New Bionic Knee Is Lighter and Helps Amputees Move Naturally

Most prosthetic knees are passive, meaning they don't help push you forward when you walk or stand up. Powered knees can do that, but earlier designs were too heavy and bulky for everyday wear. This new study describes a powered knee that weighs about as much as a small bag of sugar (2.6 kg) and is slim enough to fit under clothing. The design uses a special motor called a quasi-direct drive, which is easier to control, quieter, and lets the knee move smoothly with the user.

The research team tested the knee on benches and then with three people who had above-knee amputations. Those users walked on level ground and performed sit-to-stand transitions — something many of us do dozens of times a day without thinking. The knee produced force similar to that of a natural leg during those activities. It also delivers strong torque (145 Newton-meters), which is enough to help someone climb stairs or stand up from a chair without leaning heavily on their arms.

The big achievement here is combining strength with lightness. Previous powered knees with this kind of motor were too heavy for practical use, which kept them out of the commercial market. This version is also quiet and easy to move by hand when not powered, which adds comfort and safety. The researchers say the design meets or improves on a leading commercial powered knee in mass, size, and performance. While more testing is needed before it reaches clinics, this study is an important step toward powered prostheses that feel less like machinery and more like a natural part of the body.