Biomechanical effect of distal locking in simple two-part AO/OTA 31A1.2 pertrochanteric fractures treated with a short cephalomedullary nail: a finite element analysis

The use of distal locking screws in simple pertrochanteric fractures treated with short cephalomedullary nails is still debated. The present study aims to assess the biomechanical effect of distal locking in standardized simple two-part AO/OTA 31A1.2 pertrochanteric fracture model, focusing on construct stability and load transfer. A three-dimensional finite element model was created based on computed tomography of a fourth-generation composite femur. Five different configurations were considered: intact bone, immediate postoperative locked and unlocked constructs, and healed locked and unlocked models. The 2400-N axial force was applied to the femoral head to replicate maximum loads occurring in the single-leg stance phase. Interfragmentary angular displacement, implant micromotion, and mean and maximum non Mises stresses were measured in the fracture area, proximal metaphysis, and distal cortical region. Comparative analysis without inferential statistics was performed. Both the locked and unlocked configurations provided mechanical stability with minimal implant micromotion. In the immediate postoperative models, interfragmentary angular displacement was similar to the locked and unlocked configurations. Stress distribution in the fracture and proximal metaphyseal regions was similar for both fixation techniques. The major difference was noted in the distal diaphysis, where distal locking caused higher stress concentration at the entry and exit sites of the locking screw. In contrast, the unlocked arrangement had a more uniform load-transfer profile, similar to that of the intact femur. After fracture-healing simulation, differences between the two models attenuated, with the stress distribution gradually converging to that of the intact femur. According to a finite element analysis of a simple two-part AO/OTA 31A1.2 pertrochanteric fracture model, distal locking did not confer a significant biomechanical benefit to the stability of the construct under the applied load. However, distal locking affected the load transfer process by producing higher local stress concentrations in the distal femoral cortex. Further clinical research is needed to assess whether these biomechanical differences have clinical significance. Level V, mechanism-based reasoning (Oxford Centre for Evidence-Based Medicine 2011 Levels of Evidence).