Low back pain associated with lumbar

JULIUS GOODMAN RESIDENT AWARD Effect of Complications within 90 Days on Cost Per Quality-Adjusted Life Year Gained Following Elective Surgery for Degenerative Lumbar Spine Disease Silky Chotai, MD Ahilan Sivaganesan, MD Scott L. Parker, MD Joseph B. Wick, BA David P. Stonko, MS Matthew J. McGirt, MD Clinton J. Devin, MD Department of Orthopedics Surgery and Department of Neurological surgery, Vanderbilt University Medical Center, Nashville, Tennessee; Department of Neurological Surgery, Carolina Neurosurgery and Spine Associates, Charlotte, North Carolina This work is based on Effect of Complications Within 90 Days on Cost Utility Following Elective Surgery for Degenerative Lumbar Spine Disease, presented at the 2016 CNS Annual Meeting in San Diego, California. Correspondence: Clinton J. Devin, MD, Department of Orthopedics Surgery, Vanderbilt Spine Institute, Vanderbilt University School of Medicine, Medical Center East, South Tower, Suite 4200, Nashville, TN 37232-8774. E-mail: clinton.j.devin@vanderbilt.edu Received, January 22, 2017. Accepted, June 24, 2017. Copyright C 2017 by the Congress of Neurological Surgeons Low back pain associated with lumbar degenerative pathologies is highly prevalent and one of the costliest entity in the United States. 1-5 In the financial year 2012, for 178 789 spine surgeries the Medicare paid about $3.9 billion. 6 The frequency of lumbar spine surgery increased by about 220% over the last 2 decades and is expected to rise further with the growing population. 1 The risk of complications following lumbar spine surgery is reported as high as 10% to 20%. 7-12 Complications within 90-d postoperative global period have been utilized by several administrative databases to track safety and quality of spine care. 8,13-19 In the current era of scarce health-care resources, efforts are focused to evaluate highcost interventions, determine clinical- and costeffectiveness, and to maximize patients quality of life. Providers and payers are constantly thriving to define strategies aimed at improvement of quality of patient care, thus maximizing value of each healthcare dollar spent. The healthcare value-based equation (benefit/cost) comprises patient safety, patient-reported outcomes, and cost of care. The direct health care cost of perioperative adverse events is estimated to consume 1 dollar for every 7 dollars spent (14%-16%) on hospital care. 20-23 In addition to increased costs, the occurrence of complication creates frustration and inconvenience for patients, providers, and administrators. 24 Therefore, it is vital to account for complications and to analyze their impact on cost from patients, providers, and societal perspectives. A cost-effectiveness analysis determines the value of care of an intervention by using patient- ABBREVIATIONS: BMI, body mass index; BP, back pain; EQ-5D, EuroQol-5D; LP, leg pain; NRS, numeric rating scale; ODI, Oswestry disability index; PROs, patient reported outcome; QALY, quality-adjusted life year reported outcomes with respect to societal health care resources. Cost-utility ratios allow all stakeholders to compare treatment strategies and to identify the relative priorities, which would allow for optimal healthcare resource allocation. Costutility can also be used to compare the differences in the cost per quality-adjusted life year (QALY) gained among various patient-specific factors. 25,26 Despite increasing rates of spine surgery and associated complications, evidence of impact of complications on cost-effectiveness of commonly performed lumbar spine surgeries is lacking. 