Horses are quite prone to injuries. Many times owners examine these injuries and if they look small, people assume they aren't a big deal. However, the size of the wound is not as important as the location. Any wound at the knee, or hock, and below is potentially serious and could even be deadly as there are some really sensitive structures in this area and very little soft tissue covering the bones and joints. Even a half-inch puncture in the wrong place can be devastating because it can enter a tendon sheath or a joint. Infections in tendon sheaths and joints are emergencies. So anytime your horse has a lower leg wound and the skin is broken, call your veterinarian because if you wait to see what happens, it may be too late, besides which if treatment is possible it will be even more expensive. The vet may need to sedate the horse and use a nerve block to examine the area; it may be necessary to take samples of the joint or tendon sheath fluid, or inject these structures with an anti-inflammatory or local anesthetic drug to determine whether they are affected. If tendon sheath and joint infections are not treated early and aggressively, treatment may not be successful.
If your horse has a swollen leg or is lame, don't just assume it is a sprain or a bruise. It is important to examine the leg carefully, and if you find a wound of any type, regardless of the size, understand that it could be serious. Some of my clients would start giving their horse pain medication like bute without calling a vet, and the horse would get better for a few days and then be much worse. By then, many of those horses were so infected that treatment was unsuccessful. For this reason, if you find a wound, never give your horse bute without having your vet check your horse first.