Complications associated with pedicle screws

Accuracy of Pedicle Screw Placement with Robotic Guidance System: A Cadaveric Study

STUDY DESIGN

A cadaveric study.

OBJECTIVE

To investigate the accuracy of pedicle screw placement using a robotic guidance system (RGS).

SUMMARY OF BACKGROUND DATA

RGS is a unique surgery assistance-apparatus. Although several clinical studies have demonstrated that RGS provides accurate pedicle screw placement, very few studies have validated its accuracy.

METHODS

A total of 216 trajectories performed with the assistance of the RGS in eight cadavers were evaluated. The RGS was used, with different mounting platforms, to drill pilot holes in the thoracic and lumbosacral spine, using 3-mm diameter fiducial wires as trajectory markers. Deviation between the preoperative plan and executed trajectories was measured at the entry points to the vertebrae and at a depth of 30 mm along the wire. Both the deviation from the preoperative plan and the wire position were evaluated in the axial and sagittal planes using computed tomography (CT).

RESULTS

The average deviation from the planned wire placement was 0.64 ± 0.59 mm at the entry point and 0.63 ± 0.57 mm at a depth of 30 mm in the axial plane, and 0.77 ± 0.62 mm and 0.80 ± 0.66 mm, respectively, in the sagittal plane. The magnitude of deviation was not affected by the vertebral level or the platform used. The use of an open approach achieved greater screw placement accuracy at a depth of 30 mm in the sagittal plane, compared with the percutaneous approach. The fiducials were placed completely within the pedicle in 93.9% of trajectories in the axial plane (n = 164 pedicles with a width ≥5 mm) and 98.6% in the sagittal plane (n = 216).

CONCLUSION

In this cadaveric study, RGS supported execution of accurate trajectories that were equal or slightly superior to reports of CT-based navigation systems.

LEVEL OF EVIDENCE

N/A.

Imaging of lumbar spinal surgery complications

Abstract

Lumbar spine surgery for spinal stenosis is a frequently performed procedure and was the fastest growing type of surgery in the US from 1980 to 2000. With increasing surgical invasiveness, postoperative complications also tend to be higher. Cross-sectional imaging techniques (CT and MRI) are more sensitive than radiographs and play an increasingly important role in evaluation of patients with lumbar spine surgery. Their use in patients with metallic implants is somewhat limited by artefacts, which can obscure pathology and decrease accuracy and reader confidence. Metal artefact reduction techniques have been developed, which can significantly improve image quality and enable early detection of postoperative complications. Complications can occur throughout postoperative course. Early complications include hardware displacement, incidental durotomy, postoperative collections—most commonly seroma, and less likely haematoma and/or infection. Incidental durotomy with CSF leak causing intracranial hypotension has characteristic MR brain findings and diagnosis of occult leak sites have been improved with use of dynamic CT myelography. Haematomas, even when compressing the thecal sac, are usually asymptomatic. Early infection, with nonspecific MR findings, can be diagnosed accurately using dual radiotracer studies. Delayed complications include loosening, hardware failure, symptomatic new or recurrent disc herniation, peri-/epidural fibrosis, arachnoiditis, and radiculitis.

Teaching Points

• CT and MRI play an increasingly important role in evaluation of patients with lumbar spine surgery

• Complications can occur throughout the postoperative course and early detection is critical

• Artefact reduction techniques can improve image quality for early and improved detection of complications

Biomechanical evaluation of pedicle screw loosening mechanism using synthetic bone surrogate of various densities

Pedicle screw fixation is a well-established procedure for various spinal disorders. However, pedicle screws failures are still reported. Therefore, there is a need for a greater understanding of the pedicle screw failure mechanism. This experimental study investigates the biomechanical stability of pedicle screws using a synthetic bone surrogate with a special focus on the screw loosening mechanism. Pedicle screws have been inserted in thirty six polyurethane foam blocks of three different densities. In half of the specimens from each density group, pedicle screws were submitted to cyclic bending (toggling) before pullout. The rest of specimens were solely loaded in axial pullout. The peak pullout force and stiffness were determined from load-displacement curve of each specimen. Statistical analyses were performed to investigate on the effect of toggling and bone surrogate density on the pedicle screw's pullout force. The results suggest that the pullout force and stiffness were significantly affected by toggling and density. Higher pullout forces resulted from higher grades of density. The proposed method allowed investigating the pedicle screw loosening mechanism. However, conducing further experimental tests on animal or cadaveric vertebrae are needed to confirm these findings.

Cortical Bone Trajectory for Lumbar Pedicle Screw Placement: A Review of Published Reports

There have been a number of developments in screw design and implantation techniques over recent years, including proposal of an alternative trajectory for screw fixation aimed at increasing purchase of pedicle screws in higher density bone. Cortical bone trajectory (CBT) screw insertion follows a lateral path in the transverse plane and caudocephalad path in the sagittal plane. This technique has been advocated because it is reportedly less invasive, improves screw-bone purchase and reduces neurovascular injury; however, these claims have not been supported by robust clinical evidence. The available evidence was therefore reviewed to assess the relative merits of CBT and highlight areas for further research. To this end, a search of relevant published studies reporting biomechanical, morphometric or clinical outcomes after use of CBT screws in patients with spinal pathologies was performed via six electronic databases.

Pedicle Screw Placement in the Thoracolumbar Spine Using a Novel, Simple, Safe, and Effective Guide-Pin : A Computerized Tomography Analysis

Objective

To improve pedicle screw placement accuracy with minimal radiation and low cost, we developed specially designed K-wire with a marker. To evaluate the accuracy of thoracolumbar pedicle screws placed using the novel guide-pin and portable X-rays.

Methods

Observational cohort study with computerized tomography (CT) analysis of in vivo and in vitro pedicle screw placement. Postoperative CT scans of 183 titanium pedicle screws (85 lumbar and 98 thoracic from T1 to L5) placed into 2 cadavers and 18 patients were assessed. A specially designed guide-pin with a marker was inserted into the pedicle to identify the correct starting point (2 mm lateral to the center of the pedicle) and aiming point (center of the pedicle isthmus) in posteroanterior and lateral X-rays. After radiographically confirming the exact starting and aiming points desired, a gearshift was inserted into the pedicle from the starting point into the vertebral body through the center of pedicle isthmus.

Results

Ninety-nine percent (181/183) of screws were contained within the pedicle (total 183 pedicle screws : 98 thoracic pedicle screws and 85 lumbar screws). Only two of 183 (1.0%) thoracic pedicle screws demonstrated breach (1 lateral in a patient and 1 medial in a cadaver specimen). None of the pedicle breaches were associated with neurologic or other clinical sequelae.

Conclusion

A simple, specially designed guide-pin with portable X-rays can provide correct starting and aiming points and allows for accurate pedicle screw placement without preoperative CT scan and intraoperative fluoroscopic assistance.

A New Electromagnetic Navigation System for Pedicle Screws Placement: A Human Cadaver Study at the Lumbar Spine

Introduction

Technical developments for improving the safety and accuracy of pedicle screw placement play an increasingly important role in spine surgery. In addition to the standard techniques of free-hand placement and fluoroscopic navigation, the rate of complications is reduced by 3D fluoroscopy, cone-beam CT, intraoperative CT/MRI, and various other navigation techniques. Another important aspect that should be emphasized is the reduction of intraoperative radiation exposure for personnel and patient.

The aim of this study was to investigate the accuracy of a new navigation system for the spine based on an electromagnetic field.

