Placement of thoracolumbar pedicle screws using three-dimensional image guidance: experience in a large patient cohort

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

Accuracy of fluoroscopically-assisted pedicle screw placement: analysis of 1,218 screws in 198 patients

BACKGROUND CONTEXT

We retrospectively analyzed a total of 1,218 pedicle screws for accuracy, with postoperative computed tomography (CT), in 198 patients who were operated on between March 2004 and September 2012.

PURPOSE

To determine the incidence of screw misplacement in patients who received a transpedicular screw fixation, with intraoperative fluoroscopy in the lateral and lateral with anteroposterior (AP) positions. The results are compared between the two groups.

STUDY DESIGN

Retrospective comparative study of accuracy of pedicle screw placement in thoracic and lumbar spine.

PATIENT SAMPLE

The sample consists of 198 consecutive patients who underwent transpedicular screw fixation.

OUTCOME MEASURES

Accuracy of screw placement was evaluated by postoperative CT scan. Misplacement was defined in cases where more than 25% of the screw size was residing outside the pedicle.

METHODS

The indications for hardware placement, radiologic studies, patient demographics, and reoperation rates were recorded. Five hundred twenty-eight screws (Group A, n=81) were inserted into the vertebral body with the assistance of lateral fluoroscopy only, whereas 690 screws (Group B, n=117) were inserted with the assistance of lateral fluoroscopy, and the final positions of the screws were checked with AP fluoroscopy.

RESULTS

A total of 1,218 screws were analyzed, with 962 screws placed at the lumbosacral region and 256 screws at the thoracic region. According to the postoperative CT scan, 27 screws (2.2%) were identified as breaching the pedicle. Nineteen of them (3.6%) were in Group A, whereas 8 (1.16%) were in Group B. The rate of pedicle breaches was significantly different between Group A and B (p=.0052). In Group A, the lateral violation of the pedicle was seen in 10 screws (1.9%), whereas medial violation was seen in 9 screws (1.7%). In Group B, the lateral violation of the pedicle was seen in six screws (0.87%), whereas medial violation was seen in two screws (0.29%). The medial and lateral penetration of screws were significantly different between Groups A and B (p<.05). A pedicle breach occurred in 21 patients, and 15 of them underwent a revision surgery to correct the misplaced screw. Of these patients, 11 (13.6%) were in Group A, and 4 (3.4%) were in Group B (p=.0335).

CONCLUSIONS

In this study, we evaluated and clarified the diagnostic value of intraoperative fluoroscopy in both the lateral and AP imaging that have not yet been evaluated in any comparative study. We concluded that the intraoperative use of fluoroscopy, especially in the AP position, significantly decreases the risk of screw misplacement and the results are comparable with other advanced techniques.

The Utility of 3-Dimensional-Navigation in the Surgical Treatment of Children With Idiopathic Scoliosis

STUDY DESIGN

Ambispective study of patients undergoing surgical correction of adolescent idiopathic scoliosis.

OBJECTIVE

To evaluate the accuracy of screw placement using preoperative 3-dimensional (3D) computed tomography (CT)-based navigation with intraoperative fluoroscopic guidance compared with freehand placement.

SUMMARY OF BACKGROUND DATA

Pedicle screws placed in deformed vertebrae have a high malposition rate. The use of navigation-based systems has increased placement accuracy.

METHODS

Intraoperative registration of patient anatomy to preoperative 3D-CT was performed using anatomic landmarks. When registration accuracy was high (mean square error, <1.0 mm), screw tracts were drilled under navigation guidance; when the error was >1.0 mm, re-registration was performed. The researchers documented times for registration, navigation, and screw placement, and the number of passes. Results were compared with outcomes in cases operated on with freehand screw placement.

RESULTS

A total of 62 patients were included (54 females and 8 males; mean age was 15.1 years [range, 12-18 years]). Mean deformity was 67° (range, 52° to 80°). Mean follow-up was 35 months (range, 42-19 months). In the navigation group, 710 pedicle screws were placed. Mean times were 55 seconds for tracker placement, 94.5 seconds per vertebra for patient registration, 131.1 seconds for screw tract formation on the concave side of the deformity, and 129.5 seconds on the convex side. Average total procedure time was 3.5 hours (range, 2-7 hours). Mean overall registration accuracy was 0.7 mm. Pedicle integrity was breached in 1.6% trajectories. In the freehand group, 470 pedicle screws were placed. Average time for screw placement was 135.2 seconds (p < .001 vs. navigation). Pedicle integrity was breached in 5.1% of trajectories (p < .0001 vs. navigation). No patient developed neurological or other complications. There was no destabilization of the instrumented spine during short- or long-term follow-up.

CONCLUSIONS

Intraoperative optic fluoroscopic navigation based on anatomic landmark registration to preoperative 3D-CT spine images enables precise pedicle screw placement with only a minor increase in pedicle preparation time in patients with adolescent idiopathic scoliosis.

Techniques and accuracy of thoracolumbar pedicle screw placement

Pedicle screw instrumentation has been used to stabilize the thoracolumbar spine for several decades. Although pedicle screws were originally placed via a free-hand technique, there has been a movement in favor of pedicle screw placement with the aid of imaging. Such assistive techniques include fluoroscopy guidance and stereotactic navigation. Imaging has the benefit of increased visualization of a pedicle’s trajectory, but can result in increased morbidity associated with radiation exposure, increased time expenditure, and possible workflow interruption. Many institutions have reported high accuracies with each of these three core techniques. However, due to differing definitions of accuracy and varying radiographic analyses, it is extremely difficult to compare studies side-by-side to determine which techniques are superior. From the literature, it can be concluded that pedicles of vertebrae within the mid-thoracic spine and vertebrae that have altered morphology due to scoliosis or other deformities are the most difficult to cannulate. Thus, spine surgeons would benefit the most from using assistive technologies in these circumstances. All other pedicles in the thoracolumbar spine should theoretically be cannulated with ease via a free-hand technique, given appropriate training and experience. Despite these global recommendations, appropriate techniques must be chosen at the surgeon’s discretion. Such determinations should be based on the surgeon’s experience and the specific pathology that will be treated.

Position and complications of pedicle screw insertion with or without image-navigation techniques in the thoracolumbar spine: a meta-analysis of comparative studies

Computer-navigated pedicle screw insertion is applied to the thoracic and lumbar spine to attain high insertion accuracy and a low rate of screw-related complications. However, some in vivo and in vitro studies have shown that no advantages are gained with the use of navigation techniques compared to conventional techniques. Additionally, inconsistent conclusions have been drawn in various studies due to different population characteristics and methods used to assess the accuracy of screw placement. Moreover, it is not clear whether pedicle screw insertion with navigation techniques decreases the incidence of screw-related complications. Therefore, this study was sought to perform a meta-analysis of all available prospective evidence regarding pedicle screw insertion with or without navigation techniques in human thoracic and lumbar spine. We considered in vivo comparative studies that assessed the results of pedicle screw placement with or without navigation techniques. PubMed, Ovid MEDLINE and EMBASE databases were searched. Three published randomized controlled trials (RCTs) and nine retrospective comparative studies met the inclusion criteria. These studies included a total of 732 patients in whom 4,953 screws were inserted. In conclusion, accuracy of the position of grade I, II, III and IV screws and complication rate related to pedicle screw placement were significantly increased when navigation techniques were used in comparison to conventional techniques. Future research in this area should include RCTs with well-planned methodology to limit bias and report on validated, patient-based outcome measures.

Thoracolumbar instrumentation with CT-guided navigation (O-arm) in 270 consecutive patients: accuracy rates and lessons learned

Object

Thoracolumbar instrumentation has experienced a dramatic increase in utilization over the last 2 decades. However, pedicle screw fixation remains a challenging undertaking, with suboptimal placement contributing to postoperative pain, neurological deficit, vascular complications, and return to the operating suite. Image-guided spinal surgery has substantially improved the accuracy rates for these procedures. However, it is not without technical challenges and a learning curve for novice operators. The authors present their experience with the O-arm intraoperative imaging system and share the lessons they learned over nearly 5 years.

Methods

The authors performed a retrospective chart review of 270 consecutive patients who underwent thoracolumbar pedicle screw fixation utilizing the O-arm imaging system in conjunction with StealthStation navigation between April 2009 and September 2013 at a single tertiary care center; 266 of the patients underwent CT scanning on postoperative Day 1 to evaluate hardware placement. The CT scans were interpreted prospectively by 3 neuroradiologists as part of standard work flow and retrospectively by 2 neurosurgeons and a senior resident. Pedicle screws were evaluated for breaches according to the 3-tier classification proposed by Mirza et al.

Results

Of 270 patients, 266 (98.5%) were included in the final analysis based on the presence of a postoperative CT scan. Overall, 1651 pedicle screws were placed in 266 patients and yielded a 5.3% breach rate; 213 thoracic and 1438 lumbosacral pedicle screws were inserted with 6.6% and 5.1% breach rates, respectively. Of the 87 suboptimally placed screws, there were 13 Grade 1, 16 Grade 2, and 12 Grade 3 misses as well as 46 anterolateral or “tip-out” perforations at L-5. Four patients (1.5%) required a return to the operating room for pedicle screw revision, 2 of whom experienced transient radicular symptoms and 2 remained asymptomatic. Interestingly, the pedicle breach rate was higher than anticipated at 13.21% for the 30 patients over the initial 6-month period with the O-arm. After certain modifications to the authors' technique, the subsequent 30 patients experienced a statistically significant decrease in breach rate at 5.6% (p = 0.014).

