Critical Shoulder Angle and Acromiohumeral Distance on Radiographs and Association with Rotator Cuff Tears: A Cross-Sectional Study

Objective: To determine the associations between the critical shoulder angle (CSA) andacromiohumeral distance (AHD) measured on true anteroposterior (AP) radiographs and the presence and severity of MRI-confirmedrotator cuff tears (RCTs). Design: Retrospective cross-sectional study. Methods: We included adults with shoulder pain who underwent same-day ipsilateral shoulder MRI and true AP radiography (N=198; 94 men, 104 women; mean age 53.6"}10.9 years). MRI classified the tendons as having no tear (NT, n=87), partial-thickness rotator cuff tear (PTRCT, n=73), or full-thickness rotator cuff tear (FTRCT, n=38). CSA (deg) and AHD (mm) were electronically measured using PACS. Group differences were tested using one-way ANOVA (Bonferroni post-hoc test). The associations among age, CSA, and AHD were examined with Pearson correlations (α=0.05). Results: CSA differed by group (p<0.001); pairwise comparisonswere as follows: NT vs PTRCT (p<0.001), NT vs FTRCT (p<0.001), and PTRCT vs FTRCT (p=0.025). AHD differed by group (p<0.001); pairwise comparisons were NT vs PTRCT (p<0.001), NT vs FTRCT (p<0.001), and PTRCT vs FTRCT (p=0.461).There were Correlations between age and AHD (r=−0.28,p<0.001) and CSA and AHD (r=−0.43, p<0.001). Conclusions: Larger CSA and smaller AHD on true AP radiographs were found to be associated with MRI-confirmed RCTs. The CSA increased stepwise with tear severity, whereas the AHD primarily reflected tear presence rather than distinguishing PTRCT from FTRCT. Combined interpretation of the CSA (putative anatomic/biomechanical risk marker) and AHD (consequence marker of superior humeral migration) may aid in screening, risk stratification, and treatment decision-making in clinical practice.