Abstract: BACKGROUND: Few studies are comparing the biomechanical characteristics of three internal fixation techniques in the treatment of distal tibial fractures.  
OBJECTIVE: To compare the biomechanical properties of distal tibial fractures fixed by medial distal tibial plate, anterior-grade expert tibial nail and retrograde tibial nail.
METHODS: Based on the CT data of a SAWBONES 4th generation artificial composite tibia model, a simulation model of distal tibia fracture (AO/ASIF 43-A3) was constructed by digital 3D reconstruction technology. On this basis, three internal fixation methods including locking plate of the medial tibia, expert grade intramedullary nail and retrograde tibial nail were simulated.  Finite element analysis was carried out for three groups of implanted assembly models under axial compression and axial torsion loading conditions respectively, and the differences in stress distribution, stress peak value and fracture space displacement were compared among the three groups.  
RESULTS AND CONCLUSION: (1) When the three groups of internal fixators were loaded under two load conditions, the peak stress of the expert tibial nail group was 283.53 MPa at the unlocked main nail hole under the torsion condition. In the medial distal tibial plate group, the stress peak was located on the third screw, which was 913.07 MPa under the torsional condition. In the retrograde tibial nail group, the stress peak was at the second main nail hole under the torsion condition, which was 435.42 MPa. In the retrograde tibial nail group, the stress peak of the cortical bone around the main nail hole at the medial malleolus appeared under high axial compression condition, which was 55.34 MPa. (2) In terms of fracture gap micromovement, the expert tibial nail group had the highest tangential displacement in the four regions under axial compression load. The axial displacement of the four regions in the medial distal tibial plate group was the highest, and the maximum value was in the lateral region. The peak axial displacement of the expert tibial nail group and retrograde tibial nail group was located in the posterior region. (3) When the axial torsional load was loaded, the peak axial displacement of the medial distal tibial plate group and retrograde tibial nail group was in the lateral region, and the tangential displacement of the four regions in the retrograde tibial nail group was smaller than that in the medial distal tibial plate group and expert tibial nail group. (4) It is indicated that retrograde tibial nail has a biomechanical advantage over the medial distal tibial plate and expert tibial nail in distal tibial fractures in terms of fracture end fretting and internal fixation stress.

Key words: internal fixation, distal tibial fracture, finite element, biomechanics, fracture space micromovement, stress distribution