A healthy navicular bone is a small canoe-shaped structure that acts as a fulcrum for the important deep digital flexor tendon to pass around. As such, this tiny structure plays a big role in keeping the lower limb structures moving smoothly. But results from a new study have revealed that, in rare cases, some of these crucial bones are segmented into two or even three parts. This segmentation isn’t the result of injury or wear, though; the horses are born this way. And the effects are detrimental to the horse’s health, performance, and welfare.

“We are the first to describe three cases with clinical, radiological, and pathological images,” said Willem Back, DVM, Cert. KNMvD (CKRD), Cert. Pract. KNMvD (Equine Practice), PhD, Spec. KNMvD (Equine Surgery), Dipl. ECVS, Prof. (U Ghent), of the Utrecht University Faculty of Veterinary Medicine Department of Equine Sciences in the Netherlands.

“Usually, the clinical picture reveals a gradually developing lameness later leading to extreme, cystic changes in the bone,” Back said.

However, those later changes are associated with only minimal arthrosis (degenerative joint disease caused by wear and tear over time), unlike changes related to a trauma-related injury, he added. Furthermore, the bone-segmenting disease can occur in more than one foot in the same horse. Thus, he said, the disease is congenital (the horses are born with it) and does not result from trauma in early life