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Bariatric surgery before elective posterior lumbar fusion is associated with reduced medical complications and infection
ARTICLE IN PRESS
The Spine Journal ■■ (2018) ■■–■■
Clinical Study
Bariatric surgery before elective posterior lumbar fusion is associated with reduced medical complications and infection Deeptee Jain, MD*, Sigurd H. Berven, MD, John Carter, MD, Alan L. Zhang, MD, Vedat Deviren, MD Department of Orthopaedic Surgery, University of California, 500 Parnassus Ave, MU West 321, Box 0728, San Francisco, CA 94143, USA Received 30 August 2017; revised 11 January 2018; accepted 19 January 2018
Abstract
BACKGROUND CONTEXT: Severely obese patients with operative spinal pathology present a challenge to the spine surgeon, given the increased complication risk. PURPOSE: We aimed to determine the impact of bariatric surgery (BS) on perioperative complications of posterior lumbar fusion. STUDY DESIGN: This is a retrospective cohort study. PATIENT SAMPLE: Patients undergoing posterior lumbar fusion surgery in the State Inpatient Databases of New York, Florida, North Carolina, Nebraska, Utah, and California comprised the patient sample. OUTCOMES: Thirty-day medical complications, surgical complications (nerve injury, infection, revision), death, readmission, and hospital length of stay (LOS) were the study’s outcomes. METHODS: We analyzed 156,517 patients using International Classification of Diseases, Ninth Revision codes. Patients were categorized into three groups: Group 1: history of BS and obesity, Group 2: severe obesity, body mass index (BMI)>40 (severely obese), and Group 3: normal weight, BMI<25 (non-obese). Logistic and linear multivariate regressions were performed to compare complications and LOS, respectively, between BS and severely obese groups and BS and non-obese groups while controlling for confounders. There were no sources of funding for this study. RESULTS: There were 590 patients with BS, 5,791 severely obese, and 150,136 non-obese. Comparing BS with severely obese, BS had significantly lower rates of respiratory failure (odds ratio [OR] 0.59, p=.019), urinary tract infection (OR 0.64, p=.031), acute renal failure (OR 0.39, p=.007), overall medical complications (OR 0.59, p<.001), and infection (OR 0.65, p=.025). Bariatric surgery also had significantly lower hospital LOS (B=−0.46, p=.01). Comparing BS with non-obese, there were no significant differences in medical complications; however, BS had significantly higher rates of infection (OR 2.70, p<.001), reoperation (OR 2.05, p=.045), and readmission (OR 1.89, p<.001). CONCLUSION: Bariatric surgery before elective posterior lumbar fusion mitigates risk of medical complications and infection. However, these patients still have increased risk of infection, revision surgery, and readmission compared with patients with normal BMI. Surgeons might consider referral for BS for the severely obese patient before undergoing spine surgery. © 2018 Elsevier Inc. All rights reserved.
Keywords:
Bariatric surgery; Lumbar fusion; Obese; Readmission; Revision; Surgical site infection
FDA device/drug status: Not applicable. Author disclosures: DJ: Nothing to disclose. SB: Royalties: Medtronic (G); Stock Ownership: Baxano (A), Providence Medical (A); Consulting: Medtronic (E), Stryker (D), Globus (B), RTI (B); Research Support (Investigator Salary, Staff/Materials): AOSpine, NSF, and NIH (B, staff); Fellowship Support: NuVasive (D, Paid directly to institution/employer), AOSpine (E, Paid directly to institution/employer), Globus (E, Paid directly to institution/ employer), outside the submitted work. JC: Nothing to disclose. ALZ: Nothing to disclose. VD: Royalties: NuVasive (G), Consulting: NuVasive (C), https://doi.org/10.1016/j.spinee.2018.01.023 1529-9430/© 2018 Elsevier Inc. All rights reserved.
Guidepoint (A), Medicrea (A), BIOMET (A); Fellowship Support: NuVasive (D), Globus (E), AOSpine (E), outside the submitted work. The disclosure key can be found on the Table of Contents and at www.TheSpineJournalOnline.com. There were no sources of funding for this work. * Corresponding author. Department of Orthopaedic Surgery, University of California, 500 Parnassus Ave, MU West 321, Box 0728, San Francisco, CA 94143. Tel.: (1) 415-4761166; fax: (1) 415-4761304. E-mail address: [email protected] (D. Jain)
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Introduction Obesity is becoming increasingly prevalent in the United States, affecting an estimated 35% of the population [1]. Obesity, according to the World Health Organization, is defined by body mass index (BMI): overweight is BMI>25 kg/m2, obese is BMI >30 kg/m2, and morbid (severe) obesity is BMI>40 kg/m2 [2]. Obese patients are more likely to have disc degeneration and low back pain [3]. Not surprisingly therefore, a large percentage (80%) of patients undergoing spine surgery are either overweight or obese [4,5]. As the prevalence of obesity has increased, so has the use of bariatric surgery (BS), with 220,000 procedures performed in the United States and Canada in 2008 [6]. Bariatric surgery (BS) is indicated in patients with BMI>40, or BMI>35 with obesity-related complications, and leads to substantial decreases in BMI, on average 10–15 points of BMI [7,8]. In addition, BS also results in improvement of other obesityrelated comorbidities, such as type II diabetes mellitus, hypertension, and cardiovascular disease [9,10]. Multiple studies have demonstrated that obese patients undergoing spine surgery have greater blood loss, longer operative times, and higher rates of surgical site infection, revision rates, and mortality compared with non-obese patients [11,12]. Bariatric surgery before spine surgery may mitigate these risks. However, endocrine literature suggests that there may be detrimental effects of BS on nutritional status and bone density [13–16]. The purpose of this study was to determine the impact of BS on postoperative medical and surgical complications in patients undergoing lumbar spine fusion. In this database study, we examined patients undergoing posterior lumbar fusion, and compared patients who had a previous history of BS with those who were severely obese but with no history of BS and those who were non-obese. We hypothesized that patients with a history of BS would have lower complication rates than their obese counterparts. Methods This was a retrospective cohort study of patients undergoing posterior lumbar fusion. There were no sources of funding for this study. Data sample Administrative claims from the State Inpatient Databases (SID) were analyzed. The SID is the largest all-payer inpatient database in the United States; it contains all of each state’s hospital inpatient discharge records. Each patient is assigned a unique identification number, which can then be tracked across time points and different hospitals, thus allowing subsequent readmissions to be linked to the indexed admission. Complete data in SID were available for Florida, New York, Nebraska, and Utah from 2006 to 2010, and California from 2006 to 2011. These states represent an ethnically
