An orthosis includes a device for holding the knee cap and arranged to press against the knee by a part consisting of an elastic material surrounding the knee. The holding device includes an annular body having a central oval opening for receiving the knee cap and separate supporting bodies that protrude outwardly from the periphery of the body. Two adjacent supporting bodies are separated by a gap when the holding device in a non-constrained state. The holding device is substantially flat in the non-constrained state and non-deformable in a plane. The holding device is designed so as to be able to be deformed into a domed position, hugging the shape of the bent knee. In this position, the supporting bodies are butt jointedand the holding device forms a shell enveloping the knee.
