Friction of osteoarthritic cartilage with patient-specific synovial fluid: Effect of different loading conditions

The objective of this study was to quantify the friction coefficients of degenerated human cartilage lubricated with patient-specific synovial fluid under four different loading regimes in order to identify those regimes that cause the highest friction.

Lateral tibial plateaus and synovial fluid samples were obtained from six patients undergoing total knee replacement surgery. Friction tests were performed on cylindrical samples using an established cartilage against glass tribometer. Four different loading regimes were applied, representing physiologic loads and velocities observed during daily activities. To account for effects of osteoarthritis (OA)-related alterations in the synovial fluid (SF) on friction, patient-specific SF was used as lubricant. Friction coefficients were derived from the first (μ₀) and final 60 ​s (μ_end) of testing.

Under stance phase conditions, friction was lowest at the beginning of testing (μ₀ ​= ​0.021), but increased the most (+276 %, μ_end ​= ​0.079) compared to low (+47 %) and moderate loading regimes (+31 %). Under swing phase conditions low friction was maintained over time (+0 %, μ₀ ​= ​0.041, μ_end ​= ​0.041).

The friction properties of degenerated cartilage samples indicated a strong dependency on the loading regime, whereby prolonged stance phase loading led to the highest time-dependent increase in friction. Moreover, our data suggested that osteoarthritic synovial fluid was sufficient to provide low cartilage friction.