SPINE Volume 40, Number 8, pp 514-520 ©2015, Wolters Kluwer Health, Inc. All rights reserved.

RANDOMIZED TRIAL

Comparing Cost-effectiveness of X-Stop With Minimally Invasive Decompression in Lumbar Spinal Stenosis A Randomized Controlled Trial Greger Lønne, MD,*†‡ Lars Gunnar Johnsen, MD, PhD,†‡§ Eline Aas, PhD,¶ Stian Lydersen, PhD, Hege Andresen, MSc,†‡ Roar Rønning, MD,* and Øystein P. Nygaard, MD, PhD†‡**

Study Design. Randomized clinical trial with 2-year follow-up. Objective. To compare the cost-effectiveness of X-stop to minimally invasive decompression in patients with symptomatic lumbar spinal stenosis. Summary of Background Data. Lumbar spinal stenosis is the most common indication for operative treatment in elderly. Although surgery is more costly than nonoperative treatment, health outcomes for more than 2 years were shown to be significantly better. Surgical treatment with minimally invasive decompression is widely used. X-stop is introduced as another minimally invasive technique showing good results compared with nonoperative treatment. Methods. We enrolled 96 patients aged 50 to 85 years, with symptoms of neurogenic intermittent claudication within 250-m walking distance and 1- or 2-level lumbar spinal stenosis, randomized to either minimally invasive decompression or X-stop. Qualityadjusted life-years were based on EuroQol EQ-5D. The hospital unit costs were estimated by means of the top-down approach. Each cost unit was converted into a monetary value by dividing the overall cost by the amount of cost units produced. The analysis of costs and

From the *Department of Orthopedic Surgery, Innlandet Hospital Trust, Lillehammer, Norway; †Department of Neuroscience, Norwegian University of Science and Technology, Trondheim, Norway; ‡National Advisory Unit on Spinal Surgery, St. Olavs Hospital, Trondheim University Hospital, Trondheim, Norway; §Department of Orthopedic Surgery, St. Olavs Hospital, Trondheim University Hospital, Trondheim, Norway; ¶Institute of Health Management and Health Economics, University of Oslo, Norway; Regional Centre for Child and Youth Mental Health and Child Welfare, Norwegian University of Science and Technology, Trondheim, Norway; and **Department of Neurosurgery, St. Olavs Hospital, Trondheim University Hospital, Norway. Acknowledgment date: October 21, 2014. Revision date: December 20, 2014. Acceptance date: January 16, 2015. The device(s)/drug(s) is/are FDA approved or approved by corresponding national agency for this indication. No funds were received in support of this work. No relevant financial activities outside the submitted work. Address correspondence and reprint requests to Greger Lønne, MD, Department of Orthopaedic Surgery, Innlandet Hospital Trust, Anders Sandvigsgt 17, 2609 Lillehammer, Norway; E-mail: [email protected] DOI: 10.1097/BRS.0000000000000798

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health outcomes is presented by the incremental cost-effectiveness ratio. Results. The study was terminated after a midway interim analysis because of significantly higher reoperation rate in the X-stop group (33%). The incremental cost for X-stop compared with minimally invasive decompression was €2832 (95% confidence interval: 1886–3778), whereas the incremental health gain was 0.11 qualityadjusted life-year (95% confidence interval: −0.01 to 0.23). Based on the incremental cost and effect, the incremental cost-effectiveness ratio was €25,700. Conclusion. The majority of the bootstrap samples displayed in the northeast corner of the cost-effectiveness plane, giving a 50% likelihood that X-stop is cost-effective at the extra cost of €25,700 (incremental cost-effectiveness ratio) for a quality-adjusted life-year. The significantly higher cost of X-stop is mainly due to implant cost and the significantly higher reoperation rate. Key words: lumbar spinal stenosis, neurogenic intermittent claudication, X-stop, minimally invasive decompression, qualityadjusted life-years, cost-effectiveness study, EQ-5D, SF-6D, spine surgery, randomized controlled trial, multicenter study. Level of Evidence: 2 Spine 2015;40:514–520

L

umbar spinal stenosis (LSS) can cause neurogenic intermittent claudication and is the most common indication for spinal surgery among the elderly.1,2 Surgical decompression with laminectomy has been the “gold standard,” but minimally invasive decompression (MID) techniques are now widely used.3 Although surgery is more costly than nonoperative treatment, health outcomes for more than 2 years were shown to be significantly better among those treated surgically.4,5 MID still has the potential for complications and symptom recurrence.6 Interspinous process devices have been introduced as an alternative. By inducing a local flexion in the stenotic level, the implant can relieve symptoms. In 2005 X-stop (Medtronic, Minneapolis, MN) was introduced to the

