An association between complete and incomplete stress fractures of the humerus in racehorses.

This study investigates the link between full and partial stress fractures of the humerus in racehorses, based on data from 21 horses at a Californian racetrack over a year-long period.

Sample and Examination

• The research involved studying 21 horses that had experienced a complete, unilateral humeral fracture during race training or actual racing. This took place at a racetrack in California from 24 February 1990 to 10 July 1991.
• These fractures occurred almost equally in both left and right limbs of the horses, and were also distributed almost evenly between male and female horses. The most significant injury took place during training sessions and mostly involved 2- and 3-year-old horses.

Findings

• Among the 16 Thoroughbred horses with known racing histories, just 5 had raced more than once in the past. An analysis of their racing times revealed that the average time lapse between their races was shorter than the time span from their last race to their fracture injury, with a significance level of P = 0.07, suggesting the damaging effect of a shorter recovery time between races.
• Further examination of 13 humerus bones revealed that 10 of them had visible signs of periosteal callus bridging one segment of the fracture line, which is a reliable telltale sign of a pre-existing stress fracture. This suggests these injuries likely resulted from accumulated stress and strain rather than a single, traumatic event.

Conclusion

• Based on the findings, the study concludes that there’s a correlation between complete and incomplete stress fractures of the humerus in racehorses. The frequency and intensity of training, as well as the adequacy of rest periods between races, could have a significant impact.