The synovial response to exogenous phospholipid (synovial surfactant) injected into the equine radiocarpal joint compared with that to prilocaine, hyaluronan and propylene glycol.

The study investigates the effects of injecting surface-active phospholipid in a propylene glycol carrier into the joints of horses, on the joint’s function and fluid composition. The effects were compared against injections of prilocaine, propylene glycol and hyaluronan.

Methodology

• Twenty-four horses were randomly assigned to four treatment groups, each receiving different solutions injected into their left radiocarpal joints: surface-active phospholipid in propylene glycol, propylene glycol solely, prilocaine, and hyaluronan.
• The right radiocarpal joints of the same horses were used as controls and received a saline injection equivalent in volume to the treatment on the left joints.
• Lameness examinations, arthrocenteses (joint fluid extraction for analysis), and synovial fluid analyses were conducted before the experiment, and at intervals of 1, 3, and 7 days following treatment.

Results

• None of the horses showed signs of lameness after treatment, though there was a temporary mild to moderate development of effusions (swelling due to fluid accumulation) in the treated joints.
• Analysis of the synovial fluid showed significantly higher inflammation in treated joints than in control joints, with the difference being greatest around 24 hours post-injection.
• There were no notable differences between the effects of the four different treatments, with the exception of neutrophil counts and alkaline phosphatase activities, which were significantly elevated in joints treated with prilocaine.

Conclusions

• The intra-articular injection of surface-active phospholipid in a propylene glycol carrier caused temporary, clinically insignificant abnormalities in synovial fluid.
• The phospholipid was found to be no more harmful to synovium (joint lining) than prilocaine or hyaluronan.
• None of the administered treatments induced lameness in horses.
• The used dosage and formulation might be suitable for future research into the use of surface-active phospholipid for treating or preventing osteoarthritis in horses.