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Marjorie Bekaert Thomas
Advances in health and medicine.
Orthopedics Channel
Reported April 15, 2009

Growing New Knees -- In-Depth Doctor's Interview

Benjamin Ma, M.D., Chief of Sports Medicine and Shoulder Surgery at the University of California in San Francisco, explains how a new way of replacing knee cartilage may offer a more permanent solution to knee injuries.

Once you lose your cartilage, can you replace it?

Dr. Ma: Cartilage cells are very lazy cells, I call them. They’re very slow growing. They don’t like to reproduce very well, so when you have an injury to it, they don’t grow back very easily at all. If you had a cartilage injury when you were like 16 or 18 years old, you have that for the rest of your life, and that’s the problem that we have right now.

Was there much that you could do for cartilage injuries, before these three procedures that we’re going to talk about?

Dr. Ma: A lot of the time, we try to modify the patient’s activity, maybe do physical therapy, maybe advising to change some of the activities that they’re doing, but in terms of surgical procedures that we’re going to talk about, there’s not a lot out there. We used to do a lot of surgery where we would go and clean out the knee and take some loose cartilage out, and we can do it, but you’re not really replacing the cartilage or regenerating it. We just take the loose pieces, other abnormal pieces away.

How does the NeoCart surgery work?

Dr. Ma: The NeoCart surgery is the new procedure that allows them to grow cartilage and put it back into the patient’s knee, and hopefully resurface the knee to allow them to actually have better function down the road.

Because you’re taking the patient’s own cells and cartilage, does that eliminate the chance of rejection?

Dr. Ma: With this procedure, we can actually take some of the patient’s own cartilage, bring the cartilage and the cells back, grow those cells, and after that we put the cells back into a scaffold, almost like putting them in the house and let them grow in the house. I like to put things around it. They actually form cartilage matrix, which is what gets the couch its strength. Once it forms a piece of cartilage, then we actually re-implant it back into the patient’s knee.

How long does it take to grow a piece of cartilage?

Dr. Ma: For that particular procedure, it takes almost eight to 10 weeks to actually grow the cartilage from a cell, from the biopsy.

How big is that piece of cartilage that you’re growing?

Dr. Ma: Right now, we can actually get a cartilage piece up to a diameter of two-and-a-half centimeters, so it’s almost the size of a quarter, and that’s the size that we’re actually dealing with right now.

What kind of a difference does this procedure make for patients?

Dr. Ma: When you actually look into the person’s knee the width of the femur is probably about two to two-and-a-half centimeters only, so when you lose that much cartilage, you actually have lost the entire width of one side of the knee. That’s quite significant. You can imagine all your body weight goes through that small area.

Do patients then end up with just bones grinding against bones?

Dr. Ma: When you actually lose the cartilage, even though it’s small, you actually have exposed bone. When you have exposed bone, that’s where all your nerve fibers are, that’s when you actually feel pain. When people have bone on bone arthritis that’s so painful, it’s because they have exposed bone, don’t have the cartilage overlying the bone to protect them, so even a small area could be quite painful.

When you make this quarter-inch cartilage, how thick is it?

Dr. Ma: The ones that we have right now are about one to two millimeters thick and that’s almost the same as what the normal human cartilage is for thickness, maybe a little bit thicker than a quarter.

What does it feel like for the patient who gets it?

Dr. Ma: We’re doing a clinical trial on this particular type of cartilage resurfacing, and we actually finished Phase l and Phase ll of the clinical trials right now. So far, the patients have been doing better in terms of how they feel. We actually do these different knee scores to see how they are doing. In general, they have better results than they had before the operation. The other thing is to be able to go back to higher level type sports and activities, which in general the patients seem to be able to do it. However, we have to kind of compare this procedure to the ones that we have right now or to not do anything to see what it really does.

How does this procedure differ from the microfracture?

Dr. Ma: The microfracture is something that maybe most people may be familiar with -- athletes have the procedure done. What the procedure does is go in and look at the exposed bone where there is no cartilage. What they do is they put little poke holes into the bone to actually go into the bone marrow. Once you do that, there is access to the bone marrow. The bone marrow bleeds into the affected area, and the cells go over there and form some fake cartilage. It’s almost like forming some scar tissue over the exposed bone. It’s not normal cartilage, though. It forms fake cartilage, and usually these are softer. They’re not as durable. We do have athletes that are able to go back to very high level sports, but they tend not to do as well long-term, so the micro-fracture is what’s available right now. We want to kind of improve on that technique and hopefully the NeoCart procedure will be able to kind of put the good cartilage back in the knee and have better results.

Is the microfracture the kind of gold standard across the board right now and will the NeoCart become the new gold standard?

Dr. Ma: I think the microfracture is probably still the most common way that we deal with exposed cartilage or cartilage defect right now across the board, but there is a lot of excitement about these cell-based type scaffold surgeries that hopefully we will get our results to be better.

Another procedure that you do is mosaicplasty. How does that work?

Dr. Ma: Mosaic, which is kind of putting things together in a little mosaic fashion. Plasty means kind of a change to its shape. For example, if you have a focal cartilage defect that has some exposed cartilage, you actually borrow cartilage from around the knee to get that area covered. Basically, it’s robbing Peter to pay Paul, and it kind of puts things together. We usually borrow cartilage from areas of the knee that are not so important, for example, around the knee cap area, to cover area that’s more important, which is kind of where the main part of the knee will actually stand on. That procedure has also been quite successful. The only thing is that when you put cartilage next to each other, they don’t grow very well together. There are some interface issues to the cartilage that it is not as smooth, and there are also some issues about durability about this particular procedure.

