Obesity negatively effects cost efficiency and outcomes following adult spinal deformity surgery

Journal Pre-proof

Obesity Negatively Effects Cost Efficiency and Outcomes Following Adult Spinal Deformity Surgery Avery E. Brown BS , Haddy Alas BS , Katherine E. Pierce BS , Cole A. Bortz BA , Hamid Hassanzadeh MD , Lawal A. Labaran BS , Varun Puvanesarajah MD , Dennis Vasquez-Montes MS , Erik Wang BA , Tina Raman MD , Bassel G. Diebo MD , Virginie Lafage PhD , Renaud Lafage MS , Aaron J. Buckland MBBS, FRACS , Andrew J. Schoenfeld MD , Michael C. Gerling MD , Peter G. Passias MD PII: DOI: Reference:

S1529-9430(19)31150-7 https://doi.org/10.1016/j.spinee.2019.12.012 SPINEE 58083

To appear in:

The Spine Journal

Received date: Revised date: Accepted date:

21 March 2019 16 December 2019 17 December 2019

Please cite this article as: Avery E. Brown BS , Haddy Alas BS , Katherine E. Pierce BS , Cole A. Bortz BA , Hamid Hassanzadeh MD , Lawal A. Labaran BS , Varun Puvanesarajah MD , Dennis Vasquez-Montes MS , Erik Wang BA , Tina Raman MD , Bassel G. Diebo MD , Virginie Lafage PhD , Renaud Lafage MS , Aaron J. Buckland MBBS, FRACS , Andrew J. Schoenfeld MD , Michael C. Gerling MD , Peter G. Passias MD , Obesity Negatively Effects Cost Efficiency and Outcomes Following Adult Spinal Deformity Surgery, The Spine Journal (2019), doi: https://doi.org/10.1016/j.spinee.2019.12.012

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Inc.

Obesity Negatively Effects Cost Efficiency and Outcomes Following Adult Spinal Deformity Surgery Avery E. Brown BS1, Haddy Alas BS1, Katherine E. Pierce BS1, Cole A. Bortz BA1, Hamid Hassanzadeh MD2, Lawal A. Labaran BS2, Varun Puvanesarajah MD2, Dennis Vasquez-Montes MS3, Erik Wang BA3, Tina Raman MD3, Bassel G. Diebo MD3, Virginie Lafage PhD4, Renaud Lafage MS4, Aaron J. Buckland MBBS, FRACS3, Andrew J. Schoenfeld MD5, Michael C. Gerling MD3, Peter G. Passias MD1 Affiliations: 1. Division of Spinal Surgery/Departments of Orthopaedic and Neurosurgery, NYU Medical Center, NY Spine Institute, New York, NY, USA 2. Department of Orthopedic Surgery, University of Virginia School of Medicine, Charlottesville, VA 3. Department of Orthopaedic Surgery, NYU Langone Orthopedic Hospital, New York, NY 4. Department of Orthopaedic Surgery, Hospital for Special Surgery, New York, NY 5. Department of Orthopedic Surgery, Harvard Medical School, Boston, MA

Corresponding Author: Peter G. Passias, MD Division of Spinal Surgery/ Departments of Orthopaedic and Neurosurgery NYU Medical Center NY Spine Institute 301 East 17th St, New York, NY, 10003, USA. Tel.: (516) 357-8777 Fax: (516) 357- 0087 E-mail address: [email protected] Funding Information: No funding was received in relation to the creation of this work. Conflict of Interest Statement: Peter G Passias MD – Reports personal consulting fees for Spinewave, Zimmer Biomet, DePuy Synthes, and Medicrea outside the submitted work

ABSTRACT

Background Context: Obesity has risen to epidemic proportions within the United States. As the rates of obesity have increased, so has its prevalence among patients undergoing adult spinal deformity (ASD) surgery. The effect of obesity on the cost efficiency of corrective procedures for ASD has not been effectively evaluated.

Purpose: To investigate differences in cost efficiency of ASD surgery for patients stratified by body mass index (BMI).

Study Design/Setting: Retrospective review of a single center ASD database.

Patient Sample: 505 ASD patients Outcome Measures: Complications, revisions, costs, EuroQol-5D (EQ5D), quality adjusted life years (QALYS), cost per QALY.

