Pre-existing adjacent level foraminal stenosis does not affect the outcome of a single level lumbar interbody fusion

The aim of this study was to investigate whether or not pre-existing asymptomatic neuroforaminal stenosis adjacent to the fusion level develops adjacent segment disease (ASD) after single-level lumbar interbody fusion.

Risk factors of ASD after spinal fusion have been well investigated, but there have been few studies focused on the relationship between ASD and pre-existing asymptomatic neuroforaminal stenosis.

A total of 302 patients who had undergone a single-level lumbar interbody fusion were reviewed at a minimum of 2 year follow-up. They were 109 men and 193 women with a mean age of 68.8 years. Follow-up periods was averaged 53.5 months. ASD was defined as neurological deterioration related to adjacent segment pathologies which required an additional surgery. Based on the pathologies, patients were divided into three categories: ASD due to foraminal stenosis (ASD-FS), ASD due to central stenosis (ASD-CS), and ASD due to herniated disc (ASD-HD). Measured variables were age, gender, diagnosis, BMI, decompression procedures at adjacent segments, preoperative anterior/posterior slip, asymptomatic neuroforaminal stenosis, facet tropism, and postoperative spinopelvic parameters.

Thirty-eight patients (12.6%) developed ASD. There were 15 patients with ASD-FS, 18 patients with ASD-CS, and five patients with ASD-HD. Lumbar lordosis (LL) and sacral slope (SS) were significantly smaller and pelvic tilt (PT) was significantly larger in ASD-FS. Asymptomatic neuroforaminal stenosis was detected preoperatively in 33.3% of the ASD-FS group, and 18.6% of non-ASD group; the incidence was not significantly different.

Adjacent-level neuroforaminal stenosis was not a significant risk of ASD after single-level lumbar interbody fusion, and might not need to be fused if asymptomatic.