and socioeconomically diverse group of patients and include approximately one-third of the US population [17]. Inclusion-exclusion criteria All patients age >18 who underwent posterior lumbar fusion were included in the study. These patients were identified using International Classification of Diseases, Ninth Revision (ICD9) procedure codes 81.07 and 81.08. Patients who underwent revision surgery (ICD-9 codes 81.34–81.38) or anterior fusion (ICD-9 code 81.06) were excluded. Patients with ICD-9 diagnosis codes for bone cancer or metastases, infection, and trauma were excluded (Supplementary Table S1). Patients were then subdivided into three groups. Group 1 (BS—experimental group) included patients with a history of BS and a diagnosis of obesity; they were identified based on the presence of ICD-9 codes for BS in conjunction with ICD-9 codes for obesity. Bariatric surgery is indicated in patients with BMI>40 or BMI>35 with obesity-related comorbidities; thus it can be inferred that patients who underwent BS met these criteria at the time of BS. There were two control groups. Group 2 (severely obese—control group) included severely obese patients; they were identified based on ICD-9 codes for BMI>40 or morbid obesity with no codes for BS. Group 3 (non-obese—control group) included non-obese patients with no history of BS. These consisted of the remaining patients with no codes for obesity or BS. Thus, patients with codes for obesity or BMI>30, but no codes for morbid obesity or BMI>40 or BS, and patients with codes for BS, but no codes for obesity, were excluded (Supplementary Table S2). To ensure a minimum 30-day follow-up, patients who underwent surgery the last quarter of the dataset were excluded. Patient characteristics and outcomes Data were queried for demographic data including age and gender. Data were queried for 17 medical comorbidities that can be used to calculate a modified Charlson Comorbidity Index (CCI) score, as described previously [18]. Data were then queried for 30-day medical complications. Major medical complications included pulmonary embolism, deep vein thrombosis, acute myocardial infection, respiratory failure, and cerebrovascular accident. Minor complications included urinary tract infection, pneumonia, acute renal failure, and postoperative blood transfusion. Data were queried for surgical complications: intraoperative complications included dural tear and death, and 30-day complications included nerve injury, infection, death, revision, and reoperation (Supplementary Table S3). Data were also queried for hospital length of stay (LOS). Statistical analysis Demographics, preoperative comorbidities, complications, and LOS were described using the mean and standard deviation for continuous variables and percentages for binary
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variables. Demographics and preoperative comorbidities were compared using analysis of variance for continuous variables (age, CCI) and chi-squared for categorical variables (gender). Each complication and LOS was compared between both BS and obese groups and BS and non-obese groups. Logistic multivariate regression analyses were performed to compare complication rates, controlling for age, gender, and CCI. Results are presented as odds ratio (OR), confidence interval (CI), and p-value. Linear multivariate regression was performed to compare LOS between groups, controlling for the same confounders. Results are presented as coefficient (B) and p-value. Additionally, a subgroup analysis was performed in the severely obese group to determine risk factors for 30-day infection, revision, and readmission. Logistic multivariate models were created with demographic variables, including age, gender, and each comorbidity, and dural tear and LOS. Results are presented as OR, CI, and p-value. All analyses were performed using Stata v14 (StataCorp, College Station, TX, USA). Results There were 196,680 patients identified who underwent posterior lumbar spine fusion that met inclusion-exclusion criteria. After patients were divided into the three study groups, there were 180,425 patients remaining. After the last-quarter patients were excluded, there were a total of 176,256 patients remaining. After patients who underwent anterior surgery were excluded, there were 156,517 patients remaining who were included in the final analysis. There were 590 patients in the BS group, 5,791 in the severely obese group, and 150,136 in the non-obese group. Average age was 53.9, 56.3, and 57.9 years, respectively; this was significantly different between groups (F (2, 156,415)=47.2, p=<.001). Percent female was 74.6, 65.6, and 54.8%, respectively; this was significantly different between groups (chi-sqaure=349.0, p<.001). Average CCI was 0.70, 0.95, and 0.51 respectively; this was significantly different between groups (F (2, 156,514)=691.0, p=<.001) (Table 1). Comparing BS with severely obese, BS had significantly lower rates of respiratory failure (OR 0.59, p=.019), urinary tract infection (OR 0.64, p=.031), acute renal failure (OR 0.39, p=.007), overall medical complications (OR 0.59, p<.001), and infection (OR 0.65, p=.025). There were no significant differences found among all other complications (Tables 2 and 3). Bariatric surgery also had significantly lower LOS (BS: 4.51±3.81 vs. severely obese: 5.19±4.31 days, B=−0.46, standard error=0.18, p=.01). Comparing BS with non-obese, there were no significant differences in medical complications; however, BS had significantly higher rates of infection (OR 2.70, p<.001), reoperation (OR 2.05, p=.045), and readmission (OR 1.89, p<.001) (Tables 2 and 3). There was no significant difference in LOS (BS: 4.51±3.81 vs. non-obese: 4.30±3.34 days, B=0.08, standard error=0.14, p=.55).
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Table 1 Patient demographics and preoperative comorbidities
Age (y) Female (%) AIDS/HIV (%) Metastatic solid tumor (%) Moderate to severe liver disease (%) Any malignancy except skin (%) Hemiplegia or paraplegia (%) Renal disease (%) Diabetes with chronic comp (%) Cerebrovascular disease (%) Chronic pulmonary disease (%) Congestive heart failure (%) Dementia (%) Diabetes without chronic comp (%) Mild liver disease (%) Myocardial infarction (%) Peptic ulcer disease (%) Peripheral vascular disease (%) Rheumatic disease (%) Charlson Comorbidity Index
BS (n=590)
Severely obese (n=5,791)
Non-obese (n=150,136)
53.9 74.6 0.00 0.00 0.00 1.02 1.86 2.71 1.19 0.85 21.53 1.69 0.17 21.19 1.53 2.71 1.86 1.69 3.22 0.70
56.3 65.6 0.03 0.07 0.03 0.64 2.49 4.44 3.68 1.40 22.78 4.42 0.07 31.31 1.42 4.02 0.73 2.66 3.21 0.95
57.9 54.8 0.05 0.03 0.03 0.10 1.50 1.97 1.07 1.32 13.66 1.88 0.19 13.30 1.03 3.25 0.55 2.11 2.82 0.51
BS, bariatric surgery.
