Congenital Scoliosis

Congenital scoliosis is a lateral curvature of the spine caused by vertebral malformations present at birth. Unlike adolescent idiopathic scoliosis the deformity is structural from the outset and often rigid, and unlike neuromuscular scoliosis the problem is in the bone rather than the muscle. Where it presents as a severe curve in a small child it becomes one of the early-onset scoliosis problems, with the growth-friendly options set out in VEPTR and growing rods.

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Who. The incidence is 0.5-1 per 1000 live births, slightly more girls than boys. Most cases are sporadic with no strong genetic pattern, though familial clusters exist, and maternal diabetes and valproic acid exposure are risk factors.

Natural history. Without treatment 75% progress, and how fast depends on the balance of growth across the anomaly: the type of defect, whether it is unilateral (unilateral anomalies progress faster), its location (thoracolumbar curves progress most), an intraspinal tether (which worsens progression) and the rapid growth phases, the first five years and the adolescent spurt. The life-threatening complication of a severe early-onset deformity is thoracic insufficiency syndrome (TIS), the inability of the thorax to support normal respiration or lung growth.

Embryology. The axial skeleton forms in the mesenchymal stage, weeks 4-6. Somites form along the notochord and then re-segment: the caudal half of one somite fuses with the cranial half of the next to form a vertebra. A failure of formation leaves a hemivertebra or wedge; a failure of segmentation leaves an unsegmented bar or block.

Formation failure is not only a hemivertebra. A butterfly vertebra is a midline sagittal cleft, two alae of body that never fused. It is a formation defect, but a balanced one, so it does not act as a growing wedge. The hemivertebra is the unbalanced cousin that drives the curve.

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Growth potential. T1-S1 lengthens by 10cm in the first five years and by another 10cm in the adolescent growth spurt. Fusing the thoracic spine early stops that vertical growth, and the loss is lung volume rather than correction: adequate adult pulmonary function needs roughly 18-22cm of T1-T12 height.

Most congenital scoliosis is sporadic, but a recognised genetic mechanism now explains a meaningful minority and is increasingly examined.

The compound-inheritance model. In roughly 10% of patients with isolated congenital scoliosis (vertebral malformation without a syndrome) the cause is a rare loss-of-function TBX6 variant, commonly a 16p11.2 microdeletion, on one allele combined with a common hypomorphic TBX6 risk haplotype on the other. This compound heterozygosity drops TBX6 dosage below the threshold needed for normal somite segmentation, and because neither allele alone causes disease the inheritance looks sporadic.

The pathway. TBX6 acts in the Notch / segmentation-clock machinery that drives somitogenesis, the same pathway whose disruption (DLL3, MESP2, LFNG, HES7) causes spondylocostal dysostosis.

Why it matters. Identifying a 16p11.2 deletion has counselling implications, since it also carries developmental and neuropsychiatric associations, and it frames congenital scoliosis as a dosage-sensitive developmental disorder rather than a purely random event.

Winter's classification is read from the radiograph and sorts anomalies by what went wrong in embryology: failure of formation (Type I), failure of segmentation (Type II) or both (Type III). Its point is urgency. The type tells you how the growth is unbalanced, and therefore how fast the curve is likely to move.

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Type I, failure of formation. The subtypes differ in how the hemivertebra is joined to its neighbours:

• Fully segmented hemivertebra: a disc space above and below, so it acts as a growing wedge. Rapid progression
• Semi-segmented: fused to one adjacent vertebra, still a wedge
• Incarcerated hemivertebra: only the pedicles are deformed and the body is set into the spine. Slow progression
• Wedge vertebra: partial formation failure

Type II, failure of segmentation. A block vertebra is a bilateral failure: stable, a short segment, and usually needs no treatment. A unilateral unsegmented bar is the dangerous one, because the fused side cannot grow while the open side does, and the spine bends towards the bar.

Type III, mixed. A combination of both. A unilateral bar with a contralateral hemivertebra is the "malignant curve": the bar tethers one side while the hemivertebra pushes growth on the other, and progression is rapid and relentless.

