Abstract: A below-knee orthosis with fastening devices for fastening the orthosis to the foot and to the lower leg, and with an L-shaped support spring which is made of a resilient material and which has an upright branch that defines a contact plane and is intended to bear on the dorsal aspect of the lower leg, the lower end of which upright branch is adjoined by a horizontal branch designed to engage under the foot, said below-knee orthosis permitting an improved heel-to-toe behavior in the material of the support spring and taking account of the natural outward position of the foot by virtue of the fact that the upright branch is twisted in the lower area in such a way that the horizontal branch continuing the lower end is turned outward by an angle ? from the plane lying perpendicular to the contact plane of the upright branch above the twisted lower area.