A Research On Biomechanics Of The Hip During Triple Pelvic Osteotomy Of Developmental Dysplasia Of The Hip By Using Finite Element Analysis

BACKGROUND: The aim of this study is to use finite element method to analyze the biomechanics of the hip in children with DDH managed with triple pelvic osteotomy(TPO).METHODS: At the beginning of this study,we should confirm the acetabular rotation center and its motion during the TPO.We retrospectively reviewed 33 hips in24 patients(18 females and 6 males;9 had bilateral dislocations)between Oct 2012and Oct 2016.Both distances from the acetabular rotation center to the mid-line of body and to the horizontal line across the pubic symphysis were measured in order to access the position changes of the acetabular rotation center in all patients before and one year after surgery and in the final follow-up.Besides,T?nnis classification,acetabular index(AI),center-edge angle(CEA),distance from center of the femoral head to midline were measured at the same time points.Variance analysis was used to compare parameters among groups.Pearson coefficient analysis was calculated to evaluate the relationship between the position of the acetabular rotation center and Harris score.We selected 3 patients of these cases.According to the preoperative CT three-dimensional model was established.Based on concluded acetabulum rotation center position,we simulated TPO.Each rotation increases the LCEA by 10 degrees,and then used the method of finite element to analysis of the acetabulum and femur contact area,contact surface maximum pressure,the maximum stress of cartilages.REULTS: The mean age of the patients was 9.81±1.51 years and the mean follow-up time was 2.20±1.41 years.CE Angle and AI were significantly improved after operation.No significant statistical difference was shown in the position of acetabular rotation center postoperatively.At the final follow-up,the Severin’s rating was excellent or good,while the average Harris function score was 91.12 ± 4.12.There was no significant correlation between the change of acetabular rotation center and Harris functional score.3 model patients selected were all female,aged 11 years,13 years,and 13 years old respectively.The preoperative CEA of the affected side was 5°,the T?nnis classification was type III,and their weights were 47.3 kg,48.5 kg,and51 kg.In the biomechanical results calculated by finite element analysis,the hip cartilage stress after triple osteotomy was significantly lower than that before surgery.During the surgery,with the increase of lateral and anterior coverage,the contact area of acetabular cartilage and femoral cartilage increased gradually,and then gradually decreased after reaching the peak.The maximum contact surface pressure and the maximum cartilage stress showed a gradual decrease,and gradually increased after reaching the peak.CONCLUSION: It is crucial to keep the acetabular rotation center immovable during the procedure of TPO.TPO could not only increase the coverage of the femoral head and the contact area of hip joint,but also decrease the maximum contact pressure and stress of cartilages.All these data support that TPO could provide a better biomechanical structure of the hip and obtain satisfactory function after operation and delay the progress of hip joint degenerative osteoarthritis.