Equine Intra-Articular Osteoarthritis Treatment Options

By Raquel Baccarin, DVM, PhD, WEVA Regional Ambassador for Brazil and South America

Epidemiologic data collected from more than 100,000 horses revealed that articular lesions are the most frequent reason owners seek veterinary care for their animals (Pennell et al., 2005). Among equine joint diseases with the greatest impact and clinical relevance in orthopedics, osteoarthritis (OA) remains the most devastating. The condition is often associated with poor performance, early retirement, and a significant financial burden for owners of affected animals.

In humans, OA is classically defined as an age-related joint disease that is one of the main causes of pain and dysfunction in elderly individuals. However, in horses, the condition also affects young animals, indicating that age is not an essential factor for OA development in equids.

Equine OA is a painful and debilitating disease that can develop rapidly (when secondary to trauma) or slowly (months to years), depending on the etiology (cause). It is common in all types of horses; however, it tends to affect joints with a larger and smaller range of movement in sport horses and leisure horses, respectively.

In recent years, researchers have described equine OA not as a single disease, but as the final stage of destruction of the articular cartilage, with early stages being triggered and perpetuated by many random factors. However, the exact sequence of events leading to OA development remains unclear, and the temporal relationship between subchondral bone (located just under the cartilage surface within a joint) damage, chronic synovial membrane (the joint capsule’s inner lining, which secretes lubricating synovial fluid) inflammation, and cartilage damage remains unknown.

Pharmacological OA therapy focuses on preventing or reducing pain and improving joint function. Veterinarians have administered intra-articular (in the joint) injections of the corticosteroid triamcinolone acetonide (TA), with or without hyaluronic acid (HA), for decades. Triamcinolone provides better pain relief and functionality in the short- and medium-term, but corticosteroid alternatives are needed for horses with chronic OA.

Many studies have shown that administering at least three intra-articular HA injections results in significant improvement in joint pain and function that begins immediately after treatment and lasts for a medium- or long-term period. However, there is no evidence confirming HA injections improve structural damage to articular cartilage.

Chondroitin sulfate (CS) and glucosamine are therapeutic alternatives for OA treatment. Researchers have found evidence suggesting that CS and glucosamine could preserve or even repair damaged articular cartilage. Dietary supplements containing CS are available, as well as intra-articular formulations for managing OA clinical signs in horses. When testing CS in horses, researchers’ initial hypothesis was that it would provide the cartilage with the necessary building blocks to synthesize the extracellular matrix proteoglycans; however, study results were inconsistent and conflicting. Chondroitin sulfate penetration into chondrocytes (cells that make up articular cartilage) was very limited, indicating that CS’s primary effect on chondrocytes is mediated by cell-surface receptors through which it exerts anti-inflammatory effects.

Another therapeutic alternative for OA is polyacrylamide hydrogel (PAAG), which studies showed alleviates lameness and joint effusion in osteoarthritic horse joints. Additional studies are needed to elucidate PAAG’s mechanism of action in improving OA clinical signs.

Blood-derived products such as platelet-rich plasma (PRP), autologous conditioned serum (ACS), autologous processed plasma, and autologous blood can also be administered via intra-articular injection. Most equine clinical studies have shown that PRP has positive effects when used to treat joint injuries; however, these studies have a high risk of bias and PRP products vary greatly in composition, making it difficult to compare their efficacies. Frequently, veterinarians recommend two or three PRP treatments with intervals varying from two to three weeks. Following PRP treatment veterinarians have reported lameness improvement and reduced joint effusion (swelling). Researchers are also working to develop a more effective PRP product by combining it with other molecules such as chitosan and gelatin, and HA used in combination with PRP has shown promise as a future treatment.

Veterinarians commonly use ACS in athletic horses when corticosteroid use no longer shows beneficial effects, mainly in chronic OA cases. Lameness generally improves after the second administration, with resolution occurring after the third or fourth. The effects of ACS treatment typically last three months to a year in joints that are not responsive to other intra-articular therapies. A considerable amount of data suggests that ACS use has beneficial effects, but the findings of experimental and clinical trials are inconsistent.

Several studies have shown that intra-articular mesenchymal stem cell (MSC) injection helps reduce synovial inflammation and results in better cartilage repair from a structural point of view, when compared to other currently available therapies and surgical techniques. In horses, MSC sources include bone marrow, adipose tissue, umbilical cord, umbilical cord blood, amniotic membrane, and peripheral blood. Moreover, researchers have recently shown synovial fluid and membrane to be viable sources of MSCs. The quantity of cells obtained, the capacity for and efficiency of differentiation, the ease of collection, and low risk of complications during collection are important issues to consider when selecting an MSC source. Currently, MSCs derived from bone marrow and adipose tissue are most commonly used in therapeutic approaches.

Veterinarians can use a variety of intra-articular therapies to minimize joint damage, but it is important to identify the most effective treatments for specific equine OA cases. Furthermore, most of the therapies used to treat OA treatment have short-term effects on pain and function, and few have been tested for or exhibit long-term benefits.

Veterinarians should constantly strive to gain more experience in using such therapies, alone or in combination, to provide optimal treatment to horses recovering from joint injuries.