| Objective: In this study,two different muscle contraction methods were used to exercise intervention in mice after rotator cuff injury repair.The healing effect of tendon-bone union after rotator cuff repair in mice was examined by histomorphology,immunology,bone morphology and biomechanics.The effects of different muscle contraction methods on tendonbone interface healing were preliminarily explored.To provide theoretical support for determining the best rehabilitation treatment after rotator cuff repair in the future.Methods:(1)104 C57BL/6 mice(8 weeks old,male,20-22 g)were established as a model for acute supraspinatus tendon injury repair in the right shoulder.The mice were randomly divided into 4 groups after surgery: Control group(Con group),Horizontal running group(Horz group),+15° Uphill running group(Up group),and-15° Downhill running group(Down group),all 26 mice in each group.Adaptive running platform training was performed one week before surgery,and formal running platform training(speed: 10m/min,time: 20min/d,5d/w,5 consecutive days with two days rest)was performed on the 7th postoperative day at the respective set angles.Mice were executed at 4 and 8 weeks postoperatively,and blood was collected from the right supraspinatus-supraspinatus tendon-humerus(SSTH)specimens after removal of the eyeballs.The blood specimens were subjected to Enzyme-linked immunosorbent assay(Elisa)to detect the concentration of TGF-β1;the SSTH specimens were stained with H&E and safranin O-fast green.At 8 weeks postoperatively,SSTH specimens were subjected to bone morphology and biomechanical testing to assess the morphological parameters and mechanical properties of subchondral bone.Results: All C57BL/6 mice survived to the end of the experiment,and the incisions healed well.(1)Histological examination:(1)at 4 weeks after surgery,H&E staining and safranin O-fast green staining showed that the injured tendon-bone interface began to heal in each group.The fibrocartilage layer was obvious in Down group,and the continuity and taxis of collagen fibers in Horz group and Up group were better than those in Con group.(2)at 8 weeks after surgery,the arrangement of collagen fibers at the tendon-bone interface in each group was more orderly than that at 4 weeks.Transitional structures with obvious tide lines were observed in Down and Horz groups.The thickness of fibrocartilage layer in Down group was significantly better than that in the other three groups.Horz and Up groups were superior to Con group in the number of chondrocytes and tendon fibers.(2)Immunological assays:(1)at 4 weeks postoperatively,the TGF-β1 concentration in the Con group was significantly lower than that in the other three groups.The TGF-β1 concentration in the Down group was significantly higher than that in the Up group and the Horz group(p<0.05),and there was no significant difference between the Horz and Up groups(p>0.05).(2)at 8 weeks after surgery,TGF-β1 concentration decreased in all groups compared with that at 4 weeks.The concentration of TGF-β1 in the Down group was higher than that in the Con group(p<0.05).There was no significant difference between the other groups.(p>0.05).(3)Bone morphology: Micro-CT scan showed that at 8 weeks after operation,the tendon-bone interface of Down group healed best,followed by Horz group.BV/TV in the Down group was significantly higher than that in the Con group(p<0.05).The number and thickness of subchondral bone trabeculae in the Down group were significantly better than those in the other three groups.The number of subchondral bone trabeculae in Horz group was significantly higher than that in Con group(p<0.05).The thickness of trabecular bone in Horz group and Up group was better than that in Con group(p<0.05),and the trabecular space in Con group was significantly larger than that in Down group(p<0.05).There was no significant difference in the morphological parameters between Horz group and Up group(p>0.05).(4)Biomechanical tests: At 8 weeks after surgery,there was no statistical difference in crosssectional area between the four groups(p>0.05).The tensile load and ultimate strength in group Down were better than those in group Con,group Up(p<0.01)and group Horz(p<0.05),and those in group Horz were better than those in group Con(p<0.05).Conclusion:(1)Both eccentric and concentric contraction can promote tendon-bone interface healing after rotator cuff repair in mice.(2)Eccentric contraction promotes healing at the tendon bone interface after rotator cuff repair in mice better than a combination of centripetal contraction and centripetal centrifugal training. |
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