Progression and association with lameness and racing performance of radiographic changes in the proximal sesamoid bones of young Standardbred trotters

Radiographic examination of the metacarpo- and metatarsophalangeal joints was performed on 753 Standardbred trotters (6-21 months of age): 21 showed obvious changes in 26 proximal sesamoid bones on lateromedial projection. The radiographic changes were divided into 6 different types: (1) irregular abaxial margin (8 horses); (2) enlargement of the sesamoid bone (6 horses); (3) 'fracture' or separate centre of ossification of the apex (4 horses); (4) vertical, non-articular fracture of the plantar part of the sesamoid bone (1 horse); (5) a small bony fragment located in a defect in the apical part of the bone (2 horses); and (6) multiple areas of decreased radiodensity (1 horse). Each horse displayed only one type of radiographic change except for one which possessed those of types 3 and 5. Follow-up radiographic examination of 21 of the 26 affected proximal sesamoid bones at approximately 6-month intervals revealed a reduction in the changes in 13 bones and an unaltered condition in 8. Lameness examination was performed on 16 of the 21 horses at 3 years of age and 14 (87.5%) were observed to be lame, but detected lameness did not seem to be referrable to the sesamoid changes. Earnings after the racing season as 3- and 4-year-old horses showed no differences (P > 0.05) between horses with radiographic changes in the proximal sesamoid bones and those without such changes.