What is the optimum fusion technique for adult isthmic spondylolisthesis--PLIF or PLF? A long-term prospective cohort comparison study.

STUDY DESIGN: Long-term prospective observational cohort study.

OBJECTIVE: The objective of the study was to compare the long-term functional outcomes of posterolateral fusion (PLF) and posterior lumbar interbody fusion (PLIF) for the treatment of adult isthmic spondylolisthesis (IS).

SUMMARY OF BACKGROUND DATA: PLIF has the theoretical advantage of improving sagittal alignment and providing a larger, more consistent fusion mass in patients with IS compared with PLF. Studies to date though have not shown a clinical difference, with follow-up of 2 years.

METHODS: An prospective cohort study was performed of a single surgeon's patients with IS treated surgically over a 10-year period. Average follow-up was 7 years and 10 months. Preoperative patient characteristics between the 2 groups were not significantly different. The return rate of the long-term questionnaires was 83%. Outcome measures were the Roland Morris Disability Questionnaire (RMDQ), Low Back Outcome Score (LBOS), Short Form (SF)-12v2, and SF-6D R2.

RESULTS: PLIF provided better short-term and long-term results than PLF. The PLIF group had significantly better LBOS scores in the long term, and nonsignificantly better RMDQ scores. As measured by the RMDQ Minimal Clinically Important Difference set at 4 and 8, the LBOS Minimal Clinically Important Difference set at 7.5 points and by SF-12v2 Physical Component Score, PLIF patients performed better than PLF patients. When analyzing single-level fusions alone, the difference is more pronounced, with Physical Component Score, Mental Component Scores, and SF-6D R2 all being significantly better in the PLIF group rather than the PLF group.

CONCLUSIONS: This study strongly supports the use of PLIF to obtain equivalent or superior clinical outcomes compared with PLF for spinal fusion for lumbar IS. Although there are considerable issues when commenting on the results of observational studies, the results of this study are the first to report long-term follow-up beyond 2 years, and further larger long-term randomized studies are suggested.