Recurrent anterior shoulder instability: accuracy of estimations of glenoid bone loss with computed tomography is insufficient for therapeutic decision-making.

OBJECTIVE: To evaluate the reliability of glenoid bone loss estimations based on either axial computed tomography (CT) series or single sagittal ("en face" to glenoid) CT reconstructions, and to assess their accuracy by comparing with actual CT-based bone loss measurements, in patients with anterior glenohumeral instability.
MATERIALS AND METHODS: In two separate series of patients diagnosed with recurrent anterior glenohumeral instability, glenoid bone loss was estimated on axial CT series and on the most lateral sagittal (en face) glenoid view by two blinded radiologists. Additionally, in the second series of patients, glenoid defects were measured on sagittal CT reconstructions by an independent observer.
RESULTS: In both series, larger defects were estimated when based on sagittal CT images compared to axial views. In the second series, mean measured bone loss was 11.5% (SD = 6.0) of the total original glenoid area, with estimations of 9.6% (SD = 7.2) and 7.8% (SD = 4.2) for sagittal and axial views, respectively. Correlations of defect estimations with actual measurements were fair to poor; glenoid defects tended to be underestimated, especially when based on axial views.
CONCLUSION: CT-based estimations of glenoid bone defects are inaccurate. Especially for axial views, there is a high chance of glenoid defect underestimation. When using glenoid bone loss quantification in therapeutic decision-making, measuring the defect instead of estimating is strongly advised.