Horses with Extensive Sidebone Have an Increased Risk of Injury

Imagine that after a thorough prepurchase examination, your veterinarian turns to you and says the horse has sidebone, meaning his lateral and medial cartilages of the foot that have "ossified," or hardened into bone. What should you do?

If the condition is extensive enough, you should carefully consider this horse's future and be aware that he is at-risk for collateral ligament, distal interphalangeal (coffin) joint, and distal phalanx (pedal bone) injury, says Sue Dyson, MA, VetMB, PhD, DEO, FRCVS, head of clinical orthopaedics at the Animal Health Trust in Newmarket, England.

"The cartilages play an important role in providing support to the foot, dissipating the forces of the foot's impact with the ground, and appear to play an important hemodynamic (flow of blood) role in the foot," explained Dyson. "While several studies have suggested that ossification of the cartilages is associated with injuries to other structures in the foot, large studies were needed to see if this association was real."

Dyson and her research team examined 462 horses to determine the frequency of ossification of the cartilages and to see whether there was an association between sidebones and injury to other structures in the foot.

"Ossification of the cartilages was judged on a scale from 0 to 5, and we considered grade 3 and up to be of possible significance," relayed Dyson.

Key findings of the study were that:

  • Fifty-nine (12.8%) of the 462 feet had possible significant ossification (i.e., grade greater than 3);
  • A considerable association between horses with possible significant ossification and injury to the collateral ligaments, distal interphalangeal (coffin) joint, and distal phalanx (pedal bone) was noted;
  • Lateral cartilages were ossified more frequently than medial cartilages; and
  • Even if the ossification was highly asymmetric (i.e., one markedly more ossified than the other) there was no difference in frequency of injuries to the distal phalanx.

"This large-scale study highlights that horses with either bilateral extensive ossification or marked mediolateral asymmetry in ossification (differences in ossification between the medial and lateral cartilages) are potentially of clinical importance," concluded Dyson.

She added, "Owners should certainly consider extensively ossified cartilages during a prepurchase examination."

Despite the impressive number of horses included in this study, Dyson indicated additional studies with a larger number of horses are still needed.

The study, "Is there an association between ossification of the cartilages of the foot and collateral desmopathy of the distal interphalangeal joint or distal phalanx injury?" is scheduled to be published in an upcoming edition of the Equine Veterinary Journal.

The abstract is available online.

About the Author

Stacey Oke, DVM, MSc

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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