What could be the causes of burning and stabbing sensations in one sacroiliac (SI) joint in a 55-year-old adult?

Causes of Unilateral Sacroiliac Joint Burning and Stabbing Pain in a 55-Year-Old

The burning and stabbing sensations in one sacroiliac joint at age 55 most likely represent either sacroiliac joint dysfunction (mechanical pain) or inflammatory sacroiliitis from axial spondyloarthropathy, with the unilateral presentation favoring either mechanical dysfunction or psoriatic/reactive spondyloarthritis subtypes over ankylosing spondylitis. 1

Primary Differential Diagnoses

Inflammatory Sacroiliitis (Axial Spondyloarthropathy)

• Unilateral sacroiliitis occurs particularly in psoriatic spondyloarthritis and reactive arthritis, whereas ankylosing spondylitis typically presents bilaterally 1
• The age of 55 is slightly older than typical for axial spondyloarthropathy, which characteristically presents before age 40-45 years, though late presentations do occur 1, 2
• Look specifically for inflammatory pain characteristics: insidious onset, improvement with exercise but not rest, pain occurring at night (especially second half), morning stiffness >30 minutes, and alternating buttock pain 1, 2
• Associated features to assess: uveitis, psoriasis, inflammatory bowel disease, peripheral joint involvement (30-50% of cases), and HLA-B27 positivity (74-89% of cases) 1, 2

Sacroiliac Joint Dysfunction (Mechanical)

• Mechanical SI joint dysfunction accounts for 15-30% of mechanical low back pain and commonly presents with localized pain around the posterior superior iliac spine 3, 4, 5
• Pain typically does not extend above L5 and lacks inflammatory characteristics 5
• This diagnosis is more likely if pain worsens with rest, does not improve with exercise, and lacks morning stiffness 2
• Risk factors include pregnancy/postpartum status, physically demanding work, high-impact sports, or repetitive shear-stress injuries 6, 7

Other Considerations

• Osteitis condensans ilii: presents with bilateral iliac sclerosis (though can be asymmetric), typically in postpartum women, without erosions or bone marrow edema on MRI 6
• Osteoarthritis of the SI joint can cause localized pain, particularly in this age group 7
• Hyperparathyroidism can cause sacroiliitis-like changes 7

Diagnostic Algorithm

Step 1: Clinical Assessment

• Determine if pain has inflammatory characteristics (onset before age 45, duration ≥3 months, improvement with exercise, night pain, morning stiffness) versus mechanical features 1, 2
• Perform at least three physical provocation tests; positive responses to ≥3 tests suggest SI joint as pain source 3, 4
• Assess for extra-articular manifestations: uveitis, psoriasis, inflammatory bowel disease, peripheral arthritis 2

Step 2: Initial Imaging

• Order plain radiographs of the sacroiliac joints first (rated 9/9 appropriateness by ACR) 1, 8
• Include complementary spine radiographs (at minimum cervical and lumbar) 1, 8
• Critical limitation: radiographs have low sensitivity (19-72%) for early disease and may miss >50% of structural changes; findings lag symptoms by 3-7 years 1, 8

Step 3: If Radiographs Negative or Equivocal with High Clinical Suspicion

• Proceed to MRI of sacroiliac joints without contrast (sensitivity 79%, specificity 89%) 8
• MRI protocol must include T1-weighted sequences and fat-suppressed fluid-sensitive sequences (STIR or T2 fat-sat) 8
• Look for bone marrow edema extending ≥1 cm deep to articular surface (more specific for axSpA; superficial edema occurs in 30% of healthy controls) 8, 6
• Assess for erosions, fat metaplasia, and sclerosis 8, 6
• Contrast is generally not necessary and does not significantly increase diagnostic accuracy 8

Step 4: Laboratory Testing

• HLA-B27 testing should be ordered alongside initial radiographs if inflammatory features are present 2
• Check inflammatory markers (C-reactive protein), though these may be normal in axSpA 2
• Do not rule out spondyloarthritis based solely on negative HLA-B27 2

Step 5: Confirmatory Testing if Diagnosis Remains Unclear

• Diagnostic SI joint block with local anesthetic can confirm the joint as pain source, though false-positives and false-negatives occur 4, 5, 9

Critical Pitfalls to Avoid

• Do not rely on imaging alone: radiographs have fair to moderate interobserver agreement and miss early disease 1, 8
• Do not dismiss inflammatory sacroiliitis based on age >45 years alone, as diagnosis is frequently delayed 4.9-8 years from symptom onset 2
• Do not order CT, bone scan, ultrasound, or PET/CT as initial imaging—these are not appropriate for initial evaluation 1, 8
• Do not assume bilateral involvement is required for inflammatory sacroiliitis; unilateral presentation occurs in psoriatic and reactive arthritis 1
• Failure to inquire about pregnancy history or physically demanding work can lead to misdiagnosis 6