21,27,28 We set out to evaluate the cost per QALY gained in patients with complications within 90-d after surgery for degenerative lumbar spine disease. METHODS A retrospective review of prospective single-center longitudinal registry-based data was conducted for patients enrolled for degenerative lumbar spine diagnosis. The institutional review board approved that the study and wavier of informed consent was obtained for all the patients entered into the registry. Patients older than 18 yr who underwent 1 to 4 level lumbar surgery for symptoms of leg and back pain that failed 3 mo of multimodal conservative treatment, with confirmed imaging findings for diagnosis of degenerative stenosis, disc herniation, and spondylolisthesis, were included in the study. Patients who underwent surgery for spine tumor, trauma, and infection were excluded. Furthermore, patients for whom preoperative variables and follow-up data were not available were excluded. Outcome Measures Baseline, and postoperative 2-yr patient reported outcome (PROs) for back-related disability, back and leg pain, and quality of life were captured. Satisfaction with outcome was captured at postoperative 2-yr using North American Spine Society satisfaction questionnaire. Validated PRO instruments included: (1) back-related disability Oswestry Disability Index CLINICAL NEUROSURGERY VOLUME 64 NUMBER 1 SEPTEMBER 2017 157

CHOTAI ET AL TABLE 1. Patient Variables No complication (n = 349) Complication (n = 58) P-value Age (mean ± SD) 60 ± 13 61 ± 11.56 Gender: male 161 (46%) 25 (43%).44 BMI (mean ± SD) 31 ± 7 31.3 ± 7.46 Smoker 190 (54%) 32 (55%).46 Preoperative narcotic use 190 (54%) 32 (55%).48 Duration of symptoms > 12 mo 177 (51%) 29 (49%).58 Back pain dominant 19 (5%) 4(7%).41 Leg Pain dominant 76 (22%) 11 (19%).42 Neurogenic claudication 87 (25%) 19 (33%).12 Revision surgery 101 (29%) 22 (38%).09 Diagnosis.4 Herniated disc 80 (23%) 9 (16%) Spondylolisthesis 101 (29%) 19 (33%) Stenosis 169 (48%) 29 (50%) Comorbidities Diabetes 74 (21%) 15 (26%).24 Atrial fibrillation 11 (3%) 5(9%).06 Hypertension 206 (59%) 38 (66%).16 Congestive heart failure 8(2%) 4(7%).07 Coronary artery disease 67 (19%) 12 (21%).43 Myocardial infraction 14 (4%) 3 (5%).44 Chronic obstructive pulmonary disease 7 (2%) 3 (5%).15 Preoperative anticoagulation 11 (3%) 6(10%).02 ASA grade: 3/4 220 (63%) 42 (72%).06 Surgery.017 Microdiscectomy 51 (15%) 4 (7%) Decompression 101 (29%) 11 (19%) Decompression and fusion 198 (57%) 42 (72%) Number of levels (mean ± SD) 1.7 ± 0.8 2.0 ± 0.9.12 Length of surgery (min) 189 ± 88 230 ± 83.001 Length of hospital stay (d) 3.0 ± 2.6 4.4 ± 3.0.001 Not employed at the time of surgery 202 (58%) 38 (66%).07 ASA grade, American Society of Anesthesiologist physical status grade; SD, Standard Deviation. (ODI), 29 (2) Quality of life EuroQol-5D (EQ-5D), 30 (3) numeric rating scale pain scores (NRS) for back pain (BP) and leg pain (LP). 31 The outcomes were assessed during clinical visit or by telephone interview. Cost Data Total cost was defined as the sum of direct and indirect cost. The direct costs included costs associated with in-patient hospital stay (hospital cost), surgeons professional cost, and postdischarge health care resource utilization. The hospital costs were derived based on procedure, caseseverity, and presence or absence of complications, which determines the diagnosis related group of the procedure. Surgeons professional fees were derived from current procedural terminology codes using the resource-based relative-value scale. Postdischarge resource utilization was calculated based on the patient self-reported frequency of healthcare provider visits, medication use, and diagnostic imaging utilization. The details regarding cost data collected in the registry have been published previously. 