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WITH... PR HEINZ WAGNER
M.O. : What do you think of the metal-on-metal bearing surfaces ?
H.W.: Because the early results of total hip replacement were just spectacular, we became tempted to use prostheses also in younger patients who have a longer life expectancy; and because of that we now see the most important late complication, which is aseptic loosening. The number of cases is rapidly increasing and we can speak of a world-wide orthopaedic epidemic of aseptic loosening.
In recent times, it has been demonstrated that bone resorption is the cause of aseptic loosening and is in turn caused by debris particles from the polyethylene articulation. And you know, for a surgeon, it is so depressing to do our best for the patient and then to see an aseptic loosening twelve, fourteen or fifteen years later just because we are using an inappropriate material; and in the last years we have been searching for better materials which produce less debris particles.
There is an excellent researcher in Los Angeles, Patricia Campbell, and she made measurements of these particles and she found that a total hip prosthesis with a polyethylene acetabular component produces 370.000 particles per step. This is really a frightening figure, which also shows how small these particles are. Now, tribological measurements have been made and it has been found that the coupling of ceramic on ceramic and metal on metal have the lowest particle production, and if it is true that the particles are the cause of loosening, the longevity of the prosthesis must be better if we succeed in decreasing the amount of particle debris.
H.W.: Now, ceramic on ceramic and metal on metal both have advantages and disadvantages. Ceramic on ceramic is very popular in France, but there are two or probably three major disadvantages. One is that ceramic is a brittle material. It is as hard as glass and it can break; breakage is not very often, but when it occurs it is a real disaster for the patient. Secondly, the tribological condition in ceramic is good if you have appropriate coverage of the head, but if you have a steep acetabular component you have an equatorial load transfer and then the wear of the ceramic goes up dramatically. And the third disavantage is due to the brittelness of the material; very small acetabular components cannot be made and for particular hips and for patients from particular countries who have very small acetabula where you need an acetabular component with an outside diameter of 44 mm, this cannot be made from ceramic material. On the other hand with the metal on metal articulation we are very fortunate to have thirty years’ experience with the old designs. They had a very high failure rate because in those times the technology of manufacturing was poor. And for instance in the prostheses of McKee, the two components were made by two different manufacturers and the matching was inappropriate. But in other cases where the matching was good by chance, these prostheses lasted twenty-five years or more without visible wear.
H.W.: Our methods of measurement are so sensitive nowadays that we measure very small amounts of metal ions, and we measure metal ions even in persons who have no prostheses; now we have these values but we don't know what to do with them, we don't know whether they are important or not, and nobody is concerned about the metal ions which come from the cemented stem of the prosthesis, because at that site many more metal ions are delivered and the final question is what happens to these metal ions: do they stay in the body, or are they excreted by the kidneys? These are all issues which will have to be addressed in the near future.
H.W.: Yes, I have used more than five hundred, and my longest follow up is seven and a half years. We have evaluated these patients very carefully, but all the data we get actually do not relate to the metal on metal articulation but to the prosthesis itself . The only clear evidence we have found by now is that over a seven and a half year period, metal on metal articulations do not show new problems or disadvantages. This is all we can say. And, actually, I think we have to wait another seven years until we enter the time period where polyethylene articulations start to create problems. And if by that time the metal on metal articulation will show no signs of aseptic loosening, then this will be the proof of the superiority of the metal on metal articulation. But on the other hand we can also look at other signs, for instance McKee's prostheses have been used for thirty years, and they show excellent results, provided that the dimensions and the coupling are technically perfect.
H.W.: Well, you know, we have to distinguish which patient we are talking about. If we have a femoral neck fracture in a patient over seventy-five, we need not to discuss the matter and we can use what we've been using in the past, because it will last for the lifetime of the patient. But the question is what should be done with the younger patients, who have a longer lifespan ahead. For this group of patients we have to look for the greatest possible longevity, and it is commonly agreed now that we should use non-cemented acetabular components with titanium convex sides, which allows for osseointegration, and we should use metal on metal articulations in order to have the smallest possible particle production.
