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Neurosurgery
Research paper
Tubular discectomy versus conventional microdiscectomy for the treatment of lumbar disc herniation: long-term results of a randomised controlled trial
  1. Gijsbert M Overdevest1,2,
  2. Wilco C Peul1,2,
  3. Ronald Brand3,
  4. Bart W Koes4,
  5. Ronald HMA Bartels5,
  6. Wee F Tan6,
  7. Mark P Arts1
  8. On behalf of the Leiden-The Hague Spine Intervention Prognostic Study Group
  1. 1 Department of Neurosurgery, The Hague Medical Center, The Hague, The Netherlands
  2. 2 Department of Neurosurgery, Leiden University Medical Center, Leiden, The Netherlands
  3. 3 Department of Medical Statistics, Leiden University Medical Center, Leiden, The Netherlands
  4. 4 Department of General Practice, Erasmus Medical Center, Rotterdam, The Netherlands
  5. 5 Department of Neurosurgery, Radboud University Medical Center, Nijmegen, The Netherlands
  6. 6 Department of Neurosurgery, Medical Center Alkmaar, Alkmaar, The Netherlands
  1. Correspondence to Dr Gijsbert M Overdevest, Department of Neurosurgery, The Hague Medical Center, PO Box 432, 2501 CK, The Hague, The Netherlands; G.M.Overdevest{at}lumc.nl

Abstract

Background The reference surgical procedure for the treatment of lumbar disc herniation is open microdiscectomy. Minimal invasive discectomy with tubular retractors is hypothesised to cause less tissue damage and result in lower blood loss, less postoperative pain and faster recovery. We previously reported our 1 and 2-year results, and found no better outcomes of tubular discectomy compared with open microdiscectomy. Until now, no studies on tubular discectomy have reported results with more than 2 years of follow-up. Studies with long-term follow-up are required to determine if clinical outcomes are sustained and to assess specific long-term outcomes such as reoperation rate and iatrogenic low back pain due to impaired spinal integrity. The aim of this study is to evaluate the 5-year results of tubular discectomy compared with conventional microdiscectomy.

Methods The study was designed as a double-blind randomised controlled trial. 325 patients with a symptomatic lumbar disc herniation were randomly allocated to tubular discectomy (166 patients) or conventional microdiscectomy (159 patients). Repeated standardised follow-up measurements were performed at 2, 4, 6, 8, 12, 26, 38, 52, 78, 104, 156, 208 and 260 weeks after randomisation. Main outcomes are the Roland-Morris Disability Questionnaire for Sciatica (RDQ), Visual Analogue Scale for leg pain and low back pain, self-perceived recovery and reoperation incidence.

Results There was no clinically significant difference between tubular discectomy and conventional microdiscectomy regarding the main clinical outcomes at any time point during the 5 years of follow-up. RDQ scores at 5 years were 4.3 (95% CI 3.3 to 5.2) in the tubular discectomy group and 3.4 (95% CI 2.4 to 4.5) in the conventional microdiscectomy group. The mean difference of 0.9 (95% CI −0.6 to 2.2) was not significant. Mean differences for leg pain and back pain were 0.2 (95% CI −5.5 to 6.0) and 0.4 (95% CI −5.9 to 6.7), respectively. 77% of patients allocated to conventional discectomy reported complete or near-complete recovery of symptoms compared with 74% of patients allocated to tubular discectomy (p=0.79). The reoperation rate was 18% in the tubular discectomy group and 13% in the conventional discectomy group (p=0.29).

Conclusions Long-term functional and clinical outcome did not differ between patients allocated to tubular discectomy and conventional microdiscectomy. Primary and secondary outcome measures did not support the hypothesised advantages of tubular discectomy over conventional microdiscectomy.

Trial registration number ISRCTN51857546.

