Structure and Parts
Origin: posterior part of the iliac crest, sacrum, and spinous processes of the lumbar vertebrae.
Topographically, the muscle is divided into three columns:
- Iliocostalis muscle (m. iliocostalis) — includes the lumbar (lumborum), thoracic (thoracis), and cervical (cervicis) parts. Function: extends the vertebral column and laterally flexes it. Innervated by the dorsal rami of spinal nerves (rr. dorsales nn. spinalium, C8–L1).
- Longissimus muscle (m. longissimus) — consists of the thoracic, cervical, and cranial (capitis) parts. Inserts into the transverse processes of the vertebrae and the mastoid process. Function: extends the vertebral column and head, and rotates them to the same side.
- Spinalis muscle (m. spinalis) — also has thoracic, cervical, and cranial parts. Function: extends the vertebral column.
Topography and Fascial Sheath
The muscle lies in the groove between the spinous and transverse processes of the vertebrae, belonging topographically to the deep layer of back muscles.
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. It is 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 to form a fibrous compartment for the muscle. The aponeurosis of the transversus abdominis muscle (m. transversus abdominis) originates anteriorly from this fusion site.
Additionally, the lateral margin of the muscle forms the inner (medial) border of the lumbar quadrangle (Lesgaft–Grünfeld rhombus) — a weak point of the posterior abdominal wall through which retroperitoneal abscesses can spread to the posterior abdominal wall.
Clinical Significance
The lateral margin of m. erector spinae serves as a crucial anatomical landmark in the lumbar region.
- Paranephric block: The needle insertion point is located 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 (with the patient positioned on the healthy side with a bolster). The block is used for renal and biliary colic, pancreatitis, cholecystitis, peritonitis, dynamic ileus, and shock resulting from severe lower extremity trauma.
- Lumbotomy (Fedorov incision): A surgical approach to retroperitoneal organs. The incision begins at the apex of the angle between the 12th rib and m. erector spinae (7–8 cm lateral to the spinous processes) and extends obliquely downward toward the umbilicus, reaching the iliac crest.