OBJECTIVETo investigate the stability of internal fixation for femoral neck fracture(FNF) using two or three cannulated screws directed to different fracture lines, and to provide a theoretical basis for the clinical decision making.

METHODSFifteen fresh frozen human femur samples were selected and the FNF model was established with Pauwels angle of 30°, 50° and 70° respectively. The models were fixed with three or two cannulated screws, and their differences at tensile strength, subsidence, shear strength and composite displacement, gap distance, torsional angle and stiffness values of four types of femur were evaluated to identify their biomechanical stability.

RESULTSWith Pauwels angle of 30° and 50°, no statistical differences at the referenced outcomes were observed between two and three cannulated screw fixation for FNF(>0.05). With the Pauwels angle of 70 °, three cannulated screws fixation were significantly superior to two cannulated screws fixation for FNF(<0.05). Nevertheless, when Pauwels angle was 70°, three cannulated screws fixation turned out to be relative instable compared with Pauwels angle of 30° and 50°.

CONCLUSIONSWith Pauwels angle of 30° and 50°, two cannulated screws fixation was similarly stable as using three cannulated screws for FNF. Three cannulated screws fixation were obviously superior to two cannulated screws fixation when Pauwels angle was 70°, but the application of three cannulated screws could still be insufficiently stable when only such routine fixations were utilized. Therefore, Angle Stabilizing System or anti-sliding screws were needed to enhance the stability of FNF fixation.