Erector spinae muscle

Structure and parts of the muscle

Muscle origin: posterior part of the iliac crest, sacrum, and spinous processes of the lumbar vertebrae.

Topographically, the muscle is divided into three parts:

• Iliocostalis muscle (m. iliocostalis) — includes the lumbar (lumborum), thoracic (thoracis), and cervical (cervicis) parts. Function: extends the spine and bends it laterally. Innervated by the dorsal branches of spinal nerves (rr. dorsales nn. spinalium, C8–L1).
• Longissimus muscle (m. longissimus) — consists of the thoracic, cervical, and capital (capitis) parts. Attaches to the transverse processes of the vertebrae and the mastoid process. Function: extends the spine and head, rotates them to its side.
• Spinalis muscle (m. spinalis) — also has thoracic, cervical, and capital parts. Function: extends the spine.

Topography and fascial sheath

The muscle lies in the groove between the spinous and transverse processes of the vertebrae. Topographically, it belongs to the medial division of the second muscle layer.

M. erector spinae is enclosed in a dense aponeurotic sheath formed by two layers of the thoracolumbar fascia (fascia thoracolumbalis):

• Superficial (posterior) layer — attaches medially to the spinous processes, sacrum, and iliac crest, and laterally to the angles of the ribs. Reinforced by the tendons of the latissimus dorsi (m. latissimus dorsi) and trapezius (m. trapezius) muscles.
• Deep (anterior) layer — forms the anterior wall of the sheath, attaching to the transverse processes of the lumbar vertebrae and the 12th rib.

At the lateral margin of m. erector spinae, the superficial and deep layers fuse, forming a fibrous sheath for the muscle. From their fusion site anteriorly, the aponeurosis of the transversus abdominis muscle (m. transversus abdominis) originates.

Furthermore, the lateral margin of the muscle serves as the inner (medial) boundary of the lumbar quadrangle (Lesgaft–Greenfelt rhombus), a weak spot of the posterior abdominal wall through which abscesses from the retroperitoneal tissue can spread to the posterior abdominal wall.

Clinical significance

The outer margin of m. erector spinae serves as a landmark in the lumbar region.

• Paranephric block: the needle insertion point is at the apex of the angle formed by the 12th rib and the lateral margin of m. erector spinae. The needle is inserted perpendicular to the body surface (the patient is positioned on the healthy side with a bolster). The block is used for renal and biliary colic, pancreatitis, cholecystitis, peritonitis, paralytic ileus, and shock in severe lower extremity trauma.
• Lumbotomy (Fedorov incision): a surgical approach to the retroperitoneal organs. The incision begins at the apex of the angle between the 12th rib and m. erector spinae (7–8 cm away from the spinous processes) and extends obliquely downward toward the umbilicus, reaching the iliac crest.

Class and exam questions

What else to study on this topic

• Thoracolumbar fascia (fascia thoracolumbalis)
• Lumbar quadrangle (Lesgaft–Greenfelt rhombus)
• Topography of the retroperitoneal space
• Paranephric Block

Other topics in the "Anatomical Structures" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.