A ratio estimating glenoid bone loss

BACKGROUND: Estimating glenoid bone loss when assessing the unstable shoulder can be challenging. The aim of this article was to describe a simple derived ratio to estimate glenoid bone loss. METHODS: When the glenoid is damaged and bone is damaged because of instability, the anterior aspect of the glenoid loses its normal curvature and becomes flattened. In geometry, this represents a chord. There are 3 assumptions for the calculations: (1) the lower glenoid is a circle; (2) there is a relationship between the glenoid height and the diameter of the glenoid circle; and (3) the length of the measured bone loss of the glenoid is a chord. Two measurements are required: glenoid height and length of the glenoid defect. The calculations involved in the ratio are reviewed. RESULTS: If the ratio of the length of the bone defect to the glenoid height is 0.5 (otherwise, 50% of the height), the estimated bone loss is 12%. CONCLUSION: Glenoid bone loss can be estimated by measuring the length of the glenoid and the length of the defect.