Surgery of the anterior cruciate ligament of the knee is frequently a young patient surgery. The post-operative pain of this surgery is managed according to recommendation. In the majority of case, femoral nerve block is performed. The femoral nerve block can cause "paralysis" of the quadriceps more or less complete that no allowing a good quadriceps locking. This locking is indispensable to avoid post-operative flexima and to ensure stabilization of the knee during walking.