Introduction

Spine surgery is an operation related to pivotal body structures, such as the spinal cord, nerve root, and the surrounding vascular compositions [3, 4]. For years, different techniques have been developed for spine surgery, one of which, pedicle screw placement, is an essential method for obtaining immediate stabilization of pathologic spinal segments [7]. However, misplacement of pedicle screws and long surgical duration are the two primary issues that adversely impact the ultimate surgical outcomes. Therefore, an efficient, accurate, and reproducible strategy for faster and more precise pedicle screw placement would be of benefit to the general orthopaedic practitioner [8, 33, 35] and is why computer-aided navigation techniques were invented [11, 13, 20, 29].

The misplacement rate of pedicle screw insertion has decreased dramatically with the assistance of computer-aided navigation [6, 14, 15, 27, 28, 31]. C-arm fluoroscopic imaging has been a traditional navigation technique used for years for active guidance in spine surgery and has enabled the accurate placement of pedicle screws. Despite this progress, the conventional C-arm system only provides two-dimensional fluoroscopic images, for which additional artificial correction during the operation is required in case the patient’s position is distorted [2, 17, 18]. Another navigation system, the O-arm imaging technique, provides real-time three-dimensional surgical imaging. During the pedicle screw placement, three-dimensional images of the spine segments can be presented simultaneously on the screen, thereby eliminating the need to account for the patient’s position [1, 5, 19, 26]. In theory, the O-arm technique appears to have more advantages, than the C-arm system, for more accurate surgical navigation. However, existing studies have shown the opposite. Incidence of misplacement occurs at 1.5%–4% for conventional C-arm fluoroscopy, whereas it is 9% in navigation coupled with O-arm imaging [9, 30, 34]. Moreover, efficiency of pedicle screw placement is another major concern, but current studies do not reach a consensus whether the C-arm or O-arm navigation technique is more time saving during the pedicle screw placement. Since there has been no systemic review comparing the C-arm with the O-arm system in regard to the accuracy and efficiency in pedicle screw placement in spine surgery, we performed a systematic review to address the question of whether dose navigation coupled with O-arm technology as superiority in terms of accuracy and efficiency compared with conventional C-arm fluoroscopy.

Materials and methods

Literature retrieval was performed by searching the PubMed, Embase, and Cochrane databases, from year 2000 to June, 2019, using “C-Arm,” “O-Arm,” and their corresponding synonyms as keywords and MeSH terms. Filters were not set. A total of 93 articles were found associated with O-arm and C-arm, including studies from the three databases directly and studies extracted from the references. Duplicated articles were removed after verification of the first authors, titles, and abstracts. Further screening of the searching outcomes was conducted manually according to the inclusion and exclusion criteria previously established. Only studies that made comparisons between O-arm and C-arm technology in regard to accuracy and efficiency in pedicle screw placement were included. Eligible studies had to report at least one outcome variable of “screw placement deviation,” “screw preparation time,” “operation time,” and “screw placement time.”

Data from the included studies was extracted and imported into Microsoft Excel 2007 software for analyses by two independent investigators. Data summarization was comprised of (1) study details, including study designs and statistical methods; (2) details of the pedicle screw placement, consisting of surgical techniques, the amount, and positions of pedicle screw placements; and (3) details of outcome assessment of accuracy and efficiency, comprising grade or scored system for accuracy assessment and screw preparation time or screw placement time for efficiency evaluation. In cases where data integrity was lacking, another two investigators acquired the missing data by measuring the diagrams and charts displayed in the recruited studies or by recalculation using the original data provided. This systematic review was carried out in accordance with the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines [16].

Results

After searching the databases with keywords and MeSH terms, a total of 93 articles emerged, with 91 directly selected from the databases and 2 added from the references. Fifty-seven of the 93 articles were duplicates and removed, with 36 articles left for further assessment. Concerning the inclusion criteria and the exclusion criteria, ten of the 36 articles were eliminated because the two techniques were not compared, and another 13 articles were excluded due to the absence of reporting accuracy, preparation time, or screw placement time. In addition, five of the 36 articles did not provide enough data. Eventually, eight studies were retained for comprehensive analysis (Fig. 1).

Fig. 1
figure 1

Flowchart of article selection process

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Study designs appeared moderately heterogeneous across the eight studies. Six studies were clinical studies [22, 23, 10, 12, 25, 32], with another one being a cadaver study [24], and the last one [21] comprised a clinical and cadaveric study. The surgical methods mentioned in the five studies were different and not described in the other three. The surgical operation was performed by a single surgeon in two studies and by different surgeons in four studies, while the remaining studies did not mention. Grade systems were applied as the accuracy measurement in seven studies, whereas another one used a scoring system.