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RANDOMIZED TRIAL market as the first Food and Drug Administration–approved interspinous process device.7 This method is also minimally invasive and more effective than conservative treatment.8,9 It does not enter the spinal canal; hence, there may be a lower risk of complications. Although a structured literature review by Burnett et al10 demonstrates that laminectomy is more cost-effective than X-stop, Skidmore et al25 found in a randomized controlled trial that the X-stop is cost-effective compared with conservative treatment and dominant compared with laminectomy. To our knowledge, there are no studies comparing the costeffectiveness of X-stop with MID as part of a randomized controlled trial.

Aim The aim of this study was to compare the cost-effectiveness of X-stop with MID in LSS.

Comparing Cost-effectiveness of X-Stop • Lønne et al

this descriptive system contains 243 combinations, or health states, revised into a health-related quality of life (HRQoL) index with a range from −0.59 to 1.00, where 1.00 indicates full health. SF-6D was used for a sensitivity analysis and is a 6-dimensional health state classification system based on SF-36 (United Kingdom, standard gamble tariff).14 The 6 dimensions are physical functioning, role limitations, social functioning, pain, mental health, and vitality, revised into a HRQoL index with a range from 0.29 to 1.00 scale, were 1.00 indicates full health. QALYs were estimated by combining HRQoL index and time, calculating the area under the curve using the trapezoidal method.

Costs

This study was a randomized controlled multicenter trial in which 96 patients from 6 hospitals were enrolled either for X-stop or MID between June 2007 and September 2011. For further details, see reference Lønne et al.12

This study has the health care perspective; hence, the main analysis includes costs incurred by the health service. The main cost components in this analysis are estimated costs from a district hospital. All unit costs were calculated in Norwegian Krone (NOK) adjusted for inflation with 2010 as the reference year and converted into Euros using the rate 1 €2010= 8.47 NOK2010.

Study Population

Units and Unit Costs

Eligible patients were aged 50 to 85 years, with symptoms of neurogenic intermittent claudication within 250-m walking distance for at least 6 months, treated conservatively without sufficient effect. The patients had 1 or 2 levels of LSS between L2 and L5.

The hospital unit costs were estimated from the hospital department’s actual expenses by means of the top-down approach.15,16 Each cost unit was converted into a monetary value by dividing the overall cost by the amount of cost units produced. Data were available from the hospital electronic administrative system. Cost units are listed in Table 1. Surgery time unit (min) is the directly measured time from skin incision to skin closure. The costs are based on a standard operation team: 1 surgeon, 1 assistant surgeon, and 2 operation nurses. For the main surgeon, 30 minutes of preoperative and postoperative activity was included. The costs also include the use of disposable equipment and standard surgical instruments. The prices of all implants were withdrawn from the unit cost. Anesthetic time unit (min) was directly measured as time from start of the anesthesia to wake-up. The resources used cover the anesthesiologist and the nurse allocated to the operation. A fixed amount of €108, based on a standard procedure, was added to each procedure to account for the cost of equipment and medicine. Wake-up service unit (hr) was calculated by dividing the salary cost for the nurses allocated to this patient group by the total hours spent on operated patients. Postoperative hospital stay (d) at the care unit was counted from the day after treatment, where operation day is day zero. Nurses’ salaries and all costs belonging to the care unit are included in this unit cost, including the salary for the surgeons based on time spent at the unit. Postoperative radiography is a fixed cost based on the average time spent for the procedure, including doctors’ time to interpret the radiographical image. The cost of capital and spare capacity are included.

MATERIALS AND METHODS

Treatment Alternatives MID was performed under general anesthesia with a partial excision of the lower part of lamina and the medial aspects of the facet joint. The ligamentum flavum was resected from the central canal and lateral recesses to expose the dural sac and the nerve roots. The procedure was done bilaterally or with a crossover technique; both methods used a microscope or loupe combined with a retraction system.5 X-stop was inserted under general or local anesthesia with the patient in a right lateral decubitus position. An approximately 4- to 6-cm longitudinal midline skin incision was used and continued on both sides of the spinous process. After using a distractor, the X-stop was inserted through the interspinous ligament and locked by 2 wings located lateral on the implant. The position of X-stop was locked posteriorly by the intact supraspinous ligament and anteriorly by the lamina.

