Equine Navicular Disease

Thehorse.com - Full Article

by: Stacey Oke, DVM, MSc
January 01 2011, Article # 17730

The navicular bone is small in stature but continues to be a big pain in the foot.

The navicular bone is a small, boat-shaped bone nestled deep in the protective womb of the hoof, cushioned by the digital bursa (a small, fluid-filled sac), shrouded by the deep digital flexor tendon, and bathed in synovial fluid. It only measures approximately 6 cm wide and 2 cm deep (top to bottom) in an average 1,200-pound horse, so how can such a small bone be such a nuisance?

Part of the problem is that, despite its cushy abode and small stature, the navicular bone has a big job.

"The function of the navicular bone is to act as a fulcrum around which passes the deep digital flexor tendon (DDFT) before it inserts on the distal phalanx (pedal bone)," explains Sue Dyson, MA, VetMB, PhD, DEO, FRCVS, head of clinical orthopaedics at the Animal Health Trust's Centre for Equine Studies in Newmarket, U.K. "The navicular bone is also an integral part of the distal interphalangeal (coffin) joint, which is one of the major shock absorbing joints in the lower part of the limb. The orientation of the DDFT depends on the position of the coffin joint (flexed or extended), and the position of the coffin joint also influences the size of the forces applied to the navicular bone by the DDFT, which are maximum in the propulsion phase of the stride just before liftoff."

Navicular disease is a common cause of equine lameness, primarily in the forelimb...

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