Medical history was made in San Diego recently when a surgeon from the Scripps Clinic Division of Orthopaedic Surgery implanted into a patient a total knee prosthesis that has the ability to directly measure forces that occur within the knee. This type of prosthesis has never before been implanted in a living patient and is expected to generate information that will lead to major advances in knee implant design.
The custom-designed implant, known as an electronic knee, contains tranducers, a microtransmitter and an antenna that allow transmission of force measurements into a computer-readable format. This revolutionary technology will allow scientists at the Scripps Clinic Center for Orthopaedic Research and Education (SCORE) to measure in real-time the distribution of forces to the implant and the load-carrying capabilities of the bone as the patient walks, climbs stairs and exercises. This knowledge will give scientists, engineers and industry the ability to design better knee replacement prostheses in the future.
“Until now, engineers have mathematically estimated forces that occur across the knee joint,” explained Clifford W. Colwell, Jr., MD, director of SCORE, who performed the surgery. SCORE links pre-clinical, clinical and biomechanics research and is uniquely positioned to bring scientific discoveries like the electronic knee into existence.
“Now we will know exactly where the forces are coming from for each type of physical activity the patient engages in. These specific measurements will not only result in better implant design, but will also give us the ability to measure the effectiveness of other devices such as orthotics and braces,” Colwell added. Other possible applications include better design of sporting equipment and specialized footwear.
Jerry Ward was in need of knee replacement surgery and was selected for this groundbreaking procedure. A retired aerospace engineer, Ward is eager to go through the process and contribute to the scientific knowledge this project will provide. Ward is very active and has enjoyed tennis, golf and skiing. He understands the benefit of artificial joints, having previously received a total hip replacement and total knee replacement on his other knee.
“The last eight years of my life would have been vastly different if not for artificial joints,” said Ward, who believes he would have been dependent on a walker if he hadn’t undergone the previous surgeries. “It’s a lot more fun to go shopping for golf clubs than for a rocking chair,” he added.
The electronic knee project is the result of a unique collaboration among clinicians, scientists and industry professionals. “We spent over 13 years in the development process,” said John Slamin, an engineer with DePuy Orthopaedics, Inc., a Johnson & Johnson company, manufacturer of the implant.
“MicroStrain is proud to be part of the team that made this technology breakthrough possible,” said Steven Arms, President of MicroStrain Inc., which develops wireless microsensors. “Our wireless sensor microelectronics expertise has made it possible for new data to speed improvements in the field of knee replacements.”
Another contributor to this project is NK Biotechnical, a specialty engineering firm from Minneapolis.
According to Slamin, the electronic knee implant is similar to a standard implant on the top half where it has a typical femoral component and polyethylene articular surface. The lower metallic component, made from titanium, 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 the posts are transducers that measure the strain that changes within the metal as the patient moves. The transducers are wired to a transmitter, which is connected to an antenna. The antenna transmits the information to a receiver outside the body. A removable coil fits around the knee and externally activates the system, then transmits data into a computer system. The electronic signals are converted into actual loads in pounds at each one of the four posts as the patient moves.
“The financial investment in this project from DePuy has been substantial, in addition to the human resources spent,” indicated Slamin. Other financial supporters include the Orthopaedic Research and Education Foundation, private philanthropic foundations and individual donors. “The financial investment is minimal compared to the benefit that all total knee replacement patients will receive in the future,” Slamin added.
With approximately 400,000 knee replacement surgeries performed every year in the U.S. and the population of active seniors growing, the financial impact of designing better, longer-wearing knee implants is significant.
Colwell, who is known internationally for his work in the field of total joint replacement, relates this project to other scientific discoveries. “Implanting the prosthesis was like the Mars landing, but what we’re really looking forward to is the scientific knowledge we’ll gain from the data,” said Colwell.
Data collection will begin at the SCORE laboratory under the direction of Darryl D’Lima, MD, within a few days of the surgery and will continue on an ongoing basis both inside and outside the laboratory.
For more information about the electronic knee or knee replacement surgery call 1-800-SCRIPPS (1- 1-800-SCRIPPS).