What is posterior superior iliac spines?

The posterior superior iliac spines (PSIS) are bony protrusions located on the back of the sacrum and the upper part of the ilium (hip bone). They are easily identifiable as two small bumps above the buttocks and below the lower back. The PSIS are connected to the sacroiliac joint and serve as attachment points for various muscles and ligaments involved in the movement of the hip joint and the pelvis. In physical therapy and chiropractic practice, the PSIS are often used as landmarks for identifying asymmetry or dysfunction in the pelvis and for assessing the alignment and mobility of the spine and the lower extremities.