In the subgroup analysis of severely obese patients, significant risk factors for complications were as follows: hemiplegia, diabetes with chronic complications, rheumatic disease, female gender, and LOS for 30-day infection; diabetes with and without chronic complications, history of myocardial infarction, peptic ulcer disease, age>65, female gender, and LOS for 30 day readmission; and age>65 and female gender for 30-day revision (Table 4). Discussion It is well established that obesity is associated with increased rates of medical complications and infection after lumbar spine surgery, and this risk is further increased by severe obesity [4,19–22]. Thus, managing severely obese patients with operative spinal pathology can be challenging. In this database study, we demonstrated that patients who underwent BS before posterior lumbar spine fusion had lower rates of medical complications and infection, as well as shorter hospital LOS, compared with severely obese patients. Nonetheless, patients with BS still had higher rates of infection, reoperation, and readmission compared with non-obese patients without a history of BS surgery. The present study is the first to examine the impact of BS on complications of lumbar spine surgery and provides important insight on how best to preoperatively optimize severely obese patients with spinal pathology. Although there are no previous studies examining the influence of BS on complications after spine surgery, we can extrapolate from the total joint arthroplasty literature, which shows mixed results. Some studies demonstrate decreased risk of complications in patients with BS compared with severely
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4 Table 2 Thirty-day medical complications
BS: severely obese
Pulmonary embolism DVT Acute myocardial infarction Respiratory failure Cerebrovascular accident UTI Pneumonia Acute renal failure Postop blood transfusion Any medical complication
BS: non-obese
BS
Obese
Non-obese
OR
CI
p-Value
OR
CI
p-Value
0.17 0.34 0.51 3.73 0.17 4.41 0.17 1.53 0.17 9.83
0.83 0.66 0.79 6.92 0.54 7.37 0.17 5.04 0.02 17.61
0.37 0.33 0.40 3.42 0.55 3.46 0.12 1.30 0.02 8.36
0.24 0.62 1.11 0.59 0.52 0.64 1.41 0.39 8.33 0.59
[0.03–1.69] [0.15–2.70] [0.33–3.70] [0.38–0.92] [0.07–4.00] [0.42–0.96] [0.18–11.36] [0.20–0.78] [0.50–142.9] [0.44–0.79]
.15 .51 .87 .019 .527 .031 .75 .007 .141 <.001
0.53 1.30 1.72 1.09 0.40 1.33 1.49 1.56 9.43 1.22
[0.07–3.85] [0.32–5.26] [0.53–5.56] [0.71–1.69] [0.06–2.86] [0.89–1.75] [0.21–10.75] [0.79–3.13] [1.26–71.43] [0.93–1.61]
.52 .73 .37 .69 .36 .17 .69 .21 .029 .17
BS, bariatric surgery; CI, confidence interval; DVT, deep vein thrombosis; OR, odds ratio; UTI, urinary tract infection. p-Value in bold indicates statistical significance.
obese patients [22], whereas other studies demonstrate no difference [23,24]. Although useful as a starting point, posterior lumbar spine surgery has its own risk profile of medical and surgical complications. Not only does the present study suggest that BS mitigates complications after lumbar spine surgery, but previous studies suggest that it might obviate the need for surgery at all by improving symptoms preoperatively. In a study of 58 severely obese patients who underwent BS, Khoueir et al. demonstrated significant improvements in back pain and backrelated function after BS [25]. In another study of 30 severely obese patients who underwent BS, Lidar et al. demonstrated improvement in back and leg pain, as well as radiographic evidence of increased disc height [26]. These findings further support the recommendation for consideration of BS before lumbar spine fusion. These results must be approached with caution; they should not be interpreted as to suggest that severely obese patients should not undergo spine surgery. In fact, multiple studies have demonstrated significant clinical improvement, albeit with increased risk of complication, in obese and severely obese patients undergoing lumbar spine surgery [27–29]. In subgroup analyses of the Spine Patient Outcomes Research Trials, authors showed that obese and severely obese patients had greater treatment effects of surgery compared with their
non-obese counterparts; this was attributed primarily to poor outcomes with nonoperative care in obese and severely obese patients. Furthermore, these results also should not be interpreted to suggest that every morbidly obese should undergo BS before undergoing elective spine surgery. Initial weight management strategies should be employed before undergoing BS, centered on diet modification. In fact, indications for BS require 6 months of failed attempts at nonoperative weight loss. Nonetheless, the present study provides insight into preoperative optimization, via one option, BS. There exist concerns regarding nutritional status and bone quality after BS; patients with BS have low hydroxyproline, which is important for wound healing; low vitamin B12, D, and E; and loss of bone mineral density (BMD) [13–16]. Despite these consequences, for posterior lumbar spine fusion, it appears that in the short term at least, the benefits of improvement in medical comorbidities outweigh the risks. It remains to be seen what the long-term consequences are, for example on fusion rates or the longevity of the construct. Furthermore, the timing of BS before spine surgery was not addressed in this study as it was not available with this dataset. Although BMD has been shown to be substantially reduced up to 5 years after BS, it is possible that most of the nutritional deficits and decrease in BMD would be most severe in the first 2 years. This might be an area of future research.
Table 3 Surgical complications BS: severely obese BS Intraoperative Death 0.17 Dural tear 2.54 30-d Complications Nerve injury 4.41 Infection 39.15 Death 0.17 Revision 1.36 Readmission 10.51
Obese
BS: non-obese
Non-obese
OR
CI
p-Value
OR
CI
0.26 2.43
0.12 1.77
0.93 1.08
[0.12–7.14] [0.63–1.85]
.94 .80
2.17 1.67
[0.30–15.6] [0.98–2.76]
.45 .057
3.99 8.27 0.45 2.30 13.69
3.90 0.22 0.20 0.66 6.22
1.11 0.65 0.53 0.58 0.80
[0.74–1.69] [0.45–0.95] [0.07–4.00] [0.28–1.20] [0.61–1.05]
.60 .025 .53 .15 .11
1.14 2.70 1.27 2.05 1.89
[0.76–1.69] [1.89–4.00] [0.18–9.09] [1.02–4.17] [1.33–2.44]
.52 <.001 .82 .045 <.001
BS, bariatric surgery; CI, confidence interval; OR, odds ratio. p-Value in bold indicates statistical significance.
