Finite element analysis of a novel repair device for lumbar spondylolysis

Abstract Background This study aimed to compare the biomechanical differences between a novel repair device for lumbar spondylolysis and a nail–hook internal fixation system through three-dimensional finite element analysis. Methods Three-dimensional images of L4–S1 were constructed based on computed tomography images of a young male patient. Four finite element models were developed: Model A: intact model; Model B: bilateral spondylolysis of the L5 model; Model C: spondylolysis fixed by the nail–hook internal fixation system model; and Model D: spondylolysis fixed by the novel repair device model. A uniformly distributed 600-N vertical downward concentrated force and 10 Nm of torque were applied to the upper surface of the L4 to simulate six physiological activities of the lumbar spine. The fixation effects were evaluated by comparing the range of motion, maximum stress of the intervertebral disks, maximum displacement of the spondylolysis, and stress distribution of the internal fixation. Results The range of motions of the two internal fixation models were similar in each segment and direction. In terms of the maximum displacement of the spondylolysis, that of the fracture surface in the novel repair device model was significantly reduced compared with the nail–hook internal fixation model in each range of motion. The maximum stress of the intervertebral disks in the two models had their respective advantages in different activity directions, but the difference in stress values was not significant. The stress levels of both internal fixation devices were concentrated on the connecting rod and the junction of the pedicle screw and the connecting rod. Due to the shorter connecting rod of the nail–hook internal fixation system, the stress on the connecting rod was more concentrated, while the stress distribution on the connecting rod of the novel device was more dispersed. Conclusion The new type of lumbar pars interarticularis repair device is highly reliable in fixation, and the bone grafting area of the pars interarticularis is well exposed, providing favorable conditions for bone grafting and subsequent bone formation. It is a highly promising internal fixation device that offers a new option for pars interarticularis repair.