What are the radiographic findings on X-ray of the pelvis (Pelvic X-ray) indicative of Ankylosing Spondylitis (AS)?

From the Guidelines

X-ray findings indicative of ankylosing spondylitis in the pelvis typically include sacroiliitis, which appears as blurring, erosion, sclerosis, and eventual fusion of the sacroiliac joints, as noted in the 2021 update of the ACR Appropriateness Criteria for inflammatory back pain 1. These changes are often bilateral and symmetric, starting at the lower portion of the joint and progressing upward.

• The radiographic evaluation of the sacroiliac joints is useful in the initial evaluation of suspected axSpA, but its limitations must be acknowledged, including low sensitivity for detection of early disease and wide variability in reported sensitivity and specificity 1.
• Other characteristic findings may include squaring of the vertebral bodies, syndesmophytes (bony outgrowths) bridging the vertebrae, and calcification of spinal ligaments, giving a "bamboo spine" appearance on lateral views.
• The hip joints may show concentric joint space narrowing and eventual ankylosis in advanced cases.
• Early detection is crucial as these radiographic changes represent established structural damage that is irreversible, and MRI might be needed to detect active inflammation before structural damage occurs, as radiographs are unable to demonstrate active inflammation 1.
• These radiographic findings, combined with clinical symptoms like inflammatory back pain, morning stiffness, and limited spinal mobility, help establish the diagnosis of ankylosing spondylitis.

From the Research

X-ray Pelvis Findings Indicative of Ankylosing Spondylitis

• X-rays are the initial imaging modality of choice for diagnosing ankylosing spondylitis (AS) 2
• Sacroiliitis is a key finding on x-ray, but if it is not present, an HLA-B27 test should be obtained if suspicion of AS remains high 2
• The Assessment of SpondyloArthritis International Society (ASAS) criteria are helpful in the diagnosis of AS 2

Treatment and Management

• Continuous use of nonsteroidal anti-inflammatory drugs (NSAIDs) is the first-line therapy for AS 2
• Tumor necrosis factor-alpha inhibitors are used as a second-line therapy, followed by slow-acting antirheumatic drugs (eg, methotrexate) 2
• Physical therapy is also an important part of management, and patients should be advised to quit smoking and maintain a healthy weight 2

Complications and Associated Conditions

• Patients with AS are at increased risk of complications, such as spinal fracture 2
• Other conditions associated with AS include anterior uveitis, inflammatory bowel disease, and osteoporosis 2
• NSAIDs are effective in controlling symptoms of AS, but may have a significant side effect profile 3, 4, 5, 6