Low Back Pain

• Mechanical/Structural Dysfunction: Degeneration of intervertebral discs involves loss of proteoglycan content, decreased disc hydration, and reduced elasticity leading to annular fissuring and potential nuclear herniation. Facet joint osteoarthritis produces osteophyte formation and capsular inflammation. Ligamentous laxity and paraspinal muscle weakness (particularly multifidus and transverse abdominis) compromise spinal stabilization, generating repetitive microtrauma and inflammatory mediator release. Segmental instability results from cumulative degenerative changes, causing abnormal vertebral motion and mechanoreceptor sensitization.

• Neurobiological Mechanisms: Inflammatory mediators (interleukins, TNF-α, prostaglandins) released from damaged discs, ligaments, and surrounding tissues directly irritate nerve roots and dorsal root ganglia. Mechanical compression of neural structures increases intraneural pressure, impairing axonal transport and inducing ischemia. Central sensitization—amplification of pain signaling within the spinal cord and brain—involves wind-up phenomena, expanded receptive fields, and altered descending inhibitory control. Neuroplastic changes in the dorsolateral prefrontal cortex and anterior insula correlate with chronicity and pain catastrophizing.

• Vascular and Ischemic Factors: Disc herniation compresses nutrient vessels supplying nerve roots, causing radicular ischemia. Inflammatory exudate increases tissue pressure within fascial compartments, further compromising microvascular perfusion and perpetuating pain via hypoxia-sensitive ion channels (ASIC1a).

Mechanical/Degenerative Causes (85-90% of LBP)

• Lumbar strain/sprain: Acute musculoligamentous injury from overuse, poor lifting mechanics, or direct trauma; self-limited inflammation typically resolves in 2-4 weeks
• Intervertebral disc herniation: Nuclear material protrusion through annular defects; can compress nerve roots (radiculopathy) or cause central stenosis if large
• Degenerative disc disease (spondylosis): Age-related dehydration, fibrosis, and height loss with progressive osteophyte formation; typically asymptomatic but can generate axial LBP
• Facet joint osteoarthritis and hypertrophy: Cartilage degeneration with osteophyte proliferation causing lateral recess stenosis
• Lumbar spinal stenosis: Narrowing of vertebral canal, lateral recesses, or neural foramina from disc bulging, osteophytes, and ligamentum flavum hypertrophy; typically causes claudication-type pain
• Spondylolisthesis: Anterior vertebral displacement from isthmic defect (spondylolysis) or degenerative changes; graded I-IV by percentage of displacement

Inflammatory/Rheumatologic Causes (5-10%)

• Ankylosing spondylitis (AS): HLA-B27-associated spondyloarthropathy with inflammatory spinal fusion; presents with morning stiffness, elevated ESR/CRP, and bamboo spine on imaging
• Reactive arthritis and enteropathic spondyloarthritis: Inflammatory spinal involvement secondary to GI or GU infection/IBD
• Psoriatic spondyloarthropathy: Spinal inflammation in 5-10% of psoriasis patients

Serious Structural/Systemic Causes (1-3%, "Red Flag" Conditions)

• Spinal fracture: Compression fractures (osteoporosis, multiple myeloma, metastatic disease) or acute traumatic fractures; risk increased by age >50, corticosteroid use, osteoporosis
• Malignancy (metastatic or primary): Hematologic spread (lung, breast, prostate, renal cancers) or primary spinal tumors (myeloma, lymphoma); typically progressive pain unrelieved by rest, night pain, weight loss
• Infection (osteomyelitis/discitis): Bacterial seeding via hematogenous spread or direct inoculation; associated with fever, IV drug use, immunosuppression, or recent spinal procedures
• Cauda equina syndrome (CES): Massive disc herniation or canal stenosis compressing multiple nerve roots at L5-S1 level; presents with bilateral leg pain/paresthesias, saddle anesthesia, bowel/bladder dysfunction, and bilateral lower extremity weakness; neurosurgical emergency
• Abdominal aortic aneurysm (AAA): Rupture presents with sudden severe LBP, hypotension, and pulsatile abdominal mass; mortality >50% if ruptured

Risk Factors

• Age: Degenerative changes peak 30-50 years; stenosis more common >65 years
• Occupational/Biomechanical: Prolonged sitting, heavy lifting, vibration exposure, poor posture, repetitive bending
• Lifestyle: Sedentary behavior, obesity (BMI >30), smoking (impairs disc nutrition), deconditioning
• Psychological: Depression, anxiety, catastrophizing, somatization, poor coping mechanisms (stronger predictor of chronicity than pain severity)
• Genetic: Familial clustering of disc degeneration; twin studies suggest 40-60% heritability
• Prior Episodes: History of LBP is strongest predictor of recurrence (60-80% recurrence within 1 year)
• Medical Comorbidities: Osteoporosis, inflammatory arthropathies, immunosuppression

