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Lessons Learned From Metal-on-Metal Implants

Months ago, the idea came to me to write three articles about the lessons learned from metal-on-metal (MoM) implants. My intent was to have three authors write about three important aspects of designing orthopaedic implants: verification test methods, risk analysis and post-market surveillance.

Packard lightened

     Rob Packard
Jean Bigoney, Ph.D., a metallurgist and regulatory consultant, agreed to write about the verification test methods. I was writing about risk analysis, and was asking a Notified Body to write about post-market surveillance. “Professor Jean” was kind enough to help me with the first article, and she was able to get additional information from another scientist in Germany who has conducted a number of wear tests on MoM hip implants for OEMs. I thought enlisting her help was going to be the hard part. I soon learned an unanticipated lesson about MoM implants in the process of writing this article.

The first Notified Body I contacted refused to respond to my request. It wasn’t just a case of overlooking the email. My friend responded to all my emails—except the one about these articles. The second Notified Body I contacted responded by saying, “[NB#2] must decline at this time.” The third Notified Body I contacted responded with a phone call. This person said that [NB#3] did not have any clients with approved MoM implants, and it would be a great opportunity to show how other Notified Bodies should have done things differently. However, this person also said that [NB#3] could not write the article. What makes one Notified Body look bad makes all the Notified Bodies look bad.

In January, the FDA was the latest regulatory body to take investigative action on MoM implants. While assembling a committee to review clinical data and the benefits and risks of MoM hip implants, the FDA developed safety communication recommendations and proposed orders to require OEMs to submit premarket approval applications.

What follows is our two-part primer on metal implant test method results and risk analysis steps OEMs should consider as fallout continues over the use of MoM implants.

A Titanium Metallurgist’s Perspective on MoM

By Jean Bigoney, Ph.D.


Jean Bigoney, Ph.D.
“Titanium hip implants? Not in MY patients!” This was the pronouncement of my friend and colleague in Munich, orthopaedic surgeon Dr. Reiner Gradinger, which left no doubt as to his material of choice for his patients. As far as he was concerned, the risk of aseptic loosening from wear debris was too great. Titanium may be widely considered “biocompatible” and exhibit suitable strength in applications as endoprostheses, but titanium was notorious for having poor wear resistance. He wanted no part of it. Cobalt-based implants were, in his mind, safer due to the naturally superior wear resistance.

He wasn’t the only one. As long as surgeons performing revision surgery were seeing evidence of “wear disease,” which they sometimes called “black death” to vividly describe the metallosis of periprosthetic tissue when retrieving cemented titanium prostheses, many remained skeptical about titanium. Aseptic loosening remains the most frequent cause of revision surgery in total hip replacement (THR), according to the Swedish Hip Arthroplasty Register, and prevalence has remained unchanged over the years at roughly 70%. Along with titanium, wear debris from Ultra-high-molecular-weight polyethylene (UHMWPE) has also implicated as a cause of aseptic loosening in hip implants. Therefore, scientists have put a lot of time and effort into studying particles during the last 20 years.