How Does a Varus Deformity of the Humeral Head Affect Elevation Forces and Shoulder Function? A Biomechanical Study With Human Shoulder Specimens
Bibliographic record
Abstract
OBJECTIVES: A biomechanical study was performed to test the hypothesis that a varus deformity of the humeral head decreases supraspinatus (SSP) efficiency and increases deltoid elevation forces in human specimens. METHODS: Twenty-four fresh-frozen human shoulder specimens were prepared by preserving the rotator cuff and deltoid. A defined, medial closed-wedge osteotomy was performed and lateral locked plate applied to simulate a varus deformity of 45° in Group I (n = 8) and 20° in Group II (n = 8). The control group (n = 8) was not osteotomized. The effect of the deformities on arm elevation forces was measured in a robot-assisted shoulder simulator under a physiologically loaded rotator cuff during three elevation phases. Phase 1 encompassed 0° to 30°, Phase 2 was from 30° to 60°, and Phase 3 included 60° to 90° of shoulder elevation. RESULTS: SSP efficiency, defined as the degree of elevation attained per unit muscle force, was significantly less in Group I compared with Group II (P = 0.036) and the control group (P = 0.039) (Group I = 0.12 ± 0.03°/N, Group II 0.18 ± 0.05°/N, and control group 0.24 ± 0.10°/N). Under physiological loading of the rotator cuff, the deltoid (DELT) elevation forces were significantly greater in Group I (Pphase 1 = 0.015, Pphase 3 = 0.001) and Group II (Pphase 1 = 0.015, Pphase 3 = 0.006) compared with the control group in elevation Phase 1 (Group I: 3.20 ± 1.04 N/°, Group II: 3.03 ± 0.96 N/°, control group: 2.01 ± 0.53 N/°) and Phase 3 (Group I: 2.50 ± 0.85 N/°, Group II: 1.55 ± 0.28 N/°, control group: 1.21 ± 0.18 N/°). When the SSP was unloaded, the DELT elevation forces were significantly greater in Group l than in Group II (P = 0.040) and the control group (P = 0.004) during elevation Phase 3 (Group I: 2.12 ± 0.60 N/°, Group II: 1.47 ± 0.34 N/°, control group: 1.24 ± 0.32 N/°). CONCLUSIONS: A varus deformity of the humeral head changes the pretension of the rotator cuff and results in a significantly decreased SSP efficiency (45° varus) and significantly higher arm elevation forces (20° varus). Clinically, the study's findings are relevant because they indicate that varus deformities of more than 20° should not be accepted intraoperatively and might indicate the need for surgical correction in case of subsequent symptoms.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 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) | 0.000 | 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 teacher head, 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".