Reply to the comment of R. Härtl:

We thank professor Härtl and colleagues for their comments on our study.

In our opinion, new treatments in medicine, including new innovating surgical techniques, should be properly investigated. Tubular procedures for different indications in spine surgery need to be evaluated in randomised controlled trials. However, the assumption of Härtl and colleagues that the tubular approach in relatively easy surgical procedures does not have to be evaluated, and therefore that our hypothesis flaws, is worrisome to us. Härtl and colleagues state that ‘in order to become efficient at more complex tubular procedures it seemed justified and advantageous to adopt tubular surgery for simple spinal procedures’. First, our double-blinded randomised trial on lumbar disk herniation documented that tubular discectomy was not superior to the standard procedure. Secondly, tubular approaches in complex spine surgery should be evaluated in randomised trials as well, prior to implementation in daily practise.

The fact that tubular discectomy was not superior to conventional surgery was not due to inexperience of surgeons, as Härtl and colleagues suggest. Surgeons needed to perform at least 15 procedures before they could participate in our trial [1]. Moreover, we found a tendency of worse results in more experienced surgeons.

We strongly disagree with the suggestion to exclude the patients with recurrent disk herniation from primary analysis. First, in an intention-to-treat analysis, by definition, the primary endpoint should include all patients with all possible reasons for an unfavourable outcome. Moreover, recurrent disk herniation might very well be an important reason for difference in pain scores between the groups. To decide on new guidelines, the final clinical result of both groups, including all its determinants, is crucial. In our opinion, excluding these patients would certainly bias the primary outcome.

We agree with the statement that ‘the lack of benefit from tubular discectomy over conventional surgery does not mean that tubular surgery would not have a significant advantage when comparing potentially much more invasive procedures’. Even more in complex spine surgery, it is our duty to start a randomised controlled trial. We therefore encourage Härtl and colleagues to start enrolling their patients in randomised trials instead of relying on case series and expert opinion only, to help reinforcing evidence based guidelines in this field.

References

• 1 McLoughlin G, Gregory S, Fourney DR. et al .The learning curve of minimally-invasive lumbar microdiscectomy. In: Book The learning curve of minimally-invasive lumbar microdiscectomy. (Editor ed. eds.), vol. 35. pp. 75–78. City 2008: 75-78