Cardinal Symptom Characteristics

• Pain Quality and Location: Localized midline or unilateral LBP below 12th rib; mechanical pain worsens with movement and improves with rest (nonspecific); radicular pain follows dermatomal distribution (L5: dorsolateral foot; S1: posterior/lateral foot and sole) with sharp, burning, or electric quality; claudication-type pain develops or worsens with walking/lumbar extension and improves with sitting/lumbar flexion
• Pain Radiation: Referred pain (from facets, muscles, ligaments) typically radiates to buttock, proximal thigh, or groin but not below knee; true radiculopathy crosses knee and follows nerve root distribution
• Associated Symptoms: Morning stiffness (suggests inflammatory etiology if >30-45 minutes); night pain (concerning for malignancy or severe stenosis if sleep-disrupting); progressive neurological symptoms (weakness, numbness, incontinence—red flags); weight loss, fever, chills (infection/malignancy)

Physical Examination Findings

• Inspection/Palpation: Paraspinal muscle spasm (visible asymmetry, palpable rigidity), scoliosis, kyphosis, step-off deformity (spondylolisthesis); point tenderness over spinous processes (vertebral fracture) or facet joints
• Range of Motion: Decreased lumbar flexion, extension, lateral bending; guarding patterns suggest acute muscular dysfunction; nonorganic/Waddell signs (inconsistent effort, superficial tenderness, simulated rotation pain) suggest psychogenic contribution but don't exclude organic pathology
• Neurological Examination: Myotomal weakness (L4: quadriceps, knee extension; L5: foot dorsiflexion, hip abduction; S1: plantarflexion, hip extension); dermatomal sensory loss; hyperreflexia (upper motor neuron lesions, cord compression) vs. hyporeflexia (lower motor neuron/radiculopathy); Straight Leg Raise (SLR) positive if pain reproduces with passive hip flexion <60° (sensitive for nerve root tension, L4-L5-S1); Crossed SLR (pain on contralateral leg elevation) highly specific for large disc herniation compressing examined nerve root; Babinski sign, hyperreflexia, or clonus suggests myelopathy; Saddle anesthesia (perianal sensory loss) and anal sphincter laxity indicate CES
• Specialized Maneuvers: Femoral stretch test (prone knee flexion) sensitive for L2-L4 nerve root irritation; Patellar reflex (L3-L4), Achilles reflex (S1) diminution/absence with radiculopathy; hip/knee range of motion assesses for referred pain from hip joint

Clinical Assessment and Decision-Making

• History and Physical Examination: Most accurate initial diagnostic tool; differentiation of mechanical vs. radicular vs. claudication pain, identification of red flags, and assessment of psychosocial factors drive imaging and investigation decisions. Standard history should systematically address onset, character, radiation, severity (visual analog scale or numeric rating scale 0-10), aggravating/relieving factors, associated constitutional symptoms, and functional impact.
• Red Flag Screening: Mandatory assessment for indicators of serious pathology requiring urgent imaging/intervention: age >50 or <18 years, history of cancer, unexplained weight loss >5%, fever, IV drug use, immunosuppression, recent infection/procedure, corticosteroid use, severe night pain, progressive neurological deficit, saddle anesthesia, bowel/bladder dysfunction, bilateral leg pain/weakness. Presence of multiple red flags or acute onset with severe symptoms warrants urgent evaluation; single red flags may prompt imaging based on clinical judgment.

Imaging Studies (Selective Use to Avoid Overdiagnosis)

