Abstract
Background Given the physical and economic burden of complications in spine surgery, reducing the prevalence of perioperative adverse events is a primary concern of both patients and health care professionals. This study aims to identify specific perioperative factors predictive of developing varying grades of postoperative complications in adult spinal deformity (ASD) patients, as assessed by the Clavien-Dindo complication classification (Cc) system.
Methods Surgical ASD patients ≥18 years were identified in the American College of Surgeons’ National Surgical Quality Improvement Program from 2005 to 2015. Postoperative complications were stratified by Cc grade severity: minor (I, II, and III) and severe (IV and V). Stepwise regression models generated dataset-specific predictive models for Cc groups. Model internal validation was achieved by bootstrapping and calculating the area under the curve (AUC) of the model. Significance was set at P < 0.05.
Results Included were 3936 patients (59 ± 16 years, 63% women, 29 ± 7 kg/m2) undergoing surgery for ASD (4.4 ± 4.7 levels, 71% posterior approach, 11% anterior, and 18% combined). Overall, 1% of cases were revisions, 39% of procedures involved decompression, 27% osteotomy, and 15% iliac fixation. Additionally, 66% of patients experienced at least 1 complication, 0% of which were Cc grade I, 51% II, 5% III, 43% IV, and 1% V. The final model predicting severe Cc (IV–V) complications yielded an AUC of 75.6% and included male sex, diabetes, increased operative time, central nervous system tumor, osteotomy, cigarette pack-years, anterior decompression, and anterior lumbar interbody fusion. Final models predicting specific Cc grades were created.
Conclusions Specific predictors of adverse events following ASD-corrective surgery varied for complications of different severities. Multivariate modeling showed smoking rate, osteotomy, diabetes, anterior lumbar interbody fusion, and higher operative time, among other factors, as predictive of severe complications, as classified by the Clavien-Dindo Cc system. These factors can help in the identification of high-risk patients and, consequently, improve preoperative patient counseling.
Clinical Relevance The findings of this study provide a foundation for identifying ASD patients at high risk of postoperative complications .
Level of Evidence 4.
Introduction
Adult spinal deformity (ASD) refers to a multitude of conditions that disrupts appropriate curvature and orientation of the spine in the adult. Diagnoses encompassed in the category of ASD include scoliosis, kyphosis, sagittal malalignment, axial plane deformity, and rotary subluxation. Spinal deformity can arise de novo—as in adult idiopathic scoliosis—as well as secondary to progressive asymmetric degeneration of spinal elements such as intervertebral discs and facet joints.1,2 Spinal alignment is critical in the maintenance of upright posture, stability of the axial skeleton, and protection of neural elements; when this is compromised, many deleterious sequelae present including deformity, axial pain, and neurologic symptoms, significantly affecting health-related quality of life as well as physical function.3–5 While there is no current consensus on the prevalence of adult scoliosis in the general population, with estimates ranging from 1.4% to 36%, a 2005 prospective study by Schwab et al found the prevalence in the elderly population to be 68%. These estimates put the number of patients in the United States with ASD conservatively at 27.5 million and, given the rapid growth of the elderly US population, this number is expected to reach 60 million by 2050.6,7
Surgical intervention is the recommended treatment for certain ASD patients whose symptoms progress despite nonoperative treatment. With advancements in technology, medical understanding, and surgical technique, adult deformity surgery outcomes and morbidity have improved in the past few decades, leading to corrective procedures becoming a more utilized treatment option.3,8 McCarty et al recently illustrated this in a study, revealing a 4-fold increase in the number of ASD surgeries for Medicare patients from 2000 to 2010.9 Despite these advances, postoperative complications remain significant, affecting both outcomes and cost of care, with some studies reporting complication rates as high as 86%.8 A 2011 systematic review concluded that elderly deformity surgery has a complication rate of 38%, and a 2007 study on 51 spinal deformity patients undergoing surgical treatment demonstrated 37% had perioperative complications with 20% of them classified as major complications, including myocardial infarction, pulmonary embolism, neurologic defect, pneumonia, and deep wound infection.10,11
Given the frequency, effect on outcome, and cost of complications in ASD surgery, greater understanding of factors predictive of complications is necessary to facilitate more effective care from a patient counseling, operative patient selection, surgical, and medical standpoint. Using the Clavien-Dindo grading system, validated for general surgery to classify perioperative complications, this study investigates the use of patient factors, comorbidities, and surgical variables in predicting complications and complication severity. It is our hope that by connecting factors with not just complication predictability but the severity of said complications, we are providing more clinical relevance to the data.
