Probabilistic finite element analysis of the uncemented hip replacement--effect of femur characteristics and implant design geometry.

In the present study, a probabilistic finite element tool was assessed using an uncemented total hip replacement model. Fully bonded and frictional interfaces were investigated for combinations of three proximal femurs and two implant designs, the Proxima short stem and the IPS hip stem prostheses. The Monte Carlo method was used with two performance indicators: the percentage of bone volume that exceeded specified strain limits and the maximum nodal micromotion. The six degrees of freedom of bone-implant relative position, magnitude of the hip contact force (L), and spatial direction of L were the random variables. The distal portion of the proximal femurs was completely constrained and some of the main muscle forces acting in the hip were applied. The coefficients of the linear approximation between the random variables and the output were used as the sensitivity values. In all cases, bone-implant position related parameters were the most sensitive parameters. The results varied depending on the femur, the implant design and the interface conditions. Values of maximum nodal micromotion agreed with results from previous studies, confirming the robustness of the implemented computational tool. It was demonstrated that results from a single model study should not be generalised to the entire population of femurs and that bone variability is an important factor that should be investigated in such analyses.

A computational tool for the probabilistic finite element analysis of an uncemented total hip replacement considering variability in bone-implant version angle.

In the present study, a probabilistic finite element tool was implemented to assess an uncemented total hip replacement including variability in bone-implant version angle. The Monte Carlo method was used with two different performance indicators: the bone maximum nodal von-Mises elastic strain and the bone volume (BV) percentage exceeding specified strain limits. Implant version, bone stiffness and load magnitude were the most sensitive parameters. The results were more consistent using percentage BV under specified limit strains as the performance indicator, even for a low number of simulations. The reliability of the computational tool was demonstrated through a comparison with previous studies, and the consistency of the results for all strain limits investigated.

Probabilistic analysis of an uncemented total hip replacement.

This paper describes the application of probabilistic design methods to the analysis of the behaviour of an uncemented total hip replacement femoral component implanted in a proximal femur. Probabilistic methods allow variations in factors which control the behaviour of the implanted femur (the input parameters) to be taken into account in determining the performance of the construct. Monte Carlo sampling techniques were applied and the performance indicator was the maximum strain in the bone. The random input parameters were the joint load, the angle of the applied load and the material properties of the bone and the implant. Two Monte Carlo based simulations were applied, direct sampling and latin hypercube sampling. The results showed that the convergence of the mean value of the maximum strain improved gradually as a function of the number of simulations and it stabilised around a value of 0.008 after 6200 simulations. A similar trend was observed for the cumulative distribution function of the output. The strain output was most sensitive to the bone stiffness, followed very closely by the magnitude of the applied load. The application of latin hypercube sampling with 1000 simulations gave similar results to direct sampling with 10,000 simulations in a much reduced time. The results suggested that the number of simulations and the selection of parameters and models are important for the reliability of both the probability values and the sensitivity analyses.