The effects of contact stress and articulation amplitude on fluid load support in articular cartilage

Jamie M. Benson¹, Jordyn L. Schrader¹, David L. Burris^1,2

¹Biomedical Engineering, ²Mechanical Engineering, University of Delaware, Newark, DE

Introduction: During mechanical loading of the joint interstitial pressure gradients develop in the cartilage as fluid is forced through the matrix¹. While the matrix carries a fraction of the load, the fluid pressurization carries a bulk of it ^{2, 3}. Using the migrating contact (MCA) setup we can induce this fluid load support, which leverages the intermittent bath exposure recovery theory. In this study, we used the MCA to elucidate the fluid load support in relation to varying applied contact stresses and articulation lengths.

Methods: 19 mm diameter full thickness osteochondral plugs were extracted from the femoral condyles of adult bovine stifles, and were tested in the MCA. Explants were tested in static equilibrium and sliding equilibrium with probes of diameter sizes 6.35mm, 4.763mm, 3.969mm, 3.175mm and 2.381mm—across increasing track lengths and constant loads.

Results: The fluid load fraction of the plugs were calculated in response to the increasing probe size and track lengths. Under low contact stresses and high articulation lengths, represented by the fluid load support of the cartilage nears 100%. As the contact stresses increase, there is a reduction in the maximal fluid load support. But when articulation lengths remained low, regardless of contact stresses, the fluid load support diminished. 

Conclusions:This study demonstrates that the fluid load support of cartilage is dependent on contact forces and articulation length. Fluid load support decreases with decreased track length and increased contact stresses—impeding its cartilages’ ability to recover fluid passively.