Lameness improvement in horses with distal tarsal pain after intra-articular injection of botulinum neurotoxin type A.

Objective: To evaluate the effect of IA injections of botulinum toxin type A (BoNT-A) in horses with chronic, naturally occurring distal tarsal osteoarthritis.

Methods: 9 horses were selected after physical and radiographic assessments. Horses also underwent an objective lameness examination and were included if they had a hindlimb impact lameness (Pmin ≥ 3 mm), which positively responded (≥ 50%) to the tarsometatarsal and centrodistal joints' anesthetic block. Horses randomly received an intra-articular injection of BoNT-A or an equivalent volume of saline solution. Horses were reevaluated at postinjection days (PIDs) 1, 7, 15, 30, 60, 90, 120, 150, and 180. Success criteria included a decrease in Pmin (≤ 3 mm) or an abolishment of lameness on the baseline lame limb with lameness shifting to the contralateral limb. A percentage of lameness improvement was calculated for all horses at all timepoints.

Results: 5 horses were included in the BoNT-A group, whereas 4 individuals were allocated in the placebo group. A significant improvement (P < .05) was observed in horses from the BoNT-A group when compared to placebo at PIDs 90, 120, 150, and 180. Two of 5 horses (40%) from the BoNT-A group had an absolute improvement (100%) in lameness at all the timepoints. Higher percentages of lameness improvement were observed at PID 60.

Conclusions: The results of this study suggest that the intra-articular injection with 50 U of BoNT-A was effective in reducing lameness in horses with distal tarsal osteoarthritis, mainly 90 days after injection.

Clinical relevance: Botulinum toxin type A can be considered as an option for managing horses with chronic osteoarthritis.