Methods: ASD patients (scoliosis≥20°, SVA≥5cm, PT≥25°, or TK ≥60°) ≥18, undergoing ≥4 level fusions were included. Patients were stratified into NIH-defined obesity groups based on their preoperative BMI: underweight 18.5< (U), normal 18.5–24.9 (N), overweight 25.0–29.9 (O), obese I 30.0–34.9 (OI), obese II 35.0–39.9 (OII), and obesity class III 40.0 + (OIII). Total surgery costs for each ASD obesity group were calculated. Costs were calculated using the PearlDiver database, which reflects both private insurance and Medicare reimbursement claims. Overall complications (CC) and major complications (MCC) were assessed according to CMS.

definitions. QALYs and cost per QALY for obesity groups were calculated using an annual 3% discount up to life expectancy (78.7 years).

Results: In all, 505 patients met inclusion criteria. Baseline demographics and surgical details were: age 60.8 ± 14.8, 67.6% female, BMI 28.8 ± 7.30, 81.0% posterior approach, 18% combined approach, 10.1 ± 4.2 levels fused, op time 441.2 ± 146.1 minutes, EBL 1903.8 ± 1594.7 cc, LOS 8.7 ± 10.7 days. There were 17 U, 154 N patients, 151 O patients, 100 OI, 51 OII, and 32 OIII patients. Revision rates by obesity group were: 0% U, 3% N patients, 3% O patients, 5% OI, 4% OII, and 6% for OIII patients. The total surgery costs by obesity group were: $48,757.86 U, $49,688.52 N, $47,219.93 O, $50,467.66 OI, $51,189.47 OII, and $53,855.79 OIII. In an analysis of patients with baseline and 1Y EQ5D follow up, the cost per QALY by obesity group was: $153,737.78 U, $229,222.37 N, $290,361.68 O, $493,588.47 OI, $327,876.21 OII, and $171,680.00 OIII. If that benefit was sustained to life expectancy, the cost per QALY was $8,588.70 U, $12,805.72 N, $16,221.32 O, $27,574.77 OI, $18,317.11 OII, and $9,591.06 for OIII.

Conclusions: Among adult spinal deformity patients, those with BMIs in the obesity I, obesity II, or obesity class III range had more expensive total surgery costs. When assessing 1 year cost per quality adjusted life year, obese patients had costs 32% higher than non-obese patients ($224,440.61 vs. $331,048.23). Further research is warranted on the utility of optimizing modifiable preoperative health factors for patients undergoing corrective adult spinal deformity surgery.

Key Words: Adult Spinal Deformity; Obesity; Body Mass Index; Cost; Cost Efficiency; Quality Adjusted Life Years

INTRODUCTION

The National Institutes of Health defines obesity as a body mass index (BMI) greater than 30.0 kg/m2 and subdivides it into three different classes: obesity class I 30.0-34.9, obesity class II 35.0-39.99, and obesity class III/extreme obesity >40.0. Obesity has become a prevalent comorbidity in many parts of the developed world, and rates of obesity have increased over the past few decades, affecting an estimated 39.8% of the US population over the age of 20, including 7.6% with obesity class III.13,17,41 These rates are only expected to rise, and along with it, billions of increased direct and indirect healthcare expenditures.10,39 While still a point of contention, many studies have demonstrated an increased prevalence of spine pathology among obese patients compared to non-obese patients, with the Wakayama Spine Study in particular finding increased MRI evidence of degenerative disk disease (DDD).17,34,36,38 In addition, obese patients undergoing spine surgery are at significantly higher risk of medical and surgical complications, as well as need for revision.3–5,7,14–16,19,27,28 As both the prevalence of spine surgery and obesity increase in parallel, there is a concern that outcomes may be compromised and expenditures increase among individuals with elevated BMI. As BMI is an objective and modifiable factor, these results add to the discussion on cost efficiency and the potential utility of preoperative optimization. In this context, we sought to evaluate the total cost of surgery and cost per quality adjusted life years (QALYs) for adult spinal deformity patients undergoing corrective surgery. We

hypothesized that obesity would be associated with more costly peri-operative care and reduced cost-efficiency overall.

METHODS

Study Design and Data Source

This study was an Institutional Review Board (IRB) approved retrospective review of patients presenting to a single academic spine center between November 2013-Novemeber 2018. Inclusion criteria consisted of age >18 years, operative treatment for adult spinal deformity (ASD), with available radiographic, surgical, and health related quality of life data. ASD was defined as scoliosis ≥20°, sagittal vertical axis (SVA) ≥5cm, pelvic tilt (PT) ≥25°, or thoracic kyphosis (TK) ≥60° and undergoing ≥4 level fusions. Patients were stratified into different obesity classes according to the National Heart, Lung, and Blood Institute of the National Institutes of Health obesity definitions.24 Obesity classes were based on preoperative BMI and included: underweight 18.5<, normal 18.5–24.9, overweight 25.0–29.9, obese I 30.0–34.9, obese II 35.0–39.9, and obese III >40.0.

