In this episode of PodMD, Orthopaedic Surgeon Dr Jason Hockings will be discussing the topic of kinematic and functional alignment techniques in knee replacement. We discuss when knee replacement surgery becomes necessary, signs and symptoms GPs should look out for, what knee replacement surgery involves today, and more.
- Transcript
Please note this is a machine generated transcription and may contain some errors.
*As always, all in this PodMD podcast is intended for health professionals and the comments are of a general nature. Information given is not intended as specific medical advice pertaining to any given patient. If you have a clinical issue with one of your patients please seek appropriate advice from a colleague with expertise in the area.
Today I’d like to welcome to the PodMD studio Dr Jason Hockings.
Dr Jason Hockings is a Victorian-trained orthopaedic surgeon with subspecialist expertise in hip, knee. Jason completed his orthopaedic training in Victoria in 2021 and has since undertaken post-fellowship training at multiple locations. You can learn more about Jason on his profile page on our PodMD website.
Today, we’ll be discussing the topic of current concepts in best practice for knee replacement surgery, focusing on kinematic and functional alignment techniques.
*Please listen to our disclosure at the end of this podcast
And thank you, Jason, for talking to us once again on PodMD.
Jason: Thank you very much for having me.
All right, well, to start off from your perspective, when does a knee replacement actually become necessary?
Jason: Yeah, that’s a good question. So a knee replacement is a really good, effective operation in terms of relieving pain and restoring function for patients. So it becomes necessary when the symptoms of their knee arthritis have reached a point where it’s limiting their ability to do the daily activities and the things they want to do.
So it’s essentially a pain-relieving procedure, not a life-saving procedure. So once the patient has got to the point where it’s stopping them from playing golf or doing their other social activities, or a lot of the time because it’s keeping them up at night with pain, that’s when they should consider having their knee replaced.
What about some more clinical indications that the surgery is the right option?
Jason: Yeah, absolutely. So most of the time, by the time I’ve seen the patient, they’ve already had a number of consultations with their GP and they’ve had some forms of non-operative treatment. But basically the clinical indications for me for a knee replacement would be radiologically significant arthritis. So we’re talking about grade three or four arthritis on an x-ray, and that the patient has exhausted non-operative treatment and has not achieved a satisfactory outcome with non-operative treatment.
And that really consists of optimizing simple pain relief, which is regular paracetamol and anti-inflammatories, a good physiotherapy program such as the GLAD program, which has really good evidence behind it in terms of reducing symptoms, and any other lifestyle modifications such as weight loss or activity modification. And if the patient has done those things and has not achieved a satisfactory outcome, that’s when they’ve reached the time when they should have a knee replacement.
Are there other signs or symptoms that the GP should look for?
Jason: Yeah, absolutely. I think if they have an increasing analgesic requirement, so if they’re coming back to the GP having already taken simple analgesia, asking for stronger painkillers, that would be a real indication to consider surgery because we know that the stronger painkillers such as opiates have a lot of side effects. That’s been a very widely studied thing over the last few years and you really don’t want to start the patient down that pathway if you can avoid it. So if they’re getting to the point where they need that, that’s when I’d be discussing surgery with them.
The other thing that I would consider a strong indication for surgery is if it’s affecting their mobility to the point where they’re at risk of falls, because we know that if they have a fall, then they could sustain a hip fracture or another fracture, and that’s got really significant morbidity attached to it. And that’s avoidable if we do the surgery early enough.
Can you explain what knee replacement surgery actually involves today compared to say a decade ago?
Jason: Yeah, absolutely. Like a lot of the surgeries we do in orthopaedics, knee replacements have come a long way in the last 10 or 15 years. So the traditional way to do a knee replacement is through what’s called a medial parapatellar approach. So that’s cutting straight down through the front of the knee and attaching part of the vastus muscle from the patella, so the vastus medialis obligus, that comes off. You then evert the patella and the entire knee is on view. Now that’s a fine way to do a knee replacement. That’s how I was first trained.
But the problem with that is you’re cutting through muscle and tendon to do the operation. And that means the patient has more pain postoperatively and a slower recovery. So now a lot of us have switched to what’s called the subvastus approach, which is the same in the inferior part. But at the superior part of the incision, we don’t cut through the muscle or tendon at all. We just go next to it through the joint capsule and then we slide the patella out of the way to do the operation. So it’s technically a bit more demanding, but it means the patient’s pain afterwards is much better.
