A human or animal joint is treated by introduction of a device between the suitably prepared articulating surfaces of the joint, wherein the device is anchored in both these articular surfaces with the aid of a material having thermoplastic properties and with the aid of vibratory energy. For allowing at least limited articulation of the joint after implantation, the device comprises two articulating portions (1 and 2), wherein one of the articulating portions is anchored in each one of the articulating surfaces of the joint. On implantation a proximal face of the device is contacted with a vibrating tool (5) and the vibration is transmitted through parts of the device to locations in which the material having thermoplastic properties is near the bone tissue of the articulating surfaces of the joint and in which liquefaction is desired. The liquefied material penetrates the bone tissue and, on re-solidification forms a positive fit connection between the device and the bone tissue. For achieving targeted and efficient liquefaction and as little energy loss as possible and still allowing articulation of the articulating portions (1 and 2) of the device relative to each other after the implantation, the device is equipped at least for the implantation with a temporal connector portion (4) which connects the two articulating portions (1 and 2) to constitute together with the connector portion (4) and possibly an interface portion (3) a rigid item. The connector portion (4) is removed from the joint immediately after anchoring the articulating portions (1 and 2) or in a second surgical operation after a healing phase in which the joint is immobilized by the connector portion or the connector portion (4) consists of a bio-resorbable or bio-degradable material and is removed gradually by bio-resorption or bio-degradation.