Back Pain

1. Epidemiology and Anatomy
2. Mechanical Causes (90% of Low Back Pain)
3. Red Flags — Serious Causes Requiring Urgent Evaluation
4. Thoracic and Referred Back Pain
5. Inflammatory Back Pain — Ankylosing Spondylitis and SpA
6. Diagnostic Approach
7. Evidence-Based Treatment
8. Chronic Pain Neuroscience and Prevention
9. Key Research Papers
10. Connections
11. Featured Videos

Epidemiology and Anatomy

Back pain is the second most common reason for physician visits in the United States, trailing only upper respiratory tract infections. It is one of the most consequential conditions in all of medicine — not because it is lethal, but because of its staggering prevalence and economic footprint. 80% of adults experience at least one significant episode of back pain during their lifetime. Annual point prevalence reaches approximately 25% of the adult population, and the condition costs the US healthcare system and economy over $100 billion per year when direct medical expenses and lost workplace productivity are combined. Globally, low back pain is the leading cause of years lived with disability, outranking all other conditions in that metric.

Understanding the anatomy is essential to understanding back pain. The vertebral column consists of 33 vertebrae: 7 cervical (C1–C7), 12 thoracic (T1–T12), 5 lumbar (L1–L5), 5 sacral (fused into the sacrum), and 4 coccygeal. The lumbar spine (L1–S1) is by far the most commonly affected region, owing to its role in bearing the full weight of the upper body and its range of flexion/extension movement.

Intervertebral discs sit between each pair of adjacent vertebrae. Each disc has an inner nucleus pulposus — a gelatinous, hydrated core — enclosed by concentric rings of fibrocartilage called the annulus fibrosus. Discs function as shock absorbers and allow spinal motion. They are avascular after childhood, receiving nutrients entirely by diffusion from adjacent vertebral endplates. This limited blood supply makes discs susceptible to degeneration with age, physical load, smoking, and dehydration.

The key lumbar nerve roots and their clinical correlates are critical for localizing pathology on examination:

• L4 root: knee extension (quadriceps), medial ankle (patellar) reflex
• L5 root: dorsiflexion and big toe extension (extensor hallucis longus); no reliable reflex to test
• S1 root: plantar flexion (gastrocnemius/soleus), Achilles tendon reflex

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Mechanical Causes (90% of Low Back Pain)

Mechanical back pain — pain arising from spinal structures without a systemic or visceral cause — accounts for roughly 90% of all back pain presentations. Within this broad category, several distinct entities are recognized.

Nonspecific Low Back Pain

The most common presentation. No identifiable structural cause is found on clinical examination or imaging. The underlying substrate is typically muscle strain or ligament sprain from an acute mechanical event — lifting, twisting, or prolonged posture. Reassuringly, over 90% of acute episodes resolve within 6–8 weeks with active management and analgesia. However, recurrence rates are high: 50–85% of patients experience recurrence within one year, and a subset transitions to chronic pain.

Disc Herniation

When the nucleus pulposus extrudes through a tear in the annulus fibrosus, it can compress adjacent nerve roots and cause radiculopathy (nerve root pain). The most commonly affected levels are L4–L5 (compressing the L5 root) and L5–S1 (compressing the S1 root). The classic syndrome is sciatica: unilateral leg pain that exceeds back pain in intensity, radiating from the buttock through the posterior thigh, calf, and into the foot — typically in a dermatomal distribution.

The Straight Leg Raise (SLR) test is the most clinically useful maneuver: with the patient supine, the examiner raises the extended leg passively. Reproduction of the patient's radicular leg pain between 30° and 70° of hip flexion is a positive test, with sensitivity approximately 91% but specificity only 26% for L4–L5 or L5–S1 disc herniation. The crossed SLR — raising the contralateral leg reproduces pain in the symptomatic leg — is far more specific (approximately 88%) though less sensitive. 90% of disc herniations resolve without surgery over 6–12 weeks with conservative care.

