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