Intra-articular therapy in horses spans corticosteroids, hyaluronate sodium, polyacrylamide hydrogel, mesenchymal stem cells, local anesthetics (for diagnosis), and emerging agents including botulinum neurotoxin type A — each with distinct efficacy data and safety profiles.

Corticosteroids are the most established treatment option. Betamethasone sodium phosphate and betamethasone acetate (BME) produced clinical success with improved lameness scores in 75.53% of 119 treated horses at 5 days post-injection, compared to 52.52% of 120 saline-control horses.Journal of the… Adverse effects from the BME field trial included increased joint effusion (15%), increased lameness (6.7%), loose stool (5.9%), agitation/anxiety (4.2%), increased heat in the joint (2.5%), delayed joint swelling (2.5%), inappetence (3.4%), acute non–weight-bearing lameness (0.8%), and laminitis (0.8%).Journal of the… Methylprednisolone acetate (MPA) and triamcinolone acetonide injected into the distal tarsal joints produced improvement for a median of 56 days, with no significant difference in efficacy between the two agents.American Journa… MPA administered intra-articularly at 200 mg total (100 mg per tarsocrural joint) also improves pulmonary function in severely asthmatic horses, though the effect is mild and short-lived.Equine Veterina… Corticosteroids carry systemic absorption risks including masking of joint infections and exacerbation of laminitis in susceptible horses.Journal of the…

Hyaluronate sodium (HA) produces good-to-excellent clinical improvement in the majority of horses with carpal or fetlock lameness. In a controlled field study, overall clinical improvement was rated excellent or good in 96% of intra-articularly treated horses and 90% of intravenously treated horses.FDA DailyMed An… However, a single intra-articular injection of non-animal stabilized hyaluronic acid (NASHA) was not superior to saline for reducing lameness scores in horses with synovitis or mild osteoarthritis of the metacarpophalangeal joint (P = 0.94), though NASHA did produce greater improvement in flexion test scores compared to placebo (P = 0.01).BMC Veterinary… Concerns exist that both low and high molecular weight HA formulations can induce inflammatory responses in healthy equine joints and are often associated with lameness.BMC Veterinary… The half-life of unmodified HA solutions can be less than 1 day, yet pain-relieving effects persist beyond this, suggesting disease-modifying as well as symptom-modifying activity.BMC Veterinary… Hyaluronate sodium is also the most recommended intra-thecal therapy following digital flexor tendon sheath surgery among ACVS and ACVSMR diplomates.Frontiers in Ve…

2.5% injectable polyacrylamide hydrogel (iPAAG) has a favorable safety profile with an estimated adverse event rate of 0.04%. It is commonly used for OA management and is well tolerated when combined concurrently with BME in healthy horses.Journal of the…

Allogeneic neonatal umbilical cord-derived mesenchymal stem cells (MSCs) produce significant clinical improvement in metacarpophalangeal joint OA over 6 months, but a single injection is equivalent to two injections given one month apart — there is no significant difference in total clinical score between single and repeated administration at any time point.PLoS ONE Owner-detected adverse effects occurred in 18% of horses.PLoS ONE Radiographic OA scores did not change significantly from baseline to 6 months in either group.PLoS ONE

Autologous protein solution (APS) is the most commonly recommended intra-articular therapy among ACVS and ACVSMR diplomates for acute synovial joint pathology, consistent with evidence that APS decreases gross and histologic effects of acute inflammation on cartilage and synovial membrane in experimental models.Frontiers in Ve…

Botulinum neurotoxin type A (BoNT-A) is an emerging option for refractory distal tarsal pain, with the majority of treated horses remaining sound at 180 days post-injection — a duration that appears longer-lasting than the approximately 56-day improvement seen with corticosteroids in the same joint.American Journa…

Local anesthetics are used intra-articularly for lameness diagnosis rather than treatment. Both 2% lidocaine and 2% mepivacaine induce synovial fluid changes indicative of inflammation and a catabolic collagen response, with lidocaine producing more pronounced changes than mepivacaine — making mepivacaine the safer choice for intra-articular injection.American Journa… Synovial fluid concentrations of both agents at approximately 7 minutes post-injection (lidocaine mean 11.96 mg/mL, mepivacaine mean 8.18 mg/mL) and at approximately 23 minutes (lidocaine mean 6.31 mg/mL, mepivacaine mean 4.97 mg/mL) exceed concentrations previously associated with cytotoxic effects.Frontiers in Ve… Cytotoxicity may be mitigated by concurrent injection with HA, platelet-rich plasma (PRP), or combinations including nonsteroidal anti-inflammatories and opioids.Equine Veterina… Local anesthetics are rapidly cleared from synovial fluid after injection, often within 30 minutes.Equine Veterina…

Would you like to go deeper on the safety comparison between corticosteroid options — specifically triamcinolone acetonide versus methylprednisolone acetate — for a specific joint?