Three-Dimensional Geometry of the Normal Scapula: A Software Analysis

Recent evidence suggests that variations in overall scapular morphology may predispose individuals to specific shoulder pathologies. The purposes of this study were to provide a comprehensive 3D analysis of scapular anatomy in a healthy population and to investigate potential age-related differences and associations with pathological thresholds described in the literature.

This study included computed tomography scan data from 369 healthy scapulae of subjects ≥18 years of age without shoulder pathology. The scapulae were analyzed to measure key morphological parameters, including glenoid version, acromial coverage, posterior acromial height, coracoid angles, and scapular spine angle. Scapulae of individuals <60 years old were compared with those of individuals ≥60 years old. Morphological thresholds described in previous studies were used to identify the percentage of healthy scapulae that demonstrated values exceeding pathological thresholds.

Significant differences were observed between the scapulae of patients <60 years old and those ≥60 years old, with younger patients generally exhibiting scapular morphologies more closely resembling those reported in pathological cases. Key differences included posterior acromial height, posterior acromial coverage, scapular spine angle, and coracoacromial coverage (p < 0.05 for each). Across the cohort, a small percentage of healthy scapulae exceeded pathological thresholds published in the literature for posterior instability (posterior acromial height: 12.2%; posterior acromial coverage: 12.7%), anterior instability (coracoid pillar angle 2: 9.5%; scapular spine angle 2: 13.3%; glenoid rotation: 0.5%), and primary osteoarthritis (anterior coracoid plane coverage: 6.5%; coracoacromial plane coverage: 10.8%; posterior acromial coverage: 10.3%; critical shoulder angle: 6.0%).

This study provides a comprehensive reference for the 3D morphology of the healthy scapula. The results reveal relatively low variability in shape among healthy scapulae; however, specific morphological variations appear to predispose individuals to certain pathologies. As degenerative conditions develop over time, younger subjects with such predispositions may gradually transition out of the healthy cohort. Conversely, individuals who remain healthy beyond 60 years of age likely possess a "healthy" anatomy that does not favor pathology, representing the true cohort of healthy subjects.

Understanding the 3D morphology of the healthy scapula could enhance our knowledge of the etiology of conditions such as posterior and anterior instability and primary osteoarthritis, potentially improving their surgical management.