Computer-assisted fluoroscopic targeting system for pedicle screw insertion

SEGMENTAL SPINAL INSTRUMENTATION IN THE MANAGEMENT OF SCOLIOSIS

SPINAL INSTRUMENTATION FOR the correction of spinal deformity began with Harrington and his rod system. The use of the Harrington rods was limited, however, because of the need for long-segment instrumentation, distraction, and the potential for hood dislodgment and construct failure. Luque subsequently introduced the next generation of spinal fixation techniques via the concept of segmental instrumentation; his use of sublaminar wires allowed the construct to be fixated to the spine at every level. This arrangement allowed greater control over correction of spinal deformities and significantly lessened the incidence of hardware dislodgment. Modern instrumentation systems, including the use of pedicle screws, permit even greater control of the spine in multiple planes during deformity correction. Newer strategies have decreased the incidence of neurological injury during implant application and provide greater stability. A review of segmental fixation, including surgical techniques, is provided in this article.

Computer-assisted pedicle screw placement for thoracolumbar spine fracture with separate spinal reference clamp placement and registration

BACKGROUND

The objective of the study was to improve the accuracy of computer-assisted pedicle screw installation in the spine. This study evaluates the accuracy of computer-assisted pedicle screw placement with separate spinal reference clamp placement and registration on each instrumented vertebra for thoracolumbar spine fractures.

METHODS

Postoperative radiographs and CT scans assessed the accuracy of pedicle screw placement in 21 adult patients on each instrumented vertebra. Screw placements were graded as good if the screws were placed in the central core of the pedicle and the cancellous portion of the body. Screw placements were graded as fair if the screws were placed slightly eccentrically, causing erosion of the pedicular cortex, and with less than a 2-mm perforation of the pedicular cortex. Screw placements were graded as poor if screws were placed eccentrically with a large portion of the screw extending outside the cortical margin of the pedicle and with more than a 2-mm perforation of the pedicular cortex.

RESULTS

A total of 140 image-guided pedicle screws were placed in 21 patients: 78 in the thoracic and 62 in the lumbar spine. Of the 140 pedicle screw placements, 96.4% (135/140) were categorized as good; 3.6% (5/140), fair; and 0% were poor. All 5 fair placement screws were placed in the thoracic spine without any mobility.

CONCLUSION

Separate registration increases accuracy of screw placement in thoracolumbar pedicle instrumentation. Separate spinal reference clamp placement in the instrumented vertebra provides real-time virtual imaging that decreases the possibility of downward displacement during manual installation of the screw.

Fluoroscopy-based navigation system in spine surgery

The variability in width, height, and spatial orientation of a spinal pedicle makes pedicle screw insertion a delicate operation. The aim of the current paper is to describe a computer-assisted surgical navigation system based on fluoroscopic X-ray image calibration and three-dimensional optical localizers in order to reduce radiation exposure while increasing accuracy and reliability of the surgical procedure for pedicle screw insertion. Instrumentation using transpedicular screw fixation was performed: in a first group, a conventional surgical procedure was carried out with 26 patients (138 screws); in a second group, a navigated surgical procedure (virtual fluoroscopy) was performed with 26 patients (140 screws). Evaluation of screw placement in every case was done by using plain X-rays and post-operative computer tomography scan. A 5 per cent cortex penetration (7 of 140 pedicle screws) occurred for the computer-assisted group. A 13 per cent penetration (18 of 138 pedicle screws) occurred for the non computer-assisted group. The radiation running time for each vertebra level (two screws) reached 3.5s on average in the computer-assisted group and 11.5s on average in the non computer-assisted group. The operative time for two screws on the same vertebra level reaches 10 min on average in the non computer-assisted group and 11.9 min on average in the computer-assisted group. The fluoroscopy-based (two-dimensional) navigation system for pedicle screw insertion is a safe and reliable procedure for surgery in the lower thoracic and lumbar spine.

Thoracic pedicle screw placement: analysis using anatomical landmarks without image guidance

STUDY DESIGN

Prospective laboratory study analyzing the technique of pedicle screw placement in a cadaveric model.

OBJECTIVES

To determine whether a freehand technique without image guidance can be used to safely place pedicle screws in the thoracic spine.

SUMMARY OF BACKGROUND DATA

The use of thoracic pedicle screws for the treatment of spinal deformity has been gaining increased acceptance among surgeons. Although these implants improve deformity correction, there is still concern regarding the risks to neurological and vascular structures and regarding the experience level needed to use this implant. This study was designed to determine whether these implants could be placed safely without imaging modalities.

METHODS

Six fresh cadaveric specimens were instrumented from vertebral segments T4-T11. Ninety-six screws were placed along the anatomical axis of the pedicle. Pedicles were dissected to determine the wall violations, the position of neural structures, and the lateral coverage of the pedicle by the rib head.

RESULTS

Ninety-seven percent of screws had less than 1 mm of wall violation, with 84 screws (87.5%) fully contained within the pedicle. Four screws (4.16%) violated the medial cortex. No violations occurred superiorly, inferiorly, or anteriorly. Nerve roots were in contact with the inferior pedicle wall at all levels. The average distance from nerve to the superior pedicle ranged from 3.85 to 5.04 mm.

CONCLUSIONS

Placing pedicle screws along the anatomical axis without image guidance produced a low level of pedicle wall disruption. This technique uses a reproducible start point at each level, and the results are equal to or better than those of other cadaveric studies that have used guidance systems.

Closed Fluoroscopic-Assisted Spinal Arch External Skeletal Fixation for the Stabilization of Vertebral Column Injuries in Five Dogs

OBJECTIVE

To evaluate outcome after closed fluoroscopic-assisted application of spinal arch external skeletal fixators in dogs with vertebral column injuries.

STUDY DESIGN

Retrospective case series.

ANIMALS

Dogs with traumatic vertebral column injuries (n=5).

METHODS

Medical records of dogs with vertebral column fractures and/or luxations stabilized with spinal arch external skeletal fixator frames applied using a closed fluoroscopic-assisted technique were reviewed. Owners were contacted to obtain long-term clinical outcomes.

