Tubular discectomy for the treatment of lumbar disc herniation : new standard or transient fashion? : Results of a double-blind randomised controlled trial

randomised controlled trial

Arts, M.P.

Citation

Arts, M. P. (2010, September 23). Tubular discectomy for the treatment of lumbar disc herniation : new standard or transient fashion? : Results of a double-blind randomised controlled trial. Retrieved from https://hdl.handle.net/1887/15975

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Cost utility analysis

Tubular discectomy versus conventional

microdiscectomy for the treatment of lumbar disc related sciatica: cost utility analysis alongside a double-blind randomised controlled trial

M. Elske van den Akker Mark P. Arts

Wilbert B. van den Hout Ronald Brand

Bart W. Koes WilcoC.Peul

Submitted

ABSTRACT

Objective: To determine whether a favourable cost effectiveness for tubular discectomy compared with conventional microdiscectomy is attained.

Design:Cost utility analysis alongside a double-blind randomised controlled trial.

Setting:Seven Dutch hospitals.

Participants:325 patients with lumbar disc related sciatica lasting more than 6-8 weeks.

Interventions:Tubular discectomy compared with conventional microdiscectomy.

Main outcome measures: Quality adjusted life years (QALYs) at one year and societal costs, estimated from patient reported utilities (UK and NL EuroQol, SF-6D, and visual analogue scale) and diaries on costs (healthcare, patient costs, and prod uctivity).

Results:QALYs duri ng all fou r qua rters and accord ing to all utility meas ures were not statistica Ily different between tubular discectomy and conventionai microdiscectomy (difference UK EuroQol -0.018, 95% confidence interval -0.066 to 0.031). From the healthcare perspective, tubular discectomy resulted in non-significant higher costs (difference (401,95% confidence interval (-212 to (1015). From the societal perspective, also a non-significant difference of (1302 (95% confidence interval (-1166 to (3769) in favour of conventional microdiscectomy was found. The non significant differences in costs and QALYs in favour of conventional microdiscectomy result in a low probability that tubular discectomy is more cost effective than conventional microdiscectomy.

Conclusions:Tubular discectomy is unlikely to be cost effective compared with conventional microdiscectomy.

INTRODU eTI ON

Unilateral transflaval microdiscectomy is the most frequently performed surgical procedure for patients with lumbar disc related sciatica.¹Transmuscular tubular discectomy has been introduced to reduce postoperative back pain, faster mobilisation and resumption of daily activities with potentially a faster rate of recovery. However, scientific evidence of superiority of minimally invasive techniques is lacking. In a double-blind randomised controlled trial we compared the effectiveness of tubular discectomy with conventional microdiscectomy.2-4 This trial showed similar rates of recovery and functional outcome du ring the first two years after surgery, although patients treated with tubular discectomy reported significant more leg pain and back pain.3,4

Previous randomised trials comparing tubular discectomy and conventional microdiscectomy did not focus on an economic evaluation.5.9We therefore performed a cost utility analysis of the data from our randomised controlled trial, comparing quality adjusted life years (QALYs) with societal costs at one year, to determine whether given this similar effectiveness a favourable cost effectiveness for tubular discectomy is attained.

METHODS

Patients with sciatica due to lumbar disc herniation participated in a multicenter double- blind randomised controlled trial, comparing tubular discectomy with conventional microdiscectomy. Details of the study protocol have been published previously.2 The Medical Ethics Committees of seven participating general hospitals in the Netherlands approved the study and all participants gave written informed consent.

A total sample size of300patients was calculated to detect at least a 4-point difference in the Roland Disability Questionnaire for Sciatica.¹⁰Between January2005and October2006, 325patients were enrolled. The baseline characteristics of both groups were similar.3,4

Patients and treatment

Eligible patients, aged between 18 and 70 years, presented with sciatica lasting more than 6-8weeks, and radiologically confirmed disc herniation with distinct nerve root compression.

Patients with small contained disc herniations with doubtful nerve root compression were exc luded. Moreover, patients with cau da eq ui na synd rome, previous spi na I surge ry at the sa me

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disc level, spondylolisthesis, central canal stenosis, pregnancy, severe somatic or psychiatric diseases, inadequate knowledge of Dutch language, or emigration planned within one year of inclusion, were also excluded.

