Name: pedicle screw placement using an augmented reality head-mounted display in a porcine model
Uploaded: 2024-05-24T12:30:00
Duration: 6 min 18 s
Description: This protocol helps assess the accuracy and workflow of an augmented reality (AR) hybrid navigation system using the Magic Leap head-mounted display (HMD) ...

The procedure was performed in a conventional OR, equipped with a radiolucent OR table, a navigation platform, and a mobile CBCT device providing both 2D fluoroscopy and 3D CBCT images of high quality for AR navigation. Two porcine cadavers, which were approximately 80 cm in length and 45 kg, were used for the purpose of this study. The specimens were purchased commercially, and their use for this experiment did not require an ethical permit. All the devices, instruments, and software used within the described workflow are listed in the Table of Materials. The following step-by-step procedure was performed and repeated for each specimen.
1. Porcine cadaver specimen
<ol>
	<li>Place the porcine cadaver specimen on the operating table in the operating room.</li>
	<li>Drape the porcine cadaver specimen in sterile covers. Use incision film to cover the skin in the surgical field.</li>
</ol>
2. Identification of the vertebral levels of interest
<ol>
	<li>Using the CBCT scanner, identify the vertebral levels of interest by fluoroscopy. Use the wireless control tablet of the CBCT scanner to move the scanner to the desired position, align the x-ray beam, and to perform the fluoroscopy scan (Figure 1). 
	NOTE: The 2D scans can be immediately reviewed on the tablet. The vertebral levels are identified by looking for ribs on the fluoroscopy scan and counting upward or downward.</li>
	<li>Attach the radiolucent navigation dynamic reference clamp to a spinous process in the area of interest by exposing the spinous process and fastening the clamp using the dedicated screwdriver. Then, attach the reflective spheres of the reference frame to the clamp (Figure 2).</li>
	<li>Perform a CBCT scan, and transfer the scan to the navigation platform (via LAN) (Figure 3). The navigation system camera tracks the CBCT scanner and the dynamic reference frame, enabling automatic patient registration using the Brainlab Loop-X Automatic Registration software on the navigation platform.</li>
	<li>Start the Spine &#38; Trauma Navigation software on the navigation platform. Use the spinal pointer and the 2D navigation views to verify the accuracy of the patient registration on anatomical landmarks.</li>
</ol>
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/64474/64474fig01.jpg" /> 
Figure 1: The wireless control tablet of the CBCT scanner. The tablet showing the fluoroscopy images from the CBCT. <a href="https://www.jove.com/files/ftp_upload/64474/64474fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/64474/64474fig02.jpg" /> 
Figure 2: A schematic picture of the clamp attached to the spinous process. <a href="https://www.jove.com/files/ftp_upload/64474/64474fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/64474/64474fig03.jpg" /> 
Figure 3: The Loop-X CBCT. The CBCT performing a scan on the draped pig cadaver with the reference attached. <a href="https://www.jove.com/files/ftp_upload/64474/64474fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
3. Instrument calibration
<ol>
	<li>Calibrate a navigated drill guide and a screw driver to the navigation system. For this purpose, select the instrument in the Brainlab Spine &#38; Trauma Instrument Setup software, and then present the real instrument to the camera of the navigation system along with a calibration device. Move the instrument in a rotating motion while in contact with the calibration device until the navigation system recognizes the instrument. Once calibrated, track and visualize the instrument on both the 2D images and the 3D model in the HMD.</li>
</ol>
4. Head-mounted device fitting
<ol>
	<li>Ensure that each surgeon is fitted with a Magic Leap headset (the HMD). Ensure the HMD and the navigation platform are connected to the same network (WLAN connection for the HMD and LAN connection for the navigation platform).</li>
	<li>To establish the communication between the HMD and the Spine &#38; Trauma Navigation software, look at the QR code displayed on the screen of the navigation platform. This starts the corresponding Mixed Reality application running on the HMD and transfer of data to the HMD.</li>
	<li>Perform the mixed reality alignment by looking at the spine reference array through the&#160;HMD for a few seconds. Wait for a 3D model of the spine, rendered based on the CBCT scan, to be accurately augmented onto the specimen in the HMD. In addition to the 3D overlay, look at the 2D navigation views and a second 3D model above the 2D navigation views (hover view) that are displayed in the HMD.</li>
</ol>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/64474/64474fig04v2.jpg" /> 
Figure 4: The view through the HMD. The surgeon&#39;s view through the HMD presenting both 2D and 3D information. The 3D overlay shows the planned 3D screws with protruding trajectory lines assisting instrument alignment. The lower 3D model is augmented onto the spine of the pig; additional information is provided in the 2D and 3D representations floating above, which can be positioned freely in the virtual space and switched on and off. <a href="https://www.jove.com/files/ftp_upload/64474/64474fig04largev2.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
5. Planning the pedicle screw placement
<ol>
	<li>Plan the pedicle screw paths based on the 3D registered augmented model, aligning them with the anatomy of the spine, and visualize in the HMD (Figure 5). Perform fine-tuning of the screw paths on the touchscreen of the navigation platform.</li>
</ol>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/64474/64474fig05v2.jpg" /> 
Figure 5:&#160;Pedicle screw path planning. The paths for the pedicle screws being planned using the HMD and the navigation pointer. <a href="https://www.jove.com/files/ftp_upload/64474/64474fig05largev2.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
6. Beginning the pedicle screw placement
<ol>
	<li>Make small skin incisions approximately 2 cm long with a scalpel for minimally invasive access to the pedicles based on the superimposed 3D model visible through the HMD (Figure 6).</li>
	<li>Using a minimally invasive technique, dissect the soft tissue, and dilate the canal with dilators&#160;until the pedicle entry point on the vertebral surface is reached.</li>
	<li>Adjust the depth of the drill guide to match the length of the screw planned for the pedicle. The planned screw length is displayed on the screen of the navigation system. Position and align the navigated drill guide to the planned path.</li>
	<li>Drill the pedicle using a power drill with a 4.5 mm drill bit (Figure 7). Drill according to the planned path; the drill guide stops the drill from going deeper than the planned depth.</li>
	<li>Estimate the time from the skin incision until the canal is drilled for each pedicle.</li>
</ol>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/64474/64474fig06v2.jpg" /> 
Figure 6:&#160;Minimally invasive incisions. The pig cadaver from above showing the minimally invasive incisions along the spine. To the right is the reference with the reflective spheres clamped to the spinous process. <a href="https://www.jove.com/files/ftp_upload/64474/64474fig06largev2.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/64474/64474fig07v2.jpg" /> 
Figure 7: Drilling the pedicles. The pedicle is drilled with a power drill using the navigation visible through the HMD to align the drill guide to the pre-planned path. <a href="https://www.jove.com/files/ftp_upload/64474/64474fig07largev2.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
7. Visualization of the screw placement
NOTE: No screws were placed to avoid metal artifacts during evaluation.
<ol>
	<li>Perform a second CBCT to acquire X-ray images of the drilled vertebrae for the accuracy analysis. Ensure the drilled canal in the vertebra is clearly visible before using it for subsequent accuracy analyses.</li>
</ol>
8. Cannulating the spine
<ol>
	<li>Repeat the above procedure described in section 2, section 4, section 6, and section 7 to cover the next region of interest until the whole spine is cannulated.</li>
	<li>Repeat the same procedure (sections 1-8) using the second specimen.</li>
</ol>
9. Image analysis
<ol>
	<li>Match the obtained CBCT images to the navigation plan and make corrections according to the laboratory notes taken during the procedure.</li>
	<li>Have an independent reviewer evaluate all the images and grade the cannulations according to the Gertzbein grading scale, from 0 to 3. Grades 0 or 1 are considered accurate. Grades 2 or 3 are considered inaccurate.</li>
	<li>Fuse the trajectories of the planned paths and the cannulations, and define the technical accuracy as the deviation from the path at the entry and target. Measure the angular deviation.</li>
</ol>

