Definition of Pain

"An unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage."

• Pain is both a sensory and an emotional experience — it is not purely a physical signal.
• It can occur with actual tissue damage (e.g., a cut), potential damage (e.g., a threat), or even in the absence of demonstrable tissue damage (e.g., neuropathic or psychogenic pain).
• It is distinct from nociception, which is the unconscious neural activity induced by a harmful stimulus applied to sensory receptors — pain requires conscious awareness.

Classification of Pain

Preemptive vs. Preventive Analgesia

Preemptive Analgesia

• Defined as an analgesic intervention administered before surgical incision that is more effective than the same intervention given after surgery.
• The rationale was to prevent the establishment of central sensitization caused by the incisional injury, thereby reducing postoperative pain hypersensitivity.
• Mechanism: Block nociceptive afferent input before it reaches the CNS and triggers wind-up, facilitation, and long-term potentiation in dorsal horn neurons.
• Clinical reality: Randomized controlled trials have had mixed (largely negative) results. A single pre-incision analgesic block cannot prevent central sensitization because once the block wears off, the ongoing surgical/inflammatory injury re-initiates central sensitization. The term is now considered obsolete.

Preventive Analgesia

• A broader, more modern concept: includes any antinociceptive regimen delivered at any time during the perioperative period (before, during, or after surgery) that attenuates pain-induced sensitization.
• Timing is less critical than the intensity and duration of the intervention.
• The goal is to block NMDA receptor activation in the dorsal horn, preventing:
  • Wind-up
  • Central sensitization
  • Expansion of receptive fields
  • Long-term potentiation → chronic pain

Three Critical Principles for Preventive Analgesia to Succeed

1. Depth: Analgesia must be adequate to block all nociceptive input during surgery.
2. Extent: The analgesic technique must cover the entire surgical field.
3. Duration: Analgesia must span both the surgical and postsurgical (inflammatory) periods — because inflammatory injury continues well into the postoperative period and perpetuates central sensitization.

Key Comparison Table

Causes of Low Back Pain

1. Musculoskeletal / Mechanical (Most Common)

2. Disc-Related

• Lumbar disc degeneration (discogenic LBP): degenerative disc disease without frank herniation; axial LBP
• Prolapsed/herniated disc: nuclear material herniates through annulus fibrosus, compressing nerve roots (most commonly L4–L5 or L5–S1)

3. Degenerative / Arthritis

• Lumbar spondylosis (osteophyte formation)
• Facet joint arthropathy
• Degenerative endplate changes (Modic changes on MRI)

4. Inflammatory

• Ankylosing spondylitis: morning stiffness, sacroiliac tenderness, young males; HLA-B27 positive
• Other seronegative spondyloarthropathies

5. Infective

• Vertebral osteomyelitis / discitis: fever, local tenderness, elevated ESR/CRP; MRI confirms
• Epidural abscess: pain + fever + neurological signs → surgical emergency

6. Neoplastic

• Primary vertebral tumors (e.g., myeloma)
• Metastases (breast, prostate, lung, renal, thyroid): worsening pain in recumbent position, night pain, systemic symptoms
• Intradural/extramedullary tumors

7. Congenital / Developmental

• Spina bifida occulta
• Sacralization / lumbarization of vertebrae
• Congenital scoliosis
• Transitional vertebrae / asymmetric facet joints

8. Referred / Visceral Pain

• Renal stones, pyelonephritis, renal cysts → costovertebral angle tenderness
• Aortic aneurysm → pulsatile abdominal mass + back pain
• Retroperitoneal pathology (lymphoma, pancreatic Ca)
• Pelvic disease in women (endometriosis, PID)
• Prostate disease in men

9. Vascular

• Ischemia of lumbar spinal cord
• Aortic aneurysm (see above)

10. Osteoporotic / Traumatic

• Vertebral compression fractures (osteoporosis, trauma, malignancy)
• Transverse process fractures

11. Psychogenic / Functional

• Chronic LBP without structural pathology
• Associated with somatization, depression, compensation claims

Red Flags Requiring Urgent Imaging (MRI)

• Objective neurological deficits (radiculopathy, conus signs, sphincter dysfunction)
• Pain worsening in recumbent position / at night
• Pain aggravated by Valsalva maneuver
• History of cancer
• Fever + spinal tenderness
• Post-trauma
• Progressive pain

Management of Prolapsed Intervertebral Disc (PIVD)

Pathophysiology

• L5 root: pain/numbness down dorsomedial foot; weakness of tibialis anterior (foot drop)
• S1 root: pain/numbness to lateral foot/small toe; weakness of peroneus longus and brevis; absent ankle jerk

Investigations

• MRI lumbosacral spine: investigation of choice — confirms level, degree of herniation, nerve root compression
• CT spine: if MRI contraindicated
• EMG/NCV: may not detect early radiculopathy; useful for chronic or atypical cases
• X-ray: limited value; screens for structural anomalies, fractures

Conservative Management (First-Line, 6–12 Weeks)

Interventional / Minimally Invasive

• Lumbar epidural steroid injections (LESIs): provide fast and effective pain relief when nerve root is not severely mechanically compressed; useful if conservative treatment fails within 6–8 weeks
• Transforaminal / caudal epidural blocks: targeted root injection at the affected level
• Medial branch blocks / facet injections: if facet joint involvement coexists

Surgical Management

1. Absolute (emergency):
   • Cauda equina syndrome: bilateral leg weakness, saddle anaesthesia, bowel/bladder dysfunction → emergency microdiscectomy
2. Relative (elective):
   • Moderate-to-severe focal neurological deficit (weakness, significant numbness)
   • Severe disabling pain for >3 months not responding to aggressive pain management, with disc herniation confirmed on MRI/CT

Summary Algorithm

PIVD diagnosed (clinical + MRI)
        |
        ├── Cauda equina syndrome? → EMERGENCY SURGERY
        |
        ├── Severe/progressive neurological deficit? → Early surgery
        |
        └── Otherwise → Conservative (NSAIDs, PT, muscle relaxants) × 6–12 weeks
                            |
                    No improvement?
                            |
                    Epidural steroid injection
                            |
                    Still no improvement + confirmed herniation?
                            |
                    Elective microdiscectomy