What is the most common cause of sacral pain following a fall?

Most Common Cause of Sacral Pain After a Fall

The most common cause of sacral pain following a fall is a sacral insufficiency fracture (SIF), particularly in elderly patients with underlying osteoporosis or bone fragility.

Understanding the Clinical Context

Sacral insufficiency fractures occur when normal biomechanical forces—such as those from a fall—act on weakened bone 1, 2. These are stress fractures that predominantly affect:

• Postmenopausal women over 55 years of age (most common demographic) 2
• Patients with osteoporosis or prior fragility fractures
• Those with history of radiation therapy, long-term corticosteroid use, or metabolic bone disorders 2

Why These Fractures Are Frequently Missed

SIFs are notoriously underdiagnosed because symptoms are nonspecific 1. Patients typically present with:

• Low back, sacral, or buttock pain after a ground-level fall
• Insidious onset of symptoms
• Pain that may be mistaken for lumbar spine disorders or even metastatic disease 1

The clinical presentation often mimics other conditions, leading to significant delays in diagnosis and treatment 2.

Diagnostic Approach

Imaging Hierarchy

1. Plain radiographs have LOW sensitivity and are frequently insufficient 3, 4

2. CT scanning can identify:

   • Sclerosis of cancellous bone in the sacral ala
   • Discrete fracture lines (when present)
   • Displacement patterns 2
   • Useful for surgical planning but less sensitive for early detection 1

3. MRI is the most sensitive modality for early detection 1, 5:

   • Shows hypointense signal on T1-weighted sequences
   • Hyperintensity on T2-weighted or STIR sequences 2
   • Gold standard for diagnosis when clinical suspicion is high

High-Risk Populations Requiring Heightened Suspicion

Maintain a high index of suspicion in patients with 2:

• Osteoporosis or vitamin D deficiency
• Prior multilevel spinal fusion
• Rheumatoid arthritis
• History of pelvic radiation
• Pregnancy (rare but possible)
• Malignancy

Distinguishing from High-Energy Pelvic Trauma

While the guidelines 6, 7 extensively discuss unstable pelvic fractures from high-energy trauma (motor vehicle accidents, significant falls), the context of a typical fall in an elderly patient points toward fragility fractures rather than traumatic pelvic ring disruptions. The Young-Burgess classification system (APC, LC, VS patterns) applies to high-energy trauma, not the low-energy mechanism typical of SIFs 7.

Common Pitfall to Avoid

Do not dismiss sacral pain after a fall as simple musculoskeletal strain in elderly patients or those with risk factors for bone fragility. The "silent epidemic" nature of these fractures 3 means they remain unrecognized in many cases, leading to prolonged pain, functional impairment, and delayed mobilization.

Clinical Bottom Line

In the context of sacral pain following a fall, particularly in elderly or osteoporotic patients, sacral insufficiency fracture is the primary diagnosis to rule out 1, 2, 3. Order MRI if clinical suspicion is high and plain films are negative, as early diagnosis enables appropriate treatment—whether conservative management or surgical stabilization—and prevents the complications associated with delayed recognition.