Quantitative evaluation of subchondral bone injury of the plantaro‐lateral condyles of the third metatarsal bone in Thoroughbred horses identified using nuclear scintigraphy: 48 cases

Reasons for performing study: Increased radio‐isotope uptake (IRU) in the subchondral bone of the plantaro‐lateral condyle of the third metatarsus (MTIII) is a commonly reported scintigraphic finding and potential cause of lameness in UK Thoroughbred racehorses in training and has not been fully documented. Objectives: To characterise lameness attributable to IRU of the subchondral bone of MTIII, compare the scintigraphic findings of these horses with a normal population and evaluate the use of scintigraphy as an indicator of prognosis. Hypothesis: IRU will be in significantly higher in horses with subchondral bone injury and will be related to prognosis and future racing performance. Methods: Data were analysed from 48 horses in which subchondral bone injury of the plantaro‐lateral condyle of MTIII had been diagnosed using nuclear scintigraphy and that met the inclusion criteria. Data recorded included age, sex, trainer, racing discipline, lameness assessment, treatment regimes, radiographic and scintigraphic findings, response to diagnostic analgesia where performed and racing performance pre‐ and post diagnosis. Region of interest (ROI) counts were obtained for the plantar condyle and the mid diaphysis from the latero‐medial view, the ratio calculated and then compared with a control group of clinically unaffected horses. Results: The mean condyle mid‐diaphysis ROI ratio was significantly (P<0.001) higher in the affected population and with positively correlation (P = 0.024) with the level of lameness. The presence of radiographic findings had no significant effect on the ROI ratio. Conclusion: Subchondral bone injury of the plantar lateral condyles of MTIII is a significant cause of lameness in UK Thoroughbred racehorses. Nuclear scintigraphy is a useful diagnostic imaging modality in the detection of affected horses but is a poor indicator of prognosis for the condition. Potential relevance: Better understanding of the clinical manifestations, diagnosis of and prognosis for subchondral bone injury will benefit the Thoroughbred industry in the UK.