Degenerative Change of Adjacent Segments according to the Fusion Method after L4-5 Segmental Fusion: Comparative Study of Posterolateral Fusion and Posterior Lumbar Interbody Fusion

Purpose : We wanted to investigate the difference in the incidence of post-fusion adjacent segment degeneration between performing posterolateral fusion and posterior lumbar interbody fusion. Materials and Methods : One hundred fifty seven patients who underwent L4-5 fusion using pedicle screws for degenerative lumbar disease and followed up more than three years were analyzed retrospectively. Eighty-six cases of posterolateral fusion (group I) and 71 cases of posterior lumbar interbody fusion (group II) were compared. Sampling bias was evaluated by comparing gender, age, the preoperative degeneration of adjacent segments, the sagittal angle of fusion segments on the last follow up and the follow-up period. The differences of adjacent segments degeneration and the revision rate between the two groups were investigated multilaterally. The actual risk factors for such degeneration were investigated by performing multiple logistic regression test, which contrasted the degeneration group with the non-degeneration group for all the above factors, including whether interbody fusion was done or not. Results : Sampling bias was excluded except for the preoperative proximal adjacent segments degeneration (p=0.036). There was no statistical difference in the final proximal degeneration (31/86, 36% in group I, 26/71, 37% in group II, p=0.536) and revision (8/86, 9% in group I, 6/71, 8% in group II, p=0.536). There was no statistical difference in the final distal degeneration (9/86, 10% in group I, 8/71, 11% in group II, p=0.536) and revision (4/86, 5% in group I, 2/71, 3% in group II, p=0.435). When comparing those cases who developed degeneration on either side with the non-degeneration cases, the odds ratio of old age and an insufficient sagittal angle of the fusion segments reached statistical significance (p=0.024, 0.001). Conclusion : There were no differences in adjacent segments degeneration between the posterolateral fusion group and the posterior lumbar interbody fusion group. Rather than the operation methods, old age and insufficient sagittal angle of the fusion segments were the actual risk factors of such degeneration.