The other things we’ve changed for the operation are a lot of us have moved away from using a tourniquet. We know that that has issues in terms of quads control after the operation and pain. And so I find that a combination of not using a tourniquet and using a subvascistis approach means that on day zero and day one, postoperatively, the patients are noticeably better. They’re straight leg raising, they’re bending their knee, they’ve got a much lower opiate requirement, and they’re they’re much happier. So that’s been one of the main advances over the last 10 years.
And to put it in perspective for us, between the different surgeries, what are the measures for pain and mobility? How much better is it?
Jason: Yeah, so look, there is mixed data on this. The subvastus approach has been studied for the last 10 or 20 years. Different papers have produced different results, but it’s fairly consistent that in the first few days, the patient reported pain scores, and there’s lots of different ones, there’s visual analog scores, there’s opiate requirements, et cetera, are lower if you’ve done a subvastus approach compared to a medial parapatella approach.
And so, you know, there’s significant evidence now that particularly in those first few days, it does make a difference. Similar to the anterior approach versus posterior approach to the hip, but probably not quite as significant. And it does converge with medial parapatella by about six weeks. But in that initial recovery period, it does make a significant difference to the patient.
And we hear terms like mechanical alignment would be one, kinematic alignment I’ve heard of, and sometimes even functional alignment. Would you break these down and explain these to us in simple terms?
Jason: I’ll do my best. If you go to an arthroplasty society meeting, even senior surgeons in the country have trouble distinguishing between these terms sometimes. So look, the traditional way of doing a knee replacement is what’s called a mechanically aligned knee. So the idea of that is you do a distal femur cut and a proximal tibia cut parallel to the floor and you make the leg straight. So it’s perpendicular to the floor. And that’s how we were all sort of originally taught to do knee replacements. The problem with that is there’s been a number of studies that have come out over the last five and 10 years. that show that people’s legs are not all aligned like that. So people have different shapes and sizes essentially. So some people are a bit more knock-kneed, some people are a bit more bow-legged. So in other words, they have a native varus or valgus alignment to the knee. And that means that if you put it straight, it won’t feel right for them.
So traditionally we found, and then the data supports this, that up to 20% of knee replacements aren’t completely satisfied with their knee replacement. And that’s probably why, because we’re trying to make it a one size fits all approach. So in the last five years or so, we’ve really moved towards tailoring the alignment towards the patient’s native anatomy. And that’s where things like kinematic alignment and functional alignment come in. So kinematic alignment essentially is just, you can think of it almost like a resurfacing procedure for the knee. So you align the prosthesis to the patient’s native anatomy, and it feels like their native knee because it’s in the same position as their native knee was. The prosthesis you use if you’re doing that alignment is often different. It’s often what’s called a medial pivot knee, which mimics the anatomy of the knee and the kinematics of the knee much more closely. Functional alignment is similar but slightly different. It’s in the same vein, but typically they’re not using a medial pivot knee. They’re using a more standard knee. It’s often done with robotics and it’s more about getting the ligament tension on either side of the knee to be balanced. So similar but slightly different.
So what roles do technologies like say robotics, navigation systems or patient specific instrumentation play in achieving these alignment goals?
Jason: Yeah, look, they play a really important role and I think. that the advance in technology has been one of the main driving forces that has allowed us to develop and explore these new alignment techniques that we couldn’t do before. So previously we were just doing it with simple jigs. We had very little technological assistance and it would have been impossible to do a proper kinematic or functional knee with that technology. Australia was a very early adopter and enthusiastic adopter of navigation when that came in, and that was sort of in the 2000s, even a bit earlier. So if you look at our use of navigation, it was even higher than the US for a while. And so Australia has been at the forefront of this sort of movement in technology and orthopaedics for the last two decades.
Robotics has really changed the game again. It’s taken navigation to the next level because in addition to being able to navigate the knee, the robot will allow you to put the knee replacement in very, very accurately. So that’s been the next step. And then we’ve branched off into different areas again. So patient specific cutting guides, patient specific instrumentation, that’s really come into the fore in the last five years or so. And that allows you to do a very precisely aligned knee if you’re doing kinematic alignment because you can match it to exactly where the patient’s knee used to be. So I’ve done both. I used the robot for some knees and functional alignment. I’m starting to use more patient-specific cutting guys and kinematic alignment now with a more modern prosthesis that allows a medial pivot in the knee. And so that’s the direction I’ve been moving in.
