Summary

Future research in the biomechanics of OCDs that will utilize a goat animal model would be well served to use the medial compartment but should avoid using the lateral.

Abstract

Introduction

Treatment for osteochondral defects (OCDs) is a common part of many sports medicine practices. Given that significant research efforts have been placed on seeking new and novel treatments for OCDs and many utilize animal models to do so. One commonly used animal model in OCD research is the goat. Previous studies into the validity of the goat have found it to be a reliable model in terms of anatomy similarities however there is less known about the similarities or differences in the mechanical changes after OCD formation. The intention of this study was to determine if the caprine stifle joint, the analogous joint to the knee in a goat, is a viable model for evaluating the effect of OCD size on joint contact pressures, a commonly studied variable after OCD formation.

Methods

12 caprine stifle joints and 6 human cadaver knees were used. Circular OCDs were created in both the medial and lateral femoral condyle of the goats with diameters of 0mm, 3mm,5mm, 7.5mm. Goat specimens were placed on a custom mounting rig machine and axial loaded with 100N via pulleys in 30° of extension which represents full extension for goats. Human knees had square defects created due to larger condyles and more accurate sizing with sides equal to 3mm, 5mm, and 7mm. Human knees were then loaded onto the MTS machine and loaded with up to 600N. Pressure sensors were inserted into both the medial and lateral compartments and maximum contact pressure during loading was recorded. Plots of surface area to contact pressure were generated for both goat and human and for combined both sides, as well as medial and lateral compartments alone. Linear regression models were created for the above categories and the difference in the model coefficients were analyzed.

Results

The coefficient from the combined laterality regression model for the caprine knees was 3.985MPa/cm2 with an R2 of 0.533 and for humans it was 2.358MPa/cm2 with an R2 of 0.252. The difference between these was 1.627 (p<.001). Coefficients of the medial and lateral compartments alone were 2.341MPa/cm2 with R2 of 0.333 and 5.629MPa/cm2 with R2 of 0.737 for the goats and 2.531 MPa/cm2 with R2 of 0.263 and 2.531MPa/cm2 with R2 of 0.263 for the humans respectively. The differences between the human and goat coefficients for medial and lateral were 0.190 (p>0.1) and 3.444 (p<.01) respectively.

Conclusion

The overall coefficients differ significantly between the caprine and human knees. However, when subdivided by laterality, the medial compartment of the goat appropriately represents the pattern of the medial compartment of the human while the lateral does not. These results indicate future research in the biomechanics of OCDs would be well served to use the medial compartment of a caprine model but should avoid using the lateral.