Dr. David Rovinsky discusses the use of calibrated x-rays, a preoperative spinopelvic assessment tool (RI.HIP MODELER), and explains how software-guided surgery factors in pelvic tilt and other information to determine optimal cup placement, leg length and offset during total hip arthroplasty.
ah lo uh I'm dr. David Levinsky from the University of Hawaii and I'm going to talk to you about the use of enabling technology in total hip replacement. This is our standard disclaimer. And I am a consultant for smith nephew Ortho grid and also VR. So I come to medicine from the computer software industry and I've been Doing technology integration orthopedics for 20 years and I think it's our job to pick the best implants and the best technology to get the best outcomes for our patients. So I was trained post your approach traditional total hip replacement using acetate templates using mechanical alignment guides for anti version and inclination, doing some different types of devices to measure leg lengths and still in the recovery room. We would get occasionally some very disheartening X rays. So I want to share with you how we're using technology to make hip replacement much more precise and reproducible from preoperative planning, two interpretive enabling tools and even postoperative assessment. So we just had a nice discussion about how we use digital template ng. And this is superb for getting the static aspects of total hip replacement, correct reproducing patient anatomy, leg length and offset. But the real challenge is dealing with the dynamic aspects of hip replacement, including spinal, public mobility and public tilt and how they relate to patient activities. So what's interesting is we put the cup in in the operating room and we think that's where the cup is going to stay. But the patient's pelvis moves in space as they go through their day. And when we stand our pelvis tilts forward which actually helps us, It improves the coverage of the femoral head and that improves the contact pressures. And when we sit the pelvic rocks posterior lee and that gets the anteroom of the cup out of the way to prevent impingement and gives improved coverage of the head posterior early to prevent this location. Now a normal range of motion, It's about 30°. The challenging cases are when patients are stiff and they can be stiff and stuck in a seated position or stuck in a standing position. And the hyper mobile pelvis is really a challenge because the arc of motion is so great. The precise location where that cup is going to be stable is very, very precise and these patients almost always require dual mobility and our spinal public motion can change as we age or if we get a spinal fusion. So a cup that was in a good position when you had normal spinal public mobility can become unstable when the patient has a few spine, especially with a flat back deformity. So what we do at our clinic is we get a standing ap pelvis and this is the functional position of the patient when they're walking around. We also get a supine ap pelvis with king Mark calibration for template ng and we get a lateral pelvis standing and sitting and we measure the difference or change in the sacral slope and in this case the patient has very little change in the sacral slope. They have a flat back from degenerative disease and they have a stuck seated posture. So what we've learned is that the cup in these patients has to be placed with less anti version. If you place the cup in your typical orientation of 40° of inclination and 20° of anti version, The pelvis being stuck in a seated position is going to make that anti version actually 38° and they'll have anterior instability. So our goal orientation of the cup has to decrease introversion and our goal is going to be 10°. So this is what we did for this patient and he had a very stable hip and a nice outcome. So is the Ideal Cup position 40 and 15 relative to the table and relative to the base of the public? Probably not. And it depends on the spinal public mobility. And this is one of many Papers out there that shows that up to 60% of dislocations can have the cup in the ideal safe zone of low winnick of 40 and 15. So we have to reproduce offset. We have to reproduce leg length, but we also have to look at spinal public mobility. So what is the optimal cup position? How do we figure this out? So we can use a computer simulation to do this and we can look at the patient's actual spinal public motion and design the cup position that avoids impingement which can lead to dislocation and avoids edge loading to limit where and this is done by taking a standing and seated lateral X ray of the pelvis. We take a picture of it with an ipad or your phone and then we can measure the change in sequel slope and then we can virtually place implants and see what happens as the patient moves through their day. And we can alter the implant locations and decide on the optimal cut position for the patient. So this is a piece of software that is not FDA approved. It's not on the market yet, it's called hip pro and it uses technology from life mod. And this is the lateral projections of the pelvis standing and seated. You measure the change in sacral slope and you also define the anterior public plane with a line from the A. S. I. S. To the top of the pubic synthesis. And then the computer will help you classify into this category of normal range of motion stuck standing, stuck seated or hyper mobile. And then we can look at activities throughout the full range of motion. So golfing from the back swing all the way through, follow through and you can see what's happening to the contact pressure on the left and stem excursion on the right. And we can look at this summation slide and you can see at the end of the backswing there's actually impingement on the edge of the cup. We can look at getting out of a chair, getting on a bicycle, reaching down to the floor, going downstairs and even doing activities such as yoga so we can summarize this information and say okay what is the best position for the cup and diversion, inclination and even stem version? And we want to centralize loading and minimize impingement and optimize stability. And we can even change implants and compare implants and you'll see things like a larger head will give you more stability. A skirted neck will decrease stability. So we can calculate and determine the optimal component location. And in this case we've chosen 48° inclination And 16° of anti virgin. So what does this mean? While we define this relative to the anterior pelvic plane? So that's a plane described by the A. S. I. S. On both sides and the top of the pubic synthesis. But when the patient's lying on the table, they're not lying parallel to the entire public plane, the pelvis is generally tilted. And that change in tilt is the difference between the public plane and the functional plane. And in this case the patients changes 13°. And that's going to affect our Gold Cup position. So you can imagine if someone has a normal mobility of their spine when they're lying flat on the table they're standing in a similar posture. But if they have a stiff spine and a flat back, the change between the interpublic plane and the table can be quite significant and the impact this has on the cut position is significant. So