#217      27 min 49 sec
Joint resolution: Interrogating muscle and bone for better surgical outcomes

Biomedical engineer Marcus Pandy and orthopaedic surgeon Peter Choong discuss how modern imaging technology is shedding light on human locomotion, particularly in knees and other joints. They also explain how this new found knowledge is used to improve surgical outcomes for patients. With science host Dr Shane Huntington.

"What we know is that obesity leads to biomechanical changes that push or initiate arthritis.  When you replace their joints and bring them back to normal, and patients still are obese, it makes you ask the question does that obesity reproduce the same forces that will now grind the artificial joint in the same way that it had ground the real joint." -- Prof Peter Choong




Prof. Marcus Pandy
Prof. Marcus Pandy

Professor Marcus Pandy is appointed as Chair of Mechanical and Biomedical Engineering in the Department of Mechanical Engineering at the University of Melbourne. He received a PhD in mechanical engineering from Ohio State University, Columbus USA, and then completed a post-doctoral fellowship in mechanical engineering at Stanford University. Prior to joining the University of Melbourne, he held the Joe J. King Professorship in biomedical engineering at the University of Texas at Austin. He is a Fellow of the American Institute of Medical and Biological Engineering, the American Society of Mechanical Engineers and the Institute of Engineers Australia.

Prof Pandy's research is aimed at using computational models of the human musculoskeletal system to describe and explain muscle and joint function during functional activities such as walking. He has published over 100 journal papers on his research related to musculoskeletal biomechanics and currently serves as a principal investigator on a number of grants from the Australian Research Council and the National Health and Medical Research Council.

Publications

Prof. Peter Choong
Prof. Peter Choong

Professor Peter Choong is the Sir Hugh Devine Professor of Surgery and Director of Orthopaedics at St Vincent's Hospital and Chair of the Bone and Soft Tissue Sarcoma Service at Peter MacCallum Cancer Centre. Professor Peter Choong has a major surgical interest in advanced limb reconstruction and his research focuses on arthritis surgery, limb sparing surgery, cancer and tissue engineering. Professor Choong’s leadership roles at St Vincent's Hospital and Peter MacCallum Cancer Centre were instrumental in establishing his groups as a State Centre of Excellence for joint replacement surgery and a National Centre for musculoskeletal oncology care. His clinical and academic leadership in cancer research and advanced limb surgery makes him ideally placed to undertake this important and ground breaking research.

Publications

Credits

Host: Dr Shane Huntington
Producers: Eric van Bemmel, Kelvin Param
Associate Producer: Dr Dyani Lewis
Audio Engineer: Gavin Nebauer
Voiceover: Nerissa Hannink
Series Creators: Kelvin Param & Eric van Bemmel

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VOICEOVER
Welcome to Up Close, the research talk show from the University of Melbourne, Australia.

SHANE HUNTINGTON
I'm Shane Huntington; thanks for joining us.  The muscles, bones and other tissues that make up the musculoskeletal system enable us to walk to and run and also perform spectacular acrobatic feats for sport or dance.  We can think of the musculoskeletal system as a simple frame, the skeleton, which is moved around by muscles attached to it.  But this description belies its complexity, a complexity that has fascinated people since long before da Vinci dissected his first cadaver and continues to fascinate scientists today.  Because it is so central to our bodies, when the musculoskeletal system is damaged by injury or illness, the results can dramatically limit our ability to function.  In these cases we turn to the surgeons, who we hope will have the skills and devices needed to repair or replace our damaged parts.  Today on Up Close we speak to a biomedical engineer and a surgeon who are helping to personalise the approach to orthopaedic surgery, and in doing so are also gaining a greater understanding of the way we move.  In the studio with us are Professor Marcus Pandy, chair of mechanical and biomedical engineering in the Department of Mechanical Engineering at the University of Melbourne, and Professor Peter Choong, chair of surgery and head of the Department of Surgery at the University of Melbourne and director of orthopaedics at St Vincent's Hospital.  Welcome to Up Close, Marcus and Peter.

PETER CHOONG
Thank you, Shane.

MARCUS PANDY
Thanks, Shane.

SHANE HUNTINGTON
Peter, I'd like to start with you.  What are the typical conditions that you would see in your practice as an orthopaedic surgeon?

PETER CHOONG
So Shane, as an orthopaedic surgeon I deal with conditions that affect the joints and bones.  So for example patients who have arthritis - and what arthritis is, is the degeneration of joints over time that may also occur when people injure their joints.  I also deal with broken bones, frequently from car accidents, sometimes from sports injuries.  In any case, what we try to do is return patients and their limbs back to their normal positions to allow them to function normally.

