Terry Allen Clyburn, MD, an Orthopedic surgeon at Houston Methodist Hospital, talks about the benefits of 3-D hip modeling and the tools that help surgeons place them.
What is so great about this 3D concept in general, in particular the hip?
Dr. Clyburn: When we are planning to do a total hip, it’s very important for us to look at the x-rays and determine what the arthritic process has caused. Not only does it cause the loss of the cartilage and for the bone to rub together, but It also causes the hip to shorten or narrow. And one of the issues that you can have after a hip replacement is to have inequality of your leg links. So, when we’re planning the surgical procedure, we try very hard to do the operation in such a way that we put the hips back to the normal length and normal width that they were at originally. It’s not that easy to do that when you’re just looking at a plain single view x-ray, but when you can actually produce a three-dimensional computer model of the hip and you can see it from all directions, then you can see exactly what you need to do to make that hip perfect. In fact, the conformist hip program, the program that looks at the data from the CAT scan and designs the hip, we give it the information, we tell it specifically we want the leg to be five millimeters longer and five millimeters wider so as to produce the anatomic state that we want. Then the computer program actually designs the total hip to produce that implant that fits that patient perfectly.
You can see it in 3-D, and you can be very, very exact when you’re putting it in and making it. One almost wonders why anything is not in 3-D from the very beginning. What took us so long to get there?
Dr. Clyburn: Well, the technology really didn’t exist. First of all, there were some attempts to do this many years ago, but the quality of the CAT scans was not good enough. The pixelation and all- it just wasn’t exact. So, the fit of the implant just didn’t work out well. It took years for the technology to catch up with the concept.
So, they knew what they wanted to do, it was just a question of the implementation of it?
Dr. Clyburn: Right. Now frankly, at the same time that the work was done in this, work was being done in another arena, off-the-shelf implants. When I first started doing hip replacements you may have three or four sizes of the stem that goes in the femur and maybe three or four of the socket sizes and a couple of different lengths that you could produce, but it would be like going to a shoe store that had only four or five sizes of shoes. Those just were a struggle to get a good result with. What the off-the-shelf companies did, is they began to produce more and more sizes and more and more shapes so you could actually template in a traditional way and get a fairly close fit. So, there’s some competition there as well.
So describe to us how sensitive the human body is when something happens to be a millimeter off.
Dr. Clyburn: Well, a millimeter may not make a difference, but certainly three or four or five is definitely something that the patient can feel. So far what we’ve talked about is what’s called length and offset. If your length and offset aren’t right, you would feel your leg lengths to be a little bit different, you may limp a little bit because of that, but there’s another factor that we haven’t talked about and that is the stability of the hip. Your hip, my hip, and a person’s artificial hip are held in place, the ball in the socket is held only by the tension in the muscles and the tendons around. They don’t actually connect together. The ball just sits in the socket and is free to move. So, if the tension of the tissue isn’t exactly right and if the position of the implants within the pelvis and within the femur isn’t exactly right, it predisposes the patient to a complication called dislocation, it is not pleasant. If the patient moves the wrong direction or bends or twists a little bit, it’s possible, if this inherent stability is inadequate, for the ball to come out of the socket. And it’s quite painful. It’s not that hard to fix, we just basically give them some anesthetic, pull on the leg, pop the ball back in and tell them please don’t get in that position again- and they usually don’t.
But as a surgeon, this has got to just be a kind of nirvana for you.
Dr. Clyburn: It’s really not the call you want to get, that your patients in the emergency room with a dislocation. We’re not happy. The patient’s unhappy. We don’t want it to happen. So, getting the exact and perfect position of the implant into the human body exactly the way we want it is not easy. When we’re operating, we’re operating through a small incision, down in a deep hole, doing our best to try to position it. We may take x-rays during the surgery to see that the position is just right. One of the advantages of preplanning the implantation of the total hip and of going through this process of doing three-dimensional imaging is that they actually produce devices that we can use when we place the implant. It uses the patient’s natural shape, for instance, of the socket and puts the implant in relative to the existing anatomy- exactly the way it’s planned on the computer. On the computer, you can see where the patient’s natural socket is and you can see where the new implant needs to go relative to the natural anatomy, but when you’re in surgery, it’s a little hard to see that. So, there are guides that are custom made. Not only what you’re putting in is manufactured from a 3D standpoint, but also the tools that are necessary to implant the processes properly are 3D printed with plastic. We’re able to very accurately implant the device so the device is customized to fit the patient and the guides help us to put them in properly and exactly the way they need to be put in to get a good result.
