Proliferation and apoptosis of chondrocytes in dislocational hip of neonatal rats in the process of degeneration

Abstract

Objective To explore the proliferation and apoptosis of chondrocytes during the de genration process resulted from dislocation of the hip in neonatal rat model.Methods Neonatal Wistar rats were randomly divided into two groups (experimental and control group).Developmental dislocation of the hip (DDH) model was mimicked by swaddling position,which was to immobilize the bilat eral hips and legs at extension with medical tape for ten days.The rats were sacrificeal at 2,4 and 8 weeks of age and hips were isolated for gross measurement and sanfranin O-fast green staining.Chondrocytes were isolated for proliferation index (PI) and apoptosis ratio (AR) by flow cytometry (FCM) and CCK 8 test.Student's-t test was applied for statistical analysis.Results The gross sample showed the abnormal relationship of the hips,proving the success of model.The anatomy didn't get reduction with development.Acetabula depth ratio (ADR) of control group increased along with development,however,ADR in DDH group showed an obvious increase at 4-weeks with a deep decrease at 8-weeks and were smaller than those in the control group at each stage.Femoral head ratio (FHR) in control group didn't show significant changes along with growing up; however,FHR in DDH group decreased along with development and was smaller than those in the control group.The sanfranin O-fast green staining revealed that the cartilage in control group became thinner and showed distinct layers along with development,whereas the shape of cartilage in DDH group deformed from 4 weeks after birth and extracellular matrix (ECM) became less stained,chondrocytes disordered and clusters presented.Mankin score showed significant difference at 4 and 8 weeks after birth (P＜0.01).PI of DDH group showed higher than those in the control group at each stage,as well as proliferative ratio by CCK-8 test.AR in DDH group was higher than that in control group at 2 and 8 weeks,while no sig nificance was presented at 4 weeks.Conclusions Proliferation and apoptosis of chondrocytes are evident during the process from dislocational hip to early degeneration in neonatal rat. Key words: Hip dislocation; Cartilage, articular; Rats