Objective calculation of glenoid bone loss in anterior shoulder instability based on the contour of the posteroinferior quadrant using the best-fit circle method: an accurate and reproducible evaluation

Background Glenoid bone loss is proposed to be an important risk factor for recurrent anterior shoulder instability. The purpose of the present study was to develop an accurate and reproducible method for quantifying a bone loss in patients with anterior shoulder instability. Methods A total of 66 sets of computed tomography images of the glenoid were acquired and en face view was established. Based on the contour of the inferior half and posteroinferior quadrant of the glenoid, the best-fit circle was drawn using the least-squares method with a comparison of the radii. A bone loss was created via a simulated osteotomy, and a method for estimating the bone loss based on the contour of the posteroinferior quadrant was developed. Results The radii of the best-fit circle were 29.30±1.84 mm and 33.76±2.04 mm based on the inferior half and posteroinferior quadrant of the glenoid, respectively (P<0.01). Bone loss quantification using the contour of the inferior half or posteroinferior quadrant with simulated osteotomy showed a significant difference (P<0.01). For a 25% of glenoid bone loss, the estimated value using the traditional method on the contour of the posteroinferior quadrant was 34%. the A new method for accurate bone loss quantification was developed based on the contour of the posteroinferior quadrant of the glenoid. Conclusion Estimation of the glenoid bone loss based on the rim of the posteroinferior quadrant may overestimate the glenoid bone loss due to the difference in the radius of the curvature of the inferior half and posteroinferior quadrant. A mathematical method was developed to correct this error and may aid in more accurately measuring the glenoid bone loss using the contour of the posteroinferior quadrant in patients with anterior shoulder instability.