In vitro biomechanical analysis of a locking self-compression screw model applied to Pauwels III and comminuted femoral neck fractures

Abstract

Femoral neck fractures (FNFs) affect the young adult population and are intimately related to high-energy trauma. Despite innovations in osteosynthesis materials, the rate of complications remains at 10%–59% in Pauwels type III (PIII) fractures. The authors thus propose a fixation model with a novel self-compression screw, comparing it to a sliding hip screw plate associated with a derotation screw in the fixation of a PIII fracture with posterior inferior comminution. The finite element method (FEM) was used in this comparison along with a virtual femur model with structural characteristics similar to those of a healthy young human bone. We formed 4 groups: Group 1 (GC), intact bone; Group 2 (SHS+S), sliding hip screw plate with derotation screw; Group 3 (XS), X-pin + SS (self-compression model with superior positioning screw); Group 4 (XI), X-pin + IS (self-compression model with inferior positioning screw). A 700 N monotonic load was applied to the apex of the femur head towards the ground so that stress was mainly focused on the fracture site and osteosynthesis. Analyses included total displacement and maximum principal stress and were performed for all groups. Fracture displacement, rotation, and von Mises were assessed only in groups that underwent osteosynthesis. Total displacement values in groups with self-compression screws (XS and XI) were closer to those for healthy femurs, with a 38.5% reduction when comparing the XS group with the SHS+S group. Fracture displacement and rotation values presented reductions of over 60% when comparing the XS and XI groups with the SHS+S group. Equivalent Von Mises stress values were similar between XS and XI and presented a reduction of approximately 5.25% when compared with the SHS+S group. Our FEM analyses demonstrated that the self-compression screw model has potential biomechanical advantages over the SHS+S model.