Since the Lima Corporate 3D printing facility for complex custom orthopedic implants opened last March at Hospital for Special Surgery (HSS), HSS orthopedic surgeons like Mark P. Figgie, MD, have successfully used the new facility to produce implants for a range of patients for whom other solutions would have been inadequate. Dr Figgie, chief emeritus of the Surgical Arthritis Service and professor of orthopedic surgery at HSS, talked with Medscape about the hospital's process for using custom implants and current challenges in matching patients to the best orthopedic implant while getting them treated in a timely manner. Questions and answers in this interview have been edited for clarity.
What is the surgical planning and implant design process for using 3D-printed models and implants at HSS?
First, we identify the patient who may benefit from having a 3D model made, and that can be anything from somebody who's had previous surgery to others where the bone geometry is unusual, and we're not sure if an implant is going to fit properly. We have some patients where there's been significant wearing away of the bone in, for example, the acetabulum, and we want to see what bone is left to determine if a standard implant will fit or if we need to do any sort of patient-specific implant to make up for the bone loss.
I've had one case recently where the patient had surgery in their youth for dysplastic hips, and the femoral bone grew around the metal implants, and they were inside the bone. In order to plan for hip replacements, we had to get the hardware out first. We made a 3D model of the femur and planned where we had to make the bone cuts to get the metal out and then put the femur back together so that we could later perform the hip replacement.
Right now, most of the 3D printing we do are models, not the actual implant. But if we identify a patient who has something unusual about the geometry of their anatomy, we get a CT scan, and from that, we can create an actual model of the patient's geometry.
Now we have the technology to start making the actual implant to fit into the bone. And that's where Lima has a lot of expertise. This process has evolved from first making the actual model, and we've been doing that for a while, but now we're to the point where custom implants are 3D-printed. The advantage of that is avoiding the need to mill it from a solid block, where you've got restrictions on the geometry, the shape, and how the cuts are made because the tools have to get in there to remove the metal. It's a very slow process, and if you screw it up at any point, you've got to toss the whole thing out.
It's difficult to cut and machine a titanium block to form an implant, but with 3D printing, you're instead putting a powder base down and building off that, so they can make any shape geometry. You're not wasting material because you're just putting in what is called for, and you get exact geometries without having to machine the shape of the implant.
Can you describe a case in which printing a 3D model of the patient's bone anatomy made all the difference in planning and carrying out the surgery?
We had a 16-year-old boy who had previous hip surgery for dysplasia. He didn't really have a hip socket, and his femur was twisted and curved. No implant was going to fit in there if we were doing a hip replacement. We did a CT and a 3D reconstruction and found out that we had to rebreak the bone and take a section of it out. We had to cut the greater trochanter off to be able to get the implant in. We made a custom metal implant that would essentially fit into the two pieces to realign it. We had to plan bone cuts very carefully, determining how much to remove because in the operating room, you've got very few landmarks to measure off of. In planning the surgery, we manufactured a couple of models of the anatomy, took them to the lab, and practiced making the cuts and putting the implant in. It really helped us to prepare for the case. It was very stressful because we were trying to get things perfect and make sure it was going to last him for a long period of time. We couldn't have really done it accurately without having the planning tools that we did. The operation turned out very well, and he's doing great. I wouldn't have been able to do it without the 3D models.
How has 3D model making evolved at HSS over the years?
Before our collaboration with Lima, our ability to make 3D models was limited and slower. Our engineers would have to run the printing process over the weekend to make a model that was not even full sized.
How has the technology helped you to plan for other cases?
We're using the technology more and more because it can be very daunting to try to plan a 3D procedure on a 2D screen, especially for people who aren't used to reading blueprints. It's really helpful to have the actual model in your hands and see how the implant may fit or where the femur might impinge against the pelvis if they're taking their hip through a range of motion.
What are some of the more common uses for 3D-printed custom implants?
We see the need for them in a lot of hip replacement revisions and for the sequelae of juvenile inflammatory arthritis in the hip because it affects the bone growth, size, and dimensions. You see the need for it in some knee replacement revisions, but not as much as in the hips. It is also used in failed elbow replacements with bone loss and then in some cases of shoulder dysplasia where the glenoid has not grown properly. I know Lima has done quite a bit of custom implant work in the shoulder in Europe.
Can you describe a case in which 3D printing of a bone implant clearly facilitated the best surgical and functional outcomes for the patient?
