The sacroiliac joint is a set of paired connections between the sacrum and the wing of the ilii. It is a transition site between the pelvis and the spine.

The articulating surfaces of the sacroiliac joint are:

Auricular surface of the sacrum
Auricular surface of the ilium

The joint is surrounded by a fibrous joint capsule.

The sacroiliac joint is one of the most important weight-bearing joints, stabilized and strengthened by several ligaments. The ligaments of the sacroiliac joint are located around the sacroiliac joint, and the main ones are:

Anterior sacroiliac ligament - begins at the anterolateral part of the pelvic surface of the sacrum (third segment), the ligament ends anterior to the auricular surface of the ilium; it is thin and is more like a thickening of the fibrous capsule in the anteroinferior portion of the joint;
Posterior sacroiliac ligament - located posterior and superior to the sacroiliac joint; it is much more pronounced and thicker than the anterior ligament. The posterior sacroiliac ligament is composed of two parts:
- Short posterior sacroiliac ligament - upper portion; extends between the first and second transverse tubercles of the sacrum to the tuberosity of the ilium,
- Long posterior sacroiliac ligament - lower portion; stretches between the third and fourth transverse tubercle of the sacrum to the posterior superior iliac spine.

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Sacroiliac joint and its ligaments