Material and Method

Twenty pedicle screws were placed in the lumbar spine of human cadavers using EMF navigation. Navigation was based on data from a preoperative thin-slice CT scan. The cadavers were positioned on a special field generator and the system was matched using a patient tracker on the spinous process. Navigation was conducted using especially developed instruments that can be tracked in the electromagnetic field. Another thin-slice CT scan was made postoperatively to assess the result. The evaluation included the position of the screws in the direction of trajectory and any injury to the surrounding cortical bone. The results were classified in 5 groups: grade 1: ideal screw position in the center of the pedicle with no cortical bone injury; grade 2: acceptable screw position, cortical bone injury with cortical penetration ≤ 2 mm; grade 3: cortical bone injury with cortical penetration 2,1-4 mm, grad 4: cortical bone injury with cortical penetration 4,1-6 mm, grade 5: cortical bone injury with cortical penetration >6 mm.

Results

The initial evaluation of the system showed good accuracy for the lumbar spine (65% grade 1, 20% grade 2, 15% grade 3, 0% grade 4, 0% grade 5). A comparison of the initial results with other navigation techniques in literature (CT navigation, 2D fluoroscopic navigation) shows that the accuracy of this system is comparable.

Conclusion

EMF navigation offers a high accuracy in Pedicle screw placement with additional advantages compared to other techniques. The short set-up time and easy handling of EMF navigation should be emphasized. Additional advantages are the absence of intraoperative radiation exposure for the operator and surgical team in the current set-up and the operator’s free mobility without interfering with navigation. Further studies with navigation at higher levels of the spine, larger numbers of cases and studies with control group are planned.

Implant distribution in surgically instrumented Lenke 1 adolescent idiopathic scoliosis: does it affect curve correction?

STUDY DESIGN

Retrospective review of prospective multicenter database of patients with adolescent idiopathic scoliosis who underwent posterior spinal fusion.

OBJECTIVE

To analyze implant distribution in surgically instrumented Lenke 1 patients and evaluate how it impacts curve correction.

SUMMARY OF BACKGROUND DATA

Although pedicle screw constructs have demonstrated successful surgical results, the optimal pedicle screw density and configuration remain unclear.

METHODS

A total of 279 patients with adolescent idiopathic scoliosis treated with pedicle screws were reviewed. Implant density was computed for each side of the instrumented segment, which was divided into 5 regions: distal and proximal ends (upper/lower instrumented vertebra +1 adjacent vertebra), apical region (apex ± 1 vertebra), and the 2 regions in between (upper/lower periapical). Centralized measurement of Cobb angle and thoracic kyphosis was performed on preoperative and at 1-year postoperative radiographs as well as percent curve flexibility.

RESULTS

The mean implant density was 1.66 implants per level fused (1.08 to 2) with greater available pedicles filled on the concavity (92%, 53%-100%) compared with the convex side (73%, 23%-100%, P < 0.01). The concave distal end region had the highest density with 99% of pedicles filled (P < 0.01), followed by the other concave regions and the convex distal end region (88%-94%) (P > 0.05). Other convex regions of the construct had less instrumentation, with only 54% to 78% of pedicles instrumented (P < 0.01). Implant density in the concave apical region (69%, 23%-100%) had a positive effect on curve correction (P = 0.002, R = 0.19).

CONCLUSION

Significant variability exists in implant distribution with the greatest variation on the convex side and lowest implant density used in the periapical convex regions. Only instrumentation at the concave side, particularly at the apical region, was associated with curve correction. This suggests that for a low implant density construct, the best regions for planned screw dropout may be in the periapical convexity.

LEVEL OF EVIDENCE

3.

Computer-aided surgery does not increase the accuracy of dorsal pedicle screw placement in the thoracic and lumbar spine: a retrospective analysis of 2,003 pedicle screws in a level I trauma center

Study Design A retrospective analysis of a prospective database. Objective Meta-analyses suggest that computer-assisted systems can increase the accuracy of pedicle screw placement for dorsal spinal fusion procedures. The results of further meta-analyses report that in the thoracic spine, both the methods have comparable placement accuracy. These studies are limited due to an abundance of screw classification systems. The aim of this study was to assess the placement accuracy and potentially influencing factors of three-dimensionally navigated versus conventionally inserted pedicle screws. Methods This was a retrospective analysis of a prospective database at a level I trauma center of pedicle screw placement (computer-navigated versus traditionally placed) for dorsal spinal stabilizations. The cases spanned a 5.5-year study period (January 1, 2005, to June 30, 2010). The perforations of the pedicle were differentiated in three grades based on the postoperative computed tomography. Results The overall placement accuracy was 86% in the conventional group versus 79% in the computer-navigated group (grade 0). The computer-navigated procedures were superior in the lumbar spine and the conventional procedures were superior in the thoracic spine, but both failed to be of statistical significance. The level of experience of the performing surgeon and the patient's body mass index did not influence the placement accuracy. The only significant influence was the spinal segment: the higher the spinal level where the fusion was performed, the more likely the screw was displaced. Conclusions The computer-navigated and conventional methods are both safe procedures to place transpedicular screws at the traumatized thoracic and lumbar spine. At the moment, three-dimensionally based navigation does not significantly increase the placement accuracy.

Safety and Efficacy of Power-Assisted Pedicle Tract Preparation and Screw Placement

STUDY DESIGN

Retrospective review of 1 surgeon's posterior spinal fusion cases.

OBJECTIVES

To assess the safety and efficacy of using power tools versus using manual tools to create pedicle tracts and place pedicle screws.

SUMMARY OF BACKGROUND DATA

This is the first study to report on the safety and efficacy of pedicle tract creation and pedicle screw placement using power tools.

METHODS

The study included 442 cases and 6412 pedicle screws. The manual tool cohort included 159 cases (1,870 screws, January 1, 2004 to June 30, 2007). The power tool cohort included 283 cases (4,542 screws, January 1, 2008 to August 29, 2012). Patient charts and radiographs were reviewed. The researchers recorded the number of screws placed and their positions. Screws were classified as failed if the patient returned to surgery for revision or removal of the screw. Operating and fluoroscopy times were analyzed by cohort overall and for diagnosis-specific subsets.

RESULTS

The incidence of injury resulting from pedicle screw placement was 0.00% (0 of 1,870) with the manual method and 0.02% (1 of 4,542) with power (p = .5211). One screw, placed with power, was assumed to have caused a minor hemothorax, which was successfully treated with a chest tube. There were no neurologic or vascular injuries or other complications attributable to a pedicle screw in either group. Screws placed with power were removed or revised because of problems attributable to the pedicle screw one-sixth as often as those placed using manual tools: 2 of 1,410 (0.14%) versus 8 of 948 (0.84%) (p = .024). Fluoroscopy times in the power cohort were two-thirds as long as those in the manual cohort (p < .001). Operating times were not significantly different (p = .109).

CONCLUSIONS

The use of power tools to create pedicle tracts and place pedicle screws was associated with shorter fluoroscopy times and a lower revision rate compared with using manual tools. Both techniques posed similar low risks of injury to the patient.

