In a 45-year-old male construction worker who developed acute low back pain three days ago while lifting a 30‑kg concrete block, with deep aching lumbar pain worsened by flexion and lifting, relieved by lying supine with knees supported, no radicular symptoms, normal neurologic exam, and no systemic signs, what is the most likely diagnosis and which red‑flag findings would necessitate urgent imaging or referral?

Clinical Scenario: Acute Mechanical Low Back Pain

Most Likely Diagnosis

This 45-year-old construction worker has acute nonspecific mechanical low back pain, most likely from lumbar muscle strain or minor ligamentous injury related to the lifting mechanism. 1

Clinical Reasoning

Why This is Mechanical Low Back Pain:

• Acute onset (3 days) with clear mechanical trigger (lifting 30-kg concrete block) strongly suggests muscle or ligamentous strain 2
• Pain pattern is classic mechanical: worsens with flexion and lifting, improves with rest (supine with knee support) 2, 3
• Absence of radicular symptoms (no leg pain below the knee, no dermatomal distribution) rules out nerve root compression 4, 5
• Normal neurologic examination excludes significant neurologic compromise 1
• No systemic signs (no fever, no weight loss, no night pain) makes infection or malignancy unlikely 2, 3

What You Should NOT Do:

• Do NOT order imaging at this stage – acute uncomplicated low back pain without red flags is self-limiting and imaging provides no clinical benefit 1
• Do NOT prescribe bed rest – maintaining activity is more effective than rest 4, 3

Red Flags Requiring Urgent Imaging or Referral

You must systematically screen for these conditions that would change management immediately:

Cauda Equina Syndrome (Requires Emergency MRI):

• Urinary retention or overflow incontinence 4, 2
• Fecal incontinence 4
• Saddle anesthesia (numbness in perineum/buttocks) 4
• Bilateral leg weakness 4
• Progressive motor or sensory loss 2

Malignancy (Requires Urgent MRI):

• Age >50 years 4, 2
• History of cancer 4, 2
• Unexplained weight loss 4, 2
• Failure to improve after 1 month of conservative treatment 4
• Severe night pain unrelieved by rest 3

Infection (Requires Urgent MRI and Labs):

• Fever 4, 2
• Recent bacterial infection 4
• IV drug use 4
• Immunocompromised status (HIV, chronic steroids, transplant) 4
• Recent invasive spinal procedure 2

Fracture (Requires Plain Radiography Initially):

• Age >70 years 4
• Significant trauma relative to age (minor trauma in elderly, major trauma in young) 2
• Prolonged corticosteroid use 4
• Known osteoporosis 4

Appropriate Management for This Patient

Immediate Actions (First 4-6 Weeks):

• Reassure the patient that acute mechanical low back pain is self-limiting and typically resolves within 4-12 weeks 1
• Encourage continued activity and return to work as tolerated – avoid bed rest 4, 3
• NSAIDs as first-line medication for pain control 2, 3
• Consider physical therapy if symptoms persist beyond initial week 3

When to Image:

• Only if symptoms persist after 4-6 weeks of conservative management AND patient is a surgical candidate 4
• Plain radiography may be reasonable if symptoms persist beyond 1-2 months despite therapy 4
• MRI is NOT indicated unless red flags develop or patient fails 4-6 weeks of conservative treatment 1, 4

Common Pitfalls to Avoid

• Do not order MRI in the first 4-6 weeks unless red flags are present – imaging identifies many degenerative abnormalities that correlate poorly with symptoms and lead to unnecessary interventions 1, 4
• Do not assume imaging abnormalities equal pathology – disc protrusions occur in 29-43% of asymptomatic adults depending on age 1
• Do not overlook occupational factors – construction workers have increased risk due to repetitive lifting, bending, and twisting 6