Development of ethnicity-adjusted global alignment and proportion score to predict the risk of mechanical complications following corrective surgery for adult spinal deformity

BACKGROUND CONTEXT Surgery for degenerative scoliosis (DS) is a complex procedure with high complications and revision rates. Based on the concept that PI is a constant parameter, the GAP score was developed from sagittal alignment data collected in the Caucasian population to predict mechanical complications. However, PI varies among different ethnic groups, and the GAP score may not apply to Chinese populations. Thus, this study aims to assess the predictability of the GAP score for mechanical complications in the Chinese population and develop an ethnicity-adjusted GAP score. PURPOSE To test the predictability of the original GAP score in the Chinese population and develop a Chinese ethnicity-tailored GAP scoring system. STUDY DESIGN/SETTINGS Retrospective cohort study PATIENT SAMPLE A total of 560 asymptomatic healthy volunteers were enrolled to develop Chinese ethnicity-tailored GAP (C-GAP) scores and a total of 114 DS patients were enrolled to test the predictability of original GAP score and C-GAP score. OUTCOME MEASURES Demographic information, sagittal spinopelvic parameters of healthy volunteers and DS patients were collected. Mechanical complications were recorded at a minimum of 2-year follow-up after corrective surgery for DS patients. METHODS A total of 560 asymptomatic healthy volunteers with a mean age of 61.9±14.1 years were enrolled to develop ethnicity-adjusted GAP score. Besides, 114 DS patients (M/F=10/104) with a mean age of 60.7±7.1 years were retrospectively reviewed. Demographic data and radiological parameters of both groups, including PI, lumbar lordosis (LL), sacral slope (SS), the sagittal vertical axis (SVA), and global tilt (GT) were collected. Ideal LL, SS, and GT were obtained by calculating their correlation with PI of healthy volunteers using linear regression analysis. Relative pelvic version (RPV), relative lumbar lordosis (RLL), lordosis distribution index (LDI), and relative spinopelvic alignment (RSA) were obtained using the ideal parameters, and the Chinese population adjusted GAP score (C-GAP) was developed based on these values. The predictability of original and C-GAP for mechanical failure was evaluated using clinical and radiological data of DS patients by evaluating the area under the curve (AUC) using receiver operating characteristics. This study was supported the National Natural Science Foundation of China (NSFC) (No. 82272545), $ 8,000-10,000 and the Jiangsu Provincial Key Medical Center, and the China Postdoctoral Science Foundation (2021M701677, $ 5,000-7,000). RESULTS Ideal SS=0.53 × PI+9 (p=0.002), ideal LL=0.48 × PI+22 (p=0.023) and ideal GT=0.46 × PI-9 (p=0.011). were obtained by correlation analysis using sagittal parameters from those healthy volunteers, and RPV, RLL, RSA, and LDI were calculated accordingly. Then, the ethnicity-adjusted C-GAP score was developed by summing up the numeric value of calculated RPV, RLL, RSA, and LDI. The AUC was classified as ‘‘no or low discriminatory power’’ for the original GAP score in predicting mechanical complications (AUC=0.592, p=0.078). Similarly, the original GAP score did not correlate with mechanical complications in DS patients. According to the C-GAP score, the sagittal parameters were proportional in 25 (21.9%) cases, moderately disproportional in 68 (59.6%), and severely disproportional in 21% (18.5%) cases. The incidence of mechanical complications was statistically different among proportioned and moderately disproportional and severely disproportional portions of the C-GAP score (P=0.03). The predictability of the C-GAP score is high with an AUC=0.773 (p<0.001). In addition, there is a linear correlation between mechanical complication rate and C-GAP score (χ=0.102, P=0.02). CONCLUSION The Ethnicity-adjusted C-GAP score system developed in the current study provided a more accurate and reliable for predicting the risk of mechanical complications after corrective surgery for degenerative scoliosis.