Scoliosis

• Adolescent idiopathic scoliosis accounts for the large majority: onset around puberty, more often progressive in girls, typically a right thoracic curve. Painless — significant pain, a left thoracic curve, or neurological signs suggest a secondary cause (syrinx, tumour, tethered cord) and warrant MRI.
• Other categories: congenital (vertebral malformation, often with renal and cardiac anomalies), neuromuscular (cerebral palsy, Duchenne muscular dystrophy, spina bifida), and syndromic (Marfan, neurofibromatosis type 1).
• Screening and examination: the Adams forward bend test reveals a rib hump from vertebral rotation; a scoliometer quantifies trunk rotation. Also assess shoulder and pelvic asymmetry, leg length, skin findings (café-au-lait spots, midline hair tufts or dimples) and a full neurological examination.
• Progression risk is driven by remaining skeletal growth — assessed by Risser stage and menarchal status — and by curve magnitude. Curves progress most during the growth spurt.
• Management by Cobb angle, broadly: below 20–25° observation with serial radiographs; 25–45° in a skeletally immature patient, bracing, which reduces progression to the surgical threshold; above 45–50°, surgical correction with instrumented fusion.
• Large untreated thoracic curves can restrict pulmonary function.

Idiopathic (by far the most common)

• Adolescent idiopathic scoliosis (AIS): multifactorial and polygenic, with clustering in families. Onset near the pubertal growth spurt; the stem is almost always an 11–15-year-old girl noticed at a school or sports physical.
• Infantile (<3 years) and juvenile (3–10 years) idiopathic forms are far less common; early onset raises suspicion for an underlying neural axis abnormality.

Congenital (vertebral malformation in utero)

• Failure of formation (hemivertebra) or failure of segmentation (unilateral unsegmented bar). A unilateral bar with a contralateral hemivertebra has the highest progression risk.
• Because sclerotome and mesonephros develop together, congenital scoliosis carries renal and cardiac anomalies (VACTERL association) — screen with renal ultrasound and echocardiography.

Neuromuscular

• Cerebral palsy, Duchenne muscular dystrophy, spinal muscular atrophy, myelomeningocele, poliomyelitis. Loss of balanced trunk control yields a long C-shaped thoracolumbar curve with pelvic obliquity; risk correlates with non-ambulatory status.

Syndromic and other

• Marfan syndrome and neurofibromatosis type 1 (short, sharply angulated dystrophic curves), Ehlers–Danlos, skeletal dysplasias.
• Secondary structural causes: syringomyelia, Chiari I malformation, tethered cord, spinal cord tumour, osteoid osteoma (painful, night pain relieved by NSAIDs).

• Remaining skeletal growth — the single strongest predictor: low Risser stage (0–2), premenarchal status, Tanner stage, open triradiate cartilage.
• Female sex — small curves occur about equally in boys and girls, but girls are several times more likely to progress to a treatment threshold.
• Larger curve magnitude at presentation, thoracic curve location, double curves, and a positive family history.

Modifiable / potentially modifiable

• Brace wear adherence — the only well-supported modifiable determinant of outcome.
• Nutritional and bone-health factors (low BMI, low bone mineral density, vitamin D deficiency) are associated but not proven causal.
• Backpack weight, posture, and sleeping position do not cause structural scoliosis — a classic distractor.

Coupled motion is the core concept

• The spine cannot bend laterally without rotating. In a structural curve, vertebral bodies rotate toward the convexity while the spinous processes rotate toward the concavity. This is why scoliosis is a three-dimensional deformity and not simply a sideways bend.
• The ribs are rigidly attached to the vertebrae, so vertebral rotation drags the posterior ribs on the convex side backward — producing the rib hump (razorback deformity) unmasked by the Adams forward bend test. On the concave side the anterior chest wall protrudes.
• Rotation also flattens the normal thoracic kyphosis, so a typical AIS curve is a right thoracic curve with relative thoracic hypokyphosis/lordosis, further narrowing the anteroposterior chest diameter.

Why curves progress

• The Hueter–Volkmann principle: increased compressive load slows physeal growth, decreased load accelerates it. Once a curve exists, the concave side is compressed and grows less while the convex side grows more, deepening the curve — a self-reinforcing vicious cycle.
• Growth is the fuel. Progression is fastest during the peak height velocity of the adolescent growth spurt and largely stops at skeletal maturity, which is why Risser stage and menarchal status drive management decisions.
• Beyond skeletal maturity, curves greater than roughly 50° in the thoracic spine may continue to progress slowly in adulthood through asymmetric disc and facet degeneration and creep of ligamentous restraints.

