A replacement ligament prosthesis including an elongate replacement ligament having a femoral end and a tibial end. The prosthesis includes a bar, which in use will extend between the medial and lateral condyles of a femur and across the intercondylar notch, and to which the femoral end of the elongate replacement ligament will be fixed. The prosthesis also includes a fixing means, which in use will fasten the tibial end of the elongate replacement ligament to the tibia.