Data Collection Demographic and clinical data were abstracted, including patient age, biologic sex, BMI, and prior ASD surgery. Surgical data collected included operative time, estimated blood loss, surgical approach, off-label use of bone morphogenetic protein 2 (BMP-2), performance of an osteotomy and number of levels involved, number of levels fused, and use of instrumentation.

Patients were evaluated using full-length free-standing lateral spine radiographs (36" long-cassette) at baseline and 1 year following surgery. Radiographs were analyzed using dedicated and validated software (SpineView®; ENSAM, Laboratory of Biomechanics, Paris, France) at a single center with standard techniques. 6,25,32 Thoracolumbar and spinopelvic radiographic parameters included T4–T12 thoracic kyphosis (TK), L1–S1 lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), and pelvic incidence minus lumbar lordosis (PI– LL) mismatch.

Cost Calculation The PearlDiver database, which reflects both private insurance and Medicare reimbursement claims, was used to calculate costs using job order cost accounting (“charge analysis”). This database is one of the largest research databases with access to Medicare reimbursement charges, trends, and outcomes data. It reflects the mean costs associated with the procedures which allows for increased generalizability. Costs associated with different 2018 ASD DRG’s were assessed. Revisions, all complications (CC) and major complications (MCC) were assessed according to CMS definitions.9 One-year reimbursement consisted of a standardized estimate using Medicare pay-scales for all services rendered within a 30 day window, including estimates regarding costs of postoperative complications, outpatient healthcare encounters, and medical related readmissions.

Utility Calculation Quality-adjusted life years (QALY) was used as an assessment of outcome.30,35 The QALYs gained were calculated using the following equation (Equation 1):

QALY is a measure of health-related quality of life, which calculates the quality of life (Q) while taking into account the life expectancy (L) to determine health benefits, where e is Napier’s mathematical constant and r is the discount rate. WHO recommends a discount rate of 3%, which was used in this analysis.23,40 Total utility gained by an intervention was calculated by a change in Q (Qi – Q) and was multiplied by the life expectancy to determine total QALYs gained. Life expectancy was selected manually, based on US national averages for females (81.6 years) and males (76.9 years). QALY’s were calculated using a general health-state patientreported quality of life metric, the EuroQol Five-Dimensions questionnaire (EQ-5D).

Statistical Analysis Demographic and clinical variables were assessed using Chi-squared and t-tests for categorical and continuous variables, respectively. Utility was calculated using the EQ-5D. Cost (dollars) per QALYs gained was calculated at one-year post-operatively. Two-sided P-values less than 0.05 were considered statistically significant. All statistical analyses were conducted using SPSS Version 23 (Armonk, NY).

RESULTS

Patient Demographics We included 505 ASD patients in this analysis. The mean age of the cohort was 60.8 ± 14.8, 67.6% were female, and the mean BMI was 28.8 ± 7.30. There were 17 underweight, 154

normal weight, 151 overweight, 100 obesity class I, 51 obesity class II, and 32 obesity class III patients (table 1).

Surgical Details ASD correction for these patients involved a mean 10.1 ± 4.2 levels fused, with 82.0% undergoing a posterior approach and 18% a combined approach. Mean operative time was 441.2 ± 146.1 minutes, mean estimated blood loss was 1903.8 ± 1594.7 ccs, mean length of stay was 8.7 ± 10.7 days. Revision rates by obesity group were: 0% for underweight, 3% normal, 3% overweight, 5% obesity class I, 4% obesity class II, and 6% for obesity class III patients.

Pre- and Post-Operative Radiographic Alignment There were no observed differences in alignment between the groups, as each obesity class showed pre to postoperative improvement in multiple radiographic measures (table 2). Notably, patients with obesity class I showed less improvement in multiple global spinal alignment measures at 1 year post operation.

Health Related Quality of Life Scores Patients in the underweight and obesity class III had the lowest preoperative EQ5D scores compared to all NIH obesity classes (table 3). At 1 year, all groups showed improvement in EQ5D scores with underweight and obesity class III groups showing the greatest difference in preoperative and 1 year scores (Δ0.32 and Δ0.31, respectively).

