Risk factors for adjacent segment disease after lateral lumbar interbody fusion for lumbar spinal canal stenosis with instability.

PURPOSE: Lateral lumbar interbody fusion (LLIF) achieves indirect decompression by restoring disc height; however, excessive cage elevation may increase the risk of adjacent segment disease (ASD). This relationship remains unclear. Therefore, this study aimed to identify ASD risk factors following LLIF by focusing on intervertebral height gain and comparing outcomes of LLIF and decompression using propensity score matching (PSM).

METHODS

Seventy-six patients who underwent single-level LLIF for lumbar stenosis with instability were analyzed to identify ASD-related risk factors. Univariate and multivariate Cox regression analyses were used to determine independent predictors. A receiver-operating characteristic analysis identified the optimal cage elevation threshold. PSM of 69 patients with LLIF and 69 patients with decompression was performed. ASD-free survival was evaluated using a Kaplan-Meier analysis. The LLIF cohort was divided into low and high elevation groups based on a cutoff of 3.7 mm.

RESULTS

A multivariate analysis identified posterior cage placement (hazard ratio [HR], 1.06; p = 0.032) and greater cage elevation (HR, 1.28; p = 0.012) as independent risk factors. The 5-year ASD-free survival rates were 81.1%, 72.9%, and 46.9% for decompression, low-elevation LLIF, and high-elevation LLIF, respectively. Compared to decompression, high-elevation LLIF significantly increased the ASD risk (HR, 3.81; p < 0.001), but low-elevation LLIF did not (HR, 1.79; p = 0.279). Low-elevation LLIF resulted in greater leg numbness improvement (16.65 vs. 41.90; p = 0.023).

CONCLUSION

Excessive intervertebral elevation with LLIF increased the ASD risk. Decompression and LLIF with moderate elevation improved symptoms without a significantly different ASD incidence.