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Ankylosing Spondylitis

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Other Names

  • AS
  • Axial Spondyloarthritis
  • Bechterew disease
  • Marie Strümpell disease
  • Juvenile Rheumatoid Arthritis


  • This page refers to ankylosing spondylitis (AS), an inflammatory spondyloarthropathy primarily affecting the spine


  • First described in the 1800s with radiographic descriptions occuring in the 1930s[1]


  • Male > Female, although this discrepancy may not be as significant as initially thought
    • Men trend towards more severe disease[2]
  • Most commonly occurs in individuals in their 30s
  • The estimated prevalence of axial spondyloarthritis in the United States is 0.9 to 1.4% of the adult population[3]


  • General
    • Seronegative spondyloarthropathy
    • Results in fusion (ankylosis) of the spine and sacroiliac joints
  • HLA-B27
    • Class 1 surface antigen found in less than 89% of AS patients
    • Function is to bind antigenic peptides for presentation to cytotoxic T cells
    • Strongly associated with spondyloarthropathies
    • Exact mechanism in AS is not known at this time
  • Other proposed etiologies
    • ERAP1 has gained interest from researchers
  • Primary site of inflammation is the Sacroiliac Joint
    • Proinflammatory cytokines lead to bony destruction and new bone growth
    • Syndesmophytes develop inside ligaments which can be seen radiographically
    • In its most severe presentation, fusion occurs
  • Disease progression
    • As disease progresses, total fusion of the axial skeleton can occur
    • Leads to loss of function and mobility, chronic pain
    • Can also restrict lung function and lead to respiratory failure
  • Extra-axial manifestations
    • Can affect other joints
    • Can affect eyes, heart and lungs
    • Patients may develop anxiety or depression due to their disease
    • Can have a significant impact on quality of life, ability to work

Associated Conditions

Risk Factors

  • Genetics
    • (HLA)-B27 has the greatest association at 90% (need citation)
    • ERAP-1
    • IL23R
    • TNF-associated genes

Differential Diagnosis

Clinical Features

  • History
    • Patients most commonly report back pain
    • Inflammatory back pain is paradoxical in that it improves with activity and worsens with rest
    • Pain is often dull, insidious, nocturnal and interferes with sleep
    • Morning stiffness may last >30 minutes
    • Important to consider extra-axial symptoms
    • Patients may report joint pain elsewhere
    • May also have ophthalmic, cardiac and pulmnary symptoms
    • May endorse fatigue, weight loss
  • Physical Exam: Physical Exam Back
    • Limited chest wall expansion during inhalation
    • Limited spinal flexion
    • May have kyphotic spine deformity
  • Special Tests
    • Schobers Test: measures the degree of lumbar flexion
    • FABER Test: Figure 4 position with compression can strain SI joint



  • Standard Radiographs Lumbar Spine
    • Classically, shows the so-called "bamboo spine" or paravertebral ossification (scalloping) running parallel to the spine
    • Often normal early in disease process, can take up to a decade from disease onset for radiographic changes to occur
  • Other findings include
    • Erosions of the vertebral bodies
    • Vertebral body squaring
    • "Dagger spine" from interspious ligament ossification
  • Standardard Radiographs Sacroiliac Joint
    • First to develop, symmetric and bilateral
    • Can show characteristic changes of sacroilitis
    • Includes blurred joint margins, erosions, loss of joint space
    • In advanced cases, SI joint can be fused


  • Provides additional information beyond what plain radiographs can demonstrate
  • Active lesions: bone marrow edema, capsulitis, synovitis, enthesitis
  • Chronic lesions: sclerosis, erosions, fat deposition, bone bridges or ankylosis


  • C-reactive protein (CRP): Elevated in 50% of cases
    • Not specific or sensitive
  • Erythrocyte sedimentation rate (ESR)
    • Not specific or sensitive
  • Normocytic anemia
  • HLA-B27
    • Present in 7% - 9% of caucasians[4]
    • About 5% of people with HLA-B27 develop AS
  • Interleukin-6: Not useful
  • Calprotectin: may help, used to monitor inflammatory bowel disease
  • RF Factor: By definition, this is negative

Diagnostic Injection

  • Injection into SI joint can be diagnostic and therapeutic
  • Sensitivity is high (need citation)

