Effects of kinematic and kinetic variables on articular cartilage mechanical and biological properties

Objective: During daily activity, the knee joint experiences a range of complex joint motion and loading patterns. However, few studies have investigated the effects of combined motion and load to understand how interactions between these factors may affect articular hyaline cartilage at the tissue and cell level. Our objective was to quantify the effects of varying combinations of physiologically relevant analogs of specific knee movements and loading on cartilage mechanical and biological properties. Design: Using response surface methodology applied to an established bioreactor-indenter workflow, we quantified the effect of load (20–60N, or ∼1–3 MPa), sliding speed (1–100 mm/s) and migrating contact frequency (0.00–0.2 Hertz) on changes in cartilage stiffening ratio, cartilage deformation (i.e., surface height displacement), cell viability, histopathological score, and gene expression. All kinetic and kinematic input ranges were chosen to fall within established physiological ranges in the knee. Bioreactor testing was conducted using a ceramic counterface and a testing lubricant of culture medium. Results: Cartilage stiffening ratio increased after loading – the magnitude of the change was affected by load and sliding speed. Minimum cartilage deformation occurred at low load and high sliding speed. Superficial cell death was driven by an interaction of load and sliding speed, with the highest percentages of cell death at high loads. No terms were observed to have significant effects on histopathological score. Conclusions: Our findings provide a better understanding of how kinematic and kinetic factors modulate cartilage responses at the matrix and the cell level, by quantifying the cartilage response using physiological input parameters.