Safety and efficacy of pedicle screw placement using intraoperative computed tomography: consecutive series of 1148 pedicle screws

Clinical article

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Object

A number of imaging techniques have been introduced to minimize the risk of pedicle screw placement. Intraoperative CT has been recently introduced to assist in spinal instrumentation. The aim of this study was to study the effectiveness of intraoperative CT in enhancing the safety and accuracy of pedicle screw placement.

Methods

The authors included all cases from December 2009 through July 2012 in which intraoperative CT scanning was used to confirm pedicle screw placement.

Results

A total of 203 patients met the inclusion criteria. Of 1148 screws, 103 screws (8.97%) were revised intraoperatively in 72 patients (35.5%): 14 (18.42%) were revised in the cervical spine (C-2 or C-7), 25 (7.25%) in the thoracic spine, and 64 (8.80%) in the lumbar spine. Compared with screws in the thoracic and lumbar regions, pedicle screws placed in the cervical region were statistically more likely to be revised (p = 0.0061). Two patients (0.99%) required reoperations due to undetected misplacement of pedicle screws.

Conclusions

The authors describe one of the first North American experiences using intraoperative CT scanning to confirm the placement of pedicle screws. Compared with a similar cohort of patients from their institution who had pedicle screws inserted via the free-hand technique with postoperative CT, the authors found that the intraoperative CT lowers the threshold for pedicle screw revision, resulting in a statistically higher rate of screw revision in the thoracic and lumbar spine (p < 0.0001). During their 2.5-year experience with the intraoperative CT, the authors did not find a reduction in rates of reoperation for misplaced pedicle screws.

Object

A number of imaging techniques have been introduced to minimize the risk of pedicle screw placement. Intraoperative CT has been recently introduced to assist in spinal instrumentation. The aim of this study was to study the effectiveness of intraoperative CT in enhancing the safety and accuracy of pedicle screw placement.

Methods

The authors included all cases from December 2009 through July 2012 in which intraoperative CT scanning was used to confirm pedicle screw placement.

Results

A total of 203 patients met the inclusion criteria. Of 1148 screws, 103 screws (8.97%) were revised intraoperatively in 72 patients (35.5%): 14 (18.42%) were revised in the cervical spine (C-2 or C-7), 25 (7.25%) in the thoracic spine, and 64 (8.80%) in the lumbar spine. Compared with screws in the thoracic and lumbar regions, pedicle screws placed in the cervical region were statistically more likely to be revised (p = 0.0061). Two patients (0.99%) required reoperations due to undetected misplacement of pedicle screws.

Conclusions

The authors describe one of the first North American experiences using intraoperative CT scanning to confirm the placement of pedicle screws. Compared with a similar cohort of patients from their institution who had pedicle screws inserted via the free-hand technique with postoperative CT, the authors found that the intraoperative CT lowers the threshold for pedicle screw revision, resulting in a statistically higher rate of screw revision in the thoracic and lumbar spine (p < 0.0001). During their 2.5-year experience with the intraoperative CT, the authors did not find a reduction in rates of reoperation for misplaced pedicle screws.

Pedicle screws are a mainstay in the treatment of spinal disorders requiring instrumented arthrodesis.14,34 Their ability to stabilize the spinal column via a posterior fixation entry point has rendered them the standard to which many other fixation techniques are compared.36,37,39 However, pedicle screw placement may be challenging, particularly in the cervical and thoracic spine because of the smaller pedicle size and complex morphology.11,12,14,19,23,32,34,36,41,43 As a result, conventional methods based on anatomical landmarks and intraoperative fluoroscopy still result in pedicle breach rates of up to 39.8% in the literature.1–4,7,13,14,16,19,21,26,29–33,37,42,45

In light of the potential complications, a number of techniques such as virtual fluoroscopy and CT-based computer guidance systems have been introduced to minimize the risk of pedicle screw placement.25–27,30,31,40,41 Although image-guided surgical techniques have resulted in lower perforation rates (ranging from 9.3% to 14.3%), these technologies have their limitations.2–9 Virtual fluoroscopy is dependent on the resolution of the acquired fluoroscopic projections. On the other hand, CT-based computer guidance systems require preoperative imaging; thus, variations in patient positioning before and during the operation may alter intervertebral relationships, leading to potential navigational inaccuracies.10,12–17

To bridge the gap between preoperative and intraoperative position-dependent changes, intraoperative CT scanning has recently been introduced. Here, we summarize our experience using intraoperative CT scanning during pedicle screw placement for spinal pathologies requiring instrumented fusion. We document and categorize our misplaced screws and note the number of patients who required a postoperative revision surgery for pedicle screw revision. To compare the efficacy of intraoperative CT scanning, we also compare our results with a previous cohort of 964 patients at our institution who received 6816 pedicle screws in the thoracolumbar spine via the freehand technique coupled with postoperative CT imaging.30

Methods

Data Collection

We retrospectively reviewed the records of all patients undergoing pedicle screw placement in the cervical, thoracic, or lumbar spine from December 2009—the month that the intraoperative CT scanner was inaugurated at our institution—through July 2012. In this study, all pedicle screws, including C-2 and C-7 pedicle screws, were inserted using a free-hand technique in which anatomical landmarks are used to guide screw placement. Fluoroscopy or navigation was not used. The screws were placed by a total of 8 neurosurgeons. Patient demographics, clinical presentation, indications for hardware placement, radiological studies, operative variables, and length of follow-up were reviewed for each case.

For all patients included in this study, the location and accuracy of the pedicle screws or, in many cases, the pedicle markers, were objectively evaluated using CT imaging performed intraoperatively. The presence and extent of cortical breach by any misplaced pedicle screw or marker was determined by review of axial, sagittal, and coronal reconstructed images obtained from the intraoperative CT scan. The location and direction of cortical breach—medial, lateral, superior, inferior, or anterior—were noted in each instance. The numbers and locations of screws that were removed and replaced, or markers that then required a trajectory modification, were noted. If the marker or screw was placed properly within the pedicle but the surgeon felt it necessary to make an adjustment (such as changing the trajectory or the screw length), the screw was counted as requiring modification. In some instances, a second CT scan was obtained when the surgeon wanted to confirm placement of the newly revised instrumentation. In other instances, if the surgeon felt confident of the revision, he or she did not obtain a second scan given concerns for radiation exposure to the patient. Patients who required revision surgery due to misplacement of screws were documented.