• Plain Radiographs (AP, Lateral, Oblique Lumbar Views): Low sensitivity/specificity for disc pathology; useful for detecting fractures (especially compression fractures with kyphosis), spondylolisthesis (assess degree via Meyerding classification), gross degenerative changes, or scoliosis. Lateral view best demonstrates spondylolisthesis and disc height loss. Not routinely recommended for acute mechanical LBP without fracture risk or neurological findings.
• Magnetic Resonance Imaging (MRI): Gold standard for soft tissue visualization including disc herniation, nerve root compression, spinal cord signal abnormality (myelopathy), marrow edema (fracture, infection, metastatic disease), epidural abscess. High sensitivity but poor specificity—asymptomatic disc herniations present in 25-60% of normal individuals, limiting clinical correlation. Reserved for: (1) persistent radiculopathy unresponsive to conservative treatment, (2) suspicion of serious pathology (infection, malignancy, CES), (3) surgical planning if intervention considered, (4) progressive neurological deficit. STIR sequences detect T2 signal abnormality suspicious for infection; contrast enhancement (gadolinium) helpful for infection (rim enhancement), malignancy, and arachnoiditis.
• Computed Tomography (CT): Superior for cortical bone detail; useful for evaluating fractures, spinal stenosis degree, spondylolysis detection, and guiding interventional procedures. Lower soft tissue contrast than MRI; preferred if MRI contraindicated (pacemaker, metallic implants). CT myelography (intrathecal contrast) enhanced visualization of nerve root compression if MRI unavailable.
• Imaging Criteria—When NOT to Image: Uncomplicated acute mechanical LBP (<6 weeks) with no red flags does not warrant imaging; 90% resolve naturally with conservative care. Premature imaging increases cost, patient anxiety, and unnecessary intervention without improving outcomes. Imaging recommended if: red flags present, neurological deficit, persistent symptoms >6 weeks unresponsive to conservative measures, or preparation for interventional procedures.

Laboratory Tests (Selected Based on Clinical Context)

• Complete Blood Count (CBC): Leukocytosis suggests infection; anemia raises concern for malignancy or chronic disease
• Comprehensive Metabolic Panel: Assess renal function before contrast administration; electrolyte abnormalities may reflect spinal cord involvement
• Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP): Elevated in infection (>20 mm/hr ESR, typically), inflammatory spondyloarthropathy (AS, reactive arthritis), and malignancy; helpful for infection screening (sensitivity ~90% if both negative in early osteomyelitis, though CRP more sensitive acutely than ESR). Normal ESR/CRP does not exclude serious pathology.
• HLA-B27: Positive in 90% of ankylosing spondylitis cases but present in 6-8% of general population; ordered if spondyloarthropathy suspected (morning stiffness >45 minutes, inflammatory markers elevated, imaging changes)
• Blood Cultures: If infection suspected (fever, IV drug use, immunosuppression); positive in ~30-50% of spinal osteomyelitis/discitis
• Prostate-Specific Antigen (PSA) and Tumor Markers: Only if malignancy suspected given age, risk factors, constitutional symptoms; not screening tools

Diagnostic Criteria for Specific Entities

• Unilateral leg pain in dermatomal distribution (typically below knee)
• Positive tension signs: SLR <60°, crossed SLR, femoral stretch test
• Neurological findings: dermatomal sensory loss, myotomal weakness, hyporeflexia corresponding to same nerve root
• MRI confirmation: nerve root compression at level consistent with clinical findings

• Claudication-type pain (bilateral or unilateral leg pain, paresthesias, heaviness, or weakness)
• Symptoms worsen with lumbar extension and prolonged walking; improve with lumbar flexion and sitting
• Imaging findings: narrowed vertebral canal (<10-12 mm anteroposterior diameter), lateral recess stenosis, or neural foraminal narrowing; severity may not correlate with symptoms

• Bilateral leg pain and/or paresthesias, often with low back pain
• Saddle anesthesia (perianal/perineal sensory loss) or bilateral lower extremity sensory loss
• Bilateral leg weakness or asymmetric presentation
• Bowel/bladder dysfunction: urinary retention (most sensitive—post-void residual >150 mL), incontinence, fecal incontinence, loss of anal tone, decreased anal sensation
• Acute or rapidly progressive symptoms
• MRI shows massive central disc herniation, epidural mass, or fracture compressing cauda equina at L5-S1; myelography shows "candle dripping" appearance of contrast around compressed nerve roots

• Age <45 years at onset with insidious progressive pain and stiffness
• Morning stiffness ≥30 minutes improving with activity
• Elevated inflammatory markers (ESR, CRP)
• HLA-B27 positive
• Imaging: squared vertebral bodies, syndesmophytes (vertical bony bridges between vertebrae), "bamboo spine" appearance on lateral radiographs

Acute/Subacute Low Back Pain (Duration <6 weeks)

• First-Line Pharmacotherapy:
• NSAIDs (ibuprofen 400-800 mg TID-QID, naproxen 500-1000 mg daily, meloxicam 7.5-15 mg daily): Inhibit COX-1/COX-2, reducing prostaglandin-mediated inflammation and pain; effectiveness similar across agents. Most effective within first 2 weeks; limited evidence beyond 4 weeks. GI intolerance in 10-15%; consider gastroprotection (proton pump inhibitor) if age >65 or history of peptic ulcer disease. Cardiovascular and renal risks with prolonged use; avoid in renal impairment or heart failure. Acetaminophen (3-4 g daily in divided doses) inferior to NSAIDs but reasonable alternative if NSAIDs contraindicated; monitor for hepatotoxicity.
• Muscle Relaxants (cyclobenzaprine 5-

