Health impact and economic analysis of NGO-supported neurosurgery in Bolivia

Clinical article

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Object

Bolivia, one of the poorest countries in the world, ranks 108th on the 2013 Human Development Index. With approximately 1 neurosurgeon per 200,000 people, access to neurosurgery in Bolivia is a growing health concern. Furthermore, neurosurgery in nonindustrialized countries has been considered both cost-prohibitive and lacking in outcomes evaluation. A non-governmental organization (NGO) supports spinal procedures in Bolivia (Solidarity Bridge), and the authors sought to determine its impact and cost-effectiveness.

Methods

In a retrospective review of prospectively collected data, 19 patients were identified prior to spinal instrumentation and followed over 12 months. For inclusion, patients required interviewing prior to surgery and during at least 2 follow-up visits. All causes of spinal pathology were included. Sixteen patients met inclusion criteria and were therefore part of the analysis. Outcomes measured included assessment of activities of daily living, pain, ambulation, return to work/school, and satisfaction. Cost-effectiveness was determined by cost-utility analysis. Utilities were derived using the Health Utilities Index. Complications were incorporated into an expected value decision tree.

Results

Median (± SD) preoperative satisfaction was 2.0 ± 0.3 (on a scale of 0–10), while 6-month postoperative satisfaction was 7 ± 1.4 (p < 0.0001). Ambulation, pain, and emotional disability data suggested marked improvement (56%, 69%, and 63%, respectively; p = 0.035, 0.003, and 0.006). Total discounted incremental quality-adjusted life year (QALY) gain was 0.771. The total discounted cost equaled $9036 (95% CI $8561–$10,740) at 2 years. Computing the incremental cost-effectiveness ratio resulted in a value of $11,720/QALY, ranging from $9220 to $15,473/QALY in a univariate sensitivity analysis.

Conclusions

This NGO-supported spinal instrumentation program in Bolivia appears to be cost-effective, especially when compared with the conventional $50,000/QALY benchmark and the WHO endorsed country-specific threshold of $16,026/QALY. However, with a gross domestic product per capita in Bolivia equaling $4800 per year and 30.3% of the population living on less than $2 per day, this cost continues to appear unrealistic. Additionally, the study has several significant limitations, namely its limited sample size, follow-up period, the assumption that patients not receiving surgical intervention would not make any clinical improvement, the reliance on the NGO for patient selection and sustainable practices such as follow-up care and ancillary services, and the lack of a randomized prospective design. These limitations, as well as an unclear understanding of Bolivian willingness-to-pay data, affect the generalizability of the study findings and impede widespread economic policy reform. Because cost-effectiveness research may inevitably direct care decisions and prove that an effort such as this can be cost saving, a prospective, properly controlled investigation is now warranted.

Abbreviations used in this paper:CUA = cost-utility analysis; HUI3 = Health Utilities Index Mark 3; ICER = incremental cost-effectiveness ratio; NGO = non-governmental organization; QALY = quality-adjusted life year.

Abstract

Object

Bolivia, one of the poorest countries in the world, ranks 108th on the 2013 Human Development Index. With approximately 1 neurosurgeon per 200,000 people, access to neurosurgery in Bolivia is a growing health concern. Furthermore, neurosurgery in nonindustrialized countries has been considered both cost-prohibitive and lacking in outcomes evaluation. A non-governmental organization (NGO) supports spinal procedures in Bolivia (Solidarity Bridge), and the authors sought to determine its impact and cost-effectiveness.

Methods

In a retrospective review of prospectively collected data, 19 patients were identified prior to spinal instrumentation and followed over 12 months. For inclusion, patients required interviewing prior to surgery and during at least 2 follow-up visits. All causes of spinal pathology were included. Sixteen patients met inclusion criteria and were therefore part of the analysis. Outcomes measured included assessment of activities of daily living, pain, ambulation, return to work/school, and satisfaction. Cost-effectiveness was determined by cost-utility analysis. Utilities were derived using the Health Utilities Index. Complications were incorporated into an expected value decision tree.

Results

Median (± SD) preoperative satisfaction was 2.0 ± 0.3 (on a scale of 0–10), while 6-month postoperative satisfaction was 7 ± 1.4 (p < 0.0001). Ambulation, pain, and emotional disability data suggested marked improvement (56%, 69%, and 63%, respectively; p = 0.035, 0.003, and 0.006). Total discounted incremental quality-adjusted life year (QALY) gain was 0.771. The total discounted cost equaled $9036 (95% CI $8561–$10,740) at 2 years. Computing the incremental cost-effectiveness ratio resulted in a value of $11,720/QALY, ranging from $9220 to $15,473/QALY in a univariate sensitivity analysis.

