A biomechanical analysis of cannulated screws fixation in a configuration of "axial compression and lateral buttress" in treatment of Pauwels type Ⅱ femoral neck fractures / 中华创伤骨科杂志

ABSTRACT

Objective:To investigate the biomechanical properties of cannulated screws fixation in a configuration of "axial compression and lateral buttress" in the treatment of Pauwels type Ⅱ femoral neck fractures.Methods:Ten specimens of Sawbones artificial femur were first made into models of type Ⅱ femoral neck fracture with a Pauwells angle of 50° and then randomized into 2 equal groups ( n=5). The specimens in the experimental group were subjected to fixation with cannulated screws in a configuration of "axial compression and lateral buttress" in which the axial screw was 8.5 mm in diameter and the lateral screw 6.5 mm in diameter. The specimens in the control group were subjected to conventional fixation with cannulated screws in a configuration of "inverted triangle and parallel compression" in which the 3 screws was 7.3 mm in diameter. Finally, the specimens were placed onto a biomechanical testing machine to determine the parameters of static axial stiffness, displacement under 60 to 600 N load for 5,000 cycles, ultimate load and ultimate stiffness in turn. The 2 groups were compared to find out their differences. Results:The static axial stiffness was (1,492.00 ± 87.86) N/mm, significantly higher than that in the control group [(1,200.22 ± 228.06) N/mm] ( P<0.05). There was no significant difference between the 2 groups in the cyclic load displacement [(0.44 ± 0.01) mm versus (0.57 ± 0.17) mm] ( P>0.05), but the experimental group showed a lower trend. The ultimate load and ultimate stiffness were (4,292.61 ± 804.29) N and (1,623.55 ± 180.94) N/mm in the experimental group and (4,383.64 ± 1,423.24) N and (1,433.77 ± 289.93) N/mm in the control group, showing no significant difference between the 2 groups ( P>0.05). Conclusion:In the treatment of Pauwels type Ⅱ femoral neck fractures, fixation with cannulated screws in a configuration of "axial compression and lateral buttress" may exhibit better biomechanical properties than that in a conventional configuration of "inverted triangle" .