“Cementless fixation is an easy surgery with excellent intermediate to long term clinical performance, ” says Louis Kwong. Richard Scott counters, “Cemented TKA [total knee arthroplasty] is state of the art and has a reoperation rate of 0.5% for the first 15 years. Cementless hasn’t yet been proven to be as reliable as cemented fixation.”
This week’s Orthopaedic Crossfire® debate is “Cementless Fixation: A Contemporary Durable Solution.” For the proposition is Louis M. Kwong, M.D. from UCLA Harbor Medical Center in California; against the proposition is Richard D. Scott from Harvard Medical School in Boston. Moderating is Leo A. Whiteside, M.D. of the Missouri Bone and Joint Center in St. Louis.
Dr. Kwong: “Cementless TKA was first explored 30 years ago with the primary goals of simplifying the operation, reducing the number of interfaces for failure, increasing the longevity of the implant, and addressing the needs of the younger, active population. But the early failures of first generation knee implants were plagued by aseptic loosening of the tibial and patellar components for several reasons: poor implant design, material failure, inferior polyethylene, thin patellar poly leading to high susceptibility to edge wear and osteolysis.”
“Nevertheless, excellent survival in intermediate to long term follow-up has been seen in a number of series. Hoffman reported 93.4% survival at 12 years; Whiteside found 98.6% survival at 15-18 years (no cementless patella). And in Ritter’s cementless series at 10 years there was 100% femoral component survival, 97.4% tibial component survival, but there was a patellar failure rate of 16.4% pointing to the continued need for improvement in this area.”
“Substantial improvements have been made in both material composition and implant design. I think one of the most important biomaterials introduced in orthopedics in the last 30 years is porous tantalum. It has a reticulated trabecular geometry, an open cellular structure of 100% interconnecting pores. Each pore is shaped like a dodecahedron, a 12 sided figure with each side shaped like a pentagon. Each pore is 550 microns in size, and up to 85% of the material is porous by volume. Compared to other commonly used biomaterials such as smooth titanium, big and small sutured beads and fiber metal, porous tantalum has the highest surface friction against bone, thus imparting tremendous initial stability as a prerequisite for long term biologic fixation.”
“The first total knee implant made with this material was a monoblock porous tantalum tibia, a single piece prosthesis with direct compression molded polyethylene into the porous tantalum. It achieves fixation with these two hexagonal pegs implanted into drill holes that are dimensionally smaller in size than the pegs themselves. Followed by this was a monoblock patellar component, also with the same geometry of direct compression molding poly into the porous tantalum, using a single hexagonal peg for interference fit.”
“How have these implants performed? Mayo Clinic just reported their five year experience with the cementless tibia, and found no difference in survival against the cemented implant. There was a 3.5% overall reoperation rate and no revisions of the monoblock cementless tibia for aseptic loosening. In our own series at Harbor-UCLA we had 115 patients and 11 year follow-up of all cementless with an average BMI [body mass index] of 32.5. They all had cementless monoblock porous tantalum tibia, a monoblock porous tantalum patella, and a cobalt-chromium fiber mesh femur. This was a non-selected series all done by orthopedic residents. We had 95.7% implant survival; four were revised for periprosthetic infection; one was revised for femoral component mismatch. There was one death due to pulmonary embolism, with no cases of osteolysis, no X-ray evidence of loosening, no revisions for aseptic loosening; patient satisfaction was 91%.”
“The advantages of cementless TKA with porous tantalum are that you eliminate the concerns that exist with PMMA (polymethylmethacrylate) such as monomer induced hypotension, thermal necrosis of bone, third body wear from retained cement debris. You don’t have the cost of cement, the mixing system, the cartridge for the cement gun, or lavage and irrigation. Also, there is an 18 minute reduction in OR time, a $3, 000 reduction in hospital bill; at the end of the day of arthroplasty we typically save 1-1.5 hours, allowing us either to do an additional surgery or to finish the day early. There is also a savings in nursing and OR staff overtime. There is a reduction in anesthesia, a potential decrease in infection risk, a potential decrease in the risk of venous thromboembolism, and a decrease in overall morbidity and mortality.”
“This is an easy surgery with excellent intermediate to long term clinical performance. Cementless fixation is the future and the future is now. Thank you.”
Dr. Scott: “You have to admit that cemented TKA is the gold standard throughout most of the world. Long term survivorship is high, reoperation rates for any reason for the first 20 years run approximately .5-1% per year. Out of my own last roughly 4, 500 knees I’ve had 244 reoperations. At an average of 14 year follow-up 5.5% had been re-operated for a rate of 0.4% per year. Half of the reoperations were for poly wear issues; most were implanted in 1995 and I hope most of those issues have been resolved.”
