Consecutive patients with ADS treated surgically at the Department of Orthopedics, Beijing Chaoyang Hospital, Capital Medical University (CMU), Beijing, China, from January 1, 2014, to December 31, 2017, were included in this retrospective cohort study. The inclusion criteria were 1) ADS treated by a posterior single approach, long-segment corrective surgery, 2) age > 50 years, 3) coronal Cobb’s angle > 30° and fusion levels > 3 motion segments, 4) integrated preoperative and follow-up radiographic data, 5) complete preoperative and follow up functional evaluation data, and 6) follow-up > 2 years. The exclusion criteria were 1) previous operation of the thoracolumbar spine, 2) other scoliosis types, including ankylosing spondylitis, spinal tuberculosis, adolescent idiopathic scoliosis progressed in adulthood, and neuromuscular and congenital scoliosis, 3) spinal tumors, or 4) revision of previous ADS surgery. The study was approved by the Ethics Committee of Beijing Chaoyang Hospital (The Third Affiliated Hospital of Capital Medical University). Informed consent was waived due to the retrospective nature of the study.
Frailty assessment and surgical data
Frailty was assessed by the modified frailty index (mFI) in all patients (Supplementary Table S1), based on data extracted from the electronic medical record system. The mFI included 11 items: history of diabetes mellitus, changes in daily activity, lung problems, history of congestive heart failure, history of myocardial infarction, history of percutaneous coronary intervention, cardiac surgery or angina, hypertension, peripheral vascular disease, clouding or delirium, transient ischemic attack, and cerebrovascular accident with deficit [15, 16]. The mFI is the proportion of the total number of items present in the patient’s preoperative history divided by 11 (i.e., the total number of items used in the assessment). Each item was given equal weight (scored 0 or 1) in the scoring of the index. Patients were identified as frail with an mFI score > 0.27. This cutoff point was based on previous reports [13, 17, 18]. After frailty assessment by the mFI scale, the patients were divided into the frailty and non-frailty groups. There were 47 (29.2%) in the frailty group and 114 (70.8%) in the non-frailty group.
Laboratory data, including albumin, total-cholesterol, creatinine, white blood cells, lymphocyte, hemoglobin and platelet, and surgical data, including operation duration, intraoperative blood loss, blood transfusion, fusion levels, decompression levels, and length of stay in hospital (LOS), were recorded. All the operations were performed by the same team and included posterior instrumentation, posterior column osteotomy, nerve decompression, and fusion.
Radiographic data included the Cobb angle of the curves and coronal vertical axis (CVA) in the coronal plane, pelvic incidence minus lumbar lordosis mismatch (PI-LL), and the sagittal vertical axis (SVA) in the sagittal plane. CVA was the distance between the C7 plumb line and the central sacral vertical line. Lumbar lordosis was reflected by the Cobb angle between the T12 upper endplate and the S1 endplate. Pelvic incidence was the angle between the perpendicular to the sacral plate and a line connecting the sacral plate’s center to the femoral head center. SVA was the distance between the C7 plumb and the sacrum’s posterior superior corner [19, 20]. All radiographic measurements were performed independently by two spinal surgeons to decrease intra-observer variability; the obtained values were averaged and used for analysis.
Complication assessment and health-related quality of life
The primary outcome was the major postoperative complications. Patients with cardiac complications, pneumonia, delirium, stroke, neurological deficit, deep wound infection, acute renal dysfunction, gastrointestinal adverse events, and deep vein thrombosis (DVT) or pulmonary embolism (PE) were recorded, according to the classification method reported by Glassman . Cardiac comorbidities included acute myocardial infarction, congestive heart failure, atrial fibrillation, and malignant arrhythmia. Gastrointestinal adverse events encompassed digestive tract hemorrhage and alimentary tract perforation. Acute renal failure refers to an increase in serum creatinine ≥26.5 μmol/L or > 1.5 times the baseline value within 48 h. The radiographic and HRQOL parameters were recorded preoperatively and at 2 years postoperatively.
Continuous variables, including age, BMI, fusion levels, decompression levels, and Oswestry disability index (ODI), Japanese Orthopedic Association scores (JOA), visual analog scale (VAS) for back pain, and Scoliosis Research Society-22 questionnaire (SRS-22) scores, are presented as means ± standard deviations (SDs) and were tested for normality using the Kolmogorov-Smirnov test. They were analyzed using the Student’s t-test or the Mann-Whitney U-test according to normality. Categorical data, such as sex and smoking, are presented as proportions and were analyzed using the chi-square and Fisher’s exact tests. Logistic analysis was performed to investigate the risk factors for complications. Major postoperative complications were recorded and described as proportions. Univariable and multivariable logistic regression analyses were carried out to investigate the possible association between frailty and major complications. The odds ratios (ORs) and 95% confidence intervals (CIs) were estimated after adjustment for each covariable in the univariable analyses. SPSS 22.0 (IBM Corp., Armonk, NY, USA) was used for data analysis. Two-tailed P < 0.05 was considered statistically significant.