| Objectives To evaluate the characteristics of biomechanics of intra-segmental trans-pedicle screws and rod to spondylolysis, and the clinical application of that operation. Methods The micro- strain gages were pasted to both side of zygapophyseal surface of lower lumbar spine in vitro biomechanics. Then the strain of the gages were measured under routine stress loadings in normal condition, spondylolysis, internal fixation respectively. A Finite Element Analysis(FEA) model of spondylolysis was made up from the images of CT scans to an adolescent patient with spondylolysis. The model was validated by self-biomechanics in vitro. FEA model with two kinds of fixation(intra-segmental and inter-segmental) was under stress loadings to discover the stress distribution to adjacent endplate. The application of the intra-segmental fixation was observed from the follow-ups about recovery and lumbar isthmic fusion. Results The stabilization to lower lumbar spine was observed in biomechanics of Intra-segmental fixation in vitro. FEA model of spondylolysis was valid and show the same results of stress at adjacent endplate between intra -segmental fixation and spondylolysis only under flexion, extension and lateral bending. However, the significant increase of stress at L4 inferior endplate was observed in inter-segmental fixation model. The decrease of stress at S1 superior endplate was marked in torsion loading with intra-segmental fixation. Of 16 patients applied to intra-segmental trans-pedicle screws and rod. fixation operation, there were 15 patients were followed up average 22.4 months. All of patients with follow-up had good results and nonunion of isthmus was not exist. Conclusion Intra-segmental trans-pedicle screws and rod fixation should stabilize the lumbar spine with spondylolysis, and remain the motion of adjacent lumbar intervertebral disc. The further study should be developed.
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