Alright, I'd like to thank Praveen and Pat for putting this course on and inviting me to serve as faculty. Here are my disclosures, they won't influence my talk this afternoon. So there's three primary approaches for placing lumbar pedicle screws. The first is the traditional open approach, the mini-open approach by an expandable tube, and the third is the true MIS approach. For the purpose of this talk, we'll just concentrate on the open approach. Dr. Wang is going to give us a talk on the MIS approach tomorrow, so we'll just focus on the open approach for lumbar screw placement this afternoon. Like many of our faculty have already stated, placement of pedicle screws really starts in your preoperative planning during the clinic. So you should study the sagittal and axial angulation of the individual pedicles, and these angles are best judged using a preoperative CT or an MRI of the lumbar spine. You want to recognize if there's a coronal deformity because that's going to impact and influence the trajectories during surgery. In terms of general lumbar anatomy, the pedicle width is the most important thing to note, and it's more important than the pedicle height itself. Here is the pedicle width marked by this arrow. The pedicle width increases from L1 in size as you come down to the sacrum. The transverse pedicle angle also increases from near zero degrees, which is straight dorsal ventral at the L1 region, to nearly 30 degrees medial at L5. The sagittal pedicle angle is usually zero at L4, which means it's straight down. And then there's a rostral angulation for the upper lumbar screws, and the L5 pedicle is 5 to 10 degrees caudally inclined. So there's several measurements that you want to consider preoperatively, and you should definitely measure these on the CT scan, and like Dr. Fouad recommended, write them down so you have them for each particular level that you're going to instrument. The first measurement is the actual length of the screw, and that would be indicated by A. You don't want to be out the anterior cortex. The transverse diameter of the pedicle is here, B. And then the pedicle length is also something important to note, so you know how far you have to go before you penetrate into the vertebral body. And by doing these measurements, that will help you decide and plan which size pedicle screw you're going to place. So it's important to note the screw entry site as well. This is routinely measured and demarcated by the junction of two lines. The first line is the straight rostral caudal line, which is drawn along the lateral border of the superior articular facet that's delineated in red here. And the second line is the transverse line through the center of the transverse process, which is this horizontal line, and that intersection is routinely the screw entry site. So let's go through the steps of placing lumbar pedicle screws. The first step is selecting that screw entry site, and I find it easier to actually visualize this prior to performing a laminectomy. The second step would be to actually prepare the entry point, and you can do this in two ways. You can take a high-speed drill and drill through the cortical bone into the cancellous bone, and if you do that, you will look out for that pedicle blush. A second way is to ronger the cortical bone off the entry point, and this is often helpful, especially when you have facets that are hypertrophied and overgrown. And if you do the ronger technique, you want to make sure that you do not destabilize the facet joint, just rostral to your upper instrumented level. The third would be to insert the pedicle probe. I like to use the Lanky Pedicle Probe, but a simple blunt pedicle probe that has a nice angulation to it is very useful. You want to direct the blunt probe directly into the pedicle, and for lumbar pedicle screws, you want to ensure that the tip of the actual pedicle probe is pointing medially, whereas in the thoracic, you want to start out with the lateral tip. Here you want to make sure that it is pointing medially, and slowly advance it approximately 20 millimeters through the pedicle. And while you're advancing it, you want to maintain the correct superior-inferior trajectory as well as the medial-lateral trajectory. And at that point, you want to take a fluoro shot to ensure that your trajectory is adequate and before you go ahead and penetrate into the vertebral body. After doing that, you remove the pedicle probe and palpate the trajectory that you've made for the first 20 millimeters using a ball-tipped feeler. You want to ensure that you're completely intraosseous, so you want to check for the forewalls as well as the floor. And by doing so, you would avoid this situation here, where the pedicle screw has clearly breached medially. So that medial breach is going to be in that first 20 millimeters, so you want to look out for that. If you have a medial breach, then you want to start out with a more lateral screw entry site and then just put a new trajectory in. And so, like Praveen stated, that medial breach is going to be within that first 20 millimeters, 10 to 20 millimeters, and you'll notice it. Then you can reinsert the pedicle probe and advance it down that same trajectory into the vertebral body. If you notice that the pedicle probe is not advancing easily, then it's most likely that the probe is near cortical bone, so you want to reposition the trajectory, because you should not have to use brute force to go through the pedicle. Sometimes you may need to if it's very cortical or if the pedicle is very small and there's a cortical rim on both ends, but routinely you don't have to. It should advance with just some force. You want to advance the pedicle probe just to 40 millimeters and take a fluoro shot at that point. And by taking the fluoro shot, that would also help you determine not only that your trajectory is adequate, but you'll also be able to check the true depth of the screw that you want to place. And then finally, tap and screw. I like to tap. I use an undersized tap. And when you tap, you want to maintain the same trajectory that you used for the actual pedicle probe. You don't want to make a new trajectory. And after you tap, before you screw, you want to actually use a ball-tipped feeler again and ensure that you don't have a medial breach, a lateral breach, and you have four walls as well as a floor. And thereafter, you want to insert the pedicle screw. So the ideal screw trajectory in the sagittal plane, the pedicle screw should be parallel to the end plates or angled slightly upward to engage where the dense bone adjacent to the end plate is. And in terms of this image here on the right, the S1 screw here is clearly not in the proper trajectory. It's not parallel to the superior end plate of S1, and it's not engaging in dense bone. In terms of the axial plane here, the pedicle screw should be medialized, and that allows it to have a stronger pull-out strength. And you don't want to insert the screw close to the anterior, too far beyond the anterior cortex. It should be inside. You don't want to penetrate the anterior cortex like this screw here because there's vessels that live there, and you don't want to get into the lumen of that vessel, whether it's the vena cava, it's the iliacs, or it's the aorta. So you don't want an anterior breach, and that's why it's critical to actually feel and make sure that you have a floor. So if you do breach, then what? Well, the first thing you want to do is just stop and think, where is the breach? Is it a lateral breach? Is it a medial breach? Is it an anterior breach? Oftentimes, it's going to be a lateral breach, like in this situation here. The reason for that, particularly at the L5 level or the sacrum, is that it was difficult to medially angulate that pedicle probe, whether it's because of extensive soft tissue or maybe it's due to the position of the retractor, like in this situation. You can see here that the retractor is actually influencing where that pedicle probe can go. It's hard to actually medialize this probe even more because the trajectory is impacted by that retractor. So you may have to reposition the retractor to get an L5 or sacral screw in. That's oftentimes the case, especially when you have such a medial trajectory like you do here. If it's a medial breach, then you want to start a little bit more lateral and go from there. And if all else fails, then you can always do a laminal frame anatomy, palpate the medial wall from the inside using a Woodson elevator or a blunt nerve hook, and this will help you identify the location of the pedicle, the starting point, as well as your trajectory. And you always want to verify after the screws are placed. I use Stimulus Evoked EMG. It's controversial, but if there's a positive response at a stimulation less than 5 milliamps, then you're very suspicious and you want to check for a medial breach. Imaging-based modalities are probably the most reliable. We actually have an O-arm, and on my long segment fixations, I always spin an O-arm at the end of the case just to make sure that all the pedicle screws are in proper location and that avoids a take-back to the operating room and also potentially a readmission for a second operation. So if you have an O-arm, it's always nice to use it. And then don't forget the rods. So you want to make sure that the proximal and distal ends are visualized and they're through the screws, and you want to confirm at the end using an x-ray. Thanks a lot.

open approach

lumbar pedicle screws

preoperative planning

screw placement

fluoroscopy