Incidence and distribution of 369 proximal sesamoid bone fractures in 354 Standardbred horses (1984-1995)

Fractures of the proximal sesamoid bones are frequently observed in horses submitted to strenuous exercise, especially Standardbreds and Thoroughbreds . Different types of fractures have been classified. Apical, Basal, Abaxial , Mid-body and Comminuted. In the present study, 369 sesamoid fractures dia gnosed 354 Standardbred trotters have been examined in order to evaluate th e distribution of different types of fractures in horses of different age. Correlation between the age of the affected horses and the type of fracture was identified, as well as the tendency for some types of fracture to occu r in specific limbs. Young horses predominated (average age, 2.84 years), w ith 81% of fractures involving 2- and 3-year old horses. Hind limbs were si gnificantly more affected. A prevalence of lateral location of fractures wa s recorded, whereas non-significant differences were observed between left and right side. Apical fractures dominated (88/1%) and this type of fractur e selectively involved young Standardbreds. In older horses, other types of fractures were relatively more frequent. A mean age for each type of fract ure was then identified, ranging from 2.6 years for apical fractures to 6.5 years for mid-body fractures. Apical fractures were mainly located in the hind limb, especially on the left. Basal and mid--- body fractures occurred more frequently in the front limbs. The selective distribution of various types of proximal sesamoid fractures in specific limbs of horses characteri sed by different age can refer to different stages of bone remodelling in r esponse to training and racing. The prevalence of certain sites training an d racing. The prevalence of certain sites also play a role in fracture dist ribution.