Conclusions

This NGO-supported spinal instrumentation program in Bolivia appears to be cost-effective, especially when compared with the conventional $50,000/QALY benchmark and the WHO endorsed country-specific threshold of $16,026/QALY. However, with a gross domestic product per capita in Bolivia equaling $4800 per year and 30.3% of the population living on less than $2 per day, this cost continues to appear unrealistic. Additionally, the study has several significant limitations, namely its limited sample size, follow-up period, the assumption that patients not receiving surgical intervention would not make any clinical improvement, the reliance on the NGO for patient selection and sustainable practices such as follow-up care and ancillary services, and the lack of a randomized prospective design. These limitations, as well as an unclear understanding of Bolivian willingness-to-pay data, affect the generalizability of the study findings and impede widespread economic policy reform. Because cost-effectiveness research may inevitably direct care decisions and prove that an effort such as this can be cost saving, a prospective, properly controlled investigation is now warranted.

Bolivia, one of the poorest countries in the world, ranks 108th on the 2013 Human Development Index (http://hdr.undp.org/en/data); for comparison, Chile is 40th and the US is 3rd on the same index. There are approximately 10.2 million people living in Bolivia with a mean life expectancy of 64 years for males and 67 years for females. With approximately 1 neurosurgeon for every 200,000 people, and the majority of the population living outside urban centers, access to neurosurgery is a growing global health concern. Furthermore, neurosurgery has often been considered both cost-prohibitive and deficient in outcome valuation, especially in nonindustrialized countries. However, in most instances, these suppositions have not been methodologically examined.

Cost-effectiveness analysis requires defining, as it can include several disparate analyses. Unlike cost-minimization and cost-benefit analyses, cost-effectiveness analysis measures the output (benefit) in terms of quality-adjusted life years (QALYs), rather than in monetary terms.4,6,17–19,23 Any cost-effectiveness analysis that accounts for the perceived value of an intervention or health state is termed a cost-utility analysis (CUA).4,17–19,23 Cost-utility analysis is a type of preference-based quality of life metric. Health status instruments, such as the 36-Item (SF-36), 12-Item (SF-12), and 6-Dimension (SF-6D) Short Form Health Surveys,19,20 and other standardized questionnaires are often used as surrogates to elicit patients' valuations for their current health state. Single quality of life values are generated and expressed on a 0–1 scale. Zero represents the value of death and 1 represents the value of perfect health. This valuation of a health state is also known as “utility,” a concept developed by economists to indicate the strength of an individual's preference.

Spine surgery in the US is expensive. Microdiscectomy for lumbar disc herniation, for example, was recently shown to cost $69,403/QALY when compared with nonsurgical management.22 Given that discectomy surgery does not include instrumentation, which is invariably more costly, and the fact that the total per capita expenditure on health in Bolivia is approximately $204, it appeared unlikely that spinal instrumentation would be cost-effective in this setting. However, numerous variables influence a CUA and differences are expected when formally evaluating direct costs, indirect costs, and quality of life changes in Bolivia. To our knowledge, no CUA has ever been conducted on spinal instrumentation in Bolivia. Given this information and the fact that a local NGO, Solidarity Bridge, is supporting spinal instrumentation in Bolivia, we sought to determine the impact and cost-effectiveness of this procedure in this country.

Methods

Study Population

In a retrospective review of prospectively collected data, with the help of Solidarity Bridge, 19 patients were identified from two Bolivian cities prior to spinal instrumentation and followed prospectively over 12 months (Fig. 1). Per Solidarity Bridge inclusion criteria, patients initially met with social workers to determine socioeconomic and disability status to qualify for sponsorship. Patients also required an interview prior to surgery and during at least two follow-up visits. Because patients with malignant origins of spinal deformity are often significantly different in presentation, management, and prognosis, they were excluded from the study. All traumatic and infectious spinal injuries were included. A total of 16 patients (84%) were included in the final analysis. Outcomes measured included assessment of activities of daily living, pain, ambulation, return to work/school, and self-reported satisfaction. Cost-effectiveness was determined by CUA.

Fig. 1.
Fig. 1.

Flow diagram depicting an observational pre-post study design. A total of 19 patients were initially identified. Sixteen patients satisfied all inclusion criteria to be included in the CUA.