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None of the authors who are affiliated with clinical institutions (H.F., G.B., E.E., and A.E.-T.) have financial interests in the subject matter, materials, or equipment or with any competing materials and did not receive any payments from Brainlab. A.E.-T has been a consultant for Brainlab untill October 2022. The other authors affiliated with Brainlab (J.W., F.T., and L.W.) have financial interests in the subject matter, materials, and equipment, in the sense that they are employees of Brainlab. The extent of influence on the data, manuscript structure, and manuscript conclusions by these authors and/or Brainlab was limited to technical knowledge and support for the experiments, as well as performing the technical analysis of the image data. The authors without conflicts of interest had full control of all the data labeling, data analysis, information submitted for publication, and overall conclusions drawn in the manuscript. The prototype system described in this article is currently a research prototype and is not for commercial use.

In this study, a novel workflow for minimally invasive pedicle screw placement using an HMD in sterile conditions is described and its accuracy evaluated. There are several scientific reports on HMD systems for cranial and spinal navigation, two of which have gained FDA approval for clinical use17,18. Other studies have shown promising results in the usability of HMDs in sterile environments19,20, as well as good accuracy in phantom and cadaver studies12,13,21. The results of the current study support the usefulness and feasibility of the workflow in a sterile environment and can serve as an important basis for the clinical introduction of the current device.
This study is distinguished by the step-by-step description of the procedure in the OR. Using an integrated navigation concept, including intraoperative CBCT and HMD, the patient registration and image overlay can be automatized to save time and effort in the OR. Once the setup is completed and the surgeons are equipped with the eye-calibrated HMD, all the other steps can be performed seamlessly. A great advantage of the pre-planning of the screw trajectories is that any deviation from the correct path can immediately be visualized and corrected.
When the planning is complete, the trajectories can be seen through the pedicles and will match the anatomical angulations of the pedicles. Any trajectories not matching the angulation of the others will become evident, and the surgeon can then correct them to facilitate the subsequent rod placement. The planned trajectories are saved, and they can then be used to assess the technical accuracy after fusion to the postoperative scans. In this context, technical accuracy is a combination of the inbound error of the navigation system and the surgeon&#39;s ability to adhere to the planned path. Importantly, the possibility to perform a confirmation CBCT allows for the intraoperative revision of any screw that, despite navigation, may be incorrectly placed.
CBCT is a well-known and widely used imaging device for intraoperative navigation and postoperative verification. CBCT provides 3D images of superior quality compared to the 2D images from a C-arm, a device commonly used in spinal surgery. The image quality and diagnostic accuracy of CBCT are comparable to conventional CT. The time requirement for the setup and sterile draping is similar to that of a standard C-arm but with much better diagnostic quality imaging22,23,24,25.
The difference in technical accuracy between the entry point and the target point is a result of the fact that the accuracy at the entry point is highly dependent on the anatomy at the chosen entry point. If the entry point is placed on a slope on the bone surface, there always is a risk of skiving26,27. When the pedicle is entered, the rigid cortical walls will guide the device, and, hence, the deviation at the target will be smaller due to there being no room for wiggling.
The HMD provides a 3D model that is rendered from the intraoperative CBCT or preoperative imaging and augmented onto the actual spine. In addition, it displays 2D images in the axial, sagittal, and coronal planes, as well as a second 3D model that the surgeon can rotate and position anywhere in the virtual space, based on personal preference. Interaction with the display software is currently performed using a remote control. To use this remote control in a sterile environment, it would have to be placed in a sterile plastic bag. This is standard practice with several non-sterile handheld devices that have to be used in sterile environments. However, in a clinical environment, hand gestures or voice commands would be preferred. During navigation, virtual representations of the tracked instruments in the 2D and 3D views provide visual feedback to aid the surgeon.
The HMD itself has evolved, and the second generation of Magic Leap is lighter and has a larger field of view. The field of view is an important factor in the use of HMDs and represents one of the features that is constantly being developed further. The field of view of the Magic Leap was fully efficient for conducting this experiment and did not pose any limitations to the workflow. Each HMD has its own small computer that the surgeon needs to wear underneath their sterile gowns. The communication between the HMD and the navigation system is via Wi-Fi, and network limitations may result in latency. Despite this product being the first prototype, the current results indicate excellent clinical accuracy and submillimeter technical accuracy.
