• Ferran Pellisé, Alejandro Hernández, Xavier Vidal, Joan Minguell, Cristobal Martínez, and Carlos Villanueva.
• Unitat d'estudi de la Patología del Raquis, Hospital Universitari Vall d'Hebron, Barcelona, Spain. 24361fpu@comb.es
• Spine. 2007 Mar 1; 32 (5): 574-9.

Study DesignProspective observational single-cohort study.ObjectiveTo analyze long-term radiographic changes in all unfused lumbar segments after instrumented posterolateral lumbar fusion.Summary Of Background DataAdjacent segment degeneration (ASD) after lumbar fusion may be a consequence of biomechanical stress or result from constitutional factors. Most studies analyzing ASD only investigate the motion segments immediately above and below the fusion. None compares adjacent segments to all the other unfused segments after instrumented posterior fusion.MethodsUsing the distortion-compensated roentgen analysis method, disc height, dorsoventral displacement, and lordosis were measured in 212 unfused segments from 62 patients, on digitized standing radiographs taken before fusion surgery and after a mean follow-up of 7.5 years (range, 4-11 years). The effect of covariables, such as age, length of follow-up, fusion level, number of fused segments, and sagittal and spinopelvic parameters on the preoperative to follow-up changes, were analyzed using a repeated-measurement model.ResultsNo changes were observed at the segments located below the fusion. All the unfused segments above the fusion showed the same significant loss of disc height. Loss of disc height did not depend on fusion parameters, correlated weakly with age and length of follow-up, and correlated highly across adjacent unfused segments.ConclusionsAfter posterior lumbar instrumented fusion, radiographic changes suggesting disc degeneration appear homogeneously at several levels cephalad to fusion and seem to be determined by individual characteristics.

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