Innovative approach in the treatment of comminuted proximal phalanx fractures in horses based on biomechanical modelling.

Proximal phalanx (P1) fractures in horses are relatively common, and present significant treatment challenges, especially when the fractures are comminuted or infected. An innovative treatment approach includes attaching an external fixator to the third metacarpal bone (MC III), the healthy bone above fracture, to offload the injured P1 and protect it from load-bearing forces, particularly during post-surgical standing up. This study aims to develop the favourable mathematical and numerical models for screws configuration in this external fixator. Nine configurations (I-IX), varying in screw alignment and number, were investigated based on the experimental data from computed tomography and simulations of compression tests. Cortical and trabecular tissues were modelled as a nonlinear viscoelastic continuum, with material constants identified through uniaxial compression and stress relaxation tests. The best attachment of the external fixator was analysed in terms of stresses and strains in both trabecular and cortical bone, as well as stresses in screws. Configuration II (1 diaphysis screw, 4 distal metaphysis screws at 7°) and III (1 diaphysis screw, 4 distal metaphysis screws at 14°) were identified as mostly biomechanically favourable. This external stabilization approach could potentially reduce the rate of post-surgical failure often leading to horse euthanasia.