Surgical Technique

Free-hand pedicle screw placement was performed using anatomical landmarks as previously described.30 Pilot holes were made using the high-speed air drill. A pedicle probe was used to cannulate the pedicle. Using a pedicle feeler, evaluation for a breach was performed. Upon determining that no breach had occurred, pedicle markers were placed. If a breach was noted, the trajectory was revised using a pedicle probe. Once the trajectory was noted to be satisfactory, a pedicle marker was placed. In some instances a plain lateral radiograph was obtained intraoperatively to confirm marker position; then the holes were subsequently tapped and the screws were placed prior to CT imaging.

An intraoperative CT scanning study with sagittal and coronal reconstructions was obtained either after placement of the pedicle markers or, if the surgeon was confident of the trajectory, after placement of the pedicle screws. In some instances, a CT scan was obtained after marker placement, followed by a second scan obtained after pedicle screw placement. However, as described above, a second scan was not uniformly obtained. In cases that required intraoperative revision of a pedicle screw, multiple CT scans may have been obtained based on the number of revisions needed.

Radiation Exposure

The intraoperative scanner is a 40-slice scanner (as opposed to a 64-slice scanner). While both scanners emit similar radiation doses, we tend to scan for a shorter amount of time with the intraoperative CT because we focus on the area of instrumentation. For example, a typical lumbar spine CT would require 10 seconds of scanning time at 300 mA for a total radiation dose of 8–10 mSv. With the intraoperative CT, we can focus just on the area of instrumentation and cut down the scanning time to 4 seconds at 300 mA for a total radiation dose of 3–4 mSv. The radiation exposure to the surgeon is nonexistent as all surgeons completely leave the operating room while the CT scan is taking place.

Operative Time

At our institution, preparation of the anesthetized patient for the imaging procedure requires 15 minutes while the patient is positioned but before skin incision. Each intraoperative CT scan and interpretation of the subsequent images by the spine surgeon requires an additional 10 minutes. Therefore, radiological confirmation of the pedicle screws after 1 intraoperative CT scan adds 25 minutes to the total operative time.

Results

Patient Population

In December 2009, our institution began using an intraoperative CT scanner. Between December 2009 and July 2012, a total of 203 patients underwent posterior spinal instrumented fusion using confirmatory intraoperative CT imaging. The average patient age was 61.0 ± 11.7 years, and 45.3% were male. Of these 203 patients, 24 (11.8%) underwent surgery for trauma to the spine, 23 (11.3%) had tumors, 148 (72.9%) had degenerative spinal disease, 68 (33.5%) had spondylolisthesis, 4 (2.0%) had congenital spinal disorders, and 10 (4.9%) had infectious pathology of the spine (Fig. 1). Twenty-nine patients (16.5%) had diabetes mellitus, 78 (44.3%) had hypertension, 8 (4.5%) had coronary artery disease, 15 (8.5%) had osteoporosis, 3 (1.7%) were morbidly obese, 4 (2.3%) had chronic obstructive pulmonary disease, and 43 (24.4%) had a history of previous spinal surgery. Forty-nine patients underwent cervical pedicle screw placement at either C-2 or C-7; 184 patients had pedicle screws placed in the thoracic or lumbar region. Thirty patients had subaxial cervical constructs that extended into the thoracic region.

Fig. 1.
Fig. 1.

Indications for pedicle screw placement in 203 patients using the intraoperative CT (ioCT) scanner.

In total, 56 (4.88%) pedicle screws were placed at C-2, and 20 (1.74%) pedicle screws were placed at C-7 (Fig. 2 upper). In the thoracic spine, 72 (6.27%) pedicle screws were placed at T-1, 78 (6.79%) were inserted at T-2, 18 (1.57%) at T-3, 18 (1.57%) at T-4, 12 (1.05%) at T-5, 9 (0.78%) at T-6, 16 (1.39%) at T-7, 20 (1.74%) at T-8, 16 (1.39%) at T-9, 32 (2.79%) at T-10, 32 (2.79%) at T-11, and 22 (1.92%) at T-12. Forty pedicle screws (3.48%) were placed at L-1, 76 (6.62%) screws were placed at L-2, 128 (11.15%) at L-3, 199 (17.33%) at L-4, 195 (16.99%) at L-5, and 89 (7.75%) at S-1. Of a total of 1148 screws, 76 (6.57%) were placed in the cervical spine, 345 (29.84%) were inserted in the thoracic spine, and 727 (62.89%) were placed in the lumbar spine. Excluding the cervical cases, a total of 1072 screws were placed in the thoracic or lumbar spine. Of thoracic and lumbar screws alone, 6.71% were placed at T-1, 7.28% at T-2, 1.68% at T-3, 1.68% at T-4, 1.12% at T-5, 0.84% at T-6, 1.49% at T-7, 1.87% at T-8, 1.49% at T-9, 2.99% at T-10, 2.99% at T-11, 2.05% at T-12, 3.73% at L-1, 7.09% at L-2, 11.94% at L-3, 18.56% at L-4, 18.19% at L-5, and 8.3% at S-1 (Fig. 2 lower). In total, 32.2% of pedicle screws in this subgroup were placed in the thoracic spine, whereas 67.8% were inserted in the lumbar spine.

Fig. 2.
Fig. 2.

Upper: Number of pedicle screws placed in the cervical, thoracic, and lumbar spine as a percentage of total pedicle screws placed. Lower: Percentage of pedicle screws placed in the thoracic and lumbar spine only.

Intraoperative and Perioperative Outcomes

Within the cervical spine, 7 (12.50%) of the 56 pedicle screws or markers at C-2 were revised intraoperatively, and 7 (35.00%) of the 20 pedicle screws or markers at C-7 were revised (Fig. 3 upper). Four (5.56%) of 72 were revised at T-1, 10 (12.82%) of 78 at T-2, 2 (11.11%) of 18 at T-3, 1 (5.56%) of 18 at T-4, 1 (8.33%) of 12 at T-5, 1 (11.11%) of 9 at T-6, 1 (6.25%) of 16 at T-7, 2 (10.00%) of 20 at T-8, 1 (6.25%) of 16 at T-9, 1 (3.12%) of 32 at T-10, 0 (0.00%) of 32 at T-11, and 1 (4.55%) of 22 at T-12. Within the lumbar spine, 2 (5.00%) of 40 screws or markers were revised at L-1, 5 (6.58%) of 76 at L-2, 9 (7.03%) of 128 at L-3, 15 (7.54%) of 199 at L-4, 25 (12.82%) of 195 at L-5, and 8 (8.99%) of 89 at S-1. Thus, of 1148 pedicle screws, a total of 103 (8.97%) were revised: 14 (18.42%) of 76 were revised in the cervical spine, 25 (7.25%) of 345 were revised in the thoracic spine, and 64 (8.80%) of 727 were revised in the lumbar spine (Fig. 3 lower). Compared with screws in the thoracic and lumbar regions, pedicle screws placed in the cervical spine were statistically more likely to be revised (p = 0.0061). In contrast, there was no statistical difference between the rates of revised screws between the thoracic and lumbar regions (p = 0.4098).

