The orthosis (10) comprises: a foot portion (12)； a leg portion (14) exerting a therapeutic compression textile pressure on the leg； and a rib-knitted end portion (16) locally exerting a holding textile pressure for preventing the terminal portion from sliding downwards under the effect of the elastic return force. (F) from the leg portion that is stretched in the longitudinal direction. The method comprises obtaining data representative of: morphological characteristics of the limb； rheological characteristics of the leg portion of the orthosis； friction characteristics at the interface between the limb and the leg portion of the orthosis； rheological characteristics of the end portion of the orthosis； and friction characteristics at the interface between the limb and the end portion of the orthosis. The following step consists in numerically simulating the action on the limb of the leg portion and of the end portion of the orthosis, and in providing at least one indicator that quantifies the way the orthosis will hold on the limb.
