Characteristics of High-Risk Bipolar Bone Loss Lesions Using 3-Dimensional Imaging

Background: The concept of on-track versus off-track bone lesions in glenohumeral instability continues to evolve. Although much has been ascertained from an original biomechanical model, bony pathological changes, especially on 3-dimensional (3D) imaging, have not been fully evaluated. Purpose: To compare the differences in on-track versus off-track lesions to characterize glenoid and humeral head bone defects using 3D modeling software. Study Design: Cross-sectional study; Level of evidence, 3. Methods: A consecutive cohort of 75 patients with recurrent anterior instability, with evidence of Hill-Sachs lesions (HSLs) and glenoid bone loss (GBL) and a mean age of 27.1 years (range, 18-48 years), were reviewed. 3D models of unilateral proximal humeri and glenoids were reconstructed. The volume, surface area, width, and depth of identified HSLs were quantified, along with their location (medial, superior) and orientation (Hill-Sachs angle). The percentage, width, and length of GBL as well as the glenoid track status were calculated. The on-track and off-track groups were compared using the Mann-Whitney U test. Results: The off-track group had greater HSL surface area (374.23 vs 272.64 mm², respectively; P =.001), more HSL medialization (14.96 vs 17.62 mm, respectively; P =.028), greater HSL volume (603.08 vs 433.61 mm³, respectively; P =.007), and a greater mean HSL width (16.06 vs 11.53 mm, respectively; P =.001) than the on-track group. The off-track group also had greater GBL (22.55% vs 17.73%, respectively; P =.037), a greater GBL width (6.92 vs 3.58 mm, respectively; P <.001), and a greater GBL length (21.61 vs 16.1mm, respectively; P =.015) than the on-track group. Further analysis of large off-track lesions revealed a greater Hill-Sachs angle (33.16° vs 26.20°, respectively; P =.035) and a more superior extent of HSLs compared with borderline off-track and on-track lesions. Conclusion: Off-track lesions were found to have larger GBL, a larger HSL width, a more medialized HSL, and greater HSL surface area. This study outlines the specific characteristics of high-risk bipolar bone loss lesions to simplify the identification of patients in a clinical setting and aid in appropriate treatment planning.