Pastern Lucencies' Effect on Racing Performance (AAEP 2011)

Prior to purchasing a yearling racing prospect at a sale, a buyer typically has a veterinarian conduct a thorough examination on the horse to ensure he is in top condition. Most of these exams include a review of radiographs, or X rays, of the horse's limbs. Historically, many veterinarians have considered lucencies (bone cysts) in pastern radiographs benign; however, one researcher has determined certain lucencies--namely those located on midline--should be taken seriously because they appear to have a significant effect on racing performance.

At the 2011 American Association of Equine Practitioners Convention, held Nov. 18-22 in San Antonio, Texas, Julie Vargas, DVM, described a retrospective study in which she and colleagues examined the impact of severe pastern lucencies in Thoroughbred yearlings on 2- and 3-year-old racing performance. Vargas, a practitioner with Equine Services LTD in Wellington, Fla., noted that prior to this study the association between the presence of these lucencies and racing performance had not been evaluated.

Vargas explained that pastern lucencies typically occur on the weight-bearing surface of the joint; vary in size, shape, and depth; and can be caused by a variety of different factors, including developmental bone anomalies and/or trauma to the cartilage surface. Previous research indicates that they are detected more often in young male Thoroughbreds or Warmbloods, and they're most commonly found in the forelimb, she added.

Vargas and colleagues at Rood & Riddle Equine Hospital examined 7,226 radiograph reports from Thoroughbred yearlings at auctions in the United States from 2002 to 2007. The team took measurements of the lucencies and noted each abnormality's location within the pastern. Maternal siblings were used as controls. In total, the researchers included 171 yearlings with lucencies in the study, along with 832 maternal siblings.

Upon reviewing the results of the review, Vargas found that:

  • Sixty percent of lucencies evaluated occurred in the hind limbs while 40% occurred in the forelimbs (a statistic contrary to previous reports of forelimbs being affected more often);
  • Thirty-nine percent of affected horses were colts and 61% were fillies (refuting previous reports of males being more commonly affected);
  • Ten percent of the 171 affected yearlings had lucencies in two limbs;
  • There was no significant difference in the number of starts at 2 or 3 years, total earnings, or earnings per start between control horses and horses with lucencies located on the condyle (bulbous bottom or distal end of the bone) or facet (the smooth articular surface) of the pastern;
  • However, there was a significant difference between controls and horses with lucencies that occurred on the midline of the pastern; At 2 and 3, these horses had decreased earnings per start, and decreased total earnings as compared to control horses. Additionally, starts at 2 were fewer than sibling controls.

"It is also feasible that horses with large severe midline (pastern) lucencies race successfully," Vargas added, reminding that in general, "pastern cysts seldom cause lameness and so a direct relationship between midline cysts and decreased performance is unlikely. The reason for decreased performance with midline pastern cysts is unknown."

Vargas noted that midline lucencies are "often believed to be normal variations of synovial fossas (nonarticulating areas in synovial articular surfaces)" and, thus, aren't noted on all radiograph reports. Vargas' research indicates it could be beneficial to note these lucencies on radiographic reports more frequently.

"The ones that were noted (and, thus, the ones evaluated in the study) were therefore severe (i.e., seen on multiple radiographic views) in nature and evident on multiple radiographic views," she added.

"This is part of the ongoing research at the Rood & Riddle Equine Hospital to better define the significant radiographic findings seen on sale radiographs both at public auction and on purchase examinations," Vargas concluded. "Only when we research a radiographic finding like pastern lucencies do we know the implications of those findings on the expected performance of the horses we are evaluating."

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.