Design changes improve contact patterns and articular surface damage in total knee arthroplasty

The Optetrak PS (Exactech, Inc., Gainesville, FL) has been a well-functioning posterior stabilized knee replacement since its introduction in 1995. In 2009, the Optetrak Logic incorporated modifications to the anterior face of the tibial post and the corresponding anterior articulating surface of the femoral component to reduce edge loading on the polyethylene post. In this study, we provide the rationale for the design change and compare the damage on retrieved tibial components of both designs to demonstrate the effectiveness of the design modifications in decreasing post damage.

We integrated retrieval findings of tibial post damage with finite element analysis to redesign the anterior tibial post-femoral box articulation. We then used subsequent retrieval analysis on a 3:1 matched sample of 60 PS and 20 Logic inserts to examine the impact of the design change on polyethylene damage.

Polyethylene stresses were markedly reduced when rounded contact geometries were incorporated. The comparison of the new and old designs using retrieval analysis demonstrated that the redesign led to reduction in surface damage and deformation on the tibial post.

This study shows the use of a design cycle by which a problem is identified through retrieval analysis, analytical tools are used to suggest design solutions, and then retrieval analysis is applied again on the new design to confirm improved performance.

Anterior post damage has been markedly reduced through the introduction of design changes to the post-box geometry.