p-Value
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Table 4 Risk factors for 30-day infection, readmission, and reoperation in severely obese patients Infection
Age>65 Female AIDS/HIV Metastatic solid tumor Moderate to severe liver disease Any malignancy except skin Hemiplegia or paraplegia Renal disease Diabetes with chronic comp Cerebrovascular disease Chronic pulmonary disease Congestive heart failure Dementia Diabetes without chronic comp Mild liver disease Myocardial infarction Peptic ulcer disease Peripheral vascular disease Rheumatic disease Dural tear LOS
Readmission
OR
CI
p
OR
1.01 1.6 1 1 1 0.7 1.6 0.12 1.56 1.33 0.95 0.88 2.69 1.17 1.27 0.98 1.62 0.65 1.66 1.26 1.09
[0.99–1.01] [1.28–2.00]
.151 <.001
1.65 1.36 8.52 1.37 1 0.64 1.27 1.36 1.51 1.22 1.05 1.18 1.35 1.27 1.32 1.49 2.4 0.89 1.39 1.15 1.02
[0.21–2.25] [1.04–2.68] [0.81–1.8] [1.00–2.43] [0.67–2.63] [0.75–1.19] [0.57–1.37] [0.25–28.00] [0.95–1.44] [0.62–2.61] [0.60–1.61] [0.64–4.08] [0.34–1.27] [1.07–2.56] [0.73–2.17] [1.07–1.11]
.55 .034 .33 .049 .406 .67 .58 .41 .13 .49 .96 .30 .22 .021 .73 <.001
CI
Reoperation p
OR
CI
p
[1.41–1.95] [1.15–1.61] [0.52–139.9] [0.13–13.8]
<.001 <.001 .13 .78
[1.15–2.4] [1.12–2.56]
.007 .013
[0.86–101.3]
.066
[0.24–1.70] [0.92–1.97] [0.98–1.89] [1.05–2.16] [0.70–2.15] [0.88–1.25] [0.85–1.65] [0.13–13.65] [1.08–1.49] [0.73–2.39] [1.06–2.09] [1.21–4.80] [0.56–1.40] [0.95–2.04] [0.72–1.82] [1.004–1.03]
.37 .28 .061 .024 .47 .56 .32 .79 .004 .35 .02 .013 .62 .083 .55 .01
1.66 1.69 1 9.34 1 1.78 0.57 1.35 0.45 0.95 1.05 1.03 1 0.82 1.81 1.27 1.68 1.09 1.52 1.82 1.01
[0.37–8.43] [0.14–2.39] [0.64–2.91] [0.14–1.48] [0.23–3.98] [0.70–1.57] [0.45–2.32]
.46 .45 .43 .19 .94 .81 .94
[0.55–1.21] [0.56–5.86] [0.56–2.83] [0.36–7.82] [0.39–3.06] [0.70–3.34] [0.78–4.22] [0.97–1.04]
.32 .32 .56 .51 .86 .29 .16 .73
CI, confidence interval; LOS, length of stay; OR, odds ratio. p-Value in bold indicates statistical significance.
The subgroup analysis provides important insight into predictors of infection, readmission, and revision surgery specifically in severely obese patients. This is the first study to examine risk factors for complications in this patient population. Medical comorbidities in general, and especially diabetes, have been previously shown to increase the risk of infection and overall readmission in the general patient population [30–32]. Not surprisingly, this finding is consistent in severely obese patients. Finally, this study also speaks to a larger context of preoperative optimization regarding nutritional status. Unfortunately, there is quite limited literature on the subject. Both severely obese patients and patients with post-BS suffer from metabolic syndromes. Either way, it is the authors’ opinion that if a nutritional disorder is suspect, a full nutritional workup is warranted, which include laboratory studies such as total lymphocyte count and serum albumin. These have been linked to surgical site infection after spine surgery, although there is no evidence that nutritional optimization improves outcomes [33,34]. The limitations of this study include those suffered by any administrative claims database study. Primarily, these data are subject to errors in coding and billing. It is difficult to collect the true complexity of the patient in administrative claims; they often underreport both preoperative comorbidities and postoperative complications [35,36]. Discrepancies in rates of postoperative complications after lumbar spine fusion between the Healthcare Cost and Utilization Project and other national databases such as the National Surgery Quality Improvement Program highlight these challenges [37].
Furthermore, these data do not account for differences in instrumentation or technique for surgery. Such errors have the potential to influence the analyses. Finally, the dataset does not provide precise BMI information, and thus we do not know the BMI for the experimental group nor the control groups at the time of the index spine surgery. It would be interesting in a future study to examine the relationship between the amount of weight loss and complications. In summary, despite these limitations, with a large sample of patients, we demonstrated that patients who undergo BS before lumbar spine have significantly lower rates of medical complications and infections than their severely obese counterparts; however, they still have significantly higher rates of infection, revision, and readmission than their non-obese counterparts. This information suggests that for severely obese patients presenting for lumbar spine fusion, surgeons should consider referral for BS for preoperative optimization, but still must council patients that the risks will not be normalized to that of non-obese patients. Supplementary material Supplementary material related to this article can be found at https://doi.org/10.1016/j.spinee.2018.01.023. References [1] Flegal KM, Carroll MD, Kit BK, Ogden CL. Prevalence of obesity and trends in the distribution of body mass index among US adults, 1999–2010. JAMA 2012;307:491–7.
