During her career, Lisa Fortier, DVM, PhD, Dipl. ACVS, James Law professor of surgery at Cornell University’s College of Veterinary Medicine, in Ithaca, New York and editor of the American Veterinary Medical Association’s journals, has made, and continues to make, contributions to developing and revolutionizing orthobiologics in equine medicine. In this field, practitioners use treatments derived from biological substances, such as stem cells, to manage musculoskeletal conditions.

Fortier presented her research on the history and future of orthobiologics, providing key takeaways for veterinarians using these therapies, during her Frank J. Milne State-of-the-Art Lecture at the 2024 American Association of Equine Practitioners Convention, held Dec. 7-11, in Orlando, Florida. She described the history of the main orthobiologics used today in equine practice: autologous conditioned serum (ACS), which concentrates platelets and interleukin-1 receptor antagonist protein, or IRAP; platelet-rich plasma (PRP); autologous protein solution (APS); and bone-marrow-derived cultured mesenchymal stem cells.

Which Orthobiologics Are Best for Horses?

“The main questions I get asked about orthobiologics are: ‘Which one is best?’” said Fortier. “‘How many injections should I perform?’ And, ‘When can we get the horse back to work?’” But, despite dedicating her life’s work to studying orthobiologics and implementing these in her practice, she said she’s learned these biologics are complex and there are still no clear answers to these questions. “There are a lot of different cells in play, and they change from horse to horse,” Fortier said. “None of the biologics are miracle drugs, but I still recommend orthobiologics as first-, not last-line, therapies.”

Fortier emphasized the importance of using orthobiologics to treat acute joint injuries involving an abundance of the pro-inflammatory mediator interleukin (IL)-1 . For example, Fortier recommended administering ACS at the time of injury, then following up with either additional ACS treatments or a 2.5% polyacrylamide hydrogel.

Platelet-Rich Plasma for Soft Tissue Injuries and Equine Joint Health

Veterinarians primarily use PRP in tendon and ligament injuries in horses, although physicians typically use the approach for treating joints in human medicine. “There is no scientific reason for this, it’s just the way it evolved,” Fortier said.

Veterinarians have not developed a true definition for what constitutes PRP, but they typically believe PRP contains five times more platelets than blood. The growth factors contained in those platelets are considered the active ingredient.

One of the key advances in PRP was discovering the need for leukoreduced PRP. “Leukocytes, also known as white blood cells, and one particular population of leukocytes, called neutrophils, are lightly inflammatory,” said Fortier. “When treating a musculoskeletal injury, we don’t need further inflammation, so using a leukoreduced PRP is advisable.”

When using PRP in practice, Fortier said she delivers it using ultrasound guidance, being careful not to overfill the lesion. She collects bone marrow during the same visit in case she wants to use stem cells moving forward because the stem cell culture process takes about eight weeks to complete.

Fortier also recommends using shock wave or pulsed electromagnetic field (PEMF) therapy for soft-tissue injuries. If she sees no response (i.e., 50% improvement in lameness), she reevaluates her diagnosis rather than simply repeating the PRP injection. If she does note a response, she’ll repeat the PRP injection in two weeks. A third injection is rarely in her repertoire. Instead, she’ll use the cultured stem cells or a 2.5% polyacrylamide hydrogel.

Autologous protein solution (APS) is an alternative to ACS (IRAP) and PRP, providing a patient-side means of delivering IL-1Ra and growth factors. This orthobiologic is produced from a patient’s blood sample incubated with special beads that stimulate cytokines and chemokines in 20 minutes (rather than overnight). APS has a much lower concentration of IL-1Ra than ACS (and both have more IL-1Ra than PRP) and yields a smaller volume. 

Bone Marrow and MSCs for Equine Injury and Joint Health

Fortier said bone marrow concentrate products fulfill the requisite trilogy for tissue repair: stem cells, cytokines (proteins that help regulate inflammation), and a scaffold that provides structural support for tissue development.

One of the key messages Fortier shared was the importance of using autologous products—biologics collected from the patients themselves. “Allogeneic cells, from another horse, induce an immune response, and that response can be massive following a second injection, possibly resulting in the loss of the horse,” said Fortier.

What Horses are Good Candidates for Biologics Treatment?

Regardless of which orthobiologics a veterinarian chooses, Fortier stressed the importance of starting with a systemically healthy horse.

“Nothing is going to heal if you have bad biology,” she said. “We’re becoming much more aware of subtle endocrine abnormalities, and these horses, who have a higher risk of tendon injury, will not heal as you might expect.” For this reason, Fortier recommends routine endocrine testing of all horses as part of their wellness program.

Take-Home Message

Veterinarians should examine horses’ overall health before considering them as candidates for orthobiologic treatment. The approaches veterinarians choose vary depending on each patient’s injury, disease, and health status, but they should treat a horse in the acute injury phase to increase the likelihood of success.