Like tendons, ligaments are composed of connective-tissue bundles made primarily of collagen with some elastic fibers as well. In a ligament, the connective tissue is arranged in parallel sheets bound together tightly. The strength of a ligament is the sum of the strength of each of these sheets. Healthy ligaments have a generous margin built in between the loads they normally withstand and what it takes to damage them. However, during a progressive training program, the ligament may undergo a series of minor injuries/disruptions that lead to the formation of a stronger and bigger ligament.
When training and exercising is done correctly, you never know this occurs and the horse is never sore or swollen. However, if you go too quickly and symptoms begin to appear, you know the workload is too much. If you ignore those early symptoms, your horse can end up with a rupture of enough tissue that it becomes significantly weakened and unable to support the horse without pain, possibly even standing still.
This is called desmitis, which means inflammation of a ligament and inflammation, which, of course, is a result of damage. When extensive damage occurs, the suspensory can’t support the fetlock and the joint will sink down toward the ground. This may be the result of trauma or a condition called degenerative suspensory ligament desmitis (DSLD).
DSLD is considered a progressive, incurable disease. In DSLD, the damaged ligament areas have been replaced by cartilage or scar tissue, which can’t be returned to normal elasticity. However, interventions such as using eggbar or extended-heel shoes to help support the fetlock, the use of support boots when working the horse, and dietary supplements can help many horses and even arrest the progression of the suspensory disease.
While some horses do require euthanasia, the diagnosis of DSLD isn’t necessarily a death sentence. Some horses stabilize on their own, probably when the repair and degenerative forces, including stresses, level of exercise and conformation, reach an equilibrium.
Although it was recognized 25 years ago, DSLD remains a poorly understood syndrome where the suspensory ligament develops areas of damage that can’t repair themselves normally. Why isn’t clear.
One theory is that conformation stresses or the structural weakness of the suspensory - those small bones and ligaments supporting a large body weight - constantly overload the ligament, which then can’t keep pace with repair.
Another theory involves nutritional deficiencies, including an insufficient supply of nutrients required for repair and/or insufficient antioxidants to keep the inflammatory processes in check. Other experts believe that a basic metabolic defect resulting in the formation of defective ligament tissue will eventually be found.
Although it could be difficult to distinguish true DSLD from desmitis of other causes, there are some key features of DSLD:
Gradual and progressive appearance of lameness, unrelated to activity level, with pain on palpation of the suspensory ligaments, usually evident first over the branches, and positive fetlock flexion test.
Bilateral involvement of both front or both hind legs.
Onset before the age of 10.
The finding of a characteristic hyperechoic (white) pattern in the suspensory, rather than the hypoechoic (dark holes) usually seen with traumatic injuries and thickening of the suspensory branches. Disrupted fiber patterns may also be seen and tears can also occur in advanced cases.
In the advanced stages of DSLD, or any severe suspensory damage, the suspensory can no longer support the fetlock and it will drop closer to the ground. The pastern angle then becomes more sloping and the foot pushed in front of its normal position, further weakening the support for the fetlock. The angles of the hind leg joints, especially the hock, become much more straight up and down.
Ringbone involving the pastern joint also commonly results because the sesamoidean ligaments coming down from the base of the sesamoids and attaching to the pastern bone are an integral part of the support of the bony column of the pastern (P1 joint). When the sesamoids/fetlock drop, these ligaments loosen and the bone slips forward.
It would be nice if horses were like salamanders so that every damaged tissue would just grow back exactly the same as it was before. Unfortunately, that’s not the case. Healing can result in the rebuilding of tissues, of course, but there’s also a considerable potential for scarring. For ligament injuries to heal in a way that maximizes how functional and strong the repair will be, it’s important to walk a fine line between inflammation encouraging repair vs. inflammation leading to scarring.
In the early stages of an injury, inflammation is necessary to both remove damaged tissues and encourage good blood flow to deliver nutrients for repair. Ligaments, however, have a poor blood supply compared to other tissues, and the buildup of fluid in the spaces between the sheets of connective tissue can result in back pressure on the blood vessels and inefficient removal of both the damaged tissues and the inflammatory enzymes. The connective tissue that is formed up to 10 or 14 days after an injury is also unspecialized and can’t withstand the same forces. There’s a fine line between efforts to keep circulation and fluid removal going but not damage new tissue.
After this initial phase, the challenge becomes to encourage the healing to proceed along the lines of laying down a functional ligament repair versus a mass of unspecialized scar tissue. The stimulus for the immature tissue to become functional ligament comes from the loading it experiences. Fibers will line up according to the forces placed on them. However, these immature tissues and the damaged ligament itself are still weak and easily reinjured.
While the suspicion is there that horses that develop DSLD may have an inherent biochemical problem that prevents them from forming and repairing ligaments in a normal way, the approach to treating both traumatic desmitis and DSLD is essentially the same. While there are no miracle cures, some management practices and products can improve the outcome.
Stage I - fresh injuries: The prescription for ligament injuries in human athletes is RICE: Rest, Ice, Compression and Elevation. We can’t manage the elevation part with horses, but otherwise it’s good advice. Stall confinement is about all the rest you can provide and is definitely in order initially.