SHANE HUNTINGTON
In your surgical suite, when you open a patient up in these circumstances, can you describe the scene?  What sort of things are you seeing around the bones and the entire system that are abnormal?

PETER CHOONG
With patients with arthritis, and commonly it's arthritis of the hip and knee - in a country like Australia we have about 80,000 replacements of hips and knees each year.  In a country such as the United States there may be 600,000 joint replacements a year.  When we get in there, what we see is a joint that is diseased by a loss of smoothness, extra bits of bone, a cragginess to what should really be a very smooth surface.  So for example if you look at the knee joint, it would be like looking at a billiard ball, white and shiny, that's what a normal joint surface would look like.  In an arthritic joint we would see it as discoloured, potholes, crevices and clearly a surface that's not smooth, and that is the nature of arthritis or degeneration of a joint where it loses its smoothness.

SHANE HUNTINGTON
That lack of smoothness, that change in texture, that's what's causing the severe inflammation and pain that the patients feel?

PETER CHOONG
Sure, and what happens is the rough surfaces rub against each other, causes debris to collect, the debris causes inflammation, which is a swelling and pain of the joint and patients feel it as a loss of movement, a loss of function.  They aren't able to take their weight; they aren't able to do things with that limb and a swelling that is visible to them and a swelling that they can feel.  So altogether arthritis, which affects about 50 per cent of the population over the age of 65, is something that really reduces people's ability to function normally and to contribute; in fact, in a country like Australia, it is the third highest cause of disability caused by a chronic condition.

SHANE HUNTINGTON
How has the approach in the surgical suite changed over recent decades, for something like arthritis but also for more severe conditions like cancer and the like?

PETER CHOONG
Sure.  What we're trying to do now is return patients' limbs to as close as normal as is possible.  So what we do is we use devices that we call prostheses and these mimic the function of joints; they are made out of metals and plastics and sometimes ceramics.  We shape them in a way that simulates a joint and we put them in positions that are calculated by our bioengineering colleagues to give the patient the best function.  Over the years our research into different metals, different plastics and different ceramics has allowed us to produce durable prostheses that we hope would last the test of time.  So in general, for each patient who has new joint replacement in, we expect that 95 per cent of them would have the same joint still in place in 15 years following the surgery. 
SHANE HUNTINGTON
Is there a trade off between the functionality of these replacement joints and their longevity?

PETER CHOONG
There is that trade off, and the way it works is this.  When you give someone a joint that functions very well, they start to use it normally, and these are not normal joints, they're new joints.  A normal joint is able to tolerate the impact of life and the twists and turns but when you have a prosthetic or an artificial joint in position, it cannot tolerate the same level of daily use and that is why surfaces wear away, much like the tyres on a car will wear away.  The more carefully you use it, just like tyres the more carefully you drive, the longer they will last.

SHANE HUNTINGTON
With regards to these replacement joints and how they fit in with the existing muscles, tendons, ligaments, does that work as well as the original joints or are there still significant problems there with integration?

PETER CHOONG
There are problems with integration that the scientists and the clinicians, the surgeons, are trying to work through.  The areas of particular concern is where the prosthesis joins with the bone, how does it integrate, how does it stick itself on?  There are two ways of doing this; we can glue it on using special cement or we can use what's called biologic interlocking where the bone grows into the prosthesis and holds on to it.  Now, we reserve that type of prosthesis for the younger patients, that is those perhaps younger than the age of 65, and those older than the age of 65, they do better with the ones that are cemented in.

SHANE HUNTINGTON
Marcus, the musculoskeletal system seems like quite a simple structure from a basic physics point of view and a mechanics point of view of having hinges, pulleys, levers and so forth.  Is that actually the case, though?

