INTRODUCTION
Percutaneous iliosacral screw (IS) fixation is frequently used to treat unstable pelvic ring fractures.1 This procedure can be technically challenging, particularly in patients with sacral dysmorphism who have narrow S1 and S2 bony corridors with indentation to the anterior aspect of the sacral ala and increased alar slope.2,3 As a result, advances in imaging technology with intraoperative computed tomography (CT) scanners, such as the O-arm Surgical Imaging System (O-arm; Medtronic, Fridley, MN), have been developed to assist surgeons in safe, efficient, and accurate placement of percutaneous fixation of pelvic ring injuries.4–6 The present video (see Video, Supplemental Digital Content 1, https://links.lww.com/JOT/A387) reviews the benefits and potential drawbacks to the utilization of this type of technology. Imaging acquisition, registration for navigation, and surgical technique are described.
BENEFITS AND LIMITATIONS
The O-arm and Medtronic StealthStation navigation systems provide important operative benefits including improved accuracy of IS screw insertion and reduction of screw malposition.1,7 Improved three-dimensional pelvic imaging may be particularly helpful in cases with difficult anatomy, including sacral dysmorphism and obesity, and may help reduce the rate of screw malposition for less experienced surgeons.8,9 Furthermore, O-arm utilization has been associated with decreased operative time.6 Compared with conventional intraoperative fluoroscopy with a C-arm, the O-arm often requires less time for imaging acquisition. In addition, the use of navigation improves first-pass efficiency.6 However, the effective use of an intraoperative O-arm requires preoperative planning and ample experience with the imaging and navigations systems.
Commonly discussed limitations of the intraoperative O-arm and 3-D navigation include radiation exposure, cost, availability, and the learning curve of the surgeon and operating room staff.6,10 Although it has been reported that an O-arm uses significantly more radiation compared with conventional fluoroscopy, previous reports have demonstrated equivalent or lower cumulative radiation exposure for both patient and provider.11,12 Financial costs may also limit a system-wide incorporation of intraoperative CT and surgical navigation. The O-arm Surgical Imaging System costs approximately $700,000, whereas a C-arm costs approximately $245,000. However, Dea et al13 found that cumulative cost, including acquisition, operation, and reoperation, is comparable between both imaging systems.
SURGICAL TECHNIQUE
The patient is positioned supine on a radiolucent table, with arms taped across the chest. After routine prepping and draping of the pelvis, the referencing frame is anchored to the iliac wing contralateral to the planned entry point of the IS screws and registered with the Medtronic StealthStation navigation system and software.
Anterior–posterior (AP), inlet, outlet, and lateral views are obtained using the O-arm in two-dimensional or C-arm mode and saved to memory positions designated as 1–4. Next, the referencing frame array and the navigation trochar array are registered to the Medtronic navigation tower receiver.
Once the frames are registered, 1 spin is performed with the O-arm for the acquisition of 3-D images to use for navigation. On the navigation monitor, 4 views are chosen to base the navigation projections. The 4 options are as follows: trajectory 1, trajectory 2, synthetic AP, and synthetic lateral. The synthetic AP and synthetic lateral views can then be manipulated rotationally to provide inlet and outlet x-ray views, whereas the trajectory 1 and trajectory 2 views show the axial and coronal CT images, respectively, which help identify a safe bony corridor for pin placement. A cannulated pin sheath with an attached array is then placed at the skin to determine the optimum site for incision while looking at the navigation projection screen trajectory images. An incision is made and the pin sheath is taken down to the bone. Using the navigated projections, the guide pin for the cannulated screw system of choice is driven across the sacral corridor, keeping the trajectory on the navigation screen. The navigation system provides an option to extrapolate screw length. However, screw length should be confirmed with the cannulated depth gauge slid over the guide pin.
Two-dimensional x-ray views, including AP pelvis, inlet, and outlet views, are taken to confirm guide pin placement. If there is any question regarding the location of the guide pin, a second spin with the O-arm can be performed. Once the pin placement is confirmed, the length is checked and the cannulated drill bit is used over the guide pin. A screw of measured length is inserted, with or without a washer. A final spin of the O-arm is performed once all hardware is in to confirm intraosseous location and reduction.
CONCLUSIONS
The use of O-arm Surgical Imaging and Medtronic StealthStation navigation systems for percutaneous IS screw insertion for pelvic ring injuries has been shown to be safe and effective with potential to reduce operative time and overall radiation exposure. More importantly, in cases with difficult anatomy, 3D imaging and navigation minimizes the risk of screw malposition. The cost of this technology may currently be prohibitive for widespread utilization, but with ongoing innovation, orthopaedic trauma surgeons should be encouraged to familiarize themselves with advanced imaging modalities and surgical techniques aimed at improving accuracy and safety of IS screw placement.
REFERENCES
1. Richter PH, Gebhard F, Dehner C, et al. Accuracy of computer-assisted iliosacral screw placement using a hybrid operating room. Injury. 2016;47:402–407.
2. Miller AN, Routt ML Jr. Variations in sacral morphology and implications for iliosacral screw fixation. J Am Acad Orthop Surg. 2012;20:8–16.
3. Kaiser SP, Gardner MJ, Liu J, et al. Anatomic determinants of
sacral dysmorphism and implications for safe iliosacral screw placement. J bone Jointt Surg Am. 2014;96:e120.
4. Rosenberger RE, Dolati B, Larndorfer R, et al. Accuracy of minimally invasive navigated acetabular and iliosacral fracture stabilization using a targeting and noninvasive registration device. Archives Orthop trauma Surg. 2010;130:223–230.
5. Behrendt D, Mutze M, Steinke H, et al. Evaluation of 2D and 3D navigation for iliosacral screw fixation. Int J Comput Assist Radiol Surg. 2012;7:249–255.
6. Qureshi S, Lu Y, McAnany S, et al. Three-dimensional intraoperative imaging modalities in orthopaedic surgery: a narrative review. J Am Acad Orthop Surg. 2014;22:800–809.
7. Takao M, Nishii T, Sakai T, et al. Iliosacral screw insertion using CT-3D-fluoroscopy matching navigation. Injury. 2014;45:988–994.
8. Verma SK, Singh PK, Agrawal D, et al. O-arm with navigation versus C-arm: a review of screw placement over 3 years at a major trauma center. Br J Neurosurg. 2016;30:658–661.
9. Takao M, Nishii T, Sakai T, et al. CT-3D-fluoroscopy matching navigation can reduce the malposition rate of iliosacral screw insertion for less-experienced surgeons. J Orthop trauma. 2013;27:716–721.
10. Pitteloud N, Gamulin A, Barea C, et al. Radiation exposure using the O-arm((R)) surgical imaging system. Eur Spine J. 2017;26:651–657.
11. Verbeek J, Hermans E, van Vugt A, et al. Correct positioning of percutaneous iliosacral screws with computer-navigated versus fluoroscopically guided surgery in traumatic pelvic ring fractures. J Orthop trauma. 2016;30:331–335.
12. Desai S, Patel VJ, Lall RR, et al. Comparing radiation dose from conventional fluoroscopy to intraoperative cone beam CT (O-arm) during percutaneous lesioning procedures of the Gasserian ganglion. Cureus. 2015;7:e345.
13. Dea N, Fisher CG, Batke J, et al. Economic evaluation comparing intraoperative cone beam CT-based navigation and conventional fluoroscopy for the placement of spinal pedicle screws: a patient-level data cost-effectiveness analysis. Spine J. 2016;16:23–31.