Eight studies reported pedicle screw placement outcomes related to accuracy in both the C-arm and O-arm groups. The positions of all pedicle screws were evaluated by postoperative CT scanning. Six studies reported the same grade system, from grades 0 to 3, to evaluate the accuracy of screw placement. Grade 0 meant that screws were appropriately located, without observable vertebral cortex penetration; grades 1 to 3 indicated a cortex penetration within 2 mm, between 2 and 4 mm, and more than 4 mm, respectively. Another study of Knafo [10] was based on the Laine classification, where Laine 0 is a strictly intrapedicular screw, Laine I is a minor pedicle perforation (0–2 mm), Laine II is a moderate pedicle perforation (2–4 mm), Laine III is a severe pedicle perforation (4–6 mm), and Laine IV is a complete extrapedicular trajectory. The last study evaluated the accuracy outcome by employing a scoring system from 0 to 10.

Six studies reported pedicle screw placement outcomes related to efficiency in both the C-arm and O-arm groups. Two studies provided operation time, and five studies provided preparation time of screw placement. Besides, three studies provided insertion time of screw placement. Moreover, three studies outlined the learning curve to revealed insertion time transformation along with the operator’s clinical skill progress.

Diverse surgical procedures were performed across the eight studies, embracing standard open surgery, minimally invasive surgery, and percutaneous pedicle screw insertion surgery. After we avoided the data of cervical vertebra [32], all of the pedicle screw insertions were restricted to the thoracic and lumbar spine. Spinal segments between C-arm-and O-arm-coupled surgeries were similar in each study. All eight studies specified statistical methods. Four studies adopted SPSS software for analyzation, but the other four did not mention the individual software packages used. The overview of the study characteristics was summarized in Table 1.

Table 1 The overview of study characteristics is summarized
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Concerning the accuracy of screw insertion, the screw misplacement percentage and the grade of screw deviation were calculated in succession using data from the seven studies that employed a grading system or Laine classification to judge accuracy. Four studies showed a lower incidence of misplacement and a lesser degree of cortex penetration when using O-arm-coupled navigation, compared with conventional C-arm-coupled fluoroscopy [10, 12, 22, 25]. One study showed similar breach rates with the aid of either C-arm or O-arm technology [23]. But the last two studies did not mention this result clearly. As for the six studies using the grading system while another one using the Laine classification for accuracy measurement, we choose a criterion to define what means successful vertebral pedicle screws: that screws were appropriately located, without observable vertebral cortex penetration. The pooled results indicated that the incidence of screw misplacement in the C-arm groups is higher (I2 = 85.0%, p < 0.00001; RR = 0.49, p = 0.01; Fig. 2). Because of the large heterogeneity, we used sensitivity analyses and removed the study of Verma et al. And the pooled results also indicated that the incidence of screw misplacement in the C-arm groups is higher (I2 = 0.0%, p = 0.66; RR = 0.69, p = 0.0001; Fig. 3). This result consists of the study that used the developed score system to measure the accuracy of screw placement, which found that the O-arm group had a measurably higher mean accuracy than the C-arm group (p = 0.0001) [21].

Fig. 2
figure 2

Pooled accuracy outcomes comparing O-arm group and C-arm group. RR = relative risk; CI = confidence interval

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Fig. 3
figure 3

Pooled accuracy outcomes (without the study of Verma et al.) comparing O-arm group and C-arm group. RR = relative risk; CI = confidence interval

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In order to discuss the question about serious screws breach between two navigation, we define the serious screws breach: a cortex penetration more than 4 mm (Grade 3, Laine III, Laine IV), which were considered to have a severe risk of neuronal compromise and were always repositioned [25]. All seven studies provided data about cortex penetration, and the pooled results indicated that the incidence of screw serious breach in the C-arm groups is higher (I2 = 0.0%, p = 0.61; RR = 0.32, p < 0.0001; Fig. 4). O-arm navigation had significant superiority compared with C-arm guidance when it comes to the accuracy of screw insertion.

Fig. 4
figure 4

Pooled outcomes of the incidence of screw serious breach comparing O-arm group and C-arm group. RR = relative risk; CI = confidence interval

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Two studies reported the operation time for pedicle screw placement [12, 25]. All showed no statistically significant difference in the operating time when O-arm or C-arm were used, and the pooled results indicated no significant difference between C-arm and O-arm (I2 = 98.0%, p < 0.00001; Std. Mean Difference 0.97, 95% CI − 0.06 to 2.00; p = 0.07, random-effect model; Fig. 5).

Fig. 5
figure 5

Pooled outcomes of operation time comparing O-arm group and C-arm group. CI = confidence interval

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Five studies reported the pedicle screw insertion time [12, 21,22,23,24]. Two of them showed a longer insertion time required in the O-arm group than in the C-arm group (p < 0.05) [22, 23], but in the other two studies, the screw insertion time for the O-arm group was shorter (p < 0.05) [12, 24]. The study of Tabaraee et al. is a cadaver study, while the other three are clinical studies. Besides, the last study only provided a chart without detail data, so we used GetData Graph Digitizer software to extract data. The pooled results from five studies indicated no significant difference between C-arm and O-arm (I2 = 84.0%, p < 0.0001; Std. Mean Difference − 0.03, 95% CI − 0.36 to 0.29, p = 0.83, random-effect model; Fig. 6). O-arm navigation had no superiority compared with C-arm guidance when it comes to screw insertion time.

