Abstract: An extension deceleration orthotic fulcrum for knee and elbow braces, which simulates performance of the function of those ligaments that control joint motion and provide anteroposterior joint stability, comprising a lightweight, external spring assembly, upper and lower elongated arms, and centric or polycentric fulcrum, which is adjustable for its range of motion, adaptable for use on many different style orthoses, and whose strength can be varied to suit corrective, preventive, anthropomorphic, environmental, and usage requirements, including means both for mechanically dampening the limb's angular velocity on extension to prevent hyperextension and for accelerating the limb's angular velocity on flexion to enable quicker, smoother, less stressful motion.