Navicular Bone Fragments’ Effect on Lameness

A team evaluated a possible association between distal border fragments of the navicular bone and lameness.
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Although researchers have been studying the equine navicular bone for years, many mysteries still surround it. For instance, advanced imaging techniques give veterinarians a clearer picture than ever of irregularities or damage to the navicular bone, but it’s not always evident what such pathologies mean for a horse’s soundness. Elizabeth Yorke, DVM, of Yorke Equine Veterinary Services, in Auburn, Ala., and colleagues at Alamo Pintado Equine Medical Center, in Los Olivos, Calif., and Auburn University, recently evaluated the possible association between distal border fragments (bone fragments on the lower border) of the navicular bone and clinical lameness.

Yorke described the research at the 2012 American Association of Equine Practitioners Convention, held Dec 1-5 in Anaheim, Calif. The team hypothesized that horses with distal border fragments of the navicular bone are more likely to be lame and that larger fragment size would result in more severe lameness. To test their hypotheses, they reviewed the records of 453 horses that underwent MRI for lameness of the distal forelimb.

The researchers identified:

  • Distal border fragments in 13.25% of horses and 10% of feet.
  • In limbs without fragments, a mean lameness score of 1.8 out of 5 (with 5 being most severe); in horses with one or more fragments, a score of 1.57 out of 5.
  • In statistical tests, horses with a fragment were not more likely to be categorized as lame.
  • Mean size of 66.3 mm3 for fragments at the lateral angle (situated to the outer part of the limb) of the distal border and 41.3 mm3 for fragments at the medial (toward the horse’s midline) angle of the distal border.
  • No significant difference in fragment size across lameness grades.

In summary, the team found that limbs with distal border fragments weren’t necessarily more lame than limbs without fragments and that fragment size did not dictate lameness severity. Yorke noted that the team found limbs with fragments on both the medial and lateral angles of the distal border of the navicular bone were more likely to be classified as lame

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Written by:

Erica Larson, former news editor for The Horse, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.

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