ObjectiveTo 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. MethodsThe 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 tothe acromion medial side and was pierced out under acromion close to the deltoid trailing edge; the penetratingpartof 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 hardtissueslices was used for VanGieson staining and histological observation of the supraspinatus tendon. ResultsAll ratssurvived to the end of experiment, without infection.The rats suffered limp at 2-3 daysafter 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). ConclusionA 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.
ObjectiveTo provides an objective tool to evaluate rotator cuff function in rats. MethodsSixty adult male Sprague Dawley rats, weighing (281.21± 20.12) g, were involved in this experiment. Botulinum toxin A (6 U/kg) was injected into the infraspinatus of 12 rats in Botox group. Infraspinatus tendons of 12 rats in tear group were cut by microinvasive method. Infraspinatus tendons of 12 rats in sham-operation group were exposed but not cut. No any treatment was performed on the 12 rats in normal control group. One shoulder joint of each rat was selected randomly as treatment side. After 7 days, cadence, rate of stand phase, support pressure, swing speed, stand speed, and stride length of rats in those 4 groups were measured. Treatment side and contralateral side ratio of each gait parameter was caculated. If parameters of Botox group and tear group both showed significant differences compared with those of normal control group and sham-operation group, the gait parameter was brought into rating scale as an item. Each item was assigned from 1 point to 5 points according to gait parameter. The chronic rotator cuff injury model was established in 12 rats of verification group and rating scale was used to evaluate rotator cuff function each week for 8 weeks after surgery. ResultsAll gait parameters of tear group were significantly less than those of Botox group (P＜0.05), and Botox group was significantly less than sham-operation group and normal control group (P＜0.05), but no significant difference was found between sham-operation group and normal control group (P>0.05). All gait parameters were brought into rating scale as items. All items were rated from 1 point to 5 points, so the total score was 30 points and the lowest score was 6 points. Thirty points meant normal function of infraspinatus (rotator cuff function was normal), and 6 points meant complete loss of infraspinatus function (rotator cuff function was severely damaged). Rotator cuff functional scores of rats in verification group were 27.00±1.86, 23.75±2.83, 21.33±1.92, 18.17±2.37, 13.17±1.64, 11.67±2.50, 8.17±1.27, 6.50±0.67 from the 1st week to the 8th week respectively. ConclusionThe rating scale of rat rotator cuff function may reflect the severity of rotator cuff injury and the functional status of rotator cuff to some extent in rats.