Evaluation of equine locomotion during different degrees of experimentally induced lameness. II: Distribution of ground reaction force patterns of the concurrently loaded limbs.

Force plate and high-speed film data from a group of six walking horses were used to study the distribution of the ground reaction forces (GRF) of the concurrently loaded limbs. Three different degrees of supporting lameness were induced in a forelimb or a hindlimb using modified horse shoes. In all experiments the alterations in the distribution in the transverse horizontal GRF (Fx) were small. During unilateral forelimb lameness, the decreased longitudinal horizontal GRF (Fy) was compensated by an increase of the Fy forces of the contralateral forelimb and the ipsilateral hindlimb. The decreased vertical GRF (Fz) of the lame limb was compensated by an increase of the Fz amplitudes of the contralateral forelimb during the swing phase of the lame limb and increased Fz forces of both the diagonal and the ipsilateral hindlimbs during the stance phase of the lame limb. During unilateral hindlimb lameness the decreases in the deceleration Fy forces of the lame hindlimb were mainly compensated by increased propulsion forces in the contralateral hindlimb and small increases of the Fy forces of both forelimbs. The decreased Fz forces of the lame hindlimb were mainly compensated by increased Fz forces of the diagonal forelimb and smaller increases in Fz forces in the ipsilateral forelimb during the stance phase. During the swing phase of the lame hindlimb small compensatory increases were found in the contralateral hindlimb. Decreased peak amplitudes and impulses in the lame limb, and compensatory increases in the two or three concurrently loaded limbs, resulted in significant decreases in left-to-right symmetry percentages between forelimbs as well as hindlimbs during the different degrees of one limb lameness.