Emergencies (recognize and act before imaging is completed)

• Cauda equina syndrome: Compression of the lumbosacral roots causes sacral parasympathetic and pudendal dysfunction before motor loss becomes complete. Painless urinary retention with overflow incontinence and an elevated post-void residual is the most sensitive early sign; saddle anesthesia and loss of anal tone follow. Requires emergent MRI and surgical decompression — delay correlates with permanent bladder, bowel, and sexual dysfunction.
• Spinal epidural abscess: Hematogenous seeding (IV drug use, bacteremia, recent instrumentation; Staphylococcus aureus most common) produces the triad of fever, spinal pain, and neurologic deficit, though the full triad is uncommon. Escalating deficit signals cord/root ischemia. Urgent MRI with contrast plus blood cultures; IDSA guidance favors culture-directed antibiotics with drainage for neurologic compromise.
• Metastatic epidural spinal cord compression: Tumor in the vertebral body expands posteriorly; a known cancer history plus new thoracic band-like pain, worse at night or recumbent, with hyperreflexia and a sensory level is the signal. Give corticosteroids and obtain MRI of the entire spine, then radiation oncology/neurosurgery.
• Ruptured abdominal aortic aneurysm: Tearing back/flank pain with hypotension and pulsatile mass; bedside ultrasound, not MRI.

Complications of the disease itself

• Chronic pain and disability: Central sensitization and fear-avoidance behavior perpetuate pain after tissue healing; catastrophizing and depression predict this better than initial pain severity.
• Persistent motor deficit: Unrecovered foot drop from L5 root compression, or fixed sensory loss, when compression is prolonged.

Treatment-related complications

• NSAIDs: COX-1 inhibition causes GI ulceration/bleeding; prostaglandin-dependent afferent arteriolar tone loss causes AKI, plus fluid retention and cardiovascular risk.
• Opioids: Tolerance, opioid-induced hyperalgesia, overdose; the CDC 2022 opioid prescribing guideline discourages them as first-line for back pain.
• Muscle relaxants: Sedation and anticholinergic delirium/falls in older adults (cyclobenzaprine is on the Beers criteria list).
• Epidural steroid injection: Dural puncture headache, infection, hyperglycemia; rare cord infarct with transforaminal particulate steroid.
• Surgery: Dural tear with CSF leak, discitis, recurrent herniation, adjacent segment degeneration, and failed back surgery syndrome; new postoperative bilateral leg weakness or retention suggests epidural hematoma — an emergency.

• No imaging for uncomplicated acute LBP: The American College of Physicians and Choosing Wisely both advise against routine imaging within the first six weeks absent red flags or progressive deficit. On a stem describing mechanical LBP with a normal neuro exam, the best next step is reassurance plus continued activity — not an MRI.
• Stay active; bed rest is the classic distractor: Prolonged bed rest worsens deconditioning and delays return to function. ACP places nonpharmacologic measures (heat, exercise, massage, spinal manipulation) first for acute LBP, with NSAIDs as the preferred initial drug.
• Suspected cauda equina syndrome → emergent MRI and surgical decompression: Do not wait for the full syndrome. Saddle anesthesia, decreased anal tone, and urinary retention with a high post-void residual are the tested findings; retention is the most sensitive.
• Localize by reflex and myotome: S1 lesions lose the Achilles reflex and plantarflexion (weak toe-walking); L5 lesions cause weak dorsiflexion and great-toe extension with preserved reflexes — a favorite trap. L3–L4 lesions blunt the patellar reflex and are best elicited by the femoral stretch test.
• Crossed straight-leg raise is specific, plain SLR is sensitive: Pain in the affected leg when the unaffected leg is raised strongly suggests a large central disc herniation.
• Neurogenic vs vascular claudication: Neurogenic pain improves with lumbar flexion (shopping cart sign), is worse walking downhill, and spares the pulses; vascular claudication is reproducible at a fixed distance, relieved by standing still, with diminished pulses and a low ABI.
• MRI findings are common in asymptomatic people: Disc bulges and herniations appear in a large fraction of pain-free adults, so imaging must match the dermatome and myotome before attributing symptoms to it.
• The inflammatory pattern: Age under 45, insidious onset, morning stiffness improving with exercise and worsening with rest, and nocturnal pain point to axial spondyloarthritis (HLA-B27, sacroiliitis) — NSAIDs first, TNF inhibitors for refractory disease.