title: Descriptive epidemiology of joint injuries in Thoroughbred racehorses in training.
abstract: BACKGROUND
  No large scale epidemiological studies have previously quantified the occurrence of carpal, metacarpo- and metatarsophalangeal (MCP/MTP) joint injuries in Thoroughbred racehorses.
  
  
  OBJECTIVE
  To develop an objective classification system for carpal and MCP/MTP joint injuries and estimate the incidence of these injuries in young Thoroughbreds in flat race training.
  
  
  METHODS
  In a prospective cohort study, data on daily exercise and veterinary-diagnosed carpal and MCP/MTP joint injuries were collected from Thoroughbreds monitored since starting training as yearlings, for up to 2 years. Cases were classified in one of 4 categories: 1) localised to a carpal or MCP/MTP joint based on clinical examination and/or diagnostic analgesia; no diagnostic imaging performed; 2) localised to a carpal or MCP/MTP joint based on clinical examination and/or diagnostic analgesia; radiographs taken but no abnormalities detected; 3) evidence of abnormality of subchondral bone and/or articular margin(s) on diagnostic imaging and 4) evidence of discontinuity of the articular surface on diagnostic imaging. Incidence rates and rate ratios were estimated using Poisson regression, adjusting for trainer-level clustering.
  
  
  RESULTS
  A total of 647 horses from 13 trainers throughout England contributed 7785 months at risk of joint injury. One-hundred-and-eighty-four cases of carpal (n = 82) or MCP/MTP (n = 102) joint injury were reported in 165 horses and classified in Category 1 (n = 21), Category 2 (n = 21), Category 3 (n = 72) or Category 4 (n = 70). The overall joint injury rate was 1.8 per 100 horse months (95% CI = 1.2, 2.8); rates did not differ significantly between 2- and 3-year-olds but females sustained Category 1 injuries at triple the rate of males (P = 0.03). Joint injury rates differed significantly between trainers (P<0.001) and there was trainer variation in anatomical site and severity of injury.
  
  
  CONCLUSIONS
  Carpal and MCP/MTP joint injuries are an important cause of morbidity in Thoroughbred racehorses. Identification of modifiable risk factors for these injuries may reduce their incidence.
authors.affiliation: Department of Veterinary Clinical Sciences, Royal Veterinary College, Hawkshead Lane, North Mymms, Hatfield, Hertfordshire, UK. srreed@rvc.ac.uk
authors.forename: S R
authors.initials: SR
authors.lastname: Reed
authors.forename: B F
authors.initials: BF
authors.lastname: Jackson
authors.forename: C W
authors.initials: CW
authors.lastname: Mc Ilwraith
authors.forename: I M
authors.initials: IM
authors.lastname: Wright
authors.forename: R
authors.initials: R
authors.lastname: Pilsworth
authors.forename: S
authors.initials: S
authors.lastname: Knapp
authors.forename: J L N
authors.initials: JL
authors.lastname: Wood
authors.forename: J S
authors.initials: JS
authors.lastname: Price
authors.forename: K L P
authors.initials: KL
authors.lastname: Verheyen
mesh_terms: D000818:Animals; D015331:Cohort Studies; D004739:England / Q000453:epidemiology; D005260:Female; D005552:Forelimb; D006614:Hindlimb; D006734:Horse Diseases / Q000453:epidemiology* / Q000209:etiology; D006736:Horses; D007596:Joints / Q000293:injuries*; D007794:Lameness, Animal; D008297:Male; D010003:Osteoarthritis / Q000453:epidemiology / Q000209:etiology / Q000662:veterinary*; D010805:Physical Conditioning, Animal; D012420:Running; D013177:Sports