The disclosure relates to an orthosis comprising a tubular sleeve having an inlet opening and an outlet opening or sock. The tubular sleeve is preferably formed of a stretchable, textile-based material such that the tubular sleeve as such is radially collapsible when being in a non-worn condition and is circumferentially stretchable to adapt to a shape of a limb of a user when being worn thereon. The orthosis further comprises a circumferentially expandable reinforcement member arranged at the inlet opening and circumscribing at least approximately 135° of the inlet opening. The reinforcement member is resilient and provides a radially outwardly directed force onto the tubular sleeve and thereby retains the inlet opening in an open shape facilitating insertion of the limb through the inlet opening into the orthosis. Also described are kit of parts and the use of the orthosis.