microcrack

noun

mi·​cro·​crack -ˈkrak 

: a small or minute fracture in a material (such as bone) : microfracture sense 1

Fatigue damage in bone occurs in the form of microcracks. … The process of microcrack accumulation in bone may eventually lead to stress fractures. These fractures occur commonly in athletes and soldiers engaged in high intensity, repetitive activities such as marching or running and happen when microcracks accumulate at a rate that exceeds the capacity for bone repair.

—Fergal J. O'Brien et al., Journal of Orthopaedic Research