MARCUS PANDY
No, obviously it's a very complicated system to analyse and to pick up on the theme that Peter was describing in osteoarthritis, we know that mechanical forces at the joints exacerbate the initiation and progression of the disease, and unfortunately the loads that are placed on the joint are largely unknown.  The reason for that is we can't directly measure the forces that are developed by the muscles and therefore the forces that are transmitted by the bones through the joints.  And if we don't know the loading then we don't really understand what's happening to the joints when people, say, walk.  So we're forced to use another method to try and interrogate the system.  We can do experiments, and experiments are routinely done in facilities called gait laboratories where you have patients walk through the laboratory and you can measure the way they move very accurately.  You can even measure the external forces, say, from the ground that are applied to the body, but those measurements don't tell you the internal forces in the body which is really what we need to know to understand function at a fairly deep level.  So the approach that we and others use is we develop computational models, computer models of the body, of the musculoskeletal system, models of muscle function, models of joints and then we integrate the experiments that we can do on people, or the data we can get from these experiments with these models to try and infer the forces that are present internally.  With that information we can really understand things such as what are the stressors, which is really what breaks down cartilage tissue, what are the stresses that occur across say, joints such as the knee.  We can understand where the stresses are highest and we know that, for example, osteoarthritis always occurs on the inside of people's knees, on the medial side of the knee.  So we can use models to verify that that's so, and also if we can understand how the muscles, say, around the knee function, then that knowledge will inform treatments that we can use such as say, physiotherapy, of how to change the function of the muscles and therefore change the loading across the joint.

SHANE HUNTINGTON
I'm Shane Huntington and you're listening to Up Close.  In this episode we're talking about examining and treating the musculoskeletal system with biomedical engineer Professor Marcus Pandy and surgeon Professor Peter Choong.
Marcus, when we talk about one of these gait laboratories where you monitor the way someone walks, what sort of physical parameters are you actually able to measure in such a laboratory?

MARCUS PANDY
People have been doing gait experiments for more than a century now and routinely the variables that are measured are the major movements of the body segments.  So for example, as we walk we flex and extend our knees, hips and ankles, and we can put markers on the surface of the skin and from the measurements of the way those markers move we can calculate, in some software, how the joints flex and extend.  However, when we walk our knees don't just flex and extend, they actually slip over each other; they translate, the bones translate relative to each other.  For example, the thigh and the shank translates relative to each other and these conventional motion capture systems cannot elucidate those movements accurately.  You can't measure the very small translations of the bones at the knee - say they move by about five millimetres - by putting markers on the skin you won't be able to accurately measure the very small translations of a joint.  And that's unfortunate because it's those translations that are really going to tell us how the cartilage tissue is rubbing on each other for people, say, with osteoarthritis where the cartilage may be thinner in some regions of the joint than in others.

SHANE HUNTINGTON
Now, many of our listeners would be aware of course of the extensive use of medical x-rays.  How do you go about going that step further with your work, from the gait laboratory where everything's external, to utilising x-rays as a mechanism for getting the sort of information you've been discussing?

MARCUS PANDY
Right, so I've just alluded to, conventional systems don't allow us to measure accurately the movements of the bones at joints such as the knee.  So what we and others are doing now is trying to use dynamic x-ray imaging - and this is low doses of ionising radiation, so it's completely safe - and you aim an x-ray unit at someone's joint such as the knee, and as they walk through past the unit, the unit takes x-ray images at some frame rate.  Typically the systems that you can buy off the shelf are about 30 frames a second, so you can capture 30 x-rays per second as the subject walks.  Unfortunately that doesn't allow you to capture movements such as walking because the frame rates aren't high enough and also these systems are stationary; you can only use them, say, in conjunction with a treadmill if you want to capture motion for multiple strides of gait.  What we've been doing in my laboratory is we've developed a dual plane x-ray system that can move with the subject, so it translates alongside the subject and as it tracks the subject it images the joint as the subject walks along.  So we can capture x-rays for multiple strides of walking and also at very high frame rates.  The conventional systems operate at 30 frame rates a second; we have a system that we can go up to 1000 frames a second, so at high speeds and a mobile system, and bi-plane we can capture accurately three dimensional information about how the joint moves.  Now, these systems, by the way, work really well when you have a patient with a replacement joint, an implant, because the implants are metal and the metal shows up beautifully on x-ray.  But for a natural joint, the images are around the edges a little frayed.  So we have software where we look at the image and the software detects the outline of the image as best as it can, and we take those images and triangulate the information from the two x-rays and then reconstruct a solid model of the joint from the x-ray images.

SHANE HUNTINGTON
Now, we often hear how genetically alike we all are, but when you do these sorts of studies of various patients, how similar are we in the way we walk?  Do we all walk in the same way?

