Diagnostic accuracy of digital photography and image analysis for the measurement of foot conformation in the horse

Reasons for performing study: Rigorous evaluation of practicable methods for the objective assessment of foot conformation has not been performed. Objectives: To assess the practicability, precision and accuracy of the process of obtaining measurements of horses' feet using photography and image processing software. Methods: Precision study: Lateral photographs of horses' feet were obtained twice by 2 veterinary surgeons (image acquisition - IAc). Photographs were analysed by 2 masked veterinary surgeons on 2 occasions (image analysis - IAn). Measurements were compared within and between operators for self and non-self acquired photographs. Agreement indices (AIs) and 95% limits of agreement (LOA) were calculated for the IAn process alone and for the combined IAc + IAn processes. Accuracy study: Measurements obtained from lateral photographs were compared with those obtained from lateromedial radiographs. AIs and 95% LOA were calculated for each measurement. Results: Precision study: Mean intra- and interoperator AIs for the IAn process alone were >= 0.90 while those for the combined IAc + IAn processes were >= 0.89 for all measurements. Similar mean AIs and 95% LOA were calculated regardless of image origin. The 95% LOA for hoof angle, heel height/toe height% and coronary band angle for all comparisons were within target values. Accuracy study: Mean AIs were >= 0.89 for all measurements. The 95% LOA for heel height/toe height% and coronary band angle were within target values. Conclusions: Excellent precision was identified within and between operators regardless of image origin. High levels of accuracy were also identified, especially for heel height/toe height% and coronary band angle, indicating that photography and radiography may be used interchangeably. Potential relevance: Acquisition and analysis of photographic images is an appropriate method for the objective measurement of foot conformation, both in clinical and research settings.