Randomisation into tubular discectomy or conventional microdiscectomy was performed in the operating room after induction of anesthesia by opening a sealed envelope. The details of the treatment can be found elsewhere.2 Briefly, conventional microdiscectomy was performed after subperiosteal dissection and retraction of the ipsilateral paravertebral muscles. The herniated disc was removed by the unilateral transflaval approach with the aid of a headlight- loupe or microscope magnification, depending on the surgeon's preference. In case of tubular discectomy, the skin was retracted laterally and the guidewire and sequential dilators (METRx, Medtronic) were placed at the inferior margin of the lamina under fluoroscopic control. A14 to 18 mm working channel was introduced over the final dilator and attached to the table. The herniated disc was removed through the tubular retractor with microscopic magnification. For blinding purposes, an equally small midline incision was made in both procedures (25 to 30 mm) and patients and researchers were kept blinded for the allocated treatment during the follow-up period of 1 year.

Utilities and QALYs

Utilities represent the valuation of the quality of life of the patients, on a scale from zero (as bad as death) to one (perfect health). Patients described their quality of life using the EuroQol classification system (EQ-5D), from which we calculated utilities for the United Kingdom and The Netherlands.^{l l},12 Similarly, patients reported their quality of life using the SF-36, from which we calculated the SF-6D utilities.B Both EQ-5D and SF-6D provide societal valuation, which is preferred for economic evaluations from a societal perspective. We also obtained valuations by the patients themselves, using a Visual Analogue Scale (VAS) ranging from 0 (worst imaginable health) to 100 (perfect health). We transformed the values to a utility scale,14 using the power transformation 1-(1-VASj100)1.61.

We obtained measurements for EQ-5D and the VAS at intake, randomisation and 2,4, 6, 8, 12, 26, 38, and 52 weeks after randomisation. SF-36 measurements were obtained less often; at intake, 4, 8, 26, and 52 weeks after randomisation. For the EQ-5D, SF-36 and VAS measurements, respectively 6%, 6% and 8% of the items were missing. From the area under the utility curves we calculated the average utility during each separate quarter of the year after randomisation and during the entire year (QALYs).

Costs

We estimated the costs from the societal perspective during a follow-up period of one year.

Because of the one year time horizon, costs were not discounted. Costs were converted into 2008price levels using the general Dutch consumer price index.is

Using cost diaries, patients reported admissions to hospital, visits (specialists, general practitioner, physical therapy, and alternative health care), homecare, paid domestic help, informal care, drugs and aids, out of pocket expenses as result of sciatica, and hours of absenteeism from work.

At the follow-up examinations by the research nurse at 4, 8, 26 and 52 weeks after randomisation the research nurse collected and went through the diary with the patient. All patients completed the first diary. Of the follOWing diaries, 4%, 5% and 10%, respectively, were missing.

A micro cost approach was used to estimate the cost of the two surgical procedures.

The cost of the operating room (staff, operating room, equipment and overheads), specific operating equipment and consumables were considered. Cost of anesthesia and use of awakening room use was assumed to be equal for both procedures and therefore omitted.

In order to calculate the cost of operating room, the time of surgery was registered for each patient. Cost for 1 minute use of the operating room was obtained from each participating hospital. The mean cost per minute of ( 13,48 was increased by the personnel costs of one neurosurgeon and one anesthetist (( 3.53¹⁶). Cost of specific operating equipment of ( 17.72 and(4.84for respectively tubular discectomy and conventional microdiscectomy was calculated on the basis of initial purchasing prices of the instruments, their yearly use and depreciation, maintenance and interest cost. Costs of disposables amount to€85and(65per surgery for respectively tubular discectomy and conventional microdiscectomy.

For other health care resources we used Dutch standard prices designed to represent societal costs and to standardize economic evaluations.16-18 Health care costs are reported including the patients' time and travel costs.

We valued the reported hours of absenteeism from work during the first year follow-up period according to the friction cost method using a friction period of22weeks¹⁶at standard prod uctivity costs of ( 33 per hour for women and€42 per hour for men.

Analysis

All analyses followed the intention to treat principle. All statistical analyses were conducted with Stata 9.2 (StataCorp, College Station, TX, USA).

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5

To reduce possible bias due to missing data, we used multiple imputation by chained equations, with 5 iterations for the switching regression model.¹⁹ For each missing utility measure or cost measure, an imputation regression model was used that included age, sex, body-mass index, randomisation group, patient's reported functional disability measured by the modified Roland Disability Questionnaire for Sciatica,20 VAS for leg pain and back pain, duration of complaints, and all (other) utility measures and costs measures at all moments.

Group differences in QALYs and costs were statistically analysed using standard t- test for unequal variance.

Base case cost utility analysis compared societal costs at one year to QALYs at one year based on the UK EQ-5D. Sensitivity analyses were carried out on the use of different utility measures (US EQ-5D, NL EQ-5D, SF-6D, or VAS) and on the perspective (societal or healthcare perspective).

