Coracoid Morphology and the Risk of Posterior Shoulder Instability: A Magnetic Resonance Imaging Study

Background: Posterior shoulder instability has been associated with abnormal acromial and glenoid morphology. However, the role of coracoid morphology in posterior instability remains unclear. Hypothesis: Patients undergoing surgery for posterior shoulder instability will have more inferiorly oriented and lateralized coracoids compared to patients with anterior instability or a noninstability comparison group. Study Design: Cohort study; Level of evidence, 3. Methods: Magnetic resonance imaging measurements were collected for 3 surgical cohorts: posterior instability (n = 41), anterior instability (n = 39), and a comparison group undergoing arthroscopy for snapping scapula (n = 38). Coracoid morphology metrics included: lateral coracoid offset, sagittal coracoid angle, coronal coracoid angle (CCA), transverse coracoid length, coracoacromial length (CAL), coracohumeral distance, and inferior coracoid coverage (ICC). Glenoid version and bone loss were also measured. One-way analysis of variance with Tukey post hoc testing or Kruskal-Wallis with Dunn testing was used as appropriate to compare groups. The P value was set a priori at