The implant comprises a stem (10) terminating in a head (20). The stem is adapted to be inserted in the metacarpus of the thumb and the head to be disposed in a space obtained particularly by removing at least a portion of the trapezium. The surface of the head is constituted by a base (201) connected to the stem and adapted to rest on the proximal end of the metacarpus, a distal surface portion (202) opposite the base and serving as a contact surface with the bone located facing the proximal end of the metacarpus, and a connecting portion (203) connecting the base and the distal surface portion of the head. The distal surface portion (202) of the head is inclined relative to a longitudinal axis (104) of the stem by a predetermined angle (.alpha.), such that, when the stem (10) is mounted straight in the metacarpus, the distal surface portion (202) of the head can be located in varus.