Study design:

A retrospective study.

Objective:

The aim of this study was to investigate the ability of Global Alignment and Proportion (GAP) score to predict the occurrence of adjacent segment degeneration (ASD) after fusion surgery for lumbar degenerative diseases.

Summary of background data:

The recently developed GAP score was applied to predict postoperative complications for adult spinal deformity, as well as to facilitate future outcome-based research on optimal treatment for various spinal conditions. However, it remains unclear whether reconstruction of alignment according to GAP score can reduce the ASD rates.

Methods:

This study retrospectively reviewed 126 consecutive patients who had undergone lumbar fusion and had been followed over 2 years. Pre- and postoperative radiographs and MRI were analyzed for ASD. GAP scores were calculated based on the early postoperative spinopelvic parameters. Cochran-Armitage test of trend was performed to investigate the association between GAP score and the occurrence of ASD. Receiver-operating characteristic curves were used to analyze the predictive accuracy of the GAP score for ASD.

Results:

Radiographical ASD (R-ASD) and symptomatic ASD (S-ASD) were diagnosed in 44 (34.9%) patients and in 13 (10.3%) patients, respectively. The patients with a proportioned spinopelvic state according to the GAP score had significantly lower rates of ASD (R-ASD and S-ASD) or S-ASD than those with a moderately or severely disproportioned spinopelvic state. The area under curve for the GAP score predicting ASD and S-ASD was 0.691 (95% confidence interval [CI]: 0.596∼0.785, P < 0.01) and 0.865 (95% CI: 0.771∼0.958, P < 0.01), respectively.

Conclusion:

Our study revealed a significant association between postoperative GAP score and occurrence of ASD after lumbar fusion surgery. Setting surgical goals according to the GAP score may help reduce the occurrence of ASD, especially for S-ASD.Level of Evidence: 4.