Early Onset Scoliosis (EOS)

Early Onset Scoliosis is a time-based definition (Age less than 10). It encompasses a heterogeneous group of diagnoses.

• Pulmonary Impact: The primary concern is Thoracic Insufficiency Syndrome (TIS).
  • Alveoli multiply rapidly until age 8.
  • Severe deformity restricts lung volume, leading to restrictive lung disease to Pulmonary Hypertension to Cor Pulmonale to Early Death.
• Epidemiology:
  • Infantile Idiopathic: Rare (under 1% of all idiopathic scoliosis in most series). Male predominance. Left-sided thoracic curves are typical. Higher incidence historically reported in Europe than North America.
  • Juvenile Idiopathic: Female predominance. Right-sided thoracic curves (like AIS). Progression is common and often relentless without treatment.

The Mehta Angle (Rib-Vertebral Angle Difference - RVAD) This is the angle between the rib neck and the vertebral body.

• Measured at the apical vertebra.
• Calculation: RVAD = Angle on Concave side - Angle on Convex side.
• Significance:
  • Less than 20 degrees: 80% chance of spontaneous resolution. (Resolving).
  • Greater than 20 degrees: 80% chance of progression. (Progressive).

Rib Head Phases (Mehta)

• Phase 1: Prominent gap between rib head and vertebral body.
• Phase 2: Rib head overlaps the vertebral body. Indicates progression.

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Genetic Testing:

• Consider if syndromic features present (Microarray).

• Bracing: Most growing rod patients wear a brace post-op to protect the anchors.
• Physio: Essential to maintain flexibility (auto-fusion prevention).
• Follow-up: Lengthening schedule (MCGR: Clinic every 3 months. TGR: Surgery every 6 months).

• Pulmonary: The main goal is survival. Early fusion (less than age 5) results in severe TIS and death. Delaying fusion until age 10-12 significantly improves pulmonary volume.
• Deformity: complete correction is rarely the goal. "Control" is the goal.
• Final Fusion: Usually performed at skeletal maturity (Age 12-14 females, 14-16 males) to lock in the correction.

Global epidemiology

• EOS is a heterogeneous, time-based group (onset under age 10). Idiopathic infantile scoliosis accounts for under 1% of idiopathic curves in most series, with historically higher reported rates in Europe than North America. Congenital and neuromuscular aetiologies dominate the structural/progressive end of the spectrum worldwide.

Society guidance, side by side

Registry and multicentre evidence

• Practice is driven largely by multicentre prospective EOS registries (e.g. the Pediatric Spine Study Group / Growing Spine Study Group datasets) rather than national arthroplasty-style registries, given device diversity and small numbers. These cohorts underpin the data on dual-rod growth rates, MCGR diminishing returns, and complication profiles.

High- vs limited-resource practice variation

• High-resource settings: ready access to whole-spine MRI, MCGR (avoiding repeated open lengthenings), VEPTR, intraoperative neuromonitoring and multidisciplinary paediatric pulmonology/spine teams.
• Limited-resource settings: greater reliance on serial casting and traditional growing rods (lower implant cost but repeated GA), with MRI and MCGR access constrained. Halo-gravity traction is a valuable low-cost adjunct for severe rigid curves. Late presentation with established thoracic insufficiency is more common.

1. The Law of Diminishing Returns With traditional growing rods, every time you go in to lengthen (every 6 months), the spine gets stiffer (auto-fusion). By the time you do the final fusion, the spine may already be fused in a less-than-perfect position. MCGR helps avoid this "Law of Diminishing Returns" by avoiding open surgery.

2. Crankshaft Phenomenon If you fuse the posterior elements (or they auto-fuse) but the anterior vertebral body growth plates remain open, the spine will twist and rotate as it grows anteriorly.

• Prevention: In young children (less than 10), definitive fusion often requires Anterior and Posterior fusion to stop all growth centers.

3. Hemiepiphysiodesis For a congenital hemivertebra:

• You can fuse the convex side (epiphysiodesis). The concave side continues to grow, potentially correcting the curve over time.
• Or: Resect the hemivertebra entirely (more aggressive, better correction).

The topic lists growing rods, MCGR, VEPTR, Shilla and convex hemiepiphysiodesis as a flat menu, but the examiner's organising framework - that every growth-friendly implant works by one of three mechanisms - is never assembled. Knowing the category explains how each device behaves over time and how to choose between them.

So the device choice follows the curve: a large, progressive curve needs the corrective power of distraction; a curve where repeated surgery is undesirable may suit growth-guidance; and a small, flexible curve with lots of growth left is the candidate for compression/growth-modulation. The distinction also explains the named behaviours elsewhere in this topic - the "law of diminishing returns" and auto-fusion belong to the distraction category, while convex hemiepiphysiodesis (used for the congenital hemivertebra) is the compression category.

The topic repeatedly relies on the concept of "anchors" - anchor pull-out, hooks versus screws, "rib-to-rib or rib-to-spine", the rib-based versus spine-based debate, "extending fixation to ribs or pelvis", and avoiding proximal junctional kyphosis - but never explains the foundation concept that ties them together. A growth-friendly construct needs a stable proximal foundation and a stable distal foundation, each with several anchor points, bridging the deformity.

The foundation choice is a series of trade-offs: rib versus spine proximally (spare the spine and gain thoracic expansion but risk migration/cut-out, versus hold better but risk PJK) and spine versus pelvis distally (preserve motion versus control pelvic obliquity in neuromuscular disease). The common failure modes map onto the foundations: anchor pull-out in small/osteoporotic bone (where hooks may hold better than screws), rib migration/cut-out with rib cradles, and PJK when the proximal foundation is too low or ends at a kyphotic apex. This is why a foundation uses multiple anchor points and why a salvage of failed rods often means moving the foundation (to ribs proximally, or to the pelvis distally).

• RVAD threshold: The classic 20-degree Mehta cut-off is challenged — long-term data suggest an optimal threshold nearer 17 degrees and warn against relying on a single index measurement (Lloyd et al, 2020). Serial RVAD and Cobb trends are more reliable than any one value.
• MCGR metal ions and reliability: Magnetically controlled rods reduce open lengthenings, but elevated serum titanium, actuator/pin failure, and progressive loss of distraction (a residual "law of diminishing returns") generate ongoing debate about long-term safety and true cost-effectiveness.
• Casting vs early surgery: When to abandon casting for a growth-friendly construct is not standardised. Casting can be curative if started under age 2, but late or stiff curves respond poorly.
• Rib-based vs spine-based anchors: VEPTR (rib-based) directly expands the thorax but has high migration/cutout rates; spine-based anchors give better deformity control but less direct chest-wall benefit. The optimal hybrid is unsettled.
• Graduation strategy: Whether to perform definitive fusion, "watchful waiting" with retained rods, or remove implants at skeletal maturity remains individualised, with no consensus on the best endpoint.
• Crankshaft prevention: The need for anterior growth arrest (combined anterior/posterior fusion) in very young children is debated in the era of all-pedicle-screw posterior constructs.

The Mehta Technique Min Mehta revolutionized the treatment of infantile scoliosis.

• Principle: The spine grows rapidly in the first 2 years. If you can hold it straight, the growth will correct the deformity (Hueter-Volkmann law).
• Technique:
  • General Anaesthesia.
  • Risser Table (Traction frame).
  • Derotation: Correct the rotation, not just the lateral bend. Mold over the apical rib hump.
  • Window: Cut a large anterior "mushroom" window for belly breathing (infants are diaphragmatic breathers).
• Result: Can result in a permanent cure for idiopathic curves if started early.