OBJECTIVE MEASURES OF LAMENESS EVALUATION

Subjective evaluation of the horse in motion is the standard of practice for detection and evaluation of lameness in horses. Techniques for subjective evaluation are first learned in veterinary school and later developed by collegial transfer of knowledge, study of standard veterinary texts, and by experience. Nothing is better than experience at improving this skill. How one looks and what one looks for when detecting and evaluating lameness varies from practitioner to practitioner that is dependent somewhat on the type or breed of horse and activity being evaluated. “Head nodding”, whether it refer to the up or downward movement of the head, limb movement and the shape of the hoof flight arc, how the foot lands, stride length, joint angle changes, “hip hikes” and “hip dips”, gluteal muscle rise and “use”, certain behaviors under certain activities, like not being able to take the right lead at a canter easily; all of these and more have been described in veterinary texts and manuscripts and presentations. Frequently the examiners, through experience, know whether or not the horse is lame and the limb involved, perhaps without being able to describe what is seen exactly. It is definitely one of the “arts” of equine practice. With such variability in subjective technique it is understandable that, even between experienced practitioners, some disagreement in detecting lameness, grading severity, grading improvement after blocking or treatment, picking the limb with the primary lameness, is expected. Subtle movement signs that happen very quickly, below the temporal sampling ability of the naked human eye, and compensatory movements due to unloading the limb with primary lameness that mimic lameness in another limb, contribute to this disagreement. It has been shown that experienced clinicians are significantly more consistent, i.e. agree with themselves, at detecting mild to moderate lameness (60% above chance) than veterinarians in training (40% above chance), but agreement between experienced clinicians is no better than between younger, less experienced ones (20% above chance). Agreement between experienced clinicians for detecting a change in lameness was only 19% above chance. Detecting hind limb lameness is more difficult than detecting forelimb lameness, especially when the severity of lameness is mild. In one in depth study of over 100 horses simultaneously evaluated by 3 clinicians, detection of forelimb and hind limb lameness when the mean AAEP score was >1.5, was >90% (>40% above chance). However, when the mean AAEP score was <1.5, agreement for forelimb and hind limb lameness was only approximately 60%, or just slightly above chance. Testing after full lameness evaluation, including lunging and flexion tests, compared to testing only by observing the horse trot in a straight line, degraded agreement. It has also been shown that prior assumption of a block being performed during a lameness evaluation can bias clinicians into grading lameness less by up to 1 AAEP grade. The 95% confidence interval for repeatability between clinicians for grading lameness in horses is about 1.5 grades. Results of these studies suggest 2 broad concepts; 1) if you are going to use subjective evaluation of lameness as an assessment tool in clinical studies it is best to use one, and only one, experienced clinician, and 2) finding small, but nevertheless significant, differences between treatment groups for reduction in lameness after treatments in clinical studies will be difficult without large numbers of experimental subjects. Utilizing numerical scales with greater numbers of divisions than the