During the Kester News Hour at the 2024 American Association of Equine Practitioners Convention, held in December in Orlando, Florida, a series of experts presented current papers relevant to clinical equine medicine and surgery. Some of the material related to joint disease and therapy, which we’ve summarized here.
PAAG 2.5%
Kyla Ortved, BSc, DVM, PhD, DACVS, of the University of Pennsylvania, discussed the clinical and histologic effects of two different doses of polyacrylamide hydrogel (PAAG) injected into the fetlock and/or middle carpal joint.
Ten healthy young horses without osteoarthritis received 2.5% PAAG at either 50 or 100 miligrams into a total of 13 joints. Then, the researchers assessed the joints at Days 0, 14, 42 and 90 days following injection. Evaluation included a clinical exam, synoviocentesis, gross pathology, synovial histology, and scanning electron microscopy. A gross exam was performed on Day 240.
Neither dose produced any adverse effects. Cellular counts and total protein were within normal limits at all time points. Gross pathology appeared normal, but synovial histology showed integration of PAAG into the synovial membrane, macrophage infiltration, villus hyperplasia, and increased vascularity as early as 14 days, which progressed up to 42 days.
In another PAAG study, McClure et al. performed serial injections using 4% PAAG into normal fetlock joints of eight healthy horses aged 5-10 years. Injections were performed on Days 0, 45, 90, and 135 with gross examination of the joints on Day 250.
While the research team reported no differences between the saline-treated controls and PAAG-treated joints, they noted an increase in the percentage of large mononuclear cells in both controls and treated joints at Day 240. Effusion scores and biomarkers of cartilage health and turnover did not differ significantly between controls and treated joints. Histology of the synovial membrane showed a layer of 4% PAAG on the membrane surface with a small amount integrated into the synovial membrane.
Take-Home Message About PAAG Treatment
PAAG does not induce a significant inflammatory response in treated joints. The 2.5% product integrates into the synovium and changes its morphology and potentially improves elasticity and cellular composition with increased macrophages, which might play a role in immunomodulation of the joint. In contrast, 4% PAAG likely works as a viscoelastic supplement that remains mainly in the joint space. It adheres to synovial membrane and cartilage, especially when defects are present. Ortved noted that both studies included only normal joints, and there might be differences in inflamed joints.
Joint Pathology Scores Following APS Injection
A study presented by Katie Seabaugh, DVM, DACVS, DACVSMR, of Colorado State University’s Equine Orthopaedic Research Center, reviewed the effects of a single intra-articular injection of autologous protein solution (APS) following synovitis induction. The researchers wanted to determine whether APS injection resulted in changes in joint swelling and lameness as well as improvements in synovial fluid parameters and joint pathology.
Over 14 days, the study horses had synovitis induced in the tarsocrural joint with interleukin-1-beta. Five horses served as controls, and 12 received APS treatment. The results showed:
- No differences in clinical assessment between groups.
- No differences in serum amyloid A between groups.
- In APS-treated horses, IL-6 and IL-10 remained higher on Day 2, but IL-6 returned to normal by Day 4.
- Control joints had higher levels of hemosiderosis and higher total scores than normal joints as well as higher cellular infiltration and total histopathology scores than the APS-treated joints.
In summary, APS did not decrease lameness or joint circumference, and synovial fluid parameters did not differ between APS and controls. Histopathology scores were higher for control joints than APS-treated joints, suggesting APS has a disease-modifying effect.
References
- Lowe J, Clifford L, Julian A, Koene M. Histologic and cytologic changes in normal equine joints after injection with 2.5% injectable polyacrylamide hydrogel reveal low-level macrophage-driven foreign body response. J Am Vet Med Assoc. 2024 Feb 21;262(5):649-647. doi: 10.2460/javma.23.10.0553. PMID: 38382205
- McClure SR, Peitzmeier MD, Jackman BR, Evans RB, Ziegler CL, Ganta CK. (2024). Serial injections of 4% polyacrylamide hydrogel have no detrimental effects in equine joints following clinical, histologic, and synovial biomarker evaluation. Am J Vet Res, 1-7. https://doi.org/10.2460/ajvr.24.01.0016
- Usimaki A, Ciamillo SA, Barot D, Linardi RL, Engiles JB, Ortved KF. Single injection of intra-articular autologous protein solution in horses with acute interleukin-1B-induced synovitis decreases joint pathology scores. Equine Vet J. 2024 Jul 25. doi: 10.1111/evj.14203
Related Reading
- Systemic and Intra-Articular Therapies for Lame Horses
- Understanding the Biomechanics of the Horse’s Fetlock Joint
- Daily Vet Life: Successful IRAP Outcomes
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