The objective of this study was to apply a biodegradable dynamic fixation system (BDFS)for lumbar fusion between articular processes and compare the fusion results and biomechanical changes with those of conventional rigid fixation. Twenty-four mongrel dogs were randomly assigned to 2 groups and subjected to either posterior lumbar fusion surgery with a BDFS or titanium rods (TR) at the L5-L6 segments. Six animals in each group were sacrificed at 8 or 16 weeks . Fusion conditions were evaluated by CT, manual palpation, biomechanical tests and histological analysis. Biomechanical tests were performed at the L4-7and L5-6 segments. Histological examination was performed on organs, surrounding tissues and the fused area. The magnesium alloy components maintained their initial shape 8 weeks after the operation, but the meshing teeth were almost completely degraded at 16 weeks. The biomechanical analysis revealed an increased lateral bending ROM at 8 weeks and axial torsion ROM at 16 weeks. The L4-5 extension-flexion ROMs in BDFS group were 2.29±0.86° and 3.17±1.08° at 16 weeks, respectively, which were increased to 3.22±0.56°and 5.55±1.84° in TR group. However, both groups showed similar fusion results. The BDFS design is suitable, and its degradation in vivo is safe. BDFS can be applied for posterior lumbar fusion between articular processes to complete the fusion well. Additionally, BDFS can reduce the decline in lateral motion and hypermotion of the cranial adjacent segment in flexion-extension motion.

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