Accuracy of Computer Assisted Percutaneous Placement of Hiosacral Screws: A Cadaveric Study

Evaluation of Partial Cut-out of Sacroiliac Screws From the Sacral Ala Slope via Pelvic Inlet and Outlet View

STUDY DESIGN

An anatomic and radiographic study of placement of sacroiliac screws.

OBJECTIVE

The aim of this study was to quantitatively assess the risk of partial cut-out of sacroiliac screws from the sacral ala slope via inlet and outlet view.

SUMMARY OF BACKGROUND DATA

The partial cut-out of sacroiliac screws from the superior surface of sacral ala can jeopardize the L5 nerve root, which is difficult to identify on the pelvic inlet and outlet views.

METHODS

Computed tomography images of 60 patients without pelvic ring deformity or injury were used to measure the width (on inlet view) and height (on outlet view) of the sacral ala. The angle of the sacral ala slope was measured on lateral view. According to the measured parameters, the theoretical safe trajectories of screw placement were calculated using inverse trigonometric functions. Under fluoroscopic guidance, a sacroiliac screw was placed close to the midline on both inlet and outlet views, including posterosuperior, posteroinferior, anterosuperior, and anteroinferior regions to the midline. The incidence of screw partial cut-out from the superior surface of sacral ala was identified.

RESULTS

The measured widths and heights of the sacral alas were 28.1 ± 2.8 and 29.8 ± 3.1 mm, respectively. The average angle between the superior aspect of the S1 vertebral body and the superior aspect of the sacral ala was 37.2 ± 2.5 degrees. The rate of partial cut-out of the screws from the superior surface of sacral ala slope was 12.5% (5/40) in posterosuperior, 0% (0/40) in posteroinferior, 70% (28/40) in anterosuperior, and 20% (8/40) in anteroinferior.

CONCLUSION

To avoid the risk of partial cut-out from sacroiliac screw placement, more precise description should be added to the conventional description: the sacroiliac screws should be placed at the inferior half portion on outlet view and at the posterior half portion on inlet view.

LEVEL OF EVIDENCE

4.

Iliosacral screw placement: are uniplanar changes realistic based on standard fluoroscopic imaging?

BACKGROUND

With the aim of improving the understanding of iliosacral screw placement, two hypotheses were tested: (1) standard intraoperative inlet and outlet images are not based on orthogonal coordinates, and (2) therefore making starting point and aim changes by moving perpendicular to the c-arm beam will displace the guide wire on the other intraoperative radiographic view.

METHODS

This is a prospective case series with review of intraoperative data from consecutive patients treated at a University Level I trauma center. The study group included ten consecutive patients with nondysmorphic upper sacral segments and unstable posterior pelvic ring injuries that required surgical treatment. Posterior surgical stabilization included iliosacral screw placement using a standardized three- view technique in the supine position. The main outcome measurement included the angles from the perpendicular required to achieve what have been considered the ideal inlet and outlet views intraoperatively. The angle arc for each patient created by the recorded angles was then determined.

RESULTS

The average sagittal plane tilt required to achieve the ideal inlet view was 25 degrees (range, 21-33 degrees). The average sagittal plane tilt required to achieve the ideal outlet view was 42 degrees (range, 30-50 degrees). The average arc between the ideal inlet and outlet views was 67 degrees (range, 62-76 degrees). These views never created an orthogonal system.

CONCLUSION

We commonly work in orthogonal systems. Within these systems, it is possible to make a uniplanar correction by moving perpendicular to one plane or radiographic view. The ideal views to image the safe zone for iliosacral screw placement do not create an orthogonal system. When this average angle arc is placed on a graphic model of the pelvis, it becomes clear that the plane of the radiographic beam of the ideal inlet view is collinear with the anterior aspect of the upper two sacral bodies. The outlet view is oblique to the upper sacral bodies. Surgeons must keep this in mind when using fluoroscopic views to insert iliosacral screws.

Clinical and methodological precision of spinal navigation assisted by 3D intraoperative O-arm radiographic imaging

OBJECT

In recent years, the importance of intraoperative navigation in neurosurgery has been increasing. Multiple studies have proven the advantages and safety of computer-assisted spinal neurosurgery. The use of intraoperative 3D radiographic imaging to acquire image information for navigational purposes has several advantages and should increase the accuracy and safety of screw guidance with navigation. The aim of this study was to evaluate the clinical and methodological precision of navigated spine surgery in combination with the O-arm multidimensional imaging system.

METHODS

Thoracic, lumbar, and sacral pedicle screws that were placed with the help of the combination of the O-arm and StealthStation TREON plus navigation systems were analyzed. To evaluate clinical precision, 278 polyaxial pedicle screws in 139 vertebrae were reviewed for medial or caudal perforations on coronal projection. For the evaluation of the methodological accuracy, virtual and intraoperative images were compared, and the angulation of the pedicle screw to the midsagittal line was measured.