Fig. 3.
Fig. 3.

Upper: Number of pedicle screws revised, expressed as a percentage of the total number of pedicle screws placed at each spinal level. Lower: Number of pedicle screws revised, expressed as a percentage of total pedicle screws placed within the cervical, thoracic, or lumbar spinal regions. Compared with screws in the thoracic and lumbar regions, pedicle screws placed in the cervical region were statistically more likely to be revised (**p = 0.0061).

In total, 103 pedicle screws (8.97%) were revised in 72 patients (35.5%). Of this total, 41 pedicle screws or markers (39.81%) were classified as having a lateral breach based on intraoperative CT scanning. Twenty-nine pedicle screws or markers (28.16%) were medially breached, 7 (6.80%) were superiorly breached, and 13 (12.62%) were inferiorly breached. In these cases, the screw was removed and placed again along an improved trajectory. If the marker was found to have breached the pedicle cortex, it was removed and a new trajectory was obtained using the pedicle finder. Twelve pedicle screws or markers (11.65%) violated the anterior vertebral body cortex; they were removed and replaced with shorter screws. On the other hand, 8 screws (7.77%) were deemed too short and were replaced with longer screws (Fig. 4). Four pedicle screws were removed and not replaced. Three screws were replaced with ones with a larger diameter. Only one screw was revised to accommodate a smaller diameter screw.

Fig. 4.
Fig. 4.

Classification of 103 pedicle screw breaches in 72 patients. Short screws are ones that were deemed short based on intraoperative CT imaging and as a result were replaced with longer screws.

Of note, in 172 patients (84.73%) the pedicle screws were placed prior to intraoperative imaging, while in the remaining 31 patients (15.27%) markers were used. Of the 103 revised screws or markers, 94 trajectories (91.26%) were changed following scanning with pedicle screws versus 9 revisions (8.74%) following pedicle markers (Fig. 5).

Fig. 5.
Fig. 5.

A and B: Intraoperative CT images of the L-3 spinal level. The right pedicle screw is laterally placed outside of the vertebral body. The screw is revised for a more medial trajectory (B). C and D: Postoperative CT images of the T-11 spinal level. The left pedicle screw is anteriorly displaced. The screw tip is abutting the aorta (C). To avoid a luminal tear of the thoracic aorta, the pedicle screw was replaced with a shorter screw (D).

Intraoperatively, 17 patients (3.44%) had incidental durotomies. Perioperatively, 4 patients (1.97%) had surgical site infections, 3 (1.48%) had CSF leaks, 1 (0.49%) experienced deep venous thrombosis, and 1 (0.49%) had a pulmonary embolism. The average length of stay for patients was 6.33 ± 5.17 days.

Two patients required reoperations 3 and 4 days after the index operation because of undetected misplacement of pedicle screws. In the first case, the patient underwent an instrumented L1–3 posterolateral fusion. Intraoperatively, the left L-3 screw had been revised because of a medial breach; however, a postrevision CT scan was not obtained. Postoperatively, the patient experienced unremitting left L-3 radiculopathy. A postoperative CT scan was subsequently ordered, and the left L-3 screw was found to have inferiorly breached the pedicle. The patient was taken back to the operating room; the left L-3 screw was removed, and the fusion was extended to L-4. Intraoperative CT scanning revealed proper placement of the pedicle screws. After the revision surgery, the patient's symptoms improved and the patient was discharged to rehabilitation with no residual neurological deficit. In the second case, the patient underwent an L2–3 instrumented posterolateral fusion. Intraoperative CT imaging revealed proper placement of the pedicle markers. Pedicle screws were subsequently placed; a second intraoperative CT scan was not obtained after screw placement. Postoperatively, the patient complained of significant abdominal pain. A CT scan was obtained and revealed an anteriorly breached right L-2 screw, abutting the aorta. The vascular surgery team was consulted, and removal of the screw was recommended. The patient was taken back to the operating room; the right L-2 screw was removed and replaced with a shorter screw. The patient was subsequently discharged to home with no neurological deficit.

Discussion

Pedicle screws have become the standard by which all other posterior instrumented fixation techniques are compared.18–23 Despite being one of the predominant means of fixation in the posterior spine, the intrinsic anatomy inherent to screw placement, coupled with interpatient pedicle variability, translates into the potential for neurological risk to many patients.24–28,30,31 Rampersaud et al. demonstrated that the mean maximum permissible translational screw placement error in the thoracic spine was 0.6 mm, with a rotational error of 2.6°.32 In the lumbar spine, the translational screw placement error was 2.0 mm and the rotational error was 6.3°. In light of the small margin for error, a number of assistive techniques such as virtual fluoroscopy and CT-based computer guidance systems have been introduced to increase the accuracy of pedicle screw placement.33,34,37,39–44 The recent advent of intraoperative CT scanning offers the possibility of monitoring and visualization of pedicle screws immediately after their placement.34–37,39–45

In our experience, among the 203 patients who underwent pedicle screw placement with intraoperative CT imaging, 72.9% had degenerative spinal disease. Of 1148 pedicle screws placed, 76 (6.57%) were placed in the cervical spine, 345 (29.84%) were inserted in the thoracic spine, and 727 (62.89%) were placed in the lumbar spine. To compare the efficacy of the intraoperative CT scanner in reducing reoperations for pedicle screw revision, we compared our results with our published institutional series of pedicle screws placed via a free-hand technique confirmed with postoperative CT.

In our previous study, we reported the results of 6816 pedicle screws placed via free-hand technique in 964 patients at our institution.30 Among these screws, 3443 (50.5%) were placed in the thoracic spine and 3373 (49.5%) were placed in the lumbar spine. Upon postoperative CT scanning, 115 screws (1.7%) were identified as breaching the pedicle or vertebral body cortex. Compared with our breach rate of 103 (9.61%) of 1072 screws placed in the thoracic/lumbar spine, this was a significantly lower rate (p < 0.0001). Among the free-hand cohort, these 115 pedicle screws were misplaced in 87 patients (9.0%); in our cohort who underwent intraoperative CT scanning, screws were revised in 72 patients (35.5%). This increase in this cohort was statistically significant (p < 0.0001). The increase in breach rate—both in terms of misplaced screws and number of patients affected—is likely due to differing definitions of breached screws. In the publication describing the free-hand technique with postoperative CT scans, we defined breach as pedicle screws with more than 25% of the screw diameter residing outside the pedicle or vertebral body cortex. In contrast, in this study any perceived breach of pedicle screws or pedicle markers visualized on the intraoperative CT scan prompted surgeons to revise the screw. Additionally, screws that were too short or those that the surgeon deemed required an improved trajectory were counted as revised/breached screws. Thus, the intraoperative CT scanner is much more sensitive at detecting unfavorably placed screws than conventional intraoperative fluoroscopy or radiography and dramatically lowers the threshold for screw revision.

