Abstract: The apparatus has a thigh retaining component (1) and a leg retaining component (2) tied together by an articulation apparatus (3).The external articulation is formed of two legs (18 and 21-23-24) articulated as a knee brace to block forward extension.The external articulation has an upper articulated leg (25), set as a knee brace, with the upper part of a cross piece (27) whose lower portion is articulated at the end of a rod (31) whose other end is articulated to the lower leg (37).The leg (21-23-24) and the rod (31) are, preferably adjustable in length and their ends can turn slightly with respect to one another.The brace of the invention can be advantageously used in almost all cases of knee instability while allowing it good freedom of motion.