The invention relates to an orthosis for supporting a limb or a joint of a human or of a vertebrate animal, comprising: a sleeve (10) which is at least partly elastic and is designed to enclose a limb or a joint, a plate (12) made of a thermoformable material, and a pocket (11) formed on the sleeve in order to receive the plate, the pocket having a shape adapted to that of the plate. The adherence between the plate (12) and the inner surface of the pocket is treated in order to permit a relative movement of the plate with respect to the material (10, 11) forming the pocket during and after an operation of thermoforming of the plate, this being done by placing the orthosis on the limb or the joint with the plate present in the pocket. This orthosis is designed in particular to be fitted in place and thermoformed by the user himself.
