Ankylosing Spondylitis

KEY FACTS

Imaging

• Location

  • Discs and synovial joints of spine

  • Joints of axial skeleton, less commonly peripheral joints

  • Tendon and ligament attachments (entheses)

• Sacroiliac joints (SIJs): Bilaterally symmetric erosive arthropathy → fusion

• Facet, uncovertebral joints: Erosions → fusion

• Squaring of vertebral bodies → corner erosions → “shiny corner” (corner sclerosis) → ankylosis

• Erosions, new bone formation at tendon and ligament attachments

• Trauma

  • Often hyperextension injury, involving all 3 columns of spine

  • Fracture may occur through fused regions

  • MR should be considered to exclude occult fracture, as these may be subtle secondary to osteopenia

Top Differential Diagnoses

• Diffuse idiopathic skeletal hyperostosis

• Psoriatic arthritis and reactive arthropathy

• Rheumatoid arthritis

• Osteitis condensans ilii

Pathology

• Associated findings

  • Pulmonary interstitial fibrosis, decreased chest excursion, uveitis, aortitis, aortic valve insufficiency

• 90% of patients HLA-B27 positive

Clinical Issues

• Complications: Kyphotic deformity, fractures of fused spine

• Pain centered over SIJs, back stiffness

Diagnostic Checklist

• Normal SIJs preclude imaging diagnosis of ankylosing spondylitis

TERMINOLOGY

IMAGING