24,25,28,32 The costs of 90-d readmissions to our institution were also recorded. The costs were derived based on Medicare national payment amounts. The indirect costs were derived based on patient or family member workday losses and cost of a caregiver, if this was needed. Such calculations for indirect costs have been previously validated. 25,32-35 QALY Calculation QALYs were calculated using the EQ-5D scores with US valuation using time-weighted area under the curve approach. Mean total 2-yr cost per QALY gained after surgery was assessed. Statistical Analysis Descriptive statistics, including mean (standard deviation) or median (interquartile range; IQR), for continuous variables, and frequency for categorical variables were computed. The study population was dichotomized into those with complications and without complications to compare the PROs, QALYs gained, and cost per QALY gained in these groups. Student s t-test or Mann-Whitney U-test for continuous data and chi-square test for nominal data were used. Analysis was performed using SPSS version 20 (IBM, Armonk, New York). 158 VOLUME 64 NUMBER 1 SEPTEMBER 2017 www.neurosurgery-online.com

COMPLICATION EFFECT ON COST PER QALY GAINED TABLE 2. Frequency of 90-d Complications in the Study Cohort n(%) Surgical complications Superficial surgical site infection 17 (4.2%) Deep surgical site infection 6 (1.5%) New neurological deficits 8 (1.9%) Hardware failure/wound related 5(1.2%) CSF leaks 4 (1.0%) Hematoma 1 (0.3%) Medical complications UTI 28 (6.9%) DVT 2 (0.6%) Pulmonary Embolism 1 (0.3%) Pneumonia 1 (0.2%) MI 1 (0.2%) CSF, cerebrospinal fluid; DVT, deep venous thrombosis; MI, myocardial infraction; UTI, urinary tract infection. RESULTS A total of 407 patients were included in the study. The mean age of 186 male and 221 female patients was 60 ± 13 yr. Twentytwo percent (n = 90) had diabetes at the time of surgery. The mean body mass index (BMI) was 31 ± 7. Mean baseline ODI was 48.7 ± 15.4 percentage points, BP was 6.5 ± 2.7 points, LP was 6.7 ± 2.8 points, and EQ-5D was 0.54 ± 0.22 QALYs. Twenty-two percent (n = 89) had diagnosis of herniated disc, 29% (n = 120) spondylolisthesis, and 49% (n = 198) of patients had stenosis. Table 1 summarizes the patient variables in those with and without 90-d complication. Outcomes Fourteen percent (58) of patients developed complications within 90-d after surgery. Surgical site infection was the most frequent major complication (n = 17, 4.2%), and 1.5% (n = 6) of patients had surgical site infection requiring incision and drainage; 1.9% (n = 8) of patients had new neurological deficits. Table 2 summarizes the number and frequency of complications in the study cohort. All patients had significant improvement in postoperative 2-yr (P <.0001). The patients with and without 90-d complications had similar improvement in PROs at postoperative 2-yr (Table 3). Resource Utilization and Costs Patients with complications had higher mean length of hospital stay (4.4 ± 3.0 vs 3.0 ± 2.6, P <.001), longer length of surgery (230 ± 83 vs 189 ± 88, P <.001), higher number of surgeon visits (3 vs 2 visits, P <.0001) higher number of outpatient physical/occupational therapy visits (13 vs 9, P =.02), and higher postdischarge imaging (median number of X-ray; 2 vs 1, P =.04) compared to those without complications. The number of lost workdays following surgery was higher among patients with complications (58 vs 31 days, P =.05). Table 4 lists the postdischarge health-care resource utilization. The patients with 90-d complications had significantly higher hospital cost ($20 328 vs $15 388, P <.0001). There was no statistically significant difference in the mean indirect cost at 2 yr for patients with ($4012) and without ($3685) complications (P = 0.69). The indirect costs were $12 202 and $11 488 for patients