  • lumbar disc
  • herniation
  • minimal invasive
  • surgery
  • tubular discectomy.

https://doi.org/10.1136/jnnp-2016-315306

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    Introduction

    The lumbar radicular syndrome is typically caused by a lumbar disc herniation.1 The lifetime incidence of the lumbar radicular syndrome ranges from 12% to 43%.2 The natural history is generally favourable, with improvement of symptoms in 75% of patients after 4 weeks.3 Surgery is recommended in patients with radicular symptoms refractory to conservative management.4 The most commonly performed surgical technique is an open microdiscectomy with or without the use of an operating microscope.5 6 Alternatively, a discectomy can be performed through a tubular, muscle splitting, retractor system. Originally, this technique describes the use of an endoscope,7 but the less invasive muscle splitting approach is also preserved with microscopic visualisation.8–11 A total of 11 randomised controlled trials (RCTs) compared the clinical results of open microdiscectomy with minimal invasive discectomy using a tubular retractor system.8–19 Minimal invasive discectomy allows for smaller incisions and less disruption of back muscles than open microdiscectomy, potentially resulting in reduced blood loss, less postoperative pain, faster recovery and shorter hospitalisation. However, neither study provided convincing evidence that functional or clinical outcomes after minimal invasive discectomy are any better than after open microdiscectomy.20–22 RCTs with more than 2 years of follow-up have not been published yet. Studies with long-term follow-up are required to determine if clinical outcomes are sustained and to assess specific long-term outcomes such as reoperation rate and iatrogenic low back pain due to impaired spinal integrity. The objective of this study is to analyse the results of our previously published RCT at 5 years of follow-up.8 9 Long-term outcome regarding pain, functional outcome, perceived recovery and reoperation rates after tubular discectomy and open microdiscectomy will be assessed.

    Materials and methods

    The study design was a multicentre, double-blind, RCT. Patients with sciatica caused by lumbar disc herniation were randomly allocated to either tubular discectomy or conventional open microdiscectomy. The study’s objective was to compare clinical and functional outcome of both treatments. The study protocol was approved by the medical ethics committee at the Leiden University Medical Center and the participating hospitals, and all patients gave written informed consent prior to their participation.

    Patient population and randomisation

    Patients eligible for inclusion had sciatica due to a lumbar disc herniation for at least 8 weeks and had unsatisfactory relief of symptoms with prior conservative treatment. Patients were aged 18–70 years.

    Only patients with distinct nerve root compression due to a lumbar disc herniation were included, as evaluated by MRI. For this purpose, patients with disc herniations less than one-third of the spinal canal diameter and disc herniations with questionable nerve root compression were excluded. Other exclusion criteria were the presence of cauda equina syndrome, past surgery on the same spinal segment, spondylolisthesis, spinal stenosis, pregnancy or inability to complete follow-up examinations (eg, severe comorbid conditions, language barrier, planned emigration). Evaluation and follow-up of patients was performed by independent researchers. Random allocation was provided by a computer-generated randomisation list, and allocation was concealed by using a randomisation sequence of variable block size and a sealed opaque envelope containing treatment allocation that was opened not until in the operating theatre. Randomisation was stratified for the participating hospital and researcher. Participants and outcome assessors were blinded to treatment allocation throughout the study period. Further details can be found in the study protocol which has been published previously.23

    Study interventions

    Neurosurgeons participating in the study performed both conventional open microdiscectomies and tubular discectomies, and had ample experience with both techniques. Surgery was performed in the prone or knee-chest position with the patient under general or spinal anaesthesia. The level of the discectomy was verified using intraoperative fluoroscopy. Both techniques were performed using an equally small midline skin incision of 25–30 mm. During conventional open microdiscectomy, back muscles were detached from the spinous process and retracted unilaterally. The caudal part of the cephalad lamina and ligamentum flavum were removed to expose the compressed nerve root and herniated disc. During this procedure, visualisation was provided by an operating microscope or loupe magnification and headlight. With tubular discectomy, the midline skin incision was retracted laterally and a muscle splitting dilatator (METRx, Medtronic) was inserted with lateral fluoroscopic guidance. A tubular retractor of 14–18 mm was positioned at the caudal part of the cephalad lamina and ligamentum flavum. Visualisation was provided by an operating microscope. With both techniques, only herniated disc material and a small portion of the intervertebral disc were removed. Removal of bone was limited to gain access to the ligamentum flavum. Patients were encouraged to exercise and walk the day of surgery and were regularly discharged the day after. Patients were allowed to resume their regular activities as soon as permitted by their pain.

