Deep digital flexor tendon force and digital mechanics in normal ponies and ponies with rotation of the distal phalanx as a sequel to laminitis.
Authors: McGuigan, Walsh, Pardoe, Day, Wilson
Journal: Equine veterinary journal
Summary
# Editorial Summary McGuigan and colleagues used inverse dynamics analysis to compare deep digital flexor tendon (DDFT) force patterns between normal ponies and sound ponies displaying 6–13 degrees of distal phalanx rotation secondary to laminitis, addressing a paradox in the literature: whilst DDFT tension is implicated in causing rotational damage during acute laminitis, the shortened lever arm that follows rotation should theoretically reduce DDFT loading. Six ponies in each group were assessed at trot using forceplate and motion capture to calculate DDFT force based on the moments acting around the distal interphalangeal joint during stance. The rotated group demonstrated a striking mechanical difference—the zero moment point lay palmar to the DIP joint centre for approximately the first 40% of stance, producing zero DDFT force during early weight-bearing, whereas normal ponies generated peak DDFT forces of 1.92 N/kg early in stance. Notably, rotated ponies only approached normal DDFT force values (6.41 N/kg) during late stance, occurring substantially later in the gait cycle than controls (79.2% versus 60.7% of stance). These findings suggest that horses with established rotational damage develop altered biomechanics that naturally unload the compromised dorsal laminae early in stance, shifting demand to late stance—a distinction that may guide farriery interventions focused on modifying breakover mechanics and reducing peak DDFT loading through the vulnerable dorsal hoof capsule during the mid-to-late stance phase.
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Practical Takeaways
- •Farriery interventions should focus on reducing DDFT force through breakover in laminitic horses with DP rotation to protect healing dorsal laminae
- •The shift in peak DDFT force timing (late vs early stance) in rotated cases suggests different loading mechanics that farriery must accommodate
- •Early stance loading patterns differ significantly between normal and rotated cases, indicating need for individualized therapeutic shoeing strategies
Key Findings
- •Normal ponies showed peak DDFT force of 1.92±1.63 N/kg in early stance, while laminitic ponies with DP rotation showed zero DDFT force for the first 40% of stance
- •Peak DDFT force occurred at 60.7% of stance in normal ponies versus 79.2% of stance in laminitic ponies with rotation
- •Laminitic ponies with DP rotation demonstrated markedly reduced DDFT force until late stance phase, when forces approached normal values
- •The point of zero moment was palmar to the DIP joint centre of rotation in rotated cases, explaining the reduced early-stance DDFT tension