This lowered threshold for screw revision likely explains the equivalent rates of revision between thoracic and lumbar pedicle screws in the intraoperative CT scan cohort. Thus, whereas patients who received free-hand pedicle screws had a thoracic spine breach rate of 2.5% versus a 0.9% breach rate within the lumbar spine (p < 0.0001), patients who underwent intraoperative CT imaging had 25 screws (7.25%) revised in the thoracic spine and 64 (8.80%) revised in the lumbar spine (p = 0.4098) (Table 1). In contrast, 14 pedicle screws (18.42%) were revised in the cervical spine, with the highest percentage of revised screws at C-7 (35.0%). The cervical screw revision rate was statistically higher than the thoracic or lumbar screw revision rates in patients undergoing intraoperative CT imaging (p < 0.0001).

TABLE 1:

Comparison of revision rates and direction of pedicle screw breaches between the intraoperative CT group and the postoperative CT group (published data set)*

ParameterRate (%)
Intraop CTPostop CT
revision rate
 thoracic7.252.5
 lumbar8.800.9
direction of pedicle screw breaches
 lateral39.8161.3
 medial28.1632.8
 superior6.82.5
 inferior12.62NA
 anterior11.65NA
 short screws7.77NA

NA = not available.

A total of 1148 screws were placed in the intraoperative CT group and 6816 were placed in the postoperative CT group.

A total of 103 pedicle screw revisions were performed in the intraoperative CT group and 115 were performed in the postoperative CT group.

In patients undergoing free-hand pedicle screw placement in the previously published series, the direction of breach was lateral in 73 cases (61.3%), medial in 39 (32.8%), and superior in 3 (2.5%). For patients who had pedicle screw placement with the assistance of the intraoperative CT scanner, 41 pedicle screws (39.81%) were classified as lateral breached, 29 pedicle screws (28.16%) were medially breached, and 7 (6.80%) were superiorly breached (Table 1). These trends were consistent regardless of patient cohort, likely due to the fact that screws were placed using the free-hand technique in both the postoperative CT scan and intraoperative CT scan cohorts. Thus, although the detection of screw breaches may be made and corrected intraoperatively, the quality of the breach itself is likely to be unaltered by the presence of the intraoperative CT scanner. Nonetheless, intraoperative imaging did allow for replacement of short screws and for adjustments to the trajectory of suboptimal screws that did not have a frank breach.

In the previously published postoperative CT scan cohort, 8 patients (0.8%) underwent revision surgery to correct a malpositioned screw. In contrast, 2 patients (0.99%) in the intraoperative CT cohort required reoperations due to misplaced hardware. Compared with patients experiencing free-hand placement of screws with postoperative CT scans, patients in the intraoperative CT cohort had a similar rate of reoperation (p = 0.6881).

We also compared our results with a similar cohort of patients undergoing postoperative CT scans by the same surgeons during a matched period of time as the intraoperative CT cohort of patients (2009–2012; Tables 2 and 3). In this postoperative cohort, 4440 pedicle screws were placed via free-hand technique in 607 patients at our institution (Table 2). On postoperative CT scanning, 6 misplaced pedicle screws required reoperation for screw revision. The most common indication for revision was anterior displacement of the pedicle that extended beyond the vertebral body (3 of the 6 revisions; Table 3). In these cases, the long screw compressed the adjacent aorta with a risk of a luminal tear (Fig. 5). Of the 607 cases, the reoperation rate in the postoperative CT cohort was 0.99%, comparable to a reoperation rate of 0.99% in the intraoperative CT cohort (p = 0.997).

TABLE 2:

Comparison of perioperative characteristics in patients undergoing intraoperative versus postoperative CT scanning (matched patient data set)*

ParameterIntraop CTPostop CTp Value
no. of patients203607
mean age ± SD61.0 ± 11.759.1 ± 15.30.076
diagnosis
 congenital4 (2.0)23 (3.79)0.230
 degenerative spinal disease148 (72.9)450 (74.14)<0.001
 infection10 (4.9)18 (2.97)0.164
 spondylolisthesis68 (33.5)98 (16.14)<0.001
 trauma24 (11.8)38 (6.26)0.010
 tumor23 (23.0)94 (15.49)0.190
spinal region
 cervical only19 (9.4)154 (25.37)<0.001
 cervicothoracic30 (14.8)111 (18.29)0.233
 thoracolumbar184 (90.6)342 (56.34)<0.001
blood loss (ml)547.22527.50.924
total no. of screws11484440
mean no. of screws/op ± SD5.7 ± 2.77.3 ± 4.7<0.001
reop for misplaced screws2 (0.99)6 (0.99)0.997

Values are presented as the number of cases (%) unless specified otherwise. Values in boldface are statistically significant.

TABLE 3:

Comparison of direction of pedicle screw breaches and location between the intraoperative CT group and the postoperative CT group (matched patient data set)

ParameterIntraop CT Revisions (%)Postop CT Revisions (%)
no. of revisions1036
direction of breach
 lateral41 (39.81)2 (33.33)
 medial29 (28.16)1 (16.67)
 superior7 (6.80)NA
 inferior13 (12.62)NA
 anterior12 (11.65)3 (50.00)
 short8 (7.77)1 (16.67)
location of breach
 cervical14 (18.42)NA
 thoracic25 (7.25)1 (16.67)
 lumbar64 (8.80)5 (83.33)

Our results demonstrate that the presence of intraoperative CT scanning lowers the threshold for pedicle screw revision, resulting in statistically higher rates of pedicle screw revision in the thoracic and lumbar spine compared with postoperative CT scanning. Many of the revisions done in the intraoperative CT cohort were to correct minor breaches that would have been merely observed had intraoperative CT imaging not been available. Thus, we may have unnecessarily revised some screws in the absence of neurovascular impingement by the screw or loss of biomechanical fixation. However, given the presence of the intraoperative CT scanner and the relative ease of revising pedicle screws during the initial surgery, various spinal surgeons consistently decided to make minor adjustments to seemingly render the instrumentation perfect. Unfortunately, our results indicate that the intraoperative CT scanner is no guarantee of perfection. In our institution's 2.5-year experience with the intraoperative CT in 203 patients, we did not observe a decrease in rates of reoperation due to pedicle screw misplacement.

