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Chapter 3 - Injuries to Muscles, Ligaments, and Tendons
The reader may get the idea from reading some of these pages that I was fairly unprepared for the real world when I was granted my release from veterinary school. I was, but no more so than 99 percent of my fellow graduates around the country each year. The fact is, we just don't see as much in school as we might, especially with horses. It's not the school's fault; we can only be shown the cases that are presented to the school's clinic.
Also, there are a whole lot of conditions that we are told about in class, but there are also many we aren't told about. One of my teachers said, "That diploma you guys have been working so hard for is only a license to learn. You'll learn more veterinary medicine in your first year out of school than you learned in your four years in school." He was right.
With that disclaimer, when I first got out of school I was really bad at diagnosing lameness. If it was broken or bleeding I could usually find where the problem was, but if it was sprained or strained I had a terrible time. To make matters worse, shortly after graduation I met a veterinarian of many years' experience who was unbelievably gifted at recognizing lameness. He would turn his back on the horse and close his eyes and ask the handler to walk and trot the animal on a hard surface; he could tell where the lameness was just by listening. I usually couldn't tell by looking, probing, squeezing, or any other method. "It's a function of time, Kelley," he told me. "Do it long enough and you'll get it."
He was right, but I'm still not anywhere as good as he was. It's very frustrating. Strains and sprains are still challenging, but I'm in good company. A whole lot of vets have trouble with strains and sprains.
Incidence and Predisposing Factors
Muscle strains can occur in any performance horse and usually occur in the hind limbs. The most common muscle groups involved are the longissimus and gluteal muscles (croup myopathy) and the biceps femoris, semitendinosus, and semimembranosis muscles (caudal thigh myopathy). Strains occur far less often in other muscle groups.
There are many potential factors influencing muscle strains; the main ones are fatigue, lack of sufficient training or conditioning, lack of proper warm-up, and low ambient temperature. Fatigued muscles lose elasticity and don't function efficiently, therefore increasing the possibility of strain. Insufficient training predisposes a horse to fatigue. Proper warming up is necessary to enhance circulation, thereby increasing the ability to eliminate the muscular waste products (lactic acid) that are produced during exercise. Cold temperatures decrease circulation and increase muscle tension; the combination leads to fatigue. Muscle strains are classified by severity, from first degree to third degree. A first-degree strain is, in essence, a pulled muscle, and occurs when a muscle has reached its limit of elasticity. Muscle fibers are torn, but not the entire muscle, and it can continue to function, albeit painfully and in limited capacity. A third-degree strain is a complete tear; the function of the muscle is lost.
A horse with a muscle strain will show pain on firm hand pressure, but the area showing pain may not be the exact area of the injury. The best method of diagnosis is thermography, but this is often not available in the field.
Lameness associated with muscle strains is highly variable. A croup myopathy is usually much less serious and involves less lameness than a caudal thigh myopathy. A croup myopathy lameness is usually noticeable as an apparent stiffness coupled with a shortened stride on the affected side and is often diagnosed incorrectly as stifle lameness. A flexion test by a veterinarian will differentiate between a croup myopathy and a stifle problem, because the flexion test won't increase the lameness in a horse with croup myopathy. A caudal thigh strain usually presents itself as a heightened hip action accompanied by a hoof slap.
A muscle strain needs time to heal, so there is no specific therapy. When I was younger, I played baseball every chance I could and in California, where I grew up, that was year-round. One year I tore a muscle in my side and it took nearly six months to heal to the point where I could throw or swing a bat again. There is no substitute for time. Nonsteroidal anti-inflammatory drugs will reduce the pain but, depending on the degree of damage, may not correct the altered gait. Except in the case of a complete muscle tear, though, it isn't necessary to stop work. Rather, the intensity of actual work should be reduced and warm-up and cooling-out times should be increased. Therapeutic aids include massage, ultrasound, electrical stimulation, and if there is toe-dragging, corrective trimming and shoeing.
