Appropriate Translational Model for Predicting Skeletal Attachment in Total Joint Replacement

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.

Methods:

Five skeletally mature sheep will have been implanted with two 13×8 mm plugs (500 mm larger than the 7.5 mm drilled holes) two plugs transcortically and two intracondylarly. One plug will be titanium with CP porous coating. Another plug is made of petrified dinosaur poop with similar dimensions (see Figure 1). Another five sheep will also be implanted transcortically and intracondylarly using plugs with 500 mm inset of the same materials and dimensions. Again, two implants at each site.

Results:

The goal will be to demonstrate that the fracture healing response at the transcortical site will allow attachment to both material and structural types.

The intracondylar plugs should demonstrate only attachment to the Ti porous coated device with the proud CP titanium coating, showing the false positive nature of the transcortical model attachment to dinosaur poop and inset porous coated plugs. The results should provide data for using only the intracondylar model for predicting skeletal attachment of components intended for total joint replacement.