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AN50.1-4 | Vertebral column — Self-Directed Learning

Curvatures of the Vertebral Column (AN50.1)

Four curvatures in the sagittal plane:

Figure: Curvatures of the Vertebral Column (AN50.1)

Curvature	Direction	Onset	Classification
Cervical lordosis	Convex anteriorly	When infant lifts head (4 months)	Secondary (compensatory)
Thoracic kyphosis	Convex posteriorly	Present at birth (primary)	Primary
Lumbar lordosis	Convex anteriorly	When infant begins to stand/walk (12–18 months)	Secondary (compensatory)
Sacral kyphosis	Convex posteriorly	Present at birth (primary)	Primary

Primary curvatures (thoracic + sacral): present at birth; reflect the shape of the embryonic C-shaped flexure
Secondary (compensatory) curvatures (cervical + lumbar): develop postnatally with erect posture

Clinical curvature changes:
- Scoliosis: lateral curvature of the spine (see AN50.4)
- Kyphosis: exaggeration of the thoracic kyphosis; causes include Pott's disease (TB), osteoporotic vertebral fractures (common in Indian postmenopausal women), Scheuermann's disease (adolescent)
- Lordosis: exaggeration of lumbar lordosis; causes include pregnancy (transient), obesity, hip flexor contracture, bilateral congenital hip dislocation
- Flat back: loss of lumbar lordosis after spinal fusion or ankylosing spondylitis

Intervertebral Joints and Ligaments (AN50.2)

Two types of joints between adjacent vertebrae:

Figure: Intervertebral Joints and Ligaments (AN50.2)

1. Intervertebral (cartilaginous) joints — between vertebral bodies:
- Type: secondary cartilaginous (symphysis)
- Articular surfaces: hyaline cartilage plates on each vertebral body + fibrocartilaginous intervertebral disc between them
- Intervertebral disc structure:
- Nucleus pulposus (centre): gelatinous, high water content (90% in young adults, decreases with age); embryological remnant of the notochord; acts as a hydraulic shock absorber
- Annulus fibrosus (outer ring): concentric lamellae of obliquely oriented fibrocartilage; posterior part is thinner (predisposes to posterolateral disc herniation)

2. Zygapophyseal (facet) joints — between articular processes:
- Type: synovial plane joints
- Orientation varies by region → determines movement: cervical (oblique, allows rotation + flexion), thoracic (coronal, limits flexion), lumbar (sagittal, allows flexion/extension, limits rotation)

Key ligaments of the vertebral column:

Ligament	Attachment	Function
Anterior longitudinal ligament (ALL)	Skull → sacrum on anterior vertebral bodies	Prevents hyperextension; reinforces anterior disc
Posterior longitudinal ligament (PLL)	Skull → sacrum in vertebral canal on posterior bodies	Prevents hyperflexion; CENTRAL protection of disc (narrow → posterolateral disc bulge can bypass PLL)
Ligamentum flavum	Lamina of one vertebra to lamina below	Elastic; maintains upright posture; thick at lumbar level (can cause canal stenosis when hypertrophied)
Interspinous ligament	Between adjacent spinous processes	Limits flexion
Supraspinous ligament	Tips of spinous processes C7 to sacrum	Limits flexion (becomes ligamentum nuchae in the neck)
Intertransverse ligaments	Between transverse processes	Limits lateral flexion

Sacroiliac joint:
- Type: synovial (upper part) + syndesmosis (lower part); some cartilaginous elements
- Extremely strong anterior and posterior sacroiliac ligaments (strongest ligaments in the body)
- Movement: very limited (slight nutation/counternutation during pregnancy)
- Ankylosing spondylitis affects the sacroiliac joints first → bilateral sacroiliitis → progressive fusion ("bamboo spine")

Figure: Key ligaments of the vertebral column:

Pubic symphysis:
- Type: secondary cartilaginous (with fibrocartilaginous disc)
- Held by superior pubic ligament and inferior arcuate ligament
- Slight movement during pregnancy (relaxin → ligament relaxation)
- Osteitis pubis: inflammation of the symphysis → groin pain in footballers and multiparous women

