Biomechanical analysis of 3D correction and bone-screw forces as a function of rod insertion sequence and orientation relative to the sagittal plane in adolescent idiopathic scoliosis instrumentation
Bibliographic record
Abstract
BACKGROUND: In adolescent idiopathic scoliosis instrumentation, rods are typically aligned with the sagittal plane during the initial translation maneuver. Surgeons often empirically orient the rod slightly opposite to the scoliotic curve, but the optimal orientation and insertion sequence, as well as their influence on 3D correction and forces, remain unclear. This study investigates the biomechanical influence of these rod parameters on scoliosis correction. METHODS: Patient-specific multi-body biomechanical models were developed for 30 adolescent idiopathic scoliosis patients (11 hypo-, 12 normo-, 7 hyper-kyphotic thoracic curves) to simulate posterior instrumentation with a primary segmental translation correction maneuver. Rod insertion was tested in two sequences: concave side first, followed by the convex side, and vice versa. The construct included pedicle screws and 5.5-mm Cobalt-Chromium rods contoured to 45° (concave side) and 15° (convex side). Four rod orientations relative to the sagittal plane (0°, 10°, 20°, 30°) were analyzed for 3D correction and bone-screw forces. FINDINGS: Main thoracic Cobb angle correction improved significantly with rod orientations ≥20° (p < 0.01). Apical vertebral rotation and thoracic kyphosis correction were unaffected by rod orientation (p > 0.05). Bone-screw forces increased slightly but not significantly (p > 0.05) with greater rod orientation. Convex-side-first rod insertion reduced bone-screw forces during initial insertion, achieving corrections similar to the concave-first sequence. INTERPRETATION: Pre-contoured rods oriented up to 30° opposite the scoliotic curve significantly improved coronal plane correction, while maintaining similar thoracic kyphosis and vertebral rotation, with non-significant increases in bone-screw forces. Convex-side-first insertion may reduce mechanical stress during surgery.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".