Trusted medical expertise in seconds.

Access 1,000+ clinical and preclinical articles. Find answers fast with the high-powered search feature and clinical tools.

Try free for 5 days
Evidence-based content, created and peer-reviewed by physicians. Read the disclaimer.

Ankylosing spondylitis

Last updated: May 4, 2020

Summarytoggle arrow icon

Ankylosing spondylitis (spondyloarthritis), a type of seronegative spondyloarthropathy, is a chronic inflammatory disease of the axial skeleton that leads to partial or even complete fusion and rigidity of the spine. Males are disproportionately affected and upwards of 90% of patients are positive for the HLA-B27 genotype, which predisposes to the disease. The most characteristic early finding is pain and stiffness in the neck and lower back, caused by inflammation of the vertebral column and the sacroiliac joints. The pain typically improves with activity and is especially prominent at night. Other articular findings include tenderness to percussion and displacement of the sacroiliac joints (Mennell's sign), as well as limited spine mobility, which can progress to restrictive pulmonary disease. The most common extra-articular manifestation is acute, unilateral anterior uveitis. Diagnosis is primarily based on symptoms and x-ray of the sacroiliac joints, with HLA-B27 testing and MRI reserved for inconclusive cases. There is no curative treatment, but regular physiotherapy can slow progression of the disease. Additionally, NSAIDs and/or tumor necrosis factor-α inhibitors may improve symptoms. In severe cases, surgery may be considered to improve quality of life.

  • Sex: > (3:1)
  • Age: 15–40 years
  • Lifetime prevalence in the US: ∼0.5%


Epidemiological data refers to the US, unless otherwise specified.

  • Genetic predisposition: 90–95% of patients are HLA-B27 positive. [1]

Articular symptoms

  • Most common presenting symptoms: back and neck pain
    • Gradual onset of dull pain that progresses slowly
    • Morning stiffness that improves with activity
    • Pain is independent of positioning; , also appears at night
    • Tenderness over the sacroiliac joints
  • Limited mobility of the spine (especially reduced forward lumbar flexion)
  • Inflammatory enthesitis (e.g., of the Achilles tendon, iliac crests, tibial tuberosities): painful on palpation
  • Dactylitis
  • Arthritis outside the spine (hip, shoulder, knee joint)

Extra-articular manifestations


Diagnostic approach

  1. Physical examination, patient history, and pelvic x-ray: If results are conclusive, no additional testing is required!
  2. If inconclusive → HLA-B27 testing
  3. If still inconclusive → pelvic MRI

Clinical tests

  • Chest expansion measurement: to monitor disease severity
    • Method: measure chest circumference in full expiration and inspiration
      • Pathological difference: < 2 cm
      • Physiological difference: > 5 cm
  • Spine mobility tests
    • Schober test : Mark two points, S1 and another point 10 cm above → patient touches toes (without bending the knees) → distance between the two points increases by ≥ 4 cm → physiological test result; a smaller increase in distance between these two points is pathological
  • Examination of the hip [3]

The degree of decrease in chest expansion is an important determinant of disease severity.

Laboratory findings



  • Helps confirm a diagnosis and evaluate the severity of disease
  • Changes are generally more evident in later disease.
  • The changes usually occur symmetrically.
  • Pelvis (best initial test): to examine the sacroiliac joints
    • Signs of sacroiliitis, including ankylosis (fusion of the articular surfaces)
  • Spine
  • Thorax: ankylosis of costosternal and costovertebral joints

Mild courses may only exhibit inflammatory changes in the sacroiliac joints on x-ray after a number of years.





Radiographic features

  • Horizontal growth

Syndesmophytes grow vertically, as opposed to osteophytes, which grow horizontally!


The differential diagnoses listed here are not exhaustive.

Physical therapy is the most important treatment modality!References:[1][13]


We list the most important complications. The selection is not exhaustive.

