The Novel Acromial Angle is associated with the severity of full-thickness rotator cuff tear: a retrospective radiographic study

Purpose To investigate the relationship between the Novel Acromial Angle (NAA) and the severity of rotator cuff tears, including partial bursal-side and full-thickness tears. Methods This retrospective cohort study included 386 patients who underwent both scapular outlet-view radiography and shoulder MRI at our hospital between September 2023 and April 2025. Based on MRI findings, patients were classified into a symptomatic MRI-negative control group, a partial bursal-side tear group, or a full-thickness tear group. The NAA was measured and compared among the groups. Results The mean NAA was significantly smaller in both tear groups than in the symptomatic MRI-negative control group ( p < 0.01). A smaller NAA was significantly associated with larger full-thickness tear size ( p < 0.01). The area under the receiver operating characteristic curve (AUC) for identifying full-thickness tears was 0.76, which was higher than the AUC for partial tears (0.67). However, NAA was not significantly associated with the depth of partial bursal-side tears ( p > 0.05). Conclusion NAA was significantly associated with the presence and severity of full-thickness rotator cuff tears, with smaller angles corresponding to larger tears. NAA may be a useful radiographic parameter for preoperative planning and for evaluating the potential need for acromioplasty, particularly in patients with full-thickness tears.