A step forward for hip replacements
One of the most successful surgeries ever invented is the total hip replacement; this replaces the ball and socket joint at the top of the leg with an artificial implant. It’s performed in people with severe and debilitating hip arthritis. The downside is that these devices only have a limited lifespan before they wear out and need replacing themselves; and as people live longer and remain active for longer, more patients are needing replacement hip replacements, which tend to be more complicated than performing the surgery the first time around. So is there a better approach? Chris Smith spoke to medical engineer Sophie Williams from the University of Leeds, asking firstly how many people have total hip replacements...
Sophie - If we look at England and Wales, about 90,000 are having hip replacements every year, but if we look at the people who have hip osteoarthritis and may need one of these hip replacements we’re talking about 11% of over 45 year olds.
Chris - So very common; very, very frequently performed surgery which, as people live longer, is going to become even more common?
Sophie - Absolutely, yes. One of the drivers for my research is actually about hip replacements, seeing what we can do to make those better so only one is needed. But, also, if we can go into these patients earlier on and we can make it so that they’re less likely to need a hip replacement.
Chris - But if someone’s hip has worn out and they have arthritis, how can you avoid that happening?
Sophie - We’re starting to see increasing amounts of evidence that some people have hips that aren’t quite as round, aren’t quite as spherical as they should be, and they seem to be more likely of developing osteoarthritis. This is a condition called femoroacetabular impingement. Already now, surgeons are going in earlier when patients present with some early onset of pain and they will start looking at how they can make that hip more round again so the progression to osteoarthritis won’t be as rapid.
Chris - Right, so if you could intervene in these people and not do a complete hip replacement, but you do some kind of resurfacing or refashioning to the hip you could, potentially, prevent the need for a hip replacement and you could do it in people earlier so that they wouldn’t progress to full blown arthritis?
Sophie - Yeah, that’s exactly the case. The thing is, at the moment, whilst surgeons are very good at doing this surgery they don’t really have the scientific evidence to tell them which bits of the bone they should be removing. The problem with these hips when they’re a funny shape is that they impinge. If you imagine going into some sort of extreme of motion - and I’m not talking gymnastics here - I’m just talking maybe leaning down to tie your shoelace, that will cause an impingement between the outer round bit of your head and then the rim of the cup and that outer round will start to cause some damage. So, if we give the surgeons sort of a road map of what they need to remove to make sure we don’t get that impingement, then it’s going to be better.
Chris - How are you able to model what’s going on in a person’s hip then in order to give the surgeon that information?
Sophie - For quite a lot of years now in our labs at the University of Leeds we’ve had hip simulators. These effectively we’ve been putting total hip replacements into them which we’ll continue to do, and we can load them and put them through motion cycles. Previously, we’ve just tended to put these through walking cycles to see how they perform, but what I want to do in this grant is actually starting to take tissue that mimics the tissue in the human body and go to extremes of motion to see when you get the damage so we can then make changes to the hip as the surgeon would do and see if that actually, in reality, really does reduce the amount of damage that we get.
Chris - Will you, ultimately, end up then with a computer model where you could take the scan of the individual, plug it into your computer model, and it will then work out where all of the forces are travelling through their joint and when they were to move in certain positions when it’s likely to impinge or wrinkle up the cartilage in the joint and, therefore, you could make predictions for the surgeon without actually having to lay a finger on the patient?
Sophie - Yeah, that’s absolutely what we want to do. It’s very much about creating a bespoke sort of package for each individual patient because everyone’s got a different shaped pelvis, they move in different ways, etc. The bit we’re missing at the moment is we don’t actually know how the tissue physically behaves so we need this physical experimental simulator in the lab. We need to physically do it and cause this damage in the lab.
Chris - What have you got then: something that resembles a hip joint but it’s sort of sitting with mechanical devices attached to it so you can see exactly how it’s being loaded when it gets moved around?
Sophie - Yeah, pretty much. The exciting part of this grant is I’m going to be collaborating with some manufacturing engineers, so they’re really good at coming up with smart materials that will mimic materials that we have in the body. We can also put various sensors on that so we can look at the forces that are going through the hip. And then, as the shape is changed, we can look at what causes this optimum amounts of change and differences in that. We can actually start to use some tissue in the lab as well - human tissue - and look at the changes you get with that and the damage that’s caused.
Chris - What will you do then; three dimensionally print the structures so that you can get something which is really quite a precise and accurate representation of what’s going on in a real hip?
Sophie - Yeah, that is what we’ll do. We can create the funny shaped bits and we can start to change that shape, and then we can use natural tissue as well on the other side to see what damage you get as you start to apply those loads and motions.
Chris - And you do think the surgeon doing this kind of refashioning and resurfacing maneuver will be easier, less traumatic than doing a total hip replacement?
Sophie - Yeah. I think we'll still need total hip replacements, but it means that we can put them off and we won’t need to use them in so many patients quite so early.