Patient characteristics with underlying quality of life functioning prior to surgery are given in Table 1. The median age of our patients was 36 compared with a national median of 22.2. Twelve patients (75%) were male. Preoperatively 12 (75%) were nonambulatory, 12 (75%) were in severe pain, and 11 (69%) suffered from emotional disability. The authors received IRB approval to conduct standardized interviews and review patient data. Otherwise, the authors did not interfere with or change the ongoing work by Solidarity Bridge, which includes ensuring sustainability of patient care, follow-up, medication delivery, and support services for the patients. The project did not fall under HIPAA requirements because no protected health information was recorded or linked by code to data.

TABLE 1:

Characteristics of patients included in this study*

VariableStudy PopulationBolivian Population
no. of patients16 (84)
median age (yrs)3622.2
sex (%)
 males12 (75)F > M
 females4 (25)
mean follow-up in mos (range)7.4 (1–24)
occupation (%)
 student3 (18.8)
 farmer4 (25)11.3%
 worker6 (37.5)51.8%
 professional2 (12.5)14.2%
 none1 (6.25)7.5%
pathology (%)
 Pott's disease2 (12.5)2%
 herniation w/ spondylolisthesis3 (18.75)
 traumatic fracture11 (68.75)
  cervical1 (6.25)
  thoracic3 (18.8)
  lumbar7 (43.8)
increase in QALY (%)
 preopreferent
 postop15 (94)
not ambulating
 preop12 (75)
 postop3 (19)
 p value0.035
severe pain
 preop12 (75)
 postop1 (6)
 p value0.003
emotional disability
 preop11 (69)
 postop1 (6)
 p value0.006

p values determined by McNemar's test for paired proportions.

Values retrieved from http://www.worldbank.org/ (accessed 8/22/11).

Decision Analysis

To make cost-utility calculations, several model assumptions were made. These assumptions included the following: 1) an incremental cost-effectiveness ratio (ICER) was determined by comparing spinal instrumentation to no spinal instrumentation, given that most patients with spinal cord injury of any type in Bolivia would not receive an intervention; 2) patients without an intervention would not significantly improve given the limited resources, such as rehabilitation, physical therapy, and other ancillary services; 3) patients would be assisted by Solidarity Bridge to ensure follow-up, medication use, and sustainable care; and 4) the typical risks associated with surgery included infection, instability or incomplete arthrodesis requiring reoperation, adjacent-segment disease, intractable pain, neurological injury, persistent or worsening paraplegia, and death. Complications were incorporated into the final weighted cost analysis (Table 2).

TABLE 2:

Postoperative complications of spinal instrumentation in Bolivian cohort

ComplicationNo. of PatientsNo. of TreatmentsPercentage of Total Cohort (Based on Treatment)
repeat surgery126.25
fall106.25
instrumentation failure106.25
infections5531.25

In our sample, the 12-month surgical success rate was 87.5%. Based on data reported in the literature, the complication rate of spinal instrumentation can be as low as 3%, with a reoperation rate of 2%.21 Due to the variability in reported complication rates, however, and the dependence on procedure type, the following additional model assumptions were made: 1) 1-year surgical success, defined as intact instrumentation and bone fusion on radiographs, was set at 85%, a value lower than that reported in the literature and this sample, but considered appropriate in a nonindustrialized setting; 2) utilities were assumed to be stable; 3) the time frame chosen for the CUA was extrapolated to 2 years; 4) all patients would survive the study period, because the median patient age was 36; and 5) follow-up for all patients was assumed to be similar.

Utility Assessment

Given substantial cultural and comprehension barriers identified during presurvey testing, treatment effectiveness (using QALYs) was evaluated by obtaining health states from the Health Utilities Index Mark 3 (HUI3) and not the direct time trade-off method or other preference-based questionnaires (such as the SF-36, SF-12, and EuroQol Group–5 Dimension [EQ-5D]).5,11,13 To our knowledge, the HUI3 had not previously been administered in Bolivia, but evidence of its international generalizability does exist in the literature.12 Accordingly, we used the Spanish 40Q interviewer-administered version in our setting. The HUI3 uses preference-based scoring functions to convert descriptive measures of disability into measures of overall quality of life.

Postoperative utilities at 1, 3, 6, and 12 months were compared with preoperative health states to measure incremental change. Transitions between health states were therefore captured during the study period. The Wilcoxon rank-sum test was used to assess normality of the utility data. The total QALY gain (comparative effectiveness) was also determined by multiplying the years of utility gain by years of benefit duration and comparing it to the preoperative utility (quality of life) state.

