Improved Accuracy of Minimally Invasive Transpedicular Screw Placement in the Lumbar Spine With 3-Dimensional Stereotactic Image Guidance: A Comparative Meta-Analysis

Computer tomography-assisted 3-dimensional navigation in spine surgery: a narrative review on safety, accuracy, efficacy and reduction of complications

The computed tomography-assisted 3D navigation system is a useful tool for spinal surgeons, enabling them to enhance the effectiveness and safety of surgical procedures by providing real-time three-dimensional information during decompression, resection, and instrumentation. Specific advantages of this navigation system include precise pedicle screw placement, the capability for immediate intraoperative correction, and execution of minimally invasive surgeries with reduced radiation exposure for the surgical team. Noteworthy disadvantages of this system are the relatively high implementation costs, the need for specific training, and limited accessibility to outpatient surgery centers. Currently, spinal navigation systems are constantly being upgraded with additional innovations, such as integration with robotics and improvement of the existing tools, which will ultimately lead to a better quality of life for patients and an improved experience for surgeons.

Ex vivo comparison of pin placement with patient-specific drill guides or freehand technique in canine cadaveric spines

OBJECTIVE

To compare vertebral implant placement in the canine thoracolumbar spine between 3D-printed patient-specific drill guides (3DPG) and the conventional freehand technique (FH).

STUDY DESIGN

Ex vivo study.

ANIMALS

Cadaveric canine spines (n = 24).

METHODS

Implant trajectories were established for the left and right sides of the T10 through L6 vertebrae based on computed tomography (CT) imaging. Customized drill guides were created for each vertebra of interest. Each cadaver was randomly assigned to one of six veterinarians with varying levels of experience placing vertebral implants. Vertebrae were randomly assigned a surgical order and technique (3DPG or FH) for both sides. Postoperative CT images were acquired. A single, blinded observer assessed pin placement using a modified Zdichavsky classification.

RESULTS

A total of 480 implants were placed in 240 vertebrae. Three sites were excluded from the analysis; therefore, a total of 238 implants were evaluated using the FH technique and 239 implants using 3DPG. When evaluating implant placement, 152/239 (63.6%) of 3DPG implants were considered to have an acceptable placement in comparison with 115/248 (48.32%) with FH. Overall, pin placement using 3DPG was more likely to provide acceptable pin placement (p < .001) in comparison with the FH technique for surgeons at all levels of experience.

CONCLUSION

The use of 3DPG was shown to be better than the conventional freehand technique regarding acceptable placement of implants in the thoracolumbar spine of canine cadavers.

CLINICAL SIGNIFICANCE

Utilizing 3DPG can be considered better than the traditional FH technique when placing implants in the canine thoracolumbar spine.

Percutaneous thoraco-lumbar-sacral pedicle screw placement accuracy results from a multi-center, prospective clinical study using a skin marker-based optical navigation system

STUDY DESIGN

Prospective multi-center study.

OBJECTIVE

The study aimed to evaluate the accuracy of pedicle screw placement using a skin marker-based optical surgical navigation system for minimal invasive thoraco-lumbar-sacral pedicle screw placement.

METHODS

The study was performed in a hybrid Operating Room with a video camera-based navigation system integrated in the imaging hardware. The patient was tracked with non-invasive skin markers while the instrument tracking was via an on-shaft optical marker pattern. The screw placement accuracy assessment was performed by three independent reviewers, using the Gertzbein grading. The screw placement time as well as the staff and patient radiation doses was also measured.

RESULTS

In total, 211 screws in 39 patients were analyzed for screw placement accuracy. Of these 32.7% were in the thoracic region, 59.7% were in the lumbar region, and 7.6% were in the sacral region. An overall accuracy of 98.1% was achieved. No screws were deemed severely misplaced (Gertzbein grading 3). The average time for screw placement was 6 min and 25 secs (± 3 min 33 secs). The average operator radiation dose per subject was 40.3 µSv. The mean patient effective dose (ED) was 11.94 mSv.

CONCLUSION

Skin marker-based ON can be used to achieve very accurate thoracolumbarsacral pedicle screw placements.

CT-Navigated Spinal Instrumentations-Three-Dimensional Evaluation of Screw Placement Accuracy in Relation to a Screw Trajectory Plan

Background and Objectives: In the literature, spinal navigation and robot-assisted surgery improved screw placement accuracy, but the majority of studies only qualitatively report on screw positioning within the vertebra. We sought to evaluate screw placement accuracy in relation to a preoperative trajectory plan by three-dimensional quantification to elucidate technical benefits of navigation for lumbar pedicle screws. Materials and Methods: In 27 CT-navigated instrumentations for degenerative disease, a dedicated intraoperative 3D-trajectory plan was created for all screws. Final screw positions were defined on postoperative CT. Trajectory plans and final screw positions were co-registered and quantitatively compared computing minimal absolute differences (MAD) of screw head and tip points (mm) and screw axis (degree) in 3D-space, respectively. Differences were evaluated with consideration of the navigation target registration error. Clinical acceptability of screws was evaluated using the Gertzbein−Robbins (GR) classification. Results: Data included 140 screws covering levels L1-S1. While screw placement was clinically acceptable in all cases (GR grade A and B in 112 (80%) and 28 (20%) cases, respectively), implanted screws showed considerable deviation compared to the trajectory plan: Mean axis deviation was 6.3° ± 3.6°, screw head and tip points showed mean MAD of 5.2 ± 2.4 mm and 5.5 ± 2.7 mm, respectively. Deviations significantly exceeded the mean navigation registration error of 0.87 ± 0.22 mm (p < 0.001). Conclusions: Screw placement was clinically acceptable in all screws after navigated placement but nevertheless, considerable deviation in implanted screws was noted compared to the initial trajectory plan. Our data provides a 3D-quantitative benchmark for screw accuracy achievable by CT-navigation in routine spine surgery and suggests a framework for objective comparison of screw outcome after navigated or robot-assisted procedures. Factors contributing to screw deviations should be considered to assure optimal surgical results when applying navigation for spinal instrumentation.

Feasibility and Accuracy of Thoracolumbar Pedicle Screw Placement Using an Augmented Reality Head Mounted Device

Background: To investigate the accuracy of augmented reality (AR) navigation using the Magic Leap head mounted device (HMD), pedicle screws were minimally invasively placed in four spine phantoms. Methods: AR navigation provided by a combination of a conventional navigation system integrated with the Magic Leap head mounted device (AR-HMD) was used. Forty-eight screws were planned and inserted into Th11-L4 of the phantoms using the AR-HMD and navigated instruments. Postprocedural CT scans were used to grade the technical (deviation from the plan) and clinical (Gertzbein grade) accuracy of the screws. The time for each screw placement was recorded. Results: The mean deviation between navigation plan and screw position was 1.9 ± 0.7 mm (1.9 [0.3–4.1] mm) at the entry point and 1.4 ± 0.8 mm (1.2 [0.1–3.9] mm) at the screw tip. The angular deviation was 3.0 ± 1.4° (2.7 [0.4–6.2]°) and the mean time for screw placement was 130 ± 55 s (108 [58–437] s). The clinical accuracy was 94% according to the Gertzbein grading scale. Conclusion: The combination of an AR-HMD with a conventional navigation system for accurate minimally invasive screw placement is feasible and can exploit the benefits of AR in the perspective of the surgeon with the reliability of a conventional navigation system.

Minimally Invasive Surgery for Spinal Metastasis: A Review

OBJECTIVE

Minimally invasive surgery (MIS) techniques have advanced the treatment of metastatic diseases to the spine. The objective of this review is to describe clinical outcomes, benefits, and complications of these techniques.

METHODS

All relevant clinical studies describing the role of MIS, computer-assisted navigation (CAN), robot-assisted (RA) procedures, and laser interstitial thermal therapy (LITT) in the treatment of metastatic spine diseases were identified from PubMed, MEDLINE, and relevant article bibliographies.

