EVIDENCE LEVEL OF THE PLACEMENT OF SCREWS OUTSIDE PEDICLE IN THORACIC AND LUMBAR SPINE

ABSTRACT International recommendations in spine surgery require reproducible, safe and effective procedures. The placement of pedicle screws is technically demanding and relies on different methods of support, which result a high rate of complications related to suboptimal screw placement, with reports ranging from 15.7% to 40% according to Hansen-Algenstaedt N and Koktekir E in separate studies. This study carried out a systematic review of existing literature to identify the level of evidence of the placement of pedicle screws outside the pedicle in thoracic and lumbar spine. For the systematic review, a search of the existing literature, based on the use of MeSH terms in PubMed-Medline, Ovid, The Cochrane Library, MedicLatina, Elsevier, and EBSCO databases. According to the literature found, most authors agree that the placement of screws outside the pedicle itself does not represent a serious complication or that requires repositioning in a second surgery even when they are found to have a violation up to 50% of the medial wall of the pedicle. However, they agree that repositioning should be immediate if it is shown with imaging studies such as MRI and CT that endangers vascular and/or neurological structures, or are associated with biomechanical alterations of the spine. Level of Evidence II; Systematic Review of studies level II.


INTRODUCTION
Most high-energy accidents involve spine injuries and the most frequent are of the thoracic and lumbar spines.][8] Pedicle screw placement techniques are demanding.Transoperative navigation support is limited by its high cost.The use of a fluoroscope overexposes the health personnel and the patient to radiation and offers only limited assistance at the moment of screw placement.Anatomic vertebral modifications, especially in patients with degenerative pathology, result in a rate of complications related to suboptimal placement of the screws. 9,10Therefore, it is important to identify the level of evidence in the medical literature about the placement of pedicle screws outside of the pedicle as a complication and the level of application of the results systematically in the medical literature in patients submitted to thoracic or lumbar instrumentation surgery, 11,12 as well as its significance in the medical--legal sphere.The results were evaluated in a qualitative, retrospective, cross--sectional, observational, systematic review study, according to the recommendations of the Cochrane Group, establishing the level of evidence for the placement of pedicle screws outside of the pedicle in the thoracic and lumbar spines, including a description of the variables, a homogeneity analysis, and the identification and analysis of interobserver concordance, according to the Jada scale, the kappa value, the intraclass correlation coefficient (ICC), considering values ≥ 0.80 and p<0.05 as reliable.

RESULTS
We obtained 112 articles, from which we initially selected 46.After the first filtering, we ended up with 22 articles relating to the placement of pedicle screws outside the pedicle, which met the selection criteria and completed the full text sample.
Two observers participated independently in the qualification, methodological evaluation, level of evidence, and grade of recommendation, in accordance with Sackett's classification of levels of evidence, disagreeing on three articles regarding the level of evidence and grade of recommendation and a third observer was used to determine the proper classification for those articles.
Of the 19 articles included, twelve (63%) were from the United States of America, two (11%) from China, and one each (5%) from the United Kingdom, Turkey, Austria, Switzerland, and Greece.(Figure 1).
There is very little literature of high quality and good methodological design on the subject of the level of evidence and grade of recommendation of placement of pedicle screws outside the pedicle in the thoracic and lumbar spine as a complication.The results of our review indicate level of evidence "4" (Figure 2) and grade of recommendation "C", with a "favorable, but not conclusive recommendation".(Figure 3)

DISCUSSION
The posterior lumbar interbody fusion (PLIF) technique has become an important component of modern spine pathology treatment.Fixation with pedicle screws is an important method for internal thoracic and lumbar spine fixation.4][5] However, there is a problem associated with transpedicular fixation: the pedicle is the strongest location, but it is not the widest part of the vertebrae.This factor is fundamental in the placement of the screws in the   pedicles.A significant rate of screws placed outside of the pedicle and the resulting complications has been reported and extrapedicular placement of the screws is considered by some authors as a catastrophic failure of the procedure, In general, there is very little literature published by the other surgeons about these situations and what exists is of poor quality and poor methodological design.Thus, we consider it important to conduct a study that establishes a benchmark to determine the true severity of placement of the pedicle screws outside of the pedicle and to encourage new studies with a higher level of evidence than those published to date.

CONCLUSIONS
In disagreement with the literature found, most of the authors agree that screw placement outside of the pedicle by itself is not a serious complication or one that requires them to be repositioned in a second surgery, since this would be an additional medical risk to the patient and would increase the costs incurred by the health system, even when it would be a grade III violation of the medial wall of the pedicle.However, we agree that the repositioning of these screws should be immediate if imaging studies such as MRI and CAT studies show that they are putting vascular and/or neurological structures at risk or they are associated with biomechanical alterations of the spine, even if there is a grade II violation of the medial wall of the pedicle.The screws that present a grade I violation of the pedicle, and most of the grade II violations are rarely accompanied by vascular and nerve lesions, so the grade of recommendation for replacement of these screws is D. For grade III and IV screws, the grade of recommendation for screw replacement is C and for grade II, III, and IV screws the grade of recommendation for replacement of the screws is A.
METHODS A systematic review of the existing literature was conducted in which the level of evidence about the placement of pedicle screws outside the pedicle in the thoracic and lumbar spines was identified.It was authorized by the Institutional Review Board as No. 3401 and COFEPRIS Registration No. 13 CI 09 005 221, "Dr.Victorio de la Fuente Narváez" Orthopedic Hospital of the UMAE, IMSS, Mexico, who assigned Registration No. R-2016-3401-50 to the project.For the systematic review a search of the existing literature was performed, based on the use of MeSH terms in the PubMed-Medline, Ovid, The Cochrane Library, Medi-cLatina, Elsevier, and EBSCO databases.The MeSH terms used were Pedicle Screw Complication, Misplacement, Thoracic Spine, and Lumbar Spine.