Abstract:

BACKGROUND: There are two kinds of cannulated screws (single- and double-headed) in clinic. Common single-headed cannulated compression screw is easy to cause shortened femoral neck, and screw dropping occurs usually when osteoporosis; thereafter, choosing single- or two-headed cannulated compression screw in the treatment of femoral neck fracture remains controversial.

OBJECTIVE: To investigate the biomechanical effects of two double-headed and ordinary (single-headed) cannulated compression screws and different spatial configurations in the treatment of femoral neck fractures by finite element analysis.  

METHODS: The original DICOM data were obtained by collecting a thin layer CT scan of the proximal femur of a healthy adult volunteer (male, 30 years old). The proximal femoral model was established in MIMICS10.01 software. The model was imported into the UG 8.0 software to establish the femur neck fracture model (Pauwels angle 60°). A three-dimensional model of double-headed and ordinary cannulated compression screw was obtained by three-dimensional scanning modeling. In the UG 8.0 software, the femoral neck fracture assembly modeling was performed according to the horizontal and vertical distribution of two screws. The established model was introduced into the ANSYS 14.5 software to calculate the opening angle of the femoral neck fracture, the relative displacement of the fracture end and the stress distribution. 

RESULTS AND CONCLUSION: (1) In terms of biomechanical stability: the opening angle and displacement of the fracture end in the two screws in the horizontal position group were smaller than those in the vertical position group. The opening angle and displacement of the double-headed cannulated compression screw group were smaller than those in the ordinary cannulated compression screw. (2) Stress distribution: the stress distribution of the two screws was different. The stress distribution on the screw in the double-headed group was more dispersed than that in the ordinary group, and some stress was transmitted to the tail of the screw. In the ordinary group, the stress on the screw was mainly concentrated on the fracture end. There was also a difference in the stress distribution between horizontal and vertical position groups. When the two screws were horizontally fixed, the stress distribution on the front screw was more concentrated, while the vertical position was mainly concentrated on the upper one. (3) These results imply that the double-headed cannulated compression screw is more stable and reliable than the ordinary cannulated compression screw in the treatment of femoral neck fracture. The horizontal fixation of the two screws has better biomechanical stability than the vertical fixation. Therefore, the clinical application of double-head compression screws can be used to treat femoral neck fractures. When two screws are selected, horizontal fixation should be used.

Key words: femoral neck fracture, internal fixation, hollow compression screw, double-head compression screw, horizontal fixation, vertical fixation, biomechanics