Correlation between sagittal plane changes and adjacent segment degeneration following lumbar spine fusion

Adjacent segment degeneration following lumbar spine fusion remains a widel y acknowledged problem, but there is insufficient knowledge regarding the f actors that contribute to its occurrence. The aim of this study is to analy se the relationship between abnormal sagittal plane configuration of the lu mbar spine and the development of adjacent segment degeneration. Eighty-thr ee consecutive patients who underwent lumbar fusion for degenerative disc d isease were reviewed retrospectively. Patients with spondylolytic spondylol isthesis and degenerative scoliosis were not included in this study. Mean f ollow-up period was 5 years. Results were analysed to determine the associa tion between abnormal sagittal configuration and post operative adjacent se gment degeneration. Thirty-one out of 83 patients (36.1%) showed radiograph ic evidence of adjacent segment degeneration. Patients with normal C7 plumb line and normal sacral inclination in the immediate post operative radiogr aphs had the lowest incidence of adjacent level change compared with patien ts who had abnormality in one or both of these parameters. The difference w as statistically significant (P < 0.02). There was no statistically signifi cant difference in the incidence of adjacent level degeneration between mal e and female patients-between posterior fusion alone and combined posterola teral and posterior interbody fusions; and between fusions extending down t o the sacrum and fusions stopping short of the sacrum. It was concluded was that normality of sacral inclination is an important parameter for minimiz ing the incidence of adjacent level degeneration. Retrolisthesis was the mo st common type of adjacent segment change. Patients with post operative sag ittal plane abnormalities should preferably be followed-up for at least 5 y ears to detect adjacent level changes.