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Chapter Summary
• Context: Severe and high-angle idiopathic scoliosis represents one of the most demanding challenges in spinal deformity surgery. While a uniform angular cutoff does not exist, the entity encompasses high-magnitude, rigid curves associated with profound 3D trunk deformity and extensive anatomical distortion. The spinal cord, dysplastic pedicles, great vessels, chest wall, and paraspinal musculature are significantly displaced, sharply increasing the complexity of pedicle cannulation, corrective maneuvers, and neural protection. In many public healthcare systems, delayed access to tertiary care results in patients presenting with neglected, hyper-rigid deformities, coronal/sagittal imbalance, and severe cardiorespiratory impairment. In these high-risk scenarios, the primary surgical goal is not maximizing radiographic correction at all costs, but restoring trunk balance and pulmonary mechanics safely without exceeding the spinal cord's mechanical, vascular, and neurological tolerance.
• Chapter Objective: To establish the diagnostic, clinical, and surgical algorithms for managing severe and high-angle idiopathic scoliosis. The reader will learn to assess neurological risk factors, understand apical spinal cord morphometry and pedicle dysplasia, evaluate curve flexibility and pulmonary reserve, and master staged strategies, including halo-gravity traction, temporary internal distraction, multi-level osteotomies (PVCR vs LIEPO), and neuromonitoring safety protocols.
• Neurological risk is not defined by Cobb angle aloneSevere spinal deformities alter anatomical relationships across the chest and spine. The aorta shifts relative to the apical vertebra; thoracic pedicles exhibit severe hypoplasia or sclerosis; and the spinal cord is often displaced directly against the osseous concavity at the apex. The Sielatycki MRI classification (Figure 1) categorizes apical spinal cord morphology and CSF effacement, identifying patterns associated with heightened risk of intraoperative neuromonitoring data loss during correction. The Watanabe classification characterizes pedicle channel dysplasia, while the Deformity Angular Ratio (DAR) quantifies angular concentration over segmented levels. These tools supplement the Cobb angle in defining true risk.
• Clinical and multimodal imaging evaluationClinical assessment looks beyond standard asymmetries for gross shoulder/pelvic imbalance, severe rib humps, dyspnea, back pain in adult patients, and upper motor neuron signs indicating subclinical cord compression. Computed tomography (CT) with 3D reconstructions details pedicle morphology and facet ankylosis; full-neuraxis MRI evaluates cord compression, syrinx, and apical subarachnoid space. The authors establish CT and MRI as routine preoperative workup. Multi-positional flexibility studies (traction, suspension, bending) assess residual mobility.
• Preparing and mobilizing the curve prior to correctionFor medically fit patients, management is surgical. Preparatory strategies include preoperative halo-gravity traction, intraoperative traction, temporary internal distraction, and planned staged surgeries. Figure 2 illustrates traction timing, while Figure 3 demonstrates temporary internal distraction. In neglected adult cases with facet fusion, the authors describe a staged protocol: initial posterior release and instrumentation, followed by interval halo traction to safely loosen the curve prior to definitive correction.
• Surgical osteotomies matched to curve morphologyCombined anterior-posterior approaches have largely been supplanted by posterior-only techniques. Posterior vertebral column resection (PVCR) provides dramatic multiplanar correction, but produces major temporary spinal instability and carries high complication risks. The authors reserve PVCR primarily for sharp, short-radius angular deformities. For long-radius idiopathic curves, they advocate Lateral Intersomatic Extra Pleural Osteotomies (LIEPO), a proprietary technique providing segmental flexibility with reduced morbidity. Figures 4 and 5 contrast PVCR and LIEPO concepts. Medial pediculectomy and thoracoplasty serve as valuable adjunctive tools.
• Complication management and neuromonitoringNeurological deficit is the most critical risk, anticipated through cord morphometry, DAR, and continuous intraoperative neurophysiological monitoring (IONM). Thoracic complications (pleural tears, hemothorax) and general risks (blood loss, infection, pseudarthrosis, junctional kyphosis) require stringent perioperative protocols.
• Clinical Application: In clinical practice, surgical planning begins with estimating neurological vulnerability before applying the first corrective force. Clinical exam must screen for clonus, hyperreflexia, and sensory changes. 3D CT maps pedicle screw trajectories and identifies facet bridges; MRI evaluates whether the cord is compressed against the concave apex (Sielatycki classification). Severe pedicle dysplasia warrants skipping screws at hazardous concave levels rather than risking canal penetration. Curve correction must be executed as a gradual, multi-step process. Preoperative halo-gravity traction, wide facetectomies, temporary rod distraction, or staged releases loosen the curve, allowing gentle 3D realignment without stretching the spinal cord abruptly. Osteotomy selection must follow curve geometry: short, focal kyphoscoliotic angular curves benefit from PVCR, whereas long sweeping thoracic curves are best managed with multiple posterior column osteotomies (PCO/Ponte) or LIEPO. During corrective maneuvers, any significant drop in motor evoked potentials (MEP) or somatosensory evoked potentials (SSEP) mandates an immediate pause, restoring baseline rod contours, elevating mean arterial pressure (>80-85 mmHg), releasing excessive concave traction, or performing medial decompression if apical impingement occurs.