Evaluation of the Effect of Fixation Angle between Polyaxial Pedicle Screw Head and Rod on the Failure of Screw-Rod Connection

Introduction. Polyaxial screws had been only tested according to the ASTM standards (when they were perpendicularly positioned to the rod). In this study, effects of the pedicle screws angled fixation to the rod on the mechanical properties of fixation were investigated. Materials and Method. 30 vertically fixed screws and 30 screws fixed with angle were used in the study. Screws were used in three different diameters which were 6.5 mm, 7.0 mm, and 7.5 mm, in equal numbers. Axial pull-out and flexion moment tests were performed. Test results compared with each other using appropriate statistical methods. Results. In pull-out test, vertically fixed screws, in 6.5 mm and 7.0 mm diameter, had significantly higher maximum load values than angled fixed screws with the same diameters (P < 0.01). Additionally, vertically fixed screws, in all diameters, had significantly greater stiffness according to corresponding size fixed with angle (P < 0.005). Conclusion. Fixing the pedicle screw to the rod with angle significantly decreased the pull-out stiffness in all diameters. Similarly, pedicle screw instrumentation fixed with angle decreased the minimum sagittal angle between the rod and the screw in all diameters for flexion moment test but the differences were not significant.

Navigation of pedicle screws in the thoracic spine with a new electromagnetic navigation system: a human cadaver study

INTRODUCTION

Posterior stabilization of the spine is a standard procedure in spinal surgery. In addition to the standard techniques, several new techniques have been developed. The objective of this cadaveric study was to examine the accuracy of a new electromagnetic navigation system for instrumentation of pedicle screws in the spine.

MATERIAL AND METHOD

Forty-eight pedicle screws were inserted in the thoracic spine of human cadavers using EMF navigation and instruments developed especially for electromagnetic navigation. The screw position was assessed postoperatively by a CT scan.

RESULTS

The screws were classified into 3 groups: grade 1 = ideal position; grade 2 = cortical penetration <2 mm; grade 3 = cortical penetration ≥2 mm. The initial evaluation of the system showed satisfied positioning for the thoracic spine; 37 of 48 screws (77.1%, 95% confidence interval [62.7%, 88%]) were classified as group 1 or 2.

DISCUSSION

The screw placement was satisfactory. The initial results show that there is room for improvement with some changes needed. The ease of use and short setup times should be pointed out. Instrumentation is achieved without restricting the operator's mobility during navigation.

CONCLUSION

The results indicate a good placement technique for pedicle screws. Big advantages are the easy handling of the system.

Surgical treatment of the osteoporotic spine with bone cement-injectable cannulated pedicle screw fixation: technical description and preliminary application in 43 patients

OBJECTIVES

To describe a new approach for the application of polymethylmethacrylate augmentation of bone cement-injectable cannulated pedicle screws.

METHODS

Between June 2010 and February 2013, 43 patients with degenerative spinal disease and osteoporosis (T-score <-2.5) underwent lumbar fusion using cement-injectable cannulated pedicle screws. Clinical outcomes were evaluated using a Visual Analog Scale and the Oswestry Disability Index. Patients were given radiographic follow-up examinations after 3, 6, and 12 months and once per year thereafter.

RESULTS

All patients were followed for a mean of 15.7 ± 5.6 months (range, 6 to 35 months). The Visual Analog Scale and Oswestry Disability Index scores showed a significant reduction in back pain (p = 0.018) and an improvement in lower extremity function (p = 0.025) in patients who underwent lumbar fusion using the novel screw. Intraoperative cement leakage occurred in four patients, but no neurological complications were observed. Radiological observation indicated no loosening or pulling out of the novel screw, and bone fusion was excellent.

CONCLUSIONS

The described polymethylmethacrylate augmentation technique using bone cement-injectable cannulated pedicle screws can reduce pain and improve spinal dysfunction in osteoporotic patients undergoing osteoporotic spine surgery.

Comparison of open and percutaneous lumbar pedicle screw revision rate using 3-D image guidance and intraoperative CT

Complications arising from a malpositioned screw can be both devastating and costly. The incidence of neurologic injury secondary to a malpositioned screw is reported to be as high as 7% to 12%. The advancement of image-guided technology has allowed surgeons to place screws more accurately and confirm correct placement prior to leaving the operating room. Only a small number of studies have examined image-guided pedicle screw accuracy in terms of intraoperative revision and reoperation rates. The purpose of this study was to determine the intraoperative revision and return to surgery rates for navigated lumbar pedicle screws and to compare navigated open and percutaneous techniques. The authors reviewed 199 cases of 3-dimensional image-guided lumbar pedicle screw instrumentation from November 2006 to December 2011. Screw or K-wire removal, repositioning, or eventual abandonment of insertion were noted. Chi-square test was used to determine statistical significance in rates between the 2 groups (alpha=0.05). The authors also noted return to surgery secondary to complications from a malpositioned screw. The overall intraoperative revision rate of navigated lumbar pedicle screws was 4.6%. There were significantly more revisions in the percutaneously inserted screws (7.5%) than with the open technique (2.7%) (P=.0004). If K-wire revisions are excluded, there was no statistically significant difference in intraoperative revision rates between the percutaneous and open groups (2.1% vs 2.7%, respectively) (P=.0004). No patients underwent reoperation for a malpositioned screw. This technology has virtually eliminated the need for reoperation for screw malposition. It may suggest a more cost-effective way of preventing neurovascular injuries and revision surgeries.

Skipped versus consecutive pedicle screw constructs for correction of Lenke 1 curves

PURPOSE

Thoracic pedicle screws provide superior curve correction to hook and wire constructs in adolescent idiopathic scoliosis, while increasing cost. The number of implants required for best correction and outcome has not yet been determined.

METHODS

We retrospectively reviewed pre- and post-operative radiographs and self-reported outcome measures in an age- and curve-matched cohort of 40 patients with Lenke I AIS who underwent selective fusions between T3/4 and L1. Twenty patients were treated with thoracic pedicle screws at every level bilaterally (CON) and 20 patients with screws at every level on the concave side and skipped levels on the convex side of the curve (SKP). All patients had a minimum 2-year follow-up. Radiographs were assessed for coronal and sagittal curvatures, as well as thoracic torsion and vertebral rotation. Health-related quality of life was assessed using the SRS-22 instrument. Instrumentation cost data were collected for each case.

RESULTS

Postoperative follow-up averaged 28 months for the CON group and 29 months for the SKP group. No statistically significant differences were found between groups with respect to age and pre- and post-operative radiographic parameters. Both constructs provided acceptable correction of the main thoracic curves (66.9 vs. 66.6 %, CON group and SKP group, respectively; p = 0.92), and spontaneous correction of the proximal thoracic (41.5 vs. 41.1 %; p = 0.92) and thoracolumbar/lumbar curves (54.8 vs. 54.3 %; p = 0.92). No significant difference was found in postoperative SRS-22 scores (96 vs. 94.3; p = 0.34). The CON group cost for instrumentation was significantly higher than the SKP group ($19,500 vs. $13,300; p = 0.002). There was no statistically significant difference in operating room times between groups.

CONCLUSION

Both construct types provide excellent coronal correction and sagittal balance, with no significant differences in radiographic findings or clinical outcomes. A significant decrease in cost was found with use of skipped screw constructs.

Imaging of lumbar spine fusion

This article reviews the imaging of lumbar spinal fusion and its major indications. The most common procedures are described for the purpose of allowing understanding of postoperative imaging. Imaging options are reviewed for preoperative workup, intraoperative guidance, and postoperative purposes. Examples of hardware integrity, fusion, and loosening are provided.

