This week’s Orthopaedic Crossfire® debate was part of the 33rd Annual Current Concepts in Joint Replacement® (CCJR®), Winter meeting, which took place in Orlando. This week’s topic is “The Cemented All Poly Tibia in the Active <60 Patient.” For is Robert T. Trousdale, M.D., Mayo Clinic, Rochester, Minnesota. Opposing is Aaron A. Hofmann, M.D., Hofmann Arthritis Institute, Salt Lake City, Utah. Moderating is Thomas P. Sculco, M.D., Hospital for Special Surgery, New York, New York.
Dr. Trousdale: I’m going to advocate for the use of all polyethylene tibias in young active patients.
Fact #1 with our total knee replacements—at least to date—the best long-term results with fixed bearing knees are with monoblock tibial components…and I’ll share with you a little bit later some data that supports that fact.
And Fact #2, the results of many modular fixed bearing designs have been relatively disastrous and one of the reasons we spend a lot of time talking about osteolysis about total knees. In defense of Aaron, and what I think he’s going to tell you, is that the designs that we’ve got now are probably better than the designs we used in the ‘80s, ‘90s, and maybe early 2000s.
So, what are pros of an all polyethylene tibial component? There are a lot of them I think. You can resect less tibia for the same polyethylene thickness. I think in young, active patients there may be an advantage to that. There’s good data that suggests there’s less osteolysis than with some modular designs. There’s better long-term survivorship than in some modular designs that were used in the ’80s, ‘90s, and early 2000s. There is questionable better loading in the proximal tibia, whether it makes a clinical difference I think is unknown. And there’s no doubt they’re less expensive. That’s important, at least in the United States, and I’m sure where you practice, and the future cost of our total knees is going to be an important issue. So, if you use something cheaper with the same outcome, it may be worthwhile pursuing.
The major negative of an all polyethylene tibial component is you can’t do a poly exchange revision total knee surgery. I would argue that late poly exchanges only apply to a relatively small number of our patients. The outcome of that operation, I think, is a little unpredictable and I would ask you if it’s worth it, given all the negatives of modularity.
Here’s a little bit of data from Chit Ranawat and Jose Rodriguez. Two hundred forty-three (243) Press Fit Condylar cruciate-substituting total knee replacements: One hundred thirteen with titanium baseplates with a modular liner and 130 with all poly tibias in the monoblock design. The seven-year survivorship data with the endpoint of revision and/or osteolysis demonstrates 96% for the all poly monoblock versus 75% for the metal-backed tibias. So, early mid-term follow-up, the all poly clearly wins in this design.
Weber published a study looking at modular and monoblock tibial components, and at intermediate follow-up, the revision rates were lower in the monoblock. The radiolucencies about the tibial component were lower in the monoblock. And the osteolysis rate was 17 times lower in the monoblock tibial component at only 5- to 11-year follow-up.
We recently looked up our experience with a large number of knees, and the all poly tibias had significantly lower risk of revision versus the modular components. And the risk reduction with the all poly was not affected by age, sex or BMI [body mass index].
Across all age groups, even in those patients less than 60 or 65, monoblock had better survivorships than modular total knees except in the very elderly. In the very elderly, the results were the same with the monoblock tibial component or the modular tibial component. The argument to use only an all poly in the elderly is, I think, flawed. Across all BMI groups, except the very heavy patients, the all poly tibia has won. It has better survivorship and in the heaviest patients there was no significant difference.
Additionally, we found that the infection rate was also lower in the all poly design—so, 2.7% of the people developed postop infection. There’s a significantly increased risk for reoperation in the metal-backed group compared to the all poly group with the endpoint of infection. There may be some selection bias here, but there may also be some polyethylene synovitis issues and hyperemia issues that make the all poly a little protective against infection.
So, based on this data, we felt that the all poly tibia had a significantly improved implant survival compared to metal-backed tibias in all age groups except the very old. There is a significantly reduced rate and risk of postoperative infection compared to metal-backed tibias. And there’s a significantly reduced incidence of loosening with all poly versus metal-backed tibias.
