Does the tidemark location matter in osteochondral allograft transplantation? A finite element analysis

Introduction

While OCA has been shown to result in good long-term outcomes, there is still a considerable failure rate present with room for improvement.

Objectives

The purpose of this study is to evaluate the impact that osteochondral allograft cartilage thickness has on contact pressures, and to simulate whether a mismatch of the subchondral bony interface relative to the host-recipient site results in altered biomechanics.

Methods

Properties of articular cartilage and bone were incorporated into a finite element model to create a simulated osteochondral lesion (diameter: 10 mm, height: 10 mm, cartilage thickness: 2 mm, subchondral bone thickness: 8 mm). Five osteochondral plugs were constructed to fill the defect, with cartilage-to-bone ratios between 1:9 and 1:1. The plugs were inserted and given a static downward force of 5000 N. Resultant stresses and displacements were measured.

Results

The 2:8 cartilage-to-bone ratio plug, matched with the recipient site, was deemed optimal based on its resultant stress and displacement. The 1:9 plug displaced less than the 2:8 match and endured greater stress per unit of cartilage volume, whereas the 3:7 plug also displayed similar displacement to the 1:9 plug but had greater cartilage volume and was able to distribute less stress per unit of cartilage volume. The 4:6 plug displaced to a similar extent as the 3:7 plug but displayed a unique pattern of strain. The 5:5 plug was considered nonfunctional, as the majority of displacement was seen in the cartilage of the recipient site rather than in the plug itself.

Conclusions

The relationship between the cartilage-to-bone ratio in osteochondral allografts and that of their surroundings significantly impacts the distribution of stresses and predilection for micromotion at the repair site.