Page 280 - The Veterinary Care of the Horse

• paired collateral suspensory ligaments which originate on either side of the distal end

of the proximal phalanx (P1) and run downwards, attaching to the outside of the middle
VetBooks.ir phalanx (P2) and the upper surface of the navicular bone where they join in the midline;
a branch continues from the lateral extremity of the navicular bone to insert on the lateral

cartilage and the pedal bone.
• the distal sesamoidean impar ligament is a sheet of fibrous tissue that joins the lower

surface of the navicular bone to the pedal bone, close to the attachment of the DDFT.

Causes

The disease is thought to be caused by repeated trauma to the navicular bone from its
supporting ligaments and the DDFT. Certain types of conformation increase the

biomechanical stress on this area. These include the following.
• Long-toe, low-heel conformation with a broken back hoof-pastern axis. During

breakover, the ligaments come under excessive tension and the DDFT compresses the
upper edge of the navicular bone against the other bones making up the joint; high forces

are imposed on the lower part of the navicular bone from the very taut DDFT.
• Mediolateral hoof imbalance.

• Narrow, upright boxy feet.

• Small feet for the weight of the horse; concussion at the heels is increased.

• The shape of the navicular bone varies between different breeds of horse; a concave or
undulating upper articular border of the bone appears to be associated with a higher

incidence of navicular syndrome than a straight or convex surface; this affects the
biomechanical forces that are applied to the area.

Increased concussion from working on hard surfaces may be a contributory factor. The

disease is also associated with changes that can occur within the foot from prolonged periods
of box rest. Without normal, regular exercise, the horse’s feet tend to become contracted.

Certain breeds, e.g. Warmbloods and Thoroughbreds, appear to experience a high
incidence of the disease. This is likely to be the result of conformational factors.

What happens to the navicular bone?

• In each case, the forces induce changes in the fibrocartilage covering the back surface of

the navicular bone. In places, the cartilage is completely eroded and the bone is exposed.
This results in increased wear to the DDFT and adhesions may occur between the tendon