Stress Distribution in Interlocking and Blocking Screw Fixation for Distal Tibial Intramedullary Nailing: A Finite Element Analysis

Abstract

Background/Objectives: This study evaluates the structural strength of various fixation models for distal tibial fractures using finite element analysis, comparing the biomechanical performance of different interlocking and blocking screw configurations in intramedullary nail fixation. Methods: Finite element models were developed for three different screw configurations: two interlocking screws (T2S), three interlocking screws (T3S), and two interlocking screws combined with two blocking screws (T2SBS2). Material properties were assigned using SAWBONES (R) models, reflecting established biomechanical characteristics. The models were subjected to static axial loading (800 Nm), internal rotation (3500 Nm), and external rotation stresses. The stress distribution and structural integrity of each fixation model were analyzed. Results: The T3S model demonstrated the lowest maximum von Mises stress values across all loading conditions. Under axial loading, the maximum VMS at the medial first screw contact was the lowest in the T3S model (65.96 MPa) compared to T2S (135.68 MPa) and T2SBS2 (150.30 MPa). Similarly, internal rotation loading resulted in the lowest stress at the medial first screw site in T3S (64.86 MPa), compared to significantly higher stresses in T2S (136.29 MPa) and T2SBS2 (158.11 MPa). The T2SBS2 configuration showed effective stress reduction at the distal interlocking screws, highlighting its potential for improved load sharing. Conclusions: The findings underscore the importance of the secure fixation of the initial interlocking screw in distal tibial fractures. The fixation model utilizing three interlocking screws provided the most favorable overall stress distribution, whereas the inclusion of blocking screws effectively reduced stress concentrations at distal screw sites.