Analysis Of Developmental Dysplasia Of The Hip Acetabular Biomechanical

Objective:The simulation hip model is established by using3D digitaltechnology, and factors of finite element method on the biomechanicsanalysis, so as to obtain best when rotational osteotomy around theacetabulum bone cutting position and rotation Angle, in order to realizethe postoperative hip uniform stress distribution.Methods:To construct3D-CT finite element models of the normal adult lowerlimbs length via mimics software,including the pelvis and sacrum, on theleft side of the first half of the femur，the CT layer thickness is1.25mm.The model area are divided into cortical bone, cancellous bone, cartilageand glenoid labrum.Every part are given different index according to theliterature.To the state of acetabulum femoral head of the developmentaldysplasia of the hip,measuring the CE angle and VCA angle via plainradiography and constructing pelvic model with three different layers CEand VCA angle,0°、10°and15°.The sacrum took a vertical load about700N， straight down the strength of700N, increasing load with10-stepmethod.Boundary conditions, our posterioanterior axial modelconstrainted in sciatic, fixed completely in the distal femur. The articularsurface stress calculated by three-dimensional finite element analysissoftware MSC. MARC.The acetabulum and femoral head are defined interface.The above model arerespectively calculated.Results:The stress of anterior lateral edge of acetabulum to the top of theacetabulumin in normal hip joint distributed evenly.Compared withnormal hip, developmental dysplasia of the hip model, mises stressincreased. With the decreasing of the CE angle and VCA angle,the stresson the interfance increased a lot.In the model of the15°、10°and0°,stress of the acetabulum and femoral head contact interface. The peakstress value upper the acetabulum, respectively，is17.3MPa,18.9MPa,24.6MPa,18.9MPa；The characteristic of the acetabulum hypoplasia areas follows, the stress concentrated on the anterior lateral of theacetabulum in the model of the CE and VCA15degree、10degree;thestress concentrated on the central of the posterior acetabulum in themodel of the CE0degree and VCA0degree.Conclusions:From what we has measured the normal compare with the hipmodel,the effective weighting area of the articular cartilage graduallydecreased with the change of the CE angle and VCA angle from15degree to0degree,meanwhile,the press on the cartilage increased at thesame loading. the femoral head moved to lateral area， when lateralfemoral head moves beyond the scope of joint contact area，dislocationwill occur. Due to congenital developmental acetabulum hypoplasia of patientsphysiological anatomy structure change, make biological stress changesaround hip joint, the articular cartilage in tension than organizationaladaptability, contraction deformation of articular cartilage, and evendisappear.Around the pseudo cyst formation within the subchondral bone,bone hyperplasia, osteophyte formation, eventually develop osteoarthritis7)9).For good hip rotational acetabular osteotomy for the treatment ofDDH patients, according to the biological stress analysis of hip aroundthe best bone cutting position and rotating Angle, to achieve the desiredhead mortar cover effect, and the stress of the hip joint is uniformlydistributed，so that delay the development of the osteoarthritis.