Cost Analysis

The average cost of ASD was found to be $50,196.54. After accounting for revision surgery, and all complications following surgery obesity class III patients had the highest total costs of surgery ($53,855.79, table 4). However, when assessing the costs between all obesity classes (obesity I, II and III) vs. non obese (underweight, normal, and overweight) at 1 year, the average for obese patients was $51,837.64, vs. $48,555.44 for non-obese. At 1 year, the cost per quality adjusted life year (QALY) was highest for obesity class I patients ($493,588.47, table 5). When the cost per QALY was assessed at life expectancy, assuming the benefits gained by 1 year are maintained, all groups were below $30,000. When comparing the costs per QALY between patients defined as obesity I BMI or above and those with BMI’s classified as overweight or lower, the cost per QALY was significantly higher for obese patients at 1 year and life expectancy ($224,440.61 vs. $331,048.23, p<0.001).

DISCUSSION

Obesity rates have continued to rise in the general population and, as a result, there is a growing subset of obese patients undergoing adult spinal deformity corrective surgery.12 This investigation assessed the affect obesity had on surgical outcomes and cost efficiency, finding that patients with preoperative BMI’s in the obesity class I or higher experienced greater rates of revisions, post-operative complications, costs, and costs per quality adjusted life years. As obesity continues to grow to epidemic proportions, these results contribute to the larger discussion on healthcare efficiency and the potential role preoperative optimization may have on outcomes.

In this analysis, there was a general rise in total surgery costs which paralleled elevations in BMI, with obesity class III patients having the highest average costs. Amin et al. observed similar findings in a perioperative review of an adult spinal deformity population, with obesity class II/III patients having significantly increased odds of prolonged ICU stay, prolonged total LOS, and high cost of care episodes.2 However, they reported higher average costs of care for ASD surgery. This was likely due to the use of Medicare reimbursement data in this investigation, which is historically lower than hospital claims.11 When assessing health utility gained, as measured through baseline and 1 year EQ5D scores, there was a significantly higher cost per quality adjusted life year between obese and nonobese patients. This is in part due to the higher pre to postoperative utility gain for non-obese patients compared to obese patients, though all groups showed significant increases by 1 year. This is consistent with previous literature from Soroceanu et al. which reported that, while both obese and non-obese ASD surgery patients experienced significant improvement in their HRQL scores over time, the overall magnitude was less for obese patients.17,37 Knutsson et al. also reached similar conclusions in a population of lumbar spine surgery patients, finding that despite achieving significant pain reduction, better walking ability, and improved quality of life after surgery, obesity was associated with a higher degree of dissatisfaction and poorer outcomes.20 However, when the cost per QALY was assessed at life expectancy, all groups were below established thresholds for efficiency. The findings of sustained clinical benefits following surgery are supported throughout ASD literature.1,21,29 In one particular analysis of ASD patients 2-17 years post op (average 5 years), Dickson et al. found that patients had significantly decreased pain and fatigue, as well as a significantly improved self-image and the ability to perform physical, functional, and positional tasks.8

There is a well-established association between obesity, complications, and revisions in spine surgery.3–5,7,14–16,19,27,28 Recently, Rihn et al. reported significantly higher revision rates at 4 years for obese versus non-obese patients undergoing lumbar surgery (20% vs. 11%).31 While also reporting increased revision rates associated with obesity, Ou et al. found that up to 44% of increased BMI patients had spinal deformity 60 months post index surgery, versus 11.9% for lower BMI patients, though they used the Asian BMI categories to define obesity.26 While this investigation observed similar alignment outcomes between groups, there was an average revision rate of 2% in non-obese patients and 5% in obese patients, which was a contributing factor in the difference in cost efficiency between the groups. However, with longer follow up, it’s possible those rates could be closer to other reported values. Jensen et al. assessed outcomes after spine surgery between patients who had prior bariatric surgery and controls, finding that bariatric patients experienced greater pre-and postoperative pain as well as higher ODI/NDI scores. 18 However, the cervical spine bariatric patients had higher expectations for a complete recovery than the lumbar bariatric spine cohort. Given these findings, preoperative bariatric surgery prior to long spinal fusions may not be beneficial to obese patients. While the cost per quality adjusted life years for underweight and obesity III patients appeared to be relatively optimal, this was a reflection of higher mean preoperative disability, with underweight and obesity III patients having the worst baseline EQ5D scores of the entire cohort. As a result of the higher baseline disability, these patients had the largest pre to post changes in EQ5D scores, which drove their cost per quality adjusted life years down. These findings should be taken with caution, as it has been well established that patients at the extremes of BMI are at higher risks of surgical complications and revision.5,22,33 Saleh et al. found that underweight spine patients were at increased odds for post-operative complications and hospital

