A Novel Proportional Method for the Simplified Assessment of Glenoid Bone Loss in Patients With Anterior Shoulder Instability

Background: Surgical planning for anterior shoulder instability (ASI) necessitates accurate measurements of glenoid bone defects, but current methods are either challenging or too complex for practical use. This underscores the need for a simplified, but precise, assessment technique for anterior glenoid bone defects. Purpose: To introduce a new measurement technique that requires only computed tomography (CT) of the affected shoulder joint and simultaneously simplifies the assessment of bone defects in the anterior glenoid. Study Design: Cohort study (diagnosis); Level of evidence, 3. Methods: CT scans of the glenoid from 285 healthy participants and 43 patients with unilateral ASI were collected and reconstructed in 3 dimensions. Initially, we established the proportional relationship between the maximum height and width in the superior-inferior and anterior-posterior directions of the glenoid as well as the location of their intersection (point O) in healthy participants. Subsequently, glenoid bone defects in patients with ASI were measured using the contralateral comparison method, the best-fit circle method, the CT-specific formula method, and our novel proportional method. We analyzed the differences in defect ratios and sizes as well as glenoid track calculations among the 4 methods. Results: The mean width-to-height ratio of the glenoid was determined to be 0.69 ± 0.04, allowing for the simplification of the calculation to width = 0.7 × height for clinical convenience. Point O was consistently located at the lower one-third of the glenoid height. There was no statistical significance noted in the measurements of bone defect size and bone defect ratio when comparing the novel proportional method, the contralateral comparison method, and the best-fit circle method; however, a significant increase in bone defect size and bone defect ratio was estimated with the CT-specific formula method (defect size: F = 19.20, P < .0001; defect ratio: F = 15.99, P < .0001). Conclusion: We introduced a novel method for estimating the width of glenoid bone defects through the proportion of glenoid width to height, finding that 70% of the glenoid height at its lower one-third closely approximated its maximum width. This approach, requiring only CT data from the affected shoulder, simplified calculations and matched the accuracy of traditional methods. It offers potential clinical benefits in evaluating glenoid defects.