Causes of Sacroiliac Joint Pain
Sacroiliac joint pain is commonly caused by inflammatory conditions like axial spondyloarthritis, mechanical factors including sprains and degenerative changes, and less frequently by infections or malignancies. 1, 2
Inflammatory Causes
Axial Spondyloarthritis (axSpA)
- Accounts for approximately 5% of chronic back pain cases 1
- Includes several subtypes:
- Ankylosing spondylitis (classic radiographic-axSpA)
- Psoriatic spondyloarthritis
- Reactive arthritis
- Inflammatory bowel disease-related spondyloarthropathies
- Non-radiographic axSpA (early disease without radiographic changes)
- Characteristic findings:
- Bone marrow edema on MRI (active inflammation)
- Erosions, sclerosis, and eventual ankylosis
- Often bilateral and symmetric sacroiliitis 1
Clinical Presentation of Inflammatory SIJ Pain
- Typically presents before age 45 1
- Pain is chronic (>3 months) and insidious in onset
- Morning stiffness that improves with activity but not rest
- Pain that awakens in the second half of the night
- Alternating buttock pain 1
Mechanical/Degenerative Causes
Sacroiliac Joint Sprain
- Occurs despite the joint's inherent strength
- Diagnosis requires more than just tenderness on palpation
- Often overlooked as a cause of low back pain 3
Degenerative Changes
- Accounts for approximately 15% of low back pain cases 4, 5
- More common following:
- Trauma
- Pregnancy
- In certain athletes 5
- Patients rarely report pain above L5 level
- Most localize pain around the posterior superior iliac spine (PSIS) 4
Posterior Ligament Pain
- Can manifest in buttocks, groin, and lower extremities
- May be confused with lumbar disc herniation or spinal stenosis
- Key diagnostic features include:
- Pain at the PSIS detected by one-finger test
- Groin pain
- Pain while sitting
- Tenderness at PSIS and sacrotuberous ligament 6
Less Common Causes
Infectious Sacroiliitis
- Can cause changes resembling inflammatory sacroiliitis
- Requires prompt diagnosis and treatment 2
Malignancy
- Rare but important cause to consider
- May present with night pain, unexplained weight loss, or constitutional symptoms 2
Other Conditions
- Osteitis condensans ilii (OCI)
- Can mimic sacroiliitis radiologically
- Typically affects anterior middle region of the joint 2
- Diffuse idiopathic skeletal hyperostosis (DISH)
- Characterized by ligament ossification at joint borders 2
- Repetitive stress injuries in athletes 2
Diagnostic Approach
Imaging Considerations
Radiography - First-line imaging but has low sensitivity for early disease
MRI - Most sensitive for early inflammatory changes
- Can detect active inflammation before structural damage occurs
- STIR or T2-weighted fat-saturated sequences show bone marrow edema
- Can differentiate between inflammatory and mechanical causes 1
CT - Helpful when MRI contraindicated
- Better than radiographs for detecting subtle erosions
- Good for assessing complex SIJ anatomy
- Cannot reliably detect active inflammation 1
Distribution of Lesions Helps Determine Cause
- Inflammatory lesions can affect any part of the joint
- Mechanical lesions often occur in the anterior middle region
- Ligament ossifications found at joint borders 2
Treatment Considerations
Treatment should be directed at the underlying cause:
For inflammatory causes:
- NSAIDs
- Disease-modifying antirheumatic drugs (DMARDs)
- Biologic therapies like TNF-α antagonists for axSpA 1
For mechanical/degenerative causes:
For recalcitrant cases:
Common Pitfalls
- Misdiagnosing SIJ pain as lumbar disc disease or hip pathology
- Relying solely on radiographs which may miss early disease
- Assuming all SIJ pain is mechanical when inflammatory causes require different treatment
- Overlooking SIJ pain in patients with diffuse or referred pain patterns
- Failing to consider rare but serious causes like infection or malignancy