readmission following surgery.33 Bono et al. reported obesity III as a significantly higher predictor of post-operative complications in lumbar spine surgery.4 These findings suggests that there is likely a reasonable range of BMIs for which patients could theoretically be optimized to, further research is needed on the potential of preoperative intervention. This study is not without limitations. Our data was obtained through retrospective review, which represents inherent limitations and the introduction of biases including the potential for provider selection to confound results. We were limited to using BMI as a reflection of obesity, which is not an accurate reflection of overall physical health or the many other patient factors that may contribute to obesity. Our cost data was obtained from a database that reflected average Medicare payments, which may affect the generalizability of our results for ASD patients of private insurers. However, as Medicare generally reimburses at lower percentages than private insurers, our data may represent an underestimate of actual cost efficiency values in ASD surgery. Notably, our analysis was only able to assess patients with 1 year follow up, which was still affected by patients lost to follow up. Further longitudinal research is needed to adequately assess the impact obesity has on cost efficiency and outcomes in ASD surgery, as it’s possible that achieving lower BMI preoperatively may have comparable or even decreased cost efficiency. However, despite these limitations, these results provide valuable discussion on obesity and the potential for preoperative optimization of modifiable factors like BMI.

CONCLUSIONS

As the rates of obesity rise in both the general population and those undergoing surgical treatment for adult spinal deformity, a better understanding of its effects on adverse outcomes

and cost efficiency is necessary. This study found that obese patients had higher revision rates, total costs, and costs per quality adjusted life years as compared to non-obese patients. As BMI is both clinically modifiable and objective, more research is needed on the potential role of preoperative optimization, as it may reduce unnecessary complications and increase cost efficiency in adult spinal deformity corrective surgery. References

1.

Adogwa O, Karikari IO, Elsamadicy AA, Sergesketter AR, Galan D, Bridwell KH: Correlation of 2-year SRS-22r and ODI patient-reported outcomes with 5-year patientreported outcomes after complex spinal fusion: a 5-year single-institution study of 118 patients. J Neurosurg Spine 29:422–428, 2018

2.

Amin RM, Raad M, Jain A, Sandhu KP, Frank SM, Kebaish KM: Increasing Body Mass Index is Associated With Worse Perioperative Outcomes and Higher Costs in Adult Spinal Deformity Surgery. Spine (Phila Pa 1976) 43:693–698, 2018

3.

Azimi P, Yazdanian T, Shahzadi S, Benzel EC, Azhari S, Nayeb Aghaei H, et al: Cut-off Value for Body Mass Index in Predicting Surgical Success in Patients with Lumbar Spinal Canal Stenosis. Asian Spine J 12:1085–1091, 2018

4.

Bono OJ, Poorman GW, Foster N, Jalai CM, Horn SR, Oren J, et al: Body mass index predicts risk of complications in lumbar spine surgery based on surgical invasiveness. Spine J: 1204-1210, 2017

5.

Buerba RA, Fu MC, Gruskay JA, Long WD 3rd, 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 14:2008–18, 2013 6.

Champain S, Benchikh K, Nogier a., Mazel C, Guise J De, Skalli W: Validation of new clinical quantitative analysis software applicable in spine orthopaedic studies. Eur Spine J 15:982–91, 2006

7.

Chan AK, Bisson EF, Bydon M, Glassman SD, Foley KT, Potts EA, et al: Obese Patients Benefit, but do not Fare as Well as Nonobese Patients, Following Lumbar Spondylolisthesis Surgery: An Analysis of the Quality Outcomes Database. Neurosurgery: 80-87, 2018

8.

Dickson JH, Mirkovic S, Noble PC, Nalty T, Erwin WD: Results of operative treatment of idiopathic scoliosis in adults. J Bone Joint Surg Am 77:513–23, 1995

9.

Draft ICD-10-CM/PCS MS-DRGv28 Definitions Manual: Available: https://www.cms.gov/icd10manual/fullcode_cms/p0370.html. Accessed 9 March 2019

10.

Finkelstein EA, Trogdon JG, Cohen JW, Dietz W: Annual Medical Spending Attributable To Obesity: Payer-And Service-Specific Estimates. Health Aff 28:w822–w831, 2009

11.

Frakt AB: How much do hospitals cost shift? A review of the evidence. Milbank Q 89:90–130, 2011

12.