RESULTS

Five dogs (age range, 6-72 months; weight, 10-54 kg) had traumatic vertebral column injuries stabilized with spinal arch external skeletal fixators applied in closed fashion. Injuries involved vertebral segments of the thoracolumbar junction, lumbar spine, and lumbosacral junction. Immediately postoperatively, 4 dogs had anatomic alignment of their vertebral fracture/luxation; 1 dog had 1 mm of vertebral canal height compromise. Time to fixator removal ranged from 65 to 282 days (141+/-87 days). All dogs had regained satisfactory neurologic function by 3 months. At long-term follow-up (range, 282-780 days; mean 445+/-190 days) all dogs were judged to have good to excellent return of function by their owners.

CONCLUSION

Successful closed fluoroscopic-assisted application of external skeletal fixators using spinal arches provided satisfactory reduction with few complications in 5 dogs. Return to function was judged to be good to excellent in all dogs at long-term evaluation.

CLINICAL RELEVANCE

Closed fluoroscopic-assisted application of ESF using spinal arches provided satisfactory reduction and effective stabilization of spinal fractures with few complications and should be considered as a treatment approach.

Image-guided spinal surgery

BACKGROUND

The purpose of this review is to present a comprehensive summary of commonly used methods of spinal image guidance, including the benefits and limitations of this novel technology.

METHODS

The relevant medical literature was examined, supplemented by the author's laboratory and clinical experience with image-guided spinal surgery.

RESULTS

Spinal image guidance has undergone significant evolution and rapid technological advancement in recent years. Image guidance provides three-dimensional visualization of the spine that can be used for preoperative planning and intraoperative navigation. There are three commonly used methods of spinal image guidance: preoperative CT-based, fluoroscopy-based, and 3D fluoroscopy. Each of these methods demonstrates lower rates of spinal implant misplacement than non-image-guided techniques.

CONCLUSIONS

Image guidance provides highly accurate intraoperative navigation and the medical literature suggests that this technology increases the safety of a variety of routine and complex spinal procedures.

Computer-assisted Spinal Navigation Versus Serial Radiography and Operative Time for Posterior Spinal Fusion at L5-S1

OBJECTIVE

To review the operative time differences between computer-assisted spinal navigation versus serial radiography.

SUMMARY OF BACKGROUND DATA

There have been multiple studies describing the use of computer-assisted image guided surgery (IGS) in the application of spinal instrumentation. Techniques have evolved to allow attainment of multilevel visualization intraoperatively both successfully and safely. These have proven to result in low screw misplacement rates, low incidence of radiation exposure and excellent operative field viewing. As a result, image guidance has become an increasingly accepted and practiced form of intraoperative spinal navigation. However, potential limitations to IGS have been described including longer operating times. Many studies have looked at the success of beneficial outcomes; however, none to our knowledge have reviewed such described operative time increments with IGS.

METHODS

The authors performed a retrospective database analysis of 105 patients undergoing posterior L5-S1 spine fusion with pedicle screw instrumentation for isthmic spondylolisthesis with and without the use of fluoroscopy-based image guidance. This was followed by a chart review of anesthesia operative time documentation. Subsequent time calculations and statistical analysis were performed for comparison.

RESULTS

Computer-assisted image-guided spine surgery has overall demonstrated shorter mean operative times when compared with intraoperative serial radiography technique; an average of 40 minutes less per case (P<0.001). There is also less variation in operative times using image guidance, with 13 of 43 (30%) cases using serial x-ray lasting more than 3.75 hours compared with none of the 57 done via image guidance (P<0.001). The operative duration for both procedures trended downward over time. For both procedural cohorts operating room time continued to decrease as of the most recent year being performed. Lastly, in an attempt to minimize such a confounding factor as a learning curve, the last 20 cases in each group were compared. There was an average difference of about 22 minutes less for the image guidance group but missed being statistically significant (P=0.0503).

CONCLUSIONS

Image-guided spinal surgery did not cause an increase in operative time. In the best scenario, image navigation saved a statistically significant (P<0.001) amount of time in the operating room. At its worst, fluoroscopy-based image-guided navigation is not significantly different from standard serial radiography.

Neurosurgical robotics: a review of brain and spine applications

Neurosurgery has traditionally been at the forefront of advancing technologies, adapting new techniques and devices successfully in an effort to increase the safety and efficacy of brain and spine surgery. Among these adaptations are surgical robotics. This paper reviews some of the more promising systems in neurosurgical robotics, including brain and spine applications in use and in development. The purpose of the discussion is twofold-to discuss the most promising models for neurosurgical applications, and to discuss some of the pitfalls of robotic neurosurgery given the unique anatomy of the brain and spine.

Pedicle screw placement accuracy: a meta-analysis

STUDY DESIGN

A meta-analysis of the published literature was conducted specifically looking at accuracy and the postoperative methods used for the assessment of pedicle screw placement in the human spine.

OBJECTIVES

This study specifically aimed to identify postoperative methods used for pedicle screw placement assessment, including the most common method, and to report cumulative pedicle screw placement study statistics from synthesis of the published literature.

SUMMARY OF BACKGROUND DATA

Safety concerns have driven specific interests in the accuracy and precision of pedicle screw placement. A large variation in reported accuracy may exist partly due to the lack of a standardized evaluation method and/or the lack of consensus to what, or in which range, is pedicle screw placement accuracy considered satisfactory.

METHODS

A MEDLINE search was executed covering the span from 1966 until 2006, and references from identified papers were reviewed. An extensive database was constructed for synthesis of the identified studies. Subgroups and descriptive statistics were determined based on the type of population, in vivo or cadaveric, and separated based on whether the assistance of navigation was employed.

RESULTS

In total, we report on 130 studies resulting in 37,337 total pedicle screws implanted, of which 34,107 (91.3%) were identified as accurately placed for the combined in vivo and cadaveric populations. The most common assessment method identified pedicle screw violations simply as either present or absent. Overall, the median placement accuracy for the in vivo assisted navigation subgroup (95.2%) was higher than that of the subgroup without the use of navigation (90.3%).

