Finite element methods have been applied extensively and with much success in the analysis of orthopaedic hip and knee implants. Very recently a burgeoning interest has developed, in the finite element community, in how numerical models can be constructed for the solution of problems in contact mechanics. New developments in this area are of paramount importance in the design of implants for orthopaedic surgery. Modern techniques are described for finite element contact analysis and applied to two problems of stress analysis in a plastic tibial component. In the former, results are compared with a previous finite element analysis and with Hertzian solutions. In the latter, an estimate of the extent of convergence of the finite element solutions is provided.

Finite Element Analysis of a Total Knee Replacement by Using Gauss Point Contact Constraints

This paper is a review of different methods used to reduce the effect of strain gradients in experimental models with 3D embedded strain gauged transducers. A detailed analysis of various methods used in relation to research carried out on a prosthetic hip implant is investigated. The methods to reduce these gradient effects detail the importance of the selection of the most suitable 3D transducer pattern and establishing the locations on the model where strain gradients are least problematic. It is also shown that the use of large-scale models helps minimise the effect a gradient may have on data. Another way of avoiding strain gradients is to use axisymmetric models and embed the gauges at the same radius in the model but at a different angular orientation from the central axis. The strain gradient across the 3D embedded strain gauge transducer can be reduced using the methods described here so that significant errors in the final tensor do not materialise.

An Examination of Various Methods of Minimising Strain Gradients in 3D Embedded Strain Gauge Analysis

Finite element analysis of a total knee replacement by using Gauss point contact constraints.

This study deals with the development of a specialized finite element algorithm suitable for a non-linear contact stress analysis of a model of a plastic tibial plateau of a typical unicondylar knee prosthesis. The principle feature of the contact algorithm is the use of Lagrange multiplier methods for the application of displacement constraints to surface Gauss points of a contacting body to prevent mesh overlap. This allows the effective modelling of two- and three-dimensional contact problems, with or without friction, using higher order elements. Through the selection of suitable benchmark tests, the performance and accuracy of the algorithm was assessed prior to the model analysis. Good agreement was obtained between the finite element results for the contact model and existing theoretical and experimental data. It was found that the Hertzian theory failed to accurately predict localized stresses at the contact interface when the indenter was much stiffer than the model.

http://sdj.sagepub.com/content/30/3/195.full.pdf

E G Little

Papers

Modelling an orthopaedic knee prosthesis as a layered elastic system part 2: Finite element analysis