• Fa-Chuan Kuan, Kai-Lan Hsu, Cheng-Li Lin, Chih-Kai Hong, Ming-Long Yeh, and Wei-Ren Su.
• Department of Biomedical Engineering, National Cheng Kung University, Tainan, Taiwan; Department of Orthopaedic Surgery, National Cheng Kung University Hospital, College of Medicine, National Cheng Kung University, Tainan, Taiwan; Skeleton Materials and Bio-compatibility Core Lab, Research Center of Clinical Medicine, National Cheng Kung University Hospital, College of Medicine, National Cheng Kung University, Tainan, Taiwan.
• Injury. 2019 Nov 1; 50 (11): 1889-1894.

ObjectivesThe purpose of this study is to determine the biomechanical properties of the bicortical off-axis screw fixation for stabilizing of Pauwels III femoral neck fractures compared with other fixation methods.MethodsEighteen synthetic femurs (Sawbones Pacific Research Laboratories, Vashon, WA) were divided into three groups. The osteotomy was made vertically to mimic the Pauwels type III femoral neck fracture. Group A (n = 6) was fixed with traditional inverted triangle cannulated screws. Group B (n = 6) was fixed with a unicortical off-axis screw and two parallel cannulated screws. Group C (n = 6) was fixed with a bicortical off-axis screw and two parallel cannulated screws. Each group was tested with a nondestructive axial compression test at a 7° of valgus followed with 1000 cycles of cyclic loading test from 100 N to 1000 N. Finally, a destructive axial compression test was applied until catastrophic failure.ResultsThe average axial stiffness from group A to group C was 856.5, 934, and 1340 N/mm, respectively. The average ultimate failure load from group A to group C was 2612.7, 2508.8, and 3706 N, respectively. Group C exhibited significantly greater axial stiffness and a higher ultimate failure load than the other two groups (P < 0.05). Regarding the interfragmental displacement, the values from group A to group C were 0.41, 0.83, 0.36, respectively, and group B exhibited significantly larger fracture gap formation after the cyclic loading test.ConclusionsThe results of this biomechanical study show statistically significant increases in axial stiffness and ultimate failure load for the off-axis screw placed in bicortical fashion. Once the off-axis screw was positioned unicortically, the largest fracture diastasis was observed as compared to the other two methods.Copyright © 2019 Elsevier Ltd. All rights reserved.

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