CONCLUSIONS

Navigation does indeed provide a higher accuracy in the placement of pedicle screws for most of the subgroups presented. However, an exception is found at the thoracic levels for both the in vivo and cadaveric populations, where no advantage in the use of navigation was found.

Inserting pedicle screws in the upper thoracic spine without the use of fluoroscopy or image guidance. Is it safe?

Several studies have looked at accuracy of thoracic pedicle screw placement using fluoroscopy, image guidance, and anatomical landmarks. To our knowledge the upper thoracic spine (T1-T6) has not been specifically studied in the context of screw insertion and placement accuracy without the use of either image guidance or fluoroscopy. Our objective was to study the accuracy of upper thoracic screw placement without the use of fluoroscopy or image guidance, and report on implant related complications. A single surgeon inserted 60 screws in 13 consecutive non-scoliotic spine patients. These were the first 60 screws placed in the high thoracic spine in our institution. The most common diagnosis in our patient population was trauma. All screws were inserted using a modified Roy-Camille technique. Post-operative axial computed tomography (CT) images were obtained for each patient and analyzed by an independent senior radiologist for placement accuracy. Implant related complications were prospectively noted. No pedicle screw misplacement was found in 61.5% of the patients. In the remaining 38.5% of patients some misplacements were noted. Fifty-three screws out of the total 60 implanted were placed correctly within all the pedicle margins. The overall pedicle screw placement accuracy was 88.3% using our modified Roy-Camille technique. Five medial and two lateral violations were noted in the seven misplaced screws. One of the seven misplaced screws was considered to be questionable in terms of pedicle perforation. No implant related complications were noted. We found that inserting pedicle screws in the upper thoracic spine based solely on anatomical landmarks was safe with an accuracy comparable to that of published studies using image-guided navigation at the thoracic level.

The Development of Minimally Invasive Spine Surgery

The modern era of minimally invasive spine surgery has its roots in percutaneous techniques developed in the mid-twentieth century. The widespread application of minimally invasive techniques seen today is predicated on technologic developments of only the past 10 years, however. This article reviews the development of minimally invasive spinal surgery as it has evolved for the cervical, thoracic, and lumbar spine. Each new development has sought to equal or improve on the effectiveness demonstrated by comparable open surgical techniques while reducing iatrogenic tissue trauma and resultant postoperative pain and disability, to produce overall better outcomes for patients.

Image-guided periacetabular osteotomy: computer-assisted navigation compared with the conventional technique: a randomized study of 36 patients followed for 2 years

BACKGROUND

Periacetabular osteotomy (PAO) is an effective but technically demanding surgical procedure. We evaluated the efficiency of computer-assisted navigation in PAO and compared it with the traditional approach.

PATIENTS AND METHODS

We performed a randomized study of 36 patients undergoing PAO using either the CT-based, computer-assisted navigation technique or the conventional approach. The operative details, radiographic results, and functional outcomes were compared between groups.

RESULTS

Patients in the conventional surgery group required an average of 4.4 (2-7) images of intraoperative radiographs, whereas only 0.6 (0-1) images were required in the navigation group. The operation time was 21 min shorter with computer-assisted navigation. No significant difference with regard to operative blood loss, transfusion requirement, correction of deformity, and functional improvement was found. Complications such as intraarticular damage, osteonecrosis, or neurovascular injury were not encountered.

INTERPRETATION

A computer-assisted navigation system is a feasible tool to provide real-time image guidance and facilitate PAO. However, it offers little additional benefit when the surgery is done by an experienced surgeon.

Real-time tracking of vertebral body movement with implantable reference microsensors

OBJECTIVE

In the spine, navigation techniques serve mainly to control and accurately target insertion of implants. The main source of error is that the spine is not a rigid organ, but rather a chain of semiflexible movement segments. Any intraoperative manipulation of the patient alters the geometry and volumetry as compared to the 3D volume model created from the image data. Thus, the objective of the study was to implement the theoretical principle of microsensor referencing in a model experiment and to clarify which anatomical structures are suitable for intermittent implantation of positional sensors, as illustrated with cervical vertebral bodies.

MATERIALS AND METHODS

Laboratory tests were conducted using 70 models of human cervical vertebral bodies. The first experiment investigated whether arbitrary movements of vertebral bodies can be tracked with the positional information from the implanted microsensors. The accuracy of this movement monitoring was determined quantitatively on the basis of positional error measurement. In the second experiment, different ventral and dorsal surgical operations were simulated on five models of the cervical spine. Quantifiable measurement values such as the spatial extension of the intervertebral space and the relative positions of the planes of the upper plates were determined.

RESULTS

With respect to the differing anatomy of the individual vertebral bodies of the cervical spine, the sensors could be placed securely with a 5x2 mm drill. The registration error (RE) was determined as a root mean square error. The mean value was 0.9425 mm (range: 0.57-1.2 mm; median: 0.9400 mm; SD: 0.1903 mm). The precision of the movement monitoring of the vertebral body was investigated along its three main axes. The error tolerance between post-interventional 3D reconstruction and direct measurement on the model did not exceed 1.3 mm in the distance measurements or 2.5 degrees in the angular measurements. The tomograms on the system monitor could be updated in close to real time on the basis of the positional information from the reference sensor.

CONCLUSIONS

Motion sensors implanted into the vertebral bodies communicated any change in position to the navigation system in close to real time, thus enabling the preoperative image data set to be updated. The experiments described could ultimately show that continuous real-time visualization of individual vertebral body movements along the movement axes (flexion-extension, tilting and rotation) is possible with high accuracy using implantable microsensors. A future application of such microsensors might be the integration of robot systems into spinal microsurgery.

