What are the options for intra-articular injections in horses and how do they compare in efficacy?

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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.6 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%).6 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.10 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.7 Corticosteroids carry systemic absorption risks including masking of joint infections and exacerbation of laminitis in susceptible horses.6 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.4 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