Methods
Data Source
The American College of Surgeons’ National Surgical Quality Improvement Program (ACS-NSQIP) database was used for analysis of perioperative factors in patients undergoing ASD-corrective surgery. NSQIP was developed by the US Department of Veterans Affairs with use of information from hospitals across the United States to track the outcome of risk-adjusted surgical interventions. The NSQIP tracks 135 clinical metrics, including preoperative risk factors, intraoperative variables, 30-day postoperative outcomes, current procedural terminology (CPT) coding, and International Classification of Disease 9th Edition (ICD-9) coding. Data are collected and audited by training surgical clinical reviewers from randomly assigned patients, which ensure the database’s standardization and reliability. Additional information regarding the ACS-NSQIP program can be found at https://www.facs.org/quality-programs/acs-nsqip/about.
Study Design
This is a retrospective analysis of ACS-NSQIP data from the years 2005 to 2015. The inclusion criteria were patients older than 18 years undergoing elective ASD-corrective surgery. An ASD population undergoing corrective surgery was isolated, as previously published.12 Patients with dyspnea, esophageal varices, do-not-resuscitate status, or a history of angina within 1 month before surgery; patients in a coma 24 hours prior to surgery, and patients who were pregnant were excluded. The CPT and ICD-9 codes used for inclusion and exclusion criteria are listed in Appendix A.
FIGURE S1.
Statistical Analysis
Primary analysis tracked postoperative complications stratified through the Clavien-Dindo complication classification system by severity. This classification was established as an objective, reliable, and reproducible system to define and grade postoperative complications. Through this system, complications are categorized into 5 grades. This study grouped patients by minor Clavien complications (groups I, II, and III) and severe (groups IV and V). An individual is categorized as a grade I complication when they deviate from the normal postoperative course. Grade II classification is assigned when the patient requires pharmacological treatment, and grade III entails surgical, endoscopic, or radiological intervention. Clavien grade IV involves life-threatening complications with intensive care/intensive care unit management, and Clavien V classification is used when the complication results in the death of the patient.13
Univariate analysis was performed using χ 2 tests for categorical variables and unpaired Student t tests for continuous variables. Multivariate analysis was performed using stepwise regression models to generate dataset-specific predictive models for Clavein-Dindo complication groups. Secondary analysis of model internal validation was achieved by bootstrapping and calculating the area under the curve (AUC) of the model. All statistical analysis was performed using SPSS version 23.0 (Armonk, NY, USA). A P value of less than 0.05 was considered statistically significant.
Results
Overall Cohort Characteristics
This study analyzed 3936 patients (mean age 59 ± 16 years, 63% women, mean body mass index [BMI] 29 ± 7 kg/m2) who underwent ASD-corrective surgery from 2005 to 2015 (Table 1). Overall, operations averaged 4.4 ± 4.7 levels fused, 0.49 ± 1.31 anterior fusion, and 3.87 ± 4.74 posterior fusion. Of the included operations, 31.22% involved insertion of an interbody device, 27.11% osteotomy, 3.91% anterior decompression, 35.82% posterior decompression, 15.65% iliac fixation, and 6.68% 3-column osteotomy. By approach, 12.40% of procedures were anterior only, 66.67% posterior only, and 13.59% combined (Table 2). Prior to surgery, 94.2% had an independent functional status, indicating no reliance on others for daily living, 4.70% were partially dependent, and 0.70% were totally dependent.
Patient demographic characteristics between minor Clavien complications and severe Clavien complications.
Patient procedural characteristics between severe and minor Clavien grades.