The limitations of this study are the small sample size and the porcine, cadaveric model. The possible effects of breathing and bleeding on the accuracy could not be evaluated. Although a minimally invasive technique was used, no screws were inserted. However, the screw canals were readily visible and allowed for an accurate assessment of accuracy without interference from metal artifacts.In conclusion, this paper provides a detailed description of a novel workflow for HMD AR navigation. When used for minimally invasive pedicle cannulations in a porcine model, submillimeter technical accuracy and 100% clinical accuracy could be achieved.

The correct placement of pedicle screws is important to avoid damage to neurovascular structures in and around the spine. The placement accuracy using the free-hand technique is highly variable1. By using 3D navigation, the accuracy is improved compared to traditional image-guided methods based on intraoperative fluoroscopy. Higher accuracy reduces the risk of revision surgery2,3.
With the estimation that mean life expectancy will continue to increase, an increasing number of elderly patients will need surgical spine procedures for various pathologies4. Minimally invasive approaches are gaining ground due to their lower morbidity, especially in the elderly5,6. However, these approaches are dependent on accurate navigational solutions. As navigation is image-based, efforts are being made to reduce the intraoperative radiation exposure of patients and staff7,8,9,10.
Augmented reality (AR) is an emerging technology in surgical navigation that aims to improve the accuracy and efficacy in the operating room (OR)11. AR superimposes computer-generated information onto a real-world view. This works especially well when the superimposed information is seen through an HMD. For that purpose, HMDs using head-up display technology have gained attention due to their small size, portability, and the possibility to maintain a direct line of sight. Several HMDs are available on the market today for AR navigation12,13,14,15,16.
The Magic Leap headset is an optical see-through HMD, including several cameras, a depth sensor, and inertial measurement units, which are used to determine the position and orientation of the headset in the environment. The purpose of this study was to evaluate the workflow of the Magic Leap HMD, combined with a conventional navigation system and a state-of-the-art mobile CBCT device, for intraoperative imaging in a realistic surgical environment.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Instrument tracking array spine &#38; trauma&#160;4-marker</td>
			<td>Brainlab</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Curve Navigation System</td>
			<td>Brainlab</td>
			<td></td>
			<td>Navigation System 
			<img alt="Figure 1" src="/files/ftp_upload/64474/64474eq01.jpg" style="margin: auto;" /></td>
		</tr>
		<tr>
			<td>Disposable clip-on remote control</td>
			<td>Brainlab</td>
			<td></td>
			<td>SmartClip</td>
		</tr>
		<tr>
			<td>Drill guide tube, handle with marker spheres, drill guide depth control insertable, drill bits</td>
			<td>Brainlab</td>
			<td></td>
			<td>Drill guide and accessories</td>
		</tr>
		<tr>
			<td>Expedium</td>
			<td>DePuy Synthes</td>
			<td></td>
			<td>Screwdriver 
			<img alt="Figure 3" src="/files/ftp_upload/64474/64474eq03.jpg" style="margin: auto;" /></td>
		</tr>
		<tr>
			<td>Instrument calibration matrix</td>
			<td>Brainlab</td>
			<td></td>
			<td>Instrument Calibration Matrix 
			<img alt="Figure 4" src="/files/ftp_upload/64474/64474eq04.jpg" style="margin: auto;" /></td>
		</tr>
		<tr>
			<td>Loop-X</td>
			<td>Brainlab</td>
			<td></td>
			<td>CBCT scanner 
			<img alt="Figure 5" src="/files/ftp_upload/64474/64474eq05.jpg" style="margin: auto;" /></td>
		</tr>
		<tr>
			<td>Magic Leap 2</td>
			<td>Magic leap Inc.</td>
			<td></td>
			<td>Mixed Reality headset 
			<img alt="Figure 6" src="/files/ftp_upload/64474/64474eq06v2.jpg" style="margin: auto;" /></td>
		</tr>
		<tr>
			<td>Navigation pointer spine&#160;</td>
			<td>Brainlab</td>
			<td></td>
			<td>Navigation Pointer 
			<img alt="Figure 7" src="/files/ftp_upload/64474/64474eq07v2.jpg" style="margin: auto;" /></td>
		</tr>
		<tr>
			<td>Spine reference array for reference clamp carbon (4-Sphere Geometry)</td>
			<td>Brainlab</td>
			<td></td>
			<td>Spine Reference Array 
			<img alt="Figure 8" src="/files/ftp_upload/64474/64474eq08.jpg" style="margin: auto;" /></td>
		</tr>
		<tr>
			<td>Spine reference clamp carbon with slider</td>
			<td>Brainlab</td>
			<td></td>
			<td>Spine Reference Clamp&#160; 
			<img alt="Figure 9" src="/files/ftp_upload/64474/64474eq09.jpg" style="margin: auto;" /></td>
		</tr>
		<tr>
			<td>TruSystem 7500</td>
			<td>Trumpf</td>
			<td></td>
			<td>Operating table</td>
		</tr>
		<tr>
			<td>Software</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Mixed Reality Spine Navigation App for Magic Leap</td>
			<td>Brainlab</td>
			<td></td>
			<td>Run on Curve Navigation System 
			Version: 2.0</td>
		</tr>
		<tr>
			<td>PDM</td>
			<td>Brainlab</td>
			<td></td>
			<td>Run on Curve Navigation System 
			Version: 4.2</td>
		</tr>
		<tr>
			<td>Spine &#38; Trauma Instrument Setup</td>
			<td>Brainlab</td>
			<td></td>
			<td>Run on Curve Navigation System 
			Version: 6.2</td>
		</tr>
		<tr>
			<td>Spine &#38; Trauma Navigation 2.0</td>
			<td>Brainlab</td>
			<td></td>
			<td>Run on Curve Navigation System 
			Version: 1.6</td>
		</tr>
	</tbody>
</table>

