Description

The shin in a horse is similar to that of a human in that it is the front of cannon bone in the leg just below the knee. As with a human, too much stress leads to a sore shin. 

Shin soreness in the horse develops when the front surfaces of the cannon bones in the forelimbs are subjected to high-impact forces during early training. As young horses gallop at a fast pace on hard, compacted tracks, the increased compressive force affects the surface of the bone resulting in distortion and flexion in the cannon bones. In severe cases, the concussive force results in stress fractures.

The cannon bone's inability to adapt effectively to the stresses placed on its front surface as speed and distance training increase, result in metabolic changes in the bone structure and can result in hemorrhaging below the surface along with laying down of new bone on the front surface.

The new bone is sponge fiber bone rather than strong, dense bone. When the cannon bone is unable to carry continued overload, increased inflammation and thickening lead to shin soreness.

Symptoms

• Heat over front of cannon bones
• Swelling
• Pain when palpated
• Shortened stride
• Lameness

Causes

Shin soreness is caused by the cannon bone's attempt to repair damage to the dorsal aspect of the bone when the horse is exercised to the point of overload on the front cannon bones.

This exercise-induced bone remodeling leads to growth of new, less-dense bone, hemorrhaging below the periosteum, and stress fractures. All of these factors contribute to inflammation, swelling, and soreness of the shin bone.

Horses that are trained on compacted dirt tracks are more likely to develop shin soreness than those trained on wood fiber tracks or turf tracks.

Prevention

Preventing shin soreness relies on good horse management and not pushing young, athletic horses to work beyond their growth capacity under circumstances that contribute to a breakdown in the horse's musculature and bone systems.

Well-designed turf or wood-fiber tracks that are properly banked and don't force horses to corner end circles in a small radius will help prevent increased strain on the cannon bones. Studies in the UK show that shin soreness is less likely to develop in young horses galloped on straight tracks.

Although financial considerations often drive training that allows young horses to train and race beyond their maturational development, consideration should be given to training horses in such a way as to increase their longevity by setting performance standards that do not trade the physical well-being of the horse for an early start on any promotional circuit.

Treatment

In acute cases of shin soreness with severe swelling and lameness, the horse should be confined to stable rest to avoid the risk of long-term bone damage. Cold compression therapy with ice packs should be applied two or three times a day for fifteen to twenty minutes to help reduce swelling and discomfort.

A veterinarian may decide that a course of phenylbutazone is also needed. Once the pain and inflammation has subsided, a veterinarian should examine and assess the severity of the fibrous secondary bone deposits.

X-rays may be necessary to check for secondary bone formation and hairline fractures. The veterinarian will recommend treatment depending on the findings.

Following the veterinarian's recommendations, the horse can be reintroduced to an exercise program designed to keep the horse sound and encourage active and long-term modeling to permanently adapt the cannon bones to fast exercise.