[Computer-assisted spine surgery: principles, technique, results and perspectives]

[Electromagnetic navigation of transpedicular punctures: more precise than the standard?]

AIM

Before clinical implementation of an approved electromagnetic tracking system (CAPPA IRAD EMT) an experimental trial was performed to investigate the accuracy of the system and its safety in application for transpedicular vertebral punctures in comparison to the classical fluoroscopic method.

MATERIAL AND METHODS

A total of 110 transpedicular punctures were performed bilaterally using 11 vertebrae of 5 realistic artificial phantoms and 1 pedicle was punctured with the conventional technique using c-arm fluoroscopy and the other with the electromagnetic tracking system. As a target a radiopaque non-ferromagnetic marker was implanted bilaterally in the anterior wall of the vertebrae. For evaluation of the precision the distance from the end of the puncture to the target and the gradual deviation of the actual channel from the ideal trajectory were assessed in three-dimensional computer tomography. Calculations and statistical analysis were performed according to the Wilcoxon test by means of SPSS 16.0.1 for Windows.

RESULTS

The mean distance from the target was 6.6 mm (± 3.9 mm standard deviation SD) with electromagnetic navigation compared to 3.2 mm (± 2.8 mm SD) with fluoroscopic assistance and the mean aberration from the ideal trajectory was 18.4° (± 4.6° SD) compared to 6.5° (± 3.5° SD), respectively. The difference of accuracy was highly significant regarding both parameters (p < 0.001).

CONCLUSIONS

The minimum requirement for accuracy of transpedicular punctures could not be achieved with electromagnetic navigation. Unless proven otherwise, the lack of accuracy is attributed to unstable referencing. Despite evidence of successful employment for soft tissue punctures the system cannot currently be recommended for osseous applications of the spine.

Navigated guide tube for the placement of mini-open pedicle screws using stereotactic 3D navigation without the use of K-wires

Object

Three-dimensional spinal navigation increases screw accuracy, but its implementation in clinical practice has been difficult, mainly because of surgeons' concerns about increased operative times, disturbance of workflow, and safety. The authors present a custom-designed navigated guide that addresses some of these concerns by allowing for drilling, tapping, and placing the final screw via a minimally invasive approach without the need for K-wires. In this paper, the authors' goal was to describe the technical aspects of the navigated guide tube as well as pedicle screw accuracy.

Methods

The authors present the technical details of a navigated guide that allows drilling, tapping, and the placement of the final screw without the need for K-wires. The first 10 patients who received minimally invasive mini-open spinal pedicle screws are presented. The case series focuses on the immediate postoperative outcomes, pedicle screw accuracy, and pedicle screw–related complications. An independent board-certified neuroradiologist determined pedicle screw accuracy according to a 4-tiered grading system.

Results

The navigated guide allowed successful placement of mini-open pedicle screws as part of posterior fixation from L-1 to S-1 without the use of K-wires. Only 7-mm-diameter screws were placed, and 72% of screws were completely contained within the pedicle. Breaches less than 2 mm were seen in 23% of cases, and these were all lateral except for one screw. Breaches were related to the lateral to medial trajectory chosen to avoid the superior facet joint. There were no complications related to pedicle screw insertion.

Conclusions

A novel customized navigated guide tube is presented that facilitates the workflow and allows accurate placement of mini-open pedicle screws without the need for K-wires.

Acetabular component positioning using anatomic landmarks of the acetabulum

BACKGROUND

The acetabular cup should be properly oriented to prevent dislocation and to reduce wear. However, achieving proper cup placement is challenging with potentially large variations of cup position. We propose a new technique to position the acetabular cup.

QUESTIONS/PURPOSES

We used this technique, then determined actual cup position and subsequent dislocation rate.

METHODS

We measured acetabular abduction (α°) and anteversion (β°) on preoperative CT scans in 46 patients (50 hips) scheduled for THA. During the operation, we identified the transverse acetabular notch (TAN) and anterior acetabular notch (AAN), a notch at the anterior acetabular margin. We then marked two reference points for 40° abduction at the acetabular rim: the superior point, which is opposite the TAN, and the inferior point at |α - 40| mm inside (when α was > 40°) or outside the TAN (when α was < 40°). We also marked two reference points for 15° anteversion: the posterior point opposite the AAN and the anterior point at |β - 15| mm inside (when β was < 15°) or outside the AAN (when β was > 15°). During cup insertion, we aligned cup abduction to the line between the superior and inferior points and cup anteversion to the line between the anterior and posterior points. We measured cup abduction and anteversion and evaluated the dislocation rate. One patient was lost to followup before 60 months; the minimum followup for the other 45 patients was 60 months (mean, 62.8 months; range, 60-65 months).

