The relation between bulk (external) and internal measures of spinal stiffness
Bibliographic record
Abstract
BACKGROUND: While spinal stiffness is thought to be an important factor in the diagnosis and management of various spinal conditions, it is notoriously difficult to measure directly. As a result, clinicians often rely on posteroanterior palpation to estimate bulk stiffness as a proxy for the stiffness of internal spinal tissues. Unfortunately, the validity of this proxy remains uncertain. To investigate this, we posed two key research questions: (1) How do measurements of bulk stiffness correlate with direct measures of spinal stiffness? and (2) Can bulk stiffness measurements be normalized to more accurately reflect internal spinal stiffness? METHODS: This cross-sectional measurement study investigated the relation between bulk and internal spinal stiffness in a young, asymptomatic cohort. Bulk stiffness defined as external resistance of the spine measured through mechanical indentation at the L3 vertebra, while internal spinal stiffness was assessed concurrently using fluoroscopic imaging. Linear regression was used to analyze the relation between bulk and internal spinal stiffness measures. Bulk measures were then normalized using physical measurements (e.g. height, weight) and tissue volume measures of the multifidi obtained by MRI (i.e. muscle volume) and reanalyzed. RESULTS: Twenty-six persons (26) participated, with data from 7 of those being excluded due to fluoroscopic movement artifacts. Unnormalized bulk stiffness was found to correlate poorly with internal spinal stiffness (R2 = 0.1883). Normalization of bulk stiffness using factors such as body weight and multifidus muscle volume did not improve R2 values. Our results were further validated through post hoc analysis, suggesting en bloc movement of the lumbar spine. CONCLUSIONS: Raw bulk spinal stiffness values should not be used as a proxy for internal spinal stiffness as they measure unrelated constructs. Our results may help explain why bulk stiffness measures of the spine may not always align with clinical outcomes. Attempts to normalize bulk spinal stiffness to various human factors such as weight and paravertebral muscle volume did not improve the correlation between bulk spinal stiffness and internal spinal stiffness.
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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 | 0.006 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| 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".