Ankylosing Spondylitis

Description:

• 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

Signs/Symptoms:

• 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

Imaging:

• 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

Treatment:

• 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