Miniature robotic guidance for spine surgery — introduction of a novel system and analysis of challenges encountered during the clinical development phase at two spine centres

BACKGROUND

Instrumented spinal fusion surgery is increasingly performed. Breaching of the pedicle occurs in 3-55% of screws; clinically significant screw misplacements occur in 0-7% of all transpedicular screw placements. Several techniques have reduced this incidence but none gained popularity due to cost as well as staff issues. Surgical robots offer distinct added value in accuracy and minimal invasiveness. The aim of this study is to introduce the SpineAssist--a novel spine surgery miniature robot, to discuss the various reasons that had prevented full success with its use, to identify patients related, technical related, and surgeon related issues, and to offer ways to avoid them.

METHODS

The SpineAssist miniature robotic system is presented, including a short description of the system, its mode of action and a short summary of the surgical procedure.15 patients had undergone lumbar fusion procedures using the robotic system as part of clinical trials in two Israeli spine centres. A group of 9 procedures was identified within this prospective cohort. This group represents a wide array of technical challenges and human errors which were encountered during the clinical development phase of the SpineAssist. These 9 cases were conducted in two different sites by different surgical teams, over a period of 9 months, with an average interval of 7 weeks between consecutive cases. The cases were analysed for patient, system, surgeon and technical issues causing the difficulty. Conclusions were drawn as to how to avoid these hurdles in the future.

RESULTS

In six cases the system operated smoothly, resulting in accurate screws placement according to the pre-operative plan, this was confirmed by a post-operative CT scan. Technical and surgical challenges which are associated with the system early development stage were encountered during 9 procedures. On the technical side, the following phenomena were evident: 1) failure of the software to automatically achieve satisfying CT-to-fluoro image registration and 2) failure of the hospital's peripheral equipment/logistics preventing registration. On the clinical side of things, the following issues were encountered: 1) failure to avoid excessive pressure on the guiding arm caused by surrounding soft tissues, leading to a shift in the entry point and trajectory of the tool guide. 2) a surgeon applying too much force on the tool guide at the tip of the robotic arm, causing deviation from plan. 3) pre-operative plan out of the reach of the robot arm and 4) attachment of the clamp to the spinous process in a suboptimal orientation.

CONCLUSIONS

It is expected that following a steep learning curve in the range of 5-10 cases, recommended to take place within 2-3 weeks time, the surgical team will gain sufficient experience in operating the SpineAssist miniature robotic device in order to achieve excellent surgical results. The system may be used for wide range of applications including but not limited to pedicle screws, trans-facet and trans-laminar screws, biopsy needles, vertebroplasty or kyphoplasty tools and more. The preoperative plan has to be logical, intraoperative fluoro images taken with care, gentle surgical technique must be kept - maintaining the integrity of the posterior elements, and avoiding pressure between the robot arms and the soft tissues. During the clinical development phase discussed in this study, both teams used an early version of the system. Based on the results of this study several significant software and hardware improvements have already been implemented. It is our hope that describing and analysing our findings will help in planning and preparing for the clinical utilization of the SpineAssist system in future sites and will shorten their learning curve. By the time this article is published wider clinical experience will have been gathered and we expect to soon follow up with an analysis of clinical utilization of this system in a larger study group.

Percutaneous computer-assisted translaminar facet screw: an initial human cadaveric study

BACKGROUND CONTEXT

Translaminar facet screws are a minimally invasive technique for posterior lumbar fixation with good success rates. Computer-assisted image navigation using virtual fluoroscopy allows multiple simultaneous screens in various planes to plan and drive spinal instrumentation.

PURPOSE

This study evaluates the percutaneous placement of translaminar facet screws with the use of virtual fluoroscopy as an image guidance technique.

STUDY DESIGN/SETTING

A human cadaveric study was performed with a percutaneous reference frame applied to the iliac crest. Ten translaminar facet screws were placed bilaterally at five levels. Anteroposterior and lateral images were used to navigate 4.0-mm screws through a percutaneous portal under virtual fluoroscopy.

METHODS

An axial computed tomographic scan through the instrumented levels was obtained after the screws were placed. Screws were graded on entry, course through the lamina, and terminus. A grading system was devised to grade the course through the lamina.

RESULTS

All 10 screw-entry points were judged optimal at the spinous process laminar junction. There were five Grade I breeches with less than 1/2 the screw through the lamina, and five Grade 0 screw placements with the screw contained completely within the lamina. The termination point was acceptable in five screws. The screws that began on the right and terminated on the left were all found to have grade II breakouts. No screws placed the spinal canal or exiting nerve root at risk.

CONCLUSIONS

Virtual fluoroscopy provides significant assistance in percutaneous placement of translaminar facet screws and results in safe position of entry, lamina course, and terminus.

Use of intraoperative isocentric C-arm 3D fluoroscopy for sextant percutaneous pedicle screw placement: case report and review of the literature

BACKGROUND CONTEXT

Three-dimensional (3D) fluoroscopy-based image guidance system using an isocentric C-arm (Iso-C) fluoroscope was shown to be as effective as computed tomography-based systems in guiding the accurate percutaneous placement of lumbar pedicle screws in cadavers. To date, however, no description is available of the intraoperative use of 3D fluoroscopy to guide lumbar pedicle screw placement in an actual spinal fusion procedure.

PURPOSE

We report a case in which isocentric 3D fluoroscopic images, along with image-guidance software, were used to guide the placement of percutaneous pedicle screws for fusion in a patient with degenerative spondylolisthesis.

STUDY DESIGN/SETTING

Operating room of a large academic medical center during the placement of percutaneous pedicle screws in a patient with degenerative spondylolisthesis.

METHODS

A percutaneous dynamic reference array was attached to the L3 spinous process. A satisfactory image set was obtained and automatically registered. The L4 and L5 pedicles were localized, and pedicle holes were then cannulated, drilled and tapped. A screw was then inserted using the Sextant system for percutaneous pedicle screws. In this manner, bilateral pedicle screws were inserted into the L4-L5 pedicles. All steps of pedicle cannulation were performed under Iso-C 3D image guidance.

RESULTS

A postoperative computed tomography scan showed accurate placement of all pedicle screws. The patient experienced an improvement in leg pain with no new neurologic deficits.

CONCLUSIONS

The present case is the first case to demonstrate the intraoperative use of a 3D fluoroscopy-based image-guidance system for accurate navigation during lumbar pedicle screw placement.

