To characterize cartilage shear strain during articulation, and the effects of lubrication and degeneration.

Human osteochondral cores from lateral femoral condyles, characterized as normal or mildly degenerated based on surface structure, were selected. Under video microscopy, pairs of osteochondral blocks from each core were apposed, compressed 15%, and subjected to relative lateral motion with synovial fluid (SF) or phosphate buffered saline (PBS) as lubricant. When cartilage surfaces began to slide steadily, shear strain (E_xz) and modulus (G) overall in the full tissue thickness and also as a function of depth from the surface were determined.

In normal tissue with SF as lubricant, E_xz was highest (0.056) near the articular surface and diminished monotonically with depth, with an overall average E_xz of 0.028. In degenerated cartilage with SF as lubricant, E_xz near the surface (0.28) was 5‐fold that of normal cartilage and localized there, with an overall E_xz of 0.041. With PBS as lubricant, E_xz values near the articular surface were ∼50% higher than those observed with SF, and overall E_xz was 0.045 and 0.062 in normal and degenerated tissue, respectively. Near the articular surface, G was lower with degeneration (0.06 MPa, versus 0.18 MPa in normal cartilage). In both normal and degenerated cartilage, G increased with tissue depth to 3–4 MPa, with an overall G of 0.26–0.32 MPa.

During articulation, peak cartilage shear is highest near the articular surface and decreases markedly with depth. With degeneration and diminished lubrication, the markedly increased cartilage shear near the articular surface may contribute to progressive cartilage deterioration and osteoarthritis.