Question: I have a 7-year-old Thoroughbred mare who has developed a left front knee problem. When she came in one evening last winter, she had small abrasions on both her knees. Her left knee was mildly swollen though not painful or hot to touch. I used ice, gave medicine and did knee stretches for about a week and the problem of the swollen knee seemed to resolve itself.
However, the swelling returned when I sent her off for training for three months this spring-about six weeks after the injury. Some days are worse than others. She is never lame, and probing the swollen knee does not seem to bother her. Now she is back at home and working at Training Level. I usually longe her for 10 minutes before riding and then school for 30 to 40 minutes, three or four days a week.
Her veterinarian diagnosed hygroma and basically says this is a chronic problem and there isn’t really a whole lot I can do. Draining the fluid when it accumulates and then injecting steroids doesn’t seem to work, so he advised not doing this. She is on glucosamine. Is there anything else I can do to avoid this swelling?
Answer: The problem you describe is a common one and can involve several different structures around a horse’s “knee” or, more appropriately, the carpus. The problem could be one of three: in the skin under the carpus, in the carpal joint itself or in the extensor sheath. These three conditions all look fairly similar and each is characterized by swelling around the “knee.”
Lameness is rarely associated with any of these problems except at the beginning of the incident. A puncture of the actual carpal joint and leakage of joint fluid under the skin is called a hygroma. This is the most serious of the three conditions since bacteria can enter through the wound and infect the joint. It also is the least common one of the three.
If the skin under the carpus is swollen, the condition is called seroma. This is the most common problem with horses. It is blood and serum collecting under the skin of the carpus. A seroma can accumulate to a good size and can be difficult to stop from filling back up, even with draining and cortisone injections. Seromas easily recur with strenuous exercise or external trauma. They can, however, be opened and allowed to drain.
The third possible cause of your mare’s knee problem is a swelling of the extensor sheath. The extensor sheath surrounds the extensor tendons as they pass over the carpus. This condition is easily identified by the additional swelling that occurs in the extensor tendon sheath, extending up the horse’ s leg beyond the immediate area of the carpus. While this problem is not as common as the seroma, it is not as uncommon as the hygroma. It also is one of the more treatable conditions, since it responds well to cortisone injections.
Good clinical and ultrasound examinations and/or tapping into the swelling and performing a fluid analysis can differentiate these conditions. Some of the problems can be treated by draining and giving cortisone injections, but, as your veterinarian says, such treatments don’t always work, particularly in the case of a seroma.
If your horse is doing well and she is sound, you should leave well enough alone. Glucosamine won’t hurt anything, but it sure won’t help this condition. Fortunately, the swelling is cosmetic only and shouldn’t affect your horse’s performance.
A.Kent Allen, DVM, is a U.S. Equestrian Team (USET) veterinarian and was the highest ranking veterinary official at the 2000 Olympic Games. He is chairman of the USA Equestrian Veterinary and Drugs and Medications Committees. He practices from his Virginia Equine Imaging in Middleburg, Va.