RESULTS

The mean cup abduction was 40° (range, 32°-47°) and the mean cup anteversion was 17° (range, 8°-25°). No dislocation occurred postoperatively in 49 hips (45 patients) for a minimum of 5 years followup.

CONCLUSIONS

We obtained adequate cup position with our method and none of 45 patients (49 hips) had dislocation.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See Guidelines for Authors for a complete description of level of evidence.

Evaluation of 2D and 3D navigation for iliosacral screw fixation

PURPOSE

Image guidance is essential in some orthopedic surgical procedures, especially iliosacral screw fixation. Currently, there is no consensus regarding the best image guidance technique. An ex-vivo study was performed to compare conventional, 2-dimensional (2D), and 3D imaging techniques and determine the optimal image guidance technique for pelvic surgery.

METHODS

Plastic (n = 9) and donated cadaver pelvises (n = 8) were evaluated in the laboratory. The pelvises were positioned on radiolucent operation tables in a prone position. Transiliosacral screws were inserted without or with 2D- and 3D-navigational support. A digital mobile X-ray unit with flat-panel fluoroscopy and navigation software was used to measure precision, radiation exposure, and time requirements.

RESULTS

2D-navigation resulted in 40% incorrect screw positioning for the cadavers, 6% for the plastic phantoms, and 21% overall. The highest accuracy was accomplished with 3D-navigation (plastic: 100%; cadavers: 83%; p < 0.05). The dose-area product showed that both 2D- and 3D-navigation required increased exposure compared to the conventional technique (p < 0.01). For both plastic and cadaver specimens, navigated techniques required significantly longer times for screw insertion than the conventional technique (p < 0.01).

CONCLUSION

3D image guidance for transiliosacral screw fixation enabled more accurate screw placement in S1 and S2 vertebrae. However, radiation exposure in 3D-navigation was excessive; thus, we recommend avoiding 3D-navigation in young patients. A primary advantage of 3D-navigation was that the operating team could leave the room during the scan; thus, it reduced their radiation exposure. Moreover, the time required for screw insertion with 3D-navigation was similar to that required in the conventional technique; thus, 3D-navigation is recommended for older patients.

Navigation of artificial disc replacement: evaluation in a cadaver study

INTRODUCTION

Previous studies have shown that total disc replacement (TDR) resulted in significantly better restoration of disc-space height and significantly less subsidence than anterior interbody fusion with BAK cages. Clinical outcomes and flexion/extension range of motion correlated with the accuracy of surgical placement of the CHARITÉ™ artificial disc. False positioning of the artificial disc leads to spondylarthrosis and disc degeneration of the adjacent segment, and exclusive use of a C-arm could cause such false positioning (due to the parallax effect). The objective of this study was to test and evaluate the accuracy of navigated artificial disc replacement as performed by a spine surgeon without a prior learning curve. In each case, the placement position achieved by the surgeon was compared with the preoperatively planned position for that specimen.

MATERIALS AND METHODS

Lumbar intervertebral disc prostheses (CHARITÉ™ , DePuy Spine) were placed using an image guidance technique (BrainLAB VectorVision system) in ten human cadaveric spine specimens. A total of 15 such disc replacements were performed using navigation. Post-instrumentation accuracy was assessed by a computer on the basis of CT scans.

RESULTS

The placement of the disc was assessed as ideal (<3 mm from the planned position), suboptimal (3-5 mm from the planned position) or poor (>5 mm from the planned position). Only three disc prostheses were placed suboptimally, and none was poorly placed. Placement in the coronal plane was significantly better than in the other planes.

DISCUSSION

Navigation is a useful instrument in the hands of the spine surgeon, enabling an ideal placement of the disc prosthesis. Navigation offers greater accuracy and less inter-procedural variation than standard fluoroscopy (due to the parallax effect). As accurate (ideal or suboptimal) placement correlates with good clinical outcome, further clinical studies on the navigation of TDR are essential. In this present study, the disc replacement was performed by a surgeon without experience in total disc replacement, indicating that prior completion of a learning curve was not essential.

