Fetlock joint kinematics differ with age in Thoroughbred [was thoroughbred] racehorses.

The study investigates the differences in the movement or kinematics of the fetlock joint in Thoroughbred racehorses of different ages, specifically between 2- and 5- years old, during galloping to see if these disparities may explain why younger racehorses tend to sustain more injuries to their forelimbs compared to older ones.

Study Methodology

• The researchers conducted their study on twelve Thoroughbred racehorses of varying ages between 2 and 5 years old.
• The motion of these horses during their daily galloping workouts on a 7/8 mile sand-surface track was captured. The researchers videotaped these sequences in slow motion at 250 frames per second, focusing on the sagittal plane or side view.
• Four galloping strides were recorded for each horse, and these were then digitized to determine the angles of the fetlock joints in the leading forelimb during the support period of a stride. The support period is when the hoof makes contact with the ground and bears the horse’s weight.

Measured Variables

• The researchers measured four kinematic variables from the angular profile of each stride. These variables were: the angle of fetlock joint dorsi-flexion (bending) at the mid-stance phase, the negative angular velocity, the positive angular velocity, and the time from hoof impact to the mid-stance phase of limb support.

Findings

• It was found that the 2-year-old Thoroughbreds had a significantly faster rate of dorsi-flexion of their fetlock joints compared to the 3-, 4-, and 5-year-old Thoroughbreds. These differences were statistically significant.
• This was observed following the impact of the leading forelimb during moderate galloping, with an average speed of 14 meters per second.
• The researchers suggest that the higher rate of dorsi-flexion in the young Thoroughbreds may be caused by the immaturity of their suspensory apparatus tissues. The suspensory apparatus is a group of ligaments and tendons that support the fetlock joint, and immaturity in this context implies a lack of stiffness.

Implications

• The findings of this research could provide a possible explanation for the higher incidence of forelimb injuries observed in young Thoroughbred racehorses.
• It raises the question of whether training and racing practices for young racehorses should be modified to mitigate this risk.