Percutaneous iliosacral screw and trans-iliac trans-sacral screw with single C-arm fluoroscope intensifier is a safe treatment for pelvic ring injuries

To elucidate the accuracy, efficacy, and safety of percutaneous iliosacral screw (ISS) and trans-iliac trans-sacral screw (TITS) insertion using a single C-arm fluoroscopy intensifier. Additionally, the potential risk factors that might cause mal-positioned screws were identified. Patients with pelvic ring injuries who underwent percutaneous screw fixation in a single medical institute were divided into an ISS group (n = 59) and a TITS group (n = 62) and assessed. The angles deviated from ideal orientation (ADIO) of the implanted screw were measured, and potential risk factors for mal-positioned screws were analyzed. Overall, the reduction quality of the pelvic ring was good or excellent in 70 patients (82.4%) by Matta’s criteria and in 48 patients (56.5%) by Lefaivre’s criteria. ADIO measurements of the ISS and TITS groups via multi-planar computed tomography were 9.16° ± 6.97° and 3.09° ± 2.8° in the axial view, respectively, and 5.92° ± 3.65° and 2.10° ± 2.01° in the coronal view, respectively. Univariate statistical analysis revealed body mass index as the single potential risk factor of mal-positioned screws. With careful preoperative planning and intraoperative preparations, placing ISS and TITS under the guidance of single C-arm fluoroscopy intensifier is a reliable and safe technique. Caution should be exercised when performing this procedure in patients with a high body mass index.

www.nature.com/scientificreports/ intensifier. Since that time, several real-time image modifications have been proposed to improve the accuracy and safety of this technique, such as 2-arm fluoroscopy, O-arm fluoroscopy, intraoperative computed tomography, and navigation system [16][17][18][19] . Although reports from these new image-assisted surgery have revealed their efficacies, the advanced image tools are expensive and not routinely available to each orthopedic surgeon and facility. Therefore, the usefulness of these advanced image tools for the percutaneous treatment of posterior pelvic ring may be limited. The aim of this study was to report the surgical outcomes using the most commonly available intraoperative image evaluation, the single fluoroscopic intensifier, in treating posterior pelvic ring injuries by either iliosacral screw (ISS) or trans-iliac trans-sacral screw (TITS) insertion. Additionally, the risk factors of potentially malpositioned screws were evaluated.

