Patient Specific Technology uses pre-operative 3D imaging to create custom cutting instruments tailored to each individual patient's hip and knee anatomy - allowing surgeons to plan surgery before the operation even begins. Dr Liew is an Adelaide orthopaedic surgeon who exclusively performs hip and knee replacements and has been using this technology for over 10 years.
Dr Chien-Wen Liew and Dr Luke Mooney discuss 3D planning, femoral stem options and leg-length checks in hip replacement, filmed at a Sydney hip conference.
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0:00 · Introduction
Hi, it's Luke from Orthopaedics 360 here with Chien-Wen and we're just visiting a hip and knee symposium here in Sydney. It's been fantastic to be able to see new technology and our colleagues picking up on this technology and driving things forward. I'm excited to show you some of the technology we use for our hip replacements. Not only can we 3D plan our surgery and use cutting guys to execute that surgery, but we can use further technology like imaging in inside our theaters to demonstrate our execution of that plan.
You can see the hip replacement here with the femoral stem, the acetabular component. we can take very accurate measurements in theater in real time to see that reproduction of our plan. I think it's been quite important to have the X-ray during surgery. It's not something that we used to be able to do with posterior approach and that's something we can do quite easily because we have the carbon fibre tables and things for the anterior approach.
So that's certainly something that we've enjoyed and having the intraoperative imaging allows us to test and adjust before we implant the final prosthesis. just to verify that plan has been executed just as we set up. Just adds, I think, a lot to the accuracy. we judge how well we've placed the prosthesis by X-rays. So, it only makes sense that we X-ray during surgery. We spend all that time planning our surgery.
We've really got to make sure that we're executing on the day. And that's the exciting thing about this technology. And this new system that's sort of evolving on what we've used for years just gives us even more data, which is pretty amazing. Yeah, so, we'll show you that. What it involves is really just a three-dimensional preop scan that we already do. and then we get a huge amount of data.
2:10 · Hips
We are at the hip area now. We've getting some talks on hips and we're hearing about things from the joint registry. we're also just hearing about people's choice of implants which you know there are a vast number of implants cemented, cementless, fully coated. you know we use a few different stems just based on geometry. What about bearing choices? So the bearing is basically where you use or where the where the joint moves.
And so what you can see here that's ceramic on ceramic bearing. That's what I use. you're using something different. What do you use for most of your hips? Most of my hips would have a polyethylene liner with a ceramic head. these are these function well. They demonstrate to perform well from a registry point of view with a very low revision rate. and it's it's very tolerant of forces of daily activities and functional use of the hip which is why I really like it.
And probably I mean the thing that I get often asked is people know one person who's had a ceramic on ceramic which is what I use that has had a squeak or something like that. Yeah, you know I think we haven't noticed that as much and I think these third generation ceramics are probably a lot better than they were 20 years ago. Yeah, the rates of problems with C on C or ceramic on ceramic are very low.
What do you think about the idea of a ceramic breaking with force with the new ceramics? I think the rates of that is just so exceedingly low. that it's not really a concern. Ceramic fracture is now very rare. And I remember getting one of the ceramic heads and just throwing it at the floor and it didn't break. Yeah, it's actually I don't know how you could break one, but I know that there are cases out there of people breaking them.
I think that if you looked at those cases, it'd be the old style of ceramic or I think probably inaccurate implantation. So, putting an abnormal force on it. Yeah, I mean we know that actually in the registry the ceramic on poly does amazingly well. Yeah, but that's for a revision standpoint only and probably dates back I mean the data is 20 plus years old now. Yeah, so I wonder whether what we see coming up now is that ceramic on ceramic is just as good if we separate that data for the last 10 years.
Yeah, which is interesting. But it's just interesting. Both using different options. Yeah, great outcomes for both. Same results. Yeah, I don't think a patient could feel it. No. Yeah, that's excellent. Philosophically, I think if we look at wear rates and we look at in the lab, not in real life, ceramic on ceramic probably wins. and that's, you know, certainly not real world example, but that's why I choose to use it.
I think when we're talking in a lab where you are cycling billions of times, a million times, then you start to see a difference. I think you're probably not going to notice it unless you're a professional cyclist and you still want to be after you've had your hip replacement.