H.W.: Now, in this younger age group in most of the cases I use a non-cemented femoral stem of rough blasted titanium and with longitudinal sharp ribs which cut into the bone, providing high rotational stability. It is a prosthesis which I have designed. I think that for uncemented prostheses the proximal load transfer is extremely important. You know, there are different designs in the literature; for instance, an anatomical prosthesis is designed to preserve the normal anatomy of the femur. But if you look at total hip replacement, even in the very best results you see that the femur does not maintain the same structure as that which was present before, on normal load transmission, because normally the load is transmitted on the surface of the bone, in the cortex, and with the prosthesis the load is transmitted through the medullary canal, so the load transfer and the stress lines change and the bone has to remodel and to adapt to the new biomechanical situation. Therefore it is my conviction that we should aim for a prosthesis which has a proximal load transfer and which makes it easier for the bone to adapt to this structure.
H.W.: Titanium cementless stems with a rough blasted surface allow for osseointegration, and if you succeed in achieving osseointegration, titanium will not create problems. This is the great advantage of titanium. On the other hand, if you have smooth titanium surfaces there is some micromotion between bone and the titanium, and the passive layer of titanium oxide is very soft and is swept off the surface, so this can create problems. In recent times there has also been some concern about cemented titanium prostheses and it has been seen that if the titanium stem is too thin, corrosion can occur at the titanium surfaces. This is because titanium is more elastic than cobalt chrome and more liable to micromotion; and with the cement mantle, no oxide can penetrate toward the titanium surface to repair the passive layer and there you have corrosion in an acid medium with a pH far below 7. We have measured in some cases, a pH of 1, which is very acidic! So, I think that cemented titanium stems should be used with great care and that very thin and elastic titanium stems should not be used with cemented techniques.
H.W.: I was the chief surgeon of a very large orthopaedic hospital and we had to take care especially of complicated cases. We had patients referred from all over the country with aseptic or septic loosening with extensive bone loss, where the bone loss was so severe that no new prosthesis could be firmly fixed in the old prosthesis bed. So we had to look for a solution.
H.W.: Well, we did what everybody did. We cleaned the cavity and then we applied ostheosynthesis plates and cerclage wires and so forth, and then we fixed a new prosthesis with cement. But the life of these revisions was very short because after loosening you never get a fixation with cement as good as that which you achieve in a primary hip implantation. And then we found that we had to bypass the defect. Based on this idea, we developed a highly successful revision prosthesis. I must confess that it has also been a surprise to myself; that not only the prosthesis worked well but that there was also rapid bone repair in the old prosthesis bed.
H.W.: The idea was to have a prosthesis which can bridge the defect, which can provide high stability and which has to give a high rotational stability. I had some ingineering experience and I remembered from the machines that a cone junction was very effective and I thought when I would ream the medullary cavity to a cone and insert a conically shaped implant, then I should get very good stability. Moreover, the longitudinal ribs cut into the bone, and by doing so they give a high rotational stability.
H.W.: Yes, but between the ribs you have space for blood vessels, so that the revascularization of the medullary cavity occurs very quickly, and you have a discontinuous load transfer, because the load is transferred into the bone only on the peaks of the ridges. So you have a very high mechanical pressure per square unit, which turned out to be very advantageous for osseointegration. After a relatively short period of time, Professor Schenk from Switzerland was able to histologically investigate such a case and he found very interesting new evidence that in a cementless implantat the new bone does not grow in the grooves, but is attracted to the peaks of the implant. Therefore, we can say the design of a non-cemented prosthesis should not have many grooves, but many peaks.
H.W.: I did this only in the beginning, until I saw that the bone is reformed by itself. And now I don't put bone between the bone shell and the stem. I leave it bare. I apply bone grafts only on the lateral surface of the femur if there are bony defects, because bone repair on the lateral surface is slow. And if they have a defect of more than one and a half centimetre it might take a long time for this gap to fill up. If you have a longer defect on the medial side of the femur, surprisingly, this takes care of itself - you don't need to graft it because on the medial side new bone comes very quickly.
H.W.: In these severe cases I use the transfemoral approach. I open the femoral cavity by doing a bone window with great care not to detach the muscles. So, when I reduce the bony cover I replace also the musculature, and I can apply the bone graft underneath the musculature. In very rare cases I make a suture of the muscle just to keep the bone graft in place.
