A sudden swelling on a horse's leg is always cause for concern. Photo © EQUUS
A sudden swelling on a horse's leg is always a concern, but when that horse is in training for high-level competition, the case becomes even more urgent.
So when Reno, a 2-year-old Quarter Horse colt, developed a mysterious swelling just above his right knee in August 2011, his owner and trainer, Matt Koch, immediately called Ron Moorhead, DVM, of The Animal Clinic and Pharmacy in Ogallala, Nebraska. Reno is a working cow horse, and at that time he was in heavy training for the prestigious 2- and 3-year-old cow horse futurities.
When Moorhead arrived, he found a distinct swelling just above the colt's knee, right over one of the tendons, called the extensor carpi radialis, which connects a forearm muscle to just below the knee and helps to extend the joint with each stride. The swelling was distinct but slightly diffuse, about the size of a plum, with a texture that yielded to the touch. The good news was that Reno wasn't lame, and palpating the swelling didn't appear to cause him any pain.
Moorhead suspected minor tendon inflammation, and he and Koch discussed the treatment options. Invasive exploratory diagnostics or long stints of stall rest would have drastically interrupted Reno's competitive schedule. Fortunately, because the colt wasn't lame or in any discomfort, these measures weren't immediately necessary. But ignoring the problem wasn't an option either---if left unaddressed, the swelling could progress to the point where it interfered with flexion of the knee joint.
To strike a balance between these two extremes, Moorhead prescribed diclofenac sodium, a topical anti-inflammatory sold under the name Surpass, to control the inflammation, and he recommended daily bandaging to keep the swelling under control. Then Reno would be carefully monitored as he finished the competition season. If any lameness developed, Moorhead and Koch would re-evaluate their plan.
By October, Reno had won four futurities, including a National Reined Cow Horse Association championship. He had remained sound throughout the season, but the swelling above his knee had persisted and even increased in size a bit. Koch called Moorhead in for a follow-up visit.
The swelling was still localized to the same area, just above the knee. Starting with a conservative approach, Moorhead injected the swelling with a steroid, an antibiotic and hyaluronan0 to reduce the inflammation, and he prescribed two weeks of rest in a small pen. The hope was that this treatment would be enough to resolve the problem. It wasn't, however, so when Moorhead returned to find the knee still swollen, he referred Reno to Colorado State University (CSU) for a more in-depth diagnostic workup and treatment.
Common injury, uncommon location
I met Reno when he arrived at CSU. The red roan colt was handsome and well-mannered, making him very easy to work around. A physical exam turned up no problems beyond the swollen knee---careful training had left him in excellent physical shape.
I, too, found the swelling above Reno's right knee to be cool to the touch and nonpainful. The colt wasn't lame, and he didn't resent me repeatedly flexing the joint. I could tell from touching the swelling that it was filled with fluid, not a "knot" of scar tissue or a bony growth. I agreed with Moorhead's assessment that this was most likely a minor tendon injury, a suspicion I could confirm using an ultrasound.
Ultrasound technology works by passing sound waves into the body using a wand called a transducer. Those sound waves bounce off structures and back to the transducer, which analyzes the echoes to produce images of those structures on a monitor. Ultrasound is particularly useful for investigating soft-tissue injuries.
Sure enough, the ultrasound images revealed that Reno's right front extensor carpi radialis tendon sheath (ECRTS) was significantly distended and filled with fluid. A tendon sheath is a fibrous membrane that envelops the tendon itself. It protects the structure and holds in lubricating synovial fluid. A tendon sheath is very distensible, meaning it stretches easily, and even minor irritation or injury can cause it to balloon outward and fill with fluid to produce a distinct, soft swelling like Reno's. This condition, called tenosynovitis, is relatively common, but not in the ECRTS. In fact, a literature search for that condition in that specific location produced only three publications in the past 30 years.
Because the swelling was so close to Reno's knee, we decided to take radiographs of that joint, just to make sure there were no underlying injuries to the bones, but all of the structures looked healthy and undamaged. Also, because we had heard anecdotal reports of fluid in the ECRTS moving into the carpal (knee) joints, we took the extra step of performing a contrast study to see exactly where this extra fluid was collecting. To do this, we injected a radiopaque liquid into the swollen tendon sheath and then repeated the radiograph. The liquid appeared as a bright white area on the image that showed us exactly where the margins of the swelling were and what else might be inside there. Comparing the standard radiograph to the contrast radiograph, the huge pocket of fluid just above the knee was obvious. It was also clear that the fluid was limited to the tendon sheath, and none had made it down into the knee.
