| Objective Knee joint injuries is very common in daily life and sports,and joint immobilization is a common treatment.However,longstanding or improper immobilization are also common reasons of joint contracture.Joint contracture not only influences the daily life of patients,but also causes great medical and economic burden on family and society.The purpose of this study was to establish a rabbit model of extending knee joint contracture by joint immobilization,and to investigate the pathological characteristics of myogenic contracture and its possible mechanism.Methods According to the immobilization time,thirty New Zealand white rabbits were randomly divided into 5 groups: control group(I-0,6 rabbits,without any treatment),1-week immobilization group(I-1,6 rabbits,with left knee joint complete extending immobilization for 1 week),2-week immobilization group(I-2,6 rabbits,with left knee joint complete extending immobilization for 2 weeks),4-week immobilization group(I-4,6 rabbits,with left knee joint complete extending immobilization for 4 weeks)and 8-week immobilization group(I-8,6 rabbits,with left knee joint complete extending immobilization for 8 weeks).At the end of each immobilization time point,the rabbits were killed,and then the myogenic contracture and arthrogenic contracture were analyzed by detecting the angle of knee joint contracture after immobilization.The cross-sectional area of rectus femoris muscle fiber was analyzed by Masson staining.The protein expression levels of hypoxia inducible factor-1α(HIF-1α)and transforming growth factor-β1(TGF-β1)were analyzed by western blot.Results In the total contracture,the total contracture angle of each immobilization group increased with the immobilization time during 8 weeks(P < 0.001);in myogenic contracture,the contracture angle of each immobilization group increased with the immobilization time before the first 4 weeks(P<0.05),but there was no significant difference between I-4 group and I-8 group after 4 weeks immobilization(P > 0.05).In Masson staining and quantitative results,the cross-sectional area of rectus femoris decreased and the proportion of collagen fiber deposition increased within 4 weeks after immobilization(P < 0.05),but there was no significant difference in the cross-sectional area of rectus femoris and proportion of collagen fiber deposition in the I-8 group compared with the I-4 group after 4 weeks immobilization(P > 0.05).The expression level of hypoxia inducible factor-1αprotein increased continuously within 4 weeks after immobilization(P < 0.05),but there was no significant difference in the expression level of hypoxia inducible factor-1α protein between I-4 group and I-8 group after 4 weeks immobilization(P >0.05);the expression of transforming growth factor-β1 protein increased significantly within 2 weeks(P < 0.05);But there was no significant difference between the each group after 2 weeks immobilization(P > 0.05).Conclusion In this study,the increase of myogenic contracture angle,the decrease of rectus femoris cross-sectional area and the increase of collagen deposition ratio detected within 4 weeks of immobilization can be used to infer that the pathological characteristics of myogenic contracture in the early stage of joint contracture are mainly time-dependent changes of muscle fibrosis and atrophy.It is suggested that the mechanism of myogenic contracture may be related to the high expression of hypoxia inducible factor-1α and transforming growth factor-β1. |