Identification of Costs

All pertinent costs for the intervention were accounted for, including the surgery and its associated fees, follow-up care, medications, other health services, complications, and indirect costs, such as missed work and unpaid caregiver time. Medicare reimbursement rates, which are often used to represent societal impact in the US, were not pertinent in this setting. To estimate direct medical costs at each time point, Solidarity Bridge–reported instances of resource use were multiplied by unit costs for each component (Table 3). Health care economics in Bolivia are complex and constantly changing. Currently, 3 systems exist, and include the public sector that covers approximately 30% of the low-income population, the social security arm for salaried employees making up 27% of the population, and the private sector that accounts for approximately 10% of the population.8 In the last decade in Bolivia, approximately 22% percent of health expenditures were financed by the government, 38% by social security, and 37% paid directly by households and NGOs. Most of the nationally funded programs are directed toward women and maternal care. Providers in national hospitals are salaried and in private hospitals are reimbursed on a fee-for-service basis. Our investigation focused on the population that would otherwise have limited to no health care access. Under an almost entirely flat-fee system, we accounted for hospital charges, physician fees, and ancillary costs that were billed and paid for by the NGO (Solidarity Bridge). The cost for the donated instrumentation (estimated by the company) was also included.

TABLE 3:

Mean surgery cost and associated unit costs by cost component*

Cost ComponentsMean Costs/Unit Cost ($)
direct cost
 instrumentation supplies
  rods/screws/caps3000
 health care visit
  surgeon20
  social worker10/patient
 diagnostic tests
  radiograph16.74
 medications/month
  analgesics32.18
  antibiotics24.05
  steroids40.10
  NSAIDs8.03
surgery
  primary surgery§3000
  OR fee300
  hospital stay1000
  repeat surgery4300
 patient cost
  travel3
indirect cost (per hr)
 missed work1.58
 unpaid caregiver time0.74
 missed housekeeping0.61

NSAID=nonsteroidal antiinflammatory drug; OR=operating room.

Donated costs.

No patients were taking or paying for medications at 1-month follow-up.

Includes surgeon costs, anesthesiology costs, OR time costs, and ancillary staff costs.

Indirect costs were estimated using the standard human capital approach9 by multiplying the change in hours worked by the gross-of-tax wage rate based on self-reported wages at preoperative interviews. All costs were adjusted for inflation (http://www.bls.gov/data/inflation_calculator.htm) and are expressed in 2011 US dollars with a 3% annualized discount rate used in the analysis of both costs and QALYs.

Calculations of QALYs and Costs

For the 2-year extrapolated study period, QALY was calculated using the following formula:18

article image
in which t is the yearly spinal instrumentation survival rate (0.85), u is the average incremental utility (0.512), and dq is the discounting rate for QALYs (3%).

The equation for the total discounted cost associated with spinal instrumentation in Bolivia is:

article image
An initial cost that was incurred at or immediately prior to surgery was not discounted. Costs incurred following surgery were discounted appropriately.

Sensitivity Analysis

The model was assessed using a univariate sensitivity analysis (Table 4). The relevant parameters included utility value, retention rate (survival probability), discounting rate for QALYs, and discounting rate for costs. Each parameter was varied at fixed intervals individually. In the case of yearly survival probability and incremental utility value, values were varied by 20%, a commonly used interval when larger series are unavailable for model calibration.

TABLE 4:

Univariate sensitivity analysis of spinal instrumentation in Bolivia

Variable Adjustment Cost YieldYearly Survival ProbabilityIncremental Utility ValueDiscount Rate for QALYsDiscount Rate for Costs
high1.00.4120.050.01
current0.850.5120.030.03
low0.700.6120.010.05
range ($/QALY)9220–15,4739800–14,55111,388–12,04811,673–11,770

Results

Of the 19 patients identified, only 16 completed the per protocol study design. Two patients were lost to follow-up and 1 patient died during the study period. Because the nature of the death was considered to be unrelated to his injury or surgery, these data were censored and excluded from the CUA. As described, the HUI35 was used for patient-based utility assessment. For each patient, the difference between preoperative and postoperative utility values at each time point was calculated and the mean of these differences obtained. Decreases in function were accounted for by incorporating negative utilities into the mean incremental utility calculation. The mean (± SD) preoperative utility value was 0.128 ± 0.202, increasing to 0.640 ± 0.320 postoperatively (p < 0.001). This yields an average incremental utility gain of 0.512 (95% CI 0.313–0.711) for our Bolivian patients undergoing spinal instrumentation in this study. Median preoperative satisfaction was 2.0 ± 0.3 (on a scale of 0–10), while 6-month postoperative satisfaction was 7 ± 1.4 (p < 0.0001). Ambulation, pain, and emotional disability data suggested marked improvement (56%, 69%, and 63% gains, respectively; p = 0.035, 0.003, and 0.006, respectively). There were a mean of 47 ± 14 work days missed, while 6 patients (37.5%) reported missed homemaker or caregiver days of an unreliable duration.