Materials and methods
Patient enrollment. We retrospectively collected patients' medical records from the fracture registration database of our institute to identify those who were diagnosed with pelvic ring injury and underwent percutaneous screws fixation (ISS, TITS, or both) either through closed reduction and internal fixation or open reduction and internal fixation (ORIF) between January 2017 and June 2020. The medical records and pre-and postoperative radiological images were meticulously reviewed. All the operative procedures were performed with an established operative protocol by a single surgeon (Y.-H.Y.). The review process was approved by the Chang Gung medical foundation institutional review board (IRB No. 202100620B0).
Resuscitation and perioperative protocol. The patients were sent to the emergency department (ED) directly from trauma scenes or transferred from primary medical institutes. Advanced Trauma Life Support ® resuscitation protocol was followed in the ED, and then patients were transferred to the ordinary ward or intensive care unit, as required. Osteosynthesis for the pelvic fracture was performed immediately after the patient was hemodynamically stabilized. Image examinations, including X-rays [anteroposterior (AP), inlet, and outlet views] and multi-planar computed tomography (mpCT), were required for preoperative planning. Subsequently, the rehabilitation protocol was individualized according to the patient's concomitant injuries and fractures. Similar postoperative image examinations were performed to examine the reduction quality of the pelvic ring and the position of the implants.
Operative technique. Patients were positioned in supine or prone position, according to the planned procedures and the concomitant injuries observed on a radiolucent table (Modular Table System; Mizuho OSI, California, USA) under general anesthesia. In patients for whom a prone position was contraindicated because of concomitant injuries or anesthesia requirements, a supine position was preferred. However, a prone position was necessary for ORIF of posterior pelvic ring injuries, such as dislocated sacroiliac joint and vertical displacement of the sacral fracture. The osteosynthesis strategy for anterior and posterior pelvic ring injury could be performed simultaneously or sequentially. Posterior pelvic ring reduction and fixation was always performed prior to anterior pelvic ring procedure, except in cases with pelvic ring injury to AO B2.1 20 with significant internal rotational deformity of the affected hemipelvis.
AP, inlet, outlet, 2 Judet views, and sacrum lateral views were examined prior to surgical draping to ensure that all the images could be obtained clearly without limitations. The intraoperative images were obtained from a single-arm fluoroscopic intensifier (Ziehm Solo; Ziehm Imaging GmbH, Nuremberg, Germany). The ideal orientation of the ISS was perpendicular to the sacroiliac joint, whereas that for TITS was parallel to the groundline. After the position and orientation of the K-wire was confirmed, a 7.0-mm cannulated screw (Cannulated Screw 7.0 mm; Syntec Technology Co., Hsinchu, Taiwan) was applied as the target implant. All images were examined repeatedly throughout the procedures. Moreover, the radiation dose and time were recorded thoroughly during percutaneous screw osteosynthesis.
Analysis of screw placement and reduction quality of the pelvis. Standard X-rays (AP, inlet, outlet views) and mpCT were obtained postoperatively for each patient. Radiological interpretations were performed by two independent medical doctors (J.-P.C. and P.-J.T.), who were not involved in the surgeries, using the PACS system (Centricity Enterprise Web V3.0; GE Healthcare, Chicago, USA).
The morphology variability of the sacrum, in terms of sacral dysmorphism, was examined prior to osteosynthesis. We adapted the criteria by Routt 21 to define a dysmorphic sacrum which are the signs from X-rays, including (1) mammillary bodies; (2) tongue-in-groove morphology; (3) collinearity; (4) dysmorphic neural foramina; (5) residual sacral disc space. When the sacral dysmorphism was anticipated from preoperative image evaluation, percutaneous osteosynthesis by TITS would be applied more frequently than that by ISS because of the narrow corridor of S1.
Several classifications and grading systems for fracture pattern, reduction quality evaluation, and screw positions were adapted in this study. We classified the fracture pattern according to the Arbeitsgemeinschaft für Osteosynthesefragen (AO) system or pelvic ring injury 20 . For those fractures with sacral involvements, the Denis classification were applied 22 . The reduction qualities of the pelvic ring injuries were evaluated from the pelvic AP, inlet, and outlet X-rays, and axial and coronal views of the mpCT. We adapted the criteria from Matta and Tornetta for vertical reduction quality 15,23 and from Lefaivre for symmetrical reduction quality 24 . Accordingly, we classified the reduction quality of the pelvic ring injury as excellent, good, fair, or poor.
For ISS, we collected the angles between the screw and sacroiliac joint obtained in the axial and coronal views of the mpCT. The angular differences between the implanted screw and the ideal orientation of the ISS, which should be perpendicular to the sacroiliac joint in each view, were measured and termed as the angles deviated Scientific Reports | (2022) 12:368 | https://doi.org/10.1038/s41598-021-04351-z www.nature.com/scientificreports/ from ideal orientation (ADIO) (Fig. 1A). For TITS, the angular difference between the implanted screw and the ideal orientation, which should be parallel to the groundline in both axial and coronal views of the mpCT scan, were recorded (Fig. 1B).
To qualitatively define mal-positioned ISS and TITS, a screw that penetrated, encroached, or touched the neuroforamina of the sacrum or a newly appeared postoperative neurological deficit was defined as a malpositioned screw, and Smith's grading system (Table 1), which classified the position of the screw from grade 0 to 3, was applied to quantify those with mal-positions 25 .
Statistical analysis. The Chi-square test or the Fisher's exact test was used where appropriate to analyze categorical data. Nonparametric Mann-Whitney U test was applied for between-group comparisons in numerical data. Logistic regression was applied for analysis of risk factors. Statistical significance was defined as p < 0.05.   24 , the evaluations of ISS in both views had grade 1 mal-angulation and grade 0 perforation, whereas those of TITS showed grade 0 mal-angulation and grade 0 perforation.

Complications.
One surgical site infection from the percutaneous wound was found 7 days after the index surgery. The wound finally healed uneventfully with implant retention after surgical debridement, proper wound care, and adequate systemic antibiotic treatment.

Risk factors analyses.
To determine the potential risk factors that might cause a mal-positioned screw from this percutaneous procedure, a logistic regression analysis was carried. The chosen factors are shown in Table 4. Because of the relatively small number of enrolled patients, a stepwise method of logistic regression test was applied. However, we failed to find a significant risk factor for mal-positioned screw using logistic regression analysis. Using the receiver operating characteristic, the area under the curve in the axial and coronal views    Fig. 2A), and 0.461 and 0.792 respectively, in the TITS group (Fig. 2B). Several univariate analyses were conducted to attempt to find potential risk factors for mal-positioned screws ( Table 5). No significant risk factors were found in the ISS group, regardless of mpCT view. Although no risk factor was found in the coronal view for the TITS group, the patient's body mass index (BMI) was identified as a single significant risk factor (p = 0.02) in the axial view.