Conclusions

Image-guided spinal surgery can be a great option in the operating room and provides high pedicle screw accuracy rates. With numerous systems commercially available, it is important to develop a systematic approach regardless of the technology in question. There is a learning curve for surgeons unfamiliar with image guidance that should be recognized and appreciated when transitioning to navigation-assisted spinal surgery. In fact, the authors' experience with a large patient cohort suggests that this learning curve may be more significant than previously reported.

The effect of pedicle screw redirection after lateral wall breach--a biomechanical study using human lumbar vertebrae

BACKGROUND CONTEXT

Currently, pedicle screw segmental fixation of the spine is considered a standard of care for a number of conditions. Most surgeons employ a free-hand technique using various intraoperative modalities to improve pedicle screw accuracy. Despite continued improvements in technique, pedicle breach remains a frequent occurrence. Once a breach is detected intraoperatively, the most common corrective maneuver is to medially redirect the pedicle screw into the pedicle. To our knowledge, the biomechanical impact of medially redirecting a pedicle screw after a lateral pedicle breach has not been examined.

PURPOSE

To compare the fixation strength of perfectly placed pedicle screws to the fixation strength of pedicle screws that were correctly placed after having been redirected (RD) following a lateral pedicle breach.

STUDY DESIGN/SETTING

A biomechanical study using human lumbar vertebrae.

METHODS

Ten fresh human lumbar vertebrae were isolated from five donors. Each vertebra was instrumented with a monoaxial pedicle screw into each pedicle using two different techniques. On one side, a perfect center-center (CC) screw path was created using direct visualization and fluoroscopy. A 6.0-mm-diameter cannulated tap and a pedicle probe were used to develop the pedicle for the 7.0-mm-diameter by 45-mm-long cannulated pedicle screw, which was placed using a digital torque driver. On the contralateral side, an intentional lateral pedicle wall breach was created at the pedicle-vertebral body junction using a guide wire, a 6.0-mm-diameter cannulated tap, and a pedicle probe. This path was then redirected into a CC position, developed, and instrumented with a 7.0-mm-diameter by 45-mm-long cannulated pedicle screw: the RD screw. For each pedicle screw, we assessed four outcome measures: maximal torque, seating torque, screw loosening, and post-loosening axial pullout. Screw loosening and axial pullout were assessed using an MTS machine.

RESULTS

The biomechanical cost of a lateral pedicle breach and the requirement to redirect the pedicle screw are as follows: an overall drop of 28% (p<.002) in maximal insertion torque and 25% (p<.049) in seating torque, a drop of 25% (p<.040) in resistance to screw loosening, and a drop in axial pullout force of 11% (p<.047).

CONCLUSIONS

Compared with a CC lumbar pedicle screw, an RD lumbar pedicle screw placed after a lateral wall breach is significantly weaker in terms of maximal insertional torque, seating torque, screw loosening force, and axial pullout strength. These significant decreases in biomechanical properties are clearly important when RD pedicle screws are placed at the cephalad or caudal end of a long construct. In this situation, augmentation of the RD screw is an option.

Pedicle violation and Navigational errors in pedicle screw insertion using the intraoperative O-arm: A preliminary report

Background

Use of computer-assisted insertion of pedicle screws has some advantages owing to the reportedly decreased incidence of pedicle breach and clinical events. Registration-based methods based on preoperative computed tomography imaging, 2D fluoroscopy, and 3D fluoroscopy are the most popular, however each has its limitations. O-arm–based navigation, which uses intraoperative acquisition and registration of navigated images, may overcome many of these disadvantages. We set out to study the clinical accuracy and navigational accuracy for pedicle screw insertion using our recently acquired O-arm and present our preliminary findings.

Methods

The first 26 patients operated consecutively for L4-5 fusion were included in the study. O-arm–based navigation was used to insert the pedicle screws. Postoperative computed tomography images were acquired and assessed for pedicle breach and anterior cortical perforation. Planned trajectories of each screw were compared with the actual trajectories in the postoperative images to assess navigational accuracy in both axial and sagittal planes.

Results

A total of 104 screws were inserted. One screw (1%) breached the pedicle laterally. Nonsignificant anterolateral cortical perforations were noted in 7 screws (6.7%), all of which occurred at L5 level. The mean axial and sagittal navigational error was 2.3° (±1.7) and 3.1° (±2.3), respectively. There were no significant differences in the errors between L4 or L5 level. The occurrence of anterior perforation correlated with the degree of axial (P = .02) but not sagittal (P = .12) navigational error. There were no clinical events related to the screw insertion.

Conclusion

Use of O-arm–guided pedicle screw insertion was associated with low incidence of pedicle breach (1%) and a low range of navigational error in both sagittal and axial planes. Anterolateral vertebral body perforation was higher at L5 without any negative clinical events. Despite the high need for technical support, we found that O-arm was a very efficient tool for accurate pedicle screw insertion.

Comparison between the accuracy of percutaneous and open pedicle screw fixations in lumbosacral fusion

BACKGROUND CONTEXT

In pedicle screw fixation, accurate insertion is essential to avoid neurological injury or weak stability. The percutaneous pedicle screw system was developed for minimally invasive spine surgery, and its safety has already been reported. However, the accuracy of percutaneous pedicle screw fixation (PPF) has not been compared with that of the open system to date.

PURPOSE

To compare the accuracy of PPF with that of open pedicle screw fixation (open PF) and to investigate the risk factors associated with pedicle wall penetration.

STUDY DESIGN/SETTING

A retrospective case series.

PATIENT SAMPLE

The study group included 237 patients who underwent posterior pedicle screw fixation between January 2008 and October 2010 at a single institute with a total of 1,056 pedicle screw fixations completed. One hundred and twenty-six patients with 558 screws underwent open PF and 111 patients with 498 screws underwent PPF.

OUTCOME MEASURES

Postoperative computerized tomography, including sagittal and coronal reformatted images.

METHODS

Consecutive surgeries with either conventional open PF or PPF for anterior lumbar interbody fusion or transforaminal lumbar interbody fusion were performed. The open pedicle screw employed was from the WSH system (Winova, Seoul, Korea), and the two percutaneous pedicle screw systems were the Sextant (Medtronics, Minneapolis, MN, USA) and the Viper systems (DePuy Spine, Raynham, MA, USA). Computed tomography images were evaluated to determine pedicle wall penetration after operation. Severity was classified as mild (<3 mm), moderate (3-6 mm), and severe (≥6 mm), and the direction was assessed as medial, lateral, inferior, and superior.

RESULTS

Pedicle wall penetration occurred in 75 patients (13.4%) in the open PF group and 71 patients (14.3%) in the PPF group and was not statistically different between the groups (p=.695). Assessment of the severity of the pedicle wall penetration revealed that minor penetration was the most common (open PF group, 9.7%; PPF group, 10.6%), although the distribution of the degree of severity was not statistically different between the groups (p=.863). A relatively higher incidence of lateral penetration was observed in the open PF group (66.7% vs. 43.7%), whereas medial, superior, and inferior penetrations were higher in the PPF group (p=.033). Other parameters such as age, sex, surgical method, and surgeon factors did not influence the penetration rate, but bone mineral densitometry negatively correlated with the penetration.

CONCLUSIONS

Pedicle wall penetration during screw fixation was not different between the open PF and PPF groups. The lateral, paraspinal, muscle-splitting approach seems to lessen medial wall penetration, especially in the S1 vertebra. Distribution of the direction of penetration differs between the groups, with lateral wall penetration being more prominent in the open PF group. Careful placement of pedicle screws is necessary for a stronger construct because of the high incidence of penetration.

Routine spinal navigation for thoraco-lumbar pedicle screw insertion using the O-arm three-dimensional imaging system improves placement accuracy

Modern image-guided spinal navigation employs high-quality intra-operative three dimensional (3D) images to improve the accuracy of spinal surgery. This study aimed to assess the accuracy of thoraco-lumbar pedicle screw insertion using the O-arm (Breakaway Imaging, LLC, Littleton, MA, USA) 3D imaging system. Ninety-two patients underwent insertion of thoraco-lumbar pedicle screws guided by O-arm navigation over a 27 month period. Intra-operative scans were retrospectively reviewed for pedicle breach. The operative time of patients where O-arm navigation was used was compared to a matched control group where fluoroscopy was used. A total of 467 pedicle screws were inserted. Four hundred and forty-five screws (95.3%) were placed within the pedicle without any breach (Gertzbein classification grade 0). Sixteen screws (3.4%) had a pedicle breach of less than 2mm (Gertzbein classification grade 1), and six screws (1.3%) had a pedicle breach between 2mm and 4mm (Gertzbein classification grade 2). The grade 2 screws were revised intra-operatively. There was no incidence of neurovascular injury in this series of patients. The mean operative time for O-arm patients was 5.25 hours. In a matched control group of fluoroscopy patients, the mean operative time was 4.75 hours. The difference in the mean operative time between the two groups was not statistically significant (p=0.15, paired t-test). Stereotactic navigation based on intra-operative O-arm 3D imaging resulted in high accuracy in thoraco-lumbar pedicle screw insertion.

Operating room radiation exposure in cone beam computed tomography-based, image-guided spinal surgery: clinical article

OBJECT

Surgeon and operating room (OR) staff radiation exposure during spinal surgery is a concern, especially with the increasing use of multiplanar fluoroscopy in minimally invasive spinal surgery procedures. Cone beam computed tomography (cbCT)-based, 3D image guidance does not involve the use of active fluoroscopy during instrumentation placement and therefore decreases radiation exposure for the surgeon and OR staff during spinal fusion procedures. However, the radiation scatter of a cbCT device can be similar to that of a standard 64-slice CT scanner and thus could expose the surgeon and OR staff to radiation during image acquisition. The purpose of the present study was to measure radiation exposure at several unshielded locations in the OR when using cbCT in conjunction with 3D image-guided spinal surgery in 25 spinal surgery cases.

