Adjacent segment degeneration after posterior lumbar fusion: An analysis of possible risk factors

Many surveys have been distributed about the risk factors for adjacent segment degeneration
(ASD) after lumbar fusion. Despite myriad of risk factors recognized for ASD evolution, study results have
been inconsistent and there is not an agreement regarding which are the most important. Our study was
done to identify factors which may be important in the development of symptomatic ASD after lumbar
fusion.
Patients and methods: This retrospective study evaluated 1250 consecutive patients who underwent
posterior lumbar fusion and pedicular fixation between February 2006 and February 2009. A total of
13 patients with symptomatic ASD (clinical ASD) who underwent secondary surgery were identified.
Another group of 22 patients without symptomatic ASD (subclinical ASD) after spinal fusion were marked
as the control group. These two groups were compared for demographic data and clinical and radiographic
features to investigate the possible predictive factors of symptomatic ASD.
Results: The overall incidence rate of symptomatic ASD was 1.04%. Radiographic risk factors for the development of a symptomatic ASD were increased sagittal balance, loss of lordosis, and adjacent disc space
collapse. In the clinical ASD group, by multivariate logistic regression analysis, demonstrated that BMI,
preoperative ADD on MRI and disc bulge maintained their significance in predicting likelihood of clinical
ASD.
Conclusion: Patients with increased BMI, preoperative ADD and disc bulge on MRI have a statistically
significant increased risk of developing symptomatic ASD.