A knee brace for externally replacing the function of a torn anterior cruciate ligament. The brace has femur and tibia levers hinged proximal the knee joint. The femur lever has an upper high cuff which bears against the front of the thigh and a lower strap which applies anterior force to the back of the thigh proximal the knee, while the tibia lever has a lower calf cuff which bears against the back of the calf and an upper strap which applies posterior force to the front of the tibia proximal the knee. Thus, the two straps apply a differential force couple forwardly to the femur and rearwardly to the tibia proximal the knee joint which serves the anterior cruciate ligament function. A resilient tubular undersleeve anchors the brace against downward migration on the leg.