Mechanism in secondary scoliosis

• Congenital: an intrinsic bony growth asymmetry (hemivertebra acts as a wedge-shaped growth plate on one side only) creates unbalanced longitudinal growth from birth.
• Neuromuscular: weak or spastic paraspinal and abdominal musculature cannot balance the trunk against gravity, so the spine collapses into a long curve with pelvic obliquity; these curves progress even after skeletal maturity.
• Syringomyelia/Chiari: asymmetric anterior horn cell dysfunction produces asymmetric paraspinal tone — hence an atypical left thoracic curve, pain, or absent superficial abdominal reflexes.

Physiologic consequence

• Severe thoracic rotation deforms the rib cage and reduces chest wall compliance, generating a restrictive ventilatory defect rather than an obstructive one.

Classic findings, each from vertebral rotation

• ***Rib hump* on the Adams forward bend test: the patient bends forward at the waist with knees straight and palms together; posterior displacement of the convex-side ribs becomes visible. A scoliometer** across the apex quantifies the angle of trunk rotation; roughly 5–7° or more is the usual threshold to obtain radiographs.
• Shoulder height asymmetry and scapular prominence: the convex-side scapula rides higher and more posteriorly.
• Asymmetric waist creases and an apparent lateral trunk shift, with uneven distance between the arms and the flanks.
• Pelvic obliquity or apparent leg-length difference — measure true leg lengths, because a real discrepancy causes a functional curve.
• Truncal decompensation: a plumb line dropped from C7 falls off the gluteal cleft, indicating coronal imbalance.

Red flags that point away from idiopathic disease

• Significant or night pain, a left thoracic curve, rapid progression, or onset before age 10.
• Neurologic signs: hyperreflexia, clonus, weakness, cavovarus foot, gait abnormality, or absent superficial abdominal reflexes — the classic clue to syringomyelia or Chiari I.
• Cutaneous stigmata: midline hairy patch, dimple, or lipoma over the lumbosacral spine (tethered cord); café-au-lait macules and axillary freckling (NF1).
• Marfanoid habitus: tall stature, arachnodactyly, joint hypermobility, ectopia lentis.

Distinguishing functional from structural scoliosis

• A curve from leg-length discrepancy, muscle spasm, or poor posture corrects on forward bending or sitting and produces no rib hump. Only structural curves rotate.

Severe or late disease

• Exertional dyspnoea and exercise intolerance from restrictive chest wall mechanics; adults may present with back pain or, in lumbar curves, radicular symptoms.

Step 1 — clinical screening

• Adams forward bend test with scoliometer is the initial screen. The USPSTF (2018) issued an I statement — insufficient evidence to recommend for or against routine screening of asymptomatic adolescents — whereas the SRS, AAOS, POSNA and AAP jointly support screening (girls at about ages 10 and 12, boys once at about 13–14). Knowing this disagreement is itself testable.

Step 2 — imaging (confirmatory)

• Standing full-length posteroanterior and lateral radiographs of the entire spine are the study of choice. PA (rather than AP) positioning reduces breast and thyroid radiation; low-dose slot-scanning (EOS) systems reduce it further. Films must be standing — supine imaging underestimates the curve.
• Cobb angle is the gold-standard measurement: draw lines along the superior endplate of the most tilted upper end vertebra and the inferior endplate of the most tilted lower end vertebra; the angle between their perpendiculars is the Cobb angle. ≥10° defines scoliosis; below that, call it spinal asymmetry.
• Skeletal maturity grading determines progression risk: the Risser sign (0–5, ossification and fusion of the iliac apophysis, progressing lateral to medial), open versus closed triradiate cartilage, and the Sanders staging system using a hand radiograph. Correlate with menarchal status and Tanner stage.
• Side-bending or traction films assess curve flexibility for surgical planning.

Step 3 — advanced imaging when atypical

• Obtain MRI of the entire neuraxis for any red flag: left thoracic curve, onset under age 10, significant or night pain, rapid progression, abnormal neurologic examination, absent abdominal reflexes, or cutaneous midline lesions. Look for syrinx, Chiari I, tethered cord, diastematomyelia, or tumour.
• Congenital scoliosis: CT best characterises the bony malformation, and because of shared embryologic timing, obtain renal ultrasound and echocardiography to screen for the associated genitourinary and cardiac anomalies.
• Pulmonary function testing for large thoracic curves to document restrictive physiology before surgery.

Observation (Cobb <20–25°, or any curve at skeletal maturity)

• Serial standing PA radiographs roughly every 6 months during the growth spurt, lengthening once Risser 4–5. Progression is defined by a meaningful increase in Cobb angle between visits (conventionally ≥5°).

Bracing (Cobb ~25–45° in a skeletally immature patient, Risser 0–2)

• Thoracolumbosacral orthosis (TLSO) such as the Boston brace; a Milwaukee (CTLSO) brace for apices above roughly T7; nighttime bending braces (Providence, Charleston) are alternatives.
• Bracing does not correct an existing curve — it prevents progression to the surgical threshold. The BrAIST trial (Weinstein et al., NEJM) showed bracing significantly reduced progression to 50° versus observation, with a clear dose–response by hours worn; targets are typically ≥18 hours/day, and adherence is the modifiable variable that matters.
• Scoliosis-specific exercise programmes (e.g. Schroth) are endorsed by SOSORT as an adjunct, not a substitute.

