Infantile Idiopathic Scoliosis

Infantile idiopathic scoliosis is scoliosis diagnosed before the age of 3. It typically presents in the first year of life, usually noticed by the parents while bathing the child. Its demographics and natural history set it apart from adolescent idiopathic scoliosis, and the critical task is to tell the resolving curve from the progressive one.

Who and where. Boys are affected more often than girls, and the canonical curve is left thoracic. The condition is rare in North America (0.5%) and much more common in Europe and the UK, where it was historically associated with the prone sleeping position; the incidence dropped after the "Back to Sleep" campaign.

The atypical curve. A right thoracic curve in a male infant breaks the canonical pattern and is highly suspicious for a syrinx.

The alveolar-growth window. The number of alveoli, not merely their size, is laid down mainly in the first two to three years of life and continues to about age eight. A spine and thorax deformed during this window permanently limit alveolar number and thoracic volume, producing fixed restrictive lung disease that no later correction can recover. That window is the infantile age range, which is why an infantile curve carries a high pulmonary risk and an adolescent curve, with mature alveoli, does not.

Thoracic insufficiency syndrome. Campbell's term for the inability of the thorax to support normal respiration or lung growth, and the conceptual driver of early-onset, especially infantile, deformity care. The deformity itself can cause it, and so can treatment: an early definitive spinal fusion in the very young arrests thoracic growth and leaves a short, stiff, under-volume thorax.

What this makes the goal. Treatment aims to preserve thoracic height and lung growth, not merely to reduce the Cobb angle; spine surgery in the very young is really lung surgery. That is the rationale for early serial casting, which harnesses vigorous growth toward correction, and, when casting fails, for growth-friendly constructs, never an early definitive fusion. The growing-rod and VEPTR techniques are developed in the early-onset scoliosis topic.

The Mehta angle. Min Mehta described the rib-vertebral angle difference (RVAD) in 1972. The ribs attach to the vertebrae, so as the vertebra rotates, the rib on the convex side is pushed posteriorly into the hump and the rib on the concave side is pushed anteriorly.

Measuring it. On each side, the angle is taken between a line along the vertebral endplate and a line along the rib head and neck. The RVAD is the convex angle minus the concave angle; the step-by-step method is set out at the end of the page.

The rule of 20. An RVAD less than 20 degrees predicts a resolving curve, and one greater than 20 degrees a progressive curve. A Cobb angle greater than 25-30 degrees is also a predictor of progression.

Rib-head phase. In phase 1 the rib head does not overlap the apical corner of the vertebral body. In phase 2 it overlaps the vertebral body, which indicates severe rotation and pending progression.

A softer threshold than it looks. The rule of 20 is the number to quote and remains the standard cut-off, but treating it as a hard boundary between a curve that will resolve and one that will not claims more confidence than the evidence carries. A tertiary UK unit reviewed serial radiographs and modelled progression against the index RVAD. Progressive curves had significantly greater mean Cobb angle and RVAD at presentation than resolving ones, and the two correlated positively, so the RVAD is not measuring something wholly independent of curve magnitude.

The modelled cut-off. The optimal discriminating threshold in that model was 17.1 degrees, lower than the 20 degrees conventionally advocated, and the authors advise caution in predicting outcome from the index RVAD at presentation (DOI, level II). An infant at 18 degrees is not safely resolving: they sit near a threshold that at least one dataset places below the number you were taught.

What survives. The RVAD is still the best-established single radiographic predictor, 20 degrees is still the number to quote in an exam, and a phase 2 rib head still signals rotation and impending progression.

How to use it. Treat a single index RVAD as one input rather than a verdict, read it alongside Cobb magnitude and rib phase, and above all measure it serially. A curve whose RVAD is climbing over successive films tells you far more than any one value.

The two errors. Both do real damage, and not of the same kind. Falsely reassuring on a single sub-threshold RVAD wastes the alveolar growth window, and lung development lost in the first years is not recoverable; that is the graver harm. Over-calling progression commits an infant to serial casting under repeated general anaesthesia when most of these curves resolve on their own. The resolution is serial observation with a low threshold for reassessing, rather than a single decision made on the day of presentation.

Mehta and James classified infantile curves by prognosis into two types.

Double structural curves. Occasionally an infant presents with double major curves. These carry a worse prognosis, almost always progress, and have a high association with intraspinal pathology.

A diagnosis of exclusion. Infantile idiopathic scoliosis is diagnosed only once congenital causes (hemivertebra, bar) and neuromuscular causes have been ruled out. The differential below is the list to work through.

History. Confirm the age at onset, which must be under 3, and ask whether the child is reaching developmental milestones. Pain is rare, and suspicious when present.

