Background: The symptoms of rotator cuff tear vary and may even be absent. Thus, the symptoms cannot be explained solely by the presence of rotator cuff tear, and other factors are thought to be involved. Because the rotator cuff comes in contact with the coracoacromial ligament, the elasticity of the ligament may be a factor of the symptoms. The purpose of this study was to clarify the elasticity of the coracoacromial ligament in live shoulders with rotator cuff tears. Methods: Forty-one shoulders in 24 persons were enrolled in this study. The average age was 52 years old (range, 15 - 84 years old). We investigated the presence of rotator cuff tear and measured the elasticity of the coracoacromial ligament by ultrasound elastography (EUB-7500, HITACHI, Japan). Ultrasound elastography was a useful method to quantify the strain of soft tissue when pressure was added. The strain ratio (the ratio of strain of the coracoacromial ligament to that of the rotator cuff) was used as the index of the elasticity of coracoacromial ligament. Thus, the higher the strain ratio was, the softer the ligament was. Results: The strain ratio of the coracoacromial ligaments without rotator cuff tear showed a negative correlation to the age (r = ﹣0.825, P < 0.01). The strain ratio of the ligaments with rotator cuff tear (23.75 ± 15.05, 69.6 years old) was higher than that of the older ligaments without cuff tear (12.62 ± 7.94, 64.6 years old) (P = 0.0486). In shoulders with rotator cuff tear, the strain ratio of the ligaments with pain (14.37 ± 10.15, 66.7 years old) was lower than that of ligaments without pain (33.12 ± 13.59, 69.1 years old) (P = 0.0221). Conclusions: The coracoacromial ligament became stiffened with aging but softened with the existence of rotator cuff tear. The ligaments with symptomatic cuff tear are more stiffened than the ligaments with asymptomatic cuff tear.
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