Intraoperative Cone Beam CT in Hybrid Operating Room Set-Up as an Alternative to Postoperative CT for Pedicle Screw Breach Detection

Intraoperative Cone Beam CT in Hybrid Operating Room Set-Up as an Alternative to Postoperative CT for Pedicle Screw Breach Detection. Journal of Spine Research Surgery 4 (2022): Abstract Background: CT is considered the gold standard for detecting pedicle breach. However, CBCT may be a viable and low radiation dose alternative to provide intraoperative feedback to surgeons to permit in-room revisions of misplaced screws. Methods: To assess the ability and reliability of intr-J aoperative cone-beam CT (CBCT) from a robotic C-arm in a hybrid operating room (OR) two hundred forty-one pedicle screws were inserted in cervical, thoracic and lumbar spine of 7 cadavers followed by CBCT and CT imaging. The CT images served as the standard of reference. Agreement on screw placement between both imaging systems was assessed using Cohen’s Kappa coefficient (κ). Sensitivity, speci ficity, receiver operating characteristic (ROC), area under the empirical and fitted ROC curves (AUC) were computed to assess CBCT as a diagnostic tool compared to CT. The patient effective radiation dose (ED) was calculated for comparison. A systematic literature review was performed to provide pers-pective to the obtained results. Results: Almost perfect agreement in assessing pedicle screw grading between CBCT and CT was observed (κ=0.84). The sensitivity and specificity of CBCT were 0.84 and 0.98 respectively. The AUC derived from the empirical and fitted ROC curves were 0.95 and 0.96. Conclusion: Intraoperative CBCT by C-arm in a hybrid OR is highly reliable in identification of screw placement at significant dose reduction.


Introduction
Accurately positioned pedicle screws offer optimal biomechanical fixation, making them a well-accepted treatment choice for a variety of spine pathologies [1,2]. However, up to 42% of pedicle screws were reported to be malpositioned [3,4]. While initially clinically silent, these may eventually result in an unstable construct, reduced fusion, pseudoarthrosis and accelerated adjacent-level degeneration [5]. In comparison to CT, radiography detects only 52% of misplaced screws [6,7], making intraoperative CT imaging necessary for complex deformity, to avoid revision surgeries. Availability of intraoperative 3D imaging resulted in revision of 9% of screws intraoperatively corresponding to 35% of the treated patients. Lower threshold for intraoperative revisions based on objective intraoperatively available imaging data, leads to fewer secondary revision surgeries [8].
Avoidance of postoperative revisions makes the initial investment in intraoperative 3D imaging technologies economically more attractive [9]. Hybrid operating rooms (OR) equipped with a motorized Carm coupled with a radiolucent surgical table as well as with integrated navigation capabilities, have been recently used for spine surgery [10]. The C-arm provides intraoperative cone-beam CT (CBCT) imaging. The purpose of this cadaver study was to determine the diagnostic performance of intraoperative CBCT using a C-arm in a hybrid OR for identifying screw misplacements in comparison to gold-standard postoperative CT. To put our results in perspective, a sytematic literature review of studies comparing intraoperative 3D imaging for screw misplacements with postoperative CT was conducted.

Data analysis
The CBCT and CT images were reviewed on a PACS system with 3D volumes displayed in a multi-planar format. The width and level were set to optimize visualization. Screw position assessments were performed using the Gertzbein grading [13]: Each screw was assigned a grade from 0 to 3, for each imaging modality. Consequently, a 4x4 contingency table to compare the similarity in rating was created. Figure 3 illustrates an example of each of the 4 grades on both CBCT and CT from the diagonal of the contingency table (i.e. agreement between both imaging modality for each grade). All images in

Statistical analysis
Cohen's Kappa coefficient (κ) was calculated to assess the agreement between CBCT and CT based on the contingency tables and was classified according to Landis et al. [14] as detailed in Table 1.
Sensitivity was defined as the proportion of misplaced screws detected on CBCT which were confirmed as such on CT; whereas specificity was defined as the proportion of screws accurately placed according to CBCT which was confirmed as such on CT.

Accuracy comparison between CBCT and CT
All cadavers had their fully instrumented spine imaged with CBCT as seen in comparison with CT, Figure 2. ED reduction on CBCT.

Literature review and comparison
The initial database search identified 117 studies without any duplicates. 104 articles were excluded after scrutiny of abstracts. The two most common reasons for exclusion were articles not being comparative studies (n=35) and the study group not corresponding to an intraoperative 3D imaging such as 2D radiography, EMG, or other techniques (n=35).
Fifteen studies were not related to pedicle screws (e.g. iliac screws), and an equal amount corresponded to conference abstracts. Four abstracts corresponded to papers not written in English. From the remaining 13 articles, 5 other exclusions were applied at text screening level. The most common reason of exclusion was not using a Gertzbein-like grading with 2 mm increment for breach (n=5) [16][17][18][19][20]. One study was excluded because of inconsistency between the data in the abstract and in the text [21].
One study did not use a grading scale but revision surgery as surrogate parameter for screw misplacement [22]. Another study did not confirm whether the for breach <2mm and considered all breaches as misplaced screws [24]. Finally, there were 4 studies that were discussed in this review [25][26][27][28], Figure 4.
Details are presented in Table 3 Figure 5 shows a comparison of the ROC curves and corresponding AUC.

Discussion
Hybrid ORs support multidisciplinary use of 2D and 3D imaging and navigation for open and minimal invasive procedures [10]. This cadaver study sought to assess the diagnostic performance of CBCT from a C-arm within a hybrid OR compared to diagnostic CT. Unlike mobile C-arm with CBCT capability and mobile CT, the C-arm system in the hybrid OR has an image acquisition and processing chain comparable to diagnostic CT scanners. Thus enabling better management of image quality and radiation dose exposure [29]. While macroscopic dissection is the gold reference for evaluating pedicle screw placement, CT is the clinically viable alternative [26].

Conclusions
Intraoperative CBCT by C-arm in a hybrid OR repre-

Institutional Review Board Statement
The study was conducted according to the guidelines of the Declaration of Helsinki. Ethics approval was obtained for a cadaver study from the ethics committee of the Christian-Albrecht-University Kiel, Germany.

Informed Consent Statement
Informed consent was obtained from all subjects involved in the study before decease.

Data Availability Statement
Not applicable

Conflicts of Interest
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.