Answered by, Jen Reda, DVM, Aiken, SC and Stephanie Regan, DVM, Lexington, KY
Courtesy of AAEP
Question: My 19-year-old Thoroughbred gelding was recently diagnosed with moderate osteoarthritis in his right hind and upon ultrasound, with mild DSLD in both hinds. The number one treatment recommendation is for articular injections. Will these injections resolve the DSLD in any way? Sadly enough, he was also diagnosed with atrial fibrillation (afib) six years ago. I can’t help but wonder, are the two diagnosis related?
Answer: We are sorry to hear that your Thoroughbred has been diagnosed with these three chronic conditions. A couple points we were unclear on were which joint in the right hind was diagnosed with osteoarthritis (OA) and which two diagnoses you thought might be related. However, we will talk about OA in general, and we assume the link you are questioning is between Degenerative Suspensory Ligament Desmitis (DSLD) and OA.
OA is a disease of moveable joints whose hallmark feature is loss of articular cartilage, along with bone remodeling. This can occur for many reasons, including abnormalities in the subchondral bone underlying this cartilage due to repetitive stress or abnormal forces imposed on the joint due to soft tissue injury. OA can be the result of acute injury such as a fracture or repetitive stress from high impact work. Medical management of OA has multiple modalities that can be used in numerous combinations, including NSAID administration, such as phenylbutazone, intraarticular injections of steroids, exogenous lubricants and biologic therapies, such as corticosteroids, hyaluronic acid, and IRAP, respectively. Intramuscular injections of adequan and oral administration of neutraceuticals such as glucosamine and chondroitin sulfate may also be part of a treatment plan. Most of these therapies have published efficacies, some with better results than others, and many of them with significant side effects if not used judiciously. The basic premise is to reduce inflammation, restore lubrication, and mitigate the pro-inflammatory cytokines in the joint. Regardless of origin or management style, OA is a progressive, incurable disease that requires lifelong management.
Degenerative suspensory ligament desmitis (DSLD) is a difficult disease and one that definitely needs more research. The current best understanding of this disease is that it is likely hereditary, more commonly found in breeds like Paso Finos and Arabians, and less commonly found in Thoroughbreds. It is actually a systemic disease that involves many different connective tissues throughout the body, but often clear manifestations of it are seen in the suspensory ligaments. The current theory on DSLD is that there is an abnormal accumulation of molecules called proteoglycans in between the fibers of the connective tissue. This leads to a decrease in strength of the affected tissues and an irregular fiber pattern, which can be seen on ultrasound. Ultimately, the degeneration can lead to tendon or ligament failure. What can help to differentiate DSLD from a suspensory injury is that it occurs in more than one suspensory ligament at the same time, often in both hind or even in all four ligaments. It is also often diffusely spread throughout the whole ligament, not one focal spot of injury.
Sadly, there is no cure for DSLD either at this time. Intra-articular injections will not treat DSLD, as the problem is not within a joint. Although, potentially the OA is exacerbated by the abnormal biomechanics of the joints due to fetlock drop; it’s hard to say not knowing which joint was diagnosed. Pain management must be considered especially for horses that are currently lame, for this we would look to our nonsteroidal anti-inflammatory drugs such as phenylbutazone (Bute) or firocoxib (Previcox). Previcox can be used for longer periods of time without as great a risk of gastrointestinal side effects, so may be an option if your horse is lame. Your veterinarian may consider supplementing with MSM (methyl sulfonyl methane), which has anecdotally been reported to help restore flexibility to tissues, although to our knowledge this has not been evaluated with a formal research study. One major help to your horse may be shoeing changes; this decision will likely be a result of collaboration between your veterinarian and farrier, and may include either an eggbar or a fish tail bar shoe. Opinions vary on best course of action and will depend on severity of the DSLD and if your horse stays in work. This will provide support to the limb and relieve some of the tension on the suspensory ligament by helping to prevent the fetlock from dropping. You might also consider supportive leg wraps such as sports medicine boots to help support the tendons and ligaments in the lower limb. Most horses with DSLD will eventually not be able to continue an athletic career due to the continued degeneration of the suspensory ligaments, however pasture soundness and comfort could be a realistic goal, especially if his DSLD is mild at this stage.
For all of these separate diagnoses—the osteoarthritis, the DSLD, and the atrial fibrillation, the best advice and recommendations will come from your veterinarian. He or she has seen your horse and diagnosed these conditions. It is likely that he or she will desire follow-up appointments to monitor the progression of the osteoarthritis as well as the DSLD, and may need to perform further radiographs or ultrasounds along the way. We recommend you continue to work with him or her for the best treatment plan for your horse. Best of luck to you, and thank you for your question!