Akikazu Ishihara, BVSc; Stephen M. Reed, DVM, DACVIM; Päivi J. Rajala-Schultz, DVM, PhD; James T. Robertson, DVM, DACVS; Alicia L. Bertone, DVM, PhD, DACVS Journal of the American Veterinary Medical Association March 1, 2009 234 5 644-651 Objective—To evaluate use of kinetic gait analysis for detection, quantification, and differentiation of hind limb lameness and spinal ataxia in horses. Design—Prospective clinical study. Animals—36 horses. Procedures—Kinetic gait analysis with a force plate was performed for 12 clinically normal horses, 12 horses with hind limb lameness, and 12 horses with spinal ataxia. Kinetic variables were compared among groups, correlated to subjective grading, and used to build predictive models to assess the accuracy of discrimination. Results—Subsets of kinetic variables were characteristically altered in ataxic and lame gaits. Ataxic horses had significantly increased lateral force peak and variation in vertical force peaks in both hind limbs. Lame horses had significantly decreased vertical force peak and increased variation in vertical force peaks only in the lame hind limb. These variables were used to differentiate between spinal ataxia and hind limb lameness with excellent accuracy. There were significant correlations between a subset of kinetic variables and subjective lameness and neurologic grades. Conclusions and Clinical Relevance—Kinetic gait variables, specifically lateral force peak and the variation in vertical force, can be used to support the differential diagnosis between spinal ataxia and hind limb lameness in horses. Kinetic gait analysis may also be applied for quantification of equine hind limb gait abnormalities as well as confirming lack of lameness and ataxia in soundness examinations.