Experimental Mechanobiological Studies On Acetabular Cartilage Of Developmental Dysplasia Of The Hip

[Background and Objective]Developmental dysplasia of the hip(DDH) is one of the most common diseases in pediatric orthopedics.The commom types include acetabular dysplasia and abnormal relationship between the femoral head and acetabular bone.Mild DDH can cause a high morbility of osteoarthritis(OA) in adult,and most of the OA patients have to receive total hip arthroplasty(THA).The present studies have ensured the retrogressive changes of the acetabular cartilage in early period of DDH.But the mechanobiological studies about the retrogression mechanism of acetabular cartilage, the expression of giant molecule proteins correlated to retrogression and the expression of integrins haven't been reported.The purpose of this study is to detect the changes of the expression of collagen,matrix metalloproteinase(MMPs) and integrins of acetabular cartilage in early DDH,to study the retrogression mechanism of the acetabular cartilage,to provide theoretical evidence for early treatment to DDH, to explore a new idea for further study of DDH.[Methods]PartⅠ.To establish animal model of DDH,detect bone mineral density(BMD), observe pathohistology.1.Apply the method of knee extending,in which left lower extremity as experimental group and right lower extremity as control group,to establish successfully 16 animal model of DDH by X-ray after 5 week's cast immobilization.2.Apply the method of Dual Energy X-ray Absorptiometry(DEXA) by Norland/p-DEXA BMD analysator to detect the BMD of acetabular bone in both groups,analyze the results using SPSS 12.0.3.Using the staining of HE and Toluidine Blue to observe the changes of chondrocytes and extracellular matrix(ECM) of acetabular cartilage samples. PartⅡ.To detect the expression ofⅡtype collagen and matrix metalloproteinases-7 (MMP-7) in acetabular cartilage of DDH.Apply the technique of immunohistochemical staining and western-blot to respectively qualitate and quantitate the expression ofⅡtype collagen and MMP-7 of 8 cartilage samples from the partⅠ.Analyze the results using SPSS 12.0.PartⅢ.To detect the expression of interinα5β1 in acetabular cartilage of DDHWe established another 8 animal models of DDH to obtain the samples of acetabular cartilage.After the extraction and reverse transcription of mRNA of integrinα5β1,we used the fluorescent quantitation RT-PCR(FQ RT-PCR) to determine the changes of the DNA copy numbers.Analyze the results using SPSS 12.0.[Results]PartⅠ.To establish animal model of DDH,detect BMD,observe pathohistology.1.The achievement ratio of establishing animal model of DDH achieved 76.2%(16/21).2.The results of BMD in experimental group were lower than that of control group, but there was no significant difference between two groups(P＞0.05).3.Pathohistology observing indicated the signs of retrogressive changes of the acetabular cartilage,including loss stain of ECM in Toluidine Blue stain and cluster chondrocytes in HE stain.PartⅡ.To detect the expression ofⅡtype collagen and MMP-7 in acetabular cartilage of DDH1.Ⅱtype collagen expressed unevenly in the ECM of experimental group,especially in cylindric cell layer.The positive numbers of immunohistochemical staining were higher than that of control group.The quantitative detection by western-blot in experimental group was higher than that of control group.There was significant difference between two groups(P＜0.05).2.The positive numbers of MMP-7 intracytoplasm were higher than that of control group.The quantitative detection by western-blot in experimental group was higher than that of control group.There was significant difference between two groups(P＜0.05).PartⅢ.To detect the expression of interinα5β1 in acetabular cartilage of DDHThere was positive expression of interinα5β1 mRNA in both groups,but the DNA copy numbers in experimental group was obviously higher that of control group. There was significant difference between two groups(P＜0.05).[Conclusions]1.There were pathologic changes of retrogression in acetabular cartilage of early DDH.Meanwhile,the BMD of acetabular bone in experimental group was lower than that of control group.There was no significant difference between two groups.2.The expression ofⅡtype collagen and MMP-7 correlated to retrogression of acetabular cartilage increased obviously in early DDH.The amount and intensity ofⅡtype collagen and MMP-7 is probably the base of differential retrogression of cartilage.The possibility ofⅡtype collagen and MMP-7 as biological parameters to reflect the degree of retrogression need further studies.3.The expression of interinα5β1 of acetabular cartilage increased obviously in early DDH.Interinα5β1 probably play an important role of mechanics sensing transmitter in the signal transduction system of hip joint.4.The retrogression mechanism of acetabular cartilage during early period of DDH: First,the mechanics signal transduction system of interins responds to the mechanical stress on the acetabular cartilage and then transmits the signs into cytoskeleton;Second,the procedure of retrogression is switched on,the cell morphous and the composition of ECM begin to change;Final,the amount of the synthesis ofⅡtype collagen and MMP-7 increases obviously.Meanwhile,the combination of increased collagen with increased integrins accelerates the proceeding of retrogression again.