METHODS

Five unshielded badge dosimeters were placed at set locations in the OR during 25 spinal surgery cases in which cbCT-based, 3D image guidance was used. The cbCT device (O-ARM) was used in conjunction with the Stealth S7 image-guided platform. The radiology department analyzed the badge dosimeters after completion of the last case.

RESULTS

Fifty high-definition O-ARM spins were performed in 25 patients for spinal registration and to check instrumentation placement. Image-guided placement of 124 screws from C-2 to the ileum was accomplished without complication. Badge dosimetry analysis revealed minimal radiation exposure for the badges 6 feet from the gantry in the area of the anesthesiology equipment, as well as for the badges located 10-13 feet from the gantry on each side of the room (mean 0.7-3.6 mrem/spin). The greatest radiation exposure occurred on the badge attached to the OR table within the gantry (mean 176.9 mrem/spin), as well as on the control panel adjacent to the gantry (mean 128.0 mrem/spin).

CONCLUSIONS

Radiation scatter from the O-ARM was minimal at various distances outside of and not adjacent to the gantry. Although the average radiation exposure at these locations was low, an earlier study, undertaken in a similar fashion, revealed no radiation exposure when the surgeon stood behind a lead shield. This simple precaution can eliminate the small amount of radiation exposure to OR staff in cases in which the O-ARM is used.

Multistep pedicle screw insertion procedure with patient-specific lamina fit-and-lock templates for the thoracic spine: clinical article

OBJECT

Pedicle screw fixation is a standard procedure of spinal instrumentation, but accurate screw placement is essential to avoid injury to the adjacent structures, such as the vessels, nerves, and viscera. The authors recently developed an intraoperative screw guiding method in which patient-specific laminar templates were used, and verified the accuracy of the multistep procedure in the thoracic spine.

METHODS

Preoperative bone images of the CT scans were analyzed using 3D/multiplanar imaging software and the trajectories of the screws were planned. Plastic templates with screw guiding structures were created for each lamina by using 3D design and printing technology. Three types of templates were made for precise multistep guidance, and all templates were specially designed to fit and lock on the lamina during the procedure. Plastic vertebra models were also generated and preoperative screw insertion simulation was performed. Surgery was performed using this patient-specific screw guide template system, and the placement of screws was postoperatively evaluated using CT scanning.

RESULTS

Ten patients with thoracic or cervicothoracic pathological entities were selected to verify this novel procedure. Fifty-eight pedicle screws were placed using the screw guide template system. Preoperatively, each template was found to fit exactly and to lock on the lamina of the vertebra models, and screw insertion simulation was successfully performed. Intraoperatively the templates also fit and locked on the patient lamina, and screw insertion was completed successfully. Postoperative CT scans confirmed that no screws violated the cortex of the pedicles, and the mean deviation of the screws from the planned trajectories was 0.87 ± 0.34 mm at the coronal midpoint section of the pedicles.

CONCLUSIONS

The multistep, patient-specific screw guide template system is useful for intraoperative pedicle screw navigation in the thoracic spine. This simple and economical method can improve the accuracy of pedicle screw insertion and reduce the operating time and radiation exposure of spinal fixation surgery.

Use of the O-arm® for skull base resection in a sphenoorbital meningioma

Intraoperative imaging during skull base surgery allows the surgeon to evaluate surgical results and direct further bone resection prior to closure, avoiding the potential morbidity of inadequate surgical therapy or reoperation. Intraoperative CT (iCT) scanning has become widely available in recent years, but its neurosurgical applications have been limited mostly to spinal and functional operations. We report a patient with a sphenoorbital meningioma with adjacent hyperostosis causing proptosis and optic canal stenosis in which a portable iCT scanner (O-arm(®); Medtronic, Fridley, MN, USA) was used to guide further resection. Postoperatively, the patient experienced resolution of her proptosis, and her vision remains clinically normal. The O-arm(®) can be easily incorporated into standard operating rooms and is useful in tailoring bony skull base resections.

Placement of thoracic transvertebral pedicle screws using 3D image guidance

Object

Transvertebral pedicle screws have successfully been used in the treatment of high-grade L5–S1 spondylolisthesis. An advantage of transvertebral pedicle screws is the purchase of multiple cortical layers across 2 vertebrae, thereby increasing the stability of the construct. At the lumbosacral junction, transvertebral pedicle screws have been shown to be biomechanically superior to pedicle screws placed in the standard fashion. The use of transvertebral pedicle screws at spinal levels other than L5–S1 has not been reported in the literature. The authors describe their technique of transvertebral pedicle screw placement in the thoracic spine using 3D image guidance.

Methods

Twelve patients undergoing cervicothoracic or thoracolumbar fusion had 41 thoracic transvertebral pedicle screws placed across 26 spinal levels using this technique. Indications for placement of thoracic transvertebral pedicle screws in earlier cases included osteoporosis and pedicle screw salvage. However, in subsequent cases screws were placed in patients undergoing multilevel thoracolumbar fusion without osteoporosis, particularly near the top of the construct. Image guidance in this study was accomplished using the Medtronic StealthStation S7 image guidance system used in conjunction with the O-arm. All patients were slated to undergo postoperative CT scanning at approximately 4–6 months for fusion assessment, which also allowed for grading of the transvertebral pedicle screws.

Results

No thoracic transvertebral pedicle screw placed in this study had to be replaced or repositioned after intraoperative review of the cone beam CT scans. Review of the postoperative CT scans revealed all transvertebral screws to be across the superior disc space with the tips in the superior vertebral body. Six pedicle screws were placed using the in-out-in technique in patients with narrow pedicles, leaving 35 screws that underwent breach analysis. No pedicle breach was noted in 34 of 35 screws. A Grade 1 (< 2 mm) medial breach was noted in 1 screw without clinical consequence. Solid fusion was observed across 25 of 26 spinal levels that underwent transvertebral screw placement including 7 spinal levels located at the top of a multilevel construct.

Conclusions

This report describes the authors' initial in vivo experience with the 3D image-guided placement of 41 thoracic transvertebral pedicle screws. Advantages of thoracic transvertebral screws include the purchase of 2 vertebral segments across multiple cortical layers. A high fusion rate was observed across spinal levels in which transvertebral screws were placed. A formal biomechanical study is needed to assess the biomechanical advantages of this technique and is currently being planned.

Comparison of open and minimally invasive techniques for posterior lumbar instrumentation and fusion after open anterior lumbar interbody fusion

BACKGROUND CONTEXT

Minimally invasive techniques for spinal fusion have theoretical advantages for the reduction of iatrogenic injury. Although this topic has been investigated previously for posterior-only interbody surgery, such as transforaminal lumbar interbody fusion, similar studies have not evaluated these techniques after anteroposterior spinal fusion, a study design that can more accurately determine the effect of pedicle screw placement and decompression via a minimally invasive technique without the confounding effect of simultaneous interbody cage placement.

PURPOSE

To compare process measures that provide insight into the morbidity of surgery, such as surgical time and the length of postoperative hospital stay between open and minimally invasive anteroposterior lumbar fusion; and to compare the complications during the intraoperative and early postoperative period between open and minimally invasive anteroposterior lumbar fusion.

STUDY DESIGN

Retrospective case-control study.

PATIENT SAMPLE

One hundred sixty-two patients.

OUTCOME MEASURES

Estimated blood loss, length of surgery, intraoperative fluoroscopy time, length of postoperative hospital stay, malpositioned instrumentation on postoperative imaging, and postoperative complications, including pulmonary embolus and surgical site infection.

METHODS

Patients who underwent open anterior lumbar interbody fusion followed by either traditional open posterior fusion (Open group) or minimally invasive posterior fusion (minimally invasive surgery [MIS] group) were matched by the number of surgical levels. A chart review was performed to document the intraoperative and postoperative process measures and associated complications in the two groups. Secondary analyses were performed to compare the subgroups of patients, who did and did not undergo a posterior decompression at the time of posterior instrumentation to determine the effect of decompression.

RESULTS

Baseline characteristics were similar between the Open and MIS groups. Estimated blood loss and postoperative transfusion rate were significantly higher in the Open group, differences that the subanalyses suggested were largely because of those patients who underwent concomitant decompression. Length of stay was not significantly different between the groups but was significantly shorter for MIS patients treated without decompression than for Open patients treated without decompression. Intraoperative fluoroscopy time was significantly longer in the MIS group. There was no difference in the infection or complication rates between the groups.

CONCLUSIONS

Our case-control study comparing patients who underwent anterior lumbar interbody fusion followed by open posterior instrumentation with those who underwent anterior lumbar interbody fusion followed by minimally invasive posterior instrumentation demonstrated that patients undergoing MIS fusion without decompression had less blood loss, less need for transfusion in the perioperative period, and a shorter hospital stay. In contrast, most outcome measures were similar between MIS and Open groups for patients who underwent decompression.

Robotic-assisted pedicle screw placement: lessons learned from the first 102 patients

INTRODUCTION

Surgeons' interest in image and/or robotic guidance for spinal implant placement is increasing. This technology is continually improving and may be particularly useful in patients with challenging anatomy. Only through careful clinical evaluation can its successful applications, limitations, and areas for improvement be defined. This study evaluates the outcomes of robotic-assisted screw placement in a consecutive series of 102 patients.