Our base case analysis resulted in a total discounted incremental QALY gain of 0.771. Total mean costs incurred by Solidarity Bridge were $9651 (95% CI $8561–$10,740) at 2 years. When discounted, the total costs of Solidarity Bridge–supported spinal instrumentation were $9036 at 2 years. Societal costs include all possible charges, including donations and government subsidies, irrespective of ability or willingness to pay. Computing the ICER resulted in a cost-utility of spinal instrumentation in our sample of $11,720/QALY. The univariate sensitivity analysis demonstrated that sustainability of the instrumentation (retention) affected the ICER most dramatically, which corresponded to an ICER range of $9220–$15,473/QALY.

Discussion

Spinal instrumentation in Bolivia appears to be cost-effective, especially when compared with the conventional $50,000/QALY benchmark. This is further supported by a 2005 WHO report (http://www.who.int/choice/costs/CER_thresholds/en/index.html) on country-specific threshold values of cost-effectiveness that suggests a more appropriate threshold in the region of $16,026/QALY (adjusted for inflation).

We estimated the cost per QALY gained from the Solidarity Bridge–supported spinal instrumentation program in Bolivia to range from $9220 to $15,473/QALY. Varying patient retention had the greatest effect on the ICER, suggesting that efforts should focus on improving patient compliance, early access to surgery, surgical training and technique, hygiene, prophylaxis against infection, and follow-up care.

Although this range of ratios compares favorably with the economic value of other health care interventions, in a country in which the per capita gross domestic product is $4800 per year and 30.3% of the population lives on less than $2 per day, this appraisal hardly seems pragmatic. Many studies report ICERs that are surprising. For example, although the mean cost of pediatric heart transplantation is approximately $234,124, the benefit in returned health years is substantial, resulting in an ICER of approximately $55,321/QALY.3 In contrast, the inexpensive drug cephalexin is often given prophylactically during dental procedures in patients with prosthetic joints. However, because the likelihood of an infection in this population is marginal, at best, the ICER equals $735,284/QALY.10 Additional examples of ICERs can be found in Table 5. What is noteworthy about any ICER is its relativity. Utilities are most commonly derived from population preference weights, and the enormous variability among nations and cultures has already been described.15 Furthermore, country-specific thresholds often differ significantly from societally determined willingness to pay. In the US, for example, willingness to pay often far exceeds the $50,000/QALY convention. Choice modeling is a technique often used to estimate willingness to pay but is beyond the scope of this study.23 It therefore remains unclear if the Bolivian government would support such a program for their population.

TABLE 5:

Cost-effectiveness of various medical interventions in the US

InterventionCost in $/QALY*
keratoprosthesis surgery for severe corneal injury117,034
coronary bypass surgery for occluded left anterior descending artery746,557
chemoprophylaxis after occupational exposure to HIV1651,752
primary pediatric heart transplant355,321
MRI for equivocal neurological symptoms14142,206
1 day of chemoprophylaxis prior to receiving dental work for patients w/ prosthetic joints10735,284

Costs adjusted for inflation to 2011 US dollars (http://www.bls.gov/data/inflation_calculator.htm).

The strength of this study was use of a validated instrument for deriving individual health state values and not relying on complex statistical modeling. The HUI3 describes 972,000 unique health states and has been used in numerous international cost-effectiveness analyses.2 A further strength of this study was our ability to follow these health states prospectively during the postoperative period. Although we acknowledge that the time trade-off or standard gamble approaches would more directly measure utilities, it was culturally unfeasible in this setting. Assessing both direct and indirect costs as well as incorporating societal impact (the cost of donations) into our analysis resulted in a larger ICER than if we looked at the provider or patient perspectives alone. This augmented value represents the worst-case scenario and is appropriate when considering the sustainability of donations and future enterprises in this population.