Depending on the willingness to pay for obtained effectiveness, a strategy is cost-effective compared with an alternative strategy if it has a better net benefit (willingness to pay

*

QALYs - costs). Given the statistical uncertainty of differences between costs and QALYs, cost effectiveness acceptability curves graph the probability that a strategy is cost effective, as a function of willingness to pay.21

RESULTS

Utilities and QAlYs

The valuation of quality of life measured by the different utility measures (EQ-5D, SF-6D, VAS) was consistently similar for patients that underwent conventional microdiscectomy and patients that underwent tubular discectomy (Figure 1).

QALYs during all four quarters and according to all utility measures were also not statistically different between both groups (Table 1). The difference in QALYs according to the UK EQ- 5D was -0.018 (95% confidence interval-0.066 to 0.031), for the NL EQ-5D -0.014 (-0.056 to 0.029), for the SF-GD -0.011 (-0.037 to 0.014), and the visual analogue scale -0.021 ( -0.058 to 0.016)

Healthcare costs

The average costs of surgery, including the initial hospital admission, were € 197 (95%

confidence interval€ 37 to€ 357) higher for tubular discectomy compared to conventional

microdiscectomy (Table 2). Combined with other health care costs, a non significant difference of € 401 (€ -212 to € 1015) was found for the total healthcare costs with higher costs for tubu lar discectomy.

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Chapter

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Figure 1: Utilities according to UK, NL EO-SO, SF-GO, and visual analogue scale after tubular discectomy (TO) and conventional microdiscectomy (CM).

Societal costs

In the non-health care costs, no significant differences were found. The total non-healthcare costs after tubular discectomy were higher than after conventional microdiscectomy with a non-significant difference of€901 (€-1304 to € 3105). As the societal cost is the sum of the healthcare and non-healthcare cost, also these costs showed a non-significant difference (€ 1302, 95% Cl €-1166 to€3769) in favour of conventional microdiscectomy.

Table 1: Utility and quality of life years (QALYs) after tubular discectomy and conventional microdiscectomy.

Values are means (standard deviations).

Measure Tubular microdiscectomy Conventional microdiscectomy Difference P-value*

(N=166) (N=159)

UK EQ-50

ptquarter 0.636 0.653 -0.017

2ndquarter 0.737 0.738 -0.001

3'dquarter 0.753 0.771 -0.018

4^thquarter 0.746 0.779 -0.033

QALYs 0.718 (0.22) 0.736 (0.21) -0.018 0.51

NLEQ-SO

ptquarter 0.702 0.718 -0.016

2ndquarter 0.781 0.782 -0.001

3'dquarter 0.794 0.805 -0.012

4^thquarter 0.787 0.813 -0.026

QALYs 0.766 (0.20) 0.779 (0.19) -0.014 0.53

SF-60

ptquarter 0.680 0.680 -0.000

2ndquarter 0.754 0.766 -0.012

3'dquarter 0.762 0.776 -0.015

4^thquarter 0.762 0.782 -0.020

QALYs 0.739 (0.10) 0.751 (0.11) -0.011 0.37

Visual analogue scale

ptquarter 0.790 0.811 -0.022

2ndquarter 0.824 0.844 -0.020

3'dquarter 0.825 0.849 -0.024

4^thquarter 0.823 0.840 -0.018

QALYs 0.815 (0.16) 0.836 (0.15) -0.021 0.26

• ttest for unequal variance

Table 2: Mean healthcare costs and societal cost per patient after tubular discectomy and conventional microdiscectomy. Volumes are percentages of patients who made costs for that item, unless stated otherwise.

Tubular discectomy Conventional micro- Difference (N=166) discectomy (N=159)

Volume Costs(€) Volume Costs(€) Costs(€) P-value*

Surgery, with admission to hospital 2539 (765) 2342 (702) 197 0.02

Repeated su rgery within 1 year 10 272 6.9 248 24 0.82

Physical therapy

1'1 quarter 9S 489 90 491 -2

2nd quarter 61 282 55 307 -2S

3^rdquarter 54 199 43 155 44

4^thquarter 47 201 33 115 56

Total (SO) 95 1171 (1165) 91 1098 (1177) 73 0.61

Other admissions to hospital 18 166 16 193 -27 0.82

Neurologistt 0.4 53 0.2 21 33 0.06

Neurosu rgeont 1.5 156 1.2 129 27 0.24

Other specialists 66 239 60 164 75 0.06

General practitionert 2.5 68 2.5 63 -5 0.81

Alternative care 17 47 17 37 10 0.64

Home care* 0.3 6 0.1 2 3 0.39

Drugs 71 61 64 67 6 0.84

Aids 24 49 27 60 -11 0.61

Total healthcare costs

1'1 quarter 3510 3229 281

2nd quarter 474 516 -42

3'd quarter 433 371 62

4^thquarter 410 310 100

Total (SO) 4827 (2636) 4426 (2946) 401 0.20

Paid domestic help! 9 155 3.1 72 82 0.24

Informal caret 25 252 32 327 -74 0.43

Out of pocket expenses 19 137 19 169 -32 0.79

Productivity costs (friction costs)