As with all retrospective clinical studies, certain biases may play a confounding role. Since our university is a teaching institution, although the attending surgeons remained constant over the time course of these studies, the residents and fellows may not have been equally represented throughout. Along these lines, the surgeons in this study use the free-hand insertion technique. This method has certain advantages but it has limitations as well, namely the lack of radiographic guidance during screw placement.38 The imaging protocol that was used also varied depending on the surgeon's preference. Some surgeons obtained intraoperative CT images after pedicle marker placement, while others obtained images after pedicle screw placement. Some surgeons obtained 1 intraoperative CT scanning study, while others obtained multiple studies to confirm placement of particularly difficult pedicle screws. Finally, although indications for surgery in both the intraoperative CT as well as postoperative CT cohorts were similar, the exact percentages of underlying pathologies (trauma, tumor, degenerative, spondylolisthesis, congenital, and infection) were not the same. Thus, additional studies with more patients are needed to further confirm whether the presence of an intraoperative CT scanner can effectively reduce the rate of reoperations due to misplaced pedicle screws.

Conclusions

Pedicle screws remain technically demanding to place as a result of the intrinsic anatomy involved and considerable interpatient variability. To date, a number of technologies have aimed to increase the accuracy rate of pedicle screw placement with the ultimate goal of reducing reoperation rates due to misplaced pedicle screws. Here, we present one of the first experiences in a North American population using an intraoperative CT scanner. Our experience suggests that use of intraoperative CT scanning reduces the threshold for revising pedicle screws, increasing the overall incidence of screw revision. Our initial 2.5-year experience did not show a decreased rate of reoperation compared with the free-hand pedicle screw placement technique with postoperative CT imaging. Future studies with larger patient populations will be needed to demonstrate more concretely the effectiveness of intraoperative CT scanning in enhancing patient safety during pedicle screw placement.

Disclosure

The authors declare no conflicts of interest related to this study. The authors have upheld all ethical standards in compiling this manuscript. General disclosures for the authors are as follows: Timothy Witham is the recipient of a research grant from Eli Lilly and Company. Ali Bydon is the recipient of a research grant from DePuy Spine. He also serves on the clinical advisory board of Med-Immune, LLC. Ziya Gokaslan is the recipient of research grants from DePuy Spine, AOSpine North America, Medtronic, NREF, Integra Life Sciences, and K2M. He receives fellowship support from AOSpine North America. He also holds stock in Spinal Kinetics and US Spine. Daniel Sciubba is the recipient of a research grant from DePuy Spine. He has consulting relationships with Medtronic, NuVasive, Globus, and DePuy.

Author contributions to the study and manuscript preparation include the following. Conception and design: M Bydon. Acquisition of data: M Bydon, Xu, Wolinsky. Analysis and interpretation of data: M Bydon, Xu, Macki, A Bydon. Drafting the article: M Bydon, Xu, Amin, Kaloostian, Sciubba, Gokaslan. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Witham. Statistical analysis: M Bydon, Xu, Sciubba. Administrative/technical/material support: Witham, M Bydon, Macki. Study supervision: Witham, M Bydon, Kaloostian, A Bydon.

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    Holly LT: Image-guided spinal surgery. Int J Med Robot 2:7152006

  • 11

    Ito HNeo MYoshida MFujibayashi SYoshitomi HNakamura T: Efficacy of computer-assisted pedicle screw insertion for cervical instability in RA patients. Rheumatol Int 27:5675742007

    • Search Google Scholar
    • Export Citation
  • 12

    Kamimura MEbara SItoh HTateiwa YKinoshita TTakaoka K: Cervical pedicle screw insertion: assessment of safety and accuracy with computer-assisted image guidance. J Spinal Disord 13:2182242000

    • Search Google Scholar
    • Export Citation
  • 13

    Kim YJLenke LGCheh GRiew KD: Evaluation of pedicle screw placement in the deformed spine using intraoperative plain radiographs: a comparison with computerized tomography. Spine (Phila Pa 1976) 30:208420882005

    • Search Google Scholar
    • Export Citation
  • 14

    Kosmopoulos VSchizas C: Pedicle screw placement accuracy: a meta-analysis. Spine (Phila Pa 1976) 32:E111E1202007

  • 15

    Kotani YAbumi KIto MTakahata MSudo HOhshima S: Accuracy analysis of pedicle screw placement in posterior scoliosis surgery: comparison between conventional fluoroscopic and computer-assisted technique. Spine (Phila Pa 1976) 32:154315502007

    • Search Google Scholar
    • Export Citation
  • 16

    Laine TLund TYlikoski MLohikoski JSchlenzka D: Accuracy of pedicle screw insertion with and without computer assistance: a randomised controlled clinical study in 100 consecutive patients. Eur Spine J 9:2352402000

    • Search Google Scholar
    • Export Citation
  • 17

    Laine TSchlenzka DMäkitalo KTallroth KNolte LPVisarius H: Improved accuracy of pedicle screw insertion with computer-assisted surgery. A prospective clinical trial of 30 patients. Spine (Phila Pa 1976) 22:125412581997

    • Search Google Scholar
    • Export Citation
  • 18

    Learch TJMassie JBPathria MNAhlgren BAGarfin SR: Assessment of pedicle screw placement utilizing conventional radiography and computed tomography: a proposed systematic approach to improve accuracy of interpretation. Spine (Phila Pa 1976) 29:7677732004

    • Search Google Scholar
    • Export Citation
  • 19

    Lee GYFMassicotte EMRampersaud YR: Clinical accuracy of cervicothoracic pedicle screw placement: a comparison of the “open” lamino-foraminotomy and computer-assisted techniques. J Spinal Disord Tech 20:25322007

    • Search Google Scholar
    • Export Citation
  • 20

    Lee TCYang LCLiliang PCSu TMRau CSChen HJ: Single versus separate registration for computer-assisted lumbar pedicle screw placement. Spine (Phila Pa 1976) 29:158515892004

    • Search Google Scholar
    • Export Citation
  • 21

    Lekovic GPPotts EAKarahalios DGHall G: A comparison of two techniques in image-guided thoracic pedicle screw placement: a retrospective study of 37 patients and 277 pedicle screws. J Neurosurg Spine 7:3933982007