METHODS

Data were recorded from technical notes and operative records created immediately following each surgery case, in which the robotic system was used to guide pedicle screw placement. All cases were performed at the same hospital by a single surgeon. The majority of patients had spinal deformity and/or previous spine surgery. Each planned screw placement was classified as: (1) successful/accurately placed screw using robotic guidance; (2) screw malpositioned using robot; (3) use of robot aborted and screw placed manually; (4) planned screw not placed as screw deemed non essential for construct stability. Data from each case were reviewed by two independent researchers to indentify the diagnosis, number of attempted robotic guided screw placements and the outcome of the attempted placement as well as complications or reasons for non-placement.

RESULTS

Robotic-guided screw placement was successfully used in 95 out of 102 patients. In those 95 patients, 949 screws (87.5 % of 1,085 planned screws) were successfully implanted. Eleven screws (1.0 %) placed using the robotic system were misplaced (all presumably due to "skiving" of the drill bit or trocar off the side of the facet). Robotic guidance was aborted and 110 screws (10.1 %) were manually placed, generally due to poor registration and/or technical trajectory issues. Fifteen screws (1.4 %) were not placed after intraoperative determination that the screw was not essential for construct stability. The robot was not used as planned in seven patients, one due to severe deformity, one due to very high body mass index, one due to extremely poor bone quality, one due to registration difficulty caused by previously placed loosened hardware, one due to difficulty with platform mounting and two due to device technical issues.

CONCLUSION

Of the 960 screws that were implanted using the robot, 949 (98.9 %) were successfully and accurately implanted and 11 (1.1 %) were malpositioned, despite the fact that the majority of patients had significant spinal deformities and/or previous spine surgeries. "Tool skiving" was thought to be the inciting issue with the misplaced screws. Intraoperative anteroposterior and oblique fluoroscopic imaging for registration is critical and was the limiting issue in four of the seven aborted cases.

Role of the O-arm and Computer-assisted Navigation of Safe Screw Fixation in Children with Traumatic Rotatory Atlantoaxial Subluxation

Study Design

A retrospective analysis of 7 patients with traumatic rotatory atlanto-axial subluxation.

Overview of Literature

Cases of traumatic rotatory atlantoaxial subluxation in children are difficult to be stabilized. Surgical challenges include: narrow pedicles, medial vertebral arteries, vertebral artery anomalies, fractured pedicles or lateral masses, and fixed subluxation. The use of O-arm and computer-assisted navigation are still tested as aiding tools in such operative modalities.

Purpose

Report of clinical series for evaluation of the safety of use of the O-arm and computed assisted-navigation in screw fixation in children with traumatic rotatory atlantoaxial subluxation.

Methods

In the present study, 7 cases of rotatory atlantoaxial traumatic subluxation were operated between December 2009 and March 2011. All patient-cases had undergone open reduction and instrumentation using atlas lateral mass and axis pedicle screws with intraoperative O-arm with computer-assisted navigation.

Results

All hardware was safely placed in the planned trajectories in all the 7 cases. Intraoperative O-arm and computer assisted-navigation were useful in securing neural and vascular tissues safety with tough-bony purchases of the hardware from the first and only trial of application with sufficient reduction of the subluxation.

Conclusions

Successful surgery is possible with using the intraoperative O-arm and computer-assisted navigation in safe and proper placement of difficult atlas lateral mass and axis pedicle screws for rotatory atlantoaxial subluxation in children.

En bloc resection of sacral chordomas aided by frameless stereotactic image guidance: a technical note

BACKGROUND

The most important predictor of survival for patients with sacral chordomas is an initial en bloc resection with negative margins. However, obtaining negative margins can be technically challenging. Intraoperative navigation may be helpful in attempting an excision with negative margins.

OBJECTIVE

This is the first report of partial sacrectomy guided by frameless stereotactic navigation.

METHODS

Three patients with a mean age of 58.7 years underwent en bloc resection of sacral chordomas aided by image guidance. Intraoperatively, the reference arc was clamped to the spinous process of L5 and the bony landmarks of S1 were used for registration. Subsequently, the drill was registered, allowing the osteotomy trajectory to be visualized in real time with reference to the patients' anatomy and tumor location.

RESULTS

None of the patients had any intraoperative or postoperative complications. Two patients with smaller tumors (5 cm) had negative margins, whereas the third patient with an 11.5 cm tumor had marginal margins. With an average follow-up of 44 months, none of the patients have had a recurrence of the tumor.

CONCLUSION

The use of frameless stereotaxy during the en bloc resection of sacral tumors is safe and feasible. Frameless stereotactic navigation was a useful adjunct to preoperative imaging and to the surgeon's anatomic knowledge. Image guidance was used during the osteotomies to decrease the likelihood of injury to vital adjacent structures or violation of the tumor capsule and to increase the likelihood that the appropriate surrounding tissue was resected to attempt a wide or marginal resection.

Computer tomography assessment of pedicle screw placement in thoracic spine: comparison between free hand and a generic 3D-based navigation techniques

INTRODUCTION

Although pedicle screw fixation is a well-established technique for the lumbar spine, screw placement in the thoracic spine is more challenging because of the smaller pedicle size and more complex 3D anatomy. The intraoperative use of image guidance devices may allow surgeons a safer, more accurate method for placing thoracic pedicle screws while limiting radiation exposure. This generic 3D imaging technique is a new generation intraoperative CT imaging system designed without compromise to address the needs of a modern OR.

AIM

The aim of our study was to check the accuracy of this generic 3D navigated pedicle screw implants in comparison to free hand technique described by Roy-Camille at the thoracic spine using CT scans.

MATERIAL AND METHODS

The material of this study was divided into two groups: free hand group (group I) (18 patients; 108 screws) and 3D group (27 patients; 100 screws). The patients were operated upon from January 2009 to March 2010. Screw implantation was performed during internal fixation for fractures, tumors, and spondylodiscitis of the thoracic spine as well as for degenerative lumbar scoliosis.

RESULTS

The accuracy rate in our work was 89.8 % in the free hand group compared to 98 % in the generic 3D navigated group.

CONCLUSION

In conclusion, 3D navigation-assisted pedicle screw placement is superior to free hand technique in the thoracic spine.

Placement of thoracolumbar pedicle screws using O-arm-based navigation: technical note on controlling the operational accuracy of the navigation system

Suboptimal placements of pedicle screws may lead to neurological and vascular complications. Computer-assisted image guidance has been shown to improve accuracy in spinal instrumentation. Checking the accuracy of the navigation system during pedicle screw placement is fundamental. We describe a novel technique of using continuous accuracy check of the navigation system during O-arm-based neuronavigation to instrument the thoracolumbar region. Forty thoracic and 42 lumbar screws were inserted in 12 patients. The Mirza evaluation system was used to evaluate the accuracy of the inserted screws. There was no neurological injury and no need to reposition any screw. The accuracy of the screws placement was excellent. Our technique of continuous at will operational accuracy check of the neuronavigation system is associated with extreme accuracy of screw placement, no need to bring a patient back to the operating room to reposition a pedicle screw, and with excellent outcome.

Screw placement accuracy for minimally invasive transforaminal lumbar interbody fusion surgery: a study on 3-d neuronavigation-guided surgery

Purpose The aim of this study was to assess the impact of 3-D navigation for pedicle screw placement accuracy in minimally invasive transverse lumbar interbody fusion (MIS-TLIF). Methods A retrospective review of 52 patients who had MIS-TLIF assisted with 3D navigation is presented. Clinical outcomes were assessed with the Oswestry Disability Index (ODI), Visual Analog Scales (VAS), and MacNab scores. Radiographic outcomes were assessed using X-rays and thin-slice computed tomography. Result The mean age was 56.5 years, and 172 screws were implanted with 16 pedicle breaches (91.0% accuracy rate). Radiographic fusion rate at a mean follow-up of 15.6 months was 87.23%. No revision surgeries were required. The mean improvement in the VAS back pain, VAS leg pain, and ODI at 11.3 months follow-up was 4.3, 4.5, and 26.8 points, respectively. At last follow-up the mean postoperative disc height gain was 4.92 mm and the mean postoperative disc angle gain was 2.79 degrees. At L5-S1 level, there was a significant correlation between a greater disc space height gain and a lower VAS leg score. Conclusion Our data support that application of 3-D navigation in MIS-TLIF is associated with a high level of accuracy in the pedicle screw placement.

Morphometric analysis using multiplanar reconstructed CT of the lumbar pedicle in patients with degenerative lumbar scoliosis characterized by a Cobb angle of 30° or greater

Object

Although the anatomy of the thoracic pedicle in adolescent idiopathic scoliosis is well known, that of the lumbar pedicle in degenerative lumbar scoliosis is not. The morphometric differences between the pedicles on the concave and convex sides can result in an increased risk of malpositioned pedicle screws. The purpose of this study was to analyze the lumbar pedicle morphology in degenerative lumbar scoliosis using multiplanar reconstructed CT.

Methods

The study group comprised 16 consecutive patients (1 man and 15 women, mean age 70.9 ± 4.5 years) with degenerative lumbar scoliosis characterized by a Cobb angle of at least 30° who underwent preoperative helical CT scans. The CT data in DICOM format were reconstructed, and the following parameters were measured for each pedicle inside the curves: the inner cortical transverse pedicle width (TPWi) and outer cortical transverse pedicle width (TPWo) and axial angle, all on an axial plane, and the inner cortical minimum pedicle diameter (MPDi) and outer cortical minimum pedicle diameter (MPDo) and cephalocaudal inclination of the pedicle, all on the plane perpendicular to the pedicle axis. The cortical thickness and cortical ratio of the pedicles on the axial plane and the plane perpendicular to the pedicle axis were calculated. Data were obtained for a total of 124 pedicles; L-1, 26 pedicles in 13 patients; L-2, 32 pedicles in 16 patients; L-3, 32 pedicles in 16 patients; L-4, 28 pedicles in 14 patients; and L-5, 6 pedicles in 3 patients.

