Chips Off the Navicular Bone Not Uncommon, But Do They Cause Lameness?

Magnetic resonance imaging (MRI) of the foot is a valuable tool in diagnosing equine lameness and can clearly identify fragments or chips originating from the distal border of the navicular bone ... but researchers say, "so what?"

"These fragments are seen in both lame and non-lame horses, which makes it difficult to determine if the fragments really are important or not," explained Sue Dyson, MA, VetMB, PhD, DEO, FRCVS, head of clinical orthopaedics at the Animal Health Trust in Newmarket, England, renowned for her research using MRI in lameness diagnosis.

To better determine the importance of these fragments, Dyson and her research team reviewed the MRI scans of 427 horses with forelimb lamenesses localized to the foot.

"Fragments were noted in 111 (30%) of the horses," said Dyson.

In addition, horses with fragments off the distal border of the navicular bone had a greater number of other navicular bone abnormalities compared with horses without fragments, including:

  • An increase in the number and size of synovial invaginations on the distal border of the navicular bone (i.e., "holes" in the navicular bone that fill with synovial fluid);
  • Significantly more osseous (bone) cyst-like lesions; and
  • Larger bony growths called enthesophytes on the distal border.

Only occasionally were isolated fragments seen without other abnormalities of the navicular bone.

"This study does show that these fragments are part of 'navicular disease,'" concluded Dyson.

She did add, however, that the contribution of these fragments to pain and lameness by themselves remains unclear.

"The pain and lameness is not necessarily caused by the fragments themselves, but might be due to the other abnormalities of both the navicular bone and other components of the podotrochlear apparatus (the distal sesamoidean impar ligament and the collateral sesamoidean ligament, or a combination of both). We also hypothesize that chronic movement of a fragment adjacent to the navicular bone may contribute to pain," Dyson noted.

The study, "High-field magnetic resonance imaging investigation of distal border fragments of the navicular bone in horses with foot pain," is scheduled to be published in an upcoming edition of the Equine Veterinary Journal. The abstract is available online.

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

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