Back Pain and Its Types

1. Introduction and Epidemiology

• Approximately 80% of individuals are affected by back pain at some point in their lives.
• Impairments of the back and spine are the most frequent cause of activity limitation in individuals younger than 45 years (National Center for Health Statistics).
• The total cost of low back pain in the United States exceeds $100 billion per year - one-third from direct care costs, two-thirds from lost productivity and absenteeism.
• About 90% of patients return to work by 3 months, with most returning within 1 month. Patients off work for 6 months have only a 50% probability of ever returning; at 1 year this drops to 25%.

2. Innervation - Understanding Why the Back Hurts

• Ventral ramus - supplies all ventral structures
• Sinuvertebral nerve - a recurrent filamentous branch that innervates the posterior disc, vertebral bodies, and posterior longitudinal ligament
• Dorsal ramus - three sub-branches: lateral and intermediate (posterior musculature/skin), and medial branch (innervates facet joints at that level and adjacent levels above and below)

3. Natural History of Disc Degeneration (Three Stages)

• Disc herniation is a complication of disc degeneration occurring in the dysfunction and instability stages.
• Spinal stenosis from degenerative arthritis is a complication of bony overgrowth in the late instability and early stabilization stages.

4. Classification of Back Pain by Etiology

From Miller's Review of Orthopaedics, 9th Ed (Table 3.10) - Pediatric/General Framework:

Note: Up to 75-80% of children with low back pain have no identifiable diagnosis.

5. Specific Types of Back Pain (Campbell's & Miller's)

A. Nonspecific / Axial Lumbar Pain

• The most common type - occurs at some point in most people's lives
• Nonspecific axial pain = no identifiable structural pathology; accounts for the majority of presentations
• Management: 1-3 days relative rest, anti-inflammatory regimen, rapid progression to active exercise, expected return to full activity in 4-8 weeks
• Psychosocial factors (depression, job dissatisfaction, anxiety, marital status) are intimately intertwined with complaints and disability
• Risk factors: genetic factors, age, gender, smoking, increased intraabdominal fat, metabolic syndrome

B. Discogenic Back Pain (Miller's Review, Ch. 8)

• Paucity of physical findings
• Back pain greater than leg pain
• No radiculopathy - absence of tension signs
• Radiographs: may show disc space narrowing or spondylosis but negative for instability
• MRI: decreased signal intensity on T2-weighted images ("dark disc"), with or without annular tear or high-intensity zone (HIZ)

• Discography (controversial): needle placed into disc, concordant pain elicited upon injection confirms that disc is a pain generator; however, evidence suggests annular tears from the needle may accelerate degeneration, so this is falling out of favor

• Almost always conservative
• More than half recover within 1 week; 90% within 1-3 months
• NSAIDs, physical therapy, conditioning
• Patient education about self-limiting nature

C. Disc Herniation / Radicular Pain

• A complication of disc degeneration (dysfunction and instability stages)
• Pain radiates to extremity following dermatomal pattern
• In the lumbar spine, an L4-5 posterolateral disc herniation typically causes L5 nerve root symptoms (because the named root exits below the named pedicle)
• Favorable outcome in most patients on natural history
• Primary surgical benefit noted in first year (SPORT trial), with maintained benefit at 8-year follow-up
• Non-progressive neurologic deficits can be treated nonoperatively; surgery can usually be delayed 6-12 weeks

D. Facet-Mediated (Zygapophyseal Joint) Pain

• Mediated through the medial branch of the dorsal ramus (from Campbell's innervation anatomy)
• Associated with facet arthrosis arising from disc degeneration and secondary loading of facet joints
• Spondylotic changes in foramina result from subsequent facet joint loading (Miller's)
• Can cause segmental instability (spondylolisthesis) from disc collapse and facet incompetence
• Treatment: medial branch blocks and radiofrequency ablation if confirmed

E. Spinal Stenosis

• A complication of bony overgrowth (hypertrophic bone around disc and facet joints) in the late instability and early stabilization stages
• Compromises neural tissue (central canal or foramen)
• Presents as neurogenic claudication - pain with walking, relieved by flexion (sitting/leaning forward)

F. Mechanical Back Pain (Spondylolysis / Spondylolisthesis)

G. Postoperative Back Pain

• Residual disc material
• Epidural hematoma or abscess
• Discitis

• Scar/fibrosis enhances on T1 post-gadolinium images
• Disc material (in the absence of infection) does not enhance beyond the immediate postoperative period
• The triad of vertebral body endplate enhancement + disc space enhancement + posterior longitudinal ligament enhancement is highly suggestive of postoperative discitis

6. Red Flags for Radiography in Acute Low Back Pain

• Age >50 years
• Significant trauma
• Neuromuscular deficits
• Unexplained weight loss (>10 lb in 6 months)
• Suspicion of ankylosing spondylitis
• Drug or alcohol abuse
• History of cancer
• Use of corticosteroids
• Temperature ≥37.8°C (≥100°F)
• Recent visit (≤1 month) for same problem with no improvement
• Patient seeking compensation for back pain

7. Genetic and Risk Factors

• Aggrecan gene
• Metalloproteinase-3 gene
• Collagen type IX and alpha 2 and 3 gene forms

• Campbell's Operative Orthopaedics, 15th Ed 2026 - Chapters 3 (Imaging), 46 (Axial Lumbar Pain/Disc Degeneration)
• Miller's Review of Orthopaedics, 9th Ed - Chapter 8 (Discogenic Back Pain), Chapter 3 (Pediatric Orthopaedics - Low Back Pain Table 3.10)