The effect of botulinum toxin injection into the deep digital flexor muscle on foot biomechanics in healthy horses.

Botulinum toxin injection into the DDF muscle transiently reduces dorsal hoof loading, potentially mitigating distal phalangeal rotation in acute laminitis.

This prospective experimental study investigated the biomechanical effects of botulinum toxin (Botox) injection into the deep digital flexor (DDF) muscle in six healthy horses, with the goal of evaluating its potential as a therapeutic intervention for acute laminitis. One forelimb per horse received ultrasound-guided botulinum toxin injection, while the contralateral limb served as an untreated control. Ground reaction forces (GRF) and center of pressure (COP) were measured at baseline and at 3, 7, 14, 28, and 42 days post-injection using pressure sensors. At day 7, a significant median reduction of 122 N in peak GRF at the toe was observed, alongside a palmar shift in COP of 10 mm during static standing and 6 mm during ambulation. These changes were transient, with no statistically significant differences from control values by day 14, indicating a therapeutic window of approximately one to two weeks. No significant biomechanical changes were detected in untreated limbs. The palmar shift in COP and reduced dorsal loading are biomechanically consistent with decreased tension in the DDF tendon, which in turn would reduce mechanical stress on the dorsal lamellae — a key pathomechanical factor in distal phalangeal rotation during laminitis. The authors propose that DDF botulinum toxin injection may serve as a reversible, minimally invasive adjunct therapy in the acute phase of laminitis. Limitations include the small sample size, use of healthy rather than laminitic horses, and the short duration of effect.

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