Clavien Grades and Demographics
A total of 2581 patients from the cohort suffered at least 1 complication, 0% of which were classified as a grade I Clavien complication. Also, 1304 (50.52%) experienced a grade II complication, 139 (5.39%) grade III, 1111 (43.04%) grade IV, and 27 (1.05%) grade V (Table 3). Across the Clavien groups, there was no significant difference in age, yet those who had complications categorized as severe Clavien were significantly more likely to be women (P < 0.001) and have a larger BMI (P = 0.011) compared with minor Clavien grades. Tables 4 and 5 show differences in demographics and preoperational blood protein levels. There was an increase in patients with a history of diabetes mellitus (P < 0.001), hemiplegia/paraplegia/quadriplegia (P < 0.05), a tumor involving the central nervous system (P < 0.001), and amputation for peripheral vascular disease (P < 0.001), with an increase in severity of Clavien grade. Also, there statistically significant findings for the severely classified groups for patients with a history of disseminated cancer (P = 0.016), those with an open wound/wound infection (P = 0.016), patients with a history of a percutaneous coronary intervention (P = 0.001), individuals with bleeding disorders (P < 0.001), and patients who underwent chemotherapy treatment for malignancy less than 30 days prior to surgery (P = 0.001). Patients categorized as severe Clavien had more cigarette pack-years (P < 0.001) and were found to consume alcohol more frequently (P = 0.027) than those with minor grades. Those patients categorized as a minor Clavien grade had a greater history of transient ischemic attacks (P = 0.003) and had undergone more blood transfusions less than 72 hours prior to the operation (P = 0.002). When comparing the blood protein levels preoperatively between each Clavien classification, prothrombin time (P = 0.021), serum albumin (P < 0.001), alkaline phosphatase (P = 0.009), blood urea nitrogen (P = 0.046), hematocrit (P < 0.001), and white blood cell count (P = 0.036) were all significant. The American Society of Anesthesiologists (ASA) classification across Clavien grades was significant (P < 0.001), where minor categorization coincided with an increased mild systemic disease (II) and those in severe Clavien groups had increased severe (IV) and life-threatening (V) systemic disease. Patients with severe Clavien complications had a higher overall postoperative length of stay in the hospital (P < 0.001).
Clavien complications from the total patient population.
Patient blood protein levels across Clavien grades.
Patient comorbidity characteristics across Clavien grades.
Procedural Factors as Predictors of Clavien Grade
Patients with severe Clavien complications had more anterior decompressions (P < 0.001), interbody device placements (P < 0.001), anterior lumbar fusion procedures (16.61% vs 8.87%, P < 0.001), 2–3 levels fused anteriorly (P = 0.005), as well as (P < 0.001) and 6 levels (P = 0.048) fused posteriorly. The patients classified with minor Clavien complications underwent more iliac fixations (P < 0.001) from 2005 to 2015, as well as osteotomies (P < 0.001) and 1 (P < 0.001), 4 to 7 (P = 0.001), and 8 or more anterior fused levels. Minor Clavien had significantly more 7 to 12 (P = 0.001) and 13+ (P < 0.001) posterior levels fused. By approach, severe Clavien-grouped patients underwent more anterior and combined approach procedures (P < 0.05), and minor Clavien complications had undergone more posterior approach operations, though the difference was not found to be significant (P = 0.156) (Table 2).
Predicting Complications
Specific predictors of Clavien grade II complications were increased age (OR, 1.038; 95% CI, 1.018–1.059), ASA score (OR, 0.656; 95% CI, 0.413–1.041), decreased preoperative hematocrit (OR, 0.955; 95% CI, 0.904–1.009), posterior lumbar interbody fusion (OR, 4.245; 95% CI, 2.236–8.060), lumbar fusion (OR, 0.541; 95% CI, 0.293–0.996), and increased operative time (OR, 1.003; 95% CI, 1.002–1.005), all resulting in an AUC of 74.9%. Clavien III classified perioperative complications had preoperative dialysis (OR, 23.966; 95% CI, 1.319–435.406) and increased operative time (OR, 1.003; 95% CI, 1–1.006) as predictors (AUC 70.2%). Multivariate modeling for Clavien grade IV predictors yielded an AUC of 92.8% and included anterior decompression (OR, 5.845; 95% CI, 2.018–16.933), lumbar fusion (OR, 0.006; 95% CI, 0.002–0.020), sepsis (OR, 895.786; 95% CI, 108.551–7392.236), and inpatient length of stay (OR, 1.071; 95% CI, 1.033–1.110). Grade V complications had specific predictors of hemiplegia and paraplegia, significant weight loss prior to surgery (OR, 49.773; 95% CI, 2.229–1111.401), and increased preoperative white blood cell count (OR, 1.505; 95% CI, 1.137–1.992) with an AUC of 77.4%. The final model also predicted severe Clavien complications combined (IV–V), yielding an AUC of 75.6%, and included female sex (OR, 0.029; 95% CI, 0.012–0.071), diabetes (OR, 3.122; 95% CI, 1.364–7.143), increased operative time (OR, 1.001; 95% CI, 1.000–1.003), central nervous system tumor (OR, 6.930; 95% CI, 1.677–28.640), osteotomy (OR, 1.847; 95% CI, 0.954–3.578), cigarette pack-years (OR, 1.015; 95% CI, 1.003–1.027), anterior fusion (OR, 3.508; 95% CI, 1.349–9.123), and anterior lumbar interbody fusion (OR, 2.286; 95% CI, 0.942–5.548) (Table 6).
