An orthosis (10) has an elastic compressive distal portion (14), extending upwards from the ankle, associated with an adjacent rigid splint proximal portion (16), enveloping the region of the calf between the level of the point where the Achilles tendon joins the calf muscles and the level located below the tibial tuberosity. This rigid splint proximal portion (16) is an essentially non-elastic, deformable tubular portion, made by: placing the orthosis onto a template representative of the morphology of the patient's calf; applying in situ on the orthosis, in the region of the splint proximal portion, a hardenable biocompatible resin; hardening the resin with the orthosis maintained on the template; and removing the orthosis in its finished state.