A pendulum test as a tool to evaluate viscous friction parameters in the equine fetlock joint

This study describes an equine fetlock joint pendulum test, and investigates the influence of post mortem time and intra-articular lipid solvent on the viscous frictional response. Fresh equine digits (control group 1 (n = 6); lipid solvent group 2 (n = 6)) were mounted in a pendulum tribometer. Assuming that pendular joint damping could be modelled by a harmonic oscillator fluid damping (HOFD), damping time (t), viscous damping coefficient (c ) and friction coefficient (µ) were then followed for 5 hours under experimental conditions (400 N; 20 °C). In all experiments, pendular joint damping was found to follow an exponential decay function (R² = 0.99714), which confirms that joint damping is fluid. The evolution of t, c and µ was found to be significantly (P <0.05) different in the two groups. Indeed, t decreased and c and µ increased more rapidly and strongly in the group 2. It was concluded that pendular joint damping can be modelled by an HOFD model. The influence of post mortem time on results suggests that, ideally, joint mechanical properties should only be tested on fresh cadavers at the same post mortem time. Finally, the addition of lipid solvent was found to be responsible for upper viscous friction parameters and for a reduced damping time, which suggests that articular lubricating ability was compromised. This equine pendulum test could be used to test the efficacy of various bio-lubricant treatments.