Cervical radiculopathy can be the result of a traumatic

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1 J Neurosurg Spine 19: , 2013 AANS, 2013 Cost-effectiveness analysis: comparing single-level cervical disc replacement and single-level anterior cervical discectomy and fusion Clinical article Sheeraz A. Qureshi, M.D., M.B.A., Steven McAnany, M.D., Vadim Goz, B.A., Steven M. Koehler, M.D., and Andrew C. Hecht, M.D. Mount Sinai Hospital, Mount Sinai School of Medicine, Department of Orthopaedic Surgery, New York, New York Object. In recent years, there has been increased interest in the use of cervical disc replacement (CDR) as an alternative to anterior cervical discectomy and fusion (ACDF). While ACDF is a proven intervention for patients with myelopathy or radiculopathy, it does have inherent limitations. Cervical disc replacement was designed to preserve motion, avoid the limitations of fusion, and theoretically allow for a quicker return to activity. A number of recently published systematic reviews and randomized controlled trials have demonstrated positive clinical results for CDR, but no studies have revealed which of the 2 treatment strategies is more cost-effective. The purpose of this study was to evaluate the cost-effectiveness of CDR and ACDF by using the power of decision analysis. Additionally, the authors aimed to identify the most critical factors affecting procedural cost and effectiveness and to define thresholds for durability and function to focus and guide future research. Methods. The authors created a surgical decision model for the treatment of single-level cervical disc disease with associated radiculopathy. The literature was reviewed to identify possible outcomes and their likelihood following CDR and ACDF. Health state utility factors were determined from the literature and assigned to each possible outcome, and procedural effectiveness was expressed in units of quality-adjusted life years (QALYs). Using ICD-9 procedure codes and data from the Nationwide Inpatient Sample, the authors calculated the median cost of hospitalization by multiplying hospital charges by the hospital-specific cost-to-charge ratio. Gross physician costs were determined from the mean Medicare reimbursement for each current procedural terminology (CPT) code. Uncertainty as regards both cost and effectiveness numbers was assessed using sensitivity analysis. Results. In the reference case, the model assumed a 20-year duration for the CDR prosthesis. Cervical disc replacement led to higher average QALYs gained at a lower cost to society if both strategies survived for 20 years ($3042/QALY for CDR vs $8760/QALY for ACDF). Sensitivity analysis revealed that CDR needed to survive at least 9.75 years to be considered a more cost-effective strategy than ACDF. Cervical disc replacement becomes an acceptable societal strategy as the prosthesis survival time approaches 11 years and the $50,000/QALY gained willingness-to-pay threshold is crossed. Sensitivity analysis also indicated that CDR must provide a utility state of at least to be cost-effective. Conclusions. Both CDR and ACDF were shown to be cost-effective procedures in the reference case. Results of the sensitivity analysis indicated that CDR must remain functional for at least 14 years to establish greater costeffectiveness than ACDF. Since the current literature has yet to demonstrate with certainty the actual durability and long-term functionality of CDR, future long-term studies are required to validate the present analysis. ( Key Words cost-effectiveness cervical disc replacement anterior cervical discectomy and fusion quality-adjusted life year Cervical radiculopathy can be the result of a traumatic or degenerative condition and can cause significant pain and functional limitation. Treatment Abbreviations used in this paper: ACDF = anterior cervical discectomy and fusion; CDR = cervical disc replacement; CEA = cost-effectiveness analysis; CER = cost-effectiveness ratio; CPT = current procedural terminology; DRG = diagnosis-related group; ICER = incremental CER; NDI = Neck Disability Index; NIS = Nationwide Inpatient Sample; QALY = quality-adjusted life year; SF-36 = 36-Item Short-Form Health Survey; WTP = willingnessto-pay. options for symptomatic cervical radiculopathy include antiinflammatory medications, physical therapy, and occasionally cervical injections. Symptoms of cervical radiculopathy due to neurological compression at a single cervical level that persist despite appropriate conservative management are most often treated with anterior cervical discectomy and fusion (ACDF). 4,8,9 Despite its longterm clinical and radiographic success, the procedure This article contains some figures that are displayed in color on line but in black-and-white in the print edition. 546 J Neurosurg: Spine / Volume 19 / November 2013