The analysis has several limitations. First, our control population for ICER is based on a major assumption that these patients would not improve neurologically or functionally without surgical intervention. Although this represents the norm in Bolivia, this could dramatically mitigate our ICER and therefore the economic benefit. Furthermore, our sample size and follow-up are limited, thereby affecting our ability to capture rare surgical complications such as deep venous thrombosis/pulmonary embolism, nonunion, late revisions, and others. It is unclear if this population is at a higher risk for late failures and lower fusion rates, although an effort to capture these data are ongoing. We also depended on Solidarity Bridge funding and their ongoing work for sustainability. Ensuring adequate follow-up and resources in the developing world remains a critical barrier to introducing subspecialized care. Despite this, the authors believe that surgical capabilities in Bolivia are adequate and that there is precedent in Bolivia to adopt social programs that include NGOs such as Solidarity Bridge to provide the necessary ancillary support (although most have focused on issues such as maternal health, newborn care, and infectious diseases).24

Patient selection was directed by Solidarity Bridge, making our sample size, potential confounders, and foreseeable challenges (such as compliance) difficult to control. The result was a relatively heterogeneous cohort, comprising different pathologies that required individualized interventions, and made our analysis imprecise. We were unable to determine if one particular spine procedure was more cost-effective than others, but rather made conclusions about spine surgery in this population in general. Indirect cost assessment depended largely on patient self-reporting and was subject to cultural taboos, recall bias, and potential miscalculations, although an electronic alternative was not available. The inherent difficulties of contacting patients in a developing nation, particularly in rural areas, also made comprehensive follow-up challenging. Due to Solidarity Bridge socioeconomic requirements for receiving assistance, many patients in this study do not have telephone lines or physical addresses.

This study has only started to address the societal and payer perspectives, the national economics in Bolivia, and the long-term implications of this initiative. Although indirect costs were analyzed, it was exceedingly difficult to capture their true impact. Because the average patient in this study resided with 4–5 other members of their family, the cascade of effects that resulted from the primary earner of a household being able to return to work or resume home care activities is difficult to ascertain but can realistically be assumed to be significant. For example, in 1 instance we received a report that a patient successfully returned to her caregiver duties, which in turn allowed a grandchild (who had assumed the care of her grandparent) to return to school. This type of missed data, when quantifiable, could greatly increase the societal value of our intervention and our understanding of willingness to pay in this setting. These types of data would help determine whether national support for such a specialized initiative is realistic. Lastly, our evaluation is based on observational rather than randomized measures of outcomes. Comparing a larger cohort to a true control group that receives no surgical intervention would provide an ICER that is more indicative of the true QALY benefit of spine surgery in this population.

Conclusions

A paradigm shift is underway in medicine, but despite the increasing prominence of evidence-based practice in neurosurgery, a standardized rubric for collecting, analyzing, and presenting cost-effectiveness data from nonindustrialized countries has yet to be established. While access and costs remain problematic in these settings, cost-effectiveness research may inevitably direct care decisions and prove that an effort such as this can be cost saving. This type of research may also significantly improve patient outcomes by imposing a close examination of standard clinical practices for efficacy of treatment. Neurosurgery ought to spearhead the effort toward cost-effectiveness and health care improvement, no matter the economics. As has been shown in the past, with some creativity, investments in our patient population now can yield long-lasting returns in the future.

Disclosure

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

Author contributions to the study and manuscript preparation include the following. Conception and design: Ament, Flores, Weaver, Moser. Acquisition of data: Ament, Greene, Flores, Capobianco, Salas, Uriona, Moser. Analysis and interpretation of data: Ament, Greene, Uriona. Drafting the article: Ament, Greene, Weaver, Moser. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Ament. Statistical analysis: Ament. Administrative/technical/material support: Flores, Capobianco, Salas, Uriona, Weaver, Moser. Study supervision: Flores, Capobianco, Salas, Uriona, Weaver, Moser.

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Article Information

Address correspondence to: Jared D. Ament, M.D., M.P.H., Department of Neurological Surgery, University of California Davis, 4860 Y St., Ste. 3740, Sacramento, CA 95817. email: jared.ament@ucdmc.ucdavis.edu.

Please include this information when citing this paper: published online February 14, 2014; DOI: 10.3171/2014.1.SPINE1228.

© AANS, except where prohibited by US copyright law.

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    Flow diagram depicting an observational pre-post study design. A total of 19 patients were initially identified. Sixteen patients satisfied all inclusion criteria to be included in the CUA.

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