5:06 · Stem Options
Okay, chen, when we're just looking at the stem options that we've got available to us, how does a patient end up going from your clinic and booking for surgery to then their operation in theater? What are the steps before we get there and how do we end up? So actually a little bit of ground work and I think that's the biggest difference with you know hip replacements now compared to hip replacements 10 15 years ago where we just had the two-dimensional X-ray.
so once a patient organises with surgery they get their three-dimensional scan. The three-dimensional scan is key. It allows me to basically perform the surgery on the computer before we enter in the operating theater. So there's no surprises. we know, you know, what prosthesis, what position, what sizes, everything before we start. and then that combined with our intraoperative imaging to match that allows it to be extremely planned surgery.
But you know that's stem geometry and you know we're very lucky actually I think in this day and age to if you heard some of those talks before where we saw the stem geometries of the past you know there was one size in everyone stuff it in make it work you know what are you using we've got all the stems here what do you use I will make to match your geometry yeah I'll make a decision based on what we see in that planning so with the 3D segment of a of a femur we can best fit any of these stems and I can take my primary stem which might be an Amos stem which has a really sensitive geometry for bone for loading bone in a in a way that preserves bone.
if this stem does not make good cortical contact within the internal part of the femur then we can start to move into different stem types such as the mast lot. the on some occasions the bone just isn't up to it and we can see that on our planning where the stress of the implant on bone isn't going to be satisfactory and then we can move into a cemented stem.
The nice thing about the range that we take to theater is that any of these options are going to be ex executed on the day with a high level of accuracy. That helps us choose the implant that best fits each patient's anatomy. Well, I think that's the key here for me is that when we go into the operating theater, I don't need like in the past, if you remember when we used to do hip replacements, you know, 10 plus years ago, we would go in with plan A, but we would have plan B, plan C available at the same time, not knowing which one's going to be perfect.
And then you'd prepare everything for this stem and realise, oh, that wasn't very good. And then you would take everything out, get another kit in, and then prepare everything for this stem. And you know that when you prepare something twice, it's never perfect, nothing. So I think the big key to the 3D planning because we can see how the stem fits in. We can see the morphology, the shape, the distance, everything before we start.
We're just going in one time getting the right choice from the start. Yeah, it's predictable. Very predictable. And I think that's where that's where the STEM choices come in. You need a few. You definitely need a few. and you know, I think we heard first talk, don't be a one-trick pony, right? Yeah, it's great.
8:14 · Leg Length
So, I think, you know, some of the talks today, they go over, you know, some of the key elements of where original hip replacements had some problems. you know, leg length and position have always been something that's discussed. Leg length in particular. And you know, I think when we look at what we do, we do so many things now to ensure leg length that it's kind of not really a problem as much anymore.
you know, maybe from what we heard in the talks, maybe what's your take on that? Like what do you think is the best way because our patients often ask us what the best way, but there's so many things. Well, there's not I think for me there's not one way. There's not one technique that ensures that accuracy and reproduction of leg length. It's really having multiple tools and techniques to work through in the in the surgery process.
So, it's having that excellent plan and then working through that plan to make sure that the neck cut was correct, checking it, verifying it that the acetabular component put in as we had planned so that we know that the hip centre hasn't changed within the pelvis. it's then having the ability to put the implants in, reduce the hip, and then test it in theater and compare that to our planned leg length and offset correction.
and we know that imaging in theater is really important or at least having some sort of technology to verify and check and cross check with the technology like the it's amazing how much or how many hips we did back, you know, 10 plus years ago where we actually had no technology to help us get leg length right and it was all down to the feel of a hip.
Now with X-rays and with the 3D planning and modeling, you know, it's so easy to check and verify where we are. So, you know, you mentioned tension on the soft tissue, but that is variable amongst many people. It's a good secondary check for sure. but I find personally the 3D models really beneficial. So, we get those 3D models from our patient specific system. and I love getting the X-rays.
it's interesting to hear about what other people are using. you know, some people are using almost like a navigation system. Now, it is you know, it's a it's a good thing. It adds probably a little bit for, you know, people who are maybe just starting out and just starting their hip replacements to see some data up on the screen, but probably you know, I can't see that something as necessary in my workflow particularly.