RESULTS

For MIS articles, we filtered 1480 results and identified 26 studies. For CAN, we searched 464 articles to identify 18 articles for review. For RA, we searched 321 results to identify 7 studies for review. For LITT, we identified 21 articles for review.

CONCLUSIONS

MIS for the treatment of spine metastasis has significant potential benefits in reducing surgical site infections, hospital stay, and blood loss without compromising instrument accuracy or overall outcomes. Overall, MIS and its adjuncts have the potential to reduce the risks involved in the treatment of patients with metastatic disease to the spinal column without compromising the benefits of decompression and stabilization of the spine.

The Use of Skin Staples as Fiducial Markers to Confirm Intraoperative Spinal Navigation Registration and Accuracy

BACKGROUND

With the advent of intraoperative computed tomography (CT) for image guidance, numerous examples of accurate navigation being applied to cranial and spinal pathology have come to light. For spinal disorders, the utilization of image guidance for the placement of percutaneous spinal instrumentation, complex osteotomies, and minimally invasive approaches are frequently utilized in trauma, degenerative, and oncological pathologies. The use of intraoperative CT for navigation, however, requires a low target registration error that must be verified throughout the procedure to confirm the accuracy of image guidance.

OBJECTIVE

To present the use of skin staples as a sterile, economical fiducial marker for minimally invasive spinal procedures requiring intraoperative CT navigation.

METHODS

Staples are applied to the skin prior to obtaining the registration CT scan and maintained throughout the remainder of the surgery to facilitate confirmation of image guidance accuracy.

RESULTS

This low-cost, simple, sterile approach provides surface landmarks that allow reliable verification of navigation accuracy during percutaneous spinal procedures using intraoperative CT scan image guidance.

CONCLUSION

The utilization of staples as a fiducial marker represents an economical and easily adaptable technique for ensuring accuracy of image guidance with intraoperative CT navigation.

A cadaveric precision and accuracy analysis of augmented reality-mediated percutaneous pedicle implant insertion

OBJECTIVE

Augmented reality-mediated spine surgery (ARMSS) is a minimally invasive novel technology that has the potential to increase the efficiency, accuracy, and safety of conventional percutaneous pedicle screw insertion methods. Visual 3D spinal anatomical and 2D navigation images are directly projected onto the operator's retina and superimposed over the surgical field, eliminating field of vision and attention shift to a remote display. The objective of this cadaveric study was to assess the accuracy and precision of percutaneous ARMSS pedicle implant insertion.

METHODS

Instrumentation was placed in 5 cadaveric torsos via ARMSS with the xvision augmented reality head-mounted display (AR-HMD) platform at levels ranging from T5 to S1 for a total of 113 total implants (93 pedicle screws and 20 Jamshidi needles). Postprocedural CT scans were graded by two independent neuroradiologists using the Gertzbein-Robbins scale (grades A-E) for clinical accuracy. Technical precision was calculated using superimposition analysis employing the Medical Image Interaction Toolkit to yield angular trajectory (°) and linear screw tip (mm) deviation from the virtual pedicle screw position compared with the actual pedicle screw position on postprocedural CT imaging.

RESULTS

The overall implant insertion clinical accuracy achieved was 99.1%. Lumbosacral and thoracic clinical accuracies were 100% and 98.2%, respectively. Specifically, among all implants inserted, 112 were noted to be Gertzbein-Robbins grade A or B (99.12%), with only 1 medial Gertzbein-Robbins grade C breach (> 2-mm pedicle breach) in a thoracic pedicle at T9. Precision analysis of the inserted pedicle screws yielded a mean screw tip linear deviation of 1.98 mm (99% CI 1.74-2.22 mm) and a mean angular error of 1.29° (99% CI 1.11°-1.46°) from the projected trajectory. These data compare favorably with data from existing navigation platforms and regulatory precision requirements mandating that linear and angular deviation be less than 3 mm (p < 0.01) and 3° (p < 0.01), respectively.

CONCLUSIONS

Percutaneous ARMSS pedicle implant insertion is a technically feasible, accurate, and highly precise method.

Management of spondylolisthesis using MIS techniques: Recent advances

The authors discuss the recent advances in the understanding and management of spondylolisthesis. The two most common kinds of spondylolisthesis - Degenerative and Spondylolytic types have been elaborated in this paper, with the understanding that similar management principles can be applied to the other lesser common varieties. The impetus has been on application of minimally invasive techniques in the treatment as well as renewed interest in stand-alone decompression in degenerative spondylolisthesis.

Is bony attachment necessary for dynamic reference frame in navigation-assisted minimally invasive lumbar spine fusion surgery?

This study aimed to compare the accuracy of navigation-assisted percutaneous pedicle screw insertions between traditional posterior superior iliac spine (PSIS) fixed and cutaneously fixed dynamic reference frame (DRF) in minimally invasive surgery of transforaminal lumbar interbody fusion (MIS TLIF). This is a prospective randomized clinical study. Between May 2016 and Nov 2017, 100 patients who underwent MIS TLIF were randomly divided into bone fixed group (with PSIS fixed DRF) and skin fixed group (with cutaneously fixed DRF). The pedicel screws were inserted under navigational guidance using computed tomography (CT) data acquired intraoperatively with a Ziehm 3-dimensional fluoroscopy-based navigation system. Screw positions were immediately checked by a final intraoperative scan. The accuracy of screw placement was evaluated by a sophisticated computed tomography protocol. Both groups had similar patient demographics. Totally Five-hundred Twelve pedicle screws were placed in the lumbar spine. There were 2 moderate (2-4 mm) pedicle perforations in each group. The accuracy showed no significant difference between bone fixed and skin fixed DRF. There were no significant procedure-related complications. The skin fixed DRF provides similar accuracy in pedicle screw insertions with bone fixed DRF using intraoperative 3D image guided navigation in MIS TLIF. Skin fixed DRF not only serves as an alternative method but also saves a separate incision wound for bony attachment.

Retrospective analysis of pedicle screw accuracy for patients undergoing spinal surgery assisted by intraoperative computed tomography (CT) scanner AIRO® and BrainLab© navigation

Minimally invasive spine surgery techniques for pedicle screw instrumentation are being more frequently used. They offer shorter operative times, shorter hospital stays for patients, faster recovery, less blood loss, and less damage to surrounding tissues. However, they may rely heavily on fluoroscopic imaging, and confer radiation exposure to the surgeon and team members. Use of the AIRO Mobile Intraoperative CT by Brainlab during surgery is a way to eliminate radiation exposure to staff and may improve accuracy rates for pedicle screw instrumentation. We designed a retrospective analysis of our first 12 patients who had a total of 59 pedicle screws inserted when we began to incorporate the AIRO iCT scanner to our surgical workflow. During pedicle screw insertion, projection images were saved, and compared to CT scans gone at the end of the case. We measured the distances between the projected and postprocedural screw locations, at both the screw tips and tulip heads. We observed a mean of 2.8 mm difference between the projection and postprocedural images. None of the screws inserted had any clinically significant complications, and no patient required revision surgery. Overall, iCT guided navigation with the AIRO system is a safe adjunct to spinal surgery. It decreased operator and staff radiation exposure, and helped facilitate successful MIS surgery without fluoroscopic imaging. Additional studies and research can be done to further improve accuracy and reliability.

Design, application, and evaluation of a novel method for determining optimal trajectory of thoracic pedicle screws

Background

This is an experimental study performed on 15 adult cadavers. In this cadaveric study, we designed and evaluated a novel methodology for determining the optimal trajectory for the placement of thoracic pedicle screws. The accuracy of thoracic pedicle screw placement is critical to the spinal surgery. The concept, implement method, and significance of the optimal thoracic pedicle trajectory have not been reported.