Fryar CD, Carroll MD, Ogden CL: Prevalence of Overweight, Obesity, and Extreme Obesity Among Adults Aged 20 and Over: United States, 1960–1962 Through 2013– 2014. 2016

13.

Fryar CD, Carroll MD, Ogden CL: Prevalence of Overweight, Obesity, and Severe Obesity Among Adults Aged 20 and Over: United States, 1960–1962 Through 2015–

2016. 2018 14.

Gelalis ID, Papanastasiou EI, Pakos EE, Ploumis A, Papadopoulos D, Mantzari M, et al: Clinical outcomes after lumbar spine microdiscectomy: a 5-year follow-up prospective study in 100 patients. Eur J Orthop Surg Traumatol 29:321–327, 2019

15.

Goyal A, Elminawy M, Kerezoudis P, Lu VM, Yolcu Y, Alvi MA, et al: Impact of obesity on outcomes following lumbar spine surgery: A systematic review and meta-analysis. Clin Neurol Neurosurg 177:27–36, 2019

16.

Horn SR, Segreto FA, Ramchandran S, Poorman GR, Sure A, Marascalachi B, et al: The Influence of Body Mass Index on Achieving Age-Adjusted Alignment Goals in Adult Spinal Deformity Corrective Surgery with Full-Body Analysis at 1 Year. World Neurosurg 120:e533–e545, 2018

17.

Jain D, Berven S: Effect of Obesity on the Development, Management, and Outcomes of Spinal Disorders. J Am Acad Orthop Surg: 499-506, 2018

18.

Jensen BA, Garvey GA, Dawson JM, Garvey TA: Outcomes After Spine Surgery Among Patients Who Have Had Prior Bariatric Surgery. Glob Spine J 8:579, 2018

19.

Klineberg EO, Passias PG, Jalai CM, Worley N, Sciubba DM, Burton DC, et al: Predicting Extended Length of Hospital Stay in an Adult Spinal Deformity Surgical Population. Spine (Phila Pa 1976) 41:E798–E805, 2016

20.

Knutsson BB, Michaëlsson K, Sandén B, Michaelsson K, Sanden B: Obesity is associated with inferior results after surgery for lumbar spinal stenosis: a study of 2633 patients from the Swedish spine register. Spine (Phila Pa 1976) 38:435–41, 2013

21.

Kyrola K, Kautiainen H, Pekkanen L, Makela P, Kiviranta I, Hakkinen A: Long-Term clinical and radiographic outcomes and patient satisfaction after adult spinal deformity correction. Scand J Surg:1457496918812201, 2018

22.

Marquez-Lara A, Nandyala S V, Sankaranarayanan S, Noureldin MNB, Singh K, Sankaaranrayanan S: Body mass index as a predictor of complications and mortality after lumbar spine surgery. Spine (Phila Pa 1976) 39:798–804, 2014

23.

Murray CJ: Quantifying the burden of disease: the technical basis for disability-adjusted life years. Bull World Health Organ 72:429–445, 1994

24.

Must A, Spadano J, Coakley EH, Field AE, Colditz G, Dietz WH: The disease burden associated with overweight and obesity. JAMA 282:1523–1529, 1999

25.

O’Brien MF, Kuklo TRTR, Blanke KM, Lenke LG: Spinal Deformity Study Group Radiographic Measurement Manual. 2005

26.

Ou C-Y, Lee T-C, Lee T-H, Huang Y-H: Impact of Body Mass Index on Adjacent Segment Disease After Lumbar Fusion for Degenerative Spine Disease. Neurosurgery 76:396–402, 2015

27.

Passias PG, Horn SR, Vasquez-Montes D, Shepard N, Segreto FA, Bortz CA, et al: Prior bariatric surgery lowers complication rates following spine surgery in obese patients. Acta Neurochir (Wien) 160:2459–2465, 2018

28.

Passias PG, Poorman GW, Horn SR, Daniels AH, Hamilton DK, Sciubba DM, et al: Impact of Obesity on Radiographic Alignment and Short-Term Complications after Surgical Treatment of Adult Cervical Deformity. Spine J 17:S243, 2018

29.

Paulus MC, Kalantar SB, Radcliff K: Cost and value of spinal deformity surgery. Spine (Phila Pa 1976) 39:388–393, 2014

30.

Poorman GW, Passias PG, Qureshi R, Hassanzadeh H, Horn S, Bortz C, et al: Cost-utility analysis of cervical deformity surgeries using one-year outcome. Spine J: 1552-1557, 2018

31.