H.W.: Yes, this is also a long story; The first prostheses were made of straight rods of titanium, and titanium could not be bent more than to an angle of 145(infinity) degrees otherwise it would break. Bending was performed at a low temperature, so the engineer asked me whether or not this was acceptable and I said yes. We had a shorter offset, but when both the implants, the acetabular implant and femoral prosthesis were in an appropriate position, there was no major disadvantage. So, after a couple of years, they improved the technology of manufacturing and now they can bend it to ninety degrees if you wish. And then we discussed whether or not we should change the angle. But the engineers told me that for a more varus angle, they would refuse to produce prostheses with small diameters because they would not resist the bending forces. So in a more varus angle, we had to eliminate the small diameters. But the small diameters were very important in many patients and now we have made a compromise: in the small diameters (thirteen, fourteen, fifteen millimetres), we still have the steep angle, and with the increasing diameter of the shaft, the varus increases also, so that we have a longer offset.
H.W.: Very soon; within the first ten cases. They all made bone within three months. It was really a pleasure! You know, it is not much fun making minor modifications to something other people have made already. It is really very fascinating to develop something new.
H.W.: You know, if you do the transfemoral approach, which we do in these severe cases, and I'm speaking only about these severe cases, then you create something like a fracture, and we know from traumatology that in transtrochanteric fractures, bone formation occurs very rapidly. So I think there is an effect of the osteotomy which stimulates bone formation. Secondly, we know from experience that titanium is very good for the bone: titanium attracts bone. And then, a very important phenomenon is the remodelling of the bone, and we know, that's the law of nature, that bone will remodel only under mechanical stress. So mechanical stress must be applied to this segment of the femur to remodel.This is old evidence - Galileo published on this. And with this bone formation, the bone migrates proximally. In the beginning, we have a distal load transfer, distant from the old prosthesis bed, but then, with bone formation, the load transfer migrates proximally.So, with time, the load transfer migrates proximally. I always say because I'm asked this question very often, that with a revision stem, we have a distal load transfer: as distal as necessary, and as proximal as possible.
H.W.: Yes but, you know, you leave the whole musculature in place. The muscle pull introduces mechanical forces into the bone shell of the femur, also in the proximal segment.
H.W.: There are a number of reasons. One reason is that the bone in this segment is very poor. The second reason is that in loosening, the inside of the femur is smooth so that you don't get an interdigitation of the cement in small cavities. Then, a very important aspect is that with cementing you maintain the size of the bone defect. This bone defect, which is filled with cement, can never improve because the cement takes the place of the bone. If you have a non-cemented revision, then you have space, and bone can develop and can repair the bone loss.
H.W.: No! You have to compare it with other solutions. What other solutions do you have? There is no other solution except cement. I think it is a good compromise. It would be much better if we could avoid aseptic loosening with the metal on metal articulation; but this is a story of the future.
H.W.: I have been the medical director of a two-hundred and fifty bed orthopaedic hospital on the outskirts of Nuremberg, in Bavaria, Germany. I retired from the job of medical director two years ago, because I am sixty-seven now. Now I enjoy a new lifestyle, which is a great experience and a great pleasure, not only for myself but also for my wife and for my family. I can now go to a concert when I feel like it.
H.W.: No, I had a full-time job, and I often worked half the night.
H.W.: Yes, but you know, in the system we have in Germany, the chief is responsible for everything and you have to look after everything. In France, you have a different system; there, you have many surgeons in charge and this makes life easier. Doctors can divide their time between hospital and private practice. This was not possible in Germany; but I think it is changing now.
H.W.: Yes, but you know, my dear friend Robert Merle D'Aubigné was also a bit of a dictator. And it’s really a question of our times: a moderate dictatorship works very effectively if the dictator is good. But if you have chosen someone in such a strong position who is not good, it is a disaster for the whole system. And patient care is changing too. When I retired I found that my hospital was becoming a short-stay hospital. In the past, we had to have large orthopaedic hospitals because patients were immobilized in plaster of Paris and traction devices, and so they had to stay for months, with tuberculosis and so forth. But now we do a lot of surgery, and the patients go home after twelve days, so you have a far greater workload per day and number of beds. When I left, I felt that the big hospital should be broken down into different departments, and they now have five departments in the same place, so it is less of a dictatorship.
