“The benefits of modularity, both for surgeons and for manufacturers, are overwhelming, ” says Chitranjan Ranawat. “Not so fast, ” says Richard Jones, “All-poly tibias are for select patients…it’s just a matter of whether you want your patients to not have the very best every time.”
This week’s Orthopaedic Crossfire® debate is “The All-Poly Tibia: A Contemporary Healthcare Solution.” For the proposition was Chitranjan S. Ranawat, M.D. of the Hospital for Special Surgery in New York. Against the proposition was Richard E. Jones, M.D. of the University of Texas, Southwestern. Moderating was Robert T. Trousdale, M.D., of Mayo Clinic in Rochester, Minnesota.
Dr. Ranawat: “I’ll share with you a follow-up on a group of patients that were below age 55—a follow-up at 10-18 years. The survivorship of all-poly components at 10-20 years, as evidenced by four reports (Font-Rodriguez et al., Ranawat et al., Vince et al., Insall et al.) is quite good. If you compare head to head all-poly to metal backed there are seven reports suggesting that there is no difference between the two (Gioe et al., Muller et al., Ranawat et al., Najibi et al., Rodriguez et al., Gioe et al., Rand).”
“Level 1 evidence: two prospective randomized studies showed no difference (Gioe et al., Muller et al.); three radiostereometric analysis (RSA) studies showed equal or better fixation (Hyldahl et al., Norgren et al., Adalberth et al.). The change from all-poly to metal backed designs occurred in 1982 in a study by Bartel showing that a metal backing distributed load and is best suited for cases when there is a bone defect.”
“So our data from 2005 that was published in the Journal of Arthroplasty looked at the Knee Society Score (KSS), the Knee Society Function Score (KSFS), the Western Ontario and McMaster Universities Score (WOMAC), a patient administered questionnaire and the UCLA Activity Score. The patient questionnaire asked specifically about pain and noise in the knee, patient satisfaction, and sense of well-being. I do the procedure without a tourniquet and use it when I’m cementing.”
“You must deliver the tibia in front of the femur and cement the femur first and the tibia next; you must remove the cement behind the tibial component. So 33 patients, 46 knees, and 13 bilateral…we have followed them now out to 10-18 years. The average age then was 55, now it’s 65/66. There were good to excellent results on Knee Society and WOMAC; the mean UCLA score was 5 or greater in several patients.”
“There was anterior knee pain in 7 knees, asymptomatic crepitation in 11 knees, and 1 patient had more symptoms, but did not require surgery. Activities of daily living: most of the patients could do them, including kneeling and squatting. Sports: the majority who were active then are still active now. Satisfaction: over 9 out of 10 were satisfied. The radiographic evaluation indicated no issue except for demarcation in zones 1 and 2 in some knees.”
“One patient had a lateral liftoff of 3mm; it didn’t change over a six-year period. There was another patient with a failed ligament reconstruction who 10 years postop climbed Mount Kilimanjaro. There were no additional revisions for osteolysis or loosening; Kaplan Meyer survivorship (mechanical failure 97.6%; failure for all causes 92% plus or minus 9.4%).”
“Indications for all-poly: elderly patients, good tibial bone quality, body weight less than 180lbs, and selected younger patients. The following technical points are important: achieve a flat tibial cut, size the component properly, cement the femur first, restore the posterior offset, lateralize the femur, cement the tibia last, and clean the cement posteriorly. It is very cost effective, and in spite of good scientific evidence it’s penetration in the U.S. market is around 5%.”
“It appears that the benefits of modularity, both for surgeons and for manufacturers, are overwhelming.”
Dr. Jones: “No modularity equals no versatility. Who is this guy I’m debating? We think of him as the Dalai Lama of orthopedics, and that’s a wonderful thing. All-poly tibias are for select patients…it’s just a matter of whether you want your patients to not have the very best every time. Metal backed tibias…bone defects, poor quality bone, convenience, insert exchange, the obese patient…these have been proven to be useful in [these] patients.”
“Load transfer: with plastic you get high bending stresses, both at the post level and changes at the interface level. However, as you spread the stresses out with a metal backed metal tray and a poly modular on top of that, it’s significantly lower bending stresses and much better long term poly wear. Mono block trabecular metal: studies are showing excellent ingrowth with that.”
“The introduction of modular polyethylene inserts in the 1980s offered isolated exchange, retention of metal, and maintenance of bone. Isolated poly exchange: you’re in trouble then…you get accelerated wear and it’s a major issue. Metal backed tibias: locking mechanism problems early on (mostly been solved), titanium base plates were always a problem (solved with highly polished chrome cobalt), and we’re pretty much eliminated backside wear with much better areas.”
“Minimizing wear with highly crosslinked polyethylene (XLPE): in Hofmann’s series of 200 patients with a mean 75-month follow-up, 100 standard, 100 XLPE; 20 radiolucencies appeared in those patients with standard poly, whereas only two appeared in those with XLPE. No measurable wear was seen. Fisher from England is now showing that the kinematics can be different with a total knee, but the wear with a XLPE is significantly less.”