Health Outcome Health outcome was quality-adjusted life-years (QALYs), based on EuroQol EQ-5D utility index (United Kingdom, time trade-off tariff),13 measured at baseline, 6 weeks, 3 months, 1 year, and 2 years after index treatment. Based on responses from a questionnaire, EQ-5D evaluates 5 dimensions: mobility, self-care, activities of daily life, pain, and anxiety/depression. Each dimension is described by 3 possible problem levels (no, mild to moderate, and severe problem). Hence, Spine

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RANDOMIZED TRIAL

Comparing Cost-effectiveness of X-Stop • Lønne et al

TABLE 1. Units and Unit Costs (€) Unit Cost (€2010)

Source

Statistics and Analysis

Surgery time, min

€12

Anesthesia time, min

€6

Time at recovery, hr

€45

Hospital stay, d

€690

The implant

€3058

Manufacturer

Outpatient visit to physician

€238

Pedersen (2009)16

Outpatient visit to physiotherapist

€238

Pedersen (2009)16

Outpatient visit to nurse

€238

Pedersen (2009)16

Consultation, GP

€110

Nossen 200717

Consultation, physiotherapist

€110

Nossen 200717

Consultation, other*

€110

Nossen 200717

All prices are calculated into 2010 prices using the consumer price index on 1.094 pro year. *Includes chiropractor and acupuncturist.

The cost of the X-stop device is based on the actual price paid in NOK2010. The patient cost diary is based on data collected from each patient.17 Information, including visits to general practitioners, physiotherapists and other health care providers, and the use of painkillers, is registered and summed over the 2-year period.

Other Costs Hospital overhead costs are defined as costs not allocated to any specific department and are accounted for in the cost units allocated by percentage in a cost-weight analysis. Patient costs are accounted for in the sensitivity analysis. The Norwegian Labor and Welfare Administration tracks the number of days on sick leave and rehabilitation to get a picture of the general loss of production.

Cost-effectiveness Analysis The analysis of costs and health outcomes is presented by the incremental cost-effectiveness ratio (ICER),18 defined by ICER =

Total cost X-stop – Total cost decompression ⌬C = ´ ⌬E QALY X-stop – QALY decompression

where ΔC and ΔE are incremental costs and QALYs, respectively. The ICER expresses the costs of a QALY gained. As a negative ICER could imply 2 very different situations, either cost savings (−ΔC) or a negative health outcome (−ΔE), a net health benefit analysis was conducted. Given a certain willingness to pay (WTP) threshold for a QALY gained, defined by 516

λ, the net health benefit is defined as net health benefit = ΔE − (ΔC/λ). The suggested value of λ in Norway is €60200.19 The study was designed to have an 80% power to detect a minimal clinically important difference of 0.5 points in the primary effect score (Zürich Claudication Questionnaire).20 We then added up for the heterogeneity in multicenter studies, the risk of dropouts and a health economics evaluation. The patient population was then n = 180 (90 in each study arm). A midway interim analysis was performed as planned. The data contained repeated measurements of the EQ-5D, and arithmetic means of effect were calculated with independent Student t test at each follow-up. QALYs were calculated as the area under the curve, plotting each measurement in a time line.21,22 The costs were calculated as the product of the mean amount of units used multiplied by the cost per unit over the 2-year period (Table 2). Discounting for treatment effects or costs was not considered necessary because most of the costs occurred during the first year after index treatment. ICER was reported as a point estimate. A nonparametric bootstrap method with 1000 replications was used to account for the heterogeneity in costs and health outcomes and reported in the cost-effectiveness plane and cost-effectiveness acceptability curves. The cost-effectiveness acceptability curve reports the likelihood that X-stop is cost-effective according to different levels of WTP. An intention-to-treat method was used in the primary analysis. Missing data in EQ-5D and SF-6D were handled by multiple imputations with 100 imputed datasets, where 1 set was randomly picked for the bootstrapping process. The imputation model included the variables to be used in the analysis, as well as age, sex, treatment group, smoking habit, the duration of operation, number of levels operated, postoperative hospital stay, and secondary surgery. Sensitivity analyses were performed by applying various cost per hospital unit,16 using per-protocol analysis instead of intention-to-treat method, using SF-6D as a utility score, adding patient costs to total costs, and excluding 1 patient with a severe complication. Statistical analyses were performed via SPSS 21 for Mac and Microsoft Excel 2011 for Mac.

