This week’s Orthopaedic Crossfire® debate is “The Cementless Knee: Intermediate Term Guarantee on Parts and Labor.” For the proposition is Matthew Abdel, M.D., M.S. of The Mayo Clinic. Against the proposition is Arun Mullaji, F.R.C.S.(Ed), M.S. of the Arthritis Clinic. Moderating is Leo Whiteside, M.D. of the Missouri Bone and Joint Center.
Dr. Abdel: “From the literature we can see that there is no question that cemented total knee arthroplasty (TKA) has good long term survivorship (approximately 95% at 15 years). Historical registry data reflects a slightly decreased survivorship for cementless TKA when compared to cemented TKA. However, there is a bias in these studies given that a low proportion of the knees were cementless fixation. There have been past problems with cementless TKA, which include a lack of tibial ingrowth, metal backed patellas, screw track osteolysis, and issues with polyethylene (thin inserts and non conforming articulations).”
“Only 80% of our patients are satisfied with their TKA. I would argue that in 2014 our contemporary TKA patients are significantly different than patients of the past. Now, they are younger, more active, have increasing life expectancy, all mandating modern implant designs and surgical techniques.”
“There are multiple benefits of cementless TKA, including diminished operative times, preservation of bone stock, ease of revision surgery, elimination of third body wear, and the potential for improved biologic long term fixation…and thus, survivorship. Multiple long term studies have shown excellent long term survivorship with cementless TKA. A 2012 Cochrane review looking at five prospective randomized trials involving 300 patients with radiostereometric analysis (RSA) show that the risk of aseptic loosening with cementless fixation was half of that with cemented fixation. Knee Society and Hospital for Special Surgery scores were similar between the two groups.”
“Another contemporary analysis by Dr. Michael Mont found equal survivorship at 10 and 20 years between cemented and cementless fixation. One of the innovations that has pushed cementless TKA forward has been highly porous metals, including tantalum. Tantalum has a decreased modulus of elasticity, which leads to decreased stress shielding. In addition the increased porosity leads to improved biologic fixation, and thus, stability.”
“To test this hypothesis we undertook a prospective randomized clinical trial at Mayo Clinic from 2003-2006 with five knee arthroplasty surgeons. The goal was to assess the durability and reliability of uncemented highly porous metal tibial components in relation to cemented modular tibial components. We randomized 400 patients into three groups, either cemented modular, uncemented monoblock trabecular metal (TM) or cemented monoblock TM. At five years there was equal survivorship between the cemented and uncemented groups. No uncemented highly porous metal component was revised in this series.”
“We also examined clinical outcomes and found no statistically significant difference between Knee Society pain and function scores or range of motion (ROM). In summary, at five years uncemented highly porous metal tibial components were as durable and reliable—particularly in that concerning early period where rigid fixation is needed for bony ingrowth with cementless fixation. So it is my contention that cementless TKA has the potential for improved satisfaction and survivorship, preservation of bone stock, decreased operative time, and improved biologic fixation (in the long term) for younger, more active patients. Innovative metals have helped, in addition to utilizing surgeons with a high volume practice with cementless fixation.”
Dr. Mullaji: “I oppose cementless knees because: most of our patients are elderly, the implant costs far more, the results haven’t been superior, it doesn’t address most causes of revision, antibiotics and cement reduce sepsis, patellar resurfacing still needs cement, the technique is more demanding, and we don’t know what the optimal design is.”
“In the most recent Australian registry those under 55 are just a small proportion (8%), and yet it’s in these young patients that revision is highest. We have no data showing that cementless leads to fewer revisions in younger patients. An earlier study from Mayo Clinic showing that in a group of patients who had cementless fixation—younger patients—survivorship was far worse.”
“Cementless costs almost $600 more per implant, and $150 more if you take into account other factors. For a country that does roughly 50, 000 total knees annually, that means a huge savings that may exceed the GDP of several countries.”
“The Australian registry shows that the revision rate with cementless is significantly higher than that of cemented—not only in the medium, but in the short term. You’ve heard about the Cochran Collaboration review. If these show a migration of more than 0.2mm then there is a theoretical risk of loosening. The four papers they looked at showed similar migration or somewhat superior data for cemented.”