pedicle screw placement using an augmented reality head-mounted display in a porcine model

This protocol helps assess the accuracy and workflow of an augmented reality (AR) hybrid navigation system using the Magic Leap head-mounted display (HMD) for minimally invasive pedicle screw placement. The cadaveric porcine specimens were placed on a surgical table and draped with sterile covers. The levels of interest were identified using fluoroscopy, and a dynamic reference frame was attached to the spinous process of a vertebra in the region of interest. Cone beam computerized tomography (CBCT) was performed, and a 3D rendering was automatically generated, which was used for the subsequent planning of the pedicle screw placements. Each surgeon was fitted with an HMD that was individually eye-calibrated and connected to the spinal navigation system.
Navigated instruments, tracked by the navigation system and displayed in 2D and 3D in the HMD, were used for 33 pedicle cannulations, each with a diameter of 4.5 mm. Postprocedural CBCT scans were assessed by an independent reviewer to measure the technical (deviation from the planned path) and clinical (Gertzbein grade) accuracy of each cannulation. The navigation time for each cannulation was measured. The technical accuracy was 1.0 mm &#177; 0.5 mm at the entry point and 0.8 mm &#177; 0.1 mm at the target. The angular deviation was 1.5&#176; &#177; 0.6&#176;, and the mean insertion time per cannulation was 141 s &#177; 71 s. The clinical accuracy was 100% according to the Gertzbein grading scale (32 grade 0; 1 grade 1). When used for minimally invasive pedicle cannulations in a porcine model, submillimeter technical accuracy and 100% clinical accuracy could be achieved with this protocol.