Examination. The associations decide what to examine:

• Head: plagiocephaly (flattening of the skull)
• Neck: torticollis, with a tight sternocleidomastoid
• Spine: a left-sided prominence and its flexibility, with the child prone to assess the rotational prominence
• Hips: Ortolani and Barlow
• Neurology: tone, reflexes and clonus; the abdominal reflexes are essential

The cluster. Moulded baby syndrome, the packaging syndrome, is a constellation of asymmetric deformities attributed to intrauterine moulding or restricted fetal positioning, and historically to postnatal prone positioning before the "Back to Sleep" campaign. Its components travel together:

• Plagiocephaly (asymmetric skull flattening)
• Congenital muscular torticollis (a tight sternocleidomastoid)
• Developmental dysplasia of the hip
• Infantile (idiopathic) scoliosis
• Metatarsus adductus

They share a side. The whole spectrum reflects one direction of moulding, so the components tend to be related in side. The plagiocephaly, the head tilt of torticollis and the curve convexity cluster in the same infant and frequently relate to the same side of moulding, rather than appearing at random.

Find one, screen for the rest. Any one feature mandates a search for the others, and the one not to miss is the hip. DDH is associated in roughly 2 to 10%, so every moulded-baby infant needs Ortolani and Barlow testing and a low threshold for hip ultrasound, along with assessment of the neck for torticollis and the feet for metatarsus adductus. The relationship runs both ways: an infant referred with plagiocephaly or torticollis equally warrants a spine check.

Other associations. Intellectual disability is slightly more frequent in infantile scoliosis, and congenital heart defects are a rare association.

Postural or structural. Separate a purely postural, fully flexible curve that corrects with positioning from a true structural curve. A moulded-baby curve can be either, so it still earns the full RVAD assessment and, for curves over 20 degrees or any progression, the MRI.

Radiographs. PA and lateral views of the whole spine. Infants are usually imaged supine or sitting rather than standing. Measure the Cobb angle and the RVAD.

MRI. Whole-neuraxis MRI, from the craniocervical junction to the sacrum, is mandatory for every infant with a curve greater than 20 degrees or any progressive curve. High-quality images usually need sedation, in practice a general anaesthetic, because a feed-and-wrap scan is difficult in older infants.

The ladder. Observe the resolving curve, cast the progressive one, brace to maintain correction or in older infants, and keep surgery with growing rods as the last resort.

Observation. For an RVAD less than 20 degrees and a Cobb angle less than 30, observe with radiographs every 4-6 months, watching for the Mehta angle crossing the threshold.

Serial casting. Early derotation plastering (EDP) is the gold standard for the progressive curve, indicated for an RVAD greater than 20 degrees, a Cobb angle greater than 30, or documented progression. Results are best if casting starts before age 2, ideally at 12-18 months, and casts are changed every 8-12 weeks under general anaesthesia. A flexible curve treated early has the potential for cure, meaning complete resolution.

Growing rods. Indicated when casting fails, or when the curve is too large or stiff to cast. Magnetically controlled growing rods (MCGR) are preferred.

VEPTR. Indicated for associated rib fusions or severe thoracic insufficiency.

The steps. Mehta's technique, in order:

• General anaesthesia with intubation
• Position on a Cotrel traction frame (Risser table)
• Apply longitudinal traction
• Derotate with a posterolateral-to-anteromedial force on the rib hump, to untwist the spine
• Mould the plaster of Paris meticulously over the ribs, and over the iliac crests for grip
• Cut a large anterior "mushroom" window to let the belly expand; a posterior window for spinal cord monitoring is possible if needed but rarely done for casting

A radiograph in the cast, taken 1-2 weeks after each application, confirms the correction.

The Risser table. The frame suspends the child by the head, with a halter, and by the pelvis, giving the surgeon 360-degree access to the torso for moulding. The longitudinal traction alone provides significant correction before any rotational force is applied.

The mushroom window. Infants breathe primarily with the diaphragm and abdomen, so a tight abdominal cast will cause respiratory distress. The anterior window must be large and mushroom-shaped: wide at the bottom over the belly, narrower at the top over the sternum.

Under the arm or over the shoulder. An under-arm cast suits low thoracic and lumbar curves. Upper thoracic curves, with an apex at T6 or higher, need an over-the-shoulder cast to control the upper lever arm.

Stopping casting. Casting can stop once the curve is less than 10 degrees and the RVAD is less than 0, the concave angle now exceeding the convex. The child moves to a custom TLSO, worn full time (23 hours a day) at first and weaned gradually to night-time wear as long as the correction is maintained, with close surveillance until skeletal maturity.

Skin. Skin breakdown is the most common complication of serial casting, at the iliac crests and scapula. Pad every bony prominence (iliac crests, scapulae, clavicles, spinous processes) and cut windows that relieve pressure without losing correction. Each cast change is a chance to inspect the skin, and parents are taught to check it, keep the cast clean and dry, and recognise early signs of trouble.

Breathing. A restrictive cast can compromise an infant's diaphragmatic breathing. Watch for:

• Increased respiratory rate
• Accessory muscle use
• Poor feeding
• Irritability

Prevention is the large mushroom window and careful moulding that avoids restricting the chest. If respiratory distress is suspected, the cast comes off immediately.

When casting fails. Some curves continue to progress despite optimal casting. The risk factors for failure are:

• Initial RVAD greater than 40 degrees
• Phase 2 rib head at presentation
• Late presentation, after age 2
• An underlying syndromic or neuromuscular cause

For refractory curves, a growing-rod construct may be necessary to control the curve while preserving thoracic growth.

