Open Access

ARTICLE

Shear Deformation Kinematics During Cartilage Articulation: Effect of Lubrication, Degeneration, and Stress Relaxation

Benjamin L. Wong^*, Won C. Bae^*, Kenneth R. Gratz^*, Robert L. Sah^∗,†

∗ University of California–San Diego, La Jolla, CA.
† Correspondence author. Department of Bioengineering, Mail Code 0412, University of California–San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0412. Tel: (858) 534-0821. Fax: (858) 822-1614. E-mail: rsah@ucsd.edu.

Molecular & Cellular Biomechanics 2008, 5(3), 197-206. https://doi.org/10.3970/mcb.2008.005.197

Abstract

During joint articulation, the biomechanical behavior of cartilage not only facilitates load-bearing and low-friction, but also provides regulatory cues to chondrocytes. Elucidation of cartilage kinematics under combined compression and shearing conditions clarifies these cues in health and disease. The objectives of this study were to elucidate the effects of lubricant, tissue degeneration, and stress relaxation duration on cartilage shear kinematics during articulation. Human osteochondral cores with normal and mildly degenerate surface structures were isolated. Paired blocks from each core were apposed, compressed, allowed to stress relax for 5 or 60 min, and shear tested with a micro-scale video microscopy system using phosphate-buffered saline (PBS) or synovial fluid as lubricant. During applied lateral motion, local and overall shear strain (E_xz) of articular cartilage were determined. The applied lateral displacement at which E_xz reached 50% of the peak (Δx_1/2) was also determined. Quantitatively, surface E_xz increased at the onset of lateral motion and peaked just as surfaces detached and slid. With continued lateral motion, surface E_xz was maintained. After short stress relaxation, effects of lubrication on E_xz and Δx_1/2 were not apparent. With prolonged stress relaxation, E_xz and Δx_1/2 near the articular surface increased markedly when PBS was used as lubricant. Similar patterns were observed for overall E_xz and Δx_1/2. With degeneration, surface E_xz was consistently higher for all cases after the onset of lateral motion. Thus, cartilage shear kinematics is markedly affected by lubricant, cartilage degeneration, and loading duration. Changes in these factors may be involved in the pathogenesis of osteoarthritis.

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