Spinal Stenosis

Degenerative narrowing of the spinal canal, lateral recesses, or neural foramina causes compression of the cauda equina or individual nerve roots. The hallmark presentation is neurogenic claudication: bilateral leg pain, weakness, and numbness that is provoked by walking or standing and relieved by sitting or forward flexion (flexion increases canal diameter). The classic "shopping cart sign" — the patient who leans forward on a shopping cart and can walk much farther — reflects this positional physiology. Spinal stenosis affects older adults and has a degenerative etiology. MRI confirms the diagnosis. The SPORT trial demonstrated that surgical decompression (laminectomy) and conservative management produced similar outcomes at two years for moderate stenosis, though surgery provided faster initial relief for severe cases.

Spondylolisthesis

Forward displacement of one vertebra over the one below it. L4 on L5 is the most common level. Degenerative spondylolisthesis occurs in older adults through facet joint and disc degeneration. Isthmic spondylolisthesis results from a pars interarticularis stress fracture and is most common in young athletes subjected to repetitive hyperextension — gymnasts, football linemen, wrestlers. Severity is graded I through IV based on the degree of slip: Grade I (1–25%), Grade II (26–50%), Grade III (51–75%), Grade IV (>75%).

Facet Joint Pain

Osteoarthritis of the posterior facet (zygapophyseal) joints produces a characteristic pattern of bilateral dull aching low back pain worsened by extension and rotation, typically without significant radiculopathy. Diagnosis is confirmed with medial branch nerve blocks; if two diagnostic blocks produce >50–80% pain relief, radiofrequency ablation (neurotomy) of the medial branch nerves can provide 6–12 months of meaningful relief.

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Red Flags — Serious Causes Requiring Urgent Evaluation

While mechanical back pain is benign and self-limited in the vast majority, a small but critically important subset of presentations signals serious underlying pathology. Recognizing these "red flags" and acting promptly can prevent irreversible harm.

Cauda Equina Syndrome — A True Emergency

Cauda equina syndrome (CES) results from compression of the cauda equina nerve roots (the bundle of lumbosacral roots below the conus medullaris at L1). It demands immediate recognition and surgical decompression. The classic constellation of red flags includes:

• Saddle anesthesia — numbness or altered sensation in the perineum, inner thighs, and genitalia (the area that would contact a saddle)
• Bladder dysfunction — urinary retention is the most common and ominous feature; post-void residual >200 mL is a reliable marker; overflow incontinence may develop
• Bowel dysfunction — fecal incontinence, loss of anal sphincter tone
• Bilateral lower extremity weakness
• Sexual dysfunction

Common causes include massive central disc herniation (L4–L5 most frequently), epidural abscess, epidural hematoma, and spinal tumor. CES is a surgical emergency: emergency MRI must be obtained immediately and surgical decompression performed within 24–48 hours. Delay beyond this window significantly worsens the prognosis for recovery of bladder and bowel function, which may become permanent.

Malignancy

Back pain that is the presenting symptom of spinal metastasis or primary spinal tumor carries characteristic features: history of known cancer, unrelenting pain at rest and at night that does not improve with any position change, unexplained weight loss, and age over 50. The spine is the most common site of bony metastases. The primary cancers most likely to metastasize to bone in descending frequency are: lung, breast, prostate, kidney, and thyroid. Workup includes bone scan or whole-spine MRI with contrast.

Vertebral Osteomyelitis

Infection of the vertebral body or disc space presents with fever, severe localized back pain, elevated ESR and CRP. Risk factors include intravenous drug use, immunosuppression, diabetes mellitus, and recent spinal procedure. Contiguous spread from a psoas abscess is a recognized mechanism. Staphylococcus aureus is the most common pathogen. Workup requires MRI with contrast and blood cultures before initiating antibiotics. Biopsy may be required to identify the organism.

