Reliability of conformational measurements in the horse using a three-dimensional motion analysis system.

Abstract: The importance of a reliable method for conformation studies is generally acknowledged, but there are only limited data on the accuracy and precision of current assessment methods. Objective: To assess (1) the accuracy and repeatability of marker placement, (2) influence of stance of the horse on conformational parameters, (3) practicality of a computerised motion analysis system and (4) to compare the computerised motion analysis system to photographic systems of assessment. Methods: Twenty-eight reflective markers placed over anatomical landmarks were located in 3D using a computerised motion analysis system and their coordinates used to calculate segment lengths and joint angles. Four experiments, involving a cadaver study, a series of repeated measures on a single Thoroughbred and repeat measurements on 108 racehorses were performed. Results: Identification of anatomical landmarks was found to introduce the biggest variation in the measurements for proximal conformation parameters with the interoperator being larger than intraoperator variation. Length measurements were least influenced by stance, with distal interphalangeal and metacarpo/metatarsophalangeal joint angles being the most variable. In some measurements, the variation between stances within a horse proved to be almost as large as between horses, rendering these parameters less useful as predictors of performance or orthopaedic health. Conclusions: A computerised motion analysis system allows 3D assessment of conformation with high accuracy and precision. It eliminates 3 major sources of error associated with photography-based methods and increases accuracy of conformational assessment by allowing repeat measurements in a relatively short period. Conclusions: Studies on conformation should be viewed in the light of the limitations of the measurement technique used. The presented method maximises accuracy and precision and is a valuable basis for future studies investigating the effect of conformation on performance or orthopaedic health.