Effect of standing tarsal angle on joint kinematics and kinetics

REASONS FOR PERFORMING STUDY: The tarsal joint is a frequent site of lameness, but little objective information is available regarding the effects of tarsal conformation on joint movements or forces. OBJECTIVE: To compare tarsal kinematics and kinetics in horses with large, intermediate and small tarsal angles. METHODS: Sagittal plane standing angle of the right tarsal joint was measured in 16 horses as they stood squarely with the hind hooves vertically beneath the hip joint. Tarsal angles were classified as small (< 155.5 degrees), intermediate (155.5-165.5 degrees) or large (> 165.5 degrees). Reflective markers, attached over the centres of joint rotation, were tracked during stance as the horses trotted across a force plate at a standardised speed. Joint angles and ground reaction forces were combined with morphometric data to calculate net joint moments and net joint powers across the tarsus using inverse dynamics. RESULTS: In all horses, the tarsus flexed during the impact phase and extended in late stance. Tarsal angles were stratified according to standing tarsal angle throughout stance. Horses with large standing angles showed less flexion and less energy absorption at the tarsus during the impact phase than those with intermediate or small angles and generated less vertical impulse than horses with small standing angles. Net extensor moment at the tarsus during stance was lower for horses with large standing angles. CONCLUSIONS: In horses with large tarsal angles, less concussion was absorbed during the impact phase, which may be a factor in the development of degenerative joint disease; and the smaller vertical impulse and extensor moment later in stance may limit propulsive ability. However, the smaller net joint moment may reduce the risk of plantar ligament desmitis. CLINICAL SIGNIFICANCE: The effects of conformation on kinematics and kinetics of the tarsal joint may influence both performance and soundness.