Vertebral Compression Fracture

Sudden onset of severe, well-localized mid-thoracic or lumbar pain following minimal trauma — or no trauma at all — in a patient with osteoporosis, postmenopausal status, chronic corticosteroid use, or underlying malignancy suggests vertebral compression fracture. Plain X-ray demonstrates vertebral height loss; MRI (STIR sequence) distinguishes acute from chronic fractures and reveals marrow edema in acute injury.

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Thoracic and Referred Back Pain

Not all back pain originates in the spine. Several visceral and vascular emergencies present with back pain as a dominant or sole symptom. Failure to consider these diagnoses in the appropriate clinical context is a serious diagnostic error.

• Aortic Aneurysm / Aortic Dissection: A tearing or ripping back pain of abrupt onset, often radiating to the anterior chest or interscapular region, in a patient with a history of hypertension or known aortic disease is an emergency until proven otherwise. CT angiography of the chest, abdomen, and pelvis is the imaging of choice. Do not delay for MRI.
• Acute Pancreatitis: Epigastric pain radiating to the mid-back in a "band around the waist" pattern, often associated with nausea, vomiting, and elevated serum lipase. Causes include gallstones and heavy alcohol use.
• Pyelonephritis / Nephrolithiasis: Flank pain with costovertebral angle (CVA) tenderness is the hallmark. Pyelonephritis presents with fever and dysuria; nephrolithiasis with colicky, severe unilateral pain and hematuria. Both may be mistaken for musculoskeletal back pain.
• Posterior Penetrating Peptic Ulcer: Chronic mid-back pain that is meal-related and associated with epigastric symptoms; occurs when a gastric or duodenal ulcer erodes posteriorly toward the pancreas.
• Retroperitoneal Pathology: Lymphoma, retroperitoneal fibrosis, and inferior vena cava thrombosis can all cause dull, persistent back pain without a musculoskeletal explanation. CT with contrast of the abdomen and pelvis is the primary imaging modality.

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Inflammatory Back Pain — Ankylosing Spondylitis and SpA

A clinically important minority of patients with chronic back pain has an inflammatory arthritis of the spine and sacroiliac joints rather than a mechanical problem. Distinguishing inflammatory from mechanical back pain early is critical because the treatment differs fundamentally, and delayed diagnosis can result in irreversible spinal fusion.

The Inflammatory Back Pain Pattern

Inflammatory back pain has a characteristic profile that contrasts sharply with mechanical pain:

• Morning stiffness lasting more than 45 minutes (mechanical pain has brief stiffness)
• Improves with activity and exercise (mechanical pain typically worsens)
• Does NOT improve with rest
• Onset before age 40
• Nocturnal awakening — the patient is awakened by back pain in the second half of the night and must get up to move
• Alternating buttock pain — shifts from one buttock to the other, reflecting sacroiliac joint inflammation
• Dramatic response to NSAIDs — relief within 24–48 hours at full dose

Ankylosing Spondylitis (AS) and Axial Spondyloarthropathy (AxSpA)

Ankylosing Spondylitis is the prototypical inflammatory back pain condition. It is strongly associated with HLA-B27 (present in ~90% of AS patients vs. 6–8% of the general population). The disease begins in the sacroiliac joints and ascends. Over years, progressive ossification of spinal ligaments and discs produces the classic "bamboo spine" appearance on X-ray. Extraarticular manifestations include anterior uveitis, psoriasis, inflammatory bowel disease, and aortic regurgitation.

Biologic therapies — TNF inhibitors (etanercept, adalimumab, infliximab) and IL-17 inhibitors (secukinumab, ixekizumab) — have transformed the management of moderate-to-severe AS.

Sacroiliitis Imaging

Early sacroiliitis is the hallmark of AxSpA and the key diagnostic target:

• Plain X-ray: Changes appear late in the disease course — erosion, sclerosis, and eventual fusion of the sacroiliac joints. Normal X-rays do not exclude early disease.
• MRI of sacroiliac joints with STIR sequence: The gold standard for detecting early active inflammation. Bone marrow edema on STIR MRI may be present years before X-ray changes appear and is a criterion for non-radiographic AxSpA. This is the single most important investigation when inflammatory back pain is suspected in a young patient with normal X-rays.

