Doctors in San Diego have implanted the first electronic knee in a patient with osteoarthritis, and they’re hoping that information generated from the knee will lead to better and longer-lasting prostheses for worn out and painful joints.The electronic knee contains transducers, a microtransmitter, and an antenna that send real-time information about movement of the knee to a computer allowing doctors to measure the distribution of forces that occur within the knee. The custom-designed implant will also allow doctors to observe the load-carrying capabilities of the bones as the patient walks, climbs stairs, and exercises.
"It’s powered from an external source, not like a battery," said Dr. Clifford Colwell, Jr., who performed the surgery to implant the knee.
"So we can gather information as long as the patient’s healthy, viable, and willing to participate. You just turn this thing on electronically whenever you want to study it," he said.
Dr. Colwell is the director of the Scripps Clinic Center for Orthopaedic Research and Education in La Jolla, California. The electronic knee is the result of collaboration among Scripps clinicians, scientists, and industry that have spent 13 years in development.
The first patient who volunteered for the electronic knee study is a retired aerospace engineer who enjoys tennis, golf, and skiing. He previously had a hip replacement and had his other knee replaced in the past.
Dr. Colwell said they plan on implanting 4 to 6 more electronic knees in patients over the next several months.
"Because patients activity levels, weights, and so forth would have an influence on the forces, if we get that much information in 4 to 6 patients we should have an adequate sampling," said Dr. Colwell.
There are 400,000 total knee replacements performed in the United States every year, and the patient population it’s an even mix of men and women. Therefore they plan on studying the electronic knees in women as well.
The design of the electronic implant is not much different from a standard prosthesis. It has a typical femoral component with a polyethylene surface that attaches to the bottom of the thigh bone. The lower titanium component is customized so that it allows measurement of the loads that occur across the knee. Four metal posts separate the top and bottom plates, and underneath are transducers that measure the strain that changes within the metal when the patient moves. The transducers are wired to a transmitter which is connected to an antenna that transmits data to a computer. The electronic signals are converted into actual loads in pounds that are felt when the patient moves.
"We will watch the wear pattern because forces will change, and as it wears we will either add more plastic in one area or subtract from another place," said Dr. Colwell.
It is observations like these that will help researchers and industry develop better implants for patients.
"There’s no foreign material that’s ever going to be perfect, nor will this electronic knee make them perfect," said Dr. Colwell, "it will just make them better in the sense that we’ll know more about force distribution and wear characteristics, and we’ll be able to plan better for that."
Their research might also be used to measure the effectiveness of other devices such as orthotics and braces. It could even be used to design sporting equipment and specialized shoes.
Currently, Scripps is the only institution studying the electronic knee. An electronic hip has been studied by other institutions with similar hopes of advancing implant design.