In total, 33 navigated cannulations were performed. The time per cannulation and the clinical and technical accuracy were assessed on the postoperative CBCT scans (Figure 8).
<img alt="Figure 9" class="xfigimg" src="/files/ftp_upload/64474/64474fig09.jpg" /> 
Figure 8:&#160;The postoperative scan of a Gertzbein grade 0 cannulation. The scan includes the surgical plan for the pedicle cannulation, presented in the coronal, axial, and sagittal views. Note the close alignment of the virtual screw and the cannulated canal. <a href="https://www.jove.com/files/ftp_upload/64474/64474fig09large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
The mean insertion time per cannulation was 141 s &#177; 71 s (median [range]: 151 [43-471]; Figure 9).
<img alt="Figure 10" class="xfigimg" src="/files/ftp_upload/64474/64474fig10.jpg" /> 
Figure 9:&#160;Histogram and box of the distribution of the pedicle cannulation times. Top, histogram of the distribution of the pedicle cannulation times (n = 33); bottom, the corresponding box plot showing the median, interquartile range, and an outlier. <a href="https://www.jove.com/files/ftp_upload/64474/64474fig10large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
All 33 cannulations were considered clinically accurate according to the Gertzbein grading scale (32 grade 0; 1 grade 1; Table 1).
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td></td>
			<td>Gertzbein Grade 0</td>
			<td>Gertzbein Grade 1</td>
			<td>Gertzbein Grade 2</td>
			<td>Gertzbein Grade 3</td>
			<td>Clinically Accurate</td>
			<td>Clinically Inaccurate</td>
			<td>Accuracy</td>
		</tr>
		<tr>
			<td>Number of screws</td>
			<td>32</td>
			<td>1</td>
			<td>0</td>
			<td>0</td>
			<td>33</td>
			<td>0</td>
			<td>100%</td>
		</tr>
	</tbody>
</table>
Table 1:&#160;Clinical accuracy of implanted screws according to the Gertzbein grading scale. Grades 0 or 1 were considered accurate. Grades 2 or 3 were considered inaccurate.
To assess the technical accuracy, the deviation of each cannulation from its planned path was measured at the bone entry and at the bottom of the drill canal (Figure 10). The 3D measurements were performed by fusing the intraoperative scan, including the planned cannulation paths, with the postoperative scan of the cannulations. The angular deviation was calculated based on these data.
<img alt="Figure 11" class="xfigimg" src="/files/ftp_upload/64474/64474fig11.jpg" /> 
Figure 10:&#160;Overview of the measurement model for technical accuracy. <a href="https://www.jove.com/files/ftp_upload/64474/64474fig11large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
This method was previously described by Frisk et al.12. For the 33 pedicle cannulations performed, the technical accuracy was 1.0 mm &#177; 0.5 mm (median [range]: 1.0 [0.4-3.3]) at the entry point (Figure 11) and 0.8 mm &#177; 0.1 mm (median [range]: 0.8 [0.6-4.6]) at the bottom of the drill canal (Figure 12). The angular deviation was 1.5&#176; &#177; 0.6&#176; (median [range]: 1.5 [0.3-5.0]; Figure 13).
<img alt="Figure 12" class="xfigimg" src="/files/ftp_upload/64474/64474fig12.jpg" /> 
Figure 11:&#160;Technical accuracy at the bone entry point. Top, the technical accuracy at the entry; bottom, the corresponding box plot showing the median, interquartile range, and an outlier. <a href="https://www.jove.com/files/ftp_upload/64474/64474fig12large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 13" class="xfigimg" src="/files/ftp_upload/64474/64474fig13.jpg" /> 
Figure 12: Technical accuracy at the target (tip of drill canal). Top, technical accuracy at the target (tip of the drill canal); bottom, the corresponding box plot showing the median, interquartile range, and outliers. <a href="https://www.jove.com/files/ftp_upload/64474/64474fig13large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 14" class="xfigimg" src="/files/ftp_upload/64474/64474fig14.jpg" /> 
Figure 13: Angular deviation compared to the planned path. Top, angle deviation from the planned path; bottom, the corresponding box plot showing the median and interquartile range. <a href="https://www.jove.com/files/ftp_upload/64474/64474fig14large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Pedicle Screw Placement Using an Augmented Reality Head-Mounted Display in a Porcine Model

The augmented reality head-mounted display, Magic Leap, was used in combination with a conventional navigation system to place pedicle screws in a porcine model by adhering to a novel workflow. With a median insertion time of &lt;2.5 min, submillimeter technical accuracy and 100% clinical accuracy were achieved according to Gertzbein.

This protocol helps assess the accuracy and workflow of an augmented reality (AR) hybrid navigation system using the Magic Leap head-mounted display (HMD) ...

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Research

JoVE Journal

Medicine

A Simple Guide Screw Method for Intracranial Xenograft Studies in Mice

The grafting of human tumor cells into the brain of immunosuppressed mice is an established method for the study of brain cancers including glioblastoma (glioma) and medulloblastoma. The widely used stereotactic approach only allows for the injection of a single animal at a time, is labor intensive and requires highly specialized equipment. The guide screw method, initially developed by Lal et al.,1 was developed to eliminate cumbersome stereotactic procedures. We now describe a modified guide screw approach that is rapid and exceptionally safe; both of which are critical ethical considerations. Notably, our procedure now incorporates an infusion pump that allows up to 10 animals to be simultaneously injected with tumor cells.
To demonstrate the utility of this procedure, we established human U87MG glioma cells as intracranial xenografts in mice, which were then treated with AMG102; a fully human antibody directed to HGF/scatter factor currently undergoing clinical evaluation2-5. Systemic injection of AMG102 significantly prolonged the survival of all mice with intracranial U87MG xenografts and resulted in a number of complete cures. 
This study demonstrates that the guide screw method is an inexpensive, highly reproducible approach for establishing intracranial xenografts. Furthermore, it provides a relevant physiological model for validating novel therapeutic strategies for the treatment of brain cancers.

In order to evaluate novel therapeutic paradigms for the treatment of glioma, physiological relevant models are essential. We utilize an implantable guide screw procedure for establishment of intracranial xenograft models that is more rapid and safer than stereotactic approaches.

