Universal calibration of surgical instruments for spinal stereotaxy

Video-assisted thoracoscopic image-guided spine surgery: evolution of 19 years of experience, from endoscopy to fully integrated 3D navigation

OBJECTIVE

The purpose of this study was to describe the evolution of thoracoscopic spine surgery from basic endoscopic procedures using fluoroscopy and anatomical localization through developmental iterations to the current technology use in which endoscopy and image-guided surgery are merged with intraoperative CT scanning.

METHODS

The authors provided detailed explanations of their thoracoscopic spine surgery techniques, beginning with their early-generation endoscopy with fluoroscopic localization, which was followed with point surface matching techniques and early image guidance. The authors supplanted this with the modern era of image guidance, thoracoscopic spine surgery, and seamless integration that has reached its current level of refinement.

RESULTS

A retrospective review of single-institution thoracoscopic procedures performed by the senior author over the course of 19 years yielded a total of 160 patients, including 73 women and 87 men. The mean patient age was 55 years, and the range included patients 16-94 years of age. There were no patients with worsened neurological function. One hundred sixteen patients underwent surgery for thoracic disc herniation, 18 for underlying neoplasms with spinal cord compression, 14 for osteomyelitis and discitis, 12 for thoracic deformity with neurological changes, and 8 for traumatic etiologies.

CONCLUSIONS

More than 19 years of experience has revealed the benefits of integrating thoracoscopic spine surgery with intraoperative CT scanning and image-guided surgery, including direct decompression without manipulation of neural elements, superior 3D spatial orientation, and localization of complex spinal anatomy. With the exponential growth of machine learning, robotics, artificial intelligence, and advances in imaging techniques and endoscopic imaging, there may be further refinements of this technique on the horizon.

Stereotactic guidance for navigated percutaneous sacroiliac joint fusion

Arthrodesis of the sacroiliac joint (SIJ) for surgical treatment of SIJ dysfunction has regained interest among spine specialists. Current techniques described in the literature most often utilize intraoperative fluoroscopy to aid in implant placement; however, image guidance for SIJ fusion may allow for minimally invasive percutaneous instrumentation with more precise implant placement. In the following cases, we performed percutaneous stereotactic navigated sacroiliac instrumentation using O-arm^® multidimensional surgical imaging with StealthStation^® navigation (Medtronic, Inc. Minneapolis, MN). Patients were positioned prone and an image-guidance reference frame was placed contralateral to the surgical site. O-arm® integrated with StealthStation® allowed immediate auto-registration. The skin incision was planned with an image-guidance probe. An image-guided awl, drill and tap were utilized to choose a starting point and trajectory. Threaded titanium cage(s) packed with autograft and/or allograft were then placed. O-arm® image-guidance allowed for implant placement in the SIJ with a small skin incision. However, we could not track the cage depth position with our current system, and in one patient, the SIJ cage had to be revised secondary to the anterior breach of sacrum.

Introduction: Intraoperative spinal imaging and navigation

Image-guided surgery (IGS) has been evolving since the early 1990s and is now used on a daily basis in the operating theater for spine surgery at many institutions. In the last 5 years, spinal IGS has greatly benefitted from important enhancements including portable intraoperative CT (iCT) coupled with high-speed computerized stereotactic navigation systems and optical-based camera tracking technology.

Image-guided navigation and video-assisted thoracoscopic spine surgery: the second generation

Object

Video-assisted thoracoscopic surgery (VATS) has evolved for treatment of a variety of spinal disorders. Early incorporation with image-guided surgery (IGS) was challenged due to reproducibility and adaptability, limiting the procedure's acceptance. In the present study, the authors report their experience with second-generation IGS and VATS technologies for anterior thoracic minimally invasive spinal (MIS) procedures.

Methods

The surgical procedure is described in detail including operating room set-up, patient positioning (a lateral decubitus position), placement of the spinal reference frame and portal, radiographic localization, registration, surgical instruments, and the image-guided thoracoscopic discectomy.

