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Why do you perform partial knee replacement instead of total knee replacement?
Well, everybody who has a partial knee is also suitable for a total knee of course, and I’d only do them in patients who have pain and disability that requires a knee replacement. And I would do a partial knee for many reasons, firstly because it is less destructive, you’re retaining about two thirds of the knee joint. We know that the kinematics of the half knee works in a same vein as a normal knee, whereas a total knee replacement the kinematics are very different. You don’t touch the ligaments so you retain all the cruciates and the collateral ligaments so you know stability in itself is inherent in your partial knee. I think the short term recovery is good but that’s not the important issue, I think the long term results are good, we’ve got 20 year results now so I think it’s stood the test of time. Patients like it because there’s not as much pain. They find that the range of movement in the knee is extremely good and the complications after half knees tend to be about half that of a total knee and I think it is a truism that we tend not to have the severe complications with a half knee that we get with a total knee.
Who is an ideal patient for partial knee replacement?
I think the answer is there is no ideal patient. I think there are suitable patients. And around 20 – 30% of patients who present with osteoarthritis, where the arthritis is purely in one half of the knee, where there’s no inflammation as the cause of the arthritis, and where the x-rays show that it’s down to bone, patients have pain and disability that requires a knee replacement. Age, whether it’s a male or female patient, whether they are inactive or active patients – I don’t think that matters. Provided they have half of the knee joint affected, and they can bend their knee to more than 90 degrees, i.e. a right angle, provided they can extend within 10 degrees of full extension, then those patients are suitable for a partial knee.
Who would you not perform the operation on?
Well, certainly anybody who has something like rheumatoid arthritis, an inflammatory arthritis that we know is probably going to affect all the compartments in the knee, you shouldn’t do a half knee because it will fail. I personally would try and avoid it in the really morbidly obese patients because we have no data on them and common sense suggests that complications are probably going to be a bit higher and that we don’t really know how long the plastic is going to last and whether the femoral components will get loose, and I think those patients should really lose weight before coming to knee replacements. But I’m talking about the very large patients, and I think that’s true for total knees as well. So those are the two groups that I wouldn’t – those who have had previous high tibial osteotomy I wouldn’t.
What are the advantages of partial knee replacement?
Patients who have very good flexion will usually achieve good flexion afterwards whereas patients with very good flexion with a total knee replacement, they often lose a degree of flexion.
The recovery tends to be a lot easier because you don’t cut through the muscles because you can avoid making very big incisions because you’re only replacing part of the knee. The function afterwards, we find patients do extremely well walking up and down stairs, and walking distances and getting back to playing golf and gentle sports such as that. Long term the advantages are not any greater than total knees because we know that the 10, 15 and even 20 year results now are almost equivocal between the two, so the advantage is we know that they can last for a long period of time, but on the positive side is that you almost have 2 bites of the cherry because a partial knee can be converted to a standard primary total knee replacement, no matter when you do it, in over 90% of patients. So you don’t have to use a revision prosthesis, whereas a total knee of course, in around 70, 80, 90 % of the cases you have to convert it to a revision prosthesis. So in younger patients and no matter what the age of the patient when you come to revise them, if that becomes a probability, it tends not to be all that difficult to do and you can put in what you might have done in the beginning anyway.
Does it have an impact on hospital stay as well?
Well we’ve shown that the length of stay with this kind of procedure done through what we call a reduced invasive type of approach, the patients can be home within 24 hours or 48 hours. I think the average length of stay of my patients is between 2 and 3 days and with total knees its something around 4 to 5 days.
Is there a difference in surgical procedure between partial knee replacement and total knee replacement?
All knee surgeons get well trained in total knee replacements and they do many of them because if 20% or 30% are suitable for the partial knee then surgeons are doing around 70 - 80% total knees and they get very used to doing that. Half knee replacement or partial knee replacement, because you’re doing the procedure to work with the other half of the knee and the patello-femoral joint is technically a lot more challenging than a total knee replacement to get it right.
Is there a difference between mobile bearing and fixed bearing partial knee replacements?
With a mobile knee replacement using the partial knee of course the plastic is not bonded on to any of the metal components so it’s free to move and rotate and hence you need to get the stability of your prostheses and the gaps between them as exact as you can do otherwise the bearing can dislocate, whereas a fixed bearing one will not dislocate. That’s the big difference from a point of view of early complications.
You also have to think about the polyethylene or the plastic, and with a mobile bearing one the wear rate is much lower because you have larger areas in contact with metal by virtue of the shape and because it can move. So it’s more congruent whereas with a fixed bearing there has to be point loading you cannot have a fully congruent fixed bearing polyethylene because otherwise it becomes more constrained, and the more constrained the prosthesis the greater the chance that it’s going to loosen. So you do tend to see greater wear rates with the fixed bearing ones than with the mobile bearing ones.
Should patients be able to choose what type of knee they have?
If it was my knee I would want to have all the choices available to me and to give due diligence and thought as to what I wanted in my knee.
Patients will come along and they will rely on us to make recommendations hopefully based on what’s the best for the patient, not because we have a particular interest in something but because we believe that in their particular cases their knees, the X-rays, and the findings, that this is a very good alternative. Some patients prefer to go down the route of a total knee replacement. We have to go through the various potential complications with them. Of course if you’re doing partial knee the other half of the knee may wear over time, some patients don’t like that thought even though the incidence of that happening is quite small.
I speak to them about it and then I give them the choice having thought about it, which of the two they would prefer to have. It is my experience that once patients find out about it and read about it they get very enthusiastic about it and it’s unusual that patients would be prepared to have a total knee if they knew that they were suitable for a half knee.
Is it important for surgeons to be trained in partial knee replacement surgery?
Surgeon education I think is extremely important and I think personally with partial knee replacements as opposed to total knee replacements that surgeons should really go through an instructional surgical course before they start doing these. In the United States, the FDA, when they approved one of the more popular half knee replacements which is the Oxford Knee, they designated that surgeons in the States had to attend a live instructional course before they did them. And I think that that is something that should be copied in most other countries. Not only do you see the surgeon doing a video link live operation but you can interact with that surgeon and having done these things myself I know how instructive it is for these surgeons because they can find out the difficulties they have with the operation and even those who have done a few can then come back and learn how and where they may have gone wrong. They learn with lectures all about the principles of what they are aiming to do and then they can play around in the laboratories afterwards and do these on plastic knees. So I think surgeon education pertaining to what is actually sometimes quite a difficult operation, is very important.
And then we run master classes which are user groups, so those of us who have been doing it for a long period of time might run these classes with surgeons who’ve done maybe 10 or 20 of them, will come along and bring all their queries and they can speak to a group of more experienced surgeons and we can pool our experience and discuss problems and newer techniques and instruments.
These interviews have been conducted and are being published upon obtaining patient and surgeon consent for this purpose