A removable flexible orthosis for the middle foot comprising a) a first metatarsophalangeal collar that encircles and is fixed on the forefoot, and extends transversely from the heads of the first to the fifth metatarsi, and longitudinally from the toe's root towards the mid-diaphysis of the metatarsi, and b) a traction strap comprising at least one end fixed or fixable on the first metatarsophalangeal collar and on the portion of the orthosis designed to be applied on the rear of the foot is provided. The two ends of the stirrup-shaped traction strap can be fixed on the postero-external and postero-internal edges of the first metatarsophalangeal collar on the sides of the foot.