The good news was that this was an extensor tendon injury. These tendons run down the front of the limbs and act to extend joints---but when the horse isn't moving, they aren't under much stress. Stall rest, then, usually gives them ample opportunity to heal. The opposite is true for the flexor tendons, which run down the back of the legs and act to flex the joints. Even when the horse is at rest, these tendons continue to act as a support structure. Injuries to flexor tendons have a much more guarded prognosis. They take longer to heal, and the tendons may never fully recover their strength and function.
An inside job
Reno's injury wasn't urgent, but we needed to address it. He had been rested for two weeks with no improvement, so we knew we had to take a more aggressive approach. We scheduled the colt for surgery the following day.
The word "arthroscopy" comes from two Greek words, "arthro," meaning joint, and "skopein," to look, so the term literally means "to look into a joint." In Reno's case, we were looking into a tendon sheath so we use the term "tenoscopy." This procedure is done with an instrument called an arthroscope, which has a slender, rigid tube that holds a light source and camera that relays a magnified image back to a monitor. A surgeon inserts the arthroscope through a small incision in the skin and is able to get a direct view of the interior structures. If needed, the surgeon can also manipulate those internal structures with other instruments used in conjunction with the arthroscope. That way, diagnosis and treatment can be accomplished during the same procedure.
With Reno under general anesthesia and on his back, I inserted the scope into his leg near the bottom end of the ECRTS. Immediately I saw a mild roughening and fraying (fibrillation) of both the sheath and the tendon inside it. I could also see an adhesion---a spot where the tendon was sticking to the sheath instead of moving freely within it. Which of these issues developed first was impossible to determine. It could have been that Reno sustained a minor injury to his tendon, and the resulting inflammatory process damaged the sheath, or it could have been the other way around. But the order of those events really didn't matter. Either way, the only way forward now was to remove all of the abnormal frayed areas and the adhesion. Otherwise, they'd continue to spur the inflammatory process, leading to even more damage.
I inserted a small forceps into a second tiny incision to grasp and pull away the frayed edges of the tendon sheath and tendon. Although the structures looked huge on the monitor, the portions I removed were as small as grains of rice, and their absence would not undermine the strength or integrity of any of the structures. I was also able to remove the adhesion between the sheath and tendon. The procedure didn't take long, and Reno recovered uneventfully.
Aftercare for this type of surgery is critical to the success of the procedure. Because the tendon sheath had been stretched by the injury, and even more by the arthroscopy, it would be very vulnerable to swelling, which would set back the healing process. We placed a large compression bandage over the surgical site to prevent it from filling with fluid again, and we also started Reno on anti-inflammatory medication.
Reno went home the next day, with strict instructions for two weeks of total stall rest. Moorhead visited him when it was time to take the stitches out, and he also injected hyaluronan into the tendon sheath to help support the production of the thick, lubricating synovial fluid that naturally fills it. The hyaluronan also acts as an anti-inflammatory treatment. The colt would get two more such injections over the coming weeks.
After the stall rest, Reno was started on a program of gradually increasing hand-walking, then after another two weeks he was turned out in a small paddock and ridden lightly. It would be several more weeks before he could return to training.
We have no way of knowing how Reno had injured his tendon, but our best educated guess is that he incurred some sort of accidental blunt-force trauma as he knocked it against a fence or water trough while playing as active young colts do. Because the colt was so well-conformed, physically fit and carefully managed, we didn't suspect his injury resulted from his athletic training, and so we had no reservations about him returning to it.
A few months after he left the clinic, we heard that Reno had developed mild swelling over his right knee. Moorhead injected a small amount of steroids into the area, which seemed to be the final kick the tendon and sheath needed to heal. Reno returned to the show circuit last spring, and in the fall he won the Junior Working Cow Horse World Championship at the American Quarter Horse Association World Show in---ironically---Reno, Nevada. He and Koch have continued to show, and they already have a championship under their belt for 2013. I have no reason to anticipate anything but a long, sound career for Reno, all with a normal knee.
This article first appeared in EQUUS issue #430.