“I have had experience with cementless patellar fixation. In the old days it required metal-backing with thinner poly with possible wear through. My personal incidence with one design is a 10% wear through rate at minimum 25 year follow up. Some metal-backed patellar designs (such as mobile bearing) are less vulnerable than others.”
“I’m now going to shift a bit, and discuss hybrid fixation where there is a cementless femur, a cemented tibia—with or without patellar resurfacing. There are potential advantages of not cementing the femoral component. There’s the possibility of bone stock preservation should component removal be necessary. It’s important, however, that fixation lugs are non-porous; otherwise extraction could be difficult. Also, there’s the avoidance of possible cement debris from the femoral fixation. There’s a shorter operating time should two cementings be utilized, and there is easy access to the back of the just-cemented tibial component (to check for extruded cement). With this procedure you have superior zone 4 integration sealing that interface from wear debris.”
“We’ve studied zone 4 radiolucency in 17 paired cemented and cementless total knees; we saw 70% zone 4 radiolucency in the cemented femurs. These were all fluoroscopically controlled perfect laterals. There was 0% zone 4 radiolucency in the cementless femur. I now try to improve zone 4 interface when cementing by using what I call the smear technique. I pack and smear cement into the posterior condyles, put some on the back of the femoral component as well, and I cement with a trial rather than a real insert because I run the risk of snow plowing cement to the back of the knee with this process.”
“The disadvantages of cementless femoral components are that more precise bone cuts are essential and the prosthesis is more expensive. Regarding bone cuts rigid primary fixation of the femoral trial is the key to a successful outcome. As for cementless femoral loosening, in my experience it is relatively rare. I’ve done about 1, 200 of these with 1-26 year follow up and have had three loosenings for an incidence of .25%.”
“Ancillary screw fixation is helpful in some designs, but it introduces a portal for wear debris and subsequent osteolysis. The newer trabecular metals may have promise, but follow-up is relatively short. Thank you.”
Moderator Whiteside: “Louis?”
Dr. Kwong: “I agree with Dr. Scott in that the long term performance of the new cementless designs isn’t proven. The results we have are 5-7 years and they are excellent. And while there’s no question that Dr. Scott is an expert model of an arthroplasty surgeon when we look at a large market like the U.S., 75% of all arthroplasty is performed by a surgeon who does less than one total joint per month. So we look at the general orthopedic surgeon as performing the lion’s share of the arthroplasty and how reproducible that is. The new designs of direct compression molded poly have the best long term performance of any poly in knee. They incorporate into the tibial and patellar designs a composition where the prosthesis is isoelastic with bone, allowing good physiologic transfer. We often look at the first two years, whether there are catastrophic failures that point to whether there was a problem with the design. We haven’t seen that with the new generation type of prostheses that incorporate materials like porous tantalum.”
Dr. Scott: “I have done about 40 cementless tibias. With some I thought that I should put some bone slurry to even out the cut if it wasn’t perfect on the tibia. I don’t think that’s necessary on the femur. How do you both feel about that?”
Dr. Kwong: “Excellent point. The fact is that we want to achieve optimum contact on the interface between the cementless surface and the bone. So if it’s not a perfectly flat cut I would re-cut that with minimal bone removal. I wouldn’t advocate for putting any type of bone slurry in order to not interpose dead bone between the viable recipient bed and the porous surface.”
Moderator Whiteside: “Dick, you seem to be happy with cementless fixation of the femoral component. If you had a tibial component that gave you reliable cementless fixation would you prefer that over cement?”
Dr. Scott: “I would be interested in using it then assessing the long-term results. Some of these systems…”
Moderator Whiteside: “Wait, let me go back to being the moderator! Where did you get this term, ‘gold standard?’ Did you major in economics?”
Dr. Scott: “I think platinum standard is better.”
Moderator Whiteside: “Alright, alright! Do you ever see loosening between the cement and the metal?”
Dr. Scott: “I think that is design-related and technique-related…the actual femoral component and its surface…whether is has recesses or dovetails. I do see that.”
Moderator Whiteside: “Look for that when you have a knee that keeps swelling and hurting, but the bone-cement interface looks good. Louis, do you ever do cemented knees anymore?”
Dr. Kwong: “Yes. When the bone quality is poor, when we have our patients with inflammatory types of arthritis where we’re concerned about the compromised biologic potential.”
Moderator Whiteside: “Thank you.”
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