Learning Radiology xray montage

Ankylosing Spondylitis


General Considerations

  • Chronic inflammatory disease of unknown etiology primarily affecting spine
  • Most common spondyloarthropathy
    • Age-young adults
      • 15-35 years
    • Mostly male
      • M:F = 4:1
    • Mostly Caucasian
      • Caucasians to Blacks = 3:1

Clinical findings

  • Insidious onset of low back pain and stiffness
  • Poor chest expansion
  • Stiffness
  • Exaggerated dorsal kyphosis
  • HLA-B 27 positive in >90%


  • Axial skeleton and large, usually central, appendicular joints
  • Sacroiliac joint involvement
    • Hallmark of disease
    • Only synovial portion of SI joint is involved
      • Inferior and anterior portion of joint
        • Other enthesopathies like DISH can cause bridging of upper, non-synovial part of joint
    • Usually site of initial involvement
    • Bilaterally symmetric
    • Widened with erosions at first
    • Then ankylosis
  • Spine
    • Usually begins at either thoracolumbar or lumbosacral junctions
      • Extends symmetrically without skip areas
        • Reiter’s and psoriasis characteristically are asymmetric and have skip areas
    • Marginal syndesmophyte formation = thin vertical dense spicules bridging the vertebral bodies
      • Ossification of outer fibers of annulus fibrosus
        • Not anterior longitudinal ligament
    • Trolley-track sign on AP view = central line of ossification (supraspinous and interspinous ligaments) with two lateral lines of ossification (apophyseal joints)
    • Bamboo spine on AP view = undulating contour due to syndesmophytes
    • Prone to fracture resulting in pseudarthrosis
    • Straightening / squaring of anterior vertebral margins
      • Osteitis of anterior corners
    • Reactive sclerosis of corners of vertebral bodies = shiny-corner sign
    • Symmetric erosions of laminar and spinous process at level of lumbar spine
    • Apophyseal  and costovertebral ankylosis
    • Periosteal whiskering
      • Sites of tendinous insertion
        • Ischial tuberosity
        • Iliac crest
        • Ischiopubic rami
        • Greater femoral trochanter
        • External occipital protuberance
        • Calcaneus
        • Patella
    • Dorsal arachnoid diverticula in lumbar spine with erosion of posterior elements
    • Atlantoaxial subluxation
  • Peripheral joint involvement
    • Hip is most frequently involved
    • Concentric joint narrowing
    • Few erosions
    • Protrusio acetabuli
  • Temporomandibular joint
    • Joint space narrowing
    • Erosions
    • Osteophytosis
  • Hand (30%)
    • Target area
      • MCP, PIP, DIP
    • Exuberant osseous proliferation
    • Osteoporosis
    • Joint space narrowing
    • Osseous erosions (deformities less striking than in rheumatoid arthritis)
  • Chest
    • Bilateral upper lobe pulmonary fibrosis (1%) with upward retraction of hila
    • Resembles tuberculosis
  • Cardiovascular
    • Aortitis (5%) of ascending aorta ± aortic valve insufficiency
      • Prognosis: 20% progress to significant disability
      • Occasionally death from cervical spine fracture / aortitis


  • Reiter syndrome (unilateral asymmetric SI joint involvement, paravertebral ossifications)
  • Psoriatic arthritis (unilateral asymmetric SI joint involvement, paravertebral ossifications)
    • Inflammatory bowel disease

Associated with:

  • Ulcerative colitis
  • Regional enteritis
    • Clinically the SI joint involvement is identical to
      • Inflammatory Bowel Disease (IBD)
  • Iritis in 25%
  • Aortic insufficiency and atrioventricular conduction defect 

 ankylosing spondylitis

Ankylosing Spondylitis. Note fusion of both SI joints and thin, symmetrical syndesmophytes bridging the intervertebral disc spaces.