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[22] Buerba RA, Fu MC, Gruskay JA, Long WD, Grauer JN. Obese class III patients at significantly greater risk of multiple complications after lumbar surgery: an analysis of 10,387 patients in the ACS NSQIP database. Spine J 2014;14:2008–18. [23] Inacio MC, Paxton EW, Fisher D, Li RA, Barber TC, Singh JA. Bariatric surgery prior to total joint arthroplasty may not provide dramatic improvements in post-arthroplasty surgical outcomes. J Arthroplasty 2014;29:1359–64. [24] Nickel BT, Klement MR, Penrose CT, Green CL, Seyler TM, Bolognesi MP. Lingering risk: bariatric surgery before total knee arthroplasty. J Arthroplasty 2016;31:207–11. [25] Khoueir P, Black MH, Crookes PF, Kaufman HS, Katkhouda N, Wang MY. Prospective assessment of axial back pain symptoms before and after bariatric weight reduction surgery. Spine J 2009;9:454– 63. [26] Lidar Z, Behrbalk E, Regev GJ, et al. Intervertebral disc height changes after weight reduction in morbidly obese patients and its effect on quality of life and radicular and low back pain. Spine 2012;37:1947– 52. [27] Rihn JA, Radcliff K, Hilibrand AS, et al. Does obesity affect outcomes of treatment for lumbar stenosis and degenerative spondylolisthesis? Analysis of the Spine Patient Outcomes Research Trial (SPORT). Spine 2012;37:1933. [28] Soroceanu A, Burton DC, Diebo BG, et al. Impact of obesity on complications, infection, and patient-reported outcomes in adult spinal deformity surgery. J Neurosurg Spine 2015;23:656–64. [29] McGuire KJ, Khaleel MA, Rihn JA, Lurie JD, Zhao W, Weinstein JN. The effect of extreme obesity on outcomes of treatment for lumbar spinal conditions: subgroup analysis of the Spine Patient Outcomes Research Trial (SPORT). Spine 2014;39:1975. [30] Caputo AM, Dobbertien RP, Ferranti JM, Brown CR, Michael KW, Richardson WJ. Risk factors for infection after orthopaedic spine surgery at a high-volume institution. J Surg Orthop Adv 2012;22:295– 8. [31] Schuster JM, Rechtine G, Norvell DC, Dettori JR. The influence of perioperative risk factors and therapeutic interventions on infection rates after spine surgery: a systematic review. Spine 2010;35(9S):S125– 37. [32] Lee NJ, Kothari P, Phan K, et al. The incidence and risk factors for 30-day unplanned readmissions after elective posterior lumbar fusion. Spine 2018;43:41–8. [33] Watanabe M, Sakai D, Matsuyama D, Yamamoto Y, Sato M, Mochida J. Risk factors for surgical site infection following spine surgery: efficacy of intraoperative saline irrigation: clinical article. J Neurosurg Spine 2010;12:540–6. [34] Sponseller PD, LaPorte DM, Hungerford MW, Eck K, Bridwell KH, Lenke LG. Deep wound infections after neuromuscular scoliosis surgery: a multicenter study of risk factors and treatment outcomes. Spine 2000;25:2461–6. [35] Quan H, Parsons GA, Ghali WA. Validity of information on comorbidity derived from ICD-9-CCM administrative data. Med Care 2002;40:675– 85. [36] Lawson EH, Louie R, Zingmond DS, et al. A comparison of clinical registry versus administrative claims data for reporting of 30-day surgical complications. Ann Surg 2012;256:973–81. [37] Bohl DD, Russo GS, Basques BA, et al. Variations in data collection methods between national databases affect study results: a comparison of the nationwide inpatient sample and national surgical quality improvement program databases for lumbar spine fusion procedures. J Bone Joint Surg Am 2014;96:e193.
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Clinical Study
Bariatric surgery before elective posterior lumbar fusion is associated with reduced medical complications and infection Deeptee Jain, MD*, Sigurd H. Berven, MD, John Carter, MD, Alan L. Zhang, MD, Vedat Deviren, MD Department of Orthopaedic Surgery, University of California, 500 Parnassus Ave, MU West 321, Box 0728, San Francisco, CA 94143, USA Received 30 August 2017; revised 11 January 2018; accepted 19 January 2018
Abstract
BACKGROUND CONTEXT: Severely obese patients with operative spinal pathology present a challenge to the spine surgeon, given the increased complication risk. PURPOSE: We aimed to determine the impact of bariatric surgery (BS) on perioperative complications of posterior lumbar fusion. STUDY DESIGN: This is a retrospective cohort study. PATIENT SAMPLE: Patients undergoing posterior lumbar fusion surgery in the State Inpatient Databases of New York, Florida, North Carolina, Nebraska, Utah, and California comprised the patient sample. OUTCOMES: Thirty-day medical complications, surgical complications (nerve injury, infection, revision), death, readmission, and hospital length of stay (LOS) were the study’s outcomes. METHODS: We analyzed 156,517 patients using International Classification of Diseases, Ninth Revision codes. Patients were categorized into three groups: Group 1: history of BS and obesity, Group 2: severe obesity, body mass index (BMI)>40 (severely obese), and Group 3: normal weight, BMI<25 (non-obese). Logistic and linear multivariate regressions were performed to compare complications and LOS, respectively, between BS and severely obese groups and BS and non-obese groups while controlling for confounders. There were no sources of funding for this study. RESULTS: There were 590 patients with BS, 5,791 severely obese, and 150,136 non-obese. Comparing BS with severely obese, BS had significantly lower rates of respiratory failure (odds ratio [OR] 0.59, p=.019), urinary tract infection (OR 0.64, p=.031), acute renal failure (OR 0.39, p=.007), overall medical complications (OR 0.59, p<.001), and infection (OR 0.65, p=.025). Bariatric surgery also had significantly lower hospital LOS (B=−0.46, p=.01). Comparing BS with non-obese, there were no significant differences in medical complications; however, BS had significantly higher rates of infection (OR 2.70, p<.001), reoperation (OR 2.05, p=.045), and readmission (OR 1.89, p<.001). CONCLUSION: Bariatric surgery before elective posterior lumbar fusion mitigates risk of medical complications and infection. However, these patients still have increased risk of infection, revision surgery, and readmission compared with patients with normal BMI. Surgeons might consider referral for BS for the severely obese patient before undergoing spine surgery. © 2018 Elsevier Inc. All rights reserved.
Keywords:
Bariatric surgery; Lumbar fusion; Obese; Readmission; Revision; Surgical site infection
FDA device/drug status: Not applicable. Author disclosures: DJ: Nothing to disclose. SB: Royalties: Medtronic (G); Stock Ownership: Baxano (A), Providence Medical (A); Consulting: Medtronic (E), Stryker (D), Globus (B), RTI (B); Research Support (Investigator Salary, Staff/Materials): AOSpine, NSF, and NIH (B, staff); Fellowship Support: NuVasive (D, Paid directly to institution/employer), AOSpine (E, Paid directly to institution/employer), Globus (E, Paid directly to institution/ employer), outside the submitted work. JC: Nothing to disclose. ALZ: Nothing to disclose. VD: Royalties: NuVasive (G), Consulting: NuVasive (C), https://doi.org/10.1016/j.spinee.2018.01.023 1529-9430/© 2018 Elsevier Inc. All rights reserved.