Results

Combined IGS and VATS procedures were successfully performed and assisted in anatomical localization in 14 patients. The mean patient age was 59 years (range 32–73 years). Disc herniation pathology represented the most common indication for surgery (n = 8 patients); intrathoracic spinal tumors were present in 4 patients and the remaining patients had infection and ossification of the posterior longitudinal ligament. All patients required chest tube drainage postoperatively, and all but 1 patient had drainage discontinued the following day. The only complication was a seroma that was presumed to be due to steroid therapy for postoperative weakness. At the final follow-up, 11 of the patients were improved neurologically, 2 patients had baseline neurological status, and the 1 patient with postoperative weakness was able to ambulate, albeit with an assistive device.

The evolution of thoracoscopic surgical procedures occurring over 20 years is presented, including their limitations. The combination of VATS and IGS technologies is discussed including their safety and the importance of 3D imaging. In cases of large open thoracotomy procedures, surgeries require difficult, extensive, and invasive access through the chest cavity; using a MIS procedure can potentially eliminate many of the complications and morbidities associated with large open procedures. The authors report their experience with thoracic spinal surgeries that involved MIS procedures and the new technologies.

Conclusions

The most significant advance in IGS procedures has resulted from intraoperative CT scanning and automatic registration with the IGS workstation. Image guidance can be used in conjunction with VATS techniques for thoracic discectomy, spinal tumors, infection, and ossification of the posterior longitudinal ligament. The authors' initial experience has revealed this technique to be useful and potentially applicable to other MIS procedures.

Image-Guided Thoracoscopic Resection of Thoracic Dumbbell Nerve Sheath Tumors

BACKGROUND:

Surgical removal of dumbbell nerve sheath tumors (NSTs) remains challenging because these neoplasms occupy ≥ 2 spinal and extraspinal spaces. The presence of intraspinal extension, tumor dimension, and/or its location within the thoracic cavity have previously made the resection of these types of neoplasms difficult.

OBJECTIVE:

To describe the feasibility of performing minimally invasive thoracoscopic surgery, as facilitated by an image guidance system (IGS), to achieve gross total resection of select dumbbell NSTs located in the thoracic spine.

METHODS:

The 3 cases presented here contained small intraspinal or foraminal components. Preoperative symptoms included Horner syndrome and back and chest wall pain. We used IGS to help guide the complete thoracoscopic resection of select dumbbell NSTs, consisting of extradural, intraforaminal, and paravertebral tumor components, which previously would have been challenging with only a thoracoscopic approach.

RESULTS:

IGS provided continuous intraoperative anatomic orientation to achieve gross total resection in all 3 cases. All surgical and postsurgical outcomes were satisfactory; preoperative symptoms improved or resolved; and no adverse events were observed.

CONCLUSION:

Thoracic dumbbell NSTs that have small intraspinal or foraminal components could be resected thoracoscopically when facilitated by IGS. Image-guided thoracoscopic resection of such dumbbell tumors may not only improve the precision of resection, reduce recurrence, and avoid the need for spinal reconstruction but also obviate the need for more invasive or simultaneous posterior procedures. The IGS enhances the accuracy and safety of 2-dimensional thoracoscopic surgery and may reduce its learning curve.

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.

Computer-assisted Magerl's transarticular screw fixation for atlantoaxial subluxation

We report two patients with rheumatoid arthritis in whom posterior atlantoaxial fixation was carried out using transarticular screws with computer assistance. Two bilateral transarticular screws were inserted in one patient; however, in the other patient, only a unilateral screw was used, because computerized images showed that the vertebral artery at the other side was placed too medially to allow insertion of the screw. Neither of these patients had any neurovascular complications after surgery. Computer-assisted surgery is useful for avoiding neurovascular complications with transarticular screw fixation of C1-2.

Computerized frameless stereotactic image guidance in spinal surgery

Clinical applications of computerized frameless stereotactic image-guided spinal surgery continue to evolve. This article discusses several limiting factors regarding the use of this technology. It discusses the benefits of stereotaxy, which are better realized when there is a distortion of 'normal' anatomy because of previous surgery or severe deformity. The three-dimensional model helps the surgeon navigate the rotated and translated vertebrae. The technology can also be helpful when performing a posterior lumbar interbody fusion, to determine the orientation and depth of placement of the allograft or the cage.

