Investigation on the sensitivity of indentation devices for detection of fatigue loading induced damage in bovine cortical bone.

Daily physiological activities subject our skeletal system to cyclic loading with varying frequencies and magnitudes. These loadings interact with the microstructure of bone and create microdamage, which can cause stress-induced injuries if not repaired on the time. The early detection is required to prevent the complications associated with these fractures. In the present study, to examine fatigue loading-induced damage in cortical bone, the sensitivity of four different indentation devices was investigated. For this, cortical bone samples were fatigued in four-point bending configuration at 0.5 Hz, 2 Hz and 4 Hz frequencies. Following the fatigue loading, cyclic reference point indentation (cRPI), impact reference point indentation (iRPI), Vickers microhardness and nanoindentation tests were performed on the bone samples. Results show that indentation devices are sensitive to detect fatigue loading induced damage only in 0.5 Hz group samples on compressive region. On the other hand, the sensitivity of indentation devices for tensile stress-induced damage is not clear. Also, histological examination of fatigued bone samples shows a significant increase in the crack density and crack length with fatigue loading only for the 0.5 Hz group samples. The present study provides insight into the sensitivity of different indentation devices to fatigue loading induced damage, which could be helpful in the development of new devices for the early diagnosis of stress induced injuries.