Three Dimensional Dynamic Biomechanical Analysis Of Hip Surface Based On CT Images

Serious hip diseases especially osteoarthritis(OA)is treated by late intervention i.e.total hip replacement at present.However,currently used spherical implant is seriously worn at the joint surface,which causes a shorter lifetime.Proper stress distribution on hip joint surface would create good stress environment for joint cartilage and slow down the degradation of joint cartilage efficiently.In clinical,orthopedists still follow the concept that the hip joint surface could be represented as simple sphere to guide diagnose and treatment of hip joint diseases.Considering the importance of hip joint surface anatomical morphology and coupling structure,many researchers have studied the hip joint surface anatomy from both anatomical measurement and biomechanical perspective until now.However,former studies were usually for statics while loads in human daily life and strong wear on joint surface mainly occurs during dynamic activities.The analysis of static model can indicate the result of the problem to some extent.But it can’t describe the actual conditions or explain the biomechanical mechanism of the model fully in practice.In order to describe the hip joint surface geometry effects on surface biomechanics during human walking more accurately,hip joint surface 3D dynamic biomechanical analysis is built in this thesis.That is,combining gait analysis and finite element modelling analysis for biomechanical mechanism study of natural joint,sphere replaced and rotational ellipsoid replaced joint biomechanics on the articular surface.It provided essential basis for understanding of natural hip joint surface biomechanics more comprehensively and idea for artificial hip prosthesis geometry optimization.In this thesis,3D geometry model of natural hip joint is built based on CT sequence images of normal volunteer.Scanned CT images were imported into MIMICS software firstly.A series of operations including threshold segmentation,region growing and manually cavity filling were done to build 3D hip finite element model(FEM).Ten instants during a complete gait cycle were selected.Anatomical positions,loads and boundary conditions for each of the instants were selected referring to Bergmann’s report.Stress distribution on hip joint surface was obtained in ABAQUS and analyzed.According to current model,the joint surface was replaced with sphere and rotational ellipsoid respectively during a gait cycle.The differences of biomechanical mechanism between the three geometries were compared to find a better description of human hip joint surface anatomy,thus giving a theoretical guidance for anatomical bionic artificial hip implant development.The results indicated: 1)The trends of peak pressure under three joint surface geometries were the same during a complete gait which is consistent with that of applied loads.2)Contact stresses of natural hip were lowest among the three models for most of the instants in a gait cycle.Rotational ellipsoid replaced hip took the second place and sphere replaced one resulted in highest contact stress.The results give an indication that rotational ellipsoid prosthesis could give a better description of physiological structure compared with standard sphere prosthesis which may increase the lifetime of implant.The dynamic biomechanical method established in this paper can not only solve the problem of hip joint well,but also provide an idea for the analysis of other biomechanical problems in scientific research and clinical.