Methods

The experimental study was performed on 15 adult cadavers. The Mimics software was used to design optimal trajectory through the pedicle central axis. Using three-dimensional (3D) printing, a navigation module with a locating facet and a stabilizing facet was developed. The thoracic pedicle screws were inserted with the help of the navigation module. The three-dimensional coordinates for the entry and the exit points of the screws were compared between the planned trajectories and the postoperative trajectories. The differences in coordinates were analyzed to evaluate the precision of the screw placement.

Results

The trajectories through the pedicle central axis showed an excellent symmetry between the single segments and for all thoracic vertebrae. Out of a total of 358 screws that were inserted, 15 (4.2%) screws breached the pedicle cortex with a breach distance of <2 mm. The qualifying rate was 98.6% (353/358) for the entry point precision of ≥3.2 mm, and 98.9% (354/358) for the exit point precision of ≥6.4 mm. In comparison to the designed qualified rate of 100% (358/358), the χ² was 3.22 and 2.26, respectively (P>0.05).

Conclusions

The optimal trajectory was obtained through the pedicle central axis, which significantly reduced the risk of cortex breach. A high degree of precision was obtained for the entry and the exit points of the screws when the postoperative trajectory was compared with the designed trajectory.

Overview of Minimally Invasive Spine Surgery

Minimally invasive spine surgery (MISS) has continued to evolve over the past few decades, with significant advancements in technology and technical skills. From endonasal cervical approaches to extreme lateral lumbar interbody fusions, MISS has showcased its usefulness across all practice areas of the spine, with unique points of access to avoid pertinent neurovascular structures. Adult spine deformity has also recognized the importance of minimally invasive techniques in its ability to limit complications and to provide adequate sagittal alignment correction and improvements in patients' functional status. Although MISS has continued to make significant progress clinically, consideration must also be given to its economic impact and the learning curve surgeons experience in adding these procedures to their armamentarium. This review examines current innovations in MISS, as well as the economic impact and future directions of the field.

Cranial facet joint injuries in percutaneous lumbar pedicle screw placement: a matched-pair analysis comparing intraoperative 3D navigation and conventional fluoroscopy

PURPOSE

The violation of the cranial adjacent facet is a frequent complication in lumbar instrumentations and can induce local pain and adjacent segment disease. Minimally invasive screw implantation is often stated as risk factor in comparison with open approaches. Percutaneous pedicle screw placement (PPSP) can be performed using single X-ray images (fluoroscopy) or intraoperative 3D navigation. The study compares top-level screws in percutaneous lumbar instrumentations regarding facet violations and screw pedicle position using navigation or fluoroscopy.

METHODS

Patients after lumbar PPSP were retrospectively separated according to the intraoperative technique: navigation (NAV) or fluoroscopy (FLUORO). Two blinded investigators graded the top-level screws regarding facet violations and pedicle breach in postoperative CT scans. Subsequent matched cohort analysis was performed for comparable groups.

RESULTS

Evaluating 768 screws, we assessed 70 (9.1%) facet violations. Overall, 186 (24.2%) screws were implanted using navigation. There was no significant difference in the rate of facet violations between both imaging groups (NAV 19/186, 10.2%, FLUORO 51/582, 8.8%, p = 0.55). Totally, 728 (94.8%) of all screws showed a correct pedicle position. Most of the 40 unfavorable pedicle positions were placed by fluoroscopy (NAV 4/186, 2.2%, FLUORO 36/582, 6.6%, p = 0.03). The matched cohorts verified these results (facet violations: NAV 19/186, 10.2%, FLUORO 18/186, 9.7%, p = 0.55; pedicle penetrations: NAV 4/186, 2.2%, FLUORO 12/186, 6.9%, p = 0.04).

CONCLUSIONS

Both intraoperative imaging techniques allow lumbar PPSP with low rates of cranial facet violations if the surgeon intends to preserve facet integrity. Navigation was superior concerning accurate pedicle screw position, but could not significantly prevent facet violations.

Evolution of Minimally Invasive Lumbar Spine Surgery

Spine surgery has evolved over centuries from first being practiced with Hippocratic boards and ladders to now being able to treat spinal pathologies with minimal tissue invasion. With the advent of new imaging and surgical technologies, spine surgeries can now be performed minimally invasively with smaller incisions, less blood loss, quicker return to daily activities, and increased visualization. Modern minimally invasive procedures include percutaneous pedicle screw fixation techniques and minimally invasive lateral approach for lumbar interbody fusion (i.e., minimally invasive transforaminal lumbar interbody fusion, extreme lateral interbody fusion, oblique lateral interbody fusion) and midline lumbar fusion with cortical bone trajectory screws. Just as evolutions in surgical techniques have helped revolutionize the field of spine surgery, imaging technologies have also contributed significantly. The advent of computer image guidance has allowed spine surgeons to advance their ability to refine surgical techniques, increase the accuracy of spinal hardware placement, and reduce radiation exposure to the operating room staff. As the field of spine surgery looks to the future, many novel technologies are on the horizon, including robotic spine surgery, artificial intelligence, and machine learning to help improve preoperative planning, improve surgical execution, and optimize patient selection to ensure improved postoperative outcomes and patient satisfaction. As more spine surgeons begin incorporating these novel minimally invasive techniques into practice, the field of minimally invasive spine surgery will continue to innovate and evolve over the coming years.

Feasibility and accuracy of a robotic guidance system for navigated spine surgery in a hybrid operating room: a cadaver study

The combination of navigation and robotics in spine surgery has the potential to accurately identify and maintain bone entry position and planned trajectory. The goal of this study was to examine the feasibility, accuracy and efficacy of a new robot-guided system for semi-automated, minimally invasive, pedicle screw placement. A custom robotic arm was integrated into a hybrid operating room (OR) equipped with an augmented reality surgical navigation system (ARSN). The robot was mounted on the OR-table and used to assist in placing Jamshidi needles in 113 pedicles in four cadavers. The ARSN system was used for planning screw paths and directing the robot. The robot arm autonomously aligned with the planned screw trajectory, and the surgeon inserted the Jamshidi needle into the pedicle. Accuracy measurements were performed on verification cone beam computed tomographies with the planned paths superimposed. To provide a clinical grading according to the Gertzbein scale, pedicle screw diameters were simulated on the placed Jamshidi needles. A technical accuracy at bone entry point of 0.48 ± 0.44 mm and 0.68 ± 0.58 mm was achieved in the axial and sagittal views, respectively. The corresponding angular errors were 0.94 ± 0.83° and 0.87 ± 0.82°. The accuracy was statistically superior (p < 0.001) to ARSN without robotic assistance. Simulated pedicle screw grading resulted in a clinical accuracy of 100%. This study demonstrates that the use of a semi-automated surgical robot for pedicle screw placement provides an accuracy well above what is clinically acceptable.

Accuracy of augmented reality surgical navigation for minimally invasive pedicle screw insertion in the thoracic and lumbar spine with a new tracking device

BACKGROUND CONTEXT

Minimally invasive approaches are increasingly used in spine surgery. The purpose of navigation systems is to guide the surgeon and to reduce intraoperative x-ray exposure.

PURPOSE

This study aimed to determine the feasibility and clinical accuracy of a navigation technology based on augmented reality surgical navigation (ARSN) for minimally invasive thoracic and lumbar pedicle screw instrumentation compared with standard fluoroscopy-guided minimally invasive technique.

STUDY DESIGN/SETTING

Cadaveric laboratory study.

METHODS

ARSN was installed in a hybrid operating room, consisting of a flat panel detector c-arm with two dimensional/three dimensional imaging capabilities and four integrated cameras in its frame. The surface-referenced navigation device does not require a bony reference but uses video cameras and optical markers applied to the patient's skin for tracking. In four cadavers, a total of 136 pedicle screws were inserted in thoracic and lumbar vertebrae. The accuracy was assessed by three independent raters in postoperative conventional computed tomography.

