This horse was injured in the axillary area, between a horse's foreleg and chest. Photo by Dr. Wendy Smith Wilson.
The area between a horse's foreleg and chest, where the front leg is attached to the chest, is called the axillary area. It is a common area in which horses get injured and lacerated. A wound there can lead to an unusual condition. Axillary wounds tend to be quite deep and can extend eight to 12 inches upward from the surface of the cut as a wound in this area allows the tissue to separate easily. Because the wound in most cases is really deep, the cut tissue acts as a one way valve for outside air; it allows air to enter the wound but not exit. This can lead to an accumulation of air under the all of the horse's skin, not just the area of injury. It can look like you stuck a needle under the horse's skin and turned on an air compressor. Fortunately, in most cases the air will be resorbed after a period of time and so it's not dangerous to the horse.
However, in some cases, the air can enter the chest and lead to a pneumothorax, a serious and potentially fatal condition in which abnormal air surrounds the lungs and causes rapid and shallow breathing. If this occurs, a large needle must be placed into the horse's chest to remove the air. To prevent air from entering into the wound after it has been explored and cleaned, the wound should be packed with sterile gauze or sterile sponges. The wound can then be sutured except for a small area to remove and replace the gauze. It is likely the sutures will not hold but the time the sutures do hold allows the wound to start closing and decreases contamination of bacteria and air into the wound. Wounds that cannot be sutured should have a bandage sutured over the wound to prevent air and bacterial contamination.
If your horse develops a wound under the foreleg, call your veterinarian as these wounds can be deadly.