Osteochondral fluid transport in an ex vivo system

Objective Alterations to fluid transport from bone-to-cartilage may contribute to the development of osteoarthritis. However, many questions remain about fluid transport between these tissues. The objectives of this study were to (1) test for diffusion of 3kDa molecular tracers from bone-to-cartilage and (2) assess potential differences in bone-to-cartilage fluid transport between different loading conditions. Design Osteochondral cores extracted from bovine femurs (N=8 femurs, 10 cores/femur) were subjected to either no-load ( i . e ., pure diffusion), pre-load only, or cyclic compression (5±2% or 10±2% strain) in a two-chamber transport system with the bone compartment filled with a 3kDa tracer. Tracer concentrations in the cartilage compartment were measured every 5 minutes for 120 minutes. Tracer concentrations were analyzed for differences in beginning, peak and equilibrium concentrations, loading effects, and time-to-peak tracer concentration. Results Peak tracer concentration in the cartilage compartment was significantly higher compared to beginning and equilibrium tracer concentrations indicating fluid transport from bone to cartilage. Cartilage-compartment tracer concentration was influenced by strain magnitude, but no time-to-peak relationship was found when comparing strain magnitudes. Conclusion This study shows that osteochondral fluid transport occurs from bone-to-cartilage with 3kDa dextran molecules. These are much larger molecules to move between bone and cartilage than previously reported. Further these results demonstrate the potential for cyclic compression to impact osteochondral fluid transport. Determining the baseline osteochondral fluid transport in healthy tissues is crucial to elucidating the potential mechanisms of progression and onset of osteoarthritis.