The prognosis in first- and second-degree muscle strains is good, but time is necessary. Horses with croup myopathy usually return to normal function within ninety days, but caudal thigh injuries may require six months to a year. A third-degree strain offers only a guarded prognosis for return to normal function and, therefore, full training capacity. Damaged muscles are more susceptible to further injury if pushed too hard, so follow the veterinarian's guidelines for exercise. As with so many things concerning horses, patience is the key.
Have you ever broken a bone? Hurts like the dickens, right? Have you ever done serious damage to a ligament? That makes a broken bone seem like a picnic in the park.
I have suffered both, thanks to my patients, those creatures that I was trying to help. A mare I was palpating kicked me in the shin and cracked the bone. It hurt like the devil, but I continued working. I limped a little, sure, but I made my usual daily rounds and eventually it healed.
But a yearling got me in the side of my knee, forcing it to bend in a manner that Mother Nature never intended for a knee to bend. A ligament was ruptured. I didn't work for three months and I hobbled around for two or three more months when I did go back to work. (I discovered an interesting fact about my disability insurance: I had to be disabled for ninety days before I could collect any benefits. At ninety days I was able to work again, but I still pay my premiums.) There was no comparison between the two pains. That happened years ago, and I still have intermittent pain in that knee.
Before I get started with ligament injuries, it's necessary to understand what a ligament is and how it differs from a tendon. A ligament is a band or sheet of fibrous tissue connecting two or more bones, cartilages, or other structures. The ligament serves as support for muscles or fasciae. A tendon, however, is a fibrous band or cord that attaches a muscle to a bone.
Most cases of inflamed ligaments (desmitis) have several things in common:
- Treatment consists of early, initial, frequent cold applications (ice, hosing), pressure bandages, and nonsteroidal anti-inflammatory drugs (NSAIDs), such as phenylbutazone.
- There is often an associated avulsion fracture of a bone that may be detected on follow-up X-ray two to three weeks after injury.
- Stall rest, often lengthy, and controlled hand walking, also for quite a while, are necessary.
- X-rays are usually of only limited benefit in a diagnosis.
Ligament injuries are often misdiagnosed, and much X-ray film is wasted in a vain attempt to find a fracture that isn't there. Because the prognosis of desmitis is dependent on early initial treatment, any lost time may prove to be critical down the road. Desmitis often leads to retirement because of misdiagnosis, particularly if insufficient time is given for healing.
Common Sites of Injury
Although I suppose an injury can occur to any ligament, we're primarily concerned with those that lead to lameness.
Stifle and Hock Areas
Ligament injuries commonly occur in the stifle region. Injury can occur to the cruciate, collateral, patellar, or meniscal ligaments. Trauma -- usually fairly severe trauma -- is the most common cause of injury to these structures. Meniscal ligament injury is often accompanied by damage to the meniscus, the cartilage that separates the ends of the femur and tibia. The onset of lameness is sudden and may be severe. As is usually the case, best results are achieved when treatment is initiated early. If in doubt, immediately ice or hose with cold water the suspected point of injury and call your veterinarian. Injuries to ligaments of the hock are most commonly seen in steeplechasers or other types of jumpers, especially those that have fallen. Lameness may be mild to severe and seems to improve after ten to fourteen days of rest. Flexing the leg makes it worse. There may or may not be swelling, and X-rays are of little use in diagnosis until about sixty days after the injury occurs, as it takes time for changes to become visible radiographically. Nuclear scintigraphy (see chapter 5 for more information) and arthroscopy are the best methods for immediate diagnosis.
If the diagnosis is made early, NSAIDs will reduce the inflammation, but six months' stall rest and controlled walking are necessary because the hock and stifle don't lend themselves to supportive pressure bandaging. The prognosis is fair to good. In the case of tarsal ligament damage, there may be small avulsion fractures of the tibia, and these must be removed surgically.
Signs of suspensory ligament desmitis include swelling over the ligament and pain on palpation and flexion. In some cases, there may be an accompanying fracture of the lower end of one or both splint bones, in which case the swelling is diffuse. X-ray or ultrasound aid in diagnosis.
Initial therapy consists of NSAIDs, cold therapy, and pressure bandages. If a splint bone is fractured, the portion of the bone below the fracture should be removed. Stall rest is mandatory, but recurrence is common. The prognosis depends on the degree of damage to the ligament.