[Operative treatment of traumatic fractures of the thorax and lumbar spine. Part II: surgical treatment and radiological findings]

The Spine Study Group (AG WS) of the German Trauma Association (DGU) presents its second prospective Internet-based multicenter study (MCS II) for the treatment of thoracic and lumbar spinal injuries. This second part of the study report focuses on the surgical treatment, course of treatment, and radiological findings in a study population of 865 patients. A total of 158 (18,3%) thoracic, 595 (68,8%) thoracolumbar, and 112 (12,9%) lumbar spine injuries were treated. Of these, 733 patients received operative treatment (OP group). Fifty-two patients were treated non-operatively and 69 patients were treated with kyphoplasty/vertebroplasty without additional instrumentation (Plasty group). In the OP group, 380 (51.8%) patients were instrumented from a posterior (dorsal) position, 34 (4.6%) from an anterior (ventral) position, and 319 (43.5%) cases with a combined posteroanterior procedure. Angular stable internal spine fixator systems were used in 86-97% of the cases for posterior and/or combined posteroanterior procedures. For anterior procedures, angular stable plate systems were used in a majority of cases (51.1%) for the instrumentation of mainly one or two segment lesions (72.7%). In 188 cases (53,3%), vertebral body replacement implants (cages) were used and were mainly implanted via endoscopic approaches (67,4%) to the thoracic spine and/or the thoracolumbar junction. The average operating time was 152 min in posterior-, 208 min in anterior-, and 298 min in combined postero-anterior procedures (p<0,001). The average blood loss was highest in combined operations, measuring 959 ml vs. 650 ml in posterior vs. 534 ml in anterior operations (p<0,001).Computer-assisted intraoperative navigation systems were used in 95 cases. At the time of hospital admission, 58,7% of the patients had spinal canal narrowing of an average of 36% (5-95%) at the level of their injury. The average spinal canal narrowing in patients with a complete spinal cord injury (Frankel/ASIA A) was calculated to be 70%, vs. 50% in patients with incomplete neurologic deficits (Frankel/ASIA B-D), and 20% in patients without neurologic deficits (Frankel/ASIS E; p<0,001). The average procedure in the plasty treatment subgroup was 50 min (18-145 min) to address one (n=59) or two (n=10) injured vertebral bodies. In patients with nonoperative treatment mainly three-point-corsets (n=36) were administered for a duration of 6-12 weeks. During their hospital stay 93 of 195 (44,7%) patients with initial neurologic deficits improved at least one Frankel/ASIA grade until the day of discharge. Two patients (0,2%) showed a neurologic deterioration. The highest rate of complete spinal cord injury (n=36, 23%) was associated with thoracic spine injuries. Nine (1%) patients died during the initial course of treatment. A total of 105 (14,3%) cases with intraoperative (n=56) and/or postoperative complications (n=69) were registered. The most common intraoperative complication was bleeding (n=35, 4,8%). A higher relative frequency of intraoperative complications was noticed in combined (n=34, 10,7%) vs. isolated posterior (n=22, 5,9%; p=0,021) procedures. The most common postoperative complication was associated with wound healing problems in 14 (1,9%) patients. Except in the non-operative treatment subgroup, a correction of the posttraumatic measured radiological deformity was achieved to a different extent within every treatment subgroup. There were no statistically significant differences between the postoperative radiological results of the treatment subgroups (dorsal vs. combination), taking into consideration the influence of relevant parameters such as different fracture types, patient age, and the amount of posttraumatic deformity (p=0,34, ANOVA).

[Best matching. Experimental comparison of different matching procedures for use in computer navigation]

INTRODUCTION

Computer navigation systems are increasingly becoming an integral part of the surgical routine in orthopedic and trauma surgery due to improvements in intraoperative visualization procedures. The matching, i.e. data alignment between virtual and therapeutic objects, is however still a persisting problem. In recent years various matching procedures have been developed to attempt to solve the problem. In this study we compared three matching procedures using the VectorVision navigation system.

MATERIAL AND METHODS

For each matching procedure three artificial models of the lumbar spine (TH10-Os sacrum, Synbone, Malans CH) were used with the VectorVision system as navigation system (BrainLAB, Feldkirchen/Siemens, Erlangen, Germany). The experimental setup was standardized for the different navigational methods. First a CT scan of the models was acquired and based on this data set a master planning for all pedicle drillings was performed. A total of 48 drillings with pairpoint, region or CT fluoromatching were accomplished and evaluated. The time periods needed for the matching procedures were documented and compared with each other. The precision of the drillings was evaluated within the postinterventional CT. Altogether 144 drillings for pedicle screws were performed on artificial models based on an identical planning for all test series.

RESULTS

Within the experimental study of 144 drillings, only 2 perforations (1.3%) of the lateral cortical wall were detected. The time needed for the matching procedure was the shortest for region matching, followed by the pairpoint matching. The CT fluoromatching was the longest procedure. Variations in the distance of the individual drilling to the cortical wall were comparably large in all test series (on average 1.3 mm). Significant differences concerning the precision of the different matching procedures could only be shown for pairpoint matching.

CONCLUSION

In our study pairpoint matching was the only procedure without misplacement and on average had the largest safety margin for drillings. Thus this method was the most precise procedure. The region matching procedure offers the advantage of the fastest matching with comparable precision.