A Research On Contact Pressure Distribution Of The Hip Joint During Closed Reduction Of Developmental Dislocation Of The Hip By Using Finite Element Analysis

BACKGROUNDS: Developmental dislocaiton of the hip(DDH)is one of the most common developmental deformities of the lower extremities.For those infants who fail previous Pavlik harness,or those who present late and less than 18 months,closed reduction(CR)and spica casting,which can provide an adequate environment for femoral head and acetabular development and avoid proximal femoral growth disturbance,is still the primary treatment options.It is thought that the articular cartilage contact pressure(CCP)plays an important role in stimulating the development of hip toward normalization,however,excessive pressure inhabits growth,which may be related to avascular necrosis.Thereby,we try to provide insight into biomechanical factors potentially responsible for CR treatment success and complications by using finite element analysis at the first time.METHODS: We retrospectively analyzed 147 DDH patients treated by CR combined with percutaneous adductor tenotomy,and evaluated the risk factors of complications in our single center.FE models of one DDH patient was established based on the data of MRI scan on which CCP were measured.During CR,CCP between the femoral head and acetabulum in different abduction angles were tested to estimate the efficacy and potentially risk factors related to AVN during closed reduction for DDH children.RESULTS: As for acetabular index,T?nnis grade and IHDI grade,differences between preoperative data and the ones at the final follow-up were statistically significant(P<0.05).Age between 12 and 18 months,walking independently,IHDI grade 2-4 and acetabular index were the risk factors of potential open reduction,while previous Pavlik harness was the protective factor of close reduction.Age beyond 18 months,preoperative IHDI grade 3-4 and acetabular index were the risk factors of AVN(P<0.05).Age beyond 18 months and acetabular index were the risk factors of redislocation(P<0.05).A 3D reconstruction by finite element method was performed on a sixteen-month-old girl with dislocation of the hip on the right side.With the increase of the abduction angle,the force on the anterior and posterior of the acetabulum is more disperse,therefore the reduction is more stable.However,the force of the posterior acetabulum increases obviously,and the stress on the lateral part of the femoral head also enhances correspondingly.The changes of the force in the superior of the acetabulum were not obvious during CR.CONCLUSION: Closed reduction should be applied to patients with DDH between 6 and 18 months old with IHDI grade below Ⅲ.Age over 18 months,excessive AI,and IHDI grade Ⅲ and above will increase the risk of AVN and the failure rate of closed reduction.Pavlik harness treatment may improve the prognosis of DDH and lower the risk of potential open reduction.In the process of CR,CCP of the acetabulum is distributed in a butterfly-like style around the U-shaped notch.Meanwhile,stresses on the anterior and posterior acetabulum are more even,which means that increased abduction of the hip improves stability but compromises vascularity,thereby may cause AVN.