Risk factors for adjacent segment degeneration after PLIF

Study Design. A retrospective study of 87 patients who underwent posterior lumbar interbody fusion (PLIF) at L4 - L5 for L4 degenerative spondylolisthesis. Objective. To clarify: 1) the correlation between radiologic degeneration of cranial adjacent segment and clinical results, 2) risk factors for radiologic degeneration of cranial adjacent segment, and 3) preoperative radiologic features of patients who underwent additional surgery with cranial adjacent segment degeneration. Summary of Background Data. Whereas PLIF with pedicle screw fixation has shown satisfactory clinical results, a solid fusion has been reported to accelerate a degenerative change at unfused adjacent levels, especially in the cranial level. Although several authors have reported the adjacent segment degeneration after PLIF, there are no previous reports of risk factors for adjacent segment degeneration after PLIF. Materials and Methods. Eighty-seven patients who underwent PLIF for L4 degenerative spondylolisthesis and could be followed for at least 2 years were included in this study. We measured lumbar lordosis, scoliosis, laminar inclination angle at L3, facet sagittalization at L3 - L4, facet tropism at L3 - L4, preexisting disc degeneration at L3 - L4, and lordosis at the fused segment. Progression of L3 - L4 segment degeneration was defined as a condition in which disc narrowing, posterior opening, and progress of slippage in comparison with preoperative dynamic lateral radiographs. Patients were divided into three groups according to postoperative progression of L3 - L4 degeneration: Group 1 with neither progression of L3 - L4 degeneration nor neurologic deterioration, Group 2 with progression of L3 - L4 degeneration but no neurologic deterioration, and Group 3 with an additional surgery required for neurologic deterioration. Correlation between clinical results and radiologic progression of L3 - L4 degeneration, and risk factors for progression of radiologic degeneration were investigated. Further, preoperative radiologic features of Group 3 were studied to detect risk factors for clinical deterioration. Results. There were 58 (67%) patients classified into Group 1, 25 (29%) patients into Group 2, and 4 (4%) patients into Group 3. There was no significant difference in average age in each group. No obvious difference was observed in recovery rate between Groups 1 and 2. Laminar inclination angle and facet tropism in Group 3 were more significant than those in Groups 1 and 2. Further, apparent lamina inclination and facet tropism coexisted in Group 3. There were no obvious differences in other factors between each group. Conclusion. 1) There was no correlation between radiologic degeneration of cranial adjacent segment and clinical results. 2) Risk factors for postoperative radiologic degeneration could not be detected in terms of each preoperative radiologic factor. 3) Coexistence of horizontalization of the lamina at L3 and facet tropism at L3 - L4 may be one of the risk factors for neurologic deterioration resulting from accelerated L3 - L4 degenerative change after L4 - L5 PLIF.