Introduction

Fixation has been shown to be the primary indicator of an implant's long-term success. Failure to achieve attachment, especially in acetabular and TKR, has been attributed to a lack of initial stability and gaps between the implant and bone. Gaps greater than 150 microns allow fibrous tissue to form. Properly addressing implant design features can help avoid adverse outcomes.

ASTM International Standards (F1854-09) do not assess the relationship between porosity of the coating and that of cancellous bone, which can lead to an absence of mechanical interlock. This study developed a virtual program that uses human cancellous bone to predict potential skeletal attachment for implants properly placed for TJR. The goal of the Virtual Paradigm was to assess initial contact surface area at the time of implantation.

Introduction:

With the arrival of the 21^st century, there were clear expectations that cementless fixation in total joint replacements (TJR), and the translational animal protocols for introducing new coatings and surface treatments clinically, had been established. Despite the extensive literature in the 1980s and 1990s demonstrating a translational pathway for predicting skeletal attachment, there remain clinical reports of mechanical implant loosening in both cementless total hip acetabular and total knee components. Before screening a new porous coating or surface treatment, it is important to note that there has been only one experimental translational load-bearing model that has had human (1–3), sheep (4–5), clinical (6–8), and implant retrieval verification confirming skeletal attachment in these types of components, the intracondylar model (1–5,8).

What makes the intracondular model predictive of coating or surface treatments for implant attachment is the ability of the model to replicate the healing response of cancellous bone, the main attachment bone tissue to THR acetabular and TKA implants. A lot of the confusion rests with a lack of understanding of the bone response differences between the intracondylar and transcortical animal models.

The goal of this study was to test the hypothesis that the intracondylar model can provide positive and negative surface attachment data, whereas, the transcortical model can only provide positive and false positive attachment data.