RESULTS

The overall accuracy of ARSN was 94% compared with an accuracy of 88% for fluoroscopy. The difference was not statistically significant. In the thoracic region, accuracy with ARSN was 92% compared with 83% with fluoroscopy. With fluoroscopy, unsafe screws were observed in three normal cadavers and one with scoliosis. Using ARSN, unsafe screws were only observed in the scoliotic spine. No significant difference in the median of time for K-wire placement was recorded. As no intraoperative fluoroscopy was necessary in ARSN, the performing surgeon was not exposed to radiation.

CONCLUSIONS

In this limited cadaveric study minimally invasive screw placement using ARSN was demonstrated to be feasible and as accurate as fluoroscopy. It did not require any additional navigation time or use of any intraoperative x-ray imaging, thereby potentially permitting surgery in a protective lead garment-free environment. A well-powered clinical study is needed to demonstrate a significant difference in the accuracy between the two methods.

CLINICAL SIGNIFICANCE

ARSN offers real-time imaging of planned insertion paths, instrument tracking, and overlay of three dimensional bony anatomy and surface topography. The referencing procedure, by optical recognition of several skin markers is easy and does not require a solid bony reference as necessary for conventional navigation which saves time. Additionally, ARSN may foster the reduction of intraoperative x-ray exposure to spinal surgeons.

Towards non-invasive patient tracking: optical image analysis for spine tracking during spinal surgery procedures

Surgical navigation systems can enhance surgeon vision and form a reliable image-guided tool for complex interventions as spinal surgery. The main prerequisite is successful patient tracking which implies optimal motion compensation. Nowadays, optical tracking systems can satisfy the need of detecting patient position during surgery, allowing navigation without the risk of damaging neurovascular structures. However, the spine is subject to vertebrae movements which can impact the accuracy of the system. The aim of this paper is to investigate the feasibility of a novel approach for offering a direct relationship to movements of the spinal vertebra during surgery. To this end, we detect and track patient spine features between different image views, captured by several optical cameras, for vertebrae rotation and displacement reconstruction. We analyze patient images acquired in a real surgical scenario by two gray-scale cameras, embedded in the flat-panel detector of the C-arm. Spine segmentation is performed and anatomical landmarks are designed and tracked between different views, while experimenting with several feature detection algorithms (e.g. SURF, MSER, etc.). The 3D positions for the matched features are reconstructed and the triangulation errors are computed for an accuracy assessment. The analysis of the triangulation accuracy reveals a mean error of 0.38 mm, which demonstrates the feasibility of spine tracking and strengthens the clinical application of optical imaging for spinal navigation.

Recent Trends, Technical Concepts and Components of Computer-Assisted Orthopedic Surgery Systems: A Comprehensive Review

Computer-assisted orthopedic surgery (CAOS) systems have become one of the most important and challenging types of system in clinical orthopedics, as they enable precise treatment of musculoskeletal diseases, employing modern clinical navigation systems and surgical tools. This paper brings a comprehensive review of recent trends and possibilities of CAOS systems. There are three types of the surgical planning systems, including: systems based on the volumetric images (computer tomography (CT), magnetic resonance imaging (MRI) or ultrasound images), further systems utilize either 2D or 3D fluoroscopic images, and the last one utilizes the kinetic information about the joints and morphological information about the target bones. This complex review is focused on three fundamental aspects of CAOS systems: their essential components, types of CAOS systems, and mechanical tools used in CAOS systems. In this review, we also outline the possibilities for using ultrasound computer-assisted orthopedic surgery (UCAOS) systems as an alternative to conventionally used CAOS systems.

Computer Navigation in Minimally Invasive Spine Surgery

PURPOSE OF REVIEW

The goal of the review is to discuss the common general applications of navigation in the context of minimally invasive spine surgery and assess its value in the published literature comparing against non-navigated or navigated techniques.

RECENT FINDINGS

There is increasing utilization of computer navigation in minimally invasive spine surgery. There is synergy between navigation and minimally invasive technologies, such that one enhances or facilitates the other, thus leading to wider applications for both. Specifically, navigation has been shown to improve performance of percutaneous pedicle screw placement, vertebral augmentation, and minimally invasive fusion procedures. Overall, clinical studies have shown better accuracy and less radiation exposure with the use of navigation in spine surgery. The use of navigation in minimally invasive spine surgery enhances the accuracy of instrumentation and decreases radiation exposure. It is yet to be determined whether patient-reported outcomes will differ. Further research on its effect on clinical outcomes may further define the future impact of navigation in minimally invasive spine surgery.

Conventional Versus Stereotactic Image-guided Pedicle Screw Placement During Posterior Lumbar Fusions: A Retrospective Propensity Score-matched Study of a National Longitudinal Database

STUDY DESIGN

Retrospective 1:1 propensity score-matched analysis on a national longitudinal database between 2007 and 2016.

OBJECTIVE

The aim of this study was to compare complication rates, revision rates, and payment differences between navigated and conventional posterior lumbar fusion (PLF) procedures with instrumentation.

SUMMARY OF BACKGROUND DATA

Stereotactic navigation techniques for spinal instrumentation have been widely demonstrated to improve screw placement accuracies and decrease perforation rates when compared to conventional fluoroscopic and free-hand techniques. However, the clinical utility of navigation for instrumented PLF remains controversial.

METHODS

Patients who underwent elective laminectomy and instrumented PLF were stratified into "single level" and "3- to 6-level" cohorts. Navigation and conventional groups within each cohort were balanced using 1:1 propensity score matching, resulting in 1786 navigated and conventional patients in the single-level cohort and 2060 in the 3 to 6 level cohort. Outcomes were compared using bivariate analysis.

RESULTS

For the single-level cohort, there were no significant differences in rates of complications, readmissions, revisions, and length of stay between the navigation and conventional groups. For the 3- to 6-level cohort, length of stay was significantly longer in the navigation group (P < 0.0001). Rates of readmissions were, however, greater for the conventional group (30-day: P = 0.0239; 90-day: P = 0.0449). Overall complications were also greater for the conventional group (P = 0.0338), whereas revision rate was not significantly different between the 2 groups. Total payments were significantly greater for the navigation group in both the single level and 3- to 6-level cohorts (P < 0.0001).

CONCLUSION

Although use of navigation for 3- to 6-level instrumented PLF was associated with increased length of stay and payments, the concurrent decreased overall complication and readmission rates alluded to its potential clinical utility. However, for single-level instrumented PLF, no differences in outcomes were found between groups, suggesting that the value in navigation may lie in more complex procedures.

LEVEL OF EVIDENCE

3.

Quantification of computational geometric congruence in surface-based registration for spinal intra-operative three-dimensional navigation

BACKGROUND CONTEXT

Computer-assisted navigation (CAN) may guide spinal instrumentation, and requires alignment of patient anatomy to imaging. Iterative closest-point (ICP) algorithms register anatomical and imaging surface datasets, which may fail in the presence of geometric symmetry (congruence), leading to failed registration or inaccurate navigation. Here we computationally quantify geometric congruence in posterior spinal exposures, and identify predictors of potential navigation inaccuracy.

METHODS

Midline posterior exposures were performed from C1-S1 in four human cadavers. An optically-based CAN generated surface maps of the posterior elements at each level. Maps were reconstructed to include bilateral hemilamina, or unilateral hemilamina with/without the base of the spinous process. Maps were fitted to symmetrical geometries (cylindrical/spherical/planar) using computational modelling, and the degree of model fit quantified based on the ratio of model inliers to total points. Geometric congruence was subsequently assessed clinically in 11 patients undergoing midline exposures in the cervical/thoracic/lumbar spine for posterior instrumented fusion.