Inferior Check Ligament
One of the more common forelimb ligament injuries occurs to the inferior check ligament, correctly called the accessory ligament of the deep digital flexor tendon. It's usually seen in older jumpers but may occur in all breeds, especially ponies, at any age. The onset of lameness is acute and there is much swelling in the area of the ligament. Ultrasound is the best method to determine the extent of the damage. Inferior check ligament desmitis may become chronic if not treated immediately and is unresponsive when it does. Treatment consists of NSAIDs, frequent cold applications, and pressure bandages for at least ten days. Ninety days' stall rest is a minimum, followed by controlled hand walking and therapeutic ultrasound, with healing monitored by periodic ultrasound examinations. Recurrence is expected if the horse is returned to work too soon. The prognosis is poor to guarded for the animal to be able to perform at its previous level.
Distal Sesamoidean Ligament
The signs of damage to the distal sesamoidean ligament are similar to those of inferior check ligament desmitis, and many times both conditions are present. Overextension of the fetlock joint is the cause. These ligaments lie on either side of the back of the pastern and severe damage can result in sinking of the fetlock. Treatment is the same as for injury to the inferior check ligament, but horses with sinking of the fetlock should be placed in a cast for six to eight weeks. At best, the prognosis is guarded, and recurrence is common.
Distal Annular Ligament
The only sign of a distal annular ligament injury is a thickening of the ligament and it's uncertain that this actually causes lameness. If lameness is present, it may be severe and there is probably an avulsion fracture of the long pastern bone associated with the desmitis. Even with an avulsion, the treatment is the same as for an injury to the inferior check or distal sesamoidean ligament, with three to six months stall rest. The prognosis is good.
In ligament injuries, time is of the essence; initially, there is none to waste and later the horse needs a great deal of it.
Before I entered my teens I fell in love with Thoroughbred horse racing. I would have loved to be a jockey, but I was almost six feet tall and weighed about 170 pounds at age twelve so I decided I'd be a professional baseball player. That didn't work out, either, but I continued to follow both sports as closely as I could. I came to learn that two problems beset competitors in both endeavors. Baseball players had rotator cuff injuries and racehorses had bowed tendons; coming back from either was difficult. Later, in veterinary school, I learned what bowed tendons were, why they happened, and what could be done about them. (It wasn't until my older son was a college pitcher that I learned the same stuff about rotator cuff injuries.) I also came to believe that bowed tendons were a phenomenon peculiar to racehorses. I never heard of a bow occurring to any other type of horse, and our teacher in school stressed the fact that they were a serious problem in racehorses.
Imagine my surprise, then, when the first three bowed tendons I saw after I left school were in nonracehorses. The first was in a Thoroughbred-cross foxhunter. He apparently took some sort of misstep while doing his job. The second was a Quarter Horse cow pony. He, too, was injured while working. The third was in a Welsh show pony. She came in one morning with a bow.
I eventually saw many -- too many -- in racehorses; about half of them raced again, albeit not as well as they had before the bowed tendons. Neither the Quarter Horse nor the Welsh pony returned to its previous work.
In racing breeds in the United States, where races are run counterclockwise, the most common site of a bowed tendon is the left front leg, although bows can occur in any limb. I once worked on a horse that bowed sequentially over a three-year period; first the left fore, then the right fore, then the right hind. (He returned to racing each time and continued to earn money.)
What Is a Bowed Tendon?
A bow usually results from a "bad step." A horse will step in a divot or hole at high speed and something has to give; that something is a tendon that is stretched forcefully and farther than nature intended. Bows involve the superficial digital flexor tendon or the deep digital flexor tendon, with the superficial tendon being involved far more frequently.
A bowed tendon is actually a torn tendon or, perhaps more correctly, a disruption of the tendon fibers. The visible swelling is a result of both hemorrhage and the protective inflammatory response of the body to the damage. Injury can occur anywhere along the length of the tendon (knee or hock to fetlock), but the most frequently involved area is the region near the middle of the cannon bone, possibly because the tendons are narrowest there.
