Development of osteochondrosis in the tarsocrural joint and osteochondral fragments in the fetlock joints of Standardbred trotters. I. A radiological survey

In a longitudinal study 77 Standardbred foals were examined 6 times from birth to the age of 16 months. The radiological examination included 9 views, selected to demonstrate the time of occurrence and the appearance of early radiographic signs of osteochondrosis in the tarsocrural joints (OC), palmar/plantar osteochondral fragments in the fetlock joints (POF) and ununited proximal palmar/plantar eminences of the proximal phalanx (UPE). Subchondral bone defects with a diameter >5 mm and/or osseous fragments were considered significant radiographic findings and were correlated to clinical signs.Eight horses (10.4%) showed OC in the tarsocrural joints at the age of 12 months. All 8 horses showed radiographic changes indicating early OC lesions that were detectable before the age of 3 months. In 4 of these horses subchondral bone defects and/or fragments at the intermediate ridge of the distal tibia were visible before 1 month of age. Eleven horses showed radiographic changes first detected between 1 and 3 months of age that reverted to normal appearance at 8 months of age. In no case was a significant radiographic finding first detected between the age of 8 and 16 months. The radiographic findings of permanent hock OC were significantly correlated with the presence of tarsocrural joint effusions but did not correlate with lameness.At the age of 12 months, 11 horses (14.3%) showed significant radiographic changes with defects and/or osseous fragments in the metacarpo- and metatarsophalangeal (fetlock) joints. In all of these horses early indications of these changes were detected before the age of 5 months. In 7 horses early radiographic signs of abnormal ossification reverted to a normal appearance before the age of 8 months. No additional significant radiographic findings were detected after the age of 8 months. There was no correlation between radiographic findings and fetlock joint synovial effusion or lameness.Osteochondrosis of the tarsocrural joints and palmar/plantar intraarticular fragments in the fetlock joints develop very early in life and can be regarded as being permanent if present at 1 year of age