• A chronic seronegative inflammatory disease
  • affects the axial skeleton, especially the sacroiliac joints, hip joints, and spine
  • extraskeletal involvement of aorta, lung, uvea
  • Disease onset is during young adulthood, typically affecting adolescent boys
  • HLA-B27surface antigen is found in 88-96% of patients
  • Limited chest wall expansion best screening criteria
  • Elevated ESR (sedimentation rate) is present in 80% of patients
  • Serum creatine phosphokinase (CPK) is a good indicator of disease severity
  • Investigators postulate that an endogenic component (HLA-B27) and an exogenic component (Klebsiella or Chlamydia) are responsible for triggering the disease.

Left: Normal posture and lumbar lordosis. Right: Loss of lumbar lordosis and posture in ankylosing spondylitis


  • Insidious onset
  • Early symptoms of buttocks, heels, lower back pain
  • Morning stiffness with improvement of symptoms throughout day
  • Earliest changes involve sacroiliac (SI) joints
  • Disease then extends up the spine
  • Results in loss of spinal motion and lumbar lordosis
  • Synovitis leads to progressive fibrosis and ankylosis of joints
  • Enthesitis occurs where annulus fibrosis inserts on vertebral body with eventual calcification creating the characteristic “bamboo spine” (right)
  • Uveitis and chest tightness affect 30% of patients
  • Dilatation of aorta occurs in 5% of patients
  • Associated with renal amyloidosis and pulmonary fibrosis


  • Symmetric SI joint widening and subchondral erosions are first radiographic signs
  • Loss of anterior concavity of vertebral body, or squaring of the vertebra
  • Vertabral body marginal syndesmophyte formation (bone spurs connecting vertebral bodies – see red arrows) forming appearance of “bamboo spine”)
  • Disease and radiographic findings begin in SI joints and progress cephalad


  • Disease slowly progresses over several decades
  • Initial treatment involves exercises, and non-steroidal anti-inflammatory medications
  • 10% of patients require surgical intervention
  • Hip disease should be addressed surgically prior to spine surgery
  • Fixed bony flexion that limits ambulation and horizontal gaze after hip correction warrant surgical treatment
  • Loss of lumbar lordosis can be treated with multilevel posterior closing wedge osteotomies – the Smith-Peterson procedure – or other techniques
  • Spine is then fused in to corrected and more functional position
  • Contraindications to surgery include poor general health and significant scarring of major vessels that may be injured when spine is extended