Study Approval Each patient gave written, informed consent before inclusion. They were randomized with randomly selected block sizes by a computer-based Web solution hosted by the medical faculty at the Norwegian University of Science and Technology (NTNU). The data were entered by independent observers, and permission to store the data was granted by the Norwegian data inspectorate. Procedures performed in this trial were strictly predefined in a protocol approved by all researchers. The study was conducted in accordance with the Helsinki Declaration and approved by the Regional Committees for Medical and Health Research Ethics (REC) for

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TABLE 2. Mean Hospital Units Used and Mean Costs From Index Treatment to 2 Years of Follow-up Mean Units Used

Mean Cost (€2010)

X-Stop (n = 40)

MID (n = 41)

X-Stop (n = 40)

MID (n = 41)

No.

SD

No.

SD

Cost

SD

Cost

SD

Surgery time (min)

46.9

20.8

112.9

41.0

548

243

1319

426

Anesthesia time (min)

115.3

38.6

180.9

43.2

680

228

1067

255

Wake-up service (min)

140.9

75.4

222.9

170.6

106

57

167

128

Postoperative stay (d)

2.2

1.7

3.4

3.1

1484

1165

2323

2165

Levels treated

1.2

0.4

1.3

0.5









X-stop device (mean)

1.2

0.4

0.0

0.0

3670

1239

0

0

Planned radiography (mean)*

1.0



0.0



51

0

0

0

Initial hospital cost

6538

Initial hospital cost

4876

Hospital follow-up cost Secondary surgery†

0.33

0.47

0.12

0.33

1554

2268

425

1222

Visit to physician

0.40

1.03

0.20

0.61

95

246

48

145

Visit to physiotherapist

0.00

0.00

0.03

0.16

0

0

6

38

Visit to nurse

0.05

0.32

0.05

0.32

12

76

12

75

Unplanned MRI*

0.23

0.70

0.17

0.50

42

131

32

93

Unplanned radiography*

0.10

0.30

0.07

0.35

6

18

4

21

Hospital follow-up cost

1709

527

Total cost

8247

5415 2832

Cost difference *Excludes imaging as part of the study. †Because of postoperative complication and persistent or recurrence of symptoms. MID indicates minimally invasive decompression; MRI, magnetic resonance imaging.

central Norway. The trial is registered under ClinicalTrials. gov, number NCT00546949.

We decided to terminate the recruitment after the midway interim analysis due to a significant higher reoperation rate in the X-stop group.12

reoperated with MID. Five (12%) of the patients undergoing MID received secondary surgery, 3 during the first hospital stay due to hematoma and 2 (5%) within 2 years due to recurrent symptoms. Mean days of sick leave or rehabilitation (SD) were 66 (150) for X-stop and 48 (134) for MID, and 54.3% of the patients received age pension.

Patient Population

Difference in Cost and Effect

Full cost data were provided for 81 of 96 patients (84.4%), including 40 in the X-stop group and 41 in the MID group. For patient demographic baseline, see Table 3. In EQ-5D, 3.4% of the data values were missing. The results show significant improvement from preoperative measurement in both groups but no significant difference between the groups at any follow-up time points (Figure 1). Secondary surgery was performed in 13 (33%) of the patients receiving X-stop. Two had fracture of the spinous process and 1 had dislocation of the implant. Ten (25%) had either persistent or recurrent symptoms. They were all

Table 2 reports the differences in cost components according to treatment option for the 2-year period. The incremental cost for X-stop compared with MID was €2832 (95% confidence interval: 1886–3778), whereas the incremental health gain was 0.11 QALY (95% confidence interval: −0.01 to 0.23). Based on the incremental cost and effect, the ICER was €25,700.

RESULTS

Spine

Cost-effectiveness Acceptability Curves The cost-effectiveness plane reports the 1000 ICERs on the basis of the bootstrap method. The main share of the replicates www.spinejournal.com

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Comparing Cost-effectiveness of X-Stop • Lønne et al

TABLE 3. Basic Demographic Data at Baseline

(N = 81)

X-Stop (n = 40)

Minimally Invasive Decompression (n = 41)

Age (SD)

67 (8.8)

67 (8.7)

Female (%)

23 (56)

18 (44)

Age pension

22 (55)

21 (51)

Working

6 (15)

10 (24)

Unemployed

1 (3)

2 (5)

On sick leave

6 (15)

4 (10)

Disability pension

3 (8)

4 (10)

Unknown

2 (5)

0 (0)

Work status (%)

EQ-5D (95% CI) 0.40 (0.31–0.50)

0.42 (0.33–0.51)

SF-6D (95% CI)

0.58 (0.55–0.61)

0.58 (0.55–0.61)

EQ-5D indicates EuroQol EQ-5D utility index; SF-6D, Short Form-6 dimensions; CI, confidence interval.

is located in the northeast quadrant (Figure 2), indicating better health outcome for X-stop but to a higher cost. The costeffectiveness acceptability curve shows the probability that X-stop is cost-effective given different levels of WTP for a QALY (Figure 3). Given a WTP in Norway at €60,200, the probability that X-stop is a cost-effective alternative is about 77%.

