The Hype of the 30-Year Joint

The Hype of the 30-Year Joint

AAOS 2012

Randomized comparison of oxinium vs. metal against conventional and highly cross-linked polyethylene in THA.
Author: Hamadouche and Courpied

The purpose of this study was to compare the effect of femoral head material (oxinium vs. metal) on polyethylene wear in two consecutive prospective randomized series of low friction total hip arthroplasty.

This study demonstrated that up to five-year follow-up femoral head penetration was mainly influenced by polyethylene processing method rather than femoral head material.

Comparison of TKAs with oxidized zirconium and cobalt chromium femoral components in same patients.
Author: Kim et al.

Although it has been claimed that TKAs with an oxidized zirconium (OxZr) femoral knee replacement had beneficial wear properties in vitro (laboratory) there are conflicting clinical results.Three hundred thirty-one patients with OxZr femoral components in one knee and Co-Cr femoral component in the other.

Clinical, subjective, and radiographic results as well as the weight, size, and shape of the polyethylene particles were similar in the knees with the OxZr and Co-Cr femoral component. We found the theoretical advantages of the OxZr surface did not provide the actual advantage.

Is the 30-year TKA claim justified: Do simulator studies extrapolate to real life? - No.
Author: Vail.

While it is possible that a knee replacement could last 30 years, there is insufficient data available from clinical experience to support the claim of a 30-year knee replacement. Using wear simulator data along to predict in vivo (in the body) wear has been reportedly shown unreliable… Thus simulators modeling wear of polyethylene measure only one small part of the total knee system performance. How could it be possible to make a 30-year claim from a simulator when a simulator is modeling only one of a multitude of potential mechanisms of implant failure?

The simulator model is imperfect because it does not recapitulate all the variables of human motion, does not assess wear in the human body, and works in an artificially condensed time frame. There are countless examples of supposed design improvements that have failed to deliver in the clinical setting.

Establishing this expectation may be counterproductive to informed decision making by being biased to the best case scenario.

2012 American Academy of Orthopedic Surgeons (AAOS) Meeting – San Francisco; selected excerpts.

-JGM