Two cautions about those numbers. They are thoracic rates from McMaster's series, and the same anomaly progresses more slowly in the lumbar spine, so the site modifies the figure. And no abstract is indexed for the 1982 paper, so the per-year rates rest on the full text and decades of secondary citation: the ranking is not in doubt, the decimal precision is. In a viva, give the order and the approximate rate and say "in McMaster's series" rather than implying a figure you could look up in seconds.

What triggers the operation is the observed rate, not the predicted one. The classification tells you which child to watch closely and how alarmed to be at presentation; serial radiographs at consistent intervals tell you what the curve is really doing. A fully segmented hemivertebra behaving like a bar is treated like a bar.

Look. Start with the skin over the spine (the alert below), then shoulder balance and trunk shift, the face for asymmetry (Goldenhar) and the limbs for a radial clubhand (VACTERL).

Feel. A detailed lower-limb neurological examination and the reflexes: abdominal reflexes are often absent in an extensive syrinx, and ankle clonus suggests tethering.

Ask and listen. Auscultate the heart for murmurs, ask about renal problems or urinary tract infections, and confirm anal patency.

Radiographs. Whole-spine films are the first line. Count the vertebrae, identify bars and hemivertebrae, and measure the Cobb angle.

MRI of the whole spine is mandatory before any corrective surgery, looking for a tethered cord, syrinx, diastematomyelia or Chiari malformation. See tethered cord syndrome and Chiari malformation for the other neural-axis findings the scan is looking for.

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Renal ultrasound and echocardiography are mandatory for every child; the yield, and what each is looking for, is set out under associated anomalies.

CT with 3D reconstruction is for planning once you have already decided to operate; the MRI still comes first for the cord. It shows the complex bony anatomy and the pedicle morphology for screws: count the pedicles, see whether there is a disc above and below the hemivertebra (fully segmented) and plan the screws on it.

The task is to separate congenital scoliosis, a structural vertebral malformation present at birth, from the other early-onset curves, because management and prognosis differ sharply. The defining feature is an identifiable vertebral anomaly (hemivertebra, bar, block) on plain films, not simply an early or rigid curve.

Observation. Non-progressive curves, block vertebrae and balanced deformities are watched, with a radiograph every 6-12 months during growth. Observation requires strict radiographic intervals.

Bracing. Its role is limited to none. Congenital curves are rigid and do not respond to a brace. The one exception is the compensatory curve above or below the congenital defect, which is occasionally braced to delay surgery.

Surgical strategy. Treatment is a race between curve control and lung growth, and the strategy depends on how much growth remains. The goals are to stop progression, first of all, while keeping the thoracic height that lung volume needs, preventing thoracic insufficiency syndrome and restoring the sagittal profile.

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The options:

1. In situ fusion: fuse the curve as it is to stop progression. Best for an unsegmented bar (posterior fusion of the bar). Safe and simple, but no correction, and a short segment
2. Hemivertebra excision: remove the wedge to straighten the spine, the gold standard for an L4 or L5 hemivertebra causing trunk shift. Posterior-only (eggshell) or combined anterior and posterior. Excellent correction with a short fusion, but technically demanding
3. Growth-friendly surgery for the long early-onset curve and for thoracic insufficiency, not for a single lumbar hemivertebra:
   • Growing rods: distract the spine and lengthen every 6 months
   • MAGEC rods: magnetically controlled lengthening, with no trips to theatre
   • VEPTR: rib-to-rib expansion thoracoplasty for TIS and fused ribs
   • Shilla: guided growth, the rods sliding at their ends
4. Spinal osteotomy, vertebral column resection (VCR), for the severe rigid deformity in the older child

Convex epiphysiodesis for the unilateral bar. The logic is in the anatomy: the bar has no growth plates, the contralateral side has normal ones, and the difference is what bends the spine. Stopping growth on the convex (healthy) side matches it to the concave (bar) side, and early intervention prevents the severe deformity. Through a posterior or combined anterior and posterior approach:

• Ablate the growth plates and discs on the convex side
• Apply a fusion mass
• Expect arrest of progression, and perhaps some auto-correction

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Hemivertebra excision. The indication is a lumbosacral hemivertebra causing a severe list. The logic is Ruf and Harms': take the wedge, compress a short segment and leave the rest of the spine to grow.

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Hemivertebrae. Excision yields excellent correction and balance.

