Improved radiological diagnosis of palmar osteochondral disease in the Thoroughbred racehorse.

BACKGROUND: Palmar osteochondral disease (POD) is common in the Thoroughbred racehorse yet difficult to diagnose by radiography alone.

OBJECTIVES: To improve the sensitivity and specificity for diagnosing POD from radiographs.

STUDY DESIGN: Prospective, longitudinal study.

METHODS: Radiographs in nine different projections were made of metacarpophalangeal joints (MCPJ) of 50 Thoroughbreds. Post-mortem, MCPJs were dissected and gross pathology was scored. Three experienced Thoroughbred clinicians read each radiograph and recorded their findings. Another clinician reviewed each radiograph alongside the related gross specimens in order to correlate radiological findings with joint pathology. This served as a 'gold standard'. The performance of each clinician at detecting POD was compared with the 'gold standard'. Radiological features associated with POD were identified and presented to the clinicians in a training manual, prior to them re-reading the radiographs. The ability of each clinician to diagnose POD was reassessed.

RESULTS: Palmar osteochondral disease was a common finding (88/100 joints). All three clinicians demonstrated low sensitivity and low specificity at detecting POD (mean 0.37 and 0.75, respectively). Conversely, the sensitivity and specificity for POD in the 'gold standard' was high (0.95 and 1.0). POD was associated with primary radiological features (e.g. focal radiolucencies in the palmar condyles, disruption of the outline of subchondral bone and focal sclerosis of the palmar condyles) and secondary features (e.g. basilar and apical osteophytes on the proximal sesamoid bones, flattening of the palmar condyles and cavitation of the dorso-distal aspect of the third metacarpal bone). Secondary radiographic features were often easier to detect. Following training the performance of clinicians at identifying POD was significantly improved.

MAIN LIMITATIONS: Only two clinicians completed the study; low proportion of POD negative cases in the study.

CONCLUSIONS: Clinicians frequently overlook key radiological features related to POD. Alerting clinicians to relevant radiological features improved the sensitivity and specificity of diagnosis.