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Intra- and Interobserver Reliability of the CT-Based Glenoid Arc-Angle Method Using Injured-Side and Contralateral
Susanne Strasser1, Johannes Dominikus Pallua1, Anton Aschaber1
1Department of Orthopaedics and Traumatology, Medical University Innsbruck, 6020 Innsbruck, Austria.
Diagnostics (Basel, Switzerland)
|August 13, 2026
Summary
The contralateral-reference method for measuring glenoid bone loss showed numerically higher reliability estimates than the injured-side method in patients with shoulder instability. This suggests improved measurement reproducibility for surgical planning.
Area of Science:
- Orthopedic Surgery
- Radiology
- Biomedical Engineering
Background:
- Assessing glenoid bone loss is crucial for managing anterior shoulder instability.
- The CT-based glenoid arc-angle method is used to quantify bone loss.
- Reproducibility of measurement techniques is essential for reliable clinical decision-making.
Purpose of the Study:
- To compare the intraobserver and interobserver reliability and absolute agreement of the CT-based glenoid arc-angle method.
- To evaluate two approaches for constructing the reference circle: directly on the injured glenoid versus transferring from the contralateral (healthy) glenoid.
- To assess measurement reproducibility, not diagnostic accuracy or clinical utility.
Main Methods:
- Retrospective analysis of preoperative CT scans from 31 patients with anterior shoulder instability.
- Three observers performed measurements at two time points using both the contralateral-reference and injured-side methods.
- Intraclass correlation coefficients (ICCs), Bland-Altman analysis, standard error of measurement, and minimum detectable change were used to assess reliability and agreement.
Main Results:
- The contralateral-reference method demonstrated numerically higher interobserver ICC point estimates for both defect angle (0.890 vs. 0.603) and glenoid diameter (0.900 vs. 0.812) compared to the injured-side method.
- Smaller session-related biases and lower measurement-error estimates were observed with the contralateral-reference method.
- Confidence intervals overlapped, indicating numerical differences rather than statistically significant superiority.
Conclusions:
- The contralateral-reference method yielded numerically higher reliability estimates and lower measurement errors in this cohort.
- These findings are descriptive and do not establish statistically significant superiority, diagnostic accuracy, or clinical utility.
- Limitations include a small retrospective cohort and lack of anatomical or clinical outcome validation.
