Objective: To establish a model of chronic rotator cuff injury by inducing subacromial impingement syndrome in rats, so as to lay a foundation for further study on the mechanism and treatment of chronic rotator cuff injury.
Methods: The polyether-ether-ketone implants were designed and made with three-dimensional printing technique. In 48 male Sprague Dawley rats [weighing, (277.25 ± 22.03) g], one shoulder joint was selected randomly as the experimental group; in the experimental group, the implant was pierced into shoulder joint close to the acromion medial side and was pierced out under acromion close to the deltoid trailing edge; the penetrating part of implant was cut off after the implanting part was fixed with 4# braided silk suture. No any treatment was performed on the contralateral shoulder of 24 rats as control group; and the implants were immediately removed after they were pierced into the contralateral shoulder joint of the other 24 rats as sham- operation group. All the rats were exposed to 30 minutes of downhill running at 17 m/minute (-13.5°) every day at 4 days after operation and the general condition of rats was observed. At 2, 4, 6, and 8 weeks after operation, 12 rats were sacrificed to collect shoulder joint samples. The hard tissue slices was used for Van Gieson staining and histological observation of the supraspinatus tendon.
Results: All rats survived to the end of experiment, without infection. The rats suffered limp at 2-3 days after operation, and the gait of most rats returned to normal at 4 days after operation. The histological results showed that the supraspinatus tendon had smooth edge, without split layers or breakage in the control group and sham-operation group. In the experimental group, the implants were positioned accurately without dislocation; 4 kinds of typical pathological changes were observed. Partial-thickness tear on bursal side appeared at 2 weeks (5 rats) and 4 weeks (2 rats), showing no significant difference between at 2 and 4 weeks (P > 0.05); intratendinous gap formed mainly at 4 weeks (10 rats) and 6 weeks (11 rats), showing significant differences when compared with that at 2 weeks (2 rats) (P < 0.05) and 8 weeks (2 rats) (P < 0.05); partial-thickness tear on articular side mainly appeared at 6 weeks (8 rats), showing significant difference when compared with that at other time points (P < 0.05); full-thickness tear was found mainly at 8 weeks (10 rats), showing significant differences when compared with that at other time points (P < 0.05).
Conclusion: A model of chronic rotator cuff injury is successfully established in rats through microinvasive implantation of subacromial impingement syndrome inducing implants and the pathological changes in this model are highly similar to the clinical pathological progress.