    • Search Google Scholar
    • Export Citation
  • 22

    Li SGSheng LZhao HZhang JGZhai JLZhu Y: [Clinical applications of computer-assisted navigation technique in spinal pedicle screw internal fixation.]. Zhonghua Yi Xue Za Zhi 89:7367392009. (Chinese)

    • Search Google Scholar
    • Export Citation
  • 23

    Liu YJTian WLiu BLi QHu LLi ZY: [Accuracy of CT-based navigation of pedicle screws implantation in the cervical spine compared with X-ray fluoroscopy technique.]. Zhonghua Wai Ke Za Zhi 43:132813302005. (Chinese)

    • Search Google Scholar
    • Export Citation
  • 24

    Merloz PTonetti JPittet LCoulomb MLavalleé SSautot P: Pedicle screw placement using image guided techniques. Clin Orthop Relat Res 35439481998

    • Search Google Scholar
    • Export Citation
  • 25

    Merloz PTroccaz JVouaillat HVasile CTonetti JEid A: Fluoroscopy-based navigation system in spine surgery. Proc Inst Mech Eng H 221:8138202007

    • Search Google Scholar
    • Export Citation
  • 26

    Mirza SKWiggins GCKuntz C IVYork JEBellabarba CKnonodi MA: Accuracy of thoracic vertebral body screw placement using standard fluoroscopy, fluoroscopic image guidance, and computed tomographic image guidance: a cadaver study. Spine (Phila Pa 1976) 28:4024132003

    • Search Google Scholar
    • Export Citation
  • 27

    Nakashima HSato KAndo TInoh HNakamura H: Comparison of the percutaneous screw placement precision of isocentric C-arm 3-dimensional fluoroscopy-navigated pedicle screw implantation and conventional fluoroscopy method with minimally invasive surgery. J Spinal Disord Tech 22:4684722009

    • Search Google Scholar
    • Export Citation
  • 28

    Nolte LZamorano LArm EVisarius HJiang ZBerlerman U: Image-guided computer-assisted spine surgery: a pilot study on pedicle screw fixation. Stereotact Funct Neurosurg 66:1081171996

    • Search Google Scholar
    • Export Citation
  • 29

    Nottmeier EWSeemer WYoung PM: Placement of thoracolumbar pedicle screws using three-dimensional image guidance: experience in a large patient cohort. Clinical article. J Neurosurg Spine 10:33392009

    • Search Google Scholar
    • Export Citation
  • 30

    Parker SLMcGirt MJFarber SHAmin AGRick AMSuk I: Accuracy of free-hand pedicle screws in the thoracic and lumbar spine: analysis of 6816 consecutive screws. Neurosurgery 68:1701782011

    • Search Google Scholar
    • Export Citation
  • 31

    Rajasekaran SVidyadhara SRamesh PShetty AP: Randomized clinical study to compare the accuracy of navigated and non-navigated thoracic pedicle screws in deformity correction surgeries. Spine (Phila Pa 1976) 32:E56E642007

    • Search Google Scholar
    • Export Citation
  • 32

    Rampersaud YRSimon DAFoley KT: Accuracy requirements for image-guided spinal pedicle screw placement. Spine (Phila Pa 1976) 26:3523592001

    • Search Google Scholar
    • Export Citation
  • 33

    Rao GBrodke DSRondina MDailey AT: Comparison of computerized tomography and direct visualization in thoracic pedicle screw placement. J Neurosurg 97:2 Suppl2232262002

    • Search Google Scholar
    • Export Citation
  • 34

    Richter MCakir BSchmidt R: Cervical pedicle screws: conventional versus computer-assisted placement of cannulated screws. Spine (Phila Pa 1976) 30:228022872005

    • Search Google Scholar
    • Export Citation
  • 35

    Sakai YMatsuyama YNakamura HKatayama YImagama SIto Z: Segmental pedicle screwing for idiopathic scoliosis using computer-assisted surgery. J Spinal Disord Tech 21:1811862008

    • Search Google Scholar
    • Export Citation
  • 36

    Sakamoto TNeo MNakamura T: Transpedicular screw placement evaluated by axial computed tomography of the cervical pedicle. Spine (Phila Pa 1976) 29:251025152004

    • Search Google Scholar
    • Export Citation
  • 37

    Schnake KJKönig BBerth USchroeder RJKandziora FStöckle U: [Accuracy of CT-based navitation of pedicle screws in the thoracic spine compared with conventional technique.]. Unfallchirurg 107:1041122004. (Ger)

    • Search Google Scholar
    • Export Citation
  • 38

    Sciubba DMNoggle JCVellimana AKAlosh HMcGirt MJGokaslan ZL: Radiographic and clinical evaluation of free-hand placement of C-2 pedicle screws. Clinical article. J Neurosurg Spine 11:15222009

    • Search Google Scholar
    • Export Citation
  • 39

    Seller KWild AUrselmann LKrauspe R: [Prospective screw misplacement analysis after conventional and navigated pedicle screw implantation.]. Biomed Tech (Berl) 50:2872922005. (Ger)

    • Search Google Scholar
    • Export Citation
  • 40

    Slomczykowski MRoberto MSchneeberger POzdoba CVock P: Radiation dose for pedicle screw insertion. Fluoroscopic method versus computer-assisted surgery. Spine (Phila Pa 1976) 24:9759831999

    • Search Google Scholar
    • Export Citation
  • 41

    Tian NFHuang QSZhou PZhou YWu RKLou Y: Pedicle screw insertion accuracy with different assisted methods: a systematic review and meta-analysis of comparative studies. Eur Spine J 20:8468592011

    • Search Google Scholar
    • Export Citation
  • 42

    Tian NFXu HZ: Image-guided pedicle screw insertion accuracy: a meta-analysis. Int Orthop 33:8959032009

  • 43

    Tjardes TShafizadeh SRixen DPaffrath TBouillon BSteinhausen ES: Image-guided spine surgery: state of the art and future directions. Eur Spine J 19:25452010

    • Search Google Scholar
    • Export Citation
  • 44

    Verma RKrishan SHaendlmayer KMohsen A: Functional outcome of computer-assisted spinal pedicle screw placement: a systematic review and meta-analysis of 23 studies including 5,992 pedicle screws. Eur Spine J 19:3703752010

    • Search Google Scholar
    • Export Citation
  • 45

    Xu REbraheim NAShepherd MEYeasting RA: Thoracic pedicle screw placement guided by computed tomographic measurements. J Spinal Disord 12:2222261999

    • Search Google Scholar
    • Export Citation

If the inline PDF is not rendering correctly, you can download the PDF file here.