The grafting of human tumor cells into the brain of immunosuppressed mice is an established method for the study of brain cancers including glioblastoma ...

Using Quantitative Real-time PCR to Determine Donor Cell Engraftment in a Competitive Murine Bone Marrow Transplantation Model

Murine bone marrow transplantation models provide an important tool in measuring hematopoietic stem cell (HSC) functions and determining genes/molecules that regulate HSCs. In these transplant model systems, the function of HSCs is determined by the ability of these cells to engraft and reconstitute lethally irradiated recipient mice. Commonly, the donor cell contribution/engraftment is measured by antibodies to donor- specific cell surface proteins using flow cytometry. However, this method heavily depends on the specificity and the ability of the cell surface marker to differentiate donor-derived cells from recipient-originated cells, which may not be available for all mouse strains. Considering the various backgrounds of genetically modified mouse strains in the market, this cell surface/ flow cytometry-based method has significant limitations especially in mouse strains that lack well-defined surface markers to separate donor cells from congenic recipient cells. Here, we reported a PCR-based technique to determine donor cell engraftment/contribution in transplant recipient mice. We transplanted male donor bone marrow HSCs to lethally irradiated congenic female mice. Peripheral blood samples were collected at different time points post transplantation. Bone marrow samples were obtained at the end of the experiments. Genomic DNA was isolated and the Y chromosome specific gene, Zfy1, was amplified using quantitative Real time PCR. The engraftment of male donor-derived cells in the female recipient mice was calculated against standard curve with known percentage of male vs. female DNAs. Bcl2 was used as a reference gene to normalize the total DNA amount. Our data suggested that this approach reliably determines donor cell engraftment and provides a useful, yet simple method in measuring hematopoietic cell reconstitution in murine bone marrow transplantation models. Our method can be routinely performed in most laboratories because no costly equipment such as flow cytometry is required.

Determining donor cell engraftment presents a challenge in mouse bone marrow transplant models that lack well-defined phenotypical markers. We described a methodology to quantify male donor cell engraftment in female transplant recipient mice. This method can be used in all mouse strains for the study of HSC functions.

Murine bone marrow transplantation models provide an important tool in measuring hematopoietic stem cell (HSC) functions and determining genes/molecules ...

An Anesthesia, Surgery, and Harvest Method for the Evaluation of Transpedicular Screws Using an In Vivo Porcine Lumbar Spine Model

Pedicle screw fixation is the gold standard for the treatment of spinal diseases. However, many studies have reported the issue of loosening pedicle screws after spinal surgery, which is a serious concern. To address this problem, diverse types of pedicle screws have been examined to identify those with good fixation strength and osseointegration in spine bone. The porcine spine is a good alternative for the human spine in the evaluation of pedicle screws due to the anatomical size, mechanical characteristics, and cost. Although several studies have reported that pedicle screws are efficient in the porcine model, no study has described detailed protocols for the evaluation of a pedicle screw using the porcine model. Here, we describe a detailed method for evaluating transpedicular screws using an in vivo porcine lumbar spine model. The technical details for anesthesia, spine surgery, and harvest provided here will facilitate with the evaluation of the transpedicular screw fixation model.

An Anesthesia, Surgery, and Harvest Method for the Evaluation of Transpedicular Screws Using an In Vivo Porcine Lumbar Spine Model

Here, we introduce a method to evaluate transpedicular screws by using an in vivo porcine lumbar spine model.

Pedicle screw fixation is the gold standard for the treatment of spinal diseases. However, many studies have reported the issue of loosening pedicle ...

Isometric Contractility Measurement of the Mouse Mesenteric Artery Using Wire Myography

The wire myograph technique is used to assess the contractility of vascular smooth muscles in response to depolarization, GPCR agonists/inhibitors and drugs. It is widely used in many studies on the physiological functions of vascular smooth muscle, the pathogenesis of vascular diseases such as hypertension, and the development of smooth muscle relaxant drugs. The mouse is a widely used model animal with a large pool of disease models and genetically modified strains. We introduced this method to measure the isometric contraction of mouse mesenteric artery in detail. A 1.4-mm segment of mouse mesenteric resistance artery was isolated and mounted on a myograph chamber by passing two steel wires through its lumen. After equilibration and normalization steps, the vessel segment was potentiated by a high-K+ solution twice prior to the contraction assay. As an example of the application of this method in drug development, we measured the relaxant effect of a novel natural substance, neoliensinine, isolated from a Chinese herb, embryos of the lotus seed (Nelumbo nucifera Gaertn.) on mouse mesenteric arteries. The vessel segments mounted on the myograph chamber were stimulated with a high-K+ solution. When the force tension reached a stable sustained phase, cumulative doses of neoliensinine were added to the chamber. We found that neoliensinine had a dose-dependent relaxant effect on smooth muscle contraction, thus suggesting that it bears potential activity against hypertension. In addition, as the vessel segment can survive at least 4 hours after mounting and maintain contractility induced by the high-K+ solution for many times, we suggest that the wire myograph system may be used for the time-consuming process of drug screening.

The wire myograph technique is used to investigate vascular smooth muscle functions and screen new drugs. We report a detailed protocol for measuring the isometric contractility of the mouse mesenteric artery and for screening new relaxants of vascular smooth muscle.