Frameless stereotaxy for anterior spinal procedures

OBJECT

Intraoperative image guidance provides real-time three-dimensional visualization and has been successfully applied in many posterior spinal procedures. The feasibility of applying these techniques to anterior spinal surgery has not been studied systematically because the anterior spine, in contrast to the posterior spine, lacks distinct anatomical landmarks for registration. The authors sought to evaluate the practicality of performing stereotaxy in the anterior spine in a cadaveric model.

METHODS

Unilateral C4-L4 pedicle screws were placed posteriorly in three cadaveric specimens to serve as unknown markers within each vertebral body. The specimens then underwent computerized tomography (CT) scanning, and the CT data were transferred to an optical tracking system. The anterior surface of the spine was registered for use with the stereotactic system by using a paired point-matching technique. Attached to a surgical drill, K-wires were placed under stereotactic guidance in a tip-to-tip orientation with the posterior pedicle screws. A second postoperative CT scan was obtained, and accuracy was determined by measuring the distance between the tips of the K-wire and pedicle screw. The K-wires were placed tip to tip with pedicle screw markers in 57 vertebral levels. The mean registration error was 1.47+/-0.04 mm, and when combined with the universal instrument registration error of 0.7 mm yielded an overall registration error of 2.17+/-0.04 mm. The mean tip-to-tip distance for all K-wires placed was 2.46+/-0.23 mm. The difference between the mean tip-to-tip distance and overall registration error was not statistically significant (p > 0.05), indicating that the K-wires were placed within the expected range of error.

CONCLUSIONS

The results of this study confirmed the feasibility of performing anterior stereotactic procedures throughout the spine. The accuracy of the findings in this study indicates that anterior stereotaxy should be applicable in clinical practice.

Effect of frameless stereotaxy on the accuracy of C1-2 transarticular screw placement

OBJECT

In recent studies some authors have indicated that 20% of patients have at least one ectatic vertebral artery (VA) that, based on previous criteria in which preoperative computerized tomography (CT) and standard intraoperative fluoroscopic techniques were used. may prevent the safe placement of C1-2 transarticular screws. The authors conducted this study to determine whether frameless stereotaxy would improve the accuracy of C1-2 transarticular screw placement in healthy patients, particularly those whom previous criteria would have excluded.

METHODS

The authors assessed the accuracy of frameless stereotaxy for C1-2 transarticular screw placement in 17 cadaveric cervical spines. Preoperatively obtained CT scans of the C-2 vertebra were registered on a stereotactic workstation. The dimensions of the C-2 pars articularis were measured on the workstation, and a 3.5-mm screw was stereotactically placed if the height and width of the pars interarticularis was greater than 4 mm. The specimens were evaluated with postoperative CT scanning and visual inspection. Screw placement was considered acceptable if the screw was contained within the C-2 pars interarticularis, traversed the C 1-2 joint, and the screw tip was shown to be within the anterior cortex of the C-1 lateral mass. Transarticular screws were accurately placed in 16 cadaveric specimens, and only one specimen (5.9%) was excluded because of anomalous VA anatomy. In contrast, a total of four specimens (23.5%) showed significant narrowing of the C-2 pars interarticularis due to vascular anatomy that would have precluded atlantoaxial transarticular screw placement had previous nonimage-guided criteria been used.

CONCLUSIONS

Frameless stereotaxy provides precise image guidance that improves the safety of C1-2 transarticular screw placement and potentially allows this procedure to be performed in patients previously excluded because of the inaccuracy of nonimage-guided techniques.

Computer-assisted thoracic pedicle screw placement: an in vitro feasibility study

STUDY DESIGN

In this cadaveric study, a computer-assisted image guidance system was tested for accuracy of thoracic pedicle screw placement.

OBJECTIVES

Evaluate the system's accuracy for thoracic pedicle screw placement in vitro.

