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Traumatic dislocation most commonly occurs at the shoulder joint. After an initial dislocation of the shoulder, the labrum is usually detached from the glenoid (Bankart lesion). If this lesion fails to heal, surgical repair is necessary. The purpose of this study was to determine the histological and biomechanical healing process of a simulated Bankart lesion created in rabbits. A labral injury was surgically created in 40 Japanese White rabbits. The labrum was sharply dissected from the glenoid rim simulating a Bankart lesion, and was repositioned without sutures. The joint capsule, the supraspinatus and infraspinatus tendons, and the deltoid were anatomically repaired with sutures. Eight rabbits each were sacrificed at 1, 2, 3, 4, and 5 weeks after the surgery for histological and biomechanical examinations (4 animals each). The histology and biomechanical properties of the normal capsulolabral structure was examined in 8 control rabbits. Inflammatory cell infiltration into the gap between the glenoid and the labrum was noted from 1 week. The gap was covered with fibrous connective tissue accompanied by the collagen fibers by 3 weeks. The healing process was completed histologically by 3 weeks. Biomechanically, the tensile load, which decreased significantly at 1 week, gradually increased and returned to the level of intact shoulder at 4 weeks. At least four weeks are necessary for the healing of the labral injury in rabbits. Considering the difference between humans and rabbits, it seems reasonable to let the patients go back to sports 2 to 3 months after dislocation or surgical repair.

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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