Spinal Anatomy
| Region | Levels | Number | Key Feature |
|---|---|---|---|
| Cervical | C1–C7 | 7 | C1 (atlas) & C2 (axis); greatest mobility |
| Thoracic | T1–T12 | 12 | Rib articulations; kyphotic curve |
| Lumbar | L1–L5 | 5 | Largest bodies; load-bearing; lordotic |
| Sacral | S1–S5 | 5 fused | Sacroiliac joint; pelvic attachment |
| Coccygeal | Co1–Co4 | 4 fused | Vestigial; coccydynia if fractured |
- Annulus fibrosus — outer fibrocartilaginous rings; contains nucleus; susceptible to tears (fissures) under repeated flexion/torsional loads
- Nucleus pulposus — gelatinous core; 80% water in youth; distributes compressive load; dehydrates with age (disc desiccation)
- Endplates — cartilaginous; nourish avascular disc via diffusion
- Function — shock absorption, allow motion, distribute load
- 25 discs total — C2/3 to L5/S1; most herniations at L4/5 and L5/S1
Spinal Cord
- Extends from brainstem to conus medullaris at L1–L2
- Surrounded by dura mater, arachnoid, pia mater
- CSF in subarachnoid space
- Below L2: only nerve roots remain (cauda equina — "horse's tail")
Cauda Equina
- Bundle of L2–S5 nerve roots descending within lumbar canal
- Controls: lower limbs, bladder, bowel, sexual function
- Compression = Surgical Emergency
- Most commonly caused by large central L4/5 disc herniation
Temporal Classification of Back Pain
- Most common presentation
- >90% resolve spontaneously
- Usually mechanical in origin
- Self-limiting with conservative care
- Avoid bed rest — stay active
- Transition period — reassess
- Consider psychosocial "yellow flags"
- Fear-avoidance beliefs emerge
- Introduce structured physiotherapy
- Imaging if red flags or no improvement
- Biopsychosocial model essential
- Central sensitisation may develop
- Significant disability & socioeconomic impact
- Multidisciplinary team approach
- Psychological co-morbidity common
Pain Classification: Specific vs Non-Specific
- ~85–90% of all LBP presentations
- No identifiable structural cause on imaging
- Mechanical: worsens with movement, improves with rest
- No neurological deficits
- Includes: muscle strain, ligament sprain, facet joint pain, sacroiliac joint dysfunction
- Good prognosis with active management
- Identifiable pathological cause (~10–15%)
- Examples: disc herniation, spinal stenosis, fracture, tumour, infection, inflammatory arthritis
- Requires targeted investigation & management
- Red flags prompt urgent investigation
- Neurological deficits possible
Axial vs Radicular Pain
| Feature | Axial (Somatic) Pain | Radicular Pain (Sciatica) |
|---|---|---|
| Origin | Disc, facet joint, ligament, muscle | Nerve root irritation/compression |
| Location | Localised to lumbar/sacral region | Radiates down leg in dermatomal pattern |
| Quality | Dull, aching, stiffness | Sharp, shooting, electric, burning |
| Below knee? | Rarely | Often (L4/L5/S1 to foot) |
| Neurological signs | Absent | May be present (weakness, sensory loss, reflex change) |
| SLR test | Negative | Positive (>45° reproduction of leg pain) |
Disc Herniation Pathophysiology
Water loss from nucleus pulposus; disc height reduction; annular fissures begin; reduced shock absorption
Annulus fibrosus bulges but remains intact; nucleus does not escape; may indent thecal sac
Nucleus pulposus breaks through annulus; herniates posterolaterally; compresses nerve root → radiculopathy
Most Affected Levels
- L4/5: L5 nerve root affected → weakness of great toe/foot dorsiflexion, sensory loss medial foot/dorsum
- L5/S1: S1 nerve root affected → weakness of plantarflexion, reduced ankle reflex, sensory loss lateral foot/sole
- L3/4: L4 nerve root → reduced knee jerk, weakness of knee extension, medial leg sensory loss
Spinal Stenosis
Causes of Narrowing
- Ligamentum flavum hypertrophy/buckling
- Facet joint osteophytes
- Disc bulging
- Vertebral endplate osteophytes
- Spondylolisthesis
- Canal diameter <10mm = absolute stenosis
Neurogenic Claudication
- Bilateral leg pain/heaviness on walking
- Relieved by sitting/leaning forward (spinal flexion opens canal)
- Worse going downstairs (extension)
- Better going upstairs (flexion)
- Distinguish from vascular claudication (no positional relief, absent pulses)
- "Shopping cart sign" — leans on trolley to flex spine
Spondylolysis & Spondylolisthesis
- Spondylolysis — stress fracture/defect through pars interarticularis; common in adolescent athletes (gymnastics, cricket fast bowling); often bilateral at L5
- Spondylolisthesis — forward slip of one vertebra on another; most common L4 on L5, or L5 on S1
Meyerding Grading Scale
0–25% slip
26–50% slip
51–75% slip
76–100% slip