Fig. 6
figure 6

Pooled outcomes of screw insertion time comparing O-arm group and C-arm group. CI = confidence interval

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Three studies reported the preparation time for pedicle screw placement [22,23,24]. All showed a longer preparation time required in the O-arm group than in the C-arm group (p < 0.05). The preparation time of O-arm group was more than two times of C-arm group. Thus, although the preparation time varied among the three studies, the pooled results from five studies indicated a significantly longer time in O-arm group (I2 = 10.0%, p = 0.33; Mean Difference 6.64, 95% CI 2.39 to 10.89, p = 0.002, random-effect model; Fig. 7). The conclusion can be made that more preparation time is required for using O-arm technology, compared to C-arm technology. O-arm navigation had no superiority compared with C-arm guidance when it comes to screw preparation time.

Fig. 7
figure 7

Pooled outcomes of screw preparation time comparing O-arm group and C-arm group. CI = confidence interval

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Two studies by Shin et al. provide clues that the inferior vertebral cortex is the position most likely to be involved in screw misplacement when using either O- or C-arm-guided positioning (Fig. 8) and for which surgeons should pay further attention to decrease deviation rate of pedicle screw placement.

Fig. 8
figure 8

Deviated positions of misplaced screws. M = medial. I = inferior. L = lateral. S = superior

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Discussion

This systematic review and meta-analyses were based on eight studies associated with two techniques, namely, navigation coupled with either O-arm or conventional C-arm fluoroscopy, which were applied to guide pedicle screw placement in thoracic and lumbar spine surgeries. The eight studies were published in recent years (from 2011 to 2018). Therefore, the comparison between O-arm and C-arm technology is an emerging focus of clinical research.

In terms of accuracy, four studies gave evidence to support that spinal surgeries with O-arm guidance have higher accuracy in pedicle screw placement compared to navigation with C-arm technology. Moreover, the pooled results of seven studies indicated that the incidence of screw misplacement in the C-arm groups is higher. Concerning about the question of serious screws breach between two navigations, the pooled results indicated that the incidence of screw serious breach in the C-arm groups is higher. However, it should be pointed out that two of the seven studies stem from Shin and colleagues, and the surgeries in these two studies were performed by a single surgeon, instead of by different operators as in the other four studies, which may cause potential bias [10, 12, 22, 23]. Moreover, all studies contained only a small sample size. Sampling error is almost inevitable in every single study. The proficiency and experience of surgeons are underlying factors affecting the comparison of results.

When it came to efficiency, operation time, screw insertion time, and screw preparation time were compared between the two navigation groups. Two studies showed no statistically significant difference in the operating time when O-arm or C-arm were used. Five studies reported the pedicle screw insertion time and showed a wide divergence, and the pooled results indicated that O-arm navigation had no superiority compared with C-arm guidance when it comes to screw insertion time. Three studies all showed a longer preparation time required in the O-arm group than in the C-arm group (p < 0.05). Moreover, the pooled results from five studies indicated that more preparation time was required for using O-arm technology, compared to C-arm technology.

In summary, not only O-arm guidance had higher accuracy in pedicle screw placement compared to the C-arm group but also had a superiority in the rate of serious screws breach. In terms of efficiency, more preparation time was required for using O-arm technology compared to C-arm technology.

This study has some limitations. The included studies showed variation in study pattern, operative approach, evaluation methods, and skillfulness of operators, making it almost impossible to make an absolutely objective comparison. The two studies by Shin et al. showed almost identical results in that there were distinct outcomes between C- and O-arm technology concerning accuracy and efficiency, but the two were clinical studies comprised of a randomized controlled trial and a retrospective study. Tabaraee et al. showed no difference in the accuracy outcome, but they performed the study on cadavers instead of in-hospital patients. Sclafani et al. used a developed score system to evaluate the accuracy, while Knafo et al. used Laine classification, but the other studies applied a different grading system. Verma et al. also include patients of cervical spine disease. In addition, the surgical methods and surgeon experience varied among these studies, which is an essential factor in causing deviation of the pooled results. In fact, it is true that moderate heterogeneity occurred across the eight studies. This is the leading reason preventing us to perform a satisfying meta-analyses and is also the major factor affecting the credibility of the gross outcome.

Conclusions

Navigation coupled with O-arm imaging display slower efficiency compared to conventional C-arm fluoroscopy for pedicle screw placement. Navigation coupled with O-arm had significant advantages in accuracy over conventional C-arm fluoroscopy.