Spatial Bridge Locking Fixator versus Traditional Locking Plates in Treating AO/OTA 32-A3.2 Fracture: Finite Element Analysis and Biomechanical Evaluation

Objective To compare the biomechanical behaviors of the spatial bridge locking fixator (SBLF), single locking plate (SP), and double locking plate (DP) for AO/OTA 32-A3.2 fractures using finite element analysis and biomechanical tests. Methods Axial loading of 700 N was conducted on the AO/OTA 32-A3.2 model via finite element analysis. The von Mises stress and the interfragmentary movement (IFM) were comparatively analyzed in the three configurations above. On the mechanical tester, axial and torsional loading of 30 synthetic femurs (five specimens of each configuration for each test at random) was performed, and the interfragmentary movement, torsion angle, stiffness, and ultimate load were recorded and analyzed. Results The finite element analysis (FEA) results showed that the von Mises stress of the spatial bridge locking fixator (SBLF) was lower than that of the single locking plate (SP) and higher than that of the double locking plate (DP). At 700 N, the axial IFMs were 0.15-0.38 mm (SBLF), 0.03-0.84 mm (SP), and 0.02-0.07 mm (DP). The biomechanical experiment indicated that the axial interfragmentary movements (IFMs) were 0.44 +/- 0.23 mm (SBLF), 1.02 +/- 0.40 mm (SP), and 0.07 +/- 0.07 mm (DP) (p < 0.001). The axial IFM of the SBLF group had the highest probability (79.26%) of falling within the ideal range (0.2-0.8 mm), and the SP and DP groups had probabilities of 27.10% and 3.14%, respectively. The axial stiffness in the SBLF group (1586 +/- 130 N/mm) was significantly lower than that in the DP group (10,264 +/- 2671 N/mm) (p < 0.001) but greater than that in the SP group (725 +/- 178 N/mm) (p = 0.396). The range of axial loads to ultimate failure was 3385-4527 N (SBLF), 3377-4664 N (SP), and 3780-4804 N (DP). The shear motion of the fracture end was 0.35 +/- 0.14 mm (SBLF), 0.16 +/- 0.10 mm (SP), and 0.08 +/- 0.04 mm (DP) (p < 0.001). The torsional stiffness was 1.68 +/- 0.14 Nm/degree (SBLF), 2.32 +/- 0.29 Nm/degree (SP) (SBLF&SP, p < 0.001), and 3.53 +/- 0.73 Nm/degree (DP) (SBLF&DP, p < 0.001). Conclusions The SBLF structure may exhibit a better biomechanical performance compared with the SP and DP in providing the best quantity and more symmetrical interfragmentary movement for AO/OTA 32-A3.2 fractures.