    Study measures

    The primary outcome measure of the study was functional disability. Functional disability was measured by the modified Roland-Morris Disability Questionnaire for Sciatica (RDQ). The scores range from 0 (no disability) to 23 (severe disability). Secondary outcomes were leg pain and low back pain as measured by a 100 mm Visual Analogue Scale (VAS). Other secondary outcome measures were patient self-perceived recovery, complications and reoperation incidence. Outcomes were assessed in a standardised manner at regular follow-up intervals (2, 4, 6, 8, 12, 26, 38, 52, 78, 104, 156, 208 and 260 weeks after randomisation). Follow-up consisted of written questionnaires and visits the outpatient clinic.

    Statistical analysis

    Primary and secondary outcome measures after tubular discectomy and conventional open microdiscectomy were compared. Data are presented as means or percentages depending on the type of variable. Study data were analysed according to the intention to treat principle. Outcomes measures for functional disability, leg pain and low back pain were compared with a repeated measures analysis of variance. The main effect of treatment and the interaction between treatment and time was compared. Comparison of means and 95% CIs at consecutive follow-up moments are pointwise estimates, obtained by using models with time as a categorical covariate. Patient self-perceived recovery was defined as complete recovery or near-complete recovery of symptoms as measured with a seven-point Likert scale, and was compared using a generalised linear mixed model. Predefined predictors of treatment outcome were tested with a multivariate logistic regression model with recovery status at final follow-up as the dependent variable. The analysis of predictors was adjusted for treatment allocation by including both variables in the logistic regression model. Subsequently, the main effect of the interaction of both variables (ie, the effect of the treatment within each subgroup) was analysed, to determine if effect of tubular discectomy compared with conventional discectomy varies among the predefined subgroups. Patients were included in the subgroup analysis if follow-up data 4 or 5 years after randomisation were available. Study data were collected in a secure web-based data management system, and SPSS software (V. 21) was used for statistical analyses.

    Results

    Three hundred and twenty-five patients were randomly allocated to tubular discectomy (166 patients) or conventional microdiscectomy (159 patients). Sixty-three per cent of patients had data available at the final 5-year time point and 73% of participants had completed the 4 or 5-year follow-up assessment (figure 1). No statistically significant differences were found between baseline characteristics of both randomisation groups (table 1).

    Figure 1
    Figure 1

    Flowchart of study participants.

    View this table:
    Table 1

    Baseline characteristics of patients

    There was no significant difference between tubular discectomy and conventional microdiscectomy regarding the main clinical outcomes at any time point during the 5 years of follow-up (figure 2). Mean RDQ scores at 5 years were 4.3 (95% CI 3.3 to 5.2) in the tubular discectomy group and 3.4 (95% CI 2.4 to 4.5) in the conventional discectomy group. The mean difference of 0.9 (95% CI −0.6 to 2.2) was not statistically significant. Mean differences for leg pain and back pain were 0.2 (95% CI −5.5 to 6.0) and 0.4 (95% CI −5.9 to 6.7), respectively. During the entire follow-up period of 260 weeks, the mean RDQ score for tubular discectomy was 6.7 (95% CI 6.2 to 7.2) vs 6.3 (95% CI 5.8 to 6.9) for conventional microdiscectomy. This difference in functional disability was not statistically significant (p=0.3). The mean differences between treatment groups regarding leg pain (22.3, 95% CI 20.7 to 24.0 vs 20.5, 95% CI 18.8 to 22.2) and back pain (24.7, 95% CI 22.8 to 22.7 vs 22.7, 95% CI 20.6 to 24.7) were also not statistically significant (p=0.13 and p=0.14, respectively). Seventy-seven per cent of patients allocated to conventional discectomy reported recovery of symptoms at 5-year follow-up compared with 74% of patients allocated to tubular discectomy (p=0.79) (table 2).

    Figure 2
    Figure 2

    Comparison of functional disability, leg pain and back pain of patients allocated to conventional microdiscectomy and tubular discectomy. Error bars indicate 95% CIs and were determined with the use of repeated-measures analysis of variance. The mean scores on the Roland-Morris Disability Questionnaire (score range: 0–23; higher scores indicate worse functional status) did not differ significantly during the entire follow-up period of 260 weeks (p=0.30) between treatment groups. The Visual Analogue Scale (VAS) has a score range from 0 to 100 mm (higher scores indicate more intense pain). Patients assigned to tubular discectomy reported equal leg pain and back pain compared with patients assigned to conventional microdiscectomy during the 260 weeks of follow-up (p=0.13 and p=0.14, respectively).

