Adolescent Idiopathic Scoliosis — Management

Adolescent idiopathic scoliosis (AIS) is a three-dimensional structural deformity of the spine defined as a lateral spinal curvature of 10° or more (Cobb angle) with no identifiable underlying cause in patients aged 10 years to skeletal maturity. It is the most common form of scoliosis and a significant source of morbidity if untreated in progressive curves. Timely intervention with bracing or surgery can prevent progression and the need for more complex reconstructive surgery in adulthood.

• Prevalence: 2–3% of the adolescent population has curves >10°; significant curves (>20°) affect approximately 0.3–0.5%
• Female:male ratio for progressive curves: approximately 7–8:1 — girls far more likely to progress to surgical threshold
• Aetiology: genuinely idiopathic — multifactorial genetic predisposition; multiple candidate genes identified; no single causative mechanism established
• Most common curve pattern: right thoracic curve (Lenke 1) — convexity to the right in thoracic spine
• Prognosis for progression determined by: magnitude of curve at presentation, skeletal maturity (Risser grade), curve pattern, and age at onset — younger patient + larger curve + lower Risser = highest progression risk
• Pulmonary compromise: clinically significant in curves >70°; severe in curves >100° — thoracic scoliosis reduces lung volume by approximately 20 mL per degree of curvature beyond 70°

Skeletal maturity assessment is the cornerstone of management decisions in AIS. Remaining growth determines progression risk and urgency of treatment.

• Sanders classification (hand/wrist skeletal age): more sensitive for predicting peak height velocity and progression risk than Risser alone — Tanner-Whitehouse staging; particularly useful in early adolescence
• Tanner staging and menarche: girls experience peak curve progression in the 1–2 years before menarche; post-menarche girls rarely progress beyond 30°
• Triradiate cartilage closure: closed triradiate cartilage on pelvic X-ray correlates with Risser 0–1 transition and imminent peak height velocity

The Lenke classification (2001) is the standard system for describing AIS curve patterns and guides surgical fusion level selection.

• Each Lenke type has a lumbar modifier (A, B, C — based on lumbar curve relationship to CSVL) and a sagittal modifier (–, N, +)
• A structural curve must be fused; a non-structural (compensatory) curve need not be included in fusion — preserving motion segments is a key surgical goal
• Structural definition: >25° on side-bending X-ray OR >20° kyphosis in thoracic region

Management is guided by Cobb angle magnitude and skeletal maturity. The three treatment options are observation, bracing, and surgery.

• Goal of bracing: prevent curve progression to surgical threshold — does not correct existing curve; aims to hold curve magnitude until skeletal maturity
• BrAIST trial (Weinstein, NEJM 2013): bracing significantly reduces progression to surgical threshold — 72% success rate with bracing vs 48% in observation for curves 20–40° in Risser 0–2 patients; dose-response relationship — more hours = better outcomes
• Brace types: TLSO (thoracolumbosacral orthosis) — Boston brace (most common), Charleston bending brace (nighttime only), Providence brace (nighttime supine); Milwaukee brace (CTLSO) for high thoracic curves — poorly tolerated; largely abandoned
• Dosage: minimum 18 hours/day for maximal effectiveness; 13+ hours shows dose-response benefit; compliance is the primary determinant of success
• Weaning: brace weaning begins at Risser 4; completed by Risser 5 or 2 years post-menarche in girls
• Monitoring: clinical and radiographic reassessment every 4–6 months during bracing; in-brace Cobb should show correction of 50% or more — poor in-brace correction predicts failure

Posterior spinal fusion with pedicle screw instrumentation is the gold standard surgical treatment for AIS. The goal is to achieve a balanced, level fusion with maximum correction while preserving as many motion segments as possible.