Are there risks associated with the NeoCart procedure?

Dr. Ma: The risk of the NeoCart is that it takes two operations to do the procedure, because they have to do one operation, the biopsy of the cells, grow them, and then re-implant them afterwards.

Is the first surgery pretty minimally invasive?

Dr. Ma: The first operation could be done arthroscopically as an outpatient procedure. It’s minimally invasive, so recovery is not that difficult at all. For the second operation, the technology that we have right now, we have to do it using an incision, so we can’t do that particular procedure arthroscopically. That’s kind of the downside of the technology right now, whereas when we compare it with microfracture, it’s an arthroscopically based procedure.

How is mosaicplasty done?

Dr. Ma: The mosaicplasty can be done arthroscopically, or most practitioners feel more comfortable doing it with an open-type incision, because it’s difficult to shape the cartilage plugs around a very curved surface. We advise people to make incisions, and if it’s a small lesion, a small little area that’s exposed, we could certainly do it arthroscopically, so it really depends on the size of the lesion.

How long does the NeoCart procedure take -- the first one, and then the second one?

Dr. Ma: The first operation takes probably about 10 to 15 minutes to do. The second one probably takes about an hour.

How long does the microfracture take?

Dr. Ma: The microfracture takes about 20 or 30 minutes.

What about the mosaicplasty?

Dr. Ma: About an hour.

How long does the recovery for the NeoCart take?

Dr. Ma: All of them are very similar right now, in the sense that during the first six weeks, you can’t put any weight on the leg. We use what we call a CPM machine -- they put you on the machine and it moves your knee back and forth for about six weeks, and then we let you do more activities down the road.

Is the advantage to the NeoCart that you’re using your own cartilage and you’re building true cartilage that’s going to last forever?

Dr. Ma: That’s the plan. That’s the hope for that, whereas with the microfracture, you’re forming fake cartilage that’s not as doable, and with the mosaicplasty, you’re robbing Peter to pay Paul. When you take cartilage from somewhere else, it’s not as good, because you make the other parts weaker. Also, when you put it together, they don’t heal as well together, and that’s one of the downsides of that particular procedure.

Who is a good candidate for each one of these procedures?

Dr. Ma: Right now, the NeoCart is primarily for focal cartilage defect, and the remaining part of the knee has essentially normal ligament stability -- one part of the knee is abnormal. The microfracture is more commonly done, even when the knee has other injuries to it, but they need to be addressed. I think it works well for smaller lesions. If they have big lesions, it doesn’t have a very good area that supports the fake cartilage, they don’t feel very well, and the results are not as good. For the mosaicplasty, the large lesion, you can’t deal with it, because remember, you’ve got to rob Peter to pay Paul, and we don’t have enough cartilage to fit around it. You’re going to run out of plugs to do that, so I think that’s the difficult part.

Once you get this cartilage growing and maybe you grow more of it, do you think that you will just get rid of the microfracture and the mosaicplasty and just use the NeoCart?

Dr. Ma: I think that there is a potential that this could actually take over the area of cartilage resurfacing. The very intriguing or the enticing thing for us is that you’re actually putting cartilage back into the knee, and you’re not taking it from somewhere else, so I think that’s the advantage of that. The other thing is right now, we’re growing to about 25 millimeters or two-and-a-half centimeters, but there’s a potential to grow bigger pieces. For example if the entire knee is worn out, a larger area is injured, we could potentially use that also, but we are limited to smaller sizes because that’s what we want to look at.

Were you part of the research where you actually saw the cartilage grow for the first time?

Dr. Ma: We were the team that actually did the clinical trials with them, and we were, on the other part. On the other hand, we do cartilage growing in the lab here at UCSF, so some of the company work is kind of sharing what we learned here.

How long did it take to get to this point of growing cartilage?

Dr. Ma: The history of cartilage growth is that for about 40, 50 years we tried with not a lot of success. About 15 years ago, they actually learned how to grow cartilage very well, and we were able to kind of inject these cells back into the knee, and that’s what we call ACI, autologous chondrocyte implantation. It was an operation that was started by a surgeon in Sweden that allows students to learn the process, so 15, 17 years ago, we learned how to grow cartilage, and how to put it back in the knee. At that time, we just kind of injected it back into the knee, and did not have any type of scaffold, or things that would not let the cartilage grow. Now, we put the cells into a scaffold so they actually have time to grow, and then we process the cartilage by putting pressure on them to let them fake them out to kind of say, ‘Hey, you need to form some cartilage,’ and they formed cartilage before we put them back in the knee, so the technology has really evolved over the past two decades.

Was there anything ever made -- artificial cartilage -- that could work as well?

Dr. Ma: No. We are not very good about making artificial surfaces to actually replace cartilage. The reason why is that even as good as say, ceramic on ceramic, or metal on metal, the amount of friction you have on human surfaces is still at least 10 times higher than what normal cartilage surface friction is, so artificial surfaces don’t work as well. When you look at procedures that are say, hip replacement or knee replacement, even though there is metal on plastic, or metal on metal, or ceramic on ceramic surfaces, they are never as good as coefficient friction between the two of them.



This information is intended for additional research purposes only. It is not to be used as a prescription or advice from Ivanhoe Broadcast News, Inc. or any medical professional interviewed. Ivanhoe Broadcast News, Inc. assumes no responsibility for the depth or accuracy of physician statements. Procedures or medicines apply to different people and medical factors; always consult your physician on medical matters.


If you would like more information, please contact:


Lauren Hammit

Public Affairs

University of California, San Francisco

(415) 476-2557


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