Which is the origin of the quadratus lumborum?

• A. Posterior iliac crest
• B. Inner surfaces of lower six ribs
• C. Medial sacral crest
• D. Pubic crest, pubic symphysis

Answer: (A)

The main idea is identifying where the quadratus lumborum starts. This deep muscle of the posterior abdominal wall originates from the posterior part of the iliac crest (often with the iliolumbar ligament) and then inserts onto the 12th rib and the transverse processes of L1–L4. So, the posterior iliac crest is its origin.

The other options point to attachments of different muscles or structures. The inner surfaces of the lower six ribs are typical attachments for muscles like transversus abdominis or internal oblique, not the quadratus lumborum. The medial sacral crest and pubic crest/symphysis belong to other parts of the spine or abdominal/pelvic musculature and are not origins for the quadratus lumborum.