Differences in the Length and Thickness of the Coracoacromial Ligament between Normal Shoulders and Shoulders with Rotator Cuff Tears

Although the relationship between the material properties of the coracoacromial ligament and rotator cuff tears has been clarified, it is difficult to evaluate these properties in the clinical setting. The purpose of this study was to clarify the relationship between rotator cuff tears and the length and thickness of the coracoacromial ligament in living shoulders, in order to assess the potential use of these parameters as clinical indicators of the possible risk or progression of rotator cuff tears. Thirty-five volunteers (46 shoulders, mean age: 52 years) were enrolled. The presence or absence of rotator cuff tears and the length and thickness of the coracoacromial ligament were evaluated by ultrasonography. Longitudinal images of the coracoacromial ligaments with the acromion and coracoid process as landmarks were obtained, and the lengths of the ligaments were measured using acoustic shadows as the index. On the same screens, the thicknesses at the center of the ligaments were measured. Ligaments in shoulders with a rotator cuff tear were significantly shorter than ligaments in shoulders without a rotator cuff tear (25.9 ± 2.5 mm vs. 28.6 ± 1.7 mm, respectively; P < 0.0001). There was no significant difference in the thicknesses of the ligaments. The length and thickness of the coracoacromial ligament of living shoulders were easily evaluated with ultrasonography in the present study, and the coracoacromial ligament was found to be significantly shorter in shoulders with a rotator cuff tear. The risk and progression of rotator cuff tears can be evaluated clinically by measuring the length of the coracoacromial ligament.