Biomechanical study of femoral neck fracture fixed by cannulated screws and iliac bone graft at different angles

doi:10.3969/j.issn.1002-7386.2015.08.005

Abstract：Objective To investigate the biomechanical stability of iliac bone grafts at different angles with three cannulated screws for fixation of femoral neck fractures in order to provide scientific basis for clinical application.Methods The nine pairs of proximal femora and ipsilateral iliac bone grafts with lateral and upper surface retaining cortex were harvested from nine cadavers fixed in formalin,which were randomly divided into two groups: cannulated screw with medial bone graft fixation group ( CMB group) ,cannulated screw with cross bone graft fixation group ( CCB group) .The specimens were cut with power saw to create a standardized midcervical osteotomy perpendicular to the cervical neck.The fracture was then reduced and fixed with three parallel 7.3mm cannulated screws and an iliac bone graft.The cannulated screws were placed triangularly with one screw superior and two inferior.In the CMB group,the bone graft was in the middle of three cannulated screws and parallel with it,however,in the CCB group,the bone graft was made an angle of 30°with the screws on postero-anterior position.All the bone grafts were passed across the fracture line about 1.5cm.Every specimen was detected by Electroforce 3520-AT biomechanical machine.Results When femoral head was rotated to 3°and 5°, the torque values in CCB group were significantly higher than those in CMB group ( P <0.05) ,however,during axial displacement at the load of 700N and 1000N, the displacement values in CCB group were significantly lower than those in CMB group ( P <0.05).All the specimens underwent cycling compression test at 700N compression force successfully,without fatigue fracture or screw failure.The mean ultimate load in CMB group and CCB group was (2112.689 ±186.913)N and (2360.811 ±204.340)N,respectively,there was a significant difference between two groups ( P <0.05).Conclusion The biomechanical stability of fixation of femoral neck fracture with three cannulated screws in CCB group is superior to that in CMB group,and the experimental results provide a biomechanical basis for adopting optimal bone graft mode in the treatment of femoral neck fracture.