Percutaneous pedicle screw insertion of the spine

Abstract

With interest we read the letter by Rob D. Dickerman regarding our article “comparison of open versus percutaneous pedicle screw insertion in a sheep model” published in the ESJ. Our reply to the authors and colleagues is as follows: Percutaneous pedicle screw insertion represents a considerably novel technique, which has been recently introduced in the literature. Up to now, only a few studies have been published, most of them focused on technical matters and postoperative assessment of screw placement [2, 6–11]. Consequently, the available data about functional outcome are sparse. Grass and colleagues investigated procedure and image converter time, blood loss and muscle damage by needle-EMG in a controlled prospective setup representing an evidence level II-1 [3]. They found a higher loss of blood and neurophysiological signs of muscle damage in the open group. In a small retrospective study, Kim et al. analyzed cross sectional muscle areas by MRI in patients either treated with open or percutaneous pedicle screw insertion. They found a significant decrease of the multifidus muscle size in the group which received open pedicle screw insertion. However, clinical scores revealed no difference between the two groups [4]. In our study, we could for the first time demonstrate a clear benefit in terms of blood loss and CK liberation by percutaneous screw placement in a controlled and experimental setting. To our knowledge there are no further studies representing a similar high level of evidence on this topic. The author of the letter claims, that there was substantial literature on the benefits of minimally invasive spine surgery, including less muscle damage, faster recovery and shorter hospitalization and that open lumbar fusions had significantly higher muscle damage in comparison to minimally invasive procedures. However, looking at the cited literature it becomes clear that Arts as well as Kumbhare mainly addressed CK liberation in patients undergoing decompression or disc surgery while only a small minority of their patients was treated with pedicle screws [1, 5]. Further, the cited studies include neither a comparison between open and percutaneous pedicle screw insertion nor any data regarding recovery and hospitalization. The author of the letter mentions the alternative to deliver the pedicle screw percutaneously over a guidewire. Due to the very hard bone cortex of the sheep used in our study the pedicles had to be opened and inserted with a machine drill, so that the use of cannulated or wire guided screws was not an option in our study. The author of the letter presents preliminary results of several minimally invasive screw systems and used CK liberation as the main outcome factor. We agree with the author, that CK represents an important and feasible parameter to assess muscle damage. However, the clinical relevance of elevated serum CK levels after surgical procedures remains controversial and definitely, more data with regard to functional outcome and quality of life are required here [1]. A further concern is the longer exposure time to radiation with placement of percutaneous pedicle screws. During the open approach a clear orientation is provided by the anatomical landmarks of the lumbar spine and access to the pedicle can be easily obtained without image converter. In a percutaneous setting, those anatomical landmarks are lacking, which explains the longer radiation exposure time we found in the percutaneous group. The author of the letter disagreed with this point based on his own clinical observations. However, this statement remains speculative and unsupported, since he did not provide any evidence from own data, but only referred to previous studies, which do not necessarily match our experimental design. The author of the letter claims that, in experienced hands, percutaneous pedicle screw placement decreases operative time, blood loss, muscle damage and radiation exposure, while also significantly shortening hospitalization time and recuperative time. As outlined above, we do not believe that there is enough evidence from experimental and clinical studies, to support such a statement. Further, we would like to encourage the author to publish more of his data. We feel that this would contribute to the issue and would enable us and other interested groups to openly discuss whether percutaneous pedicle screw placement really provides an evidence based benefit or not.