BACKGROUND: Femoral neck fracture was mainly fixed by three cannulated screws. Some scholars have proposed that Pauwels III femoral neck fracture should be fixed with three cannulated screws and one antiwhirl screw to enhance the stability of fracture ends. Others suggested that open reduction should be used to treat Pauwels III fracture. Three cannulated screws combined with buttress plate of medial femoral neck is another treatment option. It was believed that open reduction could achieve anatomical reduction of the fracture end, reduce the pressure of the articular capsule, and not increase the destruction of the blood supply of the femoral head. The biomechanical effects of the two internal fixation methods have not been reported.

OBJECTIVE: To compare the biomechanical stability and stress of the four cannulated screws and three cannulated screws combined with buttress plate fixation for the treatment of the Pauwels III femoral neck fractures.

METHODS: The CT imaging results and internal fixation data of a 25-year-old healthy male volunteer were imported into the Mimics software using reverse modeling technique. The participant signed the informed consent. The protocol was approved by the Hospital Ethics Committee. Finally, finite element models of Pauwels III femoral neck fractures fixed with four cannulated screws and three screws cannulated screws combined with buttress plate were established respectively. An axial load of 500 N was applied on the femoral head to simulate one leg standing in Abaqus software. The maximum displacement, maximum Von Mises stress and stress distribution were compared between the two models.

RESULTS AND CONCLUSION: (1) The maximum displacement was 0.71 mm in four screws model, and 0.43 mm in the three screws combined with buttress plate model. (2) Von Mises stress peak was 436.6 MPa and 227.2 MPa in four and three screws combined with buttress plate models respectively. The stress distribution of the three screws combined with the plate group was more uniform, and more in line with the biomechanical characteristics of the normal femur. (3) Both two kinds of internal fixation methods demonstrate good fixation effect. The three cannulated screws combined with buttress plate model provide better stability and uniform stress distribution compared with four cannulated screws. The three cannulated screws combined with buttress plate is a good choice for the treatment of Pauwels III femoral neck fracture.