Results

Among the target vertebrae, the TPWi, MPDi, and MPDo were significantly smaller and the axial angle was significantly larger on the concave side than on the convex side (TPWi, 6.37 vs 6.70 mm, p < 0.01; MPDi, 5.15 vs 5.67 mm, p < 0.01; MPDo, 7.91 vs 8.37 mm, p < 0.05; axial angle, 11.79° vs 10.56°, p < 0.01). The cortical ratio of the pedicles was larger on the concave side than on the convex side (on the axial plane, 0.29 vs 0.26, p < 0.05; on the plane perpendicular to the pedicle axis, 0.36 vs 0.32, p < 0.01). These differences were most evident at L-4.

Conclusions

This study demonstrated lumbar pedicle asymmetry in degenerative lumbar scoliosis. The authors speculate that these asymmetrical changes were attributed to the remodeling caused by axial load imbalance and the limited space available for pedicles on the concave side. On the concave side, because of the narrower pedicle diameter and larger axial angle, surgeons should carefully determine screw size and direction when inserting pedicle screws to prevent possible pedicle wall breakage and neural damage.

Clinically relevant complications related to pedicle screw placement in thoracolumbar surgery and their management: a literature review of 35,630 pedicle screws

OBJECT

The technique of pedicle screw insertion is a mainstay of spinal instrumentation. Some of its potential complications are clinically relevant and may require reoperation or further postoperative care.

METHODS

A literature search was performed using MEDLINE (between 1999 and June 2011) for studies on pedicle screw placement in thoracolumbar surgery. The authors included randomized controlled trials, case-control studies, and case series (≥ 20 patients) from the English-, German-, and French-language literature. The authors assessed study type, the number of patients, the anatomical area, the number of pedicle screws, duration of follow-up, type of pedicle screw placement, incidence of complications, and type of complication. The management of specific complications is discussed.

RESULTS

Thirty-nine articles with 46 patient groups were reviewed with a total of 35,630 pedicle screws. One study was a randomized controlled trial, 8 were case-control studies, and the remaining articles were case series. Dural lesions and irritation of nerve roots were reported in a mean of 0.18% and 0.19% per pedicle screws, respectively. Thirty-two patients in 10 studies (of 5654 patients from all 39 studies) required further revision surgeries for misplaced pedicle screws causing neurological problems. None of the analyzed studies reported vascular complications, and only 2 studies reported visceral complications of clinical significance.

CONCLUSIONS

Pedicle screw placement in the thoracolumbar region is a safe procedure with an overall high accuracy and a very low rate of clinically relevant complications.

A prospective study on the use of intraoperative computed tomography (iCT) for image-guided placement of thoracic pedicle screws

BACKGROUND

Placement of thoracic pedicle screws is a technically demanding procedure. The risk of thoracic pedicle breaches range from 6.5 to 41%. Current image guidance systems consist of computer based systems utilizing preoperative CT scans or 2D/3D intraoperative fluoroscopy.

OBJECTIVE

The aim of this prospective study was to evaluate the clinical feasibility and accuracy of a new intraoperative CT (iCT) based image guidance system for thoracic pedicle screw instrumentation.

METHODS

We prospectively studied the use of iCT for the first 43 consecutive cases for which thoracic pedicle screws were inserted as part of the instrumentation for spinal fusion between April 2008 and July 2011. In every case, a post-instrumentation intraoperative check CT was done before wound closure to assess accuracy of implant placement. Outcomes were analysed with regards to the incidence of pedicle wall violations detected on intraoperative check CT imaging, and the rate of immediate intraoperative revision of misplaced screws. Pedicle violations were graded according to an established classification system.

RESULTS

A total of 261 thoracic pedicle screws (T1-T12) were inserted in 43 patients (age range 13-83). Mean follow-up was 12 months. There were 7 (2.7%) pedicle violations detected on the intraoperative check CT. Out of the seven, three were grade I (< 2 mm), two were grade II (2-4 mm) and rest two were grade III (> 4 mm) violations. Only four of the screws (1.5%) that breached the pedicle wall by more than 2 mm were immediately revised before wound closure.

CONCLUSION

The iCT based spinal neuronavigation system allowed for highly safe and accurate placement (97.3%) of thoracic pedicle screws in our institution with no neurovascular injury reported.

Application of intraoperative computed tomography with or without navigation system in surgical correction of spinal deformity: a preliminary result of 59 consecutive human cases

STUDY DESIGN

A retrospective analysis of patients undergoing spinal deformity correction surgery by the assistance of intraoperative computed tomography (iCT) with or without navigation system.

OBJECTIVE

To share our preliminary experience and analysis of the iCT navigation system applied to spinal deformity surgery.

SUMMARY OF BACKGROUND DATA

The iCT navigation system has been shown to improve accuracy and safety in posterior instrumentation. It not only decreased the operation time but also prevented excessive radiation exposure to the medical staff. To date, there are only few reports about the application of the iCT navigation system in spinal deformity surgery.

METHODS

From April 2009 to September 2010, 59 patients who had a diagnosis of scoliosis, kyphosis, or scoliokyphosis and underwent iCT-assisted surgical correction were included. Without randomization, 28 patients were operated with the iCT-navigation system, and the other 31 patients were operated with standard procedure under iCT assistance. The detailed procedures, preoperative and intraoperative images were illustrated. The accuracy of screw placement, time for screw insertion, postoperative correction rate, and iCT scanning data were analyzed.

RESULTS

There were significant differences between 2 groups in (1) the preoperative Cobb angle (76.2° and 62.6° in the navigation and non-navigation groups), (2) the accuracy and the revision rate of thoracic pedicle screws and total pedicle screws, and (3) the average screw insertion time. The breach rate and the revision rate of thoracic pedicle screws and total pedicle screws were significantly lower and the average screw insertion time was significantly lesser in the navigation group than in the non-navigation group. There were no statistically significant difference in (1) the breach rate and the revision rate of lumbar pedicle screws, (2) the mean iCT scanning time and time-out, (3) the mean number of fusion segments, (4) the mean number of iCT scans, and (5) the postoperative correction rate. Complications were encountered in 2 patients in the non-navigation group but none in the navigation group. There was no reoperation due to implant malposition in both groups.

CONCLUSION

The iCT navigation system provides desirable accuracy of posterior spinal instrumentation for patients during surgical correction of spinal deformity without radiation exposure to the medical staff, especially in thoracic spine instrumentation. Meanwhile, the iCT in itself is an effective means of assessing complex instrumentation of the spinal deformity.

Computed tomography-guided navigation of thoracic pedicle screws for adolescent idiopathic scoliosis results in more accurate placement and less screw removal

STUDY DESIGN

Retrospective study of computed tomography-guided navigation (CTGN) of thoracic pedicle screw placement in patients with adolescent idiopathic scoliosis (AIS).

OBJECTIVE

To compare the accuracy and safety of thoracic pedicle screw placement and frequency of intraoperative removal using CTGN versus conventional freehand technique in AIS.

SUMMARY OF BACKGROUND DATA

Even in experienced hands, more than 10% of the thoracic pedicle screws are misplaced. CTGN may improve accuracy and safety, but there is little published data on its efficacy.

METHODS

We reviewed intraoperative computed tomographic images in a consecutive series of AIS cases undergoing posterior fusion during a 1-year period. Three types of screws were identified: an optimal screw--the central axis is in the plane and axis of the pedicle with the tip completely within the vertebral body; an acceptable screw--the majority of its shank is outside the central axis of the pedicle, but not potentially unsafe; and a potentially unsafe screw--(1) the central axis of the screw traversed the canal, (2) left anterior/lateral vertebral body perforation, risking the aorta, or (3) any screw repositioned or removed after the postimplant computed tomography.

RESULTS

In 42 patients, 485 screws were evaluable with a visible pedicle and screw (300 navigated and 185 non-navigated). Screws were classified as follows: optimal screws, 74% CTGN versus 42% non-navigated; acceptable screws, 23% CTGN versus 49% non-navigated; and potentially unsafe, 3% CTGN versus 9% non-navigated (P < 0.001). A potentially unsafe screw was 3.8 times less likely to be inserted with navigation (P = 0.003). The odds of a significant medial breach were 7.6 times higher without navigation (P < 0.001). A screw was 8.3 times more likely to be removed intraoperatively in the non-navigated cohort (P = 0.003).

CONCLUSION

CTGN resulted in more optimally placed thoracic pedicle screws, fewer potentially unsafe screws, and fewer screw removals.

Worldwide survey on the use of navigation in spine surgery

OBJECTIVE

Computer-assisted surgery (CAS) can improve the accuracy of screw placement and decrease radiation exposure, yet this is not widely accepted among spine surgeons. The current viewpoint of spine surgeons on navigation in their everyday practice is an important issue that has not been studied. A survey-based study assessed opinions on CAS to describe the current global attitudes of surgeons on the use of navigation in spine surgery.

METHODS

A 12-item questionnaire focusing on the number and type of surgical cases, the type of equipment available, and general opinions toward CAS was distributed to 3348 AOSpine surgeons (a specialty group within the AO [Arbeitsgemeinschaft für Osteosynthesefragen] Foundation). Latent class analysis was used to investigate the existence of specific groups based on the respondent opinion profiles.

