“We’ve created something that allows an implant to react the way it would as an integrated part of the knee,” said Bruce White, CEO of AMTI and VST patent recipient.
Total knee replacement, the most common total joint procedure, is designed to replace the articular cartilage, which may have eroded over time or become damaged by extreme activity or accident. A largely successful procedure, TKR has reduced pain and improved mobility for a population of several million individuals. In response to patient and medical demand, designers and manufacturers are always working toward greater range of motion and longer service life.
These goals, however, are secondary to the concern for patient safety, and for good reason. Any surgery has inherent risks and requires a recovery process, but a central concern surrounding implantation is preventing implant failure requiring revision surgery.
“The natural human knee is a miracle of evolution, perfectly adapted for mobility, dexterity, and upright stance,” White said. “Engineering replacement parts for the strongest joint in the human body is challenging—it may be just as challenging to design testing that accurately shows that the parts are safe and durable enough to be implanted.”
Simulator machines are designed to test the function and durability of implants by recreating the loads and movements of almost any activity so the response of the implant can be evaluated. Over the past two decades, the role of joint motion simulation has evolved from a scientific tool into an integral part of the design, manufacturing, and quality assurance processes of implant device production.
“For fully realistic simulation, you need an accurate constraint model, information about the way the soft tissues surrounding the knee joint would respond to the joint’s motion,” White said. “Soft tissue may share as much as 50% of the shear load for the joint, so a more accurate and detailed constraint model will give you more accurate test results.” Soft tissue constraint was originally represented with simplistic linear models and mechanical springs. However, researchers found that wear results obtained using this method did not match what they observed in patients.
“The constraining force of the soft tissue is complex and asymmetrical, making it a challenge to represent,” White said. “But VST is a sophisticated model and gives us the clearest picture we have of how a new prosthetic device will respond after it is integrated with the remaining biological structure of the knee.”
That deep understanding of implant performance has become even more important as the average age of implant recipients has fallen over the past decade. This younger, more active population is driving the development of implants that offer enhanced performance and longer service life. These goals are naturally at odds: the more movement an implant allows, the greater the challenge to long-term durability. To evaluate the subtle design changes that can strike a balance, manufacturers require high-fidelity test environments.
“Implants and implant testing technology have a certain synergy—one spurring the other on to its next evolutionary stage,” White said. “In an industry that has always placed patient safety above all other considerations, simulation testing must keep pace with that development.”
AMTI (Advanced Mechanical Technology, Inc.) is a manufacturer of multi-axis biomedical testing machines and multi-axis force measurement instruments. Each year more than 80 percent of the hip and knee implants produced are man¬ufactured by companies that rely on AMTI joint simulators for implant evaluation. Located in Watertown, Mass. for the last 35 years, AMTI is an active participant in ASTM working alongside implant manufacturers to improve testing standards.
For more information, please contact:
Steven Profaizer, Marketing Manager
Advanced Mechanical Technology, Inc.
176 Waltham Street
Watertown, MA 02472
Phone: (1) 617-673-8434
Fax: (1) 617-926-5045
