Risk Factors for L5–S1 Disk Height Reduction After Lumbar Posterolateral Floating Fusion Surgery

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Study Design:

This is a retrospective study.


To investigate the risk factors for radiographic L5–S1 disk height reduction after lumbar posterolateral floating fusion surgery.

Summary of Background Data:

We investigated data from 86 patients (45 men) who underwent posterolateral floating fusion surgery from 2007 to 2010. The follow-up was from 2 to 6 years. The mean age of the patients was 65.4 years.


L5–S1 disk height was calculated and >2 mm reduction was defined as significant. Age, sex, height, weight, body mass index, number of fused levels, grade of disk degeneration, disk height and diameter, sacrolumbar alignment, alignment of fused level, achievement of union, and proximal adjacent segment disorder at final follow-up were compared. Univariate and multivariate logistic regressions were performed.


L5–S1 disk height reduction occurred in 14 patients (30.2%). The number of fused levels was significantly greater (1.8±0.8 vs. 1.4±0.6) in patients without disk height reduction. Radiology showed a significant change of L1–S1 sacrolumbar alignment after surgery in patients without disk height reduction (0.3±6.6 vs. –4.5±7.6 degrees). The height of the disk posterior to the L5–S1 intervertebral disk before surgery was significantly greater (7.3±2.1 vs. 6.1±2.1 mm) in patients without disk height reduction. In multivariate logistic regression analysis, fusion of >3 levels was a significant risk factor for L5–S1 disk height reduction.


In posterolateral floating fusion surgery, there was a higher risk of L5–S1 disk height reduction and consequent foraminal stenosis in patients with multiple-level fusion. Surgical methods and fusion levels should be chosen after considering their association with L5–S1 disk height reduction.

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