Rihn J a, Radcliff K, Hilibrand AS, Anderson DT, Zhao W, Lurie J, et al: Does obesity affect outcomes of treatment for lumbar stenosis and degenerative spondylolisthesis? Analysis of the Spine Patient Outcomes Research Trial (SPORT). Spine (Phila Pa 1976) 37:1933–46, 2012

32.

Rillardon L, Levassor N, Guigui P, Wodecki P, Cardinne L, Templier A, et al: Validation of a tool to measure pelvic and spinal parameters of sagittal balance. Rev Chir Orthop Reparatrice Appar Mot 89:218–27, 2003

33.

Saleh A, Thirukumaran C, Mesfin A, Molinari RW: Complications and readmission after lumbar spine surgery in elderly patients: an analysis of 2,320 patients. Spine J 17:1106– 1112, 2017

34.

Samartzis D, Karppinen J, Chan D, Luk KDK, Cheung KMC: The association of lumbar intervertebral disc degeneration on magnetic resonance imaging with body mass index in overweight and obese adults: a population-based study. Arthritis Rheum 64:1488–96, 2012

35.

Sassi F: Calculating QALYs, comparing QALY and DALY calculations. Health Policy Plan 21:402–408, 2006

36.

Shiri R, Karppinen J, Leino-Arjas P, Solovieva S, Viikari-Juntura E: The Association Between Obesity and Low Back Pain: A Meta-Analysis. Am J Epidemiol 171:135–154, 2010

37.

Soroceanu A, Burton DC, Diebo BG, Smith JS, Hostin R, Shaffrey CI, et al: Impact of obesity on complications, infection, and patient-reported outcomes in adult spinal deformity surgery. J Neurosurg Spine 23:656–664, 2015

38.

Teraguchi M, Yoshimura N, Hashizume H, Muraki S, Yamada H, Minamide A, et al: Prevalence and distribution of intervertebral disc degeneration over the entire spine in a population-based cohort: the Wakayama Spine Study. Osteoarthr Cartil 22:104–110, 2014

39.

Trogdon JG, Finkelstein EA, Feagan CW, Cohen JW: State- and Payer-Specific Estimates of Annual Medical Expenditures Attributable to Obesity. Obesity 20:214–220, 2012

40.

WHO-CHOICE: Making choices in health: WHO guide to cost-effectiveness analysis. Glob Program Evid Heal Policy ,World Heal Organ Geneva:71, 2003

41.

World Health Organization (WHO): Obesity: preventing and managing the global epidemic. Report of a WHO consultation. World Health Organ Tech Rep Ser 894:1– 253, 2000

Table 1. Baseline Demographic, Body Mass Index, and Radiographic Factors. Baseline Factor Age Female BMI Underweight Normal Overweight Obesity I Obesity II Obesity III Surgical Details Levels Fused Posterior Approach Combined Approach Operative Time Estimated Blood Loss Length of Stay

60.8 ± 14.8, 67.6% 17 154 151 100 51 32 10.1 ± 4.2 82% 18% 441.2 ± 146.1 minutes 1903.8 ± 1594.7 ccs 8.7 ± 10.7 days

Table 2. Baseline and Radiographic Outcomes at 1 Year. NIH Obesity CL cSVA TSClass CL Baseline Radiographic Alignment 27.3 ± Underweight -19.1 ± -38 ± Normal Overweight Obesity I Obesity II Obesity III

