Levels of active metabolites of vitamin D₃ in the callus of fracture repair in chicks

The levels of the active metabolites of vitamin D were measured in the callus and in the epiphyseal growth plate of chicks given radioactive cholecalciferol during fracture healing. Those levels were correlated with the histological findings. Three groups of chicks were studied: a control group with no fracture, chicks with fractures fixed by Kirschner wire, and chicks with unfixed fractures. A significant increase in the levels of the active metabolites was found in the callus during the first few days after fracture. The levels of 25-hydroxycholecalciferol [25(OH)D₃] and of 24,25-dihydroxycholecalciferol [24,25(OH)₂D₃] were higher when there was no fixation, while those of 1,25-dihydroxycholecalciferol [1,25(OH)₂D₃] were higher after fixation. The concentrations of these metabolites in the proximal epiphysis of the tibia were similar to those found in the callus. Based on these findings it is suggested that the active metabolites of vitamin D are directly involved in the process of fracture repair.