34th Annual Scientific Meeting proceedings

Objectives:

To evaluate the biomechanical competence of equine comminuted proximal phalanx fracture fixation using the LCP distal femoral plate (DFP) applied without a cast, and to compare it with transfixation pin cast (TFPC) or standard cast (SC).

Methods:

Comminuted proximal phalanx fractures were simulated in nine paired equine lower forelimbs by means of four osteotomies and central fragments removal. Specimens were pairwise assigned for treatment with either an LCP-DFP or TFPC. Biomechanical testing was performed with the cannon bone aligned vertically, and included initial non-destructive quasi-static loading in axial compression to 1000N, as well as internal and external torsion to 20Nm, followed by cyclic loading to failure. Interfragmentary movements and onset of implant failure were monitored by means of triggered and calibrated x-rays.

Results:

TFPC was associated with significantly higher initial axial and torsional construct stiffness versus plating (P≤0.020). However, fracture gap displacement remained without significant differences between TFPC and LCP DFP over the course of the first 10,000 cycles (P=0.684). Similarly, cycles and corresponding load to failure were insignificantly different between TFPC (14458 ±1435/8229 ± 718N) and plating (12,500 ± 2920/7250 ± 1460N; P=0.212). Plate failure appeared by bending, TFPC failure consisted of pin breakage and SC was not stable and failed at lower load.

Conclusions:

DFP construct without a cast may be recommended as a bridging plate for biological fracture fixation of highly comminuted proximal phalanx fracture. Reduced stiffness at initial load is a significant potential advantage as it may stimulate secondary bone callus via micromotion at the comminuted part of the fracture.