Diagnostic Performance of Radiography for the Evaluation of Osteoarthritis in the Equine Distal Tarsus: Comparison with Computed Tomography

The objective of the present study was to compare the diagnostic performance of radiography to computed tomography (CT) for the diagnosis of distal tarsal osteoarthritis. All images were interpreted and scored by 2 evaluators until a consensus was reached; they were blinded to the history, final imaging diagnosis, and results of the corresponding radiographic or CT study. On radiographs and CT images of 54 tarsi, 6 criteria (osteophyte/enthesophyte height, small/large subchondral bone radiolucencies, subchondral bone thickness, joint space narrowing) were scored in the proximal intertarsal (PIJ), distal intertarsal (DIJ), and tarsometatarsal joint (TMTJ). Compared to CT, mean radiographic scores were significantly lower for 1. small and large subchondral bone radiolucencies in all joints ( < 0.001-0.03); 2. subchondral bone thickness in the PIJ and DIJ ( = 0.03 and 0.005); and 3. enthesophyte and joint space narrowing score in the DIJ ( = 0.04 and 0.002). Low-to-high positive predictive values (PPV) were calculated for the individual criteria in all joints (0-100%). For the sum of scores of all criteria in the PIJ, DIJ, or TMTJ, respectively, PPVs were high (94-98%). In conclusion, radiography is a useful screening tool provided multiple criteria are assessed. However, CT offers significant advantages for the diagnosis of distal tarsal OA.