Scoliosis

Scoliosis is a three-dimensional structural deformity of the spine defined by a lateral curvature with a Cobb angle ≥10°, almost always accompanied by vertebral rotation and alteration of the normal sagittal profile. It is a favourite NEET PG topic for its crisp measurements (Cobb angle, Risser sign), clinical tests (Adam's forward bend), and clean treatment thresholds.

Definition & key concept

• A coronal-plane curve of <10° is NOT scoliosis — it is called spinal asymmetry and needs no treatment.
• True structural scoliosis is 3D: lateral deviation (coronal) + vertebral rotation (axial) + loss of normal kyphosis/lordosis (sagittal).
• The convexity of the curve defines its side (e.g., a "right thoracic curve" is convex to the right). The apex is the most laterally deviated vertebra; end vertebrae are the most tilted vertebrae at the top and bottom of the curve.

High-yield: A Cobb angle of ≥10° is the diagnostic cut-off for scoliosis. Below this, it is just asymmetry.

Classification

Scoliosis is broadly divided into structural (fixed, does not correct on bending/lying — has rotation) and non-structural / functional (flexible, corrects on bending — no rotation; e.g., due to leg-length discrepancy, painful muscle spasm, or poor posture).

Type	Cause	Key features
Idiopathic (~80%)	Unknown (polygenic)	Most common; subdivided by age of onset
Congenital	Vertebral malformation in utero	Failure of formation (hemivertebra) / failure of segmentation (bar); associated VACTERL anomalies
Neuromuscular	Cerebral palsy, polio, DMD, myelomeningocele, SMA	Long C-shaped curve, pelvic obliquity, progresses even after maturity
Syndromic	Marfan, NF-1, Ehlers-Danlos	Curve part of systemic disease
Degenerative (de novo)	Disc/facet degeneration in adults	Lumbar, older patients, with stenosis

Idiopathic scoliosis by age of onset

Subtype	Age of onset	Notes
Infantile	0–3 yrs	More in boys; left thoracic curve; many resolve spontaneously
Juvenile	4–9 yrs	High progression risk
Adolescent (AIS)	≥10 yrs to maturity	Most common overall; girls >> boys; classically right thoracic curve

High-yield: Adolescent idiopathic scoliosis (AIS) is the commonest type — typically a right thoracic curve in an adolescent girl. A left thoracic curve in a child is atypical and demands an MRI to rule out intraspinal pathology (syrinx, tethered cord, tumour).

Etiology & pathophysiology

• Idiopathic: multifactorial — genetic predisposition (polygenic), abnormal melatonin signalling, asymmetric paraspinal muscle activity, and disturbed proprioception have all been implicated. No single cause is proven.
• Congenital: defective somite formation between the 4th–6th weeks of gestation. Two mechanisms:
  • Failure of formation → hemivertebra (wedge), causing rapidly progressive sharp curves.
  • Failure of segmentation → unilateral unsegmented bar, the highest-risk congenital lesion for progression (worst when a bar is opposite a contralateral hemivertebra).
• Neuromuscular: muscle imbalance and truncal weakness produce a long, sweeping curve and pelvic obliquity, impairing sitting balance.

The mechanical consequence of vertebral rotation is the rib hump (posterior on the convex side) and an anterior chest prominence on the concave side — the basis of Adam's test.

Clinical features

• Often painless — discovered as asymmetry of shoulders/waist or on school screening. Pain should raise suspicion of a secondary cause (osteoid osteoma, tumour, infection, syrinx).
• Signs: unequal shoulder height, scapular prominence, asymmetric waist creases, trunk shift, and a rib hump on forward bending.
• Adam's forward bend test: patient bends forward at the waist with hands together; the examiner looks tangentially along the spine. A rib hump (thoracic) or paravertebral lumbar prominence confirms a structural, rotational curve. A functional curve disappears on bending.
• Scoliometer: quantifies the trunk rotation seen on Adam's test. Angle of trunk rotation (ATR) ≥7° warrants radiographic evaluation.

High-yield: Adam's forward bend test is the single best clinical screening test for structural scoliosis — it unmasks vertebral rotation (the rib hump).

Red flags mandating MRI → left thoracic curve → rapid progression → pain → neurological signs → abnormal abdominal reflexes → atypical (very early) age of onset.

Diagnosis & investigation of choice

• Investigation of choice (initial/standard): a standing full-length (whole-spine) PA and lateral radiograph. The PA (rather than AP) projection is preferred to reduce breast/gonadal radiation in young girls.
• MRI is reserved for atypical features (see red flags) to exclude intraspinal anomalies.
• CT helps delineate complex congenital bony anomalies and for surgical planning.