H.W.: Now, I was trained in the conventional way and later I went to Professor Hepp in Munster, who was very functionally oriented in his surgery. Then, I was very fortunate to get in very close contact with Professor Maurice Muller from Switzerland, who was the spiritus rector of the AO. He was interested in my collaboration because I had a histological laboratory and I did the first histological investigation for AO before Professor Schenk joined the group, and I did work on the reaction of bone tissue to metal implants, and internal fixation of fractures and osteotomies. In those years osteosynthesis gave us the possibility to perform functional anatomy. You have asked me so many questions about hip prostheses and I came into this field because there was a need: we had to do that. But my great fascination, actually, is not endoprosthetics. It is reconstructive osteotomies. I did much work on this, different types of osteotomies of the upper and lower extremities, very much in congenital dislocation of the hip.
H.W.: That is very difficult to say because the young surgeons in our times do not learn much about osteotomy; and total hip replacement, which is the most frequent indication for a joint repair, has become so easy, and early results are spectacular. People don't think very much about the distant future, this is the problem. And with osteotomies, I'm speaking especially about the hip, the results are not very often spectacular. They are good, but not spectacular. But the risk is very low. So I am very much in doubt. I think that reconstructive osteotomies at an early age are very important in improving the prognosis. But in ostearthrosis, osteotomy is a very difficult problem because there are very few people who know how to do it, how to identify the indication, and probably the patients will not be satisfied because they have friends or neighbours who have an artificial joint and who have a better result for the moment. So I'm very critical of this.
H.W.: Now, if the surgeon has experience with osteotomies, the patient has a good chance, from an anatomical point of view, of a good improvement for ten - fifteen years, and if the patient is intelligent enough to understand the problems, then I think that there is a very good place for osteotomies. I personally do acetabular osteotomies if the femoral head is round. But we also have to treat hips in young people with a deformation of the femoral head and that is a good place for the Chiari osteotomy.
H.W.: I do a spherical periacetabular osteotomy, which I have published in 1965. I recently presented the thirty years’ follow up. The results are very beautiful, and now I am very satisfied that I have had the chance to show how such a joint looks between twenty and thirty years after conservative surgery. And the result is that if you succeedin covering the femoral head with cartilage you have the chance to achieve a long lasting function of the natural joint.
H.W.: I think it should be done by people who are specialized in this field. It is not an operation that any surgeon can do. The anatomical structures must be handled with care. You must have good exposure, you must have the right instruments, and you must do it very carefully. And I think it will be also in the future a very good operation but it will be an operation, for a small group of surgeons who are specialists in this field.
H.W.: Of course. I mentioned already that I was very much in favour of osteototomy, especially in young people. But there are conditions where an osteotomy does not work, especially if the joint is not mobile. Osteotomy does not give good results in stiff joints. Then, I went to the literature and I found that there had been some research in Hungary on cartilage transplantation of the femoral head. And I thought that if we transplant joint surfaces we should transplant both, that is the acetabulum and the femoral component. And I developed an instrument with which we could prepare the joint surfaces, and the principle is to have the hyaline cartilage with a thin layer of bone of about a millimetre and to place this very tightly into the acetabulum and on the femoral head. And this gave very good results, very beautiful X-rays and very good function, but after six years the cartilage started to deteriorate.
H.W.: Yes, I've done transplantation of both articular surfaces of the hip but the transplant did not last long enough. It was a very beautiful operation, but you know, it is very time consuming to remove the implant from the donor, then to prepare it in your operating room and then to store it at low temperature and then to make the transplantation. But a life of six years is not enough, especially not if you see the large number of patients. Anyway the patients didn't lose much because when the cartilage was gone they had the same situation than before. And then, I said to myself if this surface replacement works so well, we should be able to do it with artificial material, and with this in mind I started with the resurfacing prosthesis. I used a cobalt chrome femoral cup and a polyethylene acetabular component. In those days we did not know about the polyethylene disease about which we are so concerned now. The results were initially very good, but with the thin polyethylene layer we had a high early loosening rate.