RESULTS

In cadaveric testing, increased cylindrical/spherical/planar symmetry was seen in the high-cervical and subaxial cervical spine relative to the thoracolumbar spine (p<0.001). Extension of unilateral exposures to include the ipsilateral base of the spinous process decreased symmetry independent of spinal level (p<0.001). In clinical testing, increased cylindrical/spherical/planar symmetry was seen in the subaxial cervical relative to the thoracolumbar spine (p<0.001), and in the thoracic relative to the lumbar spine (p<0.001). Symmetry in unilateral exposures was decreased by 20% with inclusion of the ipsilateral base of the spinous process.

CONCLUSIONS

Geometric congruence is most evident at C1 and the subaxial cervical spine, warranting greater vigilance in navigation accuracy verification. At all levels, inclusion of the base of the spinous process in unilateral registration decreases the likelihood of geometric symmetry and navigation error. This work is important to allow the extension of line-of-sight based registration techniques to minimally-invasive unilateral approaches.

Augmented and Virtual Reality Instrument Tracking for Minimally Invasive Spine Surgery: A Feasibility and Accuracy Study

STUDY DESIGN

Cadaveric animal laboratory study.

OBJECTIVE

To evaluate the feasibility and accuracy of pedicle cannulation using an augmented reality surgical navigation (ARSN) system with automatic instrument tracking, yielding feedback of instrument position in relation to deep anatomy.

SUMMARY OF BACKGROUND DATA

Minimally invasive spine surgery (MISS) has the possibility of reducing surgical exposure resulting in shorter hospital stays, lower blood loss and infection rates compared with open surgery but the drawback of limiting visual feedback to the surgeon regarding deep anatomy. MISS is mainly performed using image-guided 2D fluoroscopy, thus exposing the staff to ionizing radiation.

METHODS

A hybrid operating room (OR) equipped with a robotic C-arm with integrated optical cameras for augmented reality instrument navigation was used. In two pig cadavers, cone beam computed tomography (CBCT) scans were performed, a 3D model generated, and pedicle screw insertions were planned. Seventy-eight insertions were performed. Technical accuracy was assessed on post-insertion CBCTs by measuring the distance between the navigated device and the corresponding pre-planned path as well as the angular deviations. Drilling and hammering into the pedicle were also compared. Navigation time was measured. An independent reviewer assessed a simulated clinical accuracy according to Gertzbein.

RESULTS

The technical accuracy was 1.7 ± 1.0 mm at the bone entry point and 2.0 ± 1.3 mm at the device tip. The angular deviation was 1.7 ± 1.7° in the axial and 1.6 ± 1.2° in the sagittal plane. Navigation time per insertion was 195 ± 93 seconds. There was no difference in accuracy between hammering and drilling into the pedicle. The clinical accuracy was 97.4% to 100% depending on the screw size considered for placement. No ionizing radiation was used during navigation.

CONCLUSION

ARSN with instrument tracking for MISS is feasible, accurate, and radiation-free during navigation.

LEVEL OF EVIDENCE

3.

Intraoperative Error Propagation in 3-Dimensional Spinal Navigation From Nonsegmental Registration: A Prospective Cadaveric and Clinical Study

STUDY DESIGN

Prospective pre-clinical and clinical cohort study.

OBJECTIVES

Current spinal navigation systems rely on a dynamic reference frame (DRF) for image-to-patient registration and tool tracking. Working distant to a DRF may generate inaccuracy. Here we quantitate predictors of navigation error as a function of distance from the registered vertebral level, and from intersegmental mobility due to surgical manipulation and patient respiration.

METHODS

Navigation errors from working distant to the registered level, and from surgical manipulation, were quantified in 4 human cadavers. The 3-dimensional (3D) position of a tracked tool tip at 0 to 5 levels from the DRF, and during targeting of pedicle screw tracts, was captured in real-time by an optical navigation system. Respiration-induced vertebral motion was quantified from 10 clinical cases of open posterior instrumentation. The 3D position of a custom spinous-process clamp was tracked over 12 respiratory cycles.

RESULTS

An increase in mean 3D navigation error of ≥2 mm was observed at ≥2 levels from the DRF in the cervical and lumbar spine. Mean ± SD displacement due to surgical manipulation was 1.55 ± 1.13 mm in 3D across all levels, ≥2 mm in 17.4%, 19.2%, and 38.5% of levels in the cervical, thoracic, and lumbar spine, respectively. Mean ± SD respiration-induced 3D motion was 1.96 ± 1.32 mm, greatest in the lower thoracic spine (P < .001). Tidal volume and positive end-expiratory pressure correlated positively with increased vertebral displacement.

CONCLUSIONS

Vertebral motion is unaccounted for during image-guided surgery when performed at levels distant from the DRF. Navigating instrumentation within 2 levels of the DRF likely minimizes the risk of navigation error.

Accuracy in Percutaneous Transpedicular Screws Placement Using Biplane Radioscopy: Systematic Review and Meta-Analysis

STUDY DESIGN

Systematic review and descriptive data meta-analysis.

OBJECTIVE

The objective of this study was to appropriately establish the accuracy in the percutaneous transpedicular screws (PTS) placement using biplane radioscopy (Rx-2D).

SUMMARY OF BACKGROUND DATA

The Rx-2D is a widely-used technique for PTS as it is practical, ubiquitous, and cost-effective. However, the reported "acceptable" accuracy attained by this method is widely variable ranging between 76% and 100%.

METHODS

A systematic review was conducted to screen publications about PTS placement using Rx-2D guidance. PubMed/MEDLINE database was consulted using the search term "percutaneous pedicle screw" from 1977 to 2017. Previous meta-analysis and reference lists of the selected articles were reviewed. Accuracy values were assessed fulfilling the proposed criteria. Observational data meta-analysis was performed. Cochran's Q test was used to determine heterogeneity among data extracted from the series, which was quantified by I test. P-values≤0.05 were considered statistically significant. The results were depicted by Forest plots. Funnel plots were outlined to visualize a possible bias of publication among the selected articles.

RESULTS

In total, 27 articles were included in the analysis. Results of the accuracy were as follow, 91.5% (n=7993; 95% CI, 89.3%-93.6%) of the screws were placed purely intrapedicular, and 96.1% (n=8579; 95% CI, 94.0%-98.2%) when deviation from the pedicle was up to 2 mm.

CONCLUSIONS

This meta-analysis is the largest review of PTS placed with Rx-2D guidance reported up to date. We concluded that the procedure is a safe and reproducible technique. The key values obtained in this work set reliable references for both clinical and training outcome assessing.

Navigation in minimally invasive spine surgery

Minimally invasive spine (MIS) surgery is associated with limited dissection as compared to open surgical procedures and this can result in decreased visualization. The use of computer-assisted navigation technology, however, allows surgeons greater visualization of bony and soft tissue anatomy through limited MIS incisions. This article outlines the potential benefits of intraoperative navigation during minimally invasive spinal surgery procedures to reduce intra-operative radiation exposure and enhance surgical accuracy. We also offer the senior author's surgical setup and technique related to a skin-based navigation system. Future research is required into the use of augmented reality for surgeons during a navigated MIS surgery.

Endoscopic and Microscopic Segmental Decompression via Translaminar Crossover Spinal Approach in Elderly Patients

OBJECTIVE

For effective minimally invasive lumbar decompression, we changed the routine of segmental decompression. Using a high-speed drill or an ultrasound knife, we created a working channel, starting at the base of the spinous process of the upper vertebra slightly above the disc level, to target and decompress the contralateral recess, and termed it the translaminar crossover decompression (TCD). We evaluated the feasibility and compared the outcomes of a navigation-guided endoscopic translaminar crossover approach for segmental decompression (eTCD) in elderly patients with microscopic decompression using the same approach (mTCD).

METHODS

A total of 740 elderly patients were enrolled in a prospective cohort study. Of the 740 patients, 297, who had undergone mTCD, and 253, who had undergone eTCD, completed a 1-year follow-up visit. In addition to the surgical data, numerical rating scales (NRSs) for back and leg pain, the Core Outcome Measures Index and Oswestry Disability Index were recorded preoperatively and 3, 6, and 12 months after surgery. The MacNab criteria were supplemented by qualitative assessment of the patients' postoperative pain-free walking distance.

