Femoral Condyle Curvature and the Chondral Modeling Theory

The chondral modeling theory argues that the cartilage of a developing joint surface responds to mechanical loading during ontogeny, resulting in regions of low curvature where the joint is heavily loaded. This theory has been used to explain the relatively lower curvature exhibited by the anterior portions of human femoral condyles. In contrast, it has been argued that the femoral condyles of non‐human primates have constant curvatures, potentially in conflict with the chondral modeling theory, although this has never been rigorously quantified. The goal of this study was to measure the curvature across the medial femoral condyles of chimpanzees and gorillas, comparing them with humans. Three‐dimensional surface models of human (n=9), chimpanzee (n=9) and gorilla (n=9) femora were created using a white light surface scanner. Landmarks were collected on the attachment point for the collateral ligaments and across the femoral head. These points were used to estimate functional/mechanical axes of the femur which were then used to align all bones to a standardized orientation. The profile of each medial condyle, relative to the axis of knee flexion/extension, was extracted from digital images of the models and curvature was quantified across the profile. Measurements of curvature across the human profile match previous work, demonstrating a region of low curvature at the anterior portion of the condyle. While gorilla femora did not appear to exhibit an obvious low curvature region, the chimpanzee medial femoral condyle was found to show a consistent region of relatively low curvature. Furthermore, in support of the chondral modeling hypothesis, the position of low curvature regions appears to be associated with knee positions used during the stance phase of chimpanzee walking.