RESULTS

A response rate of 20% was recorded. Despite a widespread distribution of navigation systems in North America and Europe, only 11% of surgeons use it routinely. High-volume procedure surgeons, neurological surgeons, and surgeons with a busy minimal invasive surgery practice are more likely to use CAS. "Routine users" consider the accuracy, potential of facilitating complex surgery, and reduction in radiation exposure as the main advantages. The lack of equipment, inadequate training, and high costs are the main reasons that "nonusers" do not use CAS.

CONCLUSIONS

Spine surgeons acknowledge the value of CAS, yet current systems do not meet their expectations in terms of ease of use and integration into the surgical work flow. To increase its use, CAS has to become more cost efficient and scientific data are needed to clarify its potential benefits.

Accuracy of image-guided pedicle screw placement using intraoperative computed tomography-based navigation with automated referencing. Part II: thoracolumbar spine

BACKGROUND

Image-guided spinal instrumentation may reduce complications in spinal instrumentation.

OBJECTIVE

To assess accuracy, time efficiency, and staff radiation exposure during thoracolumbar screw instrumentation guided by intraoperative computed tomography (iCT)-based neuronavigation (iCT-N).

METHODS

In 55 patients treated for idiopathic and degenerative deformities, 826 screws were inserted in the thoracic (T2-T12; n = 243) and lumbosacral (L1-S1; n = 545) spine, as well as ilium (n = 38) guided by iCT-N. Up to 17 segments were instrumented following a single automated registration sequence with the dynamic reference arc (DRA) uniformly attached to L5. Accuracy of iCT-N was assessed by calculating angular deviations between individual navigated tool trajectories and final implant positions. Final screw positions were also graded according to established classification systems. Clinical and radiological outcome was assessed at 12 to 14 months.

RESULTS

Additional intraoperative fluoroscopy was unnecessary, eliminating staff radiation exposure. Unisegmental K-wire insertion required 4.6 ± 2.9 minutes. Of the thoracic pedicle screws 98.4% were assigned grades I to III according to the Heary classification, with 1.6% grade IV placement. In the lumbar spine, 94.4% of screws were completely contained (Gertzbein classification grade 0), 4.6% displayed minor pedicle breaches <2 mm (grade 1), and 1% of lumbar screws deviated by >2 to <4 mm (grade 2). The accuracy of iCT-N progressively deteriorates with increasing distance from the DRA, but allows safe instrumentation of up to 12 segments.

CONCLUSION

iCT-N using automated referencing allows for safe, highly accurate multilevel instrumentation of the entire thoracolumbosacral spine and ilium, rendering additional intraoperative imaging dispensable. In addition, automated registration is time-efficient and significantly reduces the need for re-registration in multilevel surgery.

Pediatric pedicle screw placement using intraoperative computed tomography and 3-dimensional image-guided navigation

STUDY DESIGN

A retrospective cohort study reporting the use of intraoperative computed tomography (CT) and image-guided navigation system for the placement of pedicle screws in pediatric compared with adult patients.

OBJECTIVE

To evaluate the accuracy of open pedicle screw placement in pediatric patients using intraoperative CT and 3-dimensional (3D) image-guided navigation.

SUMMARY OF BACKGROUND DATA

Pedicle screws are widely used in children for the correction of spinal deformity. Navigation systems and intraoperative CT are now available as an adjunct to fluoroscopy and anatomic techniques for placing pedicle screws and verifying screw position.

METHODS

From 2007 to 2010, 984 pedicle screws were placed in a consecutive series cohort of 50 pediatric patients for spinal deformity correction with the use of intraoperative CT (O-arm, Medtronic, Inc, Louisville, CO) and a computerized navigation system (Stealth, Medtronic, Inc, Louisville, CO). The primary outcome measure for this study is redirection or removal of screw on the basis of the intraoperative CT imaging. During the study period, 1511 screws were placed in adult patients using the same image guidance system.

RESULTS

A total of 984 pedicle screws were implanted using real-time navigation, with a mean of 20 screws per patient (range: 2-34). On the basis of intraoperative CT, 35 screws (3.6%) were revised (27 redirected and 8 removed), representing a 96.4% accuracy rate. No patients returned to the operating room because of screw malposition.Of the 1511 screws placed in adult patients, 28 (1.8%) were revised intraoperatively for malposition on CT imaging, for an overall 98.2% accuracy rate. Screw revision thus was more common in the pediatric population (P = 0.008). However, the pediatric screw accuracy rate is significantly higher than the findings from a recent meta-analysis of predominantly nonnavigated screws in children, reporting a 94.9% accuracy rate (P = 0.03).

CONCLUSION

We report 96.4% accuracy in pediatric pedicle screw placement using intraoperative CT and a 3D navigation system. This is similar to other reports and has better accuracy than a recent meta-analysis of nonnavigated screws in children.

Learning retention of thoracic pedicle screw placement using a high-resolution augmented reality simulator with haptic feedback

BACKGROUND

We evaluated the use of a part-task simulator with 3D and haptic feedback as a training tool for a common neurosurgical procedure--placement of thoracic pedicle screws.

OBJECTIVE

To evaluate the learning retention of thoracic pedicle screw placement on a high-performance augmented reality and haptic technology workstation.

METHODS

Fifty-one fellows and residents performed thoracic pedicle screw placement on the simulator. The virtual screws were drilled into a virtual patient's thoracic spine derived from a computed tomography data set of a real patient.

RESULTS

With a 12.5% failure rate, a 2-proportion z test yielded P = .08. For performance accuracy, an aggregate Euclidean distance deviation from entry landmark on the pedicle and a similar deviation from the target landmark in the vertebral body yielded P = .04 from a 2-sample t test in which the rejected null hypothesis assumes no improvement in performance accuracy from the practice to the test sessions, and the alternative hypothesis assumes an improvement.

CONCLUSION

The performance accuracy on the simulator was comparable to the accuracy reported in literature on recent retrospective evaluation of such placements. The failure rates indicated a minor drop from practice to test sessions, and also indicated a trend (P = .08) toward learning retention resulting in improvement from practice to test sessions. The performance accuracy showed a 15% mean score improvement and more than a 50% reduction in standard deviation from practice to test. It showed evidence (P = .04) of performance accuracy improvement from practice to test session.

Use of CT-based intraoperative spinal navigation: management of radiation exposure to operator, staff, and patients

OBJECTIVE

Radiation exposure represents significant risk to both operating room health care workers and their patients. The commonplace surgical implantation of spinal instrumentation often relies on fluoroscopy for guidance and verification. Advances in computerized tomography (CT)-based intraoperative navigation have improved accuracy of screw placement. The objective of this article is to quantify the radiation exposure from fluoroscopic and CT-based intraoperative navigation and to provide guidance in mitigating the exposure to patient and operating room (OR) staff.

METHODS

With radiation measurement devices in place, a female cadaver underwent pedicle screws from T7 to S1. The left side was guided by fluoroscopy, the right side by CT-based navigation. In addition, a CT-based navigation system was placed in an empty OR. Measurements of radiation while scanning phantom were undertaken at various positions around the OR.

RESULTS

The use of intraoperative CT-based navigation virtually eliminated radiation exposure to the surgeon. However, the radiation dose to the patient was increased compared with fluoroscopy. In addition, the radiation profile of the CT-based navigation system was not uniform with significantly lower radiation perpendicular to the axis of the patient on the side of the control panel.

CONCLUSIONS

Use of intraoperative CT-based navigation systems results in lower radiation dose to the surgeon compared with fluoroscopic-based methods. There is an increase in the radiation to the patient. In addition, it is necessary to consider and eliminate other perioperative sources of radiation, such as a postoperative CT scan, which are made redundant by this technology.

Validity of surgeon perception of navigated pedicle screw position: a cadaveric study

STUDY DESIGN

Human Cadaveric Experimental Study.

OBJECTIVE

To determine the validity of surgeon perception of pedicle screw position inserted using intraoperative three-dimensional (O-arm) image-guided screw insertion.

SUMMARY OF BACKGROUND DATA

A surgeon's ability to detect pedicle wall violations intraoperatively is crucial for optimal pedicle screw placement. Accuracy of use of a probe or sound to assess pedicle breach is not optimal and may require experience. Intraoperative navigation has been shown to improve screw placement accuracy. It has not been shown, however, whether navigation in combination with screw tract palpation can further increase the surgeon's ability to detect a pedicle breach in pedicle screw placement in the cervical, thoracic, and lumbosacral spine.

METHODS

Four hundred eighteen screws were inserted using three-dimensional image guidance transpedicularly from C2 to S1 in 10 fresh frozen cadavers. Screw tracts were created using navigation and then probed. After probing, the surgeon stated whether he perceived that the screw would be in, out laterally, or out medially. After screw insertion for all the levels, open dissection was then performed to determine the actual pedicle screw position. The surgeon's perception of screw position was compared to the dissection results.

RESULTS

The overall specificity, sensitivity, positive predictive value, and negative predictive value of the surgeon perception of pedicle screw position were 87%, 80%, 78% and 88%, respectively. Accuracy of surgeon perception of pedicle screw position was significantly less than in the cervical spine when compared with thoracic and lumbosacral spine.

CONCLUSION

Surgeon perception of a navigated pedicle screw position is accurate in the thoracic and lumbar spine. Detection of pedicle screw violations by surgeon perception in the cervical spine is less accurate and does not reliably lead to accurate screw placement.

Intraoperative computed tomography for deep brain stimulation surgery: technique and accuracy assessment

BACKGROUND

The efficacy of deep brain stimulation (DBS) is highly dependent on the accuracy of lead placement.

OBJECTIVE

To describe the use of intraoperative computed tomography (iCT) to confirm lead location before surgical closure and to study the accuracy of this technique.

