Background context:

Although fusion rates in posterolateral lumbar fusions with pedicle screws (PLF+PS) and anterior lumbar interbody fusions with pedicle screws (ALIF+PS) have been reported, there has been no consensus on superiority with respect to clinical outcome and nonunion rates. Most studies determine nonunion rates based on radiographic studies; however, many of these nonunions are asymptomatic and may not require reoperations. Hence, a potentially more clinically useful measure is the reoperation rate for symptomatic nonunions, which we term the operative nonunion rate.

Purpose:

To determine if there is a difference in operative nonunion rates between PLF+PS versus ALIF+PS.

Study design:

Retrospective cohort study.

Patient sample:

Adult patients (≥18 years old) with the diagnosis of lumbar spondylolisthesis or lumbar spinal stenosis who underwent primary elective PLF+PS and ALIF+PS for 1-level and 2-level fusions (L4-S1) between 2009-2018.

Outcome measures:

Reoperation rates for symptomatic nonunions (i.e. operative nonunion rates).

Methods:

Patients were followed until validated operative nonunions, membership termination, death, or 03/31/2019. Descriptive statistics and two-year incidence rates for operative nonunions were calculated by fusion-level, fusion type, and levels fused. Time-dependent multivariable Cox-Proportional Hazards regression was used to evaluate operative nonunion rates with adjustment for covariates or risk change estimates more than 10%.

Results:

We identified 2,061 patients (PLF+PS:1491, ALIF+PS:570) with average follow-up time of 4.8 (±3.1) years and average time to operative nonunion of 1.3 (±1.2) yrs. Comparatively, unadjusted 1-level and 2-level incidence rates for operative nonunions were higher in PLF+PS vs. ALIF+PS. For 1-level procedures these were 0.9% (95% CI=0.4-1.6) vs. 0.6% (95% CI=0.1-2.1); 2-level, 2.0% (95% CI=0.8-4.0) vs. 0.9% (95% CI=0.1-3.3). However, there were no observed significant differences in risks for operative nonunions in multivariable models comparing PLF+PS vs. ALIF+PS (HR=0.3, 95% CI=0.1-1.1), 1-level vs. 2-level fusions (HR=1.8, 95% CI=0.8-4.3), or by fusion level (L4-L5: HR=1.0, 95% CI=0.4-2.7; L5-S1: HR=2.0, 95% CI=0.7-5.4).

Conclusions:

A large cohort of patients with lumbar fusions between L4 to S1 and an average follow-up of > 4 years found that although there was a trend for higher operative nonunions in PLF+PS compared to ALIF+PS, this was not statistically significant. The role of spinal alignment was not investigated.