Abstract: BACKGROUND: Plate fixation is the mainstream method for the surgical treatment of distal femoral fractures. The intramedullary nailing has the advantages of minimally invasive, such as less soft tissue injury and bone blood supply destruction. At the same time, it is a central fixation and has better biomechanical effect. Therefore, retrograde intramedullary nailing has become another option for the internal fixation of distal femoral fractures.
OBJECTIVE: The biomechanical characteristics of new retrograde intramedullary nail on lateral femur condyle, common femoral retrograde intramedullary nail, and lateral femur condyle anatomical locking plate for the treatment of A2-type distal femoral fractures were compared using finite element analysis, and the advantages of new retrograde intramedullary nail on lateral femur condyle was studied.
METHODS: A new retrograde intramedullary nail on lateral femur condyle was designed, which was inserted into the bone cortex in front of the insertion point of the lateral collateral ligament of the lateral femoral condyle. A CT scan was performed on the lower limb bone of a male volunteer, and a three-dimensional model of the femur was established. The model was then segmented to create a three-dimensional model of a femoral distal A2-type fracture, The three-dimensional models of small (small group), standard type retrograde intramedullary nail on the lateral femoral condyle (standard group), common retrograde intramedullary needle (common group), and lateral femur condyle anatomical locking plate (plate group) were established respectively. The axial stresses of 600, 1 800 N and the torsional load of 4 000, 8 000 N·mm were applied to the models, and the displacement and stress of femur and the displacement, stress and shear force of internal fixators were observed in each group.
RESULTS AND CONCLUSION: (1) When subjected to axial load of 600 and 1 800 N, the femoral peak displacement, the femoral peak stress, and the peak stress of interal fixation in the standard group were the lowest among the four groups. (2) When subjected to torsional load of 4 000 and 8 000 N·mm, the femoral peak displacement and peak displacement of the internal fixation in the standard group were the lowest among the four groups. (3) Compared with femoral lateral condylar locking plate and common retrograde intramedullary needle, the new retrograde intramedullary needle on lateral femur condyle has mechanical advantages of reducing stress concentration and decreasing the risk of internal fixation failure.

Key words: distal femoral fracture, lateral femoral condyle, retrograde intramedullary nail, locking plate, internal fixation, finite element analysis, biomechanics