METHODS

Fifteen patients underwent awake microelectrode-guided DBS surgery in a stereotactic frame. A portable iCT scanner (Medtronic O-arm) was positioned around the patient's head throughout the procedure and was used to confirm lead location before fixation of the lead to the skull. Images were computationally fused with preoperative magnetic resonance imaging (MRI), and lead tip coordinates with respect to the midpoint of the anterior commissure-posterior commissure line were measured. Tip coordinates were compared with those obtained from postoperative MRI.

RESULTS

iCT was integrated into standard frame-based microelectrode-guided DBS surgery with a minimal increase in surgical time or complexity. Technically adequate 2-dimensional and 3-dimensional images were obtained in all cases. Head positioning and fixation techniques that allow unobstructed imaging are described. Lead tip measurements on iCT fused with preoperative MRI were statistically indistinguishable from those obtained with postoperative MRI.

CONCLUSION

iCT can be easily incorporated into standard DBS surgery, replaces the need for C-arm fluoroscopy, and provides accurate intraoperative 3-dimensional confirmation of electrode tip locations relative to preoperative images and surgical plans. iCT fused to preoperative MRI may obviate the need for routine postoperative MRI in DBS surgery. Technical nuances that must be mastered for the efficient use of iCT during DBS implantation are described.

Pedicle screw insertion accuracy with different assisted methods: a systematic review and meta-analysis of comparative studies

Studies revealed that navigation systems that provided intraoperative assistance might improve pedicle screw insertion accuracy, and also implied that different systems provided different pedicle screw insertion accuracy. A systematic review and meta-analysis was conducted to focus on the pedicle screw insertion accuracy with or without the assistance of image-guided system, and the variance among the different navigation systems. Comparative studies were searched on pedicle screw insertion accuracy between conventional and navigated method, and among different navigation systems. A total of 43 papers, including 28 clinical, 14 cadaveric and 1 model studies, were included in the current study. For clinical articles, there were 3 randomized clinical trials, 4 prospective comparative studies and 21 retrospective comparative studies. The incidence of pedicle violation among computer tomography-based navigation method group was statistically significantly less than that observed among the conventional group (OR 95% CI, in vivo: 0.32-0.60; in vitro: 0.24-0.75 P < 0.01). Two-dimensional fluoroscopy-based navigation system (OR 95% CI, in vivo: 0.27-0.48; in vitro: 0.43-0.88 P < 0.01) and three-dimension fluoroscopy-based navigation system (OR 95% CI, in vivo: 0.09-0.38; in vitro: 0.09-0.36 P < 0.01) also obtained significant reduced screw deviation rate over traditional methods. Between navigated approaches, statistically insignificant individual and pooled RR values were observed for all in vivo subgroups. Pooled estimate of in vitro studies show that computer tomography-based and three-dimension fluoroscopy-based navigation system provided more accurate pedicle screw insertion over two-dimension fluoroscopy-based navigation system. Our review showed that navigation provided a higher accuracy in the placement of pedicle screws compared with conventional methods. The superiority of navigation systems was obvious when they were applied to abnormal spinal structure. Although no strong in vivo evidence has detected significantly different pedicle screw placement accuracy among the three major navigation systems, meta-analysis revealed the variance in pedicle screw insertion accuracy with different navigation methods.

Accuracy of Image-Guided Pedicle Screw Placement Using Intraoperative Computed Tomography-Based Navigation With Automated Referencing, Part I: Cervicothoracic Spine

BACKGROUND:

Image-guided spinal instrumentation reduces the incidence of implant misplacement.

OBJECTIVE:

To assess the accuracy of intraoperative computed tomography (iCT)-based neuronavigation (iCT-N).

METHODS:

In 35 patients (age range, 18-87 years), a total of 248 pedicle screws were placed in the cervical (C1-C7) and upper and midthoracic (T1-T8) spine. An automated iCT registration sequence was used for multisegmental instrumentation, with the reference frame fixed to either a Mayfield head clamp and/or the most distal spinous process within the instrumentation. Pediculation was performed with navigated drill guides or Jamshidi cannulas. The angular deviation between navigated tool trajectory and final implant positions (evaluated on postinstrumentation iCT or postoperative CT scans) was calculated to assess the accuracy of iCT-N. Final screw positions were also graded according to established classification systems. Mean follow-up was 16.7 months.

RESULTS:

Clinically significant screw misplacement or iCT-N failure mandating conversion to conventional technique did not occur. A total of 71.4% of patients self-rated their outcome as excellent or good at 12 months; 99.3% of cervical screws were compliant with Neo classification grades 0 and 1 (grade 2, 0.7%), and neurovascular injury did not occur. In addition, 97.8% of thoracic pedicle screws were assigned grades I to III of the Heary classification, with 2.2% grade IV placement. Accuracy of iCT-N progressively deteriorated with increasing distance from the spinal reference clamp but allowed safe instrumentation of up to 10 segments.

CONCLUSION:

Image-guided spinal instrumentation using iCT-N with automated referencing allows safe, highly accurate multilevel instrumentation of the cervical and upper and midthoracic spine. In addition, iCT-N significantly reduces the need for reregistration in multilevel surgery.

Single-stage posterior midline approach for dumbbell tumors of the thoracic spine, with intraoperative CT guidance

BACKGROUND

Several different procedures have been advocated for thoracic spine dumbbell tumor resection, combining thoracic and neurosurgical approaches, in single and multiple stages, using various incisions and positions. These have led to controversies in the ideal management. The authors report their analysis of a series of 11 patients successfully treated through a one-step midline approach for complete resection and instrumentation when indicated under intraoperative CT (ICT) guidance.

METHODS

The patients' clinical presentations, imaging results, operative findings and follow-up were reviewed in 11 patients (age ranged from 11 to 62 years), over the period from August 2007 to May 2010. A single-stage, posterior midline incision approach with laminectomy, facetectomy, costotransversectomy, for complete resection of intraspinal and paraspinal components of tumor was used. Spinal instrumentation under ICT guidance was also carried out in relevant (six) cases with tumors involving junctional spinal regions such the cervico-thoracic or thoraco-lumbar region.

RESULTS

The initial clinical presenting symptom was pain in eight patients and paresthesia in one, while two patients were detected incidentally on routine chest X-rays. Total excision was achieved in 10 patients (9 schwanommas, 1 neurofibroma) with the exception of one patient who had a recurrent malignant peripheral nerve sheath tumor adherent to the vertebral artery. No significant postoperative complications occurred and an early mobilization/discharge was achieved in all patients with an average hospital stay of 5 days.

CONCLUSIONS

A one-step approach through a posterior midline incision is feasible, safe and efficient for complete excision of thoracic dumbbell tumors. This approach facilitates laminectomy, facetectomy, costotransversectomy and instrumentation under ICT guidance, while limiting muscle damage, blood loss, operative time, postoperative pain, thus enabling early mobilization with a reduced hospital stay.

Computer tomography assessment of pedicle screw placement in lumbar and sacral spine: comparison between free-hand and O-arm based navigation techniques

Transpedicular screw fixation has been accepted worldwide since Harrington et al. first placed pedicle screws through the isthmus. In vivo and in vitro studies indicated that pedicle screw insertion accuracy could be significantly improved with image-assisted systems compared with conventional approaches. The O-arm is a new generation intraoperative imaging system designed without compromise to address the needs of a modern OR like no other system currently available. The aim of our study was to check the accuracy of O-arm based and S7-navigated pedicle screw implants in comparison to free-hand technique described by Roy-Camille at the lumbar and sacral spine using CT scans. The material of this study was divided into two groups, free-hand group (group I) (30 patients; 152 screws) and O-arm group (37 patients; 187 screws). The patients were operated upon from January to September 2009. Screw implantation was performed during PLIF or TLIF mainly for spondylolisthesis, osteochondritis and post-laminectomy syndrome. The accuracy rate in our work was 94.1% in the free-hand group compared to 99% in the O-arm navigated group. Thus it was concluded that free-hand technique will only be safe and accurate when it is in the hands of an experienced surgeon and the accuracy of screw placement with O-arm can reach 100%.

Clinical accuracy of computer-assisted two-dimensional fluoroscopy for the percutaneous placement of lumbosacral pedicle screws

STUDY DESIGN

Clinical case series.

OBJECTIVE

The primary objective of this study was to evaluate the clinical accuracy of computer-assisted two-dimensional fluoroscopy (2D-CAS) for the percutaneous placement of lumbosacral pedicle screws.

SUMMARY OF BACKGROUND DATA

Loss of visual anatomic landmarks and reduced tactile feedback increases the risk of pedicle screw misplacement by when using minimally invasive (MIS) percutaneous techniques. However, objective data on screw misplacement in this scenario is lacking.

METHODS

A MIS-2D-CAS technique (FluoroNav) was used for the placement of pedicle screws in 41 consecutive patients undergoing MIS-interbody instrumented fusion. Postoperative computerized tomography (CT) was obtained in all patients at 6 months after surgery and was evaluated by 3 observers. The relative position of the screw to the pedicle was graded regarding pedicle breach (I, no breach; II, <2 mm; III, 2-4 mm; IV, >4 mm), breach direction, vertebral body perforation and screw trajectory. Interobserver reliability of CT grading was assessed with kappa statistics.

RESULTS

A total of 161 screws were placed. No neurologic, vascular, or visceral injuries occurred. About 37 (23%) screws breached the pedicle. The majority (83.8%, 31/37) of breaches were graded II. There were 5 Grade III and 1 Grade IV breaches. Medial versus lateral breaches occurred in 30% (11/37) and 60% (22/37), respectively; 10% (4/37) of the breaches were superior. Overall, 8 (5%) vertebral body breaches occurred. Of the pedicle screws, 19 (12%) had trajectories that deviated from acceptable, with the majority being medial (16/19, 84%). Fluoroscopy time for screw placement was typically less than 20 seconds total per case. There was 1 clinically significant breach at L5 (III, medial) which resulted in a L5 radiculopathy. Kappa statistics showed excellent overall agreement between reviewers (k = 0.73-0.92; 90%-96% agreement).