Surgery (Cobb >45–50°, or documented progression despite bracing, or unacceptable deformity)

• Posterior spinal instrumented fusion with pedicle screw constructs is definitive; anterior or combined approaches are used selectively.
• Vertebral body tethering is a growth-modulating, motion-sparing alternative in selected skeletally immature patients (FDA humanitarian device exemption).
• Growth-friendly constructs (traditional or magnetically controlled growing rods, rib-based distraction) for early-onset scoliosis, to preserve thoracic and pulmonary growth.
• Intraoperative neuromonitoring (SSEP and transcranial MEP) is standard.

Cause-specific caveats

• Congenital curves are bony and do not respond to bracing; hemivertebra excision or in-situ fusion is used early.
• Neuromuscular curves usually require fusion to the pelvis; bracing serves only for seating balance.

Of the disease

• Curve progression and cosmetic deformity: rib hump, truncal imbalance, and shoulder asymmetry drive psychosocial distress and body-image impairment, a well-documented outcome in adolescents and a legitimate indication for treatment.
• Restrictive lung disease: rib cage rotation and thoracic hypokyphosis reduce chest wall compliance and vital capacity. Clinically important restriction is generally confined to large thoracic curves (roughly beyond 70–80°); PFTs show reduced FVC and TLC with a preserved or increased FEV1/FVC ratio.
• Cor pulmonale and chronic hypoventilation: in very severe untreated thoracic curves, chronic hypoxaemia drives pulmonary vasoconstriction and right heart failure — a late, potentially fatal endpoint. Emergency if presenting with decompensated right heart failure or hypercapnic respiratory failure.
• Adult back pain and degenerative change: asymmetric loading accelerates disc and facet degeneration; lumbar curves may cause radiculopathy or degenerative stenosis.
• Missed secondary cause: an unrecognised syrinx or tethered cord can produce progressive myelopathy — new weakness, spasticity, or bladder dysfunction demands urgent MRI.

Of bracing

• Skin breakdown and pressure ulcers, contact dermatitis, transient reduction in vital capacity while worn, and psychological burden with poor adherence.

Of surgery

• Neurologic injury — cord traction or ischaemia during correction. Loss of MEP/SSEP signals intraoperatively triggers reduction of correction and the Stagnara wake-up test. A new postoperative deficit is a surgical emergency (epidural haematoma or cord ischaemia) requiring immediate imaging and return to theatre.
• Major blood loss, infection, and dural tear.
• Pseudarthrosis and implant failure: late recurrence of pain or loss of correction.
• Proximal junctional kyphosis above the construct.
• Crankshaft phenomenon: continued anterior vertebral growth after posterior-only fusion in a skeletally immature patient (open triradiate cartilage) causes recurrent rotational deformity.
• Superior mesenteric artery (Wilkie) syndrome: rapid spinal lengthening narrows the aortomesenteric angle and compresses the third part of the duodenum — postoperative bilious vomiting and epigastric distension; urgent recognition, decompression, and nutritional support are needed.

• The definition is a Cobb angle ≥10° with vertebral rotation. Below 10° is spinal asymmetry, not scoliosis.
• Painless right thoracic curve in an adolescent girl = idiopathic. Pain, a left thoracic curve, onset before age 10, rapid progression, or any neurologic finding → the single best next step is MRI of the neuraxis to look for syrinx, Chiari I, tethered cord, or tumour.
• Absent superficial abdominal reflexes in a scoliosis stem is the classic pointer to syringomyelia — a favourite one-line association.
• Adams forward bend test → rib hump is the screening manoeuvre; a scoliometer reading around 5–7° or more prompts a standing full-length PA radiograph, which is where the Cobb angle is measured. Supine films underestimate the curve.
• Progression risk = remaining growth × current curve size. Low Risser stage, open triradiate cartilage, and premenarchal status are the danger signs. A Risser 4–5 patient with a 30° curve needs observation, not a brace.
• Bracing prevents progression; it does not correct the curve. Indicated at roughly 25–45° in a skeletally immature patient, with benefit proportional to hours worn (BrAIST). Surgery — posterior instrumented fusion — is for curves beyond about 45–50°.
• Congenital scoliosis obliges a renal ultrasound and echocardiogram (shared embryology, VACTERL). Bracing does not work on a bony malformation.
• The screening controversy is testable: the USPSTF gives an I statement (insufficient evidence) while SRS/AAOS/POSNA/AAP endorse screening.
• Common distractors: a curve from leg-length discrepancy or muscle spasm is functional — it corrects on forward bending and has no rib hump; heavy backpacks and poor posture do not cause structural scoliosis; and in a post-fusion adolescent with bilious vomiting, think SMA syndrome, not ileus.