2 Cost-effectiveness of CDR and ACDF does have inherent disadvantages, including loss of motion segments, the potential for accelerated degeneration at adjacent segments, and the need for solid bony fusion. Cervical disc replacement (CDR) is a motion-preserving alternative to arthrodesis that obviates the need to achieve bony fusion and may result in reduced stress on adjacent segments. Recently, several studies have shown promising short- and medium-term results using CDR in the treatment of cervical disc disease. 18,22 On the basis of these reports, there has been an increased use of cervical disc arthroplasty in the treatment of symptomatic cervical disc disease unresponsive to appropriate conservative management. 26 Given the expanding interest in CDR, the purpose of this study was to evaluate the cost-effectiveness of CDR and ACDF using the power of decision analysis and to identify the most critical factors affecting procedure cost and effectiveness. We also aimed to define thresholds of durability and function so that they can be used to guide future research. Methods Study Design This cost-effectiveness analysis (CEA) followed the guidelines of the Panel on Cost-Effectiveness in Health and Medicine convened by the US Public Health Service in The purpose of this panel was to establish a set of methodological recommendations that when followed would provide standardization and permit consumers of CEA studies to identify consistent quality and comparable results. 29,32,37,40 We investigated the cost-effectiveness of CDR compared with the standard baseline of ACDF, the accepted treatment for single-level cervical disc disease. The analysis was performed using a common decision analysis software package (TreeAge Pro 2011, TreeAge Software Inc.). The primary effectiveness outcome was expressed in quality-adjusted life years (QALYs), and costs were denoted in 2010 dollars. Both costs and utilities were discounted at 3% to reflect their present value. Patient Population To model the elderly patient population associated with ACDF and CDR, this model assumed a target population of patients aged 45 years who had single-level cervical disc disease with associated radiculopathy. The age chosen is consistent with the typical age at which patients seek operative intervention for disease refractory to conservative treatment. Decision Model The decision tree was constructed to reflect the 2 primary treatment arms for a patient with symptomatic cervical radiculopathy that failed to respond to appropriate conservative management. It was assumed that the patient would undergo either an ACDF or CDR for single-level cervical disc disease with radiculopathy. The literature was reviewed to identify possible outcomes and their associated probabilities following each procedure. Since ACDF is one of the most common procedures J Neurosurg: Spine / Volume 19 / November 2013 performed for cervical radiculopathy, there is a tremendous body of literature on its clinical outcomes. 1,3,4,9,10,21,28 Despite the procedure s overall success, well-known short- and long-term complications are related to ACDF and were determined from the literature. The primary short-term complications are pseudarthrosis and hardware failure. Reported rates of pseudarthrosis or hardware failure following ACDF range from 1% 10% at 1 year posttreatment, with most studies documenting rates similar to the reference case assumption of 5%. 11,17,23,28,39 In the reference case analysis (Fig. 1), a patient with pseudarthrosis within 1 year of surgery could be treated conservatively or might need to undergo a revision fusion. The most notable long-term complication following ACDF is the development of adjacent segment degeneration. One study documents a rate of approximately 3% per year for the development of adjacent segment disease, and a rate of 3% per year was used in our analysis. 19 The event pathways following CDR were also constructed after reviewing the literature. Unlike ACDF, CDR is a relatively new procedure with a limited number of short- and medium-term follow-up studies. The primary outcomes following CDR are successful arthroplasty or hardware failure. A review of the literature demonstrated a hardware failure rate of 0% 2% at 1 year after hardware placement. 1 7,13 15,18 22,24 28,30,31,35,36,40 Following hardware failure, a patient could undergo either a revision arthroplasty or a revision ACDF. Effectiveness of Surgical Procedure Cost-utility analysis, a type of CEA, allows for comparison of different health outcomes by measuring them all in terms of QALYs. Utility factors were assigned to all health states in the model to adjust survival for quality of life. The utility of a disease state is graded on a scale of 0 1 with 1 being perfect health and 0 being death. The outcome of any health intervention can then be calculated as the product of the increase in utility that it may cause and the time in years over which the intervention may be enjoyed. Specific utility factors in the decision model were determined after reviewing the available literature. Though no studies have assigned a specific