Clinical accuracy of fluoroscopic computer-assisted pedicle screw fixation: a CT analysis

STUDY DESIGN

Observational cohort study with computerized tomography (CT) analysis of in vivo pedicle screw placement.

OBJECTIVE

To evaluate the clinical accuracy of computer-assisted fluoroscopy for the placement of thoracic and lumbosacral (LS) pedicle screws.

SUMMARY OF BACKGROUND DATA

Computer-assisted fluoroscopy is an adjunct for the placement of pedicle screws.

METHODS

Postoperative CT of 360 titanium pedicle screws (281 LS [L1-S1]; 79 thoracic [T2-T12]) were independently assessed. All screws were placed using the FluoroNav system (Medtronic Surgical Navigation Technologies, Louisville, CO). The relative position of the screw to the pedicle was graded as follows: A = completely in; B = <2 mm breach; C = 2-4 mm breach; and D = >4 mm breach. If an osseous breach occurred, the direction of the breach was further classified.

RESULTS

Eight-five percent of screws were completely contained within the pedicle. Fifty-five-pedicle breaches (25 medial; 30 lateral) occurred. Pedicle breaches were graded B in 13.1% (47 breaches), C in 1.9% (7), and D in 0.3% (1) of screws. Pedicle breach was significantly higher in the thoracic compared to the LS spine, 31.6% (25/79) and 10.6% (30/281), respectively (P < 0.0001). In the thoracic spine, 72% of pedicle breaches were lateral. In 49% of breaches, the screw diameter was larger than the pedicle diameter. None of the pedicle breaches were associated with neurologic or other clinical sequelae.

CONCLUSIONS

The clinical pedicle breach rate in this study is comparable to those reported using conventional techniques with or without fluoroscopic assistance. FluoroNav appears to be a safe adjunct for the placement of thoracic and LS pedicle screws.

Standard multiplanar fluoroscopy versus a fluoroscopically based navigation system for the percutaneous insertion of iliosacral screws: a cadaver model

OBJECTIVES

To compare the safety and efficiency of standard multiplanar fluoroscopy (StdFluoro) and virtual fluoroscopy (VirtualFluoro) for use in the percutaneous insertion of iliosacral screws.

DESIGN

: Human cadaver study comparing 2 imaging modalities during iliosacral screw insertion; imaging randomized from side to side.

SETTING

Bioskills laboratory in a medical school.

PARTICIPANTS

Twenty-nine embalmed whole human cadavers without prior hip or pelvic surgery.

INTERVENTION

Iliosacral screws were inserted into the S1 bodies using a percutaneous insertion technique. Screws were inserted on one side using StdFluoro, and on the other side, screws were placed using VirtualFluoro.

MAIN OUTCOME MEASUREMENTS

Time necessary for imaging preparation, screw insertion, and actual fluoroscopy were recorded. Accuracy and safety of screw placement was assessed using computed tomography and an anatomic dissection of the pelvis.

RESULTS

: Fifty-six of 58 iliosacral screws were placed within the desired bony corridor of the posterior pelvis. One screw placed using each method was inserted erroneously, but both were relatively minor deviations. There were no obvious injuries to major vessels or nerve roots. The total surgical time required for preparation of imaging and screw insertion averaged 7.3 minutes using StdFluoro and 6.7 minutes using VirtualFluoro (P = 0.4). Although the time necessary for screw insertion using VirtualFluoro averaged only 3.5 minutes, compared to 7.0 minutes for StdFluoro (P < 0.05), this time savings was offset by that required for application and calibration of tracking devices when using VirtualFluoro. The average fluoroscopy time using StdFluoro method was 26 seconds, whereas that for the VirtualFluoro was only 6 seconds (P < 0.01).

CONCLUSIONS

Most of the percutaneous iliosacral screws were safely inserted using StdFluoro and VirtualFluoro, and total surgical times were similar using both methods. As VirtualFluoro continues to evolve, improved efficiency in operative times may be expected. Currently, the most beneficial aspect of using VirtualFluoro during the insertion of percutaneous iliosacral screws appears to be significantly decreased use of fluoroscopy when compared to StdFluoro.

Traumatic C6-7 subluxation associated with C-7 fracture treated with a pedicle screw system under navigation guidance--case report

A 51-year-old female presented with traumatic C6-7 subluxation associated with C-7 fracture due to an automobile accident. She underwent pedicle screw fixation at C-6, C-7, and T-1 for stabilization of the spinal column. A neuronavigation system was used to obtain accurate placement of the pedicle screws. The patient recovered well without further neurological compromise. Postoperative cervical radiography showed reasonable restoration of the vertebral column without delayed kyphotic deformity.

Prospektive Schraubenfehllagenanalyse nach konventioneller und navigierter Pedikelschraubenimplantation / Computer Assisted Orthopedic Surgery (CAOS)

BACKGROUND

[corrected] The aim of this prospective study was (1) to evaluate the accuracy of pedicle screw placement using Computer - Assisted Orthopedic - Surgery (CAOS) in comparison to conventionelly image intensifier controlled pedicle screw instrumentation, (2) to compare our results with data from literature and (3) report our experiences with this technique.

PATIENTS AND METHODS

Between 11/00 and 11/01 sixteen patients planned for spine surgery were subsequently recruited. Pedicle screw instrumentation was done in each patient as well with computer aided surgery (CAOS, SurgiGate-System, Medivision, Stratec Medical, Swiss) as also with image intensifier control, allowing for intraindividual comparison. Evaluation of pedicle screw placement was carried out with postoperative computed tomography (CT) or magnetic resonance imaging (MRI).

RESULTS

33 of altogether 36 pedicle screws inserted with Computer-Assistance (CAOS) were correctly placed (91,7%), however only 17 of altogether 24 pedicle screws inserted under image intensifier control (70,8%). The difference of frequency of screw misplacement between Computer-aided and image intensifier controlled instrumentation was statistically significant (p<0.05; chi-square test).

