The technical problem is to provide a bi-directional power unit for a hinge assembly that can be easily reversed to provide a flexion or extension force. The gist of solution is a power unit that is threadably mounted on a hinge pin (spline) centrally located on the platform, and is latched to a catch assembly radially located thereto, the hinge pin of the platform communicating with one end of a torsion spring of the power unit and the catch assembly communicating with another end of the torsion spring, to selectively deliver the extension/flexion force. The power unit can be detached, with simple manual operation of the catch assembly, without tools, flipped over and reattached to the same platform attachment points to switch (reverse) extension torque to flexion torque and vice versa. The principal use of invention is to provide a hinge or joint assembly, at the ankle, wrist, knee or ankle, that is adapted to exert a bidirectional force at the body joint to provide dynamic shock absorption and return assistance.
