Net joint moments and powers in the equine forelimb during the stance phase of the trot

The objective of this study was to provide normative data describing the net joint moments and joint powers for the stance phase of the forelimb in trotting horses. Kinematic and force plate data, synchronised in time and space, were collected for the right forelimb of 6 Warmblood horses moving at a trot. The 3-D kinematic data were collapsed onto a sagittal plane, and were combined with the vertical and longitudinal ground reaction forces and with segment morphometric data to calculate net joint moments in the sagittal plane across the distal interphalangeal (coffin), metacarpophalangeal (fetlock), carpal, elbow and shoulder joints. The joint mechanical power was calculated as the product of the joint moment and the joint's angular velocity. Major peaks on the moment and power curves were identified. Each joint showed consistent and repeatable patterns in the net joint moments and joint powers. During most of stance the net joint moment was on the caudal/palmar side of all joints except the shoulder. At the coffin joint the power profile indicated an energy absorbing function that peaked at 74% stance, which coincided with the maximal longitudinal propulsive force. The fetlock joint behaved as an elastic spring; energy was absorbed in the first half of stance as the flexor tendons and SL stored elastic energy, which was released in the second half of stance as a result of elastic recoil. The carpus did not appear to play an important role in energy absorption or propulsion. Both the elbow and shoulder joints showed what appeared to be phases of elastic energy storage and release in the middle part of the stance phase, followed by a propulsive function at the shoulder in the later part of stance. The fetlock, carpus and elbow showed virtually no net generation or absorption of energy. The net energy generation at the shoulder joint was approximately equal to the energy absorption at the coffin joint. In human subjects specific gait pathologies produce characteristic alterations in the shape of the power profile as well as changes in the amount of energy absorbed and generated at the joints. In horses evaluation of net joint moments and joint powers will further our understanding of the mechanics and energetics of lameness, and may prove to be a useful diagnostic tool. An understanding of the function and dysfunction of different anatomical structures will facilitate the interpretation of clinical findings in terms of mechanical deficits.