CONCLUSION

Computer assisted surgery reduces significantly the misplacement rate of pedicle screws and remains for experienced spine surgeons an important support in the operative treatment of complex spinal deformities in future. Additionally it can be expected that Computer-Navigation will also spread out in the field of minimal-invasive spinal surgery, e.g. the kyphoplasty. The use of this technique supports beside the medical-technical knowledge an improved three-dimensional orientation in the education of spine surgeons.

Image-guided surgery in resection of benign cervicothoracic spinal tumors: a report of two cases

BACKGROUND CONTEXT

Osseous spinal tumors are an uncommon cause of persistent axial pain and muscle spasm, but even benign lesions may grow to cause deformity or neurological signs. Traditional treatment approaches to resection can be debilitating even when the tumor is benign.

PURPOSE

Emerging technologies allow surgeons to diagnose and treat osseous neoplasms while minimizing the collateral damage caused by surgical exposure and tumor excision.

STUDY DESIGN

Technical considerations are presented through two cases of benign osseous neoplasm occurring in the cervicothoracic spine of competitive athletes, demonstrating the meth-ods used to provide effective treatment while maintaining maximal functional capacity.

METHODS

Stereotactic imaging and intraoperative guidance was used as an adjunct to tumor care in these patients. Used in combination with minimally invasive, microsurgical techniques,stereotactic guidance localized and verified excision margins of benign vertebral lesions, minimizing soft tissue trauma and collateral damage.

RESULTS

Computer-assisted stereotactic localization allowed us to successfully ablate these lesions from their anatomically challenging locations, without disrupting the shoulder girdle or neck musculature, and without extensive bony resection.

CONCLUSIONS

Image guidance can accurately localize and guide excision of benign vertebral lesions while minimizing soft tissue trauma and collateral damage, allowing patients a rapid and complete return to high-demand function.

Open versus endoscopic lumbar pedicle screw fixation and posterolateral fusion in a sheep model: a feasibility study

BACKGROUND CONTEXT

Conventional open procedures for lumbar pedicle screw instrumentation are often associated with significant morbidity resulting in longer postoperative recovery and hence have led to the advent of less invasive techniques of spinal instrumentation and fusion.

PURPOSE

This study compares lumbar pedicle screw fixation and posterolateral fusion using endoscopic and open techniques in a sheep model.

STUDY DESIGN

Endoscopic and open techniques of lumbar pedicle screw instrumentation and posterolateral fusion are compared in a sheep model (12 sheep in each group). The safety and fusion outcome are assessed by postoperative computed tomography (CT) scans performed at 6 months.

METHODS

Twelve sheep underwent bilateral L4-L5 pedicle screw fixation and posterolateral fusion by means of endoscopic instrumentation and another 12 sheep by means of conventional open technique. For posterolateral fusions, an autologous iliac crest bone or bone graft substitute (Healos/MP52; Orquest, Mountain View, CA) was used on either the animal's left or right side. The animals were euthanized 6 months after surgery and the lumbar spines were harvested. Pedicle dimensions and screw insertion angles were measured and the two techniques were compared using CT and image analysis software. Pedicle screw misplacement was detected by means of direct inspection and CT scan, and fusions were evaluated by CT scans.

RESULTS

The endoscopic group's screw insertion angle was more convergent, corresponded more closely to the human pedicle angle and was less variable than in the open technique. Three of the endoscopic group's 48 screws were misplaced medially, whereas in the open technique, 5 screws were misplaced laterally. Posterolateral bone fusion masses were palpable 6 months after surgery for both the autologous bone grafts and graft substitutes. There were no complications. The ratio of screw to pedicle diameter was approximately 0.6, greater than in human studies.

CONCLUSIONS

Despite differences between pedicle dimensions and screw angles, most screws could be inserted into the sheep pedicle using endoscopic or open techniques. Bone fusion was successful in both groups. Thus, minimally invasive, endoscopic transpedicular screw-plate fixation and posterolateral fusion is feasible, and as effective as the conventional open technique.

Single versus separate registration for computer-assisted lumbar pedicle screw placement

STUDY DESIGN

This is a retrospective study conducted to evaluate the efficacy of single versus separate registration in assessing the pedicle screw accuracy in the computer-assisted lumbar spinal instrumentation.

OBJECTIVES

To see if separate registration reduced lumbar pedicle screw misplacement.

SUMMARY OF BACKGROUND DATA

Computer-assisted spinal instrumentation has been shown to improve pedicle screw installation accuracy, but 2.7% to 8% of screws still perforate the pedicular cortex. Suspected causes include differences in lumbar lordosis between preoperative CT scans and surgery.

METHODS

Postoperative radiographs and CT scans were used to assess the accuracy of pedicle screw placement in 47 adult patients following computer-assisted lumbar spinal instrumentation. Twenty-two patients underwent single registration at one level, while the other 25 underwent registration at each level.

RESULTS

The time required for a registration procedure on one level was 6 to 8 minutes, while the time required for application of a pedicle screw using computer-assisted techniques was an additional 6 to 10 minutes. The total number of screw placements was 118 in the single registration group and 130 in the separate registration group. In the former group, 85 (72%) pedicle screw placements were categorized as good, 28 (24%) were fair, and 5 (4%) were poor. All five poorly placed screws were placed in the lower lumbar or upper sacral spine with high mobility, and at levels without registration, with one causing root injury. In the latter group, 117 (90%) pedicle screw placements were good and 13 (10%) were fair. The difference in placement was found to be statistically significant (chi2, P = 0.0003). CONCLUSION.: Before the intraoperative real-time CT imaging is widely used, separate registration at each instrumented level during traditional computer-assisted lumbar spinal instrumentation is necessary to enhance the accuracy of screw placement.

