> Planetary roller screws are the gold standard for high-performance joints such as knees, ankles, and hips.

It's hard to understand how these are used for joints. I think of a screw as something that rotates many times. Are these used for things that rotate only a few degrees, as a knee might?

these translate rotary motion into linear motion. if you hold the screw fixed (with bearings), and let the nut float, then turning the screw moves the nut back and forth along the screw