Predictors of Clavien complications with AUC amounts.
Discussion
As the number of adult deformity surgeries continues to increase with the growth of an increasingly numerous and active elderly population, more thorough understanding of complications and their predictive factors is needed to ensure satisfactory outcomes as well as economic sustainability.1 Currently, complications status after corrective ASD surgery is a significant economic burden to both hospitals and patients.14 A 2016 study in the Journal of Neurosurgery demonstrated that ASD surgeries associated with a single complication can increase hospital charges from 1.7 to 4.3 times greater than those of patients without a complication. In the same study, inpatient charges increased by $108,387 to $313,536 for spine surgery cases complicated by deep vein thrombosis and by $127,958 to $246,637 for spine surgery cases complicated by pulmonary embolism.15 With respect to outcomes, major complications have been shown to have a significant effect on self-reported wellness as measured by the short form-12 general health subscale.14 Additionally, satisfaction scores have been demonstrated to negatively correlate with complications, further decreasing with increased complication severity.16
Previous investigations have elucidated risk factors for the development of complications in ASD surgery. These risk factors include age, extent of surgery, approach, and major intraoperative blood loss.17–19 A 2016 study specifically investigating risk factors for medical complications in ASD surgery found smoking, hypertension, heart disease, obesity (BMI >30), depression, duration of symptoms, ASA classification, and sex to be significant, with smoking, hypertension, and duration of symptoms identified as independent factors for the development of medical complications. The information on predictors of adverse events is comparatively sparse. A study on predictors of nonhome discharge in ASD surgery patients found the following factors to be significant: total relative value units, female sex, race, age ≥65 years, obesity, partially or totally functionally dependent, osteotomy, pelvis fixation, operation time ≥4 hours, recent weight loss, and ASA class ≥3. Additionally, poor long-term clinical outcomes in ASD surgical patients have been linked to predictors including BMI, severe preoperative disability, frailty, large preoperative sagittal vertical axis, and depression or anxiety.12,20–22
Our study utilized the Clavien-Dindo grading system in an effort to provide more clinical relevance to our findings by identifying complications in an evidence-based, standardized system, which grades complications by severity from I to V. By understanding which factors predict which grade of complications, more judicious preoperative counseling, patient selection, as well as surgical and medical treatment can be implemented. To our knowledge, this is the first study that has utilized a validated, standardized complication grading system to identify predictive factors for complications in ASD surgery utilizing data from a multicenter, national database.
With respect to demographic factors, age was found to be predictive of Clavien grade II complications. The fact that age is predictive of complications has been demonstrated consistently in the literature. That age was not found to be predictive of grade III, IV, V, or a combined category termed “severe” including grade IV and V complications, is a significant addition to ASD surgery understanding and is congruent with the growing body of evidence, suggesting that surgical correction of spine deformity in the elderly is more safe and appropriately indicated than was previous understood.1,3,8 Additionally, our analysis identified female sex as predictive of severe Clavien (IV and V) complications. This finding is echoed in the literature with many studies identifying female sex as a risk factor and salient predictor of complications in spine procedures as well as nonspine procedures, including higher rates of revision surgery and nonhome discharge.12,23,24
Clinically based factors were found to be predictive of complications across multiple Clavien complication classes. ASA score and decreased preoperative hematocrit were predictive of grade II complications, and current dialysis use at the time of surgery was predictive of grade III complications. Preoperative sepsis and inpatient length of stay were predictive of grade IV complications. Clinically based factors predictive of grade V complications included hemiplegia and paraplegia, preoperative weight loss >10% of body weight within 6 months, and elevated preoperative white blood cell count. Diabetes, tumor involving the central nervous system, and cigarette pack-years were significant predictors of developing a “severe” grade IV and/or V complication. Comorbidities are well established as increasing the risk of complications in corrective deformity surgery; our data bring about more complete understanding as specific comorbidities are shown to be predictive of not only the presence but also the severity of anticipated complications: findings that may have substantive impacts on preoperative counseling, patient selection, and overall outcomes.10,25,26
Surgical factors were also found to be salient predictors of the severity of complications. Time from incision start to finish, as well as total time in the OR, were significant across multiple Clavien grades. Operative time was predictive of grade II as well severe complications (grade IV and/or V). Time from incision open to close was predictive of grade III complications. Many previous investigations of complications in spine surgery have highlighted increased operative time as a risk factor. This variable is often reflective of surgical complexity and is associated with increased exposure to bacteria, among other deleterious effects.26–28 Grade IV and/or V complications, termed “severe,” were predicted by osteotomy, anterior fusion, anterior lumbar interbody fusion, as well as the aforementioned operative time. Osteotomies, including pedicle subtraction osteotomy and Smith-Peterson osteotomy, are very invasive procedures that involve removing bony segments of the spine in order to achieve correction of marked deformity. These procedures often involve extended procedural time as well as substantial blood loss and have been well described in the literature as associated with high complication rates.29–31 Interbody instrumentation, while allowing for surgical correction of degenerative discs, can lead to significant complications, each approach with its own constellation of benefits and drawbacks.30 The anterior vs posterior approach in deformity surgery remains a controversial topic with supportive literature on both sides.26,32,33 Our finding that anterior fusion and anterior lumbar interbody fusion are predictive of severe postoperative complications adds further information to this debate, and we hope for it to lead to more analysis and understanding.