    View this table:
    Table 2

    Comparison of functional disability, leg pain, back pain and self-perceived recovery of patients allocated to conventional microdiscectomy and tubular discectomy

    The reoperation rate during the 5 years of follow-up was 18% in the tubular discectomy group and 13% in the conventional discectomy group (p=0.29). Five per cent of patients had two or more reoperations. The total number of reoperations was 39 in the tubular discectomy group compared with 23 in the conventional microdiscectomy group (p=0.10). Six patients in the tubular discectomy group underwent instrumented fusion, compared with none in the conventional discectomy group (p=0.03) (table 3).

    View this table:
    Table 3

    Operative characteristics and reoperations

    The subgroup effect of all predefined prognostic variables for the recovery status at final follow-up are listed in table 4. Only level of education and having a physical demanding job were statistically significant outcome modifiers, irrespective of treatment allocation. Patients with a high level of education reported good or excellent recovery more frequently than patients with a low level of education (OR 1.93, p=0.04), and patients with a physically demanding job recovered less frequently than patients without a physically demanding job (OR 0.45, p=0.01). The OR for good outcome of patients treated with tubular discectomy compared with conventional microdiscectomy was 0.98 (95% CI 0.55 to 1.74). The effect of the treatment within each subgroup is listed in figure 3. The only subgroup which significantly modified the relative treatment effect of tubular discectomy compared with conventional discectomy was predominant low back pain. Patients with predominant low back pain had an OR of 5.69 (95% CI 1.08 to 29.0) for good outcome when comparing tubular discectomy with conventional microdiscectomy.

    View this table:
    Table 4

    Multivariate logistic regression analyses of all predefined prognostic variables and treatment for the recovery status at final follow-up

    Figure 3
    Figure 3

    Treatment effect within each subgroup for tubular discectomy versus conventional microdiscectomy. ORs and 95% CIs show the treatment effect of tubular discectomy versus conventional microdiscectomy within each predefined subgroup. Recovery is defined as complete or near-complete recovery of symptoms according to the self-perceived seven-point Likert scale.

    Discussion

    This study demonstrates no difference in functional or clinical outcome between patients randomly allocated to tubular discectomy and conventional microdiscectomy at 5 years of follow-up. These findings do not differ from the previously published 1 and 2-year results of the trial.8 9 Previous RCTs that compared conventional microdiscectomy with discectomy using tubular retractor systems had a follow-up of up to 2 years, and also reported no differences of clinical outcomes between treatment groups.10–16 19

    Long-term results of tubular discectomy compared with conventional microdiscectomy are of particular importance as the disruption of back muscles and tissue trauma caused by the surgical procedure may impair spinal integrity and result in chronic pain or need for reoperation due to surgically induced spinal instability or accelerated degeneration. Postoperative low back pain, muscle injury and tissue damage may be considered proxies for loss of spinal integrity. Postoperative low back pain was expected to be lower after tubular discectomy than after conventional microdiscectomy, but, instead, equal or even higher postoperative low back pain scores have been reported previously.9 11 14 19 In the current 5-year analysis, low back pain was equal among both treatment groups, and the significant difference found at 2 years of follow-up was no longer present at 5 years of follow-up. Studies that have reported on muscle injury and tissue damage in patients treated with tubular discectomy and conventional discectomy by measuring creatine kinase (CK) and systemic cytokine response have reported conflicting results. Studies have been published reporting no difference of CK levels between treatment groups,16 24 while a another study found significantly lower CK levels after tubular discectomy.17 Moreover, lower systemic cytokine response after tubular discectomy was described in two studies.13 16 Conflicting results regarding CK levels and cytokine response may be the result of different incision lengths and/or retraction of back muscles, but evidence is not compelling that transmuscular muscle splitting is truly less invasive than the subperiosteal muscle dissection during microdiscectomy.

