Sacroiliac joint anatomy

Structural composition

There are 2 histologically different portions in each side of the SI joint.

Synovial portion (anteroinferior)

• Axial spondyloarthopathy usually involve synovial portion first especially at inferior portion at iliac side (possibly due to thicker hyaline cartilage on iliac side)

Ligamentous portion (posterosuperior)

• More often affected by mechanical/degenerative change (e.g., osteoarthritis)