Histologic characterization of fracture repair process in wild birds in association with gross appearance of the bone lesion

This study aims to provide an in-depth examination of the histological changes that occur during the repair of untreated bone fractures in avian species, correlating these microscopic alterations with gross anatomical characteristics observed during different tissue repair phases. A total of 93 bone fractures from different wild birds were analyzed and classified based on temporality (acute, subacute, and chronic) according to the color changes of the hematoma and morphology (open or closed; simple, comminuted, or greenstick fractures). From a microscopic standpoint, a strong correlation was observed between the temporal progression observed macroscopically and the histological changes evident in each temporal category. Microscopic variations were found to depend on the nature of the fracture. Lesional patterns directly related to the macroscopic appearance of the fracture were established. Acute fractures exhibited extensive hematomas and an intense inflammatory response; subacute fractures showed immature granulation tissue and early signs of soft callus formation; and finally, chronic fractures were characterized by prominent soft calluses and hard calluses in different stages of development. The possible factors influencing each phase of the healing process, such as the characteristics of the type of fracture, the stability of the fracture site, bacterial contamination, the chronicity of the fracture, and the potential differences in the progression of histological changes between different animal species, are discussed. This association may be of clinical utility in decision-making for the treatment and prognosis of bone fractures in birds.