Research On Human Lower Limb Biomechanics Based On Multibody Dynamics And Finite Element Method

The activity and load of human lower limb joints are much greater than that of the upper limb joints,therefore the lower limb joints and soft tissues around them are more susceptible to diseases and injuries.Serious lower limb joint damage might cause other diseases and disability.Osteoarthritis(OA)is a common degenerative joint disease caused by multiple factors and clinical manifestations such as pain,limited joint motion range,muscle weakness,joint stiffness and instability etc.Total knee replacement(TKR),the most effective methods in clinic,has been widely used in the treatment of end-stage of knee OA.The study of lower limb biomechanics in patients with OA who have joint replacement surgery at different stages will have important practical significance.Using current advanced research methods in modern sport biomechanics and from the perspective of OA diagnosis,rehabilitation after joint replacement and the life of joint prosthesis,this thesis studied and focused on concerned problems of patients with early knee OA and TKA.Biomechanical behaviors of the lower limb joints and muscles were analyzed based on gait analysis,multi-body dynamic musculoskeletal(MS)simulation and finite element(FE)model.The aim of this study is to provide data support for clinical treatment and rehabilitation.The specific contents are as follows:The effects of toe-in and toe-out gait modification for early knee OA patients on lower limb kinematics,dynamics,and Electromyography(EMG)were investigated.The results showed that the maximum flexion angle of the knee and the adduction angle of hip were limited after gait modification(P<0.05).The toe-out gait increased the second peak of ground reaction force(GRF)in the medial-lateral direction(P<0.05).The toe-in and toe-out resulted in higher peak values for quadriceps and peroneus longus.The results also showed that gait modification could relieve patient pain without necessarily reduce tibiofemoral(TF)contact force,but might adjusted contact force or contact area on the medial and lateral of TF joints,and the TF total contact force is then redistributed and reduce the contact stress of articular cartilage The results suggested that the toe-in gait might be better than the toe-out gait as a conservative treatment for patients with early knee OA.Subject-specific MS multibody dynamics model and knee FE model after TKA were developed to investigate the biomechanical effects of medthust and bouncy gait modification.The building of MS model is based on geometry of the patient bone and prosthesis.Taking patient's gait analysis and the MS predicted results inputted the EF model and calculated,the FE results were finally calibrated using Hertz contact theory.The results showed that the medthrust gait reduce the TF joint contact force,but it might increase the instability of the hip joint.Both gait types increase the contact stress of the tibial insert.The results suggested that for patients with stable hip joints and in the period of early postoperative,patients could choose medthrust gait as a method to reduce the TF joint contact force and surrounding soft tissue forces,which could restore physiological functions of reconstructed joint as soon as possible.Taking into account the effective life of artificial joints in the human body,the FEM results does not recommend that patients long-term walk with the medthrust and bouncy gait.The developed subject-specific MS model also was used to explore the effects of quadriceps and hamstring muscles weakness on TF contact forces during normal gait.The results showed that weakness of all quadriceps and hamstring muscle groups reduced the TF contact force but increased muscle activations.The muscle weakness of the quadriceps had greater effect on the TF contact forces than hamstring.Considering postoperative muscle weakness in the multi-body dynamics MS model is beneficial to improve the prediction accuracy.The effect of gait modification on lower limb biomechanics studied in this paper provides reasonable advice for conservative treatment of early knee OA patients and rehabilitation of patients after TKA.The method of calibrating finite element results using Hertz contact theory could provides new ideas for the design and wear assessment of artificial joint prostheses.This paper also quantitatively analyzed the impact of quadriceps and hamstring muscle weakness on the TF joint contact force,which is helpful to improving the prediction accuracy of the multi-body dynamic MS model.The research on biomechanics of human lower limbs mentioned above could provide a powerful theoretical basis and help on many areas such as clinical diagnosis,rehabilitation engineering,medical simulation,sports etc.