H.W.: No, and it is very interesting that some joints still work after eighteen years. Because we have seen, in our experience with total hip replacement, that not everybody has the same sensitivity to polyethylene particles. There are differences, and we don't know the cause of these differences. Well, anyway, then we introduced ceramic femoral components to decrease the polyethylene wear, and this gave some improvement but still the results were not satisfactory enough in the long run. But you must know in those days, that was more than twenty five years ago, we were very much against hip replacement with a total prosthesis in young people, and the alternative for us was either to do an arthrodesis or to leave the patient suffering. And so we said: now we can do a surface replacement in the meantime. The great mistake was that I allowed the manufacturer to sell the prosthesis, and it became like an avalanche; it was popular all over the world. In very many cases it was not used carefully enough because resurfacing requires great care in surgery. And then, the new knowledge about metal on metal articulation came in, and the resurfacing which we do now is with metal on metal articulation, with a non-cemented acetabular component.
H.W.: We still do. But the indication has changed because the conventional hip prostheses, also with the metal on metal articulation, are naturally much better than twenty-five years ago, so the need, the indication for resurfacing is less than in the past. But it might surprise you that there is still a good indication for resurfacing also in older patients, for instance if the patient had a transtrochanteric fracture which has resulted in malunion, it is very difficult to apply a standard total hip prosthesis; or if a patient has had an infection at the level of the trochanter, probably after a previous internal fixation, there is a risk of infection if you apply a prosthetic stem. In these cases we see a good indication for resurfacing, also in the elderly patient,even nowadays.
H.W.: I could not make this experience. For me the problem was the granulation tissue which came from wear.
H.W.: Yes, but you must have good bone stock. If you have poor bone, this is not an indication for resurfacing.
H.W.: You know, when I started with the first design, many people were concerned about avascular necrosis of the femoral head, but if you protect the posterior vessels on the femoral neck, necrosis has never been a problem. I had one case which I remember who failed due to necrosis, because the patient had a kidney transplant. There was a small segmental necrosis, and I did the resurfacing. The patient was young and he had to continue with prednisone administration for his kidney, and after three years the necrosis became bigger and then the prosthesis failed. But I have never seen a failure from avascular necrosis due to resurfacing surgery, the problem has always been on the acetabular side.
H.W.: I performed six hundred and fifty leg lengthenings, using metal apparatus of my own design, and this has been a fascinating experience. Because, you know, in surgery in general we improve a deformity but in leg lengthening we can eliminate a deformity. The result of our efforts is able-bodied young people who can lead a normal life. So in those cases we do not do only reconstruction of the body, but reconstruction of the patient's whole life.
H.W.: Very easily. I went to England, in 1961 I guess, and I met Mr. Anderson in Edinburgh, who did work on leg lengthening. They kept the patients in bed and they had a frame, they adjusted it every day and made it slowly longer. But they had difficulties with swelling, and they had stiff legs and so on, and then I said to myself this idea to make a bone longer gradually and slowly is fantastic, but why shouldn't these people walk and move their joints? So then I went home and made a device, and I found a man who had a factory for electrical equipment. He lived in my neighbourhood and he was very helpful. In his factory he made the first distractor for me. We applied a distractor on the lateral side of the femur and on the medial side of the tibia, and with this the patients could move their joints, they could walk around. Then, you know, all the problems with stiffness of the knee and so forth got better.
H.W.: Yes. Now there has been a move from Russia, from Ilizarov with pins and rings. He left his device in place until the bone had healed. But this takes a very long time; it involves suffering for the patient and it is very inconvenient to have such rings on the thigh. And also the stiffening rate of the neighbouring joints is high. I have been observing the trend, and I have noticed that people are going back to the unilateral distractor in femoral lengthening. Many of them continue with the Ilizarov on the tibia. But you know, leg lengthening looks so easy and yet it is a very sophisticated system because you have to pay great attention to detail. You have to maintain joint mobility and you have to take care of the soft tissues; you also have to motivate the patient. I had very good facilities in the operating department, and I preferred in the majority of cases to do an internal fixation as soon as I had obtained the desired length. I had patients in particular those with dark hair, especially from Arab countries, who had more rapid bone production than the fair people from central Europe.
H.W.: Yes, this was my experience. But I could not find out why. So in some patients who had very rapid bone formation I left the device in place without internal fixation, but in the majority of cases I did plating, and then removed the device, which was more convenient for the patients. But you must have the right conditions. If you have a high infection rate, you should not do that. And then, probably, you should not do leg lengthening at all.
H.W.: Yes, all these people visited me and I showed them all the details, especially DeBastiani from Verona, and then they went home and made the modifications. But you know, this is always the case if you have something that is good. It will be copied. And if something is not copied, then as like as not it is not very good.
