Dynamic behavior of the nucleus pulposus within the intervertebral disc loading: a systematic review and meta-analysis exploring the concept of dynamic disc model
Bibliographic record
Abstract
Introduction The dynamic disc model (DDM) is a theoretical framework in spine mechanics that theorizes the behavior of the nucleus pulposus within the intervertebral disc under various loads. The model predicts displacement of the nucleus pulposus away from the bending loads, for example backward displacement of the nucleus pulposus with a flexion load. These predictions are regularly used as a theoretical basis for explaining certain disc pathologies, such as disc herniation. Methods We screened seven databases (CENTRAL, Embase, MEDLINE, CINAHL, ScienceDirect, Google Scholar, and HAL) up to July 2024, identifying studies through a PRISMA-guided approach that detailed the mechanical transformation (displacement and deformation) of the nucleus pulposus under bending load on the intervertebral disc. We conducted a double-blind data extraction and quality assessment of the body of evidence. Finally, we performed a meta-analysis of proportions. Results From the 9,269 articles screened, 14 studies were included in the systematic review and meta-analysis. Magnetic Resonance Imaging (MRI) was employed in 92.8% of the studies, revealing four strategies for assessing nucleus pulposus transformation. The meta-analysis of asymptomatic subjects’ data demonstrated that the nucleus pulposus behavior aligned with dynamic disc model predictions in 85.4% (95% CI = [79.4–91.4]) across spinal regions and bending directions. However, significant heterogeneity and low study quality were noted. Only one study used discography to assess the DDM in a discogenic pain population, identifying discrepancies in nucleus pulposus transformation and contrast agent leakage. Conclusion Evidence for the dynamic disc model for intact discs is of low strength, whereas very limited evidence challenges the dynamic disc model for fissured discs. New multiparametric MRI studies may help guiding future clinical assessment protocols. Systematic Review Registration CRD42022331774.
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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 | 0.027 | 0.067 |
| Meta-epidemiology (narrow) | 0.002 | 0.001 |
| Meta-epidemiology (broad) | 0.013 | 0.023 |
| Bibliometrics | 0.010 | 0.009 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.004 | 0.002 |
| Open science | 0.002 | 0.002 |
| Research integrity | 0.002 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 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".