There are cases where we're making a 3D representation of the bone and then the implant itself that we're going to be using is 3D printed. We've done some total elbow replacement revisions that are very challenging in which a standard implant is not going to fit, the bone has been worn away, and we've got to figure out how to fit it in. We'll make the 3D plastic model reconstruction, and then Lima will make the 3D-printed implant. Sometimes we'll take the model to the operating room with us to help in judging the anatomical landmarks and matching them to the patient.
We had a patient with juvenile idiopathic arthritis who had a total elbow replacement at a young age, and unfortunately, after 20 years it failed, and she lost some of her distal humerus. We did a CT to see how much bone and cement were left. We got the cement out and then put in a press-fit implant without cement so that the bone would grow into it. Fortunately, that worked out very well. We were able to establish the proper arm length for her, and she ended up recently having a baby. She'll be able to carry her baby around and function. It was a great salvage because in some cases in the past, we would not have been able to put an elbow replacement back in.
What are some of the differences between using 3D-printed implants and models from Lima vs custom implants from other companies?
A lot of the quality of a company's custom implant comes down to design. There's a lot that goes into designing a custom implant as far as how much leg length you can restore, how elastic the soft tissues are, and what the alignment of the legs is going to be at the end. It takes a lot of experience to determine the right questions to ask and come up with the right answers. If you're in the middle of a case and you've got one custom implant and it doesn't fit properly, you're in a tough spot. That's why I really like having the 3D modeling ahead of time so I can essentially do a trial run and see how it's going to fit.
I would say a 3D-printed implant would probably be more accurate than a manufactured one because they can build curves and other features in it as opposed to trying to cut it out of a block of titanium.
How are patients' presurgical experiences changing with the process of getting 3D-printed implants?
The problem with a lot of this is time, expertise, and planning. We'll identify a patient who may need a custom implant or a special implant. We'll do the CT and get the 3D-printed model made. Then we sit down with the engineers and figure out how to reconstruct it, what the implant's going to look like, what the size is, and that takes time. Then we'll model it, see how it fits, and see what the range of motion might be like. We'll make sure that it's not impinging anywhere and see if we can restore the anatomical alignment properly. But before the implant can be manufactured, we must get FDA approval for compassionate consent use of an unapproved device. It's a long process for the patient. I wish we could speed it up somehow because the design, approval, and manufacturing can take months. During that time, the patient could be suffering, or things could be deteriorating to the point where the implant might not fit properly because they've had further bone loss or destruction.
Is that the case for every 3D-printed custom implant?
At this stage, most of the 3D custom implants have to get FDA approval. There are some types — such as what we call a triflange, where they're reconstructing the acetabulum in the socket — where they have blanket approval for a certain number of patient-specific implants a year, so they can maybe manufacture up to 10 a year. That's a more generic type of implant. For most of the other patient-specific implants that we make, you must get compassionate consent approval and getting that through the FDA can be challenging because they've got a lot on their plate.
Another problem is a lot of the companies have gotten rid of their custom implant manufacturing, and expertise in this area has declined as a result. These companies have dropped their custom manufacturing abilities because it's time consuming, expensive, and not fiscally beneficial for the company. We're fortunate to have the Lima manufacturing here, but we still must get things approved through the FDA and that can slow everything down. I understand the need for it. I just wish there was a way to expedite it a little better.
What are some of the other current challenges and limitations of using 3D-printed implants?
Our technology is better, and so we're getting more information and more accurate manufacturing, but it has been challenging to get the implants designed properly, fit properly, and made in a timely manner. Wait times for patient-specific implants have increased in part because the expertise and experience needed to do those things exist only in certain places, and you've only got certain surgeons who have a lot of experience with this. I've got a long history of using patient-specific implants, and I'm at a stage of my career where I'm trying to teach the next generation about the pitfalls, what to avoid, and what works and what doesn't work. We try to avoid using custom implants when we can because we can get the patient to the operating room sooner to avoid further pain and bone loss. However, we don't want to get them there faster and not have the proper fit or the proper implants. It's a real tradeoff to do this because every time we say we need a custom implant, it's going to be time, money, and patient waiting, and I hate to do that. But if that's what they need to get the best fit possible, we'll do it right.
© 2022 WebMD, LLC
Cite this: 3D Printing of Complex Orthopedic Implants Fills Niche Role - Medscape - Feb 10, 2022.