Article Information

Address correspondence to: Timothy F. Witham, M.D., The Johns Hopkins Hospital, 600 N. Wolfe St., Meyer 7-109, Baltimore, MD 21205. email: twitham2@jhmi.edu.

Dr. M. Bydon and Mr. Xu contributed equally to this work.

Please include this information when citing this paper: published online June 13, 2014; DOI: 10.3171/2014.5.SPINE13567.

© AANS, except where prohibited by US copyright law.

Headings

Figures

  • View in gallery

    Indications for pedicle screw placement in 203 patients using the intraoperative CT (ioCT) scanner.

  • View in gallery

    Upper: Number of pedicle screws placed in the cervical, thoracic, and lumbar spine as a percentage of total pedicle screws placed. Lower: Percentage of pedicle screws placed in the thoracic and lumbar spine only.

  • View in gallery

    Upper: Number of pedicle screws revised, expressed as a percentage of the total number of pedicle screws placed at each spinal level. Lower: Number of pedicle screws revised, expressed as a percentage of total pedicle screws placed within the cervical, thoracic, or lumbar spinal regions. Compared with screws in the thoracic and lumbar regions, pedicle screws placed in the cervical region were statistically more likely to be revised (**p = 0.0061).

  • View in gallery

    Classification of 103 pedicle screw breaches in 72 patients. Short screws are ones that were deemed short based on intraoperative CT imaging and as a result were replaced with longer screws.

  • View in gallery

    A and B: Intraoperative CT images of the L-3 spinal level. The right pedicle screw is laterally placed outside of the vertebral body. The screw is revised for a more medial trajectory (B). C and D: Postoperative CT images of the T-11 spinal level. The left pedicle screw is anteriorly displaced. The screw tip is abutting the aorta (C). To avoid a luminal tear of the thoracic aorta, the pedicle screw was replaced with a shorter screw (D).

References

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    Assaker RReyns NVinchon MDemondion XLouis E: Transpedicular screw placement: image-guided versus lateral-view fluoroscopy: in vitro simulation. Spine (Phila Pa 1976) 26:216021642001

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    Austin MSVaccaro ARBrislin BNachwalter RHilibrand ASAlbert TJ: Image-guided spine surgery: a cadaver study comparing conventional open laminoforaminotomy and two image-guided techniques for pedicle screw placement in posterolateral fusion and nonfusion models. Spine (Phila Pa 1976) 27:250325082002

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    Benzel ECRupp FWMcCormack BMBaldwin NGAnson JAAdams MS: A comparison of fluoroscopy and computed tomography-derived volumetric multiple exposure transmission holography for the guidance of lumbar pedicle screw insertion. Neurosurgery 37:7117161995

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    Choi WWGreen BALevi AD: Computer-assisted fluoroscopic targeting system for pedicle screw insertion. Neurosurgery 47:8728782000

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    Ebmeier KGiest KKalff R: Intraoperative computerized tomography for improved accuracy of spinal navigation in pedicle screw placement of the thoracic spine. Acta Neurochir Suppl 85:1051132003

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    • Export Citation
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    Farber GLPlace HMMazur RAJones DEDamiano TR: Accuracy of pedicle screw placement in lumbar fusions by plain radiographs and computed tomography. Spine (Phila Pa 1976) 20:149414991995

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    • Export Citation
  • 9

    Fu TSWong CBTsai TTLiang YCChen LHChen WJ: Pedicle screw insertion: computed tomography versus fluoroscopic image guidance. Int Orthop 32:5175212008

    • Search Google Scholar
    • Export Citation
  • 10

    Holly LT: Image-guided spinal surgery. Int J Med Robot 2:7152006

  • 11

    Ito HNeo MYoshida MFujibayashi SYoshitomi HNakamura T: Efficacy of computer-assisted pedicle screw insertion for cervical instability in RA patients. Rheumatol Int 27:5675742007

    • Search Google Scholar
    • Export Citation
  • 12

    Kamimura MEbara SItoh HTateiwa YKinoshita TTakaoka K: Cervical pedicle screw insertion: assessment of safety and accuracy with computer-assisted image guidance. J Spinal Disord 13:2182242000

    • Search Google Scholar
    • Export Citation
  • 13

    Kim YJLenke LGCheh GRiew KD: Evaluation of pedicle screw placement in the deformed spine using intraoperative plain radiographs: a comparison with computerized tomography. Spine (Phila Pa 1976) 30:208420882005

    • Search Google Scholar
    • Export Citation
  • 14

    Kosmopoulos VSchizas C: Pedicle screw placement accuracy: a meta-analysis. Spine (Phila Pa 1976) 32:E111E1202007

  • 15

    Kotani YAbumi KIto MTakahata MSudo HOhshima S: Accuracy analysis of pedicle screw placement in posterior scoliosis surgery: comparison between conventional fluoroscopic and computer-assisted technique. Spine (Phila Pa 1976) 32:154315502007

    • Search Google Scholar
    • Export Citation
  • 16

    Laine TLund TYlikoski MLohikoski JSchlenzka D: Accuracy of pedicle screw insertion with and without computer assistance: a randomised controlled clinical study in 100 consecutive patients. Eur Spine J 9:2352402000

    • Search Google Scholar
    • Export Citation
  • 17

    Laine TSchlenzka DMäkitalo KTallroth KNolte LPVisarius H: Improved accuracy of pedicle screw insertion with computer-assisted surgery. A prospective clinical trial of 30 patients. Spine (Phila Pa 1976) 22:125412581997

    • Search Google Scholar
    • Export Citation
  • 18

    Learch TJMassie JBPathria MNAhlgren BAGarfin SR: Assessment of pedicle screw placement utilizing conventional radiography and computed tomography: a proposed systematic approach to improve accuracy of interpretation. Spine (Phila Pa 1976) 29:7677732004

    • Search Google Scholar
    • Export Citation
  • 19

    Lee GYFMassicotte EMRampersaud YR: Clinical accuracy of cervicothoracic pedicle screw placement: a comparison of the “open” lamino-foraminotomy and computer-assisted techniques. J Spinal Disord Tech 20:25322007

    • Search Google Scholar
    • Export Citation
  • 20

    Lee TCYang LCLiliang PCSu TMRau CSChen HJ: Single versus separate registration for computer-assisted lumbar pedicle screw placement. Spine (Phila Pa 1976) 29:158515892004

    • Search Google Scholar
    • Export Citation
  • 21

    Lekovic GPPotts EAKarahalios DGHall G: A comparison of two techniques in image-guided thoracic pedicle screw placement: a retrospective study of 37 patients and 277 pedicle screws. J Neurosurg Spine 7:3933982007