Yeah, but the X-rays are great. Yeah, what about you? I mean I also do robotic assisted surgery and having that technology in the room is another way to verify. So it's like a super X-ray. It's it's an excellent X-ray and it's a good execution tool. It means I'm not wearing lead in a in a in a in a robotic case. I don't sweat as much. But the technology means that we can have really high level confidence that plan has been executed.
And all of those things soft tissue pre-planning models in theater. It's about putting all of these things together and I think if you rely on one tech technology or technique or verification that you're more likely to have a trouble whereas if you're using five or six things every time then it's reproducible. you're checking the check, you know, like the carpenters say you measure twice, cut once, or is it measure three times?
I can't remember. But we do So, I think what's so obvious now is that surgeons, especially surgeons that do a lot of hip replacements, do so much more work before the surgery now than we ever have, right? I remember when we were learning hip replacements, you didn't really plan them that well. you kind of put an X-ray up a few minutes before you're about to do the hip replacement and you put some templates up which didn't account for things like magnification and things like that and you know that was the best we had at the time and I remember so many different tools especially when we were doing hip replacements posteriorly back in the day where we used to drill little pins in and have little rulers that came off the side and measuring tapes and it was amazing yesterday to hear about how they used to work out what straight up and down was by hanging a rope from the ceiling with a weight at the bottom.
I just, you know, just the how far things have come, you know, just the inserter handle to the corner of the room. I mean, just it's crazy talk now. You can't you can't do that. It has to be has to be three-dimensional and it has to be perfectly planned. So, you know, we're I think at a really good period now, right? It's exciting to see what comes and I think it'll be it'll be amazing when this meeting in like 5 years time what we're going to see there.
Yeah, whether or not that translates to different patient outcomes, but I think it'll at least give people the ability to have a really quantifiable way of knowing that they did the surgery correctly. Yeah, which is what we're getting now, right? Yeah, amazing. before.
Transcript edited lightly for readability.
Why Better Technology Matters
Technological advances are striving to improve upon current results. In the past, the focus has been more on establishing materials to avoid wear characteristics of implants, and in ensuring that the implants can be adequately secured to the bone for both hip and knee replacements. This has since become much less of a problem, with the advent of advanced coatings, where bone can grow into the implant, as well as the latest generation cementing techniques.
In general, Dr Liew will perform a total hip replacement without cement, to avoid the risks associated with fat embolisms during cementation. For total knee replacements, the tibia is cemented while the femur is usually uncemented.
The Three Methods of Hip and Knee Replacement
There are three main ways to plan a total hip and knee replacement:
- Conventional: Using alignment guides and rods during surgery to judge the alignment of cuts. These have been shown to be adequate in establishing the centre canal of bones, and providing a good guide for where the implants should sit. They have been around since the start of hip and knee replacements, and various tools have come in to help increase the accuracy of this technique over time.
- Navigation: Using a computer to judge where cuts are being made prior to insertion of the prosthesis. 5mm pins are drilled into the bone on both sides of the joint - on the pelvis and femur for a hip replacement, and in the femur and tibia for a knee replacement. This enables a navigational sensor, or robot, to know where the joint is. A sensor is then placed on various parts of the joint before starting in order to accurately map the joint before the operation begins.
- Patient Specific Instrumentation: Using a pre-operative scan to create specific custom moulds used as cutting guides during surgery. This enables pre-operative planning that allows identification of abnormal anatomy, variants, or any anatomical issues that need thought and planning before execution. It is Dr Liew’s technique for both hip and knee replacements.
Various methods aim to improve alignment and push outcomes. Original 3D jigs many years ago were not accurate enough - the scanning and production technology were not adequate to ensure 100% accuracy to a patient’s anatomy, and were often abandoned. Over the last 10 years, accuracy of 3D jigs has been 100% with no failures of the jig position to the bone in Dr Liew’s own experience.
How Patient Specific Instrumentation Works
Patient Specific Instrumentation requires a pre-operative investigation - typically a 3D CT scan - to recreate the exact anatomy of the hip or knee in a 3D environment. The 3D image is used to create specialised cutting blocks which are then used to make accurate bone cuts during surgery. This scan takes only a minute to perform.