Management of thoracolumbar spine trauma: An overview

Thoracolumbar spine fractures are common injuries that can result in significant disability, deformity and neurological deficit. Controversies exist regarding the appropriate radiological investigations, the indications for surgical management and the timing, approach and type of surgery. This review provides an overview of the epidemiology, biomechanical principles, radiological and clinical evaluation, classification and management principles. Literature review of all relevant articles published in PubMed covering thoracolumbar spine fractures with or without neurologic deficit was performed. The search terms used were thoracolumbar, thoracic, lumbar, fracture, trauma and management. All relevant articles and abstracts covering thoracolumbar spine fractures with and without neurologic deficit were reviewed. Biomechanically the thoracolumbar spine is predisposed to a higher incidence of spinal injuries. Computed tomography provides adequate bony detail for assessing spinal stability while magnetic resonance imaging shows injuries to soft tissues (posterior ligamentous complex [PLC]) and neurological structures. Different classification systems exist and the most recent is the AO spine knowledge forum classification of thoracolumbar trauma. Treatment includes both nonoperative and operative methods and selected based on the degree of bony injury, neurological involvement, presence of associated injuries and the integrity of the PLC. Significant advances in imaging have helped in the better understanding of thoracolumbar fractures, including information on canal morphology and injury to soft tissue structures. The ideal classification that is simple, comprehensive and guides management is still elusive. Involvement of three columns, progressive neurological deficit, significant kyphosis and canal compromise with neurological deficit are accepted indications for surgical stabilization through anterior, posterior or combined approaches.

Effects of rod reduction on pedicle screw fixation strength in the setting of Ponte osteotomies

BACKGROUND CONTEXT

The use of a rod reduction device can have deleterious consequences on pedicle screw pullout strength (POS) in the thoracic spine. However, posterior-only osteotomies in the thoracic spine are often performed to improve flexibility of the spine and offset forces of deformity correction maneuvers.

PURPOSE

To investigate the effect on pedicle screw POS caused by the rod reduction technique in the presence of facet osteotomies in the thoracic spine.

STUDY DESIGN/SETTING

The study is a biomechanical study using human cadaveric spine specimens.

METHODS

Thoracic Ponte osteotomies were performed on 3 thoracic levels in 15 cadaveric specimens. The right rod was contoured with a 5-mm residual gap at the middle level and was reduced using a rod reduction device. On the left side (paired control), a rod with no mismatch was placed. Biomechanical testing was performed with tensile load to failure "in line" with the screw axis and POS measured in Newtons (N).

RESULTS

After rod reduction, thoracic pedicle screw POS was significantly decreased (40%) compared with the control (419±426 N vs. 708±462 N, p=.002) and remained statistically significant after adjusting for bone mineral density (BMD) (p=.05). Eleven (73%) of the pedicle screws had visible pullout/failure during the reduction attempt and occurred irrespective of BMD.

CONCLUSIONS

Despite thoracic Ponte osteotomies and increased flexibility of the spinal segments, the rod reduction device still significantly decreased pedicle screw POS, typically resulting in outright failure of the screw-bone interface. Therefore, rod reduction technique of any kind should be performed with caution as it frequently results in suboptimal pedicle screw fixation.

Three-dimensional Intraoperative Imaging Modalities in Orthopaedic Surgery: A Narrative Review

Intraoperative imaging and navigation systems have revolutionized orthopaedic surgery for the spine, joints, and orthopaedic trauma. Imaging modalities such as the isocentric C-arm, O-arm imaging, and intraoperative MRI or navigation systems allow the visualization of surgical instruments and implants relative to a three-dimensional CT image or MRI. Studies show that these technologies lower the rates of implant misplacement and inadequate fracture reduction, thereby improving surgical outcomes and reducing reoperation rates. An additional benefit is reduced radiation exposure compared with that for conventional fluoroscopy. Concerns surrounding adoption of these technologies include cost and increased operating times, but improvements in design and protocol may improve the integration of these imaging modalities into the operating room.

Percutaneous posterior transdiscal oblique screw fixation with lateral interbody fusion: a radiological and cadaveric study

PURPOSE

To design and investigate a novel technique of percutaneous posterior transdiscal oblique screw fixation with lateral interbody fusion.

METHODS

CT scans of 45 patients were collected and imported into Mimics software for three-dimensional (3D) reconstruction. Cylinders were drawn to simulate the trajectory of the oblique screw. Six measurements were obtained for each unit to design a right size cage: a the distance between the intersection of the simulated trajectory of the screw with the inferior border of the upper vertebra and its anteroinferior corner; b the distance between the intersection of the simulated trajectory of the screw with the superior border of the inferior vertebra and its anterosuperior corner; h the height of the intervertebral space; θ the angle between simulated trajectory of screw and the upper endplate of inferior vertebra; uw: the width of the inferior endplate of upper vertebra; iw: the width of upper endplate of inferior vertebra. Three intact adult fresh-frozen cadaveric specimens were obtained, percutaneous posterior transdiscal oblique screw fixation was performed under X-ray apparatus, and interbody cage was implanted by assistance with special self-retaining retractor system and endoscope.

RESULTS

According to the results of data measured from 3D images, trapezoid shape interbody cages with suitable size were designed. Percutaneous posterior oblique screw fixation with lateral interbody fusion was performed on three cadaveric specimens successfully.

CONCLUSION

Using specially designed trapezoid shape interbody cages, assisted by intra-operative image intensification and endoscope, it is feasible to perform percutaneous posterior transdiscal oblique screw fixation with lateral interbody fusion technique.

A novel anchoring system for use in a nonfusion scoliosis correction device

BACKGROUND CONTEXT

Insertion of a pedicle screw in the mid- and high thoracic regions has a serious risk of facet joint damage. Because flexible implant systems require intact facet joints, we developed an enhanced fixation that is less destructive to spinal structures. The XSFIX is a posterior fixation system that uses cables that are attached to the transverse processes of a vertebra.

PURPOSE

To determine whether a fixation to the transverse process using the XSFIX is strong enough to withstand the loads applied by the XSLATOR (a novel, highly flexible nonfusion implant system) and thus, whether it is a suitable alternative for pedicle screw fixation.

STUDY DESIGN

The strength of a novel fixation system using transverse process cables was determined and compared with the strength of a similar fixation using polyaxial pedicle screws on different vertebral levels.

METHODS

Each of the 58 vertebrae, isolated from four adult human cadavers, was instrumented with either a pedicle screw anchor (PSA) system or a prototype of the XSFIX. The PSA consisted of two polyaxial pedicle screws and a 5 mm diameter rod. The XSFIX prototype consisted of two bodies that were fixed to the transverse processes, interconnected with a similar rod. Each fixation system was subjected to a lateral or an axial torque.

RESULTS

The PSA demonstrated fixation strength in lateral loading and torsion higher than required for use in the XSLATOR. The XSFIX demonstrated high enough fixation strength (in both lateral loading and torsion), only in the high and midthoracic regions (T10-T12).

CONCLUSIONS

This experiment showed that the fixation strength of XSFIX is sufficient for use with the XSLATOR only in mid- and high thoracic regions. For the low thoracic and lumbar region, the PSA is a more rigid fixation. Because the performance of the new fixation system appears to be favorable in the high and midthoracic regions, a clinical study is the next challenge.

CT-Guided Transfacet Pedicle Screw Fixation in Facet Joint Syndrome: A Novel Approach

Axial microinstability secondary to disc degeneration and consequent chronic facet joint syndrome (CFJS) is a well-known pathological entity, usually responsible for low back pain (LBP). Although posterior lumbar fixation (PIF) has been widely used for lumbar spine instability and LBP, complications related to wrong screw introduction, perineural scars and extensive muscle dissection leading to muscle dysfunction have been described. Radiofrequency ablation (RFA) of facet joints zygapophyseal nerves conventionally used for pain treatment fails in approximately 21% of patients. We investigated a "covert-surgery" minimal invasive technique to treat local spinal instability and LBP, using a novel fully CT-guided approach in patients with axial instability complicated by CFJS resistant to radioablation, by introducing direct fully or partially threaded transfacet screws (transfacet fixation - TFF), to acquire solid arthrodesis, reducing instability and LBP. The CT-guided procedure was well tolerated by all patients in simple analogue sedation, and mean operative time was approximately 45 minutes. All eight patients treated underwent clinical and CT study follow-up at two months, revealing LBP disappearance in six patients, and a significant reduction of lumbar pain in two. In conclusion, CT-guided TFF is a fast and safe technique when facet posterior fixation is needed.

