Medical Device Daily Washington Editor

WASHINGTON — The theme connecting the myriad topics being presented at this year's American Academy of Orthopaedic Surgeons (AAOS; Rosemont, Illinois) annual meeting, being held this week at the Washington Convention Center, seems to be technological innovation — from product development to making procedures such as knee and hip replacement much less invasive.

The electronic knee, or E-Knee, is one such technological innovation that its developers hope will revolutionize the design of knee replacement components. While the name conjures up images of a bionic body part that allows its recipient to run faster, farther, etc., E-Knee is a prosthesis that allows researchers to directly measure forces on the knee internally, something which only has been done previously through mathematical modeling.

Calling it “a real boon“ for knee replacement, Clifford Colwell Jr., MD, orthopedic surgeon and director of the Shirley Center for Orthopaedic Research and Education (SCORE) at the Scripps Clinic (La Jolla, California), said E-Knee has the potential to help device manufacturers develop a more durable and sophisticated artificial knee joint. Current knee replacement components have a life of 13 to 18 years and are difficult to replace when they wear out.

“Everyone who has a knee replacement from now on will benefit from this,“ Colwell told a gathering of press on Wednesday morning as he explained the technology.

Colwell, along with a team of researchers and industry professionals worked to create E-Knee, which was created for research purposes and is not commercially available.

The project has been a 14-year process, beginning in 1991 with concept development all the way to final implantation performed by Colwell in February of last year. For the past 12 months, Colwell and his team have been gathering data from the implant patient.

The components of E-Knee resemble traditional knee replacement parts. An additional thin layer in the lower plate of the replacement contains four small transducers that measure strain across the knee, which changes as the patient moves.

Also part of the lower plate is an elongated post that is inserted into the center of the bone. In the E-Knee, the post contains a multi-channel transmitter and antenna that sent all the force measurements to a computer. The entire process is activated by a removable electronic coil that fits outside the leg or on the patient's belt.

Most of the computer technology within the implant is smaller than a postage stamp.

Researchers began the process of data-gathering within a few weeks following surgery and the testing is ongoing. Real-time data on the distribution of forces to the implant and load-carrying capabilities of the bone were measured.

“We now have hard data on how much force is placed when the patient does any number of movements, like walking bicycling, or even swinging a golf club,“ Colwell said. “In many ways, this technology redefines the methodology of knee replacement research.“

In addition to SCORE and Scripps Clinic, the team involved in designing E-Knee included representatives from NK Biotechnical (Minneapolis), the DePuy Spine (Raynham, Massachusetts) division of Johnson & Johnson (New Brunswick, New Jersey) and MicroStrain (Williston, Vermont).

“We now have a means of knowing exactly where stress is being placed on the knee every time the patient engages in any type of physical activity,“ Colwell explained. “These specific measurements may not only result in better implant design, but could also allow us to measure the effectiveness of postoperative physical therapy, overall rehabilitation, bracing and the use of corrective orthotics.“

Colwell told Medical Device Daily that this technology could be used to design activity-specific artificial knees.

“So many of our patients want to get back on the golf course, for example,“ he said. “This could lead to replacements based on certain types of strain, tension or movement.“

Based on the information gathered from the one patient so far, Colwell said it seems that patients may be ready for more strenuous activity much sooner following total knee replacement than previously thought.

The patient in the trial run of E-Knee was described as an “active, older“ individual. In his early 80s, he already has had a knee and joint replacement, but is active in sports including skiing, golf and tennis.

The next step in the process, Colwell said, will be to implant E-Knees in younger adults, women, and individuals of varying weights and body types, which greatly affect how the artificial knee would perform. He said five or six new subjects would be receive E-Knee replacements in the near future.

Coldwell said that roughly 400,000 knee replacements are performed every year in the U.S., and the number of younger, more active knee-replacement patients continues to rise. As these numbers continue to grow, he said, so will the demand for longer-wearing knee implants that can withstand more rigorous post-surgery activity.