Finite element analysis of 3 internal fixations for distal type C3 femur fractures with medial wall bone defects

Managing 33-C3 femur fractures with medial wall bone defects poses a significant challenge for orthopedic surgeons. The gold standard treatment for arbeitsgemeinschaftfür osteosynthesefragen (AO)/orthopedic trauma association (OTA) 33-C3 distal femur fractures with medial wall bone defects remains elusive. This study employs finite element analysis to compare the stability and mechanical behavior of 3 internal fixation patterns (single lateral distal locking plate, retrograde intramedullary nail, and dual plates) for 33-C3 femur fractures with medial wall bone defects. The aim is to provide a theoretical basis for the selection of internal fixation modalities in clinical practice.

Enrollment included a 43-year-old male volunteer weighing 60 kg, without a history of femur fracture. Bilateral femur normality was verified through X-ray and CT scan assessments. A finite element simulation model of AO/OTA 33-C3 distal femur fracture with medial wall bone defect was established. Three fixation methods, named single lateral locking plate (single-plate group), retrograde intramedullary nail (retrograde intramedullary nail group), and dual plates (dual-plate group), were evaluated using finite element analysis under an axial load of 300 N. The assessment included an examination of von Mises stress distribution, shear stress, and displacement patterns at the internal fixation and femur fracture sites.

The finite element analysis revealed that dual-plate fixation effectively reduced the concentration of von Mises stress at the plate on the fracture site. Under full weight-bearing conditions, the maximum von Mises stress in the implants occurred at the distal femur defect level, with values of 149.30, 59.281, and 58.03 MPa for single-plate fixation, retrograde intramedullary nail, and dual-plate fixation methods, respectively. Similarly, the maximum shear stress in the implants was 77.867, 30.136, and 33.505 MPa for single-plate fixation, retrograde intramedullary nail, and dual-plate fixation methods, respectively, all presenting at the distal femur defect level. The maximum relative displacements of implants during compressive loading were 1.34, 1.25, and 0.83 mm for the single-plate , retrograde intramedullary nail, and dual-plate groups, respectively. Consistently, the maximum loading-point displacements of fracture sites were 1.529, 1.264, and 0.880 mm for the single-plate fixation group, retrograde intramedullary nail group, and dual-plate fixation group, respectively. Furthermore, at the distal femur defect level, the maximum von Mises stress was 72.682, 112.430, and 40.716 MPa for the single-plate, retrograde intramedullary nail, and dual-plate fixation groups, respectively.

Dual-plate fixation demonstrates superior biomechanical outcomes and exhibites the lowest maximum von Mises stress and shear stress, along with minimal relative movements between fracture fragments. This configuration offers optimal mechanical stability for managing AO/OTA 33-C3 distal femur fractures with medial wall bone defects. Consequently, dual-plate fixation emerges as a better treatment strategy for patients presenting with comminuted intra-articular distal femur fractures accompanied by medial wall bone defects.