Biomechanical study on femoral neck fracture fixation based on cortical screw support theory

Abstract

Objective To evaluate the biomechanical effect of cortical screw support technique in fixation of the femoral neck fractures. Methods The models of subcapital femoral neck fracture were made in eight matched pairs of embamled cadaver femurs and decided into experiment group and control group (four pairs per group). The side of experiment group was fixed using three cannulated compression screws with cortical screw support and that of control group with conventional screw placement. The speci-mens in two groups were tested in aspects of torsion and axial loading. Results In axial load test at load of 600 N and 800 N, the displacements in cortical screw support group were (0.677±0.135) mm and (0.907±0.132) mm respectively, while those of femoral head in conventional screw placement group were (0.899±0.160) mm and (1.202±0.152) nun respectively (P <0.05). There was signifi-cant difference between the two groups (P < 0.05). The maximal vertical loading for failure of the fixa-tion was (2 782±228) N in cortical screw support group and (1 950±281) N in conventional screw placement group (P < 0.01). In torsibility test at 4° and 6° torsibility, the torque-moments of cortical screw support group were (10.406±1.515) Nm and (15.328 ±1.471) Nm respectively and those of conventional screw placement group (6.628±1.163) Nm and (9.072±1.570) Nm respectively, with statistical difference between two groups (P <0.01). The maximal torque-moment for failure of the fixa-tion was (25.437±5.213) Nm in cortical screw support group and (13.235±3.012) Nm in conven-tional screw placement group (P < 0.01). Conclusion Fixation of femoral neck fractures by using cortical screw support can significantly enhance anti-torsion and anti-compression of internal fixation. Key words: Femoral neck fractures;  Biomechanics;  Fracture fixation,internal