Inclusion of Glenoid Anteversion Provides a More Accurate Assessment of Glenoid Stability Using a Measuring Protocol for the Modified Bony Shoulder Stability Ratio.

Purpose: To clarify whether there is a disparity between the conventional bony shoulder stability ratio (cBSSR) calculated using the method of Moroder et al. and the stability ratio (SR) obtained biomechanically and whether the modified bony shoulder stability ratio (mBSSR) calculated using the modified method, adjusted for glenoid anteversion, shows good consistency with the biomechanically determined SR.

Methods: Forty-two glenoid models were successively constructed from seven cadaveric scapular bones, each with varying degrees of bone defect (intact condition and 2-, 4-, 6-, 8-, and 10-mm defects). The cBSSR and mBSSR were calculated using the conventional and modified radiologic protocols, respectively. A biomechanical experiment was conducted to measure the biomechanical SR of the glenoid model for accuracy validation. Linear regression analysis, intraclass correlation coefficient (ICC) calculation, Bland-Altman plot generation, and repeated-measures analysis of variance were performed to compare these methods to ascertain the impact of including glenoid anteversion on the accuracy of the bony shoulder stability ratio (BSSR).

Results: The mBSSR, which included glenoid anteversion, showed a stronger correlation with the biomechanical SR compared with the cBSSR. Linear regression analysis showed R = 0.7727 and ICC = 0.726 for the mBSSR versus the biomechanical SR and showed R = 0.5507 and ICC = 0.363 for the cBSSR versus the biomechanical SR. Bland-Altman analysis revealed less bias between the mBSSR and biomechanical SR (bias, 0.0854; 95% confidence interval, -0.0762 to 0.2470) than between the cBSSR and biomechanical SR (bias, 0.1899; 95% confidence interval, 0.0039 to 0.3759). Repeated-measures analysis of variance confirmed a significant difference between the cBSSR and biomechanical SR (P = .002).

Conclusions: The inclusion of glenoid anteversion in mBSSR calculations provides a more accurate assessment of glenoid stability. Our findings indicate the need to consider anteversion adjustments in BSSR estimation.

Clinical Relevance: Our research identified that conventional methods did not take glenoid anteversion into account. Through our comprehensive biomechanical experiment, we have shown that incorporating glenoid anteversion in the BSSR calculation yields a more precise assessment of glenoid stability, which can provide a crucial methodologic foundation for clinical assessment.