utility factor to cervical disc disease, large-scale studies have consistently demonstrated that arthritis of any joint has a health state utility factor of 0.7, and neck pain has often been assigned a utility value of ,34 The base disease state of cervical disc disease was therefore assigned a utility value of 0.7 (Table 1). There has been no use of aggregate study data to generate health state utility factors for ACDF and CDR. A literature review of available evidence regarding ACDF and CDR outcomes was performed. Health state utility factors were estimated based on available evidence, including 4 randomized controlled trials and a recent meta-analysis comparing ACDF and CDR. 5,8,18,21,23 In comparing preand postoperative outcomes for both ACDF and CDR, we inferred several conclusions: 1) Postoperative 36-Item Short-Form Health Survey (SF-36) scores, Neck Disability Index (NDI) scores, and overall neurological status are improved over the preoperative state for both ACDF 547

3 S. A. Qureshi et al. Fig. 1. Decision model for the treatment of single-level degenerative disc disease (DDD) in the reference case. M = male; y/o = year old. and CDR; and 2) postoperative neurological status, range of motion, and overall success of CDR are improved, as compared with those of ACDF. 14,15,23,30,35,36 Based on these observations, ACDF was assigned a utility value of 0.8; and CDR, a value of Revision CDR was assigned a utility value (0.85) between those for CDR and ACDF. Similarly, revision ACDF was assigned a value (0.75) between those for ACDF and the base health state. Procedure-Related Costs Gross-cost methodology was used to estimate the direct costs of both ACDF and CDR. The gross-cost methodology relies on global Medicare charge and reimbursement data to estimate the costs of various procedures. Using ICD-9, diagnosis-related group (DRG), and current procedural terminology (CPT) codes specific for each surgical procedure, we were able to calculate estimates of direct costs. Gross-cost estimates for specific DRGs were determined using the Nationwide Inpatient Sample (NIS), part of the Healthcare Cost and Utilization Project. The NIS is an annual database of hospital inpatient stays that is used by researchers and policymakers to identify, track, and analyze national trends in health care utilization, access, charges, quality, and outcomes. This database encompasses hospital inpatient stays from states participating in the Healthcare Cost and Utilization Project. Discharges from 1044 hospitals from 40 states were included in the NIS in Typical discharge abstracts include demographics, diagnosis (primary and multiple secondary), procedures (primary and multiple secondary), charges, length of stay, and outcomes. The NIS sample represents approximately 20% of US community hospitals, defined by the American Hospital Association as all nonfederal, shortterm general, and other specialty hospitals, excluding hospital units of institutions. For our analysis, we used the Inpatient Core File, which contains data for 100% of the discharges from a sample of hospitals in participating states. To obtain the national prediction and account for weighting, stratification, and clustering effects, SAS survey procedures were used. Only hospitalizations with the primary procedures of interest were included in the analysis of cost. Hospitalizations were identified through ICD-9 procedure codes: CDR; revision of CDR; cervical fusion, anterior technique; and revision of cervical spine, anterior technique. The median cost of hospitalization (professional fees not included) was obtained by multiplying hospital charges by the hospitalspecific cost-to-charge ratio provided by the NIS. Specific costs associated with physician services for each surgical procedure were determined from the mean Medicare reimbursement data for All costs in this study are denominated in 2010 dollars (Table 2). Sensitivity Analysis Sensitivity analyses were used to validate the model to determine the impact of input variables across their range of reasonable values. Uncertainty in cost-effectiveness studies is inevitable, as data are combined from several sources to establish the probability of different out- TABLE 1: Utility values for health states included in the decision model* Health State Reference Case Utility Value base disease state 0.7 CDR 0.9 ACDF 0.8 revision CDR 0.85 revision ACDF 0.75 adjacent segment DDD 0.7 * DDD = degenerative disc disease. 548 J Neurosurg: Spine / Volume 19 / November 2013