At home. The cast must stay dry, so the child has sponge baths only, and Moleskin or Petal tape around the edges prevents skin irritation. Abdominal pressure from the cast can worsen gastric reflux, and smaller, more frequent feeds are recommended. Casting generally does NOT delay walking, but it may make an infant top-heavy at first.

At each cast change. The clinical review coincides with the cast change under general anaesthesia. Track the RVAD and Cobb angle, and monitor weight, length and thoracic development.

The family. Serial casting places a significant burden on families. They need a clear explanation of the rationale and expected duration, written instructions for cast care and warning signs, and access to the multidisciplinary team (physiotherapy, occupational therapy, social work). Parent support groups, online resources and psychological support for the repeated general anaesthetics all help.

Resolving curves. Most infantile curves, 80-90%, resolve spontaneously, typically within the first 2-3 years of life, with observation and periodic radiographs as the only treatment. The long-term prognosis is excellent, with no residual deformity or functional limitation, and thoracic development and lung function are unaffected.

Progressive curves treated early. With optimal casting technique, 70-80% are cured, meaning the curve is brought to less than 10 degrees. Many others can be stabilised for brace management, early treatment preserves normal thoracic development, and many children avoid growing rods or fusion altogether.

Progressive curves treated late, or refractory. Untreated, a progressive infantile curve progresses relentlessly to more than 100 degrees. The consequences are thoracic insufficiency syndrome, with restricted lung development and respiratory compromise; cor pulmonale, right heart failure from chronic hypoxia; and reduced life expectancy, with a significant impact on survival if severe deformity develops.

Follow to maturity. Every child with infantile scoliosis is monitored until skeletal maturity. The curve may progress during the adolescent growth spurt, residual deformity may require bracing or surgery, pulmonary function is monitored serially for thoracic insufficiency, and care is handed over appropriately to adult services.

Global epidemiology

• Infantile idiopathic scoliosis (onset before age 3) is the least common idiopathic form, historically more frequent in Europe/UK than North America. The European incidence fell after the "Back to Sleep" campaign shifted infants away from prone sleeping.
• Male predominance and left thoracic curves are the canonical pattern - the reverse of adolescent idiopathic scoliosis (female, right thoracic).
• Roughly 80 to 90% of curves resolve spontaneously; the minority that progress carry a high risk of thoracic insufficiency if untreated.

Society guidance, side by side

Registry / collaborative evidence

• Multicentre early-onset scoliosis registries (e.g. Children's Spine Study Group, Growing Spine Study Group) underpin most modern casting and growing-rod outcome data and pool cases across institutions because individual centre volumes are low.

High- vs limited-resource practice variation

• Well-resourced settings: repeated GA for cast changes, MCGR (fewer surgical lengthenings), and dedicated multidisciplinary scoliosis clinics (surgeon, orthotist, physiotherapist, anaesthetist).
• Limited-resource settings: late presentation is common (window for cure missed); traditional growing rods or definitive fusion may be the only options; repeated anaesthesia and magnet-rod technology may be unavailable, shifting practice toward casting/bracing for as long as feasible.

• MRI for every infant, or selective screening? Dobbs (2002) found 21.7% intraspinal anomalies and recommended MRI for all curves over 20 deg; Pahys (2009) found only 13% and argued close observation may be a reasonable alternative for some. Most units still obtain whole-neuraxis MRI before committing to treatment because a normal neuro exam does not exclude pathology.
• Casting: cure vs delay. Casting can genuinely reverse flexible curves started early (Mehta, Regan), but in older or non-idiopathic children it mainly delays surgery while preserving thoracic growth (LaValva). Where the true "window" closes is debated (commonly cited as before age 2 to 2.5).
• EDF (Cotrel) vs Mehta technique. Both use traction, derotation and a flexion/derotation moment; the relative contribution of each component and the optimal cast interval (8 to 12 weeks) are not standardised.
• MCGR vs traditional growing rods vs casting-to-rods. Magnetically controlled rods reduce repeated lengthening surgery but raise concerns over metallosis, rod failure and diminishing returns ("law of diminishing returns") with repeated distractions; long-term comparative data remain limited.
• Adolescent recurrence. Apparently cured curves can recur at the adolescent growth spurt (Regan), so the duration and intensity of surveillance to skeletal maturity is unsettled.
• RVAD reliability. The Mehta RVAD rule of 20 is the classic predictor but has measurement variability; some advocate combining it with rib-head phase and serial Cobb trend rather than a single threshold.

1. Identify the Apical Vertebra: The most rotated/deviated vertebra.
2. Draw the Endplate Line: A line along the perpendicular of the vertebral body endplate.
3. Draw the Rib Line: A line bisecting the head and neck of the corresponding rib.
4. Measure the Angle: The angle between these two lines on the Convex side and Concave side.
5. Calculate: Difference = Convex Angle minus Concave Angle.
   • Example: Convex 35 deg - Concave 10 deg = RVAD 25 deg. (Progressive).