The wire myograph technique is used to assess the contractility of vascular smooth muscles in response to depolarization, GPCR agonists/inhibitors and ...

Integrating Augmented Reality Tools in Breast Cancer Related Lymphedema Prognostication and Diagnosis

Breast cancer related lymphedema (BCRL) is a detrimental condition characterized by fluid accumulation in the upper limb in breast cancer patients subjected to axillary surgery and/or radiations. Its etiology is multifactorial and include also tumor-specific pathological features, such as lymphovascular invasion (LVI) and extranodal extension (ENE). To date, no widely employed guidelines for the early diagnosis of BCRL are available. Here, we illustrate a protocol for a digitally assisted BCRL assessment using a 3D laser scanner (3DLS) and a tablet computer. It has been specifically optimized in a discovery cohort of high-risk breast cancer patients. This study provides a proof-of-principle that augmented reality tools, such as 3DLS, can be incorporated into the clinical workup of BCRL to allow for a precise, reproducible, reliable, and cheap diagnosis.

Breast cancer related lymphedema is frequent in breast cancer survivors, but there are not widely employed guidelines for its diagnosis and quantification. Here, we introduce a reliable and cost-effective protocol to define, quantify, and compare upper limb volume in breast cancer patients.

Breast cancer related lymphedema (BCRL) is a detrimental condition characterized by fluid accumulation in the upper limb in breast cancer patients ...

A Porcine Corneal Endothelial Organ Culture Model Using Split Corneal Buttons

Experimental research on corneal endothelial cells is associated with several difficulties. Human donor corneas are scarce and rarely available for experimental investigations as they are normally needed for transplantation. Endothelial cell cultures often do not translate well to in vivo situations. Due to the biostructural characteristics of non-human corneas, stromal swelling during cultivation induces substantial corneal endothelial cell loss, which makes it difficult to perform cultivation for an extended period of time. Deswelling agents such as dextran are used to counteract this response. However, they also cause significant endothelial cell loss. Therefore, an ex vivo organ culture model not requiring deswelling agents was established. Pig eyes from a local slaughterhouse were used to prepare split corneal buttons. After partial corneal trephination, the outer layers of the cornea (epithelium, bowman layer, parts of the stroma) were removed. This significantly reduces corneal endothelial cell loss induced by massive stromal swelling and Descemet&#39;s membrane folding throughout longer cultivation periods and improves general preservation of the endothelial cell layer. Subsequent complete corneal trephination was followed by the removal of the split corneal button from the remaining eye bulb and cultivation. Endothelial cell density was assessed at follow-up times of up to 15 days after preparation (i.e., days 1, 8, 15) using light microscopy. The preparation technique used allows a better preservation of the endothelial cell layer enabled by less stromal tissue swelling, which results in slow and linear decline rates in split corneal buttons comparable to human donor corneas. As this standardized organo-typically cultivated research model for the first time allows a stable cultivation for at least two weeks, it is a valuable alternative to human donor corneas for future investigations of various external factors with regards to their effects on the corneal endothelium.

Here, a step-by-step protocol for the preparation and cultivation of porcine split corneal buttons is presented. As this organo-typically cultivated organ culture model shows cell death rates within 15 days, comparable to human donor corneas, it represents the first model allowing long-term cultivation of non-human corneas without adding toxic dextran.

Experimental research on corneal endothelial cells is associated with several difficulties. Human donor corneas are scarce and rarely available for ...

Combining Augmented Reality and 3D Printing to Display Patient Models on a Smartphone

Augmented reality (AR) has great potential in education, training, and surgical guidance in the medical field. Its combination with three-dimensional (3D) printing (3DP) opens new possibilities in clinical applications. Although these technologies have grown exponentially in recent years, their adoption by physicians is still limited, since they require extensive knowledge of engineering and software development. Therefore, the purpose of this protocol is to describe a step-by-step methodology enabling inexperienced users to create a smartphone app, which combines AR and 3DP for the visualization of anatomical 3D models of patients with a 3D-printed reference marker. The protocol describes how to create 3D virtual models of a patient&rsquo;s anatomy derived from 3D medical images. It then explains how to perform positioning of the 3D models with respect to marker references. Also provided are instructions for how to 3D print the required tools and models. Finally, steps to deploy the app are provided. The protocol is based on free and multi-platform software and can be applied to any medical imaging modality or patient. An alternative approach is described to provide automatic registration between a 3D-printed model created from a patient&rsquo;s anatomy and the projected holograms. As an example, a clinical case of a patient suffering from distal leg sarcoma is provided to illustrate the methodology. It is expected that this protocol will accelerate the adoption of AR and 3DP technologies by medical professionals.

Presented here is a method to design an augmented reality smartphone application for the visualization of anatomical three-dimensional models of patients using a 3D-printed reference marker.

Augmented reality (AR) has great potential in education, training, and surgical guidance in the medical field. Its combination with three-dimensional (3D) ...