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Diagnostic Approach

The cornerstone of evaluating back pain remains the clinical history and physical examination. A focused assessment identifies the pattern of pain (mechanical vs. inflammatory vs. referred), localizes neurological deficits, and screens for red flags. No imaging substitutes for this clinical synthesis.

When NOT to Image — The Critical Default

Routine imaging is not indicated in the first 4–6 weeks of uncomplicated low back pain without red flags. This recommendation is supported by robust evidence and endorsed by every major guideline (ACP, ACR, NICE). The reasons are:

• MRI findings of disc degeneration and disc bulges are extremely common in asymptomatic adults — prevalence exceeds 50% in people over age 40 with no back pain whatsoever
• Imaging findings do not correlate reliably with pain severity or disability
• Early routine imaging is associated with higher rates of surgery without improved outcomes, driven by incidental findings that prompt unnecessary intervention
• 70% of people who receive MRI at 6 weeks show "abnormalities" that may be incidental to their current episode

When to Image

Imaging is appropriate in the presence of:

• Any red flag feature (cauda equina, malignancy, infection, fracture)
• Failure to improve after 4–6 weeks of appropriate conservative management
• Radiculopathy accompanied by objective motor deficit
• Suspected axial spondyloarthropathy (MRI sacroiliac joints with STIR)
• Pre-operative planning
• Progressive neurological deficit

Imaging Modality Selection

• MRI (preferred): No ionizing radiation; excellent soft-tissue detail; best for disc, nerve root, spinal cord, bone marrow, and infection
• CT: Superior bone detail; preferred for fractures and post-surgical hardware evaluation; higher radiation dose
• X-ray: Limited utility for soft tissue; appropriate for acute trauma or spondylolisthesis grading
• Bone scan (technetium-99m): Whole-body screening for bony metastases, useful when spinal metastasis suspected

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Evidence-Based Treatment

Acute Low Back Pain (<12 Weeks)

The foundational principle of acute LBP management is that active movement produces better outcomes than rest. Bed rest worsens acute back pain — it leads to deconditioning, fear-avoidance, and prolonged disability. Patients should be explicitly advised to stay as active as possible within their pain tolerance.

• NSAIDs (first-line analgesic): Ibuprofen, naproxen, diclofenac. Multiple RCTs demonstrate superior pain reduction and functional improvement over acetaminophen. Use the lowest effective dose for the shortest necessary duration. Risks include GI bleeding (add PPI gastroprotection if prolonged use), cardiovascular effects in at-risk patients, and nephrotoxicity. Topical diclofenac gel offers local benefit with substantially lower systemic absorption.
• Muscle Relaxants: Cyclobenzaprine, methocarbamol, tizanidine, and baclofen are FDA-approved for acute musculoskeletal back pain. Benefit is predominantly for muscle spasm. They are sedating; use short-term (5–7 days); use with caution in elderly patients (fall risk, anticholinergic effects).
• Heat (topical): Continuous low-level heat wraps are as effective as NSAIDs for acute lumbar strain in several trials. Safe, inexpensive, and widely available.
• Massage: Effective for acute and subacute nonspecific LBP; moderate evidence for short-term pain reduction and functional improvement.
• Spinal Manipulation: Chiropractic or osteopathic manipulation produces moderate short-term benefit for acute nonspecific LBP, comparable to NSAIDs in head-to-head trials. Risk of serious adverse events (cauda equina, arterial dissection) is extremely rare for lumbar manipulation.
• Avoid Opioids: For acute nonspecific low back pain, opioids provide marginal short-term analgesic benefit that must be weighed against serious risks — dependence, addiction, opioid-induced hyperalgesia, cognitive effects, constipation, respiratory depression. There is no evidence of long-term benefit for nonspecific LBP. Guidelines from the CDC and ACP explicitly recommend against opioids as first- or second-line therapy for acute or chronic nonspecific back pain.