Sensitivity Analysis The results of the sensitivity analysis are shown in Table 4.

€25,700 for a QALY. The cost differences could mainly be explained by implant cost and the significantly higher reoperation rate in the X-stop group. A high reoperation rate is a disadvantage that undoubtedly has an influence on the assessment of X-stop. Some recently published studies report similar findings.23,24 With a reoperation rate at 33%, the X-stop may not be attractive to either clinicians or patients regardless of the result of the cost-effectiveness analysis.

Sensitivity Analysis Except from the per-protocol analysis, the conclusions were not altered by the sensitivity analysis. Per-protocol analysis excluded reoperated patients and revealed an increase in QALYs gained in the X-stop group compared with intentionto-treat method. This indicates that individuals undergoing reoperation report lower QALYs than the average in the X-stop group. One may argue for using a societal perspective, adding indirect costs from patient expenses and loss of production. Indeed, patient expenses are accounted for in the sensitivity analysis but do not alter the conclusion. Loss of production can be calculated from days of sick leave, and the results convey more days of sick leave in the X-stop group. Because more than half of the patients received age pension, the number of relevant patients is low and the result uncertain. Hence, these indirect costs are not accounted for. One patient in the MID group had a permanent nerve injury, which had a negative impact on the cost-effectiveness analysis but not the conclusion. Yet, the risk for this type of injury is low.25

Similar Studies Burnett et al10 authored a literature review on 108 publications that compares different treatments of LSS in a constructed

DISCUSSION Main Findings In this cost-effectiveness study, X-stop had significantly higher costs than MID. With a (nonsignificant) higher effect, it is 50% likely that X-stop is cost-effective, for an extra cost at

Figure 1. EQ-5D reported as mean (95% confidence interval) from initial treatment to 2 years of follow-up. MID indicates minimally invasive decompression.

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Figure 2. Plot of 1000 replications of ICER in a cost-effectiveness plane where ICER at €25,700 represents the average cost for 1 quality-adjusted life-year gained using X-stop compared with minimally invasive decompression, which is represented by the origo. WTP at €60,200 represents the Norwegian government willingness to pay for a QALY gained, and dots to the right of this line are cost-effective for X-stop within this price. Dots in the northwest corner left for the y axis represent ICER where X-stop is less effective and more costly. ICER indicates incremental cost-effectiveness ratio; WTP, willingness to pay.

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Comparing Cost-effectiveness of X-Stop • Lønne et al

directly as treated. Both groups could be operated in the lower cost outpatient setting. Skidmore et al11 compared the cost-effectiveness of X-stop with conservative care. Patients who failed conservative care were recruited to laminectomy. They observed that X-stop was more cost-effective than conservative care and dominant to laminectomy. However, selecting laminectomy patients from those who failed in conservative treatment introduces a possible selection bias.

Strength and Limitations

Figure 3. This cost-effectiveness acceptability curve shows the probability that X-stop is cost-effective given different levels of WTP for a quality-adjusted life-year. Here, the value of incremental costeffectiveness ratio at €25,700 is marked as 50% and WTP at €60,200 is marked as 77% probability for X-stop to be cost-effective. WTP indicates willingness to pay.

cost-effectiveness model. They report that laminectomy is the most effective treatment strategy, followed by X-stop and conservative treatment at a 2-year time horizon. Data were pooled from several sources and categorized into X-stop or laminectomy, regardless of decompression method and number of levels treated. All X-stop procedures were classified as “outpatient and local anesthesia” cases, and all laminectomy procedures as “inpatient and general anesthesia” cases. In our randomized controlled trial study, the groups were compared

We planned to recruit 180 patients, but the enrollment was terminated after inclusion of 96 patients because of higher reoperation rate in X-stop group. Hence, the study’s power to detect a minimal clinically important difference is low. The HRQoL reported at 2 years of follow-up may not reflect whether the patient has gone through a reoperation or not because it reports the present health state. By measuring the HRQoL prior to the reoperation and including this in the analysis, the picture could have been different. This was not a part of the protocol and may be a weakness of the study. From a health provider’s view, the higher cost and reoperation rate will have a negative impact on the X-stop’s feasibility. From the clinician’s point of view, the cost-effectiveness aspect is interesting but may not reflect the major disadvantages represented by the high risk of secondary surgery. The deviance between the clinical decision and the indication from the cost-effectiveness analysis could be explained by the fact that the health outcome does not capture the effect that reoperation has on HRQoL.