Accuracy of pedicle screw insertion using fluoroscopy-based navigation-assisted surgery : computed tomography postoperative assessment in 96 consecutive patients

Objective

Two-dimensional fluoroscopy-based computerized navigation for the placement of pedicle screws offers the advantage of using stored patient-specific imaging data in providing real-time guidance during screw placement. The study aimed to describe the accuracy and reliability of a fluoroscopy-based navigation system for pedicle screw insertion.

Methods

A total of 477 pedicle screws were inserted in the lower back of 96 consecutive patients between October 2007 and June 2012 using fluoroscopy-based computer-assisted surgery. The accuracy of screw placement was evaluated using a sophisticated computed tomography protocol.

Results

Of the 477 pedicle screws, 461 (96.7%) were judged to be inserted correctly. Frank screw misplacement [16 screws (3.3%)] was observed in 15 patients. Of these, 8 were classified as minimally misplaced (≤2 mm); 3, as moderately misplaced (2.1-4 mm); and 5, as severely misplaced (>4 mm). No complications, including nerve root injury, cerebrospinal fluid leakage, or internal organ injury, were observed in any of the patients.

Conclusion

The accuracy of pedicle screw placement using a fluoroscopy-based computer navigation system was observed to be superior to that obtained with conventional techniques.

Pedicle screw reinsertion using previous pilot hole and trajectory does not reduce fixation strength

STUDY DESIGN

Fresh-frozen human cadaveric biomechanical study.

OBJECTIVE

To evaluate the biomechanical consequence of pedicle screw reinsertion in the thoracic spine.

SUMMARY OF BACKGROUND DATA

During pedicle screw instrumentation, abnormal appearance on fluoroscopic imaging or low current reading with intraoperatively evoked electromyographic stimulation of a pedicle screw warrants complete removal to reassess for pedicle wall violation or screw malposition. However, screw fixation strength has never been evaluated biomechanically after reinsertion using a previous pilot hole and trajectory.

METHODS

Thirty-one thoracic individual fresh-frozen human cadaveric vertebral levels were instrumented bilaterally with 5.5-mm titanium polyaxial pedicle screws, and insertional torque (IT) was measured with each revolution. A paired comparison was performed for each level. Screw reinsertion was performed by completely removing the pedicle screw, palpating the tract, and then reinserting along the same trajectory. Screws were tensile loaded to failure "in-line" with the screw axis.

RESULTS

There was no significant difference for pedicle screw pullout strength (POS) between reinserted and control screws (732 ± 307 N vs. 742 ± 320 N, respectively; P = 0.78). There was no significant difference in IT between initial insertion for the test group (INI) (0.82 ± 0.40 N·m) and control (0.87 ± 0.50 N·m) (P = 0.33). IT for reinserted screws (0.58 ± 0.47 N·m) had significantly decreased compared with INI and control screws (29% decrease, P = 0.00; 33% decrease, P = 0.00, respectively). The test group screws in the thoracic spine had significant correlations between initial IT and POS (r = 0.79, P = 0.00), and moderate correlations between reinsertion IT and POS in the thoracic spine (r = 0.56, P = 0.00).

CONCLUSION

Despite a significant reduction in pedicle screw IT, there was no significant difference in pedicle screw POS with reinsertion. Therefore, when surgeons must completely remove a pedicle screw for tract inspection, reinsertion along the same trajectory may be performed without significantly compromising fixation strength.

LEVEL OF EVIDENCE

N/A.

Forces in spinal cannulation and breaches ex vivo

BACKGROUND

Pedicle screw insertion, to stabilize or correct the spine, relies on creating a probe path with the correct trajectory to prevent unsafe breaching of the cortical wall. Safe pedicle cannulation is aided when the surgeon can feel the difference between a safe and unsafe path. Pedicle probe forces and torques are currently unknown. The purpose of this study was to investigate the forces and torques encountered while cannulating the pedicle tract in both correct and incorrect cannulations.

METHODS

Two experienced surgeons used a standard lumbar probe modified to incorporate a 6 degree-of-freedom load cell to cannulate and breach the T12 to S1 vertebrae of six fresh frozen cadavers (3 males, 3 females, ages 65 to 92). A total of 76 pedicles were tested.

FINDINGS

Cannulation axial forces averaged 48 N (standard deviation = 13 N), medial breach 129 N (standard deviation = 25 N), and lateral breach 86 N (standard deviation = 27 N). Cannulation values were significantly lower than the breach values in all 6 degrees of freedom (p < 0.001). There were significant differences between specimens, including males and females, and between degrees of freedom, but no significant right and left differences or by vertebral level.

CONCLUSION

A large range of cannulation and breach forces and torques were measured due to variations in bone quality and geometry, as experienced clinically. This is the first time that the absolute and relative force and torque levels have been reported, to our knowledge.

Influence of the screw augmentation technique and a diameter increase on pedicle screw fixation in the osteoporotic spine: pullout versus fatigue testing

PURPOSE

For posterior spinal stabilization, loosening of pedicle screws at the bone-screw interface is a clinical complication, especially in the osteoporotic population. Axial pullout testing is the standard pre-clinical testing method for new screw designs although it has questioned clinical relevance. The aim of this study was to determine the fixation strength of three current osteoporotic fixation techniques and to investigate whether or not pullout testing results can directly relate to those of the more physiologic fatigue testing.

METHODS

Thirty-nine osteoporotic, human lumbar vertebrae were instrumented with pedicle screws according to four treatment groups: (1) screw only (control), (2) prefilled augmentation, (3) screw injected augmentation, and (4) unaugmented screws with an increased diameter. Toggle testing was first performed on one pedicle, using a cranial-caudal sinusoidal, cyclic (1.0 Hz) fatigue loading applied at the screw head. The initial compressive forces ranged from 25 to 75 N. Peak force increased stepwise by 25 N every 250 cycles until a 5.4-mm screw head displacement. The contralateral screw then underwent pure axial pullout (5 mm/min).

RESULTS

When compared to the control group, screw injected augmentation increased fatigue force (27 %, p = 0.045) while prefilled augmentation reduced fatigue force (-7 %, p = 0.73). Both augmentation techniques increased pullout force compared to the control (ps < 0.04). Increasing the screw diameter by 1 mm increased pullout force (24 %, p = 0.19), fatigue force (5 %, p = 0.73), and induced the least stiffness loss (-29 %) from control.

CONCLUSIONS

For the osteoporotic spine, screw injected augmentation showed the best biomechanical stability. Although pullout testing was more sensitive, the differences observed were not reflected in the more physiological fatigue testing, thus casting further doubt on the clinical relevance of pullout testing.

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.

Intraoperative three-dimensional fluoroscopy after transpedicular positioning of Kirschner-wire versus conventional intraoperative biplanar fluoroscopic control: A retrospective study of 345 patients and 1880 pedicle screws

STUDY DESIGN

Retrospective study.

OBJECTIVE

The aim was to find out whether intraoperative three-dimensional imaging after transpedicular positioning of Kirschner wire (K-wire) in lumbar and thoracic posterior instrumentation procedures is of benefit to the patients and if this technique is accurately enough to make a postoperative screw position control through computer tomography (CT) dispensable.

