Corpus: Quadratus lumborum muscle
1. Definition
The quadratus lumborum muscle is a skeletal muscle that is part of the deep abdominal musculature.
2. Course
2.1. Origin
The quadratus lumborum muscle originates from the iliac crest and the iliolumbar ligament.
2.2. Attachment
The muscle has a ventral portion that inserts at the caudal edge of the 12th rib. The dorsal portion attaches to the costal process of the lumbar vertebrae L1-L4 and also to the 12th rib.
2.3. Topography
Ventrally, the quadratus lumborum muscle is adjacent to the colon, kidneys, psoas major and minor muscles, and the diaphragm.
3. Innervation
The quadratus lumborum muscle is innervated by the anterior branches of the spinal nerves from spinal cord segments Th12 to L3.
4. Function
The quadratus lumborum muscle serves multiple functions:
- When contracted unilaterally, it pulls the 12th rib downward, contributing to the lateral flexion (sideways tilt) of the trunk.
- Bilateral contraction of the muscle results in extension of the lumbar spine.
- When the thorax is fixed, the muscle can elevate the lateral edge of the pelvis.
- It stabilizes the free-floating ribs, particularly the 12th rib, during forced expiration.