What is causing my back pain?

What's Causing Your Back Pain?

Your back pain is most likely nonspecific mechanical low back pain—a musculoskeletal condition affecting muscles, ligaments, or joints—which accounts for over 85% of cases and typically improves within 4-6 weeks with conservative management. 1, 2

Understanding the Most Common Causes

The American College of Physicians classifies back pain into three diagnostic categories to guide your evaluation: 1

• Nonspecific mechanical low back pain (>85% of cases): Pain from muscles, ligaments, discs, or facet joints without nerve compression or serious underlying disease 2, 3
• Back pain with radiculopathy or spinal stenosis (4-7% of cases): Nerve compression causing leg pain below the knee 1, 2
• Back pain from serious underlying conditions (<1% of cases): Cancer, infection, fracture, or cauda equina syndrome 1, 2

Critical Red Flags That Change Everything

Before assuming your pain is mechanical, you must exclude serious conditions that require urgent intervention: 1, 4

• Cauda equina syndrome (0.04% prevalence): Urinary retention (90% sensitive), fecal incontinence, saddle numbness, or bilateral leg weakness—this is a surgical emergency requiring MRI within hours 1, 4
• Cancer (0.7-9% prevalence): History of cancer increases probability from 0.7% to 9%, unexplained weight loss, age >50 years, or pain lasting >1 month without improvement 1, 2
• Spinal infection (0.01% prevalence): Fever, recent infection, IV drug use, or immunocompromised status 4, 2
• Vertebral compression fracture (4% prevalence): Older age, osteoporosis history, or corticosteroid use 1, 2

If any red flags are present, you need immediate MRI—not the usual 4-6 week waiting period. 4, 2

Distinguishing Mechanical Pain from Nerve Compression

Your pain pattern reveals the underlying cause: 2, 5

• Mechanical pattern: Pain worsens with activity and improves with rest, localized to back or buttocks—this suggests nonspecific mechanical pain 2, 6
• Radicular pattern: Sharp leg pain below the knee in a specific nerve distribution (sciatica), positive straight-leg-raise test between 30-70 degrees (91% sensitive for herniated disc)—this suggests nerve root compression 1
• Neurogenic claudication: Leg pain with walking that improves when sitting or bending forward—this suggests spinal stenosis 1
• Inflammatory pattern: Morning stiffness >30 minutes that improves with movement and worsens with rest, age <45 years—this suggests ankylosing spondylitis (0.3-5% prevalence in chronic cases) 4, 2

Less Common But Important Causes

Constipation can cause low back pain through mechanical pressure. Severe constipation or fecal impaction distends the rectosigmoid colon, creating pressure on lumbosacral nerves and manifesting as back discomfort. 7 If constipation is present, manage it with stimulant laxatives, osmotic laxatives, increased fluids, and physical activity, then reassess pain after bowel function normalizes. 7 However, don't assume constipation is the cause without excluding more common musculoskeletal origins first. 7

Common Diagnostic Pitfalls to Avoid

Do not routinely obtain imaging for nonspecific back pain without red flags—this does not improve outcomes and leads to unnecessary interventions. 1, 2, 3 Radiographs and MRI should be delayed for at least 1-2 months unless red flags are present. 1, 8

Do not overlook inflammatory causes in younger patients (<45 years) with chronic symptoms and morning stiffness—early diagnosis of ankylosing spondylitis allows for TNF-blocking agents which show strong efficacy when disease duration is less than 10 years. 2

Do not miss medication-induced constipation from opioid analgesics—this creates a cycle where pain treatment worsens constipation, which may worsen pain. 7

When Imaging Is Actually Needed

Imaging is indicated only in these specific situations: 3, 8, 9

• Red flags are present (cancer, infection, fracture, cauda equina syndrome) 3, 9
• Neuromuscular deficits are present on examination 3
• Pain persists beyond 4-6 weeks despite conservative therapy 3, 5
• Radicular symptoms suggest herniated disc or spinal stenosis requiring surgical evaluation 8

MRI is the preferred imaging modality when serious pathology is suspected, as it evaluates soft tissues, spinal cord, nerve roots, and discs better than CT or radiographs. 1