Minimally invasive spinal surgery: a historical perspective

The concept of minimally invasive spinal surgery embodies the goal of achieving clinical outcomes comparable to those of conventional open surgery, while minimizing the risk of iatrogenic injury that may be incurred during the exposure process. The development of microscopy, laser technology, endoscopy, and video and image guidance systems provided the foundation on which minimally invasive spinal surgery is based. Minimally invasive treatments have been undertaken in all areas of the spinal axis since the 20th century. Lumbar disc disease has been treated using chemonucleolysis, percutaneous discectomy, laser discectomy, intradiscal thermoablation, and minimally invasive microdiscectomy techniques. The initial use of thoracoscopy for thoracic discs and tumor biopsies has expanded to include deformity correction, sympathectomy, vertebrectomy with reconstruction and instrumentation, and resection of paraspinal neurogenic tumors. Laparoscopic techniques, such as those used for appendectomy or cholecystectomy by general surgeons, have evolved into procedures performed by spinal surgeons for anterior lumbar discectomy and fusion. Image-guided systems have been adapted to facilitate pedicle screw placement with increased accuracy. Over the past decade, minimally invasive treatment of cervical spinal disorders has become feasible by applying technologies similar to those developed for the thoracic and lumbar spine. Endoscope-assisted transoral surgery, cervical laminectomy, discectomy, and foraminotomy all represent the continual evolution of minimally invasive spinal surgery. Further improvement in optics and imaging resources, development of biological agents, and introduction of instrumentation systems designed for minimally invasive procedures will inevitably lead to further applications in minimally invasive spine surgery.

Electromagnetic field-based image-guided spine surgery part one: results of a cadaveric study evaluating lumbar pedicle screw placement

STUDY DESIGN

Human cadaveric.

OBJECTIVES

Compare the accuracy of electromagnetic field (EMF)-based image-guided lumbar pedicle screw insertion to conventional techniques using anatomic landmarks, and fluoroscopy.

BACKGROUND

Image-guided surgical systems that aid in spinal instrumentation seek to minimize radiation exposure and improve accuracy. EMF tracking-based image-guidance was developed in the hopes of eliminating line-of-sight restrictions seen with other systems.

MATERIALS AND METHODS

Sixteen fresh-frozen human cadavers were randomly allocated into three groups. Pedicle screws were inserted from L1 to L5 using only anatomic landmarks in group 1, fluoroscopy in group 2, and image-guidance in group 3. Insertion and total fluoroscopic time were recorded. Anatomic dissections were performed to assess screw placement.

RESULTS

Accuracy was 83%, 78%, and 95% for groups 1, 2, and 3, respectively. However, image-guided pedicle screw placement resulted in a 5% critical perforation rate whereas anatomic and fluoroscopic placement resulted in a 15% and 22% critical perforation rate, respectively. The average degree of perforation was 1.5 mm with image guidance, and 3.8 mm with fluoroscopic guidance (P < 0.05). Fluoroscopy time and insertion time per screw were not improved using image guidance.

CONCLUSIONS

Our study has shown that when EMF tracking was used for image-guided lumbar pedicle screw placement, accuracy was improved and the incidence and degree of cortical perforations that may place neurovascular structures at risk was also reduced. Current system requirements for set-up and image acquisition, however, do add time to the procedure, and when factored in, do not yet result in a decrease in the use of fluoroscopy or screw insertion time.

Prospective comparison of virtual fluoroscopy to fluoroscopy and plain radiographs for placement of lumbar pedicle screws

Fluoroscopy-based frameless stereotactic systems provide feedback to the surgeon using virtual fluoroscopic images. The real-life accuracy of these virtual images has not been compared with traditional fluoroscopy in a clinical setting. We prospectively studied 23 consecutive cases. In two cases, registration errors precluded the use of virtual fluoroscopy. Pedicle probes placed with virtual fluoroscopic imaging were imaged with traditional fluoroscopy in the remaining 21 cases. Position of the probes was judged to be ideal, acceptable but not ideal, or not acceptable based on the traditional fluoroscopic images. Virtual fluoroscopy was used to place probes in for 97 pedicles from L1 to the sacrum. Eighty-eight probes were judged to be in ideal position, eight were judged to be acceptable but not ideal, and one probe was judged to be in an unacceptable position. This probe was angled toward an adjacent disc space. Therefore, 96 of 97 probes placed using virtual fluoroscopy were found to be in an acceptable position. The positive predictive value for acceptable screw placement with virtual fluoroscopy compared with traditional fluoroscopy was 99%. A probe placed with virtual fluoroscopic guidance will be judged to be in an acceptable position when imaged with traditional fluoroscopy 99% of the time.

Image-guided frameless stereotactic biopsy sampling of parasellar lesions. Technical note

Interactive image-guided neuronavigation was used to obtain biopsy specimens of cavernous sinus (CS) tumors via the foramen ovale. In this study the authors demonstrated a minimally invasive approach in the management of these lesions. In four patients, whose ages ranged from 29 to 89 years (mean 61.2 years) and who harbored undefined lesions invading the CS, neuronavigation was used to perform frameless stereotactic fine-needle biopsy sampling through the foramen ovale. The biopsy site was confirmed on postoperative computerized tomography scanning. The frameless technique was accurate in displaying a real-time trajectory of the biopsy needle throughout the procedure. The lesions within the CS were approached precisely and safely. Diagnostic tissue was obtained in all cases and treatment was administered with the aid of stereotactic radiosurgery or fractionated stereotactic radiotherapy. The patients were discharged after an overnight stay with no complications. Neuronavigation is a precise and useful tool for image-guided biopsy sampling of CS tumors via the foramen ovale.

The accuracy and safety of image-guidance system using intraoperative fluoroscopic images: an in vitro feasibility study

The "virtual fluoroscopy" is a new navigation system that combines image-guided surgery and C-arm fluoroscopy. The purpose of this study was to evaluate the accuracy of this system in the case of pedicle screwing. The angular deviation in the axial and sagittal planes was measured using the bodies of 50 vertebral models. Another type of model was used to evaluate the positional deviation (two dimension and three dimension). The mean angular deviation on the axial plane was 1.3 degrees and that on the sagittal plane was 1.0 degree. The positional deviation was not recognised. This system provides quite accurate information. Using this system, the surgeon can insert surgical instruments, such as pedicle screws, while confirming the real time virtual image on the monitor displaying the surgical field, including the position and direction of the instruments, without being disturbed by his own hands or instruments and without radiation exposure.