C-arm-Free Simultaneous OLIF51 and Percutaneous Pedicle Screw Fixation in a Single Lateral Position

Oblique lumbar interbody fusion (OLIF) is an established technique for the indirect decompression of lumbar canal stenosis. However, OLIF at the L5-S1 level (OLIF51) is technically difficult because of the anatomical structures. We present a novel simultaneous technique of OLIF51 with percutaneous pedicle screw fixation without fluoroscopy. The patient is placed in a right lateral decubitus position. A percutaneous reference pin is inserted into the right sacroiliac joint. An O-arm scan is performed, and 3D reconstructed images are transmitted to the spinal navigation system. A 4 cm oblique skin incision is made under navigation guidance along the pelvis. The internal/external and transverse abdominal muscles are divided along the muscle fibers, protecting the iliohypogastric and ilioinguinal nerves. Using a retroperitoneal approach, the left common iliac vessels are identified. Special muscle retractors with illumination are used to expose the L5-S1 intervertebral disc. After disc preparation with navigated instruments, the disc space is distracted with navigated trials. Autogenous bone and demineralized bone material are then inserted into the cage hole. The OLIF51 cage is inserted into the disc space with the help of a mallet. Simultaneously, percutaneous pedicle screws are inserted by another surgeon without changing the lateral decubitus position of the patient.
In conclusion, C-arm-free OLIF51 and simultaneous percutaneous pedicle screw fixation are performed in a lateral position under navigation guidance. This novel technique reduces surgical time and radiation hazards.

C-arm-free oblique lumbar interbody fusion at the L5-S1 level (OLIF51) and simultaneous pedicle screw fixation are performed in a lateral position under navigation guidance. This technique does not expose the surgeon or operating staff to radiation hazards.

Oblique lumbar interbody fusion (OLIF) is an established technique for the indirect decompression of lumbar canal stenosis. However, OLIF at the L5-S1 ...

Augmented Reality Navigation-Guided Core Decompression for Osteonecrosis of Femoral Head

Osteonecrosis of the femoral head (ONFH) is a common joint disease in young and middle-aged patients, which seriously burdens their lives and work. For early-stage ONFH, core decompression surgery is a classical and effective hip preservation therapy. In traditional procedures of core decompression with Kirschner wire, there are still many problems such as X-ray exposure, repeated puncture verification, and damage to normal bone tissue. The blindness of the puncture process and the inability to provide real-time visualization are crucial reasons for these problems.
To optimize this procedure, our team developed an intraoperative navigation system on the basis of augmented reality (AR) technology. This surgical system can intuitively display the anatomy of the surgical areas and render preoperative images and virtual needles to intraoperative video in real-time. With the guide of the navigation system, surgeons can accurately insert Kirschner wires into the targeted lesion area and minimize the collateral damage. We conducted 10 cases of core decompression surgery with this system. The efficiency of positioning and fluoroscopy is greatly improved compared to the traditional procedures, and the accuracy of puncture is also guaranteed.

Augmented reality technology was applied to core decompression for osteonecrosis of the femoral head to realize real-time visualization of this surgical procedure. This method can effectively improve the safety and precision of core decompression.

Osteonecrosis of the femoral head (ONFH) is a common joint disease in young and middle-aged patients, which seriously burdens their lives and work. For ...

Porcine Liver Transplantation Without Veno-Venous Bypass As an Extended Criteria Donor Model

Liver transplantation is regarded as the gold standard for the treatment of a variety of fatal hepatic diseases. However, unsolved issues of chronic graft failure, ongoing organ donor shortages, and the increased use of marginal grafts call for the improvement of current concepts, such as the implementation of organ machine perfusion. In order to evaluate new methods of graft reconditioning and modulation, translational models are required. With respect to anatomical and physiological similarities to humans and recent progress in the field of xenotransplantation, pigs have become the main large animal species used in transplantation models. After the initial introduction of a porcine orthotopic liver transplant model by Garnier et al. in 1965, several modifications have been published over the past 60 years.
Due to specifies-specific anatomical traits, a veno-venous bypass during the anhepatic phase is regarded as a necessity to reduce intestinal congestion and ischemia resulting in hemodynamic instability and perioperative mortality. However, the implementation of a bypass increases the technical and logistical complexity of the procedure. Furthermore, associated complications such as air embolism, hemorrhage, and the need for a simultaneous splenectomy have been reported previously.
In this protocol, we describe a model of porcine orthotopic liver transplantation without the use of a veno-venous bypass. The engraftment of donor livers after static cold storage of 20 h - simulating extended criteria donor conditions - demonstrates that this simplified approach can be performed without significant hemodynamic alterations or intraoperative mortality and with regular uptake of liver function (as defined by bile production and liver-specific CYP1A2 metabolism). The success of this approach is ensured by an optimized surgical technique and a sophisticated anesthesiologic volume and vasopressor management.
This model should be of special interest for workgroups focusing on the immediate postoperative course, ischemia-reperfusion injury, associated immunological mechanisms, and the reconditioning of extended criteria donor organs.

In this protocol, a model of porcine orthotopic liver transplantation after static cold storage of donor organs for 20 h without the use of a veno-venous bypass during engraftment is described. The approach uses a simplified surgical technique with minimization of the anhepatic phase and sophisticated volume and vasopressor management.

Liver transplantation is regarded as the gold standard for the treatment of a variety of fatal hepatic diseases. However, unsolved issues of chronic graft ...