Biomechanical Study of Different Internal Fixation Devices for Femoral Neck Fractures: Finite Element Analysis Based on Different Reduction Qualities

Zhexi Zhu^1,2Zhongjian Tang^3,4Yafei Lu^1,2Tao Yang^1,2Jizhe Lu^1,4Chenglong Pang¹Bin Wang^1*

• ¹The Second Affiliated Hospital of Xuzhou Medical University, Xuzhou, China
• ²Xuzhou Medical University Graduate School, Xuzhou, China
• ³Peking University People's Hospital Department of Trauma and Orthopaedics, Beijing, China
• ⁴Graduate School, Hebei Medical University, Hebei, China

Objective: To compare and analyze the biomechanical advantages and disadvantages of four cannulated screws (4CCS) internal fixation device, biplanar double support screw (BDSF) internal fixation device, and dynamic hip screw (DHS) internal fixation device in anatomical reduction, positive reduction, and negative reduction of femoral neck fractures with a Pauwels angle of 50° using the finite element method. Results: In the femoral neck fracture model with a 50° Pauwels angle, maximum femoral displacement in the BDSF group was 3.412mm for anatomical reduction, 3.459mm for positive reduction, and 3.962mm for negative reduction—all smaller than those in the 4CCS and DHS groups.For femoral head stress, the 4CCS group showed higher stress (42.90Mpa) than BDSF (38.21Mpa) and DHS (35.91Mpa) under anatomical reduction. However, under positive and negative reduction, BDSF (23.75Mpa and 27.9Mpa) outperformed 4CCS (50.40Mpa and 34.6Mpa) and DHS (44.92Mpa and 44.6Mpa). Negative reduction models had significantly greater overall stress than positive reduction models, with positive reduction showing better stability.Under anatomical reduction, BDSF’s internal fixation stress (222.3Mpa) and displacement (3.611mm) differed notably from DHS (322.2Mpa, 3.009mm) and 4CCS (276.0Mpa, 3.346mm). Under positive and negative reduction, BDSF (247.4Mpa/3.370mm and 292.1Mpa/3.865mm) performed better than 4CCS (250.4Mpa/3.480mm and 293.1Mpa/3.897mm).BDSF and 4CCS had significantly lower internal fixation stress than DHS under positive and negative reduction, while no significant difference in internal fixation displacement was found between BDSF and DHS under these conditions. Conclusion: For femoral neck fractures with a Pauwels angle of 50° under anatomical reduction, positive reduction, and negative reduction, the BDSF internal fixation device has better biomechanical performance than the 4CCS and DHS internal fixation devices. Except for anatomical reduction, positive reduction can achieve better biomechanical results. The BDSF internal fixation technique can be considered a reliable closed reduction internal fixation technique for treating femoral neck fractures with different anatomical reductions.