But it’s thin technology that’s allowed us to sort of push these alignment techniques. And I think you’ll see a massive difference in terms of patient outcomes. You know, I mentioned earlier that in the older studies, there was up to a 20% dissatisfaction rate with knee replacements. That’s really coming down with this new technology. And there’s a study that’s just been done in the US by a proponent of the kinematic alignment and medial pivot knee. And his forgotten joint scores were the same for his knees done in that technique as for his hips, which is basically unheard of, you know, knee replacements traditionally have not been as good as hip replacements. But with these new alignment techniques and newer prostheses, we’re probably getting close to the point with our approach hip replacements.
And it must be much more satisfying for you as a surgeon to be able to get these results now.
Jason: Absolutely. It’s really satisfying for me as a surgeon, but it’s really, really good in terms of seeing the patient’s response. So when I was training, you’d see the patients at two weeks and they often weren’t particularly happy. And it wasn’t until about six weeks that they were sort of actually thanking us that they had an operation at all. Now I see them at two weeks and they’re bending their knee, they’re happy, they’re walking around, they’re off most of their pain relief, they’re really good. And yeah, that’s great. That’s really satisfying for me as a surgeon.
Are there particular patient groups, say, for example, younger patients or maybe those with complex deformities or it could be even people with higher activity levels who benefit the most from kinematic or functional alignment?
Jason: Oh, that’s a great question. I think the benefits are pretty universal. I mean, I think it’s more about the patient’s anatomy. So there was a, one of the sort of leading studies in this was called the CPAC study, and that was out of Sydney by a big orthopedic group there. And they actually modeled the different alignments that patients have. And they found that sort of about three quarters of patients closely resemble what you’d get with a mechanically aligned knee. So their knee was fairly straight.
But it’s for that 25 or 30% that don’t fit that, where the kinematic alignment or functional alignment makes a huge difference, because they’re the group that were probably going to be dissatisfied afterwards. So I’d say it’s more about the patient’s native anatomy. Having said that, though, obviously the higher demand the patient is, the more active they are, then if you give them a better functioning knee, the happier they’re going to be.
So for our GP listeners here, when should they be thinking about a referral, and in other words, what signs or symptoms would prompt them to send a patient your way or to another specialist?
Jason: Yeah, look, I think early referral is good. You know, even if the patient’s maybe not quite ready for a knee replacement, just going and talking to the surgeon about the natural history of their disease, the management plan, often gives them a bit of reassurance. So I’m always happy for sort of early referrals.
If the patient… presents with knee pain, then I’d always do an x-ray. If they’ve got arthritis in the knee, then I think that’s probably a good time to refer, even if they’re probably not quite ready for a knee replacement. It’s always good to start initiating non-operative treatment, and I’ve discussed that already, just simple things, simple analgesia, physiotherapy, et cetera. But linking them in with the surgeon early is often a really good thing, and it gives the patient that peace of mind, and I often just go through everything with them and say, look, if it gets to the point where you’re not coping with non-operative treatment, that’s the time to come back and see me, and I already know you now.
So sometimes the patients live far away and we can do that over telehealth. It just makes it easier for them. They’ve got that contact point. And then it’s much more sort of easy to link them in and get their surgery done when it comes time later on.
So for today, we want to wrap up and say the three take home messages that you could give to our listeners. What would they be, Jason?
Jason: So my take home messages would be that knee replacement has come a long way in terms of technique and technology over the last 10 years. And that’s meant that patient outcomes are better than they were before. My second take home would be the consideration of different alignment techniques for knee replacements. So a lot of patients really benefit from using these modern alignment techniques, the use of robotics, the use of patient specific instrumentation. And I’d really consider that when you’re making your referrals. And my final take home would be are urging people to refer earlier rather than later for the reasons I mentioned. If we can avoid patients getting on opiates and avoid patients having falls, that saves a lot of morbidity later on.
Thank you so much for your time again. And I’ll encourage our listeners once again to listen to Jason’s podcast on hip replacement surgery too. That’s part of the library. And I’m sure we, well, I hope we can have you on again, Jason. That was a brilliant podcast today.
Jason: I’d love to. Thank you very much for having me.
*We do hope you enjoy this podcast but please remember that the advice here is of a general nature and is not intended as specific advice about a given patient. The views and opinions expressed in this podcast are those of the doctor, not PodMD. If you do have a patient on whom you require specific advice, then please seek advice from a colleague with appropriate expertise in that area.
