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

Abstract

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. 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. Patients with ASD had significantly lower SS (p = 0.005) and higher PT values (p < 0.001). Patients with SS <39° or PT >21°, were at higher risk for symptomatic ASD (relative risk 1.73 for SS and 3.663 for PT). 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° and SS below 39° are at higher risk for symptomatic ASD.