SUMMARY OF BACKGROUND DATA

The effective use and reliability of pedicle screw instrumentation in providing short-segment stabilization and correction of deformity is well known in the lumbar spine. Pedicle screw placement in the thoracic spine is difficult because of the small dimensions of the thoracic pedicles and risk to the adjacent spinal cord and neurovascular structures. Investigators have shown the improved accuracy of computer-assisted lumbar pedicle screw placement; but the accuracy of computer-assisted thoracic pedicle screw placement, which is becoming more widely used, has not been shown.

METHODS

In five human cadavers, 120 thoracic pedicle screws were placed with computer-assisted image guidance. The largest clinically feasible screw was used based on the cross-sectional dimensions of each pedicle. The accuracy was assessed by postoperative computed tomography and visual inspection.

RESULTS

The overall pedicle cortex violation was 23 of 120 pedicles (19.2%). Nine violations (7.5%) were graded as major and 14 (11.7%) as minor. A marked and progressive learning curve was evident with the perforation rates that decreased from 37.5% in the first cadaver to 4.2% in the last two cadavers.

CONCLUSIONS

Accurate thoracic pedicle screw placement is feasible with computer-assisted surgery. However, as with any other new surgical technology, the learning curve must be recognized and incorporated into the necessary fundamental knowledge and experience for these procedures.

Image-guided thoracic pedicle screw placement: a technical study in cadavers and preliminary clinical experience

OBJECT

Thoracic pedicle screw fixation is effective and reliable in providing short-segment stabilization. Although the procedure is becoming more widely used, accurate insertion of the screws is difficult due to the small dimensions of thoracic pedicles, and the associated risk is high due to the proximity of the spinal cord. In previous studies authors have shown the accuracy of image-guided lumbar pedicle screw placement, but there have been no reported investigations into the accuracy of image-guided thoracic pedicle screw placement. The authors report their experience with such an investigation.

METHODS

To evaluate the accuracy of image-guided thoracic pedicle screw placement in vitro and in vivo, thoracic pedicle screws were placed with an image-guidance system in five human cadavers and 10 patients. In cadavers, the accuracy of screw placement was assessed by postoperative computerized tomography and visual inspection and in patients by postoperative imaging studies. Of the 120 pedicle screws placed in five cadavers pedicle violation occurred in 23 cases (19.2%); there was one pedicle violation (4.2%) in each of the last two cadavers. Of the 45 pedicle screws placed in 10 patients, pedicle violations occurred in three (6.7%).

CONCLUSIONS

In comparison with historical controls, the accuracy of thoracic pedicle screw placement is improved with the use of an image-guidance system. It allows the surgeon to visualize the thoracic pedicle and the surrounding structures that are normally out of the surgical field of view. The surgeon, however, must be aware of the limitations of an image-guidance system and have a sound basic knowledge of spinal anatomy to avoid causing serious complications.

Use of Internal Fiducial Markers in Frameless Stereotactic Navigational Systems during Spinal Surgery: Technical Note

OBJECTIVE

The use of frameless stereotaxy has expanded the spine surgeon's ability to perform surgical procedures with instrumentation in areas of narrow anatomic tolerance. In many circumstances, however, it is difficult to register the frameless stereotactic probe using known anatomic landmarks. This occurs typically because landmarks are indistinct, and congenital or surgical defects limit the availability of anatomic fiducials. We propose an accurate and efficient method for registering the frameless stereotactic probe for spinal surgery when a staged procedure is planned.

METHODS

During the first stage of a planned two-stage procedure, a minimum of four cranial fiducial screws are implanted in the posterior element of each vertebra in which stereotactic registration is desired. Stage 1 is completed, and all suture closure is performed. A computed tomographic scan formatted for the frameless stereotactic unit is obtained postoperatively. In the second stage of surgery, registration is performed using cranial screws as internal fiducial markers.

RESULTS

Registration is performed easily and quickly using cranial screws as internal fiducial markers. No more than four registration points are necessary to calibrate the system to accuracy within 1.5 mm.

CONCLUSION

Implantation of fiducial markers during Stage 1 of a complex staged spinal surgery renders the frameless stereotactic navigational system registration extremely fast and accurate. We advocate the technique to enhance the use of frameless navigational systems for reliable and quick registration of the spine.