PATIENTS AND METHODS

Lumbar and thoracic posterior instrumentation procedures conducted at our department between 2002 and 2012 were retrospectively reviewed. The patients were divided into two groups: group A, including patients who underwent intraoperative three-dimensional scan after transpedicular positioning of the K-wire and group B, including patients who underwent only intraoperative biplanar fluoroscopy. An early postoperative CT of the instrumented section was done in all cases to assess the screw position. The rate of immediate intraoperative correction of the K-wires in cases of mal-positioning, as well as the rate of postoperative screw revisions, was measured.

RESULTS

In general, 345 patients (1880 screws) were reviewed and divided into two groups; group A with 225 patients (1218 screws) and group B with 120 patients (662 screws). One patient (0.44%) (one screw [0.082%]) of group A underwent postoperative screw correction while screw revisions were necessary in 14 patients (11.7%) (28 screws [4.2%]) of group B. Twenty-three patients (10.2%) (28 K-wires [2.3%]) of group A underwent intraoperative correction due to primary intraoperative detected K-wire mal-position. None of the corrected K-wires resulted in a corresponding neurological deficit.

CONCLUSION

Three-dimensional imaging after transpedicular K-wire positioning leads to solid intraoperative identification of misplaced K-wires prior to screw placement and reduces screw revision rates compared with conventional fluoroscopic control. When no clinical deterioration emerges, a postoperative CT seems to be dispensable using this intraoperative three-dimensional control method.

Circumferential management of unstable thoracolumbar fractures using an anterior expandable cage, as an alternative to an iliac crest graft, combined with a posterior screw fixation: results of a series of 85 patients

Object

The optimal management of unstable thoracolumbar fractures remains unclear. The objective of the present study was to evaluate the results of using an expandable prosthetic vertebral body cage (EPVBC) in the management of unstable thoracolumbar fractures.

Methods

Eighty-five patients with unstable T7–L4 thoracolumbar fractures underwent implantation of an EPVBC via an anterior approach combined with posterior fixation. Long-term functional outcomes, including visual analog scale and Oswestry disability index scores, were evaluated.

Results

In a mean follow-up period of 16 months, anterior fixation led to a significant increase in vertebral body height, with an average gain of 19%. However, the vertebral regional kyphosis angle was not significantly increased by anterior fixation alone. No significant difference was found between early postoperative, 3-month, and 1-year postoperative regional kyphosis angle and vertebral body height. Postoperative impaction of the prosthetic cage in adjacent endplates was observed in 35% of the cases, without worsening at last follow-up. Complete fusion was observed at 1 year postoperatively and no cases of infections or revisions were observed in relation to the anterior approach.

Conclusions

The use of EPVBCs for unstable thoracolumbar fractures is safe and effective in providing long-term vertebral body height restoration and kyphosis correction, with a moderate surgical and sepsis risk. Anterior cage implantation is an alternative to iliac bone graft fusion and is a viable option in association with a posterior approach, in a single operation without additional risks.

Accuracy of Pedicle Screw Placement in Scoliosis Surgery: A Comparison between Conventional Computed Tomography-Based and O-Arm-Based Navigation Techniques

Study Design

Retrospective study.

Purpose

We compared the accuracy of O-arm-based navigation with computed tomography (CT)-based navigation in scoliotic surgery.

Overview of Literature

No previous reports comparing the results of O-arm-based navigation with conventional CT-based navigation in scoliotic surgery have been published.

Methods

A total of 222 pedicle screws were implanted in 29 patients using CT-based navigation (group C) and 416 screws were implanted in 32 patients using O-arm-based navigation (group O). Postoperative CT was performed to assess the screw accuracy, using the established Neo classification (grade 0: no perforation, grade 1: perforation <2 mm, grade 2: perforation ≥2 and <4, and grade 3: perforation ≥4 mm).

Results

In group C, 188 (84.7%) of the 222 pedicle screw placements were categorized as grade 0, 23 (10.4%) were grade 1, 11 (5.0%) were grade 2, and 0 were grade 3. In group O, 351 (84.4%) of the 416 pedicle screw placements were categorized as grade 0, 52 (12.5%) were grade 1, 13 (3.1%) were grade 2, and 0 were grade 3. Statistical analysis showed no significant difference in the prevalence of grade 2.3 perforations between groups C and O. The time to position one screw, including registration, was 10.9±3.2 minutes in group C, but was significantly decreased to 5.4±1.1 minutes in group O.

Conclusions

O-arm-based navigation facilitates pedicle screw insertion as accurately as conventional CT-based navigation. The use of O-arm-based navigation successfully reduced the time, demonstrating advantages in the safety and accuracy of pedicle screw placement for scoliotic surgery.

CT provides precise size assessment of implanted titanium alloy pedicle screws

BACKGROUND

After performing instrumented spinal fusion with pedicle screws, postoperative imaging using CT to assess screw position may be necessary. Stainless steel implants produce significant metal artifact on CT, and the degree of distortion is at least partially dependent on the cross-sectional area of the implanted device. If the same effect occurs with titanium alloy implants, ability to precisely measure proximity of screws to adjacent structures may be adversely affected as screw size increases.

QUESTIONS/PURPOSES

We therefore asked whether (1) CT provides precise measurements of true screw widths; and (2) precision degrades based on the size of the titanium implant imaged.

METHODS

CT scans performed on 20 patients after instrumented spinal fusion for scoliosis were reviewed. The sizes of 151 titanium alloy pedicle screws were measured and compared with known screw size. The amount of metal bloom artifact was determined for each of the four screw sizes. ANOVA with Tukey's post hoc test were performed to evaluate differences in scatter, and Spearman's rho coefficient was used to measure relationship between screw size and scatter.

RESULTS

All screws measured larger than their known size, but even with larger 7-mm screws the size differential was less than 1 mm. The four different screw sizes produced scatter amounts that were different from each other (p < 0.001).The amount of metal bloom artifact produced does increase as the size of the screw increases (rho = 0.962, p < 0.001).

CONCLUSIONS

CT of titanium alloy pedicle screws produces minimal artifact, thus making this the preferred imaging modality to assess screw position after surgery. Although the amount of artifact increases with the volume of titanium present, the degree of distortion is minimal and is usually less than 1 mm.

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.

Does higher anchor density result in increased curve correction and improved clinical outcomes in adolescent idiopathic scoliosis?

STUDY DESIGN

Retrospective review of prospectively collected data.

OBJECTIVE

To determine whether anchor density is associated with curve correction and patient-reported outcomes.

SUMMARY OF BACKGROUND DATA

There is limited information as to whether anchor density affects the results of adolescent idiopathic scoliosis surgery.

METHODS

A total of 952 patients with adolescent idiopathic scoliosis met inclusion criteria (Lenke 1, 2, and 5 curves) with predominantly screw constructs (no. of screws/no. of total anchors >75%). Anchor density was defined as the number of screws, hooks, and wires per level fused, with less than 1.54 considered low density. Analysis of covariance was undertaken to determine association of anchor density with percent curve correction, Scoliosis Research Society (SRS), and Spinal Appearance Questionnaire (SAQ) scores, controlling for flexibility, fusion length, demographics, and surgeon.