16.7 -13.6 ± 20 -13.6 ± 11.9 -10.7 ± 14.1 -11.8 ± 13.4 -2 ± 13.3

28.1 -23.8 ± 15.3 -28.6 ± 9.9 -29.7 ± 16.6 -25 ± 9 -36.9 ± 20.7

20.7 20 ± 19.4 17.8 ± 6.9 22 ± 13.4 18.2 ± 9.5 31.9 ± 15.6

1 Year Radiographic Alignment -68.5 ± 50.8 ± Underweight -0.8 ± 23.2, 0.013

Normal

-15.2 ± 18.2, 0.463

18.5, p<0.00 1 -25.2 ± 15.3, 0.33

17.0, p<0.00 1 17 ± 12.5, 0.108

SS

PT

PI

PI-LL

TK

SVA

20.6 ± 16.3 27.6 ± 14.5 28.7 ± 12.4 30.5 ± 14 33.4 ± 13.3 27.4 ± 11.3

27.2 ± 11 28.2 ± 12.9 24.3 ± 12 27.1 ± 10.3 27.7 ± 11.9 23.5 ± 11.9

47.7 ± 5.4 55.8 ± 15.7 53 ± 15

31.8 ± 24.1 15.9 ± 24.1 15 ± 25

57.6 ± 13.9 61 ± 11.4 50.9 ± 12.2

14 ± 20.1 23.8 ± 19.1 16.7 ± 16.4

34 ± 15.3 43 ± 21.2 36.1 ± 15.9 40.5 ± 19.3 30.9 ± 16.1 32.7 ± 11

-45.3 ± 6.7 -35.7 ± 58.4 -57.1 ± 81.5 -48.4 ± 54.7 -86.8 ± 40.2 -55.7 ± 70.4

38.3 ± 9.5, p<0.00 1 28.3 ± 11.4, 0.638

23.6 ± 8.2, 0.287

61.8 ± 14.5, p<0.00 1 49.2 ± 12.6, p<0.00

14.4 ± 13.1, p<0.00 1 3.6 ± 13.8, p<0.00

51.1 ± 17.6, 0.005

-44 ± 58.7, p<0.00 1 -18.7 ± 38, 0.003

20.9 ± 8.0, p<0.00

40.4 ± 15.9, 0.224

Overweight

Obesity I

Obesity II

Obesity III

-8.2 ± 13.4, p<0.00 1 -19.5 ± 17, p<0.00 1 -25 ± 11.1, p<0.00 1 -23.3 ± 5, p<0.00 1

1 27.6 ± 11.1, 0.014

1 51.1 ± 10.2, 0.199

1 21 ± 13.6, 0.010

31.7 ± 10, 0.004

-67.9 ± 58, 0.186

25.5 ± 9.1, 0.246

59.9 ± 11.7, 0.207

11.8 ± 14.6, 0.377

41.6 ± 14, 0.645

-47 ± 42.7, 0.840

8.8 ± 10.6, p<0.00 1 10 ± 6.5, 0.036

48.6 ± 17.6, p<0.00 1 47.4 ± 13.7, p<0.00 1

-56.5 ± 28.9, p<0.00 1 -63.1 ± 50.4, 0.630

-39.9 ± 11.3, p<0.00 1 -34.5 ± 19.4, 0.062

32.6 ± 21.4, p<0.00 1 17.5 ± 16.6, 0.036

23.5 ± 9.9, p<0.00 1 34.4 ± 10.7, 0.028

-26.4 ± 10.9, 0.481

9.4 ± 6.9, p<0.00 1 17.7 ± 13.6, p<0.00 1

29.5 ± 8.2, 0.078

24 ± 9.7, 0.088

53.6 ± 11.5, 0.002

23.7 ± 13.3, 0.235

20.5 ± 9.6, 0.271

44.2 ± 8, 0.012

-36.4 ± 16.1, 0.914

Table 3. EQ5D Outcomes at 1 Year by Obesity Type. NIH Obesity Class BL EQ5D Underweight 0.35 Normal 0.49 Overweight 0.43 Obesity I 0.52 Obesity II 0.45 Obesity III 0.31 Non-Obese vs Any Obesity Class Non Obese 0.42 Any Obesity Class 0.43

1Y EQ5D 0.67 0.71 0.59 0.62 0.60 0.62

Change in EQ5D 0.32 0.22 0.16 0.10 0.16 0.31

P Value p<0.001 p<0.001 p<0.001 p=0.03 p<0.001 p<0.001

0.66 0.62

0.23 0.19

p<0.001 p<0.001

Table 4. Total Surgery Costs by NIH Defined Obesity Class. NIH Obesity Class Average Total Costs Underweight $48,757.86 Normal $49,688.52 Overweight $47,219.93 Obesity I $50,467.66 Obesity II $51,189.47 Obesity III $53,855.79 Non-Obese vs Any Obesity Class Non Obese $48,555.44 Any Obesity Class $51,837.64

Table 5. Cost per Quality Adjusted Life Year at 1 Year and Life Expectancy. NIH Obesity Class

Cost per QALY at 1Y Underweight $153,737.78 Normal $229,222.37 Overweight $290,361.68 Obesity I $493,588.47 Obesity II $327,876.21 Obesity III $171,680.00 Non-Obese vs Any Obesity Class Non Obese $224,440.61 Any Obesity Class $331,048.23

Cost per QALY at LE $8,588.70 $12,805.72 $16,221.32 $27,574.77 $18,317.11 $9,591.06 $12,538.58 $18,494.31