Does a relation between bone histomorphometry and fractures exist? The case of the equine radius and tibia

Fractures of long bones in limbs are rare traumatic events in horses. This study investigates whether the incidence and types of fractures can be related to the histomorphometric features of the radius and tibia, which experience different biomechanical stresses and exhibit varying incidences and types of fractures. Clinical observations suggest that, in adults, slightly transverse and comminuted fractures are present in the radius, while the tibia shows a higher frequency of longitudinal and spiral fractures. Microscopic observations reveal no apparent distinctive characteristics between the radius and tibia, whereas the histomorphometric data highlight differences in the osteon density, eccentricity, and diameters of the osteons and Haversian canals. To sum up, tibial osteons are more numerous and smaller than those in the radius, resulting in a 15% higher total extension of the cement line in the tibia compared to the radius. These histomorphometric differences are an evolutionary adaptation to the different biomechanical stresses that involve the thoracic and pelvic limbs. Our results could help better understand numerous clinical realities detectable through retrospective analyses and aid in evaluating a specific bone's predisposition towards traumatic events in all mammals, including humans.