Accuracy of thoracic vertebral body screw placement using standard fluoroscopy, fluoroscopic image guidance, and computed tomographic image guidance: a cadaver study

STUDY DESIGN

A surgical simulation study in human cadaver spine specimens was conducted to evaluate the accuracy of thoracic vertebral body screw placement using four different intraoperative imaging techniques.

OBJECTIVE

To compare standard fluoroscopy, fluoroscopy-based image guidance with two different referencing methods, and computed tomography-based image guidance by the measuring the time required for screw placement, the radiation exposure to specimen and surgeon, and the accuracy of screw position in the thoracic spine.

SUMMARY OF BACKGROUND DATA

Image guidance provides additional anatomic information to the surgeon and may improve safety of technically difficult surgical procedures. The placement of screws in the thoracic spine is a technically demanding procedure in which inaccurate screw positioning places the spinal cord, nerve roots, and paraspinal structures such as the aorta and pleural space at risk for injury. Image-guided surgery may improve the accuracy of thoracic screw placement.

METHODS

Using four different intraoperative imaging methods, two experienced surgeons placed 337 vertebral body screws through the pedicles of thoracic vertebrae in 20 human cadaver thoracic spine specimens. The specimens then were examined with radiographs, computed tomography, and anatomic dissection to determine screw position. Measurements included procedure setup and screw insertion time, radiation exposure to the specimen, the surgeon's hand, the surgeon's body, frequency, direction, and magnitude of screw perforation through the cortical margins of thoracic vertebrae.

RESULTS

As compared with surgery using standard fluoroscopy, fluoroscopy-based image guidance that uses multiple reference marks and computed tomography-based image guidance improves the accuracy of thoracic vertebral body screws, but increases the time required for screw placement and the specimen radiation exposure. Exposure to radiation is minimal at the surgeon's body level and dependent on surgical technique at the surgeon's hand level. Screw perforation occurs most frequently in the lateral direction.

CONCLUSIONS

Fluoroscopy-based image guidance that uses only a single reference marker for the entire thoracic spine is highly inaccurate and unsafe. Systems with registration based on the instrumented vertebrae provide more accurate placement of thoracic vertebral body screws than standard fluoroscopy, but expose the patient to more radiation and require more time for screw insertion.

A comparison of the accuracy and safety of vertebral body pin placement using a fluoroscopically guided versus an open surgical approach: an in vitro study

OBJECTIVE

To compare the safety and accuracy of Steinmann pin placement in vertebral bodies T10 through L7 using either an open or closed fluoroscopic method.

STUDY DESIGN

In vitro radiographic and anatomic study.

ANIMALS

Ten medium-sized canine cadavers.

METHODS

Cadavers were randomly assigned to 2 groups: open and closed. Steinmann pins were placed in vertebral bodies through a standard dorsal incision in the open group and percutaneously with the aid of fluoroscopy in the closed group. Pins were placed bilaterally in vertebral bodies T10 through L7 at approximately 30 degrees from horizontal and driven to a uniform depth. Necropsies were performed to examine potential pulmonary, vascular, or neurological trauma as a result of pin placement. Spines were cross-sectioned through intervertebral disc spaces, and radiographs were performed to evaluate accuracy of pin placement. Descriptive statistics were determined for pin angle, percentage of bone purchase, and penetration length. Means of interest between groups were compared using a Student t test. Complication incidence was compared using Chi;(2) analysis. Significance was P <.05.

RESULTS

Mean pin insertion angle was significantly different than 30 degrees for the open group in thoracic and lumbar vertebrae and for the closed group in thoracic vertebrae. Mean pin insertion angle for all vertebrae was significantly greater than 30 degrees for the open group. Mean pin penetration distance in each vertebra was significantly different between groups with the closed group having less penetration and lower variance. Both groups were significantly different from the ideal penetration distance. The mean percentage of bone purchase was greater in the closed group for all vertebrae except T10 and T11. The complication incidence was significantly greater in the open group for thoracic vertebrae.

CONCLUSION AND CLINICAL RELEVANCE

The results of this study suggest that a closed technique for placement of Steinmann pins in lumbar vertebrae for use in external skeletal fixation is a reasonable and safer alternative to the traditional open technique. Use of either technique in thoracic vertebrae should be avoided.

The process and development of image-guided procedures

Medical imaging has been used primarily for diagnosis. In the past 15 years there has been an emergence of the use of images for the guidance of therapy. This process requires three-dimensional localization devices, the ability to register medical images to physical space, and the ability to display position and trajectory on those images. This paper examines the development and state of the art in those processes.

Fluoroscopic frameless stereotaxy for transsphenoidal surgery

OBJECTIVE

To assess the value of frameless fluoroscopy-guided stereotactic transsphenoidal surgery using the FluoroNav Virtual Fluoroscopy System (Medtronic Sofamor Danek, Inc., Memphis, TN).

METHODS

Twenty consecutive patients undergoing transsphenoidal surgery for sellar lesions were assigned to transsphenoidal surgery with or without computer-assisted fluoroscopic image guidance using the FluoroNav system. Prospective data regarding patient age, sex, lesion characteristics, operative time, and treatment cost were obtained.

RESULTS

Although patients in the FluoroNav group were, on average, 17 years younger than the patients in the control group, more patients with recurrent adenomas were treated in the image guidance group. No other significant differences between the groups were found. FluoroNav provided accurate, continuous information regarding the anatomic midline trajectory to the sella turcica as well as anatomic structures (e.g., sella, sphenoid sinus) in the lateral view. No patient required reversion to intraoperative videofluoroscopy. No statistically significant differences were found with regard to preincision setup time, operative time, or cost. FluoroNav allowed procedures to be performed with significantly fewer x-rays being taken.

CONCLUSION

Fluoroscopic computer-assisted frameless stereotaxy furnishes accurate real-time information with regard to midline structures and operative trajectory. Although it is useful in first-time transseptal transsphenoidal surgery, its primary benefit is realized in recurrent surgery.