The Kester News Hour at the annual American Association of Equine Practitioners Convention highlights key advancements in equine research. In 2024’s edition leading veterinarians shared their top picks from recent studies in their area of practice interest. This rapid-fire session offers valuable insights into the latest findings from equine scientists worldwide.
Kyla Ortved, DVM, PhD, Dipl. ACVS, ACVSMR, an associate professor of large animal surgery from the University of Pennsylvania’s New Bolton Center, in Kennett Square was once again invited to present what she considered the most interesting, influential, and clinically relevant studies pertaining to the equine musculoskeletal system.
Study 2.5% and 4% Polyacrylamide Hydrogel (PAAG) in Horses
In the first study she described (Lowe et al., 2024), researchers characterized how a 2.5% synthetic cross-linked injectable polyacrylamide hydrogel (2.5% iPAAG) integrated with synovial (joint) fluid when they injected it into joints. In total the researchers injected 13 fetlock or knee joints with either 2 or 4 milliliters of 2.5% iPAAG, said Ortved.
They performed follow-up examinations on the horses on Days 0, 4, 42, and 90 after injection and found white blood cells in the synovial membrane (the joints’ inner lining) consistent with a reaction to a foreign body. By Day 42 they found the iPAAG completely integrated into the joint’s synovial membrane lining. “No adverse effects at one or two times the recommended dose was appreciated,” she added.
Ortved presented a second study (McClure et al., 2024), in which researchers conducted serial 4% PAAG injections in horses on Days 0, 45, 90, and 135, then evaluated the clinical, microscopic, and synovial fluid biomarkers in those joints. “No significant difference in joint effusion (swelling) or synovial fluid markers were found between the control and PAAG groups,” she said. “Microscopy showed a layer of the PAAG on the surface of the synovial membrane lining the joint; however, a small amount also integrated into the synovial membrane.”
Together, she explained, these studies showed that the hydrogels neither induced significant inflammation in the joint nor resulted in any negative side effects in healthy equine joints. “The 4% product functions as a viscoelastic supplement, remaining mainly in the joint space, whereas the 2.5% gel integrates into the synovial lining,” said Ortved.
Treating Equine Joint Pathologies with APS
Katie Seabaugh, DVM, Dipl. ACVS, ACVSMR, of the Translational Medical Institute at Colorado State University, in Fort Collins, shared findings from a study coauthored by Ortved, in which
researchers investigated the effects of a single intra-articular (IA) injection of autologous protein solution (APS) in horses with synovitis—inflammation of the synovial membrane.
Ortved and her team studied 18 horses; they injected one tarsocrural (the uppermost hock) joint in 12 horses with APS one day after inducing synovitis. They left six horses untreated as controls.
“While APS did not decrease lameness or joint circumference or alter synovial fluid parameters, gross pathology and histopathology scores were lower for APS treated joints compared untreated (control) joints suggesting that APS may have a disease-modifying effect,” said Seabaugh.
Using NSAIDs With Orthobiologic Treatment in Horses
Seabaugh presented a second study co-authored by Ortved in 2024 in which the research team examined if commonly used nonsteroidal anti-inflammatory drugs (NSAIDs)—either a single intravenous (IV) dose or single oral dose—had any effect on growth factor and cytokine (cell-signaling protein) concentrations in APS and platelet-rich plasma (PRP). Clinicians might use NSAIDs in conjunction with the processing of APS and PRP to reduce pain and inflammation in the horse’s body, especially in cases of injury.
“There was no significant difference in cytokines and growth factors, but NSAIDs were found in the final product,” said Seabaugh. “This means we need to use biologic therapies carefully in athletes that will be drug tested.” More research is needed using long-term NSAID treatment.
Treating Synovial Infections in Horses
Ortved described another study in which de Souza et al. (2024) investigated long-term survival of horses after synovial lavage of contaminated and septic synovial structures. They authors included 240 horses presenting with contaminated or infected synovial structures, including fetlocks, digital flexor tendon sheets, and tarsocrural joints.
She said survival rates were excellent following lavage, with 228 of the 240 (95%) surviving to discharge and 89% alive one year later. Variables associated with not surviving included forelimb involvement, heavier body weight, an unknown cause of sepsis, longer surgery times, and tendon sheath or bursa involvement, said Ortved. However, the researchers did not note a correlation between soundness and survival rate.
Using PET in Sport Horses
Finally, Ortved discussed a study in which authors demonstrated PET imaging, commonly used in racehorses to detect early injury was beneficial for sport horses. The researchers imaged 36 fetlocks using positron emission tomography (PET) and computed tomography (CT) and scored the radionuclide—the tracer practitioners inject before capturing a PET scan—uptake blindly. Thirty-two PET scans revealed a single area of increased radionuclide uptake, most often in the subchondral bone, which is beneath the cartilage. The most common sites were the inner part of the long pastern (medial first phalanx) and the upper inside joint surface of the knee or hock (dorsomedial condyle of the third metacarpal/metatarsal bones). These findings correlated with the CT images and the researchers identified an association with increased radionuclide update on PET scans and pain in the horses.
“PET uptake is common in sport horses, but the pattern of uptake is quite different from racehorses, likely due to differences in biomechanical loading in the joint,” said Ortved. “PET may be very useful in the early identification of bone lesions.”
Take-Home Message
Leading veterinarians chose these six studies due to the impact they had on equine musculoskeletal research in 2024. In this rapid-fire session they shared 2.5% iPAAG, 4% PAAG, and APS might be beneficial in treating horses with joint disease, but case selection is crucial. They also shared research proving veterinarians should be cautious when administering NSAIDs while collecting blood for APS and PRP, but single-dose administration is not likely to affect the final biologic product. In 2024, researchers also showed that synovial lavage might be an effective treatment for synovial infections and PET is an effective diagnostic tool for sport horses.
