The AP radiograph demonstrates bilateral symmetric sclerosis with early fusion of the sacroiliac joints and loss of cortical definition.  The lateral radiograph demonstrates the “shiny corner” sign characterized by reactive sclerosis along a few anterior corners of lumbar vertebral bodies.

Bilateral symmetric SI joint disease DDx: Ankylosing spondylitis, Inflammatory Bowel Disease, CPPD, Osteitis Condensans Ilii

Ankylosing spondylitis is a seronegative spondyloarthropathy with a male predominance which is of unknown etiology resulting in eventual fusion of the SI joints with gradual ascending ankylosis of the spine due to syndesmophyte formation of the annulus fibrosis.  Early radiographic findings are usually seen to involve the SI joints with progression from erosions, sclerosis, to eventual ankylosis.  Thoracolumbar involvement may show vertebral body “squaring” with anterior vertebral body corner reactive osteitis described as the “shiny corner” sign.  Multilevel syndesmophytes may show ankylosis as a “bamboo spine”.  Late findings associated with fusion of the supraspinous and interspinous ligaments has also been described as the “dagger sign”.

Manaster BJ, Disler DG, May DA. Musculoskeletal Imaging: The Requisites, 2^nd ed. St. Louis: Mosby, 2002.

Brower AC, Flemming DJ. Arthritis in Black and White, 2^nd ed. Saunders, 1997.