Guidepoint (A), Medicrea (A), BIOMET (A); Fellowship Support: NuVasive (D), Globus (E), AOSpine (E), outside the submitted work. The disclosure key can be found on the Table of Contents and at www.TheSpineJournalOnline.com. There were no sources of funding for this work. * Corresponding author. Department of Orthopaedic Surgery, University of California, 500 Parnassus Ave, MU West 321, Box 0728, San Francisco, CA 94143. Tel.: (1) 415-4761166; fax: (1) 415-4761304. E-mail address: [email protected] (D. Jain)
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Introduction Obesity is becoming increasingly prevalent in the United States, affecting an estimated 35% of the population [1]. Obesity, according to the World Health Organization, is defined by body mass index (BMI): overweight is BMI>25 kg/m2, obese is BMI >30 kg/m2, and morbid (severe) obesity is BMI>40 kg/m2 [2]. Obese patients are more likely to have disc degeneration and low back pain [3]. Not surprisingly therefore, a large percentage (80%) of patients undergoing spine surgery are either overweight or obese [4,5]. As the prevalence of obesity has increased, so has the use of bariatric surgery (BS), with 220,000 procedures performed in the United States and Canada in 2008 [6]. Bariatric surgery (BS) is indicated in patients with BMI>40, or BMI>35 with obesity-related complications, and leads to substantial decreases in BMI, on average 10–15 points of BMI [7,8]. In addition, BS also results in improvement of other obesityrelated comorbidities, such as type II diabetes mellitus, hypertension, and cardiovascular disease [9,10]. Multiple studies have demonstrated that obese patients undergoing spine surgery have greater blood loss, longer operative times, and higher rates of surgical site infection, revision rates, and mortality compared with non-obese patients [11,12]. Bariatric surgery before spine surgery may mitigate these risks. However, endocrine literature suggests that there may be detrimental effects of BS on nutritional status and bone density [13–16]. The purpose of this study was to determine the impact of BS on postoperative medical and surgical complications in patients undergoing lumbar spine fusion. In this database study, we examined patients undergoing posterior lumbar fusion, and compared patients who had a previous history of BS with those who were severely obese but with no history of BS and those who were non-obese. We hypothesized that patients with a history of BS would have lower complication rates than their obese counterparts. Methods This was a retrospective cohort study of patients undergoing posterior lumbar fusion. There were no sources of funding for this study. Data sample Administrative claims from the State Inpatient Databases (SID) were analyzed. The SID is the largest all-payer inpatient database in the United States; it contains all of each state’s hospital inpatient discharge records. Each patient is assigned a unique identification number, which can then be tracked across time points and different hospitals, thus allowing subsequent readmissions to be linked to the indexed admission. Complete data in SID were available for Florida, New York, Nebraska, and Utah from 2006 to 2010, and California from 2006 to 2011. These states represent an ethnically
and socioeconomically diverse group of patients and include approximately one-third of the US population [17]. Inclusion-exclusion criteria All patients age >18 who underwent posterior lumbar fusion were included in the study. These patients were identified using International Classification of Diseases, Ninth Revision (ICD9) procedure codes 81.07 and 81.08. Patients who underwent revision surgery (ICD-9 codes 81.34–81.38) or anterior fusion (ICD-9 code 81.06) were excluded. Patients with ICD-9 diagnosis codes for bone cancer or metastases, infection, and trauma were excluded (Supplementary Table S1). Patients were then subdivided into three groups. Group 1 (BS—experimental group) included patients with a history of BS and a diagnosis of obesity; they were identified based on the presence of ICD-9 codes for BS in conjunction with ICD-9 codes for obesity. Bariatric surgery is indicated in patients with BMI>40 or BMI>35 with obesity-related comorbidities; thus it can be inferred that patients who underwent BS met these criteria at the time of BS. There were two control groups. Group 2 (severely obese—control group) included severely obese patients; they were identified based on ICD-9 codes for BMI>40 or morbid obesity with no codes for BS. Group 3 (non-obese—control group) included non-obese patients with no history of BS. These consisted of the remaining patients with no codes for obesity or BS. Thus, patients with codes for obesity or BMI>30, but no codes for morbid obesity or BMI>40 or BS, and patients with codes for BS, but no codes for obesity, were excluded (Supplementary Table S2). To ensure a minimum 30-day follow-up, patients who underwent surgery the last quarter of the dataset were excluded. Patient characteristics and outcomes Data were queried for demographic data including age and gender. Data were queried for 17 medical comorbidities that can be used to calculate a modified Charlson Comorbidity Index (CCI) score, as described previously [18]. Data were then queried for 30-day medical complications. Major medical complications included pulmonary embolism, deep vein thrombosis, acute myocardial infection, respiratory failure, and cerebrovascular accident. Minor complications included urinary tract infection, pneumonia, acute renal failure, and postoperative blood transfusion. Data were queried for surgical complications: intraoperative complications included dural tear and death, and 30-day complications included nerve injury, infection, death, revision, and reoperation (Supplementary Table S3). Data were also queried for hospital length of stay (LOS). Statistical analysis Demographics, preoperative comorbidities, complications, and LOS were described using the mean and standard deviation for continuous variables and percentages for binary
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variables. Demographics and preoperative comorbidities were compared using analysis of variance for continuous variables (age, CCI) and chi-squared for categorical variables (gender). Each complication and LOS was compared between both BS and obese groups and BS and non-obese groups. Logistic multivariate regression analyses were performed to compare complication rates, controlling for age, gender, and CCI. Results are presented as odds ratio (OR), confidence interval (CI), and p-value. Linear multivariate regression was performed to compare LOS between groups, controlling for the same confounders. Results are presented as coefficient (B) and p-value. Additionally, a subgroup analysis was performed in the severely obese group to determine risk factors for 30-day infection, revision, and readmission. Logistic multivariate models were created with demographic variables, including age, gender, and each comorbidity, and dural tear and LOS. Results are presented as OR, CI, and p-value. All analyses were performed using Stata v14 (StataCorp, College Station, TX, USA). Results There were 196,680 patients identified who underwent posterior lumbar spine fusion that met inclusion-exclusion criteria. After patients were divided into the three study groups, there were 180,425 patients remaining. After the last-quarter patients were excluded, there were a total of 176,256 patients remaining. After patients who underwent anterior surgery were excluded, there were 156,517 patients remaining who were included in the final analysis. There were 590 patients in the BS group, 5,791 in the severely obese group, and 150,136 in the non-obese group. Average age was 53.9, 56.3, and 57.9 years, respectively; this was significantly different between groups (F (2, 156,415)=47.2, p=<.001). Percent female was 74.6, 65.6, and 54.8%, respectively; this was significantly different between groups (chi-sqaure=349.0, p<.001). Average CCI was 0.70, 0.95, and 0.51 respectively; this was significantly different between groups (F (2, 156,514)=691.0, p=<.001) (Table 1). Comparing BS with severely obese, BS had significantly lower rates of respiratory failure (OR 0.59, p=.019), urinary tract infection (OR 0.64, p=.031), acute renal failure (OR 0.39, p=.007), overall medical complications (OR 0.59, p<.001), and infection (OR 0.65, p=.025). There were no significant differences found among all other complications (Tables 2 and 3). Bariatric surgery also had significantly lower LOS (BS: 4.51±3.81 vs. severely obese: 5.19±4.31 days, B=−0.46, standard error=0.18, p=.01). Comparing BS with non-obese, there were no significant differences in medical complications; however, BS had significantly higher rates of infection (OR 2.70, p<.001), reoperation (OR 2.05, p=.045), and readmission (OR 1.89, p<.001) (Tables 2 and 3). There was no significant difference in LOS (BS: 4.51±3.81 vs. non-obese: 4.30±3.34 days, B=0.08, standard error=0.14, p=.55).
