What is the initial management and differential diagnosis for a patient with low back pain after a fall?

Differential Diagnosis for Low Back Pain Post-Fall

After a fall, the differential diagnosis for low back pain must prioritize vertebral compression fracture, cauda equina syndrome, and other serious pathology before considering nonspecific mechanical causes, with imaging decisions guided by specific red flags rather than routine protocols. 1

Immediate Red Flag Assessment

Your first priority is ruling out conditions requiring urgent intervention:

• Cauda equina syndrome (0.04% prevalence): Check for urinary retention, fecal incontinence, saddle anesthesia, and bilateral leg weakness—this requires immediate MRI/CT and neurosurgical consultation 1, 2
• Vertebral compression fracture (4% prevalence): Particularly likely post-fall if patient has osteoporosis history, steroid use, or is older—plain radiography is the appropriate initial imaging 1, 3
• Vertebral malignancy (0.7% prevalence): Consider if age >50, history of cancer (increases probability to 9%), unexplained weight loss, or failure to improve after 1 month 1
• Spinal infection: Assess for fever, recent infection, IV drug use, or immunocompromised status 4

Differential Diagnosis Categories

The American College of Physicians classifies low back pain into three broad categories 1:

• Nonspecific mechanical low back pain (>85% of cases): Musculoligamentous injury from trauma, no specific anatomic cause identified 1, 5
• Radiculopathy or spinal stenosis (~7% combined):
  • Herniated disc with radiculopathy presents with leg pain below the knee in dermatomal distribution, positive straight leg raise, motor weakness in specific nerve root distribution 4, 1
  • Spinal stenosis causes pseudoclaudication with bilateral leg symptoms, typically in older patients 1
• Specific underlying pathology (<2% combined): Fracture, malignancy, infection, or cauda equina syndrome 1

Physical Examination Priorities

Focus your examination on identifying red flags:

• Neurologic assessment: Test motor strength in specific myotomes, sensory distribution, reflexes, and perform straight leg raise test 2, 6
• Midline tenderness: May indicate vertebral compression fracture (especially with trauma history) or infection if accompanied by fever 2
• Saddle anesthesia and rectal tone: Essential to rule out cauda equina syndrome 6
• Assess for progressive neurologic deficits: Any worsening motor or sensory function requires urgent imaging 3, 1

Imaging Strategy Post-Fall

Do NOT obtain routine imaging for nonspecific low back pain even after trauma if no red flags are present—this does not improve outcomes and leads to unnecessary interventions. 3, 4

Your imaging approach should be:

• Immediate MRI or CT if: Severe/progressive neurologic deficits, suspected cauda equina syndrome, or signs of serious underlying condition 3, 1
• Plain radiography if: Risk factors for vertebral compression fracture present (osteoporosis, steroid use, significant trauma in older patient, midline tenderness) 3, 1
• Delayed imaging (4-6 weeks): Consider plain radiography only if symptoms persist despite conservative therapy and no red flags present 4, 2
• MRI preferred over CT: Better soft tissue visualization, no ionizing radiation, superior for evaluating vertebral marrow and spinal canal 3, 2

Critical Pitfall: Radiation Exposure

A single lumbar spine plain radiograph (2 views) delivers gonadal radiation equivalent to daily chest x-rays for more than 1 year—particularly concerning in young women 3, 1. This underscores why imaging should be selective, not routine.

Initial Management Algorithm

If no red flags are identified:

• Maintain activity: Avoid bed rest, encourage activity within pain limits 2, 6
• First-line medications: Acetaminophen (up to 4g daily) or NSAIDs 2, 5
• Nonpharmacologic options: Superficial heat, massage, acupuncture, or spinal manipulation 2
• Avoid opioids for initial management due to abuse potential and lack of superior efficacy 2
• Reassess at 1 month: Earlier if older patient, severe pain, or signs of radiculopathy/stenosis 3, 2

When Symptoms Persist Beyond 4-6 Weeks

• Consider plain radiography if not previously performed and patient has not improved with conservative therapy 3, 4
• Refer for physical therapy or intensive rehabilitation 2
• Assess psychosocial factors (depression, job dissatisfaction, fear-avoidance) that predict chronicity using STarT Back tool 1, 2
• Reserve MRI for patients who are potential surgical candidates with persistent radiculopathy or spinal stenosis 3

Common Pitfalls to Avoid

• Ordering MRI in first 4-6 weeks without red flags: Identifies many abnormalities that correlate poorly with symptoms and may lead to unnecessary interventions 3, 4
• Missing cauda equina syndrome: Leads to permanent neurologic disability from delayed surgical decompression 1
• Overlooking cancer in patients with prior malignancy: History of cancer has positive likelihood ratio of 14.7 1
• Prescribing prolonged bed rest: Increases disability and worsens outcomes 2, 6