Study compares Impact of Glenoid concavity vs size of a bony
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Surgical treatment of shoulder instability caused by anterior glenoid bone loss is based on a critical threshold of the defect size. Recent studies indicate that the glenoid concavity is essential for glenohumeral stability. The aim of this study was to evaluate whether glenoid concavity allows a more precise assessment of glenohumeral stability than the defect size alone.

The stability ratio (SR) is a biomechanical measure of the stability of the glenohumeral joint. It's the maximum dislocating force a joint can withstand as compared to a medial compression force. Bony defects were gradually developed, and morphometric measurements were taken with a 3D measuring arm. Using linear models, the impact of defect size and concavity on the SR was investigated. The morphometrical-based bony shoulder stability ratio (BSSR) was also tested to see whether it could be used to estimate glenohumeral stability regardless of defect size.

--Glenoid concavity is a significant predictor for the SR, while the defect size provides minor informative value.

--The linear model featured a high goodness of fit with a determination coefficient of R2=0.98, indicating that 98% of the SR is predictable by concavity and defect size.

--The low mean squared error (MSE) of 4.2% proved a precise estimation of the SR.

--Defect size as an exclusive predictor in the linear model reduced R2 to 0.9 and increased the MSE to 25.7%.

--Furthermore, the loss of SR with increasing defect size was shown to be significantly dependent on the initial concavity. The BSSR as a single predictor for glenohumeral stability led to highest precision with MSE=3.4%.

Finally, Glenoid concavity is a significant element in the SR. The computed BSSR is an accurate biomechanical approximation of the calculated SR, regardless of defect size. The inclusion of glenoid concavity has the potential to influence clinical decision-making in the treatment of glenohumeral instability with anterior glenoid bone loss, resulting in a more personalized and effective outcome.