Chronic Low Back Pain (>12 Weeks)

Chronic LBP requires a multidisciplinary biopsychosocial approach that addresses physical, psychological, and social dimensions simultaneously. Single-modality treatment is inferior to combined programs.

• Cognitive Behavioral Therapy (CBT): The strongest evidence base for chronic LBP. CBT targets fear-avoidance beliefs, pain catastrophizing, and kinesiophobia (fear of movement). It reduces disability and improves function even when pain intensity does not fully resolve.
• Supervised Exercise: Core stabilization, aerobic conditioning, McKenzie method (extension-based), yoga, and Pilates all have demonstrated efficacy. The specific exercise program matters less than consistency and supervision — adherence is the key determinant of outcome.
• Duloxetine: An SNRI with FDA approval specifically for chronic musculoskeletal pain including chronic LBP. Acts via descending noradrenergic pain modulation. NNT approximately 10 for meaningful pain relief. Modest but real effect size.
• Gabapentinoids (Gabapentin, Pregabalin): Evidence for chronic nonspecific LBP is weak; adverse effects (sedation, dizziness, weight gain, abuse potential) are significant. Multiple guidelines recommend against or caution against routine use for chronic LBP.
• Epidural Steroid Injection (ESI): Transforaminal or interlaminar steroid injection provides 30–50% short-term (6–12 weeks) pain relief for radiculopathy due to disc herniation or foraminal stenosis. ESI is not indicated for nonspecific LBP without radiculopathy. Repeat injections have diminishing returns; most guidelines recommend limiting to 3 per year.
• Acupuncture: Moderate evidence for short-term benefit in chronic LBP; included in ACP guidelines as a nonpharmacologic option.
• Surgery: Reserved for patients with specific structural pathology (disc herniation, spinal stenosis with functional limitation, high-grade spondylolisthesis) who have failed at least 6–12 months of optimal conservative management (or sooner if progressive neurological deficit). Microdiscectomy for disc herniation has an 80–90% success rate in carefully selected patients. Decompressive laminectomy is the primary surgery for symptomatic spinal stenosis. Spinal fusion is indicated for instability, high-grade spondylolisthesis, and certain revision scenarios; outcomes are less predictable for fusion performed primarily for chronic pain without structural instability.

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Chronic Pain Neuroscience and Prevention

Central Sensitization and the Transition to Chronic Pain

In a subset of patients, acute back pain transitions to a chronic pain state that is disproportionate to, or entirely independent of, residual tissue damage. The mechanism is central sensitization: pathological amplification of pain signaling within the dorsal horn of the spinal cord and the brain. Descending inhibitory pathways from the periaqueductal gray and rostral ventromedial medulla lose efficacy. The result is that pain no longer faithfully reports tissue damage — it has become a self-sustaining neurological phenomenon. Chronic pain, in this model, is a disease in itself, not merely a symptom of ongoing injury.

The fear-avoidance model explains the behavioral reinforcement of this process: pain catastrophizing ("this pain means something terrible is wrong") generates fear of movement (kinesiophobia), which leads to physical avoidance and deconditioning, which worsens pain sensitivity, which reinforces catastrophizing — a vicious cycle.

Pain Neuroscience Education (PNE)

PNE — explaining to patients the neuroscience of how chronic pain works — is one of the most evidence-supported psychological interventions for chronic LBP. When patients understand that pain sensitivity can increase without corresponding tissue damage, that imaging findings are not necessarily meaningful, and that movement does not equal damage, catastrophizing decreases and function improves. PNE is most effective when combined with exercise.

