Mechanical comparison of straight and pre-bent interlocking nails used for the stabilization of a tibial gap fracture model.

Abstract

To compare the mechanical behavior of straight (STRT) and pre-bent (BENT) I-Loc angle-stable interlocking nails (AS-ILN) used for stabilization of canine mid-diaphyseal tibial fractures. In vitro experimental study. Tibial gap fracture models (n = 5/group). Tibial models simulating a comminuted mid-diaphyseal fracture were stabilized with either a STRT or BENT I-Loc AS-ILN. Bent nails were contoured to match the 10° tibial recurvatum of a mid-size dog. Constructs were subjected to cyclic eccentric compressive loads followed by ramp load until failure. Construct compliance, maximum compressive load and resistive torque, yield load and angular deformation at 450 N were statistically compared using t-tests (p < .05). Failure modes were described. Compliance was 45% lower in BENT than STRT groups (p < .0001). Constructs in the BENT group sustained ~20% and 34% greater maximum and yield loads, respectively, than STRT constructs. Maximum resistive torques were similar between groups (p = .16). At 450 N, sagittal plane angular deformation increased from 0° to 4° in procurvatum (STRT group) and decreased from 10° to 8° in recurvatum (BENT group-p < .0001). Construct yield failure occurred at the nail isthmus in both groups. These results demonstrated that, in a tibial gap fracture model, pre-bending I-Loc AS-ILNs provided mechanical advantages by increasing their ability to resist bending resulting from eccentric compressive loads. Pre-bending may reduce the occurrence of tibial nail yield failure. Surgeons should therefore consider pre-bending tibial I-Loc nails to match the bone anatomical recurvatum prior to implantation.