Disc height and anteroposterior translation in fused and adjacent segments after lumbar spine fusion

In a series of 46 patients the effects of spinal fusion upon intervertebral height and sagittal alignment in operated and non-operated segments were retrospectively evaluated on digitized radiographs. Data was compared with age- and gender-normalized standard values. The objective was to evaluate the influence of different types of spine fusions primarily upon adjacent segments, particularly in terms of degeneration and sagittal profile of the lumbar spine. Incidence of adjacent segment degeneration (ASD) is still highly controversial. However, not every degeneration adjacent to spinal fusion must be caused by the fusion and responsibility of the fusion for ASD may vary with its range and type. Distortion Corrected Roentgen Analysis (DCRA) was utilized. DCRA is a proven valid, reliable, observer-independent, and accurate tool for assessment of these parameters over time and in comparison with "normal" cohorts. With this method the exact posture of the patients needs not to be known. There was little evidence for serious fusion-related ASD within an average of 40 months follow-up. No difference could be detected for rigid vs. non-rigid fusion and instrumented vs. non-instrumented techniques. Temporary postoperative distraction effects could be detected in operated and non-operated segments. Absolute preoperative values for intervertebral height and vertebral slip were age-related. Retrospectively, the choice of segments for fusion was clearly based upon radiological criteria. Thus we conclude that radiological parameters have an obvious clinical relevance for decision-making and need to be quantified. Within the limitations of this pilot study, true fusion related ASD seems to be infrequent.