TABLE 4. Sensitivity Analyses Method

Mean Cost Difference (95% CI)

Mean QALY Difference (95% CI)

Point Estimate for ICER

Description

N

Different unit cost

Unit cost based on university hospital cost.

81

€1676 (416–2 935)

0.11 (−0.01 to 0.23)

€15250

Lower prices for index treatment. Follow-up costs are the same.

Per protocol analysis

Instead of ITT analysis.

64

€1721 (1191–2251)

0.16 (0.05–0.26)

€11099

Patients with reoperations and complications are excluded.

SF-6D

QALY calculated from SF-6D on the basis of transmission from SF-36.

81

€2832 (1886–3778)

0.07 (−0.01 to 0.13)

€40457

Multiple imputations on missing data (5.2%) from SF-36.

Patient cost

Patient personal costs in addition to hospital data. Includes visits to GP, physiotherapist and other, medication used and other out of the pocket costs.

Without patient with complication in the Without outlier minimally invasive decompression group.

Comments

75

€1670 (144–3196)

0.09 (−0.03 to 0.20)

€19523

Excluded are patients missing 2–3 schemas, including those missing none or 1 out of 3. Missing values set to zero since that is the typical.

80

€3103 (2262–3945)

0.11 (−0.01 to 0.23)

€27404

Excluding 1 patient with severe complication and long index stay.

QALY indicates quality-adjusted life-year; ICER, incremental cost effect ratio; CI, confidence interval; ITT, intention to treat analysis. Prices in €2010; SF-6D, Short Form-6 dimensions; SF-36, Short-form 36 Health Status Questionnaire.

Spine

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RANDOMIZED TRIAL CONCLUSION By comparing cost-effectiveness of X-stop with MID, the majority of the bootstrap samples displayed in the northeast corner of the cost-effectiveness plane, giving a 50% likelihood that X-stop is cost-effective at the extra cost of €25,700 (ICER) for a QALY. The effect of X-stop is nonsignificant higher. The significant higher cost of X-stop is mainly due to implant cost and the significantly higher reoperation rate.

➢ Key Points ‰ This is a randomized controlled multicenter trial that compares the cost-effectiveness of X-stop with minimally invasive decompression in patients with symptomatic lumbar spinal stenosis. ‰ The study was terminated after a midway interim analysis because of significantly higher reoperation rate in the X-stop group (33%). ‰ With a (nonsignificant) higher effect, there was a 50% likelihood that X-stop is cost-effective at the extra price of €25,700 (ICER) for a QALY compared with minimally invasive decompression. ‰ The significant higher costs were mainly due to implant cost and the significantly higher reoperation rate. ‰ From the clinician’s point of view, the costeffectiveness aspect may not reflect the major disadvantages represented by the high risk of secondary surgery.

References

1. Ishimoto Y, Yoshimura N, Muraki S, et al. Prevalence of symptomatic lumbar spinal stenosis and its association with physical performance in a population-based cohort in Japan: the Wakayama Spine Study. Osteoarthritis Cartilage 2012;20:1103–8. 2. Kalichman L, Cole R, Kim DH, et al. Spinal stenosis prevalence and association with symptoms: the Framingham Study. Spine J 2009;9:545–50. 3. Solberg TK, Olsen LR. [Årsrapport fra Nasjonalt kvalitetsregister for ryggkirurgi (NKR)]. 2013. 4. Tosteson ANA, 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;149:845–53. 5. Popov V, Anderson DG. Minimal invasive decompression for lumbar spinal stenosis. Adv Orthop 2012;2012:645321. 6. Podichetty VK, Spears J, Isaacs RE, et al. Complications associated with minimally invasive decompression for lumbar spinal stenosis. J Spinal Disord Tech 2006;19:161–6.

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Comparing cost-effectiveness of X-Stop with minimally invasive decompression in lumbar spinal stenosis: a randomized controlled trial.

Randomized clinical trial with 2-year follow-up...
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