Scintigraphic characterization of distal radial physeal closure in young Standardbred racehorses

A longitudinal scintigraphic and radiographic study of distal radial physeal activity in 14 Standardbred trotters was conducted to quantify and visually evaluate physeal uptake around the time of physeal closure. Initial intense 99mTc-HDP uptake was seen, followed by a rapid decrease of activity starting at a mean age of 20 months. Mean physeal to distal diaphyseal ROI and line profile ratios compared to ratios of mature horses decreased from 2.8 to 1.4 at the time of radiographic closure at 24-32 months. Ratios then gradually decreased until values of mature horses were reached at the end of the study (mean age 42 months). Visually discernible distal radial physeal activity was present with declining frequency throughout the study. This study indicates that, in the normal Standardbred trotter, there is mild distal radial physeal uptake present after radiographic evidence of physeal closure. This uptake is not likely to confound evaluation of pathologic conditions of the physeal or carpal regions.