3
Table 1 Patient demographics and preoperative comorbidities
Age (y) Female (%) AIDS/HIV (%) Metastatic solid tumor (%) Moderate to severe liver disease (%) Any malignancy except skin (%) Hemiplegia or paraplegia (%) Renal disease (%) Diabetes with chronic comp (%) Cerebrovascular disease (%) Chronic pulmonary disease (%) Congestive heart failure (%) Dementia (%) Diabetes without chronic comp (%) Mild liver disease (%) Myocardial infarction (%) Peptic ulcer disease (%) Peripheral vascular disease (%) Rheumatic disease (%) Charlson Comorbidity Index
BS (n=590)
Severely obese (n=5,791)
Non-obese (n=150,136)
53.9 74.6 0.00 0.00 0.00 1.02 1.86 2.71 1.19 0.85 21.53 1.69 0.17 21.19 1.53 2.71 1.86 1.69 3.22 0.70
56.3 65.6 0.03 0.07 0.03 0.64 2.49 4.44 3.68 1.40 22.78 4.42 0.07 31.31 1.42 4.02 0.73 2.66 3.21 0.95
57.9 54.8 0.05 0.03 0.03 0.10 1.50 1.97 1.07 1.32 13.66 1.88 0.19 13.30 1.03 3.25 0.55 2.11 2.82 0.51
BS, bariatric surgery.
In the subgroup analysis of severely obese patients, significant risk factors for complications were as follows: hemiplegia, diabetes with chronic complications, rheumatic disease, female gender, and LOS for 30-day infection; diabetes with and without chronic complications, history of myocardial infarction, peptic ulcer disease, age>65, female gender, and LOS for 30 day readmission; and age>65 and female gender for 30-day revision (Table 4). Discussion It is well established that obesity is associated with increased rates of medical complications and infection after lumbar spine surgery, and this risk is further increased by severe obesity [4,19–22]. Thus, managing severely obese patients with operative spinal pathology can be challenging. In this database study, we demonstrated that patients who underwent BS before posterior lumbar spine fusion had lower rates of medical complications and infection, as well as shorter hospital LOS, compared with severely obese patients. Nonetheless, patients with BS still had higher rates of infection, reoperation, and readmission compared with non-obese patients without a history of BS surgery. The present study is the first to examine the impact of BS on complications of lumbar spine surgery and provides important insight on how best to preoperatively optimize severely obese patients with spinal pathology. Although there are no previous studies examining the influence of BS on complications after spine surgery, we can extrapolate from the total joint arthroplasty literature, which shows mixed results. Some studies demonstrate decreased risk of complications in patients with BS compared with severely
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4 Table 2 Thirty-day medical complications
BS: severely obese
Pulmonary embolism DVT Acute myocardial infarction Respiratory failure Cerebrovascular accident UTI Pneumonia Acute renal failure Postop blood transfusion Any medical complication
BS: non-obese
BS
Obese
Non-obese
OR
CI
p-Value
OR
CI
p-Value
0.17 0.34 0.51 3.73 0.17 4.41 0.17 1.53 0.17 9.83
0.83 0.66 0.79 6.92 0.54 7.37 0.17 5.04 0.02 17.61
0.37 0.33 0.40 3.42 0.55 3.46 0.12 1.30 0.02 8.36
0.24 0.62 1.11 0.59 0.52 0.64 1.41 0.39 8.33 0.59
[0.03–1.69] [0.15–2.70] [0.33–3.70] [0.38–0.92] [0.07–4.00] [0.42–0.96] [0.18–11.36] [0.20–0.78] [0.50–142.9] [0.44–0.79]
.15 .51 .87 .019 .527 .031 .75 .007 .141 <.001
0.53 1.30 1.72 1.09 0.40 1.33 1.49 1.56 9.43 1.22
[0.07–3.85] [0.32–5.26] [0.53–5.56] [0.71–1.69] [0.06–2.86] [0.89–1.75] [0.21–10.75] [0.79–3.13] [1.26–71.43] [0.93–1.61]
.52 .73 .37 .69 .36 .17 .69 .21 .029 .17
BS, bariatric surgery; CI, confidence interval; DVT, deep vein thrombosis; OR, odds ratio; UTI, urinary tract infection. p-Value in bold indicates statistical significance.
obese patients [22], whereas other studies demonstrate no difference [23,24]. Although useful as a starting point, posterior lumbar spine surgery has its own risk profile of medical and surgical complications. Not only does the present study suggest that BS mitigates complications after lumbar spine surgery, but previous studies suggest that it might obviate the need for surgery at all by improving symptoms preoperatively. In a study of 58 severely obese patients who underwent BS, Khoueir et al. demonstrated significant improvements in back pain and backrelated function after BS [25]. In another study of 30 severely obese patients who underwent BS, Lidar et al. demonstrated improvement in back and leg pain, as well as radiographic evidence of increased disc height [26]. These findings further support the recommendation for consideration of BS before lumbar spine fusion. These results must be approached with caution; they should not be interpreted as to suggest that severely obese patients should not undergo spine surgery. In fact, multiple studies have demonstrated significant clinical improvement, albeit with increased risk of complication, in obese and severely obese patients undergoing lumbar spine surgery [27–29]. In subgroup analyses of the Spine Patient Outcomes Research Trials, authors showed that obese and severely obese patients had greater treatment effects of surgery compared with their
non-obese counterparts; this was attributed primarily to poor outcomes with nonoperative care in obese and severely obese patients. Furthermore, these results also should not be interpreted to suggest that every morbidly obese should undergo BS before undergoing elective spine surgery. Initial weight management strategies should be employed before undergoing BS, centered on diet modification. In fact, indications for BS require 6 months of failed attempts at nonoperative weight loss. Nonetheless, the present study provides insight into preoperative optimization, via one option, BS. There exist concerns regarding nutritional status and bone quality after BS; patients with BS have low hydroxyproline, which is important for wound healing; low vitamin B12, D, and E; and loss of bone mineral density (BMD) [13–16]. Despite these consequences, for posterior lumbar spine fusion, it appears that in the short term at least, the benefits of improvement in medical comorbidities outweigh the risks. It remains to be seen what the long-term consequences are, for example on fusion rates or the longevity of the construct. Furthermore, the timing of BS before spine surgery was not addressed in this study as it was not available with this dataset. Although BMD has been shown to be substantially reduced up to 5 years after BS, it is possible that most of the nutritional deficits and decrease in BMD would be most severe in the first 2 years. This might be an area of future research.