As the elderly cohort of the US population continues to grow, the prevalence of ASD will follow, leading to an increase in corrective surgery. Advances have allowed for great strides in outcomes of ASD surgical patients, especially in the elderly, but postoperative complications remain significant and costly. This study identifies specific factors that accurately predict the presence and severity of complications in the postoperative period. This understanding provides surgeons with more knowledge to utilize with respect to patient selection, thorough preoperative counseling, and effective follow-up care, leading to higher patient satisfaction and better clinical outcomes.
Our analysis is limited by the fact that the NSQIP database is not designed specifically for spine patients—lacking imaging, procedural data, baseline clinical information, or a complete list of medical comorbidities or complications—rendering our analysis vulnerable to confounding variables we were unable to control for. Other limitations include the use of ICD-9 and CPT codes to isolate our surgical populations, which may diminish the acquisition of unbiased patient populations.
This study allowed us to identify predictors of complications stratified by severity. Multivariate analysis established cigarette pack-years, diabetes, female sex, operative time, tumor involving the central nervous system, osteotomy, anterior fusion, and anterior lumbar interbody fusion as predictive of severe complications (grade IV–V). Significantly, it did not identify age as predictive of grade III IV, or V complications. Neither did it find age to predictive of severe complications (grade IV–V). We believe the insights provided in this study will lead to more effective patient selection, counseling, and overall care.
Conclusion
Specific predictors of adverse events following ASD-corrective surgery varied with regard to the severity of the complication. Multivariate modeling showed smoking rate, osteotomy, diabetes, and higher operative time, among other factors, as predictive of severe complications, as classified by the Clavien-Dindo complication classification system. These factors can help in the identification of high-risk patients, and consequently, improve preoperative patient counseling and surgical patient selection.
Footnotes
Funding The authors received no financial support for the research, authorship, and/or publication of this article.
Declaration of Conflicting Interests The authors report no conflicts of interest in this work.
Disclosures Michael Gerling reports royalties from Integrity Implants; consulting fees from Integrity Implants, RTI Surgical, and Wolf Endoscopic; and a leadership role for AAOS and the Cervical Spine Research Society. Hamid Hassanzadeh reports consulting fees from DePuy, Medtronic, and Nuvasive; a leadership role with the Scoliosis Research Society; stock/stock options from 4Web and Nuvasive; research support from Medtronic, Orthofix Inc, and Pfizer; and paid presenter/speaker for Medtronic, Nuvasive, and Orthofix Inc. Peter G. Passias reports personal consulting fees for Medtronic, Royal Biologics, Spinewave, Zimmer Biomet, DePuy Synthes, Terumo, and Medicrea; paid presenter/speaker for Globus Medical; research support from the Cervical Scoliosis Research Society; leadership role for Spine, and other financial or material support from Cerabedics and Spinevision. The remaining authors have nothing to disclose.
Ethical Review Committee Statement Each institution obtained approval from their local Institutional Review Board to enroll patients in the prospective database and informed consent was obtained from each patient.
- This manuscript is generously published free of charge by ISASS, the International Society for the Advancement of Spine Surgery. Copyright © 2023 ISASS. To see more or order reprints or permissions, see http://ijssurgery.com.
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