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

• Risk factors for ASD evolution are not known.
• This study was done to clarify risk factors.
• The overall incidence rate of symptomatic ASD was 1.04%.
• Body mass index, disc collapse and disc bulge were risk factors.

ObjectiveMany 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 methodsThis 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.ResultsThe 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.ConclusionPatients with increased BMI, preoperative ADD and disc bulge on MRI have a statistically significant increased risk of developing symptomatic ASD.