MARCUS PANDY
To a first approximation, yes, walking is very stereotypic, and what I mean by to a first approximation is that if you look at, say, the flexion extension angles of the major joints, the ankle, knee and hip, for healthy individuals, adults, then the standard deviations are fairly small and walking is really quite stereotypic.  Even the forces that you produce on the ground when you walk really fit within a very tight band.  However, the finer movements of, say, the knee joint and the way it translates, that is not so stereotypic; that's going to be different from individual to individual.  In fact, I would say that those sorts of details are still awaiting quantification because the tools that we need in order to make those measurements are just really now emerging.

SHANE HUNTINGTON
Peter, do you find the similar thing in the surgical suite?  When you open up a knee joint are they all very similar in the first all-up view, but when you drill down, you get down to the detail, they're all quite different and require different approaches?

PETER CHOONG
Yes, they are very similar; the anatomy of the bone, both at the end of the thigh bone or the top of the shin bone, look the same in many respects.  What differs perhaps is the deformity or the destruction and that is what adds the complexity.  Really stiff knees will behave at the time of surgery or look at the time of surgery very different from knees that move, because you can move knees into better positions, as it were.  So as a surgeon the degree of degeneration, destruction or a deformity of a joint adds that level of complexity that differentiates, that makes one person different from another.

SHANE HUNTINGTON
Peter, in the brain when there is an injury there's a degree of plasticity that allows the brain to recover to some degree in many patients.  Is there an equivalent in things like walking?  Are we able to relearn to walk in different ways very effectively or are there limits there?

PETER CHOONG
That's an interesting question, because we are learning more and more about those parts of the brain that we don't traditionally link in with movement, for example.  What we're finding is that people are able to learn or retrain certain parts of their brain to assist them; for example, those people who have had strokes, those people who have had significant injuries or surgeries.  In terms of those who have joint replacements they are trying their best to kick the habit; they've been walking a certain way because of their deformity for so many years that sometimes even after the best surgery they adopt the same posture and the same gait pattern because that's what they're used to, and there comes the role of the physiotherapist to help them regain what we call a normal gait.

MARCUS PANDY
Could I just add something there?  The problem of osteoarthritis, it's been shown that you can actually teach people how to walk differently in order to change the loading that is present across their knees.  For example, someone who has osteoarthritis, as I indicated previously, it usually occurs most often on the inside of your knee, and so there have been studies that have shown that if you teach people to lean to the other side, lean their torso to the other side, then you can change the loading and you can alleviate pain.  People actually end up using that; that turns out to be their regular gait pattern because it's less painful.

SHANE HUNTINGTON
I'm Shane Huntington and my guests today are biomedical engineer Professor Marcus Pandy and surgeon Professor Peter Choong.  We're talking about the musculoskeletal system, how to examine its motion and how to repair it when damaged here on Up Close.  Peter, is all this additional information that you wouldn't have had just ten years ago transforming the way in which you approach surgery innovations?

PETER CHOONG
Absolutely.  What this technology and the work that Marcus has done is that it allows us now to understand how a normal joint should work, and if you know how a normal joint should work from a bioengineering perspective, that helps you design prostheses or joints that would suit people.  It also helps us understand, if you use what we might call computer-guided surgery, what measures you aim for in having the computer guide you in the cuts that you make in the bone or the placement of the prostheses.  So at the end of the day you have what we would call a biomechanically ideal position, and that ideal position then allows the limb to work to its best advantage, and if a limb works to its best advantage you presumably would get longevity, the ability for the prostheses to survive its longest.

SHANE HUNTINGTON
Are you able to give patients a better idea of what the potential outcomes of their surgery will be as a result of this additional information?

PETER CHOONG
Yes, we can do that and particularly using IT sources now we can show avatars of patients' limbs and how they might work.  We use the internet, for example, to take people through the surgery and show how changes in biomechanics lead to the development of their disease and how we as surgeons aim to alter that and bring them back to normality.

SHANE HUNTINGTON
Marcus, when you look at some of the patients who have had their joints replaced, how does their gait and their movement differ in your studies from what it would have been prior to that replacement?

MARCUS PANDY
Well, let me give you an example.  We did a study recently on patients who have had a total knee replacement and we compared the mechanics of walking in these patients with healthy individuals, and we found that remarkably the mechanics look fairly similar with some exceptions, and the main exception that we found is that people who have a total knee replacement walk with a stiffer knee, they have less knee flexion, they bend their knees less when they walk and the reason for that is that they use their quadriceps muscle, which is the main muscle of the thigh, they use that less.  So if they don't bend their knees as much and their gait pattern, all of the dynamics, look the same then they must be doing something else to compensate, and it turns out that what they do is they tilt their pelvis as well forward a little bit and they use their back muscles.  So they use their quadriceps less and they use their back muscles more and they provide exactly the same amount of support to the body by doing that.  Why do they use their quadriceps less?  We don't really know yet.

