Which of the following describes the insertion of iliocostalis lumborum?

• A. Angles of the lower ribs (7-12) and the transverse processes of the lumbar vertebrae.
• B. Spinous processes of lumbar vertebrae
• C. Iliac crest
• D. Transverse processes of thoracic vertebrae

Answer: (A)

The part of the muscle being tested is where iliocostalis lumborum attaches. This muscle, the lateral member of the erector spinae, runs from the pelvis and lumbar region up toward the rib cage and lumbar spine. Its insertion points are the angles of the lower ribs (7 through 12) and the transverse processes of the lumbar vertebrae. From these attachments, contracting on one side helps extend and laterally flex the trunk and assists in lowering the ribs, which aligns with its role in maintaining posture and stabilizing the lower back.

Other described attachments don’t fit this muscle as well: the spinous processes are midline insertions seen with other muscles in the group, the iliac crest is typically an origin site rather than an insertion for this muscle, and the transverse processes of the thoracic vertebrae are associated with other portions of the erector spinae.