Ice is also the order of the day - the more, the better.
Opinions vary about wrapping legs. Bandaging helps control fluid accumulation but, if done incorrectly so that pressure isn’t even or there’s slippage, the results can be disastrous. Even expertly applied wraps can slip with the horse getting up and down or if the horse pulls at them.
Veterinarians often prescribe NSAIDs (non-steroidal anti-inflammatory drugs), such as phenylbutazone, flunixin or aspirin, for inflammation control. However, because of the potential for NSAIDs to interfere with connective tissue metabolism, we recommend you work to control the inflammatory response by icing as much as possible. We realize this is labor intensive . If the horse can’t be attended throughout the day and iced, NSAID use for a week or so may be necessary.
Stage II - repair: By 10 to 14 days after initial injury, the inflammatory response should be under good control and the fibroblasts will be beginning to lay down new tissue. Prolonged stall rest used to be recommended for horses with suspensory damage and, in some cases of DSLD, it’s advisable. However, ligaments heal better, stronger and with less scar tissue when controlled exercise to direct the orientation of the new tissue into a functional configuration is introduced early.
With simple strains and little actual tissue disruption, you may be back in the saddle doing light work at two weeks. With more serious injuries, a regimen of gradually increasing periods of hand walking will be the starting point. The best way to monitor the progress of repair is by serial ultrasounds. Damaged or fluid-filled areas appear as black holes on the ultrasound. With minor injuries, these can resolve quickly and, if the fiber pattern seen in that location looks good, the horse can gradually return to full work. With more serious injuries, repair can take several months to a year. Controlled exercise should be continued throughout this time.
High-tech therapy equipment: Of the various high-tech therapy options we’ve used, the strongest indication would be for infrasound and laser therapy (see April 2000, April 2001). Infrasound, such as the Alpha Sonic, is useful in the mobilization of inflammatory fluids without activating any further inflammatory response. This is a valuable adjunct to icing in the acute stages and for controlling any filling that occurs as exercise is gradually introduced.
After the initial two-week period, low-power laser therapy can be valuable. Studies on the behavior of fibroblasts in vitro show low-dose lasering enhances their activity. Get the dose too high, however, and they can be ’shut off.’ In our laser study, we found clear benefit from lasering ligament injuries. It was especially helpful with horses that seemed to have plateaued at a particular level of pain and swelling, leading to rapid reduction in both and continued improvement from that point.
Nutrition: Optimal nutrition is always important for healing. Adequate vitamin C, sulfur, copper and zinc are needed for ligament repair, as well as sufficient high-quality protein, while vitamin E, selenium, copper and zinc should be generously supplied to keep the balance between inflammation and repair.
Glucosamine should be helpful, and some manufacturers offer supplements containing proline, a key amino acid for connective-tissue formation. While many supplements for joints might hint at benefits for tendons and ligaments as well, few specifically claim to help with these injuries. MSM is popular with many for both nutrition and inflammatory control, but studies/trials to document a clear effect are lacking.
We tried SuspensorySaver, from Figuerola Laboratories (40 servings or 20 days at loading dose, $49.99). Like Figuerola’s LaminaSaver that worked well in our June 2002 laminitis trials, SuspensorySaver contains MSM, glucosamine, collagen, vitamin C, PABA, DMG and nutrients.
We used it in one horse that had a suspensory injury and was back in full work, retraining for racing. She had no problems with lameness but did show occasional filling. After starting the SuspensorySaver, the filling problems resolved and she trained down uneventfully.
Another trial was in a five-year-old racehorse, who had a history of suspensory problems and had reinjured the leg. No clear effect was seen with the supplement.
The third was an older horse with chronic suspensory damage, dropped fetlocks and soreness. The use of SuspensorySaver seemed to make him more comfortable.
The fourth trial horse was an Arabian diagnosed with DSLD behind. He had been put on several months of stall rest with stabilization and fitted with bar shoes for additional support of the fetlock. When attempts were made to reintroduce exercise in hand, with the goal of turnout, he would regress to stiffness behind, reluctance to move freely and constant weight shifting behind when in his stall.
He was started on the SuspensorySaver and, over a period of several weeks, was able to tolerate longer walks and paddock turnout, then stabilized at that point for the past six months, with no further improvement or deterioration.
While we wouldn’t call our results dramatic, SuspensorySaver certainly benefited three of our four horses. Although there’s no scientific evidence as yet that any particular nutrient(s) will enhance or jump-start tendon and ligament healing, we do think it’s a strong therapy to pursue.
More is not better, however, and it’s important to make sure you provide required levels of trace minerals, protein and antioxidant vitamins to the horse. It’s easy to fall short when horses are on restricted exercise and feed intakes.
In addition, we strongly recommend supportive measures in the form of RICE for fresh injuries and farrier care, boots, and light, gradual exercise with backup ultrasound studies to watch for any ’healing’ progress or repair.
Infrasound therapy and laser therapy should be considered when available.
Also With This Article
Click here to view "Detecting Suspensory Damage."
Click here to view "Suspensory Problems."
Click here to view "Where is the Suspensory Ligament'"
Click here to view "Use Caution If He Seems To ’Warm’ Out Of It."