The breakdown of a prosthetic knee
“This was a late-70s gentleman who presented with knee pain related to his total knee replacement, which he’d had since 2005,” explained the nurse practitioner who shared this surgical case.
The patient’s symptoms were relatively minor: The physical exam showed laxity and some instability, and imaging showed a narrowing of the artificial knee’s poly insert. The photographs taken during surgery, however, were dramatic.
Upon opening the knee, it was discovered that he had metallosis related to prosthesis break down. The synovial fluid was full of tiny metal shavings and the surrounding tissues were stained black.
This immediately reminded the healthcare professionals on Figure 1 of similar cases, including this one of a 68-year-old woman who had her knee prosthesis revised.
The discussion turned to both the TV series The Resident as well as the controversial recent Netflix documentary The Bleeding Edge, which examines the medical-device industry. While there was concern raised about industry regulations, one orthopedic surgeon took the opportunity to explain why there was no cause for alarm in these cases:
I think that people are somewhat running away with this topic. First, let’s remember that total hips and total knees are rated by patients as some of the most successful surgeries offered across the board. Next, the problem has come to light recently mostly in relation to metal on metal hips which were recalled several years ago. Yes, it’s been proven to cause metallosis and be an issue. But we do not know the extent of what metallosis can cause yet. Maybe it contributes to memory loss as the Netflix doc says but I can tell you there are almost zero studies even mentioning this. Second, in a knee it is due to catastrophic failure. In this case, likely his prosthesis was old and he just wore it out. Implants don’t last forever which is why we try to avoid putting them in young people. The other post referenced with metallosis in the knee was from early catastrophic failure that was likely from surgeon error. My point is that this is rare in knees and not due to the implant. I think the public loves a good “scandal” and tv shows are exploiting this. Personally, and having seen this, I will still not hesitate to get my total joint when I’m older and need one.
The nurse practitioner who originally shared the case explained that this was relatively rare, and that the surgeons involved” had heard of it but hadn’t seen it in person. The rep for the implant we were replacing it with had seen it but not to this extent. A few other orthopods came through to take a look and none of them had actually seen it before.”
As she explained,
The implant was about 12 years old and had just worn down to the point of being metal on metal. The poly insert that serves as the cushion between the 2 pieces has worn through on the edges, which you can see in one of the pics. The patient had both knees replaced around the same time (2005ish) and the other knee is completely fine.
Ultimately, the five-hour surgery was a success and the prosthesis was successfully removed and replaced. In response to a medical educator’s question about the extent of damaged tissue, the nurse practitioner explained:
We replaced it with a new implant, which needed extra spacers to help fill the void. The soft tissue was sharply excised along the blackened parts but there was plenty of good tissue left for a solid closure.