RESULTS

High- compared with low-anchor density was associated with increased percent curve correction in Lenke 1 curves at 1 year (69% vs. 66% correction, P = 0.0022), controlling for percent preoperative curve flexibility, length of fusion, and sex (model, P < 0.0001). Similar associations held at 2-year follow-up and for Lenke 2 curves. Decreased thoracic kyphosis was found with increased anchor density for Lenke 1 and 2 curve patterns. There were no associations found between anchor density and Lenke 5 curves. For Lenke 1 curve patterns at 2 years postoperatively, in the high- versus low-anchor density cohorts, there were statistically higher SRS Activity (4.3 vs. 4.2, P = 0.019), Appearance (4.3 vs. 4.1, P = 0.0005), Satisfaction (4.5 vs. 4.3, P = 0.028), and Total scores (4.3 vs. 4.2; P = 0.024). Similarly, the SAQ Appearance score at 1 year similarly was improved in the high-anchor density group (high: 14.1 vs. low: 15.0, P = 0.03) for Lenke 1 curve patterns only.

CONCLUSION

For Lenke 1 and 2 curve patterns, improved percent correction of major coronal curve was noted in the high-screw density cohort. Although statistical significance was reached, it is unclear whether screw density resulted in clinically significant differences in patient-reported outcomes.

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.

Postoperative spine complications

Imaging of the postoperative spine is common, although it remains a difficult task for radiologists. This article presents an overview of common surgical approaches and spinal hardware, and specific complications that may be associated with each procedure. In addition, expected postoperative changes and complications that are common among procedures, with their differential diagnosis and imaging features, are discussed.

Using the freehand pedicle screw placement technique in adolescent idiopathic scoliosis surgery: what is the incidence of neurological symptoms secondary to misplaced screws?

STUDY DESIGN

Retrospective case series.

OBJECTIVE

This study evaluated the incidence of postoperative neurological symptoms after a freehand pedicle screw insertion technique in idiopathic posterior scoliosis surgery.

SUMMARY OF BACKGROUND DATA

It is generally accepted that pedicle screws can be inserted by a freehand technique in the thoracic and lumbar spine in patients with adolescent idiopathic scoliosis (AIS) with a very low frequency of major complications. The prevalence of clinically significant screw misplacement, with or without the need for revision surgery is less well defined.

METHODS

Between January 1, 2000, and October 2, 2012, five hundred fifty-nine patients with AIS had thoracolumbar posterior instrumented spine surgery at the Children's Hospital of Pittsburgh. Each patient's chart and radiographs were reviewed and only those with AIS were included. Patients with neuromuscular and syndromic diagnoses were excluded as well as those with congenital or traumatic etiologies, incomplete charts, less than 3 months of follow-up and those without pedicle screws. The records were studied for complaints of radicular pain, neurological deficit, or severe headache that could be indicative of potential screw misplacement.

RESULTS

Four hundred eighty-one patients with 5923 pedicle screws met the inclusion criteria. Nine patients (1.9%) developed symptoms and underwent computed tomographic scanning. Six patients were found to have pedicle screw malposition (8 screws) and 3 of these patients underwent revision surgery. Of the 3 revision patients, 2 presented with radicular symptoms (leg pain) and 1 with an orthostatic headache due to cerebrospinal fluid leakage. At the final follow-up, all revision patients had complete symptom resolution. In total, there were 8 symptomatic, misplaced pedicle screws (0.14%) in 6 patients (1.25%).

CONCLUSION

During a 12-year period in a dedicated pediatric orthopedic hospital using the freehand placement technique, the incidence of symptomatic misplaced pedicle screws was exceedingly low.

LEVEL OF EVIDENCE

4.

Biomechanics of lateral lumbar interbody fusion constructs with lateral and posterior plate fixation: laboratory investigation

OBJECT

Lumbar interbody fusion is indicated in the treatment of degenerative conditions. Laterally inserted interbody cages significantly decrease range of motion (ROM) compared with other cages. Supplemental fixation options such as lateral plates or spinous process plates have been shown to provide stability and to reduce morbidity. The authors of the current study investigate the in vitro stability of the interbody cage with a combination of lateral and spinous process plate fixation and compare this method to the established bilateral pedicle screw fixation technique.

METHODS

Ten L1-5 specimens were evaluated using multidirectional nondestructive moments (± 7.5 N · m), with a custom 6 degrees-of-freedom spine simulator. Intervertebral motions (ROM) were measured optoelectronically. Each spine was evaluated under the following conditions at the L3-4 level: intact; interbody cage alone (stand-alone); cage supplemented with lateral plate; cage supplemented with ipsilateral pedicle screws; cage supplemented with bilateral pedicle screws; cage supplemented with spinous process plate; and cage supplemented with a combination of lateral plate and spinous process plate. Intervertebral rotations were calculated, and ROM data were normalized to the intact ROM data.

RESULTS

The stand-alone laterally inserted interbody cage significantly reduced ROM with respect to the intact state in flexion-extension (31.6% intact ROM, p < 0.001), lateral bending (32.5%, p < 0.001), and axial rotation (69.4%, p = 0.002). Compared with the stand-alone condition, addition of a lateral plate to the interbody cage did not significantly alter the ROM in flexion-extension (p = 0.904); however, it was significantly decreased in lateral bending and axial rotation (p < 0.001). The cage supplemented with a lateral plate was not statistically different from bilateral pedicle screws in lateral bending (p = 0.579). Supplemental fixation using a spinous process plate was not significantly different from bilateral pedicle screws in flexion-extension (p = 0.476). The combination of lateral plate and spinous process plate was not statistically different from the cage supplemented with bilateral pedicle screws in all the loading modes (p ≥ 0.365).

CONCLUSIONS

A combination of lateral and spinous process plate fixation to supplement a laterally inserted interbody cage helps achieve rigidity in all motion planes similar to that achieved with bilateral pedicle screws.

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.

Control radiografico postoperatorio de la instrumentacion con tornillos pediculares toracicos en la escoliosis idiopática del adolescente

OBJETIVO: Evaluar la eficacia intraoperatoria y postoperatoria de la radiografía en la colocación del tornillo pedícular dorsal y su relación con la tomografía computada (CT). MÉTODOS: Se evaluaron 36 pacientes con escoliosis idiopática del adolescente (EIA). Tres observadores clasifican colocación de los tornillos con radiografia . Estas respuestas se compararon con la tomografía computada. RESULTADOS: Se evaluaron un total de 280 tornillos pediculares. La evaluación interobservador fue de 0,56 (concordancia moderada). La evaluación intraobservador fue 0,79 (concordancia). No se presentaron lesiones vasculares o neurológicas. CONCLUSIONES: Según los resultados intra e interobservador, la reproductibilidad de la radiografía postoperatoria no es muy eficaz para el diagnósticar la mala posición de los tornillos de pedículo dorsales. La tomografía computada fue muy útil para determinar la posición de los tornillos pediculares dorsales.

The biomechanical consequences of rod reduction on pedicle screws: should it be avoided?

BACKGROUND CONTEXT

Rod contouring is frequently required to allow for appropriate alignment of pedicle screw-rod constructs. When residual mismatch is still present, a rod persuasion device is often used to achieve further rod reduction. Despite its popularity and widespread use, the biomechanical consequences of this technique have not been evaluated.

PURPOSE

To evaluate the biomechanical fixation strength of pedicle screws after attempted reduction of a rod-pedicle screw mismatch using a rod persuasion device.