4 Cost-effectiveness of CDR and ACDF TABLE 2: Costs of procedures used in the decision model, based on 2010 Medicare data and NIS data for DRG and CPT codes Procedure DRG CPT Code Cost Name Code Cost CDR $9,999 single-level disc $1, ACDF $12,415 anterior discectomy & decompression $1, arthrodesis $1, anterior instrumentation $ allograft $ revision CDR $11,389 removal of disc $ revision total disc $1, revision ACDF $13,848 removal of pseudarthrosis $1, exploration $ anterior discectomy & decompression $1, arthrodesis $1, anterior instrumentation $ allograft $ comes. Additionally, uncertainty regarding the assignment of utility values and costs in these studies can undermine the cost-effectiveness calculations to be conducted. Sensitivity analysis is therefore performed to assess the effect that each variable has on the outcome of the model. One-way sensitivity analyses, which change the value of a single variable at a time, were performed on all variables in which the data used were based on imperfect information or a lack of evidence-based literature. These variables included length of prosthesis survival, rate of hardware failure following arthroplasty, and the various health state utility factors. Results Procedure-Related Costs Costs were generated using the NIS to determine the DRG costs and Medicare 2010 costs with CPT codes specific for each procedure to determine surgeon fees. The DRG and CPT costs for each procedure were combined and discounted at a rate of 3% per year. Cervical disc replacement generated a total lifetime cost of $11,987. Comparatively, the ACDF pathway resulted in total lifetime cost of $16,823. Therefore, CDR had a net incremental lifetime savings of $4836. Effectiveness of Surgical Procedure Cervical disc replacement resulted in a generation of 3.94 QALYs, whereas ACDF resulted in This represents a net effective gain of 2.02 QALYs over the lifetime of the patient in the reference case. Cost-Effectiveness Over the lifetime of a patient in this cohort, CDR resulted in an average incremental cost of $4836 less than ACDF, while providing an incremental QALY gain of 2.02 compared with ACDF. The cost-effectiveness ratio (CER) associated with CDR was $3042 per QALY versus J Neurosurg: Spine / Volume 19 / November 2013 $8760 per QALY for ACDF (Table 3). The incremental CER (ICER) was -$2394 per QALY. The negative ICER for CDR indicates that ACDF is strongly dominated by CDR. In CEAs, a treatment strategy is dominated when analysis indicates that it is more costly and less effective than the alternative. Sensitivity Analysis Prosthesis Survival. For the reference case analysis, CDR prosthesis survival was assumed to be 20 years. Currently, no long-term studies with a follow-up longer than 6 years are available, although the failure rate in those with follow-ups shorter than 6 years has been between 0% and 2% annually. Prosthesis survival was therefore assumed to be similar to that seen in total hip arthroplasty, which is 20 years. Actual durability, however, may prove to be greater than or less than the assumed value in the present study. One-way sensitivity analysis was performed with respect to prosthesis survival time. The threshold value was 9.75 years, below which ACDF was found to be the more cost-effective strategy (Fig. 2). Assuming a $50,000/ QALY gained willingness-to-pay (WTP) threshold, CDR became a cost-effective strategy as the prosthesis survival time approached 11 years. For the reference case, an overall 1-year success rate of 99% for CDR was chosen. The 1-year failure rate for CDR would have to exceed 29% for ACDF to be the more cost-effective strategy. Costs of CDR. The costs of CDR calculated in this study can affect the outcome of the model. The cost of CDR would have to increase to more than $16,319 before ACDF would be less costly. As the cost of CDR approaches $17,000, ACDF becomes the more cost-effective strategy within the model (Fig. 3). Utility of CDR. No calculation of health state utility factors for either ACDF or CDR exists in the literature. On the basis of reported SF-36 scores, NDI scores, over- 549

5 S. A. Qureshi et al. TABLE 3: Results from base case analysis Procedure Average Lifetime Cost ($) Average QALY Gained Average Cost Difference ($) Average QALY Difference CER ($/QALY) ICER ($/QALY) CDR 11, ,042 2,394 ACDF 16, , ,760 all neurological improvement, and overall success, ACDF and CDR were assigned utility values higher than that for the base state. Additionally, a higher utility was assigned to CDR than ACDF, reflecting a better overall neurological status, overall success, and improved range of motion in the CDR group. 20,35 Sensitivity analysis was conducted to evaluate the effect of altering the assumed utilities on the ICER of CDR. The threshold utility value of CDR was 0.796, below which ACDF became the more cost-effective strategy. With reference to the $50,000 WTP threshold, CDR became a cost-effective strategy as the utility factor approached 0.81 (Fig. 4). Anterior cervical discectomy and fusion was the more cost-effective strategy when the utility was Variance in the utility factors for both revision CDR and revision ACDF did not affect the outcome of the model. Long-Term CDR Failure. In the reference case analysis, a hardware failure rate of 1.5% per year was used, which is consistent with published values in the literature ,23,30,35,36 Sensitivity analysis was performed to establish the failure rate at which