Measuring the curve — Cobb angle

The Cobb angle is the gold-standard measurement of curve magnitude:

1. Identify the upper end vertebra (most tilted toward the concavity at the top) and draw a line along its superior endplate.
2. Identify the lower end vertebra and draw a line along its inferior endplate.
3. Erect perpendiculars to these two lines.
4. The angle between the perpendiculars (= angle between the two endplate lines) is the Cobb angle.

High-yield: The Cobb angle quantifies curve severity and dictates management thresholds — memorise: observe <20–25°, brace 25–40° (in a skeletally immature patient), operate >45–50°.

Assessing rotation — Nash-Moe & Risser

• Nash-Moe method: grades vertebral rotation (0–IV) by the position of the pedicle shadow relative to the vertebral body on the AP film.
• Risser sign: grades skeletal maturity by ossification and fusion of the iliac apophysis, graded 0–5. It is the key prognostic indicator for residual growth and risk of progression.

Risser grade	Iliac apophysis ossification	Meaning
0	No ossification	Maximal remaining growth — highest progression risk
1	25%	Significant growth left
2	50%	Approaching peak growth velocity
3	75%	Growth slowing
4	100% (not yet fused)	Near maturity
5	Apophysis fused to ilium	Skeletal maturity reached

High-yield: Progression risk is highest at low Risser grades (0–1) and large curves. Once Risser 4–5 is reached, large progression is unlikely — bracing has little role after maturity.

King-Moe & Lenke classification (curve patterns)

The King-Moe classification describes thoracic AIS curve patterns (Types I–V) to guide selective fusion levels:

• Type I: S-shaped, lumbar curve larger/less flexible than thoracic.
• Type II: thoracic larger than lumbar (both cross midline).
• Type III: thoracic curve only (lumbar does not cross midline) — the most common King-Moe pattern.
• Type IV: long thoracic curve, L4 tilts into it.
• Type V: double thoracic (structural upper thoracic).

The Lenke classification (six curve types + lumbar modifier A/B/C + sagittal thoracic modifier) is the modern, comprehensive system that has largely superseded King-Moe for surgical planning.

Management & treatment thresholds

Management is driven by three variables: curve magnitude (Cobb), skeletal maturity (Risser/age), and curve type.

Stepwise approach (AIS): Diagnose with Cobb angle → assess maturity (Risser) → stratify risk → choose observe vs brace vs surgery → monitor with serial radiographs.

Cobb angle	Skeletal maturity	Management
<20–25°	Any	Observation — serial radiographs every 4–6 months while growing
25–40° (≈20–40°)	Immature (Risser 0–2, growth remaining)	Bracing (TLSO / Milwaukee)
25–45°	Mature	Observation (bracing futile after maturity)
>45–50°	Any	Surgery — posterior spinal fusion with instrumentation

Bracing

• Goal of bracing is to PREVENT progression, NOT to correct an existing curve.
• Indicated in the skeletally immature patient with a curve ~25–40° (or a progressing curve documented to worsen ≥5°).
• Boston brace / TLSO (thoracolumbosacral orthosis) — underarm brace for curves with apex at or below T7–T8.
• Milwaukee brace (CTLSO) — a cervicothoracolumbosacral orthosis with a neck ring, used for high thoracic curves (apex above T8).
• Efficacy is dose-dependent on wear time (the BrAIST trial showed ~18+ hrs/day significantly reduced progression to the surgical threshold).

High-yield: Bracing halts progression, it does not reduce the curve. It only works in a growing (skeletally immature) spine.

Surgery

• Indication: curve >45–50° in the immature, or progressive/large curves in the mature; severe cosmetic deformity; cardiopulmonary compromise (severe thoracic curves restrict lung volume).
• Procedure of choice: posterior spinal fusion with segmental pedicle-screw instrumentation (modern derivative of Harrington/Cotrel-Dubousset rod systems). Anterior approaches are used for selected thoracolumbar/lumbar curves.
• Congenital scoliosis: early surgery (e.g., hemivertebra excision, in-situ fusion, or growth-modulating rods) because curves progress relentlessly; bracing is ineffective for the rigid bony anomaly. For young children with rapidly progressive curves, growing-rod constructs / VEPTR allow trunk and lung growth.
• Neuromuscular scoliosis: long fusion to the pelvis to correct pelvic obliquity and restore sitting balance.

High-yield: Congenital scoliosis does not respond to bracing — the deformity is in the bone. A unilateral unsegmented bar carries the worst prognosis and warrants early surgery.

