Buckle rib fractures are typical of an anterior compressive force to the chest, most commonly external cardiac massage, but can be seen following any such traumatic injury.
Buckle rib fractures occur in all ages, even very elderly patients. Thus ribs are not the same as most adult long bones that tend to break like pencils on the tensile side when exposed to an extreme force.
Buckle fractures are usually seen in the middle ribs (anterior one-third) and in a line. The anterior force responsible for the rib injury may also cause a similar sternal fracture.
Buckle is an engineering term describing cortical disruption to the compressive (inner) side of a structure (i.e. the rib) and maintenance of the tensile (outer) side cortex.