An investigation of the mechanism of adjacent segment disease in a porcine spine model
Bibliographic record
Abstract
BACKGROUND: Fusion changes the biomechanics of the spine leading to the potential development of adjacent segment disease. Despite many studies on adjacent segment disease, it is largely unknown how spinal fixation affects the mechanical properties of the adjacent disc. The purpose of this study was to assess whether axial compression causes mechanical disruption to the annulus when the caudal spinal level is immobilized or injured. METHODS: Fifty-two porcine spines were assigned to one of four conditions: 1) control; 2) injured (18.5-gauge needle inserted into the nucleus of cervical 4/5); 3) immobilized (18-gauge steel wire wrapped around the transverse and spinous processes of cervical 4/5); and 4) injured+immobilized. Each specimen was then subjected to 0.5 Hz cyclic compression (300-1200N) for two hours. Post-compression, three annular samples were dissected from the cervical 3/4 disc (adjacent to immobilized and/or injured level) and mechanically tested. The same loading protocol and annular testing was also conducted in eight human cadaveric lumbar spines. FINDINGS: Immobilization and injury resulted in a reduction in adjacent disc lamellar strength including toe region stress (p < 0.001), initial failure stress (p = 0.03), and ultimate stress (p = 0.004), with immobilization having the greatest impact. Similar findings were observed in the human cadaver samples with reduced toe region strength in the injured+ immobilized samples compared to the control (p = 0.049). INTERPRETATION: The current study provides empirical evidence of decreased lamellar strength in the disc adjacent to an immobilized and/or injured level following prolonged cyclic axial loading, lending mechanistic insight into the development of adjacent segment disease.
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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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 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".