Discussion
In this study, we reviewed the efficacy and safety of percutaneous ISS and TITS insertion using a single-arm fluoroscopic intensifier intraoperatively in 85 patients with pelvic ring injuries. The results revealed a satisfactory fracture reduction quality and a low rate of mal-positioned screws. Although BMI was a potential risk factor of screw mal-positioning according to the Mann-Whitney U test, it failed to show significance in logistic regression analysis.
The application of ISS and TITS has been widely accepted for the treatment of posterior pelvic ring injuries [26][27][28] . However, mal-positioned screws can cause devastating consequences, such as injuries to superior gluteal vessels, iliac vessels, lumbosacral nerve roots, and sympathetic chain 4,9,[29][30][31] . Therefore, for effective and safe osteosynthesis, it is critical to perform this procedure under intraoperative real-time image guidance.
The optimal corridors of the ISS and TITS are narrow, and the procedure requires a high degree of technical skill. Therefore, several intraoperative image assessment technologies have been applied to enhance the accuracy of screw placement. Peng et al. compared the one and two C-arm fluoroscope technique, finding similar mal-positioned and clinical complication rates, but the two C-arm group had a shorter operation time (16 vs. 45 min, p < 0.001) and lower radiation exposure (4.5 vs. 5.7 min, p < 0.001) 16 . A recent study by Ciolli et al., showed satisfactory accuracy using the O-arm, with a complication rate and mal-positioning of screw varying from 0 to 15% 17 . Berger-Groch et al. compared fluoroscope-based conventional technique with 2D navigation procedures and found similar rates of malposition, but the radiation dose using the conventional technique was twice that of the 2D navigation procedure 32 . Richter et al. found that intraoperative computed tomography significantly reduced screw perforation rate compared to that when using conventional 3-dimensional navigation 18 . Although the advantages of advanced image systems cannot be ignored, the clinical utility might be limited to a few medical institutes. Because the single-arm fluoroscopic intensifier is the most common image assessment tool in most facilities, preoperative preparation is critical; personal protections from radiational exposure, such as keeping surgeon's hand out of the field, covering thyroid and body with lead cloths, wearing lead spectacles, laser guidance, and radiation awareness, are crucial for medical staff in the operation theater 33,34 .
The reduction quality of the pelvic ring injuries in this study were comparable to those of previous reports [35][36][37][38] , which could be due to the treatment sequence. Before implanting the screws percutaneously, all the fractures should be reduced as possible. For AO B2.1 injuries, the reduction of the pelvic ring was initiated from the anterior pelvic ring to externally rotate the affected hemipelvis. A similar reduction sequence was indicated for AO B3.1 and B3.2 injuries. A considerable percentage (70.8%) of the patients underwent open reduction for diastatic sacroiliac joints because as long as anatomical reduction was achieved, a well-positioned screw could be inserted despite a prone position takes additional time to correct positioning of the patients and is more bothersome to anesthesiologists 39 . Patients with vertically unstable sacral fractures underwent a cranial-caudal orientation reduction prior to osteosynthesis. Using this "reduction first" concept, we achieved a low malposition rate, with no implantation-related complications.
A high BMI may limit the application of percutaneous surgeries [40][41][42] . We identified that a higher BMI was the single risk factor of TITS screw angle error under axial view of computed tomography (p = 0.02). This finding may result from the cumbersome patient positioning, blurry fluoroscopic images, or difficulty in instrument application for obese patients. However, it failed to reveal its significance during logistic regression analysis. We postulated that the reasons of inconsistence between two statistical results were due to our relatively small case number and the low malposition rate (4.8%) of the percutaneously applied screws.
Sacral dysmorphism is defined as upper sacral segment dysplasia and have a higher risk in mal-positioned implant during percutaneously placing ISS and TITS 43 . In dysmorphic sacrum, narrow but adequate corridor for ISS at S1 segment can be found; however, it carries a considerable rate of malalignment 43,44 . Currently, it is believed that the use of a 3D navigation system during operation confers a lower rate of mal-positioned screw 44,45 . www.nature.com/scientificreports/ The incidence of sacral dysmorphism in our cohort was 6.6%. All dysmorphic sacrum underwent percutaneous TITS osteosynthesis, and there were no complications that required revised surgeries under single C-arm fluoroscope intensifier examination. Additionally, the morphology variation of the sacrum was not a factor in mal-angulation of the screws. A similar concept reported by Rommens et al. 43 showed that using 2D-fluoroscopicguided ISS osteosynthesis would be a safe procedure in clinical practice if a thorough preoperative evaluation of the morphology of the upper sacrum, recognition of all the necessary anatomical landmarks, and careful operative procedure were performed. This study has several limitations. First, its retrospective design study has inherited limitations. The cohort was treated using a single intraoperative image evaluation without a comparative method such as navigation-assisted percutaneous screw osteosynthesis. Second, only a small number of patients were enrolled. Third, the treatment protocol might have some divergence for patients with a similar fracture type such as supine or prone position and closed or open reduction. Fourth, all the operations were performed by a single surgeon, whose experience might have affected the surgical outcomes. However, we found that the radiation dose exposure and reduction quality of the pelvis was acceptable, and no screws penetrated the neuroforamen.

Conclusions
With careful preoperative planning and intraoperative preparations, percutaneous ISS and TITS implantation under a single-arm fluoroscopic intensifier examination is reliable and safe. Further prospective studies applying different intraoperative image systems should be conducted to identify their potential advantages over this surgical technique.