with and without complications. For patients that were employed preoperatively, family members took days off to care for patient, or a caregiver was hired. Table 5 summarizes the cost TABLE 3. Patient-Reported Outcomes (PROs) 2 yr After Surgery for Degenerative Lumbar Spine Disease PROs No complications (n = 349) Complications (n = 58) P-value Baseline PROs (mean ± SD) ODI 48.6 ± 15.5 49.7 ± 14.8.095 EQ-5D 0.55 ± 0.40 0.48 ± 0.44.61 NRS BP 6.4 ± 2.7 7.0 ± 2.3.14 NRS LP 6.8 ± 2.8 6.1 ± 3.2.29 PROs 24-mo (mean ± SD) ODI 24.9 ± 18.4 28.6 ± 18.7.98 EQ-5D 0.89 ± 0.31 0.91 ± 0.29.72 NRS BP 3.7 ± 3.1 3.9 ± 2.8.52 NRS LP 3.1 ± 3.3 3.1 ± 3.3.95 EQ-5D, Euro quality of life-5d; NRS-BP and LP, numeric rating scale back pain and leg pain; ODI, Oswestry disability index; SD, standard deviation. CLINICAL NEUROSURGERY VOLUME 64 NUMBER 1 SEPTEMBER 2017 159

CHOTAI ET AL TABLE 4. Two-Year Resource Utilization and Cost Breakdown for Patient With and Without Complication Median (range) No complication (n = 349) Complication (n = 58) P-value Healthcare visits Surgeon 2 (0-12) 3 (0-11) <.0001 Physician 0(0-10) 0(0-37).31 Chiropractor/acupuncture 0 (0-77) 0 (0-18).52 Outpatient PT/OT 9(0-193) 13 (0-255).02 Inpatient rehabilitation 0 (0-90) 0 (0-107).50 ERvisits 0 (0-8) 0(0-17).10 Diagnostic CT scan 0(0-10) 0(0-4).09 MRI 0 (0-4) 0 (0-6).11 X-ray 1 (0-21) 2 (0-7).04 Medication Spinal injections 0(0-15) 0(0-4).3 Narcotic 43 (0-540) 17 (4-820).2 Muscle relaxants 16 (0-725) 50 (37-725).33 NSAIDs 30 (0-339) 137 (4-725).95 No. of patient workdayslost 31 (4-293) 58 (51-65).05 No. of family member work days lost 5 (1-45) 6 (5-7).45 CT scan, computerized tomography scan; ER, emergency room; MRI, magnetic resonance imaging; NSAIDs, non-steroidal anti-inflammatory drugs; PT/OT, physical therapy/occupational therapy. TABLE 5. Summarizes the QALYs Gained and Cost per QALY for Patients With and Without Complications Mean ± SD No complication (n = 349) Complication (n = 58) P-value Direct cost Health care provider visits $2249 ± $6125 $2418 ± $2961.56 Diagnostic test $557 ± $921 $738 ± $834.13 Medication $1779 ± $1891 $2092 ± $2197.31 Surgeoncost (CPT) $2467 ± $1149 $2823 ± $1084.06 Hospital cost (DRG) $15 388 ± $8726 $20 328 ± $11 363.002 Readmission 0 $2405 ± $4541 <.0001 Total direct cost 2-yr $22 438 ± $12 781 $30 804 ± $14 197 <.0001 Indirect cost Patient lost wages $2273 ± $4263 $3148 ± $5365.74 Family lost wages $592 ± $2253 $545 ± $1318.82 Caregivercost $338± $4218 $152 ± $713.73 Total indirect cost 2-yr $3685 ± $7280 $4012 ± $5504.69 Total cost 2-yr $26 124 ± $14 752 $34 703 ± $15 220 <.0001 QALY gain 1-yr 0.37 ± 0.51 0.31 ± 0.53.35 QALY gain 2-yr 0.57 ± 0.71 0.49 ± 0.63.36 Cost per QALY gained 2-yr (direct cost) $39 364/QALY $62 632/QALY.05 Cost per QALY gained 2-yr (total cost) $45 831/QALY $70 822/QALY.03 CPT, current procedural terminology; DRG, diagnosis related group; QALY, quality-adjusted life year; SD, standard deviation. breakdown for patients in the study cohort. The total cost at 2 yr was significantly higher in patients with complications ($34 703 vs $26 124, P <.0001). Figure 1 demonstrates the cost associated with surgical complications 90 d following surgery. Cost Per QALY Gained Patients with complications had slightly lower mean QALYs gained compared to those without complications (0.46 vs 0.57, P =.36). The cost per QALY gained (for direct cost) in patients 160 VOLUME 64 NUMBER 1 SEPTEMBER 2017 www.neurosurgery-online.com