• Approach: posterior spinal fusion (PSF) with pedicle screw and rod instrumentation — hybrid constructs (hooks/wires) still used in some centres but pedicle screws provide superior three-column fixation and correction
• Fusion levels: determined by Lenke classification and end vertebra levels — fuse from upper instrumented vertebra (UIV) to lower instrumented vertebra (LIV); include all structural curves; the stable and neutral vertebra concept guides distal fusion level selection
• Stable vertebra: most cephalad vertebra bisected by CSVL (central sacral vertical line) on standing AP — this is the lowest level that should be fused for lumbar curves
• Correction techniques: rod derotation, in situ rod bending, vertebral column manipulation, direct vertebral rotation (DVR) — achieve coronal and sagittal correction simultaneously
• Anterior approach: anterior spinal fusion (ASF) via VATS (thoracoscopic) or open thoracotomy — fewer fusion levels needed for thoracic curves; anterior release for rigid curves >70°; less commonly used now with advances in posterior technique
• Expected correction: posterior fusion achieves approximately 60–70% coronal correction of Cobb angle with modern pedicle screw constructs

• Intraoperative neuromonitoring (IONM): combined SSEP (somatosensory evoked potentials) + MEP (motor evoked potentials) — mandatory for all AIS correction surgery; significant signal change warrants immediate wake-up test or reversal of correction
• Wake-up test (Stagnara): intraoperative arousal to confirm lower limb neurological function; reserved for when IONM signals are inconclusive or unavailable
• Neurological injury: incidence approximately 0.5–1% with modern monitoring; most resolve; permanent paraplegia extremely rare (<0.1%)
• Implant-related: pedicle screw malposition (medial breach risks cord/nerve root); rod fracture; pseudarthrosis (5–10%)
• Proximal junctional kyphosis (PJK): kyphosis developing above UIV after surgery; incidence 5–40%; related to UIV selection and sagittal balance; symptomatic PJK requires revision
• Crankshaft phenomenon: rotation and bending of fused posterior elements due to continued anterior growth in skeletally immature patients — prevented by anterior epiphysiodesis or anterior fusion in young patients (Risser 0, open triradiate cartilage)
• Blood loss: significant in long fusions; cell salvage, tranexamic acid, and controlled hypotension are standard

• Always exclude non-idiopathic causes before labelling as AIS: left thoracic curve (unusual), painful scoliosis, rapid progression, neurological signs, cafe-au-lait spots (neurofibromatosis), axillary freckling, abnormal reflexes, or hairy patch (diastematomyelia) — any atypical feature warrants MRI of the whole spine before treatment
• Syrinx (syringomyelia) is the most common finding on MRI in "AIS" with atypical features — present in up to 26% of left thoracic curves; requires neurosurgical referral before spinal surgery
• Distal fusion level selection: stopping too short risks adding-on phenomenon (progression of unfused curve below LIV); stopping too long sacrifices motion segments unnecessarily — careful pre-operative planning with traction X-rays helps define compensatory curve flexibility
• Sagittal balance: thoracic hypokyphosis is common in AIS — restoration of normal sagittal profile (>20° thoracic kyphosis) is as important as coronal correction; flat back after surgery leads to poor clinical outcomes
• Growing rods for young children with progressive scoliosis: magnetically controlled growing rods (MCGR) used for early onset scoliosis (<10 years); allow repeated distraction without open surgery; delayed definitive fusion until growth complete

• Risser 0 + large curve = highest progression risk; Risser 5 = skeletal maturity = minimal risk
• Bracing: >18 hours/day; effective for 20–40° curves in Risser 0–2 patients — BrAIST trial proven
• Surgery: >45° in skeletally immature; >50° in any patient — curves >50° progress 1° per year in adulthood
• Lenke 1 = right main thoracic curve = most common AIS pattern
• Left thoracic curve or atypical features = MRI whole spine before treatment; exclude syrinx, tethered cord, tumour
• IONM: combined SSEP + MEP mandatory; significant change = wake-up test or correct
• Crankshaft phenomenon: continued anterior growth rotates posterior fusion; prevent with anterior epiphysiodesis in Risser 0 with open triradiate cartilage
• Stable vertebra = most cephalad vertebra bisected by CSVL = guide to distal fusion level
• Proximal junctional kyphosis: common complication after long fusion — related to UIV selection and sagittal balance restoration
• Pulmonary compromise: significant beyond 70°; severe beyond 100° — thoracic curves reduce lung volume ~20 mL per degree