Estimating the risk for symptomatic adjacent segment degeneration after lumbar fusion: analysis from a cohort of patients undergoing revision surgery

Purpose Aim of this study is to estimate the risk for symptomatic adjacent segment degeneration (ASD) and examine the association between spino-pelvic parameters and ASD. Methods 22 patients operated upon by instrumented lumbar or lumbosacral spinal fusion and re-operated upon for ASD were enrolled in the study. 83 consecutive patients with the same surgery and never re-operated upon were the controls. Pelvic incidence, sacral slope (SS), pelvic tilt (PT), and lumbar lordosis were calculated. Results Patients with ASD had significantly lower SS (p = 0.005) and higher PT values (p < 0.001). Patients with SS <39 degrees or PT >21 degrees, were at higher risk for symptomatic ASD (relative risk 1.73 for SS and 3.663 for PT). Conclusions In patients re-operated upon for ASD, pelvic retroversion and hyperlordosis are the main mechanisms of compensation for the unbalanced spine. Patients with PT above 21 degrees and SS below 39 degrees are at higher risk for symptomatic ASD.