The bones on both sides of the waist are called the iliac bones. If you are in the standing position, the protrusions felt on both sides of the waist are called the iliac crests; if you are in the prone position or the lateral position, the protrusions felt on both sides of the waist are called the posterior superior iliac spines; and if you are in the supine position, the protrusions felt on both sides of the waist are the anterior superior iliac spines. The iliac crest refers to the highest position of the upper edge of the wing of the ilium, and the iliac crests on both sides of the waist are connected and at the same level as the L4/L5 interspace of the lumbar vertebrae. Pain in the iliac crest area is mostly caused by trauma, lumbar muscle strain, sacroiliac arthritis, and synovial tuberculosis infection. The posterior superior iliac spine and anterior superior iliac spine are the posterior and anterior ends of the iliac crest, i.e., the posterior and anterior sides of the pelvis, respectively. Both serve as attachment points for lumbar spine muscles, ligaments and other soft tissues. Causes of pain include muscle injury, lumbar intervertebral disc disease, etc., and play a role in the diagnosis of the disease.