    The reoperation rate steadily increased over the follow-up period, from 10% in the tubular discectomy group and 7% in the conventional microdiscectomy group after 1 year to 18% and 13%, respectively, after 5 years. The difference was not statistically significant. The most common indication for reoperation was a recurrent lumbar disc herniation. Patients in the tubular discectomy group underwent instrumented fusion significantly more frequently than patients treated with conventional microdiscectomy. The most frequent reported reason for instrumented fusion was loss of disc height resulting in foraminal stenosis. Although instrumented fusion was an infrequent reoperation, this finding also does not support the presumed preservation of spinal integrity with tubular discectomy. Our reoperation rate is comparable with the reoperation rates reported in large population-based studies, which reported 4 to 5-year reoperation rates varying from 12.3% to 13.8%.25–27 Furthermore, a comparison of reoperation rates after 12 816 open discectomies compared with 3001 endoscopic discectomies found no significant difference between both surgical techniques.26

    A comprehensive subgroup analysis was performed to determine whether certain subgroups may benefit from one of both operation techniques. In the current analysis, only patients with predominant low back pain, as compared with patients with predominant leg pain, recovered more frequently with tubular discectomy than with conventional microdiscectomy. This finding could support the presumption that tubular discectomy causes less disruption of back muscles and less tissue damage, but in general postoperative low back was no less after tubular discectomy than after conventional microdiscectomy. Furthermore, this subgroup has not been previously associated with outcome of tubular discectomy in our 1-year analysis or any other study.28 As the proportion of patients with predominant low back pain was also small compared with patients with predominant leg pain, this statistically significant effect modifier may have been found coincidentally due to multiple testing of possible effect modifiers.

    In case tubular discectomy yields no better functional and clinical outcome than conventional microdiscectomy, secondary outcome measures could provide decisive arguments for the choice of a particular technique. Studies comparing both techniques have been subjected to the rigorous methodological assessment of meta-analyses.20 22 29 Generally, the length of the surgical procedure was increased with tubular discectomy. Equal complication rates of both treatments were observed. Only the length of hospital stay and blood loss were significantly reduced with tubular discectomy, but the variation in length of hospital stay among studies was large and cannot be attributed to the operation technique alone, and the small reduction of blood loss seems clinically irrelevant. Therefore, there are also no convincing secondary outcome measures to support the proposed advantages of tubular discectomy.

    This study is subject to several limitations. Most importantly, only 63% of the study participants had data available at 5-year follow-up and 73% had completed the 4 or 5-year follow-up assessment. Although this lost to follow-up percentage is slightly better than another long-term follow-up study,30 this harbours the potential for bias. The percentage of participants with complete follow-up was comparable among both treatment groups, and therefore the comparison of treatments is unlikely biassed, but the generalisability of findings related to the clinical and functional improvement and reoperation incidence of the study population may be limited. Furthermore, tubular discectomy is a technically demanding procedure characterised by a learning curve and results depending on the technique favoured by the surgeon. Although we observed some heterogeneity between participation centres, differences were not significant and the mean operation time of tubular discectomy in our study was comparable with the reported advancements of operating time during the learning curve in other studies.31–33 Finally, only patients with larger herniated discs and distinct nerve root compression were included. However, there are no reasons to assume that the results of the current study do not apply to smaller herniated discs.

    Conclusions

    We found no evidence to support the superiority of less invasive tubular discectomy compared with conventional microdiscectomy. Long-term functional and clinical outcome did not differ between patients allocated to tubular discectomy and conventional microdiscectomy.

    Acknowledgments

    The authors thank the Dutch Health Insurance Board for funding the study, patients who participated, recruiting physicians and research nurses of the Spine Intervention Prognostic Study group (SIPS) for their work in making this trial possible.

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    View Abstract

    Footnotes

    • Contributors The conception and design of this study, or the analysis and the interpretation of the study data, the drafting of the article, or revising it critically for important intellectual content, the final approval of the version to be published.

    • Funding This study was supported by a grant from the Dutch Health Insurance Board.

    • Competing interests None declared.

    • Patient consent Obtained.

    • Ethics approval Leiden University Medical Center.

    • Provenance and peer review Not commissioned; externally peer reviewed.

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