Influence of the load modelling during gait on the stress distribution in a femoral implant

Introduction: When designing and installing implants, stress analyses should be performed in conditions close to those of everyday use. Specifically, for femoral implants, cyclic loading during gait has been demonstrated to produce fatigue failure. However, there is still no consensus in the literature regarding which modelling procedure is the most appropriate to simulate implant working conditions. This work proposes a method for realistic load modelling of the human body during gait based on flexible multibody dynamics. Method:The proposed dynamic method was applied to a case study of a lower limb implant that failed by fatigue. The computed stresses were compared to the stresses obtained using the other three methods found in the literature, which are principally based on static or quasi-static load modelling. Results: For all compared methods, the maximum computed stress was located in the same region of the implant. The maximum stress provided using flexible multibody dynamics was equal to 346 MPa, which was 355% greater than the maximum value given by the static method and 18% greater than the value given by the quasi-static method. Discussion and conclusion: The proposed dynamic method was in agreement with the conclusions of the previous failure analysis performed on the broken implant. Conversely, the static and quasi-static methods were not representative of the real loading conditions induced by gait. Moreover, the dynamic method emphasizes the pertinence of evaluating the fluctuations in the critical stress during the gait cycle, which is mandatory when studying fatigue failures.