COMPLICATION EFFECT ON COST PER QALY GAINED FIGURE 1. Demonstrates the direct cost at 90 d and at postoperative 2 yr associated with the most frequent surgical complications. with and without complication was $62 632 vs $39 364 (P =.05) and total cost per QALY gained was $70 822 vs $45 831 (P =.03), respectively, for patients with and without complications. Table 5 summarizes the QALYs gained and cost per QALY for the study cohort. Figure 2 displays the cost per QALY gained at 1-yr and 2-yr following surgery. DISCUSSION Complications within the 90-d global period occur at a constant frequency when looking at the large aggregate data sets. 7-11 The impact of complications on cost-effectiveness following lumbar spine surgery has not been studied previously. Utilizing prospective longitudinal registry-based data, we demonstrate that cost per QALY gained was higher in patients with complication compared to those without complication. A granular and meticulous approach to capture both direct and indirect costs was employed, allowing for more accurate determination of cost-effectiveness of degenerative lumbar surgery. Our observed mean 2-yr cost per QALY gained of $38 864 for direct costs and $58 272 including indirect costs compares favorably to other reported costs per QALY gained for commonly performed degenerative spine surgery. 25,32,34,36 These values are well below the generally accepted threshold of willingness to pay ($50 000 and $100 000, or less). 37 Furthermore, cost/qaly gained reflects the durability of the intervention. The QALY gained continues to improve when an intervention generates longlasting clinical benefit. With the expected durability of lumbar spine surgery, the cost-effectiveness is expected to increase with longer follow-up in both groups. 38-41 Tso et al 42 reported a projected lifetime incremental cost-utility ratio of $2307 per QALY gained for decompression and $7153 per QALY gained for CLINICAL NEUROSURGERY VOLUME 64 NUMBER 1 SEPTEMBER 2017 161

CHOTAI ET AL FIGURE 2. Demonstrates the cost per QALY gained at 1 and 2 yr in patients with and without complications. decompression with fusion, which is similar to $5321 per QALY for total hip arthroplasty and $11 275 per QALY for total knee arthroplasty. Despite the occurrence of complications, these patients achieved improvement across all PROs as much as those without complications. The mean 2-yr cumulative QALYs gained was lower in patients with occurrence of 90-d complications compared to those without complication. The mean 2-yr cost per QALY gain was significantly higher in those with 90-d complication. This is due to relatively less improvement and higher costs in patients with complications. The occurrence of complications within 90 d was associated with significant mean direct costs at 2 yr following lumbar surgery, regardless of the procedure. This suggests that patients with complications have higher costs of surgery and resource utilization compared to those without complications. Surgical site infection and new neurological deficits were the most common major 90-d complications observed in this cohort. The direct cost associated with surgical site infection and new neurological deficits was $9804 and $3048 higher than in patients without complications. Parker et al 28 demonstrated that a 3.4% decrease in incidence of surgical site infection results in cost savings of $98 974 per 100 minimally invasive transforaminal lumbar interbody fusion procedures performed. Clearly, measures focused on prevention of complications will be able to decrease the cost and therefore increase the cost-benefit ratio. The use of intrawound vancomycin significantly reduces the incidence of surgical site infection. 43,44 However, to date, definitive evidence of the efficacy of intrawound vancomycin in degenerative spine surgery, based on robust multicentric prospectively collected data, is not available. Limitations Numerous factors, including patient age, obesity, associated comorbidities, primary diagnosis, and surgical invasiveness and complexity are associated with higher chances of developing complications and also influence the cost and quality of life following surgery. 8,13-19,45 Therefore, these factors might confound the cost-benefit ratio in patients with complications. Further studies with larger sample size will allow robust analysis, to control for all the confounding variables, to accurately compare the cost-benefit ratio in patients with and without complications. 162 VOLUME 64 NUMBER 1 SEPTEMBER 2017 www.neurosurgery-online.com

