Permeability of bone and cartilage, and stiffness of collagen within cartilage, influence osteochondral fluid transport during cyclic compression: A study in finite elements.

Osteochondral fluid transport likely plays a critical role in joint health and disease, yet the mechanical factors influencing this transport remain incompletely understood. This study established a finite element model of osteochondral fluid transport under cyclic compression, incorporating depth-dependent material properties and osmotic swelling. Using biphasic constitutive models for bone and cartilage, we simulated fluid flux across the osteochondral interface and performed a parametric sensitivity analysis of seven different mechanical properties. Results demonstrate that bone and cartilage permeability, as well as the stiffness of the collagen fiber network within cartilage, significantly affect net osteochondral fluid transport. Specifically, decreased cartilage permeability resulted in increased bone-to-cartilage ostechondral flow, and decreased collagen stiffness resulted in decreased net cartilage-to-bone fluid flow. Conversely, relatively high bone permeability reversed the direction of osteochondral flow. Other parameters, including bone modulus, bone solid volume fraction, cartilage shear modulus, and fixed charge density, had negligible effects. These findings highlight the importance of specific mechanical properties of both bone and cartilage in regulating osteochondral fluid transport and suggest that future studies should consider the complete osteochondral unit to better understand joint mechanobiology and osteoarthritis progression.