MSC therapy shows reduced joint effusion in horses with OA, study finds

Equine osteoarthritis trials evaluating activated umbilical cord blood-derived mesenchymal stromal cells, both alone and combined with hyaluronic acid, show reductions in joint effusion after six weeks, according to a prospective, randomized study published in Frontiers on September 19, 2026.

Key Clinical Takeaways:
• Thirty client-owned horses with naturally occurring fetlock or carpal osteoarthritis completed the randomized clinical evaluation.
• Joint effusion scores decreased within both mesenchymal stromal cell treatment groups by week six, while the hyaluronic acid group showed no significant change.
• One horse was withdrawn from the study after contracting septic synovitis, which researchers attributed to contamination within a specific cell batch.

Evaluation of Mesenchymal Stromal Cells in Equine Osteoarthritis

Osteoarthritis remains a frequent cause of lameness and loss of athletic function in horses. While mesenchymal stromal cell therapy shows broad promise for joint disease, the clinical benefit of combining equine umbilical cord blood-derived mesenchymal stromal cells with hyaluronic acid had remained unknown prior to this trial.

Led by researchers including Judith B. Koenig, the study assessed client-owned horses diagnosed with naturally occurring fetlock or carpal osteoarthritis through intra-articular analgesia. Animals were evaluated at baseline and at three and six weeks following treatment.

Treatment Protocols and Trial Methodology

The prospective, randomized, owner-blinded study divided participating animals to receive one of three intra-articular treatments: 51 milligrams of hyaluronic acid in a 3-milliliter volume, 10 million activated equine umbilical cord blood-derived mesenchymal stromal cells alone, or 10 million activated cells combined with hyaluronic acid. Outcome measures tracked joint effusion scores, subjective and objective lameness, and owner-reported return to work.

Horses Experience Mild Reactions After Cell Injections

Thirty horses successfully completed the study protocol. One additional animal was withdrawn after developing septic synovitis, an adverse event that investigators traced directly to contamination of the administered cell batch.

Apart from that instance of septic synovitis, mild post-injection reactions occurred infrequently and at similar rates across all treatment arms. Specifically, reactions were recorded in one out of ten horses in the hyaluronic acid group, two out of ten in the cell-only group, and one out of ten in the combined therapy group.

Lameness Assessments and Return-to-Work Outcomes

Lameness assessments did not differ significantly between the treatment groups across the evaluation period. However, measurable differences emerged in secondary outcomes.

Joint effusion decreased within both cell-treated cohorts by week six, dropping by 0.75 grades in the mesenchymal stromal cell group and 0.50 grades in the combined group, compared to no significant change in horses receiving hyaluronic acid alone. Owners reported a return to work in eight out of ten horses treated with cells alone, six out of ten in the combined group, and five out of ten in the hyaluronic acid group. These figures yielded higher odds of return to work for cell-treated horses compared to hyaluronic acid controls, though the confidence interval spanned from 0.40 to 53.8 and did not reach statistical significance.

Small Sample Size Limits Clinical Trial Findings

Study authors noted that the primary limitation of the investigation was its small sample size. Intra-articular administration of activated equine umbilical cord blood-derived mesenchymal stromal cells appeared clinically feasible in horses with naturally occurring osteoarthritis, with no serious adverse events attributable to the cells identified outside of the single contaminated batch.

While the trial detected no significant between-group differences in lameness scores, the within-group reduction in joint effusion and the higher return-to-work rates observed in the cell-treated cohorts support further evaluation through larger, adequately powered clinical trials.

Disclaimer: The information provided in this article is for educational and scientific communication purposes only and does not constitute medical advice. Always consult with a qualified healthcare provider regarding any medical condition, diagnosis, or treatment plan.