Radiographic changes in Thoroughbred yearlings. Part 1: Prevalence at the time of the yearling sales.
BACKGROUND
Radiography in presale examinations of TB yearlings has become standard practice in recent years.


OBJECTIVE
To describe the prevalence and distribution of radiographic changes in the fetlocks, carpi, tarsi, stifles and fore feet of Thoroughbred yearlings in central Kentucky when these joints were examined as part of routine pre- and post sale evaluations.


METHODS
Horses subjected to radiographs included the fore (n = 1127) and hind (n = 1102) fetlocks, carpi (n = 1130), tarsi (n = 1101), stifles (n = 660) and fore feet (n = 300). Radiographic changes were categorised by location and type of change present (e.g. lucency, fragment) for each series.


RESULTS
In the fore fetlocks 1.6% had fragmentation of the proximal dorsal first phalanx and 0.5% fragmentation of the proximal palmar aspect. In the hind fetlocks 5.9% had fragmentation at the plantar aspect and 3.3% fragmentation dorsally. Lucencies, fragments or loose bodies were detected at the dorsal aspect of the distal third metacarpus in 2.8% and, at the same location on the third metatarsus, 3.2%. Most yearlings (98%) had vascular channels in the proximal sesamoid bones and irregular vascular channels (> 2 mm wide or with nonparallel sides) were more common (79%) than regular vascular channels (56%). The intermediate ridge of the distal tibia was the most common location for fragmentation in the tarsus (4.4%).


CONCLUSIONS
While some radiographic changes, e.g. vascular channels in proximal sesamoid bones, are very common in Thoroughbred yearlings, others, e.g. fragmentation or subchondral lucency within joints are quite rare usually affecting less than 5% of the population.


CONCLUSIONS
Veterinarians should expect to find radiographic changes in Thoroughbreds presented for examination prior to the yearling sales. The rarity of some changes thought to affect soundness or racing performance will make further invesigation of these conditions in horses without clinical signs more difficult.
Kane
A J
AJ
Equine Orthopaedic Research Laboratory, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, Colorado 80523, USA.
Park
R D
RD
McIlwraith
C W
CW
Rantanen
N W
NW
Morehead
J P
JP
Bramlage
L R
LR
D000818:Animals; D002350:Carpus, Animal / Q000000981:diagnostic imaging; D003132:Commerce; D005260:Female; D006734:Horse Diseases / Q000175:diagnosis / Q000000981:diagnostic imaging* / Q000191:economics / Q000453:epidemiology*; D006736:Horses / Q000033:anatomy & histology / Q000502:physiology; D008297:Male; D015995:Prevalence; D011859:Radiography; D013264:Stifle / Q000000981:diagnostic imaging; D013643:Tarsus, Animal / Q000000981:diagnostic imaging