PETER CHOONG
There's an interesting addition to that is how understanding a patient's gait can help us predict how a prosthesis might last into the future.  So, for example, obesity is currently a major problem in our communities; it is three times more common in patients who present with arthritis for surgery.  So in a country like Australia the community rate of obesity might be 20, 22 per cent; for those presenting for joint replacement they are over-represented, they may be 65, 70 per cent of these people.  What we know is that obesity leads to biomechanical changes that push or initiate arthritis.  When you replace their joints and bring them back to normal, and patients still are obese, it makes you ask the question does that obesity reproduce the same forces that will now grind the artificial joint in the same way that it had ground the real joint.  And that's where the work of Marcus and his team would be valuable for the research that we're doing, so this year, 2012, we're looking at a study of how patients who are obese who have had joint replacement, how their gait pattern would either be better or worse or how it may deteriorate over time by these gait studies.  If we know that pattern it may be that we can assist them with physiotherapy, shoeware, braces, or even look at ways of designing prostheses to tolerate the added stresses that such patients might impose on their joints.

SHANE HUNTINGTON
Would you go back and look at a patient that's had one of these replacements and potentially, after measuring these additional stresses, you're seeing in some parts of the body where they may not have been there before, or even were there before but you don't want them in the same location, and perhaps go through a surgery procedure again to moderate what's there to compensate for these problems?

PETER CHOONG
We tend not to go back and compensate once the surgery has been done, because what we don't want to do is create a problem if none exists at that moment in time.  But what we can learn from this is that over a period of time if we show deterioration and then we can link it up with the sorts of information that Marcus's work produces, then in the future we can design our surgery, our prostheses as well as our rehabilitation programs in a way that allows patients to maximise the new prostheses or the new joint that we implant in them.

SHANE HUNTINGTON
Marcus, we've talked a lot about responses to problems in the body.  What about health predictors?  Are we able to do these sorts of measurements on a person and make reasonable predictions as to whether or not they will end up with some of these conditions like arthritis?

MARCUS PANDY
That's the Holy Grail, obviously, in the work in that I do in computational modelling, to have a predictive model that you can use before you make any change is the ultimate.  We're not at that point yet, and the reason for that is that when we started this broadcast we said that the musculoskeletal system is very complex and what I mean by that there are many, many variables that you have to model and the dimension of the system is very high, which means that the computer model is very complicated and it takes a long time in order to make the calculations because the model is so complicated.  And if you have to predict how something is going to occur at a time in the future, you have to make a whole other set of calculations which take an extraordinary amount of time.  For example, about ten years ago we used a model to predict how humans walk, and the model just knew what the structure of the body is, and then we actually predicted with that model, given the physiological parameters of that model, could that model walk and if it did walk, did it walk anything like we know humans to walk?  It took us 15 months to solve that problem on a computer; we solved the problem on a parallel computer with 24 processors and it took three months of dedicated computer time to actually make the model walk.  So we can't really repeat studies like that; every time you make a change you'd have to solve this problem again.  So our group and others in the field are looking into faster, more computationally efficient ways of using these models to make these predictions, but we're not there yet.

SHANE HUNTINGTON
Professor Marcus Pandy, Chair of mechanical and biomedical engineering in the Department of Mechanical Engineering at the University of Melbourne, and Professor Peter Choong, Chair of surgery and head of the Department of Surgery at the University of Melbourne and director of orthopaedics at St Vincent's Hospital.  Thank you for being our guest today on Up Close and talking about personalising treatment for the musculoskeletal system.

PETER CHOONG
Thanks very much, Shane.

MARCUS PANDY
Thank you, Shane.

SHANE HUNTINGTON
Relevant links, a full transcript and more info on this episode can be found at our website at upclose.unimelb.edu.au.  Up Close is a production of the University of Melbourne, Australia.  This episode was recorded on 26 September 2012.  Our producers for this episode were Kelvin Param and Eric van Bemmel. Associate Producer Dyani Lewis, audio engineer Gavin Nebauer. Up Close is created by Eric van Bemmel and Kelvin Param. I am Shane Huntington; until next time, goodbye.

VOICEOVER You've been listening to Up Close.  We're also on Twitter and Facebook.  For more info, visit www.Up Close.unimelb.edu.au.  Copyright 2012, the University of Melbourne. 


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