Ankylosing Spondylitis: Description and Diagnosis

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Ankylosing Spondylitis (AS) is a chronic inflammatory disease characterized by pain and progressive stiffness. It is part of a group of rheumatic diseases termed seronegative spondyloarthropathies (vertebral joints) that share the human antigen HLA-B27. Ankylosing spondylitis is seronegative (serum negative) because a rheumatoid factor is not detected in the patient's blood (serum).

Ankylosing spondylitis is considered to be hereditary, although environmental factors have been suggested. Most people with the HLA-B27 antigen do not develop AS. It is known to affect white males about four times as often as females. Onset typically occurs between the ages of 15 and 45.

In the early stages of the disease, the sacroiliac joints (back of the pelvis) become inflamed and painful. As the disease progresses, ossification is triggered by the body's defense mechanism. Ossification causes new bone to grow between vertebrae eventually fusing them together increasing the risk for fracture. Further, ossification may affect spinal ligaments causing spinal canal stenosis (narrowing), which can result in neurologic deficit.

Ankylosing spondylitis picture illustrationAs the disease progresses, the patient may notice the discomfort moves up the spine. Photo Source:

Other symptoms may include:

  • Low back pain that may spread down into the buttocks and thighs. Pain varies in intensity, duration, and is episodic. Stiffness is usually worse in the morning and improves with exercise.
  • Limited motion in the lumbar spine.
  • As the disease progresses, the patient may notice the discomfort moves up the spine.
  • The thoracic region may be affected by pain, stiffness, and limited chest expansion.
  • Pain, tenderness, and stiffness in the shoulders, hips, knees, and heels.
  • Cauda Equina Syndrome (specific nerve compression) may develop causing bilateral lower extremity numbness, weakness, and incontinence.
  • Inflammation of the intervertebral disc or disc space (spondylodiscitis) is a common complication caused by the hardening/thickening of fibrous tissue (sclerosis) affecting vertebral end plates. The resultant abnormal vertebral motion almost always causes pain.
  • Spinal deformity: kyphosis (humpback), lordosis (swayback).


General health and family medical history is important because ankylosing spondylitis can be hereditary. Ankylosing spondylitis may or may not be associated with nonskeletal diseases such as uveitis (eye inflammation), prostatitis (prostate inflammation) and certain disorders affecting cardiac and pulmonary function. A blood workup will reveal the HLA-BA27 antigen. A physical examination often includes the following:

Schober Test: Limited motion in the lumbar spine is symptomatic of AS. The Schober test measures the degree of lumbar forward flexion as the patient bends over as though touching their toes. Progressive loss of spinal motion is correlated with x-ray findings.

Gaenslen Test: Sacroiliac pain is often found in the early stage of AS. Gaenslen's maneuver stresses the sacroiliac joints. Increased pain during this maneuver could be indicative of joint disease.

When ankylosing spondylitis affects the thoracic spine normal chest expansion may be compromised. The amount of chest expansion is measured from deep expiration to full inspiration. Measurements significantly less than one inch (normal chest expansion) could indicate AS.

General range of motion measures the degree to which a patient can perform movements of flexion, extension, lateral bending, and spinal rotation. Asymmetry may also be noted.

Neurologic Evaluation

A neurologic evaluation is mandatory for patients presenting with a spine disorder. The following symptoms are assessed: pain, numbness, paresthesias (e.g. tingling), extremity sensation, and motor function, muscle spasm, weakness, and bowel/bladder changes.

Radiographic Evidence

Plain radiographs (x-rays) are standard for AS. A CT Scan or MRI may be ordered to evaluate bone and soft tissues (eg, spinal canal) in greater detail. These tests reveal changes in the spine affected by AS.

Characteristic bilateral sacroiliac changes may appear as blurry erosions (wearing away) or hardening/thickening of fibrous tissue (sclerosis) on either side of the joint(s).

Loss of cartilage spacing in the facet joints, which fuse and become indistinguishable.

Natural spinal curvature lost and presentation of abnormal kyphosis (humpback) and/or lordosis (swayback).

Spinal fractures anywhere in the spinal column. A CT Scan or MRI may detect epidural bleeding common following spinal fracture. This bleeding may cause a semisolid swelling (hematoma) causing compression of neural elements. Fractures may lead to neurologic deficit and/or spinal deformity.

Lumbar vertebrae may appear abnormally square from erosion that has occurred where bone meets fibrous tissue during the inflammatory phase.

'Bamboo Spine' is typical of ankylosing spondylitis and results from ossification of the annulus fibrosus, the anterior longitudinal ligament, and bony bridges that form across the intervertebral spaces.

Commentary by Baron S. Lonner, MD

Doctor Shaffrey has presented an overview of problems manifested in the patient with ankylosing spondylitis. He has pointed out that the majority of patients do not require surgery for related spinal disorders. A number of points warrant further emphasis. First of all, these patients are prone to fracture of the rigid spinal column even with relatively trivial trauma such as a fall or a low-speed motor vehicle accident. This can result in severe instability, spinal deformity, and most importantly, deteriorating neurological function or paralysis. If an individual with AS has pain following a trauma,
further investigation with x-rays and possibly CT scan and/or MRI is warranted.

The problem of spinal malalignment, such as chin-on-chest deformity, has been discussed by Dr. Shaffrey. Once a deformity has been established, it is quite rigid or stiff and typically is not correctible. Before this occurs, exercise and stretching and even bracing may be considered to minimize these deformities which can be debilitating. The patient tends to be pitched forward and often has difficulty looking straight ahead as the head is often fixed in a downward position. If this occurs, osteotomies or cutting through the spinal column may be required to restore a more horizontal gaze and comfortable alignment.

Consultation with a spinal specialist early in the disease process may be warranted.

Updated on: 09/06/19
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Ankylosing Spondylitis: Treatment and Recovery
Baron S. Lonner, MD
Professor of Orthopaedic Surgery
Icahn School of Medicine
at Mount Sinai
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Ankylosing Spondylitis: Treatment and Recovery

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