Obesity has become a public health crisis and continues to be on the rise. An elevated body mass index has been linked to higher rates of spinal degenerative disease requiring surgical intervention. Limited studies exist that evaluate the effects of obesity on perioperative complications in patients undergoing anterior cervical discectomy and fusion (ACDF). Our study aims to determine the incidence of obesity in the ACDF population and the effects it may have on postoperative inpatient complications.
The National Inpatient Sample was evaluated from 2004 to 2014 and discharges with International Classification of Diseases procedure codes indicating ACDF were identified. This cohort was stratified into patients with diagnosis codes indicating obesity. Separate univariable followed by multivariable logistic regression analysis were performed for the likelihood of perioperative inpatient outcomes among the patients with obesity.
From 2004 to 2014, estimated 1,212,475 ACDFs were identified in which 9.2% of the patients were obese. The incidence of obesity amongst ACDF patients has risen dramatically during those years from 5.8% to 13.4%. Obese ACDF patients had higher inpatient likelihood of dysphagia, neurological, respiratory, and hematologic complications as well as pulmonary emboli, and intraoperative durotomy.
Obesity is a well-established modifiable comorbidity that leads to increased perioperative complications in various surgical specialties. We present one of the largest retrospective analyses evaluating the effects of obesity on inpatient complications following ACDF. Our data suggest that the number of obese patients undergoing ACDF is steadily increasing and had a higher inpatient likelihood of developing perioperative complications.
Anterior cervical discectomy and fusion (ACDF) is an effective surgical intervention often used to treat degenerative cervical spine pathology when more conservative methods fail to relieve symptoms [
Epidemiological literature has shown that patients with high body mass index (BMI) are amongst the most common populations to develop spine pathology [
An increased understanding of the effects of obesity on inpatient complications following ACDF would allow for improved patient selection and counseling and may ultimately lead to the circumvention of preventable perioperative complications. Our study aims to determine the incidence of obesity in the ACDF population and the effects it may have on postoperative inpatient complications.
The Nationwide Inpatient Sample (NIS) is the largest publicly available, all-payer, inpatient health care database in the United States (US) and is developed by the Healthcare Cost and Utilization Project (HCUP). The database contains a random subsample of 20% of US inpatient hospital records that represent an estimated 35 million annual discharges. The Elixhauser readmission and mortality indices are validated scoring systems that identify variables in the NIS correlated with overall patient health, mortality risk, and 30-day readmission risk [
The NIS was evaluated from 2004 to 2014 and discharges with International Classification of Diseases (ICD-9-CM) procedure codes indicating ACDF were identified (ICD-9-CM 80.51 and 81.02). This cohort was further stratified into patients with ICD9-CM diagnosis codes indicating obesity (278.0×), defined as a BMI of > 30.0kg/m2. Parameters including age, sex, frailty, obesity, weekend admission status, patient income, race, Elixhauser mortality/readmission indices, intraoperative monitoring, and number of fused levels were obtained and analyzed. Frailty, as defined in previous works, refers to patients with inpatient hypoalbuminemia and muscle weakness/fatigue [
Aggregate national estimates of yearly discharge frequencies were calculated utilizing weighted observations supplied by HCUP. For the years 2004–2011 and 2012–2014 the adjusted weights (TRENDWT) and normal weights (DISCWT) were utilized, respectively, to adjust for temporal database changes. Statistical analysis was performed with SAS 9.4 (SAS Institute Inc., Cary, NC, USA) utilizing the SURVEYMEANS, SURVEYLOGISTIC, SURVEYFREQ and SUVERYREG procedures that account for NIS stratified-cluster sampling methodology. NIS sampling is clustered by hospital identification (HOSPID) for all years and stratified by hospital region or hospital division for the years 2004–2011 and 2012–2014, respectively.
The normality of continuous variables was assessed graphically and statistically. Continuous variables with yearly nonparametric distributions were represented as yearly weighted median estimates; whereas, those with yearly normal distributions were represented as yearly weighted mean estimates. Comparisons of means/distributions of normally continuous variables were carried out using least squared means analysis; while, nonparametric distributions were compared with a modern extension of the Wilcoxon rank-sum test that adjusts for clustering, stratification, and weights [
Time trend series plots were created for the yearly incidence of ACDF-obesity patients. To yield a quantitative measurement of yearly distribution trends, yearly means/medians of continuous variables were assessed with univariable logistic regression, with year assessed separately as either a categorical or continuous variable. Separate univariable followed by multivariable logistic regression analysis were performed for the likelihood of the following dependent inpatient outcomes: inpatient mortality, neurological deficit, dysphagia, cardiac, respiratory, hematologic, gastrointestinal, or genitourinary complications, pulmonary embolus, wound infection, hardware failure, or durotomy. All available NIS hospital, patient, Elixhauser, and economic variables were utilized as covariates. Covariates that met a significance level of p < 0.2 in the univariable analysis were included in the multivariable analysis. A backwards multivariable logistic regression was performed and only variables that met significance were included in the final model. Only the results of obesity are displayed. p-values of ≤ 0.05 were considered statistically significant.
