deep (true) back muscles are located beneath it. The thoracolumbar fascia is a dense connective tissue fibrous plate that envelops the deep back muscles. It is divided into superficial (posterior) and deep (anterior) layers, and in the lumbar region it forms a fibrous sheath for the deep muscles.
To easily recall the projection of the scapula, remember the numbers 2 and 7: Superior angle — 2nd rib, Inferior angle — 7th rib.
Class and exam questions
What bony landmarks define the boundaries of the scapular region?
Key landmarks are the angles of the scapula: the superior angle is at the level of the 2nd rib, and the inferior angle projects at the level of the 7th rib.
How is the lumbar region bounded superiorly and inferiorly?
The upper boundary of the lumbar region runs along the 12th rib line, and the lower boundary is limited by the iliac crest.
What is the fundamental difference between deep and superficial back muscles?
Deep (true) muscles lie beneath the fascia and move the vertebral column. Superficial muscles are located above the fascia and provide movements of the upper limb.
What else to study on this topic
- Anatomy and functions of superficial back muscles
- Deep (true) back muscles: topography and biomechanics
- Structure and layers of back fascia
- Clinical significance of the lumbar groove
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