RESULTS

A comparison of the preoperative and postoperative clinical scores showed significant improvement after TCD in both cohorts (P < 0.01): Oswestry Disability Index, from 50.3% ± 12.6% to 15.5% ± 7.43%; NRS (back), from 6.9 ± 1.9 to 2.5 ± 1.3; NRS (leg), from 8.0 ± 0.85 to 1.6 ± 0.33; Core Outcome Measures Index (back), from 7.8 ± 2.0 to 2.7 ± 1.5. No statistically significant differences were found in the outcomes between the 2 cohorts.

CONCLUSIONS

TCD inherently eliminated central stenosis and facilitated decompression of both recesses via mutual undercutting, with preservation of facet joint integrity.

Evidence Based Medicine Review of Posterior Thoracolumbar Minimally Invasive Technology

Background

Evaluate the current evidence in meta-analyses on posterior thoracolumbar minimally invasive surgery techniques and outcomes for degenerative conditions.

Methods

A systematic review of the literature from 1950 to 2015.

Results

The review of the literature yielded 34 meta-analysis studies evaluating posterior thoracolumbar minimally invasive techniques and outcomes for degenerative conditions. There were 11 studies included which investigated minimally invasive surgery (MIS) versus open posterior lumbar decompressions. There were 14 studies included which investigated MIS versus open posterior lumbar interbody fusions. Finally, there were 9 studies focused on navigation techniques and radiation safety within MIS procedures.

Conclusions

There are 34 meta-analysis studies evaluating minimally invasive to open thoracolumbar surgery for degenerative disease. The studies show a trend toward decreased estimated blood loss, decreased length of stay, decreased complications, similar fusion rates, improved accuracy, and decreased radiation when minimally invasive techniques are used.

Comparing Lumbar Disc Space Preparation With Fluoroscopy Versus Cone Beam-Computed Tomography and Navigation: A Cadaveric Study

STUDY DESIGN

Cadaveric study.

OBJECTIVE

This cadaveric study sought to evaluate the efficacy of disc space preparation with cone beam-computed tomography with navigation (CBCT+N) for instrument placement compared with instrument placement with conventional fluoroscopy.

SUMMARY OF BACKGROUND DATA

Disc space preparation from a transforaminal lumbar approach is challenging with respect to visualization, and surgeons currently rely on tactile feel and two-dimensional imaging in the operating room to assess instrument positioning.

METHODS

Two orthopedic spine surgeons performed 40 disc space preparations after eight cadavers were randomly assigned to fluoroscopy versus CBCT+N. Digital images of each vertebral endplate were captured and the percent disc removed by area for the total disc and by quadrants was determined using digital imaging software.

RESULTS

There were 20 lumbar disc levels prepared in the fluoroscopy group. There were 3 thoracolumbar, and 17 lumbar disc levels prepared in the experimental group. Percent disc removed relative to the total area of the disc, as determined by the digital imaging software, was higher in the CBCT+N group (P ≤ 0.0001). More disc was removed in both the anterior contralateral and posterior contralateral quadrants in the CBCT+N group (P = 0.0006 and P ≤ 0.0001 respectively). The intraclass correlation coefficient among blinded reviewers for percent disc removed was 0.759 (95% confidence interval, 0.587-0.866)]. There was no difference in time to complete disc space preparation, number of instrument passes, or number of endplate violations between the two groups (P = 0.28, P = 0.92, and P = 0.34 respectively).

CONCLUSION

The results of this cadaveric investigation reveal that CBCT+N guidance may be used to assess instrument placement for interbody disc space preparation in a similar length of time, with no difference in instrument passes or endplate violations, in comparison with fluoroscopy.

LEVEL OF EVIDENCE

5.

Feasibility and Accuracy of Thoracolumbar Minimally Invasive Pedicle Screw Placement With Augmented Reality Navigation Technology

STUDY DESIGN

Cadaveric laboratory study.

OBJECTIVE

To assess the feasibility and accuracy of minimally invasive thoracolumbar pedicle screw placement using augmented reality (AR) surgical navigation.

SUMMARY OF BACKGROUND DATA

Minimally invasive spine (MIS) surgery has increasingly become the method of choice for a wide variety of spine pathologies. Navigation technology based on AR has been shown to be feasible, accurate, and safe in open procedures. AR technology may also be used for MIS surgery.

METHODS

The AR surgical navigation was installed in a hybrid operating room (OR). The hybrid OR includes a surgical table, a motorized flat detector C-arm with intraoperative 2D/3D imaging capabilities, integrated optical cameras for AR navigation, and patient motion tracking using optical markers on the skin. Navigation and screw placement was without any x-ray guidance. Two neurosurgeons placed 66 Jamshidi needles (two cadavers) and 18 cannulated pedicle screws (one cadaver) in the thoracolumbar spine. Technical accuracy was evaluated by measuring the distance between the tip of the actual needle position and the corresponding planned path as well as the angles between the needle and the desired path. Time needed for navigation along the virtual planned path was measured. An independent reviewer assessed the postoperative scans for the pedicle screws' clinical accuracy.

RESULTS

Navigation time per insertion was 90 ± 53 seconds with an accuracy of 2.2 ± 1.3 mm. Accuracy was not dependent on operator. There was no correlation between navigation time and accuracy. The mean error angle between the Jamshidi needles and planned paths was 0.9° ± 0.8°. No screw was misplaced outside the pedicle. Two screws breached 2 to 4 mm yielding an overall accuracy of 89% (16/18).

CONCLUSION

MIS screw placement directed by AR with intraoperative 3D imaging in a hybrid OR is accurate and efficient, without any fluoroscopy or x-ray imaging during the procedure.

LEVEL OF EVIDENCE

N/A.

Head-mounted display augmented reality to guide pedicle screw placement utilizing computed tomography

PURPOSE

Augmented reality has potential to enhance surgical navigation and visualization. We determined whether head-mounted display augmented reality (HMD-AR) with superimposed computed tomography (CT) data could allow the wearer to percutaneously guide pedicle screw placement in an opaque lumbar model with no real-time fluoroscopic guidance.

METHODS

CT imaging was obtained of a phantom composed of L1-L3 Sawbones vertebrae in opaque silicone. Preprocedural planning was performed by creating virtual trajectories of appropriate angle and depth for ideal approach into the pedicle, and these data were integrated into the Microsoft HoloLens using the Novarad OpenSight application allowing the user to view the virtual trajectory guides and CT images superimposed on the phantom in two and three dimensions. Spinal needles were inserted following the virtual trajectories to the point of contact with bone. Repeat CT revealed actual needle trajectory, allowing comparison with the ideal preprocedural paths.

RESULTS

Registration of AR to phantom showed a roughly circular deviation with maximum average radius of 2.5 mm. Users took an average of 200 s to place a needle. Extrapolation of needle trajectory into the pedicle showed that of 36 needles placed, 35 (97%) would have remained within the pedicles. Needles placed approximated a mean distance of 4.69 mm in the mediolateral direction and 4.48 mm in the craniocaudal direction from pedicle bone edge.

CONCLUSION

To our knowledge, this is the first peer-reviewed report and evaluation of HMD-AR with superimposed 3D guidance utilizing CT for spinal pedicle guide placement for the purpose of cannulation without the use of fluoroscopy.