Prevention

Back pain is not inevitable despite its extraordinary prevalence. Modifiable risk factors include:

• Physical inactivity: Regular moderate aerobic exercise and core strengthening are the most evidence-based preventive strategies. Sedentary individuals have substantially higher rates of back pain episodes and disability.
• Obesity: BMI >30 approximately doubles the risk of back pain. Mechanical overload, altered spinal biomechanics, and systemic inflammation all contribute.
• Smoking: Nicotine causes microvascular ischemia that accelerates intervertebral disc degeneration. Smokers have higher rates of disc herniation, chronic LBP, and pseudarthrosis (failed spinal fusion). Smoking cessation reduces future back pain risk.
• Occupational and ergonomic factors: Proper lifting technique (hip hinge, not lumbar flexion), standing desks to break prolonged sitting, monitor positioned at eye level, and avoiding sustained awkward postures. The recommendation to limit continuous sitting without breaks is approximately 30 minutes — brief movement interruptions reset lumbar muscle fatigue.
• Psychological factors: Workplace dissatisfaction, depression, and anxiety are stronger predictors of chronic back pain disability than the severity of initial injury. Addressing psychological wellbeing is part of genuine prevention.

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Key Research Papers

1. Chou R et al. "Noninvasive Treatments for Low Back Pain." Ann Intern Med. 2017. PMID 28192793. DOI: 10.7326/M16-2367
2. Deyo RA, Weinstein JN. "Low Back Pain." N Engl J Med. 2001;344(5):363–370. PMID 11172169. DOI: 10.1056/NEJM200102013440508
3. Weinstein JN et al. "Surgical vs Nonoperative Treatment for Lumbar Disk Herniation: The Spine Patient Outcomes Research Trial (SPORT)." JAMA. 2006;296(20):2441–2450. PMID 17119141. DOI: 10.1001/jama.296.20.2441
4. Pengel LH et al. "Acute low back pain: systematic review of its prognosis." BMJ. 2003;327(7410):323. PMID 12907487. DOI: 10.1136/bmj.327.7410.323
5. Buchbinder R et al. "Opioids for chronic low back pain." Cochrane Database Syst Rev. 2013;(11):CD004959. PMID 24218344. DOI: 10.1002/14651858.CD004959.pub4
6. Kamper SJ et al. "Multidisciplinary biopsychosocial rehabilitation for chronic low back pain." Cochrane Database Syst Rev. 2014;(9):CD000963. PMID 25180773. DOI: 10.1002/14651858.CD000963.pub3
7. Sieper J et al. "Ankylosing spondylitis: an overview." Ann Rheum Dis. 2002;61 Suppl 3:iii8–18. PMID 12381506. DOI: 10.1136/ard.61.suppl_3.iii8
8. van Tulder M et al. "Exercise therapy for low back pain." Cochrane Database Syst Rev. 2000;(2):CD000335. PMID 10796352. DOI: 10.1002/14651858.CD000335
9. Waddell G, Burton AK. "Occupational health guidelines for the management of low back pain at work." Occup Med (Lond). 2001;51(2):124–135. PMID 11307688. DOI: 10.1093/occmed/51.2.124
10. Koes BW et al. "Diagnosis and treatment of low back pain." BMJ. 2006;332(7555):1430–1434. PMID 16776886. DOI: 10.1136/bmj.332.7555.1430
11. Maher C et al. "Non-specific low back pain." Lancet. 2017;389(10070):736–747. PMID 27745712. DOI: 10.1016/S0140-6736(16)30970-9
12. Foster NE et al. "Prevention and treatment of low back pain: evidence, challenges, and promising directions." Lancet. 2018;391(10137):2368–2383. PMID 29573872. DOI: 10.1016/S0140-6736(18)30489-6

Search PubMed: Low Back Pain Treatment Evidence | Lumbar Disc Herniation and Sciatica

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Connections

• Joint Pain
• Numbness and Tingling
• Orthopedics
• Neurology
• Magnesium (muscle relaxation)
• Vitamin D3 (bone health)

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Featured Videos

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