CONCLUSION

The two-dimensional (2D) virtual fluoroscopy is a clinically acceptable option for percutaneous placement of pedicle screws. However, this technique requires cautious application and is particularly vulnerable to axial trajectory errors.

Triggered electromyography for placement of thoracic pedicle screws: is it reliable?

Reliable electromyography (EMG) thresholds for detecting medial breaches in the thoracic spine are lacking, and there is a paucity of reports evaluating this modality in patients with adolescent idiopathic scoliosis (AIS). This retrospective analysis evaluates the ability of triggered EMG to detect medial breaches with thoracic pedicle screws in patients with AIS. We reviewed 50 patients (937 pedicle screws) undergoing posterior spinal fusion (PSF) with intraoperative EMG testing. Postoperative CT scans were used for breach identification, and EMG values were analyzed. There were 47 medial breaches noted with a mean threshold stimulus of 10.2 mA (milliamperes). Only 8/47 breaches stimulated at 2-6 mA. Thirteen of the forty-seven screws tested at an EMG value ≤6 mA and/or a decrease of ≥65% compared with intraosseously placed screws. The sensitivity and positive predictive value for EMG was 0.28 and 0.21. A subanalysis of T10-T12 screws identified six of seven medial breaches. Using guidelines from the current literature, EMG does not appear to be reliable in detecting medial breaches from T2 to T9 but may have some utility from T10 to T12.

Clinical accuracy of three-dimensional fluoroscopy-based computer-assisted cervical pedicle screw placement: a retrospective comparative study of conventional versus computer-assisted cervical pedicle screw placement

Object

The authors performed a retrospective clinical study to evaluate the feasibility and accuracy of cervical pedicle screw (CPS) placement using 3D fluoroscopy-based navigation (3D FN).

Methods

The study involved 62 consecutive patients undergoing posterior stabilization of the cervical spine between 2003 and 2008. Thirty patients (126 screws) were treated using conventional techniques (CVTs) with a lateral fluoroscopic view, whereas 32 patients (150 screws) were treated using 3D FN. Screw positions were classified into 4 grades based on the pedicle wall perforations observed on postoperative CT.

Results

The prevalence of perforations in the CVT group was 27% (34 screws): 92 (73.0%), 12 (9.5%), 6 (4.8%), and 16 (12.7%) for Grade 0 (no perforation), Grade 1 (perforation < 1 mm), Grade 2 (perforation ≥ 1 and < 2 mm), and Grade 3 (perforation ≥ 2 mm), respectively. In the 3D FN group, the prevalence of perforations was 18.7% (28 screws): 122 (81.3%), 17 (11.3%), 6 (4%), and 5 (3.3%) for Grades 0, 1, 2, and 3, respectively. Statistical analysis showed no significant difference in the prevalence of Grade 1 or higher perforations between the CVT and 3D FN groups. A higher prevalence of malpositioned CPSs was seen in Grade 2 or higher (17.5% vs 7.3%, p < 0.05) in the 3D FN group and Grade 3 (12.7% vs 7.3%, p < 0.05) perforations in the CVT group. The ORs for CPS malpositioning in the CVT group were 2.72 (95% CI 1.16–6.39) in Grade 2 or higher perforations and 3.89 (95% CI 1.26–12.02) in Grade 3 perforations.

Conclusions

Three-dimensional fluoroscopy-based navigation can improve the accuracy of CPS insertion; however, severe CPS malpositioning that causes injury to the vertebral artery or neurological complications can occur even with 3D FN. Advanced techniques for the insertion of CPSs and the use of modified insertion devices can reduce the risk of a malpositioned CPS and provide increased safety.

Accuracy of percutaneous lumbar pedicle screw placement using the oblique or "owl's-eye" view and novel guidance technology

OBJECT

This study was conducted to assess the in vivo safety and accuracy of percutaneous lumbar pedicle screw placement using the owl's-eye view of the pedicle axis and a new guidance technology system that facilitates orientation of the C-arm into the appropriate fluoroscopic view and the pedicle cannulation tool in the corresponding trajectory.

METHODS

A total of 326 percutaneous pedicle screws were placed from L-3 to S-1 in 85 consecutive adult patients. Placement was performed using simple coaxial imaging of the pedicle with the owl's-eye fluoroscopic view. NeuroVision, a new guidance system using accelerometer technology, helped align the C-arm trajectory into the owl's-eye view and the cannulation tool in the same trajectory. Postoperative fine-cut CT scans were acquired to assess screw position. Medical records were reviewed for complications.

RESULTS

Five of 326 screws breached a pedicle cortex—all breaches were less than 2 mm—for an accuracy rate of 98.47%. Five screws violated an adjacent facet joint. All were at the S-1 superior facet and included in a fusion. No screw violated an adjacent mobile facet or disc space. There were no cases of new or worsening neurological symptoms or deficits for an overall clinical accuracy of 100%.

CONCLUSIONS

The owl's-eye technique of coaxial pedicle imaging with the C-arm fluoroscopy, facilitated by NeuroVision, is a safe and accurate means by which to place percutaneous pedicle screws for degenerative conditions of the lumbar spine. This is the largest series reported to use the oblique or owl's-eye projection for percutaneous pedicle screw insertion. The accuracy of percutaneous screw insertion with this technique meets or exceeds that of other reported clinical series or techniques.

A retrospective analysis of pedicle screws in contact with the great vessels

Object

Pedicle screws placed in the thoracic, lumbar, and sacral spine occasionally come in contact with the aorta, vena cava, or iliac vessels. When such screws are seen on postoperative imaging in an asymptomatic patient, the surgeon must decide whether it is riskier to revise the screw or to observe it. The authors hypothesized that the incidence of screw placement causing perioperative vessel injury is low and, further, that screws placed in contact with major vessels do not always result in vessel injury.

Methods

A retrospective review of the operative records of 182 consecutive patients undergoing thoracic, lumbar, and lumbosacral pedicle screw fusion was performed to determine the frequency of intraoperative vessel injury. Postoperative imaging for 107 patients was available to determine the incidence of screws in contact with major vessels. Charts were examined to determine if any adverse sequelae had resulted from malpositioned screws. Patient outcomes were documented.

Results

There were no intraoperative vessel injuries or deaths in 182 consecutive operations. One hundred seven patients with available postoperative films had 680 pedicle screws placed between T-3 and the sacrum during 115 operations. No patient had arterial screw penetration or deformation on postoperative imaging. Thirty-three of the 680 inserted screws were in contact with a major vessel on routine postoperative imaging. The contacted vessels included the aorta (4 cases), the iliac artery (7 cases), and the iliac veins (22 cases). Patients were followed up until death or November 2009, for a mean follow-up of 44 months (median 44 months, range 5–109 months). None of the patients with vessel contact was noted to suffer symptoms or sequelae as a result of vessel contact. Radiographic follow-up as long as 50 months after surgery revealed no detectable vessel abnormality at the contacted site.

Conclusions

Placing pedicle screws in contact with major vessels is a known risk of spinal surgery. The risk of repositioning a screw in contact with a major vessel but causing no symptoms must be weighed against the relative risk of leaving it in place.

Intraoperative computed tomography image-guided navigation for posterior thoracolumbar spinal instrumentation in spinal deformity surgery

OBJECT

Placement of thoracolumbar pedicle screws in spinal deformity surgery has a reported inaccuracy rate as high as 30%. At present, image-guided navigation systems designed to improve instrumentation accuracy typically use intraoperative fluoroscopy or preoperative CT scans. The authors report the prospective evaluation of the accuracy of posterior thoracolumbar spinal instrumentation using a new intraoperative CT operative suite with an integrated image guidance system. They compare the accuracy of thoracolumbar pedicle screw placement using intraoperative CT image guidance with instrumentation placement utilizing fluoroscopy.

METHODS

Between December 2007 and July 2008, 12 patients underwent posterior spinal instrumentation for spinal deformity correction using intraoperative CT-based image guidance. An intraoperative CT scan of the sterile surgical field was obtained after decompression and before instrumentation. Instrumentation was placed, and a postinstrumentation CT scan was obtained before wound closure to assess the accuracy of instrumentation placement and the potential need for revision. The accuracy of pedicle screw placement was later reviewed and recorded by independent observers. A comparison group of 14 patients who underwent thoracolumbar instrumentation utilizing fluoroscopy and postoperative CT scanning during the same time period was evaluated and included in this analysis.

RESULTS

In the intraoperative CT-based image guidance group, a total of 164 thoracolumbar pedicle screws were placed. Two screws were found to have breached the pedicle wall (1.2%). Neither screw was deemed to need revision due to misplacement. In the comparison group, 211 pedicle screws were placed. Postoperative CT scanning revealed that 11 screws (5.2%) had breached the pedicle. One patient in the fluoroscopy group awoke with a radiculopathy attributed to a misplaced screw, which required revision. The difference in accuracy was statistically significant (p = 0.031).

CONCLUSIONS

Intraoperative CT-based image guidance for placement of thoracolumbar instrumentation has an accuracy that exceeds reported rates with other image guidance systems, such as virtual fluoroscopy and 3D isocentric C-arm-based stereotactic systems. Furthermore, with the use of intraoperative CT scanning, a postinstrumentation CT scan allows the surgeon to evaluate the accuracy of instrumentation before wound closure and revise as appropriate.