Background. Using flexible tethering techniques, porcine models of scoliosis have been previously described. These scoliotic curves showed vertebral wedging but very limited axial rotation. In some of these techniques, a persistent scoliotic deformity was found after tether release. The possibility to create severe progressive true scoliosis in a big animal model would be very useful for research purposes, including corrective therapies. Methods. The experimental ethics committee of the main institution provide the approval to conduct the study. Experimental study using a growing porcine model. Unilateral spinal bent rigid tether anchored to two ipsilateral pedicle screws was used to induce scoliosis on eight pigs. Five spinal segments were left between the instrumented pedicles. The spinal tether was removed after 8 weeks. Ten weeks later the animals were sacrificed. Conventional radiographs and 3D CT-scans of the specimens were taken to evaluate changes in the coronal and sagittal alignment of the thoracic spine. Fine-cut CT-scans were used to evaluate vertebral and disc wedging and axial rotation. Results. After 8 weeks of rigid tethering, the mean Cobb angle of the curves was 24.3 ± 13.8 degrees. Once the interpedicular tether was removed, the scoliotic curves progressed in all animals until sacrifice. During these 10 weeks without spinal tethering the mean Cobb angle reached 50.1 ± 27.1 degrees. The sagittal alignment of the thoracic spine showed loss of physiologic kyphosis. Axial rotation ranges from 10 to 35 degrees. There was no auto-correction of the curve in any animal. A further pathologic analysis of the vertebral segments revealed that animals with greater progression had more damage of the neurocentral cartilages and epiphyseal plates at the sites of pedicle screw insertion. Interestingly, in these animals with more severe curves, compensatory curves were found proximal and distal to the tethered segments. Conclusions. Temporary interpedicular tethering at the thoracic spine induces severe scoliotic curves in pigs, with significant wedging and rotation of the vertebral bodies. As detailed by CT morphometric analysis, release of the spinal tether systematically results in progression of the deformity with development of compensatory curves outside the tethered segment. The clinical relevance of this work is that this tether release model will be very useful to evaluate both fusion and non-fusion corrective technologies in future research. Level of Evidence. Not apply for experimental studies

The aim of this study was to report the restauration of the normal vertebral morphology and the absence of curve progression after removal the instrumentation in AIS patients that underwent posterior correction of the deformity by common all screws construct whitout fusion. A series of 36 AIS immature patients (Risser 3 or less) were include in the study. Instrumentation was removed once the maturity stage was complete (Risser 5). Curve correction was assessed at pre and postoperative, before instrumentation removal, just post removal, and more than two years after instrumentation removal. Epiphyseal vertebral growth modulation was assessed by a coronal wedging ratio (WR) at the apical level of the main curve (MC). The mean preoperative coronal Cobb was corrected from 53.7°±7.5 to 5.5º±7.5º (89.7%) at the immediate postop. After implants removal (31.0±5.8 months) the MC was 13.1º. T5–T12 kyphosis showed a significant improvement from 19.0º before curve correction to 27.1º after implants removal (p<0.05). Before surgery, WR was 0.71±0.06, and after removal WR was 0.98±0.08 (p<0.001). At the end of follow-up, the mean sagittal range of motion (ROM) of the T12-S1 segment was 51.2±21.0º. SRS-22 scores improved from 3.31±0.25 preoperatively to 3.68±0.25 at final assessment (p<0.001). In conclusion, fusionless posterior approach using a common all pedicle screws construct correct satisfactory scoliotic main curves and permits removal of the instrumentation once the bone maturity is reached. The final correction was highly satisfactory and an acceptable ROM of the previously lower instrumented segments was observed