METHODS

Fifteen 3-level, human cadaveric thoracic specimens were prepared and scanned for bone mineral density. Osteoporotic (n=6) and normal (n=9) specimens were instrumented with 5.0-mm-diameter pedicle screws; for each pair of comparison level tested, the bilateral screws were equal in length, and the screw length was determined by the thoracic level and size of the vertebra (35 to 45 mm). Titanium 5.5-mm rods were contoured and secured to the pedicle screws at the proximal and distal levels. For the middle segment, the rod on the right side was intentionally contoured to create a 5-mm residual gap between the inner bushing of the pedicle screw and the rod. A rod persuasion device was then used to engage the setscrew. The left side served as a control with perfect screw/rod alignment. After 30 minutes, constructs were disassembled and vertebrae individually potted. The implants were pulled in-line with the screw axis with peak pullout strength (POS) measured in Newton (N). For the proximal and distal segments, pedicle screws on the right side were taken out and reinserted through the same trajectory to simulate screw depth adjustment as an alternative to rod reduction.

RESULTS

Pedicle screws reduced to the rod generated a 48% lower mean POS (495±379 N) relative to the controls (954±237 N) (p<.05) and significantly decreased work energy to failure (p<.05). Nearly half (n=7) of the pedicle screws had failed during the reduction attempt with visible pullout of the screw. After reduction, decreased POS was observed in both normal (p<.05) and osteoporotic (p<.05) bone. Back out and reinsertion of the screw resulted in no significant difference in mean POS, stiffness, and work energy to failure (p>.05).

CONCLUSIONS

In circumstances where a rod is not fully seated within the pedicle screw, the use of a rod persuasion device decreases the overall POS and work energy to failure of the screw or results in outright failure. Further rod contouring or correction of pedicle screw depth of insertion may be warranted to allow for appropriate alignment of the longitudinal rods.

Comparison of expansive pedicle screw and polymethylmethacrylate-augmented pedicle screw in osteoporotic sheep lumbar vertebrae: biomechanical and interfacial evaluations

Background

It was reported that expansive pedicle screw (EPS) and polymethylmethacrylate-augmented pedicle screw (PMMA-PS) could be used to increase screw stability in osteoporosis. However, there are no studies comparing the two kinds of screws in vivo. Thus, we aimed to compare biomechanical and interfacial performances of EPS and PMMA-PS in osteoporotic sheep spine.

Methodology/Principal Findings

After successful induction of osteoporotic sheep, lumbar vertebrae in each sheep were randomly divided into three groups. The conventional pedicle screw (CPS) was inserted directly into vertebrae in CPS group; PMMA was injected prior to insertion of CPS in PMMA-PS group; and the EPS was inserted in EPS group. Sheep were killed and biomechanical tests, micro-CT analysis and histological observation were performed at both 6 and 12 weeks post-operation. At 6-week and 12-week, screw stabilities in EPS and PMMA-PS groups were significantly higher than that in CPS group, but there were no significant differences between EPS and PMMA-PS groups at two study periods. The screw stability in EPS group at 12-week was significantly higher than that at 6-week. The bone trabeculae around the expanding anterior part of EPS were more and denser than that in CPS group at 6-week and 12-week. PMMA was found without any degradation and absorption forming non-biological “screw-PMMA-bone” interface in PMMA-PS group, however, more and more bone trabeculae surrounded anterior part of EPS improving local bone quality and formed biological “screw-bone” interface.

Conclusions/Significance

EPS can markedly enhance screw stability with a similar effect to the traditional method of screw augmentation with PMMA in initial surgery in osteoporosis. EPS can form better biological interface between screw and bone than PMMA-PS. In addition, EPS have no risk of thermal injury, leakage and compression caused by PMMA. We propose EPS has a great application potential in augmentation of screw stability in osteoporosis in clinic.

Pseudopneumothorax in scoliosis surgery diagnosed with intraoperative O-arm computed tomography

Postoperative pneumothorax in posterior fusion using pedicle screws is uncommon, but the complication needs to be kept in mind. There are reports of a pseudopneumothorax resulting from artifacts. We report a unique case of a pseudopneumothorax in a patient with scoliosis, diagnosed using O-arm intraoperative computed tomography. The pseudopneumothorax, initially appearing on a chest radiograph, turned out to be an area of partial atelectasis at the lateral border of the right lower lobe. Spine surgeons and anesthesiologists must recheck images and maintain a high degree of suspicion for a pseudopneumothorax when the radiographic image during scoliosis surgery does not match the patient's condition.

Are More Screws Better? A Systematic Review of Anchor Density and Curve Correction in Adolescent Idiopathic Scoliosis

STUDY DESIGN

Systematic review of clinical studies.

OBJECTIVES

To critically evaluate existing literature to determine whether increased anchor or implant density (screws, wires, and hooks per level fused) results in improved curve correction for adolescent idiopathic scoliosis (AIS) surgery.

SUMMARY OF BACKGROUND DATA

Wide variability exists in the number of screws used for AIS surgery. High numbers of pedicle screws are increasingly used, but there is limited evidence to support this as best practice.

METHODS

Online English-language databases were searched to identify articles addressing anchor density. Articles were reviewed for anchor type/number, radiographic measures, and patient-reported outcomes.

RESULTS

Of 196 references identified, 10 studies totaling 929 patients met the inclusion criteria. Reported mean anchor density varied from 1.06 to 2.0 implants per level fused. Mean percent coronal curve correction varied from 64% to 70%. Two studies (463 patients) analyzed hook, hybrid (combined hooks and screws), and screw constructs as a single cohort. Both found increased correction with high-density constructs (p = .01, p < .001), perhaps as a result of the hooks and hybrid constructs. Eight retrospective studies and 1 prospective randomized, controlled trial had predominantly screw constructs (466 patients). Increased anchor density was not associated with improved curve correction. The studies evaluating screw density are significantly underpowered to detect a difference in curve correction.

CONCLUSIONS

Wide heterogeneity in anchor density exists in the surgical treatment of AIS. Reports evaluating the effects of increased anchor density are mostly retrospective and significantly underpowered to detect a difference in curve correction and patient outcomes. At this time, there is insufficient evidence to show that anchor density affects clinical outcomes in AIS.

Proposed alternative revision strategy for broken S1 pedicle screw: radiological study, review of the literature, and case reports

BACKGROUND CONTEXT

There have been many reports outlining differing methods for managing a broken S1 screw. To the authors' best knowledge, the technique used in the present study has not been described previously. It involves insertion of a second pedicle screw without removing the broken screw shaft.

STUDY DESIGN

Radiological study, literature review, and two case reports of the surgical technique.

PURPOSE

To report a proposed new surgical technique for management of broken S1 pedicle screws.

METHODS

Computed tomography (CT) scans of 50 patients with a total of 100 S1 pedicles were analyzed. There were 25 male and 25 female patients with an average age of 51 years ranging from 36 to 68 years. The cephalad-caudal length, medial-lateral width, and cross-sectional area of the S1 pedicle were measured and compared with the diameter of a pedicle screw to illustrate the possibility of inserting a second screw in S1 pedicle without removal of the broken screw shaft. Two case reports of the proposed technique are presented.

RESULTS

The left and right S1 pedicle cross-sectional area in female measured 456.00 ± 4.00 and 457.00 ± 3.00 mm(2), respectively. The left and right S1 pedicle cross-section area in male measured 638.00 ± 2.00 and 639.00 ± 1.00 mm(2), respectively. There were statistically significant differences when comparing male and female S1 pedicle length, width, and cross-sectional area (p<.05). At 2-year follow-up, the two case reports of the proposed technique showed resolution of low back pain and radicular pain. Plain radiograph and CT scan showed posterolateral fusion mass and hardware in good position with no evidence of screw loosening.

CONCLUSIONS

The S1 pedicle dimensions measured on CT scan reviewed in the present study showed that it may be anatomically feasible to place a second screw through the S1 pedicle without the removal of the broken screw shaft. This treatment method will reduce the complications associated with other described revision strategies for broken S1 screws.