A new uniplanar correction strategy for severe thoracic kyphoscoliosis: concept, device design, and simulation with a...

To introduce a novel uniplanar correction concept-termed the kyphoscoliosis plane (KSP); and evaluate the feasibility of a purpose-designed external hinge (EH) correction system for vertebral column resection (VCR) in severe thoracic kyphoscoliosis using 3D-printed life-size models.

Seven life-size 3D-printed thoracic spine models were generated from CT scans of severe thoracic kyphoscoliosis patients (2 girls, 5 boys; mean age: 10.6 ± 3.7 years). The mean preoperative scoliosis and kyphosis angles were 88.1° ± 27 and 117.1° ± 22.4, respectively. Curve apices were located in the upper thoracic (T4-T7, n = 4), middle thoracic (T9-T10, n = 2), and lower thoracic (T11, n = 1) regions. The EH system, comprising a dual-axis hinge, L-shaped clamps, and a threaded reduction rod, was applied to simulate VCR correction. Pre- and post-correction measurements included Cobb angles, resection gap dimensions, apical spinal cord translation, and apical spinal cord length.

Scoliosis improved to 19.1° ± 9.7° (78.3% correction) and kyphosis to 22.7° ± 13° (80.6% correction). At the resection gap, the concave side elongated by 52%, the convex side was reduced by 66.4%, and the anterior aspect elongated by 18.2%. The KSP remained stable, with only a 1 ± 2.9° (1.8%) change. Apical spinal cord length decreased by just 1.4 ± 1.5 mm (6.7%), indicating minimal spinal cord strain. Apical spinal cord translation averaged 55.7 ± 3.3 mm along the KSP, corresponding to a 57% reduction in both coronal and sagittal displacement.

The KSP concept and EH system provide a controlled and effective uniplanar strategy for achieving 3D correction in severe thoracic kyphoscoliosis, particularly during VCR, while minimizing spinal cord tension.