By Cheryl Moder, contributor
Medical history was made in San Diego, California, recently when a surgeon
from the Scripps Clinic Division of Orthopaedic Surgery implanted into a patient
an electronic total knee prosthesis that can directly measure the forces that
occur within the knee as the patient moves.
"Until now, engineers have mathematically estimated forces that occur across
the knee joint," explained surgeon Clifford W. Colwell Jr., M.D., director of
the Scripps Clinic Center for Orthopaedic Research and Education (SCORE).
This new type of prosthesis has never before been implanted in a patient and
is expected to generate information that will lead to major advances in knee
implant design, said Colwell, who performed the e-knee implant surgery.
"Now we will know exactly where the forces are coming from for each type of
physical activity the patient engages in. This knowledge will give scientists,
engineers and industry the ability to design better knee replacement prostheses
in the future," Colwell added.
The electronic knee is the result of more than 13 years of research and
development. Contributors to the project include DePuy Orthopaedics Inc., a
division of Johnson & Johnson, MicroStrain Inc. and NK Biotechnical.
"This project represents a unique collaboration among clinicians, scientists
and industry professionals," said Pamela A. Pulido, RN, BSN, lead, clinical
studies and assistant director, at SCORE.
The custom-designed knee implant, known as an electronic knee or e-knee, is
similar to a standard implant on the top half where it has a typical femoral
component and polyethylene surface.
The lower component, made from titanium, is customized so that it allows
electronic measurement of the loads that occur across the knee. Four metal posts
separate the top and bottom plates. 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 sends the information to a
computerized receiver outside the body.
A removable coil fits around the patient’s 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. This technology allows SCORE’s scientists 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.
The e-knee is a one-of-a-kind experimental device that is unlikely to be
implanted in more patients. However, the device will produce data that will be
used to design improved conventional knee implants and other medical devices.
The data from the e-knee could also be used to make better sporting good
products and specialized footwear.
"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 said.
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.
The e-knee has already improved the life of its recipient.
Jerry Ward, a retired aerospace engineer, was in need of knee replacement
surgery and was selected to undergo the groundbreaking procedure. The e-knee was
implanted in Ward’s right leg on Feb. 27, 2004.
Ward—who is very active and enjoys skiing, golf and tennis—said he was eager
to undergo the process and contribute to medical and scientific advances. Due to
his engineering background and medical history, Ward said he understood the
benefits of artificial joints. He had already received a total hip replacement
and a total knee replacement in his left leg.
"The last eight years of my life would have been vastly different if not for
artificial joints, Ward said in a statement. "It’s a lot more fun to go shopping
for golf carts than for a rocking chair.
Ward said he believes he would have been dependent on a walker if not for his
artificial joints.
Electronic knee measurements were validated recently during testing at the
Motion Analysis Laboratory at Children’s Hospital and Health Center in San
Diego. This process involved computer technology and the use of special floor
plates to measure the amount of force the body applies to the ground.
Ward—who was attached to the special coil to receive data from the e-knee and
covered with special motion sensors attached to his legs and body—moved back and
forth in the at Children’s Hospital and Health Center Motion Analysis
Laboratory’s testing area as a computer captured data transmitted from inside
his leg.
Colwell, who is internationally known 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,"
Colwell said.
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