Effects of Restoration of Sagittal Alignment on Adjacent Segment Degeneration in Instrumented Lumbar Fusions

Study Design. Retrospective case-control study. Objective. To investigate the effects of postoperative sagittal alignment on radiographic adjacent segment degeneration (ASD) after lumbar fusion surgery. Summary of Background Data. ASD is one of inherent problems with fusion surgery. Many confounding factors are related to the development of ASD. Recently, sagittal alignment has been emphasized for its significance on ASD. Methods. Seventy-three patients who underwent four-level lumbar fusion surgery (L2-S1) were divided into two groups according to postoperative sagittal alignment (pelvic incidence-lumbar lordosis [PI-LL] >= or <9 degrees): 44 patients (matched group, including 10 patients who underwent pedicle subtraction osteotomy [PSO] at L4) and 29 patients (mismatched group). The general demographics, radiographic parameters, and clinical outcomes were recorded. Preoperative disc degeneration at L1-2 was evaluated by Pfirrmann grade and Kellgren-Lawrence (K-L) grade. Disc degeneration at L1-2 was evaluated by the K-L grade on 2-year postoperative X-rays. Results. The incidence of radiographic ASD (11 [25%] vs. 16 patients [55%], P = 0.02) and Oswestry Disability Index (ODI) scores (36.9 +/- 19.9 vs. 49.4 +/- 20.7, P = 0.015) at postoperative 2 years were significantly higher in the mismatched group. There were no significant differences in other demographic and radiographic parameters between the two groups. On subgroup analysis between 10 PSO patients and the mismatched group, the mismatched group showed a higher incidence of radiographic ASD (16 [55%] vs. 1 patient [10%], P = 0.041) and worse ODI scores (49.7 +/- 20.5 vs. 39.0 +/- 20.7, P = 0.040). Preoperative Pfirrmann grade at L1-2 (odds ratio [OR] = 4.191, 95% confidence interval [CI]: 1.754-10.013, P = 0.001) and postoperative PI-LL mismatch (OR = 4.890, 95% CI: 1.550-15.427, P = 0.007) showed significant relationships with the development of radiographic ASD at postoperative 2 years. Conclusion. The restoration of optimal sagittal alignment, even with PSO, may provide a protective effect on the development of radiographic ASD, although the preoperative disc degeneration grade was a risk factor for radiographic ASD.