Biomechanical Study Of Articular Cartilage And Surgical Planning Of Periacetabular Osteotomy Of Developmental Dysplasia Of The Hip

Developmental dysplasia of the hip(DDH)is a common congenital hip disease.The abnormal morphologies of the acetabulum and femoral head are an important reason for the unreasonable mechanical load of the hip joint.Periacetabular osteotomy(PAO)is the most commonly used surgical treatment method for young DDH patients.It can correct the deformities of the acetabulum and proximal femur,increase the weight-bearing area of the hip joint,restore the coverage of acetabular cartilage,and reconstruct the normal biomechanical relationship of the hip joint.However,the larger difficulty of PAO surgery,intraoperative cutting,adjustment,and fixation are mainly performed depending on the surgeon’s surgical experience,and the lack of systematic theoretical basis for surgical planning based on biomechanics,which have limited the accurate implementation of PAO.Therefore,studying the biomechanics of hip cartilage of DDH patients and the biomechanical response of different surgical plans have important academic value and clinical significance for understanding the pathogenesis of DDH and ensuring the accurate implementation of PAO surgery.In this study,a finite element model of the hip natural solid-liquid biphasic fiber-reinforced cartilage was established to study the differences in biomechanics of natural cartilage between different DDH patients and normal people,and to quantify the effect of PAO adjustment angle on the biomechanics of postoperative hip cartilage.Based on the biomechanical study,a PAO cuttingpositioning guide plate was designed.Firstly,based on the finite element modeling method of solid-liquid biphasic fiberreinforced cartilage,a finite element model of the simplify ball and socket model of the hip joint was established for DDH patient and normal people,and the biomechanical differences of the hip cartilage between DDH patient and normal people were studied under short-and longterm standing conditions.The results showed that fluid in the hip cartilage of DDH patient played a more important role under short-term loading condition,and the fluid flowed out more during long-term loading condition which increased the solid phase compression stress of the hip cartilage.Secondly,based on the finite element modeling method of solid-liquid biphasic fiberreinforced cartilage,the finite element models of hip cartilage of normal people and DDH patients were established,and the biomechanical differences of hip cartilage between different DDH patients and normal people under walking gait were further studied.The results showed that the fluid in the hip cartilage of DDH patients played an important bearing role during walking.The DDH patient with smaller LCEA had more obvious cartilage edge contact,higher contact stress and fluid pressure,and smaller contact area.Thirdly,the parametric finite element models of the hip joint were established for different DDH patients with different LCEAs after PAO.The effect of different acetabular correction angles on the contact mechanics of the hip joint were studied under simulated walking gait,and the optimal adjustment angles for different DDH patients were selected according to the minimum contact stress.Based on the finite element analyses,the optimal LCEA adjustment angles for patients A(LCEA = 8°),B(LCEA = 13°)and C(LCEA = 20°)were 35°,30° and40°,respectively.The results showed that PAO could improve the biomechanical properties of hip cartilage in DDH patients to a certain extent,but it could not completely restore to the level of normal hip joint.For DDH patients with different degrees of disease,it was necessary to determine a specific optimal adjustment angle,and it was not advisable to adopt uniform parameter according to the position of the acetabulum of normal people.Fourth,based on the parametric study of the optimal correction position of the acetabulum of DDH patients after PAO,the design basis of the PAO cutting-positioning guide plate was clarified.The design method of the PAO cutting-positioning guide plate was established for individual case.The results showed that compared with the traditional PAO cutting-positioning guide,the design method of PAO cutting-positioning guide based on biomechanical researches could ensure anatomical structure matching and the accuracy of cutting and positioning.In addition,the designed guide plate was smaller and more flexible to operate,and the fabrication time was reducted by 2.5 hours.This study provideed a theoretical basis and technical means for understanding the pathogenesis of hip joint of DDH patients,determining the best surgical cutting positioning parameters,accurately designing the cutting-positioning guide plates,and improving clinical outcomes.