An orthosis chosen from an elastic venous retention orthosis and an elastic venous compression orthosis is intended to treat a venous disorder of a lower limb of a patient in a service position in which it is fitted, via an opening, on the lower member, the orthosis having a ribbed top and a leg part, the ribbed top including a rim that delimits the opening, the orthosis being characterized in that the front part of the rim of the ribbed top has, on average, an altitude greater than that of the rear part of the rim of the ribbed top.