COMPLICATION EFFECT ON COST PER QALY GAINED Finally, the direct and indirect costs associated with surgery can vary in a different cohort either due to provider or patientspecific factors. In addition, there is lack of uniform methodology to track resource utilization, costs associated with surgery, and lost wages. 32,46 The direct and indirect cost estimates in the present study are evaluated based on patient-reported resource utilization and a chart biopsy. If care is sought outside of our facility, despite us questioning the patient, there is likely some level of recall bias. Therefore, some of the costs associated with complications that might occur between 90 d and 2 yr are missing in our assessment. Studies using administrative databases lack the granularity needed to comprehensively report the cost benefits associated with lumbar spine surgery from patients, providers, and societal perspectives. Our study is unique, as it provides pertinent information to clinicians, policy makers, and patients alike regarding the impact of complications during the 90-d global period on cost and cost-effectiveness at 2-yr following lumbar spine surgery. CONCLUSION Lumbar spine surgery offered significant improvement in outcomes and gain in health state utility regardless of occurrence of complications within the 90-d global period. The cost-utility was higher in patients with 90-d complications compared to those without, $70 822 and $45 831, which are considered costeffective as per the commonly accepted threshold of willingness to pay ($100 000/QALY). Clearly, measures focused on the prevention of complications might increase the cost-utility ratio after lumbar surgery. Disclosure The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 1. Deyo RA, Gray DT, Kreuter W, Mirza S, Martin BI. United States trends in lumbar fusion surgery for degenerative conditions. Spine. 2005;30(12):1441-1445; discussion 1446-1447. 2. Dagenais S, Caro J, Haldeman S. A systematic review of low back pain cost of illness studies in the United States and internationally. Spine J. 2008;8(1):8-20. 3. Frymoyer JW, Cats-Baril WL. An overview of the incidences and costs of low back pain. Orthop Clin North Am. 1991;22(2):263-271. 4. Martin BI, Deyo RA, Mirza SK, et al. Expenditures and health status among adults with back and neck problems. JAMA. 2008;299(6):656-664. 5. Martin BI, Turner JA, Mirza SK, Lee MJ, Comstock BA, Deyo RA. Trends in health care expenditures, utilization, and health status among US adults with spine problems, 1997-2006. Spine. 2009;34(19):2077-2084. 6. Levinson DR. Spinal devices supplied by physicianowned distributors: overview of prevalence and use. OEI-01-11-00660. In: General UDoHaHSOoI, ed2013. 7. Carreon LY, Puno RM, Dimar JR, 2nd Glassman SD, Johnson JR. Perioperative complications of posterior lumbar decompression and arthrodesis in older adults. J Bone Joint Surg. 2003;85-a(11):2089-2092. 8. Cassinelli EH, Eubanks J, Vogt M, Furey C, Yoo J, Bohlman HH. Risk factors for the development of perioperative complications in elderly patients undergoing lumbar decompression and arthrodesis for spinal stenosis: an analysis of 166 patients. Spine. 2007;32(2):230-235. 