Complications

• Cardiopulmonary: large thoracic curves (>60–70°) cause restrictive lung disease and, eventually, cor pulmonale.
• Progressive deformity & cosmetic disfigurement, with body-image and psychosocial impact.
• Back pain and accelerated degenerative changes in adulthood.
• Surgical complications: the most feared is neurological injury (paraplegia) — hence intra-operative neuromonitoring (SSEP/MEP) and the Stagnara wake-up test are used. Others: pseudarthrosis, infection, instrumentation failure, crankshaft phenomenon (continued anterior growth after isolated posterior fusion in very young children), and proximal junctional kyphosis.

Key differentials

The most important NEET PG differential is Scheuermann's kyphosis versus scoliosis, and distinguishing structural from postural curves.

Feature	Adolescent idiopathic scoliosis	Scheuermann's kyphosis
Plane of deformity	Coronal (lateral) curve + rotation	Sagittal — fixed thoracic kyphosis (round back)
Defining criterion	Cobb angle ≥10° (coronal)	≥3 adjacent vertebrae wedged ≥5° each
Hallmark X-ray sign	Rotation, lateral curve	Anterior vertebral wedging, Schmorl's nodes, endplate irregularity
Flexibility	Structural (rib hump on bending)	Rigid kyphosis, does not correct on extension
Typical pain	Usually painless	Often painful at apex

High-yield: Scheuermann's kyphosis = rigid thoracic round-back with ≥3 contiguous vertebrae wedged ≥5°, plus Schmorl's nodes and endplate irregularity. This wedging criterion is the classic distinguishing fact.

Other differentials: postural (functional) scoliosis from leg-length discrepancy (corrects on sitting/lying — equalise with a heel raise), painful scoliosis from osteoid osteoma (night pain relieved by NSAIDs/aspirin), and vertebral osteomyelitis/TB (Pott's spine) producing a sharp angular gibbus kyphosis rather than a smooth scoliotic curve.

Mnemonics & named eponyms

• Causes of scoliosis — "SCID": Syndromic, Congenital, Idiopathic, Degenerative/neuromuscular.
• Risser "fifth = fused" — Risser 5 means the iliac apophysis is fused, i.e., skeletal maturity.
• Treatment ladder — "20-40-45": observe up to ~20°, brace 20–40°, operate >45° (in the immature spine).
• Eponyms to recognise: Cobb angle, Risser sign, Nash-Moe rotation, Adam's forward bend, King-Moe / Lenke patterns, Milwaukee / Boston braces, Harrington / Cotrel-Dubousset rods, Stagnara wake-up test.

Recently asked / exam angle

• "Cobb angle ≥ ___ defines scoliosis" → 10°.
• "Best clinical test for scoliosis" → Adam's forward bend test (detects rotation/rib hump).
• "Risser sign assesses" → skeletal maturity via iliac apophysis ossification (grade 5 = fused).
• "Indication for bracing in AIS" → curve ~25–40° in a skeletally immature patient; goal is to prevent progression, not correct.
• "Surgical threshold" → Cobb >45–50° → posterior spinal fusion.
• "Left thoracic curve in a child — next step?" → MRI to exclude syrinx/intraspinal pathology.
• "Most common type of idiopathic scoliosis" → adolescent, classically right thoracic in girls.
• "Congenital scoliosis with worst prognosis" → unilateral unsegmented bar.
• "Wedging of ≥3 vertebrae by ≥5°" → diagnostic of Scheuermann's kyphosis (a common distractor).
• "Most feared complication of scoliosis surgery" → neurological injury; monitored by SSEP/MEP and Stagnara wake-up test.
• Image-based: identifying the Cobb angle measurement technique or Risser grade on a pelvis film.

Rapid revision

1. Scoliosis = Cobb angle ≥10° with vertebral rotation; <10° is mere asymmetry.
2. Adolescent idiopathic scoliosis is commonest — right thoracic curve, adolescent girl.
3. Cobb angle = angle between superior endplate of the upper end vertebra and inferior endplate of the lower end vertebra.
4. Risser sign grades maturity by iliac apophysis ossification (0 = none, 5 = fused).
5. Nash-Moe uses the pedicle position to grade vertebral rotation.
6. Treatment: <20° observe, 20–40° brace (if immature), >45° operate.
7. Bracing prevents progression but never corrects; works only in a growing spine.
8. Boston/TLSO for apex ≤T7; Milwaukee (CTLSO) for high thoracic curves.
9. Congenital scoliosis (hemivertebra / unsegmented bar) is brace-resistant → early surgery; unilateral bar = worst prognosis.
10. Neuromuscular scoliosis = long C-curve with pelvic obliquity → fuse to the pelvis.
11. Left thoracic curve, pain, or neuro signs → MRI to rule out syrinx/cord pathology.
12. Scheuermann's kyphosis = rigid round-back with ≥3 vertebrae wedged ≥5° + Schmorl's nodes; do not confuse with scoliosis. Surgical risk: paraplegia, monitored by Stagnara wake-up test.