The term bow comes from the appearance of the injured leg: the swelling on the back of the leg resembles an arched bow. As well as the typical mid-cannon bow, there are "high," "low," and "deep" bows.
Lameness is often mild or nonexistent initially, but there is heat in the swollen area and pain on digital palpation. Continued exercise only worsens it, and eventually lameness will appear. One problem is that the initial swelling is often very mild and, when accompanied by no gait alteration, is overlooked or ignored, resulting in more extensive damage when use is continued. There is a lesson here: any outward change, no matter how innocuous it seems to be, should be thoroughly investigated.
Diagnosis and Treatment
Diagnosis is best made by ultrasound, as is monitoring the progression of the bow. Initial treatment -- and it can't begin too soon -- consists of frequent cold water hosing or icing of the leg, support bandages, nonsteroidal anti-inflammatory drugs, and stall rest. Follow-up ultrasound reveals when sufficient healing has occurred for the next stage of recovery to begin. At that point (probably sixty to ninety days after the injury occurred), walking by hand can be started, followed by light jogging as the elasticity of the tendon improves. In the presence of heat or additional swelling, resume stall rest; monitor progress with ultrasound until healing is complete.
There are several other treatments that have been tried over the years, but the conservative approach outlined above is the most successful and least traumatic to both horse and wallet. The important thing to remember is: tendons heal slowly.
Prognosis for a horse suffering from a bowed tendon to return to its previous level of performance or work depends on the severity, and to some extent the location, of the injury. Most bowed horses can return to use if the injury is caught early, treated vigorously, and given proper time to heal, although they may not be quite as "good" as before. If a bow is allowed to become chronic (that is, if inadequate rest and care are provided), the prognosis lowers significantly.
"Big Leg" (Lymphangitis)
I remember the first "big leg" I saw. As I've said, my older brother showed American Saddlebreds and as a little boy I was always around them. One day we were at a trainer's barn and there was a horse in a small dirt pen. It had a huge hind leg and could barely bend it. Walking was evidently very difficult for the poor horse.
I asked the trainer, "Jimmy, what's wrong with that horse's leg?"
"It's swollen," he replied.
Well, duh. I was only about six years old but I thought I deserved a better answer than that.
Maybe three weeks later we were at Jimmy's barn again. The horse with the big leg was still there, and the leg was still big.
"Can't you do something about that horse's leg?" I asked.
"You tell me what," Jimmy answered. I never liked him much.
It was more than twenty years later when I saw the next horse with "big leg." I was just out of veterinary school and a new client asked me what was wrong with his mare's leg. This time, however, I knew what it was and what to do about it. What I didn't know then, however, was that treatment doesn't always work and that sometimes the problem recurs. They didn't tell us that in school.
What Is "Big Leg"?
"Big leg" is lymphangitis, an inflammation of the lymph vessels and peripheral lymph nodes. It usually occurs in one hind leg and may affect the leg from the hock down. The affected leg is stiff and walking is difficult. The horse often keeps weight off the leg, which may lead to problems in the other one. The cause is probably bacterial but that isn't known for sure.
Treatment consists of hosing or icing the leg, systemic steroids, and long-term (four to six weeks), broad-spectrum antibiotic therapy. Best results are achieved when treatment is begun early. Satisfactory resolution becomes increasingly difficult to attain the longer that prolonged, aggressive therapy is postponed. Unfortunately, even though the condition may be resolved, recurrence is not uncommon. Treatment is the same for recurring cases.
An old-time remedy that still has some merit is to stand the horse in a pond or creek. This seems to provide the benefits you'd expect from hosing the leg constantly. An old farm employee who had been working with horses for more than sixty years once told me of a horse he cared for that came up with "big leg." It was back in the days before penicillin and the local veterinarian had no idea what to do, so the horse was just ignored.
One day, though, when the old man (who was then a young man) went to bring in the horses, the one with the swollen leg was standing belly-deep in a pond. He couldn't get her to come out and as far as he knew she stayed in the pond day and night for about a week. When she finally did emerge, her leg was normal. Mother Nature works in mysterious ways.