Unsegmented bars. Early convex epiphysiodesis can halt progression but rarely corrects the deformity substantially.

Untreated. The curve can reach severe deformity (greater than 100 degrees), cor pulmonale, and early death from respiratory failure.

The reference series. Basu, Elsebaie and Noordeen screened 126 consecutive patients with congenital spinal deformity with MRI, echocardiography and renal ultrasound (PMID 12394903). 55% had at least one extraspinal defect: intraspinal anomalies in 37%, cardiac in 26% and urogenital in 21%. Cardiac is more common than urogenital, not less, and is often quoted far too low. The authors concluded that MRI and echocardiography "should be an essential part in the evaluation".

So every child is screened, not the selected few. A quarter of these children have a cardiac defect and auscultation will not find them all, so echocardiography is for every child at presentation, not for the one with a murmur. Renal ultrasound is ordered on diagnosis, and a whole-spine MRI before any corrective surgery. What each test is looking for:

• Intraspinal: diastematomyelia, tethered cord, syrinx, Chiari
• Cardiac: VSD, ASD, tetralogy of Fallot
• Renal: renal agenesis, horseshoe kidney
• VACTERL features on examination: imperforate anus, thumb hypoplasia (radial deficiency)

Named associations. Beyond VACTERL, the syndromes worth recognising at the bedside:

1. Klippel-Feil syndrome: fusion of cervical vertebrae, with the triad of low hairline, short neck and limited neck movement
2. Goldenhar syndrome: hemifacial microsomia, auricular tags and congenital scoliosis
3. Diastematomyelia: a split cord malformation in which a bony or fibrous spur divides the cord

Congenital vertebral anomalies also deform the spine in the sagittal plane. Congenital kyphosis is graded by the same formation-versus-segmentation logic but carries a distinct and dangerous complication: it is the commonest congenital cause of paraplegia. It also has the highest intraspinal anomaly rate of any congenital spinal deformity (the MRI section below gives the figures), so the two risks compound.

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Why Type I is dangerous. The deficient vertebral body lets the kyphosis angulate acutely at the apex and drapes the cord over the deformity, so a progressive Type I kyphosis can produce a gradual spastic paraparesis. Type II, an anterior bar, is slower and rounder.

Treatment. Early posterior fusion can arrest a small Type I curve in a very young child; an established or larger deformity needs combined anterior and posterior fusion, with anterior decompression if neurology is present. Bracing does not work.

Global epidemiology:

• Incidence approximately 0.5-1 per 1000 live births worldwide; one of the commonest causes of structural scoliosis presenting in infancy.
• Largely sporadic; environmental contributors (maternal pregestational diabetes, valproate, gestational hypoxia/carbon monoxide in experimental models) and genes affecting somitogenesis (e.g. the Notch/segmentation-clock pathway, TBX6 in spondylocostal/multiple-vertebral-segmentation phenotypes) are implicated.
• Slight female predominance; high rate of associated VACTERL, intraspinal, cardiac and renal anomalies across all populations.

Side-by-side guidance (no single national standard exists for this rare condition; principles are shared):

When to operate on a hemivertebra. Early excision at age 2-4 gives a short fusion and lets the compensatory curves self-correct, but it carries the anaesthetic and neurological risk of operating on tiny pedicles, and some advocate watchful waiting until progression is documented. The balance shifts toward earlier surgery for the fully segmented lumbosacral hemivertebra causing trunk decompensation.

MAGEC versus traditional growing rods. Magnetically controlled rods avoid repeated open lengthenings and anaesthetics, but face metallosis, titanium wear debris, lock-pin failure and the same law of diminishing returns. Whether they truly reduce total complications is still debated, and the question is tracked by early-onset-scoliosis collaboratives rather than by randomised trials.

Prophylactic anterior fusion for crankshaft. Whether routine anterior fusion is needed to prevent crankshaft after posterior fusion in a skeletally immature child is contested; pedicle-screw constructs with a robust posterior arthrodesis may reduce the phenomenon, but not abolish it.

Tethered cord release before correction. Whether an asymptomatic low-lying conus or filum lipoma must be released before deformity correction, or simply monitored, is unsettled. A bony diastematomyelia spur is a different matter: excising it before any distraction is not controversial.