9. Hoffman RM, Wheeler KJ, Deyo RA. Surgery for herniated lumbar discs: a literature synthesis. JGenInternMed. 1993;8(9):487-496. 10. Peter GC, Sanjay Y, Rani N, Jennifer M, Mitchell GM, John KR. Patient comorbidity score predicting the incidence of perioperative complications: assessing the impact of comorbidities on complications in spine surgery. JNeurosurgSpine. 2012;16(1):37-43. 11. Turner JA, Loeser JD, Deyo RA, Sanders SB. Spinal cord stimulation for patients with failed back surgery syndrome or complex regional pain syndrome: a systematic review of effectiveness and complications. Pain. 2004;108(1-2):137-147. 12. Nasser R, Yadla S, Maltenfort MG, et al. Complications in spine surgery. J Neurosurg Spine. 2010;13(2):144-157. 13. Bekelis K, Desai A, Bakhoum SF, Missios S. A predictive model of complications after spine surgery: the National Surgical Quality Improvement Program (NSQIP) 2005-2010. Spine J. 2014;14(7):1247-1255. 14. Campbell PG, Yadla S, Nasser R, Malone J, Maltenfort MG, Ratliff JK. Patient comorbidity score predicting the incidence of perioperative complications: assessing the impact of comorbidities on complications in spine surgery. JNeurosurg Spine. 2012;16(1):37-43. 15. Faciszewski T, Winter RB, Lonstein JE, Denis F, Johnson L. The surgical and medical perioperative complications of anterior spinal fusion surgery in the thoracic and lumbar spine in adults. A review of 1223 procedures. Spine. 1995;20(14):1592-1599. 16. Glassman SD, Alegre G, Carreon L, Dimar JR, Johnson JR. Perioperative complications of lumbar instrumentation and fusion in patients with diabetes mellitus. Spine J Society. 2003;3(6):496-501. 17. Guzman JZ, Iatridis JC, Skovrlj B, et al. Outcomes and complications of diabetes mellitus on patients undergoing degenerative lumbar spine surgery. Spine. 2014;39(19):1596-1604. 18. Schwender JD, Casnellie MT, Perra JH, et al. Perioperative complications in revision anterior lumbar spine surgery: incidence and risk factors. Spine. 2009;34(1):87-90. 19. Wang MY, Green BA, Shah S, Vanni S, Levi AD. Complications associated with lumbar stenosis surgery in patients older than 75 years of age. Neurosurg Focus. 2003;14(2):e7. 20. Ehsani JP, Duckett SJ, Jackson T. The incidence and cost of cardiac surgery adverse events in Australian (Victorian) hospitals 2003-2004. Eur J Health Econ. 2007;8(4):339-346. 21. Hellsten EK, Hanbidge MA, Manos AN, et al. An economic evaluation of perioperative adverse events associated with spinal surgery. Spine J. 2013;13(1):44-53. 22. Jha AK, Chan DC, Ridgway AB, Franz C, Bates DW. Improving safety and eliminating redundant tests: cutting costs in U.S. hospitals. Health Aff. 2009;28(5):1475-1484. 23. Jackson T. One Dollar in Seven: Scoping the Economics of Patient Safety. Ottawa, ON: Institute CPS; 2009. 24. Chotai S, Parker SL, Sivaganesan A, et al. Effect of complications within 90 days on patient-reported outcomes 3 months and 12 months following elective surgery for lumbar degenerative disease. Neurosurg Focus. 2015;39(6):E8. 25. Adogwa O, Parker SL, Shau DN, et al. Cost per quality-adjusted life year gained of laminectomy and extension of instrumented fusion for adjacent-segment disease: defining the value of surgical intervention. J Neurosurg Spine. 2012;16(2):141-146. 26. Vogl M, Wilkesmann R, Lausmann C, Plotz W. The impact of preoperative patient characteristics on the cost-effectiveness of total hip replacement: a cohort study. BMC Health Serv Res. 2014;14:342. 27. Ong KL, Auerbach JD, Lau E, Schmier J, Ochoa JA. Perioperative outcomes, complications, and costs associated with lumbar spinal fusion in older patients with spinal stenosis and spondylolisthesis. Neurosurg Focus. 2014;36(6):E5. 