Table 2.

Histological classification proposed by Allen et al. (1980) for analysis of bone healing stage.

Grade	Characteristic
4	Complete bone healing
3	Incomplete bone union due to the presence of a small amount of callus cartilage
2	Visibility of a well-formed hyaline cartilage bridge, joining the main fragments (complete cartilaginous union)
1	Incomplete cartilaginous union, with fibrous element retention in the chondral plate
0	Absence or delay in fracture repair, characterized by the presence of cartilage between fragments and remains of hematoma or other fluid (pseudoarthrosis)