Biomechanical evaluation of a new bidirectional self-locking fusion device in vitro

English Keywords:Biomechanics  Spine  Self-locking fusion device  Bidirectional

English Abstract:

  【Abstract】 Objectives: To evaluate the biomechanics of a new self-developed bidirectional self-locking fusion device in vitro. Methods: 12 fresh L3/4 segment specimens of domestic pig spine were randomly divided into 3 groups for modeling: normal group(intact state), traditional fusion device group(traditional fusion device and unilateral screw fixation) and new fusion device group(bidirectional self-locking fusion device implanted). On the basis of MTS multi-freedom(spinal motion) simulation test system and 500N preload, 8N·m load was applied to experimental specimens in each direction successively, and the stability test was carried out according to the order of forward bending, backward extension, left bending, right bending, and left and right rotation. The ranges of motion(ROMs) were compared between groups under different working conditions. The axial fatigue compression test was carried out with TT-JQ-01-106 fatigue testing machine to evaluate the stability and reliability of the self-developed fusion device. Results: Compared with the normal group, the ROM of the new fusion device group was significantly decreased under the conditions of flexion(1.67°±0.65° vs 3.46°±0.16°), extension(1.43°±1.01° vs 1.89°±0.29°), left bending(2.07°±1.32° vs 3.08°±0.09°), right bending(1.38°±0.72° vs 4.37°±0.20°), and right rotation(2.17°±1.51° vs 5.10°±0.37°)(all P<0.05); Under the left rotation condition, the ROM value(3.10°±1.57°) of the new device group was significantly higher than that of the normal group(2.36°±0.62°)(P<0.05). Compared with the conventional fusion device group, the ROM of the new fusion device group was significantly increased under flexion(1.67°±0.65° vs 1.22°±0.76°) and left rotation(3.10°±1.57° vs 1.57°±0.91°) conditions(P<0.05); However, there were no significant differences in ROMs between the two groups under extension(1.43°±1.01° vs 1.06°±0.50°), left bending(2.07°±1.32° vs 1.87°±1.41°), right bending(1.38°±0.72° vs 1.45°±0.69°), and right rotation(2.17°±1.51° vs 1.69°±1.07°) conditions(P>0.05). The ROM values of the normal group under flexion, extension, left bending, right bending, and right rotation conditions were significantly higher than those of the other two groups(P<0.05). Fatigue test: after 5 million load-displacement cycles, visual inspection revealed no deformation or cracks in the fusion device, and the axial compression fatigue test was passed. Conclusions: The bidirectional self-locking fusion device can obviously improve the stability of the fusion segment, which is equivalent to the stability of using the posterior single-sided nail rod system, meanwhile, it has good fatigue resistance, therefore its mechanical properties can meet the needs of clinical applications.