Abstract
OBJECTIVE: To investigate the coracoacromial ligament thickness measured by magnetic resonance imaging (MRI) on the inferior surface of the acromion, and to find the correlation between coracoacromial ligament thickness and rotator cuff tear size. METHODS: The coracoacromial ligament thickness of the inferior surface of the rotator cuff was assessed in 127 patients with rotator cuff tears using 3.0 MR system. The patients were grouped according to the size of the rotator cuff tear and whether the rotator cuff was degenerated or not. RESULTS: The mean coracoacoacromial ligament thickness on the inferior surface of the acromion was 3.58 ± 1.02 mm. The association between rotator cuff tear severity and coracoacromial ligament thickness was statistically significant (β=-1.531, P < 0.001), but not in the trauma cohort (β=-0.059, P = 0.731). CONCLUSION: (1) MRI is a reliable tool to assess the thickness of the coracoacromial ligament on the inferior surface of the acromion; (2) The increased degree of degenerative rotator cuff tear is associated with the decreased thickness of the coracoacromial ligament on the inferior surface of the acromion; (3) The change of the degree of traumatic rotator cuff tear is not associated with the thickness of the coracoacromial ligament on the inferior surface of the acromion. These findings provide further insight into the mechanism of injury in rotator cuff tears. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12891-025-09305-4.