“Surface cementing is all that I do, and all that Aaron does as well, and so that big cauliflower of cement that’s down in the canal with the people that do the other method is not necessarily present. This is Hofmann’s data as well with a metal backed tibia—surface cement only…100% survival at 5-10 years in the Natural Knee System.”
“Modularity gives you versatility. It gives you fixation solutions, both for primary and for revision knees. It improves the load transfer to the proximal tibia, and it makes it a lot easier to revise. And if you eliminate the causes of backside wear—titanium base plates and stronger locking mechanisms—XLPE helps solve the wear problems.”
“PCL rupture: we know this occurs in patients with cruciate retaining knees. You can readily exchange the tibia to an ultra congruent bearing to substitute for the posterior cruciate without having to do a full knee revision. About 5% of our revisions are patients—in Dallas, that is—that have had a cruciate retaining knee and develop a late rupture of the posterior ligament with significant sagittal plane instability. Tibial plateau fractures can be readily treated; acute fractures can be handled readily.”
“The perfect tibial component: metal backed titanium or chrome cobalt, porous or nonporous, spacers can be added for augmentation, stems can be added for offloading, great locking mechanism, and finally, XLPE can make a difference.”
Moderator Trousdale: “Dickie, it breaks my heart, but I’m shifting to the right on this one. Disclosure: I’m a huge monoblock tibia fan and I use all-poly tibias for the majority of my patients, especially my young, active patients. Chit, if you look at the data it is convincing that a monoblock tibia wins in that race.”
Dr. Ranawat: “The best argument for a younger patient who understands the pros and cons of using modularity or one piece all-poly. So if the patient lets me do what I think is the right thing I use all-poly. It’s a matter of what others are doing…society pressure. They may feel they have an inferior knee if you use all-poly. So all my friends and VIPs who don’t give me grief get all-poly.”
Moderator Trousdale: “Then there’s industry, which is motivated a bit to use modular knees because they’re more expensive.”
Dr. Ranawat: “In the U.S. the sale of all-poly is around 5%.”
Moderator Trousdale: “It’s amazing the data—I don’t think there’s any fixed bearing knee series past 15 years with a modular component. So if you’re using a modular total knee—which is fine—don’t give them 15 year data because there is none. Dickie, is there any long term data on modular total knees other than rotating platforms?”
Dr. Jones: “Not that I’m aware of. Two points: Chit, I’m surprised that you let your patients tell you what to do.”
Dr. Ranawat: “You are treating the patient, and you must be the advocate for the patient.”
Dr. Jones: “Yes, but you must recognize that all the information they get is from the internet. Rob, I’m going to go with you on monoblock, but I would like to see monoblock with a metal base.”
Moderator Trousdale: “Chit, one thing that poisoned the all-poly world is a series that came out of Mooresville that looked at one knee design—all poly with very poor results. Tell us why we shouldn’t be putting every all-poly knee design in one bucket.”
Dr. Ranawat: “Because there is a design issue and a fixation issue in their series. I agree that metal backing distributes the load properly. However, the published data—if you use all-poly on a patient with good bone quality, has a flat surface, no bone defect—there is no difference between metal backed and all-poly. That’s where science and clinical data don’t match.”
Moderator Trousdale: “The patient I don’t use an all-poly on is the 90-year-old with osteopenic bone. Chit, what to do with the elderly osteopenic patient?”
Dr. Ranawat: “The indications are good quality bone, flat surface (so there are no defects on the condyles), and a good cement technique. I think if you meet those requirements…”
Dr. Jones: “For sure that patient with osteopenia is a patient you wouldn’t want to put the poly in because there’s not going to be enough bone support to make the entire construct of bone, cement, and implant a stable, long term process.”
Moderator Trousdale: “Dickie, this wasn’t your slide, but the slide said XLPE in a modular base plate will decrease wear. Can we really be convinced of that?”
Dr. Jones: “The bench data from Fisher shows that. Fisher’s early stuff showed that one of the differences between a rotating platform and a fixed bearing was the fact that because of the kinematics of the rotating platform, and particularly the fact that it was a unirotational and not a multirotational axis, did make a difference…and it didn’t make a difference whether it was XLPE or not. But, as new data is coming out from his place, XLPE is better because there is less wear and it doesn’t make any difference what the kinematics are. The study I showed was Aaron’s [Aaron Hofmann, M.D.] with 75-months follow-up in which he showed significantly better X-rays than in the non XLPE.”
Moderator Trousdale: “Chit, how often do you use the modularity of a modular tibial tray?”
Dr. Ranawat: “They have value in knees with a deformity because when you are balancing the knee you may want to change from whatever you decide. In closing, modularity is like any addiction…you know it’s not good, but you do it still.”
Moderator Trousdale: “Thank you, gentlemen.”
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