RESULTS

Pedicle perforations were recorded in 3.2% of pedicle screws. None of the perforated pedicle screws damaged a nerve root. The difference in angulation between the actual and virtual pedicle screws was 2.8° ± 1.9°.

CONCLUSIONS

The use of the StealthStation TREON plus navigation system in combination with the O-arm system showed the highest accuracy for spinal navigation compared with other studies that used traditional image acquisition and registration for navigation.

Computer-assisted surgery for subtalar arthrodesis. A study in cadavers

BACKGROUND

Despite considerable recent interest in computer navigation for orthopaedic surgery, few investigations of computer-assisted surgery for foot and ankle operations have been reported. The purpose of the present study was to compare subtalar arthrodesis with and without computer navigation in a cadaver model.

METHODS

Subtalar arthrodesis was performed on thirty-six matched-pair cadaver lower extremities with intact soft tissues, with an attempt being made to orient two screws in the optimal configuration based on unpublished data from a preceding biomechanical study. Each matched pair was randomly assigned either to a group of surgeons who were experienced in subtalar arthrodesis or to a group of inexperienced operators. Neither surgical group was experienced in computer-assisted surgery. We compared optimal first-pass guidewire placement, fluoroscopic time, total operative time, screw placement accuracy, and adverse screw placement events between conventional (fluoroscopically guided) and computer-assisted subtalar arthrodesis.

RESULTS

The number of passes needed to achieve optimal guidewire placement decreased with the use of computer assistance for both experienced surgeons and inexperienced operators (p < 0.001), with ideal placement occurring on the first attempt in 95% of the procedures performed with use of computer assistance. While the experienced surgeons required less time and fewer guidewire passes during conventional subtalar arthrodesis than the inexperienced operators did (p < 0.001), both groups used less fluoroscopy with computer assistance (p < 0.001). There was no significant difference in operative time between the two techniques when performed by the inexperienced operators, yet the total procedure time doubled for the experienced surgeons when the procedure was performed with use of computer assistance (p < 0.001). There was no significant difference between experienced surgeons and inexperienced operators or between conventional and computer-assisted subtalar arthrodesis with respect to adverse screw placement events or the ability to accurately place both screws.

CONCLUSIONS

Computer-assisted subtalar arthrodesis resulted in screw placement accuracy that was equivalent to that of conventional (fluoroscopically guided) subtalar arthrodesis while decreasing the number of suboptimal guidewire passes and fluoroscopic time. The computer-assisted surgery technique increased the operative time for surgeons who were more experienced in conventional subtalar arthrodesis, but there was no difference in operative time for the group of operators who were inexperienced in subtalar arthrodesis.

Computer assisted percutaneous placement of augmented iliosacral screws: a reasonable alternative to sacroplasty

STUDY DESIGN

A technical report of fluoroscopy guided placement of augmented iliosacral screws in osteoporotic insufficiency fractures of the sacrum.

OBJECTIVE

To describe a combined approach of navigated iliosacral screw placement and screw augmentation as an option for osteosynthesis of sacral insufficiency fractures in the elderly.

SUMMARY OF BACKGROUND DATA

The incidence of sacral insufficiency fractures is increasing. Outcome of conservative treatment is inconsistent. Recently sacroplasty is propagated as an interventional therapy but the long-term outcome is still unknown. Evidence from finite element models suggests that stabilization of the sacrum achieved by sacroplasty is insufficient to restore the weight bearing capacity of the sacrum permanently.

METHODS

We suggest a minimally invasive fluoroscopically navigated iliosacral screw osteosynthesis with cement augmentation of the screws for treatment of insufficiency fractures of the sacrum.

RESULTS

The procedure, especially fluoroscopic visualization and navigation of the osteoporotic sacrum is technically feasible. A total radiograph time of 7,4 minutes, including image acquisition for navigation and fluoroscopic control of cement injection, is acceptable and can be expected to be significantly reduced with repeated applications of the procedure. The patient presented in the report was discharged to rehabilitation soon after the operation. An assistive device (delta wheel) is only needed for longer walking distances. Pain was reduced drastically immediately after surgery.

CONCLUSION

In general, fractures are treated by reduction and fixation to restore the biomechanical function of the injured bone. These principles should be applied to elderly patients with osteoporotic fractures as well. The technique reported here is adapted to the special demands of the elderly patient, i.e., minimally invasive, support of the weakened bone by cement augmentation, bone protective screw positioning and safety due to navigation support.

Navigationsgestützte Arthrodese des Iliosakralgelenks

Arthrodesis of the sacroiliac joint (SI) usually requires a large surgical exposure using the lateral approach. Computer-assisted surgery based on intraoperative 3D fluoroscopy imaging can reduce the approach to stab incisions. The clinical example shows the insertion of two screws and a cylindrical bone graft to achieve an arthrodesis of the SI joint. The intraoperatively navigated placement of implants and bone graft was performed only by stab incisions.