To assess the wear and tear on jet engine parts, mechanics used an old technology called ferrography to run the aircraft’s lubricating fluid through a magnetic device to separate out metal shavings and other ferrous engine debris. A University of Rhode Island researcher uses a similar process to assess the wear and tear on artificial hip and knee joints so patients can reduce the number of follow-up surgeries they must undergo or reduce the time spent in revision surgery.
Donna Meyer, an assistant professor of mechanical engineering, anticipates using her research to create a “wear atlas” that can be used by orthopedic surgeons as a diagnostic tool. She said the atlas could be used to help identify the potential problems that patients are having with their implants prior to revision surgery.
Most artificial hips consist of a polyethylene socket and metal ball or metal-on-metal combinations that are connected to adjoining bones with screws or cement. Total knee replacements are made of similar materials. Over time as the ball, socket and bone rub against each other, tiny debris is produced and settles between the bone and the implant interface, discouraging the much needed growth of bone around the prosthesis. This contributes to the loosening and separation of the interface, which necessitates revision surgery to repair it.
“Polyethylene wear debris can be a significant problem for patients because a loosened joint can cause great discomfort,” said Meyer, a Cranston resident. “If we can determine the number and size of wear debris contained in a patient’s synovial fluid, and also look at the ratio of polyethylene to other constituents like metal, bone, and cement particles, we can create a tool to assist in diagnosing the problem with the implant before surgery is necessary. Ultimately we would like to minimize the number of revision surgeries that patients face, or at least minimize the amount of time spent in surgery for additional operations.”
Meyer takes a sample of a patient’s synovial fluid — ” it’s a large component of the lubricating fluid around your knee or hip,” she said — and uses a process called bio-ferrography to capture the tiny particles of polyethylene, metal, bone and cement using a very strong magnet. Since most of the wear debris isn’t magnetic and therefore wouldn’t be collected by the device, she adds to the fluid sample a magnetic compound that binds to the non-magnetic particles.
“We need to capture every tiny particle in each sample to make sure the atlas is accurate,” said Meyer, whose research is funded by the National Science Foundation and the Rhode Island Biomedical Research Infrastructure Network.
Meyer’s interest in this research was sparked when she was a graduate student at Rensselaer Polytechnic Institute studying the lubrication of artificial hip joints. She talked to the chief of orthopedic surgery at the time at Albany Medical Center, who told her of his interest in bio-ferrography. She’s been researching the subject ever since.
Once she perfects the technique for collecting the wear debris, she will begin creating the atlas. Meyer said the atlas will be designed so doctors can easily compare a patient’s age, activity level, implant type and time since implantation with the size and composition of the wear debris to quickly determine which part of the implant is the likely cause of the problem. For example, small particles are more likely to lead to implant loosening. Large pieces of debris, on the other hand, contribute greatly to the wear volume, but it is not certain how much it contributes to implant loosening, if at all.
“The atlas can be used by doctors as a maintenance guide, in addition to a radiograph for example, and hopefully give more information about early wear detection, just like the guides used by aircraft mechanics,” she said.