Introducing posterior glenoid dysplasia with novel classification: comparison of proportion and morphology between young baseball players and other athletes

Posterior glenoid dysplasia (PGD) has been described as an adaptive osseous change in young throwing athletes exposed to repetitive mechanical stress. However, prior studies have lacked consistent definitions, reliable classifications, or sport-specific analysis. This study aimed to analyze and classify PGD in young athletes across various sports and compare its proportion and severity between symptomatic baseball players and athletes from other sports. We retrospectively reviewed 10 years of shoulder computed tomography imaging data from 568 young athletes presenting with shoulder pain: 418 baseball players, 50 overhead athletes, and 100 athletes from other sports. Dysplasia of posterior to posteroinferior glenoid, bone defect size, and additional bone formation were assessed. We established a five-type classification system: Type 0 (normal sharp rim), Type 1 (smooth rounded rim), Type 2 (triangular defect), Type 3 (retreated joint surface with posterior bulging), and Type 4 (new bone formation). PGD was identified in 85.4% of baseball players, 32.0% of overhead athletes, and 9.0% of nonoverhead athletes (P < .001). Type 2 was most common in baseball players (42.6%), and advanced morphologic PGD (Types 3-4) was present in 13.4% of baseball players but was absent in other groups. PGD was more commonly observed among overhead athletes, particularly baseball players, within this symptomatic imaging cohort. Advanced morphologic types were identified predominantly in baseball players. These findings provide a structured framework for describing posterior glenoid morphology in throwing athletes and may facilitate future prospective studies investigating clinical relevance and natural history.