We clarified the relations between the material properties of the coracoacromial ligament and rotator cuff tears. The material properties are affected by the length and the cross section of the ligament. The purpose of this study was to clarify the relations between the length and thickness of the coracoacromial ligament and the rotator cuff tears in live shoulders with ultrasonography as the medical examination and treatment indexes. Twenty-two persons (40 shoulders, mean age 52 years old) were studied. We investigated the presence of rotator cuff tear and measured the length and thickness of the coracoacromial ligament with ultrasound machine (EUB-7500, HITACHI, Japan). The longitudinal images of the ligaments were depicted with the acromion and coracoid process, and the lengths of the ligaments were measured by using acoustic shadows as the landmark. On the same screens, the thicknesses of the ligaments were measured at the central points of the ligaments. The length of the ligaments with rotator cuff tear (26.1±2.6 mm, 17 shoulders) was shorter than that of the ligaments without rotator cuff tear (28.9±1.6 mm, 23 shoulders) (P=0.0001). There was no significant difference in the thickness of the ligaments. The length of the coracoacromial ligaments with rotator cuff tears, which were measured with ultrasonography in live shoulders, was significantly short. These results were provided for the first time in live shoulders. The risk of outbreak and progress of rotator cuff tears may be evaluated by measuring the length of the coracoacromial ligament clinically.
