Body centre of mass movement in the lame horse

The body centre of mass (BCM) is a key factor in the analysis of equine gait, as its position and movement determines the distribution and magnitude of loads on the limbs. Changes in the BCM movement are proposed to be important factors in the lameness management of horses. In this study, changes in the position and the 3-dimensional (3-D) movement of the BCM in horses with induced forelimb lameness were studied using a kinematic, segmental method. The kinematics of 30 markers representing 20 body segments were recorded in 12 horses while trotting (3.9 m/s) on a treadmill using a high speed video system. A transient lameness model, evoking pressure-induced pain on the hoof sole, was used to induce 2 degrees of forelimb lameness. Based on segmental inertial data from Buchner et al, (1997) 3-D segmental centres of mass as well as the BCM were calculated. The changes in BCM movement due to lameness and the influence of selected segments on the total centre of mass were analysed. During moderate forelimb lameness, vertical displacement of the BCM showed a 34% reduced amplitude during the stance phase of the lame limb and a 9% increased amplitude during the stance phase of the sound forelimb. In the sagittal direction, the BCM during midstance moved 9 mm backwards during the stance phase of the lame forelimb. Transversal movements showed a slight, but significant shift of the BCM to the side of the sound forelimb. Head/neck segment movement changed in a sagittal as well as in a vertical direction, but only a small amount, insufficient for considerable BCM position changes. The results show a similar pattern of BCM and trunk movement and only small adaptations of BCM position due to lameness. The influence of the sagittal position of the BCM has to be seen as a minor factor in lameness management compared to the dynamic influences of a changed vertical BCM movement and the moment caused by the typical head and neck movement.