Which muscle attaches to the L5 transverse process, iliac crest, and iliolumbar ligament?

• A. Psoas Major
• B. Iliopsoas
• C. Latissimus Dorsi
• D. Quadratus Lumborum

Answer: (D)

Recognizing where a muscle anchors to bones helps identify it. Quadratus lumborum starts from the iliac crest and the iliolumbar ligament and travels upward to insert on the transverse processes of the lower lumbar vertebrae (often including L5), as well as interfacing with the 12th rib. That combination—iliac crest, iliolumbar ligament, and L5 transverse process—fits this muscle precisely, and its role includes stabilizing the lumbar spine and assisting with lateral flexion or rib stabilization. The other muscles have different attachment patterns (psoas major and iliacus link to the lumbar vertebrae or iliac fossa rather than the iliolumbar ligament plus the iliac crest, and latissimus dorsi attaches elsewhere), so they don’t match all three landmarks together.