Because otherwise, it would almost be the doctor fighting against what’s tailor-made for the patient, right?
Dr. Clyburn: If the implants are tailor-made for the patient, but the implant is not put in in the position in which it was intended to be placed, then you’re not going to get as good a result. So, you need both. You need the implant that recreates the patient’s natural anatomy and you have to provide the tools that are necessary for the surgeon to implant the new part in the exact proper way.
This sounds like the IKEA kit with the specialized wrench. I mean, you have been in practice for a while, give us a little comparison along the chronological timeline.
Dr. Clyburn: When I first started, as I mentioned, the implants only came in three sizes initially and they required bone cement to place them. Bone cement, we still use it and it’s a good product, is a polymer polymethylmethacrylate, but the problem with polymethylmethacrylate is that it’s like grout between bricks. Eventually, it starts to crack and break and wear out and the prosthesis can come loose. One of the first major developments during my time in practice was the concept of the un-cemented hip. Basically, it’s made out of a metal that’s porous, coated. The prosthesis is implanted in such a way that it’s very, very tight into the bone when you first put it in, but then because of the porosity of the metal on the outer surface, the bone grows into it. So, you skip having that interface of the polymer and once that bone has grown into that implant, it has every capability of staying there forever. That was a huge improvement. I mentioned the much wider array of sizes and shapes that came along because as we started to do more and more of them, the companies could spend more dollars and make more sizes and do more research and so forth. So that was very, very helpful. As I mentioned, back in the 80s there was an attempt with CAT scans to make custom devices and it didn’t work out well because of the quality of the CAT scan, but the CAT scans now are unbelievable. I mean, you see every tiny detail and the measurements that can be taken from the CAT scan are highly correct.
Do you use an MRI overlay with a CAT scan? What are you looking at in the OR?
Dr. Clyburn: There is a way to do this procedure with an MRI and there’s a way to do it with a CAT scan. What we found is that the CAT scan is more accurate. Now it’s kind of a simple concept, but the MRI is excellent for visualization of soft tissues, not so good for bones. The CAT scan is not so good for soft tissues, but much more accurate for the bone. So that’s how it evolved. The CAT scan is an older technology. The MRI is a newer technology. Both have evolved, but at the end of the day, the CAT scan is still the better way to look at the bone.
And in Ralph in particular, what was unique or unusual perhaps about his surgery?
Dr. Clyburn: One thing that I can say is that he is a great patient because he’s kept, despite the fact he had horrible hips, both sides, he stays in good shape. He’s muscular, he’s fit, which makes the recovery much more rapid, and you’ll probably see some film from him on the day of surgery practically running. That’s partially contributed to the implant because if the implant is doing exactly what it’s supposed to do, and it fits perfectly, then that helps the patient recover more rapidly. If the patient comes to surgery with good fitness, then they’ll recover more quickly, but in his case probably the most unique thing is that he just continued to work and walk and live life with two really, really stiff and bad hips.
Is it the boomer thing that we do much with the hips and now we’re paying the consequences?
Dr. Clyburn: I don’t think so. I don’t think the incidence of hip disease is that much more today than it was 50 or 60 years ago, except there’s so many more of us. Then, of course, the success of and the popularity of hip replacement- many of our grandparents or our parents didn’t have the option at all. Our parents may have had the option of an early hip replacement many years ago, but the results were just not as good as they are now. So, a lot of people just didn’t have it done and lived out their life- just with a cane and a bad limp.
Overall, what’s the greatest thing about this particular 3-D hip? Just a summary?
Dr. Clyburn: Probably the best thing about it is just everything that I just said in terms of being able to recreate the patient’s natural anatomy, and the ability of the surgeon to implant the prostheses in a reproducible way, as such that we achieve the exact position, the exact goal that we want.
Interview conducted by Ivanhoe Broadcast News.
END OF INTERVIEW
This information is intended for additional research purposes only. It is not to be used as a prescription or advice from Ivanhoe Broadcast News, Inc. or any medical professional interviewed. Ivanhoe Broadcast News, Inc. assumes no responsibility for the depth or accuracy of physician statements. Procedures or medicines apply to different people and medical factors; always consult your physician on medical matters.
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