Electrical potentials derived from articular cartilage: the significance of polarization potentials

Changes of electrical potentials in cartilage tissue under mechanical compression have been detected in several studies. As polarization potentials are known to occur at the interface between metals and electrolytes, the question remains open whether the measured electrical potentials in relation to mechanical compression are interfered with polarization potentials. Using a porcine model, whole knee joints were explanted and exposed to uniaxial loading of up to 250 N. Under similar conditions, a tube filled with normal saline was prepared with three gold-plated electrodes. Changes of voltage derived from the electrodes placed in normal saline could be detected only when the force was applied instantly by a hydraulically controlled pump. In comparison, mechanically induced electrical potentials could be derived from cartilage tissue when exposed to both sudden force and force induced more slowly by an electric engine. While the electrical response derived from cartilage tissue correlated with the extent of the applied force, there was no such correlation between the potential changes from normal saline and the applied mechanical force. In conclusion, polarization potentials derived from metal electrodes in contact with electrolyte solution are pressure dependent. However, those electrical potential changes obtained from the cartilage tissue under compressive force revealed no obvious influence by polarization potentials.