Symptomatic adjacent segment degeneration at the L3-4 level after fusion surgery at the L4-5 level: evaluation of the risk factors and 10-year incidence

There have been few studies on revision surgery for clinically symptomatic adjacent segment degeneration (CASD). We aimed to find the incidence of revision surgery due to CASD and to analyze the factors that affected CASD at the L3-4 level after L4-5 or L4-5-S1 level fusion surgery over a long-term follow-up period. Between January 2001 and October 2009, fusion surgeries were performed on 401 patients with spondylolisthesis at the L4-5 or L4-5-S1 level; 378 patients were followed up for a minimum of 2 years. We assessed CASD-free survival using Kaplan-Meier survival analysis. We also analyzed factors affecting the development of CASD, including sex, age, pelvic incidence, overall lordosis, segmental lordosis, lamina inclination angle, facet tropism, and the extent of disc and facet degeneration. Isthmic spondylolisthesis treated using total laminectomy or degenerative spondylolisthesis treated using subtotal laminectomy and interbody fusion (IBF) or posterolateral fusion (PLF) were also included in the risk factor analysis. The difference in disc height before and after initial surgery was also analyzed, as was inclusion of the sacrum in the fusion level. Fusion extension surgery was performed on 33 of these patients due to CASD at the L3-4 level during the follow-up period. Kaplan-Meier survival analysis indicated 3-, 5-, and 10-year disease-free survival rates of 99.20, 96.71, and 76.93 %. Statistically significant factors affecting CASD included old age, low overall lordosis, low segmental lordosis, progression of facet degeneration, total laminectomy-treated isthmic spondylolisthesis, and PLF-alone rather than IBF alone or IBF + PLF. We determined six significant factors affecting CASD development. Among these risk factors, facet degeneration, isthmic-type spondylolisthesis, and the type of fusion show higher hazard ratios and seem to be clinically more relevant than the other three factors (age, overall lordosis, and segmental lordosis).