Biomechanics of external fixation of distal tibial extra-articular fractures: is spanning the ankle with a foot plate desirable?

Abstract

To compare the mechanical stability of external fixation with and without spanning of the ankle joint with a foot plate in an in vitro model of extra-articular distal tibia fractures. A laboratory investigation was performed to evaluate the mechanical behavior of external fixation of extra-articular distal tibia fractures using a fixator with and without a foot plate. Ten fresh-frozen lower extremities (5 pairs) with a simulated OTA 43-A3.3 fracture were stabilized with an Ilizarov hybrid fixator with and without a foot plate. All mechanical testing was performed with a servohydraulic test frame (MTS Bionix 858, Minneapolis, MN). Deformation characteristics as a function of load were compared for an Ilizarov fixator with and without a foot plate under identical conditions of forefoot loading from 0 to 100 N. Relative interfragmentary motions (vertical and horizontal translations and rotation) were measured. There was significantly more vertical translation (2.57 +/- 0.97 mm vs. -0.83 +/- 0.64 mm) and angular displacement (4.49 +/- 0.45 degrees vs. -1.15 +/- 0.61 degrees ) of the distal fragment in the arrangement without a foot plate compared with the construct with a foot plate. The anterior translation of the distal fragment was similar with (1.12 +/- 0.98 mm) and without a foot plate (1.19 +/- 1.23 mm). This study supports the mechanical importance of spanning of the ankle with a foot plate in most cases of external fixation for unstable extra-articular and periarticular distal tibia fractures. Further studies are needed to validate these results before widespread changes in clinical treatment can be recommended.