The most widely used classification is that developed by Weber and Czech, who classified 2 types. First is hypertophic nonunion; the ends of fragments are hyper-vascular and capable of biological reaction, posses' adequate vascularity, produces abundant endosteal callus seeds off medullary canal, radiolucent gap bridged by fibrocartilagenous tissue without osteogenic capacity. Second type is avascular; incapable of biological reaction, poor blood supply to the ends of fragment, no periosteal or endosteal callus, radiolucent gap bridged by fibrous tissue without osteogenic capacity and resorbed fracture surfaces which are osteopenic.