Is Interbody Fusion Mandatory? - From Long Term Results of Posterolateral Fusion For Isthmic Spondylolisthesis

Purpose: Many spine surgeons are treating isthmic spondylolisthesis by interbody fusion with pedicle screw systems (PS). In this study, based on our long-term results of posterolateral fusion (PLF), the limitation of PLF and the best indication of interbody fusion for isthmic spondylolisthesis were discussed.

Methods: The study group comprised 100 patients of isthmic spondylolisthesis, who had underwent PLF with PS. All of them were followed up for more than 5 years. The mean age at surgery was 45 years. The site of spondylolisthesis was at L5 in 70 pts, at L4 in 20, and others in 10. The number of fusion levels was one in 83 pts, two in 17. Risk factors of unfavorable results such as pseudoarthrosis or instrument failures associated with PLF were analyzed using univariate and multivariate logistic regression models.

Results: The average follow-up was 8 years. JOA score (full score = 29 points) was 15.6 points at preop. and 25.8 points at follow-up. Fusion rate was 95 %. There were instrument breakage in 6pts, pseudoarthrosis in 5. From logistic regression analysis, preoperative slip angle (odds ratio [OR]: 4.48 per 10 degrees kyphosis, p<0.05) and preoperative %PDH (OR: 3.60 per 10 %, p<0.01) were the most important risk factors of pseudoarthrosis or instrument breakage. High risk factors of pseudoarthrosis or instrument breakage were preoperative wide disc space (%PDH > 35%) and/or segmental kyphosis (slip angle > 0 degrees).

Conclusions: PLF with PS has provided satisfactory long term results with high fusion rate. However, there were complications including instrument breakage or pseudoarthrosis in specific conditions. >From this study, it became clear that the patients with preserved disc height and presence of segmental kyphosis should be treated with interbody fusion. %PDH > 35% and/ or slip angle > 0 degrees are good indicators for interbody fusion. Conversely, severe disc-height loss and preserved segmental lordosis are good indicators for PLF without interbody fusion.