Abstract: A joint for an orthotic apparatus is disclosed. The joint includes a main block having arc-shaped grooves formed on opposite sides and a pair of rails separated by each arc-shaped groove. The joint also includes a pair of carriers slidably mounted on the opposite sides of the main block, each carrier having a main rollers in rolling engagement with the arc-shaped groove and a plurality of side rollers adapted to roll on the rails. Attached to each carrier is an arc-shaped rack arranged concentrically with the arc-shaped groove and a base plate for connecting to a long leg supporting member. The joint further includes a pinion gear installed on a bottom part of the main block and in meshing engagement with each arc-shaped rack, and an electric motor for operating the pinion gear.