From 2004 to 2014, estimated 1,212,475 ACDFs were identified in the NIS. Of these discharges, 112,144 (9.2%) were obese.
Various ACDF complication rates and outcomes stratified by obesity status are displayed in
On separate multivariable analyses that adjusted for various patient, hospital, and operative covariates (
Obesity is an increasing global public health issue. The mean worldwide BMI has been increasing by 0.4–0.5 kg/m2 per decade since 1980 [
Prior studies have examined the association between BMI and outcomes in thoracic and lumbar spinal surgery [
Some authors argue that obesity does not impact surgical outcomes. Buerba et al. [
We found no statistically significant difference in surgical site infections (SSI) between obese and nonobese patients (
Incidence rates of dysphagia after ACDF vary in the literature from 1% to 79% [
Our study found that obesity portends an increased rate of durotomy during an ACDF procedure (0.49% vs. 0.23%; OR, 2.035; 95% CI, 1.652–2.508; p ≤ 0.0001). This is likely due to the increased thickness of the prevertebral tissue in obese patients that makes the approach and surgical manipulation more challenging. In a retrospective study of lumbar spine procedures, Burks et al. [
Screw/plate loosening and nonunion are rare but known complications in ACDF. Several factors may predispose patients to hardware failure, such as osteoporosis and multilevel fixation [
This study has several imitations. Firstly, the data from the NIS is dependent on proper ICD-9 coding which can have errors and consequently alter patient selection. To that end, it has been observed that the NIS underreports obesity [
In conclusion, obesity is a well-established modifiable comorbidity that leads to increased perioperative complications in various surgical specialties. We present one of the largest retrospective analyses evaluating the effects of obesity on inpatient complications following ACDF. The incidence of obesity amongst ACDF patients has risen dramatically. Obese ACDF patients had higher inpatient likelihood of dysphagia, neurological, respiratory, and hematologic complications as well as pulmonary emboli, and intraoperative durotomy.
The authors have nothing to disclose.
Anterior cervical discectomy and fusion (ACDF)-obesity incidence from 2004–2014.
Patient and procedural characteristics for anterior cervical discectomy and fusion stratified by obesity
Characteristic | Overall | Obese | Nonobese | p-value | |
---|---|---|---|---|---|
No. of patients | 1,212,475 | 112,144 (9.2) | 1,100,331 (90.8) | ||
Age (yr), mean ± SD | 52.9 ± 0.17 | 52.9 ± 0.17 | 52.9 ± 0.17 | 0.647 | |
Female sex† | 638,070 (52.6) | 65,147 (58.1) | 572,923 (52.1) | < 0.001 | |
Frail† | 7,238 (0.60) | 893 (0.80) | 6,345 (0.58) | < 0.001 | |
Diabetic† | 179,413 (14.8) | 35,242 (31.4) | 144,171 (13.1) | < 0.001 | |
Weekend admissions† | 20,304 (1.7) | 2,091 (1.9) | 18,212 (1.7) | 0.030 | |
Zip code income quartile‡ | n = 1,185,974 | < 0.001 | |||
$1–24,999 | 278,437 (23.5) | 27,326 (9.8) | 251,111 (90.2) | ||
$25,000–34,999 | 313,993 (26.5) | 30,088 (9.6) | 283,905 (90.4) | ||
$35,000–44,999 | 310,193 (26.2) | 28,628 (9.2) | 281,565 (90.8) | ||
$45,000 or more | 283,350 (23.9) | 23,931 (8.4) | 259,419 (91.6) | ||
Hospital region‡ | n = 1,212,476 | < 0.001 | |||
Northeast | 183,529 (15.1) | 14,880 (8.1) | 168,649 (91.9) | ||
Midwest | 268,381 (22.1) | 27,362 (10.2) | 241,019 (89.8) | ||
South | 534,186 (44.1) | 47,273 (8.8) | 486,913 (91.2) | ||
West | 226,379 (18.7) | 22,629 (10.0) | 203,750 (90.0) | ||
Patient race‡ | n = 975,627 | < 0.001 | |||
White | 818,560 (81.9) | 75,445 (9.2) | 743,115 (90.7) | ||
African American | 89,526 (9.0) | 11,074 (12.4) | 78,452 (87.6) | ||
Hispanic | 51,538 (5.2) | 5,336 (10.4) | 46,202 (89.6) | ||
Asian or Pacific Islander | 11,782 (1.2) | 450 (3.8) | 11,332 (96.2) | ||
Native American | 4,220 (0.4) | 382 (9.1) | 3,838 (90.9) | ||
Elixhauser mortality index, median (range) | -0.8 (-1.8 to -0.2) | -6.0 (-3.89 to -1.5) | -0.7 (-1.5 to -0.2) | < 0.001 | |
Elixhauser readmission index, median (range) | -0.2 (-0.8 to 6.0) | 1.4 (-3.6 to 6.4) | -0.2 (-0.8 to 6.0) | < 0.001 | |
Intraoperative monitoring | 88,209 (7.3) | 11,319 (10.9) | 76,890 (7.0) | < 0.001 | |
Academic hospital status | 62,5197 (51.8) | 61,563 (55.2) | 563,634 (51.5) | 0.0004 | |
No. of levels fused† | < 0.001 | ||||
One level | 31,879 (2.6) | 2,298 (2.0) | 29,581 (2.7) | ||
Two or three levels | 101,3712 (83.6) | 92,873 (82.8) | 920,839 (83.7) | ||
Four levels or more levels | 166,884 (13.8) | 16,973 (15.1) | 149,911 (13.6) |
Values are presented as number (column %† or row %‡) unless otherwise indicated.
