Ankle joint biomechanics following transepiphyseal screw fixation of the distal tibia

Transepiphyseal screws have traditionally been removed after fixation of pediatric ankle fractures due to concerns about increased forces and contact pressures within the tibiotalar joint secondary to the implant. No study has assessed pressure across the ankle joint after such fixation. Seven adult and two pediatric cadaveric ankles underwent axial loading in a uniaxial material test machine. Each was tested before fixation (control), after fixation (screw in place), and after removal (after screw removal). Three sequential test runs at three loading conditions (approximate body weight, twice body weight, and five times body weight) were performed to simulate forces of standing and ambulation. Total force, peak contact pressure, and contact area were measured with an intra-articular sensor. After screw placement, all loads caused a significant increase in total force versus control. Peak contact pressures after placement also increased significantly. Screw removal subsequently led to a net decrease in force and peak pressure values. Total contact area was unchanged. Concerns regarding subchondral screws in the distal tibia appear warranted. Findings in this study support implant removal following union of such fractures.