“Several meta analyses have shown no significant difference in survivorship when utilizing randomized controlled trials (RCT) and when excluding design related failures, fixation techniques don’t really matter. A paper from Scandinavia looked at hydroxyapatite (HA) coated tibial components, 14 different trials. Although they were more stable after two years there was no difference in revision rates at two years, as well as at 8-10 years.”
“There is a paucity of evidence to support one method of fixation with respect to clinical outcomes. In a RCT which looked at 15 years of a single surgeon using the same implant—a PFC—there was no difference between the groups. Likewise with the NextGen—uncemented in one knee and cemented in the other knee in the same patient. At 14 years there were no differences. In fact, there have been poorer results with some of the older designs. The Freeman-Samuelson at six years showed a much higher rate of failure of the cementless fixation.”
“Cementless fixation doesn’t address: the common reasons for failure, infection, pain, instability, or lysis. We know that antibiotics in cement reduce infection (the second most common reason for revision). And we have data to support the use of antibiotic loaded cement as a prophylaxis against infection. Revision for infection is more expensive than for aseptic loosening or mechanical failure.”
“We know that patellar resurfacing needs cement, and surgeons who routinely resurface the patella would still require half a pack of cement. It’s a demanding technique…to ensure coaptation and to secure initial fixation. If it was really so easy then more surgeons would use it rather than shy away from cementless total knees.”
“The European data show that less than 10% of surgeons use cementless total knees, except in Norway and Denmark. In the U.S. less than 10% of surgeons use cementless total knees. We really don’t know what the optimum design is…whether there should be a stem, screws, mobile bearing or fixed bearing. We don’t know the potential long term hazards of HA and porous coating in the young patient…nor the effect of stress shielding. It’s a bad analogy to say that just because cementless works in the hips it will work in the knees.”
“So the weight of evidence is against cementless. The results are equivocal and we need larger trials; and we don’t have optimum data on design or long term safety.”
Moderator Whiteside: “Matt, what techniques must you learn to do cementless TKA?”
Dr. Abdel: “The most important thing is understanding your system. Also, you must have meticulous bone cuts so that you can have appropriate preparation for the cementless components.”
Moderator Whiteside: “Arun, in terms of cemented fixation, what does a new user have to know?”
Dr. Mullaji: “Not only is it important to know your device, but you must get accurate cuts, have good alignment and balance. And you have to pressurize the cement. The surfaces on the femur and the tibia are easier than in the total hip”
Moderator Whiteside: “Should there be deep penetration of the cement?”
Dr. Mullaji: “There is data to show that it matters how much cement penetration you get. That is a function of the quality of bone, the quality of preparation, and your actual pressurization technique.”
Moderator Whiteside: “Matt, how do you talk to patients about cemented versus uncemented?”
Dr. Abdel: “I am a firm proponent of having an open, honest discussion with the patient. We tell them that there are some designers who are utilizing this, but we don’t get into the details of cemented versus uncemented. We share our study data, and say that the concern with cementless fixation is with that early two year period. Our experience is that at five years they have rigid fixation, indicating that they have bony ingrowth that we would expect for the long term. To the issue of cost, the literature shows a shorter operative time with cementless fixation, which decreases the infection. That must be factored in.”
Dr. Mullaji: “It’s only when you exceed about an hour that infection starts kicking in at a higher rate. There’s no data showing an increase in infection in any of these cases.”
Moderator Whiteside: “If you’re going to base your opinions on prospective randomized controlled studies then you might as well go home because you can’t operate. So, what do you think is a bigger disaster: an acute infection postop with a well cemented total knee or with an uncemented total knee?”
Dr. Mullaji: “It depends on how well cemented it was and how well the cementless fixation incorporated. If you just wait long enough for a cemented infection then it’s going to be loose.”
Dr. Abdel: “I would argue that it’s easier with cementless because—without a stem—you cut right across the pegs. There is a concern about how much third body debris is left with the cement after a deep periprosthetic infection.”
Moderator Whiteside: “Matt, where are the pitfalls in development right now?”
Dr. Abdel: “Biomechanically, whether you have a keel or pegs or you use screws, you must have rigid fixation. The system I use has pegs that are slightly undersized when you place them. You need secondary fixation such as hexagonal pegs.”
Moderator Whiteside: “Thank you both very much.”
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