Perspective review on applications of optics in spinal surgery

Optical technologies may be applied to multiple facets of spinal surgery from diagnostics to intraoperative image guidance to therapeutics. In diagnostics, the current standard remains cross-sectional static imaging. Optical surface scanning tools may have an important role; however, significant work is required to clearly correlate surface metrics to radiographic and clinically relevant spinal anatomy and alignment. In the realm of intraoperative image guidance, optical tracking is widely developed as the current standard of instrument tracking, however remains compromised by line-of-sight issues and more globally cumbersome registration workflows. Surface scanning registration tools are being refined to address concerns over workflow and learning curves, and allow real-time update of tissue deformation; however, the line-of-sight issues plaguing instrument tracking remain to be addressed. In therapeutics, optical applications exist in both visualization, in the form of endoscopes, and ablation, in the form of lasers. Further work is required to extend the feasibility of laser ablation to multiple tissues, including disc, bone, and tumor, in a safe and time-efficient manner. Finally, we postulate some of the short- and long-term opportunities for future growth of optical techniques in the context of spinal surgery. Particular emphasis is placed on intraoperative image guidance, the area of the authors' primary expertise.

Accuracy of pedicle screw placement based on preoperative computed tomography versus intraoperative data set acquisition for spinal navigation system

AIM

To investigate the accuracy of pedicle screw placement based on preoperative computed tomography in comparison with intraoperative data set acquisition for spinal navigation system.

METHODS

The PubMed (MEDLINE), EMBASE, and Web of Science were systematically searched for the literature published up to September 2015. This review followed the Preferred Reporting Items for Systematic Reviews and Meta-analysis guidelines. Statistical analysis was performed using the Review Manager 5.3. The dichotomous data for the pedicle violation rate was summarized using relative risk (RR) and 95% confidence intervals (CIs) with the fixed-effects model. The level of significance was set at p < 0.05.

RESULTS

For this meta-analysis, seven studies used a total of 579 patients and 2981 screws. The results revealed that the accuracy of intraoperative data set acquisition method is significantly higher than preoperative one using 2 mm grading criteria (RR: 1.82, 95% CI: 1.09, 3.04, I² = 0%, p = 0.02). However, there was no significant difference between two kinds of methods at the 0 mm grading criteria (RR: 1.13, 95% CI: 0.88, 1.46, I² = 17%, p = 0.34). Using the 2-mm grading criteria, there was a higher accuracy of pedicle screw insertion in O-arm-assisted navigation than CT-based navigation method (RR: 1.96, 95% CI: 1.05, 3.64, I² = 0%, p = 0.03). The accuracy between CT-based navigation and two-dimensional-based navigation showed no significant difference (RR: 1.02, 95% CI: 0.35-3.03, I² = 0%, p = 0.97).

CONCLUSIONS

The intraoperative data set acquisition method may decrease the incidence of perforated screws over 2 mm but not increase the number of screws fully contained within the pedicle compared to preoperative CT-based navigation system. A significantly higher accuracy of intraoperative (O-arm) than preoperative CT-based navigation was revealed using 2 mm grading criteria.

Image guidance based on MRI for spinal interstitial laser thermotherapy: technical aspects and accuracy

OBJECTIVE

Image guidance for spinal procedures is based on 3D-fluoroscopy or CT, which provide poor visualization of soft tissues, including the spinal cord. To overcome this limitation, the authors developed a method to register intraoperative MRI (iMRI) of the spine into a neuronavigation system, allowing excellent visualization of the spinal cord. This novel technique improved the accuracy in the deployment of laser interstitial thermal therapy probes for the treatment of metastatic spinal cord compression.

METHODS

Patients were positioned prone on the MRI table under general anesthesia. Fiducial markers were applied on the skin of the back, and a plastic cradle was used to support the MRI coil. T2-weighted MRI sequences of the region of interest were exported to a standard navigation system. A reference array was sutured to the skin, and surface matching of the fiducial markers was performed. A navigated Jamshidi needle was advanced until contact was made with the dorsal elements; its position was confirmed with intraoperative fluoroscopy prior to advancement into a target in the epidural space. A screenshot of its final position was saved, and then the Jamshidi needle was exchanged for an MRI-compatible access cannula. MRI of the exact axial plane of each access cannula was obtained and compared with the corresponding screenshot saved during positioning. The discrepancy in millimeters between the trajectories was measured to evaluate accuracy of the image guidance

RESULTS

Thirteen individuals underwent implantation of 47 laser probes. The median absolute value of the discrepancy between the location predicted by the navigation system and the actual position of the access cannulas was 0.7 mm (range 0–3.2 mm). No injury or adverse event occurred during the procedures.

CONCLUSIONS

This study demonstrates the feasibility of image guidance based on MRI to perform laser interstitial thermotherapy of spinal metastasis. The authors' method permits excellent visualization of the spinal cord, improving safety and workflow during laser ablations in the epidural space. The results can be extrapolated to other indications, including biopsies or drainage of fluid collections near the spinal cord.

Spinal intraoperative three-dimensional navigation: correlation between clinical and absolute engineering accuracy

BACKGROUND CONTEXT

Spinal intraoperative computer-assisted navigation (CAN) may guide pedicle screw placement. Computer-assisted navigation techniques have been reported to reduce pedicle screw breach rates across all spinal levels. However, definitions of screw breach vary widely across studies, if reported at all. The absolute quantitative error of spinal navigation systems is theoretically a more precise and generalizable metric of navigation accuracy. It has also been computed variably and reported in less than a quarter of clinical studies of CAN-guided pedicle screw accuracy.

PURPOSE

This study aimed to characterize the correlation between clinical pedicle screw accuracy, based on postoperative imaging, and absolute quantitative navigation accuracy.

DESIGN/SETTING

This is a retrospective review of a prospectively collected cohort.

PATIENT SAMPLE

We recruited 30 patients undergoing first-time posterior cervical-thoracic-lumbar-sacral instrumented fusion±decompression, guided by intraoperative three-dimensional CAN.

OUTCOME MEASURES

Clinical or radiographic screw accuracy (Heary and 2 mm classifications) and absolute quantitative navigation accuracy (translational and angular error in axial and sagittal planes).

METHODS

We reviewed a prospectively collected series of 209 pedicle screws placed with CAN guidance. Each screw was graded clinically by multiple independent raters using the Heary and 2 mm classifications. Clinical grades were dichotomized per convention. The absolute accuracy of each screw was quantified by the translational and angular error in each of the axial and sagittal planes.

RESULTS

Acceptable screw accuracy was achieved for significantly fewer screws based on 2 mm grade versus Heary grade (92.6% vs. 95.1%, p=.036), particularly in the lumbar spine. Inter-rater agreement was good for the Heary classification and moderate for the 2 mm grade, significantly greater among radiologists than surgeon raters. Mean absolute translational-angular accuracies were 1.75 mm-3.13° and 1.20 mm-3.64° in the axial and sagittal planes, respectively. There was no correlation between clinical and absolute navigation accuracy.

CONCLUSIONS

Radiographic classifications of pedicle screw accuracy vary in sensitivity across spinal levels, as well as in inter-rater reliability. Correlation between clinical screw grade and absolute navigation accuracy is poor, as surgeons appear to compensate for navigation registration error. Future studies of navigation accuracy should report absolute translational and angular errors. Clinical screw grades based on postoperative imaging may be more reliable if performed in multiple by radiologist raters.

A Novel Groove-Entry Technique for Inserting Thoracic Percutaneous Pedicle Screws

STUDY DESIGN

Surgical technique.

OBJECTIVE

To evaluate the efficacy of a novel groove-entry technique for thoracic percutaneous pedicle screw (PPS) insertion.

SUMMARY OF BACKGROUND DATA

Minimally invasive spine stabilization (MISt) using posterior thoracolumbar instrumentation has many advantages over open procedures. Because of the variability among PPS entry points, the sloped cortex of the transverse process, and the narrow thoracic pedicle, thoracic PPS placement is technically challenging.

MATERIALS AND METHODS

A retrospective review of 24 patients who underwent minimally invasive spine stabilization procedures involving 165 thoracic PPS placements using the novel technique was performed. The thoracic PPS entry is a groove formed by 3 bony elements: the cranial portion of the base of the transverse process, the rib neck, and the posterolateral wall of the pedicle. This groove can be easily identified under fluoroscopy with a Jamshidi needle allowing thoracic PPS insertion in the craniocaudal direction.