CDR would no longer be the cost-effective strategy. A long-term threshold failure rate of 30.8% per year was calculated as the failure rate above which CDR no longer remains the preferred strategy. Revision CDR. No data in the literature support the use of revision CDR after the failure of an initial arthroplasty. However, many authors have noted the revision potential of CDR. For the reference case, a patient who demonstrated primary hardware failure was as likely to have revision CDR as revision ACDF. Sensitivity analysis failed to provide a threshold value above or below which the rate of revision CDR changed the outcomes of the model. Discussion Cervical disc replacement has been shown in several short- and medium-term studies to provide results at least equivalent to those for ACDF in the treatment of symptomatic single-level cervical disc disease unresponsive to appropriate conservative management A recent meta-analysis of 4 randomized controlled trials comparing ACDF and CDR demonstrated that overall procedural success and neurological improvement are better in the CDR group. 21 Although these studies have shown promising clinical results, our study demonstrates that longer-term follow-up is necessary to confirm durability and function of CDR prostheses to establish cost-effectiveness. Sensitivity analysis revealed that CDR becomes a cost-effective strategy once prosthesis survival time ap- Fig. 2. Variation in prosthesis survival time to determine threshold cost-effectiveness level. Incr. = incremental. 550 J Neurosurg: Spine / Volume 19 / November 2013

6 Cost-effectiveness of CDR and ACDF Fig. 3. Results of sensitivity analysis of the effect of the cost variance of CDR. Red line represents ACDF; blue line, CDR. J Neurosurg: Spine / Volume 19 / November 2013 proaches 11 years based on a WTP criterion of $50,000 per QALY. Although specific thresholds regarding favorable CERs have not been established, most authors have used CERs at or below $50,000 per QALY gained as indicative of cost-effective interventions. 16 A prosthesis survival time less than 9.75 years means that ACDF is the dominant strategy. While the available literature certainly shows promising results, survival over a longer period must be documented to more definitively justify the use of CDR in the treatment of cervical disc disease. 27 Functional outcome after CDR and ACDF is significant when determining cost-effectiveness. The former procedure has certain theoretical advantages with regard to function as compared with ACDF, including maintenance of segmental motion and reduction in adjacent segment degeneration. A recent meta-analysis has shown promising functional results for CDR, including greater improvement in neurological status and overall success, as compared with those for ACDF. 21 Given these findings, we assumed in the reference case that CDR results in the higher utility value of 0.9 as compared with ACDF, which was assigned a value of 0.8. Since the long-term utilities of CDR and ACDF have not been established, 1-way sensitivity analysis was used to determine the effect of the uncertainty of these utility values on our results. The threshold utility value for CDR was found to be This means that if the long-term health utility of CDR is less than 0.796, ACDF becomes the more costeffective strategy in the treatment of cervical disc disease. With reference to the WTP $50,000 per QALY threshold, CDR is a cost-effective strategy as long as the utility factor is at least Anterior cervical discectomy and fusion becomes the more cost-effective strategy if its utility is greater than Variance in the utility factors for both revision CDR and revision ACDF did not affect the outcome of the model. Long-term clinical trials to better determine the utility values of CDR and ACDF will be important to justify the higher utility value assigned to one treatment versus the other. Our reference case showed that CDR has the potential to be a more cost-effective strategy for the treatment of cervical disc disease than ACDF. Findings in the reference case are extrapolated based on the assumption that a CDR prosthesis will survive for 20 years and result in better function than that obtained with ACDF. Based on our reference case assumptions, CDR resulted in a CER of $3042 per QALY, whereas ACDF resulted in a CER of $8760 per QALY. The CERs of both ACDF and CDR compare favorably with those of other medical and surgical interventions. In the 1990s, total hip replacement demonstrated a CER of $4600 per QALY; medical treatment of hypertension, a CER of $24,900 per QALY; and lumbar discectomy, a CER of $29,200 per QALY. 6,20 More recently, total ankle arthroplasty was shown to have an ICER of $18,419 per QALY gained, as compared with ankle fusion. 33 The ICER is a comparative calculation and represents the difference in cost divided by the difference in the effectiveness of 2 procedures. Thus, the ICER summarizes the additional cost per unit of health benefit gained in switching from one medical intervention to another. In our reference case, the ICER of CDR versus ACDF was -$2394, meaning that CDR has the potential to be not only less costly but also more effective than fusion. Direct costs, as estimated using DRG and CPT codes, include a 551

