Insertion of quadratus lumborum?

• A. Inferior border of the 12th rib and transverse processes of L1-L4
• B. Spinous processes of L1-L4
• C. Superior border of the 12th rib
• D. Iliac crest

Answer: (A)

Quadratus lumborum is a muscle of the posterior abdominal wall that reaches upward to attach to the lower rib and the front of the lumbar spine. Its insertion on the inferior border of the twelfth rib and the transverse processes of the first through fourth lumbar vertebrae lets it directly influence the rib cage and the lower back. By pulling the twelfth rib downward, it helps with forced expiration and with stabilizing the trunk when the spine is flexed or laterally bent. The placement on the transverse processes of L1–L4 also makes it a key player in lateral flexion of the lumbar region.

That’s why the inferior border of the twelfth rib together with the transverse processes of L1–L4 is the proper insertion. The spinous processes of L1–L4 are not attachment sites for this muscle, so that option doesn’t fit. The superior border of the twelfth rib would imply a different action, not the downward pull this muscle performs. The iliac crest is a typical origin area, not the insertion point.