RESULTS

Of the 165 thoracic PPSs placed, "Good" or "Acceptable" PPS placement accuracy was achieved in 152 (92.1%) and 164 (99.4%) placements, respectively. No complications such as organ injury, and screw loosening or breakage were observed with thoracic PPS insertion.

CONCLUSIONS

This novel technique is both safe and reliable, with low misplacement and complication rates. In hospitals in which computer image guidance or navigation is unavailable, this groove-entry technique may become the standard for thoracic PPS insertion.

Removal of fixation construct could mitigate adjacent segment stress after lumbosacral fusion: A finite element analysis

BACKGROUND DATA

Combined usage of posterior lumbar interbody fusion and transpedicular fixation has been extensively used to treat the various lumbar degenerative disc diseases. The transpedicular fixator aims to increase stability and enhance the fusion rate. However, how the fused disc and bridged vertebrae respectively affect adjacent-segment diseases progression is not yet clear.

METHODS

Using a validated lumbosacral finite-element model, three variations at the L4-L5 segment were analyzed: 1) moderate disc degeneration, 2) instrumented with a stand-alone cage and pedicle screw fixators, and 3) with the cage only after fusion. The intersegmental angles, disc stresses, and facet loads were examined. Four motion tests, flexion, extension, bending, and twisting, were also simulated.

FINDINGS

The adjacent-segment disease was more severe at the cephalic segment than the caudal segment. After solid fusion and fixation, the increase in intersegmental angles, disc stresses and facet loads of the adjacent segments were about 57.6%, 47.3%, and 59.6%, respectively. However, these changes were reduced to 30.1%, 22.7%, and 27.0% after removal of the fixators. This was attributed to the differences between the biomechanical characteristics of the fusion and fixation mechanisms.

INTERPRETATION

Fixation superimposes a stiffer constraint on the mobility of the bridged segment than fusion. The current study suggested that the removal of spinal fixators after complete fusion could decrease the stress at adjacent segments. Through a minimally invasive procedure, we could reduce secondary damage to the paraspinal structures while removing the fixators, which is of utmost concern to surgeons.

Total 3D Airo® Navigation for Minimally Invasive Transforaminal Lumbar Interbody Fusion

Introduction. A new generation of iCT scanner, Airo®, has been introduced. The purpose of this study is to describe how Airo facilitates minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF). Method. We used the latest generation of portable iCT in all cases without the assistance of K-wires. We recorded the operation time, number of scans, and pedicle screw accuracy. Results. From January 2015 to December 2015, 33 consecutive patients consisting of 17 men and 16 women underwent single-level or two-level MIS-TLIF operations in our institution. The ages ranged from 23 years to 86 years (mean, 66.6 years). We treated all the cases in MIS fashion. In four cases, a tubular laminectomy at L1/2 was performed at the same time. The average operation time was 192.8 minutes and average time of placement per screw was 2.6 minutes. No additional fluoroscopy was used. Our screw accuracy rate was 98.6%. No complications were encountered. Conclusions. Airo iCT MIS-TLIF can be used for initial planning of the skin incision, precise screw, and cage placement, without the need for fluoroscopy. “Total navigation” (complete intraoperative 3D navigation without fluoroscopy) can be achieved by combining Airo navigation with navigated guide tubes for screw placement.

The Utility of a Digital Virtual Template for Junior Surgeons in Pedicle Screw Placement in the Lumbar Spine

This study assessed the utility of three-dimensional preoperative image reconstruction as digital virtual templating for junior surgeons in placing a pedicle screw (PS) in the lumbar spine. Twenty-three patients of lumbar disease were operated on with bilateral PS fixation in our hospital. The two sides of lumbar pedicles were randomly divided into “hand-free group” (HFG) and “digital virtual template group” (DVTG) in each patient. Two junior surgeons preoperatively randomly divided into these two groups finished the placement of PSs. The accuracy of PS and the procedure time of PS insertion were recorded. The accuracy of PS in DVTG was 91.8% and that in HFG was 87.7%. The PS insertion procedure time of DVTG was 74.5 ± 8.1 s and that of HFG was 90.9 ± 9.9 s. Although no significant difference was reported in the accurate rate of PS between the two groups, the PS insertion procedure time was significantly shorter in DVTG than in HFG (P < 0.05). Digital virtual template is simple and can reduce the procedure time of PS placement.

Effect of the percutaneous pedicle screw fixation at the fractured vertebra on the treatment of thoracolumbar fractures

PURPOSE

The purpose of this study was to evaluate the efficacy and safety of percutaneous pedicle screw fixation at the fractured vertebra in the treatment of thoracolumbar fractures.

METHODS

Thirty-two consecutive patients were enrolled in the study. All patients received percutaneous pedicle screw fixation, and they were randomly divided into two groups to undergo either the placement of pedicle screws into the fractured vertebra (fractured group) or not (control group). The operation time and intra-operative blood loss were recorded. Oswestry disability index (ODI) questionnaire and visual analogue scale (VAS) as clinical assessments were quantified. Radiographic follow-up was defined by the vertebral body index (VBI), anterior vertebral body height (AVBH), and Cobb angle (CA).

RESULTS

No significant difference was observed in the operation time and intra-operative blood loss between the two groups. Clinical results (VAS and ODI scores) showed no significant difference during all the follow-up periods. In the fractured group, there were better correction and less loss of AVBH and VBI compared with the control group. However, post-operative correction of the CA immediately after surgery and the correction loss at the final follow-up showed no significant difference between the two groups.

CONCLUSION

Percutaneous screw fixation combined with intermediate screws at the fractured vertebra could more effectively restore and maintain fractured vertebral height, and is an acceptable, minimally invasive surgical choice for patients with type A thoracolumbar fractures.

Fluoroscopy-guided pedicle screw accuracy with a mini-open approach: a tomographic evaluation of 470 screws in 125 patients

BACKGROUND

Transpedicular screws are currently placed with open free hand and minimally invasive techniques assisted with either fluoroscopy or navigation. Screw placement accuracy had been investigated with several methods reaching accuracy rates from 71.9% to 98.8%. The objective of this study was to assess the accuracy and safety for 2-D fluoroscopy-guided screw placement assisted with electrophysiological monitoring and the inter-observer agreement for the breach classification.

METHODS

A retrospective review was performed on 125 consecutive patients who underwent minimally invasive transforaminal lumbar interbody fusion and transpedicular screws placement between the levels of T-12 and S-1. Screw accuracy was evaluated using a postoperative computed tomography by three independent observers. Pedicle breach was documented when there was a violation in any direction of the pedicle. Inter-observer agreement was assessed with the Kappa coefficient.

RESULTS

A total of 470 transpedicular screws were evaluated between the levels of T-12 and S-1. In 57 patients the instrumentation was bilateral and in 68 unilateral. A substantial degree of agreement was found between the observers AB (κ=0.769) and A-C (κ=0.784) and almost perfect agreement between observers B-C (κ=0.928). There were a total of 427.33 (90.92%) screws without breach, 39.33 (8.37%) minor breach pedicles and 3.33 (0.71%) major breach pedicles. The pedicle breach rate was 9.08% Trajectory pedicle breach percentages were as follows: minor medial pedicle breach 4.68%, minor lateral pedicle breach 3.47%, minor inferior pedicle breach 0.22%, and major medial breach 0.70%. No intraoperative instrumentation-related or postoperative clinical complications were encountered and no surgical revision was needed.

CONCLUSIONS

Our study demonstrated a high accuracy (90.2%) for 2-D fluoroscopy-guided pedicle screw using electromonitoring. Only 0.71% of the 470 screws had a major breach. Knowing the radiological spine pedicle anatomy and the correct interpretation of EMG are the key factors for this technique.