7 S. A. Qureshi et al. Fig. 4. Results of sensitivity analysis of the effect of utility factor variance on the ICER of CDR. Red line represents ACDF; blue line, CDR. number of factors that influence health care resource utilization, such as average length of stay, operating room time, cost of instrumentation, billing practices, and so forth. Anterior discectomy and fusion was found to have an overall higher direct cost despite the fact that the CDR implant itself is more expensive than the instrumentation involved in ACDF. Although estimates of CDR and ACDF costs vary widely, a number of studies have found higher costs for ACDF than for CDR. 3,26,38 Anterior discectomy and fusion has been associated with longer hospital stays, which helps to explain the higher costs. Another contributing factor is the substantial range of ACDF instrumentation costs, depending on the use of interbody cages, bone morphogenetic protein, and the choice of plates, spacers, screws, and so forth. 10 A negative ICER means that based on the reference case assumptions, CDR is a truly dominant strategy as compared with ACDF. Several limitations to our study warrant consideration. One potential limitation is inaccuracy in the construction of our decision model. We constructed a decision tree using common decision analysis software. SooHoo and Kominski used a similar model and software in their CEA of total ankle arthroplasty. 33 The use of more complex techniques, such as Markov modeling, can improve accuracy when determining the likelihood of changes in outcome probabilities and health state utilities. However, these more complex models have not been shown to affect the qualitative results of CEAs. 16,24,31 Another potential limitation is the uncertainty that arises in our analysis because of the estimation of effectiveness and health state utilities as they relate to each procedure. The utility of a disease state is graded on a scale of 0 1, with 1 being perfect health and 0 being death. Unfortunately, no studies have assigned a specific utility factor to cervical disc disease. However, large-scale studies have demonstrated that arthritis of a joint and neck pain both have a health state utility factor of 0.7. Our study would certainly benefit from a more direct measure of the health state utility of cervical disc disease. Health state utility factors assigned after ACDF and CDR were also based on interpretation of outcomes data. Sensitivity analysis was thus used to identify threshold values for these unknown variables that would indicate cost-effectiveness. As more long-term data on CDR outcomes become available and as health utility factors and potential complications become better defined, the CEA of CDR will change accordingly. The current analysis is a reflection of the data available on CDR and ACDF at this time. Gross-costing methods were used in this study to estimate the direct costs related to both CDR and ACDF procedures. Although microcosting techniques could have provided a more precise estimate, sensitivity analysis showed that should the gross cost of CDR surpass $17,000, ACDF would become the more cost-effective option. Conclusions Cervical disc replacement has the potential to advance the treatment of symptomatic cervical disc disease unresponsive to appropriate conservative management. Interest and excitement in this new technology is growing based on results in the available literature comparing CDR and ACDF. Findings in our study suggest that assuming a 20-year survival, both ACDF and CDR are costeffective; however, CDR is a more cost-effective strategy. Importantly, we found that in order for CDR to be a costeffective strategy, the prosthesis must survive for at least 552 J Neurosurg: Spine / Volume 19 / November 2013

8 Cost-effectiveness of CDR and ACDF 11 years, and that if the prosthesis survival time is less than 9.75 years, then ACDF becomes the more cost-effective strategy. Surgeons and other decision makers can use these thresholds to formulate future studies and evaluate the results of longer-term follow-ups to decide whether to perform CDR. Disclosure Dr. Hecht is a consultant for Zimmer, Medtronic, Stryker, and DePuy. Dr. Qureshi is a consultant for Stryker Spine, Medtronic, Zimmer, and Orthofix. Author contributions to the study and manuscript prepara tion include the following. Conception and design: Koehler, Qureshi, McAnany, Hecht. Acquisition of data: McAnany. Analysis and in terpretation of data: Koehler, McAnany, Goz. Drafting the article: McAnany, Goz. Critically revising the article: all authors. Re viewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Koehler. 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