Diagnostic Criteria

  • Bilateral sacroiliitis
  • +/- Uveitis
  • HLA-B27 positive


Modified New York Criteria

  • Grading system for sacroiliitis
    • Grade 0: SI joint normal
    • Grade 1: Blurring of joint margins
    • Grade 2: Solitary erosions, juxta-articular sclerosis in small sacral or iliac areas
    • Grade 3: Manifested juxta-articular sclerosis, numerous erosions, widening of joint space, partial ankyloses
    • Grade 4: Complete ankylosis



  • Long term outcomes are highly variable and hard to prognosticate
  • With disease progression, pain and stiffness increase in severity and frequency
  • Some people have mild symptoms, others very severe


  • Management can be challenging
    • Lack of evidence for most treatments
    • Patients are generally working young males
  • Patient education
    • Advise the patient on lifestyle measures
  • Physical Therapy
    • Maintain mobility, posture
  • Exercise Therapy
  • Hydrotherapy
  • Smoking Cessation
    • Tobacco use associated with increased disease activity[5]
  • Medications
  • Corticosteroid Injection
    • Can target sacroiliac joint, peripheral joints
    • CT-guided SI joint injections have been shown to provide effective pain relief for up to 6 months
  • Disease Modifying Anti-Rheumatic Drugs (DMARDs)
    • Should be managed in consultation with a rheumatologist
    • Sulfasalazine may help with peripheral arthritis, early morning sickness (need citation)
    • TNF inhibitors (adalimumab, certolizumab pegol, etanercept, golimumab, and infliximab)
    • IL-17 inhibitors (secukinumab) have been shown to be efffective
    • IL-23 inhibitors
    • Janus kinase (JAK) inhibitor
    • Not routinely used due to lack of evidence: methotrexate, leflunomide
  • Associated conditions
    • Provider should be screening for anxiety, depression


  • Generally not considered a surgical condition
  • In the setting of spine trauma
    • Management will be guided by injury pattern
  • In the setting of severe deformity
    • Consider osteotomy, fusion
  • Large joint arthritis may require arthroplasty

Rehab and Return to Play


  • Needs to be updated

Return to Play

  • There are no evidence based guidelines for return to play for SA
  • Cardiac screening
    • All athletes should have a screening EKG
    • Further workup should be guided by history and physical exam
  • Spinal considerations
    • Athletes should be cautioned on risk of spinal fractures which can occur due to seemingly trivial trauma
    • Particular true of the cervical spine, strong consideration for CT prior to clearance
  • Consider asking athletes to wear a medical alert bracelet
    • Important to know about rigid spine during airway management
  • Must avoid sports with high risk of spinal injury including: football, ice hockey, wrestling, diving, skiing, snowboarding, rugby, cheerleading or baseball[6]


  • Fractures
    • Fused brittle spine is susceptible to fracture
    • One study estimated 4.6% of patients with AS develop fractures at average of 24 years after onset, with frequency increasing with disease duration[7]
  • Andersson Lesioninflammatory spondylodiskitis leading to disc pseudoarthrosis
  • Rare neurological manifestations
  • Orthopedic

See Also


  1. Bywaters E. Historical introduction. In: Moll J, ed. Ankylosing spondylitis. Edinburgh: Churchill-Livingstone, 1980:1-15
  2. Lee W, Reveille JD, Davis JC, Learch TJ, Ward MM, Weisman MH. Are there gender differences in severity of ankylosing spondylitis? Results from the PSOAS cohort. (2007) Annals of the rheumatic diseases. 66 (5): 633-8.
  3. Reveille JD, Witter JP, Weisman MH. Prevalence of axial spondylarthritis in the United States: estimates from a cross-sectional survey. Arthritis Care Res (Hoboken) 2012;64:905-910
  4. Wang YF, Teng MM, Chang CY et-al. Imaging manifestations of spinal fractures in ankylosing spondylitis. AJNR Am J Neuroradiol. 2005;26 (8): 2067-76.
  5. Jakobsen, Ane Krag, et al. "Is nephrolithiasis an unrecognized extra-articular manifestation in ankylosing spondylitis? A prospective population-based Swedish national cohort study with matched general population comparator subjects." PloS one 9.11 (2014): e113602.
  6. Feldtkaller E, Vosse D, Geusens P, van der Linden S. Prevalence and Annual Incidence of Vertebral Fractures in patients with Ankylosing Spondylitis. Rheum Int 2006;26:234–239
  7. Thumbikant P, et al. Spinal Cord Injury in Patients with Ankylosing Spondylitis. Spine 2007;32(26): 2989–2995.
Created by:
John Kiel on 3 July 2019 16:48:36
Last edited:
6 October 2022 00:02:10