**2. Tribology of articulating surfaces**

According to the ASM International handbook, tribology is defined as the science and technology of interacting surfaces in relative motion and all practices related thereto. It includes the study of wear, friction, and lubrication. Total joint replacements have bearing surfaces that must transmit normal joint loads and motions. Low friction has been an important design objective for prosthetic joints for two reasons. First, if large shear forces due to friction are applied to the articulating surfaces, the risk of loosening may be increased. Second, the addition of frictional shear increases the stresses associated with surface damage due to contact, which can result in the release of wear debris to the surrounding tissue that also increases the risk of loosening.
