Thumb orthosis with a mouldable thermoplastic stay. The orthosis is designed to restrict movement in CMC and MCP1 joints and puts the thumb in a functional position by an individually moulded thermoplastic thumb support, placed in a pocket on the orthosis. To individually mould the orthosis put the complete product into a waterbath until the plastic is soft and mouldable. Shape the orthosis on the patient. Leave the orthosis on the patient until cool.