How should I evaluate and initially manage a 55-year-old woman with localized sacral pain after a direct seat‑belt clip impact to the sacrum that worsens on sitting?

Evaluation and Initial Management of Sacral Trauma in a 55-Year-Old Woman

This patient requires immediate imaging with MRI of the pelvis without contrast to rule out sacral insufficiency fracture, as plain radiographs are inadequate in postmenopausal women with this mechanism of injury. 1

Initial Clinical Assessment

High-Risk Mechanism Recognition

• A direct seatbelt clip impact to the sacrum is a high-risk mechanism that mandates CT imaging and heightened suspicion for occult injury, even when initial examination appears benign 2
• In patients aged ≥55 years, trauma protocol activation thresholds should be lowered due to increased mortality risk and potential for under-triage 2
• The mechanism of direct sacral impact in a postmenopausal woman creates dual concern: traumatic sacral fracture versus insufficiency fracture in osteoporotic bone 1, 3

Focused Physical Examination

• Palpate directly over the sacrum for point tenderness, which is the most consistent finding in sacral fractures 3
• Assess for pain radiation to the buttocks, hips, or thighs—a characteristic pattern in sacral injuries 3, 4
• Perform a careful neurological examination including:
  • Lower extremity motor and sensory function (L5-S4 dermatomes) 4, 5
  • Rectal tone and perianal sensation (saddle anesthesia) 4, 5
  • Bladder function assessment, as neurogenic bladder can occur with central sacral fractures 4, 5

Imaging Strategy

Primary Imaging: MRI

MRI of the pelvis and hip without contrast is the gold standard and should be obtained urgently (rated 9/9 by ACR) 1:

• MRI detects bone marrow edema within hours of injury, long before plain films show changes 1
• Sensitivity and specificity approach that of bone scintigraphy but with superior anatomic detail 1
• Plain radiographs have only 15-35% sensitivity for early sacral fractures and are particularly unreliable in osteoporotic bone due to soft tissue overlap 1
• The sacrum must be specifically included in the imaging protocol, as sacral fractures frequently present with referred pain 1

Alternative if MRI Unavailable

If MRI cannot be obtained immediately:

• Contrast-enhanced CT of the abdomen/pelvis is the next best option for evaluating trauma patients with high-risk mechanisms 2
• CT has moderate sensitivity if symptoms have been present for several weeks but remains inferior to MRI 1
• Follow-up plain films at 10-14 days increase sensitivity to 30-70% but still miss many fractures 1

Risk Stratification by Fracture Zone

The Denis classification predicts neurological risk 4, 5:

• Zone I (ala sacralis): 24-33% neurological deficit risk, usually L5 radiculopathy 4, 5
• Zone II (sacral foramina): 29-43% deficit risk, typically unilateral sciatica without bladder dysfunction 4, 5
• Zone III (central canal): 57-64% deficit risk, frequently bilateral deficits with saddle anesthesia and sphincter dysfunction 4, 5

Neurological deficits correlate more strongly with overall pelvic instability than with specific fracture patterns 6

Initial Management Protocol

Immediate Actions

• Institute complete non-weight-bearing status on the affected side to prevent fracture displacement 1
• Provide adequate analgesia to facilitate early mobilization and prevent complications from prolonged bed rest 1
• Avoid sitting or any activity that loads the sacrum directly 3

Laboratory Assessment

• Obtain baseline inflammatory markers (CRP, procalcitonin) if there is concern for associated intra-abdominal injury from the seatbelt mechanism 2
• These markers are highly sensitive but not specific; use them to exclude rather than diagnose bowel injury 2

Admission Criteria

This patient requires hospital admission for observation 2:

• High-risk mechanism (seatbelt impact) with non-specific initial findings mandates serial clinical examination 2
• Serial exams should occur every 8 hours to detect evolving peritoneal signs from potential occult bowel injury 2
• Repeat imaging at 6 hours if clinical signs evolve or initial CT shows equivocal findings 2

Osteoporosis Evaluation

• Order dual-energy X-ray absorptiometry (DXA) scan to assess bone density, as insufficiency fractures indicate underlying osteoporosis requiring treatment 1
• Postmenopausal women with sacral fractures from minor trauma have a high prevalence of osteopenia requiring medical management 3

Critical Pitfalls to Avoid

• Do not rely on plain radiographs alone—they miss the majority of early sacral fractures, especially in osteoporotic bone 1, 3
• Do not dismiss pain as "just a contusion" in postmenopausal women with direct sacral trauma; insufficiency fractures are common and easily missed 3
• Do not forget to assess bladder function in all sacral fractures, particularly if imaging shows Zone III involvement; obtain cystometrography if neurogenic bladder is suspected 4
• Do not overlook associated intra-abdominal injuries—the seatbelt mechanism carries significant risk for bowel injury that may not be immediately apparent 2