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The sacroiliac joint (Latin: articulatio sacroiliaca) is a paired articulation in the pelvis, located between the sacrum and the wing of the ilium. It is also a transition site between the pelvis and the spine.
The sacroiliac joint is primarily classified as a synovial type joint, although its posterior region is more of a fibrous (syndesmosis) nature. The sacroiliac joint permits slight motion, and it is one of the most essential weight-bearing joints.
Articulating structures of sacroiliac joint
As written above, in the sacroiliac joint articulates two bones - ilium and sacrum. The structures of the bones that form the joint are as follows:
- Auricular surface of the sacrum
- Auricular surface of the ilium
Joint capsule and ligaments
The sacroiliac joint is surrounded by a fibrous joint capsule, and it is strengthened by two main ligaments - anterior and posterior sacroiliac ligaments. The posterior sacroiliac ligament is composed of two parts known as the short and long posterior sacroiliac ligaments.