The side benefit is that it does not require damage to surrounding structures: no pins are inserted into the bone as in navigation and robotics, and no rods are inserted into the medullary shaft as in conventional techniques.
Pre-Navigation - Planning Before the Operating Theatre
Dr Liew performs all of his total hip and knee replacements using patient specific technology. He believes this technique allows an element of “Pre-Navigation” - the bone cuts can be assessed, changed, and planned prior to surgery rather than making those decisions during the procedure.
With the approach to the hip and knee, combined with pre-operative planning, and the fact that each hip and knee prosthesis is placed to match the pre-arthritic state, planning is essential to ensuring the best possible outcome.
This requires a 3D environment to visualise what the new replacement will look like in the patient’s bone before any incision is made. This can reduce operative time, which in turn reduces the time the wound is open and potentially reduces infection risk.
Who is Suitable?
Not all patients are suitable for patient specific instrumentation, but it can actually be easier to use patient specific instruments in some complex cases - for example, when there are existing implants in the femur or tibia, or when someone has had pelvic realignment surgery. If a patient has significant metalwork, the scanning can be difficult if the edges of the bone cannot be adequately scanned. This can occur when patients have plates and screws from previous fractures. Patients with uni-compartmental knee replacements can still have a scan when a revision to a total knee replacement is planned.
Many surgeons use differing methods, and most will be enthusiastic about their own method. Dr Liew has performed all of his total hip replacements with the direct anterior approach and patient specific technology, and all of his knee replacements with kinematic alignment and patient specific technology for many years. He continues to refine the technique as improvements become available. As a member of the hip and knee Medacta international advisory boards, he is often the first to see the outcome of international research where tried and tested improvements can be used.
To discuss whether you are suitable for patient specific technology, speak with your GP for a referral to see Dr Liew.
The Pre-Operative Templating Advantage
Templating is the step where the operation is planned, in full, before entering the theatre. From the pre-operative 3D CT scan, a model of the patient's own bone is reconstructed, and the entire reconstruction is designed within it: the implant type and exact size, the position and orientation of each component, and how the joint is restored to its pre-arthritic state.
For a total hip replacement, this means planning the position of the socket and stem, and reconstructing leg length and offset to match the other side — two of the measurements patients notice most after surgery. For a total knee replacement, it means planning the depth and angle of each bone cut so the implant restores the natural joint line, in keeping with the kinematic alignment philosophy.
The advantage is that these decisions are made — and checked — in advance, against a model of the individual patient rather than an average. The operation then becomes the execution of a verified plan, rather than a series of judgements made in the moment. Because the difficult decisions are resolved beforehand, operative time can be reduced, which in turn reduces the time the wound is open.
Measuring Every Cut and Component During Surgery
A plan is only as good as the ability to deliver it. This is where patient-specific technology and intra-operative measurement work together. The custom cutting guides are manufactured to seat on each patient's unique bone surface in only one position, so each bone resection is made exactly where it was planned — not estimated from generic alignment rods.
During hip replacement, Dr Liew operates on a specialised traction table with a radiolucent carbon-fibre extension. This allows real-time X-ray imaging to be taken during the procedure, so component position, leg length and offset can be measured against the pre-operative plan and adjusted before the wound is closed — rather than discovered afterwards on the recovery-room X-ray. The detail of how this imaging works is covered in enhanced accuracy during hip replacement surgery, and the equipment itself in the technology I use now.
For knee replacement, each bone cut and the resulting soft-tissue balance through the full range of motion is checked against the kinematic plan, so the knee is balanced as it moves rather than only in a single position. Throughout, single-use instrumentation is opened fresh for each patient, so every instrument performs to the same specification each time. The result is that component position is confirmed by measurement during the operation, not left to be assessed only once surgery is complete.
"Planning the operation in three dimensions is only half of it. The advantage comes from measuring every cut and every implant position against that plan during the surgery — and adjusting before the wound is closed."
Dr Chien-Wen Liew — Orthopaedic Surgeon, Adelaide
Orthopaedic Surgeon, Adelaide
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