PURPOSE: To analyze the biomechanical effects of different frame configurations of the hybrid external fixators for distal tibial fractures on the frame stiffness and stress distribution with a finite element method (FEM). MATERIALS AND METHODS: Five configurations were simulated: Group I: two wires with convergence angle of 60degrees, Group II: 3rd wire on a bisector axis of the group I. Group III: two wires with 30degrees. Group IV: 3rd wire on a bisector axis. Group V: two wires with 30degree and a half pin on the distal articular fragment. Each group was simulated under compression, torsion, anterior-posterior and lateral-medial bending load. Stiffness, stress and deformation values were calculated. RESULTS: The overall stiffness was increased by 15~30% with the addition of a third wire, and by 150~400% with a anteromedial half pin on the articular fragment. The half pin decreased the stress level of the frame by about 43% and the deformation of the 5/8 ring by about 30%. CONCLUSION: The addition of a half pin on the articular fragment is not only a method of increasing the stiffness but also a way of decreasing the stress concentration and the deformation of the frame.
Axis, Cervical Vertebra ; External Fixators ; Tibial Fractures*