Three-dimensional kinematics of the tarsal joint at the trot

The tarsal joint is a common site of injury for many sport horses. Understanding the biomechanics of this complex joint begins with developing a clear picture of the kinematics during normal locomotion. This study describes the 3D kinematics of the tarsal joint by measuring the motion of the tibia and third metatarsus in 4 sound Quarter Horses with targets attached directly to the bones via steel pins. The objective was to determine if the tarsus had significant motion outside the tarsocrural joint. Two Steinmann pins were inserted into the lateral side of the right hindlimb and marker triads were fixed to the end of each pin. 3D motion of the bones was recorded as each subject trotted in hand. Three rotations were expressed using an attitude vector based on the finite helical angle method. Three translations were calculated as the motion of the tibia relative to the third metatarsus. Angular and translation data were mostly coupled with flexion angle. Internal/external rotation during stance and translations during swing showed evidence of noncoupled motion. Although the majority of tarsal motion occurs in the tarsocrural joint, there is evidence that translations and rotations occur in other locations within the tarsal joint and that some of these are related to the tarsal joint 'snapping' phenomenon. This research provides a set of reference 3D kinematics which will aid in the study of the aetiology and mechanical effects of tarsal joint lameness.