Boots or wraps on the back legs are often used in horses that work with the hind end strongly engaged, like upper-level dressage horses, to protect the cannon bone from contact. The weight of the hind boots, as well as firm pressure from an overly snug wrap, will cause the horse to travel wider behind, making some riders avoid using them.
The exact mechanism for the difference in movement is unclear, but it appears to be some type of reflex feedback from the weight and pressure of the boots, since the horse will go back to his normal way of traveling when the boots come off.
Fears that the horse will permanently alter his gait to move wider behind if boots are used for long periods are largely unfounded.
However, long-term boot use will cause the horse to develop leg musculature that complements and supports the way he moves with the boots. He will also begin to wear his shoes/hooves to suit the different gait. Fortunately, these changes are reversible over time.
If you feel your horse is starting to go too wide as a result of hind boots or wraps, discontinue their use. Make sure the hooves are trimmed level and replace any abnormally worn shoes with new ones.
Quicker results may be obtained by leaving the horse barefoot behind for a while and by making sure he gets plenty of turnout time, so he can move around in a relaxed manner.
If cannon-bone protection is necessary, we suggest you try switching to lightweight cotton sheets with light wraps to hold them in place. You can also try the cotton with a layer of lightweight foam cut to fit over the front of the cannon bone, held by the thin wrap.
Avoid heavy boots, highly elastic outer wraps and pulling the outer wraps tighter than they need to be to hold the wrap securely, as you always would.