3D kinematics of the equine metacarpophalangeal joint at walk and trot.

The metacarpophalangeal (MCP) joint and its supporting soft tissues are common sites of injury in athletic horses. Equine gait analysis has focused on 2D analysis in the sagittal plane and little information is available which describes 3D motions of the MCP joint and their possible role in the development of injuries. The aim was to characterize the 3D rotations of the equine MCP joint during walking and trotting. Three-dimensional trajectories of marker triads fixed rigidly to the third metacarpus and proximal phalanx of the right forelimb of healthy horses were recorded at walk (n = 4) and trot (n = 6) at 120 Hz using eight infra-red cameras. Kinematics of the MCP joint were calculated in terms of helical angles between the two segments using singular-value decomposition and spatial attitude methods. The ranges of motion were: flexion/extension: 62 +/- 7 degrees at walk, 77 +/- 5 degrees at trot; adduction/abduction: 13 +/- 7 degrees at walk, 18 +/- 7 degrees at trot; and axial rotation: 6 +/- 3 degrees at walk, 9 +/- 5 degrees at trot. Flexion/extension had a consistent pattern and amplitude in all horses and appeared to be coupled with adduction/abduction, such that stance phase extension was accompanied by abduction and swing phase flexion was accompanied by adduction. Axial rotation was small in amount and the direction varied between horses but was consistent within an individual for the two gaits.