an anterior hip, our goal is in the lips of about one third diameter. But we have to decrease the anti version if the patient has a large pelvic tilt and it's about 0.7° of anti version per one degree of pelvic tilt. So our goal cup position has to have lesser ellipse and a flatter position. So we can approximate this using radiographic markers. Looking at the trance teardrop line and the top of the pubic synthesis. So we can get a standing ap pelvis and this patient had a spinal fusion and we can measure the chance teardrop line and we can look at the top of the public synthesis and this is their standing posture. And we can use Flora Skopje and I like this in a supine position for direct anterior approach and we can move the table around so that the pelvis position approximates the position of the pelvis in the standing posture for the patient. So when we put the established component in we've hit our goal of decreasing the introversion and optimizing the position for their functional posture and certainly interpretive imaging helps whether you do this anti really or post. Eerily. This is using philosophy for post your hip which is a little cumbersome but possible. The challenges parallax, you know, if you're looking at the cup from different positions, the cup looks different and if you have a perfectly level pelvis and a perfectly ap of the hip, this is the ideal cup position for 20 degrees of anti virgin. However, the same cup looks very different. If you look at an ap pelvis it looks more horizontal and more introverted. And if the pelvis is rotated then you have a very odd looking lips. And if you have an inlet and an outlet view or largely a pelvic tilt again, your lips is not reliable. So I really want numbers to work with. I want to define my target with numbers. I want to hit that target and I want to be able to do my hips supine or lateral position. So we can do this with hip navigation which is integrated to the trauma cad planning software. And basically what we have to do is input 12 additional points or landmarks. When we template our total hip. And there are certain mathematical relationships based on sex and the relationship of these positions. That will tell us the patient's pelvic tilt and this public tilt again affects the position of a cup more so and aversion than inclination. But it does affect both numbers. So we can use navigation to again hit this target that we very carefully defined and we're identifying a position of our socket. And we also want information about leg length and offset. And this is suitable for any approach. You can do it through a post your approach, a lateral approach or anterior approach and this is a big advantage and the navigation tools are similar to what we've used for total leaves. There are arrays that communicate with infrared cameras, there's an invasive array and non invasive array and then we have a navigated insertion handle and a point probe for inputting data. So when we start the case we tell the patient information to the computer, male or female, supine position or lateral position and which side were operating. The next thing we do is we set up the camera so it's visible to the trackers and we put a noninvasive array on the anterior or lateral portion of the thigh and an invasive ray the iliac wing. And this array in the wing is a stable point position. So the computer has a reference point for the mapping and you just make a small incision and place two pins similar to what you do for an external fix. Later we then will do for the lateral registration. A very easy maneuver. We touch the ipsa lateral A. S. I. S. And the L. Five minus process. So this is really easy to do in the lateral position. The third point that defines the plane is the A. C. Tabula itself and then you can calculate your entire public plane. Other systems have required you in the past too touch both anterior superior iliac spines and that's really difficult to do in the lateral position so it's easy for the post your approach for the anti R. Approach of course you can touch both A. S. I. S. On the hips, lateral and contra lateral sides. And when we're doing an anterior hip the navigation equipment is at the foot of the table so does not get in the way of the cr. So now the first step is putting a checkpoint marker in the lateral aspect of the greater trot canter and we bring the leg up into a neutral position and we register where this landmark is. And what happens is after we put in our final components or trial components we can bring the leg back to this neutral position and we can identify exactly the change in leg length and offset that we've created. So after we make our formal net cut we can register the ashtabula by tracing the interior of the ashtabula rim and then we trace the faucet and this helps identify the hip center. Now we have all the information to define the anti Republic plan and you can navigate your hip relative to the entire public plane or we can navigate the hip relative to the table or the functional plane which is similar to an ap pelvis radiograph. And if you're navigating relative to the interpolate plane, the numbers will be more familiar. So this is 40 and 16 And since the patient has a 13° Pelvic tilt the numbers on the functional plane of course are different 38 and six. This is the actual screen. So if you're navigating to the entire public plane, it's a virtual pelvis. And if you're navigating relative to the table or the functional plane it's a virtual radiograph and you're trying to align the dash line to the yellow line and the numbers on the bottom tell you exactly where you're putting the cups and now we have to find our target and we can hit our target. And I finally have numbers with which to work. And then you put in your trials and once you put your trials in you reduce the hip and bring the femur back to its initial position and you can measure exactly any change in leg length and offset that you've created. So you can use your preoperative template ng and add back point five or you know .5 cm or whatever you need to do to change the leg length and offset to match your goal. And finally get this report. And this report includes all the information that you're looking for in terms of inclination. Anti version changes in leg length and offset. So what makes this really unique is that it's an integrated digital ecosystem. So we have input of patient characteristics as well as our plan, intra operative data, post operative assessment and then patient reported outcomes. So you can see changes in their functional scores. And what we want to do is integrate this information in one place and to see that if we're making changes in these parameters, are we actually getting better outcomes? So real intelligence for total hip replacement is an integration of implants and technology. I prefer the polar stem and the R. Three because it has also the dual mobility option of the R. 30. Preoperative planning. We do with trauma cad we use the hip pro to evaluate spinal public motion and understand public tilt and then inter operatively. I use Flora Skopje in conjunction with navigation to get my position my components precisely correct and reproduce leg length and offset. Thank you very much for your attention and Aloha from the University of Hawaii.