Abstract: BACKGROUND: Facet joint osteoarthritis is acknowledged as a significant contributor to lower back pain in the geriatric population. The advent of an innovative spinal facet joint fusion device presents a therapeutic option for intervening during the initial stages of facet joint osteoarthritis, and significantly reduces the incidence of a series of complications caused by poor early conservative treatment and late surgical treatment. However, its effect on the biomechanics of the lumbar spine is unknown. 
OBJECTIVE: To investigate the biomechanical disparities between the novel lumbar zygapophyseal joint fusion device and traditional fusion devices.
METHODS: A comprehensive three-dimensional finite element model of the L3-S1 lumbar spine was established and validated. Based on this intact model, three groups of surgical models were constructed: a bilateral pedicle screw fixation model, a bilateral novel facet joint fusion fixation model, and a bilateral facet screw fixation model, with the surgical segment designated as L4-5. Under a load of 500 N, a torque of 7.5 Nm was applied to all lumbar models to calculate the range of motion, displacement values, and intervertebral disc stress values at the L4-5 segment; stress values at the L3-4 and L5-S1 segments were also measured.
RESULTS AND CONCLUSION: (1) Compared with the intact model, the range of motion at the L4-5 segment was reduced in all surgical models. (2) The novel device exhibited the smallest range of motion at the L4-5 segment under left and right rotational conditions; the greatest range of motion at the L4-5 segment under extension conditions; and a greater range of motion under other conditions than the bilateral pedicle screw fixation model. (3) The novel device demonstrated the smallest displacement values at the L4-5 segment under left and right rotational conditions; under other conditions, the displacement values at the L4-5 segment were greater than those in the bilateral pedicle screw fixation model. (4) In terms of stress distribution at the L4-5 segment, the novel device consistently exhibited the smallest values across all conditions. (5) For the L3-4 segment, the novel device showed the greatest stress values under extension and left and right rotational conditions, while under other conditions, the values were lower than those in the bilateral pedicle screw fixation model. (6) Compared with pedicle screw fixation, the novel device produced smaller stress values at the L5-S1 segment. (7) This study indicates that, compared with pedicle screw fixation, the novel device impacts the biomechanics of the lumbar spine by fusing the facet joints. It provides stability while preserving the range of motion at the surgical segment and reduces stress on the intervertebral discs of the surgical and adjacent segments, thereby potentially delaying disc degeneration. This suggests that the novel device can achieve biomechanical effects similar to those of pedicle screw fixation in theory.

中国组织工程研究杂志出版内容重点：人工关节；骨植入物；脊柱；骨折；内固定；数字化骨科；组织工程

Key words: lumbar spine, facet joints, pedicle screw, fusion, finite element analysis, spine, biomechanics, fixation