Elasticity of the Coracoacromial Ligament in Shoulders with Rotator Cuff Tear

Abstract

The tissue sound speed that correlated to its elasticity changed according to the collagen fiber orientation of the coracoacromial ligament. The purpose of this study was to clarify the characteristics of the elasticity of the coracoacromial ligament in shoulders with rotator cuff tear. Twenty coracoacromial ligaments from cadaveric shoulders were studied. They were classified into 3 groups: ligaments with rotator cuff tear (RCT-group), ligaments with subacromial spur and normal rotator cuff (Spur-group) and ligaments without subacromial spur and rotator cuff tear (Control-group). Each ligament was divided into 6 parts: superficial and deep side of the acromial, central and coracoid part, and each part was classified by fiber orientation into wavy-part, straight-part, and irregular-part. The sound speed of each part was measured by scanning acoustic microscopy. The number of degenerated part and the sound speed were compared among the 3 groups (chi square test and ANOVA). The RCT-group and the Spur-group had more straight-parts (P=0.0002) and less wavy-parts (P<0.0001) than the Control-group. Significant differences of the sound speed were observed in each group (P<0.0001), the Control-group: 1596±19.1 m/s, the Spur-group: 1630±31.5 m/s, and the RCT-group: 1612±28.6 m/s. Especially in the acromial side, the sound speed of the Spur-group was higher than that of the Control-group (P=0.0050), and that of the RCT-group was lower than that of the Spur-group (P=0.018). In conclusion, the coracoacromial ligament with rotator cuff tear and the ligament with subacromial spur were stiffened. The ligament with rotator cuff tear was more softened than the ligament with subacromial spur. These differences of elasticity were remarkable in the acromial side.