1^stquarter 137 5296 145 5630 -334

2nd quarter 54 2075 48 1873 92

3'd quarter 31 1206 16 611 595

4^thquarter 20 768 8 307 462

Total (SO) 243 9346 (9662) 217 8421 (8845) 925 0.38

Total non-healthcare costs (SO) 9890 (9944) 8990 (9376) 901 0.42

Total societal costs

1" quarter 9040 9065 -25

2nd quarter 2605 2452 153

3'd quarter 1768 1136 632

4^thquarter 1305 763 541

Total (SO) 14717 (11139) 13415 (10620) 1302 0.30

*ttest for unequal variance, correcting for non-response using multiple imputation.tNumber of visits. * Number of hours

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5

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Cost utility analysis

Although no statistically significant differences were found in societal costs and QALYs between tubular discectomy and conventional microdiscectomy over the first year, the estimated nonsignificant differences in costs and QALYs were all in favour of conventional microdiscectomy. This results in a low probability that tubular discectomy is more cost effective than conventional microdiscectomy. This probability varies from 15% for low values of the willingness to pay to 22% for high values of the willingness to pay, as a result of the statistical uncertainty about costs and QALYs (Figure 2). With other utility measures, the probability of being cost effective remains in favour of conventional microdiscectomy. Also from the healthcare perspective, tubular discectomy is not preferred above conventional microdiscectomy (Figure 2).

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Figure2: Cost-effectiveness acceptability curves for tubular discectomy compared to conventional micro- discectomy.

DISCUSSION

The present double-blind randomised controlled trial on patients with herniated disc related sci atica, compa red tubu la r di scecto my with convention al m icrodi scectomy.2-4The tria I showed similar rates of recovery and functional outcome although patients treated with tubular

discectomy had less favourable results of leg pain and back pain during the first two years after su rgery.4

In the economic eva Iuation we stu died whether given this simi Iar effectiven ess, a favo ura ble cost utility of tubular discectomy was attained. The expected reduction in postoperative back pain, faster mobilisation and resumption of daily activities with consequent faster rate of recovery after tubular discectomy were not reflected by the utility measures: the utility measures reported are similar for both groups. The difference in mean healthcare costs was estimated at € 401, at a disadvantage of tubular discectomy. This non-significant difference mostly consisted of the difference in surgery costs, including tubular retractors, instruments and surgery time. The assumed faster resumption of daily activities beforehand was reflected by a lower absenteeism in the first quarter in the tubular discectomy group. However, after this initial lower absenteeism after tubular discectomy, the difference in absenteeism during the rest of the year was in favour of conventional microdiscectomy, most likely related to the patients' perceived recovery. As a result, the non-healthcare costs are also higher after tubular discectomy (€ 901). In addition, the difference in societal costs, which is the sum of the healthcare and non-healthcare costs, of€1302 is also not statistical significant. However, the non-significant differences in QALYs and costs in favour of conventional microdiscectomy result in the conclusion that tubular microdiscectomy is unlikely to be cost effective compared with conventional microdiscectomy, regardless of the economic threshold per QALY.

The study has several limitations. Firstly, other settings may differ from the seven general hospitals in the Dutch setting included in this study. Translating the results to other settings should be done with caution. Secondly, the duration of the economic evaluation is limited to one year. The difference between both treatment groups in utility as measured by the EQ 50 and SF 60, and in costs of physical therapy and productivity seems to increase during the year.

However, additional linear regression analyses of these variables against time (in quarters) and treatment group show no systematic trend in the difference between both treatment groups.

Therefore, we expect that a longer follow up will not alter our conclusions. Furthermore, a longer time horizon would have reduced the statistical power and the clinical evaluation showed no differences beyond the first years.3,4

In this study we used costs of surgery instead of hospital prices. In the Dutch funding system, individual hospitals set diagnosis-treatment prices for lumbar disc surgery to facilitate competition and price containment. However, prices do not bear a consistent relation to costs.

Surgery may be profitable (prices> costs) or subsidized by other services (prices < costs). Using the average hospital prices of the participating hospitals for both treatments resulted in a

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larger difference in mean surgery costs between the two treatments of€ 779 with tubular discectomy the most expensive treatment. So, irrespective of the use of costs or prices, the conclusion holds that tubular discectomy is not likely to be cost effective compared with conventional microdiscectomy.

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