Abstract
As the subacromial impingement phenomenon is observed not only in painful shoulders but also in normal shoulders, the elasticity of the coracoacromial ligament may relate to symptoms of shoulder disorders. The purpose of this study was to clarify the relationship between histological degeneration and elasticity of the coracoacromial ligament. Twenty coracoacromial ligaments from cadaveric shoulders (8 men and 12 women, average age 79.5 years old) were studied. Each ligament was divided into 6 parts: superficial and deep side of the acromial, central and coracoid part. These 120 parts of ligaments were evaluated about degeneration and elasticity. It was reported that the collagen fiber orientation of the coracoacromial ligament changes by aging from wavy to straight and that by further degeneration the fiber collapses and becomes irregular. So each part was classified by fiber orientation into wavy-part, straight-part, and irregular-part. And the tissue sound speed that showed a positive correlation to the elasticity was measured by scanning acoustic microscopy. The relationship between histological degeneration and elasticity of the coracoacromial ligament was investigated (ANOVA and Tukey-Kramer method). The mean sound speed of the wavy-part, the straight-part, and the irregular-part was 1592±17.2 m/s, 1626±28.0 m/s, and 1607±29.8 m/s, respectively (P<0.0001, ANOVA). The sound speed of the straight-part was higher than that of the wavy-part (P<0.0001), and that of the irregular-part was lower than that of the straight-part (P=0.0023). The coracoacromial ligament becomes stiffened as histological degeneration progresses from wavy to straight fiber orientation, and when it progresses further to collapsed fiber orientation the ligament becomes softened.