    • Search Google Scholar
    • Export Citation
  • 22

    Li SGSheng LZhao HZhang JGZhai JLZhu Y: [Clinical applications of computer-assisted navigation technique in spinal pedicle screw internal fixation.]. Zhonghua Yi Xue Za Zhi 89:7367392009. (Chinese)

    • Search Google Scholar
    • Export Citation
  • 23

    Liu YJTian WLiu BLi QHu LLi ZY: [Accuracy of CT-based navigation of pedicle screws implantation in the cervical spine compared with X-ray fluoroscopy technique.]. Zhonghua Wai Ke Za Zhi 43:132813302005. (Chinese)

    • Search Google Scholar
    • Export Citation
  • 24

    Merloz PTonetti JPittet LCoulomb MLavalleé SSautot P: Pedicle screw placement using image guided techniques. Clin Orthop Relat Res 35439481998

    • Search Google Scholar
    • Export Citation
  • 25

    Merloz PTroccaz JVouaillat HVasile CTonetti JEid A: Fluoroscopy-based navigation system in spine surgery. Proc Inst Mech Eng H 221:8138202007

    • Search Google Scholar
    • Export Citation
  • 26

    Mirza SKWiggins GCKuntz C IVYork JEBellabarba CKnonodi MA: Accuracy of thoracic vertebral body screw placement using standard fluoroscopy, fluoroscopic image guidance, and computed tomographic image guidance: a cadaver study. Spine (Phila Pa 1976) 28:4024132003

    • Search Google Scholar
    • Export Citation
  • 27

    Nakashima HSato KAndo TInoh HNakamura H: Comparison of the percutaneous screw placement precision of isocentric C-arm 3-dimensional fluoroscopy-navigated pedicle screw implantation and conventional fluoroscopy method with minimally invasive surgery. J Spinal Disord Tech 22:4684722009

    • Search Google Scholar
    • Export Citation
  • 28

    Nolte LZamorano LArm EVisarius HJiang ZBerlerman U: Image-guided computer-assisted spine surgery: a pilot study on pedicle screw fixation. Stereotact Funct Neurosurg 66:1081171996

    • Search Google Scholar
    • Export Citation
  • 29

    Nottmeier EWSeemer WYoung PM: Placement of thoracolumbar pedicle screws using three-dimensional image guidance: experience in a large patient cohort. Clinical article. J Neurosurg Spine 10:33392009

    • Search Google Scholar
    • Export Citation
  • 30

    Parker SLMcGirt MJFarber SHAmin AGRick AMSuk I: Accuracy of free-hand pedicle screws in the thoracic and lumbar spine: analysis of 6816 consecutive screws. Neurosurgery 68:1701782011

    • Search Google Scholar
    • Export Citation
  • 31

    Rajasekaran SVidyadhara SRamesh PShetty AP: Randomized clinical study to compare the accuracy of navigated and non-navigated thoracic pedicle screws in deformity correction surgeries. Spine (Phila Pa 1976) 32:E56E642007

    • Search Google Scholar
    • Export Citation
  • 32

    Rampersaud YRSimon DAFoley KT: Accuracy requirements for image-guided spinal pedicle screw placement. Spine (Phila Pa 1976) 26:3523592001

    • Search Google Scholar
    • Export Citation
  • 33

    Rao GBrodke DSRondina MDailey AT: Comparison of computerized tomography and direct visualization in thoracic pedicle screw placement. J Neurosurg 97:2 Suppl2232262002

    • Search Google Scholar
    • Export Citation
  • 34

    Richter MCakir BSchmidt R: Cervical pedicle screws: conventional versus computer-assisted placement of cannulated screws. Spine (Phila Pa 1976) 30:228022872005

    • Search Google Scholar
    • Export Citation
  • 35

    Sakai YMatsuyama YNakamura HKatayama YImagama SIto Z: Segmental pedicle screwing for idiopathic scoliosis using computer-assisted surgery. J Spinal Disord Tech 21:1811862008

    • Search Google Scholar
    • Export Citation
  • 36

    Sakamoto TNeo MNakamura T: Transpedicular screw placement evaluated by axial computed tomography of the cervical pedicle. Spine (Phila Pa 1976) 29:251025152004

    • Search Google Scholar
    • Export Citation
  • 37

    Schnake KJKönig BBerth USchroeder RJKandziora FStöckle U: [Accuracy of CT-based navitation of pedicle screws in the thoracic spine compared with conventional technique.]. Unfallchirurg 107:1041122004. (Ger)

    • Search Google Scholar
    • Export Citation
  • 38

    Sciubba DMNoggle JCVellimana AKAlosh HMcGirt MJGokaslan ZL: Radiographic and clinical evaluation of free-hand placement of C-2 pedicle screws. Clinical article. J Neurosurg Spine 11:15222009

    • Search Google Scholar
    • Export Citation
  • 39

    Seller KWild AUrselmann LKrauspe R: [Prospective screw misplacement analysis after conventional and navigated pedicle screw implantation.]. Biomed Tech (Berl) 50:2872922005. (Ger)

    • Search Google Scholar
    • Export Citation
  • 40

    Slomczykowski MRoberto MSchneeberger POzdoba CVock P: Radiation dose for pedicle screw insertion. Fluoroscopic method versus computer-assisted surgery. Spine (Phila Pa 1976) 24:9759831999

    • Search Google Scholar
    • Export Citation
  • 41

    Tian NFHuang QSZhou PZhou YWu RKLou Y: Pedicle screw insertion accuracy with different assisted methods: a systematic review and meta-analysis of comparative studies. Eur Spine J 20:8468592011

    • Search Google Scholar
    • Export Citation
  • 42

    Tian NFXu HZ: Image-guided pedicle screw insertion accuracy: a meta-analysis. Int Orthop 33:8959032009

  • 43

    Tjardes TShafizadeh SRixen DPaffrath TBouillon BSteinhausen ES: Image-guided spine surgery: state of the art and future directions. Eur Spine J 19:25452010

    • Search Google Scholar
    • Export Citation
  • 44

    Verma RKrishan SHaendlmayer KMohsen A: Functional outcome of computer-assisted spinal pedicle screw placement: a systematic review and meta-analysis of 23 studies including 5,992 pedicle screws. Eur Spine J 19:3703752010

    • Search Google Scholar
    • Export Citation
  • 45

    Xu REbraheim NAShepherd MEYeasting RA: Thoracic pedicle screw placement guided by computed tomographic measurements. J Spinal Disord 12:2222261999

    • Search Google Scholar
    • Export Citation

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