"Popped knees" is a layman's term used to describe enlargement in the front of the carpal joints of a horse. The knees look like they have "popped out." Sometimes this condition is accompanied by marked lameness, sometimes not, writes Dr. Barrie Grant in the "AAEP Answerline" column in the September edition of The Horse.The appearance of the knees usually is the result of the enlargement of synovial structures--the three tendons that go over the front of the knees (flexor carpi radialis, flexor carpi ulnaris, and extensor carpi radialis), two joints, and one bursa between the tendon and the joints. Inflammation in any of those structures will cause an enlargement to the front of the knee and therefore give the appearance the knee has "popped."Causes vary. Most commonly, popped knees occur from a chip in the joint in racehorses or horses that perform at high speed. Infection, developmental abnormalities in young foals that rupture their tendons in front of the knee, and direct trauma to the knee are other causes.It's important to identify which structures are inflamed, as treatment can vary. Sometimes, all can be involved, sometimes just one.It's also important to get an early, accurate diagnosis. In fact, it's the most important thing you can do for treatment. The sooner a veterinarian can make an accurate diagnosis, the more successful the treatment.Older horsemen might suggest do-it-yourself remedies, but such therapy is a disservice to the horse, according to Grant, who is a partner in the San Luis Rey Equine Hospital in Bonsall, Calif. Just giving anti-inflammatory drugs or putting a bandage on the knee is not addressing the problem. If the horse owner puts off getting a proper veterinary diagnosis and tries to treat the horse himself for two or three months with old-fashioned liniments and bandages for a horse with chips in the joint, the owner is going to reduce the chance of a successful repair of that knee. Untreated, the injury can become worse and develop into a severe arthritic condition.Treatment depends on the cause. Bone chips usually create inflammation in the joints, and sometimes inflammation of the tendon sheath. Bone chips usually are treated by removing them arthroscopically. This type of surgery can often be done in less than an hour with a horse under general anesthesia. Barring complications, the horse usually can return to work in 60 to 90 days.For direct trauma to the soft tissues in the tendon sheath, veterinarians usually administer anti-inflammatory medications such as Bute or Banamine, ice the injury, bandage or sweat the leg, and give the horse time off. That often takes care of soft tissue swelling, with full recovery taking a couple of weeks.Infection is treated by draining and flushing the area and putting the horse on appropriate antibiotics. Horses that are quite lame need to be rested during the recovery period, which can range from three or four weeks, to three or four months.For developmental abnormalities that cause tendon enlargement in foals, a veterinarian usually will put the affected leg in a half-cast for a couple of weeks. When the cast is removed, the leg is put in support bandages, and the foal is kept in a stall for a couple of months. The results usually are good.