Table 3 Surgical complications BS: severely obese BS Intraoperative Death 0.17 Dural tear 2.54 30-d Complications Nerve injury 4.41 Infection 39.15 Death 0.17 Revision 1.36 Readmission 10.51
Obese
BS: non-obese
Non-obese
OR
CI
p-Value
OR
CI
0.26 2.43
0.12 1.77
0.93 1.08
[0.12–7.14] [0.63–1.85]
.94 .80
2.17 1.67
[0.30–15.6] [0.98–2.76]
.45 .057
3.99 8.27 0.45 2.30 13.69
3.90 0.22 0.20 0.66 6.22
1.11 0.65 0.53 0.58 0.80
[0.74–1.69] [0.45–0.95] [0.07–4.00] [0.28–1.20] [0.61–1.05]
.60 .025 .53 .15 .11
1.14 2.70 1.27 2.05 1.89
[0.76–1.69] [1.89–4.00] [0.18–9.09] [1.02–4.17] [1.33–2.44]
.52 <.001 .82 .045 <.001
BS, bariatric surgery; CI, confidence interval; OR, odds ratio. p-Value in bold indicates statistical significance.
p-Value
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Table 4 Risk factors for 30-day infection, readmission, and reoperation in severely obese patients Infection
Age>65 Female AIDS/HIV Metastatic solid tumor Moderate to severe liver disease Any malignancy except skin Hemiplegia or paraplegia Renal disease Diabetes with chronic comp Cerebrovascular disease Chronic pulmonary disease Congestive heart failure Dementia Diabetes without chronic comp Mild liver disease Myocardial infarction Peptic ulcer disease Peripheral vascular disease Rheumatic disease Dural tear LOS
Readmission
OR
CI
p
OR
1.01 1.6 1 1 1 0.7 1.6 0.12 1.56 1.33 0.95 0.88 2.69 1.17 1.27 0.98 1.62 0.65 1.66 1.26 1.09
[0.99–1.01] [1.28–2.00]
.151 <.001
1.65 1.36 8.52 1.37 1 0.64 1.27 1.36 1.51 1.22 1.05 1.18 1.35 1.27 1.32 1.49 2.4 0.89 1.39 1.15 1.02
[0.21–2.25] [1.04–2.68] [0.81–1.8] [1.00–2.43] [0.67–2.63] [0.75–1.19] [0.57–1.37] [0.25–28.00] [0.95–1.44] [0.62–2.61] [0.60–1.61] [0.64–4.08] [0.34–1.27] [1.07–2.56] [0.73–2.17] [1.07–1.11]
.55 .034 .33 .049 .406 .67 .58 .41 .13 .49 .96 .30 .22 .021 .73 <.001
CI
Reoperation p
OR
CI
p
[1.41–1.95] [1.15–1.61] [0.52–139.9] [0.13–13.8]
<.001 <.001 .13 .78
[1.15–2.4] [1.12–2.56]
.007 .013
[0.86–101.3]
.066
[0.24–1.70] [0.92–1.97] [0.98–1.89] [1.05–2.16] [0.70–2.15] [0.88–1.25] [0.85–1.65] [0.13–13.65] [1.08–1.49] [0.73–2.39] [1.06–2.09] [1.21–4.80] [0.56–1.40] [0.95–2.04] [0.72–1.82] [1.004–1.03]
.37 .28 .061 .024 .47 .56 .32 .79 .004 .35 .02 .013 .62 .083 .55 .01
1.66 1.69 1 9.34 1 1.78 0.57 1.35 0.45 0.95 1.05 1.03 1 0.82 1.81 1.27 1.68 1.09 1.52 1.82 1.01
[0.37–8.43] [0.14–2.39] [0.64–2.91] [0.14–1.48] [0.23–3.98] [0.70–1.57] [0.45–2.32]
.46 .45 .43 .19 .94 .81 .94
[0.55–1.21] [0.56–5.86] [0.56–2.83] [0.36–7.82] [0.39–3.06] [0.70–3.34] [0.78–4.22] [0.97–1.04]
.32 .32 .56 .51 .86 .29 .16 .73
CI, confidence interval; LOS, length of stay; OR, odds ratio. p-Value in bold indicates statistical significance.
The subgroup analysis provides important insight into predictors of infection, readmission, and revision surgery specifically in severely obese patients. This is the first study to examine risk factors for complications in this patient population. Medical comorbidities in general, and especially diabetes, have been previously shown to increase the risk of infection and overall readmission in the general patient population [30–32]. Not surprisingly, this finding is consistent in severely obese patients. Finally, this study also speaks to a larger context of preoperative optimization regarding nutritional status. Unfortunately, there is quite limited literature on the subject. Both severely obese patients and patients with post-BS suffer from metabolic syndromes. Either way, it is the authors’ opinion that if a nutritional disorder is suspect, a full nutritional workup is warranted, which include laboratory studies such as total lymphocyte count and serum albumin. These have been linked to surgical site infection after spine surgery, although there is no evidence that nutritional optimization improves outcomes [33,34]. The limitations of this study include those suffered by any administrative claims database study. Primarily, these data are subject to errors in coding and billing. It is difficult to collect the true complexity of the patient in administrative claims; they often underreport both preoperative comorbidities and postoperative complications [35,36]. Discrepancies in rates of postoperative complications after lumbar spine fusion between the Healthcare Cost and Utilization Project and other national databases such as the National Surgery Quality Improvement Program highlight these challenges [37].
Furthermore, these data do not account for differences in instrumentation or technique for surgery. Such errors have the potential to influence the analyses. Finally, the dataset does not provide precise BMI information, and thus we do not know the BMI for the experimental group nor the control groups at the time of the index spine surgery. It would be interesting in a future study to examine the relationship between the amount of weight loss and complications. In summary, despite these limitations, with a large sample of patients, we demonstrated that patients who undergo BS before lumbar spine have significantly lower rates of medical complications and infections than their severely obese counterparts; however, they still have significantly higher rates of infection, revision, and readmission than their non-obese counterparts. This information suggests that for severely obese patients presenting for lumbar spine fusion, surgeons should consider referral for BS for preoperative optimization, but still must council patients that the risks will not be normalized to that of non-obese patients. Supplementary material Supplementary material related to this article can be found at https://doi.org/10.1016/j.spinee.2018.01.023. References [1] Flegal KM, Carroll MD, Kit BK, Ogden CL. Prevalence of obesity and trends in the distribution of body mass index among US adults, 1999–2010. JAMA 2012;307:491–7.
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