Three-Dimensional Quantification of Glenoid Bone Loss in Anterior Shoulder Instability: The Anatomic Concave Surface Area Method

BACKGROUND: Recurrent shoulder instability may be associated with glenoid erosion and bone loss. Accurate quantification of bone loss significantly influences the contemplation of surgical procedure. In addition, assessment of bone loss is crucial for surgical planning and accurate graft placement during surgery. PURPOSE: To quantify the concave surface area of glenoid bone loss by using 3-dimensional (3D) segmented models of the scapula and to compare this method with the best-fit circle and glenoid height/width methods, which use the glenoid rim for bone loss estimations. STUDY DESIGN: Cohort study (diagnosis); Level of evidence, 2. METHODS: A total of 36 consecutive preoperative bilateral computed tomography scans of patients eligible for a primary Latarjet procedure were selected from our institutional surgical database (mean patient age, 29 ± 9 years; 31 men and 5 women). The 3D models of both scapulae were generated using medical segmentation software and were used to map the anatomic concave surface area (ACSA) of the inferior glenoid using the diameter of the best-fit circle of the healthy glenoid. Bone loss was calculated as a ratio of the difference between surface areas of both glenoids (healthy and pathological) against the anatomic circular surface area of the healthy glenoid (the ACSA method). These results were compared with bone loss calculations using the best-fit circle and glenoid height/width methods. Inter- and intraobserver reliability were also calculated. RESULTS: The mean (± SD) bone loss calculated using the ACSA, the best-fit circle, and glenoid height/width methods was 9.4% ± 6.7%, 14.3% ± 6.8%, and 17.6% ± 7.3%, respectively. The ACSA method showed excellent interobserver reliability, with an intraclass correlation coefficient (ICC) of 0.95 versus those for the best-fit circle (ICC, 0.71) and glenoid height/width (ICC, 0.79) methods. CONCLUSION: Quantification of instability-related glenoid bone loss is reliable using the 3D ACSA method.