Joint pathologies, such as osteoarthritis, and soft tissue injuries including superficial digital flexor tendon (SDFT) injuries commonly cause lameness and poor performance in horses. Therefore, veterinarians and researchers consistently seek new treatments that might allow horses to comfortably return to work. In their roundtable discussion at the 2023 American Association of Equine Practitioners Convention, held Nov. 29-Dec. 3 in San Diego, California, mediators Kyla Ortved, DVM, PhD, Dipl. ACVS, ACVSMR, associate professor of large animal surgery at the University of Pennsylvania’s New Bolton Center, in Kennett Square, and Lauren Schnabel, DVM, PhD, Dipl. ACVS, ACVSMR, professor of equine orthopedic surgery at North Carolina State University, in Raleigh, drove discussions on how practitioners are treating common musculoskeletal conditions using orthobiologics.

There are many orthobiologic products available to equine practitioners including platelet-rich plasma (PRP), mesenchymal stem cells (MSCs), and autologous conditioned serum (ACS). Ortved and Schnabel presented a Venn diagram to help practitioners decide what products might be appropriate for treating common equine pathologies and injuries. For example, some treatment goals might be controlling inflammation, modulating the immune system, protecting cartilage, or providing viscosupplementation, for which certain products might be more fitting. This diagram highlighted the significant overlap in the various treatment options.

Choosing the Right Orthobiologic for Joint Treatment

The group discussed intra-articular (IA) therapies following arthroscopic surgery of a fetlock joint in which the treating veterinarian noted moderate joint inflammation and mild-to-moderate cartilage damage. The participants discussed blood-based products such as autologous protein solution (APS) and autologous conditioned serum (ACS). Both products use the horse’s own blood to produce an anti-inflammatory product that can be injected into the affected joint.

To minimize trips to the farm when using ACS, the participants suggested it might be possible to prepare this product in a nonemergent situation, ahead of time, so it is ready in case the patient does need it.

Participants agreed that alpha-2-macroglobulin, a large protein that inhibits factors leading to cartilage breakdown when injected IA, might be a treatment option when managing horses with joint pathologies. However, regardless of which orthobiologic the practitioner selects for IA applications, Schnabel reminded attendees there is significant inter- and intra-horse variability with these products. “Just because it works in one horse doesn’t mean it will in another,” she said. “The systemic health of a horse can affect the contents of the product. Further, if the horse was sedated, anesthetized, or heavily exercised prior to drawing blood (to make the orthobiologic), the final product could be adversely affected.”

“There is some good evidence for the use of stem cells for osteoarthritis especially if there is a soft-tissue component like a meniscal injury,” said Ortved, referring to the stifle joint. “I will lean towards stem cells in cases of more moderate to severe osteoarthritis. However, the price point is higher, so this always needs to be a consideration.”

PAAG and Orthobiologics for Equine Joints

“The polyacrylamides are inert substances that provide viscosupplementation without inherent anti-inflammatory properties,” said Schnabel when asked if polyacrylamide gels—which are nonorthobiologic therapies—can be used in conjunction with orthobiologics. She said these therapies can be combined, but “if a joint is inflamed, I would highly recommend giving an anti-inflammatory like a steroid first before a polyacrylamide.” Addressing inflammation in the joint might decrease the chances of an inflammatory flare (also called reactive synovitis, which can occur after any IA injection).

Orthobiologics for Soft Tissue Injuries in Horses

Ortved and Schnabel both described growing evidence for the use of stem cells to treat soft-tissue injuries, particularly SDFT injuries.

“There are several long-term clinical studies in racehorses that highlight the substantial benefits of using stem cells to treat these injuries,” said Otved. “Stem cell therapy for SDFT injuries appears to significantly reduce the rate of re-injury, which is one of the biggest hurdles in treating these horses.”

Some studies also show shock wave therapy could be beneficial for treating soft tissue injuries when used in conjunction with stem cells, said Schnabel. “But there is some concern that a high power may kill the stem cells,” she noted. “If that is true, we don’t want to kill those stem cells before they have had a chance to interact with the environment.”

For soft tissue injuries Ortved leans on autologous (from the horse itself) treatments rather than allogeneic (from an animal of the same species) products due to conflicting evidence regarding how host immune response to allogeneic cells might limit the products’ efficacy. She often starts treating patients with platelet-rich plasma (PRP) when she aspirates bone marrow to start stem cell culture because PRP can be completed patient-side within 30 minutes, while it takes autologous stem cells about three weeks to expand in culture.

Take-Home Message

Veterinarians and researchers still have much to learn about optimizing orthobiologics in equine patients for IA use and soft tissue injuries. Ortved and Schnabel stressed that accurate diagnosis and characterization of the injury or disease are critical for choosing the proper therapy and increasing the likelihood of success. Veterinarians should choose therapies based on the desired outcome and consider using them in combination because each therapy has different target tissues and mechanisms of action.