CORR Insights®: The 2018 Mark Coventry, MD Award: Does a Ceramic Bearing Improve Pain, Function, Wear, or Survivorship of TKA in Patients Younger Than 55 Years of Age? A Randomized Trial

Where Are We Now?

In the current study, Kim and colleagues [4] performed a randomized controlled trial to compare oxidized zirconium (ceramic) to cobalt chrome TKA femoral components in patients younger than 55 years of age. In this award-winning paper, the authors found no differences in Knee Society, function, WOMAC, or UCLA activity scores, and no difference in range of knee motion. They also found no radiographic evidence of loosening or osteolysis visible on CT scan in either group and concluded that unless there is some patient-specific reason to choose the ceramic device, surgeons should choose the less-expensive option for routine use. This is an important topic because age is a known risk-factor associated with revision TKA, and the usage of TKAs in younger patients is increasing [1-3].

Previous studies have also analyzed different TKA liners [6, 7]. In one study using the Australian Orthopaedic Association National Joint Replacement Registry, Vertullo and colleagues [7] compared 11,608 TKAs with cobalt chromium to 5969 TKAs with oxidized zirconium, and found no differences in the risk of revision, loosening, or osteolysis in any age group except among patients over the age of 75 years, where the oxidized zirconium component was found to have a greater risk of loosening than did the cobalt chrome component. The registry work by Vertullo and colleagues complements the randomized trial in the current study [4], and the two taken together seem to provide strong evidence that there is no substantial advantage of oxidized zirconium TKA components.

We should also not lose track of the counterfacing side of the bearing, where important discoveries also have been made. In a recent implant retrieval study, MacDonald and colleagues [6] found a lower risk of revision because of loosening among TKAs that used highly crosslinked polyethylene (HXLPE) when compared to conventional, gamma-inert sterilized ultra-high molecular weight polyethylene (UHMWPE) liners, but also that revisions resulting from instability were more likely in the HXLPE group than the conventional UHMWPE TKAs.

Where Do We Need To Go?

We still do not know which TKA liner is best, particularly for younger patients; this would be important to determine, since as younger patients tend to be more active and require implants for a longer duration of time [5]. In addition to age, other patient-specific factors such as weight, sex, and preoperative ROM need to be correlated with TKA survivorship and bearing wear. Furthermore, a quantitative analysis of liner wear with associated soft-tissue particle count should be performed. This measurement may help distinguish the effects of different femoral and tibial implants on polyethylene burnishing and wear at a microscopic level.

A cost analysis should be performed between newer, and therefore potentially more-expensive implants and older, and therefore, potentially less-expensive implants. This analysis could help contain overall healthcare costs while still providing the best care possible for patients. Addressing the above gaps in our knowledge may better help us identify the best implant design available for patients, and/or help direct further advancements in new designs.

How Do We Get There?

In order to help refine our approach to choosing implants, additional prospective and basic science studies focusing on patient-reported outcomes, implant survivorship, radiographic imaging, and clinical assessment need to be completed. These study results should then be correlated to patient cohorts that have (1) a wide age range, (2) balanced gender distribution, (3) varied obesity levels, including patients with morbid obesity, and (4) poor to excellent preoperative ROM. Additionally, these correlations should be made at short- and long-term followup; I emphasize this point because so many implant-design changes have looked promising early on, only to fail the test of time.

Also, as suggested by Kim and colleagues [4], implant-retrieval studies should further assess burnishing losses, and basic science studies evaluating polyethylene particle count in surrounding soft-tissue should likewise be performed. Incorporating the results of these studies to our current knowledge base will help us identify better implant designs for TKA patients, especially the younger and more active ones, who are most prone to premature implant revision.