• Jörg Franke, R Greiner-Perth, H Boehm, K Mahlfeld, H Grasshoff, Y Allam, and F Awiszus.
• Department of Orthopaedic Surgery, Otto-von-Guericke University of Magdeburg, Magdeburg, Germany. joerg.franke@med.ovgu.de
• Eur Spine J. 2009 Jul 1; 18 (7): 9921000992-1000.

AbstractA Prospective randomised controlled study was done to determine statistical difference between the standard microsurgical discotomy (MC) and a minimally invasive microscopic procedure for disc prolapse surgery by comparing operation duration and clinical outcome. Additionally, the transferability of the results was determined by a bicentric design. The microscopic assisted percutaneous nucleotomy (MAPN) has been advocated as a minimally invasive tubular technique. Proponents have claimed that minimally invasive procedures reduce postoperative pain and accelerate the recovery. In addition, there exist only a limited number of well-designed comparison studies comparing standard microdiscotomy to a tubular minimally invasive technique that support this claim. Furthermore, there are no well-designed studies looking at the transferability of those results and possible learning curve phenomena. We studied 100 patients, who were planned for disc prolapse surgery at two centres [50 patients at the developing centre (index) and 50 patients at the less experienced (transfer) centre]. The randomisation was done separately for each centre, employing a block-randomisation procedure with respect to age and preoperative Oswestry score. Operation duration was chosen as a primary outcome parameter as there was a distinguished shortening observed in a preliminary study at the index centre enabling a sound case number estimation. The following data were compared between the two groups and the centres with a 12-month follow-up: surgical times (operation duration and approach duration), the clinical results, leg and back pain by visual analogue scale, the Oswestry disability index, length of hospital stay, return to work time, and complications. The operation duration was statistically identical for MC (57.8 +/- 20.2 min) at the index centre and for MAPN (50.3 +/- 18.3 min) and MC (54.7 +/- 18.1 min) at the transfer centre. The operation duration was only significantly shorter for the MAPN technique at the index centre with 33.3 min (SD 12.1 min). There was a huge clinical improvement for all patients regardless of centre or method revealed by a repeated measures ANOVA for all follow-up visits Separate post hoc ANOVAs for each centre revealed that there was a significant time-method (MAPN vs. MC) interaction at the index centre (F = 3.75, P = 0.006), whereas this crucial interaction was not present at the transfer centre (F = 0.5, P = 0.7). These results suggest a slightly faster clinical recovery for the MAPN patients only at the index centre. This was due to a greater reduction in VAS score for back pain at discharge, 8-week and 6-month follow up (P < 0.002). The Oswestry-disability scores reached a significant improvement compared to the initial values extending over the complete follow-up at both centres for both methods without revealing any differences for the two methods in either centre. There was no difference regarding complications. The results demonstrate that a shorter operation duration and concomitant quicker recovery is comprehensible at an experienced minimally invasively operating centre. These advantages could not be found at the transfer centre within 25 minimally invasive procedures. In conclusion both procedures show equal mid term clinical results and the same complication rate even if the suggested advantages for the minimally invasive procedure could not be confirmed for the transfer centre within the framework of this study.

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