  1. Brent LH. Ankylosing Spondylitis and Undifferentiated Spondyloarthropathy. Ankylosing Spondylitis and Undifferentiated Spondyloarthropathy. New York, NY: WebMD. Updated: January 20, 2016. Accessed: April 11, 2017.
  2. Yu DT, van Tubergen A. Clinical manifestations of ankylosing spondylitis in adults. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. updated: September 28, 2015. Accessed: April 11, 2017.
  3. Stone JH. A Clinician's Pearls & Myths in Rheumatology. Springer ; 2009
  4. Ankylosing spondylitis. Updated: April 12, 2017. Accessed: April 12, 2017.
  5. Blum U, Buitrago-tellez C, Mundinger A, et al. Magnetic resonance imaging (MRI) for detection of active sacroiliitis: a prospective study comparing conventional radiography, scintigraphy, and contrast enhanced MRI. J Rheumatol. 1996; 23 (12): p.2107-2115.
  6. Yu DT, van Tubergen A. Diagnosis and differential diagnosis of ankylosing spondylitis and non-radiographic axial spondyloarthritis in adults. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. updated: October 19, 2016. Accessed: April 12, 2017.
  7. Van den berg R, De hooge M, Rudwaleit M, et al. ASAS modification of the Berlin algorithm for diagnosing axial spondyloarthritis: results from the SPondyloArthritis Caught Early (SPACE)-cohort and from the Assessment of SpondyloArthritis international Society (ASAS)-cohort. Ann Rheum Dis. 2013; 72 (10): p.1646-1653. doi: 10.1136/annrheumdis-2012-201884 . | Open in Read by QxMD
  8. Mata S, Fortin PR, Fitzcharles MA, et al. A controlled study of diffuse idiopathic skeletal hyperostosis: Clinical features and functional status. Medicine. 1997; 76 (2): p.104-117.
  9. Hutcheson CJ, Howe JW. The Low Back and Pelvis: Clinical Applications. Aspen Publications ; 1996
  10. Syndesmophyte. Updated: April 11, 2017. Accessed: April 11, 2017.
  11. Nascimento FA, Gatto LA, Lages RO, Neto HM, Demartini Z, Koppe GL. Diffuse idiopathic skeletal hyperostosis: A review. Surg Neurol Int. 2014; 5 (Suppl 3): p.S122-125. doi: 10.4103/2152-7806.130675 . | Open in Read by QxMD
  12. Maxwell LJ, Zochling J, Boonen A, et al. TNF-alpha inhibitors for ankylosing spondylitis. Cochrane Database Syst Rev. 2015 . doi: 10.1002/14651858.CD005468.pub2 . | Open in Read by QxMD
  13. Yu DT. Assessment and treatment of ankylosing spondylitis in adults. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. updated: April 21, 2016. Accessed: April 11, 2017.
  14. Ward MM, Deodhar A, Gensler LS, et al. 2019 Update of the American College of Rheumatology/Spondylitis Association of America/Spondyloarthritis Research and Treatment Network Recommendations for the Treatment of Ankylosing Spondylitis and Nonradiographic Axial Spondyloarthritis. Arthritis Rheumatol. 2019; 71 (10): p.1599-1613. doi: 10.1002/art.41042 . | Open in Read by QxMD
  15. Taurog JD, Chhabra A, Colbert RA. Ankylosing Spondylitis and Axial Spondyloarthritis. N Engl J Med. 2016; 374 (26): p.2563-2574. doi: 10.1056/nejmra1406182 . | Open in Read by QxMD
  16. Bernard SA et al. ACR Appropriateness Criteria ® Chronic Back Pain Suspected Sacroiliitis-Spondyloarthropathy. J Am Coll Radiol. 2017; 14 (5): p.S62-S70. doi: 10.1016/j.jacr.2017.01.048 . | Open in Read by QxMD
  17. Lukasiewicz AM et al. Spinal Fracture in Patients With Ankylosing Spondylitis. Spine. 2016; 41 (3): p.191-196. doi: 10.1097/brs.0000000000001190 . | Open in Read by QxMD
  18. Kim K-T et al. Results of Corrective Osteotomy and Treatment Strategy for Ankylosing Spondylitis with Kyphotic Deformity. Clin Orthop Surg. 2015; 7 (3): p.330. doi: 10.4055/cios.2015.7.3.330 . | Open in Read by QxMD
  19. Canella C, Schau B, Ribeiro E, Sbaffi B, Marchiori E. MRI in Seronegative Spondyloarthritis: Imaging Features and Differential Diagnosis in the Spine and Sacroiliac Joints. Am J Roentgenol. 2013; 200 (1): p.149-157. doi: 10.2214/ajr.12.8858 . | Open in Read by QxMD
  20. Bakland G, Nossent HC. Epidemiology of Spondyloarthritis: A Review. Curr Rheumatol Rep. 2013; 15 (9). doi: 10.1007/s11926-013-0351-1 . | Open in Read by QxMD