The Intervertebral Disc — Prolapse Anatomy (AN50.4 excerpt)

Disc prolapse (Prolapsed Intervertebral Disc / PIVD):

Figure: The Intervertebral Disc — Prolapse Anatomy (AN50.4 excerpt)

• Mechanism: The annulus fibrosus tears (usually posterolateral) → nucleus pulposus herniates through the tear → compresses adjacent nerve root
• Why posterolateral? The PLL is broad centrally but tapers laterally → posterolateral annulus is the weakest point; this is where 95% of herniations occur
• Common levels: L4–L5 (most common; compresses L5 root) and L5–S1 (compresses S1 root); together account for ~90%

Nerve root numbering rule:
- At lumbar levels, each nerve root exits BELOW the pedicle of the SAME-numbered vertebra
- The disc between L4 and L5 sits ABOVE the L4–L5 exit foramen; a posterolateral L4–L5 disc herniation compresses the L5 nerve root (which is descending to its exit foramen one level below)
- L4–L5 disc herniation → L5 nerve root compression:
- Pain: down the lateral leg to the dorsum of the foot + big toe (L5 dermatome)
- Weakness: foot dorsiflexion (tibialis anterior, L4–L5)
- Reflexes: usually preserved (ankle jerk = S1)
- Straight leg raise positive (sciatic stretch sign)
- L5–S1 disc herniation → S1 nerve root compression:
- Pain: down posterior thigh, posterior leg, lateral foot, little toe (S1 dermatome)
- Weakness: plantar flexion (gastrocnemius-soleus, S1)
- Reflex: absent ankle jerk (S1)

Cauda equina syndrome (central massive disc prolapse at L4–L5 or L5–S1):
- Bilateral leg weakness/numbness
- Saddle anaesthesia (perineum, inner thighs)
- Urinary retention or incontinence
- Reduced anal sphincter tone
- Surgical emergency — decompress within hours

Scoliosis, Lordosis, Spondylolisthesis, Spina Bifida (AN50.4)

Scoliosis:
- Lateral curvature of the spine in the coronal plane (often with rotational component)
- Idiopathic scoliosis (80%): most common in adolescent girls; right thoracic curve typical; Cobb angle >10° = scoliosis; >45–50° = surgery
- Secondary scoliosis: leg length discrepancy, hemivertebra, poliomyelitis, NF1, cerebral palsy
- Anatomical consequence: rib hump (rotation of vertebral bodies → ribs rotate posteriorly on convex side → rib prominence on forward bending — Adam's forward bending test)
- Screening: school-based scoliometer screening in India for adolescents

Figure: Scoliosis, Lordosis, Spondylolisthesis, Spina Bifida (AN50.4)

Lordosis:
- Exaggerated lumbar (or cervical) lordosis — convex anteriorly
- Common in pregnancy (shifting centre of gravity), obesity, bilateral hip dislocation
- Flat lumbar lordosis seen in ankylosing spondylitis, muscle spasm from disc prolapse

Spondylolisthesis:
- Forward (anterior) slip of one vertebra on the vertebra below
- Types:

Type	Mechanism
Isthmic (most common)	Stress fracture of the pars interarticularis (= spondylolysis) → vertebra slips forward; usually L4–L5 or L5–S1; gymnasts, fast bowlers
Degenerative	Facet joint and disc degeneration in older adults → L4–L5 most common
Dysplastic	Congenital defect in the posterior arch

Spina bifida:
- Failure of fusion of the vertebral arch (posterior neuropore closure failure) — a neural tube defect
- Spina bifida occulta: laminae fail to fuse but meninges and cord intact; often asymptomatic; may have overlying hair tuft/dimple/haemangioma
- Spina bifida cystica:
- Meningocoele: only meninges herniate through the defect; cord intact; good prognosis
- Meningomyelocoele (most common cystic form): cord + nerve roots herniate with meninges → severe neurological deficit below the level of lesion (paralysis, incontinence); associated with Arnold-Chiari malformation + hydrocephalus
- Prevention: folic acid 400 mcg/day (5 mg if previous affected child) periconceptionally → reduces NTD incidence by 70%; key public health message in India