28. Parker SL, Adogwa O, Witham TF, Aaronson OS, Cheng J, McGirt MJ. Post-operative infection after minimally invasive versus open transforaminal lumbar interbody fusion (TLIF): literature review and cost analysis. Minim Invasive Neurosurg. 2011;54(1):33-37. 29. Fairbank JC, Pynsent PB. The Oswestry disability index. Spine. 2000;25(22):2940-2952; discussion 2952. 30. EuroQol Group. EuroQol a new facility for the measurement of health-related quality of life. Health Policy. 1990;16(3):199-208. 31. Langley GB, Sheppeard H. The visual analogue scale: its use in pain measurement. Rheumatol Int. 1985;5(4):145-148. 32. Adogwa O, Parker SL, Shau DN, et al. Cost per quality-adjusted life year gained of revision neural decompression and instrumented fusion for same-level recurrent lumbar stenosis: defining the value of surgical intervention. J Neurosurg Spine. 2012;16(2):135-140. CLINICAL NEUROSURGERY VOLUME 64 NUMBER 1 SEPTEMBER 2017 163

CHOTAI ET AL 33. Bala MM, Riemsma RP, Nixon J, Kleijnen J. Systematic review of the (cost-)effectiveness of spinal cord stimulation for people with failed back surgery syndrome. Clin J Pain. 2008;24(9):741-756. 34. Tosteson AN, Lurie JD, Tosteson TD, et al. Surgical treatment of spinal stenosis with and without degenerative spondylolisthesis: cost-effectiveness after 2 years. Ann Intern Med. 2008;149(12):845-853. 35. Weinstein JN, Tosteson TD, Lurie JD, et al. Surgical versus nonsurgical therapy for lumbar spinal stenosis. NEnglJMed. 2008;358(8):794-810. 36. Kim S, Mortaz Hedjri S, Coyte PC, Rampersaud YR. Cost-utility of lumbar decompression with or without fusion for patients with symptomatic degenerative lumbar spondylolisthesis. Spine J. 2012;12(1): 44-54. 37. Owens DK. Interpretation of cost-effectiveness analyses. JGenInternMed. 1998;13(10):716-717. 38. Ghogawala Z, Whitmore RG, Watters WC, 3rd, et al. Guideline update for the performance of fusion procedures for degenerative disease of the lumbar spine. Part 3: assessment of economic outcome. JNeurosurgSpine. 2014;21(1): 14-22. 39. Rampersaud YR, Tso P, Walker KR, et al. Comparative outcomes and costutility following surgical treatment of focal lumbar spinal stenosis compared with osteoarthritis of the hip or knee: part 2 estimated lifetime incremental cost-utility ratios. Spine J. 2014;14(2):244-254. 40. Tosteson AN, Tosteson TD, Lurie JD, et al. Comparative effectiveness evidence from the spine patient outcomes research trial: surgical versus nonoperative care for spinal stenosis, degenerative spondylolisthesis, and intervertebral disc herniation. Spine. 2011;36(24):2061-2068. 41. Glassman SD, Polly DW, Dimar JR, Carreon LY. The cost effectiveness of singlelevel instrumented posterolateral lumbar fusion at 5 years after surgery. Spine. 2012;37(9):769-774. 42. Tso P, Walker K, Mahomed N, Coyte PC, Rampersaud YR. Comparison of lifetime incremental cost:utility ratios of surgery relative to failed medical management for the treatment of hip, knee and spine osteoarthritis modelled using 2-year postsurgical values. Can J Surg. 2012;55(3):181-190. 43. Hegde V, Meredith DS, Kepler CK, Huang RC. Management of postoperative spinal infections. World J Orthop. 2012;3(11):182-189. 44. Devin CJ, Chotai S, McGirt MJ, et al. Intrawound vancomycin decreases the risk of surgical site infection after posterior spine surgery-a multicenter analysis. Spine. 2015. 45. Kalanithi PS, Patil CG, Boakye M. National complication rates and disposition after posterior lumbar fusion for acquired spondylolisthesis. Spine. 2009;34(18):1963-1969. 46. Kuntz KM, Snider RK, Weinstein JN, Pope MH, Katz JN. Cost-effectiveness of fusion with and without instrumentation for patients with degenerative spondylolisthesis and spinal stenosis. Spine. 2000;25(9):1132-1139. 164 VOLUME 64 NUMBER 1 SEPTEMBER 2017 www.neurosurgery-online.com