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Trials. 2018 Feb 20;19(1):129. doi: 10.1186/s13063-018-2504-z.

Clinical and radiological effect of medialized cortical bone trajectory for lumbar pedicle screw fixation in patients with degenerative lumbar spondylolisthesis: study protocol for a randomized controlled trial (mPACT).

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Department of Neurosurgery, Medical University of Innsbruck, Anichstr. 35, A-6020, Innsbruck, Austria.
Department of Neurosurgery, Medical University of Innsbruck, Anichstr. 35, A-6020, Innsbruck, Austria.
Department of Neurology, Medical University of Innsbruck, Innsbruck, Austria.
Department of Medical Statistics, Informatics and Health Economics, Medical University of Innsbruck, Innsbruck, Austria.
Department of Neuroradiology, Medical University of Innsbruck, Innsbruck, Austria.



Spinal fusion with pedicle screw fixation represents the gold standard for lumbar degenerative disc disease with instability. Although it is an established technique, it is nevertheless an invasive intervention with high complication rates. Therefore, minimally invasive approaches have been developed, the medialized bilateral screw pedicel fixation (mPACT) being one of them. The study objective is to evaluate prospectively the efficacy and safety of the mPACT technique compared with the traditional trajectory for degenerative lumbar spondylolisthesis.


This is a single-center, randomized, controlled, parallel group, superiority trial. A total of 154 adult patients are allocated in a ratio of 1:1. Sample size and power calculation were performed to detect the minimal clinically important difference of 10%, with an expected standard deviation of 20% in the primary outcome parameter, the Oswestry Disability Index, with power of 80%, based on an assumed maximal dropout rate of 20%. Secondary outcome parameters include the EuroQoL 5-Dimension questionnaire, the Beck Depression Inventory, the painDETECT questionnaire and the "timed up and go" test. Furthermore, radiological and health economic outcomes will be evaluated. Follow up is performed until 5 years after surgery. Major inclusion criteria are lumbar degenerative spondylolisthesis with Meyerding grade I or II, which qualifies for decompression and fusion by medialised posterior screw placement with cortical trajectory (mPACT) or by a traditional trajectory for lumbar pedicle screw placement.


This trial will contribute to the understanding of the short-term and long-term clinical and radiological postoperative course in patients with lumbar degenerative disc disease, in which the mPACT technique is used.


ISRCTN registry, ISRCTN99263604 . Registered on 3 November 2016.


Cortical bone trajectory; Lumbar degenerative disc disease; Minimally invasive technique; Pedicle screw fixation; Transforaminal lumbar interbody fusion

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