What is the appropriate evaluation and management for pain over the sacrum?

Evaluation and Management of Sacral Pain

Initial Diagnostic Approach

Begin with plain radiographs of the sacrum and pelvis as the initial imaging study, though recognize that sensitivity is only 15-35% for early fractures, particularly in osteoporotic patients. 1 If radiographs are negative or equivocal and clinical suspicion remains high, proceed directly to MRI without contrast, which is the gold standard with a 9/9 appropriateness rating. 1

Key Clinical Features to Assess

Determine whether pain has inflammatory versus mechanical characteristics, as this fundamentally changes the diagnostic pathway. 1, 2

Inflammatory pain characteristics include: 2

• Insidious onset with improvement during exercise but not rest
• Pain occurring at night with morning stiffness >30 minutes
• Alternating buttock pain
• Age typically <40-45 years (though late presentations occur)

Mechanical pain characteristics suggest: 1, 3

• Trauma history (including low-energy falls in elderly)
• Localized tenderness over sacrum
• Pain worse with weight-bearing
• Older age (≥55 years) with osteoporosis risk factors

Associated features to document: 2

• History of uveitis, psoriasis, inflammatory bowel disease
• Peripheral joint involvement
• Prior lumbar fusion (adjacent segment disease risk)
• Pregnancy or recent delivery

Imaging Algorithm

When Radiographs Are Negative or Equivocal

MRI of the pelvis/sacrum without contrast is the definitive next step (appropriateness rating 8-9/9). 1 MRI demonstrates bone marrow edema within hours of injury, far earlier than other modalities, and has sensitivity approaching bone scintigraphy with superior anatomic detail. 1

For suspected inflammatory sacroiliitis with negative radiographs: 1, 2

• MRI sacroiliac joints without contrast (rating 8/9)
• MRI protocol must include T1-weighted and fat-suppressed fluid-sensitive sequences
• Look for bone marrow edema extending ≥1 cm deep to articular surface
• Sensitivity 79%, specificity 89% for inflammatory changes

CT without contrast is the alternative when MRI is contraindicated (rating 7/9), 1 particularly useful for identifying subtle erosions and cortical disruptions after several weeks of symptoms, though it remains inferior to MRI for early detection. 1

What NOT to Order Initially

Bone scintigraphy, ultrasound, and FDG-PET/CT are rated 1-4/9 (usually not appropriate) for initial evaluation. 1 Bone scintigraphy lacks specificity, with synovitis, arthritis, degenerative disease, and tumor appearing similar. 1 The "Honda sign" has only 63% sensitivity for sacral insufficiency fractures despite 94% positive predictive value. 1

Laboratory Evaluation

Order HLA-B27 and inflammatory markers (CRP, ESR) alongside initial imaging if inflammatory features are present. 2 These markers may be normal in axial spondyloarthropathy but help with risk stratification. 2

For patients ≥55 years with suspected insufficiency fracture, order DEXA scan to evaluate underlying osteoporosis requiring treatment. 3

Management Based on Etiology

Sacral Insufficiency Fracture (Elderly/Osteoporotic)

Institute complete non-weight-bearing on the injured side to prevent displacement. 3

• Provide adequate analgesia (acetaminophen, NSAIDs as first-line) 4
• Consider short-term muscle relaxants for severe spasm 4
• Hospital admission for observation if high-risk mechanism or severe pain 3
• Initiate osteoporosis treatment based on DEXA results 3

Sacroiliac Joint Pain (Mechanical)

Begin with NSAIDs, activity modification within pain limits (not bed rest), and physical therapy. 4, 5, 6

• Sacroiliac compression test and Patrick's test help confirm diagnosis 5
• Consider sacroiliac joint belt for stabilization 6
• If conservative treatment fails after 4-6 weeks, fluoroscopically-guided diagnostic/therapeutic injection with local anesthetic and corticosteroid (≥75% relief confirms diagnosis) 1, 6, 7
• Radiofrequency denervation if injection provides temporary relief 7
• Minimally invasive SI joint fusion reserved for refractory cases 7

Inflammatory Sacroiliitis (Suspected Spondyloarthropathy)

Refer to rheumatology for definitive diagnosis and initiation of disease-modifying therapy. 2

• NSAIDs provide symptomatic relief 4
• Biologic therapy typically required for inflammatory control 2
• Physical therapy to maintain mobility 4

Critical Pitfalls to Avoid

Do not rely on plain radiographs alone—they miss the majority of early sacral fractures, particularly in osteoporotic bone due to soft-tissue overlap and sacral curvature. 1, 2

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 overlook associated injuries in trauma patients—sacral fractures frequently present with referred buttock or thigh pain, and seat-belt mechanisms carry significant risk for occult bowel injury. 1, 3

Do not order imaging in the first 4-6 weeks for nonspecific low back pain without red flags (cancer history, unexplained weight loss, progressive neurologic deficits, fever). 4

In elderly patients or those on corticosteroids, bone scintigraphy may remain negative for several days post-injury, creating false reassurance. 1