INVESTIGATING THE POTENTIAL ADVANTAGES OF A NEW DESIGN OF SMALL JOINT ARTHROPLASTY USING FEA ANALYSIS

Abstract

Introduction: Current existing joint designs, principally flexible silastic spacers, satisfy the initial requirements but commonly lack durability. In particular all flexible silastic joints are prone to early breakage due to abrasion against bone and constant loading of the central section of the flexible implants. The aim of our new small joint design is to overcome many of the deficiencies of the flexible silastic designs while maintaining their main advantage of stabilising joint alignment throughout the flexion range.

Aim: To investigate the wear properties of the new small joint design in both static and dynamic applied loads using finite element analysis (FEA).

Materials: The design is essentially a cross between a flexible spacer and a surface replacement, whereby the spanning flexible spacer is located within the long axes of direct load bearing metacarpal and phalangeal ‘housings’. We have investigated a number of parameters, using finite element analysis (FEA), focussing principally upon the load bearing and wear properties of the new design to both static and dynamic applied loads with reference to the test protocol developed by the Durham group.

Results: Detailed FEA of the new joint design has highlighted the extreme potential durability of the housings and the internal flexible spacer. Our results suggest that the wear characteristics of both housings manufactured from PEEK (Polyetheretherketones) may result in the generation of considerably less wear debris compared with conventional alloy/plastic articulations. In addition, polyurethanes would appear to have better load bearing and wear characteristics than existing silastic materials.

Conclusions: Clearly, if our FEA findings were to be reproduced with biomechanical testing, we would be well placed to introduce durable and readily affordable small joint arthroplasties that may well resolve our current difficulties of treating patients with moderate joint disease in addition to being a realistic alternative for patients with advanced destructive small joint arthritis.