Evaluation of locking compression plate fixation of the distal phalanx to the hoof wall as a potential therapy for laminitis.

Abstract

Surgical stabilisation of the distal phalanx (DP) is a potential therapeutic strategy for severe acute laminitis. To evaluate the effects of locking compression plate (LCP) fixation of the DP to the dorsal hoof wall. Ex vivo and in vivo experiments. A T-shaped LCP was applied to one limb per pair in six pairs of cadaver forelimbs subjected to a combination of thermally induced lamellar failure and vertical load to simulate severe acute laminitis. Standard radiographic measurements were used to compare DP displacement. The LCP was then applied to one forefoot in 12 healthy Standardbred horses either standing (n=6) or under general anaesthesia (n=6). Lameness was evaluated daily, then horses were euthanised (day 8) and lamellar tissue analysed using light microscopy, histomorphometery and molecular markers of apoptosis. In the cadaver limb model, LCP fixation prevented the significant changes in hoof-distal phalanx distance, coronary extensor process distance and sole depth that characterised DP displacement in untreated limbs (p < 0.05). Application of the construct in vivo was well tolerated with minimal lameness (10/12 horses were sound at the trot on day 8); however, histology revealed dorsal lamellar pathology consistent with laminitis, but with extensive keratinocyte apoptosis. Adjacent to the LCP, caspase-3 positive cell counts were approximately 20-fold higher than control (p < 0.001). Pathology was evaluated at a single time point. Microvascular perfusion was not evaluated. Rigid fixation of the DP to the hoof capsule was achieved with the LCP construct in a cadaver limb laminitis model. In live horses, LCP fixation caused regional lamellar pathology with extensive apoptosis, likely due to disturbed lamellar microvascular perfusion and/or mechanostasis. Understanding these mechanisms is critical for refinement of the technique in order to avoid iatrogenic lamellar damage.