A hairline fracture is a tiny crack in a bone that is difficult to see or detect. It is like a thin line on the surface of the bone, but it is not a full break. Full definition
Jennifer Allora & Guillermo Calzadilla (born 1974, USA and 1971, Cuba) identify and stress hairline fractures in societal systems through performance, sculpture, sound, video and photography. (everythingatonce.com)
Result: hairline fractures of both the tibia and fibula. (si.com)
Bones can break in any number of ways, from small cracks known as hairline fractures to the multiple snaps of a compound fracture. (chicagolawyer.com)