A biomechanical investigation of the surface strains on the acromion and scapular spine during simulated ex-vivo arm motion
Bibliographic record
Abstract
While several biomechanical investigations have measured acromion and scapular spine strains for various pathological conditions to better understand the risk factors for fracture, no study has measured strains in the native shoulder. The objective of this study was to use an ex-vivo shoulder motion simulator to measure principal strain during continuous, unconstrained, muscle-driven motion of the native shoulder. Eight cadaveric specimens (57 ± 6 years) were used to simulate scapular plane abduction (27.5 to 80° of humerothoracic elevation), forward flexion (27.5 to 72.5° of humerothoracic elevation), external rotation (0 to 40° of external rotation), and circumduction (elliptical path) with glenohumeral rotation speeds of 10°/s. Principal strain was measured throughout motion in four clinically relevant regions of the scapular spine and acromion according to the Levy classification using tri-axial strain gauge rosettes. Increases in humeral elevation during scapular plane abduction and forward flexion were associated with increases in deltoid force and scapula strain. However, above approximately 60° of humerothoracic elevation, strains plateaued while deltoid forces continued to increase indicating that scapula strain patterns are influenced by deltoid force magnitude and direction. Scapula strain was higher during scapular plane abduction than forward flexion in all regions but was only significantly higher in Levy 3B (p = 0.038). The highest strains were observed in Levy regions 2 and 3A (p ≤ 0.01) which correspond to regions with the highest clinically observed fracture rates demonstrating that the shape of the acromion and scapular spine may influence strain distribution irrespective of the joint condition.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| 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".