SD, standard deviation.
Univariable logistic regression trends of obesity incidence in anterior cervical discectomy and fusion patients
2004 | 2006 | 2008 | 2010 | 2012 | 2014 | Yearly likelihood (OR) | p-value | |
---|---|---|---|---|---|---|---|---|
Overall | 5,787 (5.8) | 7,263 (6.8) | 8,963 (8.1) | 10,945 (9.6) | 12,665 (11.2) | 14,820 (13.4) | 1.11 | < 0.001 |
OR year (categorical) | Reference | 1.17 | 1.42 | 1.71 | 2.02 | 2.50 | - | < 0.001 |
OR, odds ratio.
Complications following anterior cervical discectomy and fusion stratified by obesity (n=1,212,475)
Variable | Overall | Obese | Nonobese | p-value |
---|---|---|---|---|
Inpatient mortality | 1,295 (0.11) | 125 (0.11) | 1,170 (0.11) | 0.8273 |
Neurological | 2,361 (0.19) | 313 (0.28) | 2,048 (0.19) | 0.0028 |
Dysphagia | 40,028 (3.3) | 4599 (4.1) | 35,430 (3.22) | < 0.001 |
Cardiac | 4,216 (0.34) | 541 (0.48) | 3,675 (0.33) | 0.0002 |
Respiratory | 21,416 (1.77) | 3,332 (2.97) | 18,084 (1.64) | < 0.001 |
Hematologic | 14,860 (1.22) | 2,035 (1.8) | 12,825 (1.17) | < 0.001 |
Gastrointestinal | 2,647 (0.22) | 211 (0.19) | 2,436 (0.22) | 0.3026 |
Genitourinary | 8,094 (0.67) | 986 (0.88) | 7,108 (0.64) | < 0.001 |
Pulmonary embolus | 1,731 (0.14) | 284 (0.25) | 1,447 (0.13) | < 0.001 |
Wound infection | 8,519 (0.70) | 940 (0.84) | 7,580 (0.69) | 0.0114 |
Hardware failure | 13,533 (1.11) | 1,082 (0.96) | 12,451 (1.23) | 0.0229 |
Durotomy | 3,102 (0.26) | 546 (0.49) | 2,556 (0.23) | < 0.001 |
Values are presented as number (%).
Adjusted effect of obesity on anterior cervical discectomy and fusion outcomes
Variable | OR | LL | UL | p-value |
---|---|---|---|---|
Inpatient mortality | - | - | - | NS |
Dysphagia | 1.121 | 1.032 | 1.218 | 0.0071 |
Neurological | 1.398 | 1.049 | 1.865 | 0.0224 |
Cardiac | - | - | - | NS |
Respiratory | 1.533 | 1.368 | 1.717 | < 0.001 |
Hematologic | 1.233 | 1.062 | 1.431 | 0.0058 |
Gastrointestinal | - | - | - | NS |
Genitourinary | - | - | - | NS |
Pulmonary embolus | 2.079 | 1.505 | 2.873 | < 0.001 |
Wound infection | - | - | - | NS |
Hardware failure | 0.788 | 0.676 